The　asymmetrical　group　III-VI　monolayer　Janus　M2XY　(M　=　Al,　Ga,　In;　X　not　equal　Y　=　S,　Se,　Te)　have　attracted　widespread　attention　due　to　their　significant　optical　absorption　properties,　which　are　the　potential　building　blocks　for　van　der　Waals　(vdW)　heterostructure　solar　cells.　In　this　study,　we　unraveled　an　In2STe/GeH　vdW　heterostructure　as　a　candidate　for　solar　cells　by　screening　the　Janus　M2XY　and　GeH　monolayers　on　lattice　mismatches　and　electronic　band　structures　based　on　first-principles　calculations.　The　results　highlight　that　the　In2STe/GeH　vdW　heterostructure　exhibits　a　type-II　band　gap　of　1.25　eV.　The　optical　absorption　curve　of　the　In2STe/GeH　vdW　heterostructure　indicates　that　it　possesses　significant　optical　absorption　properties　in　the　visible　and　ultraviolet　light　areas.　In　addition,　we　demonstrate　that　the　In2STe/GeH　vdW　heterostructure　shows　high　and　directionally　anisotropic　carrier　mobility　and　good　stability.　Furthermore,　strain　engineering　improves　the　theoretical　power　conversion　efficiency　of　the　In2STe/GeH　vdW　heterostructure　up　to　19.71%.　Our　present　study　will　provide　an　idea　for　designing　Janus　M2XY　and　GeH　monolayer-based　vdW　heterostructures　for　solar　cell　applications.