We have fabricated organic photovoltaic devices with blends of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and fullerene as an electron donor and electron acceptor, respectively. A significant improvement of the photovoltaic efficiency was found in device by using active materials with complementary spectra. The different weight ratios of composite film were also performed to correlate between morphology and the device performance. A power conversion efficiency (PCE) up to 2.0% with an open-circuit voltage of 0.85 V and a short-circuit current (J(SC)) of 5.3 mA/cm(2), was achieved by blending the F8T2 with [6,6]-phenyl-C71-butyric acid methyl ester (PC[70]BM). (C) 2009 Elsevier B.V. All rights reserved.