Efficient Thermoelectric Devices Research Articles

Comparative study of the structural, magnetic and electrical properties of cuprous delafossites CuBO2(B = Zn, Mn and Er) prepared using the flash auto-combustion technique

Abstract The flash auto-combustion method was utilized to produce Cu-based delafossites of CuBO2 (B = Zn, Mn, and Er). X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) were employed to verify the phase formation, surface morphology, and oxidation states of the synthesized delafossite samples. The crystallite sizes were determined to be 43, 16.76, and 21.66 nm for CuZnO2, CuMnO2, and CuErO2 nanoparticles (NPs), respectively. The magnetic characteristics of CuZnO2, CuMnO2, and CuErO2 samples were studied at room temperature, revealing their paramagnetic nature through the hysteresis effect. The Seebeck coefficient (S) for CuZnO2 was found to be positive, while it was negative for CuMnO2 and CuErO2. The thermoelectric power of CuZnO2 NPs was high, indicating their potential as materials for more efficient thermoelectric devices. Additionally, CuZnO2 exhibited an antimicrobial response against four-gram (+ve) bacteria, four-gram (-ve) bacteria, and the fungus Candida albicans (CA). The data obtained demonstrated that CuZnO2 NPs altered bacterial cell morphology, ultimately leading to bacterial cell death.

Enhancing performance and thermal stability in GeTe thermoelectric joints with cobalt diffusion barrier

This study investigates the influence on thermoelectric properties of p-type GeTe after depositing cobalt (Co) diffusion barrier, and its ability on inhibiting the interfacial reactions that degrades thermoelectric performance of the joint at medium temperatures. Establishing stable interconnections within the joint is essential for ensuring the reliability of the device. By examining the improved thermoelectric properties of GeTe, the research highlights a discovering that the addition of a Co diffusion barrier significantly elevates figure of merit (zT) values of GeTe. Electron probe microanalysis (EPMA) reveals the diffusion of Co into GeTe and the formation of Co–Te intermetallic compounds. As the device ages, there is a substantial increase in contact resistivity at the GeTe joint. After depositing a Co layer and subjecting it to long-term aging, electrical conductivity improves, and thermal conductivity decreases. This improvement occurs because the Co atoms, which have diffused into the GeTe lattice, occupy Ge vacancy sites. Instead of degrading the zT value, Co deposition leads to a 56 % increase in the zT value for the p-type GeTe joint. This study emphasizes the improvement of the zT value rather than pursuing a high peak zT value for GeTe. These results affirm the role of Co as an effective diffusion barrier, contributing to the stability of the joint interface and the enhancement of the thermoelectric properties of GeTe material, offering a viable route for creating more efficient and durable thermoelectric energy conversion devices.

Twist Proximity-Endowed Large Figure of Merit in a Band-Modulated CrI3/1T-MoS2 Moiré Superlattice.

Moiré superlattices with a robust twist proximity effect in the low-dimensional regime can facilitate nanoscale thermoelectric devices. In pristine systems, the low efficiency and lack of proficient control of thermoelectric properties impede desirable advancements in the field of energy conversion. In the present study, we demonstrate remarkable macroscopic thermoelectric response as a consequence of microscopic band structure modulation via the twist proximity in an engineered CrI3/1T-MoS2 moiré superlattice. The local twist effect, which leads to the microscopic phenomena of electron localization, results in a comprehensive electronic structure modulation. Consequently, these local effects convolute the macroscopic thermoelectric effect. Additionally, flat bands and angle-dependent metallic to semiconducting transitions are observed at 10.89, 23.41, and 30° twist angles. We correlate the observed phenomenon with the augmented spin-charge transport and interconversion via the twist proximity effect in its semiconducting phase. The estimated ultralow electronic and lattice thermal conductivities further corroborate with the observed large figure of merit and Seebeck coefficient. The maximum values of the Seebeck coefficient and figure of merit are estimated to be ∼413 μV/K and ∼4.3 at 200 K for 30° under the constant time relaxation approach. The twist-endowed outstanding thermoelectric effect in moiré superlattices with band modulation unveils a distinctive approach to establish efficient thermoelectric devices.

Enhanced Seebeck effect in gated O-shaped Kekulé graphene junctions

The Seebeck effect in graphene with uniform Kekulé lattice distortion has been studied using the tight-binding model combined with the nonequilibrium Green's function method. The numerical results of this work show that the Seebeck coefficient of the O-shaped Kekulé graphene can be enhanced by modulating the gate voltage. At room temperature (T≈300 K), the Seebeck coefficient for the armchair nanoribbon is Sc≈1370μV/K and for the zigzag nanoribbon is Sc≈1260μV/K. At low temperature (T≈128 K), the Seebeck coefficient for the armchair nanoribbon is Sc≈2500μV/K. In addition, the nano-structuration of the O-shaped Kekulé graphene layer induces an anisotropic behavior in the Seebeck effect. Our work provides an idea for the fabrication of efficient and controllable thermoelectric effect devices.

Disordered Ballistic Bismuth Nano-waveguides for Highly Efficient Thermoelectric Energy Conversion.

Junctions based on electronic ballistic waveguides, such as semiconductor nanowires or nanoribbons with transverse structural variations in the order of a large fraction of their Fermi wavelength, are suggested as highly efficient thermoelectric (TE) devices. Full harnessing of their potential requires a capability to either deterministically induce structural variations that tailor their transmission properties at the Fermi level or alternatively to form waveguides that are disordered (chaotic) but can be structurally modified continuously until favorable TE properties are achieved. Well-established methods to realize either of these routes do not exist. Here, disordered bismuth (Bi) waveguides are reported, which are both formed and structurally tuned by electromigration until their efficiency as TE devices is maximized. In accordance with theory, the conductance of the most efficient TE waveguides is in the sub quantum of conductance regime. The stability of these structures is found to be substantially higher than other actively studied devices such as single molecule junctions.

Theoretical study of the thermoelectric properties through a single-molecule junction of Zinc Porphyrin

A theoretical analysis was performed to investigate the transport properties of the Zinc Porphyrin molecule and its response to thermal fluctuations. The renormalization method was used for this analysis, using the Green’s functions technique through the Dyson equation, focusing on first-neighbor interactions. This study produced various results, including energy-dependent transmission probability, current-voltage characteristic curves, electrical and thermal conductance assessments, Seebeck coefficient, and figure of merit (ZT). In order to validate the method used, both the profile results in the transmission probability and the I–V curves were compared with theoretical (DFT) and experimental results, respectively, obtaining significant agreements in the HOMO and LUMO of the molecule, as well as a characteristic behavior of a rectifying device. Complementing the above by calculating the ZT through the molecular system Zn(5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrin) (ZnTPPdT), it was demonstrated that said molecule could be used as an efficient thermoelectric device that allows thermal energy to be converted into electrical energy.

Efficient Zn-based pn-junction thermoelectric device for energy harvesting

Efficient Zn-based pn-junction thermoelectric device for energy harvesting

Enhancing the thermopower of single-molecule junctions by edge substitution effects.

Heteroatom substitution and anchoring groups have an important impact on the thermoelectric properties of single-molecule junctions. Herein, thermoelectric properties of several anthracene derivative based single-molecule junctions are studied by means of first-principles calculations. In particular, we pay great attention to the edge substitution effects and find that edge substitution with nitrogen can induce a transmission peak near the Fermi energy, leading to large transmission coefficients and electrical conductance at the Fermi energy. Additionally, the steep shape of the transmission function gives rise to a high Seebeck coefficient. Therefore, an enhanced power factor can be expected. The robustness of this edge substitution effect has been examined by altering the electrode distance and introducing heteroatoms at different positions. The enhancement of the power factor due to edge substitution makes the studied single-molecule junction a promising candidate for efficient thermoelectric devices.

Minimum entropy production in inhomogeneous thermoelectric materials

Due to their potential applications in energy production based on waste heat, direct solar radiation or other energy sources, semiconductor materials have for years attracted the attention of theoretical and experimental researchers. The focus has been on improving the performance of thermoelectric devices through several strategies and special interest has been placed on materials with spatially inhomogeneous transport properties. Inhomogeneity can be achieved in various ways, all of them leading, to a greater or lesser extent, to an improvement of the thermoelectric performance. In this paper, general linear heat and electric charge transport processes in inhomogeneous materials are addressed. The guiding idea followed here is that there exists a relationship between inhomogeneity (structuring), minimum entropy production and performance which may be fruitfully exploited for designing more efficient thermoelectric semiconductor devices. We first show that the stationary states of such materials are minimum global entropy production states. This constitutes an extension of the validity of Prigogine’s minimum entropy principle. The heat and charge transport equations obtained within the framework of classical irreversible thermodynamics are solved to find the stationary profiles of temperature and self-consistent electric potential in a one-dimensional model of a silicon–germanium alloy subjected to an external temperature difference. This allows us to assess the effect of the spatial inhomogeneity on the thermoelectric performance. We find that, regardless of the value of the applied temperature difference, the system may efficiently operate in a regime of minimum entropy production and high efficiency.

Raman effect and unusual transport properties of Co-doped Mn2FeAl Heusler alloy

Semiconducting materials with a distinctive blend of high electrical and low thermal conductivity are required for efficient thermoelectric devices. In this aspect, Heusler alloys are potential candidates for thermoelectric materials. It has been observed that Co doping in Mn2FeAl enhances the electrical conductivity as well as reduces the thermal conductivity of the system leading to an improvement in figure of merit. The Seebeck coefficient suggested the p-type behavior over the whole temperature range, followed by a maximum at 150 K. Additionally, the electronic properties of the suggest that the observed Raman mode is due to the electronic excitations in the system. Interestingly, this system shows a decoupling between the Seebeck coefficient and electrical conductivity, suggesting the promising potential of as a thermoelectric material and offering valuable insights into its electronic properties.

Controlled caging, flat band and thermoelectric response in a quasi-one dimensional kagomé ribbon

A quasi-one dimensional kagomé ribbon geometry is studied in respect of its band spectrum, electronic transport as well as the thermopower within the tight-binding formalism. Analytic proposition of Bloch bands along with the dispersionless flat band states is seen to be consistent with the numerical evaluation of density of states, transmission and band dispersion. A uniform magnetic flux can act as an external agency to tune the spectral landscape and the transport at will. Flux sensitive band engineering leads to an interesting proposal of tunable thermoelectric performance of an identical model device. The tunable behavior can be explored by the calculation of Seebeck co-efficient. The external magnetic perturbation plays the key role in this demonstration and it is an easily adjustable parameter. We have critically investigated all the characteristic features using the Sommerfeld expansion within a tight-binding framework based on Green’s function formalism. The present analysis may provide useful directive for constructing efficient thermoelectric devices at the nanoscale level.

Ion migration mediated high Seebeck effect in halide perovskites and application in infrared detection

Thermoelectric materials play an important role in thermopower systems, thermal sensing and infrared photo-thermoelectric imaging. Ionic thermoelectric materials have recently attracted attentions considering their relatively high Seebeck coefficient. However, the ionic thermoelectric materials have to use liquid or hydrogels for ion conduction, and are susceptible to leakage, evaporation and portability issues. Metal halide perovskites possess low thermal conductivity and prominent ion migration characteristics, making them theoretically suitable candidates for thermoelectric conversion. Here we present the first-ever study of the ionic thermoelectric properties in typical solid perovskite composition MAPbI3, revealing an extremely high Seebeck coefficient of 35.7 mV/K. Furthermore, the assembled photo-thermoelectric detector of carbon/MAPbI3 single crystal/carbon demonstrated a high response (0.58 V/W) toward infrared light and the imaging test was well resolved. This research provides a novel avenue to investigate efficient thermoelectric devices based on ionic and electronic mixed conductors and develop photo-thermoelectric applications.

Studies on Optoelectronic and Transport Properties of XSnBr3 (X = Rb/Cs): A DFT Insight

Modern manufacturing is aiming for products that are readily available, environmentally sustainable, and energy efficient. This paper delves into the exploration of compounds meeting these criteria. Specifically, we investigate the structural, elastic, optoelectronic, and transport properties of XSnBr3 (X = Rb/Cs) compounds utilizing the full-potential linearized augmented plane wave program (FP LAPW), a component of Wien2K software. Structural optimization is carried out through the generalized gradient approximation (GGA) approach, yielding lattice constants consistent with preceding numerical and experimental studies. The explored XSnBr3 (X = Rb/Cs) materials exhibit ductility and mechanical stability. Notably, XSnBr3 (X = Rb/Cs) displays a direct bandgap, signifying its semiconducting nature. The bandgap values, as determined by the modified Becke–Johnson (mBJ) approach, stand at 2.07 eV for X = Rb and 2.14 eV for XSnBr3 (X = Rb/Cs). Furthermore, utilizing the BoltzTraP software’s transport feature, we investigate thermoelectric properties. Remarkably, XSnBr3 (X = Rb/Cs) demonstrates impressive figures of merit (ZT) at room temperature, implying its potential to serve as a material for highly efficient thermoelectric devices. This research holds promise for contributing to the development of environmentally friendly and energy-efficient technologies.

Latent and controllable doping of stimuli-activated molecular dopants for flexible and printable organic thermoelectric generators

Conjugated polymers (CPs) are a promising class of materials for organic thermoelectric generators (OTEGs); however, achieving high electrical conductivity through molecular doping while maintaining compatibility with thin-film printing processes remains a huge challenge. In this paper, we present a novel doping strategy using stimuli-activated molecular dopants (SAMDs) based on photoacid generators (PAGs) that can be activated by light of a specific wavelength. We demonstrate that this approach can effectively control the doping efficiency and optoelectronic properties of CP-PAG-blended thin films, resulting in a wide range of electrical conductivities. Our selected PAG molecules enabled efficient printing of the CP-PAG mixed solution and yielded a high thermoelectric figure of merit. To elucidate the mechanism behind this high thermoelectric performance, we systematically investigated the morphologies, microstructures, and energy structures of the PAG-doped CP thin films and performed various comparative tests. We also demonstrate the feasibility of using SAMDs to print flexible OTEG modules on thin polyimide substrates. We believe that our work represents a significant step toward the development of efficient, scalable, and sustainable thermoelectric devices for power generation and waste heat recovery, and highlights the advantages of PAG-based SAMDs for printable organic thermoelectrics.

Enhanced spin Seebeck effect via oxygen manipulation

Spin Seebeck effect (SSE) refers to the generation of an electric voltage transverse to a temperature gradient via a magnon current. SSE offers the potential for efficient thermoelectric devices because the transverse geometry of SSE enables to utilize waste heat from a large-area source by greatly simplifying the device structure. However, SSE suffers from a low thermoelectric conversion efficiency that must be improved for widespread application. Here we show that the SSE substantially enhances by oxidizing a ferromagnet in normal metal/ferromagnet/oxide structures. In W/CoFeB/AlOx structures, voltage-induced interfacial oxidation of CoFeB modifies the SSE, resulting in the enhancement of thermoelectric signal by an order of magnitude. We describe a mechanism for the enhancement that results from a reduced exchange interaction of the oxidized region of ferromagnet, which in turn increases a temperature difference between magnons in the ferromagnet and electrons in the normal metal and/or a gradient of magnon chemical potential in the ferromagnet. Our result will invigorate research for thermoelectric conversion by suggesting a promising way of improving the SSE efficiency.

Nanostructured PEDOT-based multilayer thin films with high thermoelectric performances

Intrinsically conductive polymers are considered as one of the most promising candidates for thermoelectric (TE) materials due to their outstanding properties. Prior studies have been primarily focused on conducting polymers such as polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). In particular, currently available cationic water-soluble conjugated polymers are limited because of difficulties in synthetic routes. Herein, a positively charged PEDOT nanoparticles (PEDOT:NPs) dispersed in water are synthesized to serve as a structure directing agent for the development of hierarchical architectures with high flexibility and TE performances. A completely organic composite is fabricated by alternately depositing layers of aqueous solutions of PEDOT:NPs and double-walled carbon nanotubes (DWNT) stabilized with PEDOT:PSS via a layer-by-layer methodology. A 20 bilayer thin film (≈ 2.1 µm thick), comprised of a PEDOT:NPs/DWNT-PEDOT:PSS repeating sequence, exhibits high electrical conductivities of up to 744 S cm−1 and a high Seebeck coefficient up to 83 µV K−1. As a result, the multilayer thin films achieve a power factor of 512 µW m−1 K−2. These excellent TE properties can be attributed to the formation of a three-dimensional conjugated network with a highly ordered structure, which facilitates carrier transport within the film. This organic composite, based on a newly synthesized conducting polymer, with high flexibility and power factor offers a promising route to utilize efficient thermoelectric devices on flexible surfaces.

Experimentally validated machine learning predictions of ultralow thermal conductivity for SnSe materials

Machine-learning (ML) models are used to predict optimal thermoelectric properties for efficient thermoelectric devices.

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.

Grading studies for efficient thermoelectric devices using combined 1D material and device modeling

The efficiency at which thermoelectric generators (TEGs) can convert heat into electrical energy is governed by the properties of the employed functional materials. For a given thermoelectric (TE) material, efficiency needs to be maximized by adjusting, e.g., the carrier concentration n. Usually, chemically homogeneous materials with a constant n along the leg are employed to fabricate TEG. However, for most TE materials, the optimum n has a pronounced temperature dependence, typically increasing toward the hot side of the leg. A local variation of n, either continuously (grading) or discontinuously (segmenting), thus has the potential to increase the efficiency of TEGs substantially. Predictions on efficiency gain are challenging, and an adequate physical model for the thermoelectric transport properties in the material as well as the device is required here. To address this challenge, we have combined a two-band model to describe the material properties with a device model based on the solution of the one-dimensional heat equation. Using Mg2Sn as an example, we have adjusted the n profile to maximize the thermoelectric figure of merit locally. We show that this would result in an increase in conversion efficiency by more than 7% for cold and hot side temperatures of 300 and 700 K, respectively. Using a thermoelectric self-compatibility criterion, we verify that the calculated n profile is indeed close to the best possible one. The presented methodology can be transferred to other material systems, and we show that it can also be used to calculate the effect of other, practically more feasible n profiles.

Theoretical Design of Highly Efficient 2D Thermoelectric Device Based on Janus MoSSe and Graphene Heterostructure

Two dimensional (2D) materials are emerging candidates for thermoelectric applications because of their exceptional electronic and mechanical properties. A serious impediment to improving thermoelectric (TE) efficiency is electrical (σ) and thermal (κ) conductivity, which are related and cannot be tuned separately. In this study, we have shown that the heterostructures of Janus MoSSe and graphene have a negative correlation between electrical and thermal conductivity. It is also possible to design both p-type and n-type legs by using a pure and phosphorus-doped heterostructure. We obtained a power factor of 3410 μW m–1 K–2 for p-type and 2450 μW m–1 K–2 for n-type cases at room temperature. The lattice thermal conductivity is reduced to 13.28 W m–1 K–1 for pure and 8.36 W m–1 K–1 for the P-doped heterostructure from 17.32 W m–1 K–1 for Janus MoSSe at 300 K. A promising figure of merit is obtained for the 2D TE device made by Janus MoSSe and graphene heterostructures.