A research team consisting of Professors Junsuk Rho from the Department of Mechanical Engineering, the Department of Chemical Engineering, and the Department of Electrical Engineering and PhD candidates Byoungsu Ko and Jaebum Noh from the Department of Mechanical Engineering at POSTECH collaborated with a research team led by Professor Heon Lee and PhD candidate Dongwoo Chae from the Department of Materials Science and Engineering at Korea University. Together, they developed a transparent radiative cooling film featuring a perforated structure resembling an insect screen, designed to regulate solar heat and lower interior temperatures. This breakthrough was recently published in Advanced Functional Materials, an international journal in materials science.
Typically, objects exposed to sunlight heat up, but there is a technique -- "radiative cooling" -- that allows them to release heat and cool down naturally without using any external power. Researchers have been exploring ways to integrate this cooling effect into transparent films such as glass. However, they have encountered challenges as these films often transmit solar heat, limiting their cooling effectiveness.
To address this challenge, a joint research team from POSTECH and Korea University engineered a film combining a perforated silver (Ag) substrate, a Bragg mirror, and a polydimethylsiloxane (PDMS) coating. This film achieves both transparency and radiative cooling performance.
The Bragg mirror, a multi-layer thin-film structure, is designed to reflect near-infrared light, which is responsible for much of the sun's heat. To maintain visibility, the team created a perforated design, akin to an insect screen, by puncturing micrometer-scale holes in the silver substrate to allow light to pass through. For effective emission of far-infrared radiation within the atmospheric window, they added a high-absorption, silicon-based PDMS coating.
Constructed with these three layers -- a perforated silver substrate, a Bragg mirror, and a PDMS coating -- the film effectively provides cooling while maintaining visibility. In testing, glass with this film stayed 22.1°C cooler than glass coated solely with PDMS.
Professor Junsuk Rho of POSTECH stated, "This technology is ready for mass production and has significant potential in architecture and environmental applications." He continued, "Most importantly, it efficiently dissipates heat and reduces energy consumption, positioning it as a key technology for a sustainable future."
The research was conducted with support from the POSCO Holdings N.EX.T IMPACT Metasurface-based Planar Optics Technology Lab and the Leading Research Lab of the Ministry of Science and ICT and the National Research Foundation of Korea.
