Efficient transfer of charges from a counter electrode to an electrolyte is a key process during the operation of dye-sensitized solar cells. Here, we develop a flexible counter electrode by electrochemical deposition of polyaniline nanofibers on graphitized polyimide carbon films for use in a tri-iodide reduction. As determined by the electrochemical impedance spectroscopy. the flexible counter electrode exhibited very low charge transfer resistance and series resistance. These results are due to the high electrocatalytic activity of the polyaniline nanofibers and the high conductivity of the flexible graphitized polyimide film. In combination with a dye-sensitized TiO2 photoelectrode and electrolyte, the photovoltaic device with the polyaniline counter electrode shows an energy conversion efficiency of 6.85% under 1 sun illumination. Short-term stability tests indicate that the photovoltaic device with the polyaniline counter electrode almost maintains its initial performance. (C) 2011 Elsevier Ltd. All rights reserved.