Dual back interface engineering optimized charge carrier dynamics in Sb(S,Se) photocathodes for efficient solar hydrogen production.

Antimony sulfoselenide (Sb(S,Se)) is a promising sunlight absorber material for solar energy conversion in photovoltaic (PV) cells and photoelectrochemical (PEC) photoelectrodes due to its excellent photoelectric properties. However, the obtained thin-film and back contact properties significantly influence the PEC performance of photocathodes, causing severe bulk recombination, carrier transport loss, and deteriorating half-cell solar-to-hydrogen (HC-STH) efficiency. This study introduces an intriguing dual back interface engineering strategy for Sb(S,Se) photocathodes by incorporating an intermediate MoO layer and a secondary carrier transport channel of Au to strengthen charge carrier dynamics. The synergistic assembly of these dual back interface layers improves the growth kinetics and achieves the optimal orientation of Sb(S,Se) thin films by increasing substrate wettability. Moreover, by shortening the back contact barrier height and passivating defect-assisted recombinations, these dual back underlayers simultaneously enhance carrier transport and separation efficiencies. As a result, the photocurrent density of the champion Sb(S,Se) photocathode increases from 5.89 to 32.60 mA cm, and the HC-STH conversion efficiency improves significantly from 0.30% to 3.58%, representing the highest value for Sb(S,Se)-based photocathodes. This work highlights the effectiveness of dual back interface engineering in promoting the PEC performance of chalcogenide photocathodes for solar hydrogen evolution applications.