Ternary polymer solar cells using two nonfullerene acceptors with cascading energy level and complementary absorptions

Abstract

In this paper, we have fabricated ternary PSC with BTP-eC9 as the host acceptor, IT-M as the guest acceptor, and PM6 as donor. The optimized ternary PSC (PM6:BTP-eC9:IT-M ratio is 1:1.2:0.2) has the highest power conversion efficiency (PCE) of 17.06 % compared to the PM6:BTP-eC9 binary PSC (16.46 %) and PM6:L8-BO reference binary PSC (16.92 %). We systematically investigated the effect of blend acceptors on morphology, photovoltaic performance and charge carrier dynamics. After the addition of IT-M to PM6:BTP-eC9 binary film, the highest JSC (from 26.39 to 26.82 mA cm−2) was achieved for optimized ternary PSCs compared to PM6:BTP-eC9 binary PSC, which was attributed to the high efficiency of light absorption in the medium to long-wavelength region of IT-M. Shallower lowest unoccupied molecular orbitals (LUMO) level of IT-M enlarged the optical bandgap, which leads to an increase in the open-circuit voltage (VOC, from 0.86 V to 0.875 V). In addition, a small amount of IT-M improves the surface and bulk morphology and crystallinity of the ternary film. The ternary films shown high charge mobility ability. This work demonstrates that supplementing the light absorption and broadening the optical bandgap of PM6:BTP-eC9 binary films by IT-M as third component can effectively improve the PCE and obtain higher photovoltaic performance than that of PM6:BTP-eC9 binary PSCs and PM6:L8-BO reference binary PSCs.