Electrochromic properties of thin nanocrystalline TiO2 films coated electrodes with adsorbed Co(II) or Fe(II) 2,2′-bipyridine complexes

A novel method of preparation of electrochromic cells with a cobalt(II) or iron(II)-tris-2,2'-bipyridine hexafluorophosphate dye adsorbed on a titanium dioxide coated electrode and platinum or nickel oxide thin coated counter-electrode in conjunction with quasi-solid state LiClO4 based electrolyte is presented. The operation of the cells was analyzed using cyclic voltammetry as well as by UV-vis reflectance and transmittance spectroscopy. The transition times between the tinted and bleached states are of the order of one second, while the difference between both states is clearly visible. Best characteristics were obtained with the cobalt bipyridine hexafluorophosphate complex dye adsorbed on a mesoporous TiO2 electrode in combination with NiO counter-electrode. Devices created according to the described method could potentially be used to recycle and re-use exhausted dye-sensitized solar cells for transparent smart windows, or as a new type of displays. (C) 2017 Elsevier Ltd. All rights reserved.