Exploring the Feasibility of Copper Incorporation in Halide Perovskites: Impact on CO₂ Photoreduction Performance

Abstract Double perovskite have attracted substantial attention as prospective materials for applications in optoelectronics and photocatalysis. Significant efforts are devoted to modulating the properties of double perovskites to improve their performance. One promising approach involves substituting silver (Ag) with copper (Cu), which offers favorable electronic characteristics. Despite promising theoretical predictions, the experimental synthesis of copper‐based double perovskites has presented notable challenges. Here, the challenges of Cu incorporation in double perovskites and the subsequent – impact of Cu on the photocatalytic activity of halide perovskites toward CO₂ reduction are explored. Combining detailed computational thermodynamic studies, it is found that Cu does not form the traditional double perovskite structure that is Cs₂CuBiCl₆; it stays as an interstitial dopant in its pristine Cs₃Bi₂Cl₉ structure. The Cu‐Cs₃Bi₂Cl₉ are found to exhibit enhanced CO₂ photoreduction activity than the pristine Cs₃Bi₂Cl₉. Further, transient absorption results show that Cu dopants enhance the carrier generation because of introduced sub‐bandgap states, and it is found that carrier decay lifetime is elevated in Cu‐Cs₃Bi₂Cl₉, which can enhance the participation of carriers in CO₂ photoreduction. The study explores the challenges and opportunities of copper doping in halide perovskites, offering the potential for developing efficient CO₂ reduction photocatalysts.