The ultrathin, soft, radiative-cooling interface layer enhances the heat dissipation of skin-like electronic devices. (Credit: City University of Hong Kong)

A photonic material-based “soft, ultrathin, radiative-cooling interface” that greatly enhances heat dissipation in devices, with temperature drops more than 56 °C, offers an alternative for effective thermal management in advanced wearable electronics.

In electronic devices, heat can be generated from both internal electronic components, when an electric current passes through a conductor, a process known as Joule heating, and external sources, such as sunlight and hot air. To cool down the devices, both radiative (i.e., thermal radiation — emitting heat energy from the device surface) and non-radiative (i.e. convection and conduction — losing heat to the layer of still air around the device and through direct contact with a cold object) heat-transfer processes can play a role.

However, the current technologies rely mostly on non-radiative means to dissipate the accumulated Joule heat. Moreover, the materials are usually bulky and rigid and offer limited portability, hindering the flexibility of wireless wearable devices.

To overcome these shortcomings, the research team developed a multifunctional composite polymer coating with both radiative and non-radiative cooling capacity without using electricity and with advances in wearability and stretchability.

When heat is generated in an electronic device, it flows to the cooling interface layer and dissipates to the ambient environment through both thermal radiation and air convection. The open space above the interface layer provides a cooler heat sink and an additional thermal exchange channel. The interface also exhibits excellent anti-ambient-interference capability due to its lower thermal conductivity, making it less susceptible to environmental heat sources that would affect the cooling effect and performance of the devices.

To examine its cooling capacity, the cooling interface layer was conformally coated onto a metallic resistance wire — a typical component causing a temperature rise in electronics. With a coating thickness of 75 μm, the temperature of the wire dropped from 140.5 °C to 101.3 °C, compared with uncoated wire at an input current of 0.5 A, and dropped to 84.2 °C with 600 μm thickness, achieving a temperature drop of more than 56 °C.