Fabrication of electrochromic devices in an undergraduate laboratory

This paper describes the fabrication and characterization of variable transmittance electrochromic devices in an undergraduate laboratory. These devices consist of transparent conducting oxide and electrochromic thin films deposited on transparent silica substrates. Indium-tin oxide (ITO) is the transparent conductor, WO₃ is the active electrochromic layer, and both materials are deposited by RF magnetron sputtering. Electrochromic darkening of the WO₃ is achieved by injecting Li⁺ ions from an electrolyte consisting of 1M LiClO₄, in propylene carbonate using a DC bias. Applying -2.5 V to a window reduces its average visible transmittance from 80% to less than 13%. Reversing the voltage polarity restores the window´s transparency. The fabrication of an entirely solid state device, which incorporates an ion storage/transport layer is also described. The activities described in this paper expose students to the fascinating properties of thin film transparent conductors and electrochromic materials