Optical properties of reversible electrodeposition electrochromic materials

The optical properties of a new type of electrochromic material based on the reversible electrodeposition of Bi have been investigated. This electrochromic material system is being investigated for both low and high information flat panel display applications. Electrochemical devices based on the reversible electrodeposition of bismuth were fabricated using an aqueous electrolyte gel containing bismuth chloride, copper chloride, and lithium bromide. A cell structure of glass substrate/tin oxide/gel electrolyte/porous carbon was employed. Optical measurements showed a spectral reflective contrast of greater than 60% in the visible spectrum. Visible reflectance could be controlled over a wide range of gray shades by controlling the writing voltage at a fixed write time or the writing time at a given voltage. The maximum reflective contrast was 67%. Depending on the display application, the electro-optical properties could be tailored by adding controlled amounts of Cu to the formulation.