HCl Assisted Transformation of Lead‐Free 0D Cs₃Cu₂I₅ Microcrystals to 3D Cs₃Cu₃Cl₉ Single Crystals for Self‐Powered UV Photodetection

Abstract Copper‐based halide perovskites have gained considerable interest in optoelectronic applications owing to their outstanding stability and luminescence properties. Herein, 3D structure of Cs 3 Cu 3 Cl 9 single crystals is developed from the known phase of 0D Cs 3 Cu 2 I 5 via addition of HCl. The transformed 3D Cs 3 Cu 3 Cl 9 single crystals exhibit superior material properties such as an optical bandgap of 2.39 eV, and distinct violet emission at 425 nm, making them a potential candidate for ultraviolet (UV) photodetection. The hierarchical FTO/Cs 3 Cu 3 Cl 9 /C heterostructure UV photodetector showed a remarkable responsivity of 0.13 mA W −1 and specific detectivity of 2.20 × 10 9 Jones under 372 nm UV illumination at zero bias, possessing a better performance than the 0D Cs 3 Cu 2 I 5 structure. This work brings insight into the transformation from 0D to 3D halide perovskite structure for self‐powered photodetectors via a simple solvent engineering strategy, thereby paving the way for further investigations in various optoelectronic applications.