18.7% Efficiency Ternary Organic Solar Cells Using Two Non-Fullerene Acceptors with Excellent Compatibility

In this work, a series of ternary organic solar cells (OSCs) were prepared with polymer PM6 as a donor and two non-fullerene materials, BTP-eC9 and ITIC-Th, with excellent compatibility as acceptors. The open-circuit voltage (VOC) of ternary OSCs is found to monotonically increase with increasing content of ITIC-Th, implying the formation of an alloying state between BTP-eC9 and ITIC-Th. Furthermore, the incorporation of ITIC-Th can effectively minimize energy loss, which effectively improves the VOC of ternary OSCs. Consequently, a remarkable power conversion efficiency (PCE) of 18.7% with a short-circuit current density (JSC) of 28.0 mA cm-2, a VOC of 0.87 V, and a fill factor (FF) of 77.0% is achieved from the optimal ternary OSCs with 15 wt % ITIC-Th in acceptors. Comprehensive characterizations show that the enhanced JSC and FF are likely due to enhanced photon harvesting, effective exciton dissociation, and balanced charge transport in the optimal ternary active layers. The findings provide a hopeful way to further improve the OSC performance by employing a ternary strategy with two compatible non-fullerene materials as acceptors.