Molecular dynamics simulations of fullerene derivatives diffusion in solar cells
Organic photovoltaics (OPV) is becoming a well established field for future energy winning. While the efficiencies are reaching acceptable levels at very competitive production conditions and prices, questions related to the durability still have to be addressed. Diffusion of acceptors, such as fullerene derivatives, in the active part of a polymeric solar cell is an important factor that influences the stability of the device. The principal objective of this research action is to understand the molecular mechanism that is responsible for the change in local structure in bulk-heterojunctions (BHJ) by computer simulations. A strong collaboration with experimentalists at all stages of the project will ensure a good focus of the planned simulations and a very good interpretation of the results. Within the general goal of this research proposal, we will focus on model systems of BHJ that are of direct relevance for the development of polymer solar cells. The main method of investigation is molecular dynamics simulation of the interface between donor and acceptor in a BHJ system. We propose a systematic modeling approach of this research question. We will first calculate diffusion coefficients and diffusion paths of the acceptor in solvent solution. In the next step we will perform the same calculations for the acceptor in the vicinity of the donor surface. We will investigate the role of the solvent, of the acceptor size and shape, of the donor's nature and of other external stimuli on the stability of the active layer in an OPV system. The insights obtained within this framework will contribute to the better understanding of the stability of the active layer in OPV and will provide valuable input for to the improvement of the life time of polymeric solar cells.