The influence of dopant species on transport properties in as-grown polypyrrole films prepared by electrochemical method

A transport study was made on electrochemically prepared polypyrrole (PPy) films to elucidate the influence of dopant species on the electrical transport properties. We present the experimental results on as-grown PPy films prepared with several anion species such as ClO4−, PF6−, BF6−, TsO− and HSO4−. The conductivities of these films at room temperature were between 50–200 S/cm. The temperature dependence exhibited a semiconductor-like behaviour over the whole range between 1.6–300K, with the only exception of PF6− doped PPy, which changed to a metal-like dependence at 8K. At 300K, the absolute thermoelectric power S(T) takes very small values (3–7μV/K) like ordinary metals. Characteristic behaviour was observed in their temperature dependence S(T) is linearly dependent on temperature below about 230K but becomes nearly constant above 230K. The Voltage-Shorted-Compaction (VSC) resistivity (ρvsc) showed a metallic temperature dependence with its slope definitely changed at 230K, corresponding well to the result of S(T), which implies a transition between metallic states of different nature.