Suppression of Ionic and Electronic Conductivity by Multilayer Heterojunctions Passivation Toward Sensitive and Stable Perovskite X‐Ray Detectors

Organic‐inorganic hybrid perovskites are promising candidates for direct X‐ray detection and imaging. The relatively high dark current in perovskite single crystals (SCs) is a major limiting factor hindering the pursuit of performance and stability enhancement. In this study, the contribution of dark current is disentangled from electronic ( σ e ) and ionic conductivity ( σ i ) and shows that the high σ i dominates the dark current of MAPbBr 3 SCs. A multilayer heterojunctions passivation strategy is developed that suppresses not only the σ i by two orders of magnitude but also σ e by a factor of 1.6. The multilayer heterojunctions passivate the halide vacancy defects and increase the electron and hole injection barrier by inducing surface p‐type doping of MAPbBr 3 . This enables the MAPbBr 3 SC X‐ray detectors to obtain a high sensitivity of 19 370 µC Gy air −1 cm −2 under a high electric field of 100 V cm −1 , a record high sensitivity for bromine self‐powered devices, and a low detection limit of 42.3 nGy air s −1 . The unencapsulated detectors demonstrate a stable baseline after storage for 210 days and outstanding operational stability upon irradiation with an accumulated dose of up to 1944 mGy air .