Polymeric solar cells have attracted much attention during the last years due to their lower fabrication cost and possibility of using flexible substrates. However, their efficiency is usually less than 5%. Among factors affecting polymeric solar cells efficiency, the active layer morphology related to blend preparation and annealing, is one of the most important. In this work we analyze the behavior of solar cells based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester, P3HT:PCBM blends prepared under different conditions. Basic parameters are extracted from measured characteristics in dark and under illumination, while modeling is used to understand the mechanisms involved in the device behavior and during its degradation in ambient conditions, which are associated to the active layer characteristics.