Sonication-induced J-aggregation in nonhalogenated solvents boosts exciton delocalization for high-efficiency organic solar cells

The commercialization of organic solar cells (OSCs) requires eliminating halogenated solvents. However, the disordered molecular aggregation of nonfullerene acceptors (NFAs) in nonhalogenated solvents hinders achieving high power conversion efficiencies (PCEs). Herein, this problem is addressed using an external physical field modulation strategy involving the sonication of NFA solutions to induce a transformation from disordered molecular aggregation to ordered J-aggregation via microstreaming and shear stress. The aggregation is effectively preserved within films, enhancing π-π stacking interactions. Moreover, sonication promotes the conversion of localized excitons to intra-moiety delocalized excitons and suppresses molecular vibrations. The PCEs of PM6:L8-BO-based binary and ternary devices fabricated using o-xylene are 19.43% and 20.41% (certified 19.84%), ranking among the highest values reported for nonhalogenated solvent-processed OSCs. The binary devices also exhibit high thermal stabilities (T80 lifetime > 10000 h). This universally applicable strategy effectively controls disordered aggregation in NFA solutions, thus paving the way for practical industrial applications.