Abstract

The coloration mechanism of tungsten trioxide (${\mathrm{WO}}_3$) 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 ${\mathrm{Na}}^{+}$ ions in ${\mathrm{WO}}_3$ thin films sputter-deposited on ITO/glass substrates. A unique model based on a constrained spline approach was developed and applied to draw out ${\epsilon }_1+i{\epsilon }_2$from 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, ${\mathrm{Na}}_x{\mathrm{WO}}_3(x=0.1,0.2,0.35)$, exhibits an absorption band centered at ca. 1.14 eV in ${\epsilon }_2$ governing the coloration mechanism.

© 2019 Optical Society of America

Optical constants and electrochromic characteristics of M_xWO₃ bronzes

Zahid Hussain
Appl. Opt. 57(20) 5720-5732 (2018)

Morphological and chemical dynamics upon electrochemical cyclic sodiation of electrochromic tungsten oxide coatings extracted by in situ ellipsometry

Alexandre Zimmer, Mickaël Gilliot, Laurent Broch, Clotilde Boulanger, Nicolas Stein, and David Horwat
Appl. Opt. 59(12) 3766-3772 (2020)

Investigation on the optical properties of annealed Mn-Co-Ni-O thin films by spectroscopic ellipsometry

Wei Zhou, Yi Liu, Yimin Yin, Wanli Ma, and Zhiming Huang
Opt. Lett. 44(11) 2701-2704 (2019)

WO₃/SiO₂ composite optical films for the fabrication of electrochromic interference filters

Bill Baloukas and Ludvik Martinu
Appl. Opt. 51(16) 3346-3356 (2012)

Amorphous Ga–Sb–Se thin films fabricated by co-sputtering

Tomáš Halenkovič, Jan Gutwirth, Marek Bouška, Laurent Calvez, Petr Němec, and Virginie Nazabal
Opt. Lett. 45(1) 29-32 (2020)