In Situ Phase Transition and Cu Doping Synergistically Regulate Perovskite Z‐Scheme Heterojunction for Photocatalytic CO 2 Reduction

Due to their remarkable reduction capacity and superior selectivity, metal halide perovskite nanocrystals have attracted considerable research interest in the domain of photocatalytic CO 2 reduction. However, the severe carrier recombination phenomenon and the lack of suitable reactive sites in perovskites have resulted in low photocatalytic activity. To address these challenges, this study proposes a synergistic regulation strategy based on in situ phase transition and metal doping. By precisely controlling the phase transition process of CsPbBr 3 at high temperatures, a Z‐scheme heterojunction photocatalyst of Cu‐doped CsPbBr 3 /CsPb 2 Br 5 (Cu‐CPB/125) was successfully fabricated. The heterojunction‐based composite delivered a CO evolution rate of 109.30 μmol g −1 h −1 , coupled with a CO selectivity as high as 98.90%. Based on in situ infrared spectroscopy and density functional theory calculations, the possible reaction pathway and mechanism were further elucidated. The energy barrier for *CO desorption on Cu sites was found to be considerably lower than that for further hydrogenation to *CHO, thereby favoring the high selectivity toward CO. This study provides new insights for the design of element‐doped perovskite heterojunction materials.