Polymer-based photovoltaic devices have been elaborated by blending the conjugated polymer, poly(2-methoxy-5-(2'-ethylhexyloxy)1-4-phenylenevinylene) (MEH-PPV) with the buckminsterfallerene, C-60. The solvent used has a main influence on the optical and electrical properties of the photoactive layers. This could be attributed to different dispersion abilities of C60 in the polymer layers shown by Atomic Force Microscopy and Scanning Electron Microscopy. Its effect on the transfer and transport properties has been studied. Thin film processing conditions have been modified by the preparation of blends of solutions of the polymer in Tetrahydrofuran and fullerene in Ortho-dichlorobenzene. The resulting spin casted layers show improved morphologies implying better dispersion of the fullerenes and increased short circuit currents. A decrease in the fullerene critical concentration to form percolation paths has been demonstrated. The improvement of the photovoltaic properties of the MEH-PPV/C-60 composites has been attributed to the nanosized fullerene domains formed upon phase separation. We used optical spectroscopy to study the charge transfer efficiency and electrical measurements to investigate charge transport properties in MEH-PPV:C-60. (C) 2007 Elsevier B.V. All rights reserved.