Control of Powder Microstructure for Improved Infrared Reflectance Modulation of an Electrochromic Plastic Device

The so-called plastic technology first developed for Li-ion batteries is demonstrated for its potential optical applications in infrared emissivity control. WO 3 ·H 2 O powder embedded in a plastic matrix is used as the active component in the LiCoO 2 /Li electrolyte/WO 3 ·H 2 O system. The role of the microstructure of WO 3 ·H 2 O as an electrochromic material is investigated. For instance, platelet-shaped grains with a surface area as large as 15 μm 2 induce a large improvement in device contrast properties. Reflectance measurements show a 53% contrast between the bleached and colored states over the 8−12 μm range. This effect is likely rooted in the free electron mobility in addition to scattering and phonon effects. The optical modulation performance over the range 2.5−20 μm compares favorably with literature results on solid devices built from annealed and sputtered m -WO 3 thin films.