An A–D–A′–D–A type small molecule acceptor with a broad absorption spectrum for organic solar cells

Organic molecules with wide absorption spectra exhibit great sunlight harvesting capability and are critically important for solar cell applications. In this manuscript, we develop an A-D-A'-D-A type small molecule acceptor (IID-IC) using isoindigo (IID) as the electron-deficient core unit (A'), thiophene as the electron-rich bridging units (D) and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) as the electron-deficient endcapping groups (A). IID-IC shows a wide absorption spectrum with the full width at half maximum (FWHM) of 190 nm, which is almost twice that of a typical A-D-A type molecule acceptor. The wide absorption spectrum of IID-IC is possibly due to the partially suppressed intramolecular charge transfer effect with the additional electron-deficient core unit. An organic solar cell (OSC) device based on IID-IC exhibits the power conversion efficiency of 2.82% with broad photoresponse from 320 nm to 780 nm.