Thermoelectric Materials Research Research Articles

A Novel Photo‐Activated Dopant for n‐Type Organic Thermoelectrics

AbstractEfficient and air‐stable molecular dopants are critical for optimizing the performance of thermoelectric devices. Despite significant advancements in developing p‐dopants for organic semiconductors, the quest for efficient and air‐stable n‐dopants remains challenging. Here, viologen‐tetraarylborate (VT) is introduced as a promising n‐dopant for thermoelectric applications, demonstrating its remarkable photo‐activation efficiency. After just 1 min of light exposure, a maximum power factor of 8.6 µW m−1 K−2, with a conductivity of 0.86 S cm−1 and a Seebeck coefficient of −346 µV K−1, is achieved for the VT doped PNDI2TEG‐2Tz film. Furthermore, VT exhibits excellent air stability, simplifying the device preparation process by allowing films to be prepared in ambient conditions. Additionally, the unique doping mechanism imparts good air stability to the stock solution of VT and the conjugated polymer, ensuring that the storage time of the stock solution does not affect thermoelectric performance. This innovative approach not only highlights the potential of VT as an efficient n‐dopant but also paves the way for developing novel air‐stable dopants and advancing doping methodologies in thermoelectric material research.

Thermoelectric Materials: A Scientometric Analysis of Recent Advancements and Future Research Directions

This scientometric study looks at the current trend in thermoelectric materials research and explores the evolving domain of thermoelectric materials research using a combination of bibliometric and scientometric methodologies. The analysis examines global research trends from a dataset of over 37,739 research articles, focusing on thematic evolution, annual growth rates, and significant contributions. Six principal research clusters were identified, encompassing energy conversion, material synthesis and nanostructures (the most prominent cluster), computational modeling and material properties, measurement and characterization, material performance enhancement, and material processing and microstructure. Each cluster highlights a critical aspect of the field, reflecting its broad scope and depth. The key findings reveal a marked annual increase in research output, highlighting the growing global importance of thermoelectric materials in sustainable energy solutions. This is especially evident in the significant contributions from China and the USA, emphasizing their leadership in the field. The study also highlights the collaborative nature of thermoelectric research, showing the impact of global partnerships and the synergistic effects of international collaboration in advancing the field. Overall, this analysis provides a comprehensive overview of the thermoelectric materials research landscape over the past decade, offering insights into trends, geographic contributions, collaborative networks, and research growth. The findings underscore thermoelectric materials’ vital role in addressing global energy challenges, highlighting recent advancements and industrial applications for energy efficiency and sustainability.

Predicting High‐Performance Thermoelectric Materials With StarryData2

AbstractIn recent years, machine learning (ML) has emerged as a potential tool in the exploration of thermoelectric (TE) materials. This study exploits the StarryData2 public database to construct an ML model for predicting the figure‐of‐merit ZT of TE materials. The original dataset from StarryData2 (372,480 datapoints) underwent systematic cleaning, resulting in a refined dataset of 18,126 instances with 2,761 unique compounds. The cleaned data is employed to train an XGBoost regressor model, utilizing chemical formulas of TE compounds as features to predict ZT at given temperatures. The XGBoost regressor exhibited high prediction accuracy, achieving the coefficient of determination (R2) scores of 0.815 and mean absolute error (MAE) of 0.103 for the test set, further evaluated through cross‐validation across 5 folds. The learning curve analysis demonstrated improved model performance with increased training data. Furthermore, the contributions of different chemical descriptors to ZT are analyzed based on feature importance analysis. Beyond conventional TE families in the training set, the trained model is applied to predict ZT for promising unexplored TE materials and estimate optimal doping concentrations. This comprehensive study shows the impact of ML on TE material research, offering valuable insights and accelerating the discovery of materials with enhanced TE properties.

Ultralow thermal conductivity and high thermoelectric performance induced by dimensionality reduction in chain-like compounds X2PtSe2 (X=K, rb)

Balancing low lattice thermal conductivity (κL) with a high power factor is a major challenge in the research of thermoelectric (TE) materials. In this paper, we report on a class of chain-like compounds, X2PtSe2(X = K, Rb), characterized by strong lattice anharmonicity, weak bonds, and low phonon group velocities. Using first-principles calculations in conjunction with self-consistent phonon theory and the Boltzmann transport equation, we systematically investigate the thermal and electrical transport properties of X2PtSe2(X = K, Rb). At room temperature, the κL of K2PtSe2 and Rb2PtSe2 in the direction perpendicular to the Pt–Se chains is only 0.15 and 0.10 Wm−1K−1, respectively. Additionally, due to the low-dimensional nature of the Pt–Se chains, these compounds exhibit a ‘pudding-mold type’ band structure, contributing to a TE power factor. At 300K, under n-type doping, K2PtSe2 and Rb2PtSe2 achieve TE figures of merit (ZT) values of 1.66 and 1.67, respectively, in the direction perpendicular to the Pt–Se chains. At 500K, the ZT value of Rb2PtSe2 approaches 4, far surpassing traditional TE materials. These results indicate that the chain-like compounds X2PtSe2(X = K, Rb) exhibit excellent TE performance, achieving energy conversion efficiencies comparable to commercial transducer devices.

Synergistic Combination of Sb2Si2Te6 Additives for Enhanced Average ZT and Single-Leg Device Efficiency of Bi0.4Sb1.6Te3-based Composites.

Thermoelectric materials are highly promising for waste heat harvesting. Although thermoelectric materials research has expanded over the years, bismuth telluride-based alloys are still the best for near-room-temperature applications. In this work, a ≈38% enhancement of the average ZT (300-473K) to 1.21 is achieved by mixing Bi0.4Sb1.6Te3 with an emerging thermoelectric material Sb2Si2Te6, which is significantly higher than that of most BiySb2-yTe3-based composites. This enhancement is facilitated by the unique interface region between the Bi0.4Sb1.6Te3 matrix and Sb2Si2Te6-based precipitates with an orderly atomic arrangement, which promotes the transport of charge carriers with minimal scattering, overcoming a common factor that is limiting ZT enhancement in such composites. At the same time, high-density dislocations in the same region can effectively scatter the phonons, decoupling the electron-phonon transport. This results in a ≈56% enhancement of the thermoelectric quality factor at 373 K, from 0.41 for the pristine sample to 0.64 for the composite sample. A single-leg device is fabricated with a high efficiency of 5.4% at ΔT = 164 K further demonstrating the efficacy of the Sb2Si2Te6 compositing strategy and the importance of the precipitate-matrix interface microstructure in improving the performance of materials for relatively low-temperature applications.

Optimizing Thermoelectric Performance of Hybrid Crystals Bi2O2Se1-xTex in the Bi2O2X System.

In addressing the global need for sustainable energy conversion, this study presents a breakthrough in thermoelectric materials research by optimizing the Bi2O2Se1-xTex system in the Bi2O2Se/Bi2O2Te pseudobinary series. Leveraging the principles of innovative transport mechanisms and defect engineering, we introduce tellurium (Te) doping into Bi2O2Se to enhance its thermoelectric properties synergistically. With the help of various advanced characterization tools such as XRD, SEM, TEM, XPS, FTIR, TGA, LFA, and DSC, combined with relevant resistance and density measurement techniques, we conducted an in-depth exploration of the complex interactions between various factors within thermoelectric materials. We recognize that the balance and synergy of these factors in the thermoelectric conversion process are crucial to achieving efficient energy conversion. Through systematic research, we are committed to revealing the mechanisms of these interactions and providing a solid scientific foundation for the optimal design and performance enhancement of thermoelectric materials. Finally, the advantage coefficient (ZT) of the thermoelectric material has been significantly improved. The crystallographic analysis confirms the formation of a continuous series of mixed crystals with varying Te concentrations, adhering to Vegard's law and exhibiting significant improvements in electrical and thermal conductivities. The Bi2O2Se1-xTex crystals, particularly the Bi2O2Se0.6Te0.4 composition, demonstrate a peak ZT of 0.86 at 373 K. This achievement aligns with recent advancements in defect-enabled mechanisms and band convergence and sets a new standard for high-performance thermoelectrics. The study's findings contribute significantly to the ongoing quest for efficient thermal-to-electrical energy conversion, offering a promising avenue for future sustainable energy technologies.

Achieving Compatible p/n-Type Half-Heusler Compositions in Valence Balanced/Unbalanced Mg1-xVxNiSb.

In thermoelectric and other inorganic materials research, the significance of half-Heusler (HH) compositions following the 18-electron rule has drawn interest in developing and exploiting the potential of intermetallic compounds. For the fabrication of thermoelectric modules, in addition to high-performance materials, having both p- and n-type materials with compatible thermal expansion coefficients is a prerequisite for module development. In this work, the p-type to n-type transition of valence balanced/unbalanced HH composition of Mg1-xVxNiSb was demonstrated by changing the Mg:V chemical ratio. The Seebeck coefficient and power factor of Ti-doped Mg0.57V0.33Ti0.1NiSb are -130 μV K-1 and 0.4 mW m-1 K-2 at 400 K, respectively. In addition, the reduced lattice thermal conductivity (κL < 2.5 W m-1 K-1 at 300 K) of n-type compositions was reported to be much smaller than κL of conventional HH materials. As high thermal conductivity has long been an issue for HH materials, the synthesis of p- and n-type Mg1-xVxNiSb compositions with low lattice thermal conductivity is a promising strategy for producing high-performance HH compounds. Achieving both p- and n-type materials from similar parent composition enabled us to fabricate a thermoelectric module with maximum output power Pmax ∼ 63 mW with a temperature difference of 390 K. This finding supports the benefit of exploring the huge compositional space of valence balanced/unbalanced quaternary HH compositions for further development of thermoelectric devices.

Effects of scattering mechanisms on thermoelectric properties of bismuth

This discussion explores various facets of thermoelectric materials research, focusing on bismuth (Bi) and its semiconductor form (Bi'). It highlights Bi's semiconductor nature and the importance of Bi' in thermoelectric materials. The thermoelectric properties of Bi' are examined, emphasizing temperature-dependent superiority. Electronic lifetimes and thermoelectric properties, considering scattering mechanisms like acoustic and ionized impurity scattering, is discussed. Bi's thermoelectric properties are influenced by temperature and carrier concentration, showing potential superiority over traditional Bi, especially at room temperature. The results show that ZT reaches a maximum value of 0.59 at 300K. The intricate relationship between Bi' thermoelectric performance, temperature, and scattering mechanisms, particularly ionized impurity scattering, is elucidated. In addition, Bi' holds promise for superior thermoelectric performance, offering valuable insights for future material development.

2D Materials for Photothermoelectric Detectors: Mechanisms, Materials, and Devices

Abstract2D materials, with outstanding optical, thermal, and electric properties, are emerging as promising candidates for fabricating high‐performance photodetectors. Recently, impressive progresses have been made in this area and some challenges are remaining to improve the properties of photodetectors. As one important part in the mainstream photodetection mechanisms, photothermoelectric (PTE) effect is showing unique priorities in fabricating advanced photodetectors, especially broadband detection operating in the mid‐infrared and terahertz spectral regime. Here, recent progress on PTE photodetectors based on layered 2D materials is reviewed. The physical mechanism of PTE effect is first discussed and then the optical and thermoelectric properties of various 2D materials are analyzed. Furthermore, strategies to improve the photodetection performance of PTE detectors are summarized in two major categories including enhanced photothermal conversion and thermoelectric conversion processes. Finally, the challenges and prospects for future research in 2D thermoelectric materials and PTE detectors are also provided.

Research progress and prospects of plastic thermoelectric materials

In recent years, significant progress has been made in the research of plastic thermoelectric materials, for example, Ag&lt;sub&gt;2&lt;/sub&gt;S-based alloys. These materials exhibit excellent room-temperature plasticity due to their low slipping barrier energy and high cleavage energy, with synergistic enhancements in plasticity and thermoelectric properties achievable through alloying and doping strategies. The latest study on Mg&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt;-based single crystals demonstrated superior performance in terms of plastic deformation capability and room-temperature thermoelectric properties. Microstructural characterization and theoretical calculation have revealed the crucial role of dislocation glide in the plastic deformation process of Mg&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt; single crystals, especially, the low slipping barrier energy observed in multiple slip systems. Importantly, the Te-doped single-crystalline Mg&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt; shows a power factor of ~55 μW cm&lt;sup&gt;–1&lt;/sup&gt; K&lt;sup&gt;–2&lt;/sup&gt; and &lt;i&gt;ZT&lt;/i&gt; of ~0.65 at room temperature along the &lt;i&gt;ab&lt;/i&gt; plane, which exceed those of the existing ductile thermoelectric materials. These findings not only deepen the understanding of microscopic deformation mechanisms in plastic thermoelectric materials but also establish an important foundation for optimizing material properties and developing novel flexible thermoelectric devices. Future applications of these materials in practical devices still face challenges in thermal stability, chemical stability, and interfacial contact. Addressing these issues will promote the application of plastic thermoelectric materials in the field of flexible electronics.

High-Throughput Screening of High-Performance Thermoelectric Materials with Gibbs Free Energy and Electronegativity.

Thermoelectric (TE) materials are an important class of energy materials that can directly convert thermal energy into electrical energy. Screening high-performance thermoelectric materials and improving their TE properties are important goals of TE materials research. Based on the objective relationship among the molar Gibbs free energy (Gm), the chemical potential, the Fermi level, the electronegativity (X) and the TE property of a material, a new method for screening TE materials with high throughput is proposed. This method requires no experiments and no first principle or Ab initio calculation. It only needs to find or calculate the molar Gibbs free energy and electronegativity of the material. Here, by calculating a variety of typical and atypical TE materials, it is found that the molar Gibbs free energy of Bi2Te3 and Sb2Te3 from 298 to 600 K (Gm = -130.20~-248.82 kJ/mol) and the electronegativity of Bi2Te3 and Sb2Te3 and PbTe (X = 1.80~2.21) can be used as criteria to judge the potential of materials to become high-performance TE materials. For good TE compounds, Gm and X are required to meet the corresponding standards at the same time. By taking Gm = -130.20~-248.82 kJ/mol and X = 1.80~2.21 as screening criteria for high performance TE materials, it is found that the Gm and X of all 15 typical TE materials and 9 widely studied TE materials meet the requirement very well, except for the X of Mg2Si, and 64 pure substances are screened as potential TE materials from 102 atypical TE materials. In addition, with reference to their electronegativity, 44 pure substances are selected directly from a thermochemical data book as potential high-performance TE materials. A particular finding is that several carbides, such as Be2C, CaC2, BaC2, SmC2, TaC and NbC, may have certain TE properties. Because the Gm and X of pure substances can be easily found in thermochemical data books and calculated using the X of pure elements, respectively, the Gm and X of materials can be used as good high-throughput screening criteria for predicting TE properties.

Estimation of Energy Harvesting by Thermoelectric Cement Composites with Nanostructured Graphene and Metallic Oxides

The measurement of electrical power and efficiency of a thermoelectric generator (TEG) holds significant importance in the realm of thermoelectric materials research and development. The present investigation involves the measurement of thermoelectric characteristics, namely electrical conductivity, Seebeck coefficient, and thermal conductivity, of cement composites containing graphene nanoplatelets and metallic oxides (Fe2O3, ZnO, MnO2). These properties are then utilized to determine the electrical power output and efficiency of the aforementioned composites. It is possible to estimate a power output of up to 1.5 W per square meter when utilizing GnP-ZnO-added cement composites, given a temperature differential of approximately 50 °C. This paper additionally discusses the methodology for fabricating a cement composite-based structural TEG module with the aim of augmenting the overall output voltage, power, and efficiency of the system.

High thermoelectric properties of Cu2Te[sbnd]Ag2Te composite with Fe addition and non-stoichiometric Te

Cu2Te-based materials are a type of superionic conductor belonging to the class of phonon-liquid electron-crystal materials and have achieved high ZT values by doping and nanostructuring. However, it is easy to form copper vacancies in Cu2Te which leads to an excessive carrier concentration and then results in a low Seebeck coefficient. Hence, controlling copper ion migration and optimizing carrier concentration is essential to improve the thermoelectric performance of Cu2Te. This paper reports high-performance Cu2TeAg2Te composite with high application value in the low-middle temperature region, which is achieved by fine tuning the carrier concentration using Fe addition and non-stoichiometric Te, as well as controlling the thermal conductivity of composite. A high ZT of ∼1.2 is obtained in AgCu0.97Fe0.03Te0.96 at a low temperature of 573 K. Meanwhile, the phase transition mechanism of Cu2TeAg2Te and its effect on the thermoelectric transport performance are revealed that go beyond nanostructuring and single-doping, which provides a strong theoretical basis for research and performance improvement of thermoelectric materials in this system.

A Critical Review of Machine Learning Techniques on Thermoelectric Materials.

Thermoelectric (TE) materials can directly convert heat to electricity and vice versa and have broad application potential for solid-state power generation and refrigeration. Over the past few decades, efforts have been made to develop new TE materials with high performance. However, traditional experiments and simulations are expensive and time-consuming, limiting the development of new materials. Machine learning (ML) has been increasingly applied to study TE materials in recent years. This paper reviews the recent progress in ML-based TE material research. The application of ML in predicting and optimizing the properties of TE materials, including electrical and thermal transport properties and optimization of functional materials with targeted TE properties, is reviewed. Finally, future research directions are discussed.

Recent progress of cryogenic thermoelectric materials

Solid-state thermoelectric (TE) materials can directly convert heat into electricity and vice versa without any mechanically moving parts or emissions. In recent years, the research of thermoelectric materials has made great progress, especially in the field of waste heat power generation at middle or high temperatures. However, the applications at cryogenic temperatures have not been paid much attention to. Here we review the recent progress of cryogenic thermoelectric materials. Some new trends, strategies and opportunities are discussed. Finally, some prospects for the future research of cryogenic thermoelectric materials are presented.

Thermoelectric properties of the aliovalent half-Heusler alloy Zn0.5Ti0.5NiSb with intrinsic low thermal conductivity

Aliovalent substitutions lead to bond disorder and low lattice thermal conductivities in half-Heusler thermoelectrics.

Approach to Determine the Density‐of‐States Effective Mass with Carrier Concentration‐Dependent Seebeck Coefficient

AbstractBand engineering is an effective strategy to improve the electronic transport properties of semiconductors. In thermoelectric materials research, density‐of‐states effective mass is an undoubted key factor in verifying the band engineering effect and establishing a strategy for enhancing thermoelectric performance. However, estimation of the effective mass is demanding or inaccurate depending on the methods taken. A simple equation is proposed, valid for all degeneracy: Log10 (md*T/300) = (2/3) Log10 (n) − (2/3) [20.3 − (0.00508 × |S|) + (1.58 × 0.967|S|)] that utilizes experimentally determined Seebeck coefficient (S) and carrier concentration (n) to determine the effective mass (md*) at a temperature (T). This straightforward equation, which gives an accurate analysis of the band modulation in terms of md*, is indispensable in designing thermoelectric materials of maximized performance.

Strategies to Improve the Thermoelectric Figure of Merit in Thermoelectric Functional Materials.

In recent years, thermoelectric functional materials have been widely concerned in temperature difference power generation, electric refrigeration and integrated circui, and so on. In this paper, the design and research progress of thermoelectric materials around lifting ZT value in recent years are reviewed. Optimizing the carrier concentration to improve the Seebeck coefficient, the steady improvement of carrier mobility and the influence of energy band engineering on thermoelectric performance are discussed. In addition, the impact of lattice thermal conductivity on ZT value is also significant. We discuss the general law that the synergistic effect of different dimensions, scales, and crystal structures can reduce lattice thermal conductivity, and introduce the new application of electro-acoustic decoupling in thermoelectric materials. Finally, the research of thermoelectric materials is summarized and prospected in the hope of providing practical ideas for expanding the application and scale industrialization of thermoelectric devices.

Structural Modularization of Cu2 Te Leading to High Thermoelectric Performance near the Mott-Ioffe-Regel Limit.

To date, thermoelectric materials research stays focused on optimizing the material's band edge details and disfavors low mobility. Here, the paradigm is shifted from the band edge to the mobility edge, exploring high thermoelectricity near the border of band conduction and hopping. Through coalloying iodine and sulfur, the plain crystal structure is modularized of liquid-like thermoelectric material Cu2 Te with mosaic nanograins and the highly size mismatched S/Te sublattice that chemically quenches the Cu sublattice and drives the electronic states from itinerant to localized. A state-of-the-art figure of merit of 1.4 is obtained at 850 K for Cu2 (S0.4 I0.1 Te0.5 ); and remarkably, it is achieved near the Mott-Ioffe-Regel limit unlike mainstream thermoelectric materials that are band conductors. Broadly, pairing structural modularization with the high performance near the Mott-Ioffe-Regel limit paves an important new path towards the rational design of high-performance thermoelectric materials.

Machine Learning Approach for Maximizing Thermoelectric Properties of BiCuSeO and Discovering New Doping Element

Machine learning (ML) has increasingly received interest as a new approach to accelerating development in materials science. It has been applied to thermoelectric materials research for discovering new materials and designing experiments. Generally, the amount of data in thermoelectric materials research, especially experimental data, is very small leading to an undesirable ML model. In this work, the ML model for predicting ZT of the doped BiCuSeO was implemented. The method to improve the model was presented step-by-step. This included normalizing the experimental ZT of the doped BiCuSeO with the pristine BiCuSeO, selecting data for the BiCuSeO doped at Bi-site only, and limiting important features for the model construction. The modified model showed significant improvement, with the R2 of 0.93, compared to the original model (R2 of 0.57). The model was validated and used to predict the ZT of the unknown doped BiCuSeO compounds. The predicted result was logically justified based on the thermoelectric principle. It means that the ML model can guide the experiments to improve the thermoelectric properties of BiCuSeO and can be extended to other materials.