Photophysics of charge transfer in a polyfluorene/violanthrone blend

We present a study of the photophysical and photovoltaic properties of blends of violanthrone in poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] (PF2/6). Photoluminescence quenching and photocurrent measurementsshow moderate efficiencies for charge generation, characteristic of such polymer/dye blends. Pump-probemeasurements on blend films suggest that while ,47% of the total exciton population dissociates within 4 psof photoexcitation, only ,32% subsequently results in the formation of dye anions. We attribute the discrepancyto the likely formation of complex species with long lifetimes, such as stabilized interface charge pairs orexciplexes. This conclusion is supported by the appearance of a long lifetime component of 2.4 ns in thedynamics of the photoinduced absorption signal associated to polarons in photoinduced absorption bandscentered at 560 nm