Site-Selective Ion Intercalation Controls Spectral Response in Electrochromic Hexagonal Tungsten Oxide Nanocrystals

The electrochromism of tungsten oxide occurs through electrochemical reduction, providing active solar control to smart windows, but over the spectral response is limited and largely empirical. To determine how specific chemical changes result in optical absorption processes responsible for coloration, we pair structurally well-defined electrochromic nanocrystals (NCs) with cations varying ionic radii limit intercalation into crystallographic sites. localized surface plasmon hexagonal cesium-doped (Cs:WO3) NCs enhanced, new features appear, depending on intercalate various interstitial voids. These differences were rationalized using X-ray photoelectron Raman spectroscopies reveal structural leading observed variations electrochemically induced spectra. Smaller cations, Na+ Li+, can access additional sites, a secondary, polaronic mechanism electrochromism, accounting enhanced visible light absorption.