Interface-Dependent Electronic Structure and Optical Properties of Staggered Al₂STe/Ga₂STe van der Waals Heterostructures

2D Janus monolayers and van der Waals heterostructures (vdWHs) exhibit fascinating physical properties because of the destruction of symmetry. The interface-dependent electronic and optical properties of vdWHs constructed by Janus Ga2STe and Al2STe are explored. The results reveal that all interfaces vdWHs exhibit staggered (type-II) band alignment. Specifically, the S/Te and Te/Te interfaces vdWHs are indirect bandgap semiconductors, while the S/S and Te/S interfaces vdWHs are direct bandgap semiconductors. The staggered band alignment promotes the electron transfer between the donor and acceptor in vdWHs, and the power conversion efficiency (PCE) of the Te/Te interface vdWH is as high as 25.34%. Furthermore, both S/Te and Te/Te interfaces vdWHs can provide suitable photocatalytic performance for water splitting under pristine conditions. By applying biaxial strain, S/S and Te/S interfaces vdWHs can be used as a photocatalyst. Under the compressive strain of 1%, the PCE of Te/Te reaches 28.68%. Based on the G(0)W(0) + Bethe-Salpeter equation, different interfaces vdWHs exhibit different landscapes of intralayer exciting or interlayer exciting. The revealed type-II band alignment, strong optical absorption, and superior PCE of the Al2STe/Ga2STe vdWHs imply that these new proposed materials have broad application prospects in optoelectronic devices such as excitonic solar cells.