Transiently delocalised hybrid quantum states are gateways for efficient exciton dissociation at organic donor-acceptor interfaces

The field of organic photovoltaics has witnessed a renaissance in recent years owing to the development of non-fullerene acceptor materials reaching record power conversion efficiencies of  > 20%. New computational models are needed to rationalise the regimes of photophysics reached in these materials. Here we report on a novel implementation of eXcitonic state-based Surface Hopping, a powerful non-adiabatic molecular dynamics method for the simulation of photo-induced charge generation in truly nanoscale donor-acceptor interfaces. We observe a transition from an inefficient cold to an efficient hot exciton dissociation mechanism as the electronic coupling between the molecules or the dielectric constant of the materials is increased. The hot pathway is observed to occur by Frenkel excitons converting into transiently delocalised hybrid exciton-charge transfer states that subsequently form charge separated states. This avoids the formation of kinetically trapped interfacial charge transfer states that are prone to non-radiative recombination.