Characterization of Indium Oxide for the Use as a Counter-Electrode in an Electrochromic Device
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CHARACTERIZATION OF INDIUM OXIDE FOR THE USE AS A COUNTER-ELECTRODE IN AN ELECTROCHROMIC DEVICE Phillip C. Yu*, Terry E. Haas*, Ronald B. Goldner**, and Stuart F. Cogan*** * Tufts University, Dept. of Chemistry, 62 Talbot Ave., Medford, MA. 02155 ** Tufts University, Electro-Optics Center, 4 Colby St., Medford, MA. 02155 *** EIC Laboratories, II1 Downey Rd., Norwood, MA. 02062 ABSTRACT Thin films of indium oxide, In203 (4000 A), deposited on commercially available In203: Sn (ITO)/glass by rf sputtering, have been examined for potential application as a counter-electrode material in an electrochromic Cyclic device, based on their chemical, structural, and optical properties. voltammetry experiments showed that mobile lithium ions can be inserted (chemical reduction) and removed (chemical oxidation) from the host Coulometric titrations showed that the films structure of indium oxide. exhibited a hysteresis behavior for the injection and removal of lithium ions Structural investigation of the indium oxide films, in LixIn2O3 (x=0-0.23). utilizing electron diffraction techniques, indicated that they were crystalline with a crystallite size of 175 A, in agreement with x-ray diffraction results. Differences in optical transmission between the lithiated and delithiated thin films were no more than 5% in the visible/near-infrared regions of the spectrum. INTRODUCTION Electrochromic materials are currently being investigated for potential An electrochromic window can be application as architectural glazings. thought of as a series of five thin films deposited on glass: a transparent conductor, an electrochromic material (working electrode), an ion conductor, an electrochromic material (counter-electrode), and a transparent conductor (Fig. 1). ________LI รท
GLASS
ELECTRODE
(UXwO) rlANSPARENT '/ CONDUCTOR (1n0 3:Sn)
Fig.l
CONDUCTOR
(UNbO,)
ELECTRODE
(U,1n,O) TRANSPARENT
ELECTROCHROMIC MATERIALS
CONDUCTOR (In.O:'Sn)
Electrochromic window.
By applying a current between the electrodes, the optical transmission and/or reflection of the working electrode can be modulated; such a window could offer dynamic control of visible and near-infrared solar radiation, providing significant savings for heating/cooling loads in buildings. Although much work has been done on studying the properties of promising working electrode materials (e.g. crystalline W0 3 ), there has been less work done on counter-electrode (CE) materials. The requirements for a CE material are: (1) to reversibly allow ions to be inserted/removed into/out of the host structure and (2) be optically complementary or optically passive
Mat. Res. Soc. Symp. Proc. Vol. 210. 01991 Materials Research Society
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with respect to the working electrode. There have been some optical and chemical studies reported for the CE material In203: Sn (ITO) [1, 2, 3], but there has been no work reported to this date on In20 3. This paper will address the fundamental electrochemical, chemical, structural, and optical properties of In203 for its application as a counter-electrode
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