Fluorine substituted benzothiazole-based low bandgap polymers for photovoltaic applications

Abstract

Two new D–A alternating copolymers, PBDFFBT and PBDTFBT, featuring a fluorinated benzothiazole (BT) electron-acceptor unit and the electron-donor segments of benzo[1,2-b:4,5-b′]difuran (BDF) or benzo[1,2-b:4,5-b′]dithiophene (BDT), were prepared by a standard Stille cross-coupling reaction. The resulting copolymers were characterized by TGA, GPC, UV-vis absorption spectroscopy and cyclic voltammetry measurements. PBDFFBT and PBDTFBT show good film forming properties. Bulk heterojunction polymer photovoltaic devices based on an active layer of the electron donor copolymers (PBDFFBT and PBDTFBT), blended with an electron acceptor [6,6]-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM) in three weight ratios of 1 : 1, 1 : 2 and 1 : 3 were investigated. The devices with the configuration of ITO/PEDOT:PSS/polymer:PC₇₁BM/Ca/Al demonstrated promising power conversion efficiencies of 3.3% for PBDFFBT:PC₇₁BM (1 : 3, w/w) and 4.0% for PBDTFBT:PC₇₁BM (1 : 2, w/w) under the illumination of AM 1.5, 100 mW cm⁻².