Strain-engineered Z-scheme γ-GeS/BlueP heterostructures for efficient photovoltaic-assisted hydrogen generation

The purposeful design of vertically stacked van der Waals heterostructures with high solar energy conversion efficiency offers a promising route toward carbon neutrality. Our first-principles calculations show that the γ-GeS/BlueP heterojunction is a narrow bandgap semiconductor with high carrier mobilities and strong absorption across the visible region. Modest in-plane strain transforms the heterojunction from type-I to type-II band alignment and enables overall water splitting through a Z-scheme photocatalytic mechanism. At −3 % biaxial strain, the predicted solar-to-hydrogen efficiency (η_STH) reaches 12.21 % and the power conversion efficiency (PCE) reaches 15.08 %. Increasing the compression strain to −4 % raises η_STH to 18.06 % and yields a substantially larger η_STH/PCE ratio than at −3 %. Furthermore, the hydrogen adsorption free energy (ΔG_H∗) for hydrogen evolution reaction (HER) decreases sharply from 1.14 eV at −3 % strain to 0.46 eV at −4 %, indicating markedly enhanced HER activity. Compressive strain also increases hole mobility and strengthens in-plane anisotropy, which facilitates efficient separation and transport of photoexcited electron-hole pairs. These strain-tunable properties highlight γ-GeS/BlueP as a potential bifunctional platform for solar energy conversion, particularly for photovoltaic-assisted hydrogen production.