Effect of methanol addition on the resistivity and morphology of PEDOT:PSS layers on top of carbon nanotubes for use as flexible electrodes

Overcoating carbon nanotube (CNT) films on flexible poly(ethylene terephthalate) (PET) foils with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layers reduces the surface roughness, which is interesting for use in organic electronics. Adding methanol to the PEDOT:PSS aqueous solution used for spin coating of the PEDOT:PSS layer improves the wetting behavior of the CNT/PET surface. Samples with different volume fractions of methanol (0, 33, 50, 67, and 75 vol %) are compared with respect to the transmission, horizontal, and vertical resistivity. With grazing-incidence small-angle X-ray scattering, the film morphologies are probed, which is challenging because of the substrate flexibility. At 50 vol %, methanol optimum conditions are achieved with the resistivity close to that of the bare CNT/PET substrates because of the best contact between the PEDOT:PSS film and CNT surface. At lower methanol ratios, the PEDOT:PSS films cannot adapt the CNT morphology, and at higher methanol ratios, they rupture into domains and no continuous PEDOT:PSS layers are formed.