Identification of excess charge carriers in InP-based quantum-dot light-emitting diodes

Abstract

InP-based quantum-dot light-emitting diodes (QLEDs) have recently attracted a lot of attention from academia and industry owing to their environment-friendly characteristics and have been hotly investigated as promising alternatives to toxic CdSe-based QLEDs. Although the performances of InP-QLEDs have been rapidly improved in recent years, the device mechanisms are not completely clear and there are still debates in the community regarding the details of excess charge carriers, which are expected to affect the charge balance and the efficiency of the devices. In this work, by studying the influence of charge injection on the efficiency and the charge carrier dynamics, we identify that holes are over-injected in InP-QLEDs, which is different from that in CdSe-QLEDs. By enhancing the injection of electrons and/or blocking the injection of holes, the population of excess holes is reduced, consequently enabling red and green InP-QLEDs with high external quantum efficiencies of 10.78% and 7.56%, respectively. Our work provides a practical way to identify the type of excess carrier and can serve as a useful guide for the optimization of charge balance in InP-QLEDs.