(629e) Oligothiophene/Fullerene Interfaces: Molecular Simulations of Organic Photovoltaic Materials

Organic Photovoltaic systems (OPVs) have generated considerable interest as materials relevant to the cost effective conversion of solar radiation to electrical power. One of the most interesting OPV systems is the bulk heterojunction device created by the microphase separation of oligothiophene and fullerene mixtures, in which the large interfacial area enables the dissociation of photogenerated electron-hole pairs. Although it is known that the fullerene phase in such systems acts as a substrate that affects the morphology of the conjugated polymer and influences final device efficiency, a complete understanding of the underlying mechanisms is lacking. In this regard, molecular dynamics (MD) simulations are performed to study the behavior of tetrathiophene chains adjacent to buckyball surfaces. Well tested and accurate force-fields that represent both the polymer and the fullerene phase are employed. In particular, we focus on the morphology of the polymer chains adjacent to the substrates by evaluating order parameters that probe chain orientation and interchain packing. We also examine the dynamics of backbone libration and segmental motion, since these are processes known to influence charge transport in the polymeric phase.