title: Ultrafast charge separation in organic photovoltaics enhanced by charge delocalization and vibronically hot exciton dissociation.
abstract: In organic photovoltaics, the mechanism by which free electrons and holes are generated, overcoming the Coulomb attraction, is a currently much debated topic. To elucidate this mechanism at a molecular level, we carried out a combined electronic structure and quantum dynamical analysis that captures the elementary events from the exciton dissociation to the free carrier generation at polymer/fullerene donor/acceptor heterojunctions. Our calculations show that experimentally observed efficient charge separations can be explained by a combination of two effects: First, the delocalization of charges which substantially reduces the Coulomb barrier, and second, the vibronically hot nature of the charge-transfer state which promotes charge dissociation beyond the barrier. These effects facilitate an ultrafast charge separation even at low-band-offset heterojunctions.
authors.affiliation: WPI-Advanced Institute for Material Research, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tamura
authors.forename: Irene
authors.initials: I
authors.lastname: Burghardt