Stable and Efficient White Photoluminescence from Cesium Lead Halide Perovskite Nanocrystals/Polyfluorene Organogel Composite by Suppressing of Halide Ion Migration

Abstract Luminescent perovskite nanocrystals (PNCs) receive great attention in recent years due to their sharp, intense, and easily tunable photoluminescence, suitable for optoelectronic applications. However, in reality, the emission bandgap tunability is limited due to rapid halide ion migration, commonly occurring in mixed halide perovskites. Consequently, it is challenging to produce white‐light emission by mixing PNCs having different emission colors. In this work, using a blue‐emitting polyfluorene (PF) to passivate the surface of yellow‐emitting CsPbBr_1.5I_1.5 based mixed halide PNC is reported not only to suppress the halide ion migration but also to generate stable and efficient white‐light emission through controlled excitation energy transfer from the former to the latter. PF gel arrests the detachment of capping ligands from the surface of nanocrystals, thereby hinders the halide ion migration and prevents the generation of related trap states. Consequently, the nonradiative recombination of photogenerated charge carriers has significantly reduced, resulting in the overall enhancement of the luminescence characteristics of the nanocrystals.