Suppression of Charge Recombination Induced by Solid Additive Assisting Organic Solar Cells with Efficiency over 20%

Abstract A volatile solid additive strategy, which can effectively optimize the morphology of the photoactive layer with an ideal domain size and purity, has emerged as a promising approach to improve the photovoltaic performance of organic solar cells (OSCs). However, the precise role of solid additives in modulating charge and exciton dynamics, especially the recombination process, remains not fully understand. In this study, a solid additive, 1,4‐diiodo‐2,5‐dimethoxybenzene (DIDOB), is developed to improve the photovoltaic performance of OSCs and conduct a comprehensive investigation into its effect on the charge recombination process. As a result, the PM6:L8‐BO‐X‐based binary OSC processed with DIDOB achieves an excellent efficiency of 19.75% with a remarkable fill factor of 81.9%, owing to the optimal fiber network morphology, tighter and ordered molecular packing, as well as the suppression of both bimolecular and geminate recombination. Notably, the DIDOB exhibits broad universality as an additive in other non‐fullerene acceptor‐based OSCs. Impressively, the D18:PM6:L8‐BO‐based ternary device processed with DIDOB yielded an excellent efficiency of 20.11% (certified as 20.03%). This work highlights the effect of the solid additive on the charge recombination process within active layer and provides insights for the further development of OSCs.