Traditional　strategies　for　self-powered　devices　face　limitations　in　performance　improvement　due　to　the　trade-off　relationship　between　different　parameters.　Here,　a　new　kind　of　ion-modulation　self-powered　photodetector　is　first　proposed　and　fabricated　by　depositing　superionic　conductor　RbAg4I5　on　one　side　of　monolayer　graphene.　The　graphene　homojunction　is　successfully　formed　at　the　boundary　of　the　asymmetric　structure　due　to　the　formation　of　bound　states　of　ions　and　electrons　at　the　contact　interface.　This　kind　of　homojunction　avoids　the　trade　off　between　response　parameters　of　traditional　self-powered　devices　because　the　dissociation　of　bound　states　under　light　irradiation　dominates　the　generation　of　a　photocurrent.　The　experimental　results　indicate　that　the　prepared　photodetector　can　achieve　great　photo　response　with　responsivity　of　20mA/W　and　a　response　speed　of　700　mu　s　for　ultraviolet　and　visible　light　when　no　bias　is　applied,　which　is　better　than　most　existing　graphene-based　self-powered　devices　in　single　or　overall　parameters.　Further,　a　semi-quantitative　model　is　systematically　established　according　to　the　internal　mechanism　and　realizes　a　good　consistency　with　experimental　results.　The　work　provides　a　new　idea　and　offers　the　foundation　to　develop　excellent　self-powered　devices　based　on　superionic　materials　with　good　properties　in　controllability　and　modulation.