Thermal conductive radiative cooling film for local heat dissipation

Radiative cooling has attracted lots of attention recently due to its electricity-free cooling by reflecting solar radiation and emitting thermal radiation to the cold outer space. However, how to improve heat dissipation performance at above-ambient temperatures is still a challenge for outdoor flexible devices. Here a bilayer structure was designed to achieve a thin and thermal conductive radiative cooling film for local heat dissipation in outdoor flexible devices, the local heating area can be avoided by the high in-plane thermal conductive performance and heat can be efficiently dissipated to the outer environment by daytime radiative cooling. The top layer consisted of porous hBN@PVDF-HFP film (thickness ∼ 100 μm) to realize daytime radiative cooling while the bottom layer was the directional graphene film (thickness ∼ 30 μm) to promote in-plane thermal conductive performance, high solar reflectance ${\bar{R}}_{\text{solar}}$ = 0.944, thermal emittance ${\bar{\epsilon }}_{\text{LWIR}}$ = 0.904, and in-plane thermal diffusivity 185.7 mm² s⁻¹ were obtained. Under sunlight, the designed radiative cooling film can greatly reduce the local working temperature from 130.6 °C to 63.3 °C compared with the reference radiative cooling film at the same local heating power, which also shows great local heat dissipation performance under a non-flat surface. This work provides a potential approach to developing thermal conductive radiative cooling technologies for outdoor local heat dissipation applications.