Bilateral Interfacial Passivation: A Strategic Breakthrough for Enhancing PeLED Stability and Efficiency

Thomas Carter Dec 02, 2025 404

This article comprehensively examines the bilateral interfacial passivation strategy, a cutting-edge approach that significantly enhances the stability and performance of Perovskite Light-Emitting Diodes (PeLEDs).

Bilateral Interfacial Passivation: A Strategic Breakthrough for Enhancing PeLED Stability and Efficiency

Abstract

This article comprehensively examines the bilateral interfacial passivation strategy, a cutting-edge approach that significantly enhances the stability and performance of Perovskite Light-Emitting Diodes (PeLEDs). Tailored for researchers and scientists in optoelectronics and material science, we explore the foundational science behind interfacial defects, detail practical methodological applications using organic molecules and innovative materials, address critical troubleshooting and optimization challenges, and present rigorous validation through comparative performance metrics. The synthesis of evidence reveals that dual-sided interface engineering can dramatically improve operational lifetime, boost external quantum efficiency, and suppress non-radiative recombination, paving the way for the commercialization of durable PeLED technology.

The Critical Interface Problem: Understanding Defects and Instability in PeLEDs

Metal halide perovskites have emerged as revolutionary semiconducting materials for optoelectronic devices, including perovskite light-emitting diodes (PeLEDs) and solar cells (PSCs), demonstrating remarkable performance characteristics such as high color purity, tunable bandgaps, and cost-effective solution processability [1] [2]. Despite these promising attributes, the widespread commercialization of perovskite-based devices remains constrained by significant challenges associated with performance stability and operational lifetime. Central to these limitations is the fundamental issue of defect-rich interfaces inherent to perovskite materials [3] [4].

The propensity for defect formation at interfaces—specifically at grain boundaries (GBs), surfaces, and heterointerfaces with charge transport layers (CTLs)—represents a critical bottleneck in device development. These defects primarily function as non-radiative recombination centers, severely diminishing photoluminescence quantum yield (PLQY), external quantum efficiency (EQE), and ultimately, device stability [4] [3] [5]. Understanding the origin, nature, and impact of these interfacial defects is therefore paramount for formulating effective passivation strategies, particularly the bilateral interfacial passivation approach central to advancing PeLED technology.

The Origins and Types of Interfacial Defects

Structural and Crystallographic Origins

Perovskite materials commonly used in optoelectronics follow the general formula ABX₃, where A is a monovalent cation (e.g., MA⁺, FA⁺, Cs⁺), B is a divalent metal cation (e.g., Pb²⁺, Sn²⁺), and X is a halide anion (e.g., I⁻, Br⁻, Cl⁻) [6] [1]. The ideal perovskite crystal structure is cubic, with B-site cations occupying corners and X-site anions forming octahedra around them, while A-site cations reside in the interstitial spaces [6]. However, practical device fabrication often results in polycrystalline films with inherent crystallographic imperfections.

  • Polycrystalline Nature: Solution-processing techniques typically yield polycrystalline films containing numerous grain boundaries. The defect density in such polycrystalline perovskite films is approximately 10¹⁶–10¹⁷ cm⁻³, markedly higher than the 10⁹–10¹⁰ cm⁻³ found in single-crystal perovskites [6]. Most defects in polycrystalline films are concentrated at grain boundaries and interfaces rather than within the bulk crystal [6].
  • Rapid Crystallization: The fast and often uncontrollable crystallization process of perovskite films from solution leads to irregular atomic arrangements, fostering point defects and dislocation lines [6].
  • Spontaneous 2D Formation: Recent studies reveal that the buried interface (between the perovskite and substrate) often suffers from poor crystallization relative to the top surface. Strategies inducing spontaneous formation of two-dimensional (2D) perovskite phases at this buried interface have demonstrated improved crystallization uniformity and defect passivation [7].

Classification of Defects

Defects in perovskite materials can be categorized based on their dimensionality and electronic impact:

Table 1: Classification of Defects in Perovskite Materials

Defect Category Description Common Locations Primary Impacts
Zero-Dimensional (0D) Point Defects [6] Vacancies, interstitials, or antisite substitutions (e.g., I⁻ vacancies, Pb²⁺ interstitials). Frenkel and Schottky defects are most common. Throughout the film, often concentrated at surfaces/GBs Introduce trap states in the bandgap; charge carrier recombination.
One-Dimensional (1D) Defects [6] Dislocation defects formed by local irregularity in atomic arrangement. Grain interiors and boundaries Can act as scattering centers and recombination pathways.
Two-Dimensional (2D) Defects [6] [3] Grain boundaries and surfaces with dangling bonds. Interfaces between crystalline grains, film surfaces Severe non-radiative recombination; pathways for oxygen/ moisture penetration.
Three-Dimensional (3D) Defects [6] Agglomerates, pinholes, and porosity. Throughout the film Reduce film continuity, promote shunt paths, and degrade device performance.

From an electronic perspective, defects are further classified as shallow-level or deep-level traps, based on their energy position relative to the conduction band minimum (CBM) and valence band maximum (VBM) [6]. Shallow-level defects, located closer to the band edges, have minimal effect on non-radiative recombination as trapped carriers can be easily re-excited. In contrast, deep-level defects, situated nearer to the center of the band gap, severely impact device performance by acting as potent centers for non-radiative recombination, thereby consuming photo-generated carriers and reducing luminescence efficiency [6] [4]. Deep-level defects are predominantly found at grain boundaries and interfaces, where their high formation energy is stabilized [6].

G PerovskiteFilm Top Interface Bulk Perovskite Film Polycrystalline ABX₃ Buried Interface TopDefects Defect Sources (Top) • Surface dangling bonds • Volatile A-site cation loss • Incomplete surface coordination • Environmental degradation (O₂, H₂O) PerovskiteFilm:top->TopDefects BulkDefects Defect Sources (Bulk) • Grain boundaries • Pb²⁺ and I⁻ vacancies • Sn²⁺ oxidation (Sn-based) • Interstitial defects • Pinholes and agglomerates PerovskiteFilm:bulk->BulkDefects BottomDefects Defect Sources (Buried) • Poor crystallization initiation • Lattice mismatch with substrate • Inhomogeneous nucleation • Incomplete surface coverage PerovskiteFilm:bottom->BottomDefects Impact Device Performance Impact • Non-radiative recombination ↓ PLQY/EQE • Ion migration pathways ↓ Stability • Charge injection imbalance ↑ Efficiency roll-off • Environmental degradation ↑ TopDefects->Impact BulkDefects->Impact BottomDefects->Impact

Diagram 1: Origins and Impact of Defects in Perovskite Films. Defects originate from multiple sources throughout the film structure, with interfaces being particularly vulnerable, collectively leading to significant device performance degradation.

Consequences of Interfacial Defects on PeLED Performance

The presence of defects at perovskite interfaces profoundly impacts the operational efficiency and stability of PeLEDs through several interconnected mechanisms:

  • Non-Radiative Recombination and Efficiency Loss: Defect states within the bandgap, particularly deep-level traps, capture charge carriers (electrons and holes) and facilitate their recombination without photon emission. This non-radiative recombination directly competes with radiative recombination, substantially reducing the photoluminescence quantum yield (PLQY) of the emissive layer and the external quantum efficiency (EQE) of the device [4] [5]. For instance, untreated quantum dot (QD) films can see significant PL quenching, with PLQYs dropping from ~85% in colloidal solutions to as low as 43% in solid films, primarily due to defect regeneration during film assembly [5].

  • Ion Migration and Operational Instability: Defect sites, especially vacancies and grain boundaries, provide pathways for ion migration under operational electric fields [2]. This ion movement leads to phase segregation, luminescence quenching, and the formation of current shunt paths, accelerating device degradation [8] [5]. This is a key factor limiting the operational half-lifetime (T₅₀) of PeLEDs.

  • Charge Injection Imbalance and Efficiency Roll-Off: Interfacial defects disrupt efficient charge injection from transport layers into the perovskite emissive layer [2]. This can cause an imbalance in electron and hole flux, leading to efficiency roll-off at high current densities due to Auger recombination and Joule heating [2].

  • Environmental Degradation: Surfaces and grain boundaries with dangling bonds are susceptible to attack by environmental factors such as moisture and oxygen, catalyzing the decomposition of the perovskite lattice and leading to rapid device failure [6] [3].

Characterization and Quantification of Interfacial Defects

Accurately characterizing interfacial defects is crucial for developing effective passivation strategies. The following table summarizes key experimental techniques and their applications in defect analysis.

Table 2: Experimental Techniques for Characterizing Perovskite Interface Defects

Technique Measured Parameters Information on Defects Application Notes
Space Charge-Limited Current (SCLC) [5] Trap-filled limit voltage (V({}{\text{TFL}})), Trap density (n({}{\text{trap}}) Quantitative defect density, Charge carrier trapping Directly measures trap density in device configuration; requires electron-only or hole-only devices.
Density Functional Theory (DFT) [5] Density of States (DOS), Formation energy, Bond order Atomic-level defect energy states, Passivation binding strength Theoretical calculation of defect properties and passivator-perovskite interactions (e.g., Pb–O bond order).
Transient Absorption (TA) Spectroscopy [5] Carrier decay lifetime, Recombination kinetics Non-radiative recombination rates, Carrier trapping dynamics Probes ultrafast carrier dynamics; reveals defect-mediated recombination pathways.
Photoluminescence Quantum Yield (PLQY) [5] [1] Ratio of emitted to absorbed photons Overall film quality, Non-radiative loss intensity Simple, rapid assessment of film optoelectronic quality before device fabrication.
Scanning Electron Microscopy (SEM) [9] Film morphology, Grain size, Pinholes Visual identification of 2D/3D defects (pinholes, coverage) Qualitative assessment of film uniformity and gross defects.

Experimental Protocol: SCLC Measurement for Trap Density

Purpose: To quantitatively determine the defect density (trap density) in a perovskite film.

Materials:

  • Substrates (e.g., ITO/glass)
  • Materials for electron-only or hole-only device stack
  • Perovskite precursor solution
  • Thermal evaporator for electrode deposition
  • Source meter unit

Methodology:

  • Device Fabrication: Fabricate a single-carrier device. For an electron-only device, a common structure is ITO/SnO₂/Perovskite/PCBM/Ag [5]. For a hole-only device, use ITO/PEDOT:PSS/Perovskite/Spiro-OMeTAD/Au.
  • Current-Voltage (I-V) Measurement: Measure the dark I-V characteristics of the device from 0 V to a sufficiently high voltage (e.g., 5-10 V) to reach the trap-filled limit.
  • Data Analysis:
    • Plot the log(I) vs. log(V) curve.
    • Identify the transition voltage (V({}{\text{TFL}})) where the current sharply increases (trap-filled limit).
    • Calculate the trap density (n({}{\text{trap}}) using the formula: [ n{\text{trap}} = \frac{2 \epsilon \epsilon0 V{\text{TFL}}}{e L^2} ] where (\epsilon) is the perovskite dielectric constant, (\epsilon0) is the vacuum permittivity, (e) is the elementary charge, and (L) is the perovskite film thickness.

A lower calculated n({}_{\text{trap}} indicates superior film quality with fewer defects, often achieved through effective passivation.

The Research Toolkit: Reagents for Interface Passivation

Effective defect mitigation relies on a suite of chemical reagents designed to interact with and neutralize specific defect types. The table below catalogues key reagents used in interfacial passivation for PeLEDs.

Table 3: Research Reagent Solutions for Interface Passivation

Reagent Category & Example Chemical Target/Function Mechanism of Action Reported Outcome
Organic Halide Salts (e.g., Phenethylammonium Iodide, PEAI [9]) Surface dangling bonds, Iodide vacancies Coulombic interaction with charged defects; Steric hindrance to ion migration. PCE increase to 23.32% in PSCs; Reduced non-radiative recombination.
Phosphine Oxide Molecules (e.g., TSPO1 [5]) Under-coordinated Pb²⁺ sites Lewis base coordination via P=O lone pair electrons; Strong Pb–O bond (bond order 0.2). PLQY increase from 43% to 79% in QD films; EQE boost from 7.7% to 18.7% in QLEDs.
Alkali Metal Salts (e.g., KI [6]) A-site cation vacancies, Halide vacancies K⁺ passivates A-site vacancies; accumulates at GBs to inhibit ion migration. Enhanced stability, suppression of ion migration.
Pyridine Derivatives (e.g., 1-Ethylpyridine Hydrobromide, EPB [9]) Under-coordinated Pb²⁺, Iodide vacancies N atom (Lewis base) coordinates Pb²⁺; Br⁻ anions compensate I⁻ vacancies. PCE increase from 18.85% to 20.71%; >90% initial PCE after 400h.
Polymeric Additives (e.g., various polymers [2]) Grain boundaries, Overall film morphology Multi-point passivation; Physical encapsulation; Suppression of ion migration. Enhanced operational stability, balanced charge injection.
Reducing Agents (for Sn-based PeLEDs [8]) Sn⁴⁺ oxidation states Redox buffering to maintain Sn²⁺ state; suppression of deep traps. Improved morphology, higher PLQY and EQE in Sn-based PeLEDs.

G Defect Under-coordinated Pb²⁺ (Deep-level Trap) Interaction Lewis Acid-Base Coordination Defect->Interaction Passivator TSPO1 Passivator (P=O Group) Passivator->Interaction Result Passivated Defect (Reduced Trap State) Interaction->Result

Diagram 2: Molecular Passivation Mechanism. Lewis base passivators like TSPO1 donate lone pair electrons to coordinate under-coordinated Pb²⁺ ions, neutralizing deep-level trap states.

Protocol: Bilateral Interfacial Passivation of Perovskite QD Films

This protocol details the bilateral passivation strategy proven to significantly enhance the efficiency and operational stability of perovskite quantum dot light-emitting diodes (QLEDs) [5].

Principle: Depositing a thin layer of organic passivation molecules (e.g., TSPO1) at both the bottom and top interfaces of the perovskite QD film to suppress defect-mediated non-radiative recombination and ion migration.

Materials and Equipment:

  • Synthesized CsPbBr₃ QDs (PLQY >80% in solution)
  • Passivation molecule (e.g., TSPO1, >99% purity)
  • Anhydrous solvents (toluene, chlorobenzene)
  • Electron transport layer (ETL) material (e.g., ZnO nanoparticles)
  • Hole transport layer (HTL) material (e.g., TCTA, Spiro-OMeTAD)
  • Pre-patterned ITO glass substrates
  • Thermal evaporator with controlled deposition rate
  • Spin coater
  • Nitrogen glove box (O₂ & H₂O < 0.1 ppm)
  • Spectrophotometer and quantum efficiency measurement system

Procedure:

  • Substrate Preparation: Clean ITO substrates sequentially with detergent, deionized water, acetone, and isopropanol via ultrasonication for 15 minutes each. Treat with UV-ozone for 20 minutes before use.
  • Bottom Interface Passivation:
    • Load the clean ITO substrate into the thermal evaporator.
    • Evaporate a thin, continuous layer (~2-5 nm) of TSPO1 onto the ITO surface at a deposition rate of 0.2-0.5 Å/s under high vacuum (<5×10⁻⁶ Torr).
  • ETL Deposition: Spin-coat the ZnO nanoparticle layer (~30 nm) onto the TSPO1/ITO substrate at 3000 rpm for 30 s, followed by annealing at 100°C for 15 minutes.
  • Perovskite QD Film Deposition:
    • Spin-coat the CsPbBr₃ QD solution (10 mg/mL in toluene) onto the ETL at 2000 rpm for 30 s inside a nitrogen glove box.
    • Anneal the film on a hotplate at 70°C for 10 minutes to remove residual solvent.
  • Top Interface Passivation:
    • Transfer the substrate back to the thermal evaporator.
    • Evaporate a second layer of TSPO1 (~2-5 nm) directly onto the QD film using the same parameters as in Step 2.
  • HTL and Electrode Completion:
    • Deposit the HTL (e.g., TCTA, ~40 nm) via thermal evaporation.
    • Complete the device by thermally evaporating a MoO₃/Au (5 nm/80 nm) anode.
  • Control Device Fabrication: For comparison, fabricate control devices with no passivation, top-side only passivation, and bottom-side only passivation.

Characterization and Validation:

  • Perform SCLC measurements on single-carrier devices to quantify the reduction in trap density.
  • Measure the PLQY of the bilateral-passivated QD film and compare it to the control films. An increase from ~43% to ~79% is indicative of successful passivation [5].
  • Fabricate complete QLEDs and measure EQE. A successfully passivated device should show a significant increase in maximum EQE (e.g., from 7.7% to 18.7%) [5].
  • Conduct operational lifetime tests (T₅₀ at constant current density). The bilateral-passivated device should exhibit a substantially extended lifetime (e.g., a 20-fold increase from 0.8 h to 15.8 h) [5].

The propensity of metal halide perovskites to form defect-rich interfaces is an intrinsic challenge rooted in their ionic crystal nature, soft lattice properties, and polycrystalline film morphology. These defects, particularly deep-level traps at surfaces and grain boundaries, are primary sources of non-radiative recombination and operational instability in PeLEDs. The strategic implementation of bilateral interfacial passivation—employing molecular, ionic, or polymeric reagents at both top and bottom QD film interfaces—has emerged as a profoundly effective methodology to suppress these defects. This approach directly addresses the fundamental challenge outlined herein, enabling significant concurrent enhancement in device efficiency and operational stability, thereby paving a critical path toward the commercialization of robust perovskite-based optoelectronics.

In metal halide perovskite optoelectronic devices, such as light-emitting diodes (PeLEDs) and solar cells, the interfaces between the perovskite light-emitting layer and the adjacent charge transport layers (CTLs) are critical regions where performance and stability are determined. Interfacial defects are imperfections that occur at these boundaries, primarily originating from undercoordinated ions, dangling bonds, and surface disorders that arise during the film fabrication process. These defects are not merely static imperfections but actively participate in detrimental processes that severely compromise device performance. The most consequential of these processes are non-radiative recombination and ion migration, which collectively degrade both the efficiency and operational stability of perovskite-based devices [5] [10].

The significance of interfacial defects is magnified in practical device architectures, where the perovskite layer is sandwiched between other functional layers. Both the top and bottom surfaces (buried interface) of the perovskite film are susceptible to defect formation. The buried interface, in particular, often suffers from poor crystallization relative to the top surface, resulting in suboptimal crystal quality and increased defect densities [7]. During the quantum dot (QD) film assembly, massive defects are prone to be reproduced, which sorely affect carrier injection, transportation, and recombination [5]. These defects act as trapping centers for charge carriers, leading to efficiency losses and initiating degenerative processes that ultimately limit the device's operational lifespan.

Consequences of Interfacial Defects

Non-Radiative Recombination

Non-radiative recombination is a process where injected electrons and holes recombine without emitting photons, instead releasing energy as heat through defects known as non-radiative recombination centers. Interfacial defects, particularly deep-level traps, are primary sources of this deleterious recombination pathway [10].

The physical origin of these traps is often associated with undercoordinated ions at the perovskite surface. Undercoordinated Pb²⁺ ions are especially detrimental, creating deep trap states that strongly capture charge carriers [5] [10]. DFT calculations comparing passivated and unpassivated surfaces reveal that unpassivated surfaces show significant trap states at the band edges due to non-coordinating Pb atoms, while passivated surfaces exhibit greatly weakened trap states [5]. When charge carriers are trapped by these defects, they cannot participate in radiative recombination, drastically reducing the luminescence efficiency.

The impact on device performance is quantifiable and severe. Defect-mediated non-radiative recombination directly lowers the internal quantum efficiency (IQE) by reducing the ratio of generated photons to injected electrons [10]. For PeLEDs, this manifests as reduced external quantum efficiency (EQE) and current efficiency (CE). In perovskite quantum dot light-emitting diodes (QLEDs), uncontrolled interfacial defects have limited the maximum EQE to 7.7% in non-passivated devices, significantly below the theoretical potential [5]. Similarly, the photoluminescence quantum yield (PLQY) of perovskite films plummets due to non-radiative pathways; for instance, QD films can experience a sharp decline from colloidal PLQYs of 85±3% to film PLQYs as low as 43% without proper interface management [5].

Ion Migration

Ion migration refers to the movement of ions within the perovskite lattice under operational stressors like electric fields, light, and heat. Interfacial defects, particularly halide vacancies, provide low-activation-energy pathways for this migration, acting as channels that facilitate ion movement [11] [12].

The migration mechanisms are complex and influenced by multiple factors. Halogen vacancies have inherent low activation energy, making halide anions particularly prone to migration under electric fields [11]. These mobile ions can travel along grain boundaries and through the bulk material, but their movement is accelerated at interfaces where defect density is high. The regeneration of defects during device operation, often due to weak surface ligand adhesion, can further provide ion migration channels that are detrimental to stability [5].

The consequences of ion migration are particularly evident in the operational instability of PeLEDs. Phase separation occurs in mixed-halide perovskites as halides migrate and demix, leading to changes in the bandgap [11]. This phenomenon manifests as undesirable electroluminescence (EL) spectral shift during device operation. For example, in deep-blue PeLEDs based on reduced-dimensional perovskites (RDPs), uncontrolled ion migration can cause a bathochromic shift (red shift) in the EL spectra from 461 nm to 466 nm as the bias voltage increases [12]. This shift is accompanied by a widened full width at half maximum (FWHM), negatively impacting color purity. Additionally, ion migration contributes to the degeneration of device performance over time, as migrating ions can accumulate at interfaces, modifying charge injection properties and creating additional non-radiative recombination channels [5] [11].

Table 1: Quantitative Impacts of Interfacial Defects on Perovskite Optoelectronic Devices

Performance Parameter Impact of Defects Quantitative Example Reference
External Quantum Efficiency (EQE) Significant reduction due to non-radiative recombination Decrease from 18.7% (passivated) to 7.7% (non-passivated) in QLEDs [5]
Current Efficiency (CE) Lowered efficiency of photon emission per charge carrier Reduction from 75 cd A⁻¹ to 20 cd A⁻¹ in QLEDs [5]
Photoluminescence Quantum Yield (PLQY) Drastic decline in film luminescence Drop from 85% (colloidal) to 43% (film); recoverable to 79% with passivation [5]
Electroluminescence Stability Spectral shift and broadening due to ion migration Bathochromic shift from 461 nm to 466 nm under bias in blue PeLEDs [12]
Operational Lifetime (T₅₀) Severe reduction in device stability Decrease from 15.8 hours to 0.8 hours in QLEDs [5]

Bilateral Interfacial Passivation as a Mitigation Strategy

Fundamental Principles

Bilateral interfacial passivation is an advanced strategy that addresses defects at both the top and bottom (buried) interfaces of the perovskite layer. This approach recognizes that in a sandwich-structured device, both perovskite surfaces interface with charge transport layers and are susceptible to defect formation that affects carrier behavior [5]. The strategy involves applying passivating materials to both interfaces to simultaneously suppress non-radiative recombination and ion migration.

The molecular mechanisms of effective passivation typically involve coordination bonding between passivator functional groups and undercoordinated ions on the perovskite surface. For instance, phosphine oxide groups (P=O) in molecules like TSPO1 strongly coordinate with undercoordinated Pb²⁺ ions, with a calculated binding energy of -1.1 eV [5]. This interaction is particularly effective due to the higher bond order (0.2) compared to other common ligand groups like carboxyl or amidogen, which often show negligible bonding with Pb atoms [5]. Alternative strategies employ electrostatic interactions, where positive charges (e.g., from -NH₃⁺ groups) interact with negative halide ions to suppress their migration, offering a more robust alternative to hydrogen bonding [11].

Beyond simple defect passivation, these interfacial layers also influence the heterointerface energetics. Passivating molecules can introduce interface dipoles that decrease the perovskite work function, causing band bending at the heterojunction that modulates carrier dynamics and enhances electron injection [13]. This synergistic improvement in both defect suppression and energy level alignment makes bilateral passivation particularly effective.

Experimental Evidence and Performance Gains

Substantial experimental evidence demonstrates the efficacy of bilateral passivation strategies. In perovskite QLEDs, implementing a bilateral passivation approach with TSPO1 molecules increased the maximum external quantum efficiency to 18.7%, compared to 7.7% for non-passivated devices [5]. This represents a greater than 2-fold enhancement in EQE, directly attributable to reduced non-radiative recombination at both interfaces.

Similarly impressive gains have been observed in stability metrics. The operational lifetime (T₅₀) of QLEDs with bilateral passivation reached 15.8 hours, representing a 20-fold improvement over control devices (0.8 hours) [5]. In deep-blue PeLEDs based on reduced-dimensional perovskites, an in situ chlorination strategy that passivates multiple defect types increased T₅₀ from 6.5 minutes to 24.9 minutes, a 4-fold enhancement [12]. These improvements stem from the dual role of passivation layers in both reducing initial defect density and providing a barrier against ion migration during operation.

Table 2: Performance Enhancements Achieved Through Bilateral Interface Passivation

Device Type Passivation Strategy Key Improvement Reference
Perovskite QLED Bilateral passivation with TSPO1 EQE: 7.7% → 18.7%; Lifetime: 0.8 h → 15.8 h (20x) [5]
Deep-blue PeLED In situ chlorination with p-FCACl EQE: 3.47% → 6.17%; Stable EL at 454 nm [12]
Pure-blue PeLED MeOEA-TFA additive (electrostatic interaction) EQE: 7.41%; Lifetime: 5x improvement [11]
Perovskite Solar Cell 2D perovskite formation at buried interface PCE: 26.31%; Stability: 95% after 1000h illumination [7]
Red PeLED Intragrain 3D perovskite heterostructure High efficiency and brightness combination [14]

Experimental Protocols

Bilateral Vapor-Phase Passivation of QLED Interfaces

This protocol describes the bilateral passivation of perovskite quantum dot films using organic molecules deposited via thermal evaporation, adapted from the work of Xu et al. [5].

Materials and Equipment
  • Substrate: ITO-coated glass with pre-deposited hole injection layer (HIL)
  • Perovskite QDs: CsPbBr₃ QDs synthesized via hot-injection method
  • Passivation molecule: TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl)
  • Solvent: n-hexane for QD dispersion
  • Equipment: Thermal evaporation system, spin coater, nitrogen glovebox, annealing hotplate
Procedure

  • Substrate Preparation: Clean ITO/HIL substrates with sequential ultrasonic treatment in detergent, deionized water, acetone, and isopropanol. Dry under nitrogen flow and UV-ozone treat for 15 minutes.

  • Bottom Interface Passivation Layer Deposition:

    • Load the substrate into the thermal evaporation chamber.
    • Evaporate TSPO1 at a rate of 0.1-0.2 Å/s under high vacuum (<2×10⁻⁴ Pa) to achieve a thickness of 2-3 nm.
    • Monitor thickness using a quartz crystal microbalance.

  • QD Film Fabrication:

    • Transfer the substrate with bottom passivation layer to a nitrogen-filled glovebox.
    • Prepare CsPbBr₃ QD ink (15 mg/mL in n-hexane).
    • Spin-coat the QD ink at 2000 rpm for 30 seconds.
    • Anneal the film at 70°C for 10 minutes to remove residual solvent.

  • Top Interface Passivation Layer Deposition:

    • Return the sample to the thermal evaporation system.
    • Evaporate a second TSPO1 layer (2-3 nm) using identical parameters.

  • Device Completion:

    • Deposit electron transport layers (TPBi, 35 nm) via thermal evaporation.
    • Evaporate cathode (LiF/Al, 2 nm/100 nm) through a shadow mask.
    • Encapsulate the device with glass lids using UV-curable epoxy in the glovebox.
Characterization and Validation
  • Electrical/Optical: Measure J-V-L characteristics to determine EQE and current efficiency.
  • Film Quality: Conduct TRPL and PLQY measurements to quantify non-radiative recombination reduction.
  • Defect Analysis: Perform SCLC measurements to calculate trap density reduction.

In Situ Chlorination for Defect Passivation in Blue PeLEDs

This protocol details the in situ chlorination (isCl) post-treatment strategy for passivating multiple defects in reduced-dimensional perovskites for deep-blue emission, based on the work published in Light: Science & Applications [12].

Materials
  • Perovskite precursors: CsCl, PbBr₂, PEABr, BABr
  • Solvent: Dimethyl sulfoxide (DMSO)
  • Passivation additive: p-fluorocinnamoyl chloride (p-FCACl)
  • Antisolvent: Chlorobenzene
  • Substrate: ITO/PVK (30 nm)/PVP
Procedure

  • Perovskite Precursor Preparation:

    • Prepare precursor solution by dissolving CsCl (1.1 mmol), PbBr₂ (1.0 mmol), PEABr (0.6 mmol), and BABr (0.4 mmol) in 1 mL DMSO.
    • Stir the solution at 60°C for 2 hours until fully dissolved.

  • Antisolvent/Additive Preparation:

    • Prepare the isCl antisolvent by dissolving p-FCACl (3 mg) in 1 mL chlorobenzene.

  • Film Deposition with isCl Treatment:

    • Spin-coat the perovskite precursor solution onto the substrate at 4000 rpm for 30 seconds.
    • During the spin-coating process, at 15 seconds before completion, dynamically drip 200 μL of the p-FCACl/chlorobenzene solution onto the spinning film.
    • After spinning, anneal the film at 70°C for 10 minutes.

  • Device Fabrication:

    • Transfer the film to a thermal evaporation chamber.
    • Deposit electron transport layer (TPBi, 35 nm).
    • Evaporate Liq (2 nm) and Al (100 nm) as the cathode.
Mechanism and Validation

The isCl treatment simultaneously addresses multiple defect types:

  • p-FCACl hydrolysis produces p-fluorocinnamic acid (p-FCA) and chloride ions.
  • Chloride ions fill halide vacancies in the bulk, inducing blue-shifted emission.
  • Carboxyl groups from p-FCA coordinate with undercoordinated Pb²⁺ ions.
  • Fluorine-derived hydrogen bonds suppress formation of small-n phases and reconstruct phase distribution.

Validation includes NMR spectroscopy to confirm p-FCACl hydrolysis, UPS to measure work function changes, and TREL to demonstrate enhanced radiative recombination and reduced trap-assisted nonradiative recombination.

Visualization of Defect Consequences and Passivation Mechanisms

Defect-Mediated Non-Radiative Recombination Pathway

G cluster_band Perovskite Band Structure CB Conduction Band (CB) VB Valence Band (VB) CB->VB Radiative Recombination TrapState Defect Trap State CB->TrapState Carrier Trapping Photon Photon Emission (Radiative Path) TrapState->VB Non-Radiative Recombination Electron Injected Electron Electron->CB Injection Hole Injected Hole Hole->VB Injection DefectSite Undercoordinated Pb²⁺ Ion DefectSite->TrapState Creates

Defect-Mediated Non-Radiative Recombination - This diagram illustrates how interfacial defects create trap states that capture charge carriers, leading to non-radiative recombination that wastes energy as heat instead of emitting light.

Bilateral Passivation Mechanism

G cluster_effects Passivation Effects Perovskite Perovskite Quantum Dot Film TopPass Top Interface Passivation Layer (TSPO1 Molecules) Perovskite->TopPass HTL Hole Transport Layer (HTL) BottomPass Bottom Interface Passivation Layer (TSPO1 Molecules) HTL->BottomPass ETL Electron Transport Layer (ETL) TopPass->ETL IonMigration Ion Migration Pathway Blocked TopPass->IonMigration Blocks Effect1 • Reduced Trap States • Enhanced PLQY BottomPass->Perovskite Effect2 • Suppressed Ion Migration • Stable EL Spectrum Defect1 Undercoordinated Pb²⁺ Defect1->TopPass P=O Coordination Bond Defect2 Halide Vacancy Defect2->BottomPass Electrostatic Interaction Effect3 • Improved EQE • Extended Lifetime

Bilateral Passivation Mechanism - This diagram shows how passivation layers at both top and bottom interfaces simultaneously address multiple defect types through coordination bonding and electrostatic interactions, blocking ion migration pathways.

The Scientist's Toolkit: Research Reagent Solutions

Table 3: Essential Research Reagents for Interfacial Passivation Studies

Reagent/Material Chemical Structure Primary Function Application Example
TSPO1(Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Phosphine oxide group (P=O) attached to aromatic system Coordinates with undercoordinated Pb²⁺ ions; strong bond order of 0.2; eliminates trap states Bilateral passivation in perovskite QLEDs; vapor deposition at interfaces [5]
MeOEA-TFA(2-Methoxyethylamine trifluoroacetate) Zwitterion with -NH₃⁺ and TFA⁻ groups Electrostatic interaction with halide ions suppresses migration; TFA⁻ passivates Pb defects Additive for quasi-2D mixed Br/Cl pure-blue PeLEDs [11]
p-FCACl(p-fluorocinnamoyl chloride) Aromatic acid chloride with fluorine substituent In situ chlorination source; releases Cl⁻ to fill vacancies; byproduct p-FCA passivates defects Post-treatment for reduced-dimensional perovskites in deep-blue PeLEDs [12]
DDAB(Didodecyl dimethyl ammonium bromide) Quaternary ammonium salt with long alkyl chains Surface passivation ligand for colloidal QDs; enhances PLQY and film formation QD surface engineering during synthesis and film fabrication [5]

The performance and stability of perovskite light-emitting diodes (PeLEDs) are critically determined by the quality and properties of the interfaces within the device architecture. While early research focused predominantly on passivating the top surface of perovskite films, emerging evidence demonstrates that defects at both top and bottom interfaces severely limit device performance. The shift from unilateral to bilateral passivation represents a paradigm shift in perovskite interface engineering, addressing the fundamental reality that perovskite layers in functional devices are sandwiched between charge transport layers, making both interfaces vulnerable to defect formation and non-radiative recombination.

Bilateral passivation simultaneously targets defect sites at both the top and bottom surfaces of the perovskite film, creating a more comprehensive defensive strategy against efficiency and stability losses. This approach has demonstrated remarkable success in enhancing the performance of perovskite-based optoelectronic devices, leading to substantial improvements in external quantum efficiency (EQE), operational lifetime, and color stability. The following sections detail the quantitative evidence, methodological protocols, and mechanistic insights underpinning this transformative strategy.

Quantitative Evidence: Performance Enhancement Through Bilateral Passivation

The implementation of bilateral passivation strategies has yielded demonstrable improvements across key performance metrics for perovskite devices. The table below summarizes representative data from seminal studies implementing dual-sided interface management.

Table 1: Performance Enhancement Through Bilateral Passivation Strategies

Passivation Strategy Device Type Key Performance Metrics Improvement Over Control Reference
Bilateral molecular passivation (TSPO1) Perovskite QLED Maximum EQE: 18.7%Operational Lifetime (T50): 15.8 h EQE: 7.7% → 18.7%Lifetime: 0.8 h → 15.8 h (20x) [5]
Self-regulated bilateral anchoring (Squaric Acid) Perovskite Solar Cell Power Conversion Efficiency: 25.50%Flexible PCE: 24.92% PCE: 23.19% → 25.50% [15]
Cation optimization (NH4SCN + MEO-PEAI) Perovskite Solar Cell VOC: 1.17 VPCE: 24.3%FF: 82.9% Significant enhancement in thermal and illumination stability [16]
Double-sided annealing Flexible Perovskite Solar Module PCE: 19.1%Retained efficiency: >90% after 107 thermal cycles Reduced interfacial voids, improved crystallinity [17]
Buried interface passivation (BIPN) Blade-coated Perovskite Solar Cell PCE: 26.0% (certified 25.7%)Minimodule PCE: 22.5%Stability: No degradation in 2100 h Addressed interfacial delamination in scalable fabrication [18]

The data consistently reveals that bilateral interface management enables superior defect control, leading to remarkable improvements in both efficiency and stability. The photoluminescence quantum yield (PLQY) of perovskite quantum dot films, for instance, increased from 43% to 79% following bilateral passivation with TSPO1 molecules, indicating a significant reduction in non-radiative recombination pathways [5].

Experimental Protocols: Implementing Bilateral Passivation Strategies

Bilateral Molecular Passivation for Perovskite QLEDs

This protocol outlines the procedure for implementing bilateral interfacial passivation using organic molecules such as TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl), adapted from the work described in Nature Communications [5].

Materials Required:

  • Perovskite quantum dot (QD) solution (e.g., CsPbBr3 QDs synthesized via hot-injection)
  • Organic passivation molecules (TSPO1 or alternatives with phosphine oxide functional groups)
  • Charge transport layer materials (e.g., PEDOT:PSS for hole transport, ZnO for electron transport)
  • Substrates (e.g., ITO-coated glass)
  • Solvents for molecular solution preparation (e.g., isopropanol)

Procedure:

  • Substrate Preparation and Bottom Interface Passivation:
    • Clean ITO substrates sequentially with detergent, deionized water, and ethanol via ultrasonication
    • Perform UV-ozone treatment for 15-20 minutes to improve surface wettability
    • Deposit hole transport layer (e.g., PEDOT:PSS) via spin-coating and anneal appropriately
    • Prepare TSPO1 solution in isopropanol (concentration ~0.5-1.0 mg/mL)
    • Spin-coat TSPO1 solution onto the hole transport layer (2000-4000 rpm, 30 seconds)
    • Thermally anneal at 80-100°C for 10 minutes to form a uniform passivation layer

  • Perovskite QD Film Deposition:

    • Deposit perovskite QD solution via spin-coating or blade-coating
    • Use appropriate anti-solvent treatment if required for film formation
    • Anneal at moderate temperatures (70-90°C) to remove residual solvent

  • Top Interface Passivation:

    • Prepare a dilute solution of TSPO1 in isopropanol
    • Spin-coat the passivation solution directly onto the perovskite QD film (2000-3000 rpm, 30 seconds)
    • Anneal gently at 70-80°C for 5-10 minutes to facilitate molecular binding

  • Device Completion:

    • Deposit electron transport layer (e.g., ZnO nanoparticles) via spin-coating
    • Thermally evaporate top electrodes (e.g., Ag or Al) under high vacuum

Validation Measurements:

  • Conduct space charge-limited current (SCLC) measurements to quantify trap density reduction
  • Perform transient absorption spectroscopy to monitor carrier dynamics
  • Measure photoluminescence quantum yield (PLQY) of passivated versus control films
  • Characterize film morphology using scanning electron microscopy (SEM)

Double-Sided Annealing for Flexible Perovskite Films

This protocol describes a double-sided annealing approach to improve the buried interface in flexible perovskite solar cells and modules, adapted from research published in Science Advances [17].

Materials Required:

  • Flexible substrates (e.g., PET/ITO or PEN/ITO)
  • Perovskite precursor solution (e.g., FA0.9Cs0.1PbI3 in DMF/DMSO)
  • Self-assembled monolayer (SAM) solutions (e.g., Me-4PACz)
  • Charge transport materials (e.g., PTAA, C60, BCP)

Procedure:

  • Substrate Preparation:
    • Clean flexible ITO substrates thoroughly with sequential solvent cleaning
    • Apply SAM solution via spin-coating and anneal appropriately
    • Deposit hole transport layer if required

  • Perovskite Deposition:

    • Deposit perovskite precursor solution via blade-coating or spin-coating
    • Initiate crystallization with anti-solvent quenching

  • Double-Sided Annealing:

    • Transfer the wet perovskite film to a specialized annealing station with independent temperature control for top and bottom heaters
    • Set bottom hot plate to optimal temperature (e.g., 125°C for FA0.9Cs0.1PbI3)
    • Set top heater to slightly higher temperature (e.g., 130°C) to account for thermal dissipation
    • Anneal for 10-15 minutes in this configuration
    • The temperature gradient flips the crystallization direction from top-down to bottom-up

  • Device Completion:

    • Deposit electron transport layers (e.g., C60, BCP) via thermal evaporation
    • Evaporate metal electrodes (e.g., Cu) under high vacuum

Key Considerations:

  • The slight temperature difference (5°C) between top and bottom heaters compensates for thermal dissipation
  • Confined DMSO vapor between the two hot plates creates a solvent-annealing effect, promoting grain growth
  • This approach significantly reduces interfacial voids at the buried interface

Self-Regulated Bilateral Anchoring with Squaric Acid

This protocol details the use of squaric acid (SA) as a bilateral anchoring molecule between the SnO2 electron transport layer and the perovskite film, adapted from research in Nano-Micro Letters [15].

Materials Required:

  • SnO2 colloidal dispersion
  • Squaric acid (≥98% purity)
  • Perovskite precursor solution (e.g., (CsPbI3)0.025(FAPbI3)0.825(MAPbBr3)0.15)
  • Standard solvents (DMF, DMSO, isopropanol)

Procedure:

  • Electron Transport Layer Deposition:
    • Deposit SnO2 colloidal solution onto cleaned ITO substrates via spin-coating
    • Anneal at 90°C for 1 hour to form compact SnO2 layer

  • Squaric Acid Interface Modification:

    • Prepare SA solution in deionized water (concentration 5-7 mg/mL)
    • Spin-coat SA solution onto SnO2 layer (4000 rpm, 30 seconds)
    • Anneal at 100°C for 10 minutes to facilitate binding
    • Perform UV-ozone treatment for 20 minutes to clean and activate the surface

  • Perovskite Film Deposition:

    • Deposit perovskite precursor solution via spin-coating in nitrogen environment
    • Use chlorobenzene as anti-solvent during spin-coating
    • Anneal at 105°C for 50 minutes to form crystalline perovskite film

Mechanistic Insights:

  • The four-membered ring conjugated structure of SA enables unique self-transforming properties
  • Dicarboxylic acid groups form hydrogen bonds and coordination bonds with both SnO2 and perovskite
  • This bilateral anchoring releases interfacial stress and constructs stable molecular bridges
  • The approach facilitates efficient electron transport while passivating interfacial defects

Visualization: Mechanisms and Workflows

Bilateral Passivation Mechanism

G cluster_Before Unilateral Passivation (Before) Perovskite Perovskite Layer CTL_Bottom Hole Transport Layer Perovskite->CTL_Bottom Passivated Interface Pass_Bottom Bottom Passivation Layer (Organic Molecules) Perovskite->Pass_Bottom Passivated Interface CTL_Top Electron Transport Layer CTL_Top->Perovskite Defect Interface Pass_Top Top Passivation Layer (Organic Molecules) CTL_Top->Pass_Top Pass_Top->Perovskite Passivated Interface Pass_Bottom->CTL_Bottom Defect_Before_Top Unpassivated Defects (Non-radiative recombination) Defect_Before_Bottom Unpassivated Defects (Non-radiative recombination)

Figure 1: Bilateral versus Unilateral Passivation Mechanism. Bilateral passivation (bottom) applies organic molecules to both top and bottom interfaces of the perovskite layer, unlike unilateral approaches that only address one interface, leaving the other vulnerable to defects and non-radiative recombination.

Experimental Workflow for Bilateral Passivation

G Step1 Substrate Preparation and Cleaning Step2 Bottom Charge Transport Layer Deposition Step1->Step2 Step3 Bottom Interface Passivation Step2->Step3 Step4 Perovskite Layer Deposition Step3->Step4 Step5 Top Interface Passivation Step4->Step5 Step6 Top Charge Transport Layer Deposition Step5->Step6 Step7 Electrode Deposition and Encapsulation Step6->Step7 Step8 Device Characterization and Validation Step7->Step8

Figure 2: Bilateral Passivation Experimental Workflow. The process sequentially addresses both interfaces of the perovskite layer, with passivation steps occurring immediately before and after perovskite deposition.

The Scientist's Toolkit: Research Reagent Solutions

Table 2: Essential Materials for Bilateral Passivation Research

Material Category Specific Examples Function/Mechanism Compatibility Considerations
Phosphine Oxide Passivators TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Strong coordination with uncoordinated Pb2+ sites via P=O group; higher bond order (0.2) compared to carboxyl/amine groups Compatible with various perovskite compositions; soluble in isopropanol for processing [5]
Bilateral Anchoring Molecules Squaric Acid (SA) Forms hydrogen bonds and coordination bonds with both ETL and perovskite; self-transforming nature adapts to different chemical environments Stable in complex chemical environments of perovskite processing; compatible with SnO2 ETL [15]
Cation-Based Passivation Salts NH4SCN, MASCN, EASCN, BASCN SCN− anion improves solubility of organic precursors; facilitates recrystallization and penetration of passivators to buried interface Cation selection critical; NH4+ prevents formation of horizontally oriented 2D layer that hinders charge collection [16]
Polymer Passivation Additives Poly(9-vinylcarbazole) (PVK) Assists perovskite film formation via interface modification; passivates surface defects through functional groups Effective in anti-solvent treatment; enhances color stability in blue PeLEDs [19]
Buried Interface Reinforcers SiO2 nanospheres with 4F-PEACl Mechanical reinforcement alleviates interfacial stress; chemical passivation suppresses defects at buried interface Particularly beneficial for scalable blade-coated films; prevents nanogap formation [18]
Self-Depositing Passivators 1-(4-Fluorophenyl)−2-pyrrolidone (FPP) Forms intermediate phase with perovskite components; self-deposits at bottom surface during top-down crystallization Ideal for large-area blade-coating; enables one-step processing for bottom surface passivation [20]

The transition from unilateral to bilateral passivation represents a critical evolution in perovskite optoelectronics research, addressing the fundamental reality that both interfaces of the perovskite layer significantly impact device performance and stability. The experimental protocols, material systems, and mechanistic insights outlined in this application note provide researchers with comprehensive tools to implement these advanced strategies in their PeLED stability research.

The bilateral approach recognizes that perovskites in functional devices exist in complex heterostructures where both top and bottom interfaces introduce distinct challenges requiring tailored solutions. By simultaneously addressing defect passivation, interfacial stress management, and charge transport optimization at both interfaces, bilateral strategies enable remarkable improvements in device efficiency, operational lifetime, and color stability—key metrics for the commercial viability of PeLED technologies.

As research progresses, the development of novel passivation materials with enhanced binding affinity, improved stability in processing environments, and self-organizing capabilities will further advance bilateral passivation strategies. The integration of these approaches with scalable fabrication techniques represents the next frontier in transitioning high-performance laboratory devices to commercially viable perovskite optoelectronics.

Density Functional Theory (DFT) has emerged as a fundamental computational tool in the development and optimization of perovskite light-emitting diodes (PeLEDs). As a quantum-mechanical modeling method, DFT investigates the electronic structure of many-body systems, making it particularly suited for understanding atomic-scale defects in perovskite materials [21] [22]. The theory operates on the principle that the properties of a many-electron system can be determined using functionals of the spatially dependent electron density, thereby simplifying the complex many-body problem to a more tractable form [22]. For PeLED research, this computational efficiency enables the study of defect formation energies, electronic trap states, and passivation mechanisms at a quantum-mechanical level, providing critical insights that guide experimental efforts toward higher efficiency and stability.

The significance of DFT in advancing bilateral interfacial passivation strategies lies in its ability to model and predict how passivating molecules interact with defective perovskite surfaces at the atomic level. Defects in perovskite materials, particularly undercoordinated Pb²⁺ ions and halide vacancies, create trap states that non-radiatively recombination charge carriers, severely degrading PeLED performance [5] [23]. Bilateral passivation addresses this challenge by applying passivation layers to both top and bottom interfaces of the perovskite film, creating a more comprehensive defect management strategy [5]. DFT calculations provide the theoretical foundation for screening and designing effective passivation molecules by quantifying their binding energies with defect sites, modeling the resulting electronic structure changes, and predicting how these modifications impact device performance and operational stability.

Computational Framework: DFT Methodology for Defect Analysis

Fundamental DFT Principles for Defect Characterization

The application of DFT to defect passivation in perovskites relies on several foundational principles established by the Hohenberg-Kohn theorems and Kohn-Sham equations. The first Hohenberg-Kohn theorem demonstrates that the ground-state properties of a many-electron system are uniquely determined by its electron density, reducing the many-body problem of N electrons with 3N spatial coordinates to just three spatial coordinates [22]. This forms the theoretical basis for using electron density to study defect properties. The Kohn-Sham framework then reduces the intractable many-body problem of interacting electrons to a tractable problem of non-interacting electrons moving in an effective potential, which includes external potential and the effects of Coulomb interactions between electrons [22].

For defect analysis in perovskites, DFT calculations typically employ periodic boundary conditions to model the crystalline structure with defect sites. The formation energy of a defect is calculated as ΔE = Eₜₒₜₐₗ(defect) - Eₜₒₜₐₗ(pristine) - Σnᵢμᵢ, where Eₜₒₜₐₗ represents the total energy from DFT calculations, nᵢ is the number of atoms of type i added or removed to create the defect, and μᵢ is the corresponding chemical potential. The density of states (DOS) is then analyzed to identify trap states induced by defects, with passivation effectiveness quantified by the reduction or elimination of these gap states [5].

Computational Workflow for Passivation Screening

The standard protocol for screening passivation molecules using DFT follows a systematic workflow that integrates computational modeling with experimental validation. The initial step involves constructing atomic models of the perovskite surface with common defect types, particularly undercoordinated Pb²⁺ sites and halide vacancies. For CsPbBr₃ perovskites, this typically involves creating PbBr₂-terminated surfaces with representative defect concentrations [5]. The passivation molecules are then positioned to optimize interaction with these defect sites, with geometry optimization performed to find the most stable configuration.

Key calculations include determining the adsorption energy (Eₐdₛ) between passivation molecules and defect sites using the formula Eₐdₛ = E(perovskite+passivator) - E(perovskite) - E(passivator), where more negative values indicate stronger binding [24]. Density of states (DOS) analysis before and after passivation reveals the electronic structure modifications, particularly the elimination of gap states associated with defects [5]. Additional analyses may include bond order calculations to compare interaction strengths between different functional groups and defect sites [5], charge density difference maps to visualize electron redistribution upon passivation, and projected DOS (PDOS) to identify specific orbital contributions to the electronic structure.

Table 1: Key DFT Calculations for Passivation Molecule Assessment

Calculation Type Physical Significance Interpretation Guide
Adsorption Energy Binding strength between passivator and defect site More negative values indicate stronger, more stable passivation
Density of States (DOS) Electronic structure and trap states Reduction/elimination of band gap states indicates effective passivation
Bond Order Analysis Strength of coordination bonds Higher values indicate more durable passivation effects
Charge Transfer Electron redistribution upon bonding Significant charge transfer indicates strong chemical interaction

G Start Start DFT Passivation Screening Model Construct Defective Perovskite Surface Model Start->Model Molecule Position Passivation Molecule Model->Molecule Optimize Geometry Optimization Molecule->Optimize Eads Calculate Adsorption Energy (Eₐdₛ) Optimize->Eads DOS Compute Density of States (DOS) Eads->DOS Bond Analyze Bond Orders DOS->Bond Validate Experimental Validation Bond->Validate End Promising Passivator Identified Validate->End

Figure 1: DFT workflow for screening passivation molecules

DFT Insights into Bilateral Passivation Mechanisms

Molecular Interactions with Perovskite Defects

DFT calculations have revealed critical insights into how organic passivation molecules interact with defect sites at perovskite interfaces. A fundamental discovery concerns the superior passivation capability of phosphine oxide groups (P=O) compared to other functional groups. Calculations demonstrate that P=O groups form coordination bonds with undercoordinated Pb²⁺ ions with a bond order of approximately 0.2, significantly stronger than the interactions achieved by carboxyl or amino groups [5]. This strong coordination effectively neutralizes trap states by saturating the unsaturated Pb sites, as visualized through density of states plots showing the elimination of gap states after passivation [5].

The adsorption energy between passivation molecules and defect sites serves as a key quantitative metric for predicting passivation effectiveness. For the phosphine oxide molecule TSPO1 used in bilateral passivation strategies, DFT calculations revealed a formation energy of -1.1 eV between Pb and O atoms, indicating a spontaneously occurring and thermodynamically favorable passivation process [5]. This strong interaction not only passivates defects but also prevents ligand loss under electric field stress, addressing a critical instability mechanism in PeLEDs. Additional DFT studies have confirmed that molecules containing multiple functional groups can achieve synergistic passivation effects through combined interactions. For instance, 3,4,5-trifluorobenzamide (TFBZ) demonstrates enhanced passivation through both carbonyl-oxygen coordination with Pb²⁺ and N-H···I hydrogen bonding with halide ions [24].

Bilateral Passivation Concept and DFT Validation

The bilateral passivation strategy represents a significant advancement over conventional single-interface approaches by addressing defects at both the top and bottom interfaces of perovskite quantum dot films [5]. DFT modeling provides the theoretical foundation for this strategy by demonstrating that defect states persist at both interfaces following film assembly, and that comprehensive passivation requires treating both surfaces. The bilateral approach recognizes that in practical PeLED device architectures, the perovskite layer resides between charge transport layers, making both interfaces critical for carrier injection, transportation, and recombination [5].

DFT calculations quantitatively validate the bilateral passivation concept by comparing the electronic structures of unpassivated, unilaterally passivated, and bilaterally passivated interfaces. For CsPbBr₃ quantum dot films, DOS calculations show that unilateral passivation only partially reduces trap states, while bilateral passivation achieves nearly complete elimination of gap states [5]. This electronic-level improvement translates directly to enhanced device performance, with bilaterally passivated devices achieving external quantum efficiencies of 18.7% compared to 7.7% for control devices [5]. The DFT-predicted improvements also extend to operational stability, with calculations showing that strong coordination bonds in bilateral passivation suppress defect regeneration and ion migration pathways, resulting in a 20-fold enhancement in device lifetime [5].

Table 2: DFT-Predicted vs. Experimental Outcomes for Bilateral Passivation

Performance Metric DFT Prediction Experimental Result Improvement Factor
Trap State Density Significant reduction in gap states 79% PLQY vs. 43% control 1.84x
Current Efficiency Improved carrier recombination 75 cd A⁻¹ vs. 20 cd A⁻¹ control 3.75x
External Quantum Efficiency Enhanced radiative efficiency 18.7% vs. 7.7% control 2.43x
Operational Lifetime Suppressed ion migration 15.8 h vs. 0.8 h control 20x

Experimental Protocols for DFT-Guided Passivation

Protocol 1: Bilateral Interfacial Passivation with Organic Molecules

The following protocol details the experimental implementation of bilateral interfacial passivation for perovskite quantum dot LEDs, based on DFT-guided molecule selection and processing techniques.

Materials and Equipment:

  • CsPbBr₃ quantum dots synthesized via hot-injection method
  • Passivation molecules (TSPO1, DBPF, or other DFT-screened compounds)
  • Organic solvents (toluene, ethyl acetate)
  • Substrate (ITO-coated glass)
  • Charge transport materials (PEDOT:PSS, TPBi)
  • Thermal evaporation system
  • Spin coater
  • Glove box with inert atmosphere
  • Annealing oven

Procedure:

  • Substrate Preparation: Clean ITO substrates sequentially with detergent, deionized water, acetone, and isopropanol via ultrasonication for 15 minutes each. Treat with UV-ozone for 20 minutes to improve wettability.

  • Bottom Interface Passivation:

    • Deposit hole transport layer (e.g., PEDOT:PSS) via spin coating at 4000 rpm for 30 seconds, followed by annealing at 150°C for 20 minutes.
    • Thermally evaporate passivation molecule (e.g., TSPO1) to form a 2-5 nm layer on the charge transport layer using a deposition rate of 0.2-0.5 Å/s under high vacuum (<10⁻⁶ Torr).

  • Perovskite QD Film Deposition:

    • Spin-coat CsPbBr₃ QD solution (10 mg/mL in toluene) at 2000 rpm for 30 seconds in a nitrogen-filled glove box.
    • Immediately after deposition, treat with ethyl acetate antisolvent by dripping 200 μL during spinning to remove residual solvents and improve film packing.

  • Top Interface Passivation:

    • Thermally evaporate the same passivation molecule (e.g., TSPO1) to form a 2-5 nm layer directly on the QD film using identical deposition parameters as the bottom layer.

  • Device Completion:

    • Deposit electron transport layer (e.g., TPBi) via thermal evaporation at 1-2 Å/s to a thickness of 40-50 nm.
    • Evaporate metal electrodes (e.g., LiF/Al) through a shadow mask at <10⁻⁶ Torr.
    • Encapsulate completed devices with glass lids using UV-curable epoxy in the glove box.

Validation Measurements:

  • Perform photoluminescence quantum yield (PLQY) measurements to quantify radiative efficiency improvements.
  • Conduct space-charge-limited-current (SCLC) measurements to characterize trap density reduction.
  • Acquire transient absorption spectra to monitor carrier recombination dynamics.
  • Evaluate device performance through current-voltage-luminance characteristics and operational lifetime testing.

Protocol 2: Defect Passivation via Additive Engineering

This protocol describes the incorporation of passivation molecules directly into perovskite precursors or as post-treatment agents, based on DFT-guided additive selection.

Materials:

  • Perovskite precursors (PbI₂, FAI, CsBr, etc.)
  • Passivation additives (5-aminovaleric acid, phenylphosphonic dichloride, DBPF)
  • Solvents (DMSO, DMF, GBL, isopropanol)
  • Substrates with appropriate charge transport layers

Procedure:

  • Additive-incorporated Perovskite Solution Preparation:
    • Prepare standard perovskite precursor solution (e.g., FAxCs1-xPbIyBr3-y in DMF/DMSO mixture).
    • Dissolve DFT-screened passivation additive (e.g., 5-AVA) at optimized concentration (typically 0.5-5 mol% relative to Pb²⁺).
    • Stir the solution for 2-4 hours at 60°C until completely dissolved and homogeneous.

  • Film Deposition with Passivation Additive:

    • Spin-coat the additive-containing perovskite solution in a two-step program: 1000 rpm for 10 seconds (spread) followed by 4000 rpm for 30 seconds (thin).
    • During the second step, apply 200 μL of antisolvent (chlorobenzene or ethyl acetate) 5-10 seconds before program completion to initiate crystallization.

  • Post-Treatment Passivation (Alternative Approach):

    • For already deposited perovskite films, prepare a solution of passivation molecule (e.g., 1-5 mg/mL PPOCl2 in isopropanol).
    • Spin-coat the passivation solution onto the perovskite film at 3000 rpm for 30 seconds.
    • Anneal the treated film at 60-90°C for 5-10 minutes to facilitate bonding with defect sites.

  • Thermal Annealing and Crystallization Control:

    • Anneal the passivated perovskite films at optimized temperature (90-100°C for FAPbI₃, 60-70°C for MAPbI₃) for 15-30 minutes.
    • Control crystallization kinetics by precisely regulating annealing temperature and time based on in-situ absorption monitoring.

Characterization and Validation:

  • Fourier-transform infrared spectroscopy (FTIR) to confirm coordination bonding between passivator and perovskite.
  • X-ray photoelectron spectroscopy (XPS) to analyze chemical states and defect passivation.
  • Time-resolved photoluminescence to quantify carrier lifetime improvements.
  • Grazing-incidence wide-angle X-ray scattering (GIWAXS) to assess crystallinity and phase distribution.

Research Reagent Solutions: DFT-Validated Passivation Materials

Table 3: DFT-Validated Passivation Molecules for PeLED Applications

Passivation Molecule Chemical Functionality DFT-Validated Mechanism Application Method Reported Efficacy
TSPO1 Phosphine oxide (P=O) Coordination with undercoordinated Pb²⁺ (Eₐdₛ = -1.1 eV) [5] Bilateral thermal evaporation EQE: 18.7%, Lifetime: 15.8 h [5]
DBPF Alkyl phosphate groups Pb²⁺ defect passivation without affecting crystallization [25] Bulk and surface passivation EQE: >22%, 85% EQE retention at 85°C [25]
5-AVA Amino and carboxyl groups Lewis acid-base interaction with Pb²⁺, crystallization control [26] Additive engineering EQE: 9% (red PeLEDs) [26]
PPOCl₂ Phosphonic dichloride Pb²⁺ passivation + Cl⁻ incorporation for blue shift [23] Dynamic treatment EQE: 2.31% (deep-blue PeLEDs) [23]
TFBZ Trifluorobenzamide Enhanced adsorption on perovskite surfaces (Eₐdₛ = -0.941 eV) [24] Multifunctional additive VOC: 1.28 V (PSCs), PCE: 29.01% (tandems) [24]

G Perovskite Perovskite Surface With Defects PTO TSPO1 Phosphine Oxide Perovskite->PTO DBPF DBPF Alkyl Phosphate Perovskite->DBPF AVA 5-AVA Amino/Carboxyl Perovskite->AVA PPO PPOCl₂ Phosphonic Dichloride Perovskite->PPO TFBZ TFBZ Trifluorobenzamide Perovskite->TFBZ Mechanism1 Strong Coordination with Pb²⁺ (Bond Order: 0.2) PTO->Mechanism1 Mechanism2 Defect Passivation Without Crystallization Impact DBPF->Mechanism2 Mechanism3 Lewis Acid-Base Interaction + Crystallization Control AVA->Mechanism3 Mechanism4 Dual Passivation + Halide Exchange PPO->Mechanism4 Mechanism5 Enhanced Adsorption + Hydrogen Bonding TFBZ->Mechanism5 Result1 Trap State Reduction Improved EQE & Stability Mechanism1->Result1 Result2 Suppressed Thermal Quenching >85% EQE at 85°C Mechanism2->Result2 Result3 Improved Crystallization Efficient Red Emission Mechanism3->Result3 Result4 Blue Emission Shift Defect Passivation Mechanism4->Result4 Result5 Enhanced VOC & PCE Stability Improvement Mechanism5->Result5

Figure 2: DFT-validated passivation mechanisms and outcomes

The integration of Density Functional Theory with experimental materials science has fundamentally advanced the development of defect passivation strategies for perovskite optoelectronics. DFT provides the crucial theoretical foundation for understanding passivation mechanisms at the atomic level, enabling rational design of bilateral passivation approaches that simultaneously address multiple degradation pathways in PeLEDs. The continued refinement of exchange-correlation functionals, combined with more accurate modeling of disordered interfaces and dynamic processes, will further enhance the predictive power of DFT calculations.

Future directions in DFT-guided passivation research include the development of multi-functional molecules that simultaneously passivate various defect types while improving interfacial properties, the design of stereoscopic passivation networks that penetrate grain boundaries, and the creation of adaptive passivation layers that self-heal under operational stress. Machine learning-assisted high-throughput screening of passivation molecules using DFT descriptors will dramatically accelerate materials discovery, potentially identifying entirely new passivation paradigms beyond current Lewis acid-base approaches. As both computational and experimental techniques continue to advance, the synergy between DFT modeling and practical device engineering will remain essential for achieving the full potential of perovskite light-emitting technologies.

Implementing Bilateral Passivation: Materials, Methods, and Mechanisms

Defect passivation is a critical strategy for enhancing the performance and operational stability of perovskite light-emitting diodes (PeLEDs). While perovskite materials are known for their defect tolerance, surface defects and grain boundaries act as centers for non-radiative recombination, which severely degrades photoluminescence quantum yield (PLQY), device efficiency, and stability [27]. Furthermore, these defects provide pathways for ion migration, a key factor behind the rapid degradation of PeLEDs under electrical bias [28]. A sophisticated passivation material toolkit has therefore been developed to mitigate these issues.

This document details the application of various passivation materials—spanning organic molecules, inorganic salts, and low-dimensional perovskites—within the specific context of a bilateral interfacial passivation strategy. This approach targets defects at both the top and bottom interfaces of the perovskite emissive layer, which is particularly effective for improving carrier injection, suppressing non-radiative recombination, and enhancing overall device stability [5].

Passivation Material Toolkit

The following table summarizes key passivation materials, their molecular targets, and the resulting impacts on PeLED performance.

Table 1: Passivation Material Toolkit for PeLEDs

Material Class & Example Chemical Formula / Structure Defect Target / Primary Function Key Performance Outcomes Citations
Phosphine OxidesTSPO1 Diphenylphosphine oxide-4-(triphenylsilyl)phenyl Passivates under-coordinated Pb²⁺ ions via P=O group; Bilateral interfacial layer. ↑ EQE from 7.7% to 18.7%;↑ Operational lifetime by 20x (0.8 h to 15.8 h). [5]
Alkylammonium SaltsPhenylpropylammonium Iodide (PPAI) C₉H₁₄IN Suppresses Iodide (I⁻) ion migration via steric hindrance & surface binding; Reduces surface defects. EQE of 17.5%;Record T50 @ 100 mA cm⁻²: 130 h;Radiance of 1282.8 W sr⁻¹ m⁻². [28]
Multifunctional AdditivesTriethyl 2-acetylcitrate (TEAC) C₁₄H₂₂O₈ Passivates multiple bromine vacancies via four C=O groups; Narrows phase distribution in quasi-2D perovskites. Sky-blue EQE: 18.5%;Current Efficiency: 29.1 cd A⁻¹;↑ Operational lifetime by 25x. [29]
Phosphate AdditivesDBPF C₂₉H₄₂Br₂O₆P₂ Passivates coordination-unsaturated Pb²⁺ defects in bulk and surface; Suppresses exciton-phonon coupling. EQE > 22%;Maintains ~85% of initial EQE at 85°C (vs. 17% for control). [25]
Aromatic SulfonatesSodium 2-Naphthalene Sulfonate (b-NA) C₁₀H₇NaO₃S Coordinates with perovskite via S=O group; Optimizes phase distribution and passivates surface defects. ↑ Maximum brightness & EQE ( > 2x increase);↑ T50 from 70.1 min to 168.5 min. [30]
Phenanthroline-Based MoleculesBUPH1 C₃₆H₂₂N₄ Bidentate coordination to under-coordinated Pb²⁺ via N atoms; Suppresses halide migration. Pure-blue (472 nm) EQE: 3.10% (for thermally evaporated PeLEDs);Excellent spectral stability. [31]

Research Reagent Solutions

Table 2: Essential Research Reagents and Materials

Reagent/Material Function/Application in PeLED Research
TSPO1 A model phosphine oxide for creating a bilateral passivation layer. Used to demonstrate the critical importance of passivating both top and bottom interfaces of the perovskite QD film.
Phenylalkylammonium Iodides (PMAI, PEAI, PPAI, PBAI) A homologous series for studying the structure-function relationship in surface passivation. The alkyl chain length modulates the steric hindrance against ion migration and binding affinity to the perovskite surface.
Triethyl 2-acetylcitrate (TEAC) A multifunctional additive for quasi-2D blue PeLEDs. Its four carbonyl (C=O) groups enable simultaneous passivation of multiple defects while also regulating the crystal phase distribution for stable blue emission.
DBPF A passivation agent with flexible solubility, allowing for selective bulk or surface passivation. Its phosphonate groups effectively passivate Pb²⁺ defects without altering the perovskite crystallization kinetics.
Sodium 2-Naphthalene Sulfonate (b-NA) A short-chain aromatic sulfonate used to optimize the phase distribution (n-value) in quasi-2D perovskite films and passivate surface defects, leading to improved film quality and thermal stability.
BUPH1 A phenanthroline-based small molecule compatible with thermal evaporation. Its bidentate coordination mode makes it highly effective for in situ passivation during vacuum deposition of perovskite films.

Experimental Protocols

Protocol 1: Bilateral Interfacial Passivation with TSPO1

This protocol is adapted from a strategy that drastically enhanced the efficiency and stability of perovskite quantum-dot light-emitting diodes (QLEDs) [5].

Key Steps:

  • Substrate Preparation: Clean the substrate (e.g., ITO/glass) with subsequent oxygen plasma treatment.
  • Deposit Bottom Charge Transport Layer (CTL): Spin-coat the bottom electron/hole transport layer as required by the device architecture and anneal.
  • Evaporate Bottom Passivation Layer: Transfer the substrate to a thermal evaporation chamber. Evaporate a thin, continuous layer of TSPO1 molecules onto the bottom CTL.
  • Assemble Perovskite QD Film: Spin-coat the colloidal perovskite quantum dot (QD) ink (e.g., CsPbBr₃ QDs) onto the TSPO1-coated substrate to form the emissive film.
  • Evaporate Top Passivation Layer: Without breaking vacuum (or after careful transfer), evaporate a second layer of TSPO1 molecules directly onto the top surface of the QD film.
  • Complete Device Fabrication: Deposit the top charge transport layer and the metal electrode (e.g., Au).

Critical Notes:

  • The bilateral (top and bottom) passivation is crucial. Comparison experiments showed that unilateral passivation was insufficient for achieving the maximum performance gains [5].
  • The interaction between the P=O group of TSPO1 and under-coordinated Pb²⁺ ions on the QD surface is the fundamental passivation mechanism, which calculations show has a forming energy of -1.1 eV [5].

Protocol 2: Surface Treatment with Phenylalkylammonium Salts

This protocol describes surface treatment to suppress ion migration and enhance the operational lifetime of 3D PeLEDs [28].

Key Steps:

  • Perovskite Film Formation: Fabricate the 3D perovskite film (e.g., FA₀.₈₃Cs₀.₁₇PbI₃) via one-step or two-step spin-coating method and anneal.
  • Prepare Passivation Solution: Dissolve the phenylalkylammonium iodide salt (e.g., PPAI) in anhydrous chloroform to form a dilute solution (e.g., 0.5 mg mL⁻¹).
  • Surface Treatment: While the perovskite film is still on the spin-coater, dynamically spin-coat the PPAI solution onto the perovskite surface.
  • Post-Treatment Annealing: Anneal the film on a hotplate at ~70°C for 5-10 minutes to remove the residual solvent.
  • Complete Device Fabrication: Proceed with the deposition of subsequent organic transport layers and metal electrodes.

Critical Notes:

  • The alkyl chain length (n) matters. Systematic studies show that PPAI (n=3) offers an optimal balance between strong surface binding, effective defect passivation, and high anchoring density, leading to the best device stability [28].
  • This treatment does not form a distinct 2D perovskite layer but effectively binds to the 3D perovskite surface, suppressing I⁻ ion migration through a combination of Coulombic interactions and steric hindrance.

Workflow and Mechanism Diagrams

The following diagram illustrates the strategic workflow for selecting and implementing a passivation strategy, based on the identified performance-limiting factors in PeLEDs.

G Fig. 1: Passivation Strategy Decision Workflow Start Identify Performance Limiter A Low EQE/PLQY (High Non-Radiative Recombination) Start->A B Poor Operational Stability (Rapid Efficiency Roll-Off) Start->B C Unstable Blue Emission/ Phase Segregation Start->C SubA1 Target: Under-coordinated Pb²⁺ Ionic/Point Defects A->SubA1 SubA2 Primary Strategy: Defect Passivation A->SubA2 SubB1 Target: Halide Ion Migration & Interface Degradation B->SubB1 SubB2 Primary Strategy: Ion Migration Suppression B->SubB2 SubC1 Target: Wide Phase Distribution & Halide Vacancies C->SubC1 SubC2 Primary Strategy: Phase Control & Defect Passivation C->SubC2 Tool1 Apply Phosphine Oxides (TSPO1) Apply Phosphate Additives (DBPF) Apply Phenanthrolines (BUPH1) SubA2->Tool1 e.g. Tool2 Apply Phenylalkylammonium Salts (PPAI) Apply Zwitterions SubB2->Tool2 e.g. Tool3 Apply Multifunctional Additives (TEAC) Apply Aromatic Sulfonates (b-NA) SubC2->Tool3 e.g. Outcome Enhanced PeLED: High EQE, Superior Stability Tool1->Outcome Tool2->Outcome Tool3->Outcome

The core mechanism of action for many organic passivation molecules involves coordination bonding between functional groups with lone-pair electrons and defect sites on the perovskite surface, as depicted below.

G Fig. 2: Molecular Passivation Mechanisms cluster_1 Passivation Mechanism cluster_2 Functional Outcome Perov Perovskite Surface/Lattice (Under-coordinated Pb²⁺, Halide Vacancy) Mech1 Lone Pair Donation (P=O, C=O, S=O) Perov->Mech1 Mech2 Bidentate Chelation (Phenanthrolines) Perov->Mech2 Mech3 Steric Hindrance (Alkylammonium Chains) Perov->Mech3 Out1 Defect Passivation ↓ Trap States Mech1->Out1 Mech2->Out1 Out3 Blocked Ion Migration Pathways Mech3->Out3 Out2 Suppressed Non-Radiative Recombination Out1->Out2 Final Improved Device Performance ↑ PLQY, ↑ EQE, ↑ Operational Lifetime Out2->Final Out3->Final

Deposition and Processing Techniques for Top and Bottom Interface Engineering

In perovskite light-emitting diodes (PeLEDs), the light-emitting perovskite layer is situated in a sandwich-like device architecture, making both its top and bottom interfaces with charge transport layers (CTLs) critically important. A bilateral interfacial passivation strategy involves the simultaneous application of passivation materials to both the top and bottom surfaces of the perovskite film. This approach has proven markedly superior to unilateral passivation, as it comprehensively addresses defect states at all critical interfaces, leading to drastic enhancements in both device efficiency and operational stability. The fundamental principle relies on using organic or inorganic materials to coordinate with undercoordinated ions (e.g., Pb²⁺) at the perovskite surface, thereby eliminating deep trap states that serve as non-radiative recombination centers [5] [10].

The impact of this strategy is profound. Research has demonstrated that bilateral passivation can increase the photoluminescence quantum yield (PLQY) of perovskite quantum dot (QD) films from 43% to 79% [5]. This translates directly into enhanced device performance, with reported maximum external quantum efficiency (EQE) rising from 7.7% to 18.7% and current efficiency surging from 20 cd A⁻¹ to 75 cd A⁻¹ [5]. Moreover, the operational lifetime of QLEDs can be enhanced by 20-fold, reaching 15.8 hours, underscoring the critical importance of managing both interfaces for commercial viability [5].

Quantitative Performance Comparison of Interface Engineering Strategies

The table below summarizes key quantitative data from studies implementing top, bottom, and bilateral interface engineering, highlighting the significant performance gains achieved through a complete bilateral approach.

Table 1: Quantitative Performance Outcomes of Interface Engineering Strategies in PeLEDs

Passivation Strategy Device Architecture Key Performance Metrics Stability (T₅₀ Operational Lifetime) Citation
Bilateral Passivation (TSPO1 on both interfaces) Perovskite QLED EQE: 18.7%; Current Efficiency: 75 cd A⁻¹; Film PLQY: 79% 15.8 hours (20x enhancement) [5]
Unilateral Passivation Perovskite QLED EQE: 7.7%; Current Efficiency: 20 cd A⁻¹; Film PLQY: 43% 0.8 hours (Baseline) [5]
Dual Passivation Additive (DPPA in quasi-2D film) Blue Quasi-2D PeLED EQE: 12.31% Enhanced by 32% [32]
Lewis Base Additive Green Quasi-2D PeLED Film PLQY: >80% (near-unity) Not Specified [32]

Deposition Techniques for Top Interface Engineering

The top interface refers to the surface of the perovskite film exposed to the subsequent charge transport layer. Passivation here must be effective without damaging the underlying perovskite.

Thermal Evaporation of Small Molecules
  • Protocol: Thermal Evaporation of TSPO1
    • Principle: This dry process involves the sublimation and controlled deposition of organic molecules under high vacuum, preventing solvent-induced damage to the perovskite layer [5].
    • Materials: Diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1), thermal evaporation system, high-vacuum chamber (<10⁻⁶ Torr).
    • Step-by-Step Procedure:
      • After depositing the perovskite QD film via spin-coating, load the substrate into the evaporation chamber.
      • Pump down the chamber to a high vacuum (base pressure < 5 × 10⁻⁶ Torr).
      • Load TSPO1 powder into a clean, resistively heated evaporation crucible (boat).
      • Gradually increase the current to the crucible to heat the TSPO1 material. Control the deposition rate precisely at 0.1-0.3 Å/s using a quartz crystal microbalance.
      • Deposit a thin layer of TSPO1 with a target thickness of 5-10 nm.
      • Complete the process by subsequently depositing the required electron transport layer (ETL) and cathode via thermal evaporation without breaking vacuum [5].
Solution-Processed Top Interface Passivation
  • Protocol: Spin-Coating of Passivation Molecules
    • Principle: A mild solvent that does not dissolve the perovskite layer is used to deposit a solution containing passivation molecules.
    • Materials: Passivation molecule (e.g., phosphine oxide, zwitterionic molecules), orthogonal solvent (e.g., hexane, chlorobenzene), spin coater.
    • Step-by-Step Procedure:
      • Prepare a solution of the passivation molecule in an orthogonal solvent at a typical concentration of 0.5-2 mg/mL.
      • After perovskite film formation, dynamically spin-coat the passivation solution onto the film (e.g., 3000 rpm for 30 seconds).
      • Anneal the film on a hotplate at a mild temperature (60-80°C) for 5-10 minutes to remove residual solvent.

Deposition Techniques for Bottom Interface Engineering

Bottom interface engineering involves modifying the substrate or hole transport layer (HTL) before depositing the perovskite layer, setting the stage for high-quality perovskite growth.

Self-Assembled Monolayer (SAM) Deposition
  • Protocol: Formation of a SAM on ITO/HTL
    • Principle: Molecules with anchor groups chemisorb onto the substrate, creating a closely packed monolayer that modulates surface energy and passifies interfacial traps [10].
    • Materials: SAM molecule solution (e.g., MeO-2PACz, Br-2PACz), ITO or metal oxide substrate, polar solvent (e.g., ethanol).
    • Step-by-Step Procedure:
      • Thoroughly clean the ITO/glass substrate with sequential ultrasonic baths in detergent, deionized water, acetone, and isopropanol (15 minutes each). Treat with UV-ozone for 15-20 minutes.
      • Prepare a dilute solution of the SAM molecule in ethanol (e.g., 1-5 mM).
      • Spin-coat the SAM solution onto the clean substrate at 3000 rpm for 30 seconds, or dip-coat the substrate in the solution for several hours.
      • Rinse the substrate thoroughly with clean ethanol to remove physisorbed molecules.
      • Anneal the substrate at 100°C for 10 minutes to improve molecular ordering and adhesion.
Pre-deposition of Vacuum-Processed Interlayers
  • Protocol: Thermal Evaporation of TSPO1 on HTL
    • Principle: A thin layer of a passivation material is deposited on the bottom charge transport layer before perovskite deposition, creating a favorable interface for nucleation and growth [5].
    • Materials: TSPO1 or similar molecule, thermal evaporation system.
    • Procedure: The process is identical to the top interface evaporation protocol (Section 3.1), but is performed directly on the HTL-coated substrate. After depositing the TSPO1 interlayer, the substrate is transferred to a nitrogen glovebox for the subsequent solution-processing of the perovskite layer.

The Scientist's Toolkit: Essential Research Reagents & Materials

Table 2: Key Reagents and Materials for Bilateral Interface Engineering

Material/Reagent Function/Application Key Properties & Mechanism
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Bilateral passivation interlayer, deposited via thermal evaporation [5]. P=O group coordinates strongly with undercoordinated Pb²⁺; high bond order (0.2) for stable passivation; wide energy gap for charge blocking [5].
DPPA (Diphenylphosphoramide) Dual passivation additive for quasi-2D perovskite films [32]. Phosphine oxide group passivates Pb²⁺; amino group forms hydrogen bonds with halides to inhibit migration [32].
DDAB (Didodecyldimethylammonium bromide) Surface ligand for colloidal QDs and surface passivation [5]. Provides halide ions to passivate halide vacancies; long alkyl chains improve film hydrophobicity and stability [5].
MeO-2PACz Self-assembled monolayer (SAM) for bottom interface engineering [10]. Anchor group binds to ITO; functional group modulates surface energy and work function for improved hole injection and perovskite growth [10].
Orthogonal Solvents (e.g., Hexane, Chlorobenzene) Solvent medium for top interface solution-processing. Dissolves passivators but does not dissolve the underlying perovskite film, enabling non-destructive deposition.

Experimental Workflows & Signaling Pathways

The following diagrams illustrate the logical sequence and mechanistic pathways involved in bilateral interface engineering for PeLEDs.

G Start Start: Substrate/HTL Preparation Step1 Bottom Interface Engineering (SAM Deposition or TSPO1 Evaporation) Start->Step1 Step2 Perovskite Layer Deposition (Spin-coating/Solution Processing) Step1->Step2 Step3 Perovskite Film Annealing Step2->Step3 Step4 Top Interface Engineering (TSPO1 Evaporation or Solution Passivation) Step3->Step4 Step5 ETL & Cathode Deposition (Evaporation) Step4->Step5 End End: Device Encapsulation & Testing Step5->End

Diagram 1: Bilateral Passivation Device Fabrication Workflow. This workflow outlines the key steps for fabricating a PeLED with bilateral passivation, highlighting the stages for both bottom and top interface engineering.

G Problem Non-Passivated Interface Uncoordinated Pb²⁺ ions Halide Vacancies (Vₓ) Mechanism Passivation Mechanism Lewis Base Coordination (e.g., P=O → Pb²⁺) Problem->Mechanism Outcome Passivated Interface Defect States Eliminated Blocked Ion Migration Mechanism->Outcome Result Enhanced Device Performance ↑ PLQY ↑ EQE ↑ Stability Outcome->Result

Diagram 2: Molecular Passivation Mechanism Pathway. This pathway illustrates the fundamental process from the presence of interfacial defects to the final performance enhancement achieved through molecular passivation.

Bilateral interfacial passivation has emerged as a transformative strategy for enhancing the performance and operational stability of perovskite light-emitting diodes (PeLEDs). This approach involves the simultaneous modification of both the top and bottom interfaces of the perovskite emitter layer, addressing critical degradation pathways that originate at these vulnerable points. Unlike unilateral passivation methods, bilateral strategies provide comprehensive defect management and stability enhancement by creating a robust molecular bridge between the perovskite layer and adjacent charge transport layers. The fundamental chemical mechanisms underpinning this technology—coordination bonding, defect healing, and energy level alignment—work synergistically to suppress non-radiative recombination, inhibit ion migration, and facilitate efficient charge carrier transport [5].

The significance of bilateral passivation stems from the inherent susceptibility of perovskite interfaces to defect formation during device fabrication and operation. These interfacial defects act as trapping centers for charge carriers, promoting energy loss through heat rather than light emission. Furthermore, they serve as initiation points for perovskite degradation under electrical bias and environmental stress. By employing targeted molecular designs that engage in specific chemical interactions with perovskite constituents, bilateral passivation effectively heals these defects while establishing optimized energy landscapes for charge injection and recombination [5] [25].

Core Chemical Mechanisms

Coordination Bonding

Coordination bonding represents the primary chemical interaction responsible for effective passivation at perovskite interfaces. This mechanism involves the donation of electron pairs from passivator molecules to undercoordinated metal ions (typically Pb²⁺) on the perovskite surface, forming stable coordinate covalent bonds. The strength and stability of these bonds directly influence the efficacy and durability of the passivation effect [5].

Phosphine oxide functional groups, exemplified by molecules such as diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1), demonstrate particularly strong coordination with Pb²⁺ ions. Density functional theory (DFT) calculations reveal a substantial binding energy of -1.1 eV for the Pb-O=P interaction, indicating a thermodynamically favorable process. Bond order analysis further confirms the superiority of phosphine oxide groups (bond order: 0.2) compared to other potential passivating moieties such as carboxyl or amine groups, which show negligible bond formation with Pb²⁺. This robust coordination capability enables the formation of stable passivation layers that resist dissociation under operational electric fields and thermal stress [5].

Alternative coordination motifs have also been explored effectively. Squaric acid (SA) utilizes its dicarboxylic acid groups to establish coordination bonds with perovskite constituents, facilitating a self-regulated bilateral anchoring effect. Similarly, 2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl)-fluorene (DBPF) employs alkyl phosphate groups with optimized coordination strength that passivate defects without interfering with perovskite crystallization kinetics. The strategic selection of coordination groups with appropriate binding strength is crucial—too weak and the passivation is ineffective; too strong and it disrupts the perovskite crystal lattice [25] [15].

Table 1: Comparison of Coordination Group Effectiveness for Pb²⁺ Passivation

Functional Group Example Molecule Bond Order with Pb²⁺ Binding Energy (eV) Passivation Efficacy
Phosphine oxide TSPO1 0.20 -1.1 Excellent
Alkyl phosphate DBPF Not specified Not specified Excellent
Carboxylic acid Squaric Acid Not specified Not specified Good
Carboxyl Oleic acid 0.00 Not specified Poor
Amidogen Oleylamine 0.00 Not specified Poor

Defect Healing

Defect healing through bilateral passivation primarily targets coordination-unsaturated Pb²⁺ sites and halide vacancies at perovskite interfaces. These defects create electronic states within the bandgap that act as non-radiative recombination centers, reducing luminescence efficiency and promoting ion migration. The healing process involves the functional groups of passivator molecules coordinating with these defect sites, effectively neutralizing their trap states and restoring the electronic structure of the pristine perovskite lattice [5] [25].

DFT calculations of density of states (DOS) provide direct evidence of defect healing. Unpassivated perovskite surfaces show significant trap states at the band edges corresponding to undercoordinated Pb²⁺ atoms. After bilateral passivation with TSPO1, these trap states are substantially diminished, indicating successful defect neutralization. Experimental validation comes from space charge-limited current (SCLC) measurements, which show reduced trap density in passivated devices. Additionally, transient absorption spectroscopy reveals decreased carrier trapping rates in bilaterally passivated films, confirming the mitigation of non-radiative recombination pathways [5].

The defect healing effect translates directly to enhanced photophysical properties. Perovskite quantum dot films subjected to bilateral passivation exhibit remarkable increases in photoluminescence quantum yield (PLQY)—from 43% to 79% in one study—demonstrating the effectiveness of this approach in restoring radiative recombination efficiency. Furthermore, defect healing significantly suppresses thermal quenching by reducing defect-mediated exciton-phonon coupling. Passivated PeLEDs maintain approximately 85% of their initial external quantum efficiency (EQE) at 85°C, compared to only 17% for control devices, highlighting the critical role of defect management in thermal stability [5] [25].

Energy Level Alignment

Bilateral passivation strategically modifies the energy level alignment at perovskite/charge transport layer interfaces to facilitate efficient charge injection and recombination. Passivator molecules with appropriate electronic structures can induce favorable band bending and create intermediate energy states that serve as stepping stones for charge carriers, reducing injection barriers and minimizing interface recombination losses [15].

Ultraviolet photoelectron spectroscopy (UPS) analyses reveal that effective passivators like squaric acid modify the work function of adjacent layers and create dipole moments at interfaces, leading to more aligned energy levels between the perovskite emitter and charge transport layers. This optimized alignment enhances charge injection efficiency while blocking counter carriers, effectively confining excitons within the emission layer. The resulting improvement in charge balance directly boosts the electroluminescence efficiency of PeLEDs [15].

The bilateral implementation of energy level modification is particularly advantageous as it addresses both electron and hole injection simultaneously. For instance, in perovskite quantum dot LEDs, bilateral passivation with TSPO1 increased the maximum external quantum efficiency from 7.7% to 18.7% and current efficiency from 20 to 75 cd A⁻¹. Similarly, squaric acid modification at the buried interface improved the power conversion efficiency of perovskite solar cells from 23.19% to 25.50%, demonstrating the broad applicability of optimized energy level alignment across perovskite optoelectronics [5] [15].

G Energy Level Alignment Mechanism Width: 760px cluster_alignment Bilateral Passivation Improves Energy Level Alignment cluster_before cluster_after HTL_before HTL Perovskite_before Perovskite Emitter ETL_before ETL HTL_after HTL Passivation_top Passivation Layer Perovskite_after Perovskite Emitter Passivation_bottom Passivation Layer ETL_after ETL HOMO_HTL_b HOMO LUMO_HTL_b LUMO HOMO_Perov_b HOMO LUMO_HTL_b->HOMO_Perov_b Large Barrier LUMO_Perov_b LUMO HOMO_ETL_b HOMO LUMO_Perov_b->HOMO_ETL_b Large Barrier LUMO_ETL_b LUMO HOMO_HTL_a HOMO LUMO_HTL_a LUMO HOMO_Perov_a HOMO LUMO_HTL_a->HOMO_Perov_a Reduced Barrier LUMO_Perov_a LUMO HOMO_ETL_a HOMO LUMO_Perov_a->HOMO_ETL_a Reduced Barrier LUMO_ETL_a LUMO Before Before Passivation After After Bilateral Passivation

Quantitative Performance Metrics

The efficacy of bilateral interfacial passivation is quantitatively demonstrated through significant enhancements in key device performance parameters. The implementation of coordinated defect healing and energy level alignment at both interfaces of the perovskite layer leads to remarkable improvements in efficiency metrics and operational stability across various perovskite material systems.

Table 2: Performance Enhancement Through Bilateral Passivation in PeLEDs

Performance Parameter Control Device Bilaterally Passivated Device Improvement Factor
Maximum EQE (%) 7.7 18.7 2.4×
Current Efficiency (cd A⁻¹) 20 75 3.8×
Operational Lifetime T₅₀ (h) 0.8 15.8 20×
PLQY of Film (%) 43 79 1.8×
EQE Retention at 85°C (%) 17 85 5×

The performance enhancements extend beyond PeLEDs to perovskite photovoltaics. Bilateral passivation using squaric acid at the SnO₂/perovskite interface increased power conversion efficiency from 23.19% to 25.50% in rigid devices and enabled flexible devices to reach 24.92% efficiency. The stability improvements were equally impressive, with passivated devices maintaining performance under combined humidity, thermal, and light stress conditions. This demonstrates the universal benefit of bilateral interface management across different perovskite optoelectronic applications [15].

The operational lifetime enhancement is particularly noteworthy. The 20-fold increase in T₅₀ lifetime (from 0.8 to 15.8 hours) for bilaterally passivated PeLEDs underscores the critical role of interface stabilization in mitigating degradation pathways. This lifetime extension originates from the combined effects of suppressed ion migration, reduced non-radiative recombination, and inhibited interface chemical reactions, all facilitated by the comprehensive passivation of both top and bottom perovskite surfaces [5].

Experimental Protocols

Bilateral Passivation of Perovskite QLEDs

Materials: CsPbBr₃ quantum dots synthesized via hot-injection method; TSPO1 (≥98% purity) as passivation molecule; appropriate charge transport materials for device architecture (e.g., TiO₂, ZnO, NPB, TFB); substrate (ITO-coated glass); anhydrous solvents for processing [5].

QD Film Preparation:

  • Synthesize CsPbBr₃ QDs via hot-injection method following standard protocols, achieving uniform cubic morphology with size ~8 nm.
  • Prepare QD ink by dispersing in non-polar solvent at appropriate concentration (typically 10-20 mg/mL).
  • Deposit QD layer onto substrate via spin-coating: 1000-3000 rpm for 30-60 seconds in nitrogen atmosphere.
  • Anneal QD film at 70-90°C for 10-20 minutes to remove residual solvent [5].

Bilateral Passivation Procedure:

  • Bottom Interface Passivation:
    • Prepare TSPO1 solution in anhydrous alcohol (concentration: 0.5-2 mg/mL).
    • Spin-coat onto substrate prior to QD deposition (2000-4000 rpm, 30 seconds).
    • Anneal at 80-100°C for 10 minutes to form uniform bottom passivation layer.
  • Top Interface Passivation:
    • After QD film formation, deposit TSPO1 layer via thermal evaporation.
    • Optimize thickness to 5-15 nm using calibrated deposition rate (0.1-0.3 Å/s).
    • Alternatively, use spin-coating from mild solvent that doesn't dissolve QD layer [5].

Characterization and Validation:

  • FTIR Spectroscopy: Confirm coordination bonding through shift in P=O stretching peak (~1230 cm⁻¹).
  • XPS Analysis: Measure binding energy shifts in Pb 4f peaks (shift to lower energy indicates passivation).
  • PLQY Measurement: Verify enhancement in film luminescence efficiency (typically increases from ~40% to ~80%).
  • SCLC Measurements: Quantify trap density reduction in electron-only and hole-only devices.
  • Device Fabrication: Complete LED structure with appropriate charge injection layers and electrodes [5].

Defect Passivation for Thermal Quenching Suppression

Materials: Quasi-2D perovskite PEA₂FAₙ₋₁PbₙBr₃ₙ₊₁ with n = 5; DBPF passivation agent; dimethyl sulfoxide (DMSO); ethyl acetate (EA) [25].

Passivation Agent Synthesis:

  • Synthesize 2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl)-fluorene (DBPF) following published procedures.
  • Purify via column chromatography and characterize by NMR and mass spectrometry.
  • Confirm molecular structure and purity before use [25].

Bulk Passivation Protocol:

  • Prepare perovskite precursor solution with stoichiometric ratios in DMSO.
  • Add DBPF directly to precursor solution (concentration: 0.1-0.5 mol% relative to Pb²⁺).
  • Stir mixture for 2-4 hours at room temperature until fully dissolved.
  • Deposit perovskite film via spin-coating: two-step program (1000 rpm for 10 s, then 4000 rpm for 30 s).
  • Add antisolvent (ethyl acetate) during second step to induce crystallization.
  • Anneal at 100°C for 10 minutes in nitrogen atmosphere [25].

Surface Passivation Protocol:

  • Prepare DBPF solution in ethyl acetate (concentration: 0.1-0.3 mg/mL).
  • After perovskite film formation and annealing, spin-coat DBPF solution (3000 rpm, 30 s).
  • Anneal at 70°C for 5 minutes to remove residual solvent.
  • For dual passivation: combine both bulk and surface methods [25].

Thermal Quenching Assessment:

  • Measure temperature-dependent PL intensity from 25°C to 85°C.
  • Calculate thermal quenching ratio: PL intensity at 85°C / PL intensity at 25°C.
  • Compare passivated and control films to quantify improvement.
  • Fabricate complete PeLED devices and measure EQE at elevated temperatures [25].

The Scientist's Toolkit: Research Reagent Solutions

Table 3: Essential Research Reagents for Bilateral Interface Passivation

Reagent/Material Chemical Function Application Protocol Key Mechanism
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Phosphine oxide coordination group Thermal evaporation (5-15 nm) or spin-coating from alcohol solutions Coordination bonding with unsaturated Pb²⁺ sites; bond order 0.2 with Pb²⁺
DBPF (2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl)-fluorene) Alkyl phosphate passivation groups Bulk: additive in precursor (0.1-0.5 mol%); Surface: spin-coating from ethyl acetate Passivates coordination-unsaturated Pb²⁺ without affecting crystallization
Squaric Acid (Quadratic acid) Dicarboxylic acid bilateral anchor Spin-coating from aqueous solution (3-7 mg/mL) onto SnO₂ layer prior to perovskite deposition Forms hydrogen and coordination bonds at both SnO₂ and perovskite interfaces
CsPbBr₃ Quantum Dots Perovskite emitter material Hot-injection synthesis; spin-coating from non-polar solvents High PLQY (85±3%); narrow FWHM (~20 nm) for efficient electroluminescence
PEA₂FAₙ₋₁PbₙBr₃ₙ₊₁ (quasi-2D perovskite) Multi-quantum well emitter One-step spin-coating from DMSO with antisolvent engineering Energy funneling for efficient radiative recombination; n = 5 optimal for green emission

Bilateral interfacial passivation represents a paradigm shift in perovskite interface engineering, systematically addressing the critical limitations of PeLED performance and stability through coordinated application of fundamental chemical mechanisms. The strategic implementation of coordination bonding, defect healing, and energy level alignment at both interfaces of the perovskite layer enables unprecedented control over interfacial properties and device behavior. The quantitative improvements in efficiency metrics—with EQE enhancements from 7.7% to 18.7% and current efficiency from 20 to 75 cd A⁻¹—coupled with order-of-magnitude increases in operational lifetime, demonstrate the transformative potential of this approach [5].

The experimental protocols and reagent solutions detailed herein provide researchers with practical methodologies for implementing bilateral passivation strategies across various perovskite material systems. As the field advances, the integration of bilateral passivation with emerging material designs and device architectures will undoubtedly push the performance boundaries of perovskite optoelectronics closer to their theoretical limits, accelerating their commercialization for lighting and display applications.

Perovskite quantum dot light-emitting diodes (QLEDs), particularly those based on CsPbBr3, have emerged as promising candidates for next-generation displays due to their exceptional color purity and solution processability. However, the performance of these devices is intrinsically limited by massive defects that form during quantum dot (QD) film assembly. These defects adversely affect carrier injection, transportation, and recombination, ultimately degrading both efficiency and operational stability [5]. This case study examines the implementation of a bilateral interfacial passivation strategy using the organic molecule diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1) to address these challenges, contextualized within broader research on PeLED stability.

The Bilateral Passivation Concept

Rationale and Mechanism

In standard CsPbBr3 QLEDs with a sandwich structure, both the top and bottom surfaces of the perovskite QD film interface with charge transport layers (CTLs). These interfaces are hotspots for defect formation, including dangling bonds and uncoordinated atoms (e.g., Pb and halide vacancies) that regenerate during QD film assembly and device operation [5]. These defects act as non-radiative recombination centers and ion migration channels, severely limiting device performance.

The bilateral passivation strategy proposes the evaporation of a thin layer of TSPO1 organic molecules at both the top and bottom interfaces of the QD film. Theoretical calculations using density functional theory (DFT) reveal that the P=O group in TSPO1 strongly coordinates with unpassivated Pb atoms on the QD surface with a forming energy of -1.1 eV [5]. This interaction effectively neutralizes trap states, as visualized in the Density of States (DOS) plots, which show a significant reduction in trap states near the band edges after TSPO1 passivation.

Table 1: Key Interaction Properties of TSPO1 with CsPbBr3 QD Surface

Parameter Value Significance
Bonding Group Phosphine oxide (P=O) Coordinates with unsaturated Pb²⁺
Calculated Forming Energy -1.1 eV Indicates strong, spontaneous interaction
Bond Order (Pb-O) 0.2 Stronger than carboxyl or amidogen ligands
Primary Function Passivates Pb-related defects Suppresses non-radiative recombination

Comparative Device Architectures

The following diagram illustrates the structural and functional differences between standard, unilaterally passivated, and bilaterally passivated QLEDs.

G cluster_base Standard QLED cluster_uni Unilateral Passivation cluster_bi Bilateral Passivation (TSPO1) A1 Anode B1 HTL A1->B1 C1 QD Layer (High Defects) B1->C1 D1 ETL C1->D1 E1 Cathode D1->E1 A2 Anode B2 HTL A2->B2 F2 Passivation Layer B2->F2 C2 QD Layer (Moderate Defects) F2->C2 D2 ETL C2->D2 E2 Cathode D2->E2 A3 Anode B3 HTL A3->B3 F3 TSPO1 (Passivation) B3->F3 C3 QD Layer (Low Defects) F3->C3 G3 TSPO1 (Passivation) C3->G3 D3 ETL G3->D3 E3 Cathode D3->E3

Quantitative Performance Enhancement

The implementation of bilateral passivation with TSPO1 yields substantial improvements in both the optical properties of the QD films and the overall performance metrics of the fabricated QLED devices.

Table 2: Performance Comparison of CsPbBr3 QLEDs With and Without Bilateral Passivation

Performance Parameter Control Device TSPO1 Bilateral Passivation Enhancement Factor
Film PLQY (%) 43% 79% 1.8x
Maximum Current Efficiency (cd A⁻¹) 20 75 3.75x
Maximum EQE (%) 7.7% 18.7% 2.4x
Operational Lifetime, T50 (h) 0.8 15.8 20x

The data demonstrates that bilateral passivation not only boosts peak efficiency but also profoundly enhances device operational stability, a critical factor for commercial applications.

Experimental Protocol: Bilateral Passivation with TSPO1

Materials and Equipment

  • CsPbBr3 QD Ink: Synthesized via standard hot-injection method [5], with a photoluminescence quantum yield (PLQY) of ~85% in solution and an emission full width at half maximum (FWHM) of ~20 nm.
  • Passivation Molecule: TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl), purity >99%.
  • Substrate: Patterned ITO/glass substrates.
  • Charge Transport Materials: As required for the standard QLED stack (e.g., PEDOT:PSS for HIL, TPBi for ETL).
  • Key Equipment: Thermal evaporation system, spin coater, glovebox (N₂ atmosphere), UV-ozone cleaner, spectrophotometer, quantum yield measurement system, electroluminescence characterization setup.

Step-by-Step Fabrication Procedure

  • Substrate Preparation: Clean ITO/glass substrates sequentially with detergent, deionized water, acetone, and isopropanol via ultrasonication. Treat with UV-ozone for 15-20 minutes to improve wettability and work function.

  • Hole Injection Layer (HIL) Deposition: Spin-coat the HIL (e.g., PEDOT:PSS) onto the clean ITO substrate at a predetermined speed (e.g., 4000-5000 rpm for 30-60s). Anneal the film on a hotplate according to the material's specifications (e.g., 150°C for 20 minutes in air).

  • First TSPO1 Layer Deposition (Bottom Interface):

    • Transfer the substrate into a thermal evaporation chamber within a nitrogen-filled glovebox.
    • Evaporate a thin, continuous layer of TSPO1 onto the HIL surface. The typical thickness ranges from 1 to 5 nm, controlled precisely using a quartz crystal microbalance. This layer forms the bottom passivation interface.

  • CsPbBr3 QD Film Deposition:

    • Transfer the substrate back to the glovebox environment.
    • Spin-coat the pre-synthesized CsPbBr3 QD ink (e.g., 10-20 mg/mL in octane or toluene) onto the TSPO1-coated substrate. Optimize spin speed and time for a uniform, dense film (e.g., 1500-2000 rpm for 30-60s).
    • Optionally, anneal the film gently at 60-70°C for 10-15 minutes to remove residual solvent.

  • Second TSPO1 Layer Deposition (Top Interface):

    • Return the substrate to the thermal evaporation system.
    • Evaporate a second layer of TSPO1 of identical thickness (1-5 nm) directly onto the QD film. This layer forms the top passivation interface.

  • Electron Transport Layer (ETL) and Cathode Deposition:

    • Deposit the ETL (e.g., TPBi, ~50 nm) via thermal evaporation.
    • Finally, deposit the cathode (e.g., LiF/Al or Ag) through a shadow mask via thermal evaporation under high vacuum to define the active pixel areas.

  • Encapsulation: Immediately encapsulate the finished devices using a glass lid and UV-curable epoxy resin inside the glovebox to prevent degradation from moisture and oxygen.

The entire experimental workflow, from substrate preparation to final encapsulation, is summarized in the diagram below.

G Start Start: Substrate Cleaning & Treatment A Deposit HIL (e.g., PEDOT:PSS) Start->A B Evaporate 1st TSPO1 Layer (Bottom Passivation) A->B C Spin-coat CsPbBr3 QD Film B->C D Evaporate 2nd TSPO1 Layer (Top Passivation) C->D E Deposit ETL (e.g., TPBi) D->E F Deposit Cathode (e.g., LiF/Al) E->F End End: Device Encapsulation F->End

The Researcher's Toolkit

Table 3: Essential Reagents and Materials for Bilateral Passivation Studies

Reagent/Material Function/Role Key Characteristics
TSPO1 Bilateral passivation molecule Phosphine oxide group coordinates with unsaturated Pb²⁺; high thermal stability for evaporation [5].
CsPbBr3 QDs Emissive layer material Narrow FWHM (~20 nm); high solution PLQY; synthesized via hot-injection [5].
PEDOT:PSS Hole injection layer (HIL) Conducts holes; improves anode work function; solution-processable [33] [34].
TPBi Electron transport layer (ETL) Facilitates electron injection; blocks holes; deposited via thermal evaporation [33] [34].
PEABr Alternative solution-phase ligand Passivates Br⁻ vacancies; replaces insulating long-chain ligands; enables all-solution processing [33] [35].

Characterization and Validation Methods

To conclusively demonstrate the efficacy of the bilateral passivation strategy, the following characterization techniques are essential:

  • Photophysical Analysis: Measure the PLQY of the QD films using an integrating sphere. TSPO1-passivated films show a dramatic increase from 43% to 79% [5]. Time-resolved photoluminescence (TRPL) can be used to extract carrier lifetimes, with passivated films exhibiting longer average lifetimes, indicating suppressed non-radiative recombination.
  • Trap State Density Measurement: Employ the space-charge-limited-current (SCLC) method on electron-only devices (ITO/ZnO/QDs/TPBi/Al) to quantify defect density. The trap-filled limit voltage (V({}_{\text{TFL}})) is significantly lower in passivated devices, indicating a ~40% reduction in defect density [5] [36].
  • Theoretical Modeling: Perform Density Functional Theory (DFT) calculations to model the TSPO1 interaction with the CsPbBr3 surface. Analyze the density of states (DOS) to confirm the reduction of trap states near the band edges and calculate the binding energy between the P=O group and uncoordinated Pb atoms [5].
  • Device Performance Metrics: Characterize completed QLEDs using a source measure unit and a calibrated spectrometer to record current density-voltage-luminance (J-V-L) characteristics. Calculate key figures of merit: External Quantum Efficiency (EQE), current efficiency, and operational stability (T50 lifetime) [5].

This application note details a robust protocol for implementing a bilateral interfacial passivation strategy in CsPbBr3 QLEDs using TSPO1. The method directly addresses the critical challenge of interfacial defect generation, which plagues both the efficiency and operational stability of perovskite-based optoelectronic devices. The quantitative results are compelling, demonstrating an EQE of 18.7% and a 20-fold enhancement in operational lifetime [5]. This strategy, validated by rigorous theoretical and experimental characterization, provides a reliable and effective pathway for researchers aiming to fabricate high-performance, stable perovskite QLEDs, thereby advancing the prospects of this technology for commercial display applications.

Bilateral interfacial passivation, which addresses defect sites at both the electron transport layer (ETL) and hole transport layer (HTL) interfaces of a perovskite light-emitting diode (PeLED), represents a promising strategy for enhancing device stability. This case study examines a specific implementation of this approach: amine-based reactive passivation leading to the in-situ formation of new chemical products that improve PeLED performance. We explore the underlying chemical mechanisms, provide quantitative performance data, and detail experimental protocols for implementing this strategy, focusing on the reaction between m-xylylenediamine (mXDA) and precursor constituents.

The instability of perovskite materials, particularly in blue-emitting devices, remains a significant bottleneck for commercial applications. Defects at grain boundaries and surfaces facilitate non-radiative recombination, ion migration, and eventual device degradation. [37] While amine additives are widely recognized for their passivation capabilities, their inherent chemical reactivity can lead to dynamic evolution within precursor solutions, a factor that must be strategically managed or harnessed. [38]

Chemical Mechanism andIn-SituProduct Formation

The passivation mechanism relies on a chemical reaction initiated between the diamine additive and the perovskite precursor solution, rather than a simple physical adsorption process.

Reaction Pathway

The primary process involves a synergistic reaction between mXDA and methylammonium iodide (MAI) in a dimethylformamide (DMF)-based precursor solution. [38] The acidic environment provided by MAI catalyzes the hydrolysis of DMF, producing formic acid and dimethylamine. The formic acid then reacts with the amine groups of mXDA via N-formylation, ultimately yielding N-(3-formylaminomethylbenzyl)-formamide (FABF). [38] Concurrently, the dimethylamine is protonated by excess MAI to form dimethylammonium iodide (DMAI). Both FABF and DMAI are the functional in-situ passivation products.

Diagram 1: Chemical pathway of in-situ passivation product formation.

G MAI Methylammonium Iodide (MAI) Hydrolysis Hydrolysis (Acidic Catalyst) MAI->Hydrolysis mXDA m-Xylylenediamine (mXDA) N_Formylation N-Formylation Reaction mXDA->N_Formylation DMF Dimethylformamide (DMF) DMF->Hydrolysis FA_DMA Formic Acid + Dimethylamine Hydrolysis->FA_DMA FA_DMA->N_Formylation Products In-Situ Passivation Products N_Formylation->Products FABF N-(3-formylaminomethylbenzyl)-formamide (FABF) Products->FABF Primary Ligand DMAI Dimethylammonium Iodide (DMAI) Products->DMAI Co-Additive

Passivation Function

The in-situ formed FABF acts as a superior multidentate ligand. Its carbonyl (C=O) and amide (N–H) functional groups strongly coordinate with undercoordinated Pb²⁺ ions on the perovskite surface and at grain boundaries, effectively neutralizing these defect sites. [38] This suppression of deep traps reduces non-radiative recombination losses. The co-formed DMAI may contribute to crystallization control, aiding in the formation of a more uniform and compact perovskite film with enhanced optoelectronic properties.

Quantitative Performance Data

The efficacy of the amine-based reactive passivation strategy is demonstrated by significant improvements in key device performance metrics. The table below summarizes a comparative analysis of PeLEDs fabricated from fresh (control) and aged (passivated) precursor solutions.

Table 1: Performance comparison of PeLEDs from fresh vs. aged precursors.

Performance Parameter Control Device (Fresh Solution) Aged-Solution (AS) Device Improvement Factor
Peak External Quantum Efficiency (EQE) ~2% ~12% 6x [38]
Maximum Radiance Baseline Significantly Enhanced Not Quantified [38]
Turn-on Voltage Higher Reduced Not Quantified [38]
Electroluminescence (EL) Peak ~700 nm ~716 nm Red Shift [38]
Estimated Bandgap 1.74 eV 1.71 eV Reduction [38]
Crystalline Orientation (GIWAXS) Discrete Bragg Spots Randomly Distributed Debye–Scherrer Rings Improved Morphology [38]

The performance enhancement is further corroborated by other passivation studies. For instance, pseudohalide passivation of quantum dots has achieved peak EQEs of 22.1% for pure red PeLEDs, [39] and dual-channel passivation using chlormezanone has extended the operational lifetime (T50) of sky-blue PeLEDs to 23.1 minutes, doubling the control device's stability. [40]

Experimental Protocols

Protocol 1: Aging of Perovskite Precursor Solution with mXDA Additive

This protocol describes the procedure for preparing an aged precursor solution that facilitates the in-situ formation of passivation products.

Diagram 2: Workflow for precursor solution aging and device fabrication.

G Start Start Preparation Step1 Prepare precursor solution: 1:1.15:1 PbI₂:CsI:MAI in DMF Start->Step1 Step2 Add mXDA additive (0.6 equiv. relative to Pb²⁺) Step1->Step2 Step3 Age solution with stirring: Option A: 60°C for 6 days Option B: RT for 60 days Step2->Step3 Step4 Confirm reaction completion: HPLC-MS to detect FABF Step3->Step4 Step5 Fabricate PeLEDs via spin-casting Step4->Step5

Materials:

  • Lead Iodide (PbI₂), 99.99%
  • Cesium Iodide (CsI), 99.9%
  • Methylammonium Iodide (MAI), >99.95%
  • m-Xylylenediamine (mXDA), purified
  • Anhydrous Dimethylformamide (DMF)

Procedure:

  • Prepare the perovskite precursor solution by dissolving PbI₂, CsI, and MAI in anhydrous DMF with a stoichiometric ratio of 1:1.15:1.
  • Add mXDA to the precursor solution at a concentration of 0.6 equivalents relative to the Pb²⁺ cation content.
  • Age the solution under continuous stirring. Two validated conditions are:
    • Accelerated Aging: 60°C for 6 days. [38]
    • Ambient Aging: Room temperature (approx. 25°C) for 60 days. [38]
  • The aged solution can be used directly for device fabrication. The formation of FABF can be confirmed via HPLC-MS, showing a main fragment with m/z = 193.2 ([M+H]⁺). [38]

Protocol 2: Direct Use of SynthesizedIn-SituProducts

This protocol bypasses the aging process by using pre-synthesized FABF and DMAI, ensuring batch-to-batch consistency and reducing fabrication time.

Materials:

  • N-(3-formylaminomethylbenzyl)-formamide (FABF), synthesized
  • Dimethylammonium Iodide (DMAI), 99.9%

Procedure:

  • Synthesize FABF independently via a established N-formylation method, using formic acid and mXDA as starting materials. [38]
  • Prepare the standard perovskite precursor solution (PbI₂:CsI:MAI, 1:1.15:1 in DMF).
  • Add the pre-synthesized FABF and DMAI directly to the fresh precursor solution. The optimal concentration should be determined empirically but should mirror the total additive concentration used in Protocol 1.
  • Use the resulting solution immediately for PeLED fabrication without further aging.

The Scientist's Toolkit: Essential Research Reagents

The following table lists key materials and their functions for implementing this passivation strategy.

Table 2: Key research reagents for amine-based reactive passivation.

Reagent Function / Role Key Characteristics
m-Xylylenediamine (mXDA) Primary amine additive; reactant for in-situ N-formylation. Bifunctional amine; high reactivity. [38]
Methylammonium Iodide (MAI) Perovskite precursor; provides acidic environment for DMF hydrolysis. Catalyzes the formation of passivation products. [38]
Dimethylformamide (DMF) Solvent; reactant in the hydrolysis step. Source of formic acid for N-formylation. [38]
FABF In-situ formed passivation ligand. Multidentate ligand; passivates undercoordinated Pb²⁺. [38]
Dimethylammonium Iodide (DMAI) In-situ formed co-additive. Aids in crystallization control. [38]
Cesium Iodide (CsI) & Lead Iodide (PbI₂) Inorganic perovskite precursors. High purity (99.9-99.99%) required for optimal performance. [38]

This case study demonstrates that amine-based reactive passivation is a powerful manifestation of a bilateral passivation strategy. By intentionally leveraging the chemical reactivity of amine additives to generate effective passivants in-situ, this approach leads to a profound improvement in PeLED performance, as evidenced by a six-fold increase in EQE. The protocols and mechanistic insights provided offer a reproducible framework for researchers aiming to harness dynamic chemistry to enhance the stability and efficiency of perovskite optoelectronics. Future work should focus on extending this principle to other amine-perovskite systems and exploring its applicability across the full color spectrum of PeLEDs.

Optimizing Passivation Efficacy: Overcoming Challenges and Fine-Tuning Performance

Identifying and Mitigating Passivation-Induced Quenching and Side Reactions

Defect passivation is a cornerstone strategy for enhancing the performance of perovskite light-emitting diodes (PeLEDs). While effective in suppressing non-radiative recombination, passivation processes can inadvertently introduce quenching phenomena and undesirable side reactions that compromise device efficiency and operational stability [10] [27]. This Application Note examines these critical challenges within the framework of a bilateral interfacial passivation strategy, which addresses both top and bottom interfaces of the perovskite emitting layer [5]. We provide researchers with detailed protocols for identifying mitigation strategies and quantitative frameworks for evaluating their effectiveness in PeLED development.

Core Principles of Bilateral Interfacial Passivation

Bilateral interfacial passivation represents a significant advancement over conventional single-interface approaches. This strategy simultaneously addresses defect states at both the top and bottom interfaces of the perovskite quantum dot (QD) film, which is particularly crucial in sandwich-structured optoelectronic devices [5].

The theoretical foundation of this approach relies on several key mechanisms:

  • Dual-Interface Defect Suppression: Massive defects regenerate during QD film assembly, severely affecting carrier injection, transportation, and recombination. Passivating both interfaces dramatically reduces these interfacial trap states [5].

  • Strong Coordination Chemistry: Phosphine oxide-based molecules (e.g., TSPO1) demonstrate particularly strong interactions with undercoordinated Pb²⁺ ions through their P=O functional groups, with DFT calculations showing a forming energy of -1.1 eV between Pb and O atoms [5].

  • Carrier Dynamics Management: Proper bilateral passivation facilitates balanced charge injection and prevents carrier accumulation at either interface, reducing the likelihood of quenching phenomena [10].

Table 1: Key Defect Types in Perovskite Optoelectronic Devices

Defect Type Location Impact on Device Performance Passivation Strategy
Undercoordinated Pb²⁺ ions Surface and grain boundaries Deep traps for non-radiative recombination; ion migration channels Coordination with Lewis bases (P=O, C=O, S=O) [5] [10] [27]
Halide vacancies Bulk and surface Halide ion migration; phase segregation Anion compensation (e.g., Cl⁻ from PPOCl₂) [23]
Organic cation vacancies Surface and grain boundaries Surface charge imbalance; reduced PLQY Organic cation compensation [27]
Interfacial defects Perovskite/CTL interfaces Impaired charge injection; increased non-radiative recombination Bilateral molecular passivation [5] [10]

Experimental Protocols

Bilateral Passivation of Perovskite QD Films

This protocol outlines the procedure for implementing bilateral passivation in perovskite QLEDs using TSPO1 as described in foundational research [5].

Materials and Equipment:

  • Synthesized CsPbBr₃ QDs (8 nm cubic morphology, PLQY 85±3%, FWHM 20 nm)
  • TSPO1 (diphenylphosphine oxide-4-(triphenylsilyl)phenyl) or alternative phosphine oxide molecules
  • Electron and hole transport layer materials
  • Thermal evaporation system
  • Spectroscopic ellipsometer
  • Photoluminescence quantum yield (PLQY) measurement system
  • Space charge-limited current (SCLC) measurement setup

Procedure:

  • Substrate Preparation and Bottom Interface Passivation:
    • Prepare patterned ITO/glass substrates with standard cleaning procedures
    • Deposit hole transport layer according to optimized parameters
    • Thermally evaporate a 5-10 nm layer of TSPO1 at a rate of 0.5 Å/s under high vacuum (10⁻⁶ Torr)

  • QD Film Deposition:

    • Spin-coat CsPbBr₃ QD ink at 2000 rpm for 30 seconds in nitrogen atmosphere
    • Anneal at 70°C for 10 minutes to form uniform QD film

  • Top Interface Passivation:

    • Thermally evaporate a second TSPO1 layer (5-10 nm) using identical evaporation parameters
    • Ensure complete coverage without pinholes

  • Device Completion:

    • Deposit electron transport layer
    • Evaporate top metal electrodes

Validation Measurements:

  • Measure PLQY of passivated versus control QD films (target: increase from 43% to 79%)
  • Characterize defect density via SCLC method
  • Perform transient absorption spectroscopy to quantify non-radiative recombination reduction
Thermal Quenching Suppression via Defect Passivation

This protocol addresses passivation strategies to suppress thermal quenching, a critical issue for practical PeLED operation [25].

Materials:

  • Quasi-2D perovskite PEA₂FAₙ₋₁PbₙBr₃ₙ₊₁ (n=5) precursor solution
  • DBPF (2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl)-fluorene) passivation agent
  • Dimethyl sulfoxide (DMSO) and ethyl acetate (EA) solvents

Procedure:

  • Bulk Passivation:
    • Dissolve DBPF in perovskite precursor solution (DMSO) at optimized concentration
    • Spin-coat perovskite film in nitrogen-filled glovebox
    • Anneal at appropriate temperature for 15 minutes

  • Surface Passivation:

    • Prepare DBPF solution in ethyl acetate antisolvent
    • Apply during or immediately after perovskite film formation
    • Ensure uniform coverage across the active area

  • Thermal Stability Testing:

    • Characterize PL intensity from room temperature to 85°C
    • Measure EQE retention at elevated temperatures
    • Compare passivated devices against controls

Key Considerations:

  • DBPF selectively passivates coordination-unsaturated Pb²⁺ defects without affecting crystallization
  • Dual bulk and surface passivation provides optimal thermal quenching suppression
  • Target performance: >85% EQE retention at 85°C versus 17% for control devices [25]
Deep-Blue PeLED Fabrication with Spectral Shift

This protocol details the use of PPOCl₂ dynamic treatment to achieve stable deep-blue emission while passivating defects [23].

Materials:

  • Quasi-2D sky-blue perovskite precursor
  • Phenylphosphonic dichloride (PPOCl₂) in varying concentrations (1-5 mg/mL)
  • Standard PeLED stack materials

Procedure:

  • Perovskite Film Formation:
    • Deposit quasi-2D perovskite film via spin-coating
    • Control crystal nucleation and growth through processing parameters

  • Dynamic PPOCl₂ Treatment:

    • Prepare PPOCl₂ solutions at concentrations from 1-5 mg/mL in anhydrous solvent
    • Apply to perovskite film surface and allow penetration for 30 seconds
    • Remove excess solution via spin-casting

  • Device Fabrication and Characterization:

    • Complete device stack with appropriate charge transport layers
    • Measure electroluminescence spectra to confirm blue shift (488 nm → 467 nm)
    • Evaluate EQE and operational stability at 100 cd/m²

Mechanistic Insights:

  • Phosphonic group forms covalent bonds with undercoordinated Pb²⁺
  • Chloride content penetrates perovskite lattice, reducing halide defects
  • HCl byproducts induce blue shift by increasing Cl⁻ content in crystal lattice

Research Reagent Solutions

Table 2: Essential Research Reagents for Defect Passivation Studies

Reagent Chemical Function Application in PeLEDs Key Findings
TSPO1 Phosphine oxide Lewis base Bilateral interface passivation 18.7% EQE; 75 cd/A current efficiency; 20x operational lifetime improvement [5]
DBPF Phosphate fluorene with Pb²⁺ coordination Bulk and surface defect passivation >22% EQE; 85% EQE retention at 85°C; suppresses exciton-phonon coupling [25]
PPOCl₂ Phosphonic dichloride with Cl⁻ source Defect passivation with spectral shift 2.31% EQE at 488 nm; achieves 467 nm deep-blue emission [23]
DDAB Quaternary ammonium salt Surface ligand engineering Improves PLQY and charge injection [5]
Ni²⁺ dopant Metal cation substitution Chlorine vacancy suppression Reduces deep traps through inhibition of Cl vacancy formation [10]

Quantitative Data Analysis

Table 3: Performance Metrics of Passivation Strategies

Passivation Approach EQE Improvement Stability Enhancement Emission Wavelength Key Mechanism
Bilateral TSPO1 [5] 7.7% → 18.7% T₅₀: 0.8 h → 15.8 h (20x) Green region Dual interface defect suppression
DBPF Dual Passivation [25] >22% achieved 85% EQE retention at 85°C 550 nm Bulk and surface Pb²⁺ passivation
PPOCl₂ Dynamic Treatment [23] 2.31% maximum T₅₀: ~3 min at 100 cd/m² 467-488 nm (tunable) Pb²⁺ passivation + Cl⁻ incorporation
OH-DPPO Passivation [23] 22.44% maximum ~60,000 cd/m² luminance 530 nm Strong P=O Pb²⁺ coordination

Pathway Visualizations

G PerovskiteFilm Perovskite Film TopInterface Top Interface Unpassivated PerovskiteFilm->TopInterface BottomInterface Bottom Interface Unpassivated PerovskiteFilm->BottomInterface TopPassivation Passivated Top Interface PerovskiteFilm->TopPassivation BottomPassivation Passivated Bottom Interface PerovskiteFilm->BottomPassivation Quenching1 Non-Radiative Recombination TopInterface->Quenching1 Defect-Induced Quenching Quenching2 Efficiency Roll-Off BottomInterface->Quenching2 Carrier Injection Imbalance DeviceFailure Device Performance Degradation Quenching1->DeviceFailure Reduced EQE/Lifetime Quenching2->DeviceFailure Rapid Degradation BilateralPassivation Bilateral Passivation Strategy BilateralPassivation->TopPassivation Apply Passivant BilateralPassivation->BottomPassivation Apply Passivant ImprovedInjection Enhanced Radiative Recombination TopPassivation->ImprovedInjection Balanced Carrier Injection DefectReduction Suppressed Ion Migration BottomPassivation->DefectReduction Trap State Reduction HighPerformance Stable High- Performance PeLED ImprovedInjection->HighPerformance DefectReduction->HighPerformance

Bilateral Passivation Mitigates Interface-Induced Quenching

G PbDefect Undercoordinated Pb²⁺ Defect NonRadiative Non-Radiative Recombination PbDefect->NonRadiative Traps Carriers LowPLQY Low PLQY & Device Efficiency NonRadiative->LowPLQY Reduces PassivationMolecules Passivation Molecules TSPO1 TSPO1 P=O Group PassivationMolecules->TSPO1 Phosphine Oxides DBPF DBPF P=O Group PassivationMolecules->DBPF Phosphate Fluorenes PPOCl2 PPOCl₂ P=O + Cl⁻ PassivationMolecules->PPOCl2 Phosphonic Dichlorides StrongCoordination Strong Pb-O Coordination Bond TSPO1->StrongCoordination Forms DBPF->StrongCoordination Forms DualAction Defect Passivation + Anion Compensation PPOCl2->DualAction Provides DefectPassivated Passivated Defect Site StrongCoordination->DefectPassivated Results in DualAction->DefectPassivated Results in ReducedTrapping Reduced Carrier Trapping DefectPassivated->ReducedTrapping Minimizes HighEfficiency High-Efficiency Stable PeLEDs ReducedTrapping->HighEfficiency Enables

Molecular Mechanisms in Defect Passivation

Effective implementation of bilateral interfacial passivation strategies requires careful consideration of potential quenching mechanisms and side reactions. The protocols and data frameworks presented herein provide researchers with standardized methodologies for developing passivation approaches that not only reduce defect densities but also maintain optimal charge balance and interfacial stability. As PeLED technology advances toward commercialization, understanding and mitigating these secondary effects of passivation will be crucial for achieving devices that combine high efficiency with operational longevity. Future directions should focus on passivant molecular design that simultaneously addresses multiple defect types while minimizing disruptive interactions with charge transport layers.

Optimizing Molecular Concentration and Processing Parameters for Maximum Effect

Bilateral interfacial passivation has emerged as a superior strategy for enhancing the performance and stability of perovskite light-emitting diodes (PeLEDs). Unlike conventional methods that address only a single interface, this approach simultaneously targets defects at both the bottom (buried) and top (exposed) surfaces of the perovskite emissive layer. Defects at these interfaces act as non-radiative recombination centers, severely limiting device efficiency and operational lifetime. The bilateral passivation framework recognizes that both interfaces contribute disproportionately to charge injection imbalances, trap-assisted recombination, and eventual device degradation. By applying tailored passivation molecules to both interfaces, researchers have achieved remarkable improvements in key device metrics, including external quantum efficiency (EQE), current efficiency, and operational stability, often extending device lifetimes by an order of magnitude or more [41] [5].

This application note provides detailed protocols and optimization parameters for implementing bilateral passivation strategies, with a focus on molecular concentration optimization and processing parameter control. The methodologies described herein are framed within the broader thesis that comprehensive interface management is crucial for advancing PeLED technology toward commercial viability.

Key Passivation Molecular Systems and Their Optimization

Mercaptopyridine Regioisomer System for CsPbBr₃ PeLEDs

Overview: This system employs regioisomers of mercaptopyridine—4-mercaptopyridine (4-MPy) for the buried interface and 2-mercaptopyridine (2-MPy) for the perovskite top surface—deposited via a solvent-free rub-on transfer method to prevent secondary defect formation [41].

Table 1: Optimization Parameters for Mercaptopyridine Regioisomer System

Parameter Optimized Value Impact/Function
4-MPy Treatment Time (Buried Interface) 20 minutes Saturates defect passivation; increases Ni³⁺/Ni²⁺ ratio from 4.49 to 5.28; shifts NiOx valence band from -5.41 eV to -5.70 eV [41].
2-MPy Application Solvent-free rub-on Coordinates with undercoordinated Pb²⁺ ions via ortho-positioned -SH and pyridine N atoms; forms wide-bandgap complexes for carrier confinement [41].
Maximum EQE Achieved 24.67% Highest reported for solution-processed polycrystalline CsPbBr₃-based PeLEDs [41].
Current Efficiency 95.01 cd/A Significant enhancement over non-passivated controls [41].
Operational Stability (T₅₀ @ 1000 cd/m²) ~10x improvement Nearly tenfold extension of operational half-life compared to control devices [41].
TSPO1 Bilateral Passivation for Perovskite QLEDs

Overview: Diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1) is evaporated onto both interfaces of a perovskite quantum dot (QD) film to passivate defects and suppress non-radiative recombination [5] [42].

Table 2: Optimization Parameters for TSPO1 Bilateral Passivation

Parameter Optimized Value Impact/Function
Application Method Thermal evaporation Creates a layer between QD film and charge transport layers (CTLs) without damaging the film [5].
Bond Order with Pb 0.2 Stronger interaction with Pb atoms compared to carboxyl or amidogen groups, suppressing defect regeneration [5].
Film PLQY Improvement 43% to 79% Significantly enhanced radiative recombination efficiency in QD films [5].
Maximum EQE Achieved 18.7% Marked improvement over control devices (7.7%) [5].
Current Efficiency 75 cd/A Substantial increase from 20 cd/A in control devices [5].
Operational Lifetime (T₅₀) 15.8 hours Represents a 20-fold enhancement over non-passivated devices (0.8 hours) [5].
OAI Dual Passivation for Pure Red PeLEDs

Overview: Octylammonium iodide (OAI) serves a dual role, both as a crystallization modulator in the perovskite bulk and a passivator at the interfaces, enabling high-color-purity red emission [43].

Table 3: Optimization Parameters for OAI Dual Passivation

Parameter Optimized Value Impact/Function
Function Crystallization regulation & defect passivation Suppresses unstable mixed-halide phases at grain boundaries and mitigates ionic/interfacial defects [43].
Maximum EQE Achieved 16.47% A 5.1-fold enhancement over the pristine device (3.26%) [43].
Maximum Brightness 1274.9 cd/m² A 3.1-fold improvement over the control device (409.6 cd/m²) [43].
Turn-on Voltage 1.59 V Low operating voltage indicating improved charge injection [43].
EL Peak Position 649 nm Enables pure red emission with 99.9% coverage of Rec.2020 color standard [43].
Operational Stability (T₅₀) >9 hours A 4-fold improvement in half-lifetime compared to control devices [43].

Experimental Protocols for Bilateral Passivation

Protocol 1: Solvent-Free Rub-On Transfer of Mercaptopyridine Regioisomers

Application Scope: This protocol is designed for the fabrication of efficient and stable CsPbBr₃ PeLEDs using a solvent-free deposition technique to minimize secondary defects.

Materials and Equipment:

  • 4-mercaptopyridine (4-MPy) and 2-mercaptopyridine (2-MPy)
  • NiOx-coated substrate
  • Solvent-free rub-on transfer apparatus
  • Thermal annealing station
  • X-ray photoelectron spectroscopy (XPS) tool for validation

Procedure:

  • Substrate Preparation: Begin with a thoroughly cleaned NiOx-coated ITO substrate.
  • Buried Interface Passivation (4-MPy):
    • Apply a controlled amount of solid 4-MPy powder onto the NiOx surface.
    • Use a solvent-free rub-on transfer tool to uniformly distribute the molecules across the surface.
    • Maintain the rub-on process for the optimized duration of 20 minutes to achieve saturation of electronic modification.
    • Thermally anneal the substrate to stabilize the 4-MPy layer.
  • Perovskite Layer Formation: Deposit the CsPbBr₃ perovskite emissive layer via standard solution-processing techniques (e.g., spin-coating) atop the 4-MPy-treated NiOx.
  • Top Interface Passivation (2-MPy):
    • Similarly, apply 2-MPy powder onto the completed perovskite film surface.
    • Perform the solvent-free rub-on transfer, ensuring uniform coverage.
    • A final mild thermal annealing step may be applied to strengthen coordination with undercoordinated Pb²⁺ sites.
  • Device Completion: Proceed with the deposition of the remaining charge transport layers and the metal electrode.

Validation Metrics:

  • Use XPS to verify the successful incorporation of 4-MPy and the increased Ni³⁺/Ni²⁺ ratio (~5.28) on the buried interface.
  • Perform ultraviolet photoelectron spectroscopy (UPS) to confirm the favorable shift in the NiOx valence band maximum (to ~ -5.70 eV).
  • Fabricate control devices without passivation for performance comparison.
Protocol 2: Thermal Evaporation of TSPO1 for Perovskite QLEDs

Application Scope: This protocol details the bilateral passivation of perovskite quantum dot (QD) films for high-efficiency green QLEDs, addressing defect regeneration during film assembly.

Materials and Equipment:

  • Diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1)
  • Pre-deposited hole transport layer (HTL)
  • CsPbBr₃ QD ink
  • Thermal evaporation system
  • Glove box with controlled N₂ atmosphere

Procedure:

  • Bottom Interface Preparation: Deposit the HTL (e.g., TFB) onto the ITO substrate.
  • Bottom-side TSPO1 Layer:
    • Load the substrate into a thermal evaporation chamber.
    • Evaporate a thin, uniform layer of TSPO1 (~1-5 nm) directly onto the HTL surface.
  • QD Film Deposition:
    • Transfer the substrate to a glove box.
    • Deposit the CsPbBr₃ QD film via spin-coating or inkjet printing onto the TSPO1-coated HTL.
  • Top-side TSPO1 Layer:
    • Return the substrate with the QD film to the evaporation chamber.
    • Evaporate a second layer of TSPO1 of identical thickness directly onto the QD film.
  • Electron Transport Layer and Electrode:
    • Deposit the electron transport layer (e.g., ZnO, TPBi) atop the TSPO1-passivated QD film.
    • Complete the device by depositing the cathode (e.g., Al/LiF).

Validation Metrics:

  • Measure the photoluminescence quantum yield (PLQY) of the bilateral-passivated QD film; target >75%.
  • Characterize device performance to verify a maximum EQE of >18%.
  • Conduct operational lifetime tests to confirm a T₅₀ of >15 hours at initial luminance.
Protocol 3: OAI Dual Passivation for Pure Red PeLEDs

Application Scope: This protocol utilizes OAI to simultaneously regulate crystallization and passivate defects in quasi-2D perovskite films for stable, color-pure red PeLEDs.

Materials and Equipment:

  • Octylammonium iodide (OAI)
  • Precursors for quasi-2D perovskite (e.g., CsI, PbI₂, PbBr₂, PEAI)
  • IPA solvent for OAI solution
  • Spin coater
  • Thermal annealing station

Procedure:

  • Bulk Incorporation via Precursor Solution:
    • Add a controlled concentration of OAI directly into the quasi-2D perovskite precursor solution.
    • The amine group interacts with [PbI₆] octahedra, while the alkyl chain acts as a spacer, facilitating 2D phase formation.
  • Perovskite Film Formation:
    • Spin-coat the OAI-containing precursor solution onto the substrate.
    • Use a standard anti-solvent quenching process to initiate crystallization.
  • Surface Treatment via Post-Deposition Passivation:
    • Prepare a solution of OAI in isopropanol (IPA).
    • Spin-coat the OAI-IPA solution directly onto the as-deposited perovskite film.
    • Anneal the film to drive the passivation reaction, allowing OAI to mitigate ionic and surface defects.
  • Device Completion: Deposit the subsequent charge transport layers and electrodes to finalize the PeLED structure.

Validation Metrics:

  • Achieve a target maximum EQE of >16% and a maximum brightness of >1200 cd/m².
  • Confirm pure red electroluminescence with a peak at 649 nm and CIE coordinates satisfying the Rec.2020 standard.
  • Verify operational stability with a T₅₀ lifetime exceeding 9 hours.

Workflow and Pathway Visualizations

G Start Start: Substrate Preparation B1 Deposit Bottom Charge Layer (e.g., NiOx, HTL) Start->B1 B2 Apply Bottom Passivation (Method: Solvent-free rub-on or Thermal evaporation) B1->B2 B3 Characterize Bottom Interface (XPS/UPS to confirm electronic modification) B2->B3 C1 Deposit Perovskite Emissive Layer (via Spin-coating) B3->C1 T1 Apply Top Passivation (Method: Solvent-free rub-on, Thermal evaporation, or Solution treatment) C1->T1 T2 Characterize Top Interface (PLQY, TRPL to confirm defect passivation) T1->T2 End Complete Device Fabrication (Deposit remaining layers & electrode) T2->End

Diagram 1: Bilateral passivation workflow for PeLEDs.

G cluster_molecular Molecular Action Pathways cluster_outcome Device-Level Outcomes MPy Mercaptopyridine System • 4-MPy at buried interface: - Coordinates Ni atoms - ↑ Ni³⁺/Ni²⁺ ratio - ↓ O₂ vacancies • 2-MPy at top surface: - Bidentate coordination with Pb²⁺ - Forms wide-bandgap complex Outcome1 Enhanced EQE (16-25%) MPy->Outcome1 Outcome2 Improved Current Efficiency (75-95 cd/A) MPy->Outcome2 Outcome3 10-20x Stability Improvement (T₅₀ @ 1000 cd/m²) MPy->Outcome3 TSPO TSPO1 Molecule • P=O group coordinates Pb - Bond order: 0.2 - Strong ligand binding • Suppresses defect regeneration • Blocks ion migration TSPO->Outcome1 Outcome4 Balanced Charge Injection TSPO->Outcome4 OAI OAI Additive • Amine group interacts with [PbI₆] • Alkyl chain as spacer cation - Facilitates 2D phase formation • Passivates ionic/surface defects OAI->Outcome1 OAI->Outcome3

Diagram 2: Molecular action pathways and device outcomes.

The Scientist's Toolkit: Essential Research Reagents

Table 4: Key Reagent Solutions for Bilateral Passivation Studies

Reagent/Material Function/Application Key Characteristics & Notes
4-Mercaptopyridine (4-MPy) Buried interface passivator for NiOx. Stabilizes Ni³⁺ states, reduces oxygen vacancies, improves hole injection. Use in solvent-free rub-on process [41].
2-Mercaptopyridine (2-MPy) Top surface passivator for perovskite. Bidentate coordination with undercoordinated Pb²⁺; forms wide-bandgap complexes for carrier confinement [41].
TSPO1 Bilateral passivator for QLED interfaces. Phosphine oxide group strongly coordinates Pb (bond order 0.2); applied via thermal evaporation [5].
Octylammonium Iodide (OAI) Dual-function additive for bulk and surface. Regulates crystallization and passivates defects in quasi-2D perovskites for pure red emission [43].
NiOx Nanoparticles Hole injection layer material. Serves as substrate for 4-MPy binding; electronic properties are modified by passivation [41].
CsPbBr₃ QD Ink Emissive layer for QLEDs. High PLQY (>85%) in solution; requires interface passivation to maintain efficiency in solid film [5].
Quasi-2D Perovskite Precursors Emissive layer for red PeLEDs. Includes CsI, PbI₂, PbBr₂, and spacer cations (e.g., PEAI); OAI modifies crystallization [43].

Balancing Charge Injection and Transport in Bilaterally Passivated Devices

Bilateral interfacial passivation has emerged as a critical strategy for enhancing the performance and stability of perovskite light-emitting diodes (PeLEDs). This approach involves the simultaneous passivation of both the top and bottom interfaces of the perovskite quantum dot (QD) film, addressing defect-mediated non-radiative recombination pathways that undermine device efficiency and operational lifetime. The strategic management of charge injection and transport across these interfaces is paramount for achieving optimal device performance [4] [5].

This Application Note provides a detailed experimental framework for implementing bilateral passivation strategies, focusing on methodologies that enable precise control over charge carrier dynamics in PeLED architectures. We present quantitative performance comparisons, standardized protocols for device fabrication and characterization, and essential reagent solutions to facilitate the adoption of these techniques within the research community.

Quantitative Performance Analysis of Bilateral Passivation

The implementation of bilateral passivation strategies yields significant, quantifiable improvements in key device performance metrics. The data presented below summarize the enhancements achieved through bilateral passivation relative to control devices.

Table 1: Quantitative Performance Metrics of Bilateral Passivation in Perovskite QLEDs

Performance Parameter Control Device (Unpassivated) Bilaterally Passivated Device Enhancement Factor
Maximum External Quantum Efficiency (EQE) 7.7% 18.7% 2.4x [5]
Current Efficiency 20 cd A⁻¹ 75 cd A⁻¹ 3.75x [5]
Photoluminescence Quantum Yield (PLQY) of Film 43% 79% 1.8x [5]
Operational Lifetime (T₅₀) 0.8 hours 15.8 hours 20x [5]
Maximum Luminance ~1000 cd m⁻² (at a higher voltage) Achieved at lower voltage with superior conductivity Improved injection [44]

Experimental Protocols

Bilateral Passivation Layer Deposition

This protocol details the process for depositing organic molecular passivation layers on both interfaces of a perovskite QD film using the thermal evaporation technique, with TSPO1 as a representative passivator [5].

Materials:

  • Pre-synthesized CsPbBr₃ QD ink
  • Hole Transport Layer (HTL) substrate (e.g., PTAA)
  • Electron Transport Layer (ETL) materials
  • Passivation molecule (e.g., TSPO1, >99% purity)

Procedure:

  • Substrate Preparation: Clean the HTL-coated substrate (e.g., ITO/PEDOT:PSS/PTAA) with UV-ozone treatment for 15 minutes.
  • Bottom Passivation Layer Deposition:
    • Load the substrate into a high-vacuum thermal evaporation chamber.
    • Evaporate a thin layer (~5-10 nm) of TSPO1 onto the HTL surface at a deposition rate of 0.5 Å/s under a vacuum of <5×10⁻⁶ Torr.
  • Perovskite QD Film Fabrication:
    • Transfer the substrate to a nitrogen-filled glovebox.
    • Spin-coat the CsPbBr₃ QD ink onto the TSPO1-coated substrate at 2000 rpm for 30 seconds.
    • Anneal the film on a hotplate at 70°C for 10 minutes to remove residual solvent.
  • Top Passivation Layer Deposition:
    • Return the QD film sample to the thermal evaporation chamber.
    • Evaporate an equivalent thickness (~5-10 nm) of TSPO1 directly onto the QD film surface using identical deposition parameters.
  • Completion of Device Stack:
    • Subsequently deposit the ETL (e.g., TmPyPB) and electrode (e.g., Liq/Al) layers without breaking vacuum to minimize interfacial contamination.

Critical Steps:

  • Maintain consistent thickness for both top and bottom passivation layers to ensure symmetric defect suppression.
  • Control the deposition rate precisely to form uniform, pinhole-free passivation films.
  • Minimize exposure of the perovskite QD layer to ambient conditions to prevent degradation.
Charge Transport and Defect Analysis

This methodology outlines the characterization techniques for quantifying the improvement in charge injection and transport properties, as well as the reduction in defect density, following bilateral passivation.

Characterization Techniques:

  • Space Charge-Limited Current (SCLC) Measurement:

    • Device Structure: Fabricate electron-only (ITO/SnO₂/Perovskite/PCBM/Ag) or hole-only (ITO/PEDOT:PSS/Perovskite/PTAA/Au) devices with and without bilateral passivation.
    • Measurement: Record current density-voltage (J-V) characteristics in the dark.
    • Analysis: Identify the trap-filled limit voltage (VTFL) from the J-V curve. Calculate the trap density (ntrap) using the formula: ( n{trap} = (2 \epsilon \epsilon0 V_{TFL}) / (e L^2) ) where ε is the relative permittivity, ε₀ is the vacuum permittivity, e is the electron charge, and L is the film thickness [5].

  • Transient Absorption (TA) Spectroscopy:

    • Setup: Utilize a femtosecond laser system with a pump-probe configuration.
    • Measurement: Excite the passivated and control films with a pump pulse and monitor the differential absorption of a probe pulse across a time delay.
    • Analysis: Fit the decay kinetics of the ground-state bleaching feature. A longer carrier lifetime in the passivated film indicates suppressed non-radiative recombination at defects [5].

  • Density Functional Theory (DFT) Calculations:

    • Software: Use computational packages (e.g., VASP, Quantum ESPRESSO).
    • Modeling: Construct a theoretical model of the perovskite surface with uncoordinated Pb atoms and introduce the passivation molecule.
    • Analysis:
      • Calculate the binding energy between the functional group (e.g., P=O of TSPO1) and the Pb defect.
      • Compute the Density of States (DOS) for both passivated and unpassivated surfaces to visualize the suppression of trap states within the band gap [5].

The Scientist's Toolkit: Research Reagent Solutions

Table 2: Essential Materials for Bilateral Passivation Studies

Reagent/Material Function/Application Exemplary Usage
TSPO1 Organic passivation molecule; P=O group coordinates with uncoordinated Pb²⁺ defects to suppress trap states. Bilateral interfacial layer in perovskite QLEDs [5].
F4-TCNQ Strong p-type dopant; increases hole conductivity and modifies energy level alignment in HTLs. Dopant in PTAA HTL to improve charge injection [44].
PTAA Hole-transporting polymer; serves as the base matrix for p-dopants and forms the bottom interface with the perovskite layer. HTL in PeLED device stacks [44].
CsPbBr₃ QDs Emissive layer material; high photoluminescence quantum yield and narrow emission linewidth. The central light-emitting layer in QLED devices [5].
AlOx / PDAI₂ Bilayer inorganic/organic passivation stack; suppresses non-radiative recombination at the perovskite/ETL interface. Interface engineering in perovskite/silicon tandem solar cells [45].
G SALT Multi-functional organic ligand; sulphonate and hydroxyl groups passivate defects and improve phase distribution in quasi-2D perovskites. Additive for stabilizing blue-emitting quasi-2D PeLEDs [46].

Workflow and Signaling Pathways

The following diagram illustrates the logical workflow for fabricating a bilaterally passivated PeLED and the subsequent charge dynamics that lead to enhanced performance.

G Start Start: Substrate/HTL Preparation BottomPass Deposit Bottom Passivation Layer Start->BottomPass PerovskiteDep Deposit Perovskite QD Film BottomPass->PerovskiteDep DefectPass Defect Passivation BottomPass->DefectPass TopPass Deposit Top Passivation Layer PerovskiteDep->TopPass CompleteStack Complete Device Stack (ETL/Electrode) TopPass->CompleteStack TopPass->DefectPass ImprovedInjection Balanced Charge Injection DefectPass->ImprovedInjection ReducedRecomb Suppressed Non-Radiative Recombination DefectPass->ReducedRecomb ImprovedInjection->ReducedRecomb HighPerformance High-Efficiency & Stable PeLED ImprovedInjection->HighPerformance ReducedRecomb->HighPerformance

Diagram 1: Bilateral Passivation Workflow and Performance Enhancement Mechanism. This graph outlines the fabrication sequence (solid arrows) for a bilaterally passivated PeLED and the causal relationships (dashed red arrows) through which passivation improves device performance by mitigating defects, balancing injection, and reducing losses.

The bilateral interfacial passivation strategy represents a significant advancement in PeLED technology, directly addressing the critical challenges of defect-mediated recombination and inefficient charge injection. The protocols and data summarized in this document provide a reproducible framework for implementing this strategy, demonstrating that simultaneous passivation of both perovskite interfaces leads to profound improvements in device efficiency and operational stability. The synergistic effect of defect suppression and charge balance optimization is fundamental to unlocking the full commercial potential of perovskite-based electroluminescent devices.

Strategies for Co-optimizing Efficiency and Operational Lifetime

The pursuit of commercially viable Perovskite Light-Emitting Diodes (PeLEDs) is fundamentally constrained by the inherent trade-off between achieving high efficiency and long operational lifetime. Defects at the interfaces between the perovskite emissive layer and the charge transport layers are primary culprits, acting as non-radiative recombination centers that reduce efficiency and as degradation initiation points that shorten device lifespan [47]. A bilateral interfacial passivation strategy has emerged as a powerful technique to address both challenges simultaneously. This approach involves the application of passivating materials to both the top and bottom interfaces of the perovskite layer, leading to a significant suppression of interfacial defects and a more balanced charge injection, thereby co-optimizing device performance and stability [47] [48].

This document provides detailed application notes and protocols for implementing bilateral passivation strategies, framing them within a broader thesis on enhancing PeLED stability research. It is structured to provide researchers with actionable methodologies, quantitative performance data, and essential visual guides for experimental workflows and material functions.

The following tables summarize key quantitative improvements in efficiency and operational lifetime achievable through bilateral passivation, as demonstrated in recent literature.

Table 1: Efficiency Enhancement via Bilateral Passivation

Device Parameter Unpassivated Control Device Bilaterally Passivated Device Passivation Material & Method Citation
Max. External Quantum Efficiency (EQE) 7.7% 18.7% TSPO1 (evaporated organic molecule) [47] [47]
Current Efficiency 20 cd A⁻¹ 75 cd A⁻¹ TSPO1 (evaporated organic molecule) [47] [47]
Max. EQE (Thermally Evaporated PeLED) Not Reported 8.86% 3AP-modified PEDOT:PSS (bottom) & Ammonium Salts (top) [48] [48]
Photoluminescence Quantum Yield (PLQY) of Film 43% 79% TSPO1 (evaporated organic molecule) [47] [47]

Table 2: Operational Lifetime Enhancement via Bilateral Passivation

Stability Metric Unpassivated Control Device Bilaterally Passivated Device Enhancement Factor Citation
T₅₀ Operational Lifetime 0.8 hours 15.8 hours ~20x [47]
Operational Lifetime (Thermally Evaporated PeLED) Not Reported 3.74 hours Not Reported [48]

Experimental Protocols for Bilateral Passivation

This section outlines a generalized protocol for fabricating bilaterally passivated PeLEDs, synthesizing methodologies from multiple sources [47] [49] [48].

Protocol: Bilateral Interfacial Passivation for QD-Based PeLEDs

Objective: To fabricate a high-efficiency and stable perovskite QLED by applying passivation layers to both the bottom and top interfaces of the quantum dot (QD) emissive layer.

Materials: ITO-coated glass substrates, PEDOT:PSS, Poly-TPD, synthesized CsPbBr₃ QDs, TSPO1 (or alternative phosphine oxide molecule), TPBi, LiF, Al.

Equipment: Spin coater, thermal evaporation system, glovebox, UV-Ozone cleaner.

Procedure:

  • Substrate Preparation and Hole Injection Layer (HIL) Deposition:

    • Pattern and clean the ITO substrates sequentially with detergent, deionized water, acetone, and isopropanol in an ultrasonic bath.
    • Treat the substrates with UV-ozone for 15-20 minutes.
    • Spin-coat the PEDOT:PSS solution onto the ITO at a speed of 4000-5000 rpm for 30-60 seconds.
    • Anneal the films on a hotplate at 150 °C for 15-20 minutes in air, then transfer them into a nitrogen-filled glovebox.

  • Bottom Interface Passivation and Hole Transport Layer (HTL) Formation:

    • Option A (Molecular Layer): Load the PEDOT:PSS/ITO substrates into the thermal evaporation chamber. Deposit a thin layer (e.g., 1-5 nm) of the passivation molecule (e.g., TSPO1) directly onto the PEDOT:PSS [47].
    • Option B (Modified HTL): Alternatively, mix the passivation agent directly into the HTL solution. For example, modify PEDOT:PSS with 3-amino-1-propanol (3AP) to form a less-conductive complex that also passivates the bottom interface [48].
    • If a separate HTL (e.g., Poly-TPD) is used, spin-coat it on top of the bottom passivation layer.

  • Perovskite Emissive Layer (EML) Deposition:

    • For QD-based devices, spin-coat the synthesized CsPbBr₃ QD ink (e.g., in octane) onto the prepared substrate.
    • Optimize the spin speed and time to achieve a uniform, pinhole-free film with the desired thickness (typically 30-50 nm).

  • Top Interface Passivation:

    • Without breaking vacuum (if possible), transfer the substrate with the QD film back to the thermal evaporation chamber.
    • Evaporate a second layer of the passivation molecule (e.g., TSPO1) directly onto the QD film. The thickness should be optimized, typically similar to the bottom layer [47].
    • Note: The necessity of treating both interfaces has been confirmed through comparison experiments with unilateral passivation, which show significantly lower performance gains [47].

  • Electron Transport Layer (ETL) and Cathode Deposition:

    • Deposit the ETL (e.g., TPBi, ~40-50 nm) via thermal evaporation.
    • Subsequently, deposit a thin LiF layer (~1 nm) followed by an Al cathode (~100 nm) through a shadow mask under high vacuum.

  • Device Encapsulation and Characterization:

    • Encapsulate the finished devices immediately with a glass lid and UV-curable epoxy inside the glovebox.
    • Characterize the current density-voltage-luminance (J-V-L) characteristics, EQE, and operational stability under constant current driving.
Workflow Visualization

The following diagram illustrates the logical sequence and key decision points in the bilateral passivation protocol.

G Start Start: Substrate Preparation A HIL Deposition (e.g., PEDOT:PSS) Start->A B Bottom Passivation A->B C Method Choice B->C D Evaporated Molecular Layer (e.g., TSPO1) C->D Option A E Solution-Processed Modification (e.g., 3AP in PEDOT:PSS) C->E Option B F HTL Deposition (e.g., Poly-TPD) D->F E->F G Perovskite EML Deposition (Spin-coating QDs) F->G H Top Passivation (Evaporate TSPO1) G->H I ETL & Cathode Deposition (TPBi, LiF, Al) H->I End Encapsulation & Characterization I->End

The Scientist's Toolkit: Research Reagent Solutions

This table details key materials used in bilateral passivation strategies and their critical functions in device performance.

Table 3: Essential Materials for Bilateral Passivation Experiments

Research Reagent Function / Rationale Application in Bilateral Strategy
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Phosphine oxide-based passivator. The P=O group has a strong binding affinity with uncoordinated Pb²⁺ ions on the perovskite surface, effectively neutralizing defect sites. DFT calculations show a bond order of 0.2 with Pb, which is stronger than conventional ligands [47]. Can be thermally evaporated on both the bottom interface (on HTL) and top interface (on QDs) to form a bilateral defect-passivation shield [47].
Formamidinium Bromide (FABr) with Alkylamine Salts Precursor for 2D perovskite passivation. Promotes the formation of a homogeneous 2D perovskite layer on top of a 3D perovskite, which passivates surface defects and enhances environmental stability [50]. Used as a top-surface treatment to create a stable, phase-pure 2D capping layer, improving efficiency and moisture resistance [50].
3-Amino-1-Propanol (3AP) Modifier for PEDOT:PSS. Interacts with PEDOT:PSS to form a less-conductive complex and can induce the formation of a wide-bandgap phase (e.g., Cs₄PbBr₆) at the interface, improving charge balance [48]. Applied to the bottom interface as a modifier for the HIL, aiding in hole injection and initial passivation [48].
Ammonium Salts Surface ligands for perovskites. Can bind to perovskite surface sites, passivating ionic defects. Also can manipulate crystallization kinetics [48]. Introduced at the top interface of the thermally evaporated perovskite layer to passivate surface defects and optimize charge injection [48].
Terpyridine Ligands Concentration-independent passivator. Strongly coordinates with perovskite surface sites, providing durable passivation that is less prone to leaching or degradation over time [49]. While demonstrated in solar cells, this class of ligands holds promise for enhancing the operational lifetime of PeLEDs via top-surface passivation.

Mechanism Visualization: Bilateral Passivation Function

The core principle of the bilateral strategy and its impact on device performance is summarized in the following diagram.

G Problem Problem: Interfacial Defects P1 Non-Radiative Recombination Problem->P1 Strategy Bilateral Passivation Strategy Problem->Strategy Solution P2 Unbalanced Charge Injection P1->P2 P3 Ion Migration Channels P2->P3 S1 Apply Passivator to Bottom Interface Strategy->S1 S2 Apply Passivator to Top Interface S1->S2 Mechanism Key Mechanism S1->Mechanism S2->Mechanism M1 P=O Group (e.g., TSPO1) Strongly binds to Uncoordinated Pb²⁺ Mechanism->M1 Outcome Device Outcome M1->Outcome O1 ↑ PLQY of Film ↑ Radiative Recombination Outcome->O1 O2 ↑ Charge Balance ↑ Current Efficiency/EQE O1->O2 O3 ↓ Degradation ↑ Operational Lifetime (T₅₀) O2->O3

Addressing Stability Challenges in Tin-Based and Wide-Bandgap Perovskites

Metal halide perovskites (MHPs) have emerged as a revolutionary class of semiconductors for light-emitting diodes (PeLEDs), offering exceptional photoluminescence quantum yields (PLQYs), narrow emission linewidths, and tunable bandgaps across the visible spectrum [10]. Despite rapid efficiency advancements with external quantum efficiencies (EQEs) now exceeding 20% for green and red devices, operational instability remains the primary barrier to their commercial implementation in displays and solid-state lighting [37]. The degradation processes in PeLEDs are multifaceted, originating from both internal factors (ionic migration, defect proliferation, phase segregation) and external influences (oxygen, moisture, thermal stress) [37]. This application note examines stability challenges in two strategically important material classes—tin-based perovskites (as lead-free alternatives) and wide-bandgap perovskites (for tandem applications)—within the framework of a bilateral interfacial passivation strategy. We provide detailed experimental protocols and reagent solutions to empower researchers in developing stable, high-performance PeLEDs.

Tin-Based Perovskites: Combating Oxidation and Defect Formation

Fundamental Instability Mechanisms

Tin-based perovskites represent the most promising lead-free alternatives due to their comparable electronic structure and ideal bandgaps (e.g., 1.2-1.4 eV for FASnI₃) [51]. However, the susceptibility of Sn²⁺ to oxidize to Sn⁴⁺ upon exposure to even trace oxygen presents a fundamental challenge [8] [51]. This oxidation creates Sn vacancies that act as p-type dopants, increasing non-radiative recombination and deteriorating film morphology [51]. The resulting high carrier density accelerates device degradation and compromises performance reproducibility.

Quantitative Performance Limitations

Table 1: Performance Metrics of Tin-Based PeLEDs Highlighting Stability Challenges

Device Structure Emission Wavelength (nm) Maximum EQE (%) Operational Stability Year Reference
ITO/m-PEDOT:PSS/(BTm)₂SnI₄/TPBi/LiF/Al 627 3.33 66 h at 95 cd/cm² 2021 [37]
ITO/PEDOT:PSS/PTAA/CsPbBr₃/TPBi/PO-T2T/LiF/Al 520 21.6 180.1 h at 100 cd/cm² 2021 [37]
Stabilization Strategy 1: Reducing Agent Integration

Protocol: Incorporating Tin(II) Fluoride (SnF₂) as a Reducing Agent

  • Objective: To suppress Sn²⁺ oxidation during perovskite crystallization and film formation.
  • Materials: Formamidinium iodide (FAI), tin(II) iodide (SnI₂), tin(II) fluoride (SnF₂), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF).
  • Procedure:
    • Prepare precursor solution by dissolving FAI (1.0 M) and SnI₂ (1.0 M) in 1:1 v/v DMSO:DMF solvent mixture.
    • Add SnF₂ additive at 5-10 mol% relative to SnI₂ into the precursor solution.
    • Stir the mixture at 60°C for 12 hours in an inert atmosphere glovebox (O₂ & H₂O < 0.1 ppm).
    • Deposit the solution onto substrates via spin-coating (4000 rpm for 30 s).
    • Anneal at 100°C for 10 minutes to form crystalline FASnI₃ film.
  • Mechanism: SnF₂ functions as a sacrificial agent that preferentially oxidizes over the perovskite lattice, thereby "buffering" the Sn²⁺ within the crystal structure [8] [51]. The fluoride ions may also passivate surface defects and reduce Sn vacancy concentration.
Stabilization Strategy 2: Bilateral Passivation for Tin Perovskites

Protocol: Bilateral Interface Passivation with Phosphine Oxide Molecules

  • Objective: To passivate interfacial defects at both the bottom and top interfaces of the tin perovskite film, suppressing non-radiative recombination and ion migration.
  • Materials: Tin perovskite film, diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1), anhydrous ethanol.
  • Procedure:
    • Bottom Interface Passivation: Before perovskite deposition, thermally evaporate a 1-2 nm layer of TSPO1 onto the underlying charge transport layer (e.g., PEDOT:PSS or NiOx).
    • Perovskite Deposition: Spin-coat the tin perovskite precursor solution (as prepared in Protocol 2.3) onto the passivated substrate and anneal.
    • Top Interface Passivation: After perovskite film formation and cooling, thermally evaporate a second 1-2 nm layer of TSPO1 directly onto the perovskite surface.
    • Continue with the deposition of the remaining charge transport layers and electrodes.
  • Mechanism: The P=O group in TSPO1 strongly coordinates with undercoordinated Sn²⁺ ions at both interfaces, neutralizing deep-level traps [5] [10]. This bilateral approach mitigates charge injection barriers, reduces non-radiative losses, and blocks pathways for ion migration and oxygen infiltration.

TinStabilization cluster_oxidation Sn²⁺ Oxidation Problem cluster_solutions Stabilization Strategies O2 O₂ Exposure Sn4 Oxidation to Sn⁴⁺ O2->Sn4 Sn2 Sn²⁺ Sn2->Sn4 Voids Sn Vacancies & P-type Doping Sn4->Voids ReducingAgent Reducing Agent (SnF₂) ReducingAgent->Sn2 Protects Outcomes Outcomes: • Reduced Non-Radiative Recombination • Suppressed Ion Migration • Enhanced Film Morphology ReducingAgent->Outcomes Passivation Bilateral Passivation (TSPO1 Molecules) Coordination Strong P=O  Sn²⁺ Coordination Passivation->Coordination Coordination->Outcomes

Diagram 1: Stabilization pathways for tin-based perovskites, addressing Sn²⁺ oxidation through reducing agents and bilateral passivation.

Wide-Bandgap Perovskites: Mitigating Phase Separation and VOC Loss

Fundamental Instability Mechanisms

Wide-bandgap (WBG) perovskites (Eg > 1.7 eV), typically achieved through bromine incorporation, are essential for tandem solar cells and blue-emitting PeLEDs [52]. These materials suffer from severe open-circuit voltage (VOC) losses and operational instability primarily due to halogen phase separation [52]. During film crystallization, bromine-rich phases ([PbBr₆]⁴⁻ octahedra) preferentially nucleate at the film surface due to lower solubility, while iodine-rich phases accumulate at the bottom, creating an inhomogeneous energy landscape that impedes efficient carrier extraction and promotes non-radiative recombination [52].

Quantitative Performance Limitations

Table 2: Performance Metrics of Wide-Bandgap PeLEDs and Solar Cells

Device Type Bandgap (eV) Key Challenge Best Reported VOC Best Reported PCE/EQE Reference
WBG PSC 1.75 Severe VOC loss from phase separation 1.32 V 20.80% (PCE) [52]
Blue PeLED - Efficiency & stability lagging - ~11% (EQE) [37]
Quasi-2D PeLED - Thermal quenching - 22.2% (EQE) [25]
Stabilization Strategy 1: Crystallization Control for Homogeneous Halogen Distribution

Protocol: Templated Crystallization Using Double-Layer 2P Molecules (D-2P)

  • Objective: To achieve homogeneous halogen-phase distribution in WBG perovskite films through bottom-up crystallization control.
  • Materials: ITO/NiOx substrate, 2-(9H-Carbazol-9-yl)ethyl]phosphonic acid (2P molecules), absolute ethanol, FAI, CsI, PbI₂, PbBr₂.
  • Procedure:
    • D-2P Structure Construction: a. Spin-coat a thin 2P film from solution onto a pre-cleaned ITO/NiOx substrate. b. Rinse with absolute ethanol to remove non-oriented molecules, leaving a self-assembled monolayer (S-2P). c. The exposed carbazole groups enable π-π stacking to form a stable double-layer (D-2P) structure.
    • Perovskite Deposition: Spin-coat the WBG perovskite precursor (e.g., FA₀.₈Cs₀.₁₅MA₀.₀₅Pb(I₀.₇Br₀.₃)₃) onto the D-2P-functionalized substrate.
    • Annealing: Anneal at 100°C for 30 minutes to form the crystalline film.
  • Mechanism: The D-2P structure provides nucleation sites that simultaneously reduce the formation energy of both Br-phase and I-phase perovskites. This induces a bottom-up crystallization process, resulting in a homogeneous halogen distribution that enhances VOC and operational stability [52].
Stabilization Strategy 2: Defect Passivation for Thermal Quenching Suppression

Protocol: Dual Passivation of Quasi-2D Perovskites with DBPF Molecules

  • Objective: To suppress thermal quenching by passivating coordination-unsaturated Pb²⁺ defects in both the bulk and surface of quasi-2D WBG perovskite films.
  • Materials: 2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl)-fluorene (DBPF), PEA₂FAₙ₋₁PbₙBr₃ₙ₊₁ quasi-2D perovskite precursor, dimethyl sulfoxide (DMSO), ethyl acetate (EA).
  • Procedure:
    • Bulk Passivation: Add DBPF (0.5-1.0 wt%) directly into the perovskite precursor solution in DMSO.
    • Film Deposition: Spin-coat the solution onto the substrate.
    • Surface Passivation: During spin-coating, introduce an antisolvent (EA) containing DBPF (0.1-0.3 mg/mL) for surface treatment.
    • Annealing: Anneal at 90°C for 15 minutes.
  • Mechanism: The phosphonate groups in DBPF coordinate with undercoordinated Pb²⁺ defects without altering crystallization kinetics. This passivation reduces defect-promoted exciton-phonon coupling, the root cause of thermal quenching, enabling devices to maintain ~85% of initial EQE at 85°C [25].

Diagram 2: Stabilization pathways for wide-bandgap perovskites, addressing phase separation and thermal quenching through crystallization control and defect passivation.

The Scientist's Toolkit: Essential Research Reagents and Materials

Table 3: Key Research Reagent Solutions for Perovskite Stability Enhancement

Reagent/Material Function/Application Key Mechanism Experimental Consideration
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Bilateral interfacial passivation layer P=O group coordinates with undercoordinated metal cations (Pb²⁺/Sn²⁺), passivating interface defects [5] Thermal evaporation (1-2 nm) provides uniform, pinhole-free layers on both QD film interfaces.
SnF₂ (Tin(II) Fluoride) Reducing agent for tin-based perovskites Suppresses Sn²⁺ oxidation to Sn⁴⁺, reduces Sn vacancy density [51] Optimal at 5-10 mol%; excess can lead to phase segregation. Requires strict inert atmosphere processing.
2P Molecules (2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) Templated crystallization for WBG perovskites Forms D-2P structure on NiOx, providing nucleation sites for homogeneous halogen distribution [52] Ethanol rinse after spin-coating removes non-oriented molecules for optimal D-2P formation.
DBPF (2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl)-fluorene) Defect passivator for quasi-2D perovskites Phosphonate groups passivate coordination-unsaturated Pb²⁺ defects without affecting crystallization [25] Flexible solubility allows for both bulk (via precursor) and surface (via antisolvent) passivation.
Ethanolamine-treated ZnO (E-ZnO) Electron transport layer (ETL) with enhanced interface stability In situ passivation of ZnO NPs reduces surface defects and slows degradation reaction with perovskite cations [53] Low-temperature synthesis (<65°C) suitable for flexible substrates; improves stability vs. pristine ZnO.

Integrated Experimental Workflow: Implementing Bilateral Passivation

Protocol: Comprehensive Bilateral Passivation for Enhanced PeLED Stability

  • Objective: To implement a complete bilateral passivation strategy that addresses both bottom and top interface defects in a standard PeLED architecture.
  • Materials: ITO/glass substrates, NiOx or PEDOT:PSS HTL, perovskite precursors, TSPO1, TPBi, LiF, Al.
  • Procedure:
    • Substrate Preparation: Clean ITO substrates sequentially with detergent, deionized water, acetone, and isopropanol via ultrasonication for 15 minutes each. Treat with UV-ozone for 15 minutes.
    • Bottom Interface Engineering: a. Deposit hole transport layer (HTL; e.g., NiOx or PEDOT:PSS) via spin-coating. b. Thermally evaporate a 1-2 nm layer of TSPO1 onto the HTL at a rate of 0.1 Å/s under high vacuum (<10⁻⁶ Torr).
    • Perovskite Active Layer Deposition: a. For tin-based perovskites: Follow Protocol 2.3 with reducing agents. b. For wide-bandgap perovskites: Follow Protocol 3.3 for templated crystallization or Protocol 3.4 for dual passivation.
    • Top Interface Engineering: Thermally evaporate a second 1-2 nm layer of TSPO1 directly onto the perovskite film at a rate of 0.1 Å/s.
    • Device Completion: Deposit electron transport layer (ETL; e.g., TPBi, 40 nm), followed by LiF (1 nm) and Al (100 nm) electrodes via thermal evaporation.
  • Quality Control: Characterize film quality using PLQY measurements (>80% target) and trap density via SCLC methods. Monitor device stability under constant current driving at elevated temperatures (e.g., 85°C).

Diagram 3: Comprehensive experimental workflow for implementing bilateral passivation in PeLED fabrication, including key quality control steps.

Performance Validation: Quantifying the Impact of Bilateral Passivation on PeLED Metrics

The pursuit of high-performance perovskite light-emitting diodes (PeLEDs) is often hampered by non-radiative recombination losses at the interfaces of the emissive layer. Defects, such as uncoordinated lead atoms and halide vacancies, are prone to form during quantum dot (QD) film assembly, severely affecting carrier injection, transportation, and recombination, which ultimately degrades device performance [5]. This Application Note details the implementation and validation of a bilateral interfacial passivation strategy, a method proven to drastically enhance the efficiency and operational stability of perovskite QD-based LEDs (QLEDs) [5] [42]. We provide a comprehensive experimental protocol and dataset demonstrating how passivating both the top and bottom interfaces of the perovskite QD film leads to dramatic improvements in external quantum efficiency (EQE), current efficiency, and photoluminescence quantum yield (PLQY).

Key Performance Data

The following tables summarize the quantitative enhancements in film properties and device performance achieved through bilateral passivation.

Table 1: Enhancement in Film Photoluminescence Properties

Passivation Strategy PLQY (%) FWHM (nm) Defect Density Reference
Unpassivated CsPbBr3 QD Film 43 ~20 High [5]
Bilateral Passivation (TSPO1) 79 ~20 Significantly Reduced [5]

Table 2: Enhancement in PeLED Device Performance

Passivation Strategy Max EQE (%) Current Efficiency (cd A⁻¹) Operational Lifetime (T₅₀, hours) Reference
Unpassivated Device 7.7 20 0.8 [5]
Bilateral Passivation (TSPO1) 18.7 75 15.8 (~20x improvement) [5]
Hybrid Ligand (GABr & DDAB) 10.02 36.4 Not Specified [54]

Experimental Protocol: Bilateral Interfacial Passivation

This section provides a detailed methodology for fabricating high-efficiency PeLEDs using the bilateral passivation strategy, as established in the referenced work [5].

Materials and Reagent Solutions

Table 3: Research Reagent Solutions

Reagent / Equipment Function / Specification Key Notes
CsPbBr3 QD Ink Emissive layer material Synthesized via hot-injection; PLQY ~85%, FWHM ~20 nm [5].
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Bilateral passivation molecule Phosphine oxide group passivates uncoordinated Pb²⁺ defects [5].
Diphenylphosphine Oxide-4-(triphenylsilyl)phenyl (TSPO1) Bilateral passivation molecule Phosphine oxide group passivates uncoordinated Pb²⁺ defects [5].
Spin Coater Thin-film deposition For uniform layer deposition.
Thermal Evaporator Molecular layer deposition For depositing TSPO1 and metal electrodes.
Photoluminescence Spectrometer Optical characterization For measuring PLQY and spectrum.
Quantum Efficiency Measurement System Device characterization For measuring EQE and current efficiency.

Step-by-Step Procedure

  • Substrate Preparation and HTL Deposition:

    • Begin with a pre-patterned ITO glass substrate.
    • Clean the substrate sequentially with detergent, deionized water, and ethanol via ultrasonication for 20 minutes each, then dry in an oven.
    • Subject the substrate to UV-ozone treatment for 20 minutes to improve surface wettability.
    • Deposit the Hole Transport Layer (HTL), such as PEDOT:PSS, onto the ITO via spin-coating and anneal according to standard protocols.

  • Bilateral Passivation: Bottom Interface:

    • Load the HTL-coated substrate into a thermal evaporation chamber.
    • Thermally evaporate a thin, continuous layer of TSPO1 molecules (approximately 1-5 nm) directly onto the HTL surface. This creates the bottom passivation layer.

  • Perovskite QD Film Deposition:

    • Transfer the substrate with the bottom passivation layer into a nitrogen-filled glovebox.
    • Deposit the CsPbBr3 QD ink onto the TSPO1/HTL surface via spin-coating (e.g., 3000 rpm for 30 seconds).
    • Anneal the film on a hotplate at a moderate temperature (e.g., 60-70°C for 10 minutes) to remove residual solvent.

  • Bilateral Passivation: Top Interface:

    • Transfer the substrate back to the thermal evaporation chamber.
    • Evaporate a second layer of TSPO1 molecules of similar thickness directly onto the top surface of the QD film. This completes the bilateral passivation scheme.

  • Electron Transport Layer and Electrode Deposition:

    • Deposit the Electron Transport Layer (ETL), such as TPBi, via thermal evaporation.
    • Finally, complete the device by thermally evaporating a metal cathode (e.g., LiF/Al) through a shadow mask to define the active pixel area.

Validation and Characterization

  • Film Quality Check: Use photoluminescence (PL) imaging under a UV lamp to visually confirm enhanced and uniform luminescence from the bilaterally-passivated QD film compared to an unpassivated control [5].
  • Device Performance Testing: Measure the current-voltage-luminance (J-V-L) characteristics of the completed PeLEDs using a source meter and a calibrated photodiode. Calculate EQE and current efficiency from this data.
  • Lifetime Testing: Operate the devices at a constant current density to measure the operational stability, recording the time until the luminance drops to 50% of its initial value (T₅₀).

Underlying Mechanisms and Workflow

The efficacy of the bilateral passivation strategy is rooted in the targeted chemical suppression of interfacial defects and the subsequent improvement in charge dynamics within the device.

G Start Start: Device Fabrication HTL Deposit Hole Transport Layer (HTL) Start->HTL BotPass Evaporate Bottom Passivation Layer (TSPO1) HTL->BotPass PerovQD Spin-Coat Perovskite Quantum Dot (QD) Film BotPass->PerovQD P2 Defect Passivation BotPass->P2 TopPass Evaporate Top Passivation Layer (TSPO1) PerovQD->TopPass ETL Deposit Electron Transport Layer (ETL) TopPass->ETL TopPass->P2 Electrode Deposit Metal Electrode ETL->Electrode End End: Completed PeLED Electrode->End P1 Unpassivated Interface P1->P2 P3 Improved Charge Injection P2->P3 P4 Enhanced Radiative Recombination P3->P4 P5 High EQE & Stability P4->P5

Diagram 1: Bilateral passivation experimental workflow and its functional impact on device performance.

Molecular Mechanism of Defect Passivation

The core mechanism involves the interaction between the phosphine oxide (P=O) functional group in TSPO1 and uncoordinated Pb²⁺ ions on the surface of the perovskite QDs. Density functional theory (DFT) calculations confirm a forming energy of -1.1 eV for this bond, indicating a strong and spontaneous interaction [5].

  • Defect Suppression: This coordination bond effectively neutralizes deep-level trap states associated with uncoordinated Pb, as evidenced by a significant reduction in trap state density observed in calculated density of states (DOS) plots [5].
  • Robust Interface: The P=O group exhibits a higher bond order (0.2) with Pb compared to common ligands like oleic acid or oleylamine, leading to a more stable interface that is less prone to ligand loss under electrical stress [5].

Impact on Device Charge Dynamics

The bilateral passivation layer directly influences the flow and recombination of charge carriers, as illustrated below.

G cluster_Unpassivated Unpassivated Device cluster_Passivated Bilaterally Passivated Device Cathode Cathode ETL ETL Cathode->ETL Defect1 Defect ETL->Defect1 TopPass Top Passivation Emissive Perovskite QD Emissive Layer Defect2 Defect Emissive->Defect2 BotPass Bottom Passivation HTL HTL Anode Anode HTL->Anode Defect1->Emissive NonRadiative Non-Radiative Recombination Defect1->NonRadiative Defect2->HTL Defect2->NonRadiative Cathode2 Cathode ETL2 ETL Cathode2->ETL2 TopPass2 Top Passivation ETL2->TopPass2 Emissive2 Perovskite QD Emissive Layer TopPass2->Emissive2 BotPass2 Bottom Passivation Emissive2->BotPass2 Radiative Radiative Recombination Emissive2->Radiative HTL2 HTL BotPass2->HTL2 Anode2 Anode HTL2->Anode2

Diagram 2: Charge dynamics comparison between unpassivated and bilaterally passivated PeLEDs.

In the unpassivated device, defects at both interfaces trap charge carriers, leading to non-radiative recombination and energy loss. The bilateral TSPO1 layer acts as a defect-blocking and charge-regulating layer, which smoothens carrier injection into the QD layer, reduces trapping, and promotes balanced bimolecular radiative recombination, thereby boosting efficiency and luminance [5] [10].

The bilateral interfacial passivation strategy represents a significant advancement in the fabrication of high-performance PeLEDs. The protocol outlined herein, utilizing TSPO1 molecules, has been empirically demonstrated to suppress interfacial defects, enhance radiative recombination, and improve charge injection. This results in a dramatic enhancement of key performance metrics, including a rise in EQE from 7.7% to 18.7%, a surge in current efficiency from 20 to 75 cd A⁻¹, and a 20-fold extension of operational device lifetime [5]. This approach provides a robust and effective pathway for researchers developing stable and efficient perovskite-based optoelectronic devices.

The pursuit of stable perovskite light-emitting diodes (PeLEDs) is a central focus in the field of optoelectronics. While device efficiencies have seen remarkable improvements, operational lifetime remains a significant barrier to commercialization. Within this context, the bilateral interfacial passivation strategy has emerged as a profoundly effective method for enhancing device stability. This Application Note details how this specific strategy has led to quantified, order-of-magnitude improvements in operational lifetime, exemplified by a documented 20-fold enhancement in T50, the time taken for luminance to drop to 50% of its initial value [47]. We present the supporting quantitative data, detailed experimental protocols for implementing this passivation, and essential tools for researchers aiming to replicate and build upon these stability breakthroughs.

Quantified Stability Enhancements from Bilateral Passivation

The following table summarizes key experimental results from seminal work on bilateral interfacial passivation, highlighting the dramatic improvements in both efficiency and operational stability.

Table 1: Quantified Performance Enhancements from Bilateral Interfacial Passivation in Perovskite QLEDs

Performance Metric Control Device (Unpassivated) Bilaterally Passivated Device Improvement Factor Experimental Conditions
Maximum External Quantum Efficiency (EQE) 7.7% 18.7% ~2.4x [47]
Current Efficiency 20 cd A⁻¹ 75 cd A⁻¹ ~3.75x [47]
Operational Lifetime (T₅₀) 0.8 hours 15.8 hours ~20x Initial luminance specified in the study [47]
Photoluminescence Quantum Yield (PLQY) of Film 43% 79% ~1.8x [47]

This data originates from a study where a bilateral passivation strategy was employed by evaporating a layer of organic molecules, specifically the phosphine oxide TSPO1, on both the top and bottom interfaces of the perovskite quantum dot (QD) film [47]. The 20-fold enhancement in T₅₀ is a direct result of suppressing defect-mediated non-radiative recombination and ion migration at the critical interfaces between the QD layer and the charge transport layers.

Experimental Protocol: Bilateral Passivation with TSPO1

This section provides a detailed methodology for implementing the bilateral interfacial passivation strategy, as validated by the data in Table 1.

Materials and Equipment

  • Substrate: ITO-coated glass.
  • Perovskite QDs: CsPbBr₃ QDs synthesized via hot-injection method [47].
  • Passivation Molecule: Diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1).
  • Charge Transport Layers: As required by standard PeLED/QLED architecture (e.g., PEDOT:PSS for hole injection).
  • Equipment: Thermal evaporation system, glovebox, spin-coater, spectrophotometer, electroluminescence measurement system.

Step-by-Step Procedure

  • Device Fabrication:

    • Clean and prepare ITO substrates with standard oxygen plasma treatment.
    • Deposit the bottom charge transport layer (e.g., PEDOT:PSS) via spin-coating and anneal.

  • Bottom Interface Passivation:

    • Transfer the substrate into a thermal evaporation chamber.
    • Thermally evaporate a thin, continuous layer of TSPO1 molecules directly onto the bottom charge transport layer. The typical thickness is on the order of nanometers.

  • Perovskite QD Film Deposition:

    • Transfer the substrate back to the glovebox.
    • Deposit the CsPbBr₃ QD film via spin-coating onto the TSPO1-passivated surface.

  • Top Interface Passivation:

    • Return the substrate with the QD film to the thermal evaporation chamber.
    • Evaporate a second layer of TSPO1 molecules directly onto the top surface of the QD film.

  • Device Completion:

    • Complete the device stack by depositing the top charge transport layer and metal electrodes (e.g., TPBi/LiF/Al) via thermal evaporation.

  • Characterization:

    • Perform current-voltage-luminance (J-V-L) measurements to determine EQE and current efficiency.
    • For operational stability (T₅₀), drive the device at a constant current to achieve a specific initial luminance and record the luminance decay over time until it reaches 50% of the initial value.

Underlying Mechanisms and Workflow

The effectiveness of this protocol hinges on the molecular interaction between the passivator and the perovskite. Density functional theory (DFT) calculations confirm a strong binding energy (-1.1 eV) between the uncoordinated Pb²⁺ ions on the QD surface and the P=O group of TSPO1 [47]. This interaction fills trap states, eliminating non-radiative recombination centers. Furthermore, the bilateral placement forms a protective barrier that suppresses ion migration, a key driver of device degradation [47] [55].

The Scientist's Toolkit: Essential Research Reagents

Successful implementation of bilateral passivation strategies requires specific functional materials. The table below lists key reagent solutions used in the featured and related studies.

Table 2: Key Research Reagent Solutions for Interfacial Passivation

Reagent / Material Chemical Function Role in Passivation Example Use Case
TSPO1 Phosphine oxide molecule Coordinates with uncoordinated Pb²⁺ ions via P=O group, eliminating surface trap states. Primary molecule for bilateral passivation in QLEDs [47]. Bilateral interfacial passivation in CsPbBr₃ QLEDs [47].
K-NDS (Dipotassium 7-hydroxynaphthalene-1,3-disulfonate) Organic salt with -SO₃⁻ and -OH groups -SO₃⁻ fills oxygen vacancies in metal oxide ETLs (e.g., SnO₂); -OH passivates dangling bonds in perovskite [56]. Dual-sided interface modification between SnO₂ ETL and perovskite absorber in solar cells [56].
3-Amino-1-propanol (3AP) Amino-alcohol compound Modifies PEDOT:PSS hole injection layer, suppresses non-radiative defects at the interface with the evaporated perovskite EML [57]. Part of a bilateral defect-passivation strategy in thermally evaporated PeLEDs [57].
Ammonium Salts Ionic compounds Passivate defects at the top interface of the perovskite emissive layer, improving film quality and balancing charge injection [57]. Part of a bilateral defect-passivation strategy in thermally evaporated PeLEDs [57].

The bilateral interfacial passivation strategy represents a paradigm shift in stabilizing perovskite optoelectronic devices. The quantitative data, demonstrating up to a 20-fold enhancement in operational lifetime (T₅₀), provides a compelling validation of its efficacy [47]. This Application Note has outlined the core experimental protocol, the critical reagents, and the fundamental mechanisms behind this breakthrough. By addressing defect densities at both critical interfaces of the perovskite layer, this approach simultaneously boosts efficiency and profoundly extends device longevity. Future research will undoubtedly focus on expanding the library of multifunctional passivation molecules and adapting these strategies to large-scale, industrial fabrication processes.

Within the development of perovskite optoelectronics, interfacial defects remain a primary factor limiting device performance and operational stability. This application note provides a comparative analysis of non-passivated, unilaterally passivated, and bilaterally passivated devices, quantifying the impact of these strategies on key performance metrics. We present structured experimental protocols and data to guide researchers in implementing these passivation methods, supporting a broader thesis on bilateral interfacial passivation for PeLED stability research.

The following tables consolidate key quantitative findings from comparative studies, highlighting the performance advantages of bilateral passivation.

Table 1. Comparative Performance Metrics for Perovskite Light-Emitting Diodes (PeLEDs)

Performance Parameter Non-Passivated Device Unilaterally Passivated Device Bilaterally Passivated Device Citation
Maximum External Quantum Efficiency (EQE) ~7.7% Not Reported ~18.7% [47]
Current Efficiency ~20 cd A⁻¹ Not Reported ~75 cd A⁻¹ [47]
Operational Lifetime (T₅₀) ~0.8 hours Not Reported ~15.8 hours [47]
Photoluminescence Quantum Yield (PLQY) of Film ~43% Not Reported ~79% [47]
Maximum EQE (Synergistic Passivation) Not Applicable Not Applicable ~21% [58]
Maximum Luminance (Synergistic Passivation) Not Applicable Not Applicable ~60,000 cd m⁻² [58]
Maximum EQE (Buried Interface) Not Applicable Not Applicable 25.5% (4 mm²) [59]

Table 2. Performance Metrics for Perovskite Solar Cells (PSCs) with Buried Interface Passivation

Performance Parameter Control Device Device with Bilateral Anchoring Citation
Power Conversion Efficiency (PCE) - Rigid 23.19% 25.50% [15]
Power Conversion Efficiency (PCE) - Flexible Not Reported 24.92% [15]
Power Conversion Efficiency (PCE) - 1 cm² Not Reported 24.01% [15]

Experimental Protocols for Passivation Strategies

Bilateral Interfacial Passivation for PeLEDs

This protocol details the bilateral passivation of perovskite quantum dot (QD) films, adapted from a strategy that significantly enhances efficiency and stability [47].

  • Key Reagents: CsPbBr₃ QD ink; Passivation molecules (e.g., TSPO1, DDAB).
  • Equipment: Spin coater, Thermal evaporator, Glovebox, Annealing oven.

Procedure: 1. Substrate Preparation: Clean the underlying charge transport layer (e.g., TiO₂ or SnO₂ for ETL) and treat with UV-ozone for 20 minutes. 2. Bottom Interface Passivation: Thermally evaporate a thin layer (~5-10 nm) of the organic passivation molecule (e.g., TSPO1) onto the substrate. 3. Perovskite QD Film Deposition: Spin-coat the CsPbBr₃ QD ink onto the passivated substrate inside a nitrogen-filled glovebox. Typical parameters: 1500-3000 rpm for 30-60 seconds. 4. Top Interface Passivation: Thermally evaporate the same or a different passivation molecule onto the freshly deposited QD film. 5. Device Completion: Proceed with the deposition of the subsequent charge transport layer and metal electrodes to complete the device architecture.

Validation & Analysis: - Use density functional theory (DFT) calculations to confirm the binding energy between passivation molecules and perovskite surface defects (e.g., uncoordinated Pb²⁺). - Characterize the reduced defect density via Space Charge-Limited Current (SCLC) measurements. - Measure the photoluminescence quantum yield (PLQY) of the passivated film to confirm enhanced radiative recombination.

Synergistic Passivation via Additive Engineering

This protocol utilizes a dual-functional compound, potassium bromide (KBr), added directly to the perovskite precursor to achieve bulk and surface passivation simultaneously [58].

  • Key Reagents: Perovskite precursors (e.g., PbBr₂, FABr, PEABr, MACl); KBr; Dimethyl sulfoxide (DMSO).
  • Equipment: Spin coater, Glovebox, Annealing hotplate.

Procedure: 1. Precursor Solution Preparation: Prepare the quasi-2D perovskite precursor solution in DMSO. For a standard formulation, mix PbBr₂, FABr, PEABr, and MACl in a molar ratio of 5:4:2:0.5. 2. Additive Incorporation: Add a 0.1 M KBr solution directly into the perovskite precursor solution. The concentration of KBr should be optimized, typically resulting in a final K⁺ concentration of 1-5 mol% relative to Pb²⁺. 3. Film Deposition: Spin-coat the mixture onto the prepared substrate (e.g., PVP/PVK on ITO). A typical two-step program is 1100 rpm for 10 s (spread) followed by 6000 rpm for 25 s (throw). 4. Anti-Solvent Treatment: During the final 5-10 seconds of the spin-coating process, drop-cast an anti-solvent (e.g., ethyl acetate, 100 µL) to induce rapid crystallization. 5. Annealing: Transfer the film to a hotplate and anneal at 90°C for 60 minutes.

Validation & Analysis: - Perform FTIR and XPS to confirm chemical interaction between KBr and perovskite components (passivation of halide vacancies and lead dangling bonds). - Measure UV-Vis absorption and photoluminescence (PL) spectra to observe changes in the phase distribution and energy transfer efficiency. - Use time-resolved photoluminescence (TRPL) to quantify the increase in carrier lifetime.

Buried Interface Modification for Perovskite Solar Cells

This protocol focuses on constructing a robust molecular bridge at the buried SnO₂/perovskite interface using squaric acid (SA) to enhance PSC performance and stability [15].

  • Key Reagents: SnO₂ colloidal dispersion; Squaric acid (SA); Perovskite precursors (e.g., PbI₂, FAI, MACl).
  • Equipment: Spin coater, UV-Ozone cleaner, Thermal evaporator, Glovebox.

Procedure: 1. Electron Transport Layer (ETL) Deposition: Spin-coat the SnO₂ colloidal dispersion onto a clean ITO/glass substrate (4000 rpm, 30 s). Anneal at 90°C for 1 hour. 2. Interface Modification: Prepare an aqueous SA solution (5-7 mg mL⁻¹). Spin-coat this solution onto the SnO₂ layer (4000 rpm, 30 s). Anneal at 100°C for 10 minutes. 3. Surface Treatment: Subject the SA-modified SnO₂ film to UV-ozone treatment for 20 minutes. 4. Perovskite Deposition: Transfer the substrate to a glovebox. Deposit the perovskite precursor solution (e.g., (CsPbI₃)₀.₀₂₅(FAPbI₃)₀.₈₂₅(MAPbBr₃)₀.₁₅) via a two-step spin-coating program (1100 rpm for 10 s, then 4500 rpm for 36 s). Introduce a chlorobenzene anti-solvent 15 seconds before the end of the second step. 5. Annealing and Completion: Anneal the perovskite film at 105°C for 50 minutes. Complete the device by sequentially depositing the hole transport layer (e.g., spiro-OMeTAD) and metal electrodes (e.g., Au).

Validation & Analysis: - Use X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy to verify the formation of coordination bonds and hydrogen bonds between SA, SnO₂, and the perovskite. - Perform in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) to study the impact of SA on perovskite crystallization kinetics. - Conduct steady-state and time-resolved photoluminescence (TRPL) to demonstrate improved charge extraction at the modified interface.

The Scientist's Toolkit: Essential Research Reagents

Table 3. Key Reagent Solutions for Perovskite Passivation Studies

Reagent Solution Function & Mechanism Application Context
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Passivates uncoordinated Pb²⁺ defects via strong P=O---Pb bonding. Reduces non-radiative recombination. Bilateral interfacial passivation for QLEDs [47]
Potassium Bromide (KBr) Synergistic passivation: Br⁻ anions fill halide vacancies; K⁺ cations screen charged defects via dielectric screening. Additive engineering in quasi-2D PeLEDs [58]
Lithium Bromide (LiBr) Buried interface modifier induces monodisperse perovskite phase formation, minimizing trap states. Pre-modification layer on substrate for PeLEDs [59]
Squaric Acid (SA) Self-regulated bilateral anchoring via hydrogen/coordination bonds. Releases residual stress and passivates defects at the SnO₂/perovskite interface. Buried interface modification for high-performance PSCs [15]
Deep Eutectic Solvent (DES)(e.g., Choline Chloride + Ethylene Glycol) Ionic passivation of uncoordinated Pb²⁺ and halide vacancies via multiple ionic interaction sites. Reduces interfacial recombination. Surface passivation for carbon-based PSCs in ambient air [60]

Experimental Workflow Visualization

The following diagram illustrates the logical workflow for designing and validating an effective bilateral passivation strategy, integrating the protocols and analyses described above.

G Start Define Device Performance Goal Substrate Prepare Substrate and ETL/HTL Start->Substrate PassivationChoice Select Passivation Strategy Substrate->PassivationChoice Bilateral Bilateral Interface Modification PassivationChoice->Bilateral Maximize stability & efficiency Unilateral Unilateral Interface Modification PassivationChoice->Unilateral Target single interface Additive Additive Engineering (Bulk Passivation) PassivationChoice->Additive Bulk defect passivation Depo Deposit Perovskite Active Layer Bilateral->Depo Unilateral->Depo Additive->Depo Complete Complete Device Fabrication Depo->Complete Analyze Performance Validation & Analysis Complete->Analyze

Diagram 1. Workflow for Passivation Strategy Development. This diagram outlines the decision-making process for selecting and implementing passivation strategies, from substrate preparation to final device validation. ETL: Electron Transport Layer; HTL: Hole Transport Layer.

Table 1: Essential Research Reagents for Bilateral Interface Passivation

Reagent Primary Function Application Context
4-methoxy-phenylethylammonium iodide (MEO-PEAI) Organic halide salt passivator for 3D perovskite surfaces; suppresses non-radiative recombination at interfaces [16]. Post-treatment solution applied to perovskite film surface to enhance VOC and efficiency [16].
Ammonium Thiocyanate (NH₄SCN) Facilitates perovskite recrystallization and enables passivator penetration to the buried interface without forming charge-blocking 2D phases [16]. Mixed with MEO-PEAI in a post-treatment strategy for bilateral (top and buried) interface passivation [16].
p-Fluorocinnamoyl Chloride (p-FCACl) In-situ chlorination (isCl) agent; releases Cl⁻ ions to fill halide vacancies and transforms into p-fluorocinnamic acid (p-FCA) for defect renovation [61]. Added to antisolvent for post-treatment of reduced-dimensional perovskite (RDP) films to renovate multiple defects and regulate phase distribution [61].
Thio-tributylphosphine (S-TBP) Ligand that forms stable Pb-S-P coordination bonds (Eads = -1.13 eV) on perovskite nanoplatelet surfaces, suppressing defect states [62]. Used in an acid-assisted ligand exchange process for colloidal CsPbBr₃ nanoplatelets to achieve high PLQY (96%) and stable deep-blue emission [62].
Carbonized Polymer Dots (CPDs) Modifies solid-liquid interface interaction during film formation; anchors anions to substrate, orients crystal growth, and passivates buried traps for uniform large-area films [63]. Mixed into the PEDOT:PSS hole transport layer (HTL) prior to depositing the perovskite emitter layer [63].

Detailed Experimental Protocols for Key Validation Techniques

Protocol for Space-Charge-Limited Current (SCLC) Measurement for Defect Density Analysis

The SCLC method is used to quantify the trap density (ntrap) in perovskite films, which is a critical metric for evaluating the efficacy of any passivation strategy.

  • Device Fabrication: Fabricate electron-only devices with a structure of ITO/SnO₂/Perovskite/PCBM/Ag. The key is to use charge transport layers that form ohmic contacts for electrons while blocking holes, ensuring the current is limited by space charge.
  • Current-Voltage (J-V) Measurement: Measure the dark J-V characteristics of the device. The voltage sweep should be performed from 0 V to a higher voltage (e.g., 4-5 V) to capture the different conduction regimes.
  • Data Analysis:
    • Identify the kink point between the ohmic region and the TFL region on the log J–log V plot. This voltage is the trap-fill-limit voltage (VTFL).
    • Calculate the trap density (ntrap) using the formula: ntrap = (2εrε0VTFL) / (eL²) where εr is the relative permittivity of the perovskite, ε0 is the vacuum permittivity, e is the elementary charge, and L is the thickness of the perovskite film.

Protocol for Time-Resolved Photoluminescence (TRPL) for Carrier Recombination Kinetics

TRPL measures the photoluminescence decay lifetime, providing insight into charge carrier recombination dynamics and the quality of passivation.

  • Sample Preparation: Prepare a glass/Perovskite sample, ideally with a control (unpassivated) and a passivated film.
  • Measurement Setup: Use a time-correlated single photon counting (TCSPC) system. Excite the sample with a pulsed laser source (e.g., a ~400 nm diode laser) and record the decay of the PL signal at the peak emission wavelength.
  • Data Fitting and Analysis:
    • Fit the decay curve to a bi-exponential or tri-exponential function: I(t) = A₁exp(-t/τ₁) + A₂exp(-t/τ₂) + A₃exp(-t/τ₃) + C
    • Calculate the amplitude-weighted average lifetime (τavg): τavg = (A₁τ₁² + A₂τ₂² + A₃τ₃²) / (A₁τ₁ + A₂τ₂ + A₃τ₃)
    • A significant increase in τavg after passivation indicates suppressed non-radiative recombination. For example, one study reported τavg increasing from 4.55 ns to 10.94 ns after effective passivation [61].
    • Calculate the radiative (kr) and non-radiative (knr) recombination rates using the PLQY and the average lifetime: kr = PLQY / τavg knr = (1 - PLQY) / τavg A decrease in knr (e.g., from 2.11 × 10⁸ s⁻¹ to 9.14 × 10⁷ s⁻¹ [61]) is a direct indicator of successful defect passivation.

Protocol for Transient Absorption (TA) Spectroscopy for Ultrafast Carrier Dynamics

TA spectroscopy probes ultrafast processes like hot carrier cooling, exciton dissociation, and charge trapping on femtosecond to nanosecond timescales.

  • Experimental Setup: A pump-probe setup is used. A strong "pump" pulse excites the sample, and a weaker, delayed "probe" pulse (white light continuum) monitors changes in absorption (ΔA) at various wavelengths and time delays.
  • Key Measurements:
    • Ground-State Bleach (GSB): The negative ΔA signal at the band edge corresponds to the filling of electronic states (bleaching). The recovery kinetics of the GSB report on charge carrier recombination and trapping.
    • Photoinduced Absorption (PIA): Positive ΔA signals can indicate excited-state absorption or trapped carriers.
  • Data Interpretation: Slower GSB recovery kinetics in passivated samples, as observed in CsPbBr₃ nanoplatelets, indicate a reduction in defect-assisted trapping and enhanced radiative recombination pathways [62]. Combining TA with TRPL, as done in a study on PVK/HTL interfaces, provides a comprehensive view of recombination and extraction mechanisms [64].

Protocol for Density Functional Theory (DFT) Calculations for Defect and Interaction Mechanisms

DFT calculations provide atomic-level insights into the interaction between passivator molecules and perovskite surfaces, explaining experimental observations.

  • Model Construction: Build a slab model of the relevant perovskite surface (e.g., PbI₂-terminated (100) surface for 3D perovskites). Introduce a defect of interest, such as an iodine vacancy (VI) or a Pb-I antisite defect.
  • Calculation of Adsorption Energy: Calculate the adsorption energy (Eads) of the passivator molecule on the defective surface. A more negative Eads indicates a stronger, more stable binding. Eads = E(slab+passivator) - Eslab - Epassivator For example, S-TBP on CsPbBr₃ NPLs showed a high Eads of -1.13 eV [62], while Me-4PACz demonstrated strong electrostatic interaction with iodine vacancies at the PVK interface [64].
  • Electronic Structure Analysis: Analyze the projected density of states (PDOS) before and after passivation. Effective passivation often reduces mid-gap defect states, which is the theoretical signature of suppressed non-radiative recombination [61] [64].

Integrated Experimental Workflow for PeLED Interface Analysis

The following diagram illustrates the logical relationship and workflow for applying these validation techniques in a cohesive strategy for bilateral interface passivation research.

G cluster_0 Optoelectronic Characterization Start Bilateral Passivation Strategy A Material Synthesis & Film Deposition Start->A B Apply Passivation (Post-treatment/Additive) A->B C Structural & Morphological Analysis (SEM, XRD, AFM) B->C E Optoelectronic Characterization B->E G Data Correlation & Mechanism Understanding C->G D Theoretical Investigation (DFT Calculations) D->G Validates F Device Fabrication & Performance Test E->F Informs Optimization E->G TRPL TRPL E->TRPL TA TA Spectroscopy E->TA SCLC SCLC E->SCLC PL Steady-State PL & PLQY E->PL F->G Performance Correlation

Table 2: Quantitative Data from Passivation Studies

Analysis Technique Control Sample (Unpassivated) Passivated/Treated Sample Key Parameter & Improvement Reference Context
TRPL τavg = 4.55 ns τavg = 10.94 ns Average Lifetime: 2.4x increase RDP films with isCl treatment [61]
TRPL knr = 2.11 × 10⁸ s⁻¹ knr = 9.14 × 10⁷ s⁻¹ Non-radiative Rate: 56.7% decrease RDP films with isCl treatment [61]
PLQY 38.6% 60.9% Absolute PLQY: 22.3 pt increase RDP films with isCl treatment [61]
PLQY 19% 96% Absolute PLQY: 77 pt increase CsPbBr₃ NPLs with acid-assisted ligand passivation [62]
Device Performance PCE = N/A PCE = 24.3% Champion Solar Cell Efficiency PSCs with MEO-PEAI & NH₄SCN [16]
Device Performance Max EQE = 3.46% Max EQE = 6.17% Deep-Blue PeLED EQE: 1.78x increase RDP PeLEDs with isCl treatment [61]

The pursuit of stable and efficient perovskite-based optoelectronic devices has identified interfacial passivation as a critical engineering strategy. While effective for specific material formulations, the true challenge and opportunity lie in establishing the material universality of these techniques—their ability to enhance performance and stability across diverse perovskite compositions and device architectures. This Application Note systematically validates a bilateral interfacial passivation strategy, demonstrating its efficacy in devices ranging from multi-cation mixed-halide perovskite photovoltaics to quantum dot light-emitting diodes (PeLEDs). The data and protocols herein provide a framework for researchers to implement and verify this approach, accelerating the development of robust perovskite devices.

Quantitative Performance Validation Across Compositions

The bilateral passivation strategy, which involves the application of passivating layers to both the top and bottom interfaces of the perovskite active layer, has been quantitatively assessed across several material systems. The following tables summarize key performance metrics, highlighting its universal benefits.

Table 1: Performance Enhancement from Bilateral Passivation in Perovskite QLEDs [5]

Parameter Control Device Bilateral Passivation (TSPO1) Enhancement
Maximum External Quantum Efficiency (EQE) 7.7% 18.7% ~2.4x
Current Efficiency 20 cd A⁻¹ 75 cd A⁻¹ ~3.75x
Operational Lifetime (T₅₀) 0.8 h 15.8 h ~20x
Photoluminescence Quantum Yield (PLQY) of Film 43% 79% ~1.8x

Table 2: Stability Performance of Passivated Multi-Component Perovskite Solar Cells [65] [66]

Perovskite System & Passivation Device Architecture PCE (%) Stability Performance
Cs₀.₀₅(FA₀.₈₃MA₀.₁₇)₀.₉₅Pb(I₀.₈₃Br₀.₁₇)₃ w/ CEAI 2D/3D [65] n-i-p 23.57 >96% of initial PCE after 1500 h MPPT (1 sun, N₂)
Multi-cation mixed-halide w/ Sodium Heptafluorobutyrate (SHF) [66] p-i-n 27.02 (Certified: 26.96) 100% of initial PCE after 1200 h MPPT (1-sun illumination)
Multi-cation mixed-halide w/ Sodium Heptafluorobutyrate (SHF) [66] p-i-n 27.02 (Certified: 26.96) 92% of initial PCE after 1800 h at 85°C

Table 3: Universal Performance Trends of Bilateral Passivation

Aspect Universal Impact Validated Compositions/Architectures
Electronic Defects Significant reduction in trap-state density; increased PLQY and carrier lifetime. CsPbBr₃ QDs [5]; 3D MCPs (Cs/FA/MA) [65] [66]
Ion Migration Increased activation energy (Eₐ) for ion migration, suppressing hysteresis and degradation. Mixed-halide perovskites [67]; 2D/3D systems [68]
Environmental Stability Enhanced hydrophobicity and barrier against moisture/oxygen ingress. 2D/3D perovskites with cyclohexylethylammonium [65]
Interface Energetics Favorable work function tuning and band alignment for improved charge extraction. p-i-n PSCs with SHF [66]; QLEDs with TSPO1 [5]

Experimental Protocols for Bilateral Passivation

Objective: To apply a molecular passivation layer to both the bottom and top interfaces of a spin-coated perovskite QD film to suppress non-radiative recombination and enhance operational stability.

Materials:

  • Synthesized CsPbBr₃ QD ink (e.g., via hot-injection method).
  • Passivation molecule solution (e.g., 2 mg/mL TSPO1 in anhydrous ethanol).
  • Electron transport layer (ETL) and hole transport layer (HTL) materials as required by device architecture.
  • Substrates (e.g., ITO-patterned glass).

Procedure:

  • Substrate Preparation: Clean the ITO/glass substrates with sequential sonication in detergent, deionized water, acetone, and isopropanol. Treat with UV-ozone for 15-20 minutes.
  • Deposit Bottom Charge Transport Layer: Spin-coat the bottom HTL (e.g., PEDOT:PSS) or ETL onto the clean substrate and anneal as required.
  • Apply Bottom Passivation Layer: Transfer the substrate into a thermal evaporation chamber. Thermally evaporate a thin, continuous film (e.g., 5-10 nm) of the passivation molecule (TSPO1) directly onto the bottom charge transport layer.
  • Deposit Perovskite QD Active Layer: Transfer the substrate back to a nitrogen-filled glovebox. Spin-coat the CsPbBr₃ QD ink onto the passivation layer at 2000-3000 rpm for 30-60 seconds to form a uniform film.
  • Apply Top Passivation Layer: Immediately after QD film deposition, thermally evaporate a second layer of the passivation molecule (TSPO1) of identical thickness directly onto the QD film.
  • Complete Device Fabrication: Without delay, deposit the top charge transport layer (opposite to the bottom layer) followed by the metal electrodes (e.g., Au or Ag) via thermal evaporation.

Validation Metrics:

  • Measure the steady-state PLQY of the bilateral-passivated QD film versus a control.
  • Fabricate complete QLED devices and record J-V-L characteristics and operational stability (T₅₀).

Objective: To form a thin 2D perovskite capping layer on a 3D multicomponent perovskite surface via post-treatment to passivate interfacial defects and enhance hydrophobicity.

Materials:

  • Pre-formed 3D perovskite film (e.g., Cs₀.₀₅MA₀.₁FA₀.₈₅PbI₂.₉Br₀.₁·0.05PbI₂).
  • Passivation salt solution (e.g., 20 mM cyclohexylethylammonium iodide (CEAI) in isopropyl alcohol (IPA)).

Procedure:

  • Prepare 3D Perovskite Film: Fabricate the multicomponent 3D perovskite film on a mesoporous TiO₂/FTO substrate using a one-step anti-solvent crystallization method. Anneal at 100°C for 60 minutes.
  • Post-Treatment Application: After the 3D perovskite film has cooled to room temperature, dynamically spin-coat the CEAI-IPA solution (e.g., 3000 rpm for 30 s) onto the film.
  • Form 2D Capping Layer: Immediately transfer the film to a hotplate and anneal at 100°C for 10 minutes to facilitate the reaction between CEAI and residual PbI₂ on the 3D perovskite surface, forming a 2D CEA₂PbI₄ phase.
  • Complete Device Stack: Proceed with the deposition of the hole-transporting layer (e.g., spiro-MeOTAD) and metal electrode.

Validation Metrics:

  • Use X-ray diffraction (XRD) to confirm the formation of characteristic 2D perovskite peaks (e.g., at 4.7°, 9.5°) and the consumption of residual PbI₂.
  • Perform time-resolved photoluminescence (TRPL) to observe an increased carrier lifetime in the passivated film.
  • Conduct X-ray photoelectron spectroscopy (XPS) to identify the new nitrogen species from the CEA⁺ cation.

The Scientist's Toolkit: Research Reagent Solutions

Table 4: Essential Reagents for Bilateral Interfacial Passivation

Reagent / Material Function / Role Example Composition / Notes
TSPO1 (Diphenylphosphine oxide-4-(triphenylsilyl)phenyl) Bilateral passivation molecule for QLEDs. Coordinates with undercoordinated Pb²⁺ via P=O group, suppressing defect states and blocking ion migration [5]. Solution in anhydrous ethanol (2 mg/mL). Applied via thermal evaporation.
CEAI (Cyclohexylethylammonium Iodide) Forms a 2D perovskite capping layer on 3D films. Passivates surface defects, improves energy level alignment, and enhances hydrophobicity [65]. 20 mM solution in isopropyl alcohol (IPA). Applied via spin-coating.
SHF (Sodium Heptafluorobutyrate) Forms an ion shield and dipole layer on the perovskite surface. Increases defect formation energy, tunes work function, and promotes compact ETL deposition [66]. Aqueous or methanolic solution. Optimal concentration is critical.
Multi-Component Perovskite Precursors Provides a stable, tunable base absorber layer. Synergistic A-site cation mixing (Cs, FA, MA) stabilizes the perovskite α-phase and increases ion migration activation energy [67]. e.g., Cs₀.₀₅(FA₀.₈₃MA₀.₁₇)₀.₉₅Pb(I₀.₈₃Br₀.₁₇)₃ [67] [65].
FBPA (Fluorinated Benzyl Ammonium Salt) Aromatic ammonium salt for 2D/3D heterostructures. Imparts high hydrophobicity and defect passivation at the grain boundaries and interface [65]. Solution in IPA. Can be mixed with precursor or applied as post-treatment.

Workflow and Logical Diagrams

The following diagram illustrates the logical workflow for implementing and validating the bilateral passivation strategy across different perovskite compositions.

G Start Define Target Perovskite Composition & Architecture P1 A: Multi-Cation 3D Perovskite (e.g., Cs/FA/MA) Start->P1 P2 B: Perovskite Quantum Dots (e.g., CsPbBr₃) Start->P2 P3 C: 2D/3D Heterostructure Start->P3 S1 Synthesize/Deposit Perovskite Active Layer P1->S1 P2->S1 P3->S1 D1 Apply Bilateral Passivation S1->D1 D1_Sub1 Method 1: Evaporated Small Molecule (TSPO1) D1->D1_Sub1 D1_Sub2 Method 2: Solution-Processed 2D Capping Layer (CEAI) D1->D1_Sub2 D1_Sub3 Method 3: Dipole Layer & Ion Shield (SHF) D1->D1_Sub3 C1 Fabricate Complete Device (PV Cell or LED) D1_Sub1->C1 D1_Sub2->C1 D1_Sub3->C1 V1 Validate Performance & Universality C1->V1 V1_Sub1 Metric 1: Electronic Properties (PCE, EQE, PLQY) V1->V1_Sub1 V1_Sub2 Metric 2: Operational Stability (MPPT, T₅₀) V1->V1_Sub2 V1_Sub3 Metric 3: Ionic/Structural (Ion Migration Eₐ, XRD) V1->V1_Sub3

Diagram 1: Universal Workflow for Validating Bilateral Passivation Strategies. This workflow outlines the process from material selection to final validation, demonstrating the applicability of passivation strategies across compositions A, B, and C via different methods (1, 2, 3).

This Application Note provides compelling evidence for the material universality of bilateral interfacial passivation. The consistent observation of enhanced electronic properties, suppressed ion migration, and dramatically improved operational stability across varied perovskite compositions—from multi-cation 3D absorbers to quantum dots, and in both n-i-p and p-i-n architectures—establishes this strategy as a foundational principle for advancing perovskite optoelectronics. The detailed protocols and reagent toolkit equip researchers to implement these methods, thereby accelerating the development of commercially viable, stable perovskite devices. Future work should focus on extending these principles to wider bandgap perovskites for tandem applications and purely tin-based compositions.

Conclusion

The bilateral interfacial passivation strategy represents a paradigm shift in the pursuit of stable and high-performance PeLEDs. By systematically addressing defect states at both the top and bottom interfaces of the perovskite layer, this approach simultaneously suppresses non-radiative recombination, inhibits ion migration, and balances charge injection. The synthesis of evidence confirms that this method delivers transformative improvements in key performance metrics, most notably a dramatic extension of operational lifetime by up to 20-fold and a significant boost in external quantum efficiency. Future directions should focus on the high-throughput screening of novel passivation molecules with stronger binding affinities, the development of universal passivation protocols applicable to a wider range of perovskite compositions—including tin-based and blue-emitting devices—and the integration of these strategies into scalable manufacturing processes. Overcoming the stability bottleneck through sophisticated interface engineering is the critical final step toward the successful commercialization of PeLEDs for next-generation displays and solid-state lighting.

References