Study on the Electrochromic Properties of Polypyrrole Layers Doped with Different Dye Molecules

Abstract Three dye molecules (Dye) of Acid Brilliant Scarlet 3R (AR18), Amido Naphthol Red G (AR1), Indigo Carmine (IC), as well as sodium dodecyl sulfate (SDS) as dopant agents were used for electrochemical synthesis of polypyrrole (PPy) layers onto indium doped tin oxide (ITO) coated polyethylene terephthalate (PET) electrode. The morphology, electrochemical, optical, and spectroelectrochemical properties of the layers were investigated. The study of the electrochemical behavior showed that the presence of each AR18, AR1, or IC with SDS, had shown an excellent synergistic effect on the electrochemical stability of layers. The morphological characterization of the PPy/dopant(s) using atomic force microscopy (AFM) showed that the surface roughness in the PPy/IC-SDS layer was 39% and 32% less than the PPy/AR18-SDS and PPy/AR1-SDS, respectively. The absorption spectrum of PPy/dopant(s) in the UV-Vis-NIR wavelength range showed the formation of polaron and bipolaron in PPy chains. Also, the optical bandgap energy of PPy/dopant(s) decreased, and the fully doped state in all PPy films was observed. Spectroelectrochemical properties of the films showed that the simultaneous use of each dye molecule and the surfactant as dopant in PPy layers demonstrated proper electrochemical and optical stability and satisfactory electrochromic parameters. For example, the color contrast of PPy/AR18-SDS was 50%, while this parameter in control sample (PPy doped with lithium perchlorate) was 21%. Also, the cathodic and anodic coloration efficiency showed a 6-fold increase in PPy/Dye-SDS compared to PPy/ClO4-. In general, according to the results it is likely that by increasing the number of anion groups in the dye molecules and decreasing their dimensions as dopant agents, the electrochemical and electrochromic properties of the resultant layer would be improved.