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Textile‐Based Thermoelectric Generators and Their Applications
Energy & Environmental Materials
... High electrical conductivity, low thermal conductivity, and high Seebeck coefficient are prerequisites of good TE material [9]. The converse of the Seebeck effect is the Peltier effect, which guides the conversion of electrical energy to thermal energy and is applied for refrigeration or cooling effect [9,11]. The TE power output of generators may again be defined as [11] ...
... The converse of the Seebeck effect is the Peltier effect, which guides the conversion of electrical energy to thermal energy and is applied for refrigeration or cooling effect [9,11]. The TE power output of generators may again be defined as [11] ...
... They have been broadly classified as per their physical dimensions as in 1D, which includes fibres, filaments, yarns, 2D structures as in fabrics, and 3D structures as in assembled textile products. 1D textiles have been produced using wet spinning, electrospinning, thermal drawing, gelation process, casting, and so on [11]. 2D and 3D architectures are based on woven, nonwoven, knitted fabrics, and fabrics with yarns, fibres, and filaments embroidered onto them [11]. ...
In the yesteryears, textile materials were primarily intended for apparels, home furnishing, and in few technical textile areas. But recently, the unique properties of a textile material owing to its material property, weave patterns, and different fabrication techniques have made it a promising candidate for smart applications. Therefore, smart textile materials can be used to power electronic items demanding energy on a miniscule scale, namely gadgets like electronic watches and smartphones. The drive for renewable and clean energy is the driving wheel behind exploration for areas that do not include energy sources from fossil fuels. Depletion of fossil fuels is an alarming concern, and hence, we should look for such energy sources that can be created from the surrounding environment. It cannot be much better than harvesting the immense potential out of the mechanical energy sources that are generally wasted. This chapter encompasses different concepts underlying the energy harvesting mechanisms of smart textiles. Piezoelectric, thermoelectric, photovoltaic, triboelectric, and piezoelectric nanogenerators are most promising in this segment. Lithium-ion batteries, polymer- based batteries, capacitors, and supercapacitors have catered to growing energy demands for a long time. But issues like portability, life cycle, and performance over a period of time were debatable for a while. Hence, different textile-based supercapacitors, batteries, and solar energy harvesting devices are researched nowadays and are a furore among the material scientists working in these areas. The efficiency and basic working of smart textiles are based on their unique structure and different production methods, which play an important role in upscaling their overall usability in their end use applications. Different potential applications will be one of the highlights of this chapter, along with different challenges and scopes of these segments of smart textiles
... 0.65 W/m 2 for a typical temperature difference of 55 K [83]. In many cases, however, only a maximum power is given for a textile-based thermoelectric generator [84], making it more complicated to estimate the maximum thermoelectric power that could be generated by garments. With 864 connected legs coated with PEDOT:PSS and poly([Na(NiETT)], respectively, on an area of (25 cm) 2 , a temperature difference of 3 K resulted in a power of 13 µW, whereupon the authors calculated that densely filling 8% of the whole body surface area with the legs of a thermoelectric generator would result in 1 mW power output [79]. ...
... 0.65 W/m 2 for a typical temperature difference of 55 K [83]. In many cases, however, only a maximum power is given for a textile-based thermoelectric generator [84], making it more complicated to estimate the maximum thermoelectric power that could be generated by garments. ...
Textiles are often used to protect people from cold environments. While most garments are designed for temperatures not far below 0 °C, very cold regions on the earth near the poles or on mountains necessitate special clothing. The same is true for homeless people who have few possibilities to warm up or workers in cooling chambers and other cold environments. Passive insulating clothing, however, can only retain body heat. Active heating, on the other hand, necessitates energy, e.g., by batteries, which are usually relatively heavy and have to be recharged regularly. This review gives an overview of energy-self-sufficient textile solutions for cold environments, including energy harvesting by textile-based or textile-integrated solar cells; piezoelectric sensors in shoes and other possibilities; energy storage in supercapacitors or batteries; and heating by electric energy or phase-change materials.
... Recent studies have shown that stable n-type SWCNT films can be obtained using several types of doping materials [43][44][45]. Based on these studies, it is now possible to obtain both p-and n-type SWCNT films and fabricate p-n junction SWCNT thermoelectric generators [46][47][48]. In our previous studies, n-type SWCNT films with ultra-long stability for over two years were developed using a cationic surfactant as a dopant [49], and several p-n junction SWCNT thermoelectric generator structures were developed using vacuum filtration [50]. ...
As power sources for Internet-of-Things sensors, thermoelectric generators must exhibit compactness, flexibility, and low manufacturing costs. Stretchable and flexible painted thermoelectric generators were fabricated on Japanese paper using inks with dispersed p- and n-type single-walled carbon nanotubes (SWCNTs). The p- and n-type SWCNT inks were dispersed using the anionic surfactant of sodium dodecylbenzene sulfonate and the cationic surfactant of dimethyldioctadecylammonium chloride, respectively. The bundle diameters of the p- and n-type SWCNT layers painted on Japanese paper differed significantly; however, the crystallinities of both types of layers were almost the same. The thermoelectric properties of both types of layers exhibited mostly the same values at 30 °C; however, the properties, particularly the electrical conductivity, of the n-type layer increased linearly, and of the p-type layer decreased as the temperature increased. The p- and n-type SWCNT inks were used to paint striped patterns on Japanese paper. By folding at the boundaries of the patterns, painted generators can shrink and expand, even on curved surfaces. The painted generator (length: 145 mm, height: 13 mm) exhibited an output voltage of 10.4 mV and a maximum power of 0.21 μW with a temperature difference of 64 K at 120 °C on the hot side.
... Many research works are undertaken in this regard. A very important progress in textile-based thermoelectric generators has been reported by Wang and Zhang (2020). In this work, the conversion of human body temperature into electrical energy has been reported. ...
... Recently, emerging moist electric generators that harvest energy from atmospheric moisture have attracted great attention in self-powered textiles [132]. Besides, thermoelectric generators that harvest energy from waste heat have been combined with fabric platforms [133]. Nevertheless, these textile-based generators often exhibit microwatt levels and instantaneous low-grade energy, which cannot meet the energy requirements of smart wearables. ...
Smart wearables equipped with integrated flexible actuators possess the ability to autonomously respond and adapt to changes in the environment. Fibrous textiles have been recognised as promising platforms for integrating flexible actuators and wearables owing to their superior body compliance, lightweight nature, and programmable architectures. Various studies related to textile actuators in smart wearables have been recently reported. However, the review focusing on the advanced design of these textile actuator technologies for smart wearables is lacking. Herein, a timely and thorough review of the progress achieved in this field over the past five years is presented. This review focuses on the advanced design concepts for textile actuators in smart wearables, covering functional materials, innovative architecture configurations, external stimuli, and their applications in smart wearables. The primary aspects focus on actuating materials, formation techniques of textile architecture, actuating behaviour and performance metrics of textile actuators, various applications in smart wearables, and the design challenges for next-generation smart wearables. Ultimately, conclusive perspectives are highlighted.
Graphical Abstract
... However, the production of 3D-TEG based on textiles has been very little explored because of challenging mechanical properties of the thermoelectric materials (tensile strength, flexibility, and frictional properties). Current developments for 3D textile TEG are based on manual manufacturing of pre-functionalized threads into a 3D fabric substrate or the subsequent coating of an entire textile [31,32]. For example, by stitching a p-and an n-type polymer-based TEG into a spacer fabric, an output power of 2.6 nW at a temperature difference of 66 K was achieved [33]. ...
Thermoelectric generators (TEG) offer the potential to convert waste heat into electricity and thus contribute to reduce CO2 emissions. The conversion of electrical energy is based on the Seebeck effect of two electrically conductive materials without any mechanical conversion and therefore without wear. The application of conventional TEG modules is limited due to cost-intensive materials and production technology of TEG, and a limited structure design for the integration of Thermoelectric Elements (TE). To address this research challenge, this work presents the development of thermoelectric composite modules based on glass fiber reinforced warp knitted spacer fabrics. In a double needle bed warp knitting machine, glass fibers in warp, weft and pile direction are integrated. The contacting of TE in the form of wires with 45 TE cm⁻² were implemented. A TEG module with 20.25 cm² in size showed a maximum output power of 2.7 μW at a temperature difference of 60 K. The Seebeck factor of S = 142 μV K⁻¹ was determined using this composite TEG with 10 TE strands and nearly 400 thermocouples. A thermoelectric model was developed for the calculation and the modules were characterized. For the first time, thermoelectric composite modules with sufficient structural-mechanical properties in terms of compressive and bending stiffness were realized based on spacer warp knitted fabrics, which can be used for the operation of sensors or small devices.
... Textile resistive sensors utilize changes in electrical resistance caused by the magnitude and direction of biomechanical stress and, thus, can also be integrated into e-textiles as sensor devices [40] . The equivalent circuit in Figure 2D illustrates that the variation in the output of the sensor concerning the applied pressure on the sensing surface is influenced by the alteration in relative resistance [36] . ...
In the face of pandemic infectious diseases and increasing aging trends, traditional public health systems lack the capacity for real-time monitoring, immediate clinical detection, continuous vital sign monitoring, and the implementation of long-cycle treatment protocols, among other deficiencies. On the basis of the rapid development of wearable electronic devices, the Internet of Things, and artificial intelligence, the future healthcare model will transform from a therapeutic, centralized, passive, and even one-size-fits-all treatment to a new paradigm of proactive, preventive, personalized, customized, and intelligent way. The development of wearable electronics has facilitated the evolution of healthcare from healthcare to biological monitoring, enabling continuous monitoring of critical biomarkers for diagnostic treatment, physiological health monitoring, and assessment. Electronic textiles (e-textiles) are among the rapidly developing wearable electronics in recent years. They have revolutionized the functionality of traditional textiles by incorporating smart attributes, enabling unique and multifunctional applications. Significantly, e-textiles have made notable advancements in the field of personalized healthcare. The article introduces several common e-textiles and their applications in personalized medicines, which also gives a forward-looking outlook on their future growth in infectious diseases, real-time health preventive monitoring, auxiliary therapy, and rehabilitation training.
... Textiles are seen as suitable materials to combine with TEGs due to inherent benefits like comfort, absence of impedance to movement, and assured heat transfer. Several types of TEG structures made through textiles can be distinguished: 1D (yarn/filament/fiber-based TEGs), 2D (fabric based-TEGs) and 3D (TEG yarn/filament/fiber into textile) [15][16]. In terms of materials, thermocouples can be produced from organic materials (materials based on carbon and conductive polymers), inorganic (e.g. ...
Textile integrated Thermoelectric Generators (TEG) represent a promising alternative for energy harvesting in smart textile products. Based on the Seebeck effect, textile TEGs can power sensors and devices of smart textiles, at a certain temperature gradient between the outdoor and the inner clothing. Textile TEGs are thus able to replace heavy and bulky batteries and ensure the washability of the smart textile product. The thermocouple is the functional unit of a TEG and is formed of a pair of legs of p-type and n-type material, under the same temperature gradient. Thermocouples are connected electrically in series and thermal in parallel to form a thermopile. Various scientific research solutions are available to integrate thermopiles into textile products with TEG functionality. This short review paper presents the physical principles, some of the applications of textile TEGs, the main textile integration techniques and some analytical relations of the main physical parameters in view of textile TEGs optimization.
... 6 With recent boom in wearable electronics market and Internet of Things (IoTs) technique, the urgent need for long-term, portable, and maintenance-free power supply has triggered great interest in TEGs, which hold great promise to take the advantage of the temperature difference between human body and environment as the heat source to drive low-power wearable electronics realizing self-powered electronics. [7][8][9][10] Apart from power generation applications, TE-based devices have also emerging applications as part of IoT sensors monitoring the environmental temperature in extreme conditions, body temperature for health care, providing tactile sensory in human-machine interaction applications. ...
Thermoelectrics is the simplest technology applicable for direct energy conversion between heat and electricity. After over 60 years of fruitful research efforts, recent boom in flexible electronics has promoted the rapid development of flexible thermoelectrics with rising performances, discovery of new materials and concepts, unconventional device configuration, and emerging applications not possible for traditional thermoelectric (TE) semiconductors. In this Perspective, we first overview representative flexible TE materials, then discuss recent breakthroughs for flexible TE devices assembled from various types of TE materials employing different technical routes. They exhibit promising power generation and sensing performances, and aim for applications in wearable electronics, such as the power supply harvesting heat from body for low-power electronics, temperature sensors for tactile e-skin, and newly emerged application as a thermo-haptic device in an extended reality system.
... Power output (P) produced by the Graphite/NiO composite ink-based FTEG was estimated using Eq. (1) [49,50]. ...
This work aims at optimizing the power density of Graphite/NiO composite ink-based flexible thermoelectric generators by varying the concentration of nickel oxide nanoparticles annealed at different temperatures. NiO nanoparticles containing porous structure, higher microstrain, dislocation in their lattice structure, and higher resistivity due to the varied annealing temperature reduced the carrier concentration and mobility resulting in the enhanced Seebeck coefficient, power output, and power density. Flexible thermoelectric generator screen printed with Graphite/NiO composite ink consisting of an optimum of 3.0 wt% NiO nanoparticles annealed at 400 °C exhibited superior performance. The maximum power density, Seebeck coefficient, and power output shown by this device at 100 °C temperature gradient are 4.10 mW/m², 47.06 µV/K, and 0.80 nW, respectively. This work demonstrates the suitability of graphite and nickel oxide composite for the screen-printed flexible thermoelectric generator for low-temperature applications.
Graphical abstract
... The high performance, stability, accessibility, and versatility of PEDOT:PSS has made it one of the preferred choices for the p-type semiconductor in the reported hybrid and organic TEGs. 24,47,48 In addition to PEDOT:PSS, other p-type materials, such as poly(3,4ethylenedioxythiophene) doped with iron(III) p-toluenesulfonate (PEDOT:Tos), 49,50 poly(2,5-bis(3-dodecyl-2-thienyl)thieno[3,2-b]thiophene) (PBTTT), 51,52 and poly(3-hexylthiophene) (P3HT), 53 have been shown to have excellent thermoelectric properties. There are reports of PEDOT:Tos demonstrating PF > 70 lW m À1 K À2 , 49,50 and a highly aligned PBTTT film was shown to have an electrical conductivity of up to 2400 S cm À1 and PF % 530 lW m À1 K À2 . ...
Organic thermoelectric generators (TEGs) are a prospective class of versatile energy-harvesters that can enable the capture of low-grade heat and provide power to the growing number of microelectronic devices and sensors in the Internet of Things. The abundance, low-toxicity, and tunability of organic conducting materials along with the scalability of the fabrication techniques promise to culminate in a safe, low-cost, and adaptable device template for a wide range of applications. Despite recent breakthroughs, it is generally recognized that significant advances in n-type organic thermoelectric materials must be made before organic TEGs can make a real impact. Yet, in this perspective, we make the argument that to accelerate progress in the field of organic TEGs, future research should focus more effort into the design and fabrication of application-oriented devices, even though materials have considerable room for improvement. We provide an overview of the best solution-processable organic thermoelectric materials, design considerations, and fabrication techniques relevant for application-oriented TEGs, followed by our perspective on the insight that can be gained by pushing forward with device-level research despite suboptimal materials.
... There are several benefits to using a thermoelectric generator (TEG) as the system for collecting self-powered energy. First, it is a solid-state device that has no moving parts or liquids [9]. This simplifies the structures and makes the system more efficient because the material itself will convert the energy. ...
Electro-textiles are the future of wearable technology and have the potential to revolutionise numerous industries. However, electro-textiles require a power source to sense, analyse, react, and adapt to various stimuli. While current power sources feature dry cell batteries, the research into alternative power sources, such as self-powered textiles, is growing due to the use of nanotechnology. These new textiles harness their own electrical energy to power sensors and other electronic devices. One system being investigated is thermoelectric generation because it uses human body waste heat to create electrical energy. Thermoelectric Generators (TEGs) can passively harvest energy and have the capacity to offer continuous electrical energy. Optimisation of its design parameters, fabrication methods, and materials used are necessary for this system to be commercially viable. This manuscript analyses recent advancements in textile-based TEGs, their application towards various industries, and the future of self-powered electro-textiles.
... when the scrolled F-TED was bent at 90 • , the resistivity only changed by 1.3 %, demonstrating the good flexibility and stability [439]. Therefore, such a scrolled F-TED is a good candidate for integrating with other functional textiles such as large-area thermal sensing fibers [636], thermally insulating textile [637], and insulation/phase change heat storage fibers [638] to design multi-functional smart textiles for various uses, including temperature monitoring, heat source detection, temperature regulation, thermal (infrared) stealth, and intelligent thermal insulation. ...
Owing to their capabilities of solid-state conversion between heat and electricity, zero-emission, and high flexibility, flexible thermoelectric devices (F-TEDs) have exhibited great application possibilities for both portable power generation and localized refrigeration. However, with the rapid development of thermoelectric science and technology, there is still a lack of comprehensive review on the rational design of F-TEDs from the fundamentals to structures, which critically determines the performance and conformality of F-TEDs. To address this issue, here, we timely overview the latest progress on the up-to-the-date F-TEDs with their unique designs. We carefully summarize the structure-related principles and factors that determine the performance of F-TEDs and the advanced strategies for improving their utilities. Besides, we focus on the timeliest designs for the inorganic-based devices, organic-based devices, and hybrid-based devices targeting both power generation and refrigeration. In the end, we point out the current challenges, controversies, and prospects of F-TEDs.
Одними з основних проблем сьогодення є глобальне потепління, забруднення довкілля та підвищення вартості електроенергії. Частково вирішити зазначені проблеми можна за допомогою термоелектричних генераторів і засобів термостабілізації різноманітних об’єктів, дія яких ґрунтується на ефектах Зеєбека й Пельтьє. Беззаперечними перевагами термоелектричних засобів є їхня екологічна безпечність, безшумність у роботі та тривалий термін служби, а також можливість безпосереднього виробництва електроенергії з відпрацьованого тепла різноманітних процесів і транспортних засобів. Ефекти Пельтьє й Зеєбека знаходять своє застосування в хімічній технології й споріднених галузях промисловості, відновлювальній енергетиці, будівництві, машино- та приладобудуванні, аерокосмічній й військовій техніці, мікроелектроніці, комп’ютерній техніці, медицині, пристроях особистої гігієни, побуті, а також на транспорті. Проте низький коефіцієнт корисної дії й висока вартість матеріалів перешкоджають широкому поширенню термоелектричної технології, незважаючи на її очевидні переваги. Більш широкого застосування термоелектричних технологій можна очікувати в разі розроблення нових струмопровідних матеріалів з різними рівнями енергії електронів у зоні провідності, зокрема напівпровідних, керамічних і полімерних, а також оптимізації геометрії та структури термоелектричних пристроїв.
In the pursuit of sustainable solutions to the ever-increasing demand for renewable energy, mechanically compliant Thermoelectric Generators (TEGs) have garnered significant attention owing to the promise they present for application in generating power from waste heat in mechanically challenging scenarios. This review paper examines the ongoing advancements in the efficiency and applicability of TEGs through novel material engineering and design innovations. It delves into the improvement of their thermoelectric properties via micro- and nanostructural modifications and explores architectural advancements aimed at enhancing functionality and power output. Notably, the integration of TEGs into flexible, stretchable, and wearable electronics has been a significant development, expanding their applications in various domains such as healthcare monitoring, remote sensing, and consumer electronics. The review emphasizes the critical interplay between electronic, thermal, and mechanical aspects in optimizing TEG performance. By providing an in-depth exploration of these multifaceted interactions and highlighting the significant advancements in materials and design, this review aims to underscore the importance of TEGs in a cleaner and more efficient era of energy generation, with a particular focus on their emerging applications across diverse fields.
Thermal management is essential for maintaining optimal performance across various applications, including personal comfort, electronic systems and industrial processes. Thermal management fibers and textiles have emerged as innovative solutions to manipulate heat transport, storage, and conversion efficiently. This review explores recent advancements in material innovations in this field. We summarized the novel fibers and textiles designed for controlling heat transport through different pathways, progress in developing phase change material (PCM)-based fibers and textiles for heat storage regulation, and application of photothermal conversion, Joule heating and thermoelectric effect as energy conversion routes in advanced fibers and textiles. Furthermore, we discussed the challenges and future perspectives of this field. It is believed that the ongoing research and development promise to bring about innovative thermal management solutions catering to demands across multiple sectors.
Flexible thermoelectric generators (FTEGs) represent an excellent solution for energizing wearable electronics, capitalizing on their ability to transform body heat into electrical energy. Nevertheless, their use in the wearable industry is limited by the insufficient thermoelectric (TE) efficiency of materials and the minimal temperature variation among the devices. In this study, we have developed a Lego‐like reconfigurable FTEG by combining flexible TE chips, rheological liquid‐metal electrical wiring, and a stretchable substrate in a mechanical plug‐in configuration. The flexible TE chips are constructed from n‐type all‐inorganic MXene/Bi2Te3 composite films, which have their TE properties further enhanced through heat treatment. A demonstration of the FTEG illustrates its capability to convert heat into vertical temperature difference (ΔT), leading to a substantial ΔT at the cold end in contact with the environment, resulting in a power output of 7.1 μW with a ΔT of 45 K from only 5 TE chips. The reconfigurable FTEG presents significant potential for wearable devices to harness low‐grade heat.
The rise of artificial intelligence and the Internet of Things have spurred an increasing demand for wearable, sustainable, and maintenance‐free power sources. Organic thermoelectric (OTE) devices are emerged as promising candidates because they are capable of converting heat energy into electricity directly without the need of moving parts, capable of flexible and seamless integration with multifunctional miniaturized electronics. In addition, OTE devices can perform straightforward as various self‐powered sensors, boosting their applications in the field of intelligent interactions. This review focuses on recent advances in OTE materials and devices for applications in energy harvesting and sensing. The basic knowledge and key parameters of OTE materials and devices are presented, followed by detailed introduction of recent progress of OTE generators, sensors, and other OTE‐integrated devices. Next, several aspects of optimizing OTE devices toward multifunctional applications are highlighted. Finally, an overview of the current challenges and future research directions of OTE‐based devices is addressed. It is hoped that this review can pave the way for speeding up a bright future for the development and practical applications of OTE devices.
Wearable thermoelectric generators (TEGs) have exhibited great potential to convert the temperature gradient between the human body and the environment into electrical energy for maintenance‐free wearable applications. A 2D planar device structure is widely employed for fabricating flexible TEGs due to its simple structure and facile fabrication properties. However, this device configuration is more appropriate for utilizing in‐plane temperature differences than the out‐of‐plane direction, which limits their application in wearable cases since the temperature difference between the human body and the environment is in the out‐of‐plane direction. To solve this problem, a novel fabric‐based TEG structure that can utilize the out‐of‐plane temperature gradient is proposed in this work. By introducing thermally conductive components in the generator, the out‐of‐plane temperature difference can be switched to the in‐plane direction, which can be further utilized for 2D planar devices in wearable applications. The prepared thermoelectric fabric prototype with only 12 p‐type TE legs exhibits a maximum open‐circuit voltage of 4.69 mV and an output power of 39.7 nW at a temperature difference of 30 K. This strategy exhibits a high degree of versatility and can be readily applied to other 2D planar TEGs, thus expanding their potential application in wearable technology.
Electronic textiles (e‐textiles) have emerged as a revolutionary solution for personalized healthcare, enabling the continuous collection and communication of diverse physiological parameters when seamlessly integrated with the human body. Among various methods employed to create wearable e‐textiles, printing offers unparalleled flexibility and comfort, seamlessly integrating wearables into garments. This has spurred growing research interest in printed e‐textiles, due to their vast design versatility, material options, fabrication techniques, and wide‐ranging applications. Here, a comprehensive overview of the crucial considerations in fabricating printed e‐textiles is provided, encompassing the selection of conductive materials and substrates, as well as the essential pre‐ and post‐treatments involved. Furthermore, the diverse printing techniques and the specific requirements are discussed, highlighting the advantages and limitations of each method. Additionally, the multitude of wearable applications made possible by printed e‐textiles is explored, such as their integration as various sensors, supercapacitors, and heated garments. Finally, a forward‐looking perspective is provided, discussing future prospects and emerging trends in the realm of printed wearable e‐textiles. As advancements in materials science, printing technologies, and design innovation continue to unfold, the transformative potential of printed e‐textiles in healthcare and beyond is poised to revolutionize the way wearable technology interacts and benefits.
Organic thermoelectric (OTE) devices composed of π‐conjugated molecules are the basic building blocks for self‐powered integrated organic electronics. In addition to molecular design and doping strategies, the highly tunable energy conversion process in OTE devices has drawn significant research interest. Specifically, the diverse physical properties of organic semiconductors, novel device geometry design, and advanced fabrication techniques combined enable the OTE device to be a powerful multiscale platform from single‐molecular scale to thin films for modulating the TE performance, studying the fundamental charge transport mechanism, exploring novel energy conversion phenomenon, and realizing various functionalities. Here, the authors comprehensively review the recent experimental and theoretical advances in related topics of OTE devices, including multifunctional, external physical fields, and temperature modulated, as well as quantum OTE devices. The remaining issues and perspectives toward future OTE device research are also discussed at the end.
Owing to the capability of the conversion between thermal energy and electrical energy and their advantages of lightweight, compactness, noise-free operation, and precision reliability, wearable thermoelectrics show great potential for diverse applications. Among them, weavable thermoelectrics, a subclass with inherent flexibility, wearability, and operability, find utility in harnessing waste heat from irregular heat sources. Given the rapid advancements in this field, a timely review is essential to consolidate the progress and challenge. Here, we provide an overview of the state of weavable thermoelectric materials and devices in wearable smart textiles, encompassing mechanisms, materials, fabrications, device structures, and applications from recent advancements, challenges, and prospects. This review can serve as a valuable reference for researchers in the field of flexible wearable thermoelectric materials and devices and their applications.
With the increasing interest of people to be informed at every step, to progress and overcome their limits, rapid developments have occurred in the field of IoT (Internet of Things) and miniaturized electronics. Thus, wearable power sources with high reliability and long duty cycles are required to power wearable electronic devices to meet people's needs and smart miniaturized electronics requirements. In addition, to make them truly wearable, these must be light, flexible, silent, low power consumption and adaptable to the human body. Textile materials can meet these requirements, and thermoelectric generators assembled from fibers, filaments, yarns, or fabrics (T-TEG) that allow the generation of thermoelectric energy (TE) from body heat represents a research topic of great interest today. Recent studies have demonstrated that T-TEGs have the potential to provide a sustainable and renewable energy source for a wide range of applications through the use of innovative materials and advanced yet simple manufacturing technologies. The choice of material is an important step in the manufacturing process, and it is essential to consider several factors such as thermoelectric efficiency, cost, processability and scalability. Thus, this paper outlines which methods, designs and materials have been chosen in recent years by researchers for the development and optimization of wearable thermoelectric generators (wTEG).
Self‐powered wearable thermoelectric (TE) devices significantly reduce the inconvenience caused to users, especially in daily use of portable devices and monitoring personal health. The textile‐based TE devices (TETs) exhibit the excellent flexibility, deformability, and light weight, which fulfill demands of long‐term wearing for the human body. In comparison to traditional TE devices with their longstanding research history, TETs are still in an initial stage of growth. In recent years, TETs to provide electricity for low‐power wearable electronics have attracted increasing attention. This review summarizes the recent progress of TETs from the points of selecting TE materials, scalable fabrication methods of TE fibers/yarns and TETs, structure design of TETs and reported high‐performance TETs. The key points to develop TETs with outstanding TE properties and mechanical performance and better than available optimization strategies are discussed. Furthermore, remaining challenges and perspectives of TETs are also proposed to suggest practical applications for heat harvesting from human body.
With the development and prosperity of Internet of Things (IoT) technology, wearable electronics have brought fresh changes to our lives. The demands for low power consumption and mini-type wearable power systems for wearable electronics are more urgent than ever. Thermoelectric materials can efficiently convert the temperature difference between body and environment into electrical energy without the need for mechanical components, making them one of the ideal candidates for wearable power systems. In recent years, a variety of high-performance thermoelectric materials and processes for the preparation of large-scale single-fiber devices have emerged, driving the application of flexible fiber-based thermoelectric generators. By weaving thermoelectric fibers into a textile that conforms to human skin, it can achieve stable operation for long periods even when the human body is in motion. In this review, the complete process from thermoelectric materials to single-fiber/yarn devices to thermoelectric textiles is introduced comprehensively. Strategies for enhancing thermoelectric performance, processing techniques for fiber devices, and the wide applications of thermoelectric textiles are summarized. In addition, the challenges of ductile thermoelectric materials, system integration, and specifications are discussed, and the relevant developments in this field are prospected.
Thermoelectric materials capable of converting heat into electrical energy are used in sustainable electric generators, whose efficiency has been normally increased with incorporation of new materials with high figure of merit (ZT) values. Because the performance of these thermoelectric generators (TEGs) also depends on device geometry, in this study we employ the finite element method to determine optimized geometries for highly efficient miniaturized TEGs. We investigated devices with similar fill factors but with different thermoelectric leg geometries (filled and hollow). Our results show that devices with legs of hollow geometry are more efficient than those with filled geometry for the same length and cross-sectional area of thermoelectric legs. This behavior was observed for thermoelectric leg lengths smaller than 0.1 mm, where the leg shape causes a significant difference in temperature distribution along the device. It was found that for reaching highly efficient miniaturized TEGs, one has to consider the leg geometry in addition to the thermal conductivity.
Fiber- and yarn-based thermoelectric materials play an essential role in the design of fabric-based flexible thermoelectric generators which may overcome the wearable difficulties of existing film-based flexible thermoelectric generators. In this study, we used a robust coating method to produce high-performance thermoelectric yarns for wearable applications. An organic/inorganic hybrid coating agent composed of PEDOT:PSS, MWCNT, and Bi 2 Te 3 was used to coat an alkali modified porous polyester yarn. The organic/inorganic hybrid material contributes to the improved thermoelectric properties. The porous modification of polyester yarns improves the wicking property of the fibers and enhances the adhesion stability between yarn substrate and the coating layer. A compromised optimal power factor of 12.3 μWm ⁻¹ K ⁻² could be achieved by 20 wt% Bi2Te3 loading. The corresponding electrical conductivity and Seebeck coefficient were 5526.8 S/m and 47.1 μV/K at room temperature respectively. A fabric thermoelectric generator with five yarn legs could generate an open circuit voltage of 2.95 mV at a temperature difference of 30 ℃, demonstrating its potential application in wearable applications.
Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.
Thermoelectric devices, which are usually composed of electrodes, thermoelectric materials and substrates, can directly convert electricity and heat. With the intrinsic advantages of organic materials, organic thermoelectric (OTE) devices have been widely explored for smart applications. With the rapid development of OTE materials in the past decade, construction of OTE devices received increasing attention. In this chapter, we summarize the geometries and construction methods of OTE devices, and introduce their applications in flexible generators, Peltier cooling elements, multi‐functional sensors. It will provide the readers with the basic knowledge of OTE devices and the key development trend toward their promising applications in wearable electronics and Internet of Things.
Thermal excitation causes a surge in carrier concentration in narrow bandgap semiconductors that seriously limit its application in the high-temperature zone. Therefore ，suppressing bipolar thermal conductivity and broadening the application temperature zone is vitally important for commercial Bi2Te3-based thermoelectric materials. Here, Cu0.6Ni0.4 (CN) nanoparticles synthesized via hydrothermal method are introduced into Bi0.4Sb1.6Te3 (BST) commercial materials. Then, the electrical and thermal properties of BST-CN (with x wt%, x=0, 0.1, 0.2, 0.4, BST-x-CN) materials are systematically investigated. The results exhibited that the weighted mobility could be improved and the bipolar thermal conductivity could be suppressed for all dealt samples. The maximum and average ZT (figure of merit) values were 1.3 at 393 K and 1.17 in the temperature range of 303-483 K for BST-0.1-CN sample, which exhibited an enhancement by 28.7 % and 28.6 % than that of the pure sample, respectively. And the optimal ZT values are attained at higher temperatures with the Cu0.6Ni0.4 contents increasing. Meanwhile, the sintered technique was optimized to enhance electron transport properties, the highest room-temperature power factor of 5.08 mW/m/K² was attained for the BST-0.1-CN cycle-2 sintered sample. And the optimal ZT value is 1.35 at 393 K for the BST-0.1-CN cycle-1 sintered sample. Finally, the results indicated that the thermoelectric performance could be improved and the application temperature zone could be broadened by suppressing bipolar thermal conductivity owing to the existence of CN nanoparticles.
High performance, high stretchability and high strength are the urgent demands for the wearable thermoelectric generators. This paper proposes a novel idea of the stretchable thermoelectric generator with the negative Poisson’s ratio architecture (NPR-TEG). Based on the thermoelastic fracture mechanics and the heat conduction law, the fatigue life and electric power output of the NPR-TEG under the thermo-electro-mechanical coupling loads are systematically analyzed. The theoretical analyses demonstrate that the negative Poisson’s ratio architecture can greatly improve the flexibility and strength of the thermoelectric devices. An analytical model to evaluate effect of cracking at the interface between the thermoelectric leg and the electrode on the power output is proposed. It is found that the existence of crack slightly degenerates the power output unless the entire interface is delaminated. The crack location has little effect on the power output. The critical crack length for the electrode delaminating from the thermoelectric leg increases to a peak value and then decreases with the angle between the electrode and the thermoelectric leg. Under the cyclical tensile strain of 20%, fatigue life of the NPR-TEG with an angle of 60° is around 1000 times longer than that of the traditional bulk thermoelectric devices. The angle is optimized to enhance the fatigue life of the NPR-TEG. Results show that the optimal angle is mainly determined by the length of the thermoelectric leg and the thickness of the electrode. The relevant research results can provide a guideline for designing, manufacturing and assessing performance of the NPR-TEG.
The rhombohedral α‐GeTe can be approximated as a slightly distorted rock‐salt structure along its [1 1 1] direction and possesses superb thermoelectric performance. However, the role of such a ferroelectric‐like structural distortion on its transport properties remains unclear. Herein we performed a systematic study on the crystal structure and electronic band structure evolutions of Ge1‐xSnxTe alloys where the degree of ferroelectric distortion is continuously tuned. It is revealed that the band gap is maximized while multiple valence bands are converged at x = 0.6 where the ferroelectric distortion is least but still works. Once undistorted, the band gap is considerably reduced, and the valence bands are largely separated again. Moreover, near the ferro‐to‐paraelectric phase transition Curie temperature, the lattice thermal conductivity reaches its minima because of significant lattice softening enabled by ferroelectric instability. We predict a peak ZT value of 2.6 at 673 K in α‐GeTe by use of proper dopants which are powerful in suppressing the excess hole concentrations but meanwhile exert little influence on the ferroelectric distortion.
Textiles offer the ideal platform to develop thermoelectric (TE) clothing for body heat harvesting and personal thermoregulation. Herein, textiles used in everyday clothing are adapted to fabricate a flexible and vertical TE device architecture. Selective laser patterning is used to create cavities for embedding bulk inorganic Bi2Te3 legs into a knitted polyester fabric used in next‐to‐skin sportswear. The device thermal design is optimized using fabric layering to accommodate longer legs up to 0.8 mm, and a flexible 3D‐printed heat sink is integrated to maximize heat dissipation to the ambient. Using flexible copper foil to connect the legs with a low‐temperature soldering paste, a stable and ultralow device electrical resistance (<1 Ω) is achieved, which is unprecedented for wearable textile‐based TE devices. The developed prototype demonstrates power generation of up to 3.8 μW using body heat, and it provides a cooling effect of 1 °C for personal thermoregulation. Furthermore, the prototype withstands a tensile strain up to 20%, over 1000 bend cycles (at a 23 mm radius comparable with the curvature of the human wrist), and ten wash cycles, thereby demonstrating viability for TE clothing. Strategies for optimization are also presented to enable further performance enhancements using all textile‐compatible processes.
Textile is one of the ideal substrates for function integration to develop wearable electronics. The practical application of soft electronics and smart clothes relies on soft energy harvesters as power sources. With the pursuit of practicality and aesthetics, comfortable and washable power sources are desired to replace rigid and bulky batteries with a limited lifetime and potential contamination for the environment. Tremendous research efforts have been devoted to developing selfpowered textiles for converting ambient thermal/mechanical energy into electricity, or capable of storing the energy for sustainable and friendly use. Nanotextiles, consisting of nanofibers, or daily fabrics/textiles decorated by nanostructures, showing excellent flexibility and breathability because of their intrinsic softness and high porosity, serve well as carriers or components of nanogenerators for smart wearable electronics. This chapter focuses on the progress of nanotextile‐based thermoelectric, piezoelectric, and triboelectric nanogenerators for energy harvesting from human body and environment. Their applications in power sources, self‐powered sensors, and hybrid platforms for energy harvesting and storage have been summarized, providing a perspective on performance enhancement and multiscenario application of nanotextiles for the self‐powered wearable technology.
The work presented in this paper demonstrates an experimental path to improve the performance of a screen-printed flexible thermoelectric generator through optimization of leg materials, geometrical and structural parameters of the leg, and the viscosity of screen-printed ink. A thin and porous screen-printed leg structure improves the Seebeck coefficient and power output by 11.53 and 8.52 times, respectively than a thick and denser leg structure. A trapezoidal design increases the Seebeck coefficient, and power output by 2.72 and 3.82 times, respectively, compared with a rectangular leg structure. The observed increment in the power output using silver as contact material is about 2.17 times higher than graphene. Screen ink with higher ink viscosity results in a 47% reduction of transient thermal conductivity and an increased power factor by 20.33 times. The rectangular leg produces the maximum power factor of 1.30 × 10⁻¹² µWmm⁻²K⁻². The improvement possible in the power output by controlling the leg structure's porosity is around 752.71%. The result indicates that optimization of ink viscosity and porosity of ink film has significant influence in enhancing the performance of FTEG than its leg shapes and material properties.
Researches on flexible thermoelectric materials usually focus on conducting polymers and conducting polymer-based composites; however, it is a great challenge to obtain high thermoelectric properties comparable to inorganic counterparts. Here, we report an n-type Ag2Se film on flexible nylon membrane with an ultrahigh power factor ~987.4 ± 104.1 μWm⁻¹K⁻² at 300 K and an excellent flexibility (93% of the original electrical conductivity retention after 1000 bending cycles around a 8-mm diameter rod). The flexibility is attributed to a synergetic effect of the nylon membrane and the Ag2Se film intertwined with numerous high-aspect-ratio Ag2Se grains. A thermoelectric prototype composed of 4-leg of the Ag2Se film generates a voltage and a maximum power of 18 mV and 460 nW, respectively, at a temperature difference of 30 K. This work opens opportunities of searching for high performance thermoelectric film for flexible thermoelectric devices.
Wearable thermoelectric generators are a promising energy source for powering activity trackers and portable health monitors. However, known iterations of wearable generators have large form factors, contain expensive or toxic materials with low elemental abundance, and quickly reach thermal equilibrium with a human body, meaning that thermoelectric power can only be generated over a short period of wear. Here, an all‐fabric thermopile is created by vapor printing persistently p‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐Cl) onto commercial cotton and this thermopile is integrated into a specially designed, wearable band that generates thermovoltages >20 mV when worn on the hand. It is shown that the reactive vapor coating process creates mechanically rugged fabric thermopiles that yield notably high thermoelectric power factors at low temperature differentials, as compared to solution‐processed counterparts. Further, best practices for naturally integrating thermopiles into garments are described, which allow for significant temperature gradients to be maintained across the thermopile despite continuous wear.
Flexible, large-area, and low-cost thermal sensing network with high spatial and temporal resolution are of profound importance in addressing the increasing needs for industrial processing, medical diagnosis, and military defense. Here, a thermoelectric fiber is fabricated by thermally co-drawing of a macroscopic preform containing semiconducting glass core and polymer cladding to deliver thermal sensor functionalities at fiber-optic length scales, flexibility, and uniformity. The resulting thermoelectric fiber sensor operates in a wide temperature range with high thermal detection sensitivity and accuracy, while offering ultra-flexibility with the bending curvature radius below 2.5 mm. Additionally, a single thermoelectric fiber can either sense the spot temperature variation or locate the heat/cold spot on the fiber. As a proof-of-concept, a two-dimensional 3×3 fiber array is woven into a textile to simultaneously detect the temperature distribution and the position of heat/cold source with the spatial resolution of millimeter. Achieving this may lead to the realization of large-area, flexible and wearable temperature sensing fabrics for wearable electronics and advanced artificial intelligence applications.
Flexible thermoelectric materials that enable harvesting electricity from human body heat or an ambient temperature gradient have potential applications in self‐powered flexible wearable electronics. The development of more efficient and flexible n‐type thermoelectric materials, however, is highly desired but challenging. Herein, reported is a nylon substrate supported fabric silver telluride (Ag2Te) nanowire network used as flexible n‐type thermoelectric materials, by the combination of vacuum filtrated assembly and mechanical pressing method. The prepared silver telluride nanowire films show optimal thermoelectric properties with the Seebeck coefficient of −129.5 µV K−1 and electrical conductivity of 187.78 S cm−1, leading to the highest power factor of 315.1 µW m−1 K2. Owing to the elimination of Peierls stress in the fabrics interlocking structure, the silver telluride nanowire films exhibit good flexibility, as the thermoelectric properties only have a change below 10% after 500 bending cycles. Based on the silver telluride nanowire film, a flexible self‐powered temperature sensor is fabricated for detecting the temperature from a human finger. The sensor shows high sensitivity that its response time and reset time are about 1.05 and 2.1 s, respectively. The results imply that silver telluride nanowire films have great potential applications in flexible thermoelectric energy conversion and self‐powered temperature sensing. Flexible and high‐performance n‐type thermoelectric films consisting of unique interlocking silver telluride nanowires are presented through vacuum filtrated assembly and mechanical pressing methods. The films possess a power factor as high as 315.1 µW m−1 K2 at 410 K. A self‐powered temperature sensor with high sensitivity is fabricated for detecting the temperature from a human finger.
Wearable sensor systems with ultra-thinness, light weight, high flexibility, and stretchability that are conformally in contact with the skin have advanced tremendously in many respects, but they still face challenges in terms of scalability, processibility, and manufacturability. Here, we report a highly stretchable and wearable textile-based self-powered temperature sensor fabricated using commercial thermoelectric inks. Through various combinations of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), silver nanoparticles (AgNPs), and graphene inks, we obtained linear temperature-sensing capability. The optimized sensor generates a thermoelectric voltage output of 1.1 mV for a temperature difference of 100 K through a combination of PEDOT:PSS and AgNPs inks and it shows high durability up to 800 cycles of 20% strain. In addition, the knitted textile substrate exhibits temperature-sensing properties that are dependent upon the stretching directions. We believe that stretchable thermoelectric fabric has broader potential for application in human-machine interfaces, health-monitoring technologies, and humanoid robotics.
Large amounts of waste heat generated in our fossil-fuel based economy can be converted into useful electric power by using thermoelectric generators. However, the low-efficiency, scarcity, high-cost and poor production scalability of conventional thermoelectric materials are hindering their mass deployment. Nanoengineering has proven to be an excellent approach for enhancing thermoelectric properties of abundant and cheap materials such as silicon. Nevertheless, the implementation of these nanostructures is still a major challenge especially for covering the large areas required for massive waste heat recovery. Here we present a family of nano-enabled materials in the form of large-area paper-like fabrics made of nanotubes as a cost-effective and scalable solution for thermoelectric generation. A case study of a fabric of p-type silicon nanotubes was developed showing a five-fold improvement of the thermoelectric figure of merit. Outstanding power densities above 100 W/m2 at 700 °C are therefore demonstrated opening a market for waste heat recovery.
Flexible organic−inorganic hybrids are promising thermoelectric materials to recycle waste heat in versatile formats. However, current organic/inorganic hybrids suffer from inferior thermoelectric properties due to aggregate nanostructures. Here we demonstrate flexible organic−inorganic hybrids where size-tunable Bi2Te3 nanoparticles are discontinuously monodispersed in the continuous conductive polymer phase, completely distinct from traditional bi-continuous hybrids. Periodic nanofillers significantly scatter phonons while continuous conducting polymer phase provides favored electronic transport, resulting in ultrahigh power factor of ~1350 μW m−1 K−2 and ultralow in-plane thermal conductivity of ~0.7 W m−1 K−1. Consequently, figure-of-merit (ZT) of 0.58 is obtained at room temperature, outperforming all reported organic materials and organic−inorganic hybrids. Thermoelectric properties of as-fabricated hybrids show negligible change for bending 100 cycles, indicating superior mechanical flexibility. These findings provide significant scientific foundation for shaping flexible thermoelectric functionality via synergistic integration of organic and inorganic components.
Organic materials are emerging thermoelectric candidates for flexible power generation and solid-cooling applications. Although the Peltier effect is a fundamental thermoelectric effect that enables site-specific and on-demand cooling applications, the Peltier effect in organic thermoelectric films have not been investigated. Here we experimentally observed and quasi-quantitatively evaluated the Peltier effect in a poly(Ni-ett) film through the fabrication of thermally suspended devices combined with an infrared imaging technique. The experimental and simulation results confirm effective extraction of the Peltier effect and verify the Thomson relations in organic materials. More importantly, the working device based on poly(Ni-ett) film yields maximum temperature differences as large as 41 K at the two contacts and a cooling of 0.2 K even under heat-insulated condition. This exploration of the Peltier effect in organic thermoelectric films predicts that organic materials hold the ultimate potential to enable flexible solid-cooling applications.
You can download the full article via this link: https://authors.elsevier.com/c/1X02W,L67mCF3F. Conducting fibres and yarns promise to become an essential part of the next generation of wearable electronics that seamlessly integrate electronic function into one of the most versatile and most widely used form of materials: textiles. This review explores the many types of conducting fibres and yarns that can be realised with conjugated polymers and carbon materials, including carbon black, carbon nanotubes and graphene. We discuss how the interplay of materials properties and the chosen processing technique lead to fibres with a wide range of electrical and mechanical properties. Depending on the choice of conjugated polymer, carbon nanotube, graphene, polymer blend, or nanocomposite the electrical conductivity can vary from less than 10−3 to more than 103 S cm−1, accompanied by an increase in Young’s modulus from 10 s of MPa to 100 s of GPa. Further, we discuss how conducting fibres can be integrated into electronic textiles (e-textiles) through e.g. weaving and knitting. Then, we provide an overview of some of the envisaged functionalities, such as sensing, data processing and storage, as well as energy harvesting e.g. by using the piezoelectric, thermoelectric, triboelectric or photovoltaic
effect. Finally, we critically discuss sustainability aspects such as the supply of materials, their toxicity, the embodied energy of fibre and textile production and recyclability, which currently are not adequately
considered but must be taken into account to ready carbon based conducting fibres for truly practical e-textile applications.
Bi2Te3-based materials have been reported to be one of the best room-temperature thermoelectric materials, and it is a challenge to substantially improve their thermoelectric properties. Here novel Bi2Te3 core fibers with borosilicate glass cladding were fabricated utilizing a modified molten core drawing method. The Bi2Te3 core of the fiber was found to consist of hexagonal polycrystalline nanosheets, and polycrystalline nanosheets had a preferential orientation; in other words, the hexagonal Bi2Te3 lamellar cleavage more tended to be parallel to the symmetry axis of the fibers. Compared with a homemade 3-mm-diameter Bi2Te3 rod, the polycrystalline nanosheets’ preferential orientation in the 89-μm-diameter Bi2Te3 core increased its electrical conductivity, but deduced its Seebeck coefficient. The Bi2Te3 core exhibits an ultrahigh ZT of 0.73 at 300 K, which is 232% higher than that of the Bi2Te3 rod. The demonstration of fibers with oriented nano-polycrystalline core and the integration with an efficient fabrication technique will pave the way for the fabrication of high-performance thermoelectric fibers.
The development of new flexible and stretchable sensors addresses the demands of upcoming application fields like internet-of-things, soft robotics, and health/structure monitoring. However, finding a reliable and robust power source to operate these devices, particularly in off-the-grid, maintenance-free applications, still poses a great challenge. The exploitation of ubiquitous temperature gradients, as the source of energy, can become a practical solution, since the recent discovery of the outstanding thermoelectric properties of a conductive polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). Unfortunately the use of PEDOT:PSS is currently constrained by its brittleness and limited processability. Herein, PEDOT:PSS is blended with a commercial elastomeric polyurethane (Lycra), to obtain tough and processable self-standing films. A remarkable strain-at-break of ≈700% is achieved for blends with 90 wt% Lycra, after ethylene glycol treatment, without affecting the Seebeck voltage. For the first time the viability of these novel blends as stretchable self-powered sensors is demonstrated.
The evolution of the society is characterized by an increasing flow of information from things to the internet. Sensors have become the cornerstone of the internet-of-everything as they track various parameters in the society and send them to the cloud for analysis, forecast, or learning. With the many parameters to sense, sensors are becoming complex and difficult to manufacture. To reduce the complexity of manufacturing, one can instead create advanced functional materials that react to multiple stimuli. To this end, conducting polymer aerogels are promising materials as they combine elasticity and sensitivity to pressure and temperature. However, the challenge is to read independently pressure and temperature output signals without cross-talk. Here, a strategy to fully decouple temperature and pressure reading in a dual-parameter sensor based on thermoelectric polymer aerogels is demonstrated. It is found that aerogels made of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) can display properties of semiconductors lying at the transition between insulator and semimetal upon exposure to high boiling point polar solvents, such as dimethylsulfoxide (DMSO). Importantly, because of the temperature-independent charge transport observed for DMSO-treated PEDOT-based aerogel, a decoupled pressure and temperature sensing can be achieved without cross-talk in the dual-parameter sensor devices.
Fiber-based flexible thermoelectric energy generators are 3D deformable, lightweight, and desirable for applications in large-area waste heat recovery, and as energy suppliers for wearable or mobile electronic systems in which large mechanical deformations, high energy conversion efficiency, and electrical stability are greatly demanded. These devices can be manufactured at low or room temperature under ambient conditions by established industrial processes, offering cost-effective and reliable products in mass quantity. This article presents a critical overview and review of state-of-the-art fiber-based thermoelectric generators, covering their operational principle, materials, device structures, fabrication methods, characterization, and potential applications. Scientific and practical challenges along with critical issues and opportunities are also discussed.
Thermoelectric (TE) conversion of human body heat is highly desirable for powering microelectronic devices. However, most of the existing TE generators are not practical because they contain toxic substances, are difficult to process, are rigid and impermeable, or are unable to be produced on a large scale. Previously, we have demonstrated a flexible, air-permeable TE power generator fabricated from polyester fabric coated with a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate), and fine silver wires [Y. Du, et al., Sci. Rep., 2015, 5, 06411]. Here, we show a multifold enhancement of the output power of this type of flexible thermoelectric generator using poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) coated cotton fabric, and fine Constantan wires. A fabric device consisting of 5 TE units was found to generate a voltage output (V) of 18.7 mV and maximum output electrical power of 212.6 nW at a temperature difference (ΔT) of 74.3 K. The fabric generators can be rolled up and remain operational after being bent at different bending radii and in different directions. Furthermore, a TE generator has been shown to be stable even after 10 days of continuous operation at a ΔT up to ∼78 K. This fabric-based TE generator is seen to be useful for the development of self-powered, wearable electronic devices.
Printing techniques could offer a scalable approach to fabricate thermoelectric (TE) devices on flexible substrates for power generation used in wearable devices and personalized thermo-regulation. However, typical printing processes need a large concentration of binder additives, which often render a detrimental effect on electrical transport of the printed TE layers. Here, we report scalable screen-printing of TE layers on flexible fiber glass fabrics, by rationally optimizing the printing inks consisting of TE particles (p-type Bi0.5Sb1.5Te3 or n-type Bi2Te2.7Se0.3), binders, and organic solvents. We identified a suitable binder additive, methyl cellulose, which offers suitable viscosity for printability at a very small concentration (0.45–0.60 wt.%), thus minimizing its negative impact on electrical transport. Following printing, the binders were subsequently burnt off via sintering and hot pressing. We found that the nanoscale defects left behind after the binder burnt off became effective phonon scattering centers, leading to low lattice thermal conductivity in the printed n-type material. With the high electrical conductivity and low thermal conductivity, the screen-printed TE layers showed high room-temperature ZT values of 0.65 and 0.81 for p-type and n-type, respectively.
We propose a design and fabrication process for fabrics containing thermoelectric generators (TEGs) in the form of carbon nanotube composite threads intended for energy harvesting of low-temperature waste heat. Our prototype thermoelectric fabric with an integrated p/n-stripe-patterned CNT thread shows potential as an easy-to-use power source for wearable electronics.
Durable, electrically conducting yarns are a critical component of electronic textiles (e-textiles). Here, such yarns with exceptional wear and wash resistance are realized through dyeing silk from the silkworm Bombyx mori with the conjugated polymer:polyelectrolyte complex PEDOT:PSS. A high Young’s modulus of approximately 2 GPa combined with a robust and scalable dyeing process results in up to 40 m long yarns that maintain their bulk electrical conductivity of approximately 14 S cm–1 when experiencing repeated bending stress as well as mechanical wear during sewing. Moreover, a high degree of ambient stability is paired with the ability to withstand both machine washing and dry cleaning. For the potential use for e-textile applications to be illustrated, an in-plane thermoelectric module that comprises 26 p-type legs is demonstrated by embroidery of dyed silk yarns onto a piece of felted wool fabric.
Temperature is one of the most important environmental stimuli to record and amplify. While traditional thermoelectric materials are attractive for temperature/heat flow sensing applications, their sensitivity is limited by their low Seebeck coefficient (∼100 μV K−1). Here we take advantage of the large ionic thermoelectric Seebeck coefficient found in polymer electrolytes (∼10,000 μV K−1) to introduce the concept of ionic thermoelectric gating a low-voltage organic transistor. The temperature sensing amplification of such ionic thermoelectric-gated devices is thousands of times superior to that of a single thermoelectric leg in traditional thermopiles. This suggests that ionic thermoelectric sensors offer a way to go beyond the limitations of traditional thermopiles and pyroelectric detectors. These findings pave the way for new infrared-gated electronic circuits with potential applications in photonics, thermography and electronic-skins.
Flexible thermoelectric (TE) fabrics were prepared by dip coating of a mixture solution of water base colloidal graphite and dimethyl sulfoxide doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) on polyester fabric. The phase composition and morphology of the TE fabrics were investigated by X-ray diffraction and field emission scanning electron microscopy. The TE properties of the graphite-PEDOT:PSS coated fabrics with different graphite loadings were measured in the temperature range from 298 to 398 K. As the content of graphite increased from 5 to 20 wt%, the electrical conductivity of the graphite-PEDOT:PSS coated polyester fabrics decreased, while the Seebeck coefficient increased in the measured temperature range from 298 to 398 K. A maximum power factor of ~0.025 μWm⁻¹K⁻² at 398 K was obtained for the graphite-PEDOT:PSS coated fabric with 15 wt% graphite loading.
Advanced wearable organic electronics have been widely studied for flexible textile-based strain sensors. However, two main issues to be addressed in wearable electronic sensors are the poor electron transfer under tensile conditions and water durability. In this work, we proposed an efficient strategy for the fabrication of a highly conductive commercial textiles coated with poly (3, 4-ethylenedioxythiophene) (PEDOT) via vapor phase polymerization (VPP) as a wearable thermoelectric (TE) strain sensor. The PEDOT-coated textile exhibited excellent mechanical elasticity and electrical properties in response to external strain. More importantly, the strain sensor showed a good strain after cyclic loading of an external stress. Moreover, the as-fabricated PEDOT-coated textiles show superior water durabilities due to the robust PEDOT coatings on the textiles by the in situ polymerization process. A large output voltage of 5.0 mV was achieved at a temperature gradient (ΔT) of 25 K, which is promising for textile generator applications. An optimized gauge factor (GF) of the strain sensor reached 54 at a strain of 1.5%, which has the capability to fully satisfy the demands of wearable electronic sensor devices.
Recently, organic thermoelectric (TE) materials especially conducting polymers have attracted increasing attention. In this work, we successfully synthesized ultrafine poly (3,4-ethylenedioxythiophene) (PEDOT) nanowires (NWs) (∼10 nm) by a simple self-assembled micellar soft-template method and then obtain highly flexible free-standing PEDOT NW films by vacuum-assisted filtration. The films are with very high electrical conductivity (∼1340 S cm⁻¹). After being treated with 6 M H2SO4 and then with 1 M NaOH at room temperature, the film shows an enhanced power factor of 46.51 μW m⁻¹K⁻² (Seebeck coefficient of 25.5 μV K⁻¹, electrical conductivity of 715.3 S cm⁻¹), which increases by 54% compared with that of the pristine film. To the best of our knowledge, it outperforms the TE performance of all reported one dimensional conducting polymer-based films. In addition, the TE performance of the film almost remains unchanged even after being bent for 200 times, indicating excellent flexibility. A flexible TE prototype composed of six strips (7 mm × 30 mm) of the as-prepared PEDOT NW films connected in series shows an output power of 157.2 nW at a temperature difference of 51.6 K. The free-standing PEDOT NW films show promise to a new generation of wearable TE devices.
The requirement of a portable electron is functioning as a driving force for a wearable energy instrument. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), as one of the most promising organic electron materials, has been widely studied in energy conversion devices. However, the efforts for PEDOT:PSS fibers are insufficient to boost the development of wearable thermoelectric energy harvesting. Here, a highly conductive p-type PEDOT:PSS fiber was produced by gelation process, which was 3 orders of magnitude higher than that of previous hydrogel fibers. Surprisingly, a post-treatment with organic solvents such as ethylene glycol and dimethyl sulfoxide tripled their electrical conductivity with an only 5% decreased Seebeck coefficient, consequently leading to an optimized thermoelectric power factor. Furthermore, we assembled a p-n-type thermoelectric device connecting five pairs of p-type PEDOT:PSS fibers and n-type carbon nanotube fibers. This fiber-based device displayed an acceptable output voltage of 20.7 mV and a power density of 481.2 μW·cm⁻² with a temperature difference of ∼60 K, which might pave the way for the development of organic thermoelectric fibers for wearable energy harvesting.
Triboelectric nanogenerators (TENG) are one of the most promising candidates for powering wearable and portable devices. Example TENGs have demonstrated flexibility, light weight, biocompatibility, versatility and good performance. Textiles are a potential substrate onto, or into, which wearable technology is increasingly being incorporated but supplying power remains an enduring challenge. TENGs are a potential textile based mechanical energy harvesting power supply and there has been an increasing effort to combine TENGs with fabrics. A significant challenge exists in the integration without losing the performance of the TENG or the original properties (appearance, breathability, washability, and durability) and feel of the textile. Various approaches towards the realisation of textile-based TENGs (T-TENGs) have been demonstrated. Depending on its structure, T-TENGs can be divided into two main types, fabric-based TENG and fibre-based TENG. The fabric-based TENG is composed of conventional and/or modified fabrics, which serve as a substrate and/or a triboelectric material. The fibre-based TENG is fabricated as a single fibre or a collection of interlaced fibres. This paper provides an up to date review of the progress in the research of T-TENGs. The paper covers the basic operating principles, possible operation modes, textile manufacturing methods, material selections, T-TENG fabrication process, surface modification and structural designs. Issues, such as standardised measurement parameters, the challenges and limitations of T-TENG are discussed.
High-performance thermoelectric composite fibers were prepared via simple wet-spinning of single-walled carbon nanotubes (SWCNTs)/poly(vinylidene fluoride) (PVDF) pastes using a common solvent/coagulation system. By improving the content and dispersion state of SWCNTs in the composite fibers, the thermoelectric performance could be effectively enhanced. With n-type doping of SWCNTs using polyethylenimine, high-performance n-type SWCNT/PVDF composite fibers could be prepared. The power factors of the p- and n-type SWCNT/PVDF composite fibers with the SWCNT content of 50 wt% were 378 ± 56 and 289 ± 98 μW m-1K-2, respectively. The electric power generation capability of an organic thermoelectric generator with the p- and n-type composite fibers was confirmed.
Herein, we demonstrate a concept of making flexible thermoelectric (TE) generators by applying cotton thread as the platforms for poly(3-hexylthiophene) (P3HT) and Argentum (Ag) paste through selectable coating method. The coated thermoelectric cotton thread can be sewed on the flexible fabrics with different knitting pictures and form thermoelectric devices. The most important is that the temperature gradient of the device was in the direction of cross-plane of the flexible fabrics, that is, between the inner and outer surfaces of clothing, therefore the flexible device can be easily wore on the body since the temperature gradient between the human body and surrounding environment is in the cross-plane direction. The maximum output power of the device with thirteen P–N type legs reached 1.15 μW at a temperature gradient of 50 K when the load resistance matched the resistance of the module. Cotton-based TE device coated with P3HT may be useful for the development of self-powered wearable electronics.
In this paper, inverted perovskite solar cells (PSCs) employing a novel polymer‐assisted small molecule layer as hole transport layer (HTL) are reported and the effect of mixed HTL on the device performance is investigated. It is the first time that the small molecule HTL is doped with a polymer HTL. The introduction of appropriate content of polymer into the small molecule layer will lead to a much smoother surface for the mixed HTL and largely reduced charge recombination, and most importantly, the energy level alignment is more matched with that of the perovskite via optimization of the doping content. Therefore, the hole transfer property is largely improved for the perovskite/mixed HTL composites. After the optimization of the polymer content in the mixed HTLs, an average power conversion efficiency (PCE) of 19.03 ± 0.53% is achieved, and the champion device exhibits a PCE of >21%. This work provides an effective strategy for the development of highly efficient inverted PSCs based on small molecule HTLs. The hole extraction property of the hole transport layer based on TAPC small molecule via polymer assistance is largely improved. The average power conversion efficiency is enhanced from 17.66 ± 0.52% to 19.03 ± 0.53%, and the champion efficiency reaches 21.01%.
Bismuth selenide exhibits high thermoelectric performance, which is a promising candidate for thermal-electrical energy conversion. Here, Bi2Se3 core thermoelectric fibers with K9 glass cladding were fabricated by a molten core drawing method. The 50-μm-diameter Bi2Se3 core fibers exhibit an ultrahigh Seebeck coefficient of −150.85 μV/K. In addition, it has a high dimensionless figure of merit of 0.18 (at 300 K) and a long-term stability in air. The results indicate that the drawing approach is an effective way to fabricate high-performance and high-stability thermoelectric fibers, which will have potential application in fiber-integrated thermoelectric devices.
Solution-printable and flexible thermoelectric materials have attracted great attention because of their scalable processability and great potential for powering flexible electronics, but it is challenging to integrate mechanical flexibility, solution-printability and outstanding thermoelectric properties together. In particular, such an n-type thermoelectric material is highly sought after. In this paper, 2D TiS2 nanosheets were exfoliated from layered polycrystalline powders, and then assembled with C60 nanoparticles, resulting in a new class of flexible n-type thermoelectric materials via a concurrent enhancement in the power factor and a reduction in thermal conductivity. The resultant C60/TiS2 hybrid films show a ZT ∼ 0.3 at 400 K, far superior to the state-of-the-art solution-printable and flexible n-type thermoelectric materials. In particular, such a thermoelectric property rivals that of single-crystal TiS2-based thermoelectric materials, which are expensive, difficult to synthesize, and unsuitable for solution printing. A solution of the C60/TiS2 hybrid was also used as an ink for printing large-area flexible and spatial thermoelectric devices. An outstanding output power of 1.68 W m⁻² was generated at a temperature gradient of 20 K. This work paves the way for flexible, solution-printable, high-performance thermoelectric materials for flexible electronics.
Carbon nanotube (CNT)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite fibers with the CNT content ranging from 10 to 50 wt% were prepared by a wet-spinning process using a common solvent/coagulation system for application to organic fiber-based thermoelectric generators. After post-treatments, such as immersion in hydrazine solutions and polyethyleneimine-infiltration, the thermoelectric properties of the CNT/PEDOT:PSS composite fibers were optimized, with p- and n-type power factors of 83.2 ± 6.4 and 113 ± 25 μW m⁻¹ K⁻², respectively. The electrical power generation capability of an organic fiber-based thermoelectric generator assembled with the p- and n-type CNT/PEDOT:PSS composite fibers was confirmed.
This article reviews materials developed to enable energy harvesting from textiles. It includes energy harvesting from mechanical, thermal, and light sources, and covers materials employed into yarns that can be woven into the textile and films that are deposited onto the surface of the textile. The textile places challenging constraints on the materials, for example, by limiting processing temperatures to typically less than 150°C and presenting a rough, inconsistent surface profile. Example materials include a screen-printable low-temperature composite lead zirconate titanate polymer film and poly(vinylidene fluoride) polymer fibers, both of which have been shown to harvest mechanical energy from textiles. Thermoelectric solutions demonstrated thus far are limited and challenging to implement within a textile. Photovoltaic solutions include organic and dye-sensitized solar cells fabricated into functionalized yarns and as films spray-coated onto textiles. While numerous suitable example materials and textile devices have been demonstrated, work is still needed to develop these into practical energy-harvesting solutions.
Self-powered electronic sensors and devices are suitable for use in applications such as health monitoring and information collection under battery-free conditions. Thermoelectric (TE) materials can utilize the temperature difference between the body and environment to achieve self-power. In this work, a flexible cellulose-based TE sponge (CP:PP sponge) was prepared via the electrostatic assembly of poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) on cellulose sponges crosslinked with branched polyethylenimine (CP sponge). X-ray photoelectron spectroscopy (XPS) confirmed the adsorption of the PEDOT:PSS onto the CP sponge. The 3D structures, which were composed of thin sheets, typical of cellulose sponges, were maintained within the CP:PP sponges. These CP:PP sponges exhibited reasonable piezoresistive characteristics and excellent flexibility. Upon the application of several press-release cycles, the resistance varied without attenuation. It was demonstrated that the electrical conductivity of the sponge could be enhanced from 2 mS/cm to 6.7 mS/cm via further assembly of the PEDOT:PSS using an immersive layer-by-layer (LbL) strategy, and the thermal conductivity was maintained as 0.0449 W/mK. The maximum figure-of-merit (ZT) value was 1.88 × 10⁻⁶ at 310 K. A TE generator was fabricated by sandwiching the as-prepared CP:PP sponge, with enhanced electric conductivity and inherent low thermal conductivity, between commercial cotton fabrics. At an ambient temperature of 291 K, the device was shown to generate a voltage of 0.3 mV when one side of the device was attached to forearm skin (307 K). Such CP:PP sponges could potentially be used in artificial intelligence products or remote medical monitoring devices as general, flexible thermal energy harvesting materials.
Porous modification is a general approach to endowing the rigid inorganic thermoelectric (TE) materials with considerable flexibility, however, by which the TE performances are severely sacrificed. Thus, there remains ongoing struggle against the trade-off between TE properties and flexibility. Herein, we develop a novel strategy to combine Bi2Te3 thick film with ubiquitous cellulose fibers (CFs) via unbalanced magnetron sputtering technique. Owing to the nano-micro hierarchical porous structures and the excellent resistance to crack propagation of the Bi2Te3/CF architectures, the obtained sample with nominal Bi2Te3 deposition thickness of tens of micrometers exhibit excellent mechanically reliable flexibility, of which the bending deformation radius could be as small as a few millimeters. Furthermore, the Bi2Te3/CF with rational internal resistance, tailorable shapes and dimensions are successfully fabricated for practical use in TE devices. Enhanced Seebeck coefficients are observed in the Bi2Te3/CF as compared to the dense Bi2Te3 films and the lattice thermal conductivity is remarkably reduced due to the strong phonon scattering effect. As a result, the TE figure of merit, ZT, is achieved as high as ~0.38 at 473 K, which competes the best flexible TEs and can be further improved by optimizing the carrier concentrations. We believe this developed technique not only opens up a new window to engineer flexible TE materials for practical applications, but also promotes the robust development of the fields, such as paper-based flexible electronics and thin-film electronics.
A novel method is reported for the stereoselective synthesis of highly functionalized allyl aryl sulfones. This protocol is based on a Pd‐catalyzed three‐component tandem reaction of sulfonyl hydrazides and aryl iodides with allenes and exhibits high ( Z )‐selectivity, good yields, minimal waste, ample product scope, and operational simplicity.
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High-performance flexible thermoelectric devices are increasingly demanded to efficiently convert thermal energy to electricity by covering heat sources with arbitrary and conformal geometries. However, some fundamental limitations still exist, e.g., low output power density, poor mechanical stability, and small cover area, which have largely restricted their studies and applications. Here, we fabricate crystalline thermoelectric micro/nanowires by thermally drawing hermetically sealed high-quality inorganic thermoelectric materials in a flexible fiber-like substrate. The resulting thermoelectric fibers are intrinsically crystalline, highly flexible, ultralong, and mechanically stable, while maintaining high thermoelectric properties as their bulk counterparts. Two types of thermoelectric generators covered on different curved surfaces are constructed to provide mW/cm²-level output power density. Additionally, a wearable two-dimensional cooling textile is assembled to achieve a maximum cooling of 5 °C. This approach works for a broad range of thermoelectric materials, and bridges the gap between high-performance thermoelectric micro/nanowires and their integrated devices for practical applications.
Flexible wearable electronics, when combined with outstanding thermoelectric properties, are promising candidates for future energy harvesting systems. Graphene and its macroscopic assemblies (e.g., graphene-based fibers and films) have thus been the subject of numerous studies because of their extraordinary electrical and mechanical properties. However, these assemblies have not been considered suitable for thermoelectric applications owing to their high intrinsic thermal conductivity. In this study, bromine doping is demonstrated to be an effective method for significantly enhancing the thermoelectric properties of graphene fibers. Doping enhances phonon scattering due to the increased defects and thus decreases the thermal conductivity, while the electrical conductivity and Seebeck coefficient are increased by the Fermi level downshift. As a result, the maximum figure of merit is 2.76 × 10–3, which is approximately four orders of magnitude larger than that of the undoped fibers throughout the temperature range. Moreover, the room temperature power factor is shown to increase up to 624 μW·m–1·K–2, which is higher than that of any other material solely composed of carbon nanotubes and graphene. The enhanced thermoelectric properties indicate the promising potential for graphene fibers in wearable energy harvesting systems.
As practical interest in flexible/or wearable power-conversion devices increases, the demand for high-performance alternatives to thermoelectric (TE) generators based on brittle inorganic materials is growing. Herein, we propose a flexible and ultralight TE generator (TEG) based on carbon nanotube yarn (CNTY) with excellent TE performance. The as-prepared CNTY shows a superior electrical conductivity of 3147 S/cm due to increased longitudinal carrier mobility derived from highly-aligned structure. Our TEG is innovative in that the CNTY acts as multi-functions in the same device. The CNTY is alternatively doped into n- and p-types using polyethyleneimine and FeCl3, respectively. The highly conductive CNTY between the doped regions is used as electrodes to minimize the circuit resistance, thereby forming an all-carbon TEG without additional metal deposition. A flexible TEG based on 60 pairs of n- and p-doped CNTY shows the maximum power density of 10.85 and 697 μW/g at temperature differences of 5 and 40 K, respectively, which are the highest values among reported TEGs based on flexible materials. We believe that the strategy proposed here to improve the power density of flexible TEG by introducing highly aligned CNTY and designing a device without metal electrodes shows great potential for the flexible/or wearable power-conversion devices.
Traditional textile materials can be transformed into functional electronic components upon being dyed or coated with films of intrinsically conducting polymers, such as poly(aniline), poly(pyrrole) and poly(3,4-ethylenedioxythiophene). A variety of textile electronic devices are built from the conductive fibers and fabrics thus obtained, including: physiochemical sensors, thermoelectric fibers/fabrics, heated garments, artificial muscles and textile supercapacitors. In all these cases, electrical performance and device ruggedness is determined by the morphology of the conducting polymer active layer on the fiber or fabric substrate. Tremendous variation in active layer morphology can be observed with different coating or dyeing conditions. Here, we summarize various methods used to create fiber- and fabric-based devices and highlight the influence of the coating method on active layer morphology and device stability.