Scalable All-Polymer Photonic Crystals for Daytime Radiative Cooling

Photonic crystals hold significant promise for passive daytime radiative cooling (PDRC) yet face inherent scalability-durability-performance trade-offs. Although all-polymer photonic crystals (APPCs) offer solutions, their development is constrained by limited refractive index contrasts (Δn < 0.2), sub-100-nm layer fabrication challenges, interfacial delamination, and insufficient mechanical robustness. Here, we fabricated a scalable, high-performance all-polymer photonic crystal film via the self-assembled gradient nanolayer coextrusion of poly(methyl methacrylate) and poly(ethylene naphthalate), followed by biaxial stretching. The resulting 1500-layer hierarchical architecture, featuring gradient layer thicknesses ranging from 50 to 400 nm, achieved a solar reflectance of 95.4% and mid-infrared emissivity of 93.4%, enabling sub-ambient cooling of 11°C under 980 W/m² solar irradiance. The dense nanolayer structure also imparted exceptional mechanical properties, including a tensile strength of ∼103.8 mPa, toughness of ∼54.9 mJ/m³, and Young's modulus of ∼2.9 GPa, substantially exceeding those of existing polymer-based radiative coolers. This solvent-free, continuous fabrication process bridged nanophotonic design with industrial-scale manufacturing, offering a practical fabrication route for durable, high-performance polymeric cooling films.