Generalized Brewster effect is a phenomenon where light of both TE (S-) and TM (P-) polarization transmit through a surface with no reflection for a particular incident angle. Generalized Brewster angle (GBA) in visible and near-infrared (NIR) wavelength region is very useful in many scientific and technical areas of applications. However, it is very rare to find a material having this effect as it demands both dielectric and magnetic response in that wavelength range and usually magnetic response is extremely weak in the optical wavelengths. Here we demonstrate the GBA effect of an anisotropic material composed of highly ordered high aspect ratio aluminium doped zinc oxide (AZO) nanopillar arrays. Along with the experimental demonstration, we also provide a proper numerical analysis to investigate the origin of this effect in the pillar array system which will be useful for many conventional as well as new applications in photonics including protein sensing.
Perfect light absorption (PLA) in nanophotonics has a wide range of applications from solar-thermal based applications to radiative cooling. However, most of the proposed platforms require intense lithography which makes them of minor practical relevance. On the other hand, thin-film light absorbers are lithographically free and can be deposited cheaply on large area based on matured technologies. However, thin-film light absorbers were thought to have major limitation and cannot be tailored compared to metamaterials. Here, we show how to design PLA using thin-films in terms of wavelength range, bandwidth, spatial profile of optical losses, directionality and iridescence. We also show that iridescent free, PLA can occur by simply heating metallic thin-films when the metal is of low reflectance and its oxide is of high refractive index. We theoretically and experimentally demonstrate Generalized Brewster angle effect in thin film light absorbers. In addition, we demonstrate hydrogen sensing using three different PLA strategies showing record sensitivity and figure of merit. Furthermore, we show various strategies to create ultra-pure structural colors. Finally, we demonstrate different solar-thermal applications for novel thin-film PLA designs.
KEYWORDS: Solar energy, Thin films, Thin film coatings, Optical coatings, Energy efficiency, Solar cells, Photovoltaics, Energy conversion efficiency, Beam splitters, Optical components
Increasing the efficiency and cost effectiveness of solar energy generation allowed them to compete with traditional carbon-based energy sources in many energy markets worldwide. However, a major problem facing the proliferation of solar energy generation is energy storage. Photovoltaic (PV) generators enjoy relatively high efficiency but suffer from high electric energy storage costs. On the other hand, solar-thermal energy conversion enables storing heat and dispatch electricity at lower storage costs but with less efficiency compared to photovoltaics. Hybridizing both solar energy conversion can address the energy storage problem. Furthermore, single junction PVs are unable to convert a large portion of the solar spectrum to energy which eventually lead to PV thermalization. Spectral beam splitting is a promising method to achieve high efficiency solar energy conversion while hybridizing electric and thermal solar energy generation.
Here, we use novel thin-film based optical coatings to develop single element selective light reflector/absorber that reflects within the wavelength range corresponding to a PV cell absorption band, while absorbing the remaining solar spectrum. We show that reflecting solar light on a PV cell using a silver mirror is less efficient and has higher temperature compared to using selective light reflector/absorber when using optical concentration exceeding 2 suns. We demonstrate hybrid PV generation and water sanitation/desalination using an Aluminum sheet with thin-film selective light reflector /absorber deposited on one side, while the other side is treated with femtosecond laser to become superwicking.
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