Here we report on the effect of light on surface and bulk morphology, structural and optical properties of polymer/fullerene blends used for organic solar cells. The crystallization kinetics of the organic film molecules was followed in real time during illumination, by time-resolved X-ray diffraction, applied in-situ, jointly with atomic force microscopy. The occurrence of possible phase separation of the two components was detected. This latter hypothesis was confirmed by Fourier Transform Infrared spectroscopy experiments. As a result of such cross monitoring, a comprehensive picture of the chemical/physical process concurring to the devices photo-active layers aging was gained. (C) 2011 Elsevier B.V. All rights reserved.