NH ₄ SCN Bulk and Surface Copassivation Enables High-Performance Inorganic Perovskite Photodetectors

Metal halide perovskites, particularly those with narrow bandgaps and broadband response, have emerged as promising candidates for photodetectors due to their outstanding optoelectronic properties and cost-effectiveness. Among these, CsPbI2Br films are notable for relatively high stability; however, they often suffer from phase segregation and operational instability, primarily caused by a substantial number of defects at the surface and grain boundaries. In this work, we present a bulk and surface copassivation strategy to mitigate such defects in CsPbI2Br films. This strategy involves the introduction of a pseudohalide salt, NH4SCN, in both the crystallization and post-treatment processes. The SCN– anions can substitute for I– anions or occupy iodide vacancies through strong coordination with Pb2+, thereby facilitating homogeneous crystal growth and reducing the defect density in the CsPbI2Br films by ∼60%. As a result, photodetectors fabricated from NH4SCN-passivated CsPbI2Br films exhibit a low dark current density of 1.30 × 10–10 A cm–2 at −0.1 V and a high specific detectivity of 4.09 × 1012 Jones at 10 Hz, outperforming most previously reported CsPbX3 vertical photodetectors. Moreover, these devices demonstrate excellent operational and ambient stability. This work highlights that bulk and surface copassivation using pseudohalide salts represents a facile and effective approach for developing stable and high-performance perovskite optoelectronic devices.