Novel Solution to Problematic UV Darkening of Electrochromic Glass

Nanotechnologies : Physical Science Apps

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  • Delia Milliron, Ph.D. , Chemical Engineering
  • Jongwook Kim, Ph.D. , Chemical Engineering

Background/unmet need

Many materials possess contrasting optical properties when exposed to different environmental conditions. Recent developments have focused on the application of such properties in the area of "smart windows." Thin films made of electrochromic materials, those that undergo changes to their optical properties under electrochemical bias, are applied to transparent substrates to create windows that can be tinted on demand.

Initial development of smart windows has shown tungsten trioxide (WO3) to be especially useful as an electrochromic material. However, WO3 degrades under exposure to UV light, becoming darker over time, thereby hindering its ability to be used in smart windows. Many remedies, such as Bragg filters and UV absorbing coatings have been tried, but with very limited success.

Invention Description

Researchers at The University of Texas at Austin have developed a novel concept to block the intrinsic photochromic mechanism of WO3 that causes UV darkening. The invention utilizes a very thin (<10 nm) conformal coating of high-dielectric and ion-conducting material as a protective layer on the electrochromic WO3 film. This thin protective layer efficiently shuts off photochromism by blocking the hole-transfer while it still allows the transfer of ions required for the electrochromic switching.


  • Very thin protective layer creates no detriment to performance
  • Protective layer effectively blocks UV radiation, eliminating the darkening effect of WO3
  • Extremely thin layer uses very little material and is therefore cost-effective


  • Protective layer provides significant reduction of UV darkening of WO3 films
  • Electrochromic properties show no adverse effect over thousands of cycles

Market potential/applications

Existing markets, such as computer monitors and anti-glare television screens, are in the billions of dollars worldwide. Emerging markets such as smart windows, which are expected to grow as management of energy efficiency continues to drive building design, will enhance the value of this technology. 

IP Status

  • 1 U.S. patent application filed