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The processability of organic thermoelectric materials plays a crucial role due to their clear advantages of applicability in large-scale areas compared to traditional inorganic counterparts. A promising way to process thermoelectric materials based on conductive polymers is through in situ polymerization in an insulating polymer matrix. This work shows an interpenetrating polymeric network based on polythiophene, silver nanoparticles (Ag NPs), and poly(methyl methacrylate) (PMMA) produced by the oxidative polymerization of terthiophene by an oxidizing silver salt in a PMMA matrix. Ag NPs are in situ synthesized simultaneously as a byproduct. The reaction occurs very fast in the solid state, and after only 1 min, a homogeneous interpenetrating polymer network (IPN) film is obtained, reaching electrical conductivity values of 120 S cm–1. Ag NPs play a determining role in the conducting properties of the IPN. Moreover, the thermoelectric properties were evaluated as a function of the synthesis parameters, reaching a maximum power factor of 51 μW m–1 K–2. This study shows a promising method to enhance the processability of hybrid thermoelectric materials on the basis of conductive polymers and nanofillers.

Herein, wooden-stick-based thermoelectric legs are introduced as a new type of thermoelectric legs. As a proof of concept, graphite- and bismuth-coated wooden sticks are fabricated with a green method, and their use as thermoelectric elements is successfully demonstrated by constructing a test thermoelectric generator. The generator based on 20 pairs of p–n legs shows a maximum power output of ∼18 nW on heating one side of the device to 70°C. The strategy can suitably be extended to other good thermoelectric materials. The approach can be promising due to the ultralow thermal conductivity of the wooden substrate pillars in contrast to other typical substrates such as glass, and hence, better thermal gradients across the device can be achieved. These environmentally friendly, non-toxic and low-cost wooden-stick-based thermoelectric devices with good thermoelectric material coatings can be conveniently used for low-grade industrial waste heat conversion applications.

Calculations of AgSbTe2 thermoelectric material and 2d CdS/TiS2 and their heterostructures were carried out using Density Functional Theory in Cambridge Serial Total Energy Package code as implemented in Material Studio 2018 software. The work function, thermal transport, electronic and optical properties were calculated. The results revealed that the heterostructures are possible to be achieved with improved properties. The electronic and thermal transport properties were likened with the description of equations derived from Boltzmann transport theory and Mott expressed in the maximum achievable Figure merit. Orbital contributions from the electron movement show valence and conduction band atomic shells.

Funding: Engineering and Physical Sciences Research Council EP/J000884/1, EP/W037300/1 (RAD, BFK). Materials with the TiNiSi structure have recently been highlighted as potential thermoelectric materials. Here we report the thermoelectric properties of TiNiX (X = Si and Ge). Both materials behave as defective metals or heavily doped degenerate semiconductors. Room temperature Seebeck coefficients are -45 μV K-1 (Si) and -20 μV K-1 (Ge) with electrical resistivities of 0.5-1 mΩ cm. The lattice thermal conductivities are 8 W m-1 K-1 (Si) and 6 W m-1 K-1 (Ge) at 360 K, which is promising in the absence of alloying. The calculated power factors and figures of merit remain small, with the largest S2/ρ = 0.17 mW m-1 K-2 and peak zT = 5 × 10-3 seen in TiNiSi near 300 K. Both compositions show Kondo behaviour at low-temperatures, linked to the emergence of local moment magnetism, and have substantial magnetoresistance effects at 2 K. This work provides property characterisation for two members of this large class of intermetallic materials. Publisher PDF

The application of machine learning (ML)-based methods to the study of thermoelectric (TE) materials is promising. Although conventional ML algorithms can achieve high prediction performance, their lack of interpretability severely obstructs researchers from extracting material-oriented insights from ML models. In this work, high ML-based prediction performance was achieved with respect to TE power factors (PFs), and the results were well understood by the SHapley Additive exPlanations (SHAP), a method to identify the correlations between targets and descriptors. We designed a robust PF prediction model for diamond-like compounds via a stacking technique, and the model achieved a coefficient of determination value above 0.95 on the test set. From the SHAP analysis, the PFs were negatively correlated with electronegativity and positively correlated with the descriptor “volume per atom” based on the previously reported dataset. TE domain knowledge was adopted to understand these correlations. This work shows that ML models can achieve high accuracy while exhibiting good interpretability, making them useful for materials scientists.

Bi2Te3 based alloys have been the most widely used thermoelectric material at low temperature for many decades. Here we report Se doped n-type Mg3Bi2 based materials with a thermoelectric figure-of-merit ZT of 0.82 at 300 K and a peak ZT of 1.24 at 498 K, which is comparable to the n-type Bi2Te3 and Te doped Mg3Bi1.4Sb0.6. The improved thermoelectric performance is benefited from the high carrier concentration and mobility as well as the thermal conductivity reduction. The reduced resistivity increased the power factor at all measured temperatures, leading to a higher engineering ZT (ZTeng) and engineering power factor (PFeng) for n-type Mg3Bi2. The n-type Mg3Bi1.4Sb0.6 materials are promising for thermoelectric power generation and cooling applications near room temperature.

Today, the earnest need for earth-abundant and environmentally friendly thermoelectric materials has revealed the importance of semiconductor metal oxides in order to eliminate the barrier towards their wide-ranging use in industrial applications. In the present work, we demonstrate the synthesis of p-type tin oxide thin films on quartz glass and Si substrates by using electron beam evaporation technique followed by rapid thermal annealing process at 200 °C for 20 min in Ar-atmosphere. Annealing-induced structural, electrical, optical and thermoelectric properties of pristine and annealed SnO thin films are primarily studied. The compositional and structural analysis of SnO films are performed by using X-Ray Diffraction, Scanning Electron Microscope as well as Atomic Force Microscope. Moreover, the mechanism of thermoelectric transportation at different measurement temperatures is deeply inspected via thermoelectric measurements. The Seebeck coefficient, carrier concentration and hole mobility in conjunction with the development of thin film nanostructures are discussed, predominantly. The optimal annealing may tune structural, electro-optic and thermoelectric properties of SnO films for the commercial-level maturity of thermoelectric devices for energy applications.

High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermoelectrics. Recently, the optimization of GeTe-based thermoelectric materials has been focusing on reducing lattice thermal conductivity via strengthening phonon scattering. In this study, we systematically studied thermoelectric properties of Se-alloyed Ge0.95Bi0.05Te via theoretical calculations, structural characterizations, and performance evaluations. Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge0.95Bi0.05Te matrix. Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge0.95Bi0.05Te matrix, which can strengthen Umklapp phonon scattering. Finally, a decreased lattice thermal conductivity from ∼1.02 W m−1 K−1 to ∼0.65 W m−1 K−1 at 723 K is obtained in Ge0.95Bi0.05Te1-xSex pellets with increasing the Se content from 0 to 0.3. A peak figure of merit of ∼1.6 at 723 K is achieved in Ge0.95Bi0.05Te0.7Se0.3 pellet, which is ∼77% higher than that of pristine GeTe. This study extends the understanding on the thermoelectric performance of GeTe.

The phonon transport is intensively related to microstructure defects. Herein, a unique high-pressure sintering technology (GPa-level) was applied to modify the microstructure of pristine SnTe. There are many nano-domains exist in the high pressured NaCl-type SnTe binary compounds. The fast Fourier transform images show the domain phases have two sets of reflections with comparable intensity and exhibit doublet periodicities of special lattice planes, which demonstrates the domain phases are the CuPt and CuAu-I-type variants evolved from the NaCl-type matrix phase. An in-depth investigation indicates the constructions of the domain phase are related to locally off-stoichiometric of SnTe and the introduced strong inner-stress during high pressure sintering process. Additionally, a calculation of the phonon transport discloses the nano-domains restrict the phonon relaxation time by orders of magnitude over a wide phonon frequency range. As a result, a wide frequency phonon scattering network can be established to lower the lattice thermal conductivity.

Room-temperature thermoelectric materials provide promising solutions for energy harvesting from the environment, and deliver a maintenance-free power supply for the internet-of-things (IoTs). The currently available Bi2Te3 family discovered in the 1950s, still dominates industrial applications, however, it has serious disadvantages of brittleness and the resource shortage of tellurium (1 × 10−3 ppm in the earth's crust). The novel Mg3Sb2 family has received increasing attention as a promising alternative for room-temperature thermoelectric materials. In this review, the development timeline and fabrication strategies of the Mg3Sb2 family are depicted. Moreover, an insightful comparison between the crystallinity and band structures of Mg3Sb2 and Bi2Te3 is drawn. An outlook is presented to discuss challenges and new paradigms in designing room-temperature thermoelectric materials.

SnSe-based thermoelectric materials are being explored since they have potential high thermoelectric figure of merit. We synthesized polycrystalline AlxSn1-xSe (x = 0.01, 0.02, 0.03 and 0.04) by hot-pressing method, and combined theoretical estimation with experimental measurement to investigate the influence of Al doping on thermoelectric properties of SnSe. It was found that dopant Al can effectively adjust the band structure of SnSe by introducing intermediate band. Al doping with low content (x = 0.01 and 0.02) can introduce a single intermediate band close to the valence band maximum or conduction band minimum, achieving band engineering optimization. In high temperature region (498 K

Spark plasma sintering (SPS) is an efficient method for fabricating various bulk dense materials, including ceramics. Reactive spark plasma sintering (RSPS) of the exothermic reaction systems involves an initial powder mixture that allows chemical transformation with release of an additional energy during the SPS process. Thus, a deep understanding of the chemistry is critical for controlling the microstructure and thus the properties of the obtained materials. Recent publications have revealed that the RSPS is widely used for manufacturing of variety of materials including ultrahigh-temperature ceramics, high-entropy ceramics, and thermoelectrics. However, the thermodynamics and kinetics of the chemical reactions occurring during RSPS are not well understood. The goals of the present critical review are as follows: (i) to provide the fundamental definitions of chemistry related parameters of RSPS; (ii) to analyze the thermodynamics and kinetics of the RSPS processes; (iii) to emphases the influence of the microstructure of the consolidated media on the chemistry of RSPS; (iv) briefly overview recent publications on RSPS of ceramics. We also provide some recommendations for future work in the field of RSPS.

Alloying with Se is proved to be feasible to suppress the lattice thermal conductivity (κL) of tellurium by introducing multidimensional lattice defects. However, extra ionization impurity centers induced by Se alloying are harmful to the electric transport properties of the matrix. In this paper, we propose that the incorporation of Ag could successfully compensate the lost carrier mobility (μH) due to Se alloying through the regulation of microstructure, resulting in the higher power factor (PF) than that of samples without Ag. After composition optimization, the κL decreased from 1.29 W m−1 K−1 of Te0.99Sb0.01 to 1.05 W m−1 K−1 of Te0.94Ag0.02Se0.03Sb0.01 at 350 K, while the PF remained unchanged or even slightly increased. Benefit from the synergistic effect of carrier mobility compensation and phonon scattering, a maximum zT of 0.91 at 573 K and an average zT of 0.57 (between 298 and 573 K) are achieved in Te0.94Ag0.02Se0.03Sb0.01. This work presents a new strategy for decoupling the thermal and electric parameters of Te-based thermoelectric materials.

Filled CoSb3-based skutterudites are promising middle-temperature thermoelectric materials. However, p-type skutterudites containing electropositive fillers require additional charge compensation by doping atoms at the framework, which leads to enhanced carrier scattering. In this work, p-type filled CoSb3 materials with electronegative guest Cl were successfully prepared by high-pressure high-temperature (HPHT) process. A high filling fraction of Cl in void sites reaching ∼23% was obtained without charge compensation. Cl filler exhibited p-type electron acceptor behavior and can increase hole concentration of pristine CoSb3 to a magnitude of 1019 cm−3. As the content of Cl rose, abnormal spinal morphology and fine nano grain were observed in Cl-filled skutterudites. In turn, lattice thermal conductivity of Cl0.6Co4Sb12 sample significantly reduced by 46% when compared to pristine CoSb3 at room temperature due to enhanced scattering of point defect, rattler, and grain boundary. In sum, HPHT process looks promising for using Cl as additional p-type dopant candidate to yield significantly enhanced phonon scattering.

Recently, oxide-based materials have proven to be potential thermoelectric materials at high temperatures. In this work, the thermoelectric properties of one-step solid-state sintered Sn1-xSbxO2 (x = 0, 0.005, 0.01, 0.02, 0.03, 0.04) ceramic pellets were investigated in detail. It was confirmed that the addition of Sb significantly alters the thermoelectric properties of SnO2 due to the increase in the carrier concentration, which increases the electrical conductivity. The Seebeck coefficient values of all the solid solutions were negative, which indicates that these samples have n-type conduction. The thermoelectric performance of the material was evaluated by determining the zT value and the best composition was Sn0·98Sb0·02O2 with zT ∼0.06 at 1073 K.

Bi2S3-based alloys are considered promising thermoelectric materials due to their large Seebeck coefficient and low lattice thermal conductivity. However, low electrical conductivity usually leads to poor electrical transport properties, which seriously restricts their further application in thermoelectric refrigeration and/or power generation. In this work, Bi2S3 with high electrical transport properties is synthesized hydrothermally via Se and Cl co-doping. The maximum electrical conductivity value of 483 S cm−1 was obtained for the Bi2S2.4Se0.4Cl0.20 sample at room temperature. The significant improvement of electrical conductivity gives rise to a high average power factor of 411 μW m−1 K−2 during the measuring temperature range and a peak value of 456 μW m−1 K−2 at 673 K. Benefiting from the largely improved electrical transport properties, a superior ZT value of approximately 0.66 and ZTave. of 0.36 were obtained for Bi2S2.4Se0.4Cl0.20, and the theoretically calculated conversion efficiency reached 5.7%. The results indicate that Bi2S3 is a promising candidate for thermoelectric applications at medium temperatures.

InGaO3(ZnO)m (m = 1, 2, 3, 4, and 5) ceramics are a series of n-type oxide thermoelectric materials with layered structures and low thermal conductivities. Herein, InGaO3(ZnO)m (m = 1, 2, 3, 4, and 5) ceramics were fabricated by spark plasma sintering (SPS). Two different trends in the thermoelectric properties of the InGaO3(ZnO)m (m = 1, 2, 3, 4, and 5) ceramics were observed depending on the odevity of the m value. The InGaO3(ZnO) sample exhibited a relatively high electrical conductivity and was therefore selected for vacuum annealing to further improve the electrical transport performance. Oxygen vacancy defects were introduced to the matrix during the annealing procedure, which improved the thermoelectric performance. A maximum ZT of 0.45 was obtained at 973 K for the InGaO3(ZnO) sample with a 96 h vacuum annealing treatment, which is 30 times higher than that of the pristine sample.

The first report of a DFT study on halide (I, Br, Cl) doping in Pb0.6Sn0.4Te, a topological crystalline insulator reveals an opening of band gap and band convergence without breaking crystal mirror symmetry, leading to high thermoelectric performance.

Abundant heat is generated in household, industry and natural processes, and the majority of the heat is dissipated to environment as waste heat owing to the low heat utilization efficiency. Hence, to harvest waste heat is of great significance for the sustainable development. Among the heat-harvesting technologies including organic Rankine cycles, thermo-osmotic energy conversion and thermoelectric generators (TEGs), TEGs that can directly convert heat into electricity is the only feasible technology to harvest the low-grade heat that has a temperature below 200 oC and is about 2/3 of the total waste heat. The operational principle of TEGs is the Seebeck effect of electronic thermoelectric (TE) materials such as semiconductors or semimetals. Recently, ionic conductors, such as liquid ionic conductors and gel ionic conductors, emerged as the next-generation TE materials mainly due to their high thermopower. Their thermopower can be higher than that of the electronic TE materials by 2-3 orders in magnitude. In addition, they usually have a low thermal conductivity. Because the charge carriers in ionic conductors are cations and anions, the principle for the ionic thermopower and ionic TE conversion devices are notably different from the electronic counterparts. Very exciting progress has been made on the ionic TE materials and devices. This article provides a review on the ionic TE materials, including the thermopower mechanism, TE properties, and applications.

Cu2-xSe has been known as an ideal thermoelectric material for application in the middle-high temperature range due to the outstanding electric transmission conductivity and relatively low lattice thermal conductivity. However, its performance is significantly constrained by its high thermal conductivity and thermal stability issues, as well as its difficulty in element doping because of the influence of atomic size and atomic solid solubility. Here, we prominently reduced the thermal conductivity of Cu2-xSe by addition different amounts of WS2 to the Cu2-xSe matrix, and successfully improved the power factor of the material because of the reduction of high Cu defects to coordinate the three mutually coupled parameters. The zT value of the WS2-doping Cu2-xSe sample was eventually enhanced by 56% compared with pristine Cu2-xSe, and up to ca. 1 at 823 K. Further, we found that the symmetry of the Cu2-xSe crystal had not been destroyed undergoing the doping of WS2 into its crystal lattice, and the doped sample showed good thermal stability when cycle test was carried out twice between 315 K and 823 K.

The developments of high-efficiency thermoelectric materials are extremely exigent for energy harvesting. In this study, a novel MWCNTs/Ag2Se (MCAS) composite was successfully fabricated by a typical one-pot hydrothermal method and its thermoelectric properties were discussed in the temperature range of 300-420 K. The SEM patterns revealed that the microparticle diameter of Ag2Se for MCAS was about 10 times smaller than that of pure Ag2Se, which contributed to the intimate contact and mutual effect at the MCAS interfaces. The thermoelectric measurements indicated that 1%MCAS obtained the optimal thermoelectric figure of merit (ZT) value, ascribed to the outstanding electrical conductivity of the MWCNTs and the declining thermal conductivity of the 1%MCAS. The electrical conductivity of 1%MCAS was 3.0 times higher than that of Ag2Se, and the lattice thermal conductivity was decreased by 55.3% at 300 K. This study provides a new strategy for designing Ag2Se-based thermoelectric materials and promoting thermoelectric performance.

Recently, several kinds of variable cross-section legs have been reported to improve the performance of thermoelectric generators (TEGs). This work further proposes an optimization study to maximize the output power of variable cross-section TEGs for solar energy utilization by coupling finite element method (FEM) and optimization algorithm. Six geometric variables along with the external load resistance are optimized by genetic algorithm (GA) and particle swarm optimization (PSO). Besides, Joule heating, Peltier effect, and Thomson effect are considered in the numerical model to improve the simulation accuracy. Optimization results show that distributions of the thermal resistance and the electrical resistance are significantly changed when the volumes of thermoelectric material remain constant. The optimized leg shape increases the temperature gradient in the high figure of merit (ZT) region by reducing the cross-section area. Although internal resistances of optimal TEGs are greater than those of rectangular TEGs, the improvement in electromotive force results in the enhancement of electrical performance. At heat flux of 35000 W m−2, 40000 W m−2, 45000 W m−2, and 50000 W m−2, temperature differences of optimal TEGs are increased by 12.77%, 18.36%, 41.93%, and 73.14%, while output powers are improved by 1.45%, 2.13%, 9.33%, and 20.13%, respectively.

Transparent-flexible thermoelectric materials are attractive for future small-sized consumer electronics, the internet of things, and wearable devices. The microstructural evolution and subsequent thermoelectric properties of Ti 1%.at-doped ZnO thin films, grown on polyimide flexible substrates, are presented. The thin films were grown using radio frequency a magnetron sputtering method followed by annealing for 60 min at temperatures of 200–400 °C under vacuum atmosphere. Post-annealed films demonstrate a hexagonal Wurtize structure. It is found that the annealing helped to relax residual stresses in the thin films, subsequently leading to enhanced charge concentration, carrier mobility, mean free path, and density-of-states effective mass. The thin film, annealed at 300 °C, illustrates the highest power factor of the films measured at room temperature at 19.10 μW m−1 K−2. Further increases in the annealing temperature suggest Ti2+ diffuses into the ZnO lattice and in turn disturbs the crystalline structure; this results in a reduction of the power factor to 9.32 μW m−1 K−2 at an annealing temperature of 350 °C.

CuPbBi5S9 compounds have been investigated as gladite for years. However, there have been no significant studies on their physical and chemical properties. This work demonstrates that upon alloying with moderate Cu, Pb, Bi, and S using an appropriate preparation method, quaternary CuPbBi5S9 compounds can exhibit excellent figure of merit ZT within the temperature range 298–723 K. A low average velocity, low Young’s modulus and Debye temperature, and large Gruneisen parameter, determined experimentally, indicate strong lattice anharmonicity in CuPbBi5S9 crystals. Furthermore, density functional theory calculations (local vibration of low-frequency acoustic phonons) justify the low lattice thermal conductivity of CuPbBi5S9 compounds. Because of the low thermal conductivity (0.514 W m−1K−1) and a relatively high power factor (293 μW m−1K−2), a maximum ZT of 0.42 was achieved at 723 K for CuPbBi5S9 prepared by mechanical alloying combined with solid-state melting. Thus, CuPbBi5S9 materials are promising candidates for use as high-performance thermoelectric materials in the intermediate-temperature range.

Thermoelectric materials have been extensively studied for applications in solid-state power generation and cooling. Progress has been made over the past decade in multiple materials systems, hence, it becomes increasingly valuable to be able to analytically model the transport behavior to optimize materials and compare different systems. The well-known effective mass modeling approach is often used to fit the data to the form expected for a single, parabolic band, with charge carrier scattering dominated by acoustic phonons, i.e., deformation potential scattering. However, many high-performance thermoelectric materials benefit from having multiple bands (multi-valley) and many have non-parabolic bands or complex scattering. Understanding how these effects alter properties from that given by the effective mass model provides rational strategies for new materials. In this review, we discuss how this can be done in three strategies, the first is how to evaluate the influence of point defects on charge carrier mobilities as well as thermal conductivity. Established methods are also available for considering additional scattering mechanisms for phonons and electrons. We focus on how to determine the parameters used in modeling that require the least amount of fitting. We discuss the thermoelectric transport in two different types of materials: lead chalcogenides and half Heuslers. The second strategy involves systems with multiple sets of conduction or valence bands, which are not necessarily aligned. We discuss different conditions in hypothetical materials systems by considering quality factors for each set of bands. We then demonstrate how the lessons learned are reflected in real thermoelectric materials systems. The third strategy uses resonant dopants, and lead chalcogenides have become model systems. These dopants create a distortion in the density of states inherently the parabolic dispersion assumption can no longer be used. It is possible nonetheless, to quantitatively reproduce thermoelectric transport properties, providing insights on how to best utilize resonant dopants. Finally, we provide an outlook, identifying limitations and challenges to solve in order to model, and better yet, predict the thermoelectric performance of different materials.

Tin Telluride is an efficient thermoelectric material having high power factor and low thermal conductivity. Pristine SnTe and Te rich SnTe were synthesized by using solvothermal method. Structural study of these samples was carried out by using Powder XRD and FESEM. Electron density maps show the uniformity of crystal structure in space. FESEM micrographs also show the formation of nanoparticles. There is formation of second phase of Te in Te rich SnTe. Crystallite size decreases, lattice strains, stacking faults and dislocation densities increase in Te rich SnTe. These distortions in structural properties can be useful in reduction of lattice thermal conductivity. Hence Te rich SnTe can be an efficient compound for thermoelectric power generation.

Thermoelectric (TE) materials are receiving increasing attention due to their ability to directly converting heat to electricity. They are used to harvest electrical energy from the wasted heat in order to increase the efficiency of global energy. Polymer-based TE materials are particularly fascinating to wearable and mobile devices due to their low density, good flexibility, and low toxicity. This review summarizes the recent breakthroughs and optimization strategies of polymer-based TE materials. Among a large number of different organic TE materials, those with remarkable TE performance are selected and divided into three categories, which are poly(3,4-ethylenedioxythiophene) derivatives, carbon nanotube/conductive polymer composites, and inorganic semiconductive nanomaterial/polymer composites. The effect of components and structures on the power factor are presented and discussed. Finally, some challenges are described and suggestions are provided for preparing the next-generation of polymer-based materials with high TE performance.

The ability of thermoelectric (TE) materials to convert thermal energy to electricity and vice versa highlights them as a promising candidate for sustainable energy applications. Despite considerable increases in the figure of merit zT of thermoelectric materials in the past two decades, there is still a prominent need to develop scalable synthesis and flexible manufacturing processes to convert high-efficiency materials into high-performance devices. Scalable printing techniques provide a versatile solution to not only fabricate both inorganic and organic TE materials with fine control over the compositions and microstructures, but also manufacture thermoelectric devices with optimized geometric and structural designs that lead to improved efficiency and system-level performances. In this review, we aim to provide a comprehensive framework of printing thermoelectric materials and devices by including recent breakthroughs and relevant discussions on TE materials chemistry, ink formulation, flexible or conformable device design, and processing strategies, with an emphasis on additive manufacturing techniques. In addition, we review recent innovations in the flexible, conformal, and stretchable device architectures and highlight state-of-the-art applications of these TE devices in energy harvesting and thermal management. Perspectives of emerging research opportunities and future directions are also discussed. While this review centers on thermoelectrics, the fundamental ink chemistry and printing processes possess the potential for applications to a broad range of energy, thermal and electronic devices.

In this work, we present a first-principles based investigation to analyse the effect of Hafnium (Hf) doping on thermoelectric properties of half-Heusler alloy RhTiP. In recent times, Hf based Heuser alloys are proved to be good thermoelectric (TE) materials. So, its interesting to see the effect of Hf, as dopant, on the newly propsed RhTiP. The energy bandgap of pure RhTiP is 0.810 eV. As we start doping, the bandgap first decrease for RhTi0.75Hf0.25P and then increase liearly for higher doping concentrations. We find that the material shows the high thermoelectric performance at 100% doping of Hf in place of Ti (RhHfP) at room temperature. The maximum value of power factor and electrical conductivity at room temperature are estimated, respectively, as 0.19688x 10 12 W K - 2 m - 1 s - 1 and 3.2058x1018 Ω - 1 m - 1 s - 1 which belong to RhHfP . The maximum ZT value at room temperature is found to be 0.7950 at room and it is too for RhHfP. We estimate that RhHfP can become a good thermoelectric material amongst all the studied concentrations for room temperature applications.

Thermoelectric devices enable direct conversion between thermal and electrical energy. Recent studies have indicated that the thin film/substrate heterostructure is effective in achieving high thermoelectric performance via decoupling the Seebeck coefficient and electrical conductivity otherwise adversely inter-dependent in homogenous bulk materials. However, the mechanism underlying the thin film/substrate heterostructure thermoelectricity remains unclear. In addition, the power output of the thin film/substrate heterostructure is limited to the nanowatt scale to date, falling short of the practical application requirement. Here, we fabricated the CrN/SrTiO3−x heterostructures with high thermoelectric output power and outstanding thermal stability. By varying the CrN film thickness and the reduction degree of SrTiO3−x substrate, the optimized power output and the power density have respectively reached 276 μW and 108 mW/cm2 for the 30 nm CrN film on a highly reduced surface of SrTiO3−x under a temperature difference of 300 K. The performance enhancement is attributed to the CrN/SrTiO3−x heterointerface, corroborated by the band bending as revealed by the scanning Kelvin probe microscopy. These results will stimulate further research efforts towards interface thermoelectrics.

SnTe is a lead-free and promising p-type thermoelectric material in an intermediate temperature range (500–900 K), but its intrinsic performance is poor due to excess cation vacancies and relativel...

Bi2Te3-based materials are dominating thermoelectrics for almost all of the room-temperature applications. To meet the future demands, both their thermoelectric (TE) and mechanical properties need to be further improved, which are the requisite for efficient TE modules applied in areas such as reliable micro-cooling. The conventional zone melting (ZM) and powder metallurgy (PM) methods fall short in preparing Bi2Te3-based alloys, which have both a highly textured structure for high TE properties and a fine-grained microstructure for high mechanical properties. Herein, a mechanical exfoliation combined with spark plasma sintering (ME-SPS) method is developed to prepare Bi0.5Sb1.5Te3 with highly improved mechanical properties (correlated mainly to the dislocation networks), as well as significantly improved thermoelectric properties (correlated mainly to the texture structure). In the method, both the dislocation density and the orientation factor (F) can be tuned by the sintering pressure. At a sintering pressure of 20 MPa, an exceptional F of up to 0.8 is retained, leading to an excellent power factor of 4.8 mW m-1 K-2 that is much higher than that of the PM polycrystalline. Meanwhile, the method can readily induce high-density dislocations (up to ∼1010 cm-2), improving the mechanical properties and reducing the lattice thermal conductivity as compared to the ZM ingot. In the exfoliated and then sintered (20 MPa) sample, the figure-of-merit ZT = 1.2 (at 350 K), which has increased by about ∼20%, and the compressive strength has also increased by ∼20%, compared to those of the ZM ingot, respectively. These results demonstrate that the ME-SPS method is highly effective in preparing high-performance Bi2Te3-based alloys, which are critical for TE modules in commercial applications at near-room temperature.

In this study, the continuous contact problem of thermoelectric layer resting on a rigid substrate and loaded by a rigid punch is examined. Considering the body force of the thermoelectric layer, the model of stress distribution between thermoelectric layer and rigid layer is established. The general expressions for the stress between the thermoelectric layer and the substrate are given. Using the boundary conditions, the singular integral equation of the stress distribution is obtained and solved by Gauss-Chebyshev integral formula. The numerical results of the stress distribution between the rigid punch and the thermoelectric layer are obtained. It is found that the stress between the rigid punch and the thermoelectric layer exhibits singularity at the edge of the rigid punch. The influence of the parameters of the rigid punch and the thermoelectric layer on the critical load factor between the thermoelectric layer and the substrate is analyzed. The results show that the larger rigid punch width and the body force of the thermoelectric layer make it difficult to separate the thermoelectric layer from the rigid substrate. The results of this paper will provide a reference for studying the contact behavior of thermoelectric materials.

Two-dimensional (2D)-layered atomic arrangement with ultralow lattice thermal conductivity and ultrahigh figure of merit in single-crystalline SnSe drew significant attention among all thermoelectric materials. However, the processing of polycrystalline SnSe with equivalent thermoelectric performance as single-crystal SnSe will have great technological significance. Herein, we demonstrate a high zT of 2.4 at 800 K through the optimization of intrinsic defects in polycrystalline SnSe via controlled alpha irradiation. Through a detailed theoretical calculation of defect formation energies and lattice dynamic phonon dispersion studies, we demonstrate that the presence of intrinsically charged Sn vacancies can enhance the power factor and distort the lattice thermal conductivity by phonon-defect scattering. Supporting our theoretical calculations, the experimental enhancement in the electrical conductivity leads to a massive power factor of 0.9 mW/mK2 and an ultralow lattice thermal conductivity of 0.22 W/mK through the vacancy-phonon scattering effect on polycrystalline SnSe. The strategy of intrinsic defect engineering of polycrystalline thermoelectric materials can increase the practical implementation of low-cost and high-performance thermoelectric generators.

Composites were prepared, through hot pressing, using carbon materials with different pore size distributions as additives for commercial Bi0.5Sb1.5Te3 thermoelectric material (BST, p-type). Thermoelectric properties of the composites were measured in a temperature range of 298‒473 K. Thermal conductivity of the composites, especially lattice thermal conductivity, was effectively decreased due to the mesoporous properties of the incorporated carbon additives. The electrical conductivity of the composites slightly decreased due to the electron scattering at the interface between the carbon material and the commercial BST matrix. The composite with 0.2 vol.% mesoporous carbon powder (36% mesoporosity) exhibited a figure of merit value approximately 10.7% higher than that of commercial BST without additives. This behavior resulted in 116% improved output power in the composite block-based single element compared with a bare BST thermoelectric block. The enhanced figure of merit was attributed to the effective reduction of lattice thermal conductivity by acoustic phonons scattering at the interface between the BST matrix and the mesoporous carbon as well as at the pore surfaces within the mesoporous carbon. By utilizing mesoporous carbon materials used in this study, the shortcomings and economic difficulties of the composite process with low dimensional carbon additives (carbon nanotubes, graphene, and nanodiamond) can be overcome for extensive practical applications. Mesoporous carbon powder with a tailored porosity distribution revealed the validity of bulk-type carbon additives to enhance the figure of merit of commercial thermoelectric materials.

Strain engineering of metal halide perovskites shows promise for better stability and device performance, but the impact on thermoelectric performance remains elusive. We demonstrate that the elect...

Polycrystalline BiCuSeO is considered as a promising thermoelectric material due to its intrinsically low thermal conductivity and moderate Seebeck coefficient. However, its low electrical conductivity and coupled electron-phonon transport properties restrict the further improvement of the thermoelectric performance. In this work, Pb and Yb dopants are incorporated into BiCuSeO to substitute for Bi sites via ball milling and high-pressure and high-temperature sintering, leading to a synergistic optimization of the electron and phonon transport and improved thermoelectric performance. The carrier concentration exhibits an enhancement with increasing Pb&Yb co-doping contents. Meanwhile, the decreased carrier mobility is suppressed appropriately by coordinating with the interplay of Pb and Yb dopants on the electronic structure. Besides, Pb&Yb co-doping combined with high-pressure and high-temperature sintering introduces abundant grain boundaries, dislocations, and point defects to effectively decrease the lattice thermal conductivity by scattering phonons in a broad frequency range. Coupled with the synergistic optimization of the electrical and thermal properties, a maximum zT of 1.2 is achieved in Bi0.88Pb0.06Yb0.06CuSeO at 850 K, which significantly outperforms the majority of oxygen-containing thermoelectric materials. Our study suggests that dual doping of bivalent ions and rare-earth elements at Bi sites is an effective strategy for improving the thermoelectric performance of BiCuSeO.

Lead telluride (PbTe), a narrow bandgap semiconductor commonly used in infrared detectors, exhibits anomalous vibrational and structural properties, making it appealing for thermoelectrics. Despite...

Achieving high electrical conductivity and thermoelectric power factor simultaneously for n-type organic thermoelectrics is still challenging. By constructing two new acceptor-acceptor n-type conjugated polymers with different backbones and introducing the 3,4,5-trimethoxyphenyl group to form the new n-type dopant 1,3-dimethyl-2-(3,4,5-trimethoxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (TP-DMBI) , high electrical conductivity of 11 S cm -1 and power factor of 32 μW m -1 K -2 are achieved. Calculations using Density Functional Theory show that TP-DMBI presents a higher singly occupied molecular orbital (SOMO) energy level of -1.94 eV than that of the common dopant 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzoimidazol-2-yl) phenyl) dimethylamine (N-DMBI) (-2.36 eV), which can result in a larger offset between the SOMO of dopant and lowest unoccupied molecular orbital (LUMO) of n-type polymers, though that effect may not be dominant in the present work. The doped polymer films exhibit higher Seebeck coefficient and power factor than films using N-DMBI at the same doping levels or similar electrical conductivity levels. Moreover, TP-DMBI doped polymer films offer much higher electron mobility of up to 0.53 cm 2 V -1 s -1 than films with N-DMBI doping, demonstrating the potential of TP-DMBI, and 3,4,5-trialkoxy DMBIs more broadly, for high performance n-type organic thermoelectrics.

The argyrodite compound, Ag8SnSe6 (ATS), which is one of the promising thermoelectric (TE) candidates, is receiving growing attention in thermoelectrics recently. However, its TE performance is sti...

As an ecofriendly and low-cost thermoelectric material, Cu2SnSe3 has recently drawn much attention. In this work, the thermoelectric properties of Cu2SnSe3-based materials have been synergistically...

Amorphous metal-oxide semiconductors can be readily prepared by a solution process at low temperatures, and their energy band structures and carrier concentrations can be controlled based on the oxide composition or the addition of dopants in the design of thermoelectric (TE) materials. However, research on the correlation between the charge transport and TE performance of amorphous metal-oxide semiconductors is still in its infancy. Herein, we present the energy-dependent TE performance characteristics of Li-doped ZnO thin films with different doping levels and charge carrier concentrations. Thin films were prepared by the solution process, and the Li doping level was controlled by the Li precursor concentration added to a Zn precursor solution. Subsequently, a field-effect-modulated Seebeck coefficient measurement device was built to study the energy-dependent TE performance. Notably, the higher ratio of interstitial Li (Li

Introducing functional gradients into thermoelectric materials can affect their conversion efficiency and mechanical properties. In this paper, the problem of thermal shock of an exponentially thermoelectric graded material is considered. Using the superposition principle and the method of separation of variables, expressions for the temperature and other physical quantities of the thermoelectric field are obtained. Then, other physical expressions for the thermoelectric field are derived from the expression for temperature. The effective thermoelectric coefficients of a static functionally graded material are obtained by using the equivalence principle. The numerical results describe the changes of physical quantities related to temperature with time and position. Meanwhile, the basic condition for thermoelectric conversion is analyzed based on the thermoelectric figure of merit, thermoelectric conversion efficiency, effective thermoelectric coefficient, and effective thermoelectric figure of merit. The results show that higher thermoelectric conversion efficiency can be achieved by changing the grading parameters. These results provide a theoretical basis for the production and performance optimization of thermoelectric materials.

A new series of Ba2-xBixCoRuO6 (0.0 ≤ x ≤ 0.6) hexagonal double perovskite oxides have been synthesized by a solid-state reaction method by substituting Ba with Bi. The polycrystalline materials are structurally characterized by the laboratory X-ray diffraction, synchrotron X-ray, and neutron powder diffraction. The lattice parameters are found to increase with increasing Bi doping despite the smaller ionic radius of Bi3+ compared to Ba2+. The expansion is attributed to the reduction of Co/Ru-site cations. Scanning electron microscopy further shows that the grain size increases with the Bi content. All Ba2-xBixCoRuO6 (0.0 ≤ x ≤ 0.6) samples exhibit p-type behavior, and the electrical resistivity (ρ) is consistent with a small polaron hopping model. The Seebeck coefficient (S) and thermal conductivity (κ) are improved significantly with Bi doping. High values of the power factor (PF ∼ 6.64 × 10-4 W/m·K2) and figure of merit (zT ∼ 0.23) are obtained at 618 K for the x = 0.6 sample. These results show that Bi doping is an effective approach for enhancing the thermoelectric properties of hexagonal Ba2-xBixCoRuO6 perovskite oxides.

Understanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat-transport-related devices, such as high-performance thermoelectric materials and heat dissipation in micro-nano-scale devices. In this work, the lattice thermal conductivity ( κL ) of the cage-like compounds Cu3 VSe4 and Cu3 NbSe4 was investigated by experimental measurements and first-principles calculations. The experimental κL of Cu3 NbSe4 is approximately 25 % lower than that of Cu3 VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third-order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the κL , and the other factors only play a minor role. The physical origin is the relatively "soft" lattice of Cu3 NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high-performance thermal management device and thermoelectric materials with intrinsically low κL .

Development new high-performance thermoelectric materials for more efficient power generation systems and eco-friendly refrigerating systems has been challenging. Over the past few decades, thermoelectric studies have been focused on increasing the thermoelectric properties of materials. However, for conventional applications, developing of thermoelectric devices or modules with lower cost and simpler fabrication processes is also important. Simulation models that can predict the thermoelectric efficiency of modules using the thermoelectric properties of materials are needed for this purpose. In this study, we developed a simple model for calculating the efficiency of thermoelectric modules using MATLAB/Simulink. In this model, the temperature difference between the hot source and heat sink was fixed to ensure the precise comparisons of thermoelectric efficiency. The electric resistivity and Seebeck coefficient of thermoelectric materials was used in order to predict the efficiency of the thermoelectric modules. Then, the efficiency of the thermoelectric modules was verified using measured values which had been reported in prior experimental works. In this study, the simulated values were higher than the real thermoelectric effiency values. To address this, the simulations should consider the thermal resistance or electric contact resistance between the thermoelectric materials and electrodes.

The binary compound of GeTe emerging as a potential medium-temperature thermoelectric material has drawn a great deal of attention. Here, we achieve ultralow lattice thermal conductivity and high thermoelectric performance in In and a heavy content of Cu codoped GeTe thermoelectrics. In dopants improve the density of state near the surface of Femi of GeTe by introducing resonant levels, producing a sharp increase of the Seebeck coefficient. In and Cu codoping not only optimizes carrier concentration but also substantially increases carrier mobility to a high value of 87 cm2 V-1 s-1 due to the diminution of Ge vacancies. The enhanced Seebeck coefficient coupled with dramatically enhanced carrier mobility results in significant enhancement of PF in Ge1.04-x-yInxCuyTe series. Moreover, we introduce Cu2Te nanocrystals' secondary phase into GeTe by alloying a heavy content of Cu. Cu2Te nanocrystals and a high density of dislocations cause strong phonon scattering, significantly diminishing lattice thermal conductivity. The lattice thermal conductivity reduced as low as 0.31 W m-1 K-1 at 823 K, which is not only lower than the amorphous limit of GeTe but also competitive with those of thermoelectric materials with strong lattice anharmonicity or complex crystal structures. Consequently, a high ZT of 2.0 was achieved for Ge0.9In0.015Cu0.125Te by decoupling electron and phonon transport of GeTe. This work highlights the importance of phonon engineering in advancing high-performance GeTe thermoelectrics.

Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate Ba8AlxGa16-xGe30 by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6c site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates Ba8AlxGa16-xGe30 and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties.

The severe electric and thermal environments may cause localized deterioration of the contact behavior of thermoelectric devices. The contact responses of the thermoelectricity under the joint effect of the finite size and the friction are analyzed. The law of the Coulomb friction is adopted. The obtained Fredholm kernel functions reveal the influence of the thickness and the friction. The known Jacobi polynomials are employed to discretize the obtained singular integral equation. The effects of the thermoelectric loadings (the total electric current and the total energy flux), friction coefficient, the thermoelectric strip thickness, and the elastic and thermoelectric material constants on the distribution of the normal traction and the surface in-plane stress are demonstrated in detail. The smaller thermal expansion coefficient and shear modulus will contribute to the lower stress concentration at both contact edges. The surface in-plane tensile stress behind the trailing edge can be alleviated as the thermoelectric strip becomes thinner.