(Zn,Ti)O Electron Transport Layer Enables the Highest Conversion Efficiency in Cd‐Free Sb 2 Se 3 Photocathodes for Stable Solar Hydrogen Production

ABSTRACT Antimony selenide (Sb 2 Se 3 ) has emerged as a promising photocathode material for photoelectrochemical (PEC)‐driven solar hydrogen production due to its low toxicity, cost‐effectiveness, and excellent photoelectric properties. Currently, efficient Sb 2 Se 3 photocathodes are mostly coupled with CdS electron transport layer (ETL), however, suffering from natural toxicity, parasitic light absorption, and interfacial mismatch and/or instability. In this study, we introduce a Cd‐free Sb 2 Se 3 photocathode with an atomic layer deposition‐processed (Zn,Ti)O ETL, which mitigates the respective limitations of binary oxides (i.e., ZnO and TiO 2 ). The optimized (Zn,Ti)O ETL enhances electron carrier density, establishes a favorable ‘spike‐like’ band alignment at the Sb 2 Se 3 /(Zn,Ti)O interface, significantly improves charge separation and transport efficiencies, as well as the stability. Consequently, the champion device achieves an impressive photocurrent density ( J ph ) of 31.1 mA/cm 2 , a record half‐cell solar‐to‐hydrogen (HC‐STH) efficiency of 5.27% for Cd‐free Sb 2 Se 3 photocathodes, and the highest unbiased STH efficiency of 2.50% in the Sb 2 Se 3 ‐BiVO 4 tandem cell, setting a new benchmark for eco‐friendly and high‐performance PEC processed green hydrogen production.