Bi2Te3-based Thermoelectric Modules Research Articles

Enhanced thermoelectric properties of 3D printed Bi2Te2.7Se0.3 by atomic interface engineering

The performance of n-type Bi2Te3 materials prepared by selective laser melting (SLM) 3D printing technology tends to be lower than p-type materials. Herein, a bottom-up interface engineering strategy based on Atomic Layer Deposition (ALD) is presented to improve the properties of n-type Bi2Te2.7Se0.3 (BTS) materials prepared by SLM. To validate this strategy, a ZnO ultrathin layer was applied to the grain boundaries of BTS, synergistically optimizing carrier/phonon transport. In terms of electrical transport, the energy filtering effect triggered by the constructed ZnO/BTS interface effectively enhances the Seebeck coefficient of the Bi2Te3 material printed by SLM, substantially increasing the power factor. Additionally, the high thermal stability of the ALD-deposited ZnO ultrathin layer effectively suppresses the volatilization of Te in BTS, regulating the carrier concentration. Regarding thermal transport properties, the multiscale defects introduced by the non-equilibrium solidification process during SLM printing cause effective phonon scattering across a wide frequency range, which in turn reduces the thermal conductivity of the material. Atomic-level interface modification in SLM-printed BTS enhanced the ZT value to 1.25. Exploiting this superior thermoelectric performance, a thermoelectric module was constructed. It demonstrated a conversion efficiency of 5.7 % with a temperature difference of 200 K, comparable to the advanced Bi2Te3-based thermoelectric modules. The integration of an ALD interface modification strategy with SLM technology has not only demonstrated potential applications in Bi2Te3-based thermoelectric material development, but also bears significant importance for the accelerated advancement of high-performance thermoelectric materials in other systems.

Bi2Te3-Based Thermoelectric Modules for Efficient and Reliable Low-Grade Heat Recovery.

Bismuth-telluride-based alloy has long been considered as the most promising candidate for low-grade waste heat power generation. However, optimizing the thermoelectric performance of n-type Bi2Te3 is more challenging than that of p-type counterparts due to its greater sensitivity to texture, and thus limits the advancement of thermoelectric modules. Herein, the thermoelectric performance of n-type Bi2Te3 is enhanced by incorporating a small amount of CuGaTe2, resulting in a peak ZT of 1.25 and a distinguished average ZT of 1.02 (300-500 K). The decomposed Cu+ strengthens interlayer interaction, while Ga+ optimizes carrier concentration within an appropriate range. Simultaneously, the emerged numerous defects, such as small-angle grain boundaries, twin boundaries, and dislocations, significantly suppresses the lattice thermal conductivity. Based on the size optimization by finite element modelling, the constructed thermoelectric module yields a high conversion efficiency of 6.9% and output power density of 0.31W cm-2 under a temperature gradient of 200 K. Even more crucially, the efficiency and output power little loss after subjecting the module to 40 thermal cycles lasting for 6 days. This study demonstrates the efficient and reliable Bi2Te3-based thermoelectric modules for broad applications in low-grade heat harvest.

High Carrier Mobility and Promising Thermoelectric Module Performance of N-Type PbSe Crystals.

The scarcity of Te hampers the widespread use of Bi2Te3-based thermoelectric modules. Here, the thermoelectric module potential of PbSe is investigated by improving its carrier mobility. Initially, large PbSe crystals are grown with the temperature gradient method to mitigate grain boundary effects on carrier transport. Subsequently, light doping with <1mole‰ halogens (Cl/Br/I) increases room-temperature carrier mobility to ~1600cm2V-1s-1, achieved by reducing carrier concentration compared to traditional heavy doping. Crystal growth design and light doping enhance carrier mobility without affecting effective mass, resulting in a high power factor ~40µWcm-1K-2 in PbSe-Cl/Br/I crystals at 300K. Additionally, Cl/Br/I doping reduces thermal conductivity and bipolar diffusion, leading to significantly lower thermal conductivity at high temperature. Enhanced carrier mobility and suppressed bipolar effect boost ZT values across the entire temperature range in n-type PbSe-Cl/Br/I crystals. Specifically, ZT values of PbSe-Br crystal reach ~0.6 at 300K, ~1.2 at 773K, and the average ZT (ZTave) reaches ~1.0 at 300-773K. Ultimately, ~5.8% power generation efficiency in a PbSe single leg with a maximum temperature cooling difference of 40K with 7-pair modules is achieved. These results indicate the potential for cost-effective and high-performance thermoelectric cooling modules based on PbSe.

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.

Realizing ultrahigh ZT value and efficiency of the Bi2Te3 thermoelectric module by periodic heating

Thermoelectric power generation is regarded as a promising technology to convert waste heat into electricity. This study aims to address the low conversion efficiency of thermoelectric modules and introduces a novel periodic heating method to enhance their performance. Two new indicators, time average ZTta value and effective conversion efficiency, are introduced to assess the dynamic behavior of thermoelectric modules. A Bi2Te3-based thermoelectric module with n-type Bi2Te3-xSex and p-type BixSb2-xTe3 materials is adopted as the research objective and tested on a designed transient experimental setup. Besides, a transient numerical model is developed to explore the optimal transient heat source and study the effect of various parameters on dynamic behavior. Compared with the steady-state efficiency of 3.76% and ZTta value of 0.78 at a heat supply of 60 W, the time average efficiency and ZTta value are improved by 52.93% and 43.59% respectively using the periodic heating method. Also, a smaller leg height, a larger leg area, more TE couples, and lower thermal conductivity are suggested for improving the dynamic behavior. This work offers a new periodic heating method to improve the output performance of thermoelectric modules, which may promote the broader application of thermoelectric power generation technology.

Enhanced thermoelectric properties of n-type Bi2Te2.7Se0.3 materials by TiO2 ceramic nanoparticle dispersion-induced energy filtering effect

Due to their superior thermoelectric capabilities, Bi2Te3-based materials have long been a popular area of study in the thermoelectric field. However, further advancements in the energy conversion efficiency of Bi2Te3-based thermoelectric modules are constrained by the low figure of merit of n-type Bi2Te3. Here, we describe an efficient method for enhancing the electrical and thermal characteristics of n-type Bi2Te2.7Se0.3 (BTS) material by dispersing TiO2 ceramic nanoparticles (NPs) in the matrix of the BTS. In more detail, the energy potential barrier, created by the matrix and the addition of TiO2 NPs, causes an energy filtering effect, which in turn raises the Seebeck coefficient. The lattice thermal conductivity is decreased as a result of dislocations at the TiO2/BTS interface and an increase in grain boundary density brought on by the fine grain strengthening of TiO2 ceramic NPs. Last but not least, the ZTmax for the BTS + 3 wt% TiO2 sample increased to 1.31, representing an improvement of 52% over the pristine sample. Additionally, at a maximum temperature differential of 150K, we have built a thermoelectric module with a power output and energy conversion efficiency of 7.2 W and 5.9%, respectively. This study introduces a viable approach towards the rational design of advanced n-type Bi2Te2.7Se0.3 materials.

Fe-Ni-Cr diffusion barrier for high-temperature operation of Bi2Te3

Bismuth-telluride (Bi2Te3)-based thermoelectric modules are widely used in practical applications at room temperature. However, to enable the utilization of waste heat sources, Bi2Te3-based thermoelectric modules need to operate at high efficiency levels over a medium temperature range (200–250 °C). To achieve high efficiency of Bi2Te3 modules operating at this temperature range, an optimal metallization layer should be inserted to minimize the electrical and thermal contact resistance and prevent elemental diffusion at the interface. In this work, we suggest a novel Fe-Ni-Cr layer to overcome the poor performance of the Ni layer, which is currently widely used as a metallization layer. The proposed Fe-Ni-Cr metallization resulted in a strong enough interface structure without any detachment even after thermal aging whereas the Ni-Cr metallization suffered from layer detachment problems. The specific electrical contact resistance of Fe-Ni-Cr metallization showed minor increase and remains at the ∼10−5 Ω·cm2 level after thermal aging at 250 ℃ for 100 h. The reliability of the Fe-Ni-Cr metallization layer was demonstrated with a 32-couples thermoelectric module, which showed a 5 % enhancement compared to Ni metallization thermoelectric module.

Diffusion bonding at the interface of Bi2Te3 thermoelectric modules

In production of Bi2Te3-based thermoelectric modules, Bi2Te3 materials were coated with electroless nickel (EN), electroless palladium, and immersion gold multilayers to suppress unanticipated interfacial reactions between Bi2Te3 and Sn-based solder alloys. However, the coating elements reacted with the solder alloys to yield intermetallic compounds (IMCs) at the Bi2Te3/solder and solder/Cu electrode interfaces. Significant Cu content from the Cu electrodes contributed to the IMCs along with to the coating and Sn elements. In this study, the influence of IMC composition on bonding strength and the characteristics of the Bi2Te3-based material/Cu electrode interface was investigated. An EN layer was plated onto Cu electrodes to suppress Cu diffusion from the electrodes into the solder alloy. IMCs mainly consisted of Sn and Cu elements in the case of uncoated Cu electrodes. When Cu electrodes were coated by the EN layer, Ni and Sn content prevailed in IMC composition. Additionally, IMCs at both the Bi2Te3/solder and solder/Cu electrode interfaces with Cu or Pd were thicker than those without Cu or Pd. Meanwhile, the bonding strength of the Bi2Te3-based material/Cu electrode interface with the EN layer on the Cu electrodes was lower than that of the interfaces without the EN layer.

Performance of Bi2Te3-based thermoelectric modules tailored by diffusion barriers

Fifty-pair Bi2Te3-based thermoelectric (TE) modules were produced by spreading Sn alloy solder on Cu electrodes before heating at 270 °C for 10 min to connect Bi2Te3-based legs with Cu electrodes. To suppress unexpected reactions between solder and TE materials, a conventional electroless nickel (EN) layer and a novel coating encompassing EN, electroless palladium, and immersion gold (ENEPIG) layers were adopted for Bi2Te3 materials as diffusion barriers. Influence of different diffusion barriers, namely, EN and ENEPIG, on TE performance of module was ascertained. Interfacial structure at Bi2Te3/solder/Cu electrode interface revealed that intermetallic compounds were generated owing to interdiffusion among Cu, Sn, and coating elements, and they mostly concentrated at Bi2Te3/solder and solder/Cu electrode interfaces. Additionally, ENEPIG coating exhibited much better wettability with solder than the EN coating, resulting in fewer defect sites at Bi2Te3/solder interface. When current flowed through TE modules, the ENEPIG-coated module yielded lower temperatures on both hot and cold sides than the EN-coated module. While the modules had temperature differences between two substrates, output power generated by the ENEPIG-coated module was higher than that of the EN-coated module. In addition, the ENEPIG-coated module showed a smaller internal resistance than the EN-coated module. After heating at 200 °C for 200 h, both modules presented markedly reduced output power, whereas internal resistance was escalated.

Experimental investigation of the performance of a thermoelectric generator at various operating conditions

Thermoelectric generators (TEG) is the device that can directly convert heat into electricity by the Seebeck effect, which is fascinated for waste heat recovery. An experiment was setup to study the influence of heat flux through the thermoelectric module on the power output and efficiency of a commercial Bi2Te3-based thermoelectric modules. The experimental result indicated that the power output evidently increased with the increasing heat flux through the thermoelectric module (TEM), while the conversion efficiency increased significantly at first then the tendency became mild with the increasing heat flux for a given air flow velocity and flow temperature. The temperature differences across the thermoelectric module are almost identical with various air velocity, while the power output and efficiency increased with the increase of cooling flow velocity with a fixed heat flux through the TEM. The power output and efficiency almost linearly decreased with the increase of cooling flow temperature with a fixed heat flux through the TEM and a fixed cooling flow velocity. The maximum output power can be obtained by maximization heat flux without exceeding the upper temperature limit of thermoelectric module.

Towards tellurium-free thermoelectric modules for power generation from low-grade heat

Thermoelectric technology converts heat into electricity directly and is a promising source of clean electricity. Commercial thermoelectric modules have relied on Bi2Te3-based compounds because of their unparalleled thermoelectric properties at temperatures associated with low-grade heat (<550 K). However, the scarcity of elemental Te greatly limits the applicability of such modules. Here we report the performance of thermoelectric modules assembled from Bi2Te3-substitute compounds, including p-type MgAgSb and n-type Mg3(Sb,Bi)2, by using a simple, versatile, and thus scalable processing routine. For a temperature difference of ~250 K, whereas a single-stage module displayed a conversion efficiency of ~6.5%, a module using segmented n-type legs displayed a record efficiency of ~7.0% that is comparable to the state-of-the-art Bi2Te3-based thermoelectric modules. Our work demonstrates the feasibility and scalability of high-performance thermoelectric modules based on sustainable elements for recovering low-grade heat.

Influences of different barrier films on microstructures and electrical properties of Bi2Te3-based joints

Diffusion barrier film was strongly proposed to utilize in Bi2Te3-based thermoelectric (TE) module. However, effects of different barriers on microstructures of solder joints and electrical properties of TE modules were still unclear, which were vital in practical applications. In current work, Bi2Te3-based TE modules without barrier (TM), with Ni (TMNi) and with Ni/Au (TMNi/Au) were fabricated via reflow-soldering. Experimental results revealed that at the interface between SAC305 solder and P- or N- type Bi2Te3 sample, the Ni or Ni/Au barrier could efficiently inhibit severe growth of the intermetallic compound (IMC) phase. Remarkably, a thinner IMC layer was observed at the solder/Au/Ni/Bi2Te3 interface, which was attributed to effects of Au elements on suppressing the formation of IMCs. The results of power generation ability test revealed that TMNi exhibited higher value of output power (P) under the temperature difference (ΔT) due to its higher values of open circuit voltage (V) and output current (I). On the other hand, since the lowest electrical resistance (R) and relatively low output current of TMNi/Au were measured during the test, the TMNi/Au was suggested to generate less heat, meaning it consumed less energy, and hence be theoretically more efficient in improving the conversion efficiency.

Mesoscale combustor-powered thermoelectric generator: Experimental optimization and evaluation metrics

The recent development of potable power sources is of considerable interest. A mesoscale combustor-powered thermoelectric generator integrated with a mesoscale stagnation-point reverse-flow combustor and a built-in heat exchanger was designed and optimized in this work to augment electric power and overall efficiency. The mesoscale combustor can run at a volumetric heat load of 72 MW/m3. The thickness of heat spreader, input power, equivalent ratio, fuel types, and heat exchanger channel types were explored to optimize the system performance. The optimized electric power of 30.7 W obtained at an overall efficiency of 3.21% was larger than the previous record of 18.1 W at an overall efficiency of 3.01% in 2015. The proposed thermoelectric generator, which was conducted with 13.2 kg of methane, reached an energy density of 300 Wh/kg. The novel design provided a concrete way to solve the contradiction between the availability of Bi2Te3-based thermoelectric module and its relatively low working temperature. Additionally, a new metrics, which is defined as (EFS/efTE,max) at Pin, was firstly proposed to evaluate various thermoelectric generators, in which different thermoelectric materials, combustion types, and input powers could be involved. The proposed metrics correlates the overall, running thermoelectric, maximum thermoelectric, combustion (reaction), and heat collection efficiencies under different input powers. The power of this metrics was comprehensively discussed by deducing the running thermoelectric efficiencies of various previous works and presenting the performance comparisons of different previous thermoelectric generators. The obtained metrics, that is, (75.9%/4.23%) at 957 W in this work was higher than those in previous studies.

Modeling and Experimental Study of a BiSbTeSe-Based Thermoelectric Module for Thermal Energy Recovery

Bi0.4Sb1.6Te2.7Se0.15S0.15 alloy thermoelectric material is introduced in this paper for thermoelectric power generation in the temperature range of 300–500 K. To evaluate the proposed material in a practical service environment, a BiSbTeSe-based thermoelectric module (TEM) with 254 thermoelectric elements is fabricated. Simulations and experiments are undertaken to assess the performance of the BiSbTeSe-based TEM under two different cases of constant heat source and heat flow. An analysis of heat transfer is conducted based on the temperature distribution of different cross-sections. Compared with a conventional Bi2Te3-based TEM, the proposed TEM can output a higher voltage when the temperature difference is higher than 60 K, especially in the heat flow case. When the temperature difference is 200 K, the open-circuit voltages are 10.90 V and 9.79 V, and the maximum output power is 8.8179 W and 7.1279 W under the constant temperature and heat flow cases, respectively. The maximum power is achieved when the load resistance is slightly higher than the internal resistance due to the effect of Peltier heat. The average deviation between the experimental values and simulation results is approximately 5.6%. The experiments verify the rationality and validity of the simulation model. This study reveals that the performance of the proposed BiSbTeSe-based alloy material is better than that of conventional bismuth telluride alloys within the range of 300–500 K. In addition, compared with constant heat thermal boundary conditions, it is more suitable for the heat flow case.

Impedance spectroscopy characterization of neutron irradiated thermoelectric modules for space nuclear power

The European Space Agency is currently supporting the research and development of advanced radioisotope power systems utilising thermoelectric modules. The performance of thermoelectric modules following exposure to neutron radiation is of significant interest due to the likely application of radioisotope thermoelectric generators in deep space exploration or planetary landers requiring prolonged periods of operation. This study utilises impedance spectroscopy to characterise the effects of neutron irradiation on the performance of complete thermoelectric modules, as opposed to standalone material. For a 50 We americium-241 radioisotope thermoelectric generator design, it is estimated that the TE modules could be exposed to a total integrated flux of approximately 5 × 1013 neutrons cm-2 (&amp;gt;1 MeV). In this study, an equivalent neutron dose was simulated experimentally via an acute 2-hour exposure in a research pool reactor. Bi2Te3-based thermoelectric modules with different leg aspect ratios and microstructures were investigated. Gamma-ray spectroscopy was initially used to identify activated radionuclides and hence quantify irradiation induced transmutation doping. To evaluate the thermoelectric properties pre- and post-irradiation, impedance spectroscopy characterization was employed. Isochronal thermal annealing of defects imparted by the irradiation process, revealed that polycrystalline based modules required significantly higher temperature than those with a monolithic microstructure. Whilst this may indicate a greater susceptibility to neutron irradiation, all tested modules demonstrated sufficient radiation hardness for use within an americium-241 radioisotope thermoelectric generator. Furthermore, the work reported demonstrates that impedance spectroscopy is a highly capably diagnostic tool for characterising the in-service degradation of complete thermoelectric devices.

Ni barrier in Bi2Te3-based thermoelectric modules for reduced contact resistance and enhanced power generation properties

Ni layer is widely utilized in Bi2Te3-based thermoelectric generators (TEGs) as a diffusion barrier layer. However, its influences on the contact resistance of the solder joints and the power generation properties of the TEGs are still unclear, which are of great importance in practical applications. In this study, Bi2Te3-based thermoelectric (TE) modules with Ni (NiTM) and without Ni (TM) layer were fabricated by using Sn96.5Ag3Cu0.5 (SAC305) solder. Experimental results showed that Ni layer could effectively reduce 32% of contact resistances in P-type and N-type solder joints. P-type solder joint with Ni avoided voids forming on the border of the Bi0.5Sb1.5Te3 and SAC305 by suppressing severe Te and Sb elements diffusion. In N-type solder joint, since Ni inhibited the formation of Bi-Te self-diffusion barrier layer, no cracks generated at the interface between Bi2Te2.5Se0.5 and SAC305. In terms of power generation abilities, the inherently superior performance of TE legs was maintained due to effective suppression of element diffusion. When the temperature difference was 161 °C, the open circuit voltage of NiTM exhibited an enhancement of 13% compared with that of TM. The lower contact resistance and higher open circuit voltage resulted in a much higher maximum output power (an enhancement of 90%) in NiTM.

A Novel Fabrication Method of Bi₂Te₃-Based Thermoelectric Modules by Indium Electroplating and Thermocompression Bonding.

In this study, we devised a method to bond thermoelectric elements directly to copper electrodes by plating indium with a relatively low melting point. A coating of indium, ~30 μm in thickness, was fabricated by electroplating the surface of a Bi2Te3-based thermoelectric element with a nickel diffusion barrier layer. They were then subjected to direct thermocompression bonding at 453 K on a hotplate for 10 min at a pressure of 1.1 kPa. Scanning electron microscopy images confirmed that a uniform bond was formed at the copper electrode/thermoelectric element interface, and the melted/solidified indium layer was defect free. Thus, the proposed novel method of fabricating a thermoelectric module by electroplating indium on the surface of the thermoelectric element and directly bonding with the copper electrode can be used to obtain a uniformly bonded interface even at a relatively low temperature without the use of solder pastes.

Impedance spectroscopy for assessment of thermoelectric module properties under a practical operating temperature

Impedance spectroscopy has recently received considerable attention in terms of thermoelectric module characterization. However, to date, no study has been conducted on the high-temperature measurement of the module using impedance spectroscopy. In this paper, a systematic study on the Bi2Te3-based thermoelectric module up to 150 °C is reported. Evaluation results indicated that impedance spectroscopy could be used for characterizing the thermoelectric module in a practical operation temperature range. The impedance spectroscopy data of the module changed with the increased temperature on account of the change in the characteristics of the thermoelectric legs. Analysis of the impedance spectroscopy data enabled determination of the thermoelectric module figure of merit, while enabling extraction of three key parameters—the Seebeck coefficient, thermal conductivity, and electrical conductivity—by employing a one-dimensional heat equation. The results indicated that, while the thermal conductivity increased with temperature, the electrical conductivity decreased with increasing temperature. The Seebeck coefficient increased with temperature up to 100 °C and tended to be saturated. The module figure of merit was 0.82 and peaked at 75 °C. The results obtained in this study can contribute to the rapid evaluation of thermoelectric modules for exploiting various novel thermoelectric materials, metallization layers, electrodes, and insulating plates.

Design and experimental investigation of a thermoelectric self-powered heating system

In this paper, a combustion-driven thermoelectric residential heating system, which uses Bi2Te3-based thermoelectric modules, is designed, constructed, and tested. The thermoelectric modules are integrated into a heat cell of a natural gas-fired heating boiler. The experiments are carried out to examine the influences of the main operating conditions, cold fluid flow rate, temperature difference between the inlet and outlet at the heat cell and different boiler powers, on output power, voltage, current and efficiency of boiler. The two operating parameters such as the cold fluid flow rate and temperature difference are found to significantly affect the output power, and the efficiency of the boiler. The thermoelectric generator unit has a power generation capacity of approximately 36W. This amount corresponds to about one-third of boiler’s requirement. The study shows that if the combi boiler is redesigned, and its efficiency is enhanced, it can generate sufficient electrical power for electrical components of the combi boiler, such as pump, valves, blower, fan, and control panel. The self-powered heating system provides advantages commercially, and can decrease the electrical power consumption. Also, and economical analysis was conducted for the self-powered heating system and the conventional system, and it was seen that the proposed system is economically applicable.

The temperature distribution and electrical performance of fluid heat exchanger-based thermoelectric generator

Thermoelectric generator (TEG) has great potential in waste heat recovery. In this paper a TEG system has been build up which consists of a Bi2Te3-based thermoelectric module and two fluid heat exchangers. The temperature distribution, electrical performance and heat components of the system have been investigated via both experiment and numerical simulation. It is revealed that the influence of fluid velocity on the temperature distribution is weak until the velocity is very slow, and the influence of Peltier effect on the temperature distribution is also limited in this system. Furthermore, attention should be paid to the contact electrical resistance induced by soldering, especially when the hot side temperature of the Bi2Te3 module is expected up to 473K. Besides that, heat component analysis suggests that Peltier effect should not be ignored in optimization analysis of thermoelectric module.