Rational Design of A‐Site Cation for High Performance Lead‐Free Perovskite X‐Ray Detectors

Design of hypotoxic lead‐free perovskites, e.g. Bismuth(Bi)‐based perovskites, is much beneficial for commercialization of perovskite X‐ray detectors due to their strong radiation absorption. Nevertheless, the design principles governing the selection of A‐site cations for achieving high‐performance X‐ray detectors remain elusive. Here, seven molecules (methylamine MA, amine NH3, dimethylbiguanide DGA, phenylethylamine PEA, 4‐fluorophenethylamine p‐FPEA, 1,3‐propanediamine PDA, and 1,4‐butanediamine BDA) and calculated their dipole moments and interaction strength with metal halide (BiI3) are selected. The first‐principles calculations and related spectroscopy measurements confirm that organic molecules (DGA) with large dipole moments can have strong interactions with perovskite octahedron and improve the carrier transport between the organic and inorganic clusters. Consequently, zero‐dimensional single crystal (SC) (DGA)BiI5∙H2O is synthesized. The (DGA)BiI5∙H2O SCs demonstrate an exceptional carrier mobility‐lifetime product of 6.55 × 10−3 cm2 V−1, resulting in the high sensitivity of 5879.4 µCGyair−1cm−2, featuring a low detection limit (4.7 nGyair s−1) and remarkable X‐ray irradiation stability even after 100 days of aging at a high electric field (100 V mm−1). Furthermore, the (DGA)BiI5∙H2O SCs for imaging, achieving a notable spatial resolution of 5.5 lp mm−1 are applied. This investigation establishes a pathway for systematically screening A‐site cations to design low‐dimensional SCs for high‐performance X‐ray detection. By considering the dipole moment of organic molecules and their interaction with BiI3, a suitable A‐site cation (DGA) is designed, resulting in a perovskite single crystal ((DGA)BiI5∙H2O) with high carrier transport properties. Ultimately, (DGA)BiI5·H2O is applied in X‐ray detection, achieving an optimal carrier mobility‐lifetime product of (6.55 × 10−3 cm2 V−1) and high sensitivity (5879.4 µC Gyair−1 cm−2).