Performance Of Thermoelectric Devices Research Articles

Geometric Symmetry Breaking and Nonlinearity Can Increase Thermoelectric Power.

Direct thermal-to-electric energy converters typically operate in the linear regime, where the ratio of actual maximum power relative to the ideal maximum power, the so-called fill factor (FF), is 0.25. Here, we show, based on fundamental symmetry considerations, that the leading order nonlinear terms that can increase the FF require devices with broken spatial symmetry. Studying nonlinear, thermoelectric transport across an asymmetric energy barrier defined in a single semiconductor nanowire, we find in both experiment and theory that we can increase the FF as well as maximum power. Geometric symmetry breaking combined with the design of nonlinear behavior thus represents a strategy for increasing the performance of thermoelectric or hot-carrier devices.

Integrating thermoelectric devices in pyrolysis reactors for biochar and electricity co-production

This study proposed an innovative approach to integrating thermoelectric devices with small-scale pyrolysis reactors by using Mizunara (Japanese oak) as the feedstock for biochar production. The primary objective of the study was to enhance the energy efficiency and carbon sequestration potential of the biochar production process by converting waste heat into electricity through thermoelectric devices. Comprehensive steady-state thermal balance analysis revealed that although covering the entire reactor surface with thermoelectric devices can result in excessive heat loss and reduced biochar yield, strategically limiting the installation area allows efficient power generation without considerably compromising biochar production. This balance between electricity generation and biochar yield is critical for optimizing the system’s efficiency. Historically, small-scale waste-heat power generation has been underdeveloped, but our studies have demonstrated that incorporating naturally cooled thermoelectric devices allows the generation of kilowatt-hour (kWh)-scale electricity from waste heat, which would otherwise be discarded. Furthermore, the analysis revealed that with optimized conditions, the CO2 equivalent values of the sequestered carbon can be substantially increased, providing a viable solution for long-term carbon storage. The results highlight the potential of this integrated approach to improve the energy efficiency of biochar production and provide a solution for waste-heat management. Moreover, we assessed the implementation effects by assigning reasonable values for the thermoelectric device performance and provide a robust framework for biomass utilization, waste-heat recovery, and CO2 sequestration.

A novel characteristic curve for thermoelectric cooler application in realistic thermal circumstances: Theory and experiment

On the materials level, the performance of thermoelectric (TE) devices can be defined by the thermoelectric figure of merit (zT). This, however, does not provide a complete picture due to the complex interplay between electronic and thermal transport properties and the uncertain thermal impedance matching between external and internal thermal resistances in different realistic thermal circumstances. Appropriate design of individual material properties and geometry parameters considering the realistic thermal circumstance can greatly enhance the device-level performance of TE devices. In this work, we develop a framework to clarify such interactions in thermoelectric coolers (TEC) with a newly proposed q-h characteristic curve, which can be used to identify how a TEC design is of effectiveness for a specific realistic thermal circumstance. The effects of zT, the individual TE material properties (i.e., thermal conductivity k, electrical conductivity σ and Seebeck coefficient S) as well as the geometry parameters (i.e., pillar height and filling factor) on the q-h characteristic curve are theoretically and experimentally investigated, respectively. TEC modules with higher zT, short pillars and high filling factor show stronger capability to handle high heat flux load, especially for the cases with high heat dissipation coefficient at hot side. The thermal property (k) and electrical properties (σ and S) are responsible for the low heat flux load (e.g., wearable TEC) and high heat flux load (e.g., on-chip TEC cooling), respectively. For wearable TEC, increasing the internal thermal resistance can prevent the back flow heat, which can be achieved with tall pillars, low filling factor and optimizing zT towards lowering thermal conductivity k. For on-chip TEC cooling, reducing the Joule heating and increasing the thermoelectric effect become dominant factors in lowering the code-side temperature of TEC modules. This can be achieved with short pillars, high filling factor and optimizing zT towards increasing the power factor S2σ. This work provides significant insights into the complex interplay between material-level properties, device-level parameters and the external thermal circumstance in determining the performance of TEC devices. The results enable researchers to design optimal TEC devices for realistic applications with different boundary conditions.

Unveiling the potential of Ag2S-based full-inorganic flexible thermoelectric devices for temperature sensors

Thermoelectric sensors, which are capable to convert temperature gradients into electrical signals, hold promise for use in wearable body-temperature monitors and self-powered electronic devices. However, traditional flexible thermoelectric devices constructed with organic materials have been hampered by their low energy conversion efficiency, largely stemming from the lack of ideal materials and optimized device geometry. In this study, we utilize state-of-the-art Ag2S-based inorganic materials and fine-tune the geometric parameters of full-inorganic flexible thermoelectric devices through finite element simulation. Our research reveal that these geometric parameters significantly impact the output performance of the flexible thermoelectric device. With the temperature difference set up as 25 K, the optimized device demonstrates a notable performance enhancement, particularly in terms of power density, which is 84 % higher compared to the pre-optimization state. This work introduces a novel approach for enhancing the performance of full-inorganic flexible thermoelectric devices, and also delves into the potential application of this technology in the realm of respiratory monitoring, underscoring its significance and promising prospects.

Wedge-shape Al and Mg co-doped zinc oxide thin films: A Facile Route to achieve high thermoelectric power factor

Thin film thermoelectric technology has immense potential to become a next-generation power source for small-scale electronics. However, the rapid development of thin film thermoelectric still lacks a controllable structural design to improve the performance of thermoelectric devices for required temperature applications. This work presented a controlled thermoelectric design of ZnO-based thin films by Al and Mg co-doping using ALD. Herein, the Mg-doped ZnO sample exhibits the highest Seebeck coefficient of −311.83 μVK−1 at 500oC, while the maximum thermoelectric power factor of 3.68 μWcm−1K−2 is obtained at 300oC, which drops for higher temperatures. This decrease in power factor resulted from the reduction in electrical conductivity above 300oC. Similarly, the Al and Mg co-doped ZnO sample (Mg/Al ≈2 at%) exhibits a high thermoelectric power factor of 3.85 μWcm−1K−2 for ZnO based material due to its moderate electrical conductivity and Seebeck coefficient value at 325oC and behave monotonically for elevated temperatures. Scanning electron microscope (SEM) images show the formation of wedge-shaped structures for Al-incorporated samples, which helps to boost the overall thermoelectric performance. Additionally, we performed XRD, UV–Vis, Hall, and AFM analysis to get a deep insight into structural, optical, electrical, and surface features of the grown thin films and their linkage with the thermoelectric properties.

Atomic-Resolution Interfacial Reaction Mechanism between Bi2Te3-Based Alloys and Ni Electrodes.

Interdiffusion and solid-solid phase reaction at the interface between thermoelectric (TE) materials and the electrode critically influence interfacial transport properties and the overall energy conversion efficiency during service. Here, the microstructural evolution and diffusion mechanisms at the interfaces between the most widely used Bi2Te3-based TE materials, n-type Bi2Te2.7Se0.3 (BTS) and p-type Bi0.5Sb1.5Te3 (BST), and Ni electrodes were investigated at atomic resolution using spherical aberration-corrected scanning transmission electron microscopy (STEM). The BTS(0001)/Ni and BST(0001)/Ni interfaces were constructed by depositing Ni nanoparticles on mechanically exfoliated BTS and BST bulk materials and subsequent annealing. The interfacial reaction is initially dominated by Ni diffusion into the TE matrix to form NiAs-type NiM intermetallics, while Ni trans-quintuple-layer diffusion only occurs in Sb-rich BST. The Bi-rich BTS is more influenced by the Ni-Te preferential reaction, resulting in NiM abnormal grain growth and the formation of tilted and rotated interfaces. Bi diffusion into the BTS matrix forms a Bi double layer at the interface or Bi2[Bi2(Te,Se)3] as the annealing temperature increases, while Bi diffusion into the Ni thin film greatly accelerates the interfacial reaction rate, as elucidated by in situ heating STEM. The results provide essential structural details to understand and prevent the degradation of TE device performance.

InP3 facilitating high thermoelectric performance in Te-based composites via high pressure

Thermoelectric devices as eco-friendly candidates for energy conversion have attracted increasing interest as a sustainable and emission free solution to solve the environmental problem. Tellurium, is expected to be a suitable candidate, nevertheless, due to the poor electrical property, it has severely hampered the further development in practical application. This work proposes a new fabrication route for bulk Te via high pressure and high temperature method to enhance its power factor by compositing a certain quality of InP3. As InP3 decomposed into indium and black phosphorus under high pressure conditions, both the carrier concentration and Seebeck coefficient was enhanced significantly, leading to a maximum power factor of 11.4 μWcm-1K-2 at 460 K, which increase by 44.2 % compared to the peak value of pristine Te. Moreover, the induced defects, such as point defects, abundant grain boundaries and heterojunctions, strongly influence the thermoelectric performance, with a substantial decrease in lattice thermal conductivity. Consequently, the ZT values are sharply enhanced by InP3 compositing with the highest value reaching ∼0.76 of Te + 0.25 wt% InP3 at 490 K. Importantly, the average ZT value within the 300 K - 600 K range reaches to 0.48, which is 3.5 times that of the pristine Te. This work mark a step toward developing high performance thermoelectric devices for energy conversion, making elemental Te more competitive with high-performance in medium temperature range.

Effect of lattice defects on electronic structure and thermoelectric properties of 2D monolayer MoS2

Molybdenum disulfide (MoS2) is considered as a promising economical and non-toxic thermoelectric material due to its low thermal conductivity and high Seebeck coefficient. However, its power factor is not ideal, which limits its energy conversion efficiency in thermoelectric applications. In this paper, the electronic structure of pure and lattice-defect MoS2 2D monolayer is studied by using the first principles method and non-equilibrium Green's function (DFT-NEGF). The effects of atom substitution and vacancy defect on the thermoelectric properties of MoS2 2D monolayer are also investigated. The result shows that the S-vacancy changes the bandgap by introducing donor and acceptor levels, while the substitution of Se and Te atoms slightly increases the bandgap value. In the case of n-type doping, the ZT value of the S atom substituted MoS2 reaches 1.19 at 300 K, while the Te atom substitution MoS2 has a higher ZT value of almost 2.26 at 800 K. The analysis shows that the thermal conductivity of MoS2 decreases due to the presence of S-vacancy, while the atomic substitution of Se and Te increases the power factor of MoS2. This work may provide a new method and theoretical guidance for achieving high performance of thermoelectric devices in the energy industry.

Investigating the Thermal Conductance of the Cu/Si Interface Using the Molecular Dynamics Method

Investigating thermal transport at the Cu/Si interface holds significant importance, as understanding interface thermal conductance is crucial for enhancing materials interface thermal management, designing thermal interface materials, and improving the performance of thermoelectric devices. In this study, we conducted molecular dynamics simulations in conjunction with the Green–Kubo relation to calculate the thermal conductance of the Cu/Si interface. We successfully obtained Cu/Si interface potentials using the lattice inversion method. Our findings revealed that the thermal conductance of the Cu/Si interface is notably influenced by the interface structure. Specifically, the thermal conductance of the Cu(001)/Si(001) interface and the Cu(111)/Si(111) interface are similar, and both are higher than that of the Cu(110)/Si(110) interface. Furthermore, through first-principles calculations of the adhesion energy, we discovered that interface binding strength plays a critical role in determining interface thermal transport properties, and the influence of pressure was also discussed. This study contributes not only to the understanding of the thermal transport mechanisms at the Cu/Si interface but also provides important insights for designing novel interface materials.

Vertically designed high-performance and flexible thermoelectric generator based on optimized PEDOT:PSS/SWCNTs composite films

To solve the long-lasting challenge of low thermoelectric performance of flexible thermoelectric device (F-TEG), in this work, we report a three-dimensional vertically structured F-TEG composed of flexible, stable, and high-performing p- and n-type single-walled carbon nanotube (SWCNT)-based composite films. The p-type SWCNT-based composite film exhibits a high room-temperature power factor of >500 μW m−1 K−2, benefiting from the effective de-doping of the hybridized poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) using a binary co-doping agent composed of NaHCO3 and the polar solvent ethylene glycol (EG). Simultaneously, the n-type SWCNT-based film doped with the amine-rich electron donor polyethyleneimine (PEI) is prepared, exhibiting a high room-temperature power factor of 185.4 μW m−1 K−2 and excellent air stability. By employing flexible supporting foam, vertical p-n thermoelectric legs are realized, and the F-TEG based on these legs exhibits a maximum open-circuit voltage of 23.2 mV and a maximum output power of 2.6 μW at a temperature difference of 48 K, demonstrating a competitive normalized power density of >2.5 μW cm−2 K−2, which advances the low-power flexible wearable field.

High efficient personal thermoregulatory device: Metallized interface layer between flexible polyimide substrate and foam copper heat sink enables thermal resistance reduction

Customizable flexible thermoelectric devices (f-TED) designed for personal thermal management (PTM) have the potential to substantially diminish energy consumption while enhancing comfort. Currently, studies focus on optimizing thermoelectric device performance and reducing radiator thermal resistance, neglecting the crucial interface between them. In this innovative work, the interface layer between the flexible polyimide substrate of f-TED and the foam copper heat sink was metallized, thereby significantly mitigating the thermal resistance at the interface. In contrast to the conventional thermal conductive adhesive, the metallized welding thermoelectric system (4 × 4 cm² in the plane) demonstrates a 37.0 % augmentation in cooling temperature difference (5.4 ℃ → 7.4 ℃) at 0.3 A. When bending 1000 times (r: ∞ → 20 mm → ∞ → …), the change rate of internal resistance is less than 1.5 %. At a temperature difference of 20 K, it reaches a maximum output power as high as 4.45 mW. Furthermore, an intelligent personal thermal management system was developed. Users can monitor and adjust the working status of the f-TED in real-time via a mobile terminal, achieving personalized thermoregulation. In actual human wear tests, the highest cooling temperature difference reached 13.7 °C, which is one of the highest reported values. This work holds significant implications for advancing f-TED technology innovation, personalized thermoregulation, energy conservation, and environmental protection.

Thermal transport and thermoelectric properties of transition metal dichalcogenides MoX 2 from first-principles calculation

The properties of two-dimensional (2D) materials have been extensively studied and applied in various applications. Our interest is to theoretically investigate the thermal transport and thermoelectric properties of the 2D transition metal dichalcogenides MoX 2 (X=S, Se, Te). We employ density functional theory and Boltzmann transport theory with relaxation-time approximation to calculate the electronic and transport properties. We also implemented the kinetic-collective model to improve the calculation of lattice thermal conductivity. Our calculations indicate that MoTe2 has the highest ZT of 2.77 among the other MoX 2 at 550 K due to its low thermal conductivity and high electrical conductivity. Consequently, we suggest that MoX 2 monolayers hold promise as materials for energy conversion devices due to their relatively high ZT. Moreover, these results could be beneficial to design 2D material-based high-performance thermoelectric devices.

Improvement of heating and cooling performance for thermoelectric devices in medical storage application

Thermoelectric devices provide several advantages over typical refrigeration systems, including compact size, quiet operation, minimal energy use, and environmentally friendly. By harnessing these benefits, we have developed a blood storage system that has the potential to transform the way blood products are preserved and safeguarded. Thermal performance was evaluated using a variety of scenarios, including thermal fin material and emissivity, voltage operation, heat sink type (I, U, O type), and tube load. This research used thermoelectric devices, Styrofoam materials, thermal fin and the heatsink to design the thermoelectric storage cabinet with heat insulation function. The aims to improve the performance of thermoelectric devices by optimizing the thermal fin design during heating/cooling storage mechanisms. Our findings emphasize the importance of thermal radiation, particularly in circumstances with low natural convection and high surface emissivity. Thermal performance is optimized when heating storage elements are incorporated into aluminum finned tubes and run at an input voltage of 8V in a 25 °C ambient temperature. In addition, using U-shaped cooling fins in cooling conditions results in superior cooling performance. The outcomes of this study highlight the possibility and potential benefits of using thermoelectric devices to heat and cool medical storage, notably blood storage applications. The insights gained here contribute to advancing the efficiency and sustainability of medical storage systems, ultimately benefiting healthcare and the environment.

Precipitation enhancement of liquid thermoelectric conversion with Fe(ClO4)2/Fe(ClO4)3 dissolved in DMF

Oxidant precipitation in the electrolyte significantly enhances the open circuit voltage and output power in a liquid thermoelectric conversion device.

Output and mechanical performance of thermoelectric generator under transient heat loads

Geometry optimization and pulsed inputs have been introduced as some of the effective methods to enhance the performance of thermoelectric devices. In this work, the geometric structure of a Bi2Te3-based thermoelectric module is optimized systematically using two-step integrated optimization method in steady state, and then the effect of transient heat flux on the output and mechanical performance is investigated deeply. The simulative results show that the optimization directions for mechanical and output performance are usually opposite. The optimal Ap/An, H/Anp and N of the Bi2Te3-based module are 1.6, 1.5 and 8, respectively. Moreover, the thicker He and thinner Hcs favor the improvement of output performance, however, considering the mechanical property, the optimal He and Hcs are regarded as 0.3 mm. In addition, using pulsed heat flux can improve the output performance and obtain a smaller average stress in a long period. The suitable duty cycle, smaller amplitude ratio and rectangular heat flux are beneficial for power enhancement and stress optimization. However, pulsed input brings frequent and repeated temperature changes, which is a challenge to the lifespan of thermoelectric modules. These simulated results will benefit the enhancement of output and mechanical performance of thermoelectric devices in the practical operation process.

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.

Influence and comprehensive evaluation of porous metal foam filled fins on the performance of power cable surface waste heat recovery thermoelectric power generation device

Cables are essential components in power systems. Certain amount of heat is generated during the energy transfer process. Effective recovery and utilization of waste heat generated by cables is a helpful proposition. In this study, a cable waste heat recovery thermoelectric generation device (CTEG) is proposed. By installing cooling fins and thermoelectric generation devices on the cable surface, the waste heat on the cable surface is converted into electric energy. To improve the power generation efficiency of the device, a method of filling porous metal foam material in the fin teeth gap is used. The results demonstrate that filling the fin teeth gap with porous metal foam material with high porosity and low pore density (PPI) can significantly increase heat transfer efficiency and benefit the output power of the thermoelectric generation device. The flow field in the pipeline of thermoelectric generation device is also analyzed in this study. A comprehensive evaluation method is proposed to consider the power generation efficiency and heat transfer efficiency of the thermoelectric generation device. It is shown that filling porous metal foam material with high porosity and low pore density can maximize the power generation efficiency of the thermoelectric generation device, and at the same time, the pipe pressure drop loss can be compensated by the improvement of heat transfer. This research is significant because it provides useful information for enhancing the energy conversion efficiency of thermoelectric generation devices that recover waste heat from cable surfaces and generate electrical power.

Enhanced thermoelectric performance via quantum confinement in a metal oxide semiconductor field effect transistor for thermal management

The performance of thermoelectric devices is gauged by the dimensionless figure of merit {{{{{boldsymbol{ZT}}}}}}. Improving {{{{{boldsymbol{ZT}}}}}} has proven to be a formidable challenge given the interdependence of its constitutive quantities, namely Seebeck coefficient, electrical conductivity, thermal conductivity, and temperature. Here, we use quantum confinement to decouple Seebeck coefficient and electrical conductivity to demonstrate an order of magnitude quantum-based enhancement to the thermoelectric figure of merit {{{{{boldsymbol{ZT}}}}}} in complimentary metal-oxide-semiconductor field-effect transistors. While most quantum-based enhancement is done through physical confinement using two-dimensional materials, our approach uses electrical confinement. Because of this, our device is more robust than the two-dimensional materials currently used. We further articulate that improvement by as much as a factor of 50 could be achieved in a practical setting. Our approach further provides a path for monolithic integration of on-chip coolers and energy scavengers with virtually no deviation from the fabrication flow of standard electronics.

Exploring the ultra-low lattice thermal conductivity of a two-dimensional compound Tl2Se3

Two-dimensional (2D) materials have attracted extensive attention in the field of thermoelectric (TE) materials, where heat transport properties play an important role in determining the performance of TE devices. In this paper, we investigate the thermal transport properties of novel 2D Tl2Se3 by means of first-principles approach combined with the Boltzmann transport equation (BTE). The small phonon sound group speed and strong anharmonicity are responsible for an ultra-low kl of 0.28 W/mK of 2D Tl2Se3 at room temperature. Meanwhile, the lattice thermal conductivity gradually decreases with the increase of temperature, indicating its potential value at high-temperature. The anti-bonding orbital filling between the Se-4p and Tl-6p states leads to the weak chemical bonds using the crystal orbital Hamiltonian population (COHP) analysis, which results in low phonon group velocities. Also, due to the strong acoustic-optical coupling in 2D Tl2Se3, the scattering processes of different acoustic modes is further studied to analyze how kl is suppressed. These findings demonstrate that 2D Tl2Se3 has potential applications in TE devices, which will motivate Tl2Se3 based experimental investigations.

Characterizing the thermoelectric cooling performance across a broad temperature range.

Thermoelectric cooling plays an essential role in precisely controlling the temperature of electronics. Characterizing the performance of thermoelectric coolers (TECs) is of great significance for the development of advanced solid-state cooling devices. However, the existing setup for characterizing the cooling performance of TECs has mainly been limited to the near room temperature range. Herein, we report the development of a new setup that is capable of characterizing thermoelectric cooling performance across a broad temperature range (80-350K). With precise and steady control of the hot-side temperature, measurements of the coefficient of performance and maximum temperature difference at room temperature have been conducted on commercial devices. By comparing the results with the commercial datasheet, it shows that our setup can accurately evaluate the cooling performance of thermoelectric devices. In addition, we further extend the characterization to different hot-side temperatures, e.g., 173, 325, and 350K, thus demonstrating the capability of our setup for evaluating the thermoelectric performance across a broad temperature range.