We investigated the effect of varying polymer crystallinity, morphology, and optical property, produced by adding four different co-solvents in to the poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C-61-butyric acid methyl ester (PCBM) active layer blend solution, on the functioning of an inverted polymeric solar device. Photovoltaic devices primed with cyclohexanone co-solvent showed the best performance with power conversion efficiency (PCE) reaching a value of 3.01 +/- 0.04%. Improvement in efficiency is related to an increase in photocurrent which is due to a combined result of ordered P3HT crystallite growth, as well as of the precise size and phase separation of domains. POLYM. ENG. SCI., 55:1382-1388, 2015. (c) 2015 Society of Plastics Engineers