New alkoxylphenyl substituted benzo[1,2-b:4,5-b '] dithiophene-based polymers: synthesis and application in solar cells

Two new alkoxylphenyl substituted benzo[1,2-b:4,5-b'] dithiophene (BDTPO)-based polymers (PBDTPO-DTBO and PBDTPO-DTBT) were synthesized. Their structures were verified by NMR spectroscopy, the molecular weights were determined by gel permeation chromatography (GPC), and the thermal properties were investigated by thermogravimetric analysis (TGA). UV-Vis absorption spectra of the polymers show broad and strong absorption bands from 300-750 nm both in CHCl3 solutions and films. The resulting copolymers exhibit relatively deep HOMO energy levels (-5.56 and -5.46 eV) and surprisingly high hole mobilities (2.2 x 10(-1) and 3.3 x 10(-2) cm(2) V-1 s(-1)) for PBDTPO-DTBO and PBDTPO-DTBT, respectively. Preliminary photovoltaic properties of the copolymers blended with [6,6]-phenyl-C-71 ((or) (61))-butyric acid methyl ester (PCBM) as an electron acceptor were investigated. The polymer solar cell (PSC) based on the single layer device structure of ITO/PEDOT:PSS/PBDTPO-DTBO:PC71BM (1 : 1.5, w/w)/Ca/Al demonstrates a high power conversion efficiency of 6.2% under the illumination of AM 1.5G, 100 mW cm(-2).