Bulk heterojunction organic solar cells based on soluble poly(thienylene vinylene) derivatives

We report on the comparison of photophysical and photovoltaic properties of three different soluble alkyl derivatives of the low bandgap poly(2,5-thienylene vinylene) (PTV), synthesized using the dithiocarbamate precursor route. The solubility of the precursor material in dichlorobenzene is enhanced by the addition of hexyl, dihexyl and dodecyl sidegroups to the polymer chain. The materials were characterized in solid state by means of absorption, ellipsometry and atomic force microscopy of films made from both the pristine alkyl-PTVs and alkyl-PTVs:([6,6]-phenyl C61-butyric acid methyl ester) (PCBM) mixtures in a 1:1 ratio. The materials showed an optical bandgap below 1.7 eV, derived from the absorption spectrum of the polymers. Field-effect transistors made of these materials showed hole mobilities in the range of 10−7 to 10−6 cm2/Vs. Bulk heterojunction solar cells made with the polymer:PCBM blend reached efficiencies above 0.6%.