Constructing built-in electric field within CsPbBr/sulfur doped graphitic carbon nitride ultra-thin nanosheet step-scheme heterojunction for carbon dioxide photoreduction.

Lead halide perovskites are promising for photocatalysis due to their excellent optoelectronic properties, high extinction coefficients, and long electron-hole diffusion lengths. However, severe recombination of photogenerated carriers limits their photocatalytic activity. Herein, we describe a perovskite-based step-scheme (S-scheme) heterojunction by interfacing CsPbBr perovskite nanocrystals with sulfur (S) doped graphitic carbon nitride (g-CN) ultrathin nanosheet. The formation of S-scheme heterojunction was substantiated by in-situ x-ray photoelectron spectra, showing a negative shift for Cs 1s, Pb 4f, and Br 3d binding energy in CsPbBr, while a positive shift for C 1s, N 1s, and S 2p in S-doped g-CN upon light irradiation. Moreover, alignment of Fermi levels in both semiconductors results in constructing a built-in electric field in the heterojunction, which enhances S-scheme electron transfer from g-CN to CsPbBr, favorable for electron (CsPbBr) and hole (g-CN) separation for enhanced carbon dioxide (CO) photoreduction. Indeed, compared with CsPbBr, the developed CsPbBr/S doped g-CN composite showed a ∼16-fold improvement in the photocatalytic CO reduction rate (∼83.6 μmol h g), thus holding great potential for photocatalysis applications in environmental and energy fields.