Thickness-Dependent Coloration Properties of Glass-Substrate Viologen-Based Electrochromic Devices

Blue viologen-based electrochromic devices on glass substrates were constructed with different internal active layer thickness by means of a thermoplastic spacer (DuPontTM surlyn1702). Optical measurements, chronoamperometry, and cyclic voltammetry (CV) were the techniques used for characterization. Coloration properties such as switching times for coloring and bleaching processes, coloration efficiency, and effective charge density, previously studied for a single device, are now obtained for several devices with different thicknesses. Dependence on thickness in the response times and in voltage-dependent parameters of device equivalent electric circuit model was studied in previous works. In this paper, some of those parameters, such as Warburg diffusion, double-layer capacitance, and charge transfer resistance, obtained with electrochemical impedance spectroscopy, are related with the coloration properties and their dependence on the thickness obtained by the aforementioned chronoamperometric and CV characterization.