Near-Infrared Electron Acceptors with Cyano-Substituted 2-(3-Oxo-2,3-dihydroinden-1-ylidene)malononitrile End-Groups for Organic Solar Cells

Near-infrared (NIR) electron acceptors are critical components for constructing organic solar cells (OSCs). Herein, we report a set of A-DA′D-A-type electron acceptors with end-groups of cyano-substituted 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (CN-IC), which possesses the strongest electron-withdrawing ability among the end-groups reported to date. An optical bandgap as low as 1.29 eV was obtained for the electron acceptors with CN-IC end-groups, which is decreased by 0.12 eV with respect to that of the reference electron acceptor. Meanwhile, deep-lying frontier molecular orbital energy levels were maintained in these electron acceptors. These advantages endow the electron acceptors with a broad light-harvesting range and the capacity to match prevalent polymer donors. Consequently, OSCs with a power conversion efficiency of 18.1% were obtained. These results suggest the huge potential of CN-IC in constructing NIR electron acceptors.