Wide-Bandgap Polymers with a C(sp³)DF Polyfluoride Backbone Enable High-Efficient Ternary Organic Solar Cells

Fluorination strategy is demonstrated to be a successful approach for optimizing the electron distribution and morphology of organic photovoltaic materials. The previous works focus on introducing only a few C(sp(2))& horbar;F bonds into conjugated backbone or C(sp(3))& horbar;F bonds into sidechains. Herein, a new strategy by introducing C(sp(3))& horbar;F polyfluoride unit into the backbone is proposed, wherein the fluorine atoms are not involved into the conjugation but can promote the intermolecular interaction between backbones. Two wide-bandgap fluoropolymers are prepared and employed as the third component for ternary organic solar cells. As expected, even if there are six fluorine atoms in a single repeat unit, the relevant fluoropolymers possess complementary absorption and aligned energy levels. More importantly, the polyfluoride backbone affords adequate non-covalent interactions, consequently enhancing the polymer aggregation and packing order, which is verified by a fibril-like morphology in the blend film with the host polymer PM6 and only 10 wt.% fluoropolymer. In addition, the decreased surface energy caused by polyfluoride unit is beneficial for the improvement of domain purity and the formation of nanoscale phase separation between donor and acceptor materials. As a result, the fluoropolymer-assisted ternary device displays a higher efficiency of 18.74% compared with the binary device (17.39%).