Tin　(Sn)-based　perovskite　solar　cells　(PSCs)　stand　out　as　a　promising　low-toxicity　alternative　to　lead　(Pb)-based　PSCs.　However,　their　progress　is　hindered　by　oxygen-induced　degradation　and　inherent　crystal　defects,　challenging　their　efficiency　and　durability.　Through　density　functional　theory　(DFT)　calculations,　it　is　found　that　oxyacid　anions　including　HCOO−,　HSO3−,　and　H2PO2−　can　strongly　coordinate　with　the　SnI2　precursor　to　form　adducts.　These　complexes　help　inhibit　Sn2+/Sn4+　oxidation　in　the　precursor　solution,　slow　down　the　crystallization　process,　and　ultimately　improve　the　crystal　quality　of　CsSnI3.　Moreover,　these　oxyacid　anions　bind　to　the　iodine　vacancies　(IV)　and　alloy　within　the　crystal　lattice,　thereby　preventing　oxygen　molecules　from　generating　detrimental　superoxide　ions　at　these　sites.　Electron　structure　analysis　and　nonadiabatic　molecular　dynamics　(NAMD)　simulations　show　that　these　anions　not　only　eliminate　trap　states　by　disrupting　the　5p-5p　orbitals　interaction　of　Sn　atoms　near　IV,　but　also　reduce　the　oscillation　of　key　energy　states　and　weaken　nonadiabatic　coupling　(NAC).　These　effects　collectively　contribute　to　the　extended　lifetime　of　charge　carriers.　Notably,　the　charge　carrier　lifetime　in　the　system　passivated　with　H2PO2−　is　extended　by　more　than　15　times.　Consequently,　the　oxyacid　anions　are　seen　to　synergistically　enhance　the　performance　of　Sn-based　PSCs.　©　2025　Wiley-VCH　GmbH.