Plasmonic Metal Oxide Nanocrystals and Their Near Infrared Electrochromism

Degenerately doped metal oxide semiconductors, like ITO, exhibit plasmonic resonance at near and mid-infrared wavelengths tunable by varying their composition. Nanocrystals of many such materials have now been synthesized and applications are emerging that leverage the responsiveness of their localized surface plasmon resonance (LSPR) to electronic charging and discharging. One such application is electrochromic glass that can dynamically control heat loads in buildings as the plasmonic absorption of the nanocrystals is electrochemically modulated. I will discuss the principles of electrochromic switching in such materials and describe our efforts to integrate plasmonic nanocrystals into full electrochromic devices. Fundamental understanding of the nature of the electronic states giving rise to infrared absorption is also being pursued.  For example, near-edge x-ray absorption spectroscopy is illuminating the charge state of the metal cations in as-prepared doped nanocrystals and in electrochemically-charged materials. Localization of charge upon lithium insertion gives rise to visible tinting, useful for controlling daylight intensity in smart windows. Finally, fabrication strategies compatible with flexible substrates are explored, opening the door to low cost manufacturing.