Graphene oxide (GO) was synthesized, and converted to reduced graphene oxide (rGO) during the preparation of electron collecting layers (TiOx) on ITO substrates in inverted P3HT:PCBM organic solar cells. The solar cells based on TiOx/rGO exhibited an open-circuit voltage and a power conversion efficiency of 0.659V and 2.70%, enhanced by 6.8% and 8%, respectively, as compared with the devices based on TiOx. Impedance spectra revealed that the devices based on TiOx/rGO composite have a smaller charge transport time constant than of devices based on TiOx. The electron collecting efficiency was improved significantly, resulting in high open circuit voltage. Moreover, the stability properties of the cells based on TiOx/rGO showed that energy conversion efficiency decreased 27% of the first day value after 90 days under ambient conditions. (C) 2013 Elsevier Ltd. All rights reserved.