COMPARATIVE SPECTROELECTROCHEMICAL INVESTIGATION OF VACUUM-EVAPORATED AND ELECTROCHEMICALLY SYNTHESIZED ELECTROCHROMIC POLYANILINE FILMS

A spectroelectrochemical study of thin electrochromic polyaniline (PAN) films deposited on SnO2 glass substrates by a vacuum thermal evaporation method has been carried out. The films obtained were studied by means of spectral, spectroelectrochemical and electrochemical methods, and the results were compared with those obtained for PAN films prepared by electrochemical polymerization. Spectroelectrochemical data (obtained under a potential step) and cyclic voltammetry data showed that the evaporated PAN films did not undergo a second oxidation stage resulting in formation of a quinoid structure. Current vs. time dependences processed according to the Cottrell equation showed that the diffusion coefficient for the evaporated PAN layers was almost a factor of 3 lower than that for the electrochemically deposited films. During cyclic tests in a real electrochromic optical filter the evaporated PAN layers exhibited a stability more than 2.5 times higher than that of the electrochemically deposited films.