The influence of thickness and preparation temperature of doped polypyrrole films on the electrical and chemical sensing properties of polypyrrole/gold Schottky barrier diodes

A gold contact with polypyrrole (PPy) doped with the copper phthalocyanine toluenesulfonate (CuPcTS) anion (Au/PPy-CuPcTS) was studied using complex impedance spectroscopy, current density voltage (J-V) and capacitance voltage (C-V) measurements. The J-V characteristics of these junctions are asymmetrical and nonlinear. The junction parameters extracted from the J-V characteristics (the saturation current density, the rectification ratio and the ideality factor) and from the C-V characteristics (the built-in voltage and the charge carrier concentration) are strongly influenced by the thickness and by the preparation temperature of the PPy layer. These Schottky diodes show high sensitivity to NO_x in the parts per million concentration range, which was explained by changes in the contact potential and in the carrier concentration of the PPy layer due to NO_x exposure. The NO_x sensitivity is influenced by the thickness as well as by the preparation temperature of the PPy layer. The junction parameters and the gas sensitivity can be improved largely by increasing the preparation temperature of the PPy films up to the glass transition temperature of PPy.