Boosting Solar Water Splitting Performance of Cu3BiS3‐Based Photocathode via Ag Doping Strategy

A photovoltaic wittichenite semiconductor of Cu3BiS3, due to its optimal bandgap, high light absorption coefficient, and various advantages of low cost and environmental‐friendliness, has been considered a competitive candidate for solar absorber materials of photocathode for photoelectrochemical water splitting. However, the presence of various deleterious defects in the Cu3BiS3 lattice and its high conduction band minimum are detrimental factors that restrict further enhancements in the conversion efficiency of Cu3BiS3‐based photocathode. Herein, a one‐step solution‐based Ag element doping strategy is proposed to improve the crystalline quality of Cu3BiS3 films, which includes enlarging the grain size and reducing the intergranular gaps. Additionally, the Ag‐doped Cu3BiS3 layer can form a more favorable band alignment with the buffer layer. Ultimately, the fabricated composite Cu3BiS3‐based photocathode doped with 3% Ag delivers a remarkable photocurrent density of 13.6 mA cm−2 under 0 VRHE, an applied bias photon‐to‐current efficiency of 2.85%, and long‐term stability exceeding 12 h. Furthermore, with the assistance of a BiVO4 photoanode, the tandem cell also achieves an unbiased solar‐to‐hydrogen efficiency of 2.64%, with no significant decline observed within 20 h. In this work, a one‐step solution‐based Ag doping strategy is employed to enhance the PEC water‐splitting performance of Cu3BiS3‐based photocathodes. The improvement in the crystalline quality of the Cu3BiS3 absorber and the formation of favorable band alignment at the buffer/Cu3BiS3 interface are demonstrated as underlying enhancement mechanisms.