Tight-binding model describes frontier orbitals of non-fullerene acceptors

Optoelectronic properties of organic photovoltaics, including light absorption, intramolecular and intermolecular charge transfer, depend on the energetics of the frontier molecular orbitals of constituent organic materials. We develop a tight-binding model for an indacenodithiophene-based small molecule non-fullerene acceptor - IDTBR, which gives a high-efficiency organic photovoltaic cell in combination with poly(3-hexylthiophene) as donor. By choosing stiff conjugated ring moieties as sites, we obtain tight-binding parameters that are local to each moiety, and transferable to other chain architectures. In particular, parameters from homo-oligomers and alternating co-oligomers of constituent moieties can be used, without adjustment, to define the tight-binding model for IDTBR, which reasonably predicts the energies and wavefunctions of its frontier molecular orbitals. Transferability of model parameters will enable efficient screening and selection of molecular architectures with desirable optoelectronic properties.