  In organic photovoltaics, charges can separate efficiently even if their
Coulomb attraction is an order of magnitude greater than the available thermal
energy. Delocalization has been suggested to explain this fact, because it
could increase the initial separation of charges in the charge-transfer (CT)
state, reducing their attraction. However, understanding the mechanism requires
a kinetic model of delocalized charge separation, which has proven difficult
because it involves tracking the correlated quantum-mechanical motion of the
electron and the hole in large simulation boxes required for disordered
materials. Here, we report the first three-dimensional simulations of
charge-separation dynamics in the presence of disorder, delocalization, and
polaron formation, finding that even slight delocalization, across less than
two molecules, can substantially enhance the charge-separation efficiency, even
starting with thermalized CT states. Delocalization does not enhance efficiency
by reducing the Coulomb attraction; instead, the enhancement is a kinetic
effect produced by the increased overlap of electronic states.
