Controlling photovoltaic performances of trifluoromethylated quinoxaline-based polymers via fluorine substitution

Abstract

In this study, three D–A-type trifluoromethylated quinoxaline-based polymers, with different numbers of fluorine (F) atoms on the quinoxaline unit, were developed to clarify the impact of strongly electron-attracting F substituents on the photovoltaic characteristics of polymers. The unfluorinated reference quinoxaline-based polymer PTB-QxCF3, was prepared by coupling an alkylated benzodithiophene donor to a trifluoromethylated quinoxaline acceptor via a thiophene bridge. Subsequently, one and two fluorine atoms were attached to the vacant 6,7-positions of the trifluoromethylated quinoxaline unit to generate the fluorinated polymers PTB-FQxCF3 and PTB-2FQxCF3, respectively. An inverted-type polymer solar cell was constructed with Y6BO as a non-fullerene acceptor, to examine the photovoltaic characteristics of the polymers. Devices made from fluorinated PTB-FQxCF3 and PTB-2FQxCF3 exhibited higher power conversion efficiencies (PCEs) of 11.95% and 13.50%, respectively, than that comprising unfluorinated PTB-QxCF3 (4.80%). This noticeable advancement in the PCEs of devices with fluorinated polymers originates from the rapid increase in their photovoltaic parameters. These results demonstrate the usefulness of the fluorination strategy for promoting photovoltaic responses of trifluoromethylated quinoxaline-based polymers.