Near-Unity Solar Reflectance and Mid-Infrared Transparency via Microwave-Engineered 2D Y2O3 for Passive Radiative Cooling

Abstract

Radiative cooling requires high visible-to-near-infrared (VIS–NIR) reflectance to block solar input and strong mid-infrared (MIR) emission to release heat through the atmospheric window. Compared to dual-functional materials, multilayer structures combining a VIS–NIR reflective and MIR transparent top layer with an emissive substrate allow each layer to perform optimally without trade-offs. Polyethylene (PE), with excellent MIR transparency, is widely used as the top layer. However, its VIS–NIR reflectance is limited by weak scattering, leaving room for further enhancement. Herein, we report a white, two-dimensional (2D) yttrium oxide (Y2O3) nanosheet material synthesized via a microwave pulse method, which overcomes these limitations. The 2D morphology enhances VIS-NIR reflectance through directional scattering, while the defect-free crystallinity achieved by microwave-assisted synthesis preserves MIR transparency by minimizing phonon scattering and absorption. Integrated with high-emissivity blackbody substrates, this composite structure delivers superior cooling performance, surpassing conventional materials in both spectral efficiency and scalability(RVIS–NIR = 0.97，εMIR = 0.94). Furthermore, the nanosheets exhibit excellent rheological properties, enabling scalable fabrication via printable inks. This study establishes a robust platform for next-generation radiative cooling technologies with transformative applications in energy-efficient architecture, electronics, and industrial thermal management.