High-efficiency organic solar cells with low voltage loss induced by solvent additive strategy

High voltage loss (V_loss) limits further improvements of organic solar cells (OSCs), and thus developing effective approaches to reduce V_loss is important. Herein, a solvent additive strategy was employed to reduce V_loss in PM6:L8-BO OSCs. The use of diiodomethane (DIM) instead of 1,8-diiodooctane (DIO) led to a reduction in energetic difference between the single excited state of L8-BO and the charge transfer state in PM6:L8-BO blend, and thereby a reduced V_loss. Meanwhile, the morphology, charge transport property, and quantum efficiency are not deteriorated. Consequently, the DIM-processed OSCs showed a high power conversion efficiency (PCE) of 18.60% (certified as 18.20%) with a high V_oc of 0.893 V, higher than those (PCE = 18.23%, V_oc = 0.869 V) of the DIO-processed devices, representing the highest efficiency for binary OSCs thus far. DIM has also been successfully applied in PM6:BTP-eC9 and PM6:3TP3T-4F blends, and high PCEs with reduced V_loss were also achieved.