Stability issues of conjugated polymer / fullerene solar cells from a chemical viewpoint

The efficiency of energy conversion and the stability or lifetime of ‘plastic’ photovoltaic cells, based on conjugated polymer/ fullerene blends, are the two main issues to be improved for this type of devices. The stability of these PV cells depends potentially on a large number of factors. A brief layer-by-layer overview of these factors is given, with main emphasis on the factors possibly playing a role in the active photovoltaic layer consisting of the interpenetrating network of a conjugated polymer and a fullerene derivative. Complicated sets of photochemical processes can take place in the pure materials and in the donor-acceptor blends, both in the absence and in the presence of oxygen. Especially, photochemical [2+2] cycloaddition and cycloreversion processes have been observed for fullerene derivatives and in certain mixtures containing an oligomer and a fullerene derivative. These and other (photo) chemical processes are very likely to have an influence on the performance of the photovoltaic cell