Organic solar cells convert light into electricity. The active layer, a bulk-heterojunction, consisting of an intimately mixed blend of a semiconducting polymer and a fullerene derivative is sandwiched between two electrodes. Light is absorbed by the polymer, creating tightly bound electron-hole pairs called excitons. At the interface between electron donor (polymer) and electron acceptor (fullerene) these excitons are separated, generating free charge carriers and producing current. In order to optimize the performance of the solar cell additional layers such as electron transport layers (ETL) or hole transport layers (HTL) can be inserted between the electrodes and the active layer.
The color of the resulting solar device depends on the light-absorbing polymer and can be tuned from red to green, including neutral shades. Highest efficiencies of ~8% are currently achievable with a blue to green appearance.
The combination of a high degree of design freedom, as well as the reduced weight of the resultant device, enables new application fields to become accessible for organic solar cells, such as integration into clothes, photovoltaic membranes for the building industry, and foldable mobile solar cells. Furthermore, target sectors such as automotive applications and building integrated photovoltaics can be addressed as the technology matures.