Recent Progress in Quantum Dot Light-Emitting Diodes: Degradation Mechanisms and Strategies for Improving Device Stability and Reliability

Authors & Affiliations

Wenxin Lin^a, Bangxiong Kang^a, Paul W. M. Blom*^b, Quan Niu*^a, Yuguang Ma^a
* Corresponding Authors | Quan Niu ORCID: 0009-0007-3024-7222

^a State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, Guangdong 510641, P. R. China
^b Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
E-mail: blom@mpip-mainz.mpg.de (P. W. M. Blom), qqniu@scut.edu.cn (Q. Niu)

Abstract

Quantum dot light-emitting diodes (QLEDs) have emerged as core devices for next-generation solution-processed printed displays, owing to their size-tunable emission, high color purity, and low-cost fabrication. However, their commercialization is hindered by critical challenges: operational instability (characterized by initial luminance increase/positive aging followed by irreversible decay/intrinsic degradation) and unpredictable shelf-storage behavior (uncontrolled efficiency enhancement causing batch-to-batch inconsistency).

This review systematically summarizes recent advances in three key aging mechanisms of QLEDs: 1. Operation-induced positive aging: Originating from optimized charge balance (e.g., enhanced hole injection, suppressed electron leakage) but leading to unpredictable luminance fluctuations; 2. Operation-induced intrinsic degradation: Driven by trap formation in quantum dots (QDs), electron leakage-induced hole transport layer (HTL) damage, interfacial charge accumulation, and ion migration in electron transport layers (ETLs); 3. Shelf-storage-induced positive aging: Caused by acid/water-mediated defect passivation or spontaneous reactions at ZnMgO/Al interfaces, undermining long-term stability.

The review highlights cutting-edge characterization techniques (in situ electrical/optical spectroscopy, transient electroluminescence, impedance spectroscopy, depth profiling) that enable mechanistic insights beyond conventional methods. Corresponding mitigation strategies are also concluded, spanning material engineering (ligand optimization, QD structure design) and device architecture optimization (bilayer HTLs/ETLs, interface passivation). These findings provide a critical guideline for fabricating shelf-stable QLEDs with long operational lifetimes, particularly addressing the bottlenecks of blue and Cd-free QLEDs.

Review Highlights

Systematic Mechanism Summarization: First to comprehensively dissect three distinct aging behaviors of QLEDs (operation-induced positive aging/intrinsic degradation, shelf-storage-induced positive aging) and their interconnections, filling the gap in unified mechanistic understanding.
Advanced Characterization Focus: Emphasizes the role of state-of-the-art techniques (e.g., electrically excited transient absorption, in situ impedance spectroscopy) in resolving degradation sites (QD layer/HTL/ETL/interfaces) and quantifying trap density.
Targeted Strategy Framework: Concludes a "material-device-characterization" integrated strategy: ligand engineering (stable RNH₂ ligands) for QDs, bilayer HTLs (poly-TPD/PF8Cz) for charge balance, and Al₂O₃ passivation for ETLs to suppress ion migration.
Industry-Oriented Insights: Pinpoints key bottlenecks for commercialization (blue QLED T₉₅ lifetime < 500 h vs industrial requirement > 5000 h; Cd-free QLED stability gap) and proposes future research directions.
Cross-Disciplinary Perspective: Bridges QD material chemistry (core/shell/ligand design) with device physics (charge transport/recombination) and characterization technology, providing a holistic view for researchers in optoelectronics.

Research Background & Significance

QLEDs have achieved remarkable progress in efficiency (red/green QLED EQE > 35%/28%, comparable to OLEDs) and lifetime (red QLED T₉₅ > 60,000 h @ 1000 cd m⁻²). However, two critical issues impede commercialization:

1. Performance Instability: Unlike conventional devices with monotonic luminance decay, QLEDs exhibit non-monotonic luminance evolution (initial positive aging → intrinsic degradation) under electrical stress, complicating lifetime measurement and display consistency. For example, blue QLEDs show T₉₅ lifetimes as low as 227 h @ 1000 cd m⁻², far below industrial standards.

2. Batch-to-Batch Inconsistency: Shelf storage induces uncontrolled efficiency enhancement (positive storage aging) due to acid/water reactions with ETLs, leading to brightness discrepancies across production batches—a major barrier for mass manufacturing.

This review addresses these challenges by: (1) clarifying the root causes of each aging mechanism (e.g., hole trap formation in QDs, Mg ion migration in ZnMgO); (2) highlighting advanced techniques to quantify degradation (e.g., impedance spectroscopy for trap density, ToF-SIMS for ion diffusion); (3) providing actionable strategies (e.g., Cl⁻ passivation for blue QDs, acid-free encapsulation for shelf stability). It serves as a critical reference for optimizing QLED reliability and accelerating their industrialization.

Funding Support

Guangdong Innovative and Entrepreneurial Research Team Program (Grant No.: 2021ZT09L392)
Guangdong Basic Research Center of Excellence for Energy and Information Polymer Materials

Core Review Framework

1. Degradation Mechanisms of QLEDs

Operation-Induced Positive Aging: Arises from improved charge balance (e.g., interfacial dipoles enhancing hole injection, degraded ZnO/Ag interfaces reducing electron leakage).
Intrinsic Degradation:
- QD layer: Trap formation via ligand detachment (OA ligands) or electron-exciton interactions;
- HTL: Electron leakage-induced bond cleavage (C-N bonds in TFB/PF8Cz);
- ETL: ZnMgO ion migration (Mg²⁺) and oxygen vacancy formation;
- Interfaces: ITO corrosion by PEDOT:PSS, AlOₓ formation at ZnMgO/Al.
Shelf-Storage Aging: Acid (from encapsulation resin) or water-induced n-doping of ZnMgO, size-focusing ripening of ZnMgO NPs.

2. Characterization & Optimization Strategies

Advanced Characterization Techniques:
- In situ EL/PL: Distinguishes QD vs HTL degradation;
- Transient electroluminescence: Measures hole transit time in QD layers;
- Impedance spectroscopy: Quantifies trap density;
- ToF-SIMS/XPS depth profiling: Tracks ion diffusion and interfacial reactions.
Stability Enhancement Strategies:
- QD engineering: Alloyed ZnSeTeS (suppresses Te aggregation), Cl⁻/Zn(OA)₂ ligand passivation;
- Device design: Bilayer HTLs (poly-TPD/PF8Cz), Al₂O₃-passivated ZnMgO ETLs;
- Encapsulation: Acid-free epoxy resin, water vapor pre-treatment.