Halogenated diphenyl ether solvent additives enable ∼20% efficiency organic solar cells and high-performance opaque/semitransparent modules

Solvent additives are considered as versatile tools to optimize morphology for boosting power conversion efficiency (PCE) of organic solar cells (OSCs). Here, three halogenated diphenyl ether (DPE) solvent additives (fluorinated DPE-F, chlorinated DPE-Cl and brominated DPE-Br) are developed to optimize active-layer (PM6:L8-BO) morphology. With the halogen atomic weight increases, three additives show a gradually increasing boiling point, while DPE-Cl and DPE-Br have similar but a much higher dipole moment compared to DPE-F. The higher boiling point and dipole moment of DPE-Br are expected to enhance the non-covalent interaction between the additive and L8-BO during the active layer film-forming process, offering improved intermolecular packing, charge transport, exciton dissociation and charge collection. As a result, the DPE-Br-treated OSC achieves a higher PCE (18.40%) compared to the DPE-F- and DPE-Cl-treated ones (17.73% and 18.03%). Impressively, using D18 as the donor, the OSCs based on DPE-Br-processed D18:L8-BO:BTP-eC9 obtain a further boosted PCE of ∼20%, while their 11.6 cm² opaque and semitransparent modules also achieve high PCEs of 16.42% and 10.50%, respectively, which are among the top values in OSCs and opaque/semitransparent modules. This work highlights that the halogenation in DPE-derived additives is a promising strategy to optimize morphology for obtaining efficient OSCs and modules.