Boosting the Photoelectrochemical Performance of ZnIn2S4 Photoanodes Via Antimony-Induced Defect and Surface Homojunction Engineering

Ternary metal sulfide (ZnIn2S4) is a promising photoanode material for photoelectrochemical (PEC) applications, yet its performance suffers from intrinsically low charge mobility and high defect density. Introducing oxygen (O)-related defects can improve carrier concentration and suppress recombination, but conventional air annealing lacks precise control over O incorporation. Here, we report an antimony (Sb)-induced defect and surface homojunction engineering strategy for ZnIn2S4 using a simple spin-coating and annealing process. Sb incorporation increases the content of O-related shallow-level donor states, which improves carrier concentration and mitigates defect-related recombination. Moreover, the surface-enriched Sb and O form a favorable surface/bulk homojunction with the intrinsic ZnIn2S4 interior, facilitating efficient carrier separation and transport. As a result, the optimized photoanode delivers an impressive photocurrent density of 4.30 mA cm-2 at 1.23 V versus the reversible hydrogen electrode (V vs. RHE) and a maximum applied bias photon-to-current efficiency (ABPE) of 2.00% in 0.5 M Na2SO4 electrolyte under AM 1.5G illumination, representing the highest reported value for ZnIn2S4-based photoanodes in neutral electrolyte without sacrificial agents. These findings highlight a promising defect engineering strategy to improve PEC performance of ternary metal chalcogenides.