In this work, we have used spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) to characterize the properties of blend films commonly used in organic solar cells, namely poly[3-hexylthiophene-2,5-diyl] (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blends. The blend films were prepared using different solvents, and for different ratios of P3HT:PCBM in order to change the Surface roughness and phase separation in the blends. The obtained SE results were analyzed with and without the surface toughness correction to examine how the morphology affects the optical properties. (C) 2008 Elsevier B.V All rights reserved.