Strongly Emissive Lead‐Free 0D Cs3Cu2I5 Perovskites Synthesized by a Room Temperature Solvent Evaporation Crystallization for Down‐Conversion Light‐Emitting Devices and Fluorescent Inks

Abstract Lead‐free 0D metal halide perovskites are emerging environmentally friendly materials exhibiting large exciton binding energy, which have recently attracted great attention for their excellent light emission properties and favorable stability. Herein, solvent evaporation crystallization at room temperature is adopted to fabricate 0D Cs 3 Cu 2 I 5 perovskite millimeter‐sized crystals, which show strong blue photoluminescence (PL) with quantum yield of up to 89%, a large Stockes shift and long (microsecond) PL lifetime, originating from self‐trapped excitons. UV pumped light‐emitting diodes are demonstrated by using Cs 3 Cu 2 I 5 powder as a solid‐state phosphor, and the precursor solution of these perovskite crystals is used as a fluorescent ink. Furthermore, blue‐emitting composite Cs 3 Cu 2 I 5 /polyvinylidene fluoride films are produced by spin coating through the solvent evaporation and followed patterning using a direct laser writing technology, which are potentially useful for displays. Finally, the solvent evaporation crystallization method is expanded to fabricate yellow emissive CsCu 2 I 3 crystals by changing the chemical molar ratio of precursor.