A wide bandgap conjugated polymer based on a vertically connected benzodithiophene unit enabling efficient non-fullerene polymer solar cells

We report a wide bandgap polymer PvBDTffBT based on a new building block: a vertical-benzodithiophene (vBDT) unit. Compared to traditional BDT based polymers, the vBDT unit in PvBDTffBT is connected via the phenyl group instead of the thiophene unit. Such modification leads to stronger torsion between the vBDT unit and the adjacent thiophene, which increases the bandgap of the polymer and introduces significant changes in the film morphology. When blended with a state-of-the-art narrow-bandgap small molecular acceptor (ITIC-Th), we find that this polymer modulation strategy significantly improves the photovoltaic performances from 3% to over 8%.