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Journal ArticleDOI

Thermoelectric Cooling and Power Generation

30 Jul 1999-Science (American Association for the Advancement of Science)-Vol. 285, Iss: 5428, pp 703-706
TL;DR: Improved materials would not only help to cool advanced electronics but could also provide energy benefits in refrigeration and when using waste heat to generate electrical power.
Abstract: In a typical thermoelectric device, a junction is formed from two different conducting materials, one containing positive charge carriers (holes) and the other negative charge carriers (electrons). When an electric current is passed in the appropriate direction through the junction, both types of charge carriers move away from the junction and convey heat away, thus cooling the junction. Similarly, a heat source at the junction causes carriers to flow away from the junction, making an electrical generator. Such devices have the advantage of containing no moving parts, but low efficiencies have limited their use to specialty applications, such as cooling laser diodes. The principles of thermoelectric devices are reviewed and strategies for increasing the efficiency of novel materials are explored. Improved materials would not only help to cool advanced electronics but could also provide energy benefits in refrigeration and when using waste heat to generate electrical power.
Citations
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Journal ArticleDOI
TL;DR: A new era of complex thermoelectric materials is approaching because of modern synthesis and characterization techniques, particularly for nanoscale materials, and the strategies used to improve the thermopower and reduce the thermal conductivity are reviewed.
Abstract: Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.

8,999 citations


Cites background or methods from "Thermoelectric Cooling and Power Ge..."

  • ...Accurate assessment of κe is important, as κl is often computed as the difference between κ and κe (equation (3)) using the experimental electrical conductivity....

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  • ...(1) (3) Carrier concentration (cm−3) 0 0....

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  • ...The reoptimized zT is shown at point (3)....

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Journal ArticleDOI
12 Sep 2008-Science
TL;DR: Thermoelectric materials are solid-state energy converters whose combination of thermal, electrical, and semiconductor properties allows them to be used to convert waste heat into electricity or electrical power directly into cooling and heating.
Abstract: Thermoelectric materials are solid-state energy converters whose combination of thermal, electrical, and semiconducting properties allows them to be used to convert waste heat into electricity or electrical power directly into cooling and heating. These materials can be competitive with fluid-based systems, such as two-phase air-conditioning compressors or heat pumps, or used in smaller-scale applications such as in automobile seats, night-vision systems, and electrical-enclosure cooling. More widespread use of thermoelectrics requires not only improving the intrinsic energy-conversion efficiency of the materials but also implementing recent advancements in system architecture. These principles are illustrated with several proven and potential applications of thermoelectrics.

4,700 citations

Journal ArticleDOI
TL;DR: In this paper, an angle-resolved photo-emission spectroscopy study was conducted to reveal the first observation of a topological state of matter featuring a single surface Dirac cone realized in the naturally occurring Bi-2Se-3 class of materials.
Abstract: Recent experiments and theories have suggested that strong spin–orbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topological insulator, which can show macroscopic quantum-entanglement effects. Such systems feature two-dimensional surface states whose electrodynamic properties are described not by the conventional Maxwell equations but rather by an attached axion field, originally proposed to describe interacting quarks. It has been proposed that a topological insulator with a single Dirac cone interfaced with a superconductor can form the most elementary unit for performing fault-tolerant quantum computation. Here we present an angle-resolved photoemission spectroscopy study that reveals the first observation of such a topological state of matter featuring a single surface Dirac cone realized in the naturally occurring Bi_2Se_3 class of materials. Our results, supported by our theoretical calculations, demonstrate that undoped Bi_2Se_3 can serve as the parent matrix compound for the long-sought topological device where in-plane carrier transport would have a purely quantum topological origin. Our study further suggests that the undoped compound reached via n-to-p doping should show topological transport phenomena even at room temperature.

3,006 citations


Cites background from "Thermoelectric Cooling and Power Ge..."

  • ...The undoped Bi 2 Se 3 is a semiconductor that belongs to the class of thermoelectric materials Bi 2 X 3 with a rhombohedral crystal structure (space group ; refs&nbs...

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Journal ArticleDOI
05 May 2011-Nature
TL;DR: It is demonstrated that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition, leading to an extraordinary zT value of 1.8 at about 850 kelvin.
Abstract: Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems—such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known, that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe_(1) − _(x)Se_(x) alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.

2,964 citations

Journal ArticleDOI
02 Jan 2015-Science
TL;DR: Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices.
Abstract: Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.

2,850 citations


Cites background from "Thermoelectric Cooling and Power Ge..."

  • ...The majority of explored materials in thermoelectric devices have zT ~ 1 (69)....

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  • ...LMs such as Bi2Te3, PbTe, and their alloys (29) and, in particular, the (Bi1–xSbx)2(Se1–yTey)3 alloy family have been in commercial use for several decades because of their room-temperature zT ~ 1 and Carnot conversion efficiencies ~5 to 6% (69)....

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  • ...In order to optimize zT, phonons must experience a high scattering rate, thus lowering thermal conductivity [like in a glass (69, 70)], whereas electrons must experience very little scattering, maintaining high electric conductivity (as in a crystal) (70)....

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  • ...The effectiveness of a thermoelectric device is assessed in twoways: by its Carnot efficiency (the fraction of absorbed heat that is converted into work) and by a material-dependent figure of merit, known as zT; zT = TS2s/k (69), where S is the Seebeck coefficient, T is the temperature, s is the electric conductivity, k is the thermal conductivity, and z = S2s/k (69)....

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  • ...Thus, thermoelectric materials require high S and s and low k (69)....

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References
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Journal ArticleDOI
TL;DR: In this paper, a model of the thermal conductivity and phonon transport in the direction perpendicular to the film plane of superlattices is established based on solving the phonon Boltzmann transport equation (BTE).
Abstract: Significant reductions in both the in-plane and cross-plane thermal conductivities of superlattices, in comparison to the values calculated from the Fourier heat conduction theory using bulk material properties, have been observed experimentally in recent years. Understanding the mechanisms controlling the thermal conductivities of superlattice structures is of considerable current interest for microelectronic and thermoelectric applications. In this work, models of the thermal conductivity and phonon transport in the direction perpendicular to the film plane of superlattices are established based on solving the phonon Boltzmann transport equation (BTE). Different phonon interface scattering mechanisms are considered, including elastic vs inelastic, and diffuse vs specular scattering of phonons. Numerical solution of the BTE yields the effective temperature distribution, thermal conductivity, and thermal boundary resistance (TBR) of the superlattices. The modeling results show that the effective thermal conductivity of superlattices in the perpendicular direction is generally controlled by phonon transport within each layer and the TBR between different layers. The TBR is no longer an intrinsic property of the interface, but depends on the layer thickness as well as the phonon mean free path. In the thin layer limit, phonon transport within each layer is ballistic, and the TBR dominates the effective thermal conductivity of superlattices. Approximate analytical solutions of the BTE are obtained for this thin-film limit. The modeling results based on partially specular and partially diffuse interface scattering processes are in reasonable agreement with recent experimental data on GaAs/AlAs and Si/Ge superlattices. From the modeling, it is concluded that the cross-plane thermal conductivity of these superlattices is controlled by diffuse and inelastic scattering processes at interfaces. Results of this work suggest that it is possible to make superlattice structures with thermal conductivity totally different from those of their constituting materials.

1,032 citations

Journal ArticleDOI
TL;DR: In this article, it has been shown theoretically that it may be possible to increase the thermoelectric figure of merit (Z$) of certain materials by preparing them in the form of two-dimensional quantum-well structures.
Abstract: Recently, it has been shown theoretically that it may be possible to increase the thermoelectric figure of merit ($Z$) of certain materials by preparing them in the form of two-dimensional quantum-well structures. Using $\mathrm{PbTe}/{\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{Te}$ multiple-quantum-well structures grown by molecular-beam epitaxy, we have performed thermoelectric and other transport measurements as a function of quantum-well thickness and doping. Our results are found to be consistent with theoretical predictions and indicate that an increase in $Z$ over bulk values may be possible through quantum confinement effects using quantum-well structures.

702 citations

Journal ArticleDOI
05 Feb 1999-Science
TL;DR: The thermoelectric materials have been investigated with the goal of maximizing electrical conductivity while minimizing thermal conductivity, which is required for good thermal performance as discussed by the authors, and the results suggest that important further improvements are on the horizon with promising applications in the computer and other high-tech industries.
Abstract: Thermoelectric materials, which have applications in refrigeration and power generation, are experiencing a surge in research activity. Many different materials are investigated with the goal of maximizing electrical conductivity while minimizing thermal conductivity, which is required for good thermoelectric performance. Only recently was a 30-year deadlock in thermoelectric performance overcome. Predictions for the new materials suggest that important further improvements are on the horizon, with promising applications in the computer and other high-tech industries.

680 citations

Journal ArticleDOI
TL;DR: In this paper, the expression for the figure of merit of a semi-conductor of given carrier mobility and lattice thermal conductivity expressed in terms of generalized Fermi-Dirae functions has been numerically evaluated for various scattering indices.
Abstract: The expression for the figure of merit of a semi-conductor of given carrier mobility and lattice thermal conductivity expressed in terms of generalized Fermi-Dirae functions has been numerically evaluated for various scattering indices. The results are presented graphically enabling the maximum figure of merit to be found. High-temperature limitations due to minority carrier production are considered in relation to the energy gap of the semi-conductor. The results are discussed in connection with bismuth telluride and other sulphides, selenides and telluridos of the heavy metals.

312 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the thermoelectric figure of merit is strongly enhanced in quantum wells and superlattices due to two-dimensional carrier confinement, which leads to an increase of the phonon relaxation rates and a significant drop in the lattice thermal conductivity.
Abstract: Recently, it has been shown that the thermoelectric figure of merit is strongly enhanced in quantum wells and superlattices due to two-dimensional carrier confinement. We predict that the figure of merit can increase even further in quantum well structures with free-surface or rigid boundaries. This additional increase is due to spatial confinement of acoustic phonons and corresponding modification of their group velocities. The latter leads to an increase of the phonon relaxation rates and thus, a significant drop in the lattice thermal conductivity.

230 citations