Centimeter-sized single crystals of 3D perovskitoid (4-AP)Pb₂X₆ (X = Br, I) for efficient and stable X-ray detection

Three-dimensional (3D) metal halide perovskites (MHPs) have been widely studied in the field of X-ray detection, due to their easy synthesis, strong X-ray absorption and high carrier transport capability. However, the conventional 3D ABX₃ MHPs have fatal problems of large dark current drift, severe ion migration and poor environmental stability, which calls for extensive research on the design and modulation of novel 3D perovskitoids to address these issues. In this study, two AB₂X₆-type 3D perovskitoids (4-AP)Pb₂X₆ (4-AP = 4-amidinopyridinium, X = Br, I) with centimeter-sized single crystals have been synthesized for X-ray detection. Thorough studies disclose unique inorganic frameworks composed of both corner-sharing and edge-sharing octahedra, while multi-ammonium aromatic 4-AP²⁺ cations are situated within the expansive cavities of the inorganic network. Strikingly, both of these compounds are characterized by elevated activation energy (E _a) of ionic conductivity, reduced dark current drift, and superior stability compared to the conventional 3D perovskite MAPbI₃. In particular, (4-AP)Pb₂I₆ with a flatter framework achieves a high sensitivity of 2512 µC Gy^-1 cm^-2 and a low detection limit of 0.72 µGy s^-1, due to the better carrier transmission channels and stronger X-ray absorption. This work highlights the potential of the 3D AB₂X₆ perovskitoid family in high-performance optoelectronics.