Atomic-Layer Controlled Interfacial Band Engineering at Two-Dimensional Layered PtSe/Si Heterojunctions for Efficient Photoelectrochemical Hydrogen Production.

Platinum diselenide (PtSe) is a group-10 two-dimensional (2D) transition metal dichalcogenide that exhibits the most prominent atomic-layer-dependent electronic behavior of "semiconductor-to-semimetal" transition when going from monolayer to bulk form. This work demonstrates an efficient photoelectrochemical (PEC) conversion for direct solar-to-hydrogen (H) production based on 2D layered PtSe/Si heterojunction photocathodes. By systematically controlling the number of atomic layers of wafer-scale 2D PtSe films through chemical vapor deposition (CVD), the interfacial band alignments at the 2D layered PtSe/Si heterojunctions can be appropriately engineered. The 2D PtSe/Si heterojunction photocathode consisting of a PtSe thin film with a thickness of 2.2 nm (or 3 atomic layers) exhibits the optimized band alignment and delivers the best PEC performance for hydrogen production with a photocurrent density of -32.4 mA cm at 0 V and an onset potential of 1 mA cm at 0.29 V versus a reversible hydrogen electrode (RHE) after post-treatment. The wafer-scale atomic-layer controlled band engineering of 2D PtSe thin-film catalysts integrated with the Si light absorber provides an effective way in the renewable energy application for direct solar-to-hydrogen production.