The interplay of efficiency and morphology in photovoltaic devices based on interpenetrating networks of conjugated polymers with fullerenes

Photophysical phenomena in composites of fullerenes and non-degenerate ground state conjugated polymers with highly extended π-electrons in their main chain can be explained by the ultrafast electron transfer from the conjugated polymer (donor) to the fullerene (acceptor) upon illumination. In this work we present current/voltage characteristics, efficiency data and surface morphology studies of large area (6 cm×6 cm) flexible plastic solar cells with a photoactive layer consisting of poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene), (MDMO-PPV) or poly(3-octylthiophene), (P3OT) as donor and fullerene C60 or a highly soluble methanofullerene, (phenyl-[6,6]-C61)-butyric acid methyl ester (PCBM) as electron acceptor. Solar cell devices have been fabricated showing monochromatic energy conversion efficiencies ηe about 1.5% and carrier collection efficiency (incident photon-to-collected electron, IPCE) of 20% at 488 nm under 10 mW/cm2. Furthermore, we have investigated the quality and homogeneity of the photoactive composite films made from the various components. It is shown that among the combinations of materials both open circuit voltage and short circuit current are maximal for blends of P3OT/C60 and MDMO-PPV/PCBM.