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

Abstract

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 π–π stacking for the design of PDI-based acceptors. We synthesized and systematically studied two isomeric PDI-tetramers with different functionalization positions (α- and β-positions) of naphthalene, and thus different extents of intramolecular packing. Interestingly, both PDI molecules exhibit two π–π stacking peaks with intramolecular and intermolecular stacking distances of 3.7–3.8 Å and 4.6–4.7 Å, respectively. Most importantly, the α-positioned PDI shows stronger intramolecular π-stacked features as evidenced by UV-Vis and photoluminescence, and morphological measurements. Consequently, the α-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 π–π stacking in the design of novel PDI-based SMAs.