[Image above] New smart windows quickly change from clear to dark and back again. Credit: Michael McGehee; Stanford University
Wouldn’t it be great if the windows in your home had the built-in capability of darkening on bright sunny days, keeping your air conditioning from constantly running?
A Stanford University research team has created a new type of smart window that blocks light by using electrodeposition to shoot an electrical current through conductive glass containing metal ions. Electrodeposition, or electroplating, is a process that uses an electric current to coat a material with a thin layer of metal.
The window changes from transparent to dark in less than a minute.
Self-tinting windows are not new—in fact we recently reported on electrochromic windows back in May. But this process is a significant improvement over existing technology, according to a Stanford News article.
Current smart windows change color when charged with electricity. Michael McGehee, professor of materials science and engineering at Stanford and lead researcher, says tungsten oxide, a typical metal used in commercial smart windows, tends to give the windows a bluish tint and is more expensive. It also takes at least 20 minutes for commercial windows to dim and, over time, they become less opaque.
“We’re excited because dynamic window technology has the potential to optimize the lighting in rooms or vehicles and save about 20% in heating and cooling costs,” McGehee says in the article.
The team’s paper describes a process of a “reversible electrodeposition of Cu and a second metal on transparent indium tin oxide electrodes modified by Pt nanoparticles.” Copper solution is spread over an indium tin oxide sheet that has been modified with platinum nanoparticles. When the window is completely clear, 80% of light can pass through—when it’s darkened, less than 5% of light is able to get through.
McGehee explains that the main differences between the team’s windows and current smart windows are in the materials that are used and how well the windows work. “Electrochromic windows have a metal oxide that changes color when it is oxidized and reduced by applying a voltage to the transparent electrode,” he writes in an email. “The advantage of our approach is that the metals are very good at blocking all colors by the same amount. We also think that our design is simpler and that our windows are likely to be cheaper when they are manufactured.”
The research team tested the windows by switching them on and off more than 5,000 times, with no degradation in the light transmission. They’ve already filed a patent for their research.
McGehee says the next step involves testing larger samples, as the scientists only used 4-in.2 size models in their study. “Our next steps for developing the dynamically tinting window technology are to figure out how to have large windows that switch quickly and to demonstrate that the windows will be stable under real world operating conditions for the necessary lifetime of the product,” he adds in the email.
“We are optimistic that the windows can be stable because metals are not damaged by high temperature or sunlight. We hope that the polymer electrolyte can be engineered to be sufficiently stable.”
The paper, published in Joule, is “Dynamic windows with neutral color, high contrast, and excellent durability using reversible metal electrodeposition” (DOI: 10.1016/j.joule.2017.06.001).
Watch the video below to see how quickly the smart glass changes.
Credit: Stanford Precourt Institute for Energy; YouTube