  The separation of photogenerated polaron pairs in organic bulk heterojunction
solar cells is the intermediate but crucial step between exciton dissociation
and charge transport to the electrodes. In state-of-the-art devices, above 80%
of all polaron pairs are separated at fields of below $10^7$V/m. In contrast,
considering just the Coulomb binding of the polaron pair, electric fields above
$10^8$V/m would be needed to reach similar yields. In order to resolve this
discrepancy, we performed kinetic Monte Carlo simulations of polaron pair
dissociation in donor--acceptor blends, considering delocalised charge carriers
along conjugated polymer chain segments. We show that the resulting fast local
charge carrier transport can indeed explain the high experimental quantum
yields in polymer solar cells.
