Exciton Dynamics within Active Layers of Organic Bulk Heterojunction Solar Cells

P3HT is one of the most studied -conjugated polymers from the beginning of realistic polymeric photovoltaic research and development history. There are already numbers of alternative polymers with which significantly higher PCE can be obtained. However, clear understanding about the internal relation between the number of incident photons and extracted electrons is still sparse. Especially the initial electron transfer process to bridge exciton dissociation and charge carrier formation is still controversial mainly due to its ultra-fast and complex nature. Therefore we have performed another set of transient absorption spectroscopy for the well-known thin film blend system consists with the poly-3-thiophene and a fullerene derivative especially at lower blending concentrations. The results are compared with the conventional photovoltaic device parameters for which same materials and preparation conditions were used. In addition, those results are compared with our previous results using a narrow band-gap polymer blend system. According to those comparisons, limiting factors of organic photovoltaic devices is discussed.