Abstract

The coloration mechanism of tungsten trioxide (WO3) upon insertion of alkali ions is still under debate after several decades of research. This Letter provides new insights into the reversible insertion and coloration mechanisms of Na+ ions in WO3 thin films sputter-deposited on ITO/glass substrates. A unique model based on a constrained spline approach was developed and applied to draw out ε1+iε2from spectroscopic ellipsometry data from 0.6 to 4.8 eV, whatever the state of the electrochromic active layer, i.e., as-deposited, colored, or bleached. It is shown that electrochemically intercalated sodium-tungsten trioxide, NaxWO3(x=0.1,0.2,0.35), exhibits an absorption band centered at ca. 1.14 eV in ε2 governing the coloration mechanism.

© 2019 Optical Society of America

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Supplementary Material (3)

NameDescription
» Data File 1       Tabulated real (n) and imaginary (k) parts of the complex refraction index of Na0.1WO3 vs. energy (eV) and wavelength (nm).
» Data File 2       Tabulated real (n) and imaginary (k) parts of the complex refraction index of Na0.2WO3 vs. energy (eV) and wavelength (nm).
» Data File 3       Tabulated real (n) and imaginary (k) parts of the complex refraction index of Na0.35WO3 vs. energy (eV) and wavelength (nm).

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