Organic materials steadily break into the market of electronic devices (see organic electronics) as cost effective solution. Ease of production and recycling, enhanced molecular engineering, light weight and flexibility are additional advantages of organic electronics over inorganic. The electronic properties of these materials are determined by the π-conjugated system (see conductive polymer).
One of the most promising applications is in photovoltaics. A low-cost implementation of organic solar cells is based on bulk-heterojunction of π-conjugated molecular donor and fullerene-based acceptor: the solar radiation is absorbed by the first component resulting in the creation of an exciton migrating to the interface where the exciton is split into the hole and electron transported to the electrodes by the donor and acceptor respectively. The complex multiscale morphology of this device limits the ability of experimental approaches to pinpoint the power conversion losses and thus to avoid the blind search of highly efficient devices. In this situation a theoretical study becomes an essential complementary tool of investigation.
We perform first-principles study of light absorption, exciton and charge carrier transport in polycrystalline small-molecule based donors. Our results show that there are no power conversion losses on a single-crystallite scale. Thus the main efforts should be put in improving the mesoscale morphology of the active layer.