With rapid development of sustainable energies and energy conversion technologies, application prospect of thermoelectric (TE) materials in power generation and cooling has received increasing attention. The requirement of improving TE materials with high figure of merit becomes much more important. How to obtain the low lattice thermal conductivity is one of the main concerns in TE materials. In this review, the influences of specific heat, phonon group velocity and relaxation time on the lattice thermal conductivity are discussed, respectively. Several typical features of TE materials with intrinsic low lattice thermal conductivity are introduced, such as strong anharmonicity, weak chemical bonds and complex primitive cells. Introducing multiscale phonon scatterings to reduce the lattice thermal conductivity of known TE materials is also presented and discussed, including but not limited to point defect scattering, dislocation scattering, boundary scattering, resonance scattering and electron-phonon scattering. In addition, some theoretical models of the minimum lattice thermal conductivity are analyzed, which has certain theoretical significance for rapid screening of TE materials with low lattice thermal conductivity. Finally, the efficient ways to obtain the low lattice thermal conductivity for TE property optimization are proposed.

Thermoelectric (TE) power generation technology is highly expected for various applications such as special power supply, green energy, energy harvesting from the environment and harvesting of industrial waste heat. Over the past years, the record of zT values of TE materials has been continuously updated, which would bode well for widespread practical applications of TE technology. However, the TE device as the core technology for the TE application lags behind the development of TE materials. Especially, the large-scale application of TE power generation technology is facing bottlenecks and new challenges. This reviewpresents an overview of the recent progress on TE device design and integration with particular attentions on device optimization design, electrode fabrication, interface engineering, and service behavior. The future challenges and development strategies for large-scale application ofthermoelectric power generation are also discussed.

Interface stability is one of the key issues determining the service reliability and life of thermoelectric devices. For skutterudite-based thermoelectric devices, the barrier layer is required in order to restrain the inter-diffusion between the hot-side electrode and skutterudite matrix. In this work, Ti₈₈Al₁₂ was selected as the barrier layer. N-type Yb_0.3Co₄Sb₁₂/Ti₈₈Al₁₂/Yb_0.3Co₄Sb₁₂ and p-type CeFe_3.85Mn_0.15Sb₁₂/Ti₈₈Al₁₂/CeFe_3.85Mn_0.15Sb₁₂ thermoelectric joints were prepared by one-step hot pressing sintering method. The evolution processes of contact resistivity and microstructure were studied through accelerated aging experiments. The results show that the contact resistivity of n-type joints increases slower than that of p-type joints under the same aging condition. Activation energy for n-type and p-type joints is 84.1 kJ/mol and 68.8 kJ/mol, respectively. Growth of the inter-metallic compound layer and cracking at the AlCo/TiCoSb interface result in rapidly increased contact resistivity of n-type joints. For p-type joints, the difference of coefficient of thermal expansion between CeFe_3.85Mn_0.15Sb₁₂ and Ti₈₈Al₁₂ becomes the main reason for the cracks.

Thermal diffusivity can be measured by the laser flash method. Previous study showed that Cu₂S has extremely low thermal diffusivity during the first-order phase transition. However, when laser is applied on the measured sample, both the absorption/emission of light and the increase of temperature on the measured sample will occur. Their effects on the measurement accuracy of the thermal diffusivity during the phase transition have not been investigated yet. In this study, it is found that the absorption/emission of light has neglectable influence on the thermal diffusivity measurement of Cu₂S. However, the increase of temperature can significantly influence the measurement results and shift the temperature when the thermal diffusivity of Cu₂S starts to decrease below the starting temperature of the phase transition determined by DSC. This can be solved by building a Cu₂S/graphite double-layer structure via using the graphite to absorb part of the laser’s energy. Furthermore, a thermal transport model is developed to extract the real thermal diffusivity from the measured thermal diffusivity of the Cu₂S/graphite double-layer structure. This work is meaningful for accurate characterization and understanding of the thermal diffusivity of phase transition materials, photosensitive materials, and heat sensitive materials.

High-throughput experiments aimed to promptly obtain the relationship among composition-phase-structure-performance with fewer experiments and screen out optimal material systems with optimized compositions. Up to now, high-throughput experiments are successfully applied in superconducting materials, fluorescent materials and giant magnetoresistance materials. Thermoelectric materials are functional materials that can realize the direct conversion between thermal energy and electrical energy and can be potentially applied in the fields of thermoelectric power generation and waste heat utilization. However, traditional preparation and characterization methods for thermoelectric materials have disadvantages of time consuming and low efficiency. Therefore, it is of great theoretical and practical significance to introduce methods and concepts of high-throughput experiments into development and optimization of new thermoelectric materials. In this paper, we summarize and discuss the existing high-throughput experimental preparation and characterization techniques with great application prospects in thermoelectric materials, including high-throughput sample preparation, composition-structure, and electro-thermal transport properties characterization, and then analyze the advantages and limitations of these high-throughput techniques. We hope to provide a reference for future high-throughput optimization and screening of thermoelectric materials.

Thermoelectric materials are a kind of energy conversion materials, which are extensively used in power generation or refrigeration. The key parameter that measure the performance of thermoelectric materials is the figure of merit ZT value, which requires material excellent electrical transport performance and low thermal conductivity. Standard first principles calculations on thermoelectric materials focus on small samples of materials, which is difficult to conclude general rules and propose new candidates. The Materials Genome Initiative speeds up the discovery and design of materials based on big data and high-throughput computational methods, which is promising in novel material screening. In thermoelectrics, first principles high-throughput calculations play an increasingly important role in the predicting and designing new materials. However, there are some drawbacks in the current high-throughput efforts for thermoelectric material screening, such as the demand of efficient high-throughput algorithms for transport properties, suitable tools for analyzing big data, etc. Solving these challenges strongly determines the efficiency and accuracy of high-throughput applications in thermoelectrics. This review summarizes several high-throughput theoretical methods and cases study on electrical and thermal transport properties in thermoelectric materials, and prospects the future trend of the combination of high-throughput and thermoelectric material research.

Thermoelectric power generation via Seebeck effect features an unique advantage in converting large amount of distributed and low-grade waste heat into electricity. Thermoelectric materials have become a hot topic of research in the field of new energy materials, guided by the high figure of merit ZT. Although various mid-temperature thermoelectric materials were discovered, the industrial application of these materials, especially in power generation applications, progressed very slowly. The staggering interface technology associated with thermoelectric device restricted the advance of thermoelectric conversion technology. In this review, the bottleneck issues of utilizing Bi₂Te₃-based devices for power generation were used as an example to illustrate the critical interface technologies. The key issues at designing electrode contact interfaces were summarized, including low contact resistance, high bonding strength, and superior thermal chemical stability at high temperature. The recent progress on the metallization and interfacial barrier layer for typical materials of Bi₂Te₃, PbTe and CoSb₃ were also reviewed.

Ternary chalcogenides I-V-VI₂ compounds attract extensive attentions for thermoelectric applications due to their intrinsically low lattice thermal conductivity. AgBiSe₂, as one of a few n-type semiconductors among these compounds, shows the potential to be a promising thermoelectric material. Therefore, this work focuses on its thermoelectric properties. According to the phase diagram of Ag₂Se-Bi₂Se₃ system, the single phase region of (Ag₂Se)_1-x(Bi₂Se₃)_x allows x to be varied in the range of 0.4~0.62. This large variation of x suggests a tunability of carrier concentration for this material. A broad carrier concentration of 1.0×10¹⁹~5.7×10¹⁹ cm^-3 for single phased (Ag₂Se)_1-x(Bi₂Se₃)_x is obtained through a composition manipulation, which enables a comprehensive assessment on electronic transport properties based on a single parabolic band model with acoustic scattering. The highest carrier concentration obtained in this work, approaching to the theoretical optimal one, leads to a peak ZT of 0.5 at 700 K. This work offers a well understanding of its transport properties and underlying physical parameters determining the thermoelectric performance.

Cu₂S shows excellent thermoelectric properties as a material with phonon liquid-electron crystal characteristics. However, traditional preparation methods are cumbersome and difficult to afford bulk Cu₂S with uniform composition, high density and excellent thermoelectric properties. In this study, a novel method named Pulsed Electric Current Sintering was introduced to synthesize and sinter Cu₂S materials in one step consuming only 30 s. The synthesis of Cu₂S under intense pulsed electric field includes three steps. A small amount of CuS and Cu₂S forms in the first step; most of Cu₂S and part of Cu_1.96S are produced in the second step; finally, the remained Cu_1.96S and Cu react to form completely pure Cu₂S. The Cu₂S bulk obtained by this method is a dense bulk with homogeneous composition, and contained abundant multi-scale microstructures. The thermoelectric performance is optimized by regulation of Cu-deficient Cu_2-xS. The maximum ZT of Cu_1.97S bulk at 873 K is 0.72, which is 49% higher than that of the pristine sample.