Optical simulation and fabrication of HfMoN/HfON/Al2O3 spectrally selective coating

Detailed ellipsometric studies were carried out to measure the refractive indices (n) and extinction coefficients (k) of the HfMoN(H)/HfMoN(L)/HfON/Al2O3 tandem absorber in the wavelength range of 300-1000 nm. The experimentally measured ellipsometric parameters have been fitted with simulated spectra using the Tauc-Lorentz model for generating dispersion of optical constants of the individual layers. Using these n and k values a three layer HfMoN/HfON/Al2O3 spectrally solar selective coating was designed and simulated using Essential Macleod software. The optical constants and thicknesses obtained from the simulation were used to develop the three layer tandem absorber with high absorptance and low emittance. The three layer tandem absorber has been deposited on stainless steel (SS) substrates using a magnetron sputtering system. The spectrophotometric data showed that the three layer tandem absorber exhibits high absorptance of 0.95 with low emittance of 0.14 on SS substrate and these values are similar to that of four layer HfMoN(H)/HfMoN(L)/HfON/Al2O3 tandem absorber.