1,8-Diiodooctane as a Critical Additive: Elucidating its Influence on the Performance of PM6:BTP-eC9-Based Nonfullerene Organic Solar Cells

In PM6:BTP-eC9-based nonfullerene organic solar cells (OSCs), incorporating 1,8-diiodooctane (DIO) is a common approach to enhance OSC's performance, yet the underlying mechanisms remain poorly understood. In this study, the correlations between DIO and charge dynamics, together with the morphological characteristics of the active layer, are comprehensively explored. Experimental studies show that the DIO solvent additive treatment was beneficial to improve exciton dissociation and balance the charge transport. While the comprehensive analysis of experimental researches also reveals that the DIO solvent additive may go against the charge transport and charge collection to some extent. Overall, DIO addition treatment has a positive effect on the whole photoelectric conversion process for PM6:BTP-eC9-based nonfullerene OSCs. Upon adding DIO, the short-circuit current density (J_SC) increases from 25.34 to 26.51 mA/cm², and the fill factor (FF) rises from 68.61% to 73.14%, resulting in a power conversion efficiency (PCE) boost from 14.88% to 15.89%. Notably, the devices with DIO demonstrate remarkable stability, retaining 80% of their initial efficiency after 576 h when stored in a nitrogen-filled glove box and tested in air. This research may provide some theoretical and experimental reference for researchers who are committed to improving the performance of PM6:BTP-eC9-based OSCs.