Designing a Transparent CdIn2S4/In2S3 Bulk‐Heterojunction Photoanode Integrated with a Perovskite Solar Cell for Unbiased Water Splitting

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%. CdIn2S4/In2S3 bulk heterojunction nanosheet arrays are designed as photoanodes of photoelectrochemical cells, which have high transparency and high separation efficiency up to 90%. This photoanode is integrated with a perovskite solar cell to form an unbiased solar water‐splitting system, delivering a solar to hydrogen conversion efficiency of 3.3%.