WO3-Based Electrochromic Windows - Problems and Status

An electrochromic (EC) window based upon the reversible formation of lithium tungsten bronze is described in terms of its component layers as well as an over-all device. The requirements and restrictions imposed upon window design and behaviour by the materials available are considered, as is the inter-relation between their properties. The sheet conductance of transparent tin oxide coated glass and the conductivity of the lithium electrolyte are considered, and shown to be important in determining uniformity and speed of window behaviour during colour/bleaching operations. The relation between thin film preparative methods and the resulting film properties is emphasised. Some basic scientific problems are considered, and particular stress is placed upon the importance of knowing about the structure of the thin film WO(3). The absence of an hermetic seal is seen as a possible barrier to commercial exploitation. But the field is ready for the bold investor.