The absorption spectra and the photovoltaic effect in thin films consisting of a blend of p-type poly(3-hexylthiophene) and n-type acceptor [6,6]-phenyl C60 butyric acid methyl ester have been studied and a decrease in inter-band absorption in the wavelength range of 450-600 nm is observed. This absorption quenching is attributed to the disordering of the poly(3-hexylthiophene) chains and a charge transfer between poly(3-hexylthiophene) and [6,6]-phenyl C60 butyric acid methyl ester, as evidenced by FTIR and Xray photoelectron spectra. Finally, photovoltaic cells were fabricated utilizing the blend as the active layer and the device characteristics were studied. (c) 2005 Elsevier B.V. All rights reserved.