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

Abstract

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 V-OC. The PB-DFQx:ITIC-based PSC exhibited the best power conversion efficiency of 6.31%, with its V-OC of 0.99 V, JSC of 10.61 mA/cm(2), FF of 60%.