Anisotropic optical properties of doped poly(3,4-ethylenedioxythiophene)

Anisotropic optical properties of doped poly(3,4-ethylenedioxythiophene) (PEDOT) thin films have been determined by using variable-angle spectroscopic ellipsometry together with intensity reflectance and transmission spectrophotometry. The optical anisotropy of the PEDOT films are of uniaxial character with the optic axis normal to the film surface. The (ordinary) index of refraction in the plane shows a metallic state behavior while the out of plane (extraordinary) index of refraction shows a near dielectric character. The metallic state behavior in the surface plane agrees well with the high electrical conductivity measured for this material. The anisotropic optical properties of doped PEDOT thin films in terms of the complex indices of refraction together with results from grazing incidence X-ray diffraction studies allow us to deduce a preferential orientation of the polymer chains.