Tight-binding approach describes polaron transport in organic semiconductors

Excitons and polarons are key elements of the electronic and optical properties of π-conjugated semiconductors, which are the building blocks of organic electronic devices. For organic photovoltaics, conjugated molecules are designed as acceptors, while polymeric π-conjugated semiconductors such as poly(3-hexylthiophene) [P3HT] are used as donors. Charge transport in these materials is often described by thermally activated hopping, with a rate given by Marcus theory, which depends on interchain electronic coupling and activation barriers. Recently, we have shown that tight-binding models can predict the frontier orbitals and describe the energetics and structure of excitons on π-conjugated semiconductors. Here, we use a tight-binding polaron model to calculate activation barriers for interchain polaron hopping in amorphous P3HT. The barrier is a dielectric-stabilized transition state delocalized over chain A (initial state) and chain B (final state) with charge fraction f on chain A. We examine different initial and final chain configurations in amorphous P3HT to explore the heterogeneity of barrier states and activation energies. Our computationally efficient approach can be used to average over disorder and predict polaron hopping rates and charge carrier mobilities for various conjugated semiconducting materials.