The effect of 1,8-diiodooctane (DIO) on the performance enhancement of polymer solar cells (PSCs) based on [6,6]phenyl-C-71-butyric acid methyl ester (PCTIBM) as the acceptor and poly[(4,8-bis-(2-ethylhexyloxy)-benzo Kdithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoy1)thieno[3,4-b]thiophene)-2,6-diy1KPBDTTT-C) as the donor was investigated from the device physics researches. The short circuit current density (Jsc) was increased from 8.84 to 12.11 mA/cm2, fill factor (FF) was increased from 44.5% to 63.1%, resulting in power conversion efficiency (PCE) with 80% improvement from 2.95% to 5.35% by adding DIO with 3% volume ratio. The enhancement of performance of PSCs could be mainly attributed to the improved charge carrier transport and increased optical field strength in the active layer by adding DIO additive. (C) 2014 Elsevier B.V. All rights reserved.