Excellent Thermoelectric Performance Research Articles

Optimizing the thermoelectric performance of n-type PbSe through dynamic doping driven by entropy engineering

This work utilized a collaborative optimization approach combining dynamic doping and entropy engineering to enhance the band degeneracy, enabling Pb0.875Sn0.125Se0.5Te0.25S0.25-2at%Cu to achieve excellent thermoelectric performance.

Magnetism-induced diffuse scattering effect triggers excellent thermoelectric performance

This work demonstrates a robust magnetism-induced diffuse scattering effect in improving the room-temperature thermoelectric performance.

Ultralow lattice thermal conductivity and excellent thermoelectric performance of monolayer CdGaInS4: a first-principles investigation.

Monolayer CdGaInS4 is an excellent optoelectronic material, but its thermoelectric properties remain unexplored. Through first-principles studies, we investigate the thermoelectric transport properties of monolayer CdGaInS4. The results show that the degenerate weakly dispersive valence band results in an ultrahigh Seebeck coefficient, and the small parabolic electron pockets lead to good electron mobility and conductivity. The ultralow lattice thermal conductivity is attributed to the complete decoupling and softening of the low frequency out-of-plane mode and the strong bonding anharmonicity, giving rise to significant phonon scattering. These results provide good physical descriptors for the search for and theoretical design of excellent two-dimensional thermoelectric materials, and motivate relative measurements in monolayer CdGaInS4 and its applications as a promising thermoelectric material.

Lone-pair electron-induced low lattice thermal conductivity and excellent thermoelectric performance of AuX (X = S, Se, Te) monolayers

We present a detailed study on the phonon thermal transport and thermoelectric (TE) properties of gold monochalcogenide AuX (X = S, Se, Te) monolayers via first-principles calculations and the Boltzmann transport theory. At room temperature, the calculated lattice thermal conductivity (κl) values in the x-direction (y-direction) were determined to be 12.66 (3.59), 6.06 (1.23), and 3.02 (0.40) W/(m·K) for the AuS, AuSe, and AuTe monolayers, respectively. The analysis of scattering matrix elements and anharmonic scattering rates suggested that the presence of strong bond anharmonicity leads to low κl values. This anharmonicity was induced by the nonlinear electrostatic repulsive force between lone-pair electrons (LPEs) surrounding the chalcogen atom and adjacent bonding electron. Furthermore, the AuS monolayer exhibited the highest bond anharmonicity among the three monolayers. This can be attributed to the reduced strength of the electrostatic repulsive force when electronegativity decreased from S to Se and Te. Although the AuS monolayer exhibited the strongest bond anharmonicity, its κl was still the largest, demonstrating that among the factors that influence κl, harmonic factors have a greater effect than anharmonic parameters. When the atomic mass was increased, the phonon frequencies, phonon group velocities, and κl decreased. Benefiting from low κl induced by LPEs, the maximum ZT values of p-type doped AuSe and AuTe monolayers exceeded 1.0 and 2.0 at T = 800 K, respectively. These results not only confirmed that the introduction of LPEs can reduce the lattice thermal conductivity and enhance the TE performance of 2D materials, but also demonstrated the promising potential of the 2D AuX family for applications in high-temperature TE devices.

Enhanced thermoelectric performance and mechanical strength in GeTe enable power generation and cooling

AbstractFinding a real thermoelectric (TE) material that excels in various aspects of TE performance, mechanical properties, TE power generation, and cooling is challenging for its commercialization. Herein, we report a novel multifunctional Ge0.78Cd0.06Pb0.1Sb0.06Te material with excellent TE performance and mechanical strength, which is utilized to construct candidate TE power generation and cooling devices near room temperature. Specifically, the effectiveness of band convergence, combined with optimized carrier concentration and electronic quality factor, distinctly boosts the Seebeck coefficient, thus greatly improving the power factor. Advanced electron microscopy observation indicates that complex multi‐scale hierarchical structures and strain field distributions lead to ultra‐low lattice thermal conductivity, and also effectively enhance mechanical properties. High ZT ~ 0.6 at 303 K, average ZTave ~ 1.18 from 303 to 553 K, and Vickers hardness of ~200 Hv in Ge0.78Cd0.06Pb0.1Sb0.06Te are obtained synchronously. Particularly, a 7‐pair TE cooling device with a maximum ΔT of ~45.9 K at Th = 328 K, and a conversion efficiency of ~5.2% at Th = 553 K is achieved in a single‐leg device. The present findings demonstrate a unique approach to developing superior multifunctional GeTe‐based alloys, opening up a promising avenue for commercial applications.image

Thermoelectric performance of 1T-ZrS2 bilayer using stacking engineering

Stacking engineering have played the very important role in tuning the structural, electronic and thermoelectric properties of 1 T ZrS2 bilayer. All these calculations are performed by using first principles calculations in conjunction with the Boltzmann transport theory. The structural properties of bilayer with all possible stackings i.e., AA1, AA2, AA3, AB1, AB2 and AB3 along with their respective interlayer distance (d) are calculated. Electronic properties of these stacking bilayers have showed the indirect band gap in all the stacking pattern. The dynamical stability of AA1, AA2 and AA3 stackings are more in comparison to other stacking bilayers. The lattice thermal conductivity with values 0.57 W mK−1, 0.47 W mK−1 and 1.45 W/mK for stackings AA1, AA2 and AA3, are obtained, respectively. The obtained values of ZT are 0.86, 0.83 and 0.82 for AA1, AA2 and AA3 stackings, respectively, at room temperature, for n-type doping. The present study has provided the effective approach for selecting the good stacking pattern of 1 T ZrS2 bilayer for various applications with excellent thermoelectric performance.

Intrinsically large effective mass and multi-valley band characteristics of n-type Bi2[sbnd]Bi2Te3 superlattice-like films

Thermoelectric superlattices are expected to decouple the strong correlation between various thermoelectric parameters, and are an important strategy for excellent thermoelectric performances. The superlattices of (Bi2)m(Bi2Te3)n homologous series are well-known for low lattice thermal conductivity and intriguing topological surface states. However, the impacts of electronic structure on the thermoelectric performance were still not well-understood in (Bi2)m(Bi2Te3)n. To cope with this issue, Bi2Bi2Te3 superlattice-like films with adjustable Bi2/(Bi2+Bi2Te3) molar ratio (R) were successfully fabricated by the molecular beam epitaxy technique. Angle-resolved photoemission spectroscopy measurements combined with theoretical calculations revealed the conduction band evolution from single-valley to multi-valley as R ≥ 0.30, leading to intrinsically high carrier effective mass and improved thermoelectric power factor. Also, the superlattice film (R = 0.46) with the structure close to Bi4Te3 possesses the topological surface state feature around the high symmetry point. As a result of the high effective mass of 3.9 m0 and very high electron density of 2.31 × 1021 cm−3, the film with R = 0.46 acquired the highest power factor of 1.49 mW·m−1·K−2 at 420 K, outperforming that of other (Bi2)m(Bi2Te3)n superlattices. This work lays an essential foundation on understanding the electronic structure and further improving thermoelectric performances of (Bi2)m(Bi2Te3)n homologous series.

Lenaite (AgFeS2): A dynamically stable mineral with excellent thermoelectric performance

Diamond-like chalcopyrites have gained superior attention in thermoelectrics due to their attractive thermal transportation. On the mark of exploring environmental-friendly thermoelectric (TE) materials, this work unveils the suitability of lenaite (AgFeS2) through first-principles calculations. Owing to the beneficial band features leading to favourable effective mass, AgFeS2 exhibits good electron transport characteristics. Concurrently, the ultra-low lattice thermal conductivity of 0.47 W m−1 K−1 is realized at 500 K; ascribed to the large Grüneisen parameter, moderate phonon velocity, and Debye temperature. The combinations of these transport properties yield significant figure of merit of 0.87 at 500 K for 1.39 × 1020 holes per cm3. This study not only emphasis the TE properties of lenaite but also facilitates to understand its fundamental properties, including structural, electron and phonon-related properties.

Anomalous Nernst effect in honeycomb and kagome magnet LaCo5 at room temperature

Magnetic order-induced time reversal symmetry breaking in the kagome lattice is predicted to generate Weyl semimetal and Chern insulating phases. The two-dimensional (2D) honeycomb lattices with spin orbit coupling (SOC) and ferromagnetism are also known to host the Chern insulating phase. Here, we study the transport properties of the ferromagnetic topological material LaCo5 crystals with TC = 840 K, which is the highest among the reported magnetic topological materials up to now. It is composed of 2D Co2 kagome layers that are separated by La–Co1 layers, in which the Co1 atoms exhibit a honeycomb structure. Both the 2D kagome and honeycomb layers exhibit out-of-plane magnetization. The large intrinsic anomalous Hall effect and anomalous Nernst effect of about 4.6 μVK−1 are observed in the ab plane with the B//c configuration at room temperature, which can be attributed to non-zero Berry curvature according to the first-principles calculations. Our results enrich the magnetic topological materials with honeycomb and kagome lattices, providing a good platform for the further study of the QAHE. The excellent thermoelectric performance, high TC, nontoxicity, and low cost also make LaCo5 a promising candidate for the applications of thermoelectric generators and heat flow sensors at high temperatures.

Excellent Thermoelectric Performance in KBaTh (Th = Sb, Bi) Based Half-Heusler Compounds and Design of Actuator for Efficient and Sustainable Energy Harvesting Applications

To examine the structural, optoelectronic, thermodynamic, and thermoelectric properties of KBaTh (Th = Sb, Bi) half-Heuslers, we used the full potential, linearized augmented plane wave (FP_LAPW) approach as in the Wien2K simulator. Generalized gradient approximation (GGA), technique, was used for the structural optimization. Mechanical stability and ductility were inherent characteristics of the studied KBaTh (Th = Sb, Bi). Having band gaps of 1.31 eV and 1.20 eV for the KBaTh (Th = Sb, Bi) compounds, they have a semiconducting character. The KBaTh (Th = Sb, Bi) compounds are suggested for use in optoelectronic devices based on studies of their optical characteristics. Thermoelectric properties were investigated using the Boltzmann transport provided by the BoltzTraP software. Since the acquired figures of merit (ZT) values for the KBaTh (Th = Sb, Bi) compounds are all almost equal to one at room temperature, this demonstrates that these substances can be used in thermoelectric devices. Additionally, we used the Slack method to determine the lattice thermal conductivity of KBaTh (Th = Sb, Bi). Our research shows that the half-Heusler compounds under investigation increase actuator response time and hence can be considered as good materials for actuators.

Excellent thermoelectric transport performance in semiconducting hhk-silicene

Unlike graphene-like silicene, a recently reported hybrid honeycomb-kagome (hhk) silicene is a semiconductor instead of a gapless Dirac-cone, which has great potential applications in semiconducting devices. Here, using first-principles calculations combined with Boltzmann transport equation, we find that hhk-silicene has high Seebeck coefficient and power factor as arising from the moderate band-gap and low effective mass. Meanwhile, compared to graphene-like silicene, the soften acoustic branches and enhanced anharmonicity lead to the extremely low lattice thermal conductivity, i.e., 0.68 W mK−1 at 300 K. Calculated thermoelectric figure of merit reaches 1.98 at 300 K, which is a recorded value among two-dimensional materials, indicating the potential of hhk-silicene as a thermoelectric material.

Realizing excellent thermoelectric performance in Ag-doped Cu2SnSe3-ZnSe solid solution by symmetry modification and stacking promotion

Ternary Cu2SnSe3 exhibits an inherent low symmetry and an unfavorable Seebeck coefficient. By strategic alloying with the highly symmetrical ZnSe, the transformation of a monoclinic structure into a tetragonal one was realized, yielding a higher band degeneracy in the electronic band. Therefore, the highest power factor in Cu2SnSe3-ZnSe solid solution reached 7.39 μW cm−1 K−2 at 773 K. Accompanied by this, the energy barrier for slip initiation during the stacking formation decreased, enabling a higher possibility of stacking faults and twins and a low lattice thermal conductivity as 0.79 W m−1 K−1 at 773 K for (Cu2SnSe3)0.6(ZnSe)0.4. Based on ZnSe alloying, the weaker covalent AgSe bonds are introduced to reduce the phonon velocities and facilitate mass fluctuation by Ag-substitution for Cu, resulting in a very low lattice thermal conductivity as 0.49 W m−1 K−1 at 773 K for (Ag0.2Cu1.8SnSe3)0.6(ZnSe)0.4. Eventually, an excellent ZT of 0.98 was achieved at 773 K for (Ag0.2Cu1.8SnSe3)0.6(ZnSe)0.4 through a progressive optimization on thermoelectric properties. Our work underscored the pivotal role of enhancing structural symmetry, increasing stacking nucleation probability and weakening covalent bonds in realizing excellent thermoelectric performance.

High thermoelectric performance of flexible Ag/Ag2Se composite film on nylon for low-grade energy harvesting

In this work, Ag/Ag2Se composite films with excellent thermoelectric (TE) properties and flexibility are prepared based on a simple one-pot method. By adjusting the nominal ratios of Ag/Se, an optimal Ag/Ag2Se composite film shows a large power factor of ∼2275 μW m−1 K−2 at 300 K. Such an outstanding TE performance of the composite film is due to the unique microstructure and the synergistic effect between the Ag and Ag2Se. Meanwhile, the composite film also shows outstanding flexibility (∼91.8% of the initial electrical conductivity is maintained, and the S is unchanged after 1500 bending cycles with a bending radius of 4 mm). Furthermore, a 4-leg flexible TE generator assembled with the optimal film produces a voltage of 14.06 mV and 4.96 μW at a temperature difference of 30.4 K. This work provides a new inspiration for the preparation of flexible Ag2Se-based films with excellent TE performance near room temperature.

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.

High performance and low thermal conductivity in Bi2Se3 induced by the synergistic regulation of a resonant energy level and microstructure prepared by Se slow-release method

In this study, Bi2Se3 thermoelectric materials with high density, low thermal conductivity, and excellent thermoelectric performance are prepared using a Se slow-release method. It was found that the number of Se defects in the material could be effectively reduced by changing the content of NaCl solvent, and a certain number of Na atoms are introduced into the Bi2Se3 matrix. The carrier concentration of Bi2Se3 is greatly optimized due to the synergistic effect of the two, leading to a gradual increase in the Seebeck coefficient from −94 to −122 μV K−1 at room temperature. Simultaneously, we conducted an in-depth investigation into the effects of Na doping and Se vacancies on the electronic structure of the materials. Our findings indicate that the presence of these two defects gives rise to resonance energy levels and sharpens the density of state peaks near the Fermi level. This discovery further underscores the potential for enhancing thermoelectric performance. Finally, the Bi2Se3(NaCl)10 sample achieved the maximum ZT value of 0.69 at 550 K, and the average ZT within the temperature detection range reached 0.36, increasing the thermoelectric performance of the material.

Cubic phase stabilization and thermoelectric performance optimization in AgBiSe2–SnTe system

AgBiSe2 is a lead-free thermoelectric (TE) material that demonstrates excellent TE performance in its high-temperature cubic phase. However, the known order-disorder transition at around 580 K induces internal stress caused by the sudden change in thermal expansion coefficient, negatively impacting TE device operation. In this study, we heavily alloyed AgBiSe2 with SnTe to increase configurational entropy (ΔS) and maintain disordered cubic phase throughout the entire temperature range. This structure variation from hexagonal to cubic increased the density-of-state effective mass as demonstrated by experimental results and first-principles calculations. Additionally, the lattice thermal conductivity was reduced by multiple point defects. Overall, the average ZT value from 300 K to 773 K increased to 0.3 after SnTe alloying. Our study provides an additional perspective of entropy engineering on thermoelectric properties beyond the conventional phonon scattering, which helps to tailor properties in other TE materials with phase transition.

Magnetic ordering boost excellent thermoelectric performance of flexible films

The poor electrical transport performance of flexible thermoelectric (TE) films is a major bottleneck for the development of in-plane heat dissipation technology based on Peltier effect. Herein, ordered Fe nanoparticles (Fe-NPs) and in-situ Fe3O4 nanoparticles (Fe3O4-NPs) as magnetic functional elements (MFEs) were embedded into Bi0·5Sb1·5Te3 (BST)/epoxy flexible films in order to enhance the TE performance. The remarkable increases in electrical conductivity of BST/MFEs/BST/epoxy flexible films have been confirmed to originate from the carrier mobility increases. The retention of large Seebeck coefficient is attributed to the negative magnetoresistance (MR−) induced by spin-dependent scattering and weak localization effect from MFEs. As a result, the maximum power factor of BST/MFEs/BST/epoxy flexible films increased by 45%, and the maximum cooling temperature difference enhanced by 1.6 times. This work reveals that the ordered MFEs can significantly boost the electro-thermal conversion performance of flexible TE films and the magnetoresistance theory can reveal the scattering mechanism of charge carriers in thermo-electromagnetic flexible films.

Enhanced in-plane thermoelectric properties achieved through the vertical van der Waals stacking of black phosphorus and Ti2C

Vertical van der Waals heterostructures (vdWHs) exhibit considerable freedom in integrating two-dimensional layered materials for achieving excellent performance. In this study, we construct a double-layer Ti2C/BP vdWH by stacking pristine monolayer black phosphorus (BP) and Ti2C vertically. The in-plane thermoelectric properties of BP, Ti2C and Ti2C/BP vdWHs at different temperatures are investigated using density functional theory combined with the non-equilibrium Green's function method. Results showed that the thermoelectric figure of merit (ZT) of Ti2C/BP vdWHs at room temperature (300 K) was approximately 103 and 104 times that of Ti2C and BP, respectively. Because of the mutual compensation of the electronic energy bands and interfacial phonon scattering, Ti2C/BP vdWHs have higher electron conductance and lower phonon conductance than both BP and Ti2C, which significantly enhances the ZT value of these structures. More importantly, the prominent thermoelectric properties of Ti2C/BP vdWHs maintain greater stability as the temperature rises (300–900 K), which leads to a high thermoelectric power factor and ZT value without relying on high temperatures. These results provide a new idea for designing two-dimensional functionalised nanoscale devices with excellent thermoelectric performance.

Multiple approaches of band engineering and mass fluctuation of solution-processed n-type Re-doped MoS2 nanosheets for enhanced thermoelectric power factor

The thermoelectric (TE) performance of Molybdenum disulpide (MoS2) can be improved by the incorporation of nanomaterials. MoS2 has been reported as promising thermoelectric materials due to their large bandgap and low thermal conductivity. In the present work, n-type MoS2 was successfully synthesized by facile hydrothermal route with an excellent thermoelectric performance by introducing rhenium (Re) dopant. The structural and morphological analyses confirmed the incorporation of Re into Mo (Molybdenum) lattice. The thermoelectric results showed that both the electrical conductivity (σ) and Seebeck coefficient (S) has been increased with the increase in Re content (2.5, 5, 7.5 and 10 at%) and temperature (303 K to 700 K), while the thermal conductivity (κ) was low. Doping with Re on MoS2 enhances the electrical conductivity through band engineering, improving carrier concentration and shifting the Fermi level to the conduction band. Introducing a heavy atomic element can reduce the total thermal conductivity by facilitating mass fluctuation. The maximum Seebeck coefficient was obtained as −100 μVK−1 at 500 K for Re 5 at% sample, which is 3.7 times greater than undoped MoS2. In addition, introducing electrons through Re doping induced bipolar conduction. These enhancements have increased the power factor of 8 μWm-1K−2 at 650 K.

Highly Stretchable, Resilient, Adhesive, and Self‐Healing Ionic Hydrogels for Thermoelectric Application

AbstractHarvesting low‐grade waste heat from the natural environment with thermoelectric materials is considered as a promising solution for the sustainable energy supply for wearable electronic devices. For practical applications, it is desirable to endow the thermoelectric materials with excellent mechanical and self‐healing properties, which remains a great challenge. Herein, the design and characterization of a series of high‐performance ionic hydrogels for soft thermoelectric generator applications are reported. Composed of a physically cross‐linked network of polyacrylic acid (PAA) and polyethylene glycol (PEO) doped with sodium chloride, the resulting PAA‐PEO‐NaCl ionic hydrogels demonstrates impressive mechanical strength (breaking stress >1.3 MPa), stretchability (>1100%), and toughness (up to 7.34 MJ m−3). Moreover, the reversible hydrogen bonding interaction and chain entanglement render the ionic hydrogels with excellent mechanical resilience, adhesion properties, and self‐healing properties. At ambient conditions, the electrochemical and thermoelectric performance of the ionic hydrogels can be restored immediately from physical damage such as cutting, and the mechanical healing can be completely restored within 24 h. At the optimized composition, the Seebeck coefficient of the ionic hydrogels can reach 3.26 mV K−1 with a low thermal conductivity of 0.321 W m−1 K−1. Considering the excellent mechanical properties and thermoelectric performance, it is believed that the ionic hydrogels are widely applicable in ionic thermoelectric capacitors to convert low‐grade heat into electricity for soft electronic devices.