  We present a fully quantum-mechanical model of the electronic dynamics of
primary photoexcitations in a polymeric semiconductor heterojunction, which
includes both polymer stacking and phonon relaxation. By examining the
phonon-induced fluctuations in the state-to-state energy gaps and the exact
golden-rule rate constants, we conclude that resonant tunnelling between the
primary exciton to delocalized interchain charge-transfer states may be the
initial step in the formation of charge-carriers in polymer-based
bulk-heterojunction photovoltaic diodes.
