We report on a solution processed reduced graphene oxide (rGO) thin films as anode buffer layer in organic solar cells. The spin-coated rGO, and zinc oxide (ZnO) thin films have been used to fabricate bulk heterojunction organic solar cells employing [poly({4,8-di(2-ethylhexyloxyl)benzo[1,2-b:4,5-b']dithiophene}-2,6-diyl)-alt-({5-octythieno[3,4-c]pyrrole-4,6-dione}-1,3-diyl):fullerene (PBDTTPD:PCBM) blends as a photoactive layer. Atomic force microscopy, X-ray diffraction, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and photovoltaic measurements were performed to investigate the morphology, materials of processed thin films, and device performance of the fabricated devices. The ZnO also plays an important role in blocking holes, collecting electrons and serves as conducting channels to the cathode top electrode. A short-circuit current density (J(sc)) and fill factor (FF), increase when the rGO was introduced, which directly contributed to the improved efficiency to 4.8%. (C) 2012 Elsevier B.V. All rights reserved.