All-Small-Molecule Organic Solar Cells Based on Pentathiophene Donor and Alkylated Indacenodithiophene-Based Acceptors with Efficiency over 8%

Three small molecules IDIC8-M, IDIC8-H, and IDIC8-F with alkylated indacenodithiophene unit as the central building block and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) or its derivations as end groups have been synthesized as nonfullerene acceptors to fabricate solar cells with small molecule donor DRCN5T. The devices based on IDIC8-H incorporating INCN as the end group give a power conversion efficiency (PCE) up to 8.00%. Upon terminal unit fluorination, IDIC8-F based devices exhibit an impressive PCE of 8.42% attributed to the much improved short-circuit current density and fill factor. For DRCN5T:IDIC8-M-based device, a PCE of 6.31% is obtained with high open-circuit voltage over 1 V. The minor structural changes of acceptors have made large difference to the devices performance with the same donor DRCN5T, mainly attributed to the difference of their absorption properties, energy levels and blend film morphologies. These results give a valuable insight on the nonfullerene acceptors based all-small-molecule solar cells.