Space‐Confined Growth for Thickness‐Controlled Cs ₃ Bi ₂ I ₉ Perovskite Single Crystal Wafers for X‐Ray Detectors

Abstract The Cs ₃ Bi ₂ I ₉ single crystal, as an all‐inorganic non‐lead perovskite, offers advantages such as stability and environmental friendliness. Its superior photoelectric properties, attributed to the absence of grain boundary influence, make it an outstanding X‐ray detection material compared to polycrystals. In addition to material properties, X‐ray detector performance is affected by the thickness of the absorption layer. Addressing this, a space‐confined method is proposed. The temperature field is determined through finite element simulation, effectively guiding the design of the space‐confined method. Through this innovative method, a series of thickness‐controlled perovskite single crystal wafers (PSCWs) are successfully prepared. Corresponding X‐ray detectors are then prepared, and the impact of single crystal thickness on device performance is investigated. With an increase in single crystal thickness, a rise followed by a decline in device sensitivity is observed, reaching an optimal value at 0.7 mm thickness at 40V mm ⁻¹ with a device performance of 11313.6µC Gy ⁻¹ cm ⁻² . This space‐confined method enables the direct growth of high‐quality perovskite single crystals with specified thickness, eliminating the need for slicing or etching.