Smart windows block light in less than a minute
Such windows have the potential to substantially decrease energy consumption of buildings, and have other applications in vehicles and even wearable glasses. Currently, say the researchers, most commercial dynamic windows – which use electrochromic materials (such as polymers or metal oxides) to effect their light transmission changes – have limited feasibility due to durability, color, switching speed, and cost.
The smart windows created by the Stanford engineers instead rely on “reversible metal electrodeposition,” and consist of conductive glass plates outlined with metal ions that, in response to electrical current, spread out over the surface to block light. In this case, the prototype used a copper solution that moves over a sheet of indium tin oxide modified with platinum nanoparticles.
When in transparent mode, the smart window allows about 80% of the surrounding natural light to pass through. When set to block light, the window transmits less than 5% of the surrounding light. Each transition – from transparent to dark and vice versa – takes only about 30 seconds.
The researchers tested their windows for durability by switching them on and off more than 5,000 times and saw no degradation in their uniformity or contrast. In addition, the windows also possess neutral color and high contrast, say the researchers, making them a promising alternative to those using traditional electrochromic materials.
“We’ve had a lot of moments where we’ve thought, how is it even possible that we’ve made something that works so well so quickly?” says Michael McGehee, a professor of materials science and engineering at Stanford and senior author of a study on the windows. “We didn’t tweak what was out there. We came up with a completely different solution.”
The prototypes used in the research are about four square inches in size, and more work is needed to increase the surface area to where it is large enough for commercial use. The researchers also hope to reduce manufacturing costs to make them competitive with dynamic windows currently on the market. In the meantime, they have filed a patent for the new technology and are looking for potential commercial partners.
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