Inorganic-Based Printed Thermoelectric Materials and Devices

One of the simplest ways to generate electric power from waste heat is thermoelectric (TE) energy conversion. So far, most of the research on thermoelectrics has focused on inorganic bulk TE materials and their device applications. However, high production costs per power output and limited shape conformity hinder applications of state-of-the-art thermoelectric devices (TEDs). In recent years, printed thermoelectrics has emerged as an exciting pathway for their potential in the production of low-cost shape-conformable TEDs. Although several inorganic bulk TE materials with high performance are successfully developed, achieving high performance in inorganic-based printed TE materials is still a challenge. Nevertheless, significant progress has been made in printed thermoelectrics in recent years. In this review article, it is started with an introduction signifying the importance of printed thermoelectrics followed by a discussion of theoretical concepts of thermoelectricity, from fundamental transport phenomena to device efficiency. Afterward, the general process of inorganic TE ink formulation is summarized, and the current development of the inorganic and hybrid inks with the mention of their TE properties and their influencing factors is elaborated. In the end, TEDs with different architecture and geometries are highlighted by documenting their performance and fabrication techniques.     

Zero‐Field Nernst Effect in a Ferromagnetic Kagome‐Lattice Weyl‐Semimetal Co3Sn2S2

The discovery of magnetic topological semimetals has recently attracted significant attention in the field of topology and thermoelectrics. In a thermoelectric device based on the Nernst geometry, an external magnet is required as an integral part. Reported is a zero‐field Nernst effect in a newly discovered hard‐ferromagnetic kagome‐lattice Weyl‐semimetal Co₃Sn₂S₂. A maximum Nernst thermopower of ≈3 µV K^?1 at 80 K in zero field is achieved in this magnetic Weyl‐semimetal. The results demonstrate the possibility of application of topological hard magnetic semimetals for low‐power thermoelectric devices based on the Nernst effect and are thus valuable for the comprehensive understanding of transport properties in this class of materials.     

Band Engineering of Thermoelectric Materials

Lead chalcogenides have long been used for space‐based and thermoelectric remote power generation applications, but recent discoveries have revealed a much greater potential for these materials. This renaissance of interest combined with the need for increased energy efficiency has led to active consideration of thermoelectrics for practical waste heat recovery systems—such as the conversion of car exhaust heat into electricity. The simple high symmetry NaCl‐type cubic structure, leads to several properties desirable for thermoelectricity, such as high valley degeneracy for high electrical conductivity and phonon anharmonicity for low thermal conductivity. The rich capabilities for both band structure and microstructure engineering enable a variety of approaches for achieving high thermoelectric performance in lead chalcogenides. This Review focuses on manipulation of the electronic and atomic structural features which makes up the thermoelectric quality factor. While these strategies are well demonstrated in lead chalcogenides, the principles used are equally applicable to most good thermoelectric materials that could enable improvement of thermoelectric devices from niche applications into the mainstream of energy technologies.     

Field-assisted sintering of effective materials for alternative power engineering

The process of field-assisted sintering of nanostructured thermoelectrics for the formation of effective materials for alternative power engineering has been numerically simulated. Functionally graded thermoelectrics and segmented thermoelement branches have been sintered in a temperature-gradient field. Modified die tooling elements are proposed that allow the desired thermal conditions to be created for the sintering of inhomogeneous effective materials.     

Nanostructuring of metals by severe plastic deformation for advanced properties

Despite rosy prospects, the use of nanostructured metals and alloys as advanced structural and functional materials has remained controversial until recently. Only in recent years has a breakthrough been outlined in this area, associated both with development of new routes for the fabrication of bulk nanostructured materials and with investigation of the fundamental mechanisms that lead to the new properties of these materials. Although a deep understanding of these mechanisms is still a topic of basic research, pilot commercial products for medicine and microdevices are coming within reach of the market. This progress article discusses new concepts and principles of using severe plastic deformation (SPD) to fabricate bulk nanostructured metals with advanced properties. Special emphasis is laid on the relationship between microstructural features and properties, as well as the first applications of SPD-produced nanomaterials.     

Indium Selenides: Structural Characteristics,Synthesis and Their Thermoelectric Performances

Indium selenides have attracted extensive attention in high‐efficiency thermoelectrics for waste heat energy conversion due to their extraordinary and tunable electrical and thermal properties. This Review aims to provide a thorough summary of the structural characteristics (e.g. crystal structures, phase transformations, and structural vacancies) and synthetic methods (e.g. bulk materials, thin films, and nanostructures) of various indium selenides, and then summarize the recent progress on exploring indium selenides as high‐efficiency thermoelectric materials. By highlighting challenges and opportunities in the end, this Review intends to shine some light on the possible approaches for thermoelectric performance enhancement of indium selenides, which should open up an opportunity for applying indium selenides in the next‐generation thermoelectric devices.     

聚3, 4-乙烯二氧噻吩: 聚苯乙烯磺酸盐基柔性复合热电材料研究进展

热电材料可以实现热能与电能的直接转化,是一种安全环保的新型能源材料。近年来,随着可穿戴电子设备的发展,柔性热电材料成为研究人员关注的焦点。传统无机热电材料具有优异的热电性能,但由于自身固有的脆性,限制了在柔性领域的发展。聚3, 4-乙烯二氧噻吩: 聚苯乙烯磺酸盐(PEDOT: PSS)具有高电导率、低热导率和良好的柔性,在柔性热电领域具有巨大的潜力。当选择合适的无机填料与PEDOT: PSS进行复合,可以得到优异的热电性能和良好的力学性能。本文综述了PEDOT: PSS基纳米复合薄膜的最新进展,并详细介绍了提高PEDOT: PSS基纳米复合薄膜热电性能的有效方法。最后,本文总结了实现高性能PEDOT: PSS基柔性热电材料的途径及面对的挑战。      

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

The urgent need for ecofriendly, stable, long‐lifetime power sources is driving the booming market for miniaturized and integrated electronics, including wearable and medical implantable devices. Flexible thermoelectric materials and devices are receiving increasing attention, due to their capability to convert heat into electricity directly by conformably attaching them onto heat sources. Polymer‐based flexible thermoelectric materials are particularly fascinating because of their intrinsic flexibility, affordability, and low toxicity. There are other promising alternatives including inorganic‐based flexible thermoelectrics that have high energy‐conversion efficiency, large power output, and stability at relatively high temperature. Herein, the state‐of‐the‐art in the development of flexible thermoelectric materials and devices is summarized, including exploring the fundamentals behind the performance of flexible thermoelectric materials and devices by relating materials chemistry and physics to properties. By taking insights from carrier and phonon transport, the limitations of high‐performance flexible thermoelectric materials and the underlying mechanisms associated with each optimization strategy are highlighted. Finally, the remaining challenges in flexible thermoelectric materials are discussed in conclusion, and suggestions and a framework to guide future development are provided, which may pave the way for a bright future for flexible thermoelectric devices in the energy market.     

热电材料的第一性原理高通量研究

热电材料是一种新型能量转换材料, 在温差发电或通电制冷等领域具有广泛应用。热电优值ZT值是衡量热电材料能量转换效率的关键参数, ZT值要求热电材料具有优异的电输运性能及较低的热导率。传统第一性原理热电材料研究往往关注少量样本下的电热输运性质理解与优化, 很难得到系统性的规律, 也不利于新体系的设计优化。材料基因组计划力求通过大数据、高通量手段去加速材料设计与发现, 具有广阔的发展前景。在热电材料研究领域, 第一性原理高通量计算也将在新材料预测与性能优化等方面起到越来越重要的作用。另一方面, 高通量研究也带来了新的挑战, 譬如电热输运性质的高通量算法发展、大数据分析手段等等, 这些方面的问题决定了高通量方法在材料应用中的效率与准确性。本文综述了热电材料中现有的电热输运性质高通量计算方法, 介绍了这些方法具体的应用案例, 并对高通量与热电材料结合的未来发展趋势进行了展望。     

聚合物热电复合材料的研究进展

本文综述了碳纳米材料/聚合物、半导体合金/聚合物、金属纳米粒子/聚合物以及聚合物/聚合物等热电复合材料的研究进展。简要分析了热电复合材料的性能提升机理及现有材料尚存在的问题,并指出了聚合物热电复合材料今后的发展方向。     

Advanced Multimaterial Electronic and Optoelectronic Fibers and Textiles

The ability to integrate complex electronic and optoelectronic functionalities within soft and thin fibers is one of today's key advanced manufacturing challenges. Multifunctional and connected fiber devices will be at the heart of the development of smart textiles and wearable devices. These devices also offer novel opportunities for surgical probes and tools, robotics and prostheses, communication systems, and portable energy harvesters. Among the various fiber‐processing methods, the preform‐to‐fiber thermal drawing technique is a very promising process that is used to fabricate multimaterial fibers with complex architectures at micro‐ and nanoscale feature sizes. Recently, a series of scientific and technological breakthroughs have significantly advanced the field of multimaterial fibers, allowing a wider range of functionalities, better performance, and novel applications. Here, these breakthroughs, in the fundamental understanding of the fluid dynamics, rheology, and tailoring of materials microstructures at play in the thermal drawing process, are presented and critically discussed. The impact of these advances on the research landscape in this field and how they offer significant new opportunities for this rapidly growing scientific and technological platform are also discussed.     

Carbon‐Nanotube‐Based Thermoelectric Materials and Devices

Conversion of waste heat to voltage has the potential to significantly reduce the carbon footprint of a number of critical energy sectors, such as the transportation and electricity‐generation sectors, and manufacturing processes. Thermal energy is also an abundant low‐flux source that can be harnessed to power portable/wearable electronic devices and critical components in remote off‐grid locations. As such, a number of different inorganic and organic materials are being explored for their potential in thermoelectric‐energy‐harvesting devices. Carbon‐based thermoelectric materials are particularly attractive due to their use of nontoxic, abundant source‐materials, their amenability to high‐throughput solution‐phase fabrication routes, and the high specific energy (i.e., W g^?1) enabled by their low mass. Single‐walled carbon nanotubes (SWCNTs) represent a unique 1D carbon allotrope with structural, electrical, and thermal properties that enable efficient thermoelectric‐energy conversion. Here, the progress made toward understanding the fundamental thermoelectric properties of SWCNTs, nanotube‐based composites, and thermoelectric devices prepared from these materials is reviewed in detail. This progress illuminates the tremendous potential that carbon‐nanotube‐based materials and composites have for producing high‐performance next‐generation devices for thermoelectric‐energy harvesting.     

Nanoscience and nanotecnology on the balance

A number of advantages of nanostructured materials over bulk materials and their potential applications in many scientific and technological fields have been revealed in recent years. To find out the main growth and trends of this exciting new scienence and technology fields the growth rate of the nano-prefixed terms in the title of journal papers has been measured. It has been shown that the investigations dealing with graphite nanotubes represent kinetically the most active field of research in the nanosciences.     

Composite thermoelectric materials with embedded nanoparticles

The current status of the development of composite thermoelectric materials with embedded nanoparticles is reviewed. An introduction is given to the suggested mechanisms of improving thermoelectric properties by inclusions of nanoparticles and to experimental methods used to prepare such composites. The progress made in the development of thermoelectric materials with embedded nanoparticles is then covered, grouping the studies according to the optimal temperature range of operation of the materials investigated. Most studies have been devoted to materials within the medium temperature range, followed by low temperature materials, whereas high temperature materials have not yet received much attention within this area. In the majority of the materials systems studied, reports of improved thermoelectric performance upon introduction of nanoparticles in bulk thermoelectrics are found. However, for continued progress in this area, there is a need for systematic experimental studies that unambiguously correlate the resulting physical effects of the nanoinclusions to the measured materials properties.     

New Directions for Low‐Dimensional Thermoelectric Materials

Many of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena found both in bulk samples containing nanoscale constituents and in nanoscale samples themselves. Prior theoretical and experimental proof‐of‐principle studies on quantum‐well superlattice and quantum‐wire samples have now evolved into studies on bulk samples containing nanostructured constituents prepared by chemical or physical approaches. In this Review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications, thus bringing together low‐dimensional and bulk materials for thermoelectric applications. Particular emphasis is given in this Review to the ability to achieve 1) a simultaneous increase in the power factor and a decrease in the thermal conductivity in the same nanocomposite sample and for transport in the same direction and 2) lower values of the thermal conductivity in these nanocomposites as compared to alloy samples of the same chemical composition. The outlook for future research directions for nanocomposite thermoelectric materials is also discussed.     

Device Physics of Dye Solar Cells

Design of new materials for nanostructured dye solar cells (DSC) requires understanding the link between the material properties and cell efficiency. This paper gives an overview of the fundamental and practical aspects of the modeling and characterization of DSCs, and integrates the knowledge into a user‐friendly DSC device model. Starting from basic physical and electrochemical concepts, mathematical expressions for the IV curve and differential resistance of all resistive cell components are derived and their relation to electrochemical impedance spectroscopy (EIS) is explained. The current understanding of the associated physics is discussed in detail and clarified. It is shown how the model parameters can be determined from complete DSCs by current dependent EIS and incident‐photon‐to‐collected‐electron (IPCE) measurements, supplemented by optical characterization, and used to quantify performance losses in DSCs. The paper aims to give a necessary theoretical background and practical guidelines for establishing an effective feedback‐loop for DSC testing and development.     

陶瓷科学中的若干重要基础问题

新型陶瓷的发展及剪裁已有陶瓷的能力以满足新的、苛求的应用将是在新世纪内继续对人类社会产生重大影响的源头之一,而陶瓷材料的发展又依赖于对相关基础问题的理解。基于近来的有关报告,综合列举了陶瓷材料中的一些热点基础问题。     

Lattice Softening Significantly Reduces Thermal Conductivity and Leads to High Thermoelectric Efficiency

The influence of micro/nanostructure on thermal conductivity is a topic of great scientific interest, particularly to thermoelectrics. The current understanding is that structural defects decrease thermal conductivity through phonon scattering where the phonon dispersion and speed of sound are assumed to remain constant. Experimental work on a PbTe model system is presented, which shows that the speed of sound linearly decreases with increased internal strain. This softening of the materials lattice completely accounts for the reduction in lattice thermal conductivity, without the introduction of additional phonon scattering mechanisms. Additionally, it is shown that a major contribution to the improvement in the thermoelectric figure of merit (zT > 2) of high‐efficiency Na‐doped PbTe can be attributed to lattice softening. While inhomogeneous internal strain fields are known to introduce phonon scattering centers, this study demonstrates that internal strain can modify phonon propagation speed as well. This presents new avenues to control lattice thermal conductivity, beyond phonon scattering. In practice, many engineering materials will exhibit both softening and scattering effects, as is shown in silicon. This work shines new light on studies of thermal conductivity in fields of energy materials, microelectronics, and nanoscale heat transfer.     

低维纳米热电材料研究进展

低维纳米热电材料具有优良的热电性能,近年来受到大量研究者的喜爱。本文讨论低维纳米热电材料的机理,综述了零维纳米热电材料、一维纳米热电材料、二维纳米热电材料的最新研究进展,为低维纳米热电材料的进一步深入研究做了初步的总结和预测。     

One-dimensional van der Waals quantum materials

The advent of graphene and other two-dimensional van der Waals materials, with their unique electrical, optical, and thermal properties has resulted in tremendous progress for fundamental science. Recent developments suggest that taking one more step down in dimensionality — from mono-layer atomic sheets to individual atomic chains — can bring exciting prospects in fundamental science and practical applications. The atomic chain is the ultimate limit in material downscaling, a frontier for establishing an entirely new field of one-dimensional quantum materials. Here, we review this emerging area of one-dimensional van der Waals quantum materials and anticipate its future directions. We focus on quantum effects associated with the charge-density-wave condensate, strongly-correlated phenomena, topological phases, and other unique physical characteristics, which are attainable specifically in van der Waals materials of lower dimensionality. Possibilities for engineering the properties of quasi-one-dimensional materials via compositional changes, vacancies, and defects, as well as their potential applications in composites are also discussed.