Toward high-energy-density, high-efficiency, and moderate-temperature chip-scale thermophotovoltaics

Research Laboratory of Electronics, Institute for Soldier Nanotechnologies, Department of Physics, Center for Materials Science and Engineering, and Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 02/2013; 110(14). DOI: 10.1073/pnas.1301004110
Source: PubMed


The challenging problem of ultra-high-energy-density, high-efficiency, and small-scale portable power generation is addressed here using a distinctive thermophotovoltaic energy conversion mechanism and chip-based system design, which we name the microthermophotovoltaic (μTPV) generator. The approach is predicted to be capable of up to 32% efficient heat-to-electricity conversion within a millimeter-scale form factor. Although considerable technological barriers need to be overcome to reach full performance, we have performed a robust experimental demonstration that validates the theoretical framework and the key system components. Even with a much-simplified μTPV system design with theoretical efficiency prediction of 2.7%, we experimentally demonstrate 2.5% efficiency. The μTPV experimental system that was built and tested comprises a silicon propane microcombustor, an integrated high-temperature photonic crystal selective thermal emitter, four 0.55-eV GaInAsSb thermophotovoltaic diodes, and an ultra-high-efficiency maximum power-point tracking power electronics converter. The system was demonstrated to operate up to 800 °C (silicon microcombustor temperature) with an input thermal power of 13.7 W, generating 344 mW of electric power over a 1-cm(2) area.

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Available from: Ivan Celanovic, Jan 03, 2014
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    • "The low experimental overall efficiency is mostly due to low TPV conversion efficiency (radiator to electricity) [4] [10] [11]. In particular, Datas and Algora [11] pointed out that the low TPV conversion efficiency is largely caused by thermal losses leading to an overheating of the cell. "
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    ABSTRACT: Optimal radiator thermal emission spectra maximizing thermophotovoltaic (TPV) conversion efficiency and output power density are determined when temperature effects in the cell are considered. To do this, a framework is designed in which a TPV model that accounts for radiative, electrical and thermal losses is coupled with a genetic algorithm. The TPV device under study involves a spectrally selective radiator at a temperature of 2000 K, a gallium antimonide cell, and a cell thermal management system characterized by a fluid temperature and a heat transfer coefficient of 293 K and 600 Wm-2K-1. It is shown that a maximum conversion efficiency of 38.8% is achievable with an emission spectrum that has emissivity of unity between 0.719 eV and 0.763 eV and zero elsewhere. This optimal spectrum is less than half of the width of those when thermal losses are neglected. A maximum output power density of 41708 Wm-2 is achievable with a spectrum having emissivity values of unity between 0.684 eV and 1.082 eV and zero elsewhere when thermal losses are accounted for. These emission spectra are shown to greatly outperform blackbody and tungsten radiators, and could be obtained using artificial structures such as metamaterials or photonic crystals.
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    ABSTRACT: Narrow-bandgap (<0.25 eV) photovoltaic (PV) devices are demonstrated at room temperature and above. These PV devices are based on interband cascade (IC) structures and can achieve a high open-circuit voltage (∼0.65 V at 300 K) that significantly exceeds the single bandgap limited value. This work demonstrates the capabilities and advantages of ICPV devices designed to effectively convert long wavelength (>5 μm) infrared photons from relatively low-temperature radiation sources (<1000 K) into electricity. Detailed characteristics of these PV devices are presented and discussed.
    Applied Physics Letters 03/2013; 102(21). DOI:10.1063/1.4807938 · 3.30 Impact Factor
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    ABSTRACT: We present the results of extensive characterization of selective emitters at high temperatures, including thermal emission measurements and thermal stability testing at 1000°C for 1h and 900°C for up to 144h. The selective emitters were fabricated as 2D photonic crystals (PhCs) on polycrystalline tantalum (Ta), targeting large-area applications in solid-state heat-to-electricity conversion. We characterized spectral emission as a function of temperature, observing very good selectivity of the emission as compared to flat Ta, with the emission of the PhC approaching the blackbody limit below the target cut-off wavelength of 2 μm, and a steep cut-off to low emission at longer wavelengths. In addition, we study the use of a thin, conformal layer (20 nm) of HfO<sub>2</sub> deposited by atomic layer deposition (ALD) as a surface protective coating, and confirm experimentally that it acts as a diffusion inhibitor and thermal barrier coating, and prevents the formation of Ta carbide on the surface. Furthermore, we tested the thermal stability of the nanostructured emitters and their optical properties before and after annealing, observing no degradation even after 144h (6 days) at 900°C, which demonstrates the suitability of these selective emitters for high-temperature applications.
    Optics Express 05/2013; 21(9):11482-91. DOI:10.1364/OE.21.011482 · 3.49 Impact Factor
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