Optical and electrical characteristics of acid-doped thin polyaniline films

Abstract

Conjugated conducting polymers, such as polypyrrole (PPY), polyaniline (PANI), and polythiophene (PT), are the most interesting conducting polymers due to their excellent chemical and electrochemical stability. In this work, three samples of thin PANI films were synthesized by chemical oxidative polymerization of aniline in the presence of hydrochloric acid using ammonium peroxydisulfate as an oxidizing agent. Two samples of the synthesized thin PANI films were doped with tetraoxosulphate(VI) acid (H2SO4) and citric acid, while the third sample was left undoped to serve as a control. We used a VeecoDektak 150 profiler to measure the film thickness; a UV-Visible spectrometer Shimadzu UV-1601 was used to determine the optical absorption spectra of the films. The measurement of DC conductivities was accomplished through the four-point probe technique with a Signatone V3.7 QuadPro resistance mapping system using a Keithley 2400 source meter. The thin films were found to be of the same thickness (0.2 μm); their absorption spectra revealed two absorption peaks at around 300 and 650 nm for the pure and citric acid-doped samples, while the H2SO4-doped PANI exhibited peaks at 300 and 880 nm. Doping reduced the direct band gap of the PANI from 2.75 to 2.4 eV. In addition, the results obtained from electrical characterization revealed that the H2SO4-doped PANI has the best conductivity among the doped samples, while the pure sample showed no value for electrical conductivity.