More Than 9% Efficient ZnSeTe Quantum Dot-Based Blue Electroluminescent Devices

We explore both the synthesis of Cd-free blue quantum dots (QDs) with high-quality photoluminescence (PL) characteristics and the fabrication of high-efficiency QD light-emitting diodes (QLEDs). True blue (445 nm)-emissive, multishelled ZnSeTe QDs with a high PL quantum yield of 84% and a sharp bandwidth of 27 nm are prepared. To obtain a better electron transport layer (ETL) material, the surface of ZnMgO nanoparticles (NPs) is modified by additional Mg reaction, leading to the possible formation of a Mg­(OH)2 layer on the surface-modified ZnMgO (m-ZnMgO) NPs. The presence of a Mg­(OH)2 overlayer, the origin of the desirably reduced electron mobility, is supposedly responsible for the improved charge balance of the QD emissive layer (EML). The Mg­(OH)2 layer is further found to alleviate the emission quenching of the QD EML. Via combination of blue ZnSeTe QDs and m-ZnMgO NP ETL, highly bright, efficient blue QLEDs with the record luminance of 2904 cd/m2 and an external quantum efficiency of 9.5% are demonstrated.