A discovery by researchers from Berkeley University in California may, in the near future, offer the potential to build windows that automatically become darker when exposed to sunlight, in order to keep the heat out (a development that was already described in Science), while generating electricity at the same time.
A group under the leadership of professor Peidong Yang has adapted the chemical structure of perovskite (a versatile material that hold much promise for solar cells) in such a way that it changes from transparent to tinted under the influence of heat.
This discovery could be the foundation for energy-producing smart windows for buildings, cars and displays. The researchers have published their discovery in Nature Materials.
The efficiency of the conversion from sunlight into electricity is currently low and for the transition from transparent to tinted it is necessary to heat the window to 100 °C; the group under the leadership of Yang is, however, already working on versions that operate at lower temperatures and have a higher efficiency.
Perovskites are currently enjoying a great deal of attention because they – with the addition of appropriate chemical elements – are able to convert light into electricity at very high efficiency. By changing the chemical composition it is also possible to change the transparency. Some time ago a perovskite was discovered that became transparent when heated, but the efficiency of electricity generation reduced dramatically after a few cycles.
The new material from Yang (a halide-perovskite with added caesium, lead, iodine and bromine), however, continues to maintain its efficiency even after many cycles (changing from transparent into a reddish tint).