Enhancing Open-Circuit Voltage of High-Efficiency Nonfullerene Ternary Solar Cells with a Star-Shaped Acceptor

The ternary strategy has been widely used in high-efficiency organic solar cells (OSCs). Herein, we successfully incorporated a mid-band-gap star-shaped acceptor, FBTIC, as the third component into the PM6/Y6 binary blend film, which not only achieved a panchromatic absorption but also significantly improved the open-circuit voltage (V_OC) of the devices due to the high-lying lowest unoccupied molecular orbital (LUMO) of the FBTIC. Morphology characterizations show that star-shaped FBTIC molecules are amorphously distributed in the ternary system, and the finely tuned ternary film morphology facilitates the exciton dissociation and charge collection in ternary devices. As a result, the best PM6/Y6/FBTIC-based ternary OSCs achieved a power conversion efficiency (PCE) of 16.7% at a weight ratio of 1.0:1.0:0.2.