Synergistic Enhancement of Cu ₂ AgBiI ₆ Self‐Powered Ultraviolet Photodetector Performance by Doping Effects and Interfacial Engineering

Abstract Lead‐free metal halide perovskites emerge as promising materials for ultraviolet (UV) photodetectors (PDs), addressing the challenges in cost, fabrication, and performance associated with traditional materials. Nevertheless, critical performance parameters such as responsivity, detectivity, and response speed remain substantially limited. This work demonstrates high‐performance, self‐powered UV photodetectors based on Cu 2 AgBiI 6 (CABI) thin films, achieved through synergistic optimization of the photosensitive layer and interfacial layer. The incorporation of 15% chlorine (Cl) into pristine CABI markedly improves film coverage and crystallinity, reducing defect density and enhancing carrier mobility. Further interface modification with 0.25 m formamidinium iodide (FAI) synergistically refines film quality, leading to superior device performance. The resulting self‐powered UV photodetector (CABI:15% Cl / 0.25 m ‐FAI) achieves a record‐high specific detectivity of 3.20 × 10 13 Jones at 365 nm, coupled with excellent stability and rapid response. This study offers valuable insights for developing high‐performance, cost‐effective, and solution‐processable perovskite photodetectors.