In this work, we have fabricated heterojunction solar cells between layers of p-type CuS and n-type Ag2S deposited through successive ionic layer adsorption and reaction (SILAR) method. We have introduced Sn2+ and Al3+ as heterovalent-dopants in the cationic sites of Ag2S and studied their effect on the photovoltaic performance of the heterojunctions. As evidenced from the band diagrams drawn from scanning tunneling spectroscopy (STS) of the components, such doping shifted the Fermi energy of pristine Ag2S towards the conduction band-edge influencing the solar cell activities of the heterojunction in turn. While the trivalent Al-dopants introduced defects states in Ag2S and hence deteriorated the cell efficiency, doping with 5 at% of Sn at the silver site resulted in band-engineered pn-junction solar cells with a power conversion efficiency of 2.85%.