Strengthening the Hetero-Molecular Interactions in Giant Dimeric Acceptors Enables Efficient Organic Solar Cells.

Giant dimeric acceptor (G-Dimer) is becoming one of the most promising organic solar cell (OSC) materials because of its definite structure, long-term stability, and high efficiency. Strengthening the hetero-molecular interactions by monomer modification greatly influences the morphology and thus the device performance, but lacks investigation. Herein, two novel quinoxaline core-based G-Dimers, Dimer-QX and Dimer-2CF, are synthesized. By comparing trifluoromethyl-substituted Dimer-2CF and non-substituted Dimer-QX, the trifluoromethylation effect on the G-Dimer is investigated and revealed. The trifluoromethyl with strong electronegativity increases electrostatic potential and reduces surface energy of the G-Dimer, weakening the homo-molecular ordered packing but reinforcing the hetero-molecular interaction with the donor. The strong hetero-molecular interaction suppresses the fast assembly during the film formation, facilitating small domains with ordered molecular packing in the blend, which is a trade-off in conventional morphology control. Together with favorable vertical phase separation, efficient charge generation, and reduced bimolecular recombination are concurrently obtained. Hence, the Dimer-2CF-based OSCs obtain a cutting-edge efficiency of 19.02% with fill factor surpassing 80%, and an averaged extrapolated T80 of ≈12 000 h under continuous 80 °C heating. This study emphasizes the importance of hetero-molecular interaction and trifluoromethylation strategy, providing a facile strategy for designing highly efficient and stable OSC materials.