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

High voltage loss (Vloss) limits further improvements of organic solar cells (OSCs), and thus developing effective approaches to reduce Vloss is important. Herein, a solvent additive strategy was employed to reduce Vloss 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 Vloss. 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 Voc of 0.893 V, higher than those (PCE = 18.23%, Voc = 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 Vloss were also achieved.