Barrierless Free Carrier Formation in an Organic Photovoltaic Material Measured with Ultrafast Vibrational Spectroscopy

摘要

Free carrier formation, the escape of electrons and holes from Coulombically bound radical pairs at donor/acceptor interfaces, is an essential step in the cascade of photochemical reactions in organic photovoltaic (OPV) materials.Electrons and holes are believed to be Coulombically bound to donor/acceptor interfaces by a few tenths of an electronvolt (eV).The efficiency of free carrier formation can strongly influence the charge collection characteristics of organic solar cells. Two mechanisms have been proposed for this process. One proposal suggests that excess vibrational energy remaining in bound radical pairs following electron transfer provides the energy needed to overcome the electron-hole Coulombic attraction.