Regulating Molecular Packing and Crystallization Kinetics via Trifluoromethyl-Functionalized Solid Additives for Efficient Organic Solar Cells

Abstract

Precise control over crystallization kinetics and molecular packing is crucial for achieving high-efficiency organic solar cells (OSCs), yet balancing controllable morphology evolution with process compatibility remains a key challenge. Here, we develop a trifluoromethyl-functionalized volatile solid additive (DBTFE) based on an ester-substituted thiophene unit to regulate active-layer morphology. Compared with its non-fluorinated counterpart DBTE, DBTFE exhibits a stronger interaction with the acceptor Y6, promoting tighter π-π stacking and more ordered molecular packing, as revealed by theoretical calculations. During film formation, DBTFE prolongs the crystallization process and optimizes the vertical phase distribution, leading to a more balanced crystalline morphology with enhanced crystallinity. Consequently, the DBTFE-treated PM6:Y6 device achieves a power conversion efficiency (PCE) of 18.6%, accompanied by suppressed trap-assisted and bimolecular recombination, improved exciton dissociation, and more balanced charge transport. Notably, this additive strategy demonstrates excellent universality across multiple systems, including PM6:L8-BO, PM6:BTP-eC9, and D18:L8-BO, all exhibiting improved efficiencies, with a peak PCE of 20.1% achieved in the D18:L8-BO system. This work provides an effective strategy for regulating crystallization behavior and morphology via trifluoromethyl-functionalized volatile solid additives, offering a generalizable pathway toward high-performance OSCs.