Radiative Cooling with Transparent Microstructured Hybrid Organic–Inorganic Polymer Film Fabricated by Nanoimprint Lithography

Radiative cooling is a passive cooling technology that could potentially address critical sustainability challenges by improving energy efficiency across different applications, including building materials, coatings, electronics, and outdoor devices. Photonic radiative coolers are a discrete category that utilizes photonic structures to optimize the emission properties of the material in the atmospheric transparency window (ATW) regime (8-13 μm). Due to their efficiency and adaptive nature, photonic radiative coolers offer a promising avenue as an adaptable cooling technology. However, a major challenge in transitioning this technology from laboratory to practical use remains. To address this barrier, large area, scalable and low-cost methods and materials need to be implemented. In this study, we demonstrate the fabrication of a transparent microstructured polymer-based radiative cooling (MPRC) film using nanoimprint lithography with a hybrid organic-inorganic UV-curable resist, namely, Ormocomp. We report the optical properties of Ormocomp within the atmospheric transparency window, which had not been previously characterized and utilize them to reveal the underlying mechanisms leading to emissivity enhancement. The MPRC film has over 90% transmission in the visible-NIR wavelengths and provides an─above ambient─cooling effect of -3 °C compared to bare Si reference sample under direct sunlight even though the solar absorptivity of silicon is lower. Our suggested design and fabrication approach is suitable for applications that need optical transparency or can be paired with reflective substrates to further enhance cooling performance, offering a practical and scalable radiative cooling solution.