Near-Infrared Electron Acceptors with Unfused Architecture for Efficient Organic Solar Cells

摘要： Nonfullerene acceptor (NFA) with near-infrared (NIR) region absorption is crucial for obtaining high current densities in organic solar cells (OSCs). Herein, two narrow bandgap NFAs with unfused backbones possessing broad (600-900 nm) and strong absorption are developed by the conjugation of a benzothiadiazole (BT) core to halogenated end-groups through cyclopentadithiophene (CPDT) bridge. Compared with the fluorinated counterpart BCDT-4F, the chlorinated NFA BCDT-4Cl appears stronger J-aggregation and closer molecular packing, leading to the optimized blend morphology when paired with polymer donor, PBDB-T. Thus, an obvious improvement of external quantum efficiency response was obtained for BCDT-4Cl based OSCs, presenting a higher efficiency of 12.10% than that (9.65%) based on BCDT-4F. This work provides a design strategy for NIR acceptors in the combination of electron deficient core and halogenated terminal in unfused backbone, which results in not only fine-tuning of optoelectronic properties, but also the simplified synthetic complexities of molecule.