Bi₂S₃-Cu₃BiS₃ Mixed Phase Interlayer for High-Performance Cu₃BiS₃-Photocathode for 2.33% Unassisted Solar Water Splitting Efficiency

To realize practical solar hydrogen production, a low-cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu₃BiS₃-based photocathode. By exploiting the crystallographic similarities between Bi₂S₃ and Cu₃BiS₃, a one-step solution process with two sulfur sources is used to prepare the Bi₂S₃–Cu₃BiS₃ blended interlayer. The elongated Bi₂S₃-Cu₃BiS₃ mixed-phase 1D nanorods atop a planar Cu₃BiS₃ film enable a high photocurrent density of 7.8 mA cm⁻² at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 V_RHE. The increased performance over the single-phase Cu₃BiS₃ thin-film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n-type CdS layer. A solar-to-hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state-of-the-art Mo:BiVO₄ photoanode, with excellent stability exceeding 21 h.