Spectrally selective TiAlN/CrAlON/Si3N4 tandem absorber for high temperature solar applications

摘要

A new spectrally selective TiAlN/CrAlON/Si3N4 tandem absorber was deposited on copper substrates using a reactive direct current magnetron sputtering system. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance (a = 0.941-0.958) and low emittance (e = 0.05-0.07). The tandem absorber was characterized using solar spectrum reflectometer and emissometer, X-ray photoelectron spectroscopy, phase-modulated spectroscopic ellipsometry, atomic force microscopy and micro-Raman spectroscopy techniques. The experimental spectroscopic ellipsometric data have been fitted with the theoretical models to derive the dispersion of the optical constants (n and k). The n and k of the three layers indicate that the TiAlN layer is the main absorber layer, Si3N4 acts as an antireflection coating and CrAlON acts as a semi-absorber layer. In order to study the thermal stability of the tandem absorbers, they were subjected to heat treatment (in air and vacuum) at different durations and temperatures. The tandem absorber deposited on copper substrate exhibited high solar selectivity (a/e = 9) even after heat-treatment in air up to 550°C for 2 hrs. Studies on the accelerated aging tests indicated that the absorber coatings on copper were stable in air up to 300°C for 150 hrs.