Balancing Charge Injection for Enhanced Efficiency in Inverted InP Quantum Dot Light-Emitting Diodes

Abstract

Indium phosphide (InP) quantum dots (QDs) have emerged as promising candidates for next-generation display and solid-state lighting technologies. However, InP-based quantum dot light-emitting diodes (QLEDs) using zinc oxide nanoparticles (ZnO NPs) as the electron transport layer (ETL) suffer from performance degradation due to unbalanced carrier injection. This is mainly caused by the high electron mobility of ZnO, which leads to excessive electron injection into the emissive layer. In this study, Poly(4-vinylpyridine) (PVPy) is introduced as an electron-blocking interlayer between the ZnO ETL and the InP-QD emissive layer to mitigate this imbalance. The insulating nature of PVPy effectively limits electron injection, reducing charge accumulation and enhancing device performance. To further evaluate the role of hole transport layers (HTLs) in conjunction with PVPy, devices incorporating solution-processed HTLs such as TFB (in p-xylene), PTAA (in chlorobenzene), and a PTAA-PVK blend are fabricated. A thermally evaporated MoO3 layer is used as the hole injection layer with Ag as the anode. Devices incorporating the PVPy interlayer consistently outperform those without, confirming the interlayer's role in improving charge balance and overall QLED performance. This strategy provides valuable insight into interface engineering for high-performance, cadmium-free QLEDs.