Structure, optical properties and thermal stability of TiC-based tandem spectrally selective solar absorber coating

A new spectrally selective solar absorber coating of TiC/Al2O3 is prepared on stainless steel substrate using a magnetron sputtering method. The new coating exhibits a high absorptance of 0.92 and a low emittance of 0.13 (82 °C). The tandem absorber is characterized using ultra-high resolution scanning electron microscope, UV-vis-NIR spectrophotometer, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The formation of amorphous carbon is due to the dissociation of TiC layer deposited under high substrate temperature (300 °C). The diffused carbon at 600-800 °C with mixed sp2 and sp3 bonds is further demonstrated by XPS and Raman spectra. With an increase in annealing temperature, the surface structure becomes more graphitic. The tandem absorber is stable in vacuum up to 650 °C for 2 h, indicating its importance for high temperature solar selective applications.