New Multi-color Electrochromic Layer by Polypyrrole Doped with Azo Dye

A multi-color electrochromic layer was produced using polypyrrole (PPy) doped with an azo dye (AR18). PPy/AR18 was electrochemically deposited on to Indium doped tin oxide (ITO) coated/polyester electrode by chronopotentiometry method. The morphology of the electrochromic layer (PPy/AR18) was studied using SEM-EDX and AFM analysis. The layer showed spherical morphology with particles size smaller than 10 nm, 6.4 μm thickness and 45 nm surface roughness. Spectroelectrochemical study showed that the optical band gap of PPy/AR18 layer was decreased to 1.75 eV. The color of the layer was rapidly changed to orange, violet and gray when the film is in reduced, neutral and oxidized forms, respectively, by applying linear (Cyclic voltammetry method) or step potential ramps (Chronoamperometry method). Also, the study of electrochromic properties of the electrochromic layer indicated very good behavior such as optical contrast 57%, anodic and cathodic response time 15 and 23 respectively, anodic and cathodic coloration efficiency 279 and 124 respectively and good optical stability after 100 cycles. The color coordinates of the reduced form (L*=85.71, a*=3.45 and b*=31.84) and oxidized form (L*=71.44, a*=4.98 and b*= -1.60) of PPy/AR18 layer in CIELAB space was calculated. Also, the color difference in CIELAB was obtained (ΔE*ab=37).