Organic photovoltaics (OPVs) rely on the heterojunction between electron donating and electron accepting molecules to separate excitons into free electrons and holes.  This interface is therefore critical to the performance of an OPV device, with the molecular conformation at this interface playing a key role in the charge separation and recombination dynamics.  As has been shown theoretically, the rates of electron transfer and the energetic landscape are predicted to vary greatly depending on the molecular conformation at the donor-acceptor interface.  Many OPV donor polymers tend to be based on a donor-acceptor structure, whereby an electron rich �donor� unit (D) is copolymerized with an electron deficient �acceptor� unit (A), and in looking at these molecular structures a common trend begins to emerge in the high-performing derivatives.  That is the polymer tends to have a branched substituent on the donor moiety and a linear or no substituent on the acceptor moiety, thereby making this acceptor unit more sterically accessible to the fullerene.  The prevalence of this structural trend led us to hypothesize that a more favorable polymer:fullerene conformation occurs when the fullerene is in closer proximity and interacting more strongly with the acceptor moeity than the donor moiety.  We present experimental evidence that the molecular conformation at the D-A interface and the resulting energetic landscape is a key parameter governing the performance of OPV  material systems.

Role of molecular conformation at the donor-acceptor interface in organic photovoltaics

247th National Meeting (2014)

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