Structurally, L8-BO-F has the same thienothienopyrrolo-thienothienoindole (TTP-TTI) core units as L8-BO (L8-BO-2F) with mono-fluorinated peripheral 2-(5 or 6-fluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile end-groups.
L8-BO-F is another highly efficient non-fullerene acceptor that belongs to Y6 family. Similar to L8-BO, it has a branched 2-butyloctyl side chain which not only promotes solubility but also improves the morphology to achieve better packed film with higher intermolecular stackings, balanced charge transport and to reduce charge combination. L8-BO-F is also believed to suppresses the non-radiative recombination leading to a reduce the voltage loss.
Outstanding device performance with PCE of 18.66% has achieved while a binary BTP-eC9 and L8-BO-F non-fullerene acceptors were used with polymer donor PM6. The polymer donor and mixed NFAs give complementary absorptions in the visible and NIR region with well matched energy alignment.
Device structure: ITO/PEDOT:PSS AI 4083/PM6:BTP-eC9:L8-BO-F (1:1.2)/PNDIT-F3N/Ag