Ternary non-fullerene polymer solar cells with an efficiency of 11.6% by simultaneously optimizing photon harvesting and phase separation

Ternary non-fullerene polymer solar cells (PSCs) were fabricated with J71 as a donor and mixed ITIC:MeIC2 as acceptors. The power conversion efficiency (PCE) of the ternary PSCs reaches 11.6% for 20 wt% MeIC2 in the acceptors, which is larger than the 10.7% or 10.2% for binary PSCs with ITIC or MeIC2 as an acceptor. The PCE improvement of ternary PSCs is mainly attributed to the simultaneously enhanced short circuit current density (J_SC) of 18.1 mA cm^-2 and fill factor (FF) of 70.5%. The photon harvesting of ternary active layers can be optimized by adjusting MeIC2 content due to the complementary asborption of ITIC and MeIC2, leading to the enhanced JSC. Meanwhile, phase separation of ternary active layers can be further optimized for efficient exciton dissociation and more balanced charge transport. The improved FF can be well explained from the more balanced charge transport evaluated by the ratios of hole mobility to electron mobility in the active layers.