Tracking localised exciton formation in organic semiconductor material

Here, using single-material OPV device and laser system with sub-10fs time resolution, we track in time the formation of localised excitonic states. For this we employ a combination of pump-probe (PP) spectroscopy, sensitive to concentration of excited states, and pump-push-photocurrent (PPPC) technique, sensitive to the state localisation. Combining both methods to monitor charge dynamics at real operation condition allows to separate and track the evolution of strongly bound and spontaneously dissociating excited states. Our data show that PP and PPPC measurement do not follow the same trend, and the discrepancy between the states probed by PP and PPPC indicates that excitons acquire localised character within first 50fs after formation. Results may be useful for a new realisation of efficient donor-acceptor OPV design.