Showing papers on "Thermoelectric effect published in 2020"

Advanced Thermoelectric Design: From Materials and Structures to Devices

Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Thermosensitive crystallization-boosted liquid thermocells for low-grade heat harvesting.

Abstract: Low-grade heat (below 373 K) is abundant and ubiquitous, but mostly wasted due to the lack of cost-effective recovery technologies. The liquid-state thermocell (LTC), an inexpensive and scalable thermoelectric device, may be commercially viable for harvesting low-grade heat energy if its Carnot-relative efficiency (ηr) reaches ~5%, which is a challenging metric to achieve experimentally. We used a thermosensitive crystallization and dissolution process to induce persistent concentration gradient of redox ions, a highly enhanced Seebeck coefficient (~3.73 mV K–1), and suppressed thermal conductivity in LTCs. As a result, we achieved a high ηr of 11% for LTCs near room temperature, and a substantially decreased cost-performance of our LTC. Our device demonstration offers promise for cost-effective low-grade heat harvesting.

Recent Progress of Two-Dimensional Thermoelectric Materials

Abstract: Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power. Moreover, the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades. Among these compounds, layered two-dimensional (2D) materials, such as graphene, black phosphorus, transition metal dichalcogenides, IVA–VIA compounds, and MXenes, have generated a large research attention as a group of potentially high-performance thermoelectric materials. Due to their unique electronic, mechanical, thermal, and optoelectronic properties, thermoelectric devices based on such materials can be applied in a variety of applications. Herein, a comprehensive review on the development of 2D materials for thermoelectric applications, as well as theoretical simulations and experimental preparation, is presented. In addition, nanodevice and new applications of 2D thermoelectric materials are also introduced. At last, current challenges are discussed and several prospects in this field are proposed.

Stretchable fabric generates electric power from woven thermoelectric fibers.

Abstract: Assembling thermoelectric modules into fabric to harvest energy from body heat could one day power multitudinous wearable electronics. However, the invalid 2D architecture of fabric limits the application in thermoelectrics. Here, we make the valid thermoelectric fabric woven out of thermoelectric fibers producing an unobtrusive working thermoelectric module. Alternately doped carbon nanotube fibers wrapped with acrylic fibers are woven into π-type thermoelectric modules. Utilizing elasticity originating from interlocked thermoelectric modules, stretchable 3D thermoelectric generators without substrate can be made to enable sufficient alignment with the heat flow direction. The textile generator shows a peak power density of 70 mWm−2 for a temperature difference of 44 K and excellent stretchability (~80% strain) with no output degradation. The compatibility between body movement and sustained power supply is further displayed. The generators described here are true textiles, proving active thermoelectrics can be woven into various fabric architectures for sensing, energy harvesting, or thermal management. Despite recent advances in flexible thermoelectric generators for wearable devices, current designs are unable to efficiently harvest heat flowing from human body. Here, the authors report high thermoelectric performance and stretchability in interlocked fiber-based modules for wearable devices.

Realizing record high performance in n-type Bi2Te3-based thermoelectric materials

Abstract: The application of Bi2Te3-based power generation is seriously hindered by the poor n-type samples, demonstrating a strong demand for high-performance n-type Bi2Te3-based thermoelectric (TE) materials. However, the strong relationship between thermal and electrical transport limits the improvement of the TE properties. Here, we propose a strategy to enhance the Seebeck coefficient while retaining a large electrical conductivity in n-type (Bi,Sb)2(Te,Se)3 materials through introducing electron transport potential wells and texturing. The thermal conductivity was also successfully decreased by constructing multi-scale phonon scattering structures. Consequently, a record maximum and average thermoelectric figure of merit (ZT) of ∼1.4 and ∼1.3 were achieved in the Bi1.8Sb0.2Te2.7Se0.3 + 15 wt% Te sample at a temperature of 300–575 K. A TE power generation module was fabricated with this n-type material and a home-made p-type Bi2Te3 sample. It demonstrated a record conversion efficiency of 6.6% at a temperature gradient of 235 K, representing about an 88% improvement compared with a commercial zone-melt Bi2Te3-based module.

Promising and Eco-Friendly Cu 2 X-Based Thermoelectric Materials: Progress and Applications

Abstract: Due to the nature of their liquid-like behavior and high dimensionless figure of merit, Cu2 X (X = Te, Se, and S)-based thermoelectric materials have attracted extensive attention. The superionicity and Cu disorder at the high temperature can dramatically affect the electronic structure of Cu2 X and in turn result in temperature-dependent carrier-transport properties. Here, the effective strategies in enhancing the thermoelectric performance of Cu2 X-based thermoelectric materials are summarized, in which the proper optimization of carrier concentration and minimization of the lattice thermal conductivity are the main focus. Then, the stabilities, mechanical properties, and module assembly of Cu2 X-based thermoelectric materials are investigated. Finally, the future directions for further improving the energy conversion efficiency of Cu2 X-based thermoelectric materials are highlighted.

High-Performance GeTe-Based Thermoelectrics: from Materials to Devices

Abstract: High-performance GeTe-based thermoelectrics have been recently attracting growing research interest. Here, an overview is presented of the structural and electronic band characteristics of GeTe. Intrinsically, compared to low-temperature rhombohedral GeTe, the high-symmetry and high-temperature cubic GeTe has a low energy offset between L and sigma points of the valence band, the reduced direct bandgap and phonon group velocity, and as a result, high thermoelectric performance. Moreover, their thermoelectric performance can be effectively enhanced through either carrier concentration optimization, band structure engineering (bandgap reduction, band degeneracy, and resonant state engineering), or restrained lattice thermal conductivity (phonon velocity reduction or phonon scattering). Consequently, the dimensionless figure of merit, ZT values, of GeTe-based thermoelectric materials can be higher than 2. The mechanical and thermal stabilities of GeTe-based thermoelectrics are highlighted, and it is found that they are suitable for practical thermoelectric applications except for their high cost. Finally, it is recognized that the performance of GeTe-based materials can be further enhanced through synergistic effects. Additionally, proper material selection and module design can further boost the energy conversion efficiency of GeTe-based thermoelectrics.

Review of current high-ZT thermoelectric materials

Abstract: Thermoelectric materials are capable of converting heat and electricity to each other Thermoelectric devices can be miniaturized and highly integrated with existing semiconductor chip systems with microgenerators or microrefrigerators After years of research and accumulation, BiTe series, SnSe series, CuSe series, half-Heusler series, multicomponent oxides series, organic–inorganic composites series, and GeTe/PbTe series have been found to have excellent thermoelectric properties According to theoretical calculation, when the diameter of Bi2Te3 nanowires is 5 A, the ZT value reaches 14, and graphdiyne has a ZT value of 48 at 300 K Experimental measurements revealed that the ZT value of n-type SnSe reached 28 This review would focus on the updated experimental and theoretical achievements of seven kinds of materials, including BiTe series, SnSe series, CuSe series, multicomponent oxides, half-Heusler alloys, organic–inorganic composites, and GeTe/PbTe series The preparation method, microstructure characteristics, device structure, and thermoelectric properties of each material will be described in detail By analyzing the performance of these materials, three possible development directions are put forward for how to further improve the thermoelectric properties of materials

Iron-based binary ferromagnets for transverse thermoelectric conversion

Abstract: Thermoelectric generation using the anomalous Nernst effect (ANE) has great potential for application in energy harvesting technology because the transverse geometry of the Nernst effect should enable efficient, large-area and flexible coverage of a heat source. For such applications to be viable, substantial improvements will be necessary not only for their performance but also for the associated material costs, safety and stability. In terms of the electronic structure, the anomalous Nernst effect (ANE) originates from the Berry curvature of the conduction electrons near the Fermi energy1,2. To design a large Berry curvature, several approaches have been considered using nodal points and lines in momentum space3–10. Here we perform a high-throughput computational search and find that 25 percent doping of aluminium and gallium in alpha iron, a naturally abundant and low-cost element, dramatically enhances the ANE by a factor of more than ten, reaching about 4 and 6 microvolts per kelvin at room temperature, respectively, close to the highest value reported so far. The comparison between experiment and theory indicates that the Fermi energy tuning to the nodal web—a flat band structure made of interconnected nodal lines—is the key for the strong enhancement in the transverse thermoelectric coefficient, reaching a value of about 5 amperes per kelvin per metre with a logarithmic temperature dependence. We have also succeeded in fabricating thin films that exhibit a large ANE at zero field, which could be suitable for designing low-cost, flexible microelectronic thermoelectric generators11–13. Aluminium- and gallium-doped iron compounds show a large anomalous Nernst effect owing to a topological electronic structure, and their films are potentially suitable for designing low-cost, flexible microelectronic thermoelectric generators.

High-Performance Thermoelectric SnSe: Aqueous Synthesis, Innovations, and Challenges

Abstract: Tin selenide (SnSe) is one of the most promising candidates to realize environmentally friendly, cost-effective, and high-performance thermoelectrics, derived from its outstanding electrical transport properties by appropriate bandgaps and intrinsic low lattice thermal conductivity from its anharmonic layered structure. Advanced aqueous synthesis possesses various unique advantages including convenient morphology control, exceptional high doping solubility, and distinctive vacancy engineering. Considering that there is an urgent demand for a comprehensive survey on the aqueous synthesis technique applied to thermoelectric SnSe, herein, a thorough overview of aqueous synthesis, characterization, and thermoelectric performance in SnSe is provided. New insights into the aqueous synthesis-based strategies for improving the performance are provided, including vacancy synergy, crystallization design, solubility breakthrough, and local lattice imperfection engineering, and an attempt to build the inherent links between the aqueous synthesis-induced structural characteristics and the excellent thermoelectric performance is presented. Furthermore, the significant advantages and potentials of an aqueous synthesis route for fabricating SnSe-based 2D thermoelectric generators, including nanorods, nanobelts, and nanosheets, are also discussed. Finally, the controversy, strategy, and outlook toward future enhancement of SnSe-based thermoelectric materials are also provided. This Review guides the design of thermoelectric SnSe with high performance and provides new perspectives as a reference for other thermoelectric systems.

High-performance compliant thermoelectric generators with magnetically self-assembled soft heat conductors for self-powered wearable electronics.

Abstract: Softening of thermoelectric generators facilitates conformal contact with arbitrary-shaped heat sources, which offers an opportunity to realize self-powered wearable applications. However, existing wearable thermoelectric devices inevitably exhibit reduced thermoelectric conversion efficiency due to the parasitic heat loss in high-thermal-impedance polymer substrates and poor thermal contact arising from rigid interconnects. Here, we propose compliant thermoelectric generators with intrinsically stretchable interconnects and soft heat conductors that achieve high thermoelectric performance and unprecedented conformability simultaneously. The silver-nanowire-based soft electrodes interconnect bismuth-telluride-based thermoelectric legs, effectively absorbing strain energy, which allows our thermoelectric generators to conform perfectly to curved surfaces. Metal particles magnetically self-assembled in elastomeric substrates form soft heat conductors that significantly enhance the heat transfer to the thermoelectric legs, thereby maximizing energy conversion efficiency on three-dimensional heat sources. Moreover, automated additive manufacturing paves the way for realizing self-powered wearable applications comprising hundreds of thermoelectric legs with high customizability under ambient conditions.

Ultrahigh power factor and flexible silver selenide-based composite film for thermoelectric devices

Abstract: Herein, an n-type Ag2Se/Ag/CuAgSe thermoelectric (TE) composite film supported by a porous nylon membrane with a record power factor (2231.5 μW m−1 K−2 at 300 K) is obtained via a simple approach. The ultrahigh power factor mainly originates from the optimized carrier transport of the composite material and the interfacial energy filtration effect. HAADF-STEM observations of a focused ion beam (FIB) prepared sample reveal that the Ag and CuAgSe in the composite exist as nanoparticles and most of the Ag nanoparticles and CuAgSe nanoparticles are randomly distributed at the surfaces and grain boundaries of the Ag2Se grains. Bending tests demonstrate superior flexibility of the hybrid film and the power factor decreases by only 10% after bending for 1000 cycles along a rod with a radius of 4 mm. The excellent flexibility is attributed to a synergetic effect of the nanocomposite film with numerous submicron-sized pores and the flexible nylon membrane. A flexible TE module is assembled using the optimum hybrid film, which generates an outstanding power density of 5.42 W m−2 at a temperature difference of 45 K. This work not only demonstrates the tremendous potential of inorganic TE materials for flexible application, but also provides an effective strategy to design high-performance TE composites.

A Review on Thermoelectric Generators: Progress and Applications

Abstract: A thermoelectric effect is a physical phenomenon consisting of the direct conversion of heat into electrical energy (Seebeck effect) or inversely from electrical current into heat (Peltier effect) without moving mechanical parts. The low efficiency of thermoelectric devices has limited their applications to certain areas, such as refrigeration, heat recovery, power generation and renewable energy. However, for specific applications like space probes, laboratory equipment and medical applications, where cost and efficiency are not as important as availability, reliability and predictability, thermoelectricity offers noteworthy potential. The challenge of making thermoelectricity a future leader in waste heat recovery and renewable energy is intensified by the integration of nanotechnology. In this review, state-of-the-art thermoelectric generators, applications and recent progress are reported. Fundamental knowledge of the thermoelectric effect, basic laws, and parameters affecting the efficiency of conventional and new thermoelectric materials are discussed. The applications of thermoelectricity are grouped into three main domains. The first group deals with the use of heat emitted from a radioisotope to supply electricity to various devices. In this group, space exploration was the only application for which thermoelectricity was successful. In the second group, a natural heat source could prove useful for producing electricity, but as thermoelectricity is still at an initial phase because of low conversion efficiency, applications are still at laboratory level. The third group is progressing at a high speed, mainly because the investigations are funded by governments and/or car manufacturers, with the final aim of reducing vehicle fuel consumption and ultimately mitigating the effect of greenhouse gas emissions.

All-Inorganic Halide Perovskites as Potential Thermoelectric Materials: Dynamic Cation off-Centering Induces Ultralow Thermal Conductivity.

Abstract: Halide perovskites are anticipated to impact next generation high performance solar cells because of their extraordinary charge transport and optoelectronic properties. However, their thermal transport behavior has received limited attention. In this work, we studied the thermal transport and thermoelectric properties of the CsSnBr3-xIx perovskites. We find a strong correlation between lattice dynamics and an ultralow thermal conductivity for series CsSnBr3-xIx reaching 0.32 Wm-1K-1 at 550 K. The CsSnBr3-xIx also possess a decent Seebeck coefficient and controllable electrical transport properties. The crystallography data and theoretical calculations suggest the Cs atom deviates from its ideal cuboctahedral geometry imposed by the perovskite cage and behaves as a heavy atom rattling oscillator. This off-center tendency of Cs, together with the distortion of SnX6 (X = Br or I) octahedra, produces a highly dynamic and disordered structure in CsSnBr3-xIx, which gives rise to a very low Debye temperature and phonon velocity. Moreover, the low temperature heat capacity data suggests strong coupling between the low frequency optical phonons and heat carrying acoustical phonons. This induces strong phonon resonance scattering that induces the ultralow lattice thermal conductivity of CsSnBr3-xIx.

Establishing the Golden Range of Seebeck Coefficient for Maximizing Thermoelectric Performance.

Abstract: The coupling nature of thermoelectric properties determines that optimizing the Fermi level is the priority to achieve a net increase in thermoelectric performance. Conventionally, the carrier concentration is used as the reflection of the Fermi level in the band structure. However, carrier concentration strongly depends upon the material’s effective mass, leading to that the optimal carrier concentration varies over a large scale for different materials. Herein, inspired by the big data survey, we develop a golden Seebeck coefficient range of 202–230 μV K–1 for thermoelectric semiconductors with lattice thermal conductivity of 0.4–1.5 W m–1 K–1. When the measured Seebeck coefficient reaches this range, the corresponding figure of merit is maximized. Using this approach, we exemplarily analyze the characteristics of n-type Pb1–xBixSe thermoelectric materials. With detailed electron microscopy and property characterizations, the high densities of dislocations and pores are found to be responsible for a low...

Band Sharpening and Band Alignment Enable High Quality Factor to Enhance Thermoelectric Performance in n-Type PbS

Abstract: Low-cost and earth-abundant PbS-based thermoelectrics are expected to be an alternative for PbTe, and have attracted extensive attentions from thermoelectric community. Herein, a maximum ZT (ZTmax) ≈ 1.3 at 923 K in n-type PbS is obtained through synergistically optimizing quality factor with Sn alloying and PbTe phase incorporation. It is found that Sn alloying in PbS can sharpen the conduction band shape to balance the contradictory interrelationship between carrier mobility and effective mass, accordingly, a peak power factor of ∼19.8 μWcm-1K-2 is achieved. Besides band sharpening, Sn alloying can also narrow the band gap of PbS so as to make the conduction band position between Pb0.94Sn0.06S and PbTe well aligned, which can benefit high carrier mobility. Therefore, incorporating the PbTe phase into the Pb0.94Sn0.06S matrix can not only favorably maintain the carrier mobility at ∼150 cm2V-1s-1 but also suppress the lattice thermal conductivity to ∼0.61 Wm-1K-1 in Pb0.94Sn0.06S-8%PbTe, which contributes to a largely enhanced quality factor. Consequently, an average ZT (ZTave) ≈ 0.72 in 300-923 K is achieved in Pb0.94Sn0.06S-8%PbTe that outperforms other n-type PbS-based thermoelectric materials.

Facile in situ solution synthesis of SnSe/rGO nanocomposites with enhanced thermoelectric performance

Abstract: Constructing nanostructured composite architectures has been considered as an effective strategy to reduce the lattice thermal conductivity (κL) and enhance the dimensionless figure of merit (ZT) of thermoelectric materials. Herein, a series of SnSe/reduced graphene oxide (rGO)-x (x = 0.1, 0.3, 0.5, 0.7 wt%) nanocomposites are controllably synthesised in situ via a facile single-step bottom-up solution method, where rGO nanosheets are incorporated intimately into the SnSe matrix. Nanocompositing performs two key functions: (i) significantly reducing the lattice thermal conductivity of the material, which can be attributed to enhanced phonon scattering from high-density SnSe/rGO interfaces, and (ii) improving the electrical conductivity over the low temperature range, as result of an increased carrier concentration. The subsequent thermoelectric performance of SnSe/rGO sintered pellets has been optimised by tuning the rGO mass fraction, with SnSe/rGO-0.3 achieving κL = 0.36 W m−1 K−1 at 773 K (cutting the κL of SnSe by 33%) to yield a maximum ZT of 0.91 at 823 K (representing a ∼47% increase compared to SnSe). This study provides a new pathway to improve the thermoelectric performance of polycrystalline SnSe by way of engineering metal chalcogenide/rGO composite architectures at the nanoscale.

Metallic n-Type Mg3Sb2 Single Crystals Demonstrate the Absence of Ionized Impurity Scattering and Enhanced Thermoelectric Performance

Abstract: Mg3 (Sb,Bi)2 alloys have recently been discovered as a competitive alternative to the state-of-the-art n-type Bi2 (Te,Se)3 thermoelectric alloys. Previous theoretical studies predict that single crystals Mg3 (Sb,Bi)2 can exhibit higher thermoelectric performance near room temperature by eliminating grain boundary resistance. However, the intrinsic Mg defect chemistry makes it challenging to grow n-type Mg3 (Sb,Bi)2 single crystals. Here, the first thermoelectric properties of n-type Te-doped Mg3 Sb2 single crystals, synthesized by a combination of Sb-flux method and Mg-vapor annealing, is reported. The electrical conductivity and carrier mobility of single crystals exhibit a metallic behavior with a typical T-1.5 dependence, indicating that phonon scattering dominates the charge carrier transport. The absence of any evidence of ionized impurity scattering in Te-doped Mg3 Sb2 single crystals proves that the thermally activated mobility previously observed in polycrystalline materials is caused by grain boundary resistance. Eliminating this grain boundary resistance in the single crystals results in a large enhancement of the weighted mobility and figure of merit zT by more than 100% near room temperature. This work experimentally demonstrates the accurate understanding of charge-carrier scattering is crucial for developing high-performance thermoelectric materials and indicates that single-crystalline Mg3 (Sb,Bi)2 solid solutions can exhibit higher zT compared to polycrystalline samples.

Electronic and thermoelectric properties of the layered Zintl phase CaIn2P2: first-principles calculations

Abstract: We have studied the doping concentration dependence of the thermoelectric (TE) properties for the n- and p-doped CaIn2P2 layered Zintl phase at two fixed temperatures: T = 600 and 900 K through fir...