Giant Molecule Acceptors Based on A-D-A-Type Small Molecule Acceptor Subunits for Medium-Bandgap Organic Solar Cells

Medium-bandgap organic solar cells (OSCs) have attracted significant attention for indoor applications and ternary devices as the second acceptor. Here, we designed and synthesized a new medium-bandgap giant molecule acceptor (GMA) DF-4TC based on A-D-A type small molecule acceptor (SMA) subunits. To the best of our knowledge, DF-4TC is the first GMA constructed from A-D-A type SMA building blocks, where the reported GMAs are all based on A-DA'D-A type SMA subunits. The OSCs based on PM6:DF-4TC possess a high open-circuit voltage (V_oc) of 1.037 V, among the highest V_oc reported for GMA-based OSCs. But the weak aggregation of DF-4TC constrains the molecular packing and device performance. To strengthen molecular aggregation, another GMA DF-4IC was synthesized by replacing the end groups. Benefiting from the strengthened molecular aggregation of DF-4IC, the PM6:DF-4IC-based OSCs show higher exciton dissociation efficiency, better charge transport, and less recombination behaviors and achieve a higher power conversion efficiency (PCE) of 12.44%. Incorporating DF-4IC as the secondary acceptor into the PM6:BTP-eC9 system, the PM6:BTP-eC9:DF-4IC-based ternary OSCs exhibit increased V_oc, contributing to a higher PCE of 19.71%. This work explored medium-bandgap GMAs, opening new opportunities for the rational design of high-performance OSCs.