Prof. Dr. Peter Müller-Buschbaum
One potential alternative to crystalline silicon photovoltaic (PV) cells is cells made from thin films (<1 micometer) of conjugated (semiconducting) and photoactive polymers, which can easily be cast onto flexible substrates over a large area using wet-processing techniques. These photoactive polymers are attractive semiconductors for photovoltaic cells because they are strong absorbers and can be deposited on flexible substrates at low cost.
Regarding all polymer photovolatic structures both components, the p- and the n-conducting one, are polymeric. Past work made clear that the type of structure installed is crucial for the potential device. Excitons generated by the incoming light need to be split into isolated charges at interfaces between p- and n-type polymers. Due to the short exciton diffusion length (for example, on the order of 20 nm for P3HT) a non-morphology is desirable. However, charge generation, charge separation and charge transport need to be balanced. So far still the inner structure in polymer films used in organic photovoltaics is widely unknown and the optimal type of structure is far from being reached. Based on two different approaches, using either polymer blends or diblock copolymers, this issue is addressed. Different parameters such as the type of solvent and annealing are under investigation (see figure). In future work aging mechanism on the meso- and nano-scale will be focussed, because so far most work was devoted to the molecular level only. Other open questions are the amount of residual solvent and its influence on the aging and performance.
