Microemulsion‐Induced Stable CsPbBr3/PbWO4 Nanocrystals for Light‐Emitting Diodes

All‐inorganic cesium lead halide perovskite colloidal nanocrystals (NCs) (CsPbX3, X = Cl, Br, I) have emerged as potential candidates for next‐generation light‐emitting diodes (LEDs). However, high trap states on the surface of CsPbX3 NCs caused by ionic nature and dynamic bonding of organic ligands limit the performance of CsPbX3 NCs‐based LEDs. Herein, a microemulsion (ME)‐modified strategy to decorate CsPbBr3 NC cores with inorganic PbWO4 is developed. It is demonstrated that ME‐assisted modification plays a crucial role in bridging the WO42− anion solution and the CsPbBr3 NC suspension. Compared with pristine CsPbBr3 NCs, the obtained PbWO4‐modified NCs exhibit improved photoluminescence efficiency. The corresponding NC films also show enhanced stability at elevated temperature and also in humid atmosphere. Consequently, the PbWO4‐modified NCs‐based LED exhibits a pronounced improvement of electroluminescence with an external quantum efficiency from 0.2% to 5.7% and twofold enhancement of the operational lifetime through PbWO4 passivation in comparison with that of pristine CsPbBr3 NCs‐based LED. These results show a promising pathway by ME‐induced anionic modification for high‐performance and stable LEDs based on perovskite NCs.