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:PC 71 BM (1:1, w/w) reaches up to 3.8   ×   10 −3   cm 2 /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:PC 71 BM (1:1, w/w)/Ca/Al demonstrates a power conversion efficiency of 2.70% with V oc   =   0.70   V, J sc   =   7.23   mA/cm 2 and FF   =   47.08%, under the illumination of AM 1.5   G, 100   mW/cm 2 .