Spherulitic Crystallization of CsCu₂I₃ for High Performance Ultraviolet Photodetectors

Ternary copper halides have become promising materials for UV photodetection due to their stability and eco-friendliness. However, the uncontrollable crystallization induces high-concentration defects in these films, inherently limiting further improvement in device performance. Herein, we reveal the antisolvent-assisted crystallization kinetics mechanism of CsCu₂I₃ during the film-forming process. The nucleation rate is manipulated by adjusting precursor supersaturation using different antisolvents, resulting in decreased density and preferential orientation of the nuclei within the wet film. Subsequent annealing leads to a homogeneous and low-defect CsCu₂I₃ film with 40-μm-scale spherulites. A resulting visible-blind ultraviolet photodetector exhibits a responsivity of 8.73 A W^-1, a specific detectivity of 5.28 × 10¹² jones, and a response speed of 1.12 ms. The unencapsulated photodetector shows negligible degradation of responsivity in ambient air (∼70% humidity) for one month. Moreover, the flexible device with a responsivity of 420.2 mA W^-1 and a detectivity of 1.18 × 10¹² jones also shows excellent bending stability.