Cesium‐Based Molecular Perovskites With Superior Stability for High‐Performance X‐Ray Detection

Abstract Metal‐free molecular perovskites have shown great potential for X‐ray detection due to their tunable chemical structures, low toxicity, and excellent photophysical properties. However, their limited X‐ray absorption and environmental instability restrict their practical application. In this study, cesium‐based molecular perovskites (MDABCO‐CsX 3 , X = Cl, Br, I) are developed by introducing Cs + at the B‐site to enhance X‐ray absorption while retaining low toxicity. The effects of halide modulation on the physical properties and device performance are systematically investigated. Among the variants, MDABCO‐CsBr 3 exhibited superior environmental stability, attributed to the optimal ionic radius and high chemical stability of Br − . This stability is further enhanced by a higher tolerance factor, which promotes a stable 3D cubic structure and suppresses ion migration within the crystal. Consequently, MDABCO‐CsBr 3 ‐based X‐ray detectors demonstrated reduced ionic migration, minimal dark current drift, and a stable current response under X‐ray exposure, achieving a high sensitivity of 4124 µC Gy −1 cm −2 and a low detection limit of 0.45 µGy s −1 . Moreover, the devices exhibit excellent thermal stability, operating effectively at temperatures up to 130 °C. These results highlight MDABCO‐CsBr 3 as a promising candidate for stable and efficient X‐ray detection, expanding the applicability of molecular perovskites in advanced radiation detection technologies.