A research group has introduced an innovative transparent cooling film that utilizes the principles of radiative cooling.
This collaborative effort involved Professors Junsuk Rho from the Departments of Mechanical Engineering, Chemical Engineering, and Electrical Engineering at POSTECH, alongside PhD candidates Byoungsu Ko and Jaebum Noh from the same department. They teamed up with Professor Heon Lee and PhD candidate Dongwoo Chae from the Department of Materials Science and Engineering at Korea University. Their joint effort resulted in a transparent radiative cooling film designed with a perforated structure similar to an insect screen, effectively managing solar heat and lowering indoor temperatures. This significant advancement was published recently in Advanced Functional Materials, an international materials science journal.
When exposed to sunlight, objects usually get warm; however, a method known as “radiative cooling” allows them to naturally cool down by releasing heat without any external power. Researchers have been trying to incorporate this cooling effect into transparent films like glass, but they’ve faced difficulties since these films tend to transmit solar heat, which limits their cooling ability.
To overcome this issue, the joint team from POSTECH and Korea University developed a film that integrates a perforated silver (Ag) substrate, a Bragg mirror, and a polydimethylsiloxane (PDMS) coating. This film effectively combines transparency with radiative cooling capabilities.
The Bragg mirror is a layered thin-film structure that reflects near-infrared light, which contributes significantly to the sun’s heat. To ensure visibility, the researchers crafted a perforated design similar to an insect screen by creating micrometer-scale holes in the silver substrate to let light pass. Additionally, to enhance the emission of far-infrared radiation within the atmospheric window, they applied a silicon-based PDMS coating with high absorption.
With these three layers—a perforated silver substrate, a Bragg mirror, and a PDMS coating—the film successfully offers cooling while retaining visibility. Tests indicated that glass with this film remained 22.1°C cooler than glass that was only coated with PDMS.
Professor Junsuk Rho from POSTECH remarked, “This technology is primed for mass production and holds great promise for architectural and environmental applications.” He added, “Most importantly, it effectively dissipates heat and lowers energy consumption, positioning it as a pivotal technology for a sustainable future.”
The research received backing from the POSCO Holdings N.EX.T IMPACT Metasurface-based Planar Optics Technology Lab and also received support from the Leading Research Lab of the Ministry of Science and ICT along with the National Research Foundation of Korea.
