Side chain engineering plays a vital role in fine tuning of non-fullerene acceptors for the contemporary organic solar cells. In this work, we compare central alkyl side chains in the modification of photophysical and photovoltaic properties of difluorinated benzothiadiazole flanked non-fullerene acceptors. With a hexyl side chain, the resulting non-fullerene H-FFBR possesses more compact intermolecular interaction, leading to narrower bandgap, higher-lying HOMO level and stronger self-aggregation, if compared to O-FFBR with octyl side chain. For the photovoltaic performances, with PTB7-Th as the donor polymer, the O-FFBR-based solar cells exhibit power conversion efficiency of 9.4%, which is higher than that of 9.1% for the H-FFBR-based devices. Bulk-heterojunction morphologies of the O-FFBR- and H-FFBR-based active layers were compared by atomic force microscopy (AFM) and transmission electron microscope (TEM), revealing that O-FFBR is likely to give lower surface roughness and smaller phase separation. Our work demonstrates that varying alkyl side chain of a non-fullerene acceptor is valuable to tune the bulk-heterojunction morphology and resulting photovoltaic performance.

侧链工程在微调当代有机太阳能电池的非富勒烯受体中起着至关重要的作用。在这项工作中，我们比较了中央烷基侧链在二氟苯并噻二唑侧接非富勒烯受体的光物理和光电性质的改性。与具有辛基侧链的O-FFBR相比，具有己基侧链的非富勒烯H-FFBR具有更紧密的分子间相互作用，从而导致更窄的带隙，更高的HOMO能级和更强的自聚集。对于光伏性能，以PTB7-Th作为供体聚合物，基于O-FFBR的太阳能电池的功率转换效率为9.4％，高于基于H-FFBR的器件的9.1％。通过原子力显微镜（AFM）和透射电子显微镜（TEM）比较了基于O-FFBR和H-FFBR的有源层的体-异质结形态，发现O-FFBR可能具有较低的表面粗糙度和较小的相分离。我们的工作表明，非富勒烯受体的烷基侧链的变化对于调节本体-异质结的形态和由此产生的光伏性能非常有价值。