Two-dimensional　(2D)　perovskites　and　InX　(X=Se,　Te)　monolayers　have　garnered　global　attention　due　to　their　extraordinary　performance　as　environment-friendly　and　low-cost　candidates　for　photoelectric　and　photocatalytic　applications.　Herein,　we　provided　a　comprehensive　understanding　on　the　crystal　structures,　stabilities,　electronic　and　optical　properties　of　lead-free　Cs3Bi2I9/InX　(X=Se,　Te)　van　der　Waals　(vdW)　heterostructures　as　well　as　their　potential　applications　in　photoelectric　conversion　and　photocatalysis　based　on　density　functional　theory　calculations.　It　is　highlighted　that　Cs3Bi2I9/InX　heterostructures　exhibit　significantly　reduced　bandgaps　and　enhanced　light　absorption　capacity,　along　with　noticeable　improvements　in　carrier　mobilities　compared　to　their　corresponding　monolayers.　By　combining　the　type-II　band　edge　natures　with　appropriate　bandgap　vales,　Cs3Bi2I9/InX　heterostructures　hold　tremendous　potential　in　the　fields　of　photoelectric　conversion　and　photocatalysis　applications.　It　is　worth　emphasizing　that　the　maximum　photoelectric　conversion　efficiencies　of　Cs3Bi2I9/InSe　and　Cs3Bi2I9/InTe　heterostructure　film　solar　cells　are　24.11　%　and　26.23　%,　respectively.　The　present　results　will　provide　fundamental　understanding　and　good　theoretical　guidance　for　rationally　constructing　vdW　heterostructures　based　on　2D　perovskites　in　the　field　of　photo　energy　conversion.　©　2024　Elsevier　B.V.