Designing Z-Scheme Type-II ZnSe/GeH van der Waals Heterostructure with High Solar-to-Hydrogen Efficiency for Photocatalytic Water Splitting.

In this work, the structural, electronic, optical, transport, and photocatalytic properties of a ZnSe/GeH heterostructure are systematically investigated using first-principles calculations. The ZnSe/GeH heterostructure exhibits a type-II direct band alignment and a suitable band gap for overall photocatalytic water splitting. Driven by interfacial charge redistribution and the built-in electric field, the heterostructure forms an efficient direct Z-scheme charge-transfer pathway that preserves the strong redox capabilities of photogenerated electrons and holes. The ZnSe/GeH heterostructure also exhibits a high intrinsic carrier mobility of 2330.09 cm2 V-1 s-1, facilitating efficient charge transport. In addition, it demonstrates strong optical absorption in the visible and near-ultraviolet regions, reaching up to 6 × 105 cm-1, which benefits light harvesting and photocatalytic applications. Moreover, the band-edge positions simultaneously straddle the hydrogen and oxygen evolution reaction potentials over a broad pH range, yielding a theoretical solar-to-hydrogen (STH) efficiency of up to 32.22%. Furthermore, the electronic properties can be effectively tuned by external biaxial and uniaxial strains. These findings highlight the ZnSe/GeH heterostructure as a promising candidate for high-efficiency solar-driven photocatalysis.