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In the development of wearable electronic devices, the composite modification of conductive polymers and single-walled carbon nanotubes (SWCNTs) has become a burgeoning research area. This study presents the synthesis of a novel polythiophene derivative, poly(3-alkoxythiophene) (P3(TEG)T), with alkoxy side chains. Different molecular weight variants of P3(TEG)T (P1-P4) were prepared and combined with SWCNTs to form composite materials. Density functional theory (DFT) calculations revealed a reduced bandgap for P3(TEG)T. Raman spectroscopy demonstrated π-π interactions between P3(TEG)T and SWCNTs, facilitating the dispersion of single-walled carbon nanotubes and the formation of a continuous conductive network. Among the composite films, P4/SWCNTs-0.9 exhibited the highest thermoelectric performance, with a power factor (PF) value of 449.50 µW m-1 K-2. The fabricated flexible thermoelectric device achieved an output power of 3976.92 nW at 50 K, with a tensile strength of 59.34 MPa for P4/SWCNTs. Our findings highlight the strong interfacial interactions between P3(TEG)T and SWCNTs in the composite material, providing an effective charge transfer pathway. Furthermore, an improvement in the tensile performance was observed with an increase in the molecular weight of the polymer used in the composite, offering a viable platform for the development of high-performance flexible organic thermoelectric materials.
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Conjugated polymers (CPs) are widely used as conductive materials in various applications, with their conductive properties adjustable through chemical doping. While doping enhances the thermoelectric properties of CPs due to improved main-chain transport, overdoping can distort the polymer structure, increasing energy disorder and impeding intrinsic electrical transport. This study explored how different dopants affect the structural integrity and electrical transport properties of CPs. We found that dopants vary in their impact on CP structure, consequently altering their electrical transport capabilities. Specifically, ferric chloride (FeCl3)-doped indacenodithiophene-co-benzothiadiazole (IDTBT) shows superior electrical transport properties to triethyloxonium hexachloroantimonate (OA)-doped IDTBT due to enhanced backbone planarity and rigidity, which facilitate carrier transport and lower energetic disorder. These results highlight the critical role of dopant selection in optimizing CPs for advanced applications, suggesting that strategic dopant choices can significantly refine the charge transport characteristics of CPs, paving the way for their industrialization.
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We investigated the thermoelectric and thermal behavior of Fe-V-W-Al-based thin films prepared using the radio frequency magnetron sputtering technique at different oxygen pressures (0.1-1.0 × 10-2 Pa) and on different substrates (n, p, and undoped Si). Interestingly, at lower oxygen pressure, formation of a bcc-type Heusler structure was observed in deposited samples, whereas at higher oxygen pressure, we have noted the development of an amorphous structure in these samples. Our findings indicate that the moderately oxidized Fe-V-W-Al amorphous thin film deposited on the n-Si substrate possesses a large magnitude of S â¼ -1098 ± 100 µV K-1 near room temperature, which is almost double the previously reported value for thin films. Additionally, the power factor (PF) indicated an enormously large value of â¼33.9 mW m-1 K-2 near 320 K. The thermal conductivity of the amorphous thin film is also found to be 2.75 Wm-1 K-1, which is quite lower compared to bulk alloys. As a result, the maximum figure of merit is estimated to be extremely high, i.e., â¼3.9 near 320 K, which is among one of the highest reported values so far. The anomalously large value of Seebeck coefficient and PF has been ascribed to the unusual composite effect of the metallic amorphous oxide phase and insulating substrate possessing a large Seebeck coefficient.
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Doping narrow-gap semiconductors is a well-established approach for designing efficient thermoelectric materials. Semiconducting half-Heusler (HH) and full-Heusler (FH) compounds have garnered significant interest within the thermoelectric field, yet the number of exceptional candidates remains relatively small. It is recently shown that the vacancy-filling approach is a viable strategy for expanding the Heusler family. Here, a range of near-semiconducting Heuslers, TiFexCuySb, creating a composition continuum that adheres to the Slater-Pauling electron counting rule are theoretically designed and experimentally synthesized. The stochastic and incomplete occupation of vacancy sites within these materials imparts continuously changing electrical conductivities, ranging from a good semiconductor with low carrier concentration in the endpoint TiFe0.67Cu0.33Sb to a heavily doped p-type semiconductor with a stoichiometry of TiFe1.00Cu0.20Sb. The optimal thermoelectric performance is experimentally observed in the intermediate compound TiFe0.80Cu0.28Sb, achieving a peak figure of merit of 0.87 at 923 K. These findings demonstrate that vacancy-filling Heusler compounds offer substantial opportunities for developing advanced thermoelectric materials.
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Flexible thermoelectric materials have drawn significant attention from researchers due to their potential applications in wearable electronics and the Internet of Things. Despite many reports on these materials, it remains a significant challenge to develop cost-effective methods for large-scale, patterned fabrication of materials that exhibit both excellent thermoelectric performance and remarkable flexibility. In this study, we have developed an Ag2Se-based ink with excellent printability that can be used to fabricate flexible thermoelectric films by screen printing and low-temperature sintering. The printed films exhibit a Seebeck coefficient of -161 µV/K and a power factor of 3250.9 µW/m·K2 at 400 K. Moreover, the films demonstrate remarkable flexibility, showing minimal changes in resistance after being bent 5000 times at a radius of 5 mm. Overall, this research offers a new opportunity for the large-scale patterned production of flexible thermoelectric films.
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CONTEXT AND RESULTS: In this work, we perform a systematic study on the thermoelectric properties of Zr1-xNiSnHfx using first-principles calculations combined with Boltzmann transport equations. The power factor of Zr1-xNiSnHfx increases as the temperature increases from 300 to 1200 K, because the increase in electrical conductivity is greater than the decrease in the Seebeck coefficient. The power factor of Zr7/8NiSnHf1/8 is larger than that of other Zr1-xNiSnHfx thermoelectric materials, but the thermoelectric figure of merit (ZT) is similar to that of others materials. This is due to the higher electronic thermal conductivity of Zr7/8NiSnHf1/8 compared to other materials. The maximum ZT of p-type (n-type) Zr1-xNiSnHfx is 0.98 (0.97), 0.9 (0.89), 0.83 (0.80), and 0.72 (0.73) at 300 K, 600 K, 900 K, and 1200 K, respectively, which are greater than those of the pure ZrNiSn. In conclusion, Hf-doped ZrNiSn can enhance the thermoelectric performance and are promising candidates for thermoelectric materials. COMPUTATIONAL METHOD: This paper uses FP-LAPW implemented in the WIEN2K code. The thermoelectric performance is calculated based on the semi-classical Boltzmann theory implanted using the BoltzTraP code. The electronic thermal conductivity (κe) and the carrier concentration (n) have been calculated using the density functional theory.
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Soft pneumatic actuation is widely used in wearable devices, soft robots, artificial muscles, and surgery machines. However, generating high-pressure gases in a soft, controllable, and portable way remains a substantial challenge. Here, a class of programmable chemical reactions that can be used to controllably generate gases with a maximum pressure output of nearly 6 MPa is reported. It is proposed to realize the programmability of the chemical reaction process using thermoelectric material with programmable electric current and employing preprogrammed reversible chemical reactants. The programmable chemical reactions as soft pneumatic actuation can be operated independently as miniature gas sources (â¼20-100 g) or combined with arbitrary physical structures to make self-contained machines, capable of generating unprecedented pressures of nearly 6 MPa or forces of about 18 kN in a controllable, portable, and silent manner. Striking demonstrations of breaking a brick, a marble, and concrete blocks, raising a sightseeing car, and successful applications in artificial muscles and soft assistive wearables illustrate tremendous application prospects of soft pneumatic actuation via programmable chemical reactions. The study establishes a new paradigm toward ultrastrong soft pneumatic actuation.
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Using Monte Carlo electronic transport simulations, coupled self-consistently with the Poisson equation for electrostatics, we explore the thermoelectric power factor of nanoengineered materials. These materials consist of alternating highly doped and intrinsic regions on the scale of several nanometers. This structure enables the creation of potential wells and barriers, implementing a mechanism for filtering carrier energy. Our study demonstrates that by carefully designing the nanostructure, we can significantly enhance its thermoelectric power factor compared to the original pristine material. Importantly, these enhancements stem not only from the energy filtering effect that boosts the Seebeck coefficient but also from the utilization of high-energy carriers within the wells and intrinsic barrier regions to maintain relatively high electronic conductivity. These findings can offer guidance for the design and optimization of new-generation thermoelectric materials through improvements in the power factor.
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Organic-inorganic hybrid thermoelectric (TE) materials have attracted tremendous interest for harvesting waste heat energy. Due to their mechanical flexibility, inorganic-organic hybrid TE materials are considered to be promising candidates for flexible energy harvesting devices. In this work, enhanced TE properties of Tellurium (Te) nanowires (NWs)- poly (3-hexylthiophene-2, 5-diyl) (P3HT) hybrid materials are reported by improving the charge transport at interfacial layer mediated via controlled oxidation. A power factor of ≈9.8 µW (mK2)-1 is obtained at room temperature for oxidized P3HT-TeNWs hybrid materials, which increases to ≈64.8 µW (mK2)-1 upon control of TeNWs oxidation. This value is sevenfold higher compared to P3HT-TeNWs-based hybrid materials reported in the literature. MD simulation reveals that oxidation-free TeNWs demonstrate better templating for P3HT polymer compared to oxidized TeNWs. The Kang-Snyder model is used to study the charge transport in these hybrid materials. A large σE0 value is obtained which is related to better templating of P3HT on oxygen-free TeNWs. This work provides evidence that oxidation control of TeNWs is critical for better interface-driven charge transport, which enhances the thermoelectric properties of TeNWs-P3HT hybrid materials. This work provides a new avenue to improve the thermoelectric properties of a new class of hybrid thermoelectric materials.
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The possibility of directly growing carbon nanofibers (CNFs) and carbon nanotubes (CNTs) on half-Heusler alloys by Chemical Vapour Deposition (CVD) is investigated for the first time, without using additional catalysts, since the half-Heusler alloys per se may function as catalytic substrates, according to the findings of the current study. As a carbon source, acetylene is used in the temperature range of 700-750 °C. The n-type half-Heusler compound Zr0.4Ti0.60.33Ni0.33Sn0.98Sb0.020.33 is utilized as the catalytic substrate. At first, a computational model is developed for the CVD reactor, aiming to optimize the experimental process design and setup. The experimental process conditions are simulated to investigate the reactive species concentrations within the reactor chamber and the activation of certain reactions. SEM analysis confirms the growth of CNFs with diameters ranging from 450 nm to 1 µm. Raman spectroscopy implies that the formed carbon structures resemble CNFs rather than CNTs, and that amorphous carbon also co-exists in the deposited samples. From the characterization results, it may be concluded that a short reaction time and a low acetylene flow rate lead to the formation of a uniform CNF coating on the surface of half-Heusler alloys. The purpose of depositing carbon nanostructures onto half-Heusler alloys is to improve the current transfer, generated from these thermoelectric compounds, by forming a conductive coating on their surface.
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Thermoelectric devices have received significant attention because of their potential for sustainable energy recovery. In these devices, a thermal design that optimizes heat transfer and dissipation is crucial for maximizing the power output. Heat dissipation generally requires external active or passive cooling devices, which often suffer from inevitable heat loss and heavy systems. Herein, the design of heat-sink integrated thermoelectric legs is proposed to enhance heat dissipation without external cooling devices, realized by finite element model simulation and 3D printing of ternary silver chalcogenide-based thermoelectric materials. Owing to the self-induced surface charges of the synthesized AgBiSe2 (n-type) and AgSbTe2 (p-type) particles, these particle-based colloidal inks exhibited high viscoelasticity, which enables the creation of complex heat-dissipation architectures via 3D printing. Power generators made from 3D-printed heat-dissipating legs exhibit higher temperature differences and output power than traditional cuboids, offering a new strategy for enhancing thermoelectric power generation.
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Se-free n-type (Bi,Sb)2Te3 thermoelectric materials, outperforming traditional n-type Bi2(Te,Se)3, emerge as a compelling candidate for practical applications of recovering low-grade waste heat. A 100% improvement in the maximum ZT of n-type Bi1.7Sb0.3Te3 is demonstrated by using melt-spinning and excess Te-assisted transient liquid phase sintering (LPS). Te-rich sintering promotes the formation of intrinsic defects (TeBi), elevating the carrier concentration and enhancing the electrical conductivity. Melt-spinning with excess Te fine-tunes the electronic band, resulting in a high power-factor of 0.35 × 10-3 W·m-1 K-2 at 300 K. Rapid volume change during sintering induces the formation of dislocation networks, significantly suppressing the lattice thermal conductivity (0.4 W·m-1 K-1). The developed n-type legs achieve a high maximum ZT of 1.0 at 450 K resulting in a 70% improvement in the output power of the thermoelectric device (7.7 W at a temperature difference of 250 K). This work highlights the synergy between melt-spinning and transient LPS, advancing the tailored control of both electronic and thermal properties in thermoelectric technology.
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Thermoelectric generators (TEGs) are environmentally friendly energy harvesting technologies that hold great promise in the field of self-powered electronics and sensing. However, the current development of thermoelectric (TE) devices has largely lagged behind the development of thermoelectric materials, especially in the preparation of thermoelectric components with customizable shapes and excellent properties, which largely limits their practical applications. These issues can be effectively addressed by using 3D printing technology. Here, we print multiple p-type thermoelectric legs (pins) consecutively with this simple technique, and the printed TEGs have excellent thermal potential (288 µV K-1 at room temperature) and excellent temperature response properties, which exhibited an output voltage of 127.94 mV at a temperature difference (ΔT) of 40 K. The 3D-printed thermoelectric generator enables the collection of thermal energy. In addition, the device has excellent temperature sensing characteristics, and this temperature signal to electrical signal conversion is very rapid, which enables temperature sensing alarms in a wide temperature domain. Combining these features, an energy harvesting and electrical alarm concept for home-scale applications is proposed, which is expected to provide a diverse research idea for the application of next-generation thermoelectric devices.
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Thermoelectricity has been considered as the most important solution of generating electricity, particularly from low-grade heat below 300 °C. Despite efforts in recent years on exploring alternative materials to only commercialized Bi2Te3, the practical implementation of these new materials has been hindered by inadequate investigation into device design. Given that the utilization of weldable electrodes offers advantages in technical compatibility for a large-scale assembly of thermoelectric elements into modules, a thorough investigation into the potential of weldable metal electrodes at T < 300 °C is imperative. In this work, the diffusion of 11 kinds of thermoelectric materials in common weldable metals (Ni, Fe, Cu, and Ag) was screened. Ag is sorted out as a promising weldable electrode that can directly bond to thermoelectric Ag2Se in this temperature range, leading to a minimization of an interfacial contact resistivity down to 11 µΩ cm2 in a design of the Ag/Ag2Se/Ag structure. The conversion efficiency of â¼3% at ΔT of 95 K with an excellent stability indicates Ag2Se as a top alternative to n-type Bi2Te3 for low-grade heat recovery.
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To improve thermoelectric efficiency, various tactics have been employed with considerable success to decouple intertwined material attributes. However, the integration of magnetism, derived from the unique spin characteristic that other methods cannot replicate, has been comparatively underexplored and presents an ongoing intellectual challenge. A previous research has shown that vacancy-filling Heuslers offer a highly adaptable framework for modulating thermoelectric properties. Here, it is demonstrated how intrinsic magnetic-electrical-thermal coupling can enhance the thermoelectric performance of vacancy-filling Heusler alloys. The materials, Nb0.75Ti0.25FeCrxSb with 0 ≤ x ≤ 0.1, feature a fraction of magnetic Cr ions that randomly occupy the vacancy sites of the Nb0.75Ti0.25FeSb half-Heusler matrix. These alloys achieve a remarkable thermoelectric figure of merit (zT) of 1.21 at 973 K, owing to increased Seebeck coefficient and decreased thermal conductivity. The mechanism is primarily due to the introduction of magnetism, which increases the density-of-states effective mass (reaching levels up to 15 times that of a free electron's mass) and simultaneously reduces the electronic thermal conductivity. Mass and strain-field fluctuations further reduce the lattice thermal conductivity. Even higher zT values can potentially be achieved by carefully balancing electron mobility and effective mass. This work underscores the substantial prospects for exploiting magnetic-electrical-thermal synergies in cutting-edge thermoelectric materials.
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Sb2Te3, a binary chalcogenide-based 3D topological insulator, attracts significant attention for its exceptional thermoelectric performance. We report the vibrational properties of magnetically doped Sb2Te3thermoelectric material. Ni doping induces defect/disorder in the system and plays a positive role in engineering the thermoelectric properties through tuning the vibrational phonon modes. Synchrotron powder x-ray diffraction study confirms good crystalline quality and single-phase nature of the synthesized samples. The change in structural parameters, includingBisoand strain, further corroborate with structural disorder. Detailed modification of phonon modes with doping and temperature variation is analysed from temperature-dependent Raman spectroscopic measurement. Compressive lattice strain is observed from the blue shift of Raman peaks owing to Ni incorporation in Sb site. An attempt is made to extract the lattice thermal conductivity from total thermal conductivity estimated through optothermal Raman studies. Hall concentration data support the change in temperature-dependent resistivity and thermopower. Remarkable increase in thermopower is observed after Ni doping. Simulation of the Pisarenko model, indicating the convergence of the valence band, explains the observed enhancement of thermopower in Sb2-xNixTe3. The energy gap between the light and heavy valence band at Γ point is found to be 30 meV (for Sb2Te3), which is reduced to 3 meV (in Sb1.98Ni0.02Te3). A significant increase in thermoelectric power factor is obtained from 715 µWm-1K-2for pristine Sb2Te3to 2415 µWm-1K-2for Ni-doped Sb2Te3sample. Finally, the thermoelectric figure of merit,ZTis found to increase by four times in Sb1.98Ni0.02Te3than that of its pristine counterpart.
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Bi-Sb-Te-based thermoelectric materials have the best room-temperature thermoelectric properties, but their inherent brittleness and rigidity limit their application in the wearable field. In this study, W-doped p-type Bi0.5Sb1.5Te3 (W-BST) thin films were prepared using magnetron sputtering on polyimide substrates to create thermoelectric generators (TEGs). Bending tests showed that the thin film has excellent flexibility and mechanical durability, meeting the flexible requirements of wearable devices. W doping can significantly increase the carrier concentration, Seebeck coefficient, and electrical conductivity of BST thin films. At 300 K, the power factor of the W-BST film is 2.25 times higher than that of the undoped film, reaching 13.75 µW cm-1 K-2. First-principles calculations showed that W doping introduces significant impurity peaks in the bandgap, in which W d electrons remarkably hybridize with the Sb and Te p electrons, leading to an improved electrical conductivity of BST films. Furthermore, W doping significantly reduces the work function of BST films, thereby improving the carrier mobility. A TEG module fabricated from four layers of W-BST thin films achieved a maximum output power density of 6.91 mW cm-2 at a temperature difference of 60 K. Application tests showed that the flexible TEG module could power a portable clock using the temperature difference between body temperature and room temperature. At a medium temperature of 439 K, the assembled TEG module can provide a stable output voltage of 1.51 V to power a LED. This study demonstrates the feasibility of combining inorganic thermoelectric materials with flexible substrates to create high-performance flexible TEGs.
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Since the implementation of the Materials Genome Project by the Obama administration in the United States, the development of various computational materials' databases has fundamentally expanded the choice of industries such as materials and energy. In the field of thermoelectric materials, the thermoelectric figure of merit (ZT) quantifies the performance of the material. From the viewpoint of calculations for vast materials, the ZT values are not easily obtained due to their computational complexity. Here, we show how to build a database of thermoelectric materials based on first-principle calculations for the electronic and heat transport of materials. Firstly, the initial structures are classified according to the values of bandgap and other basic properties using the clustering algorithm K-means in machine learning, and high-throughput first principle calculations are carried out for narrow-bandgap semiconductors which exhibit a potential thermoelectric application. The present framework of calculations mainly includes a deformation potential module, an electrical transport performance module, a mechanical and a thermodynamic properties module. We have also set up a search webpage for the calculated database of thermoelectric materials, providing search facilities and the ability to view the related physical properties of materials. Our work may inspire the construction of more computational databases of first-principle thermoelectric materials and accelerate research progress in the field of thermoelectrics.
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Defect structure is pivotal in advancing thermoelectric performance with interstitials being widely recognized for their remarkable roles in optimizing both phonon and electron transport properties. Diverse interstitial atoms are identified in previous works according to their distinct roles and can be classified into rattling interstitial, decoupling interstitial, interlayer interstitial, dynamic interstitial, and liquid interstitial. Specifically, rattling interstitial can cause phonon resonance in cage compound to scatter phonon transport; decoupling interstitial can contribute to phonon blocking and electron transport due to their significantly different mean free paths; interlayer interstitial can facilitate out-of-layer electron transport in layered compounds; dynamic interstitial can tune temperature-dependent carrier density and optimize electrical transport properties at wide temperatures; liquid interstitial could improve the carrier mobility at homogeneous dispersion state. All of these interstitials have positive impact on thermoelectric performance by adjusting transport parameters. This perspective therefore intends to provide a thorough overview of advances in interstitial strategy and highlight their significance for optimizing thermoelectric parameters. Finally, the profound potential for extending interstitial strategy to various other thermoelectric systems is discussed and some future directions in thermoelectric material are also outlined.
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Oxides are of interest for thermoelectrics due to their high thermal stability, chemical inertness, low cost, and eco-friendly constituting elements. Here, adopting a unique synthesis route via chemical co-precipitation at strongly alkaline conditions, one of the highest thermoelectric performances for ZnO ceramics ( P F max = $PF_{\text{max}} =$ 21.5 µW cm-1 K-2 and z T max = $zT_{\text{max}} =$ 0.5 at 1100 K in Zn 0.96 Al 0.04 O ${\rm Zn}_{0.96} {\rm Al}_{0.04}{\rm O}$ ) is achieved. These results are linked to a distinct modification of the electronic structure: charge carriers become trapped at the edge of the conduction band due to Anderson localization, evidenced by an anomalously low carrier mobility, and characteristic temperature and doping dependencies of charge transport. The bi-dimensional optimization of doping and carrier localization enable a simultaneous improvement of the Seebeck coefficient and electrical conductivity, opening a novel pathway to advance ZnO thermoelectrics.