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

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.