3.U.S. scientists develop new type of color-changing glass that can be turned into solar cells after heating

According to foreign media New Atlas, windows are a good daylighting tool, but in summer, this also brings unnecessary heat, causing many people to have to turn on air conditioning. Now, researchers have developed windows that can automatically change color when the sun heats up to keep buildings cool - most importantly, they are also solar panels.

The color-changing glass has been around for a long time, and the most common one is as a transition lens of glasses, which automatically adjusts color under strong light. Recent developments have made it electronic, which can be switched on demand and enlarged to the size of a window. At the same time, the efficiency of transparent (or translucent) solar cells is getting higher and higher, and they can even be installed on windows.


In this new study, researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) combined these two technologies into a single window. What they call "thermochromic photovoltaic" technology can switch colors when heated by sunlight to block glare and reduce the need for cooling. When it does so, it also starts to collect energy from this light.


This kind of window is made of a thin film of perovskite-a new type of solar cell material-sandwiched between two pieces of glass, and solvent vapor is injected into the gap. When the humidity is low, the perovskite film remains transparent, allowing the windows to transmit light normally. But at a certain temperature, steam will rearrange the perovskite crystals, first into chains, then flakes, and then cubes. Each new shape will change the color and block the light to varying degrees. It is hoped that the room will be cooled by a few degrees in the process.


When the glass temperature reaches 35°C to 46°C, the window can switch between several different colors, from transparent to yellow, orange, red and brown, it takes about 7 seconds. This is a considerable improvement over the early prototype developed by the NREL team. When the temperature reaches 65.5°C to 79.4°C, it can only switch between transparent and a reddish brown, and it takes 3 minutes to complete.


Ideally, “thermochromic photovoltaic” windows can help reduce the need for air conditioning, because air conditioning is a huge energy consumer in hot times and climates, and even a little extra electricity can be raised to help it operate. The team stated that a prototype window using the new technology can be developed within a year.