Optical and Electrical Real-Time Characterization of the Color-Switching Process in Thin Film Electrochromic Devices
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OPTICAL AND ELECTRICAL REAL-TIME CHARACTERIZATION OF THE COLOR-SWITCHING PROCESS IN THIN FILM ELECTROCHROMIC DEVICES J. MARTI, S. GIMENO, A. LOUSA and E. BERTRAN Departament de Fisica Aplicada i Electr6nica, Universitat de Barcelona, Av.Diagonal 647, E08028, Barcelona, Catalonia, SPAIN, [email protected] ABSTRACT Multilayer structures for electrochromic devices have been produced using vacuum evaporation and electrochemical deposition, and have been optically and electrically characterized by real time measurements. The deposited structures consist of a five layer stack comprising a transparent electrode (indium tin oxide) on glass substrates, an electrochromic active layer (W0 3), an electrolyte, a complementary electrochromic film (prussian blue) acting as a reservoir for the active layer, and a second transparent or reflecting electrode. In order to determine the process dynamics, real time transmittance and reflectance spectral analysis on the visible range have been performed using a multiple analysis system (OMA), during colorswitching of the device, in coordination with electrical characterizations of the switching process by current and charge transfer measurements. These measurements were performed as a function of time and of the driving voltage, and provide a means of determining the structural parameters of the device through the switching time and the current transient. INTRODUCTION Electrochromic devices (ECD) have received much attention in recent years due to their practical applications in large-area and slow-response devices for which liquid crystal displays are not practical, like energy-saving windows for buildings, solar roofs for cars, anti-glare rearview mirrors or low consumption advertising panels [1-3]. Several materials, either organic or inorganic, are known to exhibit electrochromic behavior. Among them there are some transition metal oxides like MoO 3, NiO 2, IrO 2, V20 5 and W0 3 [4], some more complex inorganic compounds like Prussian Blue [5] and some organic polymers [6]. These materials can be reversibly oxidized and reduced, being in one case transparent and in the other case opaque, according to a reaction of the kind: xMW+xe'+EC
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