Anthracene-containing PPE-PPV 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. IV‐characteristics of partly optimized photovoltaic devices based on [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) blends with a blending ratio of 1:1 under solar simulator illumination.