A Tantalum diffusion barrier layer to improve the thermal stability of AlxOy/Pt/AlxOy multilayer solar absorber

• A thin Ta layer was used as a diffusion barrier to improve the thermal stability.
• The thermal stability of AlxOy/Pt/AlxOy solar absorber coatings was improved.
• AlxOy/Pt/AlxOy solar absorber was thermally stable in air up to 700 °C for 2 h.
• The coatings were thermally stable in air up to 550 °C for 24 h.

The effect of a thin Tantalum layer on the thermal stability of AlxOy/Pt/AlxOy multilayered selective solar absorber coatings has been investigated. The resulting samples were annealed at different temperatures for different durations in air. These were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, Atomic force microscopy, Raman spectroscopy, UV–vis–NIR spectrophotometer and emissometer. The Cu/Ta/AlxOy/Pt/AlxOy multilayer solar absorber coatings were found to be thermally stable up to 700 °C in air for 2 h with good spectral selectivity (α/ε) of 0.932/0.10. At 800 °C, the spectral selectivity decreased to 0.870/0.12, which is attributed to the diffusion of Cu and formation of CuO phase. The formation of CuO phase was confirmed by X-rays diffraction, energy dispersive spectroscopy and Raman spectroscopy. Long term thermal stability study showed that the coatings were thermally stable in air up to ∼550 °C for about 24 h.