Room‐Temperature Crystallization of Ultralong (≈3.5 mm) CsCu ₂ I ₃ Microbelt to Suppress Carrier Recombination for High‐Performance UV Heterojunction Photodetector

Abstract Lead‐free ternary copper iodide perovskite analogues demonstrate great potential in photodetector, due to their nontoxity and excellent photophysical properties. However, the fast carrier recombination limits the photoelectric conversion efficiency. Herein, a room‐temperature growth strategy with the selected raw ratio is adopted to enhance carrier dynamics. The optimized‐grown CsCu ₂ I ₃ single crystal exhibits longer carrier lifetime of 157 ns, and its switch ratio and response time are enhanced by 20 000% and 600% compared with those of stoichiometric‐grown single crystal, respectively. Furthermore, space‐confined method is introduced to prepare ultralong single‐crystalline CsCu ₂ I ₃ microbelt, with the aspect ratio up to 600. The sensitivity and self‐powered performance of the UV photodetector are improved through constructing heterojunction with p‐CuI and asymmetric electrodes. The enhanced performance is ascribed to superior type‐II band alignment between CsCu ₂ I ₃ and CuI, which effectively promotes the separation of photogenerated carriers. This work not only provides an efficient way to boost the photoresponse in low‐dimensional metal halide perovskite analogue, but also displays 1D anisotropic growth for potential application in large‐area vapor‐assisted patterned devices.