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

Abstract

We investigate how facet orientation and sulfur vacancies influence the interfacial charge trans- fer properties of CdS/MoS₂ heterojunctions. Using density functional theory, we find that 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 the (001)-CdS/MoS₂ may instead limit desired interfacial charge transfer. Finally, we find that defect formation energy differences reveal a facet-dependent tendency to form sulfur vacancies in CdS/MoS₂.