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.