The use of combinatorial materials development for polymer solar cells

We use a combinatorial approach to develop molecular plastic solar cells based on soluble fullerene derivatives blended with conjugated polymers. A combinatorial way of sample preparation is well suited to deal with the multitude of possible combinations of the components of such blends. We use high mobility poly(thiophene) and poly(phenylenevinylene) derivatives to be combined with acceptors. Gradients of methanofullerene/polymer concentration were formed by diffusion of the low molecular weight component in the spin‐cast polymer matrix. Likewise the gradients of zinc phthalocyanine/C₆₀ were prepared by co‐evaporation of the two materials from two sources to make a linear array of photodiode devices. Photo‐ and electrophysical properties, such as absorption, luminescence, short circuit photocurrent and open circuit photovoltage, were measured using a specially designed installation with a resolution of 70–100 µ. Clear evidence was obtained that the photoconversion efficiency increased with the amount of methanofullerene up to very high levels, in the case of methanofullerene/polymer blends, verifying the important role of the acceptor in the photoconversion. By choosing the optimal ratio between C₆₀ and ZnPc in the evaporated layer it is possible to obtain high photocurrent in the 600–700 nm range, due to the added contribution from photoinduced electron transfer between the two molecules. Copyright © 2000 John Wiley & Sons, Ltd.