Halide‐Precursor‐Controlled Defect Engineering in Mixed‐Halide CsPb(Cl, Br) ₃ Perovskite Nanocrystals for Enhanced Photoresponse

Amine‐based synthesis of mixed‐halide perovskite nanocrystals often suffers from dynamic surface‐ligand desorption, leading to defect formation, reduced photophysical properties, and poor environmental stability. Herein, we report an amine‐free strategy for synthesizing CsPb(Cl, Br) ₃ mixed‐halide perovskite nanocrystals using 1‐bromo‐3‐chloropropane (CBP) as a bifunctional halide precursor that simultaneously supplies Cl and Br within a single reaction system. This approach enables the formation of phase‐pure mixed‐halide perovskite nanocrystals without separate halide precursors or amine ligands. Systematic variation of CBP concentration promotes the formation of Br‐rich CsPb(Cl, Br) ₃ nanocrystals, as confirmed by UV–visible absorption, photoluminescence spectroscopy, and X‐ray diffraction analyses. Increasing the CBP concentration enhances the photoluminescence quantum yield (PLQY) from 5% to 70% and improves ambient stability, attributed to reduced defect densities under optimized halide‐rich conditions. However, excessive CBP concentration decreases the PLQY, indicating an optimal composition. The enhanced PLQY of Br‐rich nanocrystals promotes stronger visible‐light absorption and more efficient photogenerated exciton generation, resulting in improved photocurrent response. Defect‐rich samples exhibit slower photocurrent rise and decay due to increased charge trapping and recombination, whereas optimized compositions demonstrate faster and more stable photoresponse. Overall, this work provides a facile and versatile amine‐free route for compositionally tunable mixed‐halide perovskite nanocrystals for photodetector and optoelectronic applications.