Performance of an electrochromic window based on polyaniline, prussian blue and tungsten oxide

In our laboratory various electrochromic windows (ECWs) have been investiga ted using mainly tungsten oxide (WO,), polyaniline (PANI) and prussian blue (PB) as electrochromic materials in combination with poly(2-acrylamido-2-m ethyl-propane-sulphonic acid) (PAMPS) as a solid proton-conducting electrol yte. The ECWs have been characterized by AC-impedance, linear sweep voltamm etry and spectroelectrochemical studies in the 290-3300 nm spectral region. The ECWs have the following general multilayered structure: Glass/ITO/EC1/ IC/ EC2/ITO/Glass, where ITO = indium oxide doped with tin, IC = ionic cond uctor, EC1 is either PANI or PANI including PB, and EC2 is WO3. The best of these ECWs has been able to regulate up to 56% (typical 50%) of the transm ission of the total solar energy in the 290-3300 nm spectral range. The com bination of the two electrochromic materials PANI and PB has been shown to be mutually beneficial in such a way that the colouration of the window is enhanced by the addition of a layer of PB onto PANI, while the adhesion of PB is improved by the presence of PANI. The energy consumption of the ECW i s about 0.01 Wh/m(2) for one complete cycle (-1.8 V/1.2 V). The switching t ime for 90% colouring/bleaching is typically 10-30 s. A PANI/PB//WO3 window has been operated for about 50 days ( similar to 3700 complete cycles) wit hout substantial loss of transmission regulation, though with an increase i n switching time (10 min.). Spectra from individual layers in the ECWs have been recorded by making holes in one or two of the electrochromic layers. In this way (the hole method), it has been possible to study the transmissi on regulation properties for each electrochromic material separately in com plete solid state windows. In addition, spectra for complete windows have b een simulated by adding contributions from individual electrochromic layers . (C) 1999 Elsevier Science B.V. All rights reserved.