Electrical studies on the doping dependence and electrode effect of metal–PANI–metal structures

Abstract

Current versus voltage (I versus V) and complex impedance, z*(f) = z'(f) − iz''(f), measurements for polyaniline (PANI) films were carried out in samples with different doping levels and gold and/or aluminium as electrodes. The complex impedance of Au/PANI/Au presents the typical behaviour of a somewhat solid disordered material with negligible electrode influence. DC measurements confirm this evidence. However, some additional influence of the interface was observed to occur when Al was used as the electrode. A phenomenological model employing the Cole–Cole dielectric function for generating the conduction process is developed and the calculated z'(f) and z''(f) as functions of the polymer doping level and the bias polarization are found to be in good agreement with experimental data, thereby separating bulk and interface contributions to the complex impedance, as well as providing approximate values of the PANI–Al interface thickness and resistivity, around 10 nm and 1013 Ω cm, respectively.