H-Bonds-Assisted Molecular Order Manipulation of Nonfullerene Acceptors for Efficient Nonannealed Organic Solar Cells

Various substituents have been incorporated into nonfullerene acceptors (NFAs) to modulate absorption scopes and energy levels for boosting efficiencies of organic solar cells (OSCs). The manipulation of the NFAs' molecular order and crystallinity via those substitutions is equally crucial to OSC performances, which yet remains interesting and challenging. The hydroxyl group, which can potentially form strong intermolecular hydrogen bonds (H-bonds) for improving molecular arrangements, has, however, never been considered. Herein, two hydroxyl-functionalized NFAs, IT-OH with one hydroxyl and IT-DOH with two hydroxyls, are synthesized to tune the molecular packing and crystallinity. The ordered molecular arrangement and higher crystallinity are observed for the IT-OH and IT-DOH than the parent ITIC. This is assigned to the formation of intermolecular H-bonds induced by the hydroxyls, which elongates molecular conjugated planes leading to long-range-ordered structures via pi-pi stacking. By the appropriate crystallinity and miscibility with donor polymer, an IT-DOH-based nonannealed OSC affords an efficiency of 12.5% with good device stability. This work provides a promising strategy to tune the molecular packing and crystallinity to design NFAs by introducing hydroxyl groups.