Intramolecular π-stacked perylene-diimide acceptors for non-fullerene organic solar cells

Proper molecular packing is key to improving the performance of non-fullerene organic solar cells (OSCs) based on perylene diimides (PDI). Herein, we implement a novel concept of introducing intramolecular - stacking for the design of PDI-based acceptors. We synthesized and systematically studied two isomeric PDI-tetramers with different functionalization positions (- and -positions) of naphthalene, and thus different extents of intramolecular packing. Interestingly, both PDI molecules exhibit two - stacking peaks with intramolecular and intermolecular stacking distances of 3.7-3.8 angstrom and 4.6-4.7 angstrom, respectively. Most importantly, the -positioned PDI shows stronger intramolecular -stacked features as evidenced by UV-Vis and photoluminescence, and morphological measurements. Consequently, the -positioned PDI achieved a higher device efficiency of 8.6% with an open-circuit voltage of 1.15 V and a reasonably high fill factor of 60%. Our work highlights the importance of intramolecular - stacking in the design of novel PDI-based SMAs.