The integration of photoelectrochemical photoanodes and solar cells to build an unbiased solar‐to‐hydrogen (STH) conversion system provides a promising way to solve the energy crisis. The key point is to develop highly transparent photoanodes, while its bulk separation efficiency (ηsep.) and surface injection efficiency are as high as possible. To resolve this contradiction, first a novel CdIn2S4/In2S3 bulk heterojunctions in the interior of nanosheets is designed as a photoanode with high transparency and an ultrahigh ηsep. up to 90%. Furthermore, decorating the ultrathin amorphous SnO2 layer by atomic layer deposition, the surface oxygen‐evolution kinetics of the photoanode are increased significantly. As a result, the onset potential of the photoanode shifts negatively to 0.02 V vs RHE, and the photocurrent density boosts to 2.98 mA cm−2 at 1.23 V vs RHE, which is ten times higher than that of pristine CdIn2S4. Such a high‐performance photoanode enables the integrated metal sulfide photoanode–perovskite solar cell system to deliver a STH conversion efficiency of 3.3%.

Hematite (α-Fe 2 O 3 ) material is regarded as a promising candidate for solar-driven water splitting because of the low cost, chemical stability, and appropriate bandgap; however, the corresponding system performances are limited by the poor electrical conductivity, short diffusion length of minority carrier, and sluggish oxygen evolution reaction. Here, we introduce the in situ Sn doping into the nanoworm-like α-Fe 2 O 3 film with ultrasonic spray pyrolysis method. We show that the current density at 1.23 V vs. RHE (J ph@1.23V ) under one-sun illumination can be improved from 10 to 130 μA/cm 2 after optimizing the Sn dopant density. Moreover, J ph@1.23V can be further enhanced 25folds compared to the untreated counterpart via the post-rapid thermal process (RTP), which is used to introduce the defect doping of oxygen vacancy. Photoelectrochemical impedance spectrum and Mott-Schottky analysis indicate that the performance improvement can be ascribed to the increased carrier density and the decreased resistances for the charge trapping on the surface states and the surface charge transferring into the electrolyte. Xray photoelectron spectrum and X-ray diffraction confirm the existence of Sn and oxygen vacancy, and the potential influences of varying levels of Sn doping and oxygen vacancy are discussed. Our work points out one universal approach to efficiently improve the photoelectrochemical performances of the metal oxide semiconductors.

Both the bulk and surface electrical properties of the α-Fe2O3 photoanode are obviously self-improved under continuous irradiation.

The contributions of different underlayers in the hematite photoanode are revealed, and the underlayers can impact the top/bottom surfaces and bulk properties.