Sputtered SiC coatings for radiative cooling and light absorption

Abstract

The outstanding thermomechanical and broadband spectral absorptance of silicon carbide (SiC) coatings makes it a promising material for high-performance optoelectronics devices and photothermal applications. We propose sputtered SiC coatings to develop: (i) broadband infrared emitters for passive radiative cooling and (ii) a spectrally selective ultrathin nanocomposite absorber. For radiative cooling, a proof of concept device has been fabricated by topping the as-sputtered 2.5-μm-thick SiC films with a single pair of distributed Bragg’s reflector (DBR). Owing to the infrared surface polariton resonances of SiC, broadband infrared emissivity of 0.8 is achieved in atmospheric transparency window (8 to 14 μm). The higher refractive index contrast (Δn) in DBR is achieved by depositing high refractive index dense Si film on top of low refractive index nanoporous SiO2, which was fabricated by oblique angle deposition approach. A single pair of DBR on top of SiC considerably reduces the absorption of the overall solar spectrum by 18%. In addition, impact of various materials and number of pairs of DBRs on radiative cooling are also numerically investigated. We also designed and fabricated SiC-based spectrally selective solar absorber coatings. An ultrathin SiC-based nanocomposite absorber with sandwich-like configuration consisting of SiC/Ag-SiC/SiC on reflective substrate has exhibited an outstanding absorptance of 91.24% in the wavelength range of 280 to 2000 nm. The surface plasmon polaritons of metal inclusion within the SiC matrix of an ultrathin nanocomposite (40 nm) layer has contributed to broadband light absorption, whereas the top most layer of SiC (40 nm) acts as antireflection layer. Conclusively, the versatility of sputtered SiC coatings has proven to be promising for radiative cooling and spectrally selective solar absorbers.