Molecular Acceptors Based on a Triarylborane Core Unit for Organic Solar Cells

摘要： Triarylboranes that exhibit p-π* conjugation serve as versatile building blocks to design n-type organic/polymer semiconductors. Here, we report a series of new molecular acceptors based on triarylborane. These molecules are designed with a boron atom that bears a bulky 2,4,6-tri-tert-butylphenyl substituent at the core and strong electron-withdrawing 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile units as the endcapping groups that are linked to the core by bithiophene bridges. Butyl or butoxy groups are introduced to tune the optoelectronic properties. These molecules show nearly planar backbones with highly localized steric hindrance at the core, low LUMO/HOMO energy levels, and broad absorption bands spanning the visible region, which are all very desirable characteristics for use as electron acceptors in organic solar cell (OSC) applications. The attachment of butyl groups to the bithiophene bridges brings about a slightly twisted backbone, which in turn promotes good solubility and homogeneous donor/acceptor blend morphology, while the introduction of butoxy groups leads to improved planarity, favorable stacking in the film state and a greatly reduced bandgap. OSC devices based on these molecules exhibit encouraging photovoltaic performances with power conversion efficiencies reaching up to 4.07%. These results further substantiate the strong potential of triarylboranes as the core unit of small molecule acceptors for OSC applications.