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

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.