Improving Performance of InP-Based Quantum Dot Light-Emitting Diodes by Controlling Defect States of the ZnO Electron Transport Layer

ZnO nanoparticles (NPs) are currently the benchmark of electron transport materials for preparing indium phosphide (InP)-based environmentally friendly quantum dot light-emitting diodes (QLEDs). However, the defect-dependent exciton quenching and charge injection limiting behavior at the ZnO/quantum dot (QD) interface seriously restrict the improvement in device performance. Herein, we report a strategy based on Li doping and MgO shell coating to regulate the defect state of ZnO to improve the performance of InP-based QLEDs. It is found that Li doping passivates the intrinsic defect states of ZnO NPs and improves the electron mobility and reduces the spontaneous charge transfer at the ZnO/QD interface and the current leakage of QLEDs. The MgO shell passivates the surface oxygen defects of ZnO NPs, thus reducing the exciton quenching and non-radiative recombination centers at the ZnO/QD interface, resulting in enhanced QLED performance. As a result, the optimized QLED prepared by Li-doped and MgO shell-coated ZnO NPs shows an external quantum efficiency of 9.7% and a brightness of 22,200 cd m–2 at 4.2 V, which are, respectively, 2.6 and 7 times higher than those of a QLED based on pure ZnO. This work shows that controlling the defect states of the ZnO electron transport layer by ion doping and shell coating provides an effective way to obtain high-performance environment-friendly QLEDs.