Interface‐Dependent Electronic Structure and Optical Properties of Staggered Al 2 STe/Ga 2 STe 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 Ga 2 STe and Al 2 STe 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 Al 2 STe/Ga 2 STe vdWHs imply that these new proposed materials have broad application prospects in optoelectronic devices such as excitonic solar cells.