p-Flurophenyldicyanovinyl as electron-withdrawing group for highly soluble and thermally stable donor–acceptor small molecules

Solution-processed small molecule-based solar cells have demonstrated high power conversion efficiencies in recent years. However, several challenges have yet to be overcome, including achieving of low cost and excellent long-term stability of donor small molecules. Therefore, development of stable blocks to design organic semiconductors with optimal properties remains an actual problem. We report an alkyl-free star-shaped donor–acceptor (D–A) molecule, N(Ph-2T-DCV-PhF)3, containing p-fluorophenyldicyanovinyl (FPh-DCV) electron-withdrawing groups, triphenylamine as the donor core, and 2,2′-bithiophenes as the π-bridges between them. The study of thermal, optical, and electrochemical properties of the molecule in comparison to the direct analog with phenyldicyanovinyl groups, N(Ph-2T-DCV-Ph)3, made it possible to demonstrate the effect of the fluorine substituent on such key parameters as solubility, bandgap, lowest unoccupied molecular orbital energy level, phase behavior, thermal stability, and wettability. This work suggests that usage of the FPh-DCV block is an effective and simple tool to tune physical and physicochemical properties of stable D–A small molecules.