Scalable On-Chip Radiative Coolers for Concentrated Solar Energy Devices

Radiative coolers spectrally tailored at mid-infrared wavelengths (5-30 μm) achieve passive and efficient heat dissipation, thereby working together with existing conduction and convection channels. However, radiative coolers developed to date are structurally too complex to be scalable, too thick for monolithic integration, visibly opaque or reflective, or thermally unstable, particularly when integrated into optoelectronic devices. Here, we report wafer-scale, submicron-thick, on-chip radiative coolers designed for high-temperature concentrated solar energy devices. A hexagonally arranged SiO2/AlOx (500/300 nm) double-shell-covered array on a wafer exhibited an emissivity larger than 0.8 at omnidirectional incidence via optical-resonance coupled photon-tunneling effects, that is, uniform absorption distribution and reduced surface reflectivity. Daytime experiments showed that the double-shell hollow cavity film lowered the Si wafer temperature by 10 °C at one-sun intensity, concurrently boosting the Si absorptivity by 19% compared to a bare Si wafer. To reveal the feasibility of applying our developed film to concentrated solar energy devices, we performed concentrated solar simulator experiments at various illumination intensities up to twenty-sun. The radiative cooling performance became progressively significant by increasing the illumination intensity; at twenty-sun intensity, the hollow-cavity film yielded a 31 °C temperature drop when the Si wafer was heated at 200 °C. These economically viable, on-chip radiative coolers will help overcome the saturated quantum efficiencies of current optoelectronic devices that are fundamentally limited by thermal effects.