Yang Li1 Chongjia Lin1 Dezhao Li1 Shihe Yang1 Baoling Huang1

1, HKUST, Kowloon, , Hong Kong

Concentrated solar power (CSP), also known as high-temperature solar-thermal energy conversion, is a promising solar energy harvesting technology due to its efficient sunlight utilization, and high availability in energy storage. For the sake of higher Carnot efficiency and greater cost reduction, next-generation CSP plants are expected to operate at higher temperatures (≥900 K) than those conventional systems. Selective solar absorbers, as the key components in CSP systems, are required to offer high stability and great selectivity at such high temperatures. Selective solar absorbers based on multilayer metal/ceramic thin films are a kind of low-cost and scalable absorbers fabricated by facile processes such as sputtering deposition. However, their thermal stability and spectral selectivity fall behind those state-of-the-art cermets and photonic absorbers. Previously works demonstrated that multilayer absorbers suffered from a variety of high-temperature degradation cases associated with the metal/ceramic interfaces, including delamination, surface oxidation, and atom diffusion.
In this work, we introduced a TiN IR reflector into the multilayer absorbers to replace refractory metals (W, Ta, Mo, etc.) used in conventional designs; meanwhile, another ceramic material, titanium oxy-nitride (TiNO), was utilized as the absorptive layer due to its tunable absorption properties and excellent compatibility with TiN. Two ceramic anti-reflection layers, ZrO2 and SiO2, with gradient refractive indexes were adopted to reduce the surface reflection, and enhance the sunlight absorption. The fabricated all-ceramic absorber displayed highly selective absorption with a high solar absorptance of 91.2% and an ultralow IR emittance of 15.7% at 1000 K. Consequently, a high solar-thermal conversion efficiency of 82.1% was achieved under the irradiation of 100 suns. This value is on par with or exceeds the record of state-of-the-art selective absorbers. As expected, the all-ceramic absorber was able to sustain its superior performance at high temperatures up to 800 °C. Both SEM-EDX and depth profiles of elements results reveal that the diffusion and oxidation were effectively suppressed in the all-ceramic structure. Moreover, the delamination was also avoided in the ceramic/ceramic interfaces. Compared with previous multilayer absorbers, this all-ceramic absorber boosted the operating temperature of such low-cost multilayer absorbers by ~300 °C, rendering it suitable for the high-temperature applications in next-generation CSP plants.