Influence of hole trapping on the electroluminescence of Cu-In-Zn-S quantum dots

Charge dynamics plays a fundamental and critical role in the performance of quantum-dot light-emitting diodes (QLEDs). While extensive research has been conducted on charge dynamics in CdSe-based QLEDs, the influence of charge behavior on multinary Cu-In-Zn-S (CIZS) quantum dots (QDs) remains largely unexplored. In this study, we demonstrate that hole transport in CIZS QD films is more efficient than electron transport. Notably, a fraction of the injected holes is trapped within the QDs even after the driving voltage is removed, leading to significant degradation in device efficiency. By incorporating an n-type small molecule hole-blocking layer at the interface between the QDs and the hole transport layer, we mitigated hole injection, resulting in a substantial improvement in QLED efficiency (from 5.5 to 6.5 cd/A). Our findings underscore the importance of a thorough understanding of charge dynamics within the QD emission layer for optimizing device design.