Synthesis and Photovoltaic Properties of Benzothiadiazole-Based Copolymer Containing Fluorinated Benzene as Weak Electron Donating Unit for Polymer Solar Cells

Abstract

1,4-Di(thiophene-2-yl)benzene (DTB), which is a phenyl compound flanked with thiophene, was synthesized via a simple synthetic route and utilized as a weak electron-donating unit in D?A type copolymer for lowering the HOMO of the copolymer. A copolymer (PDTBDTBT) was synthesized by reacting DTB with 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT). Fluorination of benzene moiety between thiophenes (F2DTB) was carried out for further lowering the HOMO energy level of the copolymer due to the strong electron-withdrawing property of fluorine. When the F2DTB is used as an electron-rich unit for conjugated copolymers (PF2DTBDTBT) which exhibits a deep HOMO energy level of ?5.5 eV, the PSCs fabricated from PFDTBDTBT exhibit a high VOC, leading to a promising PCE.