Anthracene-containing PPE-PPV applications and materials science copolymers: Effect of side-chain nature and length on photophysical and photovoltaic properties

High-molecular weight anthracene containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) copolymers bearing linear and/or branched alkyl side chains have been synthesized and investigated for use in polymer-fullerene bulk heterojunction solar cells. By variation of the nature and length of alkyl side chains the ordering in thin films could be tuned. Besides the basic photophysical characterization, small-angle X-ray scattering on extruded fibers and cyclovoltammetry measurements are reported. The photovoltaic characterization indicates that improved ordering due to linear side chains on the arylene-ethynylene segment as well as lower side-chain volume fraction yield higher photocurrents. Power conversion efficiencies of nearly 2.5% are reported for the best devices with a polymer:fullerene composition of 1:1 by weight.