Constructing built-in electric field within CsPbBr₃/sulfur doped graphitic carbon nitride ultra-thin nanosheet...

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 CsPbBr₃ perovskite nanocrystals with sulfur (S) doped graphitic carbon nitride (g-C₃N₄) 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 CsPbBr₃, while a positive shift for C 1s, N 1s, and S 2p in S-doped g-C₃N₄ 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-C₃N₄ to CsPbBr₃, favorable for electron (CsPbBr₃) and hole (g-C₃N₄) separation for enhanced carbon dioxide (CO₂) photoreduction. Indeed, compared with CsPbBr₃, the developed CsPbBr₃/S doped g-C₃N₄ composite showed a ∼16-fold improvement in the photocatalytic CO₂ reduction rate (∼83.6 μmol h^-1 g^-1), thus holding great potential for photocatalysis applications in environmental and energy fields.