Solar cells based on poly(3-hexylthiophene) (P3HT):TiO2 nanocomposite films were studied. The influence of nanoparticle concentration, solvent used for spin coating, and the film morphology on the device properties was investigated. For low nanoparticle concentration (20-30%) the device performance was worse compared to pure P3HT, while for higher concentrations (50% and 60%) significant improvements were obtained. It was found that the change of solvent (from chloroform to xylene) yields one to two orders of magnitude improvement in the nanocomposite photovoltaic cell efficiency. For optimal fabrication conditions, external quantum efficiency up to 15% and AM1 power conversion efficiency of 0.42% were obtained. (C) 2003 Elsevier B.V. All rights reserved.