Influence of methane in the electrical properties of polypyrrole films doped with dodecylbenzene sulfonic acid

Films of polypyrrole doped with dodecylbenzene sulfonic acid (DBSA) with a concentration of 0.5 mol/L were studied using complex impedance spectroscopy, current density measurements as a function of voltage (J–V) at temperature of 293 K and capacitance voltage (C–V) measurements at low frequency. The J–V characteristics of these junctions were asymmetrical and non-linear, and there was no tendency to saturate for the reverse current. Under both forward and reverse bias, these junctions exhibited a significant, fast and reversible response to methane gas, which was explained by changes in the Schottky barrier height and in the carrier concentration of polypyrrole samples. Also the junction parameters were strongly influenced by the gas. From the C–V characteristics the built-in voltage and the charge concentration were also found to be influenced by the presence of the gas. Complex impedance spectroscopy showed two semicircular arc, which could be represented by a very simple equivalent circuit characteristic of a metal–semiconductor contact. The parameters extracted from these measurements were in good agreement with the proposed mechanism.