Synergetic optimizing quinoxaline and selenophene substitution in non-fullerene acceptors for efficient organic solar cells

Selenophene-fused non-fullerene acceptors (Se-NFAs) usually exhibited improved short circuit current density (JSC) in organic solar cells, while acceptors bearing quinoxaline (Qx) unit as the central core could achieve enhanced open circuit voltage (VOC). Herein, we incorporated the advantages of the above two strategies and synthesized four nonfullerene acceptors (Qx-Se-NFAs), including Qx-Se-F, Qx-Se-Cl, p-2FQx-Se-F, and p-2FQx-Se-Cl. Compared with CH1007 (the symmetrical selenium analog of Y6), the four acceptors-based devices showed evidently improved VOC and fill factor (FF) with well-maintained JSC, achieving excellent power conversion efficiency (PCE). Qx-Se-NFAs-based devices with the fluorinated terminal group exhibit evidently advantages on VOC and FF compared with the chlorinated terminal group due to the up-shifted LUMO energy level and optimized blend film. In addition, the acceptors with fluorination on the central core could further endow device with improved carrier properties and film morphology. Consequently, the device based on Qx-Se-F exhibited the highest VOC of 0.867 V among the reported PM6:Se-NFA systems. The p-2FQx-Se-F-based device yielded a champion PCE of 18.67% by using 2PACz as the hole transport layer, which is the highest PCE in the reported Se-NFAs among the single-junction binary OSCs. This work demonstrated a promising strategy that could better trade-off JSC, FF, and VOC in Se-NFAs.