Ultra‐Stable and Highly Efficient White Light Emitting Diodes through CsPbBr₃ Perovskite Nanocrystals−Silica Composite Phosphor Functionalized with Surface Phenyl Molecules

Abstract Poor stability of CsPbBr₃ perovskite nanocrystals (NCs) to moisture/heat/light has significantly limited their application as a green phosphor, despite their outstanding luminescent properties. Here, a remarkably stable CsPbBr₃ NCs−silica composite phosphor functionalized with surface phenyl molecules (CsPbBr₃−SiO₂^Ph) is synthesized by controlling low‐temperature hydrolysis and condensation reaction of perhydropolysilazane in the presence of CsPbBr₃ NCs followed by phenyl‐functionalization. Through the process, CsPbBr₃ NCs are confined in a compact silica matrix, which is impermeable to H₂O. The synthesis strategy is extended to a classical red quantum dot, CdZnSeS@ZnS NCs, to fabricate a white light emitting diode (WLED) consisting of CsPbBr₃−SiO₂^Ph and CdZnSeS@ZnS−SiO₂^Ph phosphor and silicone resin packaged on a commercial blue InGaN chip with luminous efficacy (LE) of 9.36 lm W⁻¹. The WLED undergoes enhancements in both green and red photoluminescence over time to achieve a highly efficient performance of 38.80 lm W⁻¹. More importantly, the WLED exhibits unprecedented operational stability of LE/LE₀ = 94% after 101 h‐operation at 20 mA (2.56 V). The ultra‐high operational stability and efficient performance are mainly attributed to thermal curing and aging through which grain growth occurs as well as deactivation of defect states by permeated atmospheric O₂.