New material for smart window that can control penetration ratio on its own depending on the amount and temperature of light. This new material is expected to be utilized in commercializing windows that become dark when the sun is bright and brightened when the weather is gloomy.
Pohang University of Science and Technology (POSTECH, Chancellor Kim Moo-hwan) announced on Wednesday that a research team led by Professor Lee Dong-hwa of Materials Science and Engineering Department and Lee Joon-ho, who holds a doctoral degree, found a new material that is able to adjust the amount of light penetration on its own.
The research team proposed that perovskite mineral that is based on copper using ab initio quantum chemistry methods is able to easily control phase transition temperature and can be used as a new material that has high light transmittance at low temperature.
Smart window is seen as an eco-friendly product that is able to save heating and cooling costs of a building as it is able to adjust light transmittance on its own depending on the outside temperature. Metal-insulator phase transition material is a perfect material for smart window as it becomes metal (low penetration ratio) at high temperature and insulator (high penetration ratio) at low temperature.

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<Window that has its light transmittance adjusted based on the outside temperature>

Vanadium dioxide that has been used as the material for smart window has low efficiency in energy reduction as it has high phase transition temperature and has low light transmittance as an insulator. Although relatively low band gap is needed because phase transition needs to take place at room temperature for smart window, there is a contradiction that argues that low band gap reduces light transmittance at low temperature.
The research team hypothesized that a material with a band gap with polarized spins does not affect light transmittance based on “selection rule”. It believed that it would be able to argue the contradiction and started on the research by using ad initio quantum chemistry methods in order to verify its hypothesis and the contradiction.
After conducting ad initio quantum chemistry methods, the research team confirmed that copper-based halide perovskite has a band gap with polarized spins and that this band gap does not have any negative impact on light transmittance. It also confirmed that a band gap with polarized spins can be easily adjusted through transition of element or external stress and that it is easy to adjust phase transition temperature of the material.
“It was difficult to satisfy conditions of smart window with materials that have ordinary band gaps.” said Professor Lee Dong-hwa. “The material that we have developed is expected to overcome limitations that current exist.”
Results from the research, which was backed by three different projects, were recently published on the Journal of the American Chemical Society.
Staff Reporter Jung, Jaehoon |