Performance of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) bulk-heterojuction organic photovoltaics was improved by incorporationg a small portion of an additive, 3-fluoro-4-cyanophenol (FCP). The addition of 5wt% FCP to the P3HT:PC61BM blend film resulted in an improvement of all parameters such as short circuit current, open circuit voltage and fill factor without even post-thermal annealing, and hence increased the overall power conversion efficiency by over 80% compared to that of reference cell without FCP. Optical measurement revealed that FCP additive in the P3HT:PC61BM blend film facilitates the crystallization (ordering) of P3HT chains, leading to increasing the exciton generation and charge transport efficiency.