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Solar-thermal energy conversion can be useful in many applications, including water desalination, and thermal energy storage. In this regard, using spectrally-selective solar absorbers is vital due to their high solar absorptance and low thermal emittance. While selective absorbers can be created using a wide range of nanomaterials, the underlying geometry may control the overall performance of solar-thermal energy conversion. With different geometries, it is possible to obtain a wide range of optical responses ranging from broadband to selective absorption of light. In this study, we focus on the role of nanostructure morphology of nickel-infused alumina (Ni/NPA) based spectrally-selective solar absorbers. This study demonstrates the use of the design of experiments to analyze the effect of various geometric factors on the resulting optical response of Ni/NPA in the context of solar-thermal energy conversion. We show how this approach can provide a unique insight into the role of various geometric factors on the solar absorptance and thermal emittance of Ni/NPA-based absorbers, and demonstrate how it can guide the development of spectrally-selective materials. We believe a similar approach can be useful in the development of other optical materials for different applications. 

Thermophotovoltaics (TPVs) are a potential technology for waste-heat recovery applications and utilize IR sensitive photovoltaic diodes to convert long wavelength photons (>800nm) into electrical energy. The most common conversion regions utilize Gallium Antimonide (GaSb) as the standard semiconductor system for TPV diodes due to its high internal quantum efficiencies (close to 90%) for infrared radiation (~1700nm). However, parasitic losses prevent high conversion efficiencies from being achieved in the final device. One possible avenue to improve the conversion efficiency of these devices is to incorporate metallic photonic crystals (MPhCs) onto the front surface of the diode. In this work, we study the effect of MPhCs on GaSb TPV diodes. Simulations are presented which characterize a specific MPhC design for use with GaSb. E-field intensity vs. wavelength and depth are investigated as well as the effect of the thickness of the PhC on the interaction time between the e-field and semiconductor. It is shown that the thickness of MPhC has little effect on width of the enhancement band, and the depth the ideal p-i-n junction is between 0.6􀈝m and 2.1um. Additionally, simulated results demonstrate an increase of E-field/semiconductor interaction time of approximately 40% and 46% for a MPhC thickness of 350nm and 450nm respectively.