Abstract
<h2>Summary</h2> High voltage loss (<i>V</i><sub>loss</sub>) limits further improvements of organic solar cells (OSCs), and thus developing effective approaches to reduce <i>V</i><sub>loss</sub> is important. Herein, a solvent additive strategy was employed to reduce <i>V</i><sub>loss</sub> 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 <i>V</i><sub>loss.</sub> 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 <i>V</i><sub>oc</sub> of 0.893 V, higher than those (PCE = 18.23%, <i>V</i><sub>oc</sub> = 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 <i>V</i><sub>loss</sub> were also achieved.
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