Reflectance studies of soluble polypyrrole doped with dodecylbenzene sulfonic acid

Recent progress in the processing of conducting polypyrrole (PPy) from solution has made possible the spin-casting of optical quality films of varying thickness. We present the results of reflectance studies of soluble PPy films doped with dodecylbenzene sulfonic acid (DBSA) over a wide spectral range (.01 eV - 6 eV) at room temperature. The reflectance exhibits a plasma resonance at 1.7 eV and increases sharply at the lowest frequencies. These are the spectral features expected for a material with a partially filled conduction band. However, the corresponding optical conductivity and the real part of the dielectric function show low-frequency features characteristic of a conductor on the insulating side of the metal-insulator (M-I) transition. We conclude that there exists a finite density of localized states at the Fermi level, typical of a Fermi glass. The processibility and stability of this material make it attractive for applications such as transparent electrodes.