Design and fabrication of highly thermally stable HfMoN/HfON/Al2O3 tandem absorber for solar thermal power generation applications

• Published in: Solar energy materials and solar cells Vol. 102; pp. 86 - 92
• Main Authors: Selvakumar, N., Manikandanath, N.T., Biswas, A., Barshilia, Harish C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2012; Elsevier
• Subjects: Absorptance; Absorptivity; Aluminum oxide; Applied sciences; Ellipsometry; Energy; Exact sciences and technology; Hafnium molybdenum nitride; Hafnium oxynitride; Heat treatment; High temperature solar selective coatings; Natural energy; Optical properties; Refractivity; Solar collectors; Solar energy; Solar thermal conversion; Tandem absorber; Thermal stability; Thermoelectricity; Hafnium molybdenum nitride; High temperature solar selective coatings; Hafnium oxynitride; Tandem absorber; Optical properties; Heat treatment; Absorbent material; Spectroscopic ellipsometry; Optical constant; Absorption coefficient; High temperature; Solar absorbers; Molybdenum; Optimization; Hafnium Nitrides oxides; Hafnium; Selective coating; Heliothermy; Alumina; Antireflection coating; Protective coatings; Double layers
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2012.03.021

A new HfMoN(H)/HfMoN(L)/HfON/Al2O3 tandem absorber is designed and developed for high temperature solar thermal applications. The first absorber layer, HfMoN(H) is designed to have higher metallic content than the second HfMoN(L) layer. By varying the nitrogen flow rate, two different HfMoN layers with different refractive indices were deposited on SS substrates. The optical constants (n and k) measured using spectroscopic ellipsometry showed that HfMoN(H) and HfMoN(L) are the main absorber layers and HfON/Al2O3 acts as a double layer antireflection coating. The gradual decrease in the refractive indices from the substrate to the top resulted in increase in the absorptance, which was confirmed by the ellipsometric measurements. The optimized four layer tandem absorber exhibited high absorptance (α=0.94–0.95) and low thermal emittance (ε82°C=0.13–0.14). The four layer tandem absorber was thermally stable up to 600°C for 450h and 650°C for 100h in vacuum. Whereas, coatings heat-treated in air were thermally stable up to 475°C for 34h. ► Novel HfMoN(H)/HfMoN(L)/HfON/Al2O3 tandem absorber for high temperature solar applications. ► The tandem absorber exhibited high absorptance of 0.94–0.95 and emittance of 0.14–0.15. ► The tandem absorber was thermally stable in air at 500°C for 7h. ► The tandem absorber was thermally stable up to 600°C for 450h and 650°C for 100h in vacuum.