High‐Density Post‐Perovskite for Ultra‐Sensitive Hard X‐Ray Detection

Abstract The density properties of semiconductors play a crucial role in applications, such as radiation detection, electronic devices, and aerospace technologies. However, controlling the density of semiconductors often leads to significant alterations in their electronic structure, which can result in the loss of their original semiconductor properties. Perovskite semiconductors, known for their excellent carrier transport properties, face limitations in hard X‐ray detection due to their relatively low density and loose atomic packing. This study explores a series of post‐perovskite semiconductors with densities exceeding 5 g cm⁻ 3 , achieved through edge‐ and face‐sharing connectivity of octahedra and strong polarization between metal and chalcogenide ions. These dense materials retain semiconductor properties while exhibiting superior electrical transport characteristics. When applied to hard X‐ray detection, the post‐perovskite materials demonstrated superior attenuation cross‐sections compared to the heaviest 3D CsPbI 3 perovskite and 0D Cs 3 Bi 2 I 9 perovskite. Specifically, the BiCuSCl 2 post‐perovskite detector exhibited a high sensitivity of 4126 µC Gy air −1 cm −2 and a minimum detection limit of 4.3 nGy air s −1 . The enhanced density also mitigates ionic migration, ensuring excellent electrical stability. These findings underscore the potential of post‐perovskite semiconductors for advanced optoelectronic and radiation detection applications.