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Universal Electrochromic Smart Window Coating




Delia Milliron and colleagues at Berkeley Lab have developed an electrochromic nanoscomposite material to dynamically control heat and light through windows depending on comfort demands and environmental fluctuations. Specifically, the technology modulates both the visible and near infrared (NIR) light transmittance to control the heat that enters a building as well as the light.

The electrochromic film consists of transparent conducting oxide (TCO) nanocrystals of either tin-doped indium oxide (ITO) or aluminum-doped zinc oxide (AZO) embedded in a solid matrix. The matrix is typically a conventional electrochromic material, such as a transition metal oxide that darkens under applied voltage to adjust the shading of visible light. This offers the added possibility of separable control over the amount of heat and light transmitted through the window to potentially maximize cost savings for lighting and heating/cooling while providing glare control. Alternatively, the matrix may be a solid electrolyte, which is optically passive and simply facilitates the modulation of NIR transmission by the embedded TCO nanocrystals. A solid electrolyte is preferred over a liquid or gel for the greater durability and stability that may be required for building applications.

The Berkeley Lab material is prepared by solution-based methods, which reduce production costs compared with conventional physical deposition techniques. At the same time, the technique offers excellent control of the nanoinclusion composition, size, morphology and volume fraction, with implications for the optical transmission characteristics.

Current energy efficient window technologies are based on solar control and low-emissivity coatings, limiting them to a particular climate (either hot or cold). Electrochromic materials, materials that switch optical properties reversibly when a voltage is applied, are the most promising for universal energy efficient windows. WO3 is the most widely used electrochromic coating, however it modulates the visible part of the light spectrum while the near infrared light remains either unchanged or switches simultaneously with the visible. By offering control of both the visible and NIR ranges, the Berkeley Lab material is a superior solution.

DEVELOPMENT STAGE: Bench scale demonstration.
Voltage-selective modulation of visible and NIR light by a nanocomposite employing a conventional electrochromic matrix has been demonstrated.  Using a solid electrolyte matrix, selective NIR modulation has been demonstrated.  Cyclic voltammograms correlate the current flow with these optical changes.

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


Spectrally-selective Near Infrared Electrochromic Device, IB-2938

Aluminum-doped Zinc Oxide Nanoink, IB-2967

Modular Inorganic Nanocomposites, IB-2749


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