Enhancing Molecular Stacking Through “Strengthened Aggregation in Pseudo-Dry Film” Strategy by Bromothiazol Additive for Efficient Organic Solar Cells

Regulating the morphology and molecular ordering of the active layer is crucial for developing high-performance organic solar cells (OSCs). However, enhancing the molecular stacking is challenging as non-fullerene acceptors (NFAs) are confined within the polymer network owing to the well donor/acceptor miscibility and fast solvent evaporation. Herein, the 2,5-dibromothiazol (DBrTz) removable solid additive is chosen to optimize the film-forming kinetics for enhancing molecular aggregation of the PM6:L8-BO blends. During the film formation process, chloroform evaporates first, trapping DBrTz in the film (pseudo-dry film state). Thereafter, DBrTz will gradually volatilize, persistently prompting the L8-BO to stack and aggregate orderly until the volatilization of DBrTz is completed. The behavior is designated as “enhanced aggregation in pseudo-dry film,” an occurrence hitherto unobserved in other solid additives. This results in more compact π–π stacking and orderly long-range aggregation of L8-BO. Furthermore, DBrTz facilitated increased face-on orientations and improved vertical component distributions. This optimized morphology facilitates charge generation, transport, and extraction. Consequently, DBrTz-processed PM6:L8-BO OSCs achieved a power conversion efficiency (PCE) of 19.4%. This work elucidates the principles of solid additives and offers valuable insights for fostering the development of novel additives to improve the morphology and the efficiency of OSCs.