Comparison of Linear- and Star-Shaped Fused-Ring Electron Acceptors

A star-shaped nonfullerene electron acceptor, FBTIC, and a linear-shaped nonfullerene acceptor, FBDIC, with the same electron-deficient end groups and p-hexylphenyl side chains but different fused-ring electron-rich cores (benzotrithiophene and benzodithiophene) are designed, synthesized, and compared. Terminal groups 2FIC in FBTIC form intermolecular π–π stacking, leading to the complex 3D conjugated framework, while 2FIC units in FBDIC form double hydrogen bonding. Relative to that of FBDIC, FBTIC shows an 81 nm blue-shifted absorption, a 0.21 eV larger optical bandgap, a 0.13 eV lower highest occupied molecular orbital, a 0.1 eV higher lowest unoccupied molecular orbital, and double electron mobility. Paired with the donor PM6, the optimized PM6/FBDIC-based organic photovoltaic cells show an efficiency of 12.3%, while the cells based on PM6/FBTIC exhibit an efficiency of 10.1% with a fill factor of 75.4%, much better than those of the reported star-shaped fused-ring electron acceptors.