| The operation of a transparent electrochromic device can be viewed
in a very simple way. The core of the device usually consists of 3 layers like a
thin-film battery: Two electrodes or ion-storage layers separated by an electrolyte or ion
conductor. Under the influence of a small voltage, ions flow from one electrode to the
other. A chemical reaction occurs in the electrodes transforming them into different
compounds with different optical properties. In most cases this is a continuous process so
that the transmittance varies until the voltage is removed. The outer two layers are
transparent conducting materials that serve as contacts. There are many possible variants on this theme. For example, the layers may be inorganic or organic, they may be deposited by a variety of different techniques and the ionic species may be either H+ or Li+. Both electrodes may change optical properties or one may be a passive storage electrode or counterelectrode. The coloration mechanism itself may follow one of several completely different physical principles. A complete discussion is beyond the scope of this discussion. For more information, see for example, C.-G. Granqvist Handbook of Inorganic Electrochromic Materials, Elsevier, 1995 or visit the LBNL publications search to download full text of various articles on the subject of electrochromics. |