Electrochimica Acta 46 (2001) 2145 – 2150 Advanced electrochromic devices based on WO 3 thin films S. Papaefthimiou *, G. Leftheriotis, P. Yianoulis Department of Physics, Uniersity of Patras, Patras 26500, Greece Received 21 August 2000; received in revised form 2 November 2000 Abstract We present work on the development of advanced materials suitable for use as electrochromic thin films (EC), ion storage layers and transparent conductors (TC) in electrochromic devices. These thin film layers were prepared in our laboratory by thermal evaporation and electron gun deposition. They were incorporated into electrochromic devices, which were subsequently characterized by optical and electrochemical techniques such as transmission spectroscopy, cyclic voltammetry and galvanostatic intermittent titration. WO 3 films 300–600 nm thick have been used as EC layers. They are amorphous and near-stoichiometric with a packing density of about 0.8. We have also developed textured WO 3 films. Their structure enhances Li + intercalation into the oxide matrix, thus doubling the diffusion coefficient. V 2 O 5 ion storage thin films were Li + doped both electrochemically and in vacuum leading to a 23% increase of the EC device coloration efficiency. We have fabricated electrochromic devices with ZnS/Ag/ZnS coatings as TCs. The use of multilayer ZnS/Ag/ZnS films was found to improve the electrical characteristics and to lower the emittance of the devices. All the devices described above can withstand more than 5000 coloration – bleaching cycles and have an open-circuit memory of several days. They are suitable for advanced glazing and other switching applications. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Electrochromics; Textured WO 3 films; V 2 O 5 films; ZnS/Ag/ZnS transparent conductors; Glazing www.elsevier.nl/locate/electacta 1. Introduction Electrochromic (EC) windows present an attractive alternative to conventional solar control and shading devices. They do not impede visibility as blinds and curtains do, while they provide glare control and ther- mal comfort. Furthermore, they have no moving parts and as a result the maintenance costs are minimal. They have practically infinite coloration stages and can block both direct and diffuse solar radiation, unlike passive shading devices. EC windows can become transparent during the early morning and afternoon hours, to im- prove natural lighting conditions, unlike tinted glass. They require low voltage power supply and can be integrated into the central power management of build- ings. Their energy consumption is low (typically 8 W/m 2 [1]), and becomes nearly zero when they are kept at constant conditions, due to their considerable open circuit memory [1]. An electrochromic window can outperform the best currently available window systems (in most applications). Compared to an opaque insulat- ing wall, electrochromic glazing combines high thermal insulation and reduced heating – lighting cost due to solar gains and daylighting. Thus, they have up to 40% better annual energy performance [2]. The primary energy benefits of EC windows are: reduced cooling, heating and ventilating loads and the ability to reduce electric lighting use by managing daylight admittance. Last but not least, the architectural and aesthetic ap- peal of a dynamic coating that the electrochromic tech- nology offers is difficult to quantify but it could be a * Corresponding author. Tel.: +30-61-997449; fax: +30- 61-997472. E-mail address: spapaef@physics.upatras.gr (S. Pa- paefthimiou). 0013-4686/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(01)00393-0