Transparent Metamaterial Films with Multimodal Radiative Cooling for Outdoor Flexible Electronic Devices

Effective thermal management presents a critical challenge for next-generation, high-power, flexible electronics, requiring innovative and energy-efficient strategies to safeguard device reliability and performance. Passive radiative cooling, a zero-energy carbon-free solution, has emerged as a highly promising approach. However, integrating heat conduction, radiation, and convection into a unified thermal management system for electronic displays without compromising optical transparency remains challenging. Here, we design a multimodal transparent radiative cooling film fabricated by embedding diamond microparticles into a poly(dimethylsiloxane) elastomer matrix and patterning its surface with a pyramidal micronano array (PDMS/D-PA). The optimized film exhibits high solar spectral transmittance of 81.8%, broadband mid-infrared emissivity of 98%, and enhanced thermal conductivity of 3.33 W m^-1 K^-1. Outdoor tests show that the film-coated device achieves a steady-state temperature reduction of 14.8 °C compared to a bare counterpart under a solar irradiance of 820.8 W m^-2. An alkylation treatment further renders the film superhydrophobicity with a water contact angle of 153.4°, providing self-cleaning capability and environmental durability. This composite film bridges the gap between esthetic needs and functional demands, offering a sustainable, passive thermal management strategy for ensuring the reliability and longevity of flexible outdoor electronic devices, such as wearable sensors, foldable displays, e-skin, and drone components.