Over 15% efficiency all-small-molecule organic solar cells enabled by a C-shaped small molecule donor with tailorable asymmetric backbone

In the past few years, compared with the rapid development of polymer solar cells (PSCs), the research progress of all-small-molecule organic solar cells (ASM-OSCs) lags far behind. Herein, two kinds of C-shaped SM donors named FBD-S3 and TBD-S4, bearing subtly tailorable asymmetric central core, are firstly reported. Both the two SMs show broad as well as matched absorption and energy level with classical acceptor Y6. The introduction of asymmetric core endows SM with Y6-similar bending skeleton and a unique network assembly in which the SM donor can easily interpenetrate into neighboring Y6 via strong intermolecular interaction and facile stacking direction. These features would hinder rapid aggregation and prevent to form large domains of single component in blends, resulting in an extraordinary power conversion efficiency of 15.10% in TBD-S4:Y6-based device, which is one of the highest values for ASM-OSCs. In addition, our comparative study demonstrates that although the donor material TBD-S4 exhibits reduced crystallinity, such a molecule matches better with acceptor Y6 and works more efficiently for ASM-OSCs. This work indicates that conformation tailorable by asymmetric central core is a novel and powerful method to design SM donor, which open a new avenue for highly efficient ASM-OSCs.