High-efficiency Thermoelectric Devices Research Articles

Band engineering of phosphorene/graphene van der Waals nanoribbons toward high-efficiency thermoelectric devices

Band engineering of phosphorene/graphene van der Waals nanoribbons toward high-efficiency thermoelectric devices

Thermoelectric enhancement of a parallel double quantum dot system connecting to Luttinger liquid leads

In this work, we study the thermoelectric properties of the parallel-coupled double quantum dot connected to Luttinger liquid (LL) leads. By applying nonequilibrium Green's function methods, the expressions of the electron current, heat currents, and transport coefficients are derived. We mainly focus on the effect of intralead Coulomb interaction and the spatial asymmetry of the system. Various causes for the enhancement of the thermoelectric efficiency are investigated. We find that Coulomb interactions in the LL not only enhance quantum interference but also considerably enhance thermoelectric effects. For moderately strong intralead interaction, the figure of merit can be considerably high and reach over 60 in the case of weakly coupled to LL leads and detuning of the energy levels, while in the case of strongly coupled to LL leads and the two aligned levels, the figure of merit approaches 8. The quantum interference induced by the Coulomb interaction yields a very high thermoelectric efficiency when the intralead interaction is very strong. These results may provide a design rule for the development of high-efficiency thermoelectric devices and facilitate optimization of device performance.

Mg-Ag-Sb thin films produced by solid-state reactive diffusion

α-MgAgSb is a tellurium-free thermoelectric material that exhibits good thermoelectric properties near room temperature. Being made of relatively abundant elements compatible with the complementary metal oxide semiconductor (CMOS) technology, it is considered as a possible solution for the development of high-efficiency thermoelectric devices for heat waste harvesting in microelectronic setups. This study presents a first attempt to investigate the structural properties of MgAgSb thin films prepared by solid-state reactive diffusion. X-ray diffraction (XRD) was used to follow phase formation in thin films, first, in the case of the binary Ag3Sb and Mg3Sb2 compounds, and then, in the case of the ternary system Mg-Ag-Sb. For the later, in situ XRD was used to follow real-time phase formations during the reaction of the bilayerAg3Sb/Mg3Sb2. The results show that the phase α-MgAgSb can be produced by reactive diffusion at the interface of the bilayer. Furthermore, the three phases α, β, and γ are shown to coexist at 360 °C, which can be the result of the thin film geometry (surface and interface effects) or due to a different stoichiometry between these three phases contrasting with usual belief. At temperatures higher than 450 °C, γ-MgAgSb is the only phase stabilized in the film. This study serves as a benchmark for the production of pure α-MgAgSb thermoelectric thin films by reactive diffusion.

The Influence of Thermoelectric Properties of Nanomaterial and Applications

To assess the thermoelectric qualities of low-dimensional materials, a nanomaterial was created. Due to its inherent nanoscale structure, a one-dimensional thermoelectric material is predicted to have superior thermoelectric characteristics and low heat conductivity. High efficiency thermoelectric energy conversion devices can be realised by taking use of these better features. Graphene and hexagonal boron nitride (h-BN), two-dimensional nanomaterials, are thermally efficient. Due to the differences in the crystal lattice and electrical structure between graphene and h-BN, a new material with novel thermal properties is created when the two join to produce a planar C-BN hybrid structure or a van der Waals heterostructure. We concentrate on these new qualities while reviewing the two new materials, as their thermal properties affect their structure, size, and number of layers. To assess the thermoelectric qualities of low-dimensional materials, a micro-instrument was created. Due to its inherent nanoscale structure, a one-dimensional thermoelectric material is predicted to have superior thermoelectric characteristics and low heat conductivity. High efficiency thermoelectric energy conversion devices can be realised by taking use of these better features. In this study, we used micromachining to create microdevices to examine the thermoelectric characteristics of low-dimensional materials. The system comprises of a tiny thermocouple with a freely suspended heating element acting as the sensing element. Manipulation was used to place an array of Bi2Te3 nanowires made using the silicon template approach on the microdevice. To show the device’s ability to assess the thermoelectric properties of nanomaterials, measurements of the Bi2Te3 bundle’s electrical, thermal, and Beck coefficients were made. More information about this source text source text necessary for further translation details. We offer a synthetic method for producing Cu2ZnGeSe4 nanocrystals with a limited size range and a predetermined composition. By hot pressing, these nanocrystals were employed to create nanomaterials that were tightly packed. These nanoparticles’ Cu2ZnGeSe4 thermoelectric characteristics have been demonstrated to be very good. A figure of merit of up to 0.55 at 450 °C has already been achieved through early refinement of the nanocrystal composition. The performance of thermoelectric (TE) materials is currently the subject of intense research. One of the suggestions for enhancing their TE performance is nanostructuring. However, a nanomaterial’s shape can have a big impact on how it behaves under tension. In this study, we showed that this action uses a microwave-assisted chemical pathway to create zinc oxide (ZnO) in two distinct forms. The molar ratios of the initial precursors were altered to create nanoparticles (NPs) and nanorods (NRs). According to the results, NRs have better TE properties than NPs, especially at higher temperatures.

Nanostructural manipulations for achieving record-high room temperature figure of merit in the ZnSb thin films

Recently, fabrication of high-efficiency miniature thermoelectric devices with thin films has attracted great attention. ZnSb-based thin films have been widely studied owing to their advantages of earth-abundant, eco-friendly, and excellent electron transport properties. However, its thermoelectric performance at room temperature is still low which extremely restricts its application. In this work, we report a high-power factor of 6.2 μWcm−1K−2 and a record-high thermoelectric figure of merit, ZT of 0.35 at room temperature from the non-stoichiometric ZnSb-based thin film, fabricated by a facile magnetron cosputtering technique. Extensive characterizations reveal that all the prepared films have a primary ZnSb phase with good crystallinity, leading to high electrical conductivity. Meanwhile, the carrier concentration is optimized with Zn addition, which contributes to a high Seebeck coefficient, resulting in a decent power factor. Simultaneously, the Zn-rich films also show nanopores, Zn-rich nanophases, and Zn4Sb3 nano inclusions. These induced nanostructures enhance the scattering of medium- and long-wavelength phonons, contributing to the reduction of lattice thermal conductivity. This work demonstrates that rational nanostructure manipulations can achieve high performance in ZnSb thin films, which possess potential applications for the fabrication of miniature thermoelectric devices.

Correction: Computer-aided design of high-efficiency GeTe-based thermoelectric devices

Correction for ‘Computer-aided design of high-efficiency GeTe-based thermoelectric devices’ by Min Hong et al., Energy Environ. Sci., 2020, DOI: 10.1039/d0ee01004a.

Computer-aided design of high-efficiency GeTe-based thermoelectric devices

Enhanced thermoelectric performance by band convergence and superlattice precipitates combined with geometry optimization by computer-aided design produced a segmented thermoelectric device with a record-high conversion efficiency.

Realizing Excellent Thermoelectric Performance of Sb2Te3 Based Segmented Leg with a Wide Temperature Range Using One‐Step Sintering

AbstractTo achieve a wide temperature range and a high figure‐of‐merit, segmented assembling is considered as the most effective method based on optimized low‐temperature and medium‐temperature thermoelectric materials. In this work, divalent magnesium (Mg) as acceptor doping in both Bi0.5Sb1.5Te3 and indium (In) alloyed Sb2Te3 play an important role in improving thermoelectric performance, including enhanced power factor by balancing the electrical conductivity and Seebeck coefficient, reduced bipolar thermal conductivity by delaying occurrence of intrinsic excitation, and reduced lattice thermal conductivity due to point defects. Finally, both the figure‐of‐merit (ZT) value and the corresponding operating temperature range are improved. Typically, Mg0.01Bi0.5Sb1.49Te3 with a ZTave of 1.16 from 300 to 520 K and a ZTave of 0.84 for Mg0.02In0.1Sb1.88Te3 from 500 to 680 K are obtained. To further obtain wide‐temperature high ZT value, p‐type Mg0.01Bi0.5Sb1.49Te3/Mg0.02In0.1Sb1.88Te3 segmented leg with excellent interface bonding and extremely low contact resistivity is successfully fabricated by only one‐step sintering process. The corresponding average ZT value is up to 1.02 with a broad temperature range from 300 to 680 K, and a maximum theoretical conversion efficiency of 12.7% with a temperature difference of 380 K is obtained. This provides guidelines for high efficiency thermoelectric devices.

Engineering Nanoscale Thermal Transport: Size- and Spacing-Dependent Cooling of Nanostructures

Author(s): Frazer, TD; Knobloch, JL; Hoogeboom-Pot, KM; Nardi, D; Chao, W; Falcone, RW; Murnane, MM; Kapteyn, HC; Hernandez-Charpak, JN | Abstract: Nanoscale thermal transport is becoming ever more technologically important with the development of next-generation nanoelectronics, nanomediated thermal therapies, and high efficiency thermoelectric devices. However, direct experimental measurements of nondiffusive heat flow in nanoscale systems are challenging, and first-principle models of real geometries are not yet computationally feasible. In recent work, we used ultrafast pulses of short-wavelength light to uncover a previously-unobserved regime of nanoscale thermal transport that occurs when the width and separation of heat sources are comparable to the mean free paths of the dominant heat-carrying phonons in the substrate. We now systematically compare thermal transport from gratings of metallic nanolines with different periodicities, on both silicon and fused-silica substrates, to map the entire nanoscale thermal transport landscape - from closely spaced through increasingly isolated to fully isolated heat-transfer regimes. By monitoring the surface profile dynamics with subangstrom sensitivity, we directly measure thermal transport from the nanolines into the substrate. This allows us to quantify for the first time how the nanoline separation significantly impacts thermal transport into the substrate, making it possible to reach efficiencies that are within a factor of 2 of the diffusive (i.e., thin-film) limit. We also show that partially isolated nanolines perform significantly worse, because cooling occurs in a regime that is intermediate between close-packed and fully isolated heat sources. This work thus confirms the surprising prediction that closely spaced nanoscale heat sources can cool more quickly than when far apart. These results show that our predictive model is validated by experiment over a broad parameter space, which is important for benchmarking theories that go beyond the Fourier model of heat diffusion, and for informed design of nanoengineered systems.

Key parameters for enhancing the thermoelectric power factor of PEDOT:PSS/PANI-CSA multilayer thin films.

Among the conducting polymers, poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been extensively investigated for organic thermoelectric device applications owing to its high electrical conductivity (σ), flexibility and easy processability. The thermoelectric (TE) power factor – a factor that determines the efficiency of a thermoelectric material, is very critical in developing high-efficiency thermoelectric devices. The TE power factor of PEDOT:PSS requires further enhancement in realizing efficient organic TE devices. Recently, we have reported a layer-by-layer deposition technique to deposit PEDOT:PSS and poly aniline-camphor sulfonic acid (PANI-CSA) forming a PEDOT:PSS/PANI-CSA multilayer (ML) thin film structure with an enhanced thermoelectric power factor up to 49 μW m−1 K−1. However, there exist several ambiguities regarding the parameters that control the TE power factor in (ML) thin films. In order to identify the parameters that control the TE power factor of ML thin films, PEDOT:PSS/PANI-CSA ML thin films have been deposited by varying the deposition conditions such as spin speed, the number of layers, solvent treatment, and thickness of each layer. A thermoelectric power factor up to 325 μW m−1 K−1 is achieved by properly optimizing the spin speed, number of layers, and the thickness of each layer in ML thin films. The enhanced thermoelectric power factor is the result of multiple factors such as stretching of PEDOT chains, structural conformation change from benzoid to quinoid, and excess PSS removal from the top of the PEDOT:PSS layer through solvent treatment and at the PEDOT:PSS/PANI-CSA interface. Our study provides the basis for realizing an enhanced thermoelectric power factor of organic thermoelectric multilayer structures consisting of ultra-thin polymer thin films similar to inorganic superlattices having 2D confinement.

In-Plane Anisotropic Thermal Conductivity of Few-Layered Transition Metal Dichalcogenide Td-WTe2.

2D Td-WTe2 has attracted increasing attention due to its promising applications in spintronic, field-effect chiral, and high-efficiency thermoelectric devices. It is known that thermal conductivity plays a crucial role in condensed matter devices, especially in 2D systems where phonons, electrons, and magnons are highly confined and coupled. This work reports the first experimental evidence of in-plane anisotropic thermal conductivities in suspended Td-WTe2 samples of different thicknesses, and is also the first demonstration of such anisotropy in 2D transition metal dichalcogenides. The results reveal an obvious anisotropy in the thermal conductivities between the zigzag and armchair axes. The theoretical calculation implies that the in-plane anisotropy is attributed to the different mean free paths along the two orientations. As thickness decreases, the phonon-boundary scattering increases faster along the armchair direction, resulting in stronger anisotropy. The findings here are crucial for developing efficient thermal management schemes when engineering thermal-related applications of a 2D system.

The influence of side-coupled quantum dots on thermoelectric effect of parallel-coupled double quantum dot system

The thermoelectric transport properties of a parallel-coupled double quantum dot (PCDQD) system with side-coupled quantum dots (QDs) is investigated by using the Keldysh non-equilibrium Green's function technique. The thermoelectric quantities, including the thermal conductance, thermopower, and thermoelectric figure of merit denoted by ZT, are sensitive to the inter-dot coupling strength. With the help of side-coupled QD, unusual double Fano resonances are created in the conductance spectra to largely enhance the thermoelectric effect at low-temperature. Benefited from the coexistence of local bipolar effect and Fano resonance, the ZT can be improved by one-fold higher than that of original PCDQD system. Moreover, when the asymmetry parameter α, which indicates the geometric arrangement of coupled QDs with a given lead, takes appropriate value, the optimization of ZT can be achieved at high temperature. Our work suggests that the side-coupled QDs scheme holds promise for the designing of high-efficiency thermoelectric conversion devices.

Layered material GeSe and vertical GeSe/MoS2 p-n heterojunctions

Group-IV monochalcogenides are emerging as a new class of layered materials beyond graphene, transition metal dichalcogenides (TMDCs), and black phosphorus (BP). In this paper, we report experimental and theoretical investigations of the band structure and transport properties of GeSe and its heterostructures. We find that GeSe exhibits a markedly anisotropic electronic transport, with maximum conductance along the armchair direction. Density functional theory calculations reveal that the effective mass is 2.7 times larger along the zigzag direction than the armchair direction; this mass anisotropy explains the observed anisotropic conductance. The crystallographic orientation of GeSe is confirmed by angleresolved polarized Raman measurements, which are further supported by calculated Raman tensors for the orthorhombic structure. Novel GeSe/MoS2 p-n heterojunctions are fabricated, combining the natural p-type doping in GeSe and n-type doping in MoS2. The temperature dependence of the measured junction current reveals that GeSe and MoS2 have a type-II band alignment with a conduction band offset of ~0.234 eV. The anisotropic conductance of GeSe may enable the development of new electronic and optoelectronic devices, such as high-efficiency thermoelectric devices and plasmonic devices with resonance frequency continuously tunable through light polarization direction. The unique GeSe/MoS2 p-n junctions with type-II alignment may become essential building blocks of vertical tunneling field-effect transistors for low-power applications. The novel p-type layered material GeSe can also be combined with n-type TMDCs to form heterogeneous complementary metal oxide semiconductor (CMOS) circuits.

The structural properties of InGaN alloys and the interdependence on the thermoelectric behavior

The III-Nitrides are promising candidate for high efficiency thermoelectric (TE) materials and devices due to their unique features which includes high thermal stability. A systematic study of the room temperature TE properties of metalorganic chemical vapor deposition grown InxGa1-xN were investigated for x = 0.07 to 0.24. This paper investigated the role of indium composition on the TE properties of InGaN alloys in particular the structural properties for homogenous material that did not show significant phase separation. The highest Seebeck and power factor values of 507 μV K−1 and 21.84 × 10−4 Wm−1K−1 were observed, respectively for In0.07Ga0.93N at room temperature. The highest value of figure-of-merit (ZT) was calculated to be 0.072 for In0.20Ga0.80N alloy at room temperature.

Integration of low-dimensional materials for energy-harvesting applications: current progress, scope, challenges, and opportunities

AbstractDuring the past few years, scientists have shown that climate change is a serious problem that mandates adequate solutions. Greenhouse gas emissions such as carbon dioxide contribute to heat trapping in the atmosphere, which increases the global temperature. Reducing greenhouse gas emissions and the carbon footprint to zero is an essential step toward maintaining a 2°C temperature change. In doing so, researchers and scientists have focused much attention on finding alternative technologies that provide clean and sustainable energy. In particular, nanotechnology can offer this alternative solution to the ongoing energy crisis. The recent progress in nanomaterial research has focused on the development of high-efficiency optoelectronics, batteries, low-power electronics, and thermoelectric devices for energy generation applications. With the emergence of new nanomaterials, such as carbonaceous materials and transition metal dichalcogenides, new physics have emerged. Scientists and engineers are still eager to answer some of the fundamental issues concerning these nanomaterials, including optical, electrical, and thermal properties. Yet, to this day, nanotechnology solutions to provide a sustainable energy are hinged by the ability to control and fully understand the properties of these nanomaterials. Here, we highlight some of the recent progress carried out in nano-optoelectronics, and share our thoughts on the opportunities and challenges facing low-dimensional devices to generate clean and sustainable energy.

Heat Conduction in Nanostructured Materials Predicted by Phonon Bulk Mean Free Path Distribution

We develop a computational framework, based on the Boltzmann transport equation (BTE), with the ability to compute thermal transport in nanostructured materials of any geometry using, as the only input, the bulk cumulative thermal conductivity. The main advantage of our method is twofold. First, while the scattering times and dispersion curves are unknown for most materials, the phonon mean free path (MFP) distribution can be directly obtained by experiments. As a consequence, a wider range of materials can be simulated than with the frequency-dependent (FD) approach. Second, when the MFP distribution is available from theoretical models, our approach allows one to include easily the material dispersion in the calculations without discretizing the phonon frequencies for all polarizations thereby reducing considerably computational effort. Furthermore, after deriving the ballistic and diffusive limits of our model, we develop a multiscale method that couples phonon transport across different scales, enabling efficient simulations of materials with wide phonon MFP distributions length. After validating our model against the FD approach, we apply the method to porous silicon membranes and find good agreement with experiments on mesoscale pores. By enabling the investigation of thermal transport in unexplored nanostructured materials, our method has the potential to advance high-efficiency thermoelectric devices.

On the interplay between phonon-boundary scattering and phonon-point-defect scattering in SiGe thin films

This paper provides theoretical understanding of the interplay between the scattering of phonons by the boundaries and point-defects in SiGe thin films. It also provides a tool for the design of SiGe-based high-efficiency thermoelectric devices. The contributions of the alloy composition, grain size, and film thickness to the phonon scattering rate are described by a model for the thermal conductivity based on the single-mode relaxation time approximation. The exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield an expression for the rate at which phonons scatter by the thin film boundaries in the presence of the other phonon scattering mechanisms. The rates at which phonons scatter via normal and resistive three-phonon processes are calculated by using perturbation theories with taking into account dispersion of confined acoustic phonons in a two dimensional structure. The vibrational parameters of the model are deduced from the dispersion of confined acoustic phonons as functions of temperature and crystallographic direction. The accuracy of the model is demonstrated with reference to recent experimental investigations regarding the thermal conductivity of single-crystal and polycrystalline SiGe films. The paper describes the strength of each of the phonon scattering mechanisms in the full temperature range. Furthermore, it predicts the alloy composition and film thickness that lead to minimum thermal conductivity in a single-crystal SiGe film, and the alloy composition and grain size that lead to minimum thermal conductivity in a polycrystalline SiGe film.

Disentangling the magnetoelectric and thermoelectric transport in topological insulator thin films

We report transport studies on (Bi,Sb)2Te3 topological insulator thin films with tunable electronic band structure. We find a doping and temperature regime in which the Hall coefficient is negative indicative of electron-type carriers, whereas the Seebeck coefficient is positive indicative of hole-type carriers. This sign anomaly is due to the distinct transport behaviors of the bulk and surface states: the surface Dirac fermions dominate magnetoelectric transport while the thermoelectric effect is mainly determined by the bulk states. These findings may inspire new ideas for designing topological insulator-based high efficiency thermoelectric devices.

Review of nanostructured devices for thermoelectric applications.

A big research effort is currently dedicated to the development of thermoelectric devices capable of a direct thermal-to-electrical energy conversion, aiming at efficiencies as high as possible. These devices are very attractive for many applications in the fields of energy recovery and green energy harvesting. In this paper, after a quick summary of the fundamental principles of thermoelectricity, the main characteristics of materials needed for high efficiency thermoelectric conversion will be discussed, and a quick review of the most promising materials currently under development will be given. This review paper will put a particular emphasis on nanostructured silicon, which represents a valid compromise between good thermoelectric properties on one side and material availability, sustainability, technological feasibility on the other side. The most important bottom-up and top-down nanofabrication techniques for large area silicon nanowire arrays, to be used for high efficiency thermoelectric devices, will be presented and discussed.

Thermoelectric properties of two-dimensional topological insulators doped with nonmagnetic impurities

We present a theoretical study on the thermoelectric properties of two-dimensional topological insulators (2DTIs) doped with nonmagnetic impurities. We develop a tractable model to calculate the electronic band structure without additional input parameters and to evaluate the thermoelectric properties of 2DTIs based on CdTe/HgTe quantum wells. We find that with increasing the doping concentration of nonmagnetic impurity, the edge states dominate the thermoelectric transport and the bulk-state conduction is largely suppressed. For typical sample parameters, the thermoelectric figure of merit ZT (a quantity used to characterize the conversion efficiency of a thermoelectric device between the heat and electricity) can be much larger than 1, which is a great advance over conventional thermoelectric materials. Furthermore, we show that with decreasing the 2DTI ribbon width or the Hall-bar width, ZT can be considerably further improved. These results indicate that the CdTe/HgTe 2DTIs doped with nonmagnetic impurities can be potentially applied as high-efficiency thermoelectric materials and devices.