Phase Transition in Halide Double Perovskites for Solar‐To‐Chemical Energy Conversion

Abstract Halide double perovskites have recently garnered significant interest in solar energy conversion applications owing to their non‐toxic and high solar absorption properties. However, unanticipated structural distortion within these materials can compromise their performance, suppressing the structural distortion is essential and remains challenging. Here, it is reported that using phenylethylamine triggering the disorder‐order phase transition can largely increase the ordering extent of octahedra in double perovskite Cs 2 AgBiBr 6 , which can suppress self‐trapped exciton and defect and enable rapid charge separation, leading to exceptional photo‐physics/chemistry properties with over sixfold photoactivity enhancement in the photocatalytic C−H bond activation compared to less ordered structures. This work provides an effective strategy to solve the challenging problem of the disorder phenomenon of halide double perovskites for boosting solar‐to‐chemical energy conversion.