Non-fullerene polymer solar cells based on quinoxaline units with fluorine atoms

In this study, low bandgap polymers containing a monofluoroquinoxaline (FQx) or a difluoroquinoxaline (DFQx) as the electron-deficient unit and 2-thiophenylbenzo[1,2-b:4,5-b']dithiophene as the electron-rich unit were synthesized by Stille polymerization. The polymers exhibit satisfactory thermal stability and a broad absorption band from 300 to 650 nm. The HOMO/LUMO energy levels of PB-FQx and PB-DFQx were − 5.62/− 3.64 and − 5.70/− 3.63 eV, respectively. We found that for a high number of fluorine atoms in the conjugated backbone, the HOMO energy levels were deeper, which led to increased VOC. The PB-DFQx:ITIC-based PSC exhibited the best power conversion efficiency of 6.31%, with its VOC of 0.99 V, JSC of 10.61 mA/cm2, FF of 60%. •Synthesis of low bandgap polymers with a difluoroquinoxaline unit.•The HOMO energy levels of the fluorinated polymers were lower.•Polymers with deeper HOMO energy levels are conductive for achieving a higher VOC.•Efficient polymer solar cells were fabricated by blending the synthesized copolymers with ITIC, and the PCE increased up to 6.31%.