Tight-binding model accurately describes frontier orbitals of conjugated oligomer acceptors for organic solar cells.

Conjugated organic oligomers are designed as acceptor materials for organic photovoltaic [OPV] cells. OPV optoelectronic properties, including light absorption, intramolecular and intermolecular charge transfer, depends on the properties of frontier molecular orbitals of these conjugated molecules. Recently, we have shown that tight-binding models can efficiently describe a broad range of optoelectronic properties for copolymers. Tight-binding parameters derived from density functional theory [DFT] calculations on constituent homopolymers reasonably predict copolymer valence and conduction bands. Here, we extend this approach to heterogeneous oligomers designed for non-polymeric acceptors including IDTBR, which gives high-efficiency OPVs in combination with various polymeric donors. IDTBR consists of 7 aromatic moieties: an indacenodithiophene [IDT] core, flanked by benzothiadiazole and 3-ethylrhodadine on either side. We show that tight-binding parameters fitted to frontier orbital energies of alternating oligomers of these constituent moieties can be used without adjustment in a tight-binding model to predict the energies and wavefunctions of IDTBR frontier orbitals.