π-Extended giant dimeric acceptor as a third component enables highly efficient ternary organic solar cells with efficiency over 19.2%

Ternary strategy with a suitable third component is a successful strategy to improve the photovoltaic performance of organic solar cells (OSCs). Very recently, Y-series based giant molecule acceptors or oligomerized acceptors have emerged as promising materials for achieving highly efficient and stable binary OSCs, while application as third component for ternary OSCs is limited. Here a novel π-extended giant dimeric acceptor, GDF, is developed based on central Y series core fusion and rigid BDT as linker, and then incorporated into the state-of-the-art PM1:PC6 system to construct ternary OSCs. The GDF has a near planar backbone, resulting in increased π-conjugation, excellent crystallinity, and good electron transport capacity. When GDF is introduced into the PM1:PC6 system, it ensues in a cascade like the lowest unoccupied molecular orbitals (LUMO) energy level alignment, a complementary absorption band with PM1 and PC6, higher and balanced hole and electron mobility, slightly smaller domain size, and a higher exciton dissociation probability for PM1:PC6:GDF (1:1.1:0.1) blend film. As a consequence, the PM1:PC6:GDF (1:1.1:0.1) ternary OSC achieves a champion PCE of 19.22%, with a significantly higher open-circuit voltage and short-circuit current density, compared to 18.45% for the PM1:PC6 (1:1.2) binary OSC. Our findings show that employing a π-extended giant dimeric acceptor as a third component significantly improves the photovoltaic performance of ternary OSCs.