Conjugated Starbursts with Acceptor-?-Donor-?-Acceptor Architectures as Nonfullerene Acceptors for High-Efficiency Organic Solar Cells

A set of acceptor-pi-donor-pi-acceptor-based star -burst macromolecular acceptors (SMAs), BTTIDC8IC and BTTIDC8IC-F, are reported for efficient nonfullerene organic solar cells (OSCs). The tiny variation in intermolecular stacking and distortion of molecular structures in the three dimensions of SMAs largely affect their inherent properties. Noncovalent interactions are introduced into the peripheral groups of BTTIDC8IC to explore the effect on the regulation of the distortion of the fused-ring long arms in three dimensions. Compared to BTTIDC8IC, the fluorinated starburst molecule BTTIDC8IC-F exhibits broader (500-800 nm) light absorption and higher extinction coefficients (2.22 x 105 M-1 cm-1). BTTIDC8IC-F spin-coated films from chlorobenzene solutions exhibit crystalline rather than amorphous characteristics. X-ray diffraction and grazing incident wide-angle X-ray scattering results indicate that the BTTIDC8IC-F molecules show increased packing structures and enhanced intermolecular interactions, which may contribute to the crystallinity of its films. As a result, OSCs based on BTTIDC8IC-F SMA achieve a higher power conversion efficiency (8.24%) with improved fill factor and short-circuit current density, as compared to that based on BTTIDC8IC SMA (6.26%). The results show that subtle control of the three-dimensional structures by incorporating fluorine units in the peripheral groups allows the development of high-performance nonfullerene starburst acceptors for efficient OSCs.