Central Aromatic Ring Substitution on Non-Fullerene Acceptors Boosts Performance of Organic Photovoltaics

Abstract

Molecular packings of non-fullerene acceptors (NFAs), which are determined by not only end groups but also central cores, affect the power conversion efficiency (PCE) of organic solar cells (OSCs) greatly. Compared to typical halogen and alkyl substitutions, aromatic moieties are usually more powerful to tune molecular packing due to their π–π stacking ability. Herein, two NFAs of CH-Ph and CH-Th were designed and synthesized with phenyl and thiophene substitutions on central phenazine cores, respectively. A systematic investigation reveals that different aromatic substitutions on central core result in diverse molecular planarity and frontier orbital distributions, which greatly influences the crystallinity of NFAs and their photo-dynamics in blend films. Benefiting from the enhanced crystallinity, the PM6:CH-Th-based binary organic solar cells achieved a high PCE of 18.96%, outperforming the PM6:CH-Ph-based devices (PCE = 17.89%). By incorporating CH-Th as a third component, the ternary OSCs of PM6:CH6F:CH-Th further attained an excellent PCE of 19.94%. Our findings emphasize the crucial role of aromatic substituents on the central core in tuning the crystallinity of non-fullerene acceptors and enhancing the PCE of organic solar cells.