Unraveling the Transformation from Type-II to Z-Scheme in Perovskite-Based Heterostructures for Enhanced Photocatalytic CO 2 Reduction.

The ability to create perovskite-based heterostructures with desirable charge transfer characteristics represents an important endeavor to render a set of perovskite materials and devices with tunable optoelectronic properties. However, due to similar material selection and band alignment in type-II and Z-scheme heterostructures, it remains challenging to obtain perovskite-based heterostructures with a favorable electron transfer pathway for photocatalysis. Herein, we report a robust tailoring of effective charge transfer pathway in perovskite-based heterostructures via a type-II to Z-scheme transformation for highly efficient and selective photocatalytic CO 2 reduction. Specifically, CsPbBr 3 /TiO 2 and CsPbBr 3 /Au/TiO 2 heterostructures are synthesized and then investigated by ultrafast spectroscopy. Moreover, taking CsPbBr 3 /TiO 2 and CsPbBr 3 /Au/TiO 2 as examples, operando experiments and theoretical calculations confirm that the type-II heterostructure could be readily transformed into a Z-scheme heterostructure through establishing a low-resistance Ohmic contact, which indicates that a fast electron transfer pathway is crucial in Z-scheme construction, as further demonstrated by CsPbBr 3 /Ag/TiO 2 and CsPbBr 3 /MoS 2 heterostructures. In contrast to pristine CsPbBr 3 and CsPbBr 3 /TiO 2 , the CsPbBr 3 /Au/TiO 2 heterostructure exhibits 5.4- and 3.0-fold enhancement of electron consumption rate in photocatalytic CO 2 reduction. DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy unveil that the superior CO selectivity is attributed to the lower energy of *CO desorption than that of hydrogenation to *HCO. This meticulous design sheds light on the modification of perovskite-based multifunctional materials and enlightens conscious optimization of semiconductor-based heterostructures with desirable charge transfer for catalysis and optoelectronic applications.