(Invited) Ultrafast Infrared Spectroscopy of Charge Generation in Organic Photovoltaic Materials

Ultrafast infrared spectroscopy is used to examine the mechanism of charge generation in organic photovoltaic materials.  We examine archetypal classes of electron acceptors in organic photovoltaic (OPV) materials and reveal how their molecular structures determine whether hot CT state dissociation can influence the dynamics and yield of photo-generated electrons and holes.  Furthermore, we tune the degree of aggregation and therefore charge carrier delocalization in OPV materials and elucidate the corresponding influence on the yield of photogenerated charge carriers.  The data suggest that a distribution of local molecular environments exist at donor/acceptor interfaces.  Some of these are able to support greater degrees of charge delocalization and therefore more efficient dissociation CT states into independent charge carriers.  Molecular structure and domain composition influence the density of interfacial sites capable of separating charge, which determines the overall quantum yield for charge generation of a given OPV material.