Dc electrical conduction and morphological behavior of counter anion-governed genesis of electrochemically synthesized polypyrrole films

Highly conducting polypyrrole (PPY) films, doped with various anions [pTS-, ClO4-, and NO3- and mixed electrolyte system (pTS- + ClO4-)], have been electrochemically synthesized in aqueous solution at similar to 275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X-ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultravioletvisible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2320 K)-dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable-range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS-) and inorganic (ClO4- and NO3-) counter anions