Solar Energy, Vol.111, 350-356, 2015
The spectral selective absorbing characteristics and thermal stability of SS/TiAlN/TiAlSiN/Si3N4 tandem absorber prepared by magnetron sputtering
Spectrally selective TiAlN/TiAlSiN/Si3N4 multilayer coatings were deposited on stainless steel (SS) plate using a reactive direct current magnetron sputtering technique. In this tandem absorber system, TiAlN, TiAlSiN and Si3N4 act as the main absorbing layer, the semi-absorbing layer and the antireflection layer, respectively. An average absorptance (alpha) of 0.938 and emittance (epsilon) of 0.099 were achieved in coatings prepared under optimized conditions, which exhibit a fine-grained morphology and an amorphous microstructure as evidenced by SEM and XRD analysis, respectively. Absorptance and emittance data, as well as Raman spectra were collected for coatings exposed to different levels of thermal stresses (2 h in air @200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C, 600 degrees C). These heat treated coatings showed negligible to small degradations in their selective absorbing capabilities as compared with the as-grown ones. There was no significant change of the coatings in their morphology or composition after the heat treatments, as evidenced by the SEM and Raman spectra analysis, respectively. The spectral selectivity of the coatings remained stable after a heat-treatment at 272 degrees C in air for 300 h. (C) 2014 Elsevier Ltd. All rights reserved.