Enhancement Of Thermoelectric Power Factor Research Articles

Electron-Phonon Interaction Mediated Gigantic Enhancement of Thermoelectric Power Factor Induced by Topological Phase Transition.

We propose an effective strategy to significantly enhance the thermoelectric power factor (PF) of a series of 2D semimetals and semiconductors by driving them toward a topological phase transition (TPT). Employing first-principles calculations with an explicit consideration of electron-phonon interactions, we analyze the electronic transport properties of germanene across the TPT by applying hydrogenation and biaxial strain. We reveal that the nontrivial semimetal phase, hydrogenated germanene with 8% biaxial strain, achieves a considerable 4-fold PF enhancement, attributed to the highly asymmetric electronic structure and semimetallic nature of the nontrivial phase. We extend the strategy to another two representative 2D materials (stanene and HgSe) and observe a similar trend, with a marked 7-fold and 5-fold increase in PF, respectively. The wide selection of functional groups, universal applicability of biaxial strain, and broad spectrum of 2D semimetals and semiconductors render our approach highly promising for designing novel 2D materials with superior thermoelectric performance.

Understanding of isoelectronic alloying induced energy gap variation for a large enhancement of thermoelectric power factor

Understanding of isoelectronic alloying induced energy gap variation for a large enhancement of thermoelectric power factor

High Thermoelectric Performance in Solution-Processed Semicrystalline PEDOT:PSS Films by Strong Acid-Base Treatment: Limitations and Potential.

Thermoelectric (TE) generation with solution-processable conducting polymers offers substantial potential in low-temperature energy harvesting based on high tunability in materials, processes, and form-factors. However, manipulating the TE and charge transport properties accompanies structural and energetic disorders, restricting the enhancement of thermoelectric power factor (PF). Here, solution-based strong acid-base treatment techniques are introduced to modulate the doping level of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films with preserving its molecular orientation, enabling to achieve a remarkably high PF of 534.5µWm-1 K-2 . Interestingly, theoretical modeling suggested that further de-doping can increase the PF beyond the experimental value. However, it is impossible to reach thisvalue experimentally, even without any degradation of PEDOT crystallinity. Uncovering the underlying reason for the limitation, an analysis of the relationship among the microstructure-thermoelectric performance-charge transport property revealed that inter-domain connectivity via tie-chains and the resultant percolation for transport are crucial factors in achieving high TE performance, as in charge transport. It is believed that the methods and fundamental understandings in this work would contribute to the exploitation of conducting polymer-based low-temperature energy harvesting.

Anomalous enhancement of thermoelectric power factor in multiple two-dimensional electron gas system.

Toward drastic enhancement of thermoelectric power factor, quantum confinement effect proposed by Hicks and Dresselhaus has intrigued a lot of researchers. There has been much effort to increase power factor using step-like density-of-states in two-dimensional electron gas (2DEG) system. Here, we pay attention to another effect caused by confining electrons spatially along one-dimensional direction: multiplied 2DEG effect, where multiple discrete subbands contribute to electrical conduction, resulting in high Seebeck coefficient. The power factor of multiple 2DEG in GaAs reaches the ultrahigh value of ~100 μWcm-1 K-2 at 300 K. We evaluate the enhancement rate defined as power factor of 2DEG divided by that of three-dimensional bulk. The experimental enhancement rate relative to the theoretical one of conventional 2DEG reaches anomalously high (~4) in multiple 2DEG compared with those in various conventional 2DEG systems (~1). This proposed methodology for power factor enhancement opens the next era of thermoelectric research.

Achieving significant enhancement of thermoelectric power factor of hexagonal PdTe2 monolayer by using strain engineering

Hexagonal PdTe2, one of the two-dimensional transition metal dichalcogenies, has drawn substantial exploration as a potential thermoelectric material for low-temperature applications. However, how to further enhance its thermoelectric properties has still not been systematically investigated. In this paper, we research the electronic and thermoelectric properties of h-PdTe2 tuning by uniaxial and biaxial strains using first-principles calculations. The indirect bandgap of the unstrained h-PdTe2 is 0.195eV. It is found that both uniaxial and biaxial strains can reduce the bandgap and influence the Pd-d orbitals and Te-p orbitals near the Fermi level, leading a transition from semiconductor to conductor. It is worth noting that under biaxial strains, the power factor of h-PdTe2 is significantly improved. At the temperature of 300 K, the maximum power factors of n-type and p-type h-PdTe2 under strains of −4% and 2% are 97.56% and 61.26% higher than those without strain, respectively. Therefore, biaxial strains at low temperature can greatly enhance the thermoelectric properties of h-PdTe2. Our research not only offers a practical method for significantly enhancing the thermoelectric properties of 2D TMDs, but also promote its application in the field of thermoelectricity.

Enhancement of thermoelectric power factor in nanostructured cadmium oxide via zinc doping for high-temperature thermoelectric applications

Enhancement of thermoelectric power factor in nanostructured cadmium oxide via zinc doping for high-temperature thermoelectric applications

Enhancement of thermoelectric power factor in Cu2Se superionic conductor via high energy electron beam irradiation

The modification in the Cu2Se thermoelectric system by electron beam irradiation has been carried out in this work. Samples were prepared using the solid-state reaction technique. The prepared samples were irradiated with various energy dosages viz. 50, 100, and 150 kGy. XRD studies reveal that the synthesized samples crystallized in a monoclinic structure. The micro-hardness of the samples decreased with an increase in irradiation dosage. The sample irradiated at 100 kGy dose exhibits the lowest electrical resistivity, moderate Seebeck coefficient, and highest power factor.

Temperature dependences of thermoelectric properties of bulk SiGeAu composites

Recently, we have demonstrated thermoelectric power factor enhancement of bulk SiGeAu composites at room temperature by thermal management with resonant level effect. In terms of the application to the thermoelectric generation from low temperature wasted heat, the thermoelectric properties in the low temperature range should be investigated. In this study, we evaluate the temperature dependences of thermoelectric properties of P- and B-doped SiGeAu samples. Accompanying the thermoelectric power factor enhancement of P-doped SiGeAu sample by thermal management with resonant level effect, ZT was higher than practically-used SiGe in the range from room temperature to 200 ºC. This study indicates that SiGeAu composites can be used for reusing low temperature wasted heat.

Effect of Large Uniaxial Stress on the Thermoelectric Properties of Microcrystalline Silicon Thin Films

This study reports on the behaviour of the thermoelectric properties of n- and p-type hydrogenated microcrystalline silicon thin films (µc-Si: H) as a function of applied uniaxial stress up to ±1.7%. µc-Si: H thin films were deposited via plasma enhanced chemical vapour deposition and thermoelectric properties were obtained through annealing at 200 °C (350 °C) for n-(p-) type samples, before the bending experiments. Tensile (compressive) stress was effective to increase the electrical conductivity of n-(p-) type samples. Likewise, stress induced changes in the Seebeck coefficient, however, showing an improvement only in electron-doped films under compressive stress. Overall, the addition of elevated temperature to the bending experiments resulted in a decrease in the mechanical stability of the films. These trends did not produce a significant enhancement of the overall thermoelectric power factor, rather it was largely preserved in all cases.

Enhancement of thermoelectric power factor in Si-doped Mg3Sb2 compoundfor thermoelectric converting applications

Mg3Sb2 is a narrow band gap semiconductor with electrical conductivity and thermoelectric properties dependent on structure and doping elements. In this study, to improve the thermoelectric properties of Mg3Sb2, the authors doped Si at different ratios (x=0.05, 0.1, 0.15, 0.25, and 0.3) into Sb sites as the formula Mg3Sb2-xSix to improve the electrical conductivity of doping samples while maintaining a high value of the Seebeck coefficient. The results exhibited that Mg3Sb2 and Mg3Sb2-xSixcompounds prepared by solid phase reaction method (high energy grinding combined with hot pressing and sintering) showed hexagonal structure. The electrical conductivity of the Si-doped samples increased significantly compared to the undoped Mg3Sb2 sample, while the Seebeck coefficient slightly decreased in the low doping contents samples and highest increase in the Mg3Sb1.75Si0.25 sample. The power factor of all doping samples increased compared to undoped samples. The power factor values at 673K of Mg3Sb1.9Si0.1, Mg3Sb1.75Si0.25, and Mg3Sb1.7Si0.3 increased around 1.7 times compared to the Mg3Sb2

Enhancement of thermoelectric power factor via electron energy filtering in Cu doped MoS2 on carbon fabric for wearable thermoelectric generator applications

The design and construction of state-of-the-art wearable thermoelectric materials are important for the development of self-powered wearable thermoelectric generators (WTEGs). Molybdenum disulfide (MoS2) has been reported as a noteworthy thermoelectric (TE) material because of its large intrinsic bandgap and high carrier mobility. In this work, Cu-doped two-dimensional layered MoS2 nanosheets were grown on carbon fabric (CF) via a hydrothermal method. The electrical conductivity, Seebeck coefficient, and power factor for the Cu-doped MoS2 were found to increase with increasing temperature. The maximum Seebeck coefficient was obtained for a MoS2 sample doped with 4 at% of Cu (CM4) was ∼10 μV/K at 303 K and ∼13 μV/K at 373 K. The enhancement in the Seebeck coefficient was attributed to an energy-filtering effect caused by the interfacial barrier between MoS2 and Cu. In addition, a thermoelectric device was designed with four pairs of TE materials, where CM4 (4 at%) was used as a p-type material and Cu wire was used as an n-type material. These p- and n-type materials were connected electrically in series and thermally in parallel to generate a voltage of 190.7 μV at a temperature gradient of 8 K.

Effect of MWCNTs surface functionalization group nature on the thermoelectric power factor of PPy/MWCNTs nanocomposites

This work aims to put forward the role of multiwalled carbon nanotubes (MWCNTs) surface functionalization on the enhancement of thermoelectric (TE) power factor of new nanocomposite-based polypyrrole/surface modified multiwalled carbon nanotubes (PPy/MWCNTs), prepared by a facile in-situ oxidative polymerization process. In fact, MWCNTs’ content was fixed to ∼11 wt%, and their surfaces were respectively modified with different functional groups (benzoic acid (-D1), benzene tricarboxylic acid (-D3), -O, -COOH, -NH2 and -SH). After running all the required, spectral, structural, morphological, and thermoelectrical characterizations, it is revealed that the nanocomposites-based functionalized MWCNTs remarkably increase the Seebeck coefficient, and thus enhancing the material’s power factor. This improvement of TE power factor was attributed to the coating homogeneity and the good interaction between PPy and MWCNTs mainly through π–π stacking between the polymer chains and the nanotubes as well as electrostatic, hydrogen bonding, and electrons donor/acceptor groups interactions due to the functional groups grafted on the nanotube’s sidewall. The highest power factor value (0.51 μWm−1K−2) was obtained with PPy/MWCNTs-SH, which means an enhancement of 8 folds compared to pure PPy. Considering the content of MWCNTs and the ease of preparation process, these results might help to develop future TE materials and devices.

Simultaneous Enhancement of Thermoelectric Power Factor and Phase Stability of Tin-Based Perovskites by Organic Cation Doping

Simultaneous Enhancement of Thermoelectric Power Factor and Phase Stability of Tin-Based Perovskites by Organic Cation Doping

Enhancement of thermoelectric power factor of zinc oxide by nickel and indium dual doping

Enhancement of thermoelectric power factor of zinc oxide by nickel and indium dual doping

Enhanced thermoelectric power factor led by isovalent substitution in Sr2CrMoO6 double perovskite

The strategy of using aliovalent substitution in A2B2O6 double perovskites remained the popular choice to enhance the charge carrier concentration in order to increase their electrical conductivity. In the present investigation, we have shown that the isovalent substitution in A-site can facilitate in manipulating the oxidation states of B-site transition metal cations in double perovskites, which in turn helps in increasing the carrier concentration. Further, using the strategy of manipulating valence states of B-site cations, we could enhance the thermoelectric (TE) power factor of double perovskites. Ceramic samples of Ba x Sr2−x CrMoO6 (x = 0.0, 0.1, 0.2, and 0.3) double perovskites have been synthesized via solid-state reaction route. The phase constitution and morphological study have been carried out via x-ray diffraction (XRD) and field scanning electron microscope (FESEM). Rietveld refinement of XRD data confirms the polycrystalline cubic structure with Pmm space group. Negative values of Seebeck coefficient have been observed for these oxides in the temperature range from room temperature to 1100 K, confirming electrons as the majority charge carriers. The electrical conductivity of Sr2CrMoO6 double perovskite is found to be increased by more than an order of magnitude due to isovalent Ba2+ doping in place of Sr2+. As a result, 5 times enhancement of TE power factor has been attained in Ba x Sr2−x CrMoO6. Charge transport mechanism of these double perovskites is found to be governed by the small polaron hopping conduction model. x-ray photoelectron spectroscopy spectra validate the presence of multivalent cations of Mo5+, Mo6+, Cr3+, and Cr6+ in these double perovskites. Furthermore, the detailed defect chemistry analysis suggests that owing to Ba substitution, Cr is oxidized from Cr3+ to Cr6+ oxidation states, which enhances the electron concentration and reduces the low mobility oxygen vacancies leading to dramatically improved electrical conductivity.

Enhancement of thermoelectric power factor by modulation doping of bulk polycrystalline SnS / thin film PEDOT:PSS bilayer

Modulation doping occurs in a heterojunction where a charge carrier-rich material transfers charge to a carrier-deficient material. The modulation-doped material is intentionally selected to have higher charge carrier mobility than the modulation dopant material, so that the overall electrical conductivity can be boosted. Although this modulation doping strategy has proven effective in enhancing power factor in thermoelectrics, selection criteria for such semiconductor couples have not been explicitly clarified, resulting in only a few discovered semiconductor couples available for modulation doping-driven thermoelectric systems [1-4]. Here, we (i) report an electronic band structure-based guideline to actualize modulation doping, (ii) reveal that hole-rich PEDOT:PSS can modulation dope otherwise undoped tin monosulfide (SnS) in their bilayered structure, (iii) prove that modulation doping is responsible for thermoelectric power factor enhancement by comparing computational and experimental Seebeck coefficient and electrical conductivity values. The optimized PEDOT:PSS thin film / SnS pellet bilayered structure had a 134.7 fold improvement in electrical conductivity and a 93.6 fold power factor enhancement over those of undoped SnS, with only a ~ 20 % decrease in Seebeck coefficient. The modulation doping effect can result in further power factor improvement when SnS becomes a nanoscale thin film or nanoparticles in the future.

A significant enhancement in thermoelectric power factor of In2Te3 thin films by Se doping and Te composition tuning

Thermoelectric power factor of a material significantly relies on its electrical conductivity, thermal conductivity, and Seebeck coefficient. Herein, an attempt has been made to enhance the thermoelectric power factor of In2Te3 thin films by tuning their Te composition and via Se doping. The optimum Se-doping concentration and Te composition enhanced the power factor of pristine In2Te3 films by 14 and 7.4 times, respectively. The modified chemical composition, structural characteristics, and surface morphological features of In2Te3 films are observed to be pivotal in improving their thermoelectric power factor. Overall, this study offers a facile approach to control the thermoelectric power factor of In2Te3 thin films which is significant for their futuristic applications.

Thermoelectric power factor enhancement of calcium-intercalated layered silicene by introducing metastable phase

It has been theoretically predicted that the thermoelectric properties of silicene can be enhanced by deforming its atomic structure. In CaSi2, calcium-intercalated layered silicene, the silicene structure of the metastable 3R phase is a deformed silicene structure of the stable 6R phase. In this paper, our first-principle calculation reveals that the Seebeck coefficient is enhanced by transformation from stable 6R- to metastable 3R-CaSi2. We experimentally enhance the Seebeck coefficient by endotaxially introducing metastable 3R-CaSi2 into single-crystalline 6R-CaSi2, leading to a high thermoelectric power factor. This study demonstrates that introducing the metastable phase can become an effective way to enhance the thermoelectric power factor.

Augmentation of thermoelectric power factor of p-type chromium nitride thin films for device applications

The transformation of the n-type chromium nitride (CrN) thin films into p-type by intrinsic point defects using reactive radio frequency magnetron sputtering is explored in this report. The formation of the acceptor point defects with increasing nitrogen pressure transformed the n-type conductivity of CrN into p-type along with variation of preferred orientation from (111) to (200). To improve the mobility of holes and hence to decrease the resistivity, the CrN thin films with preferred orientation along (220) was fabricated by precisely tuning the sputtering parameters. The root cause behind the reduction in resistivity of CrN thin films with orientation of crystallites was explored by surface charge density mapping using conductive atomic force microscopy. The reduction in resistivity resulted in the enhancement of thermoelectric power factor and the p-type CrN thin film showed a power factor of 24.43 μW/m K2 with Seebeck coefficient of 301 μV/K and resistivity of 3.71 mΩ m at RT.

Significant enhancement of thermoelectric properties of conducting PTB7 polymer by addition of appropriate dopants

AbstractThermoelectric properties of poly({4,8‐bis [(2‐ethylhexyl)oxy] benzo [1,2‐b:4,5‐b'] dithiophene‐2,6‐ diyl}{3‐fluoro‐2‐ [(2‐ethylhexyl) carbonyl] thieno[3,4‐b] thiophenediyl}), commonly known as PTB7 conducting polymer was investigated for the first time by the first author in 2017, and it showed higher electrical conductivity or Seebeck coefficient (or even both) and hence, higher thermoelectric power factor than a variety of organic semiconductors. Therefore, it is worth working more on this semiconductor to improve its thermoelectric power factor. In this work, for the first time, 4 new dopants are introduced to PTB7 polymer to improve its thermoelectric properties. The materials are famous oxidants that are inexpensive and easily available with no need to perform any synthesis process, including antimony pentachloride (SbCl5), iron trichloride (FeCl3), thionyl chloride (SOCl2), and iodine (I2). As a result, significant enhancement of thermoelectric power factor after doping with antimony pentachloride (from 0.224 to 25.5 μWK−2 m−1,) and iron trichloride (from 0.224 to 18.2 μWK−2 m−1,) and moderate enhancement with thionyl chloride was obtained. For the case of iodine doping, simultaneous enhancement of electrical conductivity and Seebeck coefficient was observed due to increasing the mobility.