Band Positions and Photoelectrochemical Properties of Solution-Processed Silver-Substituted Cu₂ZnSnS₄ Photocathode

Ag-substituted Cu2ZnSnS4 (ACZTS) thin films were fabricated using a solution-processed method. The effects of Ag-substituted Cu sites on the crystallinity, band gap, band positions, and photoelectrochemical water splitting performance of Cu2ZnSnS4 (CZTS) were investigated. Compared to pure CZTS, the grain sizes and band gap of ACZTS are gradually increased as the Ag content increases. More importantly, the valence band maximum position of ACZTS is deeper than pure CZTS, which is beneficial to improve the onset potential. When the Ag/(Ag+Cu) molar ratio is 30%, the highest photocurrent of Pt/CdS/ACZTS photocathode reaches 3.78 mA/cm2 at 0 VRHE and the most positive onset potential is 0.33 VRHE, which are much higher than those of pure CZTS. The study will deepen understanding of the band structure of Ag-substituted CZTS and its effect on the photoelectrochemical performance of CZTS.