We propose solar selective absorbers with β-FeSi_2-containing SiO_2 composites on low-emissivity Mo base layers for high temperature receiver tubes. The stacking structure of the multilayer was designed based on the optical constants of the β-FeSi_2+SiO_2 composites, and the optical absorptance spectra of the fabricated absorbers were obtained to investigate the solar-thermal conversion efficiency. Because the composite with a high volume fraction of the semiconducting β-FeSi_2 showed a high extinction coefficient k only in the solar spectrum region, the interband absorption provided a desirable selective absorbing behaviour with a steep transition curve from high solar absorption to low infrared absorption in the near-infrared region. Adjusting the β-FeSi_2 content in the SiO_2 matrices was effective to control the optical constant spectra, which was useful for a gradual decline of refractive index n towards the surface. The interface between the β-FeSi_2 and Mo base layer had low thermal stability because of Si diffusion, thus a thin SiO_2 barrier was inserted at the interlayer to suppress the interaction. The optical absorption spectrum of the designed and prepared absorber "SiO_2/β-FeSi_2+SiO_2 composites/SiO_2 barrier/Mo base" achieved high photo-thermal conversion efficiencies of over 72.1 % at high temperatures below 700 °C. The β-FeSi_2 nanoparticles dispersed in the SiO_2 matrices were stable even after annealing at 750 °C for 1 h, and the fabricated multilayer showed good thermal stability at 600 °C for 500 h.
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