Pinhole-free CsCu₂I₃ thin films by I₂-modification for solar-blind ultraviolet photodetector and application to free-space optical communication

Recently, copper-based lead-free perovskites have emerged as a promising material due to their unique physical properties, abundance on earth, and lower toxicity. Among them, CsCu₂I₃ has received extensive attention for optoelectronic device applications due to its excellent air stability and stable self-trapped exciton-based yellow emission. However, the inherent one-dimensional crystal structure of CsCu₂I₃-based perovskite makes it difficult to control the morphology during the synthesis process, which results in a high density of pinhole defects on the thin films. Here, we reported a strategy to obtain a high-quality and pinhole-free CsCu₂I₃ thin film by modifying growth kinetics by adding I₂ during synthesis. The I₂-modified CsCu₂I₃ film improved surface morphology while preserving crystalline and optical properties. Therefore, the ultraviolet (UV) photodetector based on the I₂-modified CsCu₂I₃ film showed enhanced performances in the solar-blind waveband, including a high responsivity of 1.74 μA/W and fast response and recovery times of 0.684 and 0.686 s, respectively. Finally, the solar-blind UV photodetector based on the I₂-modified CsCu₂I₃ thin film exhibited outstanding demonstration in optical communication systems without ambient interference, indicating its potential for various optoelectronic applications.