Organic photovoltaic cells based on P3HT:PCBM bulk heterojunctions were fabricated with different drying durations of 0, 30, 60, and 80 min before annealing. The 60 min drying of the active layer was optimal to form perfect P3HT crystals, and to achieve the power conversion efficiency of 3.97%, increased by 10.3% compared with the device without drying. AC impedance analysis indicated the 60 min drying of the active layer formed the electrically perfect interface between P3HT and PCBM for efficient charge transport and dissociation of excitons. (C) 2013 Elsevier Ltd. All rights reserved.