Halogenation Strategy of Thiophene Derived Solvent Additives Enables Optimized Morphology for Organic Solar Cells with 19.17% Efficiency

As simple and versatile tools, additives have been widely used to refine active layer morphology and have played a crucial role in boosting the power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, three novel solvent additives named Th-FSi, Th-ClSi, and Th-BrSi with the same backbone of 2,5-bis(trimethylsilyl)thiophene are designed and synthesized by substituting different halogens of fluorine, chlorine, and bromine, respectively. Notably, Th-ClSi exhibits the more significant dipole moment and engages in non-covalent interactions with a small-molecule acceptor (SMA) L8-BO, which slight adjustments in intermolecular interaction, crystallinity, and molecular packing in the PM6:L8-BO active layer. Consequently, the OSCs incorporating Th-ClSi outperform their Th-FSi and Th-BrSi counterparts in photo-capturing, reduced energy loss, superior exciton dissociation, and charge transfer properties, out-coming yields in an enhanced PCE of 18.29%. Moreover, by integrating a near-infrared absorbing SMA (BTP-eC9) guest into the PM6:L8-BO matrix, the absorption spectrum to span 880–930 nm, and the resultant ternary OSCs achieve a commendable PCE of 19.17%, ranking among the highest efficiencies reported to date is expanded. These findings underscore the promise of halogenated thiophene-based solvent additives as a potent avenue for morphological fine-tuning and consequent PCE enhancement in OSCs.