Improvement Of Thermoelectric Performance Research Articles

A Zn-doped Sb2Te3 flexible thin film with decoupled Seebeck coefficient and electrical conductivity via band engineering.

Sb2Te3-based flexible thin films can be utilized in the fabrication of self-powered wearable devices due to their huge potential in thermoelectric performance. Although doping can significantly enhance the power factor value, the process of identifying suitable dopants is typically accompanied by numerous repeating experiments. Herein, we introduce Zn doping into thermally diffused p-type Sb2Te3 flexible thin films with a candidate dopant validated using the first-principles calculations. Subsequent experiments further corroborated the successful introduction of a Zn dopant and the improvement of thermoelectric performance. Specifically, p-type doping and the increase in the calculated effective mass can significantly increase the Seebeck coefficient, achieving the decoupling of the Seebeck coefficient and electrical conductivity in Sb2Te3 flexible thin films. An outstanding power factor of ∼22.93 μW cm-1 K-2 at room temperature can be obtained in the 0.58% Zn doped Sb2Te3 sample with significant flexibility. The subsequent fabrication of a flexible thermoelectric generator provides the maximum output voltage and output power of ∼53.0 mV and ∼1100 nW with a temperature difference of 40 K, respectively, pointing out the huge potential of Zn-doped Sb2Te3 materials for thermoelectric applications in self-powered wearable devices.

Thermoelectric materials—Challenges, approaches and classes

Thermoelectric (TE) materials have gained significant attention in recent days for their ability to convert waste heat energy into electrical energy. Numerous advances in new and a unique thermoelectric materials have been developed during the last decades due to their ease of device fabrication technique and technology. Thermoelectric research has become a hotspot in materials science over the recent years due to its promising global necessity in energy generation, energy conservation and subsequent utilization. Here this article seeks to highlight some of the recent advances in thermoelectric research such as criteria for ideal TE materials, various strategies that are in practice to improve TE performance and different methodologies adopted in the preparation of TE-based materials. This article also highlights some of the explored state-of-art materials in thermoelectric research to layout a grid for future purposes.

Machine‐Learning‐Assisted Process Optimization for High‐Performance Organic Thermoelectrics

AbstractOptimizing the processing conditions of conjugated polymers is a key step in improving the performance of various organic electronic devices, including organic thermoelectric (TE) devices that are capable of harvesting energy from waste heat. However, the inherent structural and energetic disorders in these materials and their unpredictable property changes after processing complicate the optimization principles, requiring numerous trial‐and‐error experiments to maximize the TE performance. Here, a machine‐learning (ML)‐based design of experiments approach is introduced to address these challenges, and its effectiveness is demonstrated using a representative thiophene‐based doped polymer system for organic TE. This approach not only helps to quantitatively understand how each processing parameter affects the TE properties of the polymer but also facilitates the prediction of optimal processing conditions, leading to achieve maximum TE performance with minimal experiments within a large parameter space. Furthermore, the ML‐based approach is validated by revealing the origins of the power factor maximization at the ML‐predicted processing conditions through analysis of the morphology and electronic states of the doped polymer films. The proposed methodology is applicable to the majority of polymer systems for organic thermoelectric energy conversion and will provide guidelines for determining optimal process conditions and improving TE performance with minimal effort.

Realizing high thermoelectric performance and thermal stability in CuInTe2 through heavy dose Mg doping

Cu based ternary compounds have received intensive attentions as thermoelectric materials but their carrier mobility and thermal stability are subject to native Cu vacancy. In this work, the synergistic improvement in thermoelectric performance and stability in CuInTe2 is presented, facilitated by local chemical bond enhancement. Heavy dose Mg doping on In site can successfully suppress the formation of Cu vacancy in CuInTe2 and its thermal stability is significantly improved. As a result, In comparison to alternative dopants, Mg doping demonstrates a notable capacity for reinforcing the lattice structure through the inhibition of copper vacancies, thereby yielding a considerable enhancement in mobility by 20 %∼50 %, and the zT value of CuIn0.94Mg0.06Te2 exceeds 1.2 at 873 K. By further alloying with Ga on In site, the thermal conductivity is greatly reduced and more surprisingly the thermal stability is continuously enhanced. Notably, in Cu(In0.4Ga0.6)0.94Mg0.06Te2, a peak zT value of 1.72 at 973 K is achieved, while in Cu(In0.6Ga0.4)0.94Mg0.06Te2, an average zT value of 0.82 is attained. This study offers valuable insights into optimizing the thermoelectric performance and thermal stability of Cu-based ternary compounds through effective doping and defect regulation, providing guidance for future research in this field.

Improved Thermoelectric Properties of Selenium Functionalized Pedot

AbstractPolymer‐based chalcogenide composites are gaining attention for thermal energy storage thermoelectric (TE) applications due to their high Seebeck coefficient (S) and electrical conductivity (σ), compared to low thermal conductivity of polymers without electrical optimization. This combination can enhance power factor and ZT while suppressing drawbacks. The energy‐filtering effect of polymer/chalcogenide interfaces may also improve TE performance, further enhancing the potential for improved TE applications. In this work, Poly(3,4‐ethylenedioxythiophene) (PEDOT) was functionalized with selenium (Se), and its structural and thermoelectric (TE) properties were studied. The variations of σ and S, with higher percent of Se content, displays a simultaneous rise in both σ and S values, which is noteworthy. The probable reason behind this increment of both σ and S values is due to the improvement in charge transport in the composites due to a percolating network formed between the Se nanoparticles and PEDOT along with the carrier energy filtering interaction between PEDOT and Se. The highest room temperature ZT value obtained is 0.027 for 82 % of Se content in PEDOT, which is comparable with bulk nanostructured organic‐inorganic hybrid composite materials. This work presents an efficient technique for enhancing the TE properties of polymers through inorganic functionalization.

Enhancing Thermoelectric Performance of n-Type Bi2Te2.7Se0.3 through Incorporation of Amorphous Si3N4 Nanoparticles.

Bi2Te3-based thermoelectric (TE) materials are the state-of-the-art compounds for commercial applications near room temperature. Nevertheless, the application of the n-type Bi2Te2.7Se0.3 (BTS) is restricted by the comparatively low figure of merit (ZT) and intrinsic embrittlement. Here, we show that through dispersion of amorphous Si3N4 (a-Si3N4) nanoparticles both 14% increase in power factor (at 300 K) and 48% decrease in lattice thermal conductivity are simultaneously realized. The increased power factor comes from enhanced thermopower and reduced electrical resistivity while the reduced lattice thermal conductivity originates mainly from scattering of middle- and low-frequency phonons at the incorporated a-Si3N4 nanoparticles. As a result, a large ZTmax = 1.19 (at 373 K) and an average ZTave ∼ 1.12 (300-473 K) with better mechanical properties are achieved for the BTS/0.25 wt % Si3N4 sample. Present results demonstrate that the incorporation of a-Si3N4 is a promising way to improve TE performance.

Enhancement of thermoelectric performance in Mg3(Sb,Bi)2 through engineered lattice strain and controlled carrier scattering

Mg3(Sb,Bi)2 emerges as a promising thermoelectric (TE) material due to its rich elemental composition and high TE performance, offering potential for industrial applications. In this study, we found out that the elevated sintering temperatures can introduce dislocations, vacancies, and nanoscale precipitates in the lattice, inducing desirable lattice strain. Higher lattice strain broadens the phonon dispersion, effectively reducing lattice thermal conductivity. Simultaneously, high-temperature sintering increases grain size, significantly mitigating grain boundary carrier scattering and enhancing carrier mobility. As a result, we observe a 31.4 % increase in lattice strain, a 30 % reduction in lattice thermal conductivity, a 200 % rise in room temperature mobility, ultimately achieving an outstanding figure of merit (zT) of 1.7 at 750 K for Mg3.22Ho0.03Sb1.5Bi0.5. The synergistic effect of engineering lattice strain to minimize lattice thermal conductivity and controlling carrier scattering mechanisms to enhance mobility significantly provides a novel strategy to improve TE performance of Mg3(Sb,Bi)2-based materials.

Structure relations with transport properties in p-type thermoelectric materials: Iron silicides

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe1-xMnxSi2 (0≤x≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe2Si5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi2) through heat treatment. The amount of β-FeSi2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (nH of holes) but decrease the mobility (μH). By substituting Mn to β-FeSi2, the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties.

Enhanced Thermoelectric Performance in Ca-doped AgSbTe2

Thermoelectric materials play a crucial role in applications such as recovering waste heat and refrigeration. We report a thermoelectric figure of merit (zT) of 1.17 at 623 K for AgSb1-xCaxTe2, representing a 31% enhancement compared to pristine AgSbTe2. The improved thermoelectric performance arises from enhancements in both the power factor and lattice thermal conductivity. Dopant substitution of element Ca at the Sb site in AgSbTe2 suppresses the formation of Ag2Te and increases the concentration of p-type charge carriers, leading to enhanced electrical transport properties. Additionally, Ca doping introduces solid solution point defects that enhance phonon scattering, consequently reducing the lattice thermal conductivity of the sample. This work demonstrates that a doping effectively modulates the electrical and thermal transport properties of AgSbTe2, thereby realizing improvements in thermoelectric performance.

Enhanced thermoelectric performance of copper iodide particles/nanowires composite in the low-temperature range.

Thermoelectric (TE) energy harvesting presents a viable method for reducing energy waste by transforming waste thermal energy into electricity. In this study, we fabricated copper iodide (CuI) composites using synthesized CuI nanowires (NWs) and particles to enhance TE performance in the low-temperature range. The Seebeck coefficient (S) was notably higher when a combination of CuI particles and NWs was used, reaching a maximum S of 1614.24 μV K-1 with a 60% NWs content at RT. Electrical conductivity (σ) exhibited an inverse correlation with S, with higher values detected when either particles or NWs were used only. The highest power factor (PF) of 128.44 μW m-1K-2 was recorded at RT with 60% NWs content, demonstrating improved TE performance. Thermal conductivity (κ) diminished when different material structures were employed, enhancing phonon scattering. The maximum figure of merit (ZT) achieved was ∼0.14 with 60% NWs content at 425 K, indicating the potential of this method for improving TE performance. This study offers valuable insights into optimizing TE performance using CuI composites, proposing a promising strategy for energy harvesting from low-temperature sources.

Multifunctional GeMnTe2 Synergistically Optimizes Thermoelectric Properties of SnTe-In2Te3 Alloys.

SnTe-In2Te3 alloys ensure excellent electrical properties in the whole temperature region due to the resonant level. Nevertheless, temperature-sensitive resonance states and single phonon scattering restrict further improvement of thermoelectric performance. Consequently, it is anticipated that additional electrically independent scattering sources should be introduced to impede phonon transport. Here, the SnTe-In2Te3-GeMnTe2 alloy is prepared by further solidifying cubic GeMnTe2, which demonstrates multiple modulation effects. The highly redissolved Mn2+ promotes the valence band convergence, enhances the Seebeck coefficient at higher temperature, and balances the possible weakened resonance level effect at higher carrier concentrations, and a high average power factor (1.94 mW m-1 K-2) is realized over the entire temperature range. Additionally, compensatory vacancies, substitutions, and Ge/Mn precipitates are easily constructed with GeMnTe2 alloying, leading to a further reduction in lattice thermal conductivity, which reaches κl ∼ 0.6 W m-1 K-1 at 850 K. Ultimately, a high peak zT of ∼1.25 (850 K) and a zTave of 0.72 (300-850 K) are realized in (SnTe)2.91(In2Te3)0.03(Ge0.5Mn0.5Te)1.2, and the maximum thermoelectric conversion efficiency of ∼2.8% (ΔT ∼ 450 K) is achieved. The present results indicate multiple effects of GeMnTe2 in enhancing the thermoelectric performance of SnTe-In2Te3 alloys.

Isovalent co-alloying contributes to considerable improvement in thermoelectric performance of BiSe bulks with weak anisotropy

BiSe with intrinsic low thermal conductivity has considered as a promising thermoelectric (TE) material at nearly room temperature. To improve its low thermoelectric figure of merit (zT), in this work, Sb and Te isovalent co-alloying was performed and significantly optimized its TE property with weakly anisotropic characteristic. After substituting Sb on Bi sites, the carrier concentration is suppressed by introduction of Sb Se site defects, which contributes to the increased absolute value of Seebeck coefficient (|S|). Further co-alloying Te on Se of the optimized composition Bi0.7Sb0.3Se, the carrier concentration increased without affecting the |S| due to the enhanced effective mass, which leads to a highest power factor of 12.8 μW/(cm·K2) at 423 K. As a result, a maximum zT of ∼0.54 is achieved for Bi0.7Sb0.3Se0.7Te0.3 along the pressing direction and the average zT (zTave) (from 300 K to 623 K) are drastically improved from 0.24 for pristine BiSe sample to 0.45. Moreover, an energy conversion efficiency ∼4.0% is achieved for a single leg TE device of Bi0.7Sb0.3Se0.7Te0.3when applied the temperature difference of 339 K, indicating the potential TE application.

Thermoelectric performance of chalcogenide-free CaAl-layered double hydroxide–antimony trioxide nanowire composites with low thermal conductivity

Thermoelectric (TE) materials have attracted considerable interest for their potential and the figure of merit ZT serves as a crucial metric for evaluating TE performance. Chalcogenide materials, such as tellurium (Te) and selenium (Se), have been favored for high-performance TE applications. However, their toxic nature raises concerns, demanding exploration of non-toxic alternatives suitable for human-contacting devices.This study focused on antimony trioxide (Sb2O3) due to its high Seebeck coefficient and explored the potential of layered double hydroxide (LDH) materials as a non-toxic alternative for efficient TE materials. Composites of Sb2O3 nanowires integrated with 2D CaAl-LDH were synthesized to reduce thermal conductivity and improve TE performance. The composites displayed enhanced electrical conductivity, resulting in a significantly improved power factor. The introduction of CaAl-LDH facilitated the charge carrier transport paths, leading to better electrical performance. Furthermore, the composites exhibited reduced thermal conductivity due to phonon scattering at the heterointerfaces between Sb2O3 and CaAl-LDH. As a result, the Sb2O3/CaAl-LDH_70 composite achieved a maximal ZT value of 0.0485 at 473 K, demonstrating promising potential for LDH-based composites as environmentally friendly TE materials. These findings contribute to sustainable energy conversion technologies, ensuring progress towards more efficient and biocompatible TE materials.

Ab initio study of mechanical and thermal properties of GeTe-based and PbSe-based high-entropy chalcogenides

GeTe-based and PbSe-based high-entropy compounds have outstanding thermoelectric (TE) performance and crucial applications in mid and high temperatures. Recently, the optimization of TE performance of high-entropy compounds has been focused on reducing thermal conductivity by strengthening the phonon scattering process to improve TE performance. We report a first-principles investigation on nine GeTe-based high-entropy chalcogenide solid solutions constituted of eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) and 13 PbSe-based high-entropy chalcogenide solid solutions: Pb0.99-ySb0.012SnySe1-2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and y = 0) and Pb0.99-ySb0.012SnySe1-2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 and x = 0.25). We have investigated the mechanical properties focusing on Debye temperature (ΘD), thermal conductivity (κ), Grüneisen parameter (γα), dominant phonon wavelength (λdom), and melting temperature (Tm). We find that the lattice thermal conductivity is significantly reduced when GeTe is alloyed into the following compositions: Ge0.75Sb0.13Pb0.12Te, Ge0.61Ag0.11Sb0.13Pb0.12Bi0.01Te, and Ge0.61Ag0.11Sb0.13Pb0.12Mn0.05Bi0.01Te. This reduction is due to the mass increase and strain fluctuations. The results also show that Ge0.61Ag0.11Sb0.13Pb0.12Bi0.01Te solid solution has the lowest Young’s modulus (30.362 GPa), bulk and shear moduli (18.626 and 12.359 GPa), average sound velocity (1653.128 m/sec), Debye temperature (151.689 K), lattice thermal conductivity (0.574 W.m–1.K–1), dominant phonon wavelength (0.692 Å), and melting temperature (535.91 K). Moreover, Ge0.61Ag0.11Sb0.13Pb0.12Bi0.01Te has the highest Grüneisen parameter with a reduced and temperature-independent lattice thermal conductivity. The positive correlation between ΘD and κ is revealed. Alloying of PbSe-based high-entropy by Sb, Sn, Te, and S atoms at the Se and Pb sites resulted in much higher shear strains resulted in the reduction of phonon velocity, a reduced ΘD, and a lower lattice thermal conductivity.

Band engineering enhances thermoelectric performance of Ag-doped Sn0.98Se

Ag doping can effectively increase the carrier concentration of p-type SnSe polycrystalline, thereby enhancing the thermoelectric (TE) performance. However, the key role of the transport valence band in Ag-doped SnSe remains unclear. Particularly, understanding the influence of evaluating the optimal balance between band convergence and carrier mobility on weighted mobility is a primary consideration in designing high-performance TE materials. Here, we strongly confirm through theoretical and experimental evidence that Ag-doped Sn0.98Se can promote the evolution of valence bands and achieve band convergence and density of states distortion. The significantly increased carrier concentration and effective mass result in a dramatic increase in weighted mobility, which favors the achievement of superior power factors. Furthermore, the Debye model reveals the reasons for the evolution of lattice thermal conductivity. Eventually, a superior average power factor and average zT value are obtained in the Ag-doped samples in both directions over the entire test temperature range. This strategy of improving TE performance through band engineering provides an effective way to advance TEs.

Synergistic Improvement in Thermoelectric Performance by Forming Environmentally Benign Transition Metal Oxide Composites with Graphite

Synergistic Improvement in Thermoelectric Performance by Forming Environmentally Benign Transition Metal Oxide Composites with Graphite

Enhancing the Thermoelectric Performance of GeSb4Te7 Compounds via Alloying Se.

Ge-Sb-Te compounds (GST), the well-known phase-change materials, are considered to be promising thermoelectric (TE) materials due to their decent thermoelectric performance. While Ge2Sb2Te5 and GeSb2Te4 have been extensively studied, the TE performance of GeSb4Te7 has not been well explored. Reducing the excessive carrier concentration is crucial to improving TE performance for GeSb4Te7. In this work, we synthesize a series of Se-alloyed GeSb4Te7 compounds and systematically investigate their structures and transport properties. Raman analysis reveals that Se alloying introduces a new vibrational mode of GeSe2, enhancing the interatomic interaction forces within the layers and leading to the reduction of carrier concentration. Additionally, Se alloying also increases the effective mass and thus improves the Seebeck coefficient of GeSb4Te7. The decrease in carrier concentration reduces the carrier thermal conductivity, depressing the total thermal conductivity. Finally, a maximum zT value of 0.77 and an average zT value of 0.48 (300-750 K) have been obtained in GeSb4Te5.5Se1.5. This work investigates the Raman vibration modes and the TE performance in Se-alloyed GeSb4Te7 sheddinglight on the performance optimization of other GST materials.

ZnSe Nanoparticles for Thermoelectrics: Impact of Cu-Doping

The present study investigates the impact of copper doping on the thermoelectric properties of zinc selenide (ZnSe) nanoparticles synthesized by the hydrothermal method. Nanoparticle samples with varying copper concentrations were prepared and their thermoelectric performances were evaluated by measuring the electrical transport properties, the Seebeck coefficient, and extracting the power factor. The results demonstrate that the thermoelectric properties of Cu-doped ZnSe nanoparticles are significantly enhanced by doping, mainly as an effect of an improved electrical conductivity, providing a promising avenue for energy applications of these nanomaterials. To gain further insights into the fundamental mechanisms underlying the observed improvements in thermoelectric performance of the samples, the morphological, structural, and vibrational properties were characterized using a combination of scanning electron microscopy, X-ray diffraction, and Raman spectroscopy.

Doping by Design: Enhanced Thermoelectric Performance of GeSe Alloys Through Metavalent Bonding.

Doping is usually the first step to tailor thermoelectrics. It enables precise control of the charge-carrier concentration and concomitant transport properties. Doping should also turn GeSe, which features an intrinsically a low carrier concentration, into a competitive thermoelectric. Yet, elemental doping fails to improve the carrier concentration. In contrast, alloying with Ag-V-VI2 compounds causes a remarkable enhancement of thermoelectric performance. This advance is closely related to a transition in the bonding mechanism, as evidenced by sudden changes in the optical dielectric constant ε∞ , the Born effective charge, the maximum of the optical absorption ε2 (ω), and the bond-breaking behavior. These property changes are indicative of the formation of metavalent bonding (MVB), leading to an octahedral-like atomic arrangement. MVB is accompanied by a thermoelectric-favorable band structure featuring anisotropic bands with small effective masses and a large degeneracy. A quantum-mechanical map, which distinguishes different types of chemical bonding, reveals that orthorhombic GeSe employs covalent bonding, while rhombohedral and cubic GeSe utilize MVB. The transition from covalent to MVB goes along with a pronounced improvement in thermoelectric performance. The failure or success of different dopants can be explained by this concept, which redefines doping rules and provides a "treasure map" to tailor p-bonded chalcogenides.

Enhancing Carrier Mobility and Seebeck Coefficient by Modifying Scattering Factor

AbstractThermoelectric materials possess the potential for refrigeration and power generation due to their ability to directly convert heat and electricity. Carrier mobility and the Seebeck coefficient are key properties of thermoelectric materials. Improving the effective mass is the most effective and frequent way to optimize the Seebeck coefficient. However, carrier mobility deteriorates dramatically with increasing effective mass and thus limits further improvement of thermoelectric performance. Here, the focus is on the importance of modifying the scattering factor (r) to enhance the electrical properties, and it is found that the anisotropic scattering factor enhances the carrier mobility and Seebeck coefficient of anion‐doped n‐type tin selenide crystals along the out‐of‐plane direction, indicating the potential of modifying r to improve electrical properties. Following this strategy, the average dimensionless figure of merit (ZTave) for iodine‐doped SnSe crystals is significantly improved from 0.84 to 1.57 in 300–773 K. The results emphasize the critical role of scattering factor and propose a new perspective for enhancing carrier mobility, providing a novel strategy to optimize thermoelectric performance.