Electrochromism of Conducting Polymer Polypyrrole Films and the Elucidation of its Deterioration Mechanism

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Conducting polymers such as polypyrrole are expected to utilize as electrochromic devices, because they change in their electrical conductivity and absorption of light, corresponding to doping and undoping of ions. However, it has been difficult to fit them for practical use, because these polymers are mechanically hard and brittle and they have only a short cycle-life when used repeatedly. In order to overcome the difficulty, it is very effective to clarify the deterioration mechanism of electrochromism of conducting polymers. In this study, the transition of the characteristics of polypyrrole (PPy) films while applying cyclic voltage in electrolyte solution was studied by the microscopic observation with a CCD video camera, a density gradient centrifugation method, and atomic force microscopy (AFM).From this study we conclude as follows. (1) Pin holes were observed in the PPy film with cyclic doping/undoping of electrochrolyte ions. (2) The the number of the pin holes and the total a … More rea of the pin holes were increased as the increase of the cyclic number of the voltage application. (3) The density of PPy films were increased after cyclic doping/undoping of electrochrolyte ions. (4) The surface morphology observed by AFM shows that the grain size of PPy films shrunk after cyclic doping/undoping of electrochrolyte ions. (5) The deterioration of electrochromism appeared on the electrodeposited PPy films was caused by the shrinkage of PPy films during cyclic doping and undoping of electrochrolyte ions.And also, to overcome these defects and to improve their practical performance, we developed a new method of conducting polymer films of good durability ; composite films of Polypyrrolc (PPy) and the Poly vinyl-alcohol (PVA). By using this PPy/PVA composite, we developed a solid-state device of electrochromic display. The device showed color change (black & transparent yellow) more than 2X10<@D15@>D1 times under repeated and alternate application of DC voltages of (]SY.+-。[) 0.9. Less