An A-D-D-A-type non-fullerene small-molecule acceptor with strong near-infrared absorption for high performance polymer solar cells

An acceptor-donor-donor-acceptor (A-D-D-A)-type near-infrared non-fullerene small-molecule acceptor IDT2-DFIC with indacenodithiophene-indacenodithiophene (IDT2) as a donating core and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) as electron withdrawing end groups has been synthesized. Compared to A-D-A-type small-molecule acceptor IDIC-4F, IDT2-DFIC exhibits a low optical bandgap of 1.42 eV with strong absorption in the 450-874 nm region, and upshifted energy levels as an electron acceptor. Furthermore, the IDT2-DFIC-based devices exhibited higher and more balanced charge transport and smoother surface morphology. The power conversion efficiency (PCE) of the IDT2-DFIC-based devices is 10.06%, which is higher than that of the IDIC-4F-based devices (5.17%). Our work provides an efficient molecular design strategy to construct small molecule acceptors with near-infrared absorption.