Fluorinated Benzodipyrrole-Based Non-Fullerene Acceptors with Chlorinated End Groups Exhibiting Fluorine-Chlorine Interactions for Suppressed Charge Recombination in Organic Photovoltaics.

Two terminal-chlorinated -benzodipyrrole (-BDP)-based non-fullerene acceptors (NFAs), CFB-Cl and CMB-Cl, were designed and synthesized by incorporating fluorine or methyl substituents on the -BDP core, respectively. Compared to their terminal-fluorinated counterparts, both NFAs exhibit red-shifted absorption, higher melting points, and stronger intermolecular interactions, attributed to the introduction of chlorinated end groups. Single-crystal X-ray analysis of CFB-Cl revealed a compact three-dimensional kaleidoscopic packing network stabilized by unique F···Cl halogen interactions between the fluorinated -BDP core and the chlorinated end group, leading to a short π-π stacking distance of 3.38 Å and enhanced charge transport. Consequently, PM6:CFB-Cl devices achieved a PCE of 16.62% with a fill factor (FF) of 75.54%, outperforming PM6:CMB-Cl PCE = 16.13%. To further improve device performance, a ternary blend strategy was employed by introducing the fluorinated CMB into PM6:CFB-Cl blends to extend the absorption range and improve the morphology. The resulting PM6:CFB-Cl:CMB inverted device exhibited excellent miscibility χ = 0.02 K, balanced carrier transport μ/μ = 1.38, suppressed recombination, and a highest PCE of 17.26% with = 26.02 mA cm and = 0.892 V. This work highlights the importance of halogen engineering in regulating molecular packing and charge dynamics, providing insights into the structure-morphology-performance relationship of o-BDP-based NFAs for next-generation organic photovoltaics.