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 Cs3Cu3Cl9 single crystals is developed from the known phase of 0D Cs3Cu2I5 via addition of HCl. The transformed 3D Cs3Cu3Cl9 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/Cs3Cu3Cl9/C heterostructure UV photodetector showed a remarkable responsivity of 0.13 mA W−1 and specific detectivity of 2.20 × 109 Jones under 372 nm UV illumination at zero bias, possessing a better performance than the 0D Cs3Cu2I5 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.