Significant Enhancement In Thermoelectric Performance Research Articles

Improving Thermoelectric Performance of AgSbTe2 through Suppression of Ag2Te and Band Convergence via Mg and Ti Codoping.

In this study, the impact of codoping Mg and Ti on the thermoelectric performance of AgSbTe2 materials was investigated. Through a two-step synthesis process involving slow cooling and spark plasma sintering, AgSb0.98-xMg0.02TixTe2 samples were prepared. The introduction of Mg and Ti dopants effectively suppressed the formation of the undesirable Ag2Te phase. Density functional theory (DFT) calculations confirmed that Ti doping facilitated the band convergence, leading to a reduction in the effective mass of the carriers. This optimization enhanced carrier mobility and, consequently, electrical conductivity. Additionally, the codoping strategy resulted in the reinforcement of point defects, which contributed to a decrease in lattice thermal conductivity. The AgSb0.98-xMg0.02TixTe2 sample achieved a maximum figure of merit (ZT) value of 1.45 at 523 K, representing an 87% improvement over the undoped AgSbTe2 sample. The average ZT value over the temperature range of 323-573 K was 1.09, marking a significant enhancement in thermoelectric performance. This research demonstrates the potential of Mg and Ti codoping as a strategy to improve the thermoelectric properties of AgSbTe2-based materials.

Phonon mode softening and band convergence induced significant enhancement of thermoelectric performance in strained CdI2-type SnI2 monolayer

Monolayer group IVA metal halides have attracted intensive attention for their excellent thermoelectric performance. Recently, the CdI2-type SnI2 monolayer has been successfully fabricated by molecular beam epitaxy for the first time. The universal two-dimensional growth behavior on different substrates, motivates strain engineering on its thermoelectric performance. Herein, the structure stability and thermoelectric properties of SnI2 monolayer under different strains are systematically investigated, based on first-principles calculations combined with Boltzmann transport theory. The investigation shows that the tensile strain can simultaneously induce phonon mode softening and band convergence, resulting in a significant enhancement in thermoelectric performance. The phonon mode softening for ZA and optical branches further enhances lattice anharmonicity and a reduced thermal conductivity of ∼0.14 Wm−1K−1 at 300 K (∼0.05 Wm−1K−1, 800 K) can be obtained. Additionally, band convergence in valence band improves the Seebeck coefficient and increases power factor. Under +2 % tensile strain, the optimal ZT values of SnI2 monolayer for p-type doping are substantially enhanced up to 3.05 (300 K) and 5.06 (800 K), which are increased by ∼98 % and ∼50 % compared to the case without strain. Our results reveal the close relationship between the phonon mode softening and enhanced anharmonicity, and provide the physical insights into the understanding of the modulation of thermoelectric properties of monolayer SnI2, shedding light on substantially optimizing the thermoelectric performance of monolayer group IVA metal halides family.

Improved Thermoelectric Performance of Sb2Te3 Nanosheets by Coating Pt Particles in Wide Medium-Temperature Zone.

The p-type Sb2Te3 alloy, a binary compound belonging to the V2VI3-based materials, has been widely used as a commercial material in the room-temperature zone. However, its low thermoelectric performance hinders its application in the low-medium temperature range. In this study, we prepared Sb2Te3 nanosheets coated with nanometer-sized Pt particles using a combination of solvothermal and photo-reduction methods. Our findings demonstrate that despite the adverse effects on certain properties, the addition of Pt particles to Sb2Te3 significantly improves the thermoelectric properties, primarily due to the enhanced electronic conductivity. The optimal ZT value reached 1.67 at 573 K for Sb2Te3 coated with 0.2 wt% Pt particles, and it remained above 1.0 within the temperature range of 333-573 K. These values represent a 47% and 49% increase, respectively, compared to the pure Sb2Te3 matrix. This enhancement in thermoelectric performance can be attributed to the presence of Pt metal particles, which effectively enhance carrier and phonon transport properties. Additionally, we conducted a Density Functional Theory (DFT) study to gain further insights into the underlying mechanisms. The results revealed that Sb2Te3 doped with Pt exhibited a doping level in the band structure, and a sharp rise in the Density of States (DOS) was observed. This sharp rise can be attributed to the presence of Pt atoms, which lead to enhanced electronic conductivity. In conclusion, our findings demonstrate that the incorporation of nanometer-sized Pt particles effectively improves the carrier and phonon transport properties of the Sb2Te3 alloy. This makes it a promising candidate for medium-temperature thermoelectric applications, as evidenced by the significant enhancement in thermoelectric performance achieved in this study.

Significant Enhancement of Thermoelectric Performance in Bi0.5 Sb1.5 Te3 Thin Film via Ferroelectric Polarization Engineering.

The Bi0.5 Sb1.5 Te3 (BST) thin film shows great promise in harvesting low-grade heat energy due to its excellent thermoelectric performance at room temperature. In order to further enhance its thermoelectric performance, specifically the power factor and output power, new approaches are highly desirable beyond the common "composition-structure-performance" paradigm. This study introduces ferroelectric polarization engineering as a novel strategy to achieve these goals. A Pb(Zr0.52 Ti0.48 )O3 /Bi0.5 Sb1.5 Te3 (PZT/BST) hybrid film is fabricated via magnetron sputtering. Density functional theory calculationsdemonstrate PZT polarization's influence on charge redistribution and interlayer charge transfer at the PZT/BST interface, facilitating adjustable carrier transport behavior and power factor of the BST film. As a result, a 26.7% enhancement of the power factor, from unpolarized 12.0 to 15.2 µWcm-1 K-2 , is reached by 2kV out-of-plane downward polarization of PZT. Furthermore, a five-leg generator constructed using this PZT/BST hybrid film exhibits a maximum output power density of 13.06Wm-2 at ΔT = 39 K, which is 20.8% higher than that of the unpolarized one (10.81Wm-2 ). The research presents a new approach to enhance thermoelectric thin films' power factor and output performance by introducing ferroelectric polarization engineering.

Significant enhancement in thermoelectric performance of S-shaped germanene nanoribbon devices

Due to the advantages including high efficiency and environmental friendliness, the two-dimensional thermoelectric materials have received huge attention. However, the energy conversion efficiency is not high enough for application. In this work, we have theoretically investigated the thermoelectric performance for both zigzag (ZGeNRs) and armchair (AGeNRs) germanene nanoribbons with edge defects by nonequilibrium Green's function method. For perfect germanene nanoribbons (GeNRs), it is shown that with its width increasing, the maximum of ZT values (ZTmax) decreases monotonously while the phononic thermal conductance increases linearly. For both ZGeNRs and AGeNRs, with increasing defect numbers in longitudinal direction, ZTmax increases monotonously while the phononic thermal conductance decreases. In particular, by introducing periodic defects, the ZTmax of both ZGeNRs and AGeNRs has been raised to above 2, which is due to higher Seebeck coefficient and lower thermal conductance. Our findings provide an effective way to enhance thermoelectric performance, which is beneficial for the design of ultra-thin thermoelectric devices.

Significant enhancement in thermoelectric performance of bulk CrSi2 employing quasi-binary solid solution CrSi2/MnSi1.73

Transition metal silicides, as thermoelectric (TE) materials, offer significant advantages necessary for commercialization of TE technology beyond their niche applications. In the present study, we examine the TE prospects of a quasi-binary solid solution of CrSi2 and MnSi1.73, which are both well-known chemically stable TE materials consisting of earth-abundant and non-toxic constituent elements, synthesized using spark plasma sintering at optimized processing parameters. A state-of-the-art TE figure of merit (ZT) ~ 0.29 at 673 K at an optimized solid solution composition of CrSi2/5 wt% MnSi1.73, which is ~140% higher compared to pristine CrSi2.

Grape juice: an effective liquid additive for significant enhancement of thermoelectric performance of Cu2Se

Grape juice provides a fine-scale and well-mixed dispersion of elemental carbon in a Cu2Se matrix for ultra-high thermoelectric performance.

Selenium-Substituted Diketopyrrolopyrrole Polymer for High-Performance p-Type Organic Thermoelectric Materials.

Development of high-performance organic thermoelectric (TE) materials is of vital importance for flexible power generation and solid-cooling applications. Demonstrated here is the significant enhancement in TE performance of selenium-substituted diketopyrrolopyrrole (DPP) derivatives. Along with strong intermolecular interactions and high Hall mobilities of 1.0-2.3 cm2 V-1 s-1 in doping-states for polymers, PDPPSe-12 exhibits a maximum power factor and ZT of up to 364 μW m-1 K-2 and 0.25, respectively. The performance is more than twice that of the sulfur-based DPP derivative and represents the highest value for p-type organic thermoelectric materials based on high-mobility polymers. These results reveal that selenium substitution can serve as a powerful strategy towards rationally designed thermoelectric polymers with state-of-the-art performances.

Selenium‐Substituted Diketopyrrolopyrrole Polymer for High‐Performance p‐Type Organic Thermoelectric Materials

AbstractDevelopment of high‐performance organic thermoelectric (TE) materials is of vital importance for flexible power generation and solid‐cooling applications. Demonstrated here is the significant enhancement in TE performance of selenium‐substituted diketopyrrolopyrrole (DPP) derivatives. Along with strong intermolecular interactions and high Hall mobilities of 1.0–2.3 cm2 V−1 s−1 in doping‐states for polymers, PDPPSe‐12 exhibits a maximum power factor and ZT of up to 364 μW m−1 K−2 and 0.25, respectively. The performance is more than twice that of the sulfur‐based DPP derivative and represents the highest value for p‐type organic thermoelectric materials based on high‐mobility polymers. These results reveal that selenium substitution can serve as a powerful strategy towards rationally designed thermoelectric polymers with state‐of‐the‐art performances.

Significant enhancement in thermoelectric performance of Mg3Sb2 from bulk to two-dimensional mono layer

Thermoelectric materials can effectively convert waste heat into electrical energy and receive more and more attention. Zintl phase Mg3Sb2 is a typical layered thermoelectric material and the anisotropy in crystalline structure induces strong anisotropy in its thermoelectric properties. As a result, polycrystalline Mg3Sb2 usually can not achieve the maximum thermoelectric performance. Our research proves that the dimensionality reduction in material structure can not only avoid certain crystalline direction's poor thermoelectric properties but also effectively reduce the lattice thermal conductivity. Within the framework of the density functional theory, the thermoelectric performance of two-dimensional Mg3Sb2 mono layer is accurately investigated. The ZT value of the Mg3Sb2 nano-thin film can reach 2.5 at 900 K, which is larger than that of the bulk. The theoretical results indicate that the process of nano-engineered structure can significantly enhance the energy conversion efficiency of thermoelectrics.

Realized high power factor and thermoelectric performance in Cu3SbSe4

We report the realization of high thermoelectric performance in Cu3SbSe4-based materials through Sn-doping and inclusion of Cu3Sb0.94Sn0.06Se2.5S1.5 nanostructure. This significant enhancement in thermoelectric performance is attributed to simultaneous modulation of the electrical and thermal transport. Sn doping can reduce electrical resistivity, maintaining its high power factor. Cu3Sb0.94Sn0.06Se2.5S1.5 nanoparticles dispersed in the matrix can strengthen interface scattering at the phase boundaries, which can effectively scatter the heat-carrying phonons and thus yielding low lattice thermal conductivity. As a result, the figure of merit reaches ∼0.87 at 673 K for Cu3Sb0.96Sn0.04Se4–3% Cu3Sb0.94Sn0.06Se2.5S1.5.

Enhanced thermoelectric performance of P-type Sb2Te3 thin films through organic-inorganic hybridization on flexible substrate

In this work, a new idea of organic-inorganic hybridization was proposed to fabricate flexible p-type - Sb2Te3/CH3NH3I thin films. The CH3NH3I has a strong adsorption which can promote the growth of organic molecules, improve the crystallization, and finally increase electrical conductivity. Post-annealing of the fabricated films increased the phonon scattering, thus resulting in a reduction of thermal conductivity and an increased ZT value. The annealed hybrid-composite film showed a significant enhancement in thermoelectric performance, with a maximum ZT value of 0.94 at a temperature of 413 K, which is twice as large as that of the as-deposited film.

Flexible n-type thermoelectric composite films with enhanced performance through interface engineering and post-treatment

Flexible thermoelectric (TE) materials, which are devices that convert thermal gradients to electrical energy, have attracted interest for practical energy-harvesting/recovery applications. However, as compared with p-type materials, the progress on the development of n-type TE flexible materials has been slow due to difficulties involved in n-type doping techniques. This study used high mobility carbon nanotubes (CNTs) to a uniformly mixed hybrid-composite, resulting in an enhanced power factor by increasing electrical conductivity. The energy filtering effect and stoichiometric composition of the material used, bismuth telluride (Bi2Te3) correlated to a significant enhancement in TE performance, with a power factor of 225.9 μW m−1K−2 at room temperature: a factor of 65 higher than as-fabricated composite film. This paper describes a simplified synthesis for the preparation of the composite film that eliminates time-intensive and cost-prohibitive processing, traditionally seen during extrusion and dicing inorganic manufacturing. The resulting post-annealed composite film consisting of Bi2Te3 nanowire and CNTs demonstrate a promising candidate for material that can be used for an n-type TE device that has improved energy conversion efficiency.

Se substitution and micro-nano-scale porosity enhancing thermoelectric Cu2Te**Project supported by the National Natural Science Foundation of China (Grant Nos. 51771126 and 11774247), the Youth Foundation of Science and Technology Department of Sichuan Province, China (Grant No. 2016JQ0051), Sichuan University Outstanding Young Scholars Research Funding (Grant No. 2015SCU04A20), the World First-Class University Construction Funding, and the Fundamental and Frontier Research Project

Binary Cu-based chalcogenide thermoelectric materials have attracted a great deal of attention due to their outstanding physical properties and fascinating phase sequence. However, the relatively low figure of merit zT restricts their practical applications in power generation. A general approach to enhancing zT value is to produce nanostructured grains, while one disadvantage of such a method is the expansion of grain size in heating-up process. Here, we report a prominent improvement of zT in Cu2Te0.2Se0.8, which is several times larger than that of the matrix. This significant enhancement in thermoelectric performance is attributed to the formation of abundant porosity via cold press. These pores with nano- to micrometer size can manipulate phonon transport simultaneously, resulting in an apparent suppression of thermal conductivity. Moreover, the Se substitution triggers a rapid promotion of power factor, which compensates for the reduction of electrical properties due to carriers scattering by pores. Our strategy of porosity engineering by phonon scattering can also be highly applicable in enhancing the performances of other thermoelectric systems.

Significant enhancement in thermoelectric performance of nanostructured higher manganese silicides synthesized employing a melt spinning technique.

The limited thermoelectric performance of p-type Higher Manganese Silicides (HMS) in terms of their low figure-of-merit (ZT), which is far below unity, is the main bottle-neck for realising an efficient HMS based thermoelectric generator, which has been recognized as the most promising material for harnessing waste-heat in the mid-temperature range, owing to its thermal stability, earth-abundant and environmentally friendly nature of its constituent elements. We report a significant enhancement in the thermoelectric performance of nanostructured HMS synthesized using rapid solidification by optimizing the cooling rates during melt-spinning followed by spark plasma sintering of the resulting melt-spun ribbons. By employing this experimental strategy, an unprecedented ZT ∼ 0.82 at 800 K was realized in spark plasma sintered 5 at% Al-doped MnSi1.73 HMS, melt spun at an optimized high cooling rate of ∼2 × 107 K s-1. This enhancement in ZT represents a ∼25% increase over the best reported values thus far for HMS and primarily originates from a nano-crystalline microstructure consisting of a HMS matrix (20-40 nm) with excess Si (3-9 nm) uniformly distributed in it. This nanostructure, resulting from the high cooling rates employed during the melt-spinning of HMS, introduces a high density of nano-crystallite boundaries in a wide spectrum of nano-scale dimensions, which scatter the low-to-mid-wavelength heat-carrying phonons. This abundant phonon scattering results in a significantly reduced thermal conductivity of ∼1.5 W m-1 K-1 at 800 K, which primarily contributes to the enhancement in ZT.

Decoupling of thermal and electrical conductivities by adjusting the anisotropic nature in tungsten diselenide causing significant enhancement in thermoelectric performance

A polycrystalline WSe2 nanocompound was produced via a brief thermal reaction between the atomic elements. It should grow along the in-plane direction with covalent bonds rather than along the through-plane direction with van der Waals forces, leading to both crystallographic and morphological anisotropies. Not only the anisotropies should structurally induce strong phonon scattering but they alleviate possible electron scattering at the van der Waals forces; thus, we greatly reduced thermal conductivity while minimizing electrical conductivity loss. The decoupled conductivities resulted in enhancement in figure of merit, by approximately 70% at 350°C, thus affording a promising material for mid-temperature thermoelectric operations.

Selective generation of Ag interstitial defects in Te-rich Bi2(Te,Se)3 using Ag nanoparticles causing significant improvement in thermoelectric performance

We report significant enhancement in thermoelectric performance of n-type Bi2(Te,Se)3 prepared via conventional melting process. We deposited chemically synthesized Ag nanoparticles onto Te-rich Bi2(Te,Se)3 and sintered the resulting substance to obtain a bulk product. The Ag nanoparticles and excessive Te elements should be converted to interstitial and antisite defects in the product, respectively, which possibly interacted to vary thermoelectric transport properties of the product. We endeavored to balance the concentration of the defects to optimize the properties, and thus we strengthened phonon glass electron crystal characteristic of the product, resulting in the improvement in thermoelectric performance.

Extraordinary Thermoelectric Performance Realized in n-Type PbTe through Multiphase Nanostructure Engineering.

Lead telluride has long been realized as an ideal p-type thermoelectric material at an intermediate temperature range; however, its commercial applications are largely restricted by its n-type counterpart that exhibits relatively inferior thermoelectric performance. This major limitation is largely solved here, where it is reported that a record-high ZT value of ≈1.83 can be achieved at 773 K in n-type PbTe-4%InSb composites. This significant enhancement in thermoelectric performance is attributed to the incorporation of InSb into the PbTe matrix resulting in multiphase nanostructures that can simultaneously modulate the electrical and thermal transport. On one hand, the multiphase energy barriers between nanophases and matrix can boost the power factor in the entire temperature range via significant enhancement of the Seebeck coefficient and moderately reducing the carrier mobility. On the other hand, the strengthened interface scattering at the intensive phase boundaries yields an extremely low lattice thermal conductivity. This strategy of constructing multiphase nanostructures can also be highly applicable in enhancing the performance of other state-of-the-art thermoelectric systems.

Enhanced thermoelectric performance of Se-doped PbTe bulk materials via nanostructuring and multi-scale hierarchical architecture

The combination of feasible bottom-up hydrothermal synthesis is demonstrated to notably enhance thermoelectric performance of the PbTe matrix with different Se-doped contents. The instinct electrical properties are improved by annealing with reducing gas to achieve relatively high power factor. Furthermore, multi-scale hierarchical architecture is established together with the point defects and dislocations introduced by doping Se and the formation of nanoscale participates, couple with increased boundaries and a large grain size scale from 20 nm to 1.5 μm and, resulting in scattering an even broader frequency spectrum of phonon mean free path to reduce the lattice thermal conductivity effectively. Consequently, it plays an essential synergistic optimization to achieve a maximum ZT value of 0.98 at 625 K from the as-prepared n-type PbTe1-xSex (x = 0.06) alloys. This study provides a facile and low-cost method to fabricate multi-scale hierarchical architecture materials on a large scale with significant enhancement of thermoelectric performance.

Usefulness of Mesoporous Silica as a Template for the Preparation of Bundles of Bi Nanowires with Precisely Controlled Diameter Below 10 nm

The reduction of the diameter of Bi nanowires below 10 nm has been an important target because of the theoretical prediction with regard to significant enhancement in thermoelectric performance by size reduction. In this study, we have demonstrated the usefulness of mesoporous silica with tunable pore size as a template for the preparation of thin Bi nanowires with diameters below 10 nm. Bi was deposited within the templates through a liquid phase deposition using hexane and 1,1,3,3-tetramethyldisiloxane as a solvent and reducing agent, respectively. Bundles of thin Bi nanowires with non-crystalline frameworks were successfully obtained after the template removal. The diameter was precisely controlled between about 6 nm and 9 nm. The judicious choices of mesoporous silica and deposition conditions are critical for the successful preparation. The reliable formation of such thin Bi nanowires reported here opens up exciting new possibilities.