Regioregular poly(3-hexylselenophene) (P3HS) is used in combination with zinc oxide (ZnO) to make hybrid polymer–metal oxide solar cells with a photoresponse up to 740 nm. Intimately mixed ZnO:P3HS layers were prepared by casting P3HS and diethylzinc as a reactive precursor from a common solvent in a moist atmosphere, followed by conversion to ZnO in the film. Photoinduced absorption spectroscopy was used to identify the electron transfer reaction occurring from P3HS to ZnO under illumination. The performance of ZnO:P3HS solar cells was optimized for composition, layer thickness, and conversion temperature to a final power conversion efficiency of 0.4% in simulated solar light. The performance is primarily limited by a low short-circuit current. By comparing the spectrally resolved external quantum efficiency with the optical absorption, we find that the abundant semicrystalline phase of P3HS gives a negligible contribution to the photocurrent, which is dominated by the scarce amorphous P3HS regions in direct contact with the ZnO.