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 from their production. However, the disordered molecular aggregation of nonfullerene acceptors in nonhalogenated solvents hinders the realization of OSCs with high power conversion efficiencies (PCEs). Herein, this problem is addressed using an external physical field modulation strategy involving the sonication of nonfullerene acceptor solutions. The application of ultrasound field induces a transformation from disordered molecular aggregation to ordered J-aggregation via microstreaming and shear stress in nonhalogenated solvents. The aggregation is effectively preserved within films, causing the formation of a fibril network with enhanced π-π stacking interactions. Moreover, sonication promotes the conversion of localized excitons to intra-moiety delocalized excitons and suppresses molecular vibrations, thus favoring charge separation and reducing nonradiative recombination. Consequently, the PCEs of PM6:L8-BO-based binary and ternary devices fabricated using o-xylene as a nonhalogenated solvent are 19.43% and 20.41% (certified 19.84%), which is among the highest values reported for OSCs produced without halogenated solvents. The binary devices also exhibit high thermal stabilities, with the T₈₀ lifetime exceeding 10000 h. The developed strategy is applicable to various small-molecule acceptor and polymer acceptor systems, facilitating control disordered aggregation in nonfullerene acceptor solutions and thus paving the way for practical industrial applications.