Mixed Halide Formation in Lead‐Free Antimony‐Based Halide Perovskite for Boosted CO₂ Photoreduction: Beyond Band Gap Tuning

Abstract Photocatalytic conversion of carbon dioxide (CO₂) into value‐added fuels is a vastly promising anthropogenic chemical carbon cycle to combat the greenhouse effect while meeting the ever‐increasing energy demand. Recently, lead‐based halide perovskites have demonstrated great potential in various applications including photochemical reduction of CO₂. However, in view of lead toxicity, the exploration of a lead‐free alternative is crucial for long term application. Herein, a series of lead‐free mixed halide perovskites Cs₃Sb₂Cl_xBr_9−x (0 ≤ x ≤ 9) is prepared via a facile antisolvent recrystallization technique, where the incorporation of a secondary halide enhances the charge transfer and separation while allowing precise tuning of bandgap between 2.59 and 2.90 eV. Theoretical calculations further reveal that the formation of mixed Cl/Br halides engenders favorable charge redistribution due to lower octahedral distortion, which in turn strengthens CO₂ adsorption and activation. Under visible light illumination, the optimal dual halide perovskite, Cs₃Sb₂Cl₄Br₅ manifests substantial twofold and fourfold enhancements of CH₄ yield over the single halide perovskite, Cs₃Sb₂Br₉ and Cs₃Sb₂Cl₉, respectively. In brief, this study provides a compelling demonstration of lead‐free mixed halide perovskites for photocatalytic CO₂ reduction, and it is anticipated to drive further application of perovskite‐based photocatalysts toward a diverse range of artificial photoredox reactions.