Minimalist integrated, ultrathin, scalable design of thermo-optical interfaces for above-ambient cooling

Radiative cooling (RC) exhibits substantial potential for energy conservation and sustainable development, leveraging its dual mechanism of sunlight reflection and passive thermal emission to deep space without consuming any energy. However, RC remains a fundamental challenge for objects with substantial self-generated heat and operating above ambient temperature in both indoor and outdoor environments (e.g., electronic devices and communication base stations). To address this limitation, this work proposes an integrated and ultrathin thermal photonic interface (TPI) through thermo-optical design, which incorporates 2D hexagonal boron nitride (h-BN) nanoplates with high backward scattering efficiency into a polymer/metal oxide RC framework. The optimized TPI demonstrates exceptional solar reflectivity (>93%) and mid-infrared emissivity (96%). Indoors under high thermal loading, the object coated with the TPI demonstrates temperatures 11.5 °C and 13.2 °C lower than the commercial paint and polymer matrix systems, respectively. Additionally, under daytime with high thermal loading in summer, the TPI system maintains temperatures 5-8 °C below the other two. Notably, the TPI demonstrates excellent cooling performance above the ambient temperature. This work establishes a scalable design strategy for above-ambient radiative coolers, offering an innovative paradigm for implementing 2D planar materials to RC applications.