Deep Ultraviolet Photodetection Based on Cs 2 AgBiBr 6– x Cl x with a Gradient Bandgap

Lead-free halide perovskites have garnered significant attention in photodetection applications due to their nontoxic nature and exceptional stability, especially the Cs 2 AgBiBr 6 double perovskite. However, the deep ultraviolet (DUV) photodetection capability of Cs 2 AgBiBr 6 -based photodetectors (PDs) remains largely unexplored. Herein, we propose, for the first time, a combined strategy of halogen regulation and gradient bandgap engineering to enhance the photoelectric performance of Cs 2 AgBiBr 6 PDs, achieving broadband detection from deep ultraviolet light to visible light. By constructing the Cs 2 AgBiBrCl 5 /Cs 2 AgBiBr 2 Cl 4 /Cs 2 AgBiBr 3 Cl 3 multilayer, the bandgap-gradient PDs exhibit a maximum responsivity ( R ) of 40 mA/W, a detectivity ( D ) of 2.4 × 10 11 Jones, and an external quantum efficiency (EQE) of 18% under 265 nm illumination at 0 V bias. Furthermore, the response times at 265 nm are 16 ms (rise) and 22 ms (fall), respectively. The devices also demonstrate exceptional stability, showing a marginal photocurrent decay after continuous operation cycles or atmospheric exposure. This work demonstrates the excellent ultraviolet–visible photodetection potential of the Cs 2 AgBiBr 6– x Cl x PDs with a bandgap-gradient structure, providing a promising approach to improve the performance of the halide perovskite-based photodetectors for future practical applications.