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

Abstract 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 V_RHE, 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.