A phenyl compound with electron withdrawing substituents, 3-fluoro-4-cyanophenol (FCP), was used as an additive in polymer solar cells with a P3HT [poly(3-hexyl thiophene)]:PCBM [[6,6]-phenyl-C61-butyric acid methyl ester] blend film. Under simulated solar illumination of AM 1.5 (100 mW/cm2), the devices fabricated using a P3HT:PCBM (1:0.9 w:w) layer blended with 5 wt% of FCP achieved an enhanced power conversion efficiency (PCE) of 4.8% due to the improved short circuit current and fill factor, as compared to reference cells with PCE = 4.1%. UV-visible absorption spectra, X-ray measurements and carrier mobility studies revealed that FCP facilitated the ordering of the P3HT chains, resulting in higher absorbance, larger crystal size, closer packing and enhanced hole mobility.