The effect of solvent vapor treatment on the characteristics of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/C-60/poly (3-hexylthiophene) (PAT6)/Au was studied. Interpenetrating film of C-60 and PAT6 fabricated by using chloroform (CF) as a solvent was exposed to vaporized CF atmosphere at different concentrations, temperatures and time periods before an evaporation of metal electrode. Solvent vapor treatment caused an increase in the open-circuit voltage, the fill factor and the external quantum efficiency; these were discussed by taking the surface morphology and crystallinity of the PAT6 layer which underwent a change after it was treated by this method. (C) 2009 Elsevier B.V. All rights reserved.