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Polymer Nanocrystal Composite Electrochromic Window Coating





Berkeley Lab’s Delia Milliron, U. C. Berkeley’s Evan Runnerstrom, and colleagues have developed a low cost, thin film window coating that, compared to current electrochromic devices, holds the promise of delivering faster switching speeds, stronger infrared modulation, higher coloration efficiency, and a longer lifetime.

At the heart of this innovative architecture is a thin film mixture made of transparent electron-conducting nanocrystals embedded in a lithium salt-containing polymer electrolyte matrix. When deposited on a window glass surface, this nanocomposite layer performs as a solid-state electrochromic device capable of blocking solar heat during hot days and admitting it when it is cold outside. Unlike traditional electrochromic windows, which are tinted blue in their colored state, this transparent coating can be tuned to allow the full spectrum of visible light while blocking infrared rays. This selectivity offers not only a technical advantage over current technologies, but improved aesthetics.

In addition, these thin film devices can be fabricated using low cost, earth-abundant, and environmentally friendly materials. The nanocomposite can be manufactured and deposited on glass with cost effective and energy efficient room temperature solution processing using well-established nanofabrication techniques such as spin casting, doctor-blading, and spray coating.

Key elements of this design include a network of transparent conducting tin-doped indium oxide (ITO) nanocrystals, the surfaces of which have been stripped bare of ligands to enable interaction and electron conduction between particles. The nanocomposite is formed by suspending these nanocrystals in an organic polymer solution containing electronically insulating polyethylene oxide and lithium salts. Deposited on a glass surface and, upon solvent evaporation, the solution forms a solid polymer matrix that not only physically supports the network of nanocrystals, but also acts a solid-state electrolyte for the ion transport necessary for device operation.

When subjected to a negative voltage, the nanocrystals attract the lithium ions to their surfaces while electrons flow into the nanocrystals. This changes the nanocomposite layer’s optical properties and allows it to block only near infrared radiation. When the voltage is reversed, the ions are repulsed and electrons flow out of the nanocrystals as the nanocomposite returns to its off state, becoming transparent to infrared radiation.

Windows are responsible for 30 percent of the heating and cooling requirements of U.S. homes and businesses — adding up to $40 billion annually. Improved technologies and better window designs could significantly reduce this energy loss.

Lawrence Berkeley National Laboratory’s Molecular Foundry, one of the world’s premier nanotechnology research institutions, provides outside researchers with the state-of-the-art instrumentation, in-house expertise and multidisciplinary environment they need to pursue research benefitting nanoscience. For more information about access to this outstanding nanotechnology researcher facility, go here or email

DEVELOPMENT STAGE:  Bench-scale demonstration. 

STATUS: Patent pending.  Available for licensing or collaborative research.


Universal Electrochromic Smart Window Coating, IB-3072

Spectrally-selective Near Infrared Electrochromic Device, IB-2938


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