The generation of charge carriers from excited states in organic donor/acceptor junctions is still a topic of debate. The standard rules for obtaining charge separation in these junctions have been shown to be erroneous. The role of delocalization of charge carriers over acceptor domains has been argued for some binary donor/fullerene blends. But mechanisms are still not clear. We have studied ternary blends of donor1/donor2/fullerene composition. In some of these blends, we find improved power conversion efficiency, which we cannot pinpoint to changes of optical or electrical parameters.
In transient spectroscopy studies we find such high performance blends to demonstrate an oscillatory signature, with a period which matches a Raman mode. DFT calculations indicate that this is a breathing mode of a donor polymer. Thus vibronic coupling, coupled electronic and vibrational coherence, could assist in the charge separation process generating free charges from excited states in donor/acceptor junctions.