Narrow Bandgap Perovskite Enabled by Heterovalent Co‐Doping for Visible‐NIR Light Photocatalytic CO₂ Reduction

Metal halide perovskites have garnered significant attention due to their vast potential in various optoelectronic applications. While their tunable bandgap properties allow for light absorption across the ultraviolet and much of the visible spectrum, the coverage in the near-infrared (NIR) region remains limited. Here, we demonstrate a heterovalent co-doping method for synthesizing Ag and Bi doped CsSnBr₃ crystals with absorption edge up to 1300 nm, making it one of the narrowest bandgap perovskite materials. The incorporation of trivalent Bi (p) orbitals is responsible for the band narrowing, while the monovalent Ag stabilizes the entire perovskite lattice. Taking advantage of the new energy states within the bandgap, the absorption edge of the co-dopants is extended to NIR region, so they can efficiently utilize sunlight. Moreover, the co-dopants exhibit significantly better antioxidation capability than the pristine CsSnBr₃. When applied to CO₂ photoreduction, the co-dopants achieved highly selective CO production performance, with an apparent quantum yield (AQY) of 7.56 % at 700 nm, representing a 94 % improvement over CsSnBr₃. Overall, this study provides effective strategies for optimizing tin-based perovskites and holds significant implications for future research in enhancing stability, reducing toxicity, and optimizing optoelectronic performance.