The effect of increasing Si content in the absorber layers (CrAlSiNx/CrAlSiOyNx) of solar selective absorbers upon their selectivity and thermal stability

Abstract

In this work, the effect of increasing Si content in the absorber layers (CrAlSiN x /CrAlSiO y N x) of solar selective absorbers upon their selectivity and thermal stability are studied. The two optical stacks presented consist of four magnetron sputtered layers on stainless steel substrates. In both cases, tungsten is used as back-reflector, CrAlSi x N/CrAlSiO y N x as absorber layers with different Si/(Cr+Al+Si) atomic ratio (0.15 and 0.30, respectively) and finally the SiAlO x antireflection layer. The structures were theoretically designed by SCOUT software depended on experimental transmittance (T) and reflectance (R) of thin single layers deposited on glass substrates. It is observed that optical stack coatings with higher silicon content show better selectivity values, high solar absorptance, α= 95.9%, and low emissivity, ε= 9.7 % (calculated for 400 ºC), with higher thermal stability at 600 ºC in vacuum, for 650 h. Additionally, with the annealing at 600 ºC an increase of surface roughness was found, which was smaller for sample with higher Si content.

High-temperature solar-selective coatings based on Cr(Al)N. Part 1: Microstructure and optical properties of CrNy and Cr1-xAlxNy films prepared by DC/HiPIMS

“…%) had similar reflectance and absorbance characteristics to those of TiN-based films in the solar spectrum region. A recent work published by Al-Rjoub et al [25], about SSC based on CrAlSiN and CrAlSiON, doped with different amount of silicon, showed that the higher silicon content SSC present better selectivity, high solar absorptance, α = 95.9%, and low emissivity, ε = 9.7% (calculated for 400 °C), and thermal stability at 600 ºC in vacuum for 650 h. In other hand, similar to Ti(Al)N, it is expected that the optical properties of Cr(Al)N could be tuned by controlling the chemical composition.…”

High-temperature solar-selective coatings based on Cr(Al)N. Part 2: Design, spectral properties and thermal stability of multilayer stacks

“…In recent years, transition-metal nitrides, oxides and oxynitrides have received significant attention for use in mid-and high-temperature SSC due to their excellent mechanical, chemical, thermal and optical properties [7] which can be tailored by controlling the stoichiometry ( [8] and references therein). The combination of these materials into multiple configurations as semiconductor-metal tandem, metal-dielectric composite (cermet) in single, gradient or multilayer structures can achieve outstanding performance [2][3][4][9][10][11][12][13][14][15][16][17][18][19]. The material selection, the individual layer thickness and the stacking sequence play a vital role to determine the solar selective properties providing high absorptance (up to 98%) and low emittance (<15%).…”