The need to develop renewable energy sources has stimulated a rapid growth of photovoltaic technology which uses solar energy to directly convert the daylight into electricity. Photovoltaic cells based on π-conjugated organic materials, also known as organic solar cells, potentially offer a significant reduction cost compared to inorganic solar cells and allow for large-scale production since organic materials can be solution-processed. However, the fundamental processes that determine the efficiency of these organic photovoltaic cells are still not understood. In particular, a deeper molecular-level comprehension of the exciton transport and charge generation mechanisms that take place in these photovoltaic devices is crucial to rationally design novel and enhance organic semiconducting materials for highly-efficient photovoltaic devices.The aim of this project is to develop a theoretical model able to give an appropriate description of the exciton transport mechanism in molecular crystals and to explore the connections between this mechanism and the free charge generation in photovoltaic junctions. Emphasis will be made on the role of the dynamic disorder but the other elements highlighted in the recent literature (vibronic effects, charge transfer excitons) will be included as well. The formalism will be complemented by atomistic study of the nuclear dynamics and electronic structure calculations so that accurate parameters can be feed into the model. Finally, the improved understanding of the exciton wavefunction will be used to provide a microscopic picture of the exciton dynamics in bulk and near the interface with an electron acceptor.