Recent Advances in Hole Transport Layer Engineering for High-Performance Quantum Dot Light-Emitting Diodes

Owing to their superior color purity and solution-processability, quantum dot light-emitting diodes (QLEDs) have garnered significant attention as promising candidates for next-generation displays. However, overcoming efficiency degradation and limited operational lifetime, which stem from charge transport imbalance, remains a critical challenge. Herein, we systematically discuss the role of the hole transport layer (HTL) in mitigating this imbalance. We classify HTL engineering strategies into four key categories: energy-level alignment, hole mobility and carrier concentration control, improvement in solvent stability, and multilayer architectures. Furthermore, we discuss hybrid HTL architectures that integrate multiple strategies to achieve synergistic improvement. Ultimately, this review highlights the pivotal role of HTL engineering in realizing high-performance QLEDs and provides insightful perspectives on future research directions.