Low-Temperature Vapor-Phase Anion-Exchange Strategy for Wide-Bandgap Double-Perovskite Cs₂AgBiCl₆ Films toward Weak...

Low-temperature synthesis of high-quality, high-stability, wide-bandgap perovskite films by solution methods is still challenging. Herein, large-scale wide-bandgap Cs₂AgBiCl₆ (CABC) double perovskite films are synthesized by a vapor-phase anion-exchange strategy. By dedicatedly designing an ultrathin TiO₂ modification layer between the substrate and double perovskites, high-quality heterojunctions with matched energy band alignment are formed, contributing to a remarkably enhanced ON/OFF ratio of 2.4 × 10⁴ (86 times) and a responsivity of 16 mA W^-1 (12 times). Additionally, the ultraviolet photodetectors (UV PDs) exhibit an excellent UV detection limit of 1.18 μW cm^-2 (20 nW), a broad linear dynamic range of 146 dB, and a high specific detectivity of 2.06 × 10¹¹ Jones, as well as long-term stability. Finally, we further demonstrate a weak UV imaging system using CABC UV PDs as imaging sensors. The system is capable of imaging weak UV signals as low as 2.94 μW cm^-2 (50 nW). Our results provide a feasible approach for low-temperature fabrication of wide-bandgap perovskite UV PDs and explore the promising application for weak UV detection and imaging.