We report a metamaterial design for a thermophotovoltaic (TPV) emitter. TPVs are similar to photovoltaic solar cells, but they convert heat to electricity instead of sunlight. The focus of this paper is on the emitter stage of the TPV system, which converts the heat into a spectral band which is easily absorbable by the TPV photodiode. The proposed structure consists of a platinum metallic element, an alumina dielectric spacer, and platinum grounding plane on a sapphire substrate. This perfect absorber based metamaterial emitter is shown to robustly operate at 600 °C. This temperature is high enough to enable TPV use for many industrial applications.
Applying thermophotovoltaic (TPV) technologies to existing energy generators allows us to increase energy output while utilizing present infrastructure by reclaiming the heat lost during the production process. In order to maximize the efficiency of these sources, the conversion efficiency of the TPV system needs to be optimized. Selective emitters are often used to tailor the spectrum of incident light on the diode, blocking any undesirable light that may lead to device heating or recombination. Over the years, many different technologies have been researched to create an ideal selective emitter. Plasmas and rare‐earth emitters provided highly selective spectra early on, but their fixed peaks required tailoring the diode's band gap to the emitter's characteristic wavelength. Recent advances in engineerable materials, such as photonic crystals and metamaterials, allow the opposite to take place; an appropriate selective emitter can be designed to match the TPV diode, allowing the diode structure to be optimized independently from the emitter.
The vast majority of power generation in the United States today is produced through the same processes as it was in the late-1800s: heat is applied to water to generate steam, which turns a turbine, which turns a generator, generating electrical power. Researchers today are developing solid-state power generation processes that are more befitting the 21st-century. Thermophotovoltaic (TPV) cells directly convert radiated thermal energy into electrical power, through a process similar to how traditional photovoltaics work. These TPV generators, however, include additional system components that solar cells do not incorporate. These components, selective-emitters and filters, shape the way the radiated heat is transferred into the TPV cell for conversion and are critical for its efficiency. Here, we present a review of work performed to improve the components in these systems. These improvements will help enable TPV generators to be used with nearly any thermal source for both primary power generation and waste heat harvesting.
We report the gain, noise, and dark current characteristics of random alloy Al0.79In0.21As0.74Sb0.26 (hereafter AlInAsSb)-based avalanche photodiodes (APDs) on InP substrates. We observe, at room temperature, a low excess noise corresponding to a k value (ratio of impact ionization coefficients) of 0.018 and a dark current density of 82 μA/cm2 with a gain of 15. These performance metrics represent an order of magnitude improvement of the k-value over commercially available APDs with InAlAs and InP multiplication layers grown on InP substrates. This material is also competitive with a recently reported low noise AlAsSb on InP [Yi et al., Nat. Photonics 13, 683 (2019)], with a comparable excess noise and a room temperature dark current density almost three orders of magnitude lower at the same gain. The low excess noise and dark current of AlInAsSb make it a candidate multiplication layer for integration into a separate absorption, charge, and multiplication layer avalanche photodiode for visible to short-wavelength infrared applications.
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