Photodeposited Silver‐Driven Phase Engineering of Bismuth‐Based Halide Perovskite Enabling Tunable Heterojunctions for Efficient CO 2 Photoreduction

ABSTRACT Cs 3 Bi 2 Br 9 has emerged as a competitive lead‐free photocatalyst owing to its low toxicity and favorable stability. However, its practical application is still limited by the rapid recombination of photogenerated carriers and a narrow photoresponse range. Herein, we report a facile in situ photodeposition strategy to engineer Cs 3 Bi 2 Br 9 with controlled silver loadings, enabling the selective construction of S‐scheme Cs 3 Bi 2 Br 9 @AgBr and Type I Cs 3 Bi 2 Br 9 @Cs 2 AgBiBr 6 heterojunctions. Among these, the optimized S‐scheme heterojunction (CBB‐Ag 2 ) delivers a CO yield 4.7 times higher than that of pristine Cs 3 Bi 2 Br 9 , achieving superior CO 2 photoreduction performance. Mechanistic investigations reveal that the built‐in electric field within the S‐scheme heterojunction establishes efficient interfacial charge transfer channels, effectively suppressing carrier recombination and promoting • OH generation, which collectively lower the energy barrier for *COOH formation—the rate‐determining step in CO 2 ‐to‐CO conversion. This work presents a scalable and phase‐controllable strategy for constructing high‐performance, lead‐free perovskite photocatalysts, offering valuable insights into rational heterojunction design for efficient CO 2 valorization toward carbon neutrality.