Effect of dopant concentration on the properties of HCl-doped PANI thin films prepared at different temperatures

Polyaniline thin film doped with hydrochloric acid (PANI-HCl) has been prepared by chemical oxidative polymerization at three different temperatures (4 °C, 13 °C and 31 °C) with two different dopant concentrations (1 M, 2 M). Fourier transform infrared spectroscopy indicated the presence of dopant and increase in degree of polymerization with decrease in temperature. X-ray diffraction revealed that all the films are of amorphous nature. Scanning electron microscopy showed fiber morphology with high dense inter-fiber fusion. Hall-effect analysis showed that appreciable increase in conductivity of the PANI-HCl films with 2 M-dopant concentration prepared at low temperatures (4 °C, 13 °C) occurs due to increase in carrier concentration. It also indicates the films as P-type semiconductors. UV–vis absorption spectra and photoluminescence spectra revealed that the role of dopant concentration is highly effective in the films prepared at low temperatures. High intense absorption cum emission peaks observed for the films with 2 M dopant concentration prepared at low temperatures is due to the decreased fiber diameter which increased the surface to volume ratio of the fibers and increased localized defect states. Photoluminescence spectra of the films excited using 300 nm show high intense emission peaks at 360 nm, 494 nm and a weak peak at 409 nm confirming the semiconductor nature.