This data corresponds to the demonstration of the photovoltaic effect in an ultrathin heterojunction of monolayer MoS2 and poly[[4,8-bis[(2- ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-flu-oro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7). Tuning of the PTB7 thickness enables complete quenching of the MoS2 photoluminescence. Solar cells made from the heterojunction on transparent indium tin oxide demonstrate exceptional current density per absorbing thickness. DOI: 10.1021/acsnano.6b06592