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Linearly Polarized Thermal Emitter for More Efficient Thermophotovoltaic Devices

Iowa State University and Ames Laboratory researchers have developed fabrication methods for a polarized thermal emitter than can be used to create more efficient thermophotovoltaic devices for power generation.
Thermophotovoltaic (TPV) devices can be used to generate power from photons, and consist of a thermal emitter and photodiode. These devices can be used to help overcome limitations of photovoltaic (PV) devices solar cells—since sunlight is composed of many different wavelengths, not all incident photons have an energy larger than the energy band gap (Eg) of the semiconducting material of the photodiode and thus, not all photons can contribute to the photo-current. If the thermal emitter of a TPV can absorb all incoming photons without discrimination and re-emit photons within a narrow range of energy that is optimized for the Eg of the photodiode, in principle, all energy carried by the incident photons can contribute for electricity generation, which leads results in enhanced energy conversion efficiency. While thermal radiation from a thermal source is usually unpolarized, a class of micro-structures termed polarized thermal emitters can emit polarized thermal radiation; polarized thermal emitters avoid the energy loss usually incurred by filtering because they preferentially emit photons via their structural anisotropy, and thus can improve the efficiency of TPVs. ISU and Ames Laboratory researchers have now fabricated layer-by-layer photonic crystals that can be used for linearly polarized thermal emission. This thermal emitter in conjunction with a sub-wavelength grating shows properties that are desirable for polarized thermal emitters for TPVs, including a high extinction ratio and high emissivity. In addition, the emission range can be tuned by controlling the periodicity of the sub-wavelength grating. The linearly polarized thermal emitter may thus have utility for improving the efficiency of TPVs used for power generation.
* Highly polarized thermal emission available at normal emergence * High thermal radiation power * Tunable emission range
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