Design and computational characterization of non-fullerene acceptors for use in solution-processable solar cells

In an effort to seek high-performance small molecule electron acceptor materials for use in heterojunction solar cells, computational chemistry was used to examine a variety of terminal acceptor-conjugated bridge-core acceptor-conjugated bridge-terminal acceptor small molecules. In particular, we have systematically predicted the geometric, electronic, and optical properties of 16 potential small-molecule acceptors based upon a series of electron deficient π-conjugated building blocks that have been incorporated into materials exhibiting good electron transport properties. Results show that the band gap, HOMO/LUMO energy levels, orbital spatial distribution, and intrinsic dipole moments can be systematically altered by varying the electron properties of the terminal or core acceptor units. In addition, the identity of the conjugated bridge can help fine-tune the electronic properties of the molecule, where this study showed that the strongest electron affinity of the conjugated π-bridge increased the stability in the HOMO and LUMO energies and increased the band gap of these small-molecule acceptors. As a result, this work points toward an isoindigo (C5) core combined with C2-thienopyrrole dione (A5) terminal units as the most promising small molecule acceptor material that can be fine-tuned with the choice of conjugated bridge and may be considered as reasonable candidates for synthesis and incorporation into organic solar cells.