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 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%.

Automated summary

Low bandgap polymers with monofluoroquinoxaline or difluoroquinoxaline 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. These polymers exhibit good thermal stability and broad absorption band, with the HOMO energy levels affected by the number of fluorine atoms in the conjugated backbone. PB-DFQx:ITIC-based PSC achieved the best power conversion efficiency.