Professor Jun-suk Rho (ME, CE, EE), Dr. Byeong-Su Ko (ME), and Jae-beom Noh (ME) research team developed a radiative cooling film that reduces internal temperature by regulating sunlight through hole-shaped structures like insect net. This work was conducted in collaboration with Prof. Heon Lee (Korea University), and Dr. Dong-woo Chae (Korea University) team at Korea University. The research was recently published in the international material science journal Advanced Functional Materials.

Generally, the temperature goes up when the material receives sunlight, but there is a technology where the material emits heat on its own without using electricity. It is called radiative cooling. Recently, research on applying this technology to transparent films such as glass has been actively conducted, but there remains a limitation: the cooling effect is insufficient as sunlight goes through. 

To solve this problem, the joint POSTECH-Korea University team successfully developed a film that has radiative cooling and transparency at the same time using a punctured Argentum board and Bragg mirror.

A Bragg mirror is a multilayered structural mirror designed to reflect near-infrared rays that absorb much solar heat. Additionally, the team made micrometer scale holes on the Argentum board, resembling an insect net, to maintain transparency. They used PDMS coating based on silicon which has a high absorption rate to emit far-infrared radiation on atmospheric window area.

Holed Argentum board, Bragg mirror, and PDMS-coated multilayered film serve both outstanding cooling effects and transparency. When applied to glass, the film kept the temperature at 22.1 degrees Celsius - lower than PDMS-coated glass. 

Prof. Rho, the lead researcher, noted “This technology is highly applicable to the industry since it allows for mass production and holds significant potential in architectural and environmental fields. Above all, it is meaningful as a key technology for a sustainable future, as it effectively emits heat and reduces energy consumption.”

Meanwhile, the research was supported by POSCO Holdings’ N.EX.T IMPACT – Center for Flat Optics and Metaphotonics.