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, CsPbI 2 Br 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 CsPbI 2 Br films. This strategy involves the introduction of a pseudohalide salt, NH 4 SCN, in both the crystallization and post-treatment processes. The SCN – anions can substitute for I – anions or occupy iodide vacancies through strong coordination with Pb 2+, thereby facilitating homogeneous crystal growth and reducing the defect density in the CsPbI 2 Br films by ∼60%. As a result, photodetectors fabricated from NH 4 SCN-passivated CsPbI 2 Br 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 × 10 12 Jones at 10 Hz, outperforming most previously reported CsPbX 3 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.