Orientation Regulation of One-Dimensional CsCu₂I₃Perovskites for Visible-Blind Ultraviolet Photodetectors

Ternary copper halides with a formula of CsCu2X3 (X = Cl, Br, I) have been considered as prospective materials for ultraviolet (UV) photodetectors, due to their suitable band gaps, environmental stability, eco-friendliness, and low cost. However, the crystal orientation of one-dimensional (1D) CsCu2X3 perovskites significantly affects the exciton/carrier transport in the films and thus the photodetector performance. Here, we tune the crystal orientation and exciton/charge transport of 1D CsCu2I3 perovskite films by using antisolvents during the film formation process. Compared to the randomly oriented film treated by ethyl acetate, the CsCu2I3 film using toluene as antisolvent exhibits preferential (221)-oriented growth, which induces enhanced vertical exciton diffusion/charge transport and suppressed nonradiative recombination. On the basis of this strategy, we demonstrate a self-powered, stable, and visible-blind UV photodetector with significantly enhanced response speed and detectivity. Our work clarifies that tuning the crystal orientation of 1D CsCu2X3 perovskites is the key to achieve efficient exciton diffusion/charge transport and thus high-performance lead-free perovskite optoelectronic devices.