Energy Band Gap and the Refractive Index for Polyaniline Thin Films of Polyaniline in Thin Films on Polyethylene Surface

Abstract

e-mail: yuliia.stetsiv@lnu.edu.ua Polyaniline (PAn) films, doped with citric acid, were synthesized on a polyethylene substrate by chemical oxidative polymerization using ammonium peroxydisulfate as an oxidant. The influence of monomer concentration on the optical properties of PAn films was investigated. Optical band gap, absorption coefficient, extinction coefficient, refractive index were calculated as a function of wavelength. Different methods for determining the energy of the energy gap (Tauc method and absorption spectrum fitting) were considered. It was found that the optical band gap for all thin PAn films is due to the direct allowed optical transitions. It was found that the band gap of PAn films decreases with increasing thickness of deposited PAn films. It is established that the optical energies of the band gap of PAn films of different thickness, estimated by the results of optical absorption measurements using Tauc methods and absorption spectrum fitting, are practically commensurate and are in the range of 3.13–2.36 eV for film thicknesses equal to 18.7–137.4 nm, respectively. Based on the correlations between the optical energy of the band gap and the refractive index of semiconductors using Moss, Ravindra, Ravindra-Gupta, Reddy-Ahammed, Gerve-Vandamme, Kumar-Singh, Annani and Duffy-Reddy ratios, the value of the refractive index of PAn films was calculated and these results were compared with the values obtained from the experimental results. From the obtained results it is seen that the refractive index of PAn films increases with increasing polyaniline film thickness on a polyethylene substrate. The values obtained from the Ravindra and Ravindra-Gupta relations are the closest to the experimental ones. Therefore, the synthesized PE/PAn films can be an available material for the production of optoelectronic devices, for example, for organic field transistors and LEDs.