Noncovalently Fused-Ring Electron Acceptors with C_2v Symmetry for Regulating the Morphology of Organic Solar Cells

Four noncovalently fused-ring electron acceptors p-DOC6-2F, o-DOC6-2F, o-DOC8-2F, and o-DOC2C6-2F have been designed and synthesized. p-DOC6-2F and o-DOC6-2F have the same molecular backbone but different molecular shapes and symmetries. p-DOC6-2F has an S-shaped molecular backbone and C2h symmetry, whereas o-DOC6-2F possesses a U-shaped molecular backbone and C2v symmetry. The molecular shape and symmetry can influence the dipole moment, solubility, optical absorption, energy level, molecular packing, and film morphology. Compared with the corresponding p-DOC6-2F, o-DOC6-2F exhibits better solubility, a wider band gap, and a larger dipole moment. When blended with the donor polymer PBDB-T, the C2v symmetric o-DOC6-2F can form an appropriate active layer morphology, whereas the C2h symmetric p-DOC6-2F forms oversized domains. Organic solar cells (OSCs) based on p-DOC6-2F, o-DOC6-2F, o-DOC8-2F, and o-DOC2C6-2F obtained power conversion efficiencies of 9.23, 11.87, 11.23, and 10.80%, respectively. The result reveals that the molecular symmetry can facilely regulate the performance of OSCs.