Highly Sensitive X‐Ray Detector Made of Large Lead‐Free Perovskite Cs₃Bi₂I₉ Single Crystals with Anisotropic Response

Abstract Direct X‐ray detectors require high‐quality and large‐size materials to reduce radiation hazards. As an all‐inorganic lead‐free perovskite, Cs 3 Bi 2 I 9 has good prospects for research and applications in the field of X‐ray detection. A refined evaporation method is proposed for the growth of Cs 3 Bi 2 I 9 single crystals (SCs), and a high‐quality SC with a size of 18 × 20.5 × 3 mm 3 is obtained. Due to the anisotropy of Cs 3 Bi 2 I 9 SCs, two different device structures, vertical and coplanar, are designed. The coplanar device has a higher sensitivity of 59 464.4 µC Gy air −1 cm −2 , while the vertical device performs better on the limit of detection (LoD), with an LodD as low as 1.27 nGy air s −1 .