First-Principles Study on Janus GaS/Ga2SSe Heterojunctions as Photocatalysts for Water Splitting

This study employs first-principles calculations to construct two van der Waals heterojunction models, namely GaS/Ga2SSe-S (Heterojunction A) and GaS/Ga2SSe-Se (Heterojunction B). Their structural stability, electronic structure, photocatalytic and optical properties, as well as the regulatory effects of biaxial strain, are systematically investigated. The results demonstrate that both heterojunctions exhibit a low lattice mismatch of only 2.45%, accompanied by excellent thermodynamic and dynamic stability. Both are indirect bandgap semiconductors, featuring Type-I and Type-II band alignments, respectively. Notably, Heterojunction B possesses a stronger built-in electric field and more efficient charge transfer. Biaxial strain can effectively modulate the performance of the heterojunctions: tensile strain reduces the bandgap, and under 4%-8% tensile strain, the light absorption coefficients in the ultraviolet and infrared regions are significantly enhanced. Both heterojunctions satisfy the band edge potential requirements for photocatalytic water splitting, indicating that GaS/Ga2SSe heterojunctions hold great promise as high-performance photocatalysts for water splitting.