Equal-Proportion Organic–Inorganic-Mixed Cation Perovskite Single Crystalline Heterojunctions Enable High-Performance X-ray Detection

Abstract Metal halide perovskite single crystal (SC) heterojunctions have attracted great attention in X-ray detection owing to their merits of current rectification and surface-defect passivation. However, the exploration of innovative heterostructures with superior X-ray detection performance still faces considerable challenges. In this study, we report the epitaxial growth of FA0.5Cs0.5PbBr3 SC thin films with an FA-to-Cs molar ratio of 1:1 on CsPbBr3 SC substrates through temperature-lowering crystallization, constructing FA0.5Cs0.5PbBr3/CsPbBr3 heterojunctions. Compared with CsPbBr3 SCs, the FA0.5Cs0.5PbBr3/CsPbBr3 heterojunctions exhibit a distinct rectification effect and a larger ion migration activation energy (0.556 eV), suppressing leakage current and baseline drift. In particular, the FA0.5Cs0.5PbBr3/CsPbBr3 heterojunction drastically enhances the X-ray response of CsPbBr3 SCs, delivering an outstanding sensitivity of 235,161 μC Gyair–1 cm–2 under 120 keV X-ray irradiation. Furthermore, the detector achieves a low detection limit of 83.61 nGyair s–1 and maintains excellent stability over 160 days without encapsulation. This work provides an effective strategy to suppress ion migration through the construction of mixed-cation perovskite heterojunctions, which effectively enhances the performance of the X-ray detectors.