A new polymer from fluorinated benzothiadiazole and alkoxylphenyl substituted benzo[1,2-b:4,5-b′]dithiophene: Synthesis and photovoltaic applications

A new donor–acceptor conjugated polymer (PBDTPO-FBT), which consists of a fluorinated benzothiadiazole (FBT) electron-acceptor unit and an electron-donor segment of alkoxylphenyl substituted benzo[1,2-b:4,5-b′]dithiophene (BDTPO), was synthesized according to the Stille cross-coupling reaction. The resulting copolymer was characterized by TGA, GPC, UV–vis absorption spectroscopy and cyclic voltammetry measurements. PBDTPO-FBT possesses good thermal stability with 5% weight loss temperature of 410 °C and shows broad absorption at 300–800 nm with an optical bandgap of 1.53 eV. Cyclic voltammetry measurement exhibits HOMO and LUMO energy levels of −5.43 eV and −3.72 eV, respectively. The hole mobility of PBDTPO-FBT:PC71BM (1:1, w/w) reaches up to 3.8 × 10−3 cm2/V/s by the space-charge-limited current (SCLC) method. By using 3% 1,8-diiodooctane (DIO) as the solvent additive, the polymer solar cell with the configuration of ITO/PEDOT:PSS/PBDTPO-FBT:PC71BM (1:1, w/w)/Ca/Al demonstrates a power conversion efficiency of 2.70% with Voc = 0.70 V, Jsc = 7.23 mA/cm2 and FF = 47.08%, under the illumination of AM 1.5 G, 100 mW/cm2.

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