Solid State Electrochromic Switchable Window Glazings

Multilayer, solid state electrochromic coatings based on a-WO3 (amorphous WO3) have been tested. A typical coating on glass consists of indium-tin oxide (520 nm), WO3 (410 nm), 3 MgF2 (170 nm) and gold (15 nm) all deposited by vacuum evaporation. Optical spectra and solar weighted, integrated transmission values are given for the component films and complete multilayer devices. Electricalcharacteristics and electrooptic responses are reported. Devices with MgF2 layers deposited at low pressures have high internal resistances and exhibit long term optical memories suitable for diurnal switching. The replacement of the gold electrode layer with an indium-tin oxide layer greatly increases the transmittance of the electrochromic coating stack (from solar weighted transmission of 22%to 53%). Electrochromic coatings have promise for solar gain control windows, but further improvements in optical and electrical efficiencies are needed.