Reduced Coulomb interaction in organic solar cells by the introduction of high-k SrTiO₃ nanoparticles

A concept is introduced which allows for reduced Coulomb interaction in organic solar cells and as such for enhanced power conversion efficiencies. The concept is based on the introduction of electrically insulating, nanostructured high-k materials into the organic matrix, which do not contribute to the charge carrier transport, however, enhance the effective permittivity of the organic active layer. Using an analytical model, it is demonstrated that even at a distance of 20 nm to the organic/inorganic interface of the nanostructure, the Coulomb interaction in the organic semiconductor can be reduced by more than 15 %. The concept is substantiated experimentally by realizing P3HT:PCBM solar cells with integrated SrTiO₃ nanoparticles. It could be demonstrated that in comparison to a reference cells without nanoparticles, the power conversion efficiency is improved by ∼17 %. This effect is interpreted to be the result of an organic active layer effective permittivity enhancement, which is supported by the result of transient absorption as well as grazing incidence wide angle x-ray scattering measurements.