OPTICAL INDEXES OF LITHIATED ELECTROCHROMIC OXIDES

Optical indices have been determined for thin films of several electro chromic oxide materials. One of the most important materials in electr ochromic devices, WO3, was thoroughly characterized for a range of ele ctrochromic states by sequential injection of Li ions. Another promisi ng material, Li0.5Ni0.5O, was also studied in detail. Less detailed re sults are presented for three other common lithium-intercalating elect rochromic electrode materials: V2O5, LiCoO2, and CeO2-TiO2. The films were grown by sputtering, pulsed laser deposition (PLD) and sol-gel te chniques. Measurements were made using a combination of variable-angle spectroscopic ellipsometry and spectroradiometry. The optical constan ts were then extracted using physical and spectral models appropriate to each material. Optical indices of the underlying transparent conduc tors, determined in separate studies, were fixed in the models of this work. The optical models frequently agree well with independent physi cal measurements of film structure, particularly surface roughness by atomic force microscopy. Inhomogeneity due to surface roughness, gradi ent composition, and phase separation are common in both the transpare nt conductors and electrochromics, resulting sometimes in particularly complex models for these materials. Complete sets of data are present ed over the entire solar spectrum for a range of colored states. These data are suitable for prediction of additional optical properties suc h as oblique transmittance and design of complete electrochromic devic es. (C) 1998 Elsevier Science B.V. All rights reserved.