Low‐Temperature Grown FAPb _0.5 Sn _0.5 I ₃ Single Crystals for Sensitive X‐Ray Detectors with Low Dark Current and Detection Limit

Abstract Ion migration is a universal and pending issue that hinders performance and stability of metal halide perovskite (MHP) X‐ray detectors. Lead‐tin (Pb‐Sn) perovskite single crystals hold potential for suppressing ion migration, but they face unideal Sn 2 ⁺ oxidation during crystal growth. Herein, a low‐temperature crystal growth strategy using 2‐methoxyethanol (2ME) as solvent is developed to mitigate oxidation of Sn 2 ⁺ and suppress formation of vacancy traps. The as‐grown FAPb 0.5 Sn 0.5 I 3 (FA = CH(NH 2 ) 2 + ) single crystals exhibit a high ion migration activation energy ( E a ) of 0.95 eV, which is distinctly larger than those of lead‐based perovskite crystals. As a result, the detectors exhibit a low dark current density of 0.75 nA cm −2 and small drift 4.2 × 10 −7 nA cm −1 s −1 V −1 as well as low detection limit of 0.81 nGy air s −1 , outperforming those of lead perovskite detectors. Besides, the FAPb 0.5 Sn 0.5 I 3 crystals possess high carrier mobility‐lifetime ( µτ ) product of 2.7 × 10 −3 cm 2 V −1 , resulting in self‐powered X‐ray detectors with high sensitivity of 8.1 × 10 3 µC Gy air −1 cm −2 under 0 V bias. This work reports X‐ray detectors based on Pb‐Sn single crystals for the first time and shows their potential for inhibiting ion migration and dark current without sacrificing device sensitivity, which may promote stable and low‐dose X‐ray detection.