Comparison of two D-A type polymers with each being fluorinated on D and A unit for high performance solar cells

Abstract

Recently, polymers with fluorinated building block have recently attracted great interest because high power conversion efficiencies (PCEs) over 7% have been achieved by fluorination of A unit. In this work, we synthesized two kinds of D-A polymers with each being fluorinated on A and D unit, where quaterthiophene and benzothiadiazole are used as D and A unit, respectively, in order to investigate the effects of fluorination position on photophysical properties of polymers and their device performances of polymer solar cells. Although the fluorination on either D or A unit effectively enhances intermolecular interaction, exhibiting strong vibronic shoulder in UV?Visible absorption spectra, and lowers energy levels, retaining a low bandgap of 1.58 eV, the polymer with fluorinated D unit exhibits a PCE of 7.10%, while the polymer with fluorinated A unit exhibits a PCE of 6.75%. Therefore it can be concluded that the fluorination on D unit in D?A polymer is a very promising method for achieving high performance solar cells.