Fluorinated and methylated <i>ortho</i>-benzodipyrrole-based acceptors suppressing charge recombination and minimizing energy loss in organic photovoltaics

The elimination of the A' unit from -type Y6-derivatives has led to the development of a new class of <i>ortho</i>-benzodipyrrole (<i>o</i>-BDP)-based A-D_NB_ND-A-type NFAs. In this work, two new A-D_NB_ND-A-type NFAs, denoted as CFB and CMB, are designed and synthesized, where electron-withdrawing fluorine atoms and electron-donating methyl groups are substituted on the benzene ring of the <i>o</i>-BDP moiety, respectively. CFB exhibits a blue-shifted absorption spectrum, stronger intermolecular interactions, shorter π-π stacking distances, and more ordered 3D intermolecular packing in the neat and blend films, enabling it to effectively suppress charge recombination in the PM6:CFB device showing a higher PCE of 16.55% with an FF of 77.45%. CMB displays a higher HOMO/LUMO energy level, a smaller optical bandgap, and a less ordered 3D packing, which contributes to its superior ability to suppress energy loss in the PM6:CMB device with a high <i>V</i> _oc of 0.90 V and a PCE of 16.46%. To leverage the advantages of CFB and CMB, ternary PM6:Y6-16:CFB and PM6:Y6-16:CMB devices are fabricated. The PM6:Y6-16:CFB device exhibits the highest PCE of 17.83% with an increased <i>V</i> _oc of 0.86 V and a <i>J</i> _sc of 27.32 mA cm^-2, while the PM6:Y6-16:CMB device displayed an elevated <i>V</i> _oc of 0.87 V and an improved FF of 74.71%, leading to a PCE of 17.44%. The high PCE was achieved using the non-halogenated greener solvent <i>o</i>-xylene, highlighting their potential for facilitating more eco-friendly processing procedures. C-shaped disubstituted <i>o</i>-BDP-based A-D-A type acceptors open up new avenues for tailoring electronic properties and molecular self-assembly, achieving higher OPV performance with enhanced charge recombination suppression and reduced energy loss.