Synthesis and photovoltaic properties of new conjugated polymers based on benzo[1,2-b:4,5-b']dithiophene

New conjugated polymers based on benzo[1,2-b:4,5-b']dithiophene, poly(benzo[1,2-b:4,5-b'] dithiophene-alt-bithiophene) (PBT-2T) and poly(benzo[1,2-b:4,5-b']dithiophene-alt-terthiophene) (PBT-3T), have been synthesized via the Stille coupling reaction and their optical and electrochemical properties were characterized by UV-vis, photoluminescence (PL) and cyclic voltammetry (CV) measurements. Compared to PBT-2T, PBT-3T film showed clearly red-shifted UV-visible absorption and PL spectra with maxima at 511 and 653 nm, respectively. Especially, PBT-3T containing terthiophene showed very small optical band gap of 1.65 eV. The PBT-2T and PBT-3T showed the power conversion efficiencies of 0.25% and 0.34%, respectively, under AM 1.5 (100 m/cm ²).