The influence of dielectric screening on bimolecular recombination in binary and ternary organic solar cells

Semiconducting polymer-based solar cells (PSCs) have attracted great interest due to its potential for manufacturing at low cost and large quantity. While the performance of PSCs has significantly improved in the past twenty years, the state-of-the-art efficiency around 12 % is still much lower than the theoretical efficiency limit, which is above 31%. One of the major bottlenecks to PSC efficiency is bimolecular recombination, which limits the active layer thickness and thus sunlight harvesting of the solar cell. Reduced bimolecular recombination, in which the bimolecular recombination rate is one to three orders of magnitude lower than predicted by a model based on Langevin theory, has been shown to have beneficial effects most notably allowing large fill factors at large active layer thicknesses. Reduced recombination has been observed only in a few confirmed cases of conjugated polymer / fullerene blends. Initially, this study was motivated to find additional examples of material systems with reduced recombination in order to establish general design guides for new high-performance materials.