Performance improvement of orgaic photovoltaics (OPV) based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk-heterojuction has been achieved by incorporating a small amount of additive, 3,4,5,6-tetrafluorophthalonitrile (TFP) even without post-thermal annealing. The OPV with non-annealed P3HT:PCBM:TFP blend film showd an increase in short-circuit current and open-circuit voltage, resulting in a 33% enhancement in power conversion efficiency, compared to that of reference cell without TFP additive. It was revealed that the addition of 5wt% TFP to the P3HT:PCBM blend film facilitated the crystallization (ordering) of P3HT chains without even post-thermal annealing, leading to increasing the exciton generation and charge transport efficiency.