Berkeley Lab researchers develop perovskite ‘smart window’ material

Berkeley Lab scientists working with halide perovskites have discovered a material, which acts a stable solar semiconductor, and can be switched between transparent and non-transparent appearances, with just slight changes to temperature or moisture levels.

The material, described in the paper, ‘Thermochromic Halide Perovskite Solar Cells’, published in the journal Nature Materials, was discovered serendipitously as the researchers sought to improve stability of the perovskite material methylammonium lead iodide, replacing methylammonium with cesium.

“This class of inorganic halide perovskite has amazing phase transition chemistry,” said Peidong Yang, Professor in UC Berkeley’s departments of Chemistry, and Materials Science and Engineering. “It can essentially change from one crystal structure to another when we slightly change the temperature or introduce a little water vapor.”

The researchers say that the material’s two states have exactly the same composition, but very different crystalline structures. The phase change discovered was initially seen as a drawback, but the researchers were able to turn it into something potentially useful.

The material is triggered to change from transparent to non-transparent with the application of heat. In lab experiments, the required temperature was around 100°C. The scientists say they are working to get this down to 60°C. The reverse transition is achieved by adding moisture to the material. The researchers say they will also work on alternatives to this, such as voltage.

“The solar cell shows fully reversible performance and excellent device stability over repeated phase transition cycles without any color fade or performance degradation,” said Minliang Lai, a graduate student in Yang’s group. “With a device like this, a building or car can harvest solar energy through the smart photovoltaic window.”