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Smart Glass Nano coating Selectively Filters Heat and Light
Researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have designed a new material to make smart windows even smarter. The material is a thin coating of nanocrystals embedded in glass that can dynamically modify sunlight as it passes through a window. Unlike existing technologies, the coating provides selective control over visible light and heat-producing near-infrared (NIR) light, so windows can maximize both energy savings and occupant comfort in a wide range of climates.
This is achieved using a composite of two separate radiation-absorbing materials with different properties. The bulk glass material is made from niobium oxide, which darkens when an electrical current is applied to it.
Embedded into this electrochromic glass are nanocrystals of ITO (indium tin oxide), a common transparent conducting ceramic used in touch screens and solar panels. When these nanocrystals are triggered with a voltage spike, they jump into a state which can filter out around 35% of the incoming NIR radiation.
This nanocomposite coating provides a three-stage filter for external light and heat - in it's normal state, the glass will act as normal. With a small voltage, the ITO crystals will absorb some of the heat, without reducing the amount of light passing through. Increasing the voltage will darken the niobium oxide glass, filtering out the light as well.
The researchers also discovered an additional effect, which enhances the performance of the coating even further. The ITO nanocrystals actually alter the structure of the niobium oxide glass slightly, opening up space in the matrix and allowing charge to flow more readily - making the electrical triggers more effective and strengthening the electrochromic effect.