P-type Legs Research Articles

Realizing N-type SnTe Thermoelectrics with Competitive Performance through Suppressing Sn Vacancies.

Due to the intrinsically plentiful Sn vacancies, developing n-type SnTe thermoelectric materials is a big challenge. Herein, n-type SnTe thermoelectric materials with remarkable performance were successfully synthesized through suppressing Sn vacancies, followed by electron-doping. Pb alloying notably depressed the Sn vacancies via populating Sn vacancies in SnTe (supported by transmission electron microscopy), and the electrical transports were shifted from p-type to n-type through introducing electrons using I doping. In the n-type SnTe, we found that the electrical conductivity could be enhanced by increased carrier mobility through sharpening conduction bands after alloying Pb, while the lattice thermal conductivity could be reduced via strong phonon scattering after introducing defects by Pb alloying and I doping. Resulting from these enhancements, the n-type Sn0.6Pb0.4Te0.98I0.02 achieves a notably high ZTmax ∼ 0.8 at 573 K and a remarkable ZTave ∼ 0.51 at 300-823 K, which can match many excellent p-type SnTe. This work indicates that n-type SnTe could be experimentally acquired and is a promising candidate for thermoelectric generation, which will stimulate further research on n-type SnTe thermoelectric materials and even devices on the basis of both n- and p-type SnTe legs.

Generic Approach for Contacting Thermoelectric Solid Solutions: Case Study in n- and p-Type Mg2Si0.3Sn0.7.

Metallization (known as contacting) of thermoelectric (TE) legs is vital to the long-term performance of a TE device. It is often observed that the compositional changes in a TE solid solution may render a given contact material unsuitable due to a mismatch in the thermal expansion coefficient values. Finding suitable contact materials for TE solid solutions (which often are the best TE materials) remains a challenge. In this work, we propose a multilayer single-step approach in which the same combination of contact materials can be used for a wide compositional range in a solid solution. The outer layer is a metal foil, which helps in creating an Ohmic contact with the interconnects. The intermediate layer is a mixture of the TE material and a metal powder, which results in the formation of the diffusion barrier. The innermost layer is the TE material, which is the active component of the device. The strategy was applied on n- and p-doped Mg2Si0.3Sn0.7 with elemental Cu and Ni providing the desired interface functionalities. Single-step compaction was carried out using the monoblock sintering technique. Microscopic investigation reveals the formation of a well-bonded crack-free interface. Various intermetallic phases were identified at the interface, and the formation of the MgNi2Sn phase was found to be critical to prevent any interdiffusion of elements. Electrical contact resistance (rc) measurements were conducted, and low values of 3 and 19 μΩ cm2 were measured in n- and p-type legs, respectively. The contacted TE legs were further annealed at 400 °C for 7 days to check their stability. Microstructural and electrical resistance measurements reveal minimal changes in the interface layer and rc values, indicating the workability of the multilayer technique.

Development of a solid-state multi-stage thermoelectric cooler

In this work, a unique thermoelectric solid-state multi-stage cooler for operating temperatures up to ~140 K was developed. The extrusion technology was applied to fabricate thermoelectric legs with sufficient mechanical properties for the device construction. A cooling prototype was designed and fabricated using a four-stage commercial module and a two-stage ultra-low temperature module. The ultra-low temperature module, operating in the temperature range of 180–140 K, was fabricated using Bi0·91Sb0.09 alloys as an n-type leg and an optimized composition of Bi1·6Sb0·4Te3 as a p-type leg. The four-stage commercial thermoelectric module based on n- and p-type Bi2Te3 based alloys was utilized for operation in the temperature range of 180–300 K. The solid-state cooler was tested at a hot temperature Th = 300 K in a vacuum. At the cold temperature of the fourth stage 180 K, the maximum temperature difference of the ultra-low temperature module achieves high values of maximum temperature difference ΔT = 45 K and maximum cooling capacity Qc = 85 mW. Furthermore, we demonstrated the applicability of the ultra-low cooler for refrigeration up to 150 K for a mid-infrared sensor based on a PbTe photodiode with a cut-off wavelength λc ≈ 4.2 μm and a detectivity D ≈ 1010 cm Hz1/2/W revealing the potential of the developed device for practical applications.

Interface effect and band engineering in Bi2Te3:C and Bi2Te3:Ni-Cu with enhanced thermopower for self-powered wearable thermoelectric generator

The evolution of flexible thermoelectric generators (TEGs) is an alternative source for driving wearable thermoelectric (TE) devices. Though, commercial fabric based wearable TEGs have not been realized yet. In this study, Bi2Te3 nanostructure was synthesized by a one-step hydrothermal method and deposited on carbon and nickel-copper (Ni-Cu) fabrics to form TE legs. The structural and morphological analyses confirmed the formation of Bi2Te3 and the coating of Bi2Te3 on the fabrics. The electrical conductivity and Seebeck coefficient of Bi2Te3 coated Ni-Cu fabric was 1.5 and 5.4 times higher than Bi2Te3 coated carbon fabric. Then these p-type (Bi2Te3 coated carbon fabric) and n-type (Bi2Te3 coated Ni-Cu fabric) TE legs were fabricated as an integrated array of 2 thermocouples. The Bi2Te3 modified p-type and n-type thermocouples showed an output voltage oscillating from ~25 μV to ~42 μV with a different body temperature varying from 303 to 312 K. The analysis showed the temperature ranging from below 300 K to and above 293 K will be the more suitable environmental temperature for energy harvesting from the human body.

Effect of Refractory Tantalum Metal Filling on the Microstructure and Thermoelectric Properties of Co4Sb12 Skutterudites.

We report a systematic investigation of the microstructure and thermoelectric properties of refractory element-filled nanostructured Co4Sb12 skutterudites. The refractory tantalum (Ta) metal-filled Co4Sb12 samples (TaxCo4Sb12 (x = 0, 0.4, 0.6, and 0.8)) are synthesized using a solid-state synthesis route. All the samples are composed of a single skutterudite phase. Meanwhile, nanometer-sized equiaxed grains are present in the Ta0.2Co4Sb12 and Ta0.4Co4Sb12 samples, and bimodal distributions of equiaxed grains and elongated grains are observed in Ta0.6Co4Sb12 and Ta0.8Co4Sb12 samples. The dominant carrier type changes from electrons (n-type) to holes (p-type) with an increase in Ta concentration in the samples. The power factor of the Ta0.6Co4Sb12 sample is increased to 2.12 mW/mK2 at 623 K due to the 10-fold reduction in electrical resistivity. The lowest lattice thermal conductivity observed for Ta0.6Co4Sb12 indicates the rattling action of Ta atoms and grain boundary scattering. Rietveld refinement of XRD data and the analysis of lattice thermal conductivity data using the Debye model confirm that Ta occupies at the voids as well as the Co site. The figure of merit (ZT) of ∼0.4 is obtained in the Ta0.6Co4Sb12 sample, which is comparable to single metal-filled p-type skutterudites reported to date. The thermoelectric properties of the refractory Ta metal-filled skutterudites might be useful to achieve both n-type and p-type thermoelectric legs using a single filler atom and could be one of replacements of the rare earth-filled skutterudites with improved thermoelectric properties.

Design and Performance Analysis of Powering a Wireless Earphone by a Thermoelectric Generator

A wireless earphone requires a portable power source to keep it operational for long time. Currently, small batteries are integrated with the earphones that are used until the stored energy is completely diminished. When a user uses an earphone, its front side temperature remains near 305 K, and the rear side experiences ambient temperature. A route can be designed to dissipate the heat from the front side to the rear side using thermoelectric materials. The deposition of an organized thermoelectric material inside an earphone can help produce some electrical energy to enhance the durability of the battery. Thermoelectric generators (TEGs) are used to convert heat into electrical energy. In this paper, we present a numerical analysis of a thermoelectric generator in conjunction with an earphone. The TEG model consists of p-type and n-type Bismuth Telluride ( ${Bi}_{2}{Te}_{3}$ ) semiconductor legs connected thermally in parallel and electrically in series. COMSOL Multiphysics 5.4 was used to simulate and predict the power output by the TEG. Three different temperature conditions ( $\Delta \text{T}\,\,=10.5$ , 7.5, and 4.5 K) were analyzed to investigate the performance of the TEG. Finally, the outputs at two additional temperature differences (( $\Delta \text{T}\,\,=3$ , and 20 K) were examined by considering situations where the earphone wearer is exposed to summer and winter environments, respectively.

Heat and work fluxes in thermoelectric coolers

Thermodynamics considers heat and work as the observables of energy. Then, in a non-equilibrium process, the fluxes of heat, work and energy are related. The expressions for the heat and energy flux densities are well known; although several conventions have been adopted. The work flux density defined from the heat and energy flux densities can be very useful in describing the energy balance when chosen to emphasize observable quantities. This paper discusses the advantages of the use of the conduction heat flux density given by Fourier’s law and a work flux density defined from it. As a case study, heat and work fluxes are evaluated in the elements of a thermoelectric cooler using both the observable formalism and the electrochemical formalism. Two components, Thomson and Joule, are distinguished in the work rate of the semiconductors. In the p-type leg, absorption due to the Thomson effect of up to 33% of the electric power dissipated by Joule’s effect is observed. It is also concluded that the observable voltage drop is proportional to the electrical power consumed in the TEC and in its connectors, but not in the semiconductor legs and in the semiconductor/connector junctions.

Flexible thermoelectric nanodevices based on three-dimensional networks of poly(3,4-ethylenedioxythiophene) nanowires and graphene

Freestanding poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires (NWs) were synthesized using a facile, self-assembled, micellar soft-template method. Thermoelectric properties of the PEDOT NWs under different reaction conditions were measured, and optimal experimental conditions were confirmed. To obtain preferential thermoelectric performance, PEDOT NWs/graphene composite films with various graphene mass fractions were fabricated. The maximum power factor of the hybrids was observed to reach 42.0 μWm−1K−2 with 3 wt% graphene loading, corresponding to a 200% improvement compared with pure PEDOT NWs. The thermoelectric devices were investigated using the PEDOT NWs/graphene hybrids as a p-type leg and PEDOT NWs/nitrogen-doped graphene as an n-type leg. The device, in series, shows a preferable cooling effect with an approximate temperature decrease of 0.5°C after energization. Our work provides a novel means of fabricating n-type PEDOT hybrids and promotes their practical applications as thermoelectric coolers. These findings indicate a new means of developing high-performance, flexible, organic thermoelectric materials and devices.

Shape-Versatile 3D Thermoelectric Generators by Additive Manufacturing

Additive manufacturing (AM) is a recent growing technology, which is currently implemented for different application fields, from rapid prototyping to cost-effective manufacturing of industrial components with complex shapes. Printable thermoelectric materials offer synergies with AM and can be integrated into 3D printed thermoelectric generators (TEGs). In this work, we have formulated an Ag2Se-based n-type printable thermoelectric (TE) ink with a high figure-of-merit of ∼1 at room temperature. Three scaffolds with different shapes have been printed using 3D printing. The developed ink as n-type legs and commercially available PEDOT as p-type legs were then painted on the 3D printed scaffolds to fabricate three TEGs with a different number of legs and shapes. The performance of the TEGs was studied for different temperature differences between ΔT = 10 and 70 K. Power output (Pmax) levels of several microwatts and output voltages of several millivolts can be easily achieved.

Flexible and wearable wristband for harvesting human body heat based on coral-like PEDOT:Tos-coated nanofibrous film

A flexible and wearable thermoelectric wristband consisting of a poly(3,4-ethylenedioxythiophene):p-toluenesulfonic acid (PEDOT:Tos)-coated nanofibrous film (P-type legs) and a Ag nanoparticle-coated nanofibrous film (N-type legs) is constructed to realize the thermoelectric conversion by harvesting of the human body heat. Here, P-type legs are prepared via low-temperature in-situ interfacial polymerization, and a coral-like structure is formed on nanofiber. The resultant P-type leg exhibits a high electrical conductivity of 24.50 S cm−1 and a Seebeck coefficient of 13.67 μV K−1 at a temperature difference (ΔT) of 30 °C. Meanwhile, the N-type legs are fabricated via facile wet electroless deposition exhibits an electrical conductivity of 100 S cm−1. Thus, the constructed fiber-based wristband comprises of seven pairs of P-N legs, and can generate a maximum voltage of ∼0.18 mV at ΔT = 10 °C between user’s skin and the environment. Meanwhile, power is up to 101.51 pW after swinging the arm for 5 min. This thermoelectric wristband successfully completes the recycling of the human body heat and provides a new strategy for developing textile-based thermoelectric devices and monitoring human intelligence.

Economy, energy, exergy and mechanical study of co-axial ring shape configuration of legs as a novel structure for cylindrical thermoelectric generator

The n-type and p-type leg structure of any conventional thermoelectric module are in the form of filled rectangular shape which are placed next to the each other (see graphical abstract). In this paper, hollow cylindrical configuration is investigated as a novel leg structure for thermoelectric module in which the n-type and p-type legs are placed co-axial inside each other. A validated 3D numerical simulation was employed to investigate the proposed structure from thermal, economic, exergetic and mechanical viewpoints. The cylindrical ring-shape co-axial configuration can be made in different azimuthal angle, slant angle and width ratio all of which are probed in this research under different boundary conditions. The ring shape structure is able to reduce the thermal-stresses level without the reduction of thermal efficiency. Results indicate that the increment of hot side temperature can improve the output power and conversion efficiency of the cylindrical thermoelectric generator (CTEG) device but reduces the mechanical reliability of the system. It addition, with increment of slant angle of thermoelectric legs, the maximum Von Mises stress in the legs increases and power output of the CTEG is improved. The increase of the width ratio leads to the improvement of the output power and reduction of conversion and exergy efficiencies. Moreover, it is proved that the azimuthal angle of CTEG device has minor impact on the conversion and exergy efficiencies. It is found that the Von Mises stress attains the peak values in the contact regions between wielding layers and hot sides of the legs.

Enhanced thermoelectric performance of P-type CaMg2Bi1.98 and optimized CaAl2Si2-type Zintl phase module with equal cross-section area

Recently, Zintl phase Mg3Sb2 has displayed superior n-type thermoelectric properties. However, the corresponding p-type thermoelectric materials with high thermoelectric properties are still in urgent need. CaMg2Bi2-based Zintl compound attracts increasing enthusiasm in recent years due to its high carrier mobility and low lattice thermal conductivity. Here, Yb is used to replace Ca to further tune thermoelectric transport behavior of CaMg1.9Zn0.1Bi1.98, an optimized composition according to previous work. The synergistic effect of the enhanced carrier concentration caused by electronegativity difference in cation site and the suppressed lattice thermal conductivity induced by the stronger point defects scattering leads to the peak ZT of 1.0 in Ca0.65Yb0.35Mg1.9Zn0.1Bi1.98, which exceeds most of reported CaMg2Bi2-based materials. The maximum ZTeng of single p-type leg Ca0.65Yb0.35Mg1.9Zn0.1Bi1.98 is up to 0.54 between Tc = 300 K and Th = 773 K, catching up with the current highest level in 1-2-2 Bi-based materials. Moreover, the interrelationship between conversion efficiency and p-n pair cross-section area ratio (An/Ap) is considered. For n-type Mg3.1Co0.1Sb1.5Bi0.49Te0.01/p-type Ca0.65Yb0.35Mg1.9Zn0.1Bi1.98 pair, a maximum conversion efficiency of ~12% is obtained at the optimum An/Ap approaching to 1. This prominent conversion efficiency and equal cross-section area facilitate the module fabrication process and exhibit bright prospect of CaMg2Bi2-based thermoelectric materials.

Economical and Facile Route to Produce Gram-Scale and Phase-Selective Copper Sulfides for Thermoelectric Applications

Producing thermoelectric materials without energy-intensive processes is essential to reduce the production costs and for wide-scale applications. Copper sulfides have recently been identified as new and promising environmentally friendly thermoelectric materials. Here, an economical synthetic route for the gram-scale preparation of copper sulfide is developed that enables selective control of the copper oxidation state, in turn allowing the stoichiometry to be tuned to optimize the thermoelectric characteristics of the product. Through this facile and scalable protocol, CuS, Cu1.75S, Cu1.80S, and Cu2S powders have been synthesized in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy to verify the stoichiometry of each material. The as-prepared compounds were further characterized by thermoelectric measurements and the performance of a test generator module containing ten p-type Cu2S legs was subsequently investigated. Upon heating one side of the module to 70 °C, the device produced an output voltage of 30.9 mV and a corresponding power output of 3.4 μW, which is comparable to the power outputs of many of devices fabricated with expensive and toxic thermoelectric elements. This work presents a novel pathway for the development of low-cost thermoelectric devices by introducing a facile, tunable, and high-yield CuxS synthesis procedure that may be readily adapted to other metal sulfides.

Thermally Induced Delamination of PV-TEG: Implication of Leg’s Joule and Thomson Heating

The thermal implication of peel stresses and Joule and Thomson heating on the delamination of photovoltaic-thermoelectric generator (PV-TEG) layers is modelled and established numerically. The scope of the study embraces simulation of the hybrid system with and without electric potential difference. Furthermore, the results obtained from the interfacial peel stresses demonstrate that uneven contractions occur in the layers of the hybrid system, resulting in delamination. In addition, the conductor strip/TEG interface has the highest peel stress with a numerical value of 0.13 GPa, while the glass/ethyl vinyl acetate (EVA) interface presents a contrasting stress pattern in comparison to the EVA/cell, EVA/back plate and conductor strip/TEG interface. However, the n-type leg of the TEG has a higher thermal stress in comparison to the entire system components resulting from the application of 7 mV electric potential. Finally, this paper demonstrates that thermal stress is extremely deleterious in the TEG in comparison to the PV module. As a result, device failures will commence from the thermoelectric legs, with the n-type leg having a shorter operational life in comparison to the p-type leg.

Structure and thermoelectric properties of higher manganese silicides synthesized by pack cementation

Higher manganese silicides (HMS) are promising alternative materials for middle to high temperature thermoelectric applications as a low-cost, non-toxic and highly stable p-type leg. Many of the preparation methods that have been reported previously require long-time and energy consuming processes, as well as expensive equipment, and often do not result in a material of sufficient quality. In this study, the simple, cost-effective and eco-friendly technique of pack cementation is applied. HMS powders synthesized at different experimental conditions are studied and compared considering their structure, composition, short-term thermal stability in air and thermoelectric properties. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetry and thermoelectric measurements (in terms of Seebeck coefficient, electrical and thermal conductivity) were employed for the characterization of the material and evaluation of its performance. All samples were identified as HMS and only some negligible traces of MnSi were detected. They moderately oxidize when heated non-isothermally under air atmosphere up to 1473 K, while the presence of HMS remains dominant even at such high temperatures. Their thermoelectric properties were remarkable for an undoped material, with a maximum figure of merit (ZT) of 0.47 at 777 K. Pack cementation appeared to have a great potential as the synthesis route of high-efficiency HMS.

Origins of the enhanced thermoelectric performance for p-type Ge1-xPbxTe alloys

GeTe crystallizes with a strong deviation from the stoichiometric composition (in the direction of Te excess), which results in a growth of free carrier concentration (holes) up to p ~ 1021 cm−3. Such concentration is too high from the viewpoint of thermoelectric applications (maximum value of the figure of merit Z). The work demonstrates the possibility of increasing the thermoelectric efficiency of the GeTe-based material, used for the p-type leg of the thermoelectric couple over the temperature range of 600–825 K. The samples were prepared using Spark Plasma Sintering (SPS) technique. A systematic analysis of thermoelectric properties for Ge1-xPbxTe alloys (x up to 5 at.%) has been performed. An increase in the lead content in Ge1-xPbxTe alloys creates two parallel processes. The first process is a decrease of the lattice thermal conductivity κlat, which acts up to T ≈ 550 K, when the lead content in Ge1-xPbxTe alloys increases up to 5 at. %. However, the main process is to reduce deviation from the stoichiometric composition, which consequently leads to lower hole concentration p. Therefore, at a high temperature of T ≥ 550 K Fermi level EF is approaching the edge of the valence band Ev. As a result, the thermoelectric dimensionless figure of merit ZT increases up to 1.1 at the temperature of 825 K.

Thermoelectric modules built using ceramic legs grown by laser floating zone

The present work reports the first attempt of thermoelectric module design, based on oxide materials grown through the laser floating zone technique. Two modules with 4-legs thermoelectric were assembled using Bi2Ba2Co2Oy fibres as p-type legs, while Ca0.9La0.1MnO3 and CaMn0.95Nb0.05O3 fibres were used as n-type legs. Structural and electrical characterisation of the individual fibres was performed, and the results compared to the literature. The evolution of open-circuit voltage on heating and cooling up to 723 K, present the expected trends based on the Seebeck coefficient of the individual fibres, suggesting good reliability of the modules during temperature cycling. The power generation performance was evaluated for a temperature difference up to 500 K under different electric loads. The maximum measured power was ~2.2 mW for a module volume of ~39 mm3. Nevertheless, the module here studies possess better performance than those commercially available.

Fully direct written organic micro-thermoelectric generators embedded in a plastic foil

Abstract Organic materials have attracted great interest for thermoelectric applications due to their tuneable electronic properties, solution processability and earth-abundance, potentially enabling high-throughput realization of low-cost devices for low-power energy harvesting applications. So far, organic thermoelectricity has primarily focused on materials development, with less attention given to integrated generators. Yet, future applications will require the combination of efficient generators architectures and scalable manufacturing techniques to leverage the advantages of such promising materials. Here we report the realization of a monolithic organic micro-thermoelectric generator (μ-OTEG), using only direct writing methods, embedding the thermoelectric legs within a plastic substrate through a combination of direct laser writing and inkjet printing techniques. Employing PEDOT:PSS for the p-type legs and a doped fullerene derivative for the n-type ones, we demonstrate a μ-OTEG with power density of 30.5 nW/cm2 under small thermal gradients, proving the concrete possibility of achieving power requirements of low-power, distributed sensing applications.

Anisotropic thermoelectric figure-of-merit in Mg3Sb2

In view of the tensor nature of thermoelectric (TE) figure of merit ZT, the lack of experimental data on its anisotropic transport properties, and the recent advances in theoretical modeling, here we calculated the TE properties of n-type and p-type Mg3Sb2 as a function of temperature along major crystallographic axes using a parameter-free first principles algorithm of electron–phonon interactions and phonon-phonon interactions limited Boltzmann transport equations for charge carriers and phonons, respectively. The calculated ZT curves of n-type Mg3Sb2 are found to be nearly isotropic, and the highest calculated ZT is about 2.1 at 750 K, in reasonable agreement with the experimental results and thus validating our calculations. In contrast, we found strong anisotropy of ZT in p-type Mg3Sb2, with the highest calculated ZT value attaining 1.5 at 750 K along the c-axis and 0.6 in the ab-plane at 750 K, respectively. The strong anisotropy in p-type ZT is mainly dominated by the electrical conductivity along different directions which relies on the anisotropic charge carrier effective mass. In light of the fact that the experimentally measured ZT values are less than unity in polycrystalline p-type Mg3Sb2, these results attest the key role of texture in the performance improvement of polycrystalline p-type Mg3Sb2 so as to mitigate the performance imbalance between the n-type and p-type Mg3Sb2 legs toward higher device performance.

High-Temperature Thermoelectric Energy Conversion Devices Using Si-Ge Thick Films Prepared by Laser Sintering of Nano/Micro Particles

Silicon-germanium (Si-Ge) is used as a high-temperature thermoelectric material due to its high figure of merit and good thermal stability at high temperatures. This article focuses on the high-temperature thermoelectric energy conversion devices using Si80Ge20 thick films prepared by laser sintering of nano/micro particles. The Si80Ge20 thick films were prepared by ball milling of Si-Ge material to achieve nano/micro particles and then laser sintering to achieve thick films. The device consists of three pairs of n-type phosphorus-doped Si80Ge20 legs and p-type boron-doped Si80Ge20 legs. The maximum temperature difference of 200 K was achieved when the hot-side temperature was 873 K and the cold-side was kept in the air (no water cooling). The corresponding maximum thermovoltage and output-power were 311.6 mV and 15.85 $\mu \text{W}$ . The effective power density was calculated as 8.8 mW/cm2. The performance of the device could be further improved by increasing the hot side temperature to about 1000 °C and cooling the cold side by water circulation, to generate a larger temperature difference. We demonstrate that this novel fabrication method as an easier, faster, and lower-cost way to fabricate the thick film type thermoelectric devices with high performance. Our demonstrated approach will be suitable for thermoelectric devices for large-area applications on arbitrary shapes. The presented method will also find applications for on-chip cooling and powering, which could substitute MEMS-based fabrication methods for $\mu $ -thermoelectric generators (TEGs) or other microthermoelectric modules with a simpler, cheaper, and faster fabrication process.