High-performance nonfused ring electron acceptor with a steric hindrance induced planar molecular backbone

Three nonfused ring electron acceptors (NFREAs) TTC6, TT-C8T and TT-TC8 were purposefully designed and synthesized. The molecular geometry can be adjusted by the steric hindrance of lateral substituents. According to the DFT calculations, from TTC6 to TT-C8T and TT-TC8, planarity of the molecular backbone is gradually improved, accompanying with the enhancing of intramolecular charge transfer effect. As for TT-TC8, the two phenyl substituents are almost perpendicular to the molecular backbone, which endues the acceptor with good solubility and suppresses it to form over-aggregation. Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film. As a result, TT-TC8 based devices afford the highest PCE of 13.13%, which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs.

Automated summary

Three nonfused ring electron acceptors (NFREAs) were purposefully designed and synthesized, with TTC6, TT-C8T, and TT-TC8. The molecular geometry can be adjusted by the steric hindrance of lateral substituents, resulting in improved planarity and intramolecular charge transfer effect. TT-TC8, with its perpendicular phenyl substituents, exhibits good solubility and suppresses over-aggregation. It forms multidirectional regular molecular orientation and closer molecular stacking in the film, leading to the highest power conversion efficiency (PCE) of 13.13% among NFREAs.