Universal Vapor‐Phase Synthesis of Centimeter‐Scale Lead‐Free Halide Perovskite Single Crystals for X‐Ray/UV Radiation Detection

The scalable preparation of high‐quality, composition‐tunable lead‐free perovskite single crystals with ultrathin geometries exhibits significant research value for next‐generation optoelectronic integrated microdevices in diverse environmental applications. However, the controlled growth of large‐area halide perovskite single crystals with sub‐10 µm thickness while maintaining excellent crystallinity remains a great challenge. Here, a one‐step vapor phase growth strategy to achieve centimeter‐scale Cs 3 Bi 2 Br 9 single crystals with a thickness of ∼4 µm is reported. Besides, the methodology exhibits remarkable universality, extending to the synthesis of thin Cs 3 Bi 2 X 9 (X = Cl, I) single crystals and novel mixed‐halide variants through compositional engineering. Furthermore, the growth mechanism via chemical vapor transport (CVT) is elucidated through classical nucleation theory. The fabricated X‐ray and ultraviolet photodetectors utilizing these Cs 3 Bi 2 Br 9 thin single crystals demonstrate exceptional performance metrics, including an ultra‐low dark current of 5.81 × 10 −13 A and a high photosensitivity of 2600. These results show the tremendous potential of thin perovskite single crystals for high‐performance radiation detection applications. The study not only establishes a versatile platform for low‐dimensional halides perovskite crystals growth but also opens new avenues for the development of multifunctional optoelectronic devices.