Morphological and electrochemical properties of PPy, PAni bilayer films and enhanced stability of their electrochromic devices (PPy/PAni–PEDOT, PAni/PPy–PEDOT)

Polyaniline (PAni), polypyrrole (PPy) and their bilayer coatings on ITO coated glass were prepared by electropolymerization method. Morphological and spectroelectrochemical properties of these films depending on the thickness and the sequence of the coated polymers (PAni/PPy or PPy/PAni) were analyzed. Cyclic voltammetry, UV–vis spectroscopy and scanning electron microscopy techniques were conducted to investigate the properties of bilayer coatings. Thickness of the second layer varies, depending on the thickness and type of the first layer. Furthermore, the optical transmittance varies with the sequence of the polymers. ΔT% values obtained from thin coatings of PAni/PPy bilayers are higher than the values obtained from the single layer films of each polymer. These differences have been attributed to morphological differences of bilayer films. Mono and bilayer ECDs have been constructed and investigated comparatively. As a result of the study, we have seen that bilayer films of PPy and PAni have better electrochemical stability than monolayer ECDs of each polymer.

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► Thickness of PAni for PPy/PAni bilayer decreases with increasing thickness of PPy.
► As a second layer PPy occurs as a film that is thicker than PPy coated directly on ITO-glass.
► ΔT% values of PAni/PPy bilayers are higher than that of the single layer films of each polymer.
► Morphologies of the films are affected by the thickness and sequence of bilayers.
► ECDs of bilayer films have higher stability than monolayer ECDs.