Abstract
Spectrally selective CrAlN–CrAlON based tandem absorber was deposited by magnetron sputtering and the effects of antireflection layers on the optical and thermal stability properties of tandem absorber were investigated. The thickness of the individual component layers was optimized by matrix method to achieve high solar absorptance and low thermal emittance. TEM, XRD and XPS results confirmed the microstructure of the nanocomposite CrAlN and CrAlON coatings was consisted of nanocrystalline CrN embedded in amorphous matrix of AlN or Al2O3. The optimized CrAlN/CrAlON/Al2O3 tandem absorber exhibited a high absorptance of 0.984 and a low emittance of 0.07 at 82°C. The high absorptance value of this CrAlN–CrAlON based tandem can be partially attributed to the nanocomposite structure of the CrAlN and CrAlON coatings. Accelerated aging tests indicated that the CrAlN/CrAlON/Al2O3 tandem absorbers had high thermal stability in air up to 550°C for 100h with high solar selectivity of 11.5. However, for CrAlN/CrAlON/Si3N4 tandem absorber, the emittance coefficient increased drastically above 500°C which can be attributed to the increased surface roughness and oxidation of Si3N4 antireflection layer. The CrAlN/CrAlON/Al2O3 tandem absorber with high thermal stability has great potential for application in high temperature solar selective field.
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