Fluorinated oligothiophene donors for high-performance nonfullerene small-molecule organic solar cells

Thiophene is widely used in organic photovoltaics due to its excellent charge transport properties, simple synthesis, and high stability. In this paper, two simple oligothiophenes, namely,DC5Tand2FDC5Twith rhodanine-flanked structures were synthesized and used as donors in nonfullerene small-molecule organic solar cells (NSM-OSCs). Compared toDC5T,2FDC5Twith fluorine atoms substituted on the conjugated backbone exhibited a downshifted highest occupied molecular orbital (HOMO) energy level and blue-shifted light absorption. WithIDIC-4Fas a small-molecule acceptor, the2FDC5T-based device exhibited much higher short-circuit current density and open-circuit voltage than theDC5T-based device. As a result, a promising power conversion efficiency (PCE) of 9.02% was achieved for the2FDC5T/IDIC-4Fdevice, which was 28% higher than that of theDC5T/IDIC-4Fdevice (PCE = 7.03%). Further research indicated that fluorination on the oligothiophene donor assisted the optimization of the active layer morphology and the reduction in the trap-assisted recombination in the device, which could deeply explain the improvement in efficiency.