Electrochromic tungsten oxide films for variable infrared reflectance devices

The dependence of the infrared spectral optical constants, n(lambda) and k(lambda), of electrochromic tungsten oxide thin films, prepared by reactive magnetron sputtering at different substrate temperatures, on the quantities of charge, q, inserted has been determined from spectrophotometric measurements of transmittance and reflectance. For WO3 films deposited at temperatures > 200 degreesC significant infrared absorption is observed to rise with increasing levels of charge insertion. For the most crystalline films prepared at temperatures > 350 degreesC the rates of change dn(lambda)/dq and dk(lambda)/dq are greatest. The results provide essential design data for variable reflectance/emittance devices. Rear surface devices, which mask the reflectance of a highly reflective rear surface mirror through a charge dependent increase in k(lambda), have been successfully demonstrated using either liquid or solid electrolytes. Monolithic devices have been prepared using a hybrid combination of sputtered and electron-beam evaporated coatings.