Energy Loss in Organic Photovoltaics: Nonfullerene Versus Fullerene Acceptors

The energy loss E_l00exo00exs00exs seen in organic photovoltaics sets a fundamental limit to their open-circuit voltage, and hence power conversion efficiency. This study compares molecular structures of fullerene and nonfullerene acceptors and quantifies the relationship between E_l00exo00exs00exs, exciton binding energy, and intra- and intermolecular electron-phonon couplings. Molecular design strategies derived from this analysis provide elementary approaches to reduce E_l00exo00exs00exs yet also achieve efficient exciton dissociation. While addressing the source of E_l00exo00exs00exs is particularly relevant for solar cells, it has wide-ranging implications for any system with an organic heterojunction.