Cellulose Fiber-Based Hierarchical Porous Bismuth Telluride for High-Performance Flexible and Tailorable Thermoelectrics

High-performance flexible p-type Ce-filled Fe3CoSb12 skutterudite thin film for medium-to-high-temperature applications

P-type Fe3CoSb12-based skutterudite thin films are successfully fabricated, exhibiting high thermoelectric performance, stability, and flexibility at medium-to-high temperatures, based on preparing custom target materials and employing advanced pulsed laser deposition techniques to address the bonding challenge between the thin films and high-temperature flexible polyimide substrates. Through the optimization of fabrication processing and nominal doping concentration of Ce, the thin films show a power factor of >100 μW m-1 K-2 and a ZT close to 0.6 at 653 K. After >2000 bending cycle tests at a radius of 4 mm, only a 6 % change in resistivity can be observed. Additionally, the assembled p-type Fe3CoSb12-based flexible device exhibits a power density of 135.7 µW cm-2 under a temperature difference of 100 K with the hot side at 623 K. This work fills a gap in the realization of flexible thermoelectric devices in the medium-to-high-temperature range and holds significant practical application value.

Flexible temperature-pressure dual sensor based on 3D spiral thermoelectric Bi2Te3 films

Dual-parameter pressure-temperature sensors are widely employed in personal health monitoring and robots to detect external signals. Herein, we develop a flexible composite dual-parameter pressure-temperature sensor based on three-dimensional (3D) spiral thermoelectric Bi2Te3 films. The film has a (000l) texture and good flexibility, exhibiting a maximum Seebeck coefficient of -181 μV K-1 and piezoresistance gauge factor of approximately -9.2. The device demonstrates a record-high temperature-sensing performance with a high sensing sensitivity (-426.4 μV K-1) and rapid response time (~0.95 s), which are better than those observed in most previous studies. In addition, owing to the piezoresistive effect in the Bi2Te3 film, the 3D-spiral deviceexhibits significant pressure-response properties with a pressure-sensing sensitivity of 120 Pa-1. This innovative approach achieves high-performance dual-parameter sensing using one kind of material with high flexibility, providing insight into the design and fabrication of many applications, such as e-skin.

Flexible power generators by Ag2Se thin films with record-high thermoelectric performance

Exploring new near-room-temperature thermoelectric materials is significant for replacing current high-cost Bi2Te3. This study highlights the potential of Ag2Se for wearable thermoelectric electronics, addressing the trade-off between performance and flexibility. A record-high ZT of 1.27 at 363 K is achieved in Ag2Se-based thin films with 3.2 at.% Te doping on Se sites, realized by a new concept of doping-induced orientation engineering. We reveal that Te-doping enhances film uniformity and (00l)-orientation and in turn carrier mobility by reducing the (00l) formation energy, confirmed by solid computational and experimental evidence. The doping simultaneously widens the bandgap, resulting in improved Seebeck coefficients and high power factors, and introduces TeSe point defects to effectively reduce the lattice thermal conductivity. A protective organic-polymer-based composite layer enhances film flexibility, and a rationally designed flexible thermoelectric device achieves an output power density of 1.5 mW cm-2 for wearable power generation under a 20 K temperature difference.

Advances in Cellulose-Based Composites for Energy Applications

The various forms of cellulose-based materials possess high mechanical and thermal stabilities, as well as three-dimensional open network structures with high aspect ratios capable of incorporating other materials to produce composites for a wide range of applications. Being the most prevalent natural biopolymer on the Earth, cellulose has been used as a renewable replacement for many plastic and metal substrates, in order to diminish pollutant residues in the environment. As a result, the design and development of green technological applications of cellulose and its derivatives has become a key principle of ecological sustainability. Recently, cellulose-based mesoporous structures, flexible thin films, fibers, and three-dimensional networks have been developed for use as substrates in which conductive materials can be loaded for a wide range of energy conversion and energy conservation applications. The present article provides an overview of the recent advancements in the preparation of cellulose-based composites synthesized by combining metal/semiconductor nanoparticles, organic polymers, and metal-organic frameworks with cellulose. To begin, a brief review of cellulosic materials is given, with emphasis on their properties and processing methods. Further sections focus on the integration of cellulose-based flexible substrates or three-dimensional structures into energy conversion devices, such as photovoltaic solar cells, triboelectric generators, piezoelectric generators, thermoelectric generators, as well as sensors. The review also highlights the uses of cellulose-based composites in the separators, electrolytes, binders, and electrodes of energy conservation devices such as lithium-ion batteries. Moreover, the use of cellulose-based electrodes in water splitting for hydrogen generation is discussed. In the final section, we propose the underlying challenges and outlook for the field of cellulose-based composite materials.

Intelligent wearable devices based on nanomaterials and nanostructures for healthcare

Emerging classes of flexible electronic sensors as alternatives to conventional rigid sensors offer a powerful set of capabilities for detecting and quantifying physiological and physical signals from human skin in personal healthcare. Unfortunately, the practical applications and commercialization of flexible sensors are generally limited by certain unsatisfactory aspects of their performance, such as biocompatibility, low sensing range, power supply, or single sensory function. This review intends to provide up-to-date literature on wearable devices for smart healthcare. A systematic review is provided, from sensors based on nanomaterials and nanostructures, algorithms, to multifunctional integrated devices with stretchability, self-powered performance, and biocompatibility. Typical electromechanical sensors are investigated with a specific focus on the strategies for constructing high-performance sensors based on nanomaterials and nanostructures. Then, the review emphasizes the importance of tailoring the fabrication techniques in order to improve stretchability, biocompatibility, and self-powered performance. The construction of wearable devices with high integration, high performance, and multi-functionalization for multiparameter healthcare is discussed in depth. Integrating wearable devices with appropriate machine learning algorithms is summarized. After interpretation of the algorithms, intelligent predictions are produced to give instructions or predictions for smart implementations. It is desired that this review will offer guidance for future excellence in flexible wearable sensing technologies and provide insight into commercial wearable sensors.

From Brittle to Ductile: A Scalable and Tailorable All-Inorganic Semiconductor Foil through a Rolling Process toward Flexible Thermoelectric Modules

Inorganic thermoelectric (TE) materials with outstanding capacity for energy conversion are expected to be promising eco-friendly and renewable power sources, but they are always intrinsically brittle, restricting their development in flexible TE electronics. Therefore, we have developed a facile manufacturing method of large-scale all-inorganic silver chalcogenide foils and flexible TE generators in this work. A rolling process, as an effective and facile molding technique, is applied in ductile TE materials. The figure-of-merit for flexibility of this free-standing foil is in the range of 0.02-0.13, suggesting the superior flexibility of the all-inorganic TE foils. A high TE figure-of-merit ZT of 0.47 at room temperature is reached for Ag₂S_0.45Se_0.45Te_0.1, which is one of the most promising room-temperature ZTs among flexible TE materials. A proof-of-concept flexible TE generator based on silver chalcogenide foils achieves an open-circuit voltage of 1.19 mV and an output power density of 1.8 mW/m² with a temperature difference of 2.7 °C across the TE leg, showing great potential in heat-to-electricity conversion.

Carbon Nanotube Ink Dispersed by Chitin Nanocrystals for Thermoelectric Converter for Self-Powering Multifunctional Wearable Electronics

The screen-printing process of conductive ink can realize simple and large-scale manufacture of micro/nano patterns for producing wearable electronic products. Herein, chitin nanocrystals (ChNCs) are used as a dispersant for the preparation of multiwalled carbon nanotube (MWCNT) ink with high viscosity and uniformity by ultrasound treatment. ChNCs can interact with MWCNT in noncovalent ways, including π-π and hydrophobic interactions. ChNCs/MWCNT (CCNT) ink does not aggregate even after standing for 3 months with a maximum MWCNT concentration of 33 mg mL^-1 and dispersion efficiency of 91.1%. Using CCNT ink, a paper-based thermoelectric generator (TEG) is manufactured by screen-printing technology. With good thermoelectric and strain sensing properties, CCNT coated paper can stably collect human energy at room temperature to realize self-powering. The CCNT coated paper-based TEG can convert thermal voltage signals into musical notes, monitor the changes in human behavior and respiratory rate, and monitor joint movements. Moreover, CCNT coated paper has no cytotoxicity by CCK-8 and live/dead staining. This work puts forward a strategy of green preparation of MWCNT-based ink by adding renewable chitin, which opens up a new way to apply MWCNT-based ink in self-powering wearable multifunctional sensors.

A Bi2Te3-Filled Nickel Foam Film with Exceptional Flexibility and Thermoelectric Performance

The past decades have witnessed surging demand for wearable electronics, for which thermoelectrics (TEs) are considered a promising self-charging technology, as they are capable of converting skin heat into electricity directly. Bi₂Te₃ is the most-used TE material at room temperature, due to a high zT of ~1. However, it is different to integrate Bi₂Te₃ for wearable TEs owing to its intrinsic rigidity. Bi₂Te₃ could be flexible when made thin enough, but this implies a small electrical and thermal load, thus severely restricting the power output. Herein, we developed a Bi₂Te₃/nickel foam (NiFoam) composite film through solvothermal deposition of Bi₂Te₃ nanoplates into porous NiFoam. Due to the mesh structure and ductility of Ni Foam, the film, with a thickness of 160 μm, exhibited a high figure of merit for flexibility, 0.016, connoting higher output. Moreover, the film also revealed a high tensile strength of 12.7 ± 0.04 MPa and a maximum elongation rate of 28.8%. In addition, due to the film’s high electrical conductivity and enhanced Seebeck coefficient, an outstanding power factor of 850 μW m⁻¹ K⁻² was achieved, which is among the highest ever reported. A module fabricated with five such n-type legs integrated electrically in series and thermally in parallel showed an output power of 22.8 nW at a temperature gap of 30 K. This work offered a cost-effective avenue for making highly flexible TE films for power supply of wearable electronics by intercalating TE nanoplates into porous and meshed-structure materials.

Sustainable Natural Bio-Origin Materials for Future Flexible Devices

Flexible devices serve as important intelligent interfaces in various applications involving health monitoring, biomedical therapies, and human-machine interfacing. To address the concern of electronic waste caused by the increasing usage of electronic devices based on synthetic polymers, bio-origin materials that possess environmental benignity as well as sustainability offer new opportunities for constructing flexible electronic devices with higher safety and environmental adaptivity. Herein, the bio-source and unique molecular structures of various types of natural bio-origin materials are briefly introduced. Their properties and processing technologies are systematically summarized. Then, the recent progress of these materials for constructing emerging intelligent flexible electronic devices including energy harvesters, energy storage devices, and sensors are introduced. Furthermore, the applications of these flexible electronic devices including biomedical implants, artificial e-skin, and environmental monitoring are summarized. Finally, future challenges and prospects for developing high-performance bio-origin material-based flexible devices are discussed. This review aims to provide a comprehensive and systematic summary of the latest advances in the natural bio-origin material-based flexible devices, which is expected to offer inspirations for exploitation of green flexible electronics, bridging the gap in future human-machine-environment interactions.

A New Class of Electronic Devices Based on Flexible Porous Substrates

With the advent of the Internet of Things era, the connection between electronic devices and humans is getting closer and closer. New-concept electronic devices including e-skins, nanogenerators, brain-machine interfaces, and implantable medical devices, can work on or inside human bodies, calling for wearing comfort, super flexibility, biodegradability, and stability under complex deformations. However, conventional electronics based on metal and plastic substrates cannot effectively meet these new application requirements. Therefore, a series of advanced electronic devices based on flexible porous substrates (e.g., paper, fabric, electrospun nanofibers, wood, and elastic polymer sponge) is being developed to address these challenges by virtue of their superior biocompatibility, breathability, deformability, and robustness. The porous structure of these substrates can not only improve device performance but also enable new functions, but due to their wide variety, choosing the right porous substrate is crucial for preparing high-performance electronics for specific applications. Herein, the properties of different flexible porous substrates are summarized and their basic principles of design, manufacture, and use are highlighted. Subsequently, various functionalization methods of these porous substrates are briefly introduced and compared. Then, the latest advances in flexible porous substrate-based electronics are demonstrated. Finally, the remaining challenges and future directions are discussed.

Advanced Functional Materials for Intelligent Thermoregulation in Personal Protective Equipment

The exposure to extreme temperatures in workplaces involves physical hazards for workers. A poorly acclimated worker may have lower performance and vigilance and therefore may be more exposed to accidents and injuries. Due to the incompatibility of the existing standards implemented in some workplaces and the lack of thermoregulation in many types of protective equipment that are commonly fabricated using various types of polymeric materials, thermal stress remains one of the most frequent physical hazards in many work sectors. However, many of these problems can be overcome with the use of smart textile technologies that enable intelligent thermoregulation in personal protective equipment. Being based on conductive and functional polymeric materials, smart textiles can detect many external stimuli and react to them. Interconnected sensors and actuators that interact and react to existing risks can provide the wearer with increased safety, protection, and comfort. Thus, the skills of smart protective equipment can contribute to the reduction of errors and the number and severity of accidents in the workplace and thus promote improved performance, efficiency, and productivity. This review provides an overview and opinions of authors on the current state of knowledge on these types of technologies by reviewing and discussing the state of the art of commercially available systems and the advances made in previous research works.

Fiber-Based Thermoelectric Materials and Devices for Wearable Electronics

Fiber-based thermoelectric materials and devices have the characteristics of light-weight, stability, and flexibility, which can be used in wearable electronics, attracting the wide attention of researchers. In this work, we present a review of state-of-the-art fiber-based thermoelectric material fabrication, device assembling, and its potential applications in temperature sensing, thermoelectric generation, and temperature management. In this mini review, we also shine some light on the potential application in the next generation of wearable electronics, and discuss the challenges and opportunities.

Inorganic Thermoelectric Fibers: A Review of Materials, Fabrication Methods, and Applications

Thermoelectric technology can directly harvest the waste heat into electricity, which is a promising field of green and sustainable energy. In this aspect, flexible thermoelectrics (FTE) such as wearable fabrics, smart biosensing, and biomedical electronics offer a variety of applications. Since the nanofibers are one of the important constructions of FTE, inorganic thermoelectric fibers are focused on here due to their excellent thermoelectric performance and acceptable flexibility. Additionally, measurement and microstructure characterizations for various thermoelectric fibers (Bi-Sb-Te, Ag₂Te, PbTe, SnSe and NaCo₂O₄) made by different fabrication methods, such as electrospinning, two-step anodization process, solution-phase deposition method, focused ion beam, and self-heated 3ω method, are detailed. This review further illustrates that some techniques, such as thermal drawing method, result in high performance of fiber-based thermoelectric properties, which can emerge in wearable devices and smart electronics in the near future.

Lightweight and Flexible Bi@Bi-La Natural Leather Composites with Superb X-ray Radiation Shielding Performance and Low Secondary Radiation

A high-shielding, low secondary radiation, lightweight, flexible, and wearable X-ray protection material was prepared by coimpregnating La₂O₃ and Bi₂O₃ nanoparticles in natural leather (NL) with an additional Bi₂O₃ coating at the bottom surface of the leather. The prepared Bi_28.2@Bi_3.48La_3.48-NL (28.2 and 3.48 mmol·cm^-3 are the loading contents of elements) showed excellent X-ray shielding ability (65-100%) in a wide energy range of 20-120 keV with reduced scattered secondary radiation (30%). The bottom surface coating played a critical role in enhancing the X-ray attenuation and reducing the scattered secondary radiation by reflecting and deflecting incident X-ray photons. Excellent mechanical property with superb bending resistance of the NL matrix was properly maintained, and its tensile strength and tearing load were 15.39 MPa and 25.81 N·mm^-1, respectively. This lightweight and wearable high-performance protection material can facilitate safety and comfortability during intensive activities of practitioners in the health care industry.

A high-performance and flexible thermoelectric generator based on the solution-processed composites of reduced graphene oxide nanosheets and bismuth telluride nanoplates

The fabrication of a flexible thermoelectric generator (TEG) with both high power output and good flexibility has drawn considerable attention. Solution-processed inorganic nanocrystals have good processibility in interface to retain excellent electrical properties of nanocrystals and can be processed into thin films on a flexible substrate by an easy scale-up printing or coating method. However, a high-performance TEG device based on inorganic solution-processed materials also poses challenges when it comes to flexibility of the whole device. Herein, flexible planar TEG devices are fabricated by printing an ink mixture comprising solution-processed bismuth telluride (Bi₂Te₃) nanoplates with reduced-graphene oxide (rGO) nanosheets onto flexible polyimide substrates. The interface treatment by hot ethylenediamine and the appropriate amount of rGO contribute to the high electrical properties of the material. Also, when rGO nanosheets of 1% mass ratio are added, the optimum power output of the corresponding rGO/Bi₂Te₃ TEG device with six elements reaches ∼1.72 μW at a temperature difference of 20 K. Moreover, owing to the contribution from flexible rGO nanosheets, the suitable thickness of each element, and the artful connection of elements with a soft copper wire in the devices, the 1% rGO/Bi₂Te₃ TEG device was found to be robust, and its electrical resistance merely changes by 2% after bending 1000 cycles on 5 mm in bending. These inorganic-based TEGs with both high performance and good flexibility will promote the development of new generation energy devices in the field of flexible electronics.

Ultrahigh Performance of n-Type Ag2Se Films for Flexible Thermoelectric Power Generators

Due to the limited thermoelectric (TE) performance of conducting polymers and rigidity of inorganic materials, it is still a huge challenge to prepare low-cost, highly flexible, and high-performance TE materials. Herein, we fabricated n-type Ag₂Se films using a porous nylon membrane as a flexible substrate by vacuum-assisted filtration, followed by hot pressing. A very high power factor of ∼1882 μW m^-1 K^-2 at room temperature is obtained. The high power factor is mainly the result of the high density of the Ag₂Se film and the tuned grain orientation, which is realized by the synthesis of multisized Ag₂Se nanostructures. The film also exhibits excellent flexibility with 90.7% retention of the power factor after bending around a rod of 4 mm radius for 1000 times. A four-leg TE generator is assembled with the Ag₂Se film, and its maximum output power is up to 3.2 μW at a temperature difference of 30 K, corresponding to the maximum power density of 22.0 W m^-2 and a normalized maximum power density of 408 μW m^-1 K^-2. This work provides an effective route to achieve high-power-factor, high-flexibility, and low-cost TE films.

High-Performance Ag-Modified Bi0.5Sb1.5Te3 Films for the Flexible Thermoelectric Generator

Bi-Sb-Te-based semiconductors possess the best room-temperature thermoelectric performance, but are restricted for application in the wearable field because of their inherent brittleness, rigidity, and nonscalable manufacturing techniques. Therefore, how to obtain thermoelectric materials with excellent thermoelectric properties and flexibility through the batch production process is a serious challenge. Here, we report the fabrication of flexible p-type thermoelectric Ag-modified Bi_0.5Sb_1.5Te₃ films on flexible substrates using a facile approach. Their optimized power factors are ∼12.4 and ∼14.0 μW cm^-1 K^-2 at 300 and 420 K, respectively. These high-power factors mainly originate from the optimized carrier transport of the composite system, through which a high level of electrical conductivity is achieved, whereas a remarkably improved Seebeck coefficient is simultaneously obtained. Bending tests demonstrate the excellent flexibility and mechanical durability of the composite films, and their power factors decrease by only about 10% after bending for 650 cycles with a bending radius of 5 mm. A flexible thermoelectric module is designed and constructed using the optimized composite films and displays a power density of ∼1.4 mW cm^-2 at a relatively small ΔT of 60 K. This work demonstrates the potential of inorganic thermoelectric materials to be made on flexible/wearable substrates for energy harvesting and management devices.

Tailoring Nanoporous Structures in Bi2Te3 Thin Films for Improved Thermoelectric Performance

Thin-film thermoelectrics (TEs) with unique advantages have triggered great interest in thermal management and energy harvesting technology for ambient temperature microscale systems. Although they have exhibited a good prospect, their unsatisfactory performances still seriously hamper their widespread application. Tailoring the porous structure has been demonstrated to be a facile strategy to significantly reduce thermal conductivity and enhance the figure of merit (ZT) of bulk TE materials; however, it is challenging for thin-film TEs. Here, the nanoporous Bi₂Te₃ thin films with faceted pore shapes and various porosities, pore sizes, and pore intervals are carefully designed and fabricated by evacuating the over-stoichiometry Te atoms. The dependence of the carrier mobility and lattice thermal conductivity on the pore characteristics is investigated. In the case of the pore interval longer than the electron mean free path, the porous structure greatly reduces the lattice thermal conductivity without affecting the electrical conductivity obviously. Phonon specular backscattering that is highly related to the pore characteristics is suggested to be mainly responsible for thermal conductivity reduction, resulting in ∼60% enhancement in ZT at room temperature, that is, from ∼0.42 for the dense film to ∼0.67 for the nanoporous film. The enhanced ZT value is comparable to that of commercial bulk TEs and can be further improved by optimizing the carrier concentrations. This work provides a general approach to fabricate high-performance chalcogenide TE thin-film materials.

A honeycomb-like paper-based thermoelectric generator based on a Bi2Te3/bacterial cellulose nanofiber coating

The intrinsic properties of paper, such as its light weight, flexibility, foldability, portability and degradability, have led to increasing interest in fabricating flexible energy storage devices and power supply devices on paper-based substrates. Hereby, a robust honeycomb-like thermoelectric generator (TEG) inspired by the origami and kirigami techniques was established in the present study. A thermoelectric ink with the properties of high electrical conductivity and low thermal conductivity was formulated by Bi2Te3 and bacterial cellulose (BC). The formulated ink was printed on a paper surface using a facile processing method. The manufactured paper was further folded and bonded to fabricate a honeycomb-like TEG. This honeycomb-like paper-based TEG exhibited 96 p-n junctions, achieving a maximum voltage and output power of ∼70.5 mV and ∼596 nW, respectively, at a 55 K temperature difference. Moreover, the honeycomb structure was able to withstand a large number of bending and stretching cycles while maintaining its pristine structure. This unique honeycomb structure thus provides a new strategy for future development of paper-based TEGs.

High Performance and Flexible Polyvinylpyrrolidone/Ag/Ag2Te Ternary Composite Film for Thermoelectric Power Generator

In this work, polyvinylpyrrolidone (PVP) coated Ag-rich Ag₂Te nanowires (NWs) were synthesized by a wet chemical method using PVP coated Te NWs as templates, and a flexible PVP/Ag/Ag₂Te ternary composite film on a nylon membrane was prepared by vacuum assisted filtration, followed by heat treatment. TEM and STEM observations of the focused ion beam prepared sample reveal that the composite film shows a porous network-like structure and that the Ag and Ag₂Te exist as nanoparticles and NWs, respectively, both bonded with PVP. The Ag nanoparticles are formed by separation of the Ag-rich Ag₂Te NWs during the heat treatment. For the composite film starting from a Ag/Te initial molar ratio of 6:1, a high power factor of 216.5 μW/mK² is achieved at 300 K, and it increases to 370.1 μW/mK² at 393 K. Bending tests demonstrate excellent flexibility of the hybrid film. A thermoelectric (TE) prototype composed of five legs of the hybrid film is assembled, and a maximum output power of 469 nW is obtained at a temperature gradient of 39.6 K, corresponding to a maximum power density of 341 μW/cm². This work provides an effective route to a composite film with high TE performance and excellent flexibility for wearable TE generators.

Design, Performance, and Application of Thermoelectric Nanogenerators

Thermal energy harvesting from the ambient environment through thermoelectric nanogenerators (TEGs) is an ideal way to realize self-powered operation of electronics, and even relieve the energy crisis and environmental degradation. As one of the most significant energy-related technologies, TEGs have exhibited excellent thermoelectric performance and played an increasingly important role in harvesting and converting heat into electric energy, gradually becoming one of the hot research fields. Here, the development of TEGs including materials optimization, structural designs, and potential applications, even the opportunities, challenges, and the future development direction, is analyzed and summarized. Materials optimization and structural designs of flexibility for potential applications in wearable electronics are systematically discussed. With the development of flexible and wearable electronic equipment, flexible TEGs show increasingly great application prospects in artificial intelligence, self-powered sensing systems, and other fields in the future.

Fabrication of Transparent Paper-Based Flexible Thermoelectric Generator for Wearable Energy Harvester Using Modified Distributor Printing Technology

Paper-based substrates have been increasingly attractive in flexible electronics technology as flexible support substrates due to their advantages of availability, environmental friendliness (as disposable, degradable, and renewable materials), and foldability. Hereby, a facile method for installation of p-type and n-type semiconductor legs in the thickness direction of a paper substrate was established. A transparent paper-based thermoelectric generator prototype by impregnating the paper with resin was then fabricated. The resulting transparent paper-based thermoelectric generator with 10 thermocouples showed excellent mechanical flexibility. The generator maintained a maximum voltage and an output power of ∼8.3 mV and ∼10 nW, respectively, at a temperature difference of 35 K after 1000 bending cycles. This work offers a promising strategy for the development of paper-based thermoelectric generators that are adaptable to a wide variety of complex curved surface heat source. Therefore, the heat recovery efficiency in both human and natural environments can be greatly improved.

High performance n-type Ag2Se film on nylon membrane for flexible thermoelectric power generator

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.

Highly (00l)-oriented Bi2Te3/Te heterostructure thin films with enhanced power factor

Introducing nanoscale heterostructure interfaces into material matrix is an effective strategy to optimize the thermoelectric performance by energy-dependent carrier filtering effect. In this study, highly (00l)-oriented Bi2Te3/Te heterostructure thin films have been fabricated on single-crystal MgO substrates using a facile magnetron co-sputtering method. Bi2Te3/Te heterostructure thin films with Te contents of 63.8 at% show an optimized thermoelectric performance, which possess a Seebeck coefficient of -157.7 μV K-1 and an electrical conductivity of 9.72 × 104 S m-1, leading to a high power factor approaching 25 μW cm-1 K-2. The partially decoupled behavior of the Seebeck coefficient and electrical conductivity is contributed to Bi2Te3/Te heterostructure interfaces, which causes interfacial barrier filtering and scattering effects; thus, a high level of the Seebeck coefficient is obtained. Meanwhile, carrier transport in a-b plane can benefit from the highly preferred orientation, which guarantees a remarkably high electrical conductivity. We anticipate that our strategy may guide the way for preparing high-performance thermoelectric materials by microstructure design and regulation.