An ab-initio framework for phonon-mediated exciton diffusion in crystals

摘要: The dynamics of excitons in complex materials upon photoexcitation are important for energy applications, eg, light-emitting diodes and photovoltaics. As a specific example, in organic photovoltaics, strongly-bound photo-excited excitons must diffuse to donor-acceptor interfaces where charge separation may occur before the rest of the energy conversion process can proceed. Describing phonon-mediated exciton transport in these materials is complicated by the fact that exciton bandwidth and exciton-phonon coupling strengths are similar in magnitude. In turn it is unclear a priori whether exciton diffusion is best described by phonon-limited Boltzmann-like or thermally activated hopping-like theories. In this talk, using density functional perturbation theory and the ab initio Bethe-Salpeter equation approach, we describe a self-contained framework for computing exciton diffusion coefficients in both the band-like and …