New symmetrical electrochromic devices were constructed, with PEDOT acting as electrochromic layer or as counter electrode layer depending on the polarity of the applied voltage. Devices of around 500 mm(2) were analysed in this work. They can switch from 0.5 to 2 V, obtaining a spectral change of around 21% mainly in the red wavelength interval. Measured electrochemical impedance was fitted to an equivalent circuit, made by a Randles circuit, with Warburg impedance simulating ionic diffusion at low frequencies. Results show problems in the contact layers, not seen in normal operation. This will serve as a method to improve the devices construction. (c) 2007 Elsevier B.V. All rights reserved.