Hybrid perovskites, as emerging multifunctional semiconductors, have demonstrated dual electronic/ionic conduction properties. We report a metal/ion interaction induced p-i-n junction across slightly n-type doped MAPbI3 single crystals with Au/MAPbI3/Ag configuration based on interface dependent Seebeck effect, Hall effect and time-of-flight secondary ion mass spectrometry analysis. The organic cations (MA+) interact with Au atoms, forming positively charged coordination complexes at Au/MAPbI3 interface, whereas iodine anions (I-) can react with Ag contacts, leading to interfacial ionic polarization. Such metal/ion interactions establish a p-doped region near the Au/MAPbI3 interface due to the formation of MA+ vacancies, and an n-doped region near the Ag/MAPbI3 interface due to formation of I- vacancies, consequently forming a p-i-n junction across the crystal in Au/MAPbI3/Ag configuration. Therefore, the metal/ion interaction plays a role in determining the surface electronic structure and semiconducting properties of hybrid perovskites.