We report here the fabrication of a p–n junction diode in a single nanostructure by synthesizing a heterostructure involving n-type AgInS₂ and p-type Ag₂S. The quasi type-II band alignment between these ternary–binary semiconductors in the p–n junction heterostructures also slows down the carrier recombination rate and the heterostructures show rectification behavior. Hence, they can be used as an active material for fabrication of bulk heterojunction photovoltaic devices without any additional semiconductor material or dye required for charge separation or formation of a p–n junction.