Efficient strategies to improve photovoltaic performance of A-D-A type small molecules by introducing rigidly fluorinated central cores

Abstract

For the purpose of exploring the subtle photophysical property on fluorine atom influence, in this work, two simple conjugated small molecules (SMs) with an acceptor-donor-acceptor (A-D-A) molecular backbone, DFPh(DPP)2 and DFDT(DPP)2, based on fluorinated benzene (DFPh) or fluorinated 2,2′-bithiophene (DFDT) as the central donor units, and the electron deficient diketopyrrolopyrrole (DPP) as the terminal acceptor moieties, were designed and synthesized. Due to introducing noncovalent attractive interactions between the fluorine and sulfur atoms (F⋯S), both SMs exhibited a strong absorption in the wavelength region of 300–800 nm, deep HOMO energy level of −5.39 ∼ −5.50 eV, and narrow optical band gap of 1.60–1.66 eV in comparison with those of non-fluorinated analogues. After optimization, the DFDT(DPP)2/PCB71M-based device presented a higher PCE of 7.87% with Voc of 0.86 V, Jsc of 12.6 mA cm−2, and FF of 72.6% in comparison with the PCE of 6.45% with Voc of 0.97 V, Jsc of 10.50 mA cm−2, and FF of 63.8% for DFPh(DPP)2/PCB71M-based device. Notably, the PCE of 7.87% is one of the highest PCEs reported for the A-D-A type SMs-based on DPP as terminal acceptor groups. These primary studies indicated that the incorporating fluorine atom on rigidity skeleton central units is an efficient approach to improve photovoltaic performance of A-D-A type SMs.