Interfacial Electronic Structure Modulation by Facet Orientation and Sulfur Vacancies in CdS/MoS2 Heterojunctions

We investigate how facet orientation and sulfur vacancies influence the interfacial charge transfer properties of CdS/MoS2 heterojunctions. Using density functional theory, we find that the heterojunctions are primarily stabilized by van der Waals interactions. The (001)-CdS/MoS2 interface exhibits a Type-III band alignment, while the (100)-CdS/MoS2 forms a homojunction-like alignment that straddles the water redox potentials, making it more suitable for overall water splitting. Furthermore, sulfur vacancies induce localized charge redistribution in the (100)-CdS/MoS2 interface, with select configurations introducing shallow defect states that may aid in the charge transfer pathways of hydrogen evolution reactions through favorably aligned dipole moments. In contrast, sulfur vacancy configurations in the (001)-CdS/MoS2 interface produce a more uniform charge redistribution and minimal changes to the electronic structure. The resulting dipole moments in this facet may instead limit interfacial charge transfer. Finally, the calculated defect formation energies reveal facet-dependent tendencies to form sulfur vacancies.