Large Seebeck Coefficient Research Articles

Ionic Gelatin-Based Flexible Thermoelectric Generator with Scalability for Human Body Heat Harvesting

The prosperity of intelligent wearables brings an increasingly critical problem of power supply. Regular rechargeable lithium or disposable button batteries have some problems, such as limited capacity, frequent replacement, environmental pollution, etc. Wearable energy harvester (WEH) can fundamentally solve these problems. Among WEHs, thermoelectric generator (TEG) is a promising option due to its independence of light condition or the motion of the wearer, and thermoelectric conversion (TEC) has the characteristics of quietness and continuity. Therefore, TEG has become a suitable choice for harvesting low-grade heat energy such as human body heat. Ionic thermoelectric gel (iTEG) has the advantages of a large Seebeck coefficient, freely defined shape and size, low processing cost, wide material sources, easy encapsulation, etc. In this paper, the gelatin-based iTEG is regulated and optimized by silica nanoparticles (SiO2 NPs). The optimal compound quantity of SiO2 NPs is determined, and the optimization mechanism is discussed through a series of characterization tests. Based on the iTEG, a kind of scalable flexible TEGs is proposed, and its preparation method is described in detail. A small wristband TEG (STEG) was made, and its Seebeck coefficient is 74.5 mV/K. Its bendability and stretchability were verified, and the impedance matching experiment was carried out. By charging a capacitor, the STEG successfully lights up an LED at a temperature difference (ΔT) of ~15.5 K. Subsequently, a large extended oversleeve TEG (LTEG) was prepared, and a set of heat sinks was added at the cooling end of the LTEG. Being worn on a volunteer’s forearm, the LTEG output a voltage of more than 3 V at ~20 °C. Through storing the converted energy in a capacitor, the LTEG directly drove a calculator without a DC–DC booster. The proposed iTEG and TEGs in this paper have the prospect of mass production, extending to people’s clothes, harvesting human body heat and directly powering wearable electronics.

Large Seebeck coefficient resulting from chiral interactions in triangular triple quantum dots

We theoretically study thermoelectric transport properties through a triangular triple-quantum-dot (TTQD) structure in the linear response regime using the hierarchical equations of motion approach. It is demonstrated that large Seebeck coefficient can be obtained when properly matching the interdot tunneling strength and magnetic flux at the electron–hole symmetry point, as a result of spin chiral interactions in the TTQD system. We present a systematic investigation of the thermopower (the Seebeck coefficient) dependence on the tunneling strength, magnetic flux, and on-site energy. The Seebeck coefficient shows a clear breakdown of electron–hole symmetry in the vicinity of the Kondo regime, accompanied by the deviation from the semiclassical Mott relation in the Kondo and mixed-valence regimes, which result from the many-body effects of the Kondo correlated induced resonance together with spin chiral interactions.

Suppressed atomic diffusion in flash sintering of bismuth telluride

Bi2Te3 materials were synthesised by the recently developed flash sintering (FS) method, and the rapid densification effect was studied. Whereas a fully densified sample can be obtained with a feeding current of 1.2 kA for 1 s, the limited heating effect reduces grain growth and atomic diffusion. Interestingly, the significant chemical reaction suppression with oxygen contaminants, which induces electron doping, has a meaningful electronic properties impact. The large negative Seebeck coefficient of − 138.9 μV/K in the sample prepared by conventional current sintering of 773 K for 3 min, in which the oxygen diffuses into the Bi2Te3 phase, is significantly reduced to − 8.5 μV/K in the FS sample, much closer to the intrinsic p-type conduction in Bi2Te3 raw powder. These results suggest that the limited FS heating effect may contribute to preserving the intrinsic raw powder properties in the sintered material by avoiding excess atomic diffusion and undesirable reactions.

Electronic structure and thermoelectric properties of orthorhombic spinel-derived AgInSnS4 compound: First-principles investigation

The electronic structure and thermoelectric properties of the orthorhombic spinel-derived AgInSnS4 compound were investigated using the Linearized Full-Potential Augmented Plane Wave Method (FP-LAPW), which is fundamentally based on density functional theory (DFT), in combination with semi-classical Boltzmann transport theory. According to the electronic band structure calculation, the AgInSnS4 compound is a semiconductor with a fundamentally reduced indirect bandgap of about 0.50 eV and 1.27 eV obtained within the GGA-PBE and TB-mBJ approaches, respectively. Moreover, the evaluation of the thermoelectric properties shows that the AgInSnS4 compound has a large Seebeck coefficient combined with high electrical conductivity, resulting in a high figure of merit (ZT) value of 0.81 at high temperature, making it a suitable candidate for thermoelectric applications.

Realizing High‐Performance BiSbTe Magnetic Flexible Films via Acceleration Movement and Hopping Migration of Carriers

AbstractImproving the thermoelectric (TE) performance of Bi2Te3‐based flexible films remains a huge challenge. Herein, high‐performance Ni/epoxy/Bi0.5Sb1.5Te3 magnetic flexible TE films are prepared by incorporating Ni nanoparticles (Ni‐NPs). Atomic‐resolution STEM investigation demonstrates that Te vacancies induced by the orientation reaction between Ni‐NPs and Te from Bi0.5Sb1.5Te3 trigger the presence of negatively charged and anti‐site defects and atomic‐sized electric field in the magnetic flexible TE films and further cause the acceleration movement and hopping migration of carriers. The transport measurements indicate an increased carrier concentration due to the anti‐site defects, while the significant increase of carrier mobility originates from the acceleration movement of carriers. The magnetic scattering and hopping migration of carriers are responsible for maintaining large Seebeck coefficient. As compared to epoxy/Bi0.5Sb1.5Te3 flexible TE film, the maximum power factor of the magnetic flexible TE film with 0.1% Ni‐NPs reaches 2.74 mW m−1 K−2 at 300 K and increases by 61%, while the cooling temperature difference increases by 250%.

Thin films of topological nodal line semimetals as a candidate for efficient thermoelectric converters

Thermoelectric materials intrigue much interest due to their wide range of application such as power generators and refrigerators. The efficiency of thermoelectric materials is quantified by the figure of merit, and a figure greater than unity is desired. To achieve this, a large Seebeck coefficient and low phonon thermal conductivity are required. We show that this can be achieved with a thin film of topological nodal line semimetals. We also discusses the correlation effect and spin current induced by a temperature gradient. The obtained results provide insight for the improvement of thermoelectric materials.

High thermoelectric properties realized in earth abundant Bi2S3 bulk materials via Se and Cl co-doping in solution synthesis process

• Se and Cl co-doped nanostructured Bi 2 S 3 powders were successfully synthesized via hydrothermal. • A high σ value of 483 S cm −1 is obtained at 300 K for the Bi 2 S 2.4 Se 0.4 Cl 0.20 sample. • A high PFave. of 411 μW m −1 K −2 is achieved for the Bi 2 S 2.4 Se 0.4 Cl 0.20 . • The highest ZT value of 0.66 is achieved at 673 K for the Bi 2 S 2.4 Se 0.4 Cl 0.20 sample. Bi 2 S 3 -based alloys are considered promising thermoelectric materials due to their large Seebeck coefficient and low lattice thermal conductivity. However, low electrical conductivity usually leads to poor electrical transport properties, which seriously restricts their further application in thermoelectric refrigeration and/or power generation. In this work, Bi 2 S 3 with high electrical transport properties is synthesized hydrothermally via Se and Cl co-doping. The maximum electrical conductivity value of 483 S cm −1 was obtained for the Bi 2 S 2.4 Se 0.4 Cl 0.20 sample at room temperature. The significant improvement of electrical conductivity gives rise to a high average power factor of 411 μW m −1 K −2 during the measuring temperature range and a peak value of 456 μW m −1 K −2 at 673 K. Benefiting from the largely improved electrical transport properties, a superior ZT value of approximately 0.66 and ZT ave . of 0.36 were obtained for Bi 2 S 2.4 Se 0.4 Cl 0.20 , and the theoretically calculated conversion efficiency reached 5.7%. The results indicate that Bi 2 S 3 is a promising candidate for thermoelectric applications at medium temperatures. A high ZT value in Bi2S3 system of ∼0.66 was achieved at 673 K for Bi2S3 with Se and Cl co-doped through a facile hydrothermal followed by spark plasma sintering.

Electronic structure, optical and thermoelectric properties of Ge2SeS monolayer via first-principles study

The electronic, optical and thermoelectric properties of the Ge 2 SeS monolayer were detailed using the first-principle calculations. The dynamic stability of the Ge 2 SeS structure monolayer has been confirmed by the phonon dispersion curve. Our electronic calculations indicate that the Ge 2 SeS monolayer is a semiconductor at equilibrium state with an indirect bandgap lower/larger than that of the GeS/GeSe monolayer calculated by generalized gradient approximation (GGA) of Perdew Burke Ernzerhof (PBE) functional. The optical properties such as dielectric constant, reflectivity , extinction coefficient, and absorption coefficient versus the energy were investigated. In addition, the thermoelectric properties are obtained using the semi-classical Boltzmann transport theory. The results show a large Seebeck coefficient of 2470 μV/K at 300K, the electronic figure of merit ( ZT e ) is 0.91 in Ge 2 SeS monolayer at 300 K. The predicted optical and thermoelectric properties could make the Ge 2 SeS monolayer a potential candidate for applications in optoelectronic and energy conversion technologies at room temperature. • First-principles calculations on electronic structure, optical and thermoelectric properties of Ge 2 SeS monolayer. • Dynamic stability of the Ge 2 SeS structure monolayer has been confirmed by the phonon dispersion curve. • Ge 2 SeS monolayer is a semiconductor with an indirect bandgap of 1.47 eV. • A high electronic figure of merit (ZT e ) of 0.91 have been predicted in Ge 2 SeS monolayer at 300 K. • Optical properties of the Ge 2 SeS monolayer have been investigated in agreement with reported experimental results.

Phase Analysis and Thermoelectric Properties of Cu-Rich Tetrahedrite Prepared by Solvothermal Synthesis.

Because of the large Seebeck coefficient, low thermal conductivity, and earth-abundant nature of components, tetrahedrites are promising thermoelectric materials. DFT calculations reveal that the additional copper atoms in Cu-rich Cu14Sb4S13 tetrahedrite can effectively engineer the chemical potential towards high thermoelectric performance. Here, the Cu-rich tetrahedrite phase was prepared using a novel approach, which is based on the solvothermal method and piperazine serving both as solvent and reagent. As only pure elements were used for the synthesis, the offered method allows us to avoid the typically observed inorganic salt contaminations in products. Prepared in such a way, Cu14Sb4S13 tetrahedrite materials possess a very high Seebeck coefficient (above 400 μVK−1) and low thermal conductivity (below 0.3 Wm−1K−1), yielding to an excellent dimensionless thermoelectric figure of merit ZT ≈ 0.65 at 723 K. The further enhancement of the thermoelectric performance is expected after attuning the carrier concentration to the optimal value for achieving the highest possible power factor in this system.

Impacts of Ga doping on structural and thermoelectric properties of ZnO bulks sintered by solid-state reaction

Introduction: ZnO-based bulks have been known as high-temperature thermoelectric materials due to their high thermal stability and large Seebeck coefficient. The biggest handicaps of pure ZnO are normally low electrical conductivity and weak thermoelectric power factor. This work aims to improve the electrical and thermoelectric properties of pure ZnO bulks by Ga doping. Methods: The pure ZnO and Zn0.98Ga0.02O bulks were fabricated by solid-state reaction in air at high temperature. The crystalline and microstructural properties of the samples were analyzed by using X-ray diffraction and field-emission scanning electron microscopy, respectively. The dependences on temperature of electrical conductivity, Seebeck coefficient, and power factor were recorded by using a commercial LSR-3 system. Results: The Ga doping increases carrier concentration and density-of-state effective mass, leading to simultaneous improvements in electrical conductivity and Seebeck coefficient of ZnO. At 500oC, the thermoelectric power factor of the Zn0.98Ga0.02O bulk is remarkably enhanced by 36% to 169.8 µV/mK2 as compared to the ZnO. Conclusion: The Ga doping shows not only the significant improvement in power factor, but also the potential for reducing thermal conductivity due to spinel phase segregation. Thus, this work provides a promising solution for controlling the thermoelectric performance of ZnO by doping Ga.

Peierls distortion, large Seebeck coefficient, and dispersibility of green solution phase synthesized tellurium nanoparticles

Tellurium (Te) is an appealing material for thermoelectric and many other applications due to its layered structures and highly anisotropic nature.

Carriers: the Less, the Faster

Thermoelectric (TE) community has long believed that high TE performance requires an optimal carrier concentration traditionally locating in the range of ~1019 to ~1021 cm−3. Herein, we propose that potential high TE performance might also be achieved at lower carrier concentrations of ~1018 to ~1019 cm−3. At this range, extremely large Seebeck coefficient with low thermal conductivity can be effortlessly obtained. The next step to achieve high ZT values is boosting the carrier mobility. We then propose two aspects for carrier mobility optimization, including the strategies of preparing single crystals, improving crystal symmetry, texturing, controlling microscopic defects, sharpening bands, aligning bands, and modulation doping. We also suggest it rather essential to utilize multiple of the strategies to achieve the significant optimization of carrier mobility. Our proposal will be the important guidance for realizing promising performance in new TE materials as well as revisiting the TE performance for traditional systems.

First-principles study on bilayer SnP3 as a promising thermoelectric material.

The bilayer SnP3 is recently predicted to exfoliate from its bulk phase, and motivated by the transition of the metal-to-semiconductor when the bulk SnP3 is converted to the bilayer, we study the thermoelectric performance of the bilayer SnP3 using first-principles combined with Boltzmann transport theory and deformation potential theory. The results indicate that the bilayer SnP3 is an indirect band gap semiconductor and possesses high carrier mobility. The high carrier mobility results in a large Seebeck coefficient observed in both n- and p-doped bilayer SnP3, which is helpful for acquiring a high figure of merit (ZT). Moreover, by analyzing the phonon spectrum, relaxation time, and joint density of states, we found that strong phonon scattering makes the phonon thermal conductivity extremely low (∼0.8 W m-1 K-1 at room temperature). Together with a high power factor and a low phonon thermal conductivity, the maximum ZT value can reach up to 3.8 for p-type doping at a reasonable carrier concentration, which is not only superior to that of the monolayer SnP3, but also that of the excellent thermoelectric material SnSe. Our results shed light on the fact that bilayer SnP3 is a promising thermoelectric material with a better performance than its monolayer phase.

High thermoelectric performance of ZrTe2/SrTiO3 heterostructure

Achieving high thermoelectric performance in thin film heterostructures is essential for integrated and miniatured thermoelectric device applications. In this work, we demonstrate a mechanism and device performance of enhanced thermoelectric performance induced by interfacial effect in a transition metal dichalcogenides-SrTiO3 (STO) heterostructure. Owing to the formed conductive interface and elevated conductivity, the ZrTe2/STO heterostructure presents large thermoelectric power factor of 3.7 × 105 μWcm−1K−2 at 10 K. Formation of quasi-two-dimensional conductance at the interface is attributed for the large Seebeck coefficient and high electrical conductivity, leading to high thermoelectric performance which is demonstrated by a prototype device attaining 3 K cooling with 100 mA current input to this heterostructure. This superior thermoelectric property makes this heterostructure a promising candidate for future thermoelectric device.

Emergence of 1/3 magnetization plateau and successive magnetic transitions in Zintl phase Eu3InAs3

Single crystals of ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ have been successfully synthesized by indium flux reactions. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ crystallizes in the ${\mathrm{Ca}}_{3}\mathrm{Al}{\mathrm{As}}_{3}$-type structure with an orthorhombic space-group $Pnma$. Theoretical calculations indicate that ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ is a semiconductor with a direct band gap of 0.3 eV. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ has large negative Seebeck coefficients in the range of 300--450 \ensuremath{\mu}V/K at room temperature. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ displays two antiferromagnetic transitions (${T}_{N1}=13$ and ${T}_{N2}=10$ K) for both $H\ensuremath{\parallel}b$ and $H\ensuremath{\perp}b$ which can be suppressed by magnetic fields. At 2 K, field-induced ferromagnetic states are reached for both $H\ensuremath{\parallel}b$ and $H\ensuremath{\perp}b$. Particularly, the $H\ensuremath{\parallel}b$ magnetization curves show a plateau at 1/3 of the saturated magnetization and an anomaly at 2/3 of the saturated magnetization. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ is a Zintl phase material showing a 1/3 magnetization plateau here.

Excellent Thermoelectric Performance from In Situ Reaction between Co Nanoparticles and BiSbTe Flexible Films.

Low-cost flexible thermoelectric (TE) films with excellent cooling performance are critical for the in-plane heat dissipation application based on the TE film refrigeration technology. In this work, a flexible film epoxy/Bi0.5Sb1.5Te3 is developed by the incorporation of ferromagnetic Co nanoparticles to improve the electrical transport and cooling performance. The magnetic properties and microstructures clearly indicate that part of Co nanoparticles in situ reacts with Te from Bi0.5Sb1.5Te3 to form CoTe2, as well as BiTe' antisite defects. The electric conductivity is greatly enhanced because of the increased carrier density, while a large Seebeck coefficient is well maintained because of the extra magnetic scattering. The power factor of the flexible film with 0.2 wt % Co nanoparticles reached 2.28 mW·m-1·K-2 at 300 K, increased by 34% compared to the epoxy/Bi0.5Sb1.5Te3 film. The maximum cooling temperature difference is 1.5 times higher compared with the epoxy/Bi0.5Sb1.5Te3 film. This work provides a general method to improve the electrothermal conversion performance of BiSbTe-based flexible films through in situ reaction.

Modulating the optoelectronic and thermoelectric properties of chalcopyrite AgXTe2 (X: Ga, In) via in-plane biaxial strain

The influence of biaxial-in-plan strain on optoelectronic and thermoelectric characteristics of AgXTe2 (X: Ga, In) chalcopyrite type compound has been investigated using density function theory base on full potential linear augmented plane wave technique. The generalized Perdew-Burke-Ernzerhof gradient approximation (PBEsol GGA) is used to optimize unit cell and the Tran-Blaha modified Becke-Johnson (TB-mBJ) approach is employed to improve the electronic, optical and thermoelectric properties. The effects of biaxial strains of the tensile (1%, 2%, 3%) and compression (-1%, -2%, -3%) have been calculated along with contribution of two cations (Ga and In). The calculated band gap of AgGaTe2 and AgInTe2 without strain is 1.17 and 1.13 eV that decreases with applied tensile strain and increases with compressive strain. Without strain maximum absorption is obtained at 1.3 eV and 1.1 eV AgGaTe2 and AgInTe2 respectively, however, tensile and compressive strain shows red and blue shift accordingly. The increase in flatness of valance band with compressive strain results in a large Seebeck coefficient due the large hole effective mass. This identifies AgGaTe2 as a possible efficient thermoelectric material. Consequently, the present study is very useful for developments of desired characteristics by applying strain for optoelectronic and thermoelectric devices.

CuI/Nylon Membrane Hybrid Film with Large Seebeck EffectSupported by the International Scientific and Technological Innovation Cooperation Project between the Governments of Key National R&D Program of China (Grant No. 2018YFE0111500), and the National Natural Science Foundation of China (Grant No. 51972234).

Room-temperature thermoelectric materials are important for converting heat into electrical energy. As a wide-bandgap semiconductor material, CuI has the characteristics of non-toxicity, low cost, and environmental friendliness. In this work, CuI powder was synthesized by a wet chemical method, then CuI film was formed by vacuum assisted filtration of the CuI powder on a porous nylon membrane, followed by hot pressing. The film exhibits a large Seebeck coefficient of 600 μV · K−1 at room temperature. In addition, the film also shows good flexibility (∼95% retention of the electrical conductivity after being bent along a rod with a radius of 4 mm for 1000 times). A finger touch test on a single-leg TE module indicates that a voltage of 0.9 mV was immediately generated within 0.5 s from a temperature difference of 4 K between a finger and the environment, suggesting the potential application in wearable thermal sensors.

Highly Efficient, Ultrabroad PdSe2 Phototransistors from Visible to Terahertz Driven by Mutiphysical Mechanism.

The noble transition metal dichalcogenide palladium diselenide (PdSe2) is an ideal candidate material for broad-spectrum photodetection owing to the large bandgap tunability, high mobility, low thermal conductivity, and large Seebeck coefficient. In this study, self-powered ultrabroadband PdSe2 photodetectors from the visible-infrared to terahertz (THz) region driven by a mutiphysical mechanism are reported. In the visible-infrared region, the photogenerated electron-hole pairs in the PdSe2 body are quickly separated by the built-in electric field at the metal-semiconductor interface and achieve a photoresponsivity of 28 A·W-1 at 405 nm and 0.4 A·W-1 at 1850 nm. In the THz region, PdSe2 photodetectors display a room-temperature responsivity of 20 mA·W-1 at 0.10 THz and 5 mA·W-1 at 0.24 THz based on efficient production of hot carriers in an antenna-assisted structure. Owing to the fast response speed of ∼7.5 μs and low noise equivalent power of ∼900 pW·Hz-1/2, high-resolution transmission THz imaging is demonstrated under an ambient environment at room temperature. Our research validates the great potential of PdSe2 for broadband photodetection and provides a possibility for future optoelectronic applications.

Defect promoted photothermoelectric effect in densely aligned ZnO nanorod arrays for self-powered position-sensitive photodetection

Sustainable light energy from ambient environment has attracted particular attention to meet the ever-growing need of small-scale electronics. The modulation of intercorrelated thermal and electronic transport is one of the crucial aspects for reliable photothermoelectric electronics. Herein, a defect-promoted photothermoelectric effect is demonstrated in densely aligned ZnO nanorod array with rich lattice defects. The defect-rich ZnO device delivers high electrical conductivity and large Seebeck coefficient to enable significant improvement of photothermoelectric energy conversion and self-powered photodetection. The position sensitivity reaches approximately 0.19 mV mm−1, and the temperature gradient induced electric field makes up for the suppression in the photothermoelectric process. The synergism between intrinsic defects and extra temperature field plays an important role in promoting the photothermoelectric properties of dense ZnO nanorod array. This study is interesting for interpreting the thermo-phototronic phenomena as well as demonstrating the possibility of defect engineering and phonon engineering to enable highly efficient light energy scavenging and self-powered photodetection.