Thin-film Thermoelectric Generators Research Articles

Investigating thin-film thermoelectric generators: Leg shape, TEG configuration, and contact resistance analysis

Thermoelectric generators (TEGs) are made of parallel p-type and n-type semiconducting legs which can directly convert temperature gradients into electricity. Theoretical studies have extensively explored the impact of the thermoelectric (TE) leg size and shape on the conversion efficiency of such bulk TEGs. However, in recent years, geometrically thin and film-shaped TEGs have gained attention for integration into wearable and flexible electronic devices, tapping into body heat as a power source. There is currently a lack of research on film-shaped TEGs, particularly regarding the performance of asymmetric TE leg shapes. This study investigates seven different TE leg shapes in thin-film TEGs, analyzing their electrical performance using COMSOL Multiphysics software. Results show that certain asymmetric TE leg shapes can yield over a 30% improvement in the produced open circuit voltage, as compared to conventional rectangular-shape TE legs. Furthermore, various configurations of thin-film TEGs were designed and analyzed, aiming to maximize device output power. Additionally, the study delves into the influence of electrical contact resistance on the performance of the optimal asymmetric TEGs. The proposed thin TE leg shapes and TEG configurations ae easily manufacturable and scalable using printing technology.

Fabrication of low-cost flexible thermoelectric generator using conductive HB graphite paint operated by solar radiation

Paper-based flexible thin film thermoelectric generators have emerged as a promising and feasible alternative to organic and inorganic conductors due to their ability to operate at room temperature within a limited temperature range. Here, a flexible solar thermoelectric generator (STEG) designed from a single material has been introduced, prepared by a simple painting method. We prepared HB graphite-based conductive paint and demonstrated a very unique method to design flexible STEG devices. The graphite paint shows p-type semiconductive behaviour, while, in conjunction with the polyethyleneimine (PEI) polymer, it acts as an n-type material. Based on the transport properties, the paint appears to be a good candidate for designing STEG devices. At room temperature, the power factor of 378 nW m−1 K−2 for p-type paint and 1.51 nW m−1 K−2 for n-type paint is obtained. In order to examine flexibility over the long term, the performance of the material was inspected through 300 repeated cycles, and transport properties (conductivity) were found to increase from 21 700 S m−1 to 73 500 S m−1 due to the excellent emulsifying properties of gum Arabic, which were confirmed by field emission scanning electron microscope analysis. To evaluate the performance of the thermoelectric (TE) generator, eight pairs of p–n legs are fabricated on normal copier (80 GSM) paper, and an output voltage of ∼0.1 mV K−1 (∼5.5 mV) for a temperature gradient T of up to ∼60 K was achieved. Further, the performance of flexible TE devices can be improved by increasing the number of thermoelectric legs and by sandwiching the device between Kapton tapes. Our work suggests a promising and simple approach to achieving cost-effective conversion of solar energy into electricity and highlights the potential of flexible STEGs for low-power applications.

High thermoelectric performance in polycrystalline Yb3Ge5 thin films

The development of eco-friendly thin-film thermoelectric generators for microenergy harvesting applications is highly desired. Ge-based materials have recently attracted significant research interest because of their superior performance at room temperature as human-compatible thermoelectric constituents. We examined the synthesis of Yb3Ge5 thin films and assessed their thermoelectric properties, considering the exceptional ability of Yb as a heavy metal to scatter phonons. The components of the resulting thin film were strongly dependent on the Yb/Ge deposition ratio and the subsequent annealing temperature. An increase in the Yb content augmented the formation of Yb2O3, whereas an increase in the Ge content facilitated the formation of Ge crystals. These trends were more evident at higher annealing temperatures. By controlling the YbGe composition, a power factor of 1470 µW m−1 K−2 was obtained at an annealing temperature of 700 °C, along with a low thermal conductivity of 3.1 W m−1 K−1. Machine-learning-facilitated data analysis revealed that the high power factor originated from Yb3Ge5. Notably, the power factor reached 1370 µW m−1 K−2 even at a temperature of 500 °C, causing the expansion of heat-resistant plastic films. Thus, we established the impressive potential of Yb3Ge5 as a suitable material for eco-friendly thin-film thermoelectric generators.

Thermoelectric properties of low-temperature-grown polycrystalline InAs1−xSbx films

The development of thin-film thermoelectric generators for micro-energy harvesting is highly anticipated. In this study, we have investigated the synthesis and thermoelectric applications of ternary alloy InAs1−xSbx thin films, which are narrow-gap III–V compound semiconductors. Polycrystalline InAs1−xSbx thin films with sub-micrometer grain size were synthesized on glass using molecular-beam deposition at 400 °C with all composition x. The InAs1−xSbx thin films exhibited n-type conduction, and their electrical and thermoelectric properties were strongly dependent on x and the amount of Sn doping. The ternary alloying reduced the power factor and contributed to a reduction in thermal conductivity. The InAs0.2Sb0.8 thin film on a glass substrate exhibited a power factor of 100 μW m−1 K−2 and a thermal conductivity of 2.0 W m−1 K−1 at room temperature. Furthermore, a comparable performance was demonstrated for an InAs0.2Sb0.8 thin film grown on a plastic film. These achievements will pave the way for the application of III–V compound semiconductors in flexible thermoelectric generators.

Development of the Photolithography Process for the Fabrication of a Flexible Thin Film Thermoelectric Generator

Development of the Photolithography Process for the Fabrication of a Flexible Thin Film Thermoelectric Generator

Regulation of electrical properties via ferroelectric polarization for high performance Sb2Te3 thermoelectric thin films

Sb2Te3 based thermoelectric thin films play a crucial role in energy conversion, whose thermoelectric performance highly depends on electrical properties. Herein, we proposed a new electrical properties regulation approach by ferroelectric polarization, which extracted polarization charges and achieved an in-situ modulation of the carrier concentration in Sb2Te3 thermoelectric thin films. In the positively polarized (Pr+) state, the power factor (PF) of Sb2Te3 thin films reached 14.16 μW cm−1 K−2, 19.0 % higher than the unpolarized one. The corresponding Sb2Te3 thin film thermoelectric generator (TEG) demonstrated a high output power density (ωout) of 2.22 mW cm−2 in the Pr+ state at ΔT = 42 K, demonstrating the promising potential for low-grade heat harvesting.

Recent Progress in Colloidal Quantum Dot Thermoelectrics.

Semiconducting colloidal quantum dots (CQDs) represent an emerging class of thermoelectric materials for use in a wide range of future applications. CQDs combine solution processability at low temperatures with the potential for upscalable manufacturing via printing techniques. Moreover, due to their low dimensionality, CQDs exhibit quantum confinement and a high density of grain boundaries, which can be independently exploited to tune the Seebeck coefficient and thermal conductivity, respectively. This unique combination of attractive attributes makes CQDs very promising for application in emerging thermoelectric generator (TEG) technologies operating near room temperature. Herein, recent progress in CQDs for application in emerging thin-film thermoelectrics is reviewed. First,the fundamental concepts of thermoelectricity in nanostructured materials are outlined, followed by an overview of the popular synthetic methods used to produce CQDs with controllable sizes and shapes. Recent strides in CQD-based thermoelectrics are then discussed with emphasis on their application in thin-film TEGs. Finally, the current challenges and future perspectives for further enhancing the performance of CQD-based thermoelectric materials for future applications are discussed.

Single-material MoS2 thermoelectric junction enabled by substrate engineering

To realize a thermoelectric power generator, typically, a junction between two materials with different Seebeck coefficients needs to be fabricated. Such differences in Seebeck coefficients can be induced by doping, which renders it difficult when working with two-dimensional (2d) materials. However, doping is not the only way to modulate the Seebeck coefficient of a 2d material. Substrate-altered electron–phonon scattering mechanisms can also be used to this end. Here, we employ the substrate effects to form a thermoelectric junction in ultrathin, few-layer MoS2 films. We investigated the junctions with a combination of scanning photocurrent microscopy and scanning thermal microscopy. This allows us to reveal that thermoelectric junctions form across the substrate-engineered parts. We attribute this to a gating effect induced by interfacial charges in combination with alterations in the electron–phonon scattering mechanisms. This work demonstrates that substrate engineering is a promising strategy for developing future compact thin-film thermoelectric power generators.

Thin Film Thermoelectric Generators for Powerful Applications

The power output of thin film thermoelectric generators (TEG) is not sufficient for large scale applications and is mainly used for low power applications. A thin-film TEG for high-power applications based on a new structure is proposed. The proposed new structure of the TEG ensures the mutual arrangement of flat thermocouples on a thin-film substrate of each layer with the formation of areas of hot and cold junctions, to which heat is efficiently supplied and removed, respectively. Layers are superimposed on each other and stacked in a package. TEGs generate electricity both from the heat of the sun and external heat sources. TEG, due to the high density of thermocouples that generate electricity on the substrates of many layers, generates sufficient power for their use in high-power applications and can be used in various fields as an autonomous source of electricity. Substrates and thermocouples are made of thin films. It is possible to manufacture them in nanoscale.

Economic and thermal performance analysis of two-stage thin-film solar thermoelectric power generator

One of the performance enhancement strategies in thermoelectric technology is application of two-stage leg instead of normal single stage leg structure. However, for a thin-film solar thermoelectric generator applying this strategy requires many in-depth considerations including economic -cost and reliability aspects. In this research, attempts are made to identify the economic and performance characteristics of a two-stage thin-film solar thermoelectric generator under various geometrical conditions and then compare with normal single stage configuration. Generally, in addition to being cost-effective compared to the single-stage design, the double-stage design can produce more power if the appropriate material is selected. The results of numerical simulations show that the use of bismuth tellurides in single stage thermoelectric generator (SATEG) legs improves the performance of the system in terms of power generation. But the use of skutterudites in the lower layer and bismuth tellurides in the upper layer of the two-stage case, in addition to increasing the output power, significantly reduces the dollar/watt value. Furthermore, the highest output power and exergy efficiency are obtained in the lower layer angle ratio of 0.8–1 and in the upper layer angle ratio of 2. Among the geometrical parameters, the radius of heated area (Rh) has the greatest effect on the performance of double-stage solar annular thermoelectric generator (DSATEG). The highest power output is obtained at Rh = 1.5, which is equal to 1.323W.

A novel economic-cost and thermal comparative case study between segmented and non-segmented thin-film solar annular thermoelectric generator

One of the key effective parameters on the efficiency of thermoelectric generator is the material of n-type and p-type semiconductors. Thermoelectric generator works based a huge temperature difference between two sides semiconductors. Unfortunately, the suitable efficient materials for high temperature range (hot side of thermoelectric) are not efficient for low temperature range (cold side of thermoelectric) and vice versa. That is why researchers have recently suggested segmented thermoelectric generator meaning the semiconductors are made of two different separate materials for each side of thermoelectric. This strategy has not been investigated for ultra-thin solar annular thermoelectric generator. Hence, in this research, a comparative case study is provided to clarify the efficiency of the segmented in-plane solar annular thermoelectric generator from economic, energetic and exergetic point of views. The results reveal that for a high range of heat flux, the segmented thermoelectric is more efficient even from economic cost aspect. For heat fluxes greater than 40 kW/m^2, Case 1 provides the lowest dollar/watt value, and for heat fluxes less than 40 kW/m^2, Case 4 shows the minimum dollar/watt value.

High performance flexible thin-film thermoelectric generator heated by methanol catalytic combustion

A flexible thin-film micro combustion-thermoelectric coupled (tf-MTC) device is proposed as a power supply for wireless sensors with small scale. Which is composed of thin-film thermoelectric generator (TEG) and catalytic layer. A simple but effective method is proposed for the integration of catalytic layer and thin-film TEG. With consideration of power generation system miniaturization, methanol is chosen as the fuel of catalytic combustion for its special characteristic of room-temperature self ignition and steady performance during catalytic combustion based on platinum catalyst. The centralized device with high output performance shows potential as a portable power. To make full use of the catalytic combustion energy, the integration method of catalytic layer and the electrode is proposed to form decentralized device, which greatly improves the flexible tf-MTC device output performance. The open voltage increases by nearly 103%, the value reaches 0.65 V at temperature difference 171.2 °C during steady catalytic combustion at flow rate of 1000 mL/min, and the corresponding maximum output power is 13.18 μ W with a load resistance of 8 k Ω . And the response of device to methanol, including temperature and open voltage are recorded to identify the stability of self-ignition characteristic with the fuel of methanol. • Energy system with combination of thin-film TEG and catalytic combustion. • Integration of catalytic layer and electrode of thin-film TEG. • Rapid response of the energy system to methanol-air.

Fabrication and Performance Analysis of AZO and MCCO as Thin Film-Thermoelectric Generator Materials

The purpose of this research was to determine the performance of AZO and MCCO materials as constituents of the thin film-thermoelectric generator module. The method used for fabrication is DC Magnetron Sputtering. The electrode material used is Ag and the substrate used is SiO2 glass. The arrangement of the thin film used for the fabrication of the thermoelectric module is P-N-P-N-P-N-P-N-P-N (5 couples of p-n junctions). Based on the test results, the thickness of the thin film type N is 74.72 nm and type P is 90.34 nm. At the highest test temperature (300 oC), the AZO Seebeck coefficient value is -108 µV/K while the MCCO Seebeck coefficient value is 350 µV/K, and the AZO electrical resistivity value is 0.07 Ω.m while the MCCO electrical resistivity value is 0.36 Ω.m. The highest temperature difference given in the test of the AZO and MCCO thin film thermoelectric module is 1.538 °C and the thermoelectric module can produce a voltage of 1,842 ± 0.047 mV, a Seebeck coefficient of 4 µV/K, and an efficiency of 0.44%. Based on this research, it can be concluded that the performance of AZO and MCCO thin film-thermoelectric modules will have better performance at temperatures around 300 - 350 °C.

High Thermoelectric Performance in Polycrystalline GeSiSn Ternary Alloy Thin Films.

Group IV materials are promising candidates for highly reliable and human-friendly thin-film thermoelectric generators, used for micro-energy harvesting. In this study, we investigated the synthesis and thermoelectric applications of a Ge-based ternary alloy thin film, Ge1-x-ySixSny. The solid-phase crystallization of the highly densified amorphous precursors allowed the formation of high-quality polycrystalline Ge1-x-ySixSny layers on an insulating substrate. The small compositions of Si and Sn in Ge1-x-ySixSny (x < 0.15 and y < 0.05) lowered the thermal conductivity (3.1 W m-1 K-1) owing to the alloy scattering of phonons, while maintaining a high carrier mobility (approximately 200 cm2 V-1 s-1). The solid-phase diffusion of Ga and P allowed us to control the carrier concentration to the order of 1019 cm-3 for holes and 1018 cm-3 for electrons. For both p- and n-type Ge1-x-ySixSny, the power factor peaked at x = 0.06 and y = 0.02, reaching 1160 μW m-1 K-2 for p-type and 2040 μW m-1 K-2 for n-type. The resulting dimensionless figure of merits (0.12 for p-type and 0.20 for n-type) are higher than those of most environmentally friendly thermoelectric thin films. These results indicate that group IV alloys are promising candidates for high-performance, reliable thin-film thermoelectric generators.

High-performance, thin-film thermoelectric generator with self-healing ability for body-heat harvesting

Flexible thermoelectric generators (TEGs) are attractive for their ability to power wearable electronics utilizing the temperature difference between the human body and the environment. Here, we present a self-healing flexible TEG assembled with high-performance Ag 2 Se films. A room temperature power factor (PF) as high as 20.8 μW cm −1 K −2 is obtained via isoelectronic copper doping. The relative resistance change of the film is less than 5% of the initial value after 1,000 bending cycles, and the resistance of the Ag 2 Se film recovers to its initial value within a few hours of the bending test. The 6-leg flexible TEG demonstrates a maximum power density of 80 W m −2 at a temperature difference of 50 K. An output voltage of 1.5–2.8 mV can be achieved on the arm in different motion states. These results demonstrate the promising application of Ag 2 Se-based flexible TEGs for wearable electronics. • RT power factor of 20.8 μW cm −1 K −2 is obtained in the Cu-doped Ag 2 Se film • The film exhibits self-healing capability • The 6-leg TEG demonstrates output power density of 80 W m −2 at Δ T of 50 K Hou et al. report a wearable thermoelectric generator (TEG) based on a copper-doped silver selenide flexible thermoelectric film. This TEG demonstrates a high output power density, excellent flexibility, and self-healing ability and is promising for wearable electronic applications.

Toward High-Power Output of Generators: High-Power-Factor Ag2Te-Ag Thermoelectric Thin Films Using a Layer-by-Layer Method.

The power factor is key to improving the performance of thin-film thermoelectric generators as power sources. The expected large power factor of Ag2Te testifies to its application potential. In this study, Ag2Te-Ag thin films were fabricated using a layer-by-layer method for controlling their composition and improving their thermoelectric properties. In contrast to the traditional low-temperature monoclinic structure, orthorhombic Ag2Te thin films with Ag nanoparticles on top were obtained by the reaction between Ag and Te nanorod thin films. Analysis of the structural and thermoelectric properties showed increased carrier concentration and enhanced electrical properties of the films, while the structural transition between the orthorhombic structure and the face-centered cubic structure improved the films' electrical stability over a wide range of temperatures. Owing to the special structure, a competitive high power factor of 4.66 mW m-1 K-2 at 668 K was achieved. The proposed approach improves the electrical properties of n-type Ag2Te thin films, owing to the special Ag2Te-Ag structure, and provides guidance for designing high-output-power thin-film thermoelectric generators.

Roll-to-roll manufacture of flexible thin-film thermoelectric generators using flexography with vacuum vapour deposition

Exploring processes for industrial large-scale manufacture of low-cost electronic devices is timely for the upcoming era of the Internet of Things. In this study, a roll-to-roll process using selective metallisation (a combination of flexographic printing of an oil liquid-mask and physical vapour deposition: sputtering and evaporation) is explored for the large-scale manufacture of flexible electronics, with a wearable thermoelectric generator as an exemplar device. Two post-treatments (electron beam and infrared) are trialled to remove the residual oil after selective metallisation. Both are effective for the removal of oil, however, the oil used in selective metallisation degrades the functional thermoelectric material severely, causing a dramatic increase in the internal resistance of the device. This is attributable to (1) the doping and oxidation issues in the semiconductor film; (2) the existence of oil at the interface between the two coatings. The fabricated thermoelectric generator with post-treatments shows a good voltage output comparable to a standard device fabricated using shadow mask, providing an option for portable devices requiring a voltage source. This study reports an industrially compatible roll-to-roll manufacturing process for large-scale manufacture of flexible electronics. Further studies are under way to optimise the device performance.

Thermal Concentration on Thermoelectric Thin Film for Efficient Solar Energy Harvesting

Thermoelectric generators can directly harvest and convert ambient thermal energy into electricity, which makes it ideal for thermal energy conversion. However, the limited working temperature gradient developed by direct solar radiation severely restricts the performance and the application of solar thermoelectric generators. Here, we report a multilayer thin film integrating a solar selective absorbing coating and a thermoelectric layer, where an in-plane temperature gradient was established. The temperature gradient was relatively large since the absorbed solar energy could only flow through the restricted cross-section of the thin film, representing a high thermal concentration. The fabricated thin-film solar thermoelectric generators (100 mm × 15 mm) achieve an open-circuit voltage of about 300 mV, and an output power of 0.83 μW under AM 1.5G conditions. Our work opens up a promising new strategy to achieve the simple and cost-effective conversion of solar energy into electricity by thermal concentration.

First principles study of monolayer Sb2S2Te and a mathematical model of a thin-film thermoelectric generator with maximum power point tracing

The result of the structural, electronic and thermoelectric performance of monolayer Sb2S2Te, which is a bran-new material, is calculated by using the method of full-potential linearized augmented plane-wave (FP-LAPW), and the exchange-correlation potential selected in this paper is generalized gradient approximation (GGA) scheme. There are no negative frequencies in the calculated phonon spectra, which demonstrates that dynamics of monolayer Sb2S2Te is stable in theory. The average value of lattice thermal conductivity (κl) is smaller than that of other thermoelectric (TE) materials, and monolayer Sb2S2Te has larger figure of merit (ZT) comparing with other well-known materials. According to the TE parameters (Seebeck coefficient S, electrical conductivity σ, electronic thermal conductivity κe and lattice thermal conductivity κl) of monolayer Sb2S2Te, an idealized model of thermoelectric generator (TEG) and a realistic model of maximum power point tracking (MPPT) are built. In addition, this paper studies the influence of different temperature zones, different temperature differences, cross sectional area, height and the number of P–N junction on output power and conversion efficiency of TEG. The results of physical calculation and simulation models show that the conversion efficiency of TEG of monolayer Sb2S2Te is larger than or close to that of other well-known materials, and the tracking accuracy of MPPT proposed in this paper is higher than or close to that of other researches.

Kirigami‐Based Stretchable, Deformable, Ultralight Thin‐Film Thermoelectric Generator for BodyNET Application (Adv. Energy Mater. 5/2022)

Stretchable Electronics In article number 2102993, Wei Zhu, Yuan Deng and co-workers develop a general scheme to extend a system from a thin-film thermoelectric generator into a 3D adjustable form by rational cut designs and unique patterning procedures inspired by kirigami. The kirigami-based thermoelectric generator with high specific energy output takes the advantages both from the superior fabrication capabilities existing for planar thin-film devices and a compliant mechanism with deformability.