Morphology evaluation of a polymer-fullerene bulk heterojunction ensemble generated by the fullerene derivatization

We investigated a series of bulk heterojunction solar cells and corresponding thin films by blending of an anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) copolymer with various fullerene derivatives. The so-called AnE-PVab copolymer was equipped with octyloxy side-chains at the PPE part and ethylhexyloxy side-chains at the PPV part, and has been chosen for this investigation due to its previously demonstrated superior performance in combination with phenylene-C60-butyric-acid-methyl-ester (PCBM). It is shown that the performance of bulk heterojunction solar cells strongly depends on the nature of the fullerene derivative, in particular the side-chain attached to the fullerene cage. In fact the intermolecular interaction between the polymer and fullerene derivative controls the blend morphology to a large extent, which has been interpreted on the basis of a novel approach for combining structural, topographical, photophysical, electrical and electro-optical characterizations.