Metal halide perovskite (MHP) nanocrystals (NCs) have shown promising application in photocatalytic CO₂ reduction, but their activities are still largely restrained by severe charge recombination and narrow solar spectrum response. Assembly of heterojunctions can be beneficial to the charge separation in MHPs while the assembly process usually brings native interfacial defects, impeding efficient charge separation between two materials. Herein, an in-situ generation strategy was developed to prepare CsPbBr₃ /WO₃ heterojunction, using WO₃ nanosheets (NSs) as growing substrate for the growth of CsPbBr₃ NCs. The developed CsPbBr₃ /WO₃ heterojunction exhibited a high-quality interface, greatly facilitating charge transfer between two semiconductors. The hybrid photocatalyst displayed an excellent activity toward CO₂ reduction, which was about 7-fold higher than pristine CsPbBr₃ NCs and 3.5-fold higher than their assembled counterparts. The experimental results and theoretical simulations revealed that a Z-scheme mechanism with a favorable internal electric field was responsible for the good performance of CsPbBr₃ /WO₃ heterojunction. By using O-defective WO₃ NSs as a near-infrared (NIR) light absorber, the CsPbBr₃ /WO₃ heterojunction could harvest NIR light and showed an impressive activity toward CO₂ reduction. This work demonstrates a new strategy to design MHP-based heterojunctions by synergistically considering the interface quality, charge transfer mode, interfacial electric field, and light response range between two semiconductors.

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