26 September 2016 Application of high refractive index and/or chromogenic layers to control solar and thermal radiations
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Abstract
In this presentation, we demonstrate that high refractive index materials such as β-FeSi2 and/or chromogenic materials such as VO2 are the key to control solar and thermal radiations. β-FeSi2 is known as an eco-friendly semiconductor and for sputtered polycrystalline β-FeSi2 thin films, we recently found that λ~0.3 in IR region, while n is higher than 5. On the other hand, another interesting optical property of β-FeSi2 is that both n and k are considerably high in visible to NIR region ( λ ≤ 1.55 μm). Using these optical properties in IR and VIS, we designed multilayers consisting of β-FeSi2/SiO2/β-FeSi2/W, where the upper β-FeSi2 layer absorbs VIS and NIR (λ ≤ 1.0 μm) and the bottom β-FeSi2 layer/W absorbs IR (1.0 ≤ λ ≤2.0 μm). The optimized multilayers absorb more than 90% of solar energy and the eminence at 450 °C is lower than 10%. The perfect absorbers with high refractive index layers are useful for applications to solar selective absorbers for solar thermal power generation and spectrally selective thermal emitters for thermophotovoltaic power generation, IR heaters, radiation cooling. Replacing one of β-FeSi2 layers with a chromogenic material allows active control of solar and thermal radiation. In the presentation, we also demonstrate the active perfect absorbers including a VO2 layer in NIR region.
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Motofumi Suzuki, Kensuke Nishiura, Shoma Masunaka, Naoto Muroi, Kyoko Namura, "Application of high refractive index and/or chromogenic layers to control solar and thermal radiations", Proc. SPIE 9929, Nanostructured Thin Films IX, 99290G (26 September 2016); doi: 10.1117/12.2237410; https://doi.org/10.1117/12.2237410
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