(October 3, 2015) Electrochromic
windows, so-called ‘smart windows’, share a well-known problem with
rechargeable batteries – their limited lifespan. Researchers at Uppsala
University have now worked out an entirely new way to rejuvenate smart windows
which have started to show signs of age. The study, published in the distinguished
science journal Nature Materials, may open the way to other areas of
application.
Smart windows make it possible to control how much visible
light and solar energy enter a building. This energy often leads to too high
indoor temperatures in commercial buildings the world over, even in Sweden, so
there is a need for air conditioning. Smart windows can drastically reduce
energy consumption for air conditioning, and they can also help create a more
pleasant indoor environment by reducing the amount of dazzling light coming
through them.
The electrochromic smart windows are controlled
electrically. This kind of window is the result of research carried out at
Uppsala University. Commercial production has recently been started by the
company ChromoGenics AB.
The electrochromic smart window is made up of a series of
thin layers on top of each other. The most important of these are two layers of
tungsten oxide and nickel oxide, both about a third of a micrometer thick. They
are separated by an electrolyte layer. The window’s opacity to visible light
and solar energy varies when an electrical current flows between the oxide
layers.
“The principle is the same as for an electric battery. Here
the tungsten-oxide is the cathode and the nickel-oxide the anode. Opacity
depends on how much the ‘battery’ is charged,” says Rui-Tao Wen, a doctoral
student who carried out the study as part of his thesis.
The lifespan of both electric batteries and electrochromic
smart windows is a well-known problem. They need to work after being charged
and discharged many times if they are to be really profitable.