Photon-enhanced thermionic emission from heterostructures with low interface recombination

Schwede, Jared; Sarmiento, Tomás; Narasimhan, V.; Rosenthal, Samuel; Riley, Daniel C.; Schmitt, Felix; Bargatin, Igor; Sahasrabuddhe, Kunal; Howe, Roger T.; Harris, James S.; Melosh, Nicholas A.; Shen, Zhi‐Xun

doi:10.1038/ncomms2577

Cited by 159 publications

(92 citation statements)

References 32 publications

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“…The PETE effect has been reported for gallium nitride:cesium surfaces and for silicon/ diamond double layer structures (Schwede et al, 2010;Sun et al, 2014). The role of surface and interface recombination has also been explored in III-V heterostructures (Schwede et al, 2013). PETE-like behavior has also been observed in carbon nanotube arrays (Vahdani Moghaddam et al, 2015).…”

Section: Photon-enhanced Thermionic Emission (Pete)mentioning

confidence: 81%

“…The PETE effect for emitters that incorporate a semiconductor absorbing layer, takes advantage of both the total energy of the photon flux and the flux of photons with sufficient energy to excite electrons directly into the conduction band of the emitter (Schwede et al, 2010(Schwede et al, , 2013. The effect provides a substantial enhancement of the emitter current density for moderate temperatures (i.e., at temperatures below the point where pure thermionic emission dominates).…”

Section: Photon-enhanced Thermionic Emission (Pete)mentioning

confidence: 99%

“…The creation of nanostructured emitters that take advantage of the promising properties of nanotubes and nanowires, the development of novel grid structures to minimize space-charge effects (Meir et al, 2013), molecular/ion-enhanced emission (Koeck et al, 2011), and the use of microplasmas (Go and Venkattraman, 2014) are examples of the former, while the use of photon-enhanced thermionic emission (PETE) (Schwede et al, 2010(Schwede et al, , 2013Sun et al, 2014), the efficient light-induced heating of one-dimensional materials through unusual heat localization (Heat Trap), which enable new possibilities for solar thermionics (Yaghoobi et al, 2011(Yaghoobi et al, , 2012, and the combination of the thermionic and tunneling phenomena (the field-emission heat engine) to increase efficiency (Pan et al, 2014), are examples of the latter.…”

Section: New Ideas and Areasmentioning

confidence: 99%

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Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

Haase

George

et al. 2017

Front. Mech. Eng.

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Thermionic energy conversion (TEC) is the direct conversion of heat into electricity by the mechanism of thermionic emission, the spontaneous ejection of hot electrons from a surface. Although the physical mechanism has been known for over a century, it has yet to be consistently realized in a manner practical for large-scale deployment. This perspective article provides an assessment of the potential of TEC systems for space and terrestrial applications in the twenty-first century, overviewing recent advances in the field and identifying key research challenges. Recent developments as well as persisting research needs in materials, device design, fundamental understanding, and testing and validation are discussed.Keywords: thermal energy conversion, thermionic energy conversion, thermionic emission, heat engine, electron emission iNTRODUCTiON The direct conversion of heat to electricity without any intermediate steps or moving parts remains one of the most promising, yet challenging, methods of power production. The promise of high conversion efficiency, device simplicity, and robust operation continues to push research and technology development at the cutting edge. Furthermore, because of the wide variety of possible heat sources, ranging from combustion of fossil or other fuels, nuclear reactors, solar heat, or even waste heat from the human body, the applications for thermal-to-electric energy convertors are vast, spanning many orders of magnitude of possible temperature and power ranges.Thermionic energy conversion (TEC) for direct conversion of heat to electrical energy occurs when electrons thermally emit from a hot surface, traverse a gap, and are collected by another surface. This process, starting with thermionic emission, produces a current of electrons that can subsequently drive an electrical load to produce work. Particularly well suited for high-temperature applications, since it was first proposed by Schlichter (1915), thermionic emission has been pursued as a power generation method for over a century Gyftopoulos, 1973, 1979), yet has seldom been realized in either space or terrestrial applications. However, recent advances in material science and nanotechnology as well as our evolving understanding of the underlying physical processes afford new opportunities to develop practical thermionic convertors, reinvigorating the field. Thermionic energy conversion has a long and storied history, particularly in the space programs of the United States and the former Soviet Union. However, while the field was vibrant and much progress was made during the 1960s through 1980s, including space flight demonstrations, TEC has largely been supplanted by alternative energy conversion technologies, specifically thermoelectrics and photovoltaics, in both the public and research community consciences. Much of thermionic-based research tapered off after a 2001 report by the National Research Council titled Thermionics Quo Vadis? An Assessment of the DTRA's Advanced Thermionics Research and Development Program (Na...

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Section: Photon-enhanced Thermionic Emission (Pete)mentioning

confidence: 81%

Section: Photon-enhanced Thermionic Emission (Pete)mentioning

confidence: 99%

Section: New Ideas and Areasmentioning

confidence: 99%

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Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

Haase

George

et al. 2017

Front. Mech. Eng.

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“…The collector is placed at 500 μm to 1 mm from the emitter, separated by an insulating spacer, instead of a few microns separation as proposed recently in advanced TEC. 16 The very low separation 1 μm is expected to minimize the effect of the space-charge problem but is very tedious to fabricate. However, when the space-charge problem is tackled with a magnetic field and gate, such a low separation will not be needed and a larger separation as high as 1 mm could do.…”

Section: Theoretical Analysis Of Performance Of Solar Thermionic Enermentioning

confidence: 99%

“…4,9,10,[15][16][17] The SLAC/ Stanford University research team is creating a new solid-state energy conversion technology based on microfabricated heterostructure semiconductor cathodes with appropriate band engineering and photon-enhanced thermionic energy converters (PETECs). The microfabrication allows very small gaps (a few microns) between the emitter and the collector and thus reduces the space-charge effect drastically.…”

Section: New Development In Thermionic Energy Conversionmentioning

confidence: 99%

Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector

Olawole

2018

J. Photon. Energy

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, "Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector," J. Photon. Energy 8(1), 018001 (2018), doi: 10.1117/1.JPE.8.018001. Abstract. Thermionic energy conversion (TEC) using nanomaterials is an emerging field of research. It is known that graphene can withstand temperatures as high as 4600 K in vacuum, and it has been shown that its work function can be engineered from a high value (for monolayer/ bilayer) of 4.6 eV to as low as 0.7 eV. Such attractive electronic properties (e.g., good electrical conductivity and high dielectric constant) make engineered graphene a good candidate as an emitter and collector in a thermionic energy converter for harnessing solar energy efficiently. We have used a modified Richardson-Dushman equation and have adopted a model where the collector temperature could be controlled through heat extraction in a calculated amount and a magnet can be attached on the back surface of the collector for future control of the spacecharge effect. Our work shows that the efficiency of solar energy conversion also depends on power density falling on the emitter surface, and that a power conversion efficiency of graphenebased solar TEC as high as 55% can be easily achieved (in the absence of the space-charge effect) through proper choice of work functions, collector temperature, and emissivity of emitter surfaces. Such solar energy conversion would reduce our dependence on silicon solar panels and offers great potential for future renewable energy utilization. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Understanding and Controlling the Work Function of Perovskite Oxides Using Density Functional Theory

Jacobs

Booske

Morgan

2016

Adv Funct Materials

152

116

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Perovskite oxides containing transition metals are promising materials in a wide range of electronic and electrochemical applications. However, neither their work function values nor an understanding of their work function physics have been established. Here, we predict the work function trends of a series of perovskite (ABO 3 formula) materials using Density Functional Theory, and show that the work functions of (001)-terminated AO-and BO 2 -oriented surfaces can be described using concepts of electronic band filling, bond hybridization, and surface dipoles. The calculated range of AO (BO 2 ) work functions are 1.60-3.57 eV (2.99-6.87 eV). We find an approximately linear correlation (R 2 between 0.77-0.86, depending on surface termination) between work function and position of the oxygen 2p band center, which correlation enables both understanding and rapid prediction of work function trends. Furthermore, we identify SrVO 3 as a stable, low work function, highly conductive material. Undoped (Ba-doped) SrVO 3 has an intrinsically low AO-terminated work function of 1.86 eV (1.07 eV). These properties make SrVO 3 a promising candidate material for a new electron emission cathode for application in high power microwave devices, and as a potential electron emissive material for thermionic energy conversion technologies.2

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Photon-enhanced thermionic emission from heterostructures with low interface recombination

Cited by 159 publications

References 32 publications

Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector

Understanding and Controlling the Work Function of Perovskite Oxides Using Density Functional Theory

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