Electrochromic Transition Metal Oxide Nanocrystals

Transition metal oxide thin films are the active elements of electrochromic smart glass used in commercial building applications and more. Colloidal nanocrystal synthesis can produce and tune structures at both the atomic and nanoscale that are not readily accessible by conventional physical vapor deposition, providing new opportunities to develop structure-property relationships for electrochromic materials. Nanocrystal inks are readily coated to make optical quality films, facilitating spectroelectrochemical analysis and potentially providing a pathway for low-cost manufacturing compatible with flexible form factors. We discovered that the crystal structure and morphology of niobium oxide nanocrystals play a dominant role in controlling their spectral response upon electrochemical reduction. Depending on the atomic scale structure, niobium oxide can darken selectively in the range of visible wavelengths or near infrared wavelengths or both, selectively as a function of the applied bias. The coloration efficiency can also vary by about 5 fold. Combining experimental and computational analysis, we relate these dramatic differences in electrochromic response to the nature of the electronic states populated when ions are electrochemically inserted. The most promising niobium oxide nanocrystals have been incorporated in prototype electrochromic devices.<br/>Transition metal oxide thin films are the active elements of electrochromic smart glass used in commercial building applications and more. Colloidal nanocrystal synthesis can produce and tune structures at both the atomic and nanoscale that are not readily accessible by conventional physical vapor deposition, providing new opportunities to develop structure-property relationships for electrochromic materials. Nanocrystal inks are readily coated to make optical quality films, facilitating spectroelectrochemical analysis and potentially providing a pathway for low-cost manufacturing compatible with flexible form factors. We discovered that the crystal structure and morphology of niobium oxide nanocrystals play a dominant role in controlling their spectral response upon electrochemical reduction. Depending on the atomic scale structure, niobium oxide can darken selectively in the range of visible wavelengths or near-infrared wavelengths, or both, selectively as a function of the applied bias. The coloration efficiency can also vary by about 5-fold. Combining experimental and computational analysis, we relate these dramatic differences in electrochromic response to the nature of the electronic states populated when ions are electrochemically inserted. The most promising niobium oxide nanocrystals have been incorporated into prototype electrochromic devices.