Achieving 20% Toluene-Processed Binary Organic Solar Cells via Secondary Regulation of Donor Aggregation in Sequential Processing

• Isomeric molecules fine-tune secondary nucleation of donor underlayer, enabling precise control of swelling in sequential processing. • Binary organic solar cells processed with non-halogen toluene solvent achieve a champion efficiency of 20.0% (certified 19.7%). • High dipole moment isomer promotes earlier nucleation of PM6, improving bulk morphology and vertical phase segregation. • The study proposes solvent design rules for sequential processing, advancing green-solvent-based organic photovoltaics.