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Improved Thermal Emitters for Thermophotovoltaic Energy Conversion
| Content Provider | Semantic Scholar |
|---|---|
| Author | Stelmakh, Veronika Chan, Walker R. |
| Copyright Year | 2015 |
| Abstract | Thermophotovoltaic (TPV) energy conversion enables millimeter scale power generation required for portable microelectronics, robotics, etc. In a TPV system, a heat source heats a selective emitter to incandescence, the radiation from which is incident on a low bandgap TPV cell. The selective emitter tailors the photonic density of states to produce spectrally confined selective emission of light matching the bandgap of the photovoltaic cell, enabling high heat-to-electricity conversion efficiency. The selective emitter requires: thermal stability at high-temperatures for long operational lifetimes, simple and relatively low-cost fabrication, as well as spectrally selective emission over a large uniform area. Generally, the selective emission can either originate from the natural material properties, such as in ytterbia or erbia emitters, or can be engineered through microstructuring. Our approach, the 2D photonic crystal fabricated in refractory metals, offers high spectral selectivity and high-temperature stability while being fabricated by standard semiconductor processes. In this work, we present a brief comparison of TPV system efficiencies using these different emitter technologies. We then focus on the design, fabrication, and characterization of our current 2D photonic crystal, which is a square lattice of cylindrical holes fabricated in a refractory metal substrate. The spectral performance and thermal stability of the fabricated photonic crystal thermal emitters are demonstrated and the efficiency gain of our model TPV system is characterized. ∗Address all correspondence to this author INTRODUCTION The increasing power demands of communication equipment, sensors, micro robotics platforms, and portable electronics has driven recent interest in microand millimeter-scale generators. Thermophotovoltaic (TPV) energy conversion is one approach to harness the high specific energy of hydrocarbon fuels [1–3]. In a TPV system, combustion heats an emitter to incandescence and the resulting thermal radiation is converted to electricity by a low-bandgap TPV cell. The difference between a solar photovoltaic system and a TPV system is that a TPV system produces its own light—the spectrum does not need to be the solar spectrum or even blackbody and the cells do not need to be silicon. The selective emitter however is the crucial component of any practical TPV system. One of the key challenges of TPV is making efficient use of the thermal radiation by matching the thermal radiation spectrum to the quantum efficiency of the TPV cell. The TPV cell can convert in-band radiation (photon energies above its bandgap) reasonably efficiently to electricity but out-of-band (photon energies below its bandgap) radiation is wasted. This spectral matching can be accomplished using a selective emitter (either natural or engineered) that strongly emits at some wavelengths and weakly emits at others, using a cold side filter that transmits some wavelengths to the cell and reflects others back to the selective emitter, or using both. However cold side filters require a low loss emitter-filter-cell optical cavity, which is difficult to achieve in a practical system. Natural emitters tend to have low overall emissivity, allowing parasitic heat loss mechanisms to dominate the Proceedings of the ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer MNHMT2016 January 4-6, 2016, Biopolis, Singapore |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://dspace.mit.edu/openaccess-disseminate/1721.1/109185 |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Body cavities Efficiency Emitter Device Component Energy, Physics Heat (physical force) Hydrocarbons Incandescence Lambert's cosine law MATCHING Metals Mobile computing Out-of-band agreement Parasites Photons Robotics Selectivity (electronic) Semiconductor Silicon Solar cell millimeter sensor (device) wavelength |
| Content Type | Text |
| Resource Type | Article |
