Journal of Non-Crystalline Solids 121 (1990) 319-322 319 North-Holland DIP-COATED TiOz-CeO 2 FILMS AS TRANSPARENT COUNTER-ELECTRODE FOR TRANSMISSIVE ELECTROCHROMIC DEVICES P. BAUDRY, A.C.M. RODRIGUES and M.A. AEGERTER lnstituto de F~sica e Qulrnica de S~o Carlos, University of S~o Paulo, S~o Carlos, SP, Brazil L.O. BULHOES Departamento de Quimica, Federal University of S~o Carlos, SP, Brazil The dip-coating process is an attractive way for the preparation of thin films used in the field of electrochromism. The scope of the present paper is focused on the TiO2-CeO 2 compounds since they exhibit a reversible electrochemical insertion of lithium ions maintaining a high optical transmissivity. These films can be used as transparent counter-electrode in an all solid state electrochromic transmissive device with, for example, WO 3 as electrochromic material and a lithium conductive polymer as electrolyte. 1. Introduction Interest has been increasing during the last years in the preparation of thin films by the sol-gel process. With this method, multicompo- nent large scale oxide films can be obtained easily and with lower cost than with other methods of deposition such as CVD, sputtering or vacuum evaporation. Investigations are also very active in the field of electrochromism for developing all solid state energy efficient windows. For this pur- pose, various electrochromic materials such as tungsten trioxide or vanadium pentoxide have al- ready been prepared by the sol-gel method [1,2]. This work presents a new electrode material TiO2-CeO 2 deposited by dip-coating onto ITO coated glass and which can be used as transparent counter-electrode in a transmissive electrochromic device. 2. Electrochromic window The electrochromic phenomenon is the prop- erty of some materials to change their optical transmission (reflection) spectrum and especially their colouration by application of an electric field or current. It has been extensively studied during the past two decades for its application to electro- optic displays and recently for the realization of energy efficient windows [3,4]. This latter kind of device allows the modulation of the window's transmission and reflection properties and, thus, a regulation of the heat transfer rate. The main electrochromic materials are transition metal oxides such as WO 3 or MOO3, but organic films can also exhibit the property of electrochromism. Taking WO 3 as the electrochromic material, the colouration reaction corresponds to an insertion process with electrons and ions injection: WO 3 + x e-+ xM+~ MxWO 3 (M+= Li +, H+). Although the colouration is faster with protonic conduction due to high chemical diffusion coeffi- cient of H + in WO 3, corrosion of the films in acid media occurs limiting the life of the device. There- fore, chemically inactive lithium conductors are preferred. A schematic cross-section of an electrochromic window is shown in fig. 1. It is a succession of five laminated layers sandwiched between two glass substrates. The two conductive ITO layers are the current collectors. A good compatibility of both 0022-3093/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)