Efficient\nCadmium-Free Inverted Red Quantum Dot Light-Emitting\nDiodes

Abstract

Here, we report an\nefficient inverted red indium phosphide (InP)\ncomprising QD (InP/ZnSe/ZnS, core/shell structure) light-emitting\ndiode (QLED) by modulating an interfacial contact between the electron\ntransport layer and emissive InP-QDs and applying self-aging approach.\nThe red InP-QLED with optimized interfacial contact exhibits a significant\nimprovement in maximum external quantum efficiency and current efficiency\nfrom 4.42 to 10.2% and 4.70 to 10.8 cd/A, respectively, after 69 days\nof self-aging, which is an almost 2.3-fold improvement compared to\nthe fresh device. The analysis indicates the consecutive reduction\nin electron injection and accumulation in the emissive QD due to changes\nin the conduction band minimum of ZnMgO (0.1 eV after 10 days of storage)\nthrough a downward vacuum-level shift according to the aging times.\nDuring the device aging periods, the oxygen vacancy of ZnMgO reduces,\nwhich leads to lower the conductivity of ZnMgO. As a result, charge\nbalance of the device is improved with the suppression of exciton\nquenching at the interface of ZnMgO and InP-QD.