WAlSiN-based solar selective coating stability-study under heating and cooling cycles in vacuum up to 800 °C using in situ Rutherford backscattering spectrometry and spectroscopic ellipsometry

In situ Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE) were applied to study the compositional and optical stability of a WAlSiN-based solar-selective coating (SSC) at high temperatures in vacuum. The samples were exposed to heating-cooling cycles between quasi room temperature and stepwise-increased high temperatures of 450 °C, 650 °C, and 800 °C, respectively. In situ RBS revealed full compositional stability of the SSC during thermal cycling. In situ SE indicated full conservation of the optical response at 450 °C and 650 °C, and minimal changes at 800 °C. The analysis of the ex situ optical reflectance spectra after the complete thermal cycling gave an unchanged solar absorptance of 0.94 and a slightly higher calculated thermal emittance at 800 °C of 0.16 compared to 0.15 after deposition. Cross-sectional element distribution analysis performed in scanning transmission electron microscopy mode confirmed the conservation of the SSC’s microstructure after the heating – cooling cycles. The study demonstrates compositional, optical, and structural stability of the WAlSiN-based solar-selective coating at temperatures targeted for the next generation of concentrated solar power plants.