Carrier Scattering at Alloy Nanointerfaces Enhances Power Factor in PEDOT:PSS Hybrid Thermoelectrics

Morphological Ordering of the Organic Layer for High-Performance Hybrid Thermoelectrics

Inorganic-organic hybrids, such as Te-PEDOT:PSS core/shell nanowires, have emerged as a class of promising thermoelectric materials with combined attributes of mechanical flexibility and low cost. However, the poorly understood structure-property relationship calls for further investigation for performance enhancement. Here, through precise treatments of focused electron beam irradiation and thermal annealing on individual Te-PEDOT:PSS nanowires, new, nonchemical mechanisms are introduced to specifically engineer the organic phase, and the measured results provide an unprecedented piece of evidence, confirming the dominant role of organic shell in charge transport. Paired with the Kang-Snyder model and molecular dynamics simulations, this work provides mechanistic insights in terms of heating-enabled morphological ordering of the polymer chains. The measured results show that thermal annealing on the 42 nm nanowire results in a ZT value of 0.78 at 450 K. Through leveraging the interfacial self-assembly of the organic phase to construct a high electrical conductivity domain, this work lays out a clear framework for the development of next-generation soft thermoelectrics.

The cross-interface energy-filtering effect at organic/inorganic interfaces balances the trade-off between thermopower and conductivity

The energy-filtering effect has been widely employed to elucidate the enhanced thermoelectric properties of organic/inorganic hybrids. However, the traditional Mott criterion cannot identify the energy-filtering effect of organic/inorganic hybrids due to the limitations of the Hall effect measurement in determining their carrier concentration. In this work, a carrier concentration-independent strategy under the theoretical framework of the Kang-Snyder model is proposed and demonstrated using PANI/MWCNT composites. The result indicates that the energy-filtering effect is triggered on increasing the temperature to 220 K. The energy-filtering effect gives a symmetry-breaking characteristic to the density of states of the charge carriers and leads to a higher thermopower of PANI/MWCNT than that of each constituent. From a morphological perspective, a paracrystalline PANI layer with a thickness of 3 nm is spontaneously assembled on the MWCNT network and serves as a metallic percolation pathway for carriers, resulting in a 5.56-fold increase in conductivity. The cooperative 3D carrier transport mode, including the 1D metallic transport along the paracrystalline PANI and the 2D cross-interface energy-filtering transport, co-determines a 4-fold increase in the power factors of PANI/MWCNT at 300 K. This work provides a physical insight into the improvement of the thermoelectric performance of organic/inorganic hybrids via the energy-filtering effect.

Ultra-low lattice thermal conductivity and anisotropic thermoelectric transport properties in Zintl compound β-K2Te2

A good thermoelectric (TE) performance is usually the result of the coexistence of an ultralow thermal conductivity and a high TE power factor in the same material. In this paper, we investigate the thermal transport and TE properties of the Zintl compound β-K₂Te₂ based on a combination of first-principles calculations and the Boltzmann transport equation. Remarkably, the calculated lattice thermal conductivity κ_L in hexagonal β-K₂Te₂ is ultralow with a value of 0.19 (0.30) W m^-1 K^-1 along the c (a and b) axis at 300 K due to the small phonon group velocity and phonon lifetime, which is comparable to the κ_L for wood and promises possible good TE performance. By taking the fully anisotropic acoustic deformation potential scattering, polar optical phonon scattering, and ionized impurity scattering into account, the rational electron scattering and transport properties are captured, which indicates a power factor exceeding 2.0 mW m^-1 K^-2. As a result, the anomalously high n-type ZT of 2.62 and p-type ZT of 3.82 at 650 K along the c axis are obtained in the hexagonal β-K₂Te₂, breaking the long-term record of ZT < 3.5 in the majority of the reported TE materials until now. These findings support that hexagonal β-K₂Te₂ is a potential candidate for high-efficiency TE applications.

Significantly Enhanced Thermoelectric Properties of Copper Phthalocyanine/Single-Walled Carbon Nanotube Hybrids by Iodine Doping

The copper phthalocyanine/single-walled carbon nanotube (CuPcI/SWCNT) hybrids were fabricated through doping the CuPc/SWCNT mixture using iodine vapor. It was found that both CuPc and SWCNTs were oxidized by iodine vapor resulting in great increase in carrier concentration. Moreover, the strong π-π conjugation interactions between CuPcI- and I-doped SWCNTs make the CuPcI molecules to assemble on the surface of SWCNTs in an ordered face-on packing, which benefits decreasing the carrier transport barrier across the CuPcI/SWCNT interfaces. The combination of iodine bidoping and the ordered face-on packing of CuPcI on the SWCNT surface realizes the synergetic enhancement of carrier concentration and carrier mobility and therefore the great improvement of electrical conductivity. The maximum electrical conductivity (6281 S cm^-1) and thermoelectric power factor (∼304 μW m^-1 K^-2) at room temperature were obtained at a composition of 60 wt % SWCNTs. The power factor value is 3 orders of magnitude higher than the pure CuPcI and 1 order of magnitude higher than SWCNTs. Consequently, the highest ZT value of CuPc/SWCNT hybrids is up to 0.03, which is among the highest value of organic small-molecule complexes.

Unconventional Thermoelectric Materials for Energy Harvesting and Sensing Applications

Heat is an abundant but often wasted source of energy. Thus, harvesting just a portion of this tremendous amount of energy holds significant promise for a more sustainable society. While traditional solid-state inorganic semiconductors have dominated the research stage on thermal-to-electrical energy conversion, carbon-based semiconductors have recently attracted a great deal of attention as potential thermoelectric materials for low-temperature energy harvesting, primarily driven by the high abundance of their atomic elements, ease of processing/manufacturing, and intrinsically low thermal conductivity. This quest for new materials has resulted in the discovery of several new kinds of thermoelectric materials and concepts capable of converting a heat flux into an electrical current by means of various types of particles transporting the electric charge: (i) electrons, (ii) ions, and (iii) redox molecules. This has contributed to expanding the applications envisaged for thermoelectric materials far beyond simple conversion of heat into electricity. This is the motivation behind this review. This work is divided in three sections. In the first section, we present the basic principle of the thermoelectric effects when the particles transporting the electric charge are electrons, ions, and redox molecules and describe the conceptual differences between the three thermodiffusion phenomena. In the second section, we review the efforts made on developing devices exploiting these three effects and give a thorough understanding of what limits their performance. In the third section, we review the state-of-the-art thermoelectric materials investigated so far and provide a comprehensive understanding of what limits charge and energy transport in each of these classes of materials.

New Progress on Fiber-Based Thermoelectric Materials: Performance, Device Structures and Applications

With the rapid development of wearable electronics, looking for flexible and wearable generators as their self-power systems has proved an extensive task. Fiber-based thermoelectric generators (FTEGs) are promising candidates for these self-powered systems that collect energy from the surrounding environment or human body to sustain wearable electronics. In this work, we overview performances and device structures of state-of-the-art fiber-based thermoelectric materials, including inorganic fibers (e.g., carbon fibers, oxide fibers, and semiconductor fibers), organic fibers, and hybrid fibers. Moreover, potential applications for related thermoelectric devices are discussed, and future developments in fiber-based thermoelectric materials are also briefly expected.

Wearable Thermoelectric Devices Based on Three-Dimensional PEDOT:Tosylate/CuI Paper Composites

Thermoelectric composites of organic and inorganic materials exhibit significantly enhanced thermoelectric properties compared with pristine organic thermoelectrics so they might be better suited as core materials of wearable thermoelectric devices. This study describes the development of three-dimensional (3D) paper PEDOT:tosylate/CuI composites that could be shaped as 3 mm thick blocks to convert a temperature difference between their bottom and top sides into power; the majority of organic thermoelectric materials are shaped as thin strips usually on a planar substrate and convert a temperature difference between the opposite edges of the strips into power. The 3D paper PEDOT:tosylate/CuI composites can produce a power density equal to 4.8 nW/cm² (ΔΤ = 6 Κ) that is 10 times higher than that of the pristine paper PEDOT:Tos composites. The enhanced thermoelectric properties of the paper PEDOT:tosylate/CuI composites are attributed to the CuI nanocrystals entrapped inside the composite that increases the Seebeck coefficient of the composite to 225 μV K^-1; the Seebeck coefficient of paper PEDOT:Tos is 65 μV K^-1. A proof-of-concept wearable thermoelectric device that uses 36 blocks of the paper PEDOT:tosylate/CuI composites (as p-type elements) and 36 wires of monel (as n-type elements) can produce up to 4.7 μW of power at ΔΤ = 20 K. The device has a footprint of 64 cm² and can be placed directly over the skin or can be embedded into clothing.

Organic/Inorganic Hybrid Boosting Energy Harvesting Based on the Photothermoelectric Effect

Attracted by the capability of light to heat and electricity conversion, the photothermoelectric (PTE) effect has drawn great attention in the field of energy conversion and self-powered electronics. However, it still requires effective strategies to convert electricity from light based on the corresponding photothermoelectric generator. Herein, considering the broad photoresponse and large Seebeck effect of tellurium nanowires (Te NWs) as well as the high electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), PEDOT:PSS/Te NW hybrid thin films were fabricated to enhance the conversion efficiency by the photothermoelectric effect with respect to single thermoelectric performance. A detailed comparison has been achieved between the photothermoelectric and thermoelectric properties induced by light illumination and heating plates through current-voltage (I-V) transport, respectively. PEDOT:PSS/Te NW hybrid films also show an enhanced photothermal harvesting compared to pure PEDOT:PSS. A photothermoelectric device was assembled based on the as-fabricated PEDOT:PSS/Te NW hybrid films with 90 wt% Te NWs and achieved a competitive output power density with good stability, which may provide insights into improving solar energy harvesting-based photothermoelectric conversion by organic/inorganic hybrids.

Effects of carbon nanomaterials hybridization of Poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) on thermoelectric performance

The influence of multiple dimensional carbon nanomaterials, such as graphene quantum dots (GQD), multi-walled carbon nanotubes (MWCNT), and graphene sheets (GNS) of the thermoelectric properties in poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS)-based hybrids have been investigated. PEDOT: PSS matrix was successfully used to prepare PEDOT: PSS/GQDs (PGQD), PEDOT: PSS/MWCNT (PCNT) and PEDOT: PSS/GNS (PGNS) composite films. According to structural characteristics, strongπ-πinteractions existed between carbon materials and PEDOT: PSS, and PEDOT: PSS layers with organized and arranged morphology were easier templated by GNS than GQD or MWCNT. It was found that besides energy filtering effect, hole-phonon interaction occurred with further addition of GNS and GQDs in PGNS and PGQD composite films. The optimal power factor (PF) of approximately 580 and 103μW m^-1K^-2at 363 K were acquired in PGNS composite films at 5 wt% GNS and PGQD films with 1 wt% GQD filling, respectively. Unlike PGNS and PGQD films, electrical conductivity of PCNT reduced upon the addition of MWCNT, while the Seebeck coefficient decreased firstly, and then increased and reached to the highest value at 10 wt% MWCNT. The optimal PF of 381.8μW m^-1K^-2at 363 K was obtained with weight fraction of 0.1 wt% in PCNT films.

Decoupling electron and phonon transport in single-nanowire hybrid materials for high-performance thermoelectrics

Organic-inorganic hybrids have recently emerged as a class of high-performing thermoelectric materials that are lightweight and mechanically flexible. However, the fundamental electrical and thermal transport in these materials has remained elusive due to the heterogeneity of bulk, polycrystalline, thin films reported thus far. Here, we systematically investigate a model hybrid comprising a single core/shell nanowire of Te-PEDOT:PSS. We show that as the nanowire diameter is reduced, the electrical conductivity increases and the thermal conductivity decreases, while the Seebeck coefficient remains nearly constant-this collectively results in a figure of merit, ZT, of 0.54 at 400 K. The origin of the decoupling of charge and heat transport lies in the fact that electrical transport occurs through the organic shell, while thermal transport is driven by the inorganic core. This study establishes design principles for high-performing thermoelectrics that leverage the unique interactions occurring at the interfaces of hybrid nanowires.

An Approach toward the Realization of a Through-Thickness Glass Fiber/Epoxy Thermoelectric Generator

The present study demonstrates, for the first time, the ability of a 10-ply glass fiber-reinforced polymer composite laminate to operate as a structural through-thickness thermoelectric generator. For this purpose, inorganic tellurium nanowires were mixed with single-wall carbon nanotubes in a wet chemical approach, capable of resulting in a flexible p-type thermoelectric material with a power factor value of 58.88 μW/m·K². This material was used to prepare an aqueous thermoelectric ink, which was then deposited onto a glass fiber substrate via a simple dip-coating process. The coated glass fiber ply was laminated as top lamina with uncoated glass fiber plies underneath to manufacture a thermoelectric composite capable of generating 54.22 nW power output at a through-thickness temperature difference οf 100 K. The mechanical properties of the proposed through-thickness thermoelectric laminate were tested and compared with those of the plain laminates. A minor reduction of approximately 11.5% was displayed in both the flexural modulus and strength after the integration of the thermoelectric ply. Spectroscopic and morphological analyses were also employed to characterize the obtained thermoelectric nanomaterials and the respective coated glass fiber ply.

Observation of Energy-Dependent Carrier Scattering in Conducting Polymer Nanowire Blends for Enhanced Thermoelectric Performance

Without sacrificing the intrinsic softness and flexibility of conducting polymers, their blends have been demonstrated to be promising to improve thermoelectric properties of conducting polymers. However, the underlying mechanism for the thermoelectric enhancement is hitherto far from clear and is worthy of being explored deeply. In this work, we report novel conducting polymer nanowire blends by physically mixing poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires and polypyrrole (PPy) nanowires. By carefully tuning the energetic structure of PPy nanowires (nanofillers), the Seebeck coefficients and power factors of nanowire blends are surprisingly increased by ∼20 and ∼32% (compared to PEDOT nanowires), respectively. By means of first-principles calculations and experimental characterizations, we qualitatively confirm that the improved thermoelectric property is a consequence of a built-in energy barrier at nanowire interfaces rather than the commonly used doping/de-doping effect. Subsequently, we further employ the Kang-Snyder transport model and quantitatively demonstrate that the energy barrier involves energy-dependent carrier scattering (thus, a change of total relaxation time) at nanowire heterojunctions, which contributes to the enhanced Seebeck coefficients and power factors. Our work sheds light on the mechanism that can be adopted to design soft but high-performance thermoelectric materials with conducting polymer blends.

Highly Integrable Thermoelectric Fiber

The integration of thermoelectric (TE) device on fabrics is a challenge. Instead of using adhesive tape to fix traditional filmlike TE devices onto the fabrics, which sacrifices the breathability of fabrics, here we report a flexible TE fiber based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/tellurium nanowires (Te NWs) composites, which can be woven and integrated into the fabric directly. The TE fibers have a tunable content and orientation of Te NWs and also the potential to be scaled up based on the wet-spinning process. The TE fibers exhibit desirable wearable TE performances, including high power factor (78.1 μW m^-1 K^-2), high mass-specific power (9.48 μW g^-1), excellent mechanical flexibility, and superior integrability.

Advanced Thermoelectric Design: From Materials and Structures to Devices

The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Recent Progress of Two-Dimensional Thermoelectric Materials

Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power. Moreover, the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades. Among these compounds, layered two-dimensional (2D) materials, such as graphene, black phosphorus, transition metal dichalcogenides, IVA-VIA compounds, and MXenes, have generated a large research attention as a group of potentially high-performance thermoelectric materials. Due to their unique electronic, mechanical, thermal, and optoelectronic properties, thermoelectric devices based on such materials can be applied in a variety of applications. Herein, a comprehensive review on the development of 2D materials for thermoelectric applications, as well as theoretical simulations and experimental preparation, is presented. In addition, nanodevice and new applications of 2D thermoelectric materials are also introduced. At last, current challenges are discussed and several prospects in this field are proposed.

Thermoelectric enhancement in multilayer thin-films of tin chalcogenide nanosheets/conductive polymers

Te-Substituted SnSe nanosheets (Te-s-SnSe NSs) with a lateral size of ∼500 nm are fabricated and their surfaces are then coated with a poly(3,4-ethylenedioxythiophene) PEDOT nanolayer. The 3,4-ethylenedioxythiophene loading is optimized for achieving outstanding thermoelectric performance and the resulting PEDOT-coated nanosheets (PEDOT-Te-s-SnSe NSs) are alternately stacked with PEDOT:poly(styrenesulfonate) (PSS) using a solution-processable method to obtain multilayer inorganic/organic composite films. The as-fabricated multilayer films exhibit outstanding electrical conductivity and Seebeck coefficient. This is due to the enhanced interchain interaction and charge-carrier hopping of the stretched PEDOT chains as well as the presumable energy-filtering effect at the interfacial potential barriers between inorganic and organic layers. The multilayer film consisting of three-repeated stacking allows a maximum thermoelectric power factor of 222 μW m-1 K-2, which is 5.5 times larger than that achieved with pristine PEDOT:PSS. This strategy of combining inorganic and organic materials into multilayer films is promising for the achievement of high-performance thin-film thermoelectrics.

Ink Processing for Thermoelectric Materials and Power-Generating Devices

The growing concern over the depletion of hydrocarbon resources, and the adverse environmental effects associated with their use, has increased the demand for renewable energy sources. Thermoelectric (TE) power generation from waste heat has emerged as a renewable energy source that does not generate any pollutants. Recently, ink-based processing for the preparation of TE materials has attracted tremendous attention because of the simplicity in design of power generators and the possibility of cost-effective manufacturing. In this progress report, recent advances in the development of TE inks, processing techniques, and ink-fabricated devices are reviewed. A summary of typical formulations of TE materials as inks is included, as well as a discussion on various ink-based fabrication methods, with several examples of newly designed devices fabricated using these techniques. Finally, the prospects of this field with respect to the industrialization of TE power generation technology are presented.

Good Performance and Flexible PEDOT:PSS/Cu2Se Nanowire Thermoelectric Composite Films

Herein, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coated Cu _xSe _y (PC-Cu _xSe _y) nanowires are prepared by a wet-chemical method, and PEDOT:PSS/Cu _xSe _y nanocomposite films on flexible nylon membrane are fabricated by vacuum assisted filtration and then cold-pressing. XRD analysis reveals that the Cu _xSe _y with different compositions can be obtained by adjusting the nominal Cu/Se molar ratios of their sources. For the composite film starting from a Cu/Se nominal molar ratio of 3, an optimized power factor of ∼270.3 μW/mK² is obtained at 300 K. Moreover, the film exhibits a superior flexibility with 85% of the original power factor retention after bending for 1000 cycles around a rod with a diameter of 5 mm. TEM and STEM observations of the focused ion beam (FIB) prepared sample reveal that it is mainly attributed to a synergetic effect of the nylon membrane and the composite film with nanoporous structure formed by the intertwined nanowires, besides the intrinsic flexibility of nylon. Finally, a thermoelectric prototype composed of nine legs of the optimized hybrid film generates a voltage and a maximum power of 15 mV and 320 nW, respectively, at a temperature gradient of 30 K. This work offers an effective approach for high TE performance inorganic/polymer composite film for flexible TE devices.

Fabrication of one-dimensional Cu2Te/Te nanorod composites and their enhanced thermoelectric properties

Cu₂Te/Te nanorod composites were fabricated and their thermoelectric properties were investigated.

Polymer morphology and interfacial charge transfer dominate over energy-dependent scattering in organic-inorganic thermoelectrics

Hybrid (organic-inorganic) materials have emerged as a promising class of thermoelectric materials, achieving power factors (S²σ) exceeding those of either constituent. The mechanism of this enhancement is still under debate, and pinpointing the underlying physics has proven difficult. In this work, we combine transport measurements with theoretical simulations and first principles calculations on a prototypical PEDOT:PSS-Te(Cu_x) nanowire hybrid material system to understand the effect of templating and charge redistribution on the thermoelectric performance. Further, we apply the recently developed Kang-Snyder charge transport model to show that scattering of holes in the hybrid system, defined by the energy-dependent scattering parameter, remains the same as in the host polymer matrix; performance is instead dictated by polymer morphology manifested in an energy-independent transport coefficient. We build upon this language to explain thermoelectric behavior in a variety of PEDOT and P3HT based hybrids acting as a guide for future work in multiphase materials.

To realize the potential of soft hybrid (inorganic-organic) materials for thermoelectrics, the underlying transport-related physics must be understood. Here, the authors extend the Kang-Synder framework with experimental analysis to gain insight on the thermoelectric transport in hybrid materials.

Preparation and Characterization of Te/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)/Cu7Te4 Ternary Composite Films for Flexible Thermoelectric Power Generator

In this work, Te/poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/Cu₇Te₄ ternary thermoelectric (TE) nanocomposite films were successfully fabricated by physical mixing and then drop casting. An optimum power factor of 65.3 μW/mK² was acquired from a composite film containing 95 wt % PEDOT:PSS-coated Te (PC/Te) nanorods at 300 K, which was about 5 times as large as that of the PC/Cu₇Te₄ nanorod film and about 3 times as large as that of the PC/Te nanorod film. The power factor reached 112.3 μW/mK² when the temperature was 380 K. Scanning transmission electron microscopy (STEM) and high-resolution STEM were used to observe the detailed internal microstructure of the composite film, revealing that the Te nanorods were single crystalline and the Cu₇Te₄ rods polycrystalline. The composite film was in fact a three-dimensional network interconnected with the PC/Te and PC/Cu₇Te₄ nanorods. The enhancement of the TE properties was ascribed to the synergetic effect of the two kinds of nanorods and the double-carrier filtering effect at the two heterointerfaces of Te/PEDOT:PSS and Cu₇Te₄/PEDOT:PSS. An eight single-leg flexible TE device consisting of the optimized composite film was fabricated, which produced a voltage of 31.2 mV and a maximum output power of 94.7 nW at a temperature gradient of 39 K.

Nanoscale self-assembly of thermoelectric materials: a review of chemistry-based approaches

This review is concerned with the leading methods of bottom-up material preparation for thermal-to-electrical energy interconversion. The advantages, capabilities, and challenges from a material synthesis perspective are surveyed and the methods are discussed with respect to their potential for improvement (or possibly deterioration) of application-relevant transport properties. Solution chemistry-based synthesis approaches are re-assessed from the perspective of thermoelectric applications based on reported procedures for nanowire, quantum dot, mesoporous, hydro/solvothermal, and microwave-assisted syntheses as these techniques can effectively be exploited for industrial mass production. In terms of energy conversion efficiency, the benefit of self-assembly can occur from three paths: suppressing thermal conductivity, increasing thermopower, and boosting electrical conductivity. An ideal thermoelectric material gains from all three improvements simultaneously. Most bottom-up materials have been shown to exhibit very low values of thermal conductivity compared to their top-down (solid-state) counterparts, although the main challenge lies in improving their poor electrical properties. Recent developments in the field discussed in this review reveal that the traditional view of bottom-up thermoelectrics as inferior materials suffering from poor performance is not appropriate. Thermopower enhancement due to size and energy filtering effects, electrical conductivity enhancement, and thermal conductivity reduction mechanisms inherent in bottom-up nanoscale self-assembly syntheses are indicative of the impact that these techniques will play in future thermoelectric applications.

Exceptional thermoelectric properties of flexible organic-inorganic hybrids with monodispersed and periodic nanophase

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.

The potential of flexible organic/inorganic hybrids for thermoelectrics is limited by the inability to control their microstructure. Here, the authors demonstrate polymer-nanoparticle hybrids with a monodispersed, periodic nanophase that shows high thermoelectric performance at room temperature.

One-step Synthesis and Enhanced Thermoelectric Properties of Polymer-Quantum Dot Composite Films

Conventional syntheses of polymer-inorganic composite thermoelectric materials suffer major problems such as inhomogeneity, large particle size, and oxidation that result in ineffective loading. Now a one-step synthesis can be used to fabricate high-quality small-sized anions codoped poly(3,4-ethylenedioxythiophene):dodecylbenzenesulfonate/Cl-tellurium (PEDOT:DBSA/Cl-Te) composite films using a series of novel Te^IV -based oxidants. The synchronized production of PEDOT and Te results in thick and homogeneous films containing evenly distributed and well-protected Te quantum dots. Owing to the heavily doped crystalline polymer matrix as well as the <5 nm unoxidized Te quantum dot loading, at low Te concentrations as 2.1-5.8 wt %, the films exhibits high power factors of about 100 μW m^-1  K^-2 , which is 50 % higher compared to a pure PEDOT:DBSA film.

High-performance thermoelectric materials based on ternary TiO2/CNT/PANI composites

High-performance thermoelectric materials with a thermoelectric power factor of 114.5 μW mK⁻² were obtained by using the ternary composite of TiO₂/CNT/PANI.

Manufacturing Te/PEDOT Films for Thermoelectric Applications

In this work, flexible Te films have been synthesized by electrochemical deposition using PEDOT [poly(3,4-ethylenedioxythiophene)] nanofilms as working electrodes. The Te electrodeposition time was varied to find the best thermoelectric properties of the Te/PEDOT double layers. To show the high quality of the Te films grown on PEDOT, the samples were analyzed by Raman spectroscopy, showing the three Raman active modes of Te: E₁, A₁, and E₂. The X-ray diffraction spectra also confirmed the presence of crystalline Te on top of the PEDOT films. The morphology of the Te/PEDOT films was studied using scanning electron microscopy, showing a homogeneous distribution of Te along the film. Also an atomic force microscope was used to analyze the quality of the Te surface. Finally, the electrical conductivity and the Seebeck coefficient of the Te/PEDOT films were measured as a function of the Te deposition time. The films showed an excellent thermoelectric behavior, giving a maximum power factor of about 320 ± 16 μW m^-1 K^-2 after 2.5 h of Te electrochemical deposition, a value larger than that reported for thin films of Te. Qualitative arguments to explain this behavior are given in the discussion.