High Power Factor Research Articles

High thermoelectric performance in p-type ZnSb upon increasing Zn vacancies: an experimental and theoretical study

Zn-vacancy driven high power factor and strong coupling of acoustic and optical modes enhance the zT in p-type ZnSb.

A first-principles study on the promising thermoelectric properties of SnX (X = S, Se, Te) compounds.

SnSe has emerged as an outstanding thermoelectric material due to its exceptional performance. In this study, first-principles calculations are employed to investigate the thermoelectric properties of materials within the SnX family, where X can be either S, Se, or Te. Initially, we assessed the stability of SnX (X = S, Se, Te). We found that SnS exhibits better mechanical and thermal stability than SnSe and SnTe. We then conduct phonon and electronic transport analysis. Following the general rule that heavier atoms have lower thermal conductivity, SnTe demonstrates lower thermal conductivity due to its low group velocity compared with SnS and SnSe. Regarding electrical transport properties, the band gaps for SnS, SnSe, and SnTe are 0.56, 0.54, and 0.35 eV, respectively. Notably, the small band gap and higher degeneracy in its band valleys for SnTe make it more effective for achieving a high power factor. The maximum ZT values are determined to be 1.41, 1.41, and 1.87 for SnS, SnSe, and SnTe, respectively. Remarkably, ZTmax of SnTe exceeds that of SnSe by 32.6%. Overall, the results clearly demonstrate that SnTe exhibits superior thermoelectric properties compared to SnSe and SnS. This study provides valuable insights into the electronic structure, thermal conductivity, and mechanical and thermal stability of materials within the SnSe family, such as SnS or SnTe, without the need for extensive and costly experimental work.

A van der Waals p-n heterostructure of GaSe/SnS2: a high thermoelectric figure of merit and strong anisotropy.

In recent years, van der Waals heterostructures (vdWHs) with controllable and peculiar properties have attracted extensive attention in the fields of electronics, optoelectronics, spintronics and electrochemistry. However, vdWHs with good thermoelectric performance are few due to the complex coupling of thermoelectric coefficients. Here, we employ density functional theory and Boltzmann's transport equation to explore the thermoelectric properties of the p-n vdWH of GaSe/SnS2, which has been experimentally observed to exhibit high performance as an optoelectronic device. We reveal that GaSe/SnS2 possesses strong anisotropy in terms of electronic transport resulting from the anisotropic carrier relaxation time. The longer carrier relaxation time in the y-direction for n-type induces a high power factor of 0.084 W m-1 K-2 at 300 K, while it is only 0.0087 W m-1 K-2) in the x-direction. The strong coupling of low-mid frequency phonon branches and the relatively weak Sn-S bond-induced anharmonicity hinder the phonon transport, which results in the lattice thermal conductivity of GaSe/SnS2 (14.61 and 15.43 W m-1 K-1 along the x- and y-directions at 300 K) being much smaller than the average value of GaSe and SnS2 (43.44 W m-1 K-1 at 300 K). The optimal thermoelectric figure of merit at 700 K for GaSe/SnS2 reaches 2.99, which is significantly higher than those of the constituents of GaSe (0.58) and SnS2 (1.04). The present work highlights the potential thermoelectric applications and the understanding of the thermoelectric transport mechanism for the recently synthesized p-n vdWH of GaSe/SnS2 with a high thermoelectric figure of merit and strong anisotropy.

Effects of loosely bound electrons and electron–phonon interaction on the thermoelectric properties of electrenes

The interstitial charge in 2D HfI2 exhibits high mobility due to weak lattice perturbation, and the high mobility induces a high power factor and ZT value.

Production of (Fe,Co)Si2 and (Fe.Mn)Si2 Thermoelectric Materials by Spark Plasma Sintering

In this study, FeSi2 bulk specimens were prepared by mechanical alloying, spark plasma sintering, and subsequent annealing. The annealed FeSi2 bulk specimens consisted of the β-FeSi2 phase and exhibited high Seebeck coefficient values. The maximum Seebeck coefficient of 356 μVK−1 was achieved in the FeSi2 bulk specimen annealed at 1173 K for 6 h. However, the power factor of the FeSi2 bulk specimen was quite small due to its high electrical resistivity, and a drastic improvement is required. Therefore, Mn- and Co-substituted specimens, Fe1−xMnxSi2 (x = 0.2–0.8) and Fe1−xCoxSi2 (x = 0.2–0.8), were produced, and their thermoelectric properties were evaluated. The Mn- and Co-substituted specimens exhibited lower electrical resistivity and a higher power factor than the FeSi2 bulk specimen. The Fe1−xMnxSi2 (x = 0.2–0.8) bulk specimens were p-type thermoelectric materials, and a Seebeck coefficient of 262 μVK−1 and a power factor of 339 μWm−1K−2 were achieved in the Fe0.94Mn0.06Si2 bulk specimen. On the other hand, the Fe1−xCoxSi2 (x = 0.2–0.8) bulk specimens were n-type thermoelectric materials, and a Seebeck coefficient of −180 μVK−1 and a power factor of 667 μWm−1K−2 were achieved in the Fe0.96Co0.04Si2 bulk specimen.

Universal Input Single-Stage High-Power-Factor LED Driver with Active Low-Frequency Current Ripple Suppressed

In this paper, a light-emitting diode (LED) driver with a high power factor (PF) and low-frequency current ripple suppression over a wide input range is presented, and a flyback converter is designed to operate in the discontinuous conduction mode (DCM), with a digital controller used to keep the duty cycle constant for half of the utility cycle under a fixed load and input voltage. This method ensures that the input current is in phase with the universal input voltage, thus achieving a high power factor without utilizing feedforward control. Furthermore, on the secondary side, the time of the zero point of the utility voltage can be attained so that the duty cycle can be updated at this time. In addition, a simple auxiliary circuit is connected parallel to the output side to absorb the excess output current of the flyback converter or to release the current to the load to make up for the shortage of the output current of the flyback converter so that the low-frequency ripple of the output current can be inhibited. There are only two current-detecting resistors used in this study: one is the output current-sensing resistor of the flyback converter, and the other is the output current-sensing resistor of the auxiliary circuit.

Janus 2D B2P6: A promising anisotropic thermoelectric material with high power factor

A two-dimensional (2D) material with high thermoelectric (TE) performance is of great interest for the energy conversion device. In this study, by using first-principles calculations, we show that the Janus 2D B2P6 has an extremely high TE power factor of 0.10 and 0.07 W/mK2 for p-type and n-type at room temperature, respectively, which are higher than that of conventional 2D TE materials. We also investigate lattice thermal conductivity, κph, of B2P6 by using the Boltzmann transport theory with phonon–phonon interaction. With κph of 41.45 and 133.3 W/mK for the armchair and zigzag directions, respectively, the optimized values of the TE figure of merit are up to 0.7 at 900 K. Moreover, the Janus 2D B2P6 exhibits anisotropic mechanical properties, in which the ideal strength of B2P6 is 10.7 and 18.63 N/m for the armchair and zigzag directions, respectively. Thus, our results suggest that the Janus 2D B2P6 is the potentially promising flexible anisotropic TE material.

Boosting room-temperature thermoelectric performance of Mg3Sb1.5Bi0.5 material through breaking the contradiction between carrier concentration and carrier mobility

Recently, low-cost Mg3Sb2-yBiy-based materials with high performance near room temperatures have been reported, which are considered to be promising candidates for replacing commercial Bi2Te3-based materials. Herein, we report a high power factor of ∼3000 μW m−1 K−1 and a ZT value of 0.82 at room temperature in Ti0.05Mg3.15Sb1.5Bi0.49Te0.01. Ti dopant entering into the Mg1 sublattice slightly increases the carrier concentration by the introduction of impurity states and enhances the carrier mobility by the promotion of grain size growth. The two-donor doping strategy breaks the contradiction between carrier concentration and carrier mobility, thus significantly improving the electrical transport properties near room temperatures. In addition, the introduction of defects by Ti dopant contributes to the decreased lattice thermal conductivity. Consequently, a ZTavg value of 1.19 is obtained at 50–250 ℃, ranking the top among reported n-type thermoelectric materials. Moreover, the as-fabricated single-leg device shows an high engineering efficiency considering the radiation calibration, i.e., 7.2 % and 11.8 % at temperature differences of 250 ℃ and 500 ℃ with Tc = 0 ℃, respectively, demonstrating the great potential of substituting the commercial Bi2Te3-family.

Inverse-Perovskite Ba3 BO (B = Si and Ge) as a High Performance Environmentally Benign Thermoelectric Material with Low Lattice Thermal Conductivity.

High energy-conversion efficiency (ZT) of thermoelectric materials has been achieved in heavy metal chalcogenides, but the use of toxic Pb or Te is an obstacle for wide applications of thermoelectricity. Here, high ZT is demonstrated in toxic-element free Ba3 BO (B = Si and Ge) withinverse-perovskite structure. The negatively charged B ion contributes to hole transport with long carrier life time, and their highly dispersive bands with multiple valley degeneracy realize both high p-type electronic conductivity and high Seebeck coefficient, resulting in high power factor (PF). In addition, extremely low lattice thermal conductivities (κlat ) 1.0-0.4Wm-1 K-1 at T = 300-600 K are observed in Ba3 BO. Highly distorted O-Ba6 octahedral framework with weak ionic bonds between Ba with large mass and O provides low phonon velocities and strong phonon scattering in Ba3 BO. As a consequence of high PF and low κlat , Ba3 SiO (Ba3 GeO) exhibits rather high ZT = 0.16-0.84 (0.35-0.65) at T = 300-623 K (300-523 K). Finally, based on first-principles carrier and phonon transport calculations, maximum ZT is predicted to be 2.14 for Ba3 SiO and 1.21 for Ba3 GeO at T = 600 K by optimizing hole concentration. Present results propose that inverse-perovskites would be a new platform of environmentally-benign high-ZT thermoelectric materials.

Research of electric vehicle battery packs and charging stations based on an active three-phase rectifier

Problem. The proliferation of electric vehicles has underscored the need for the development of energy-efficient charging stations and systems. These systems must deliver high efficiency, maintain a power factor close to unity, adhere to electromagnetic compatibility standards, emit low levels of higher harmonics, and enable fast charging capabilities. Current electric vehicle charging devices encounter issues such as significant power losses, high harmonic emissions to the power grid, and challenges in implementing fast charging modes. Consequently, enhancing the energy efficiency of charging stations – by reducing power losses, minimizing harmonic emissions, ensuring a high power factor, and supporting modes for regulated current and voltage sources for fast charging – is a pressing concern. Goal. The aim of this work is to perform a comparative analysis of different types of batteries for electric vehicles, exemplified by TESLA cars, presenting comparative characteristics of lithium-ion, lithium-iron-phosphate, and lithium-titanate batteries. Methodology. The study showcases an evaluation of battery units for electric vehicles and outlines a comparative assessment of lithium-ion, lithium-iron-phosphate, and lithium-titanate batteries. The research focuses on enhancing the energy efficiency of electric vehicle charging station systems through the use of active rectifiers, with modes for active power factor correction and optimal configuration. Results. An examination of the quality of converters for electric vehicle charging stations was conducted, proposing schemes for a three-phase active voltage source rectifier and an active current source rectifier. Power circuitry and space-vector switching states for power transistors are introduced. Analysis concludes that an active current rectifier may be a more promising topology. Originality. A model of a charging station based on an active current source rectifier was developed using Matlab/Simulink. Transient processes of the converter's operation and the charging of a 60 kWh battery pack were examined. It was found that the active rectifier facilitates regulation of the battery charging current, achieves a power factor close to unity, and maintains a low level of higher harmonic emissions with a harmonic distortion factor of 2.52%. Practical value. The advancement of electric vehicles necessitates the ongoing development and enhancement of the energy indicators for electric vehicle batteries and the converters of charging stations, especially those that enable fast charging. Active progress is being made in each of these areas.

Impact of terbium (Tb) on ferromagnetism and thermoelectric behaviour of spinels MgTb2(S/Se)4 for spintronic

The ferromagnetism due to rare earth elements-based spinel chalcogenides has become emerging aspirant for spintronic devices. Therefore, theoretically computed electronic properties of MgTb2(S/Se)4 spinels are analyzed to comprehend the structural, magnetic, and thermoelectric characteristics. Thermodynamic stability is elucidated using the computed enthalpy of formation (ΔH), phonons dispersion band structures. Using structural optimizations, difference in the energy states has revealed the ferromagnetic (FM) state stability. The computed band structures (BS) and density of states (DOS) both depict a half-metallic ferromagnetic state exhibiting a net spin polarization at the Fermi energy level. The underlying ferromagnetic state has been suggested due to carrier mediated indirect RKKY exchange mechanism. The thermoelectric properties are calculated to evaluate their potential for wasted-heat to useful-electricity conversion applications. The small thermal conductivity, and high-power factor exhibited by MgTb2S4 at room temperature suggest it significant for applications in thermoelectric generators.

Effects of substitutional doping CsSn0.75A0.25I3 (A=B, Sb) in the thermoelectric properties of the B-γ phase from first principles

Among hybrid and all-inorganic halide perovskites, CsSnI3 has stood out with moderate electrical conductivity and ultralow thermal conductivity. Nevertheless, the former is still low compared to values of traditional thermoelectric materials, this makes its applications scarce. Herein, we wish to present a DFT study combined with the application of the Boltzmann transport equation, to determine the effects of p and n-type substitutional doping in the lattice structure, electronic and thermoelectric properties of CsSn0.75A025I3 (A = B, Sb). Our calculations show that doping increases the thermoelectric power factor to 181.2 µW m−1 K−2 under Sb-doping, which represents a twofold value compared to 78.3 µW m−1 K−2 of the pristine lattice; under B-doping we obtained a value of 145.6 µW m−1 K−2. CsSnI3 has higher power factor upon n-type doping. Finally, yet importantly, we further examine the shifts in the Fermi level using the effective mass model framework. In doing so, our work predicts a performance enhancement by achieving a Fermi energy level close to the VBM, or CBM. Similarly, our work demonstrates that doping represents an effective way to improve the thermoelectric power factor of CsSnI3, this being attributed to the increase of charge carriers and the modification of the band structure.

Prominent texturing and enhanced thermoelectric performance of misfit layered (PbS)1.18(TiS2)2 via an exfoliation-restacking approach

Micro-texturing engineering has been taken to manipulate the thermoelectric performance of (PbS)1.18(TiS2)2 via an exfoliation-restacking approach coupled with spark plasma sintering. The resultant polycrystalline material showed remarkably promoted (00l) texturing together with a noticeable reduction in grain size, leading to prominently prior transport properties along the in-plane direction. Particularly, the electrical conductivity was much improved due to the increased carrier mobility without affecting carrier concentration and DOS effective mass, which gave rise to a maintained Seebeck coefficient and consequently a high power factor of 8.8–11.4 μW·cm−1·K−2 in the range of 323 – 773 K. Despite the slightly increased thermal conductivity due to electronic component and the limited suppression of phonon transport, a record-high ZT value of 0.52 has been achieved with an increase by ∼20% compared to that of the pristine one, demonstrating the significant effectiveness of exfoliation-restacking on boosting the thermoelectric performance for misfit layered materials.

Effect of B-site doping on the thermoelectric performances of Ca0.97Y0.01 La0.01 Yb0.01Mn1-2xNbxMoxO3 thermoelectric ceramics

A-, and B-site multiple-doped Ca0.97Y0.01La0.01Yb0.01Mn1–2xNbxMoxO3 was studied for improving its thermoelectric thermoelectric performance. Samples were prepared from planetary milled precursors and sintered at 1310ºC for 12 h. XRD showed that sintered samples are nearly single phase, with small amounts of CaMn2O4. SEM analysis revealed that grain size decreases with Nb and Mo content, leading to lowered electrical resistivity, reaching 6.1 mΩ cm at 800ºC in x = 0.03 samples, 60% lower than that of pristine samples. The highest Seebeck coefficient for doped samples has been obtained for x = 0.005, 210μV/K at 800ºC. A high power factor (0.46 mW/K2 m at 800ºC) has been reached for x = 0.01 samples. However, thermal conductivity did not significantly vary with composition, leading to ZT∼0.27 at 800ºC for x = 0.005 samples, among the best reported in the literature. These results suggest that multi-doping approach opens new paths for integrating calcium manganite-based materials in thermoelectric modules for power generation at high temperatures.

Effect of Ag-addition on the thermoelectric properties of Cu12Sb4S13 tetrahedrite

Tetrahedrite, Cu12Sb4S13, an eco-friendly thermoelectric material with earth-abundant and low-cost constituents, has garnered global interest. This study investigated the thermoelectric characteristics of Ag-added tetrahedrites, which were prepared through solid-state synthesis and subsequently hot-pressed. The minimal temperature dependence of the transport coefficient indicated the presence of strong electron–phonon coupling in the samples. It was observed that Ag addition in tetrahedrite could successfully scatter acoustic phonons, reducing the lattice thermal conductivity while minimally affecting the power factor. The enhanced anharmonicity induced by Ag addition is the primary cause of reduced lattice thermal conductivity. Raman spectroscopy data showed that Ag addition could weaken the Sb–S bond, further supporting the previous argument. Consequently, the lattice thermal conductivity was lowered to ∼0.27 W m−1 K−1 and obtained for the composition Ag0.025 added Cu11.975Sb4S13. A relatively high power factor of ∼1.3 mW m−1 K−2 was obtained for the same composition. Owing to the lowest total thermal conductivity ∼1.09 W m−1 K−1, the sample with composition Ag0.025 added Cu11.975Sb4S13 showed the highest thermoelectric figure of merit of 0.87 at 738 K.

High power factor and ultra-low lattice thermal conductivity in Sn1−xWxTe alloys via interstitial defects modulation

SnTe, a potential substitute for excellent medium-temperature thermoelectric (TE) material PbTe, has recently attracted much attention in TE energy conversion. Herein, we demonstrate a rare and effective strategy to synergistically optimize the electrical and thermal transport properties of SnTe by introducing Tungsten(W) interstitial defects. Concretely, the formation energy of intrinsic Sn vacancy defects is reduced by introducing W-interstitial defects, thus increasing the hole carrier concentration and overall electrical conductivity. Meanwhile, the increase of band degeneracy (band flattening and valence band convergence) markedly enhances the Seebeck coefficient, which exhibits the high average power factor of ∼17.79 μWcm−1K−2. Moreover, the lattice thermal conductivity is significantly reduced to 0.46 Wm−1K−1, which arises from the enhancement of phonon scattering caused by various processes including dislocations, crystal defects and multiscale nanoprecipitation. These combined effects lead to a maximum ZT value of ∼0.79 at 823 K for Sn0.97W0.03Te, especially the average ZT value remarkably increased to 0.26. Conclusively, unlike conventional work to optimize electrical transport performance (reducing hole carrier concentration), this work provides an innovative strategy to significantly improve the electrical properties of SnTe through the modulation of W-interstitial defects.

Effects of preparation method on thermoelectric properties of poly(aniline‐co‐3,4‐ethylenedioxythiophene)/SWCNT composites

AbstractComposites of conducting polymer and single‐walled carbon nanotubes (SWCNTs) are attracting great attentions in harvesting low‐grade waste heat. Prefabricated SWCNTs film used as the working electrode was placed at the liquid interface between the inorganic phase (dilute sulfuric acid solution) and the organic phase consisting of dichloromethane (DCM), aniline (ANI), and 3,4‐ethylenedioxythiophene (EDOT), together with a platinum wire (the counter electrode) and a silver chloride (AgCl/Ag) electrode (the reference electrode), to perform electrochemical polymerization of ANI and EDOT at the liquid interface. Thermoelectric (TE) composites of poly(ANI‐co‐EDOT) and SWCNTs were produced. Compared with composites from ultrasonic mixing and coating methods, the 10 wt% SWCNTs‐composites in situ formed in electrochemical polymerization have the highest power factor (PF) of 41.56 ± 3.58 μW m−1 K−2, higher than the PF values of the composites formed by other two methods. The work indicates that the TE properties of ANI‐EDOT copolymer/SWCNT (poly[ANI‐co‐EDOT]/SWCNT) composites prepared by electrochemical polymerization were better than those of the composites obtained by physical mixing the electrochemically synthesized poly(ANI‐co‐EDOT) with SWCNTs. Moreover, SWCNTs treated with sodium dodecylbenzene sulfonate (SDBS) could further improve the TE properties of the composites.

Tuning Anisotropic Thermoelectric Properties of TiS2–δ Compounds via Intercalating Iron

Layered TiS2 is of great potential in thermoelectrics for room temperature and medium temperature applications due to its tunable transport properties, low environmental impact, low cost, and lightweight. Herein, we prepared FexTiS2–δ with x varying from 0 to 0.05 through a two-step process, involving initial synthesis in sealed tubes followed by spark plasma sintering. Mössbauer spectroscopy indicated that Fe atoms occupy the octahedral sites in the van der Waals gaps and exist in the form of Fe2+ with a high spin state. FexTiS2–δ with x ≤ 0.02 exhibit high in-plane power factors, reaching an average of ~ 1.2 mWm–1K–2. The structural disorder caused by Fe intercalation leads to a significant decrease in out-of-plane lattice thermal conductivity. The anisotropy in the figure of merit, ZT, of FexTiS2–δ is suppressed due to Fe intercalation. Fe0.01TiS2–δ possesses the highest ZT of 0.39 at 625K along the in-plane direction.

Twinning behavior and thermoelectric performance of Cu2SnS3

With the perfect and orderly atomic arrangement, nanotwins could effectively scatter mid- and low-frequency phonons while minimizing the scattering for carriers, beneficial for enhancing the thermoelectric properties of materials. To unlock these features, we explored the twin structural characteristics in Cu2SnS3 and found that nanotwins formed along [100] direction on the glide-set plane, and further delved into the mechanism of twin formation and found that twinning possessed a lower nucleation barrier than the slipping. In addition, we reduced the unstable stacking fault energy in the stacking stage and amplified the probability of twin formation by introducing Se atoms at the S sites. In spite of more nanotwins, a slight increase in carrier mobility was realized, leading to a maximum power factor of 5.5 μW cm−1 K−2 at 773 K for the Cu2SnS2Se material. Meanwhile, the lattice thermal conductivity across the entire temperature range was effectively reduced due to the introduction of nanotwins and SeS points defects, which is approximately 0.46 W m−1 K−1 at 773 K for Cu2SnS2Se. Further optimization of the power factor was realized by utilizing a high-efficient doping strategy via introducing Sn vacancies. The carrier concentration became significantly augmented while minimizing ionized impurities scattering, giving rise to an exceptionally high power factor of 8.2 μW cm−1 K−2 and a highly-ranked thermoelectric figure of merit of 0.98 at 773 K for Cu2Sn0.99S2Se. Our work demonstrates an intriguing route towards the high thermoelectric performance of Cu2SnS3 through the introduction of nanotwins as well as high-efficient doping techniques.

Computations on platinum based ternary ferromagnetic half metals for spin valve diodes and green energy technology based thermoelectric

The ab initio method commonly known as wavefunction method is used to calculate the structural, mechanical, electronic, magnetic, lattice dynamical and thermoelectric properties of the half metallic half-Heusler alloys VPtZ (Z = Si, Ge, Sn). The equilibrium lattice constants and corresponding ground state energies of the studied alloys are computed in stable ferromagnetic γ-phase with a cubic structure. The electronic properties suggest that the compounds are half metals with indirect band gap having the band energies of 1.02 eV, 1.04 eV and 0.9 eV for VPtSi, VPtGe and VPtSn, respectively, in the spin down channel. The materials have spin magnetic moment of 1 μB, suggest that the materials are suitable for making spintronic devices such as spin valve diodes. Temperature dependent heat transport properties were studied by using classical Boltzmann theory. The materials have high power factor at high temperatures. Thermoelectric performance of the materials is calculated between the temperature range 100–1200 K respectively. The obtained thermoelectric figure of merit for p-type VPtSi, VPtGe and VPtSn are 0.4, 0.7 and 0.3, respectively, at 1200 K. Similarly, the figure of merit obtained for n-type VPtSi, VPtGe and VPtSn are 0.41, 0.75 and 0.3, respectively, at the same temperature. The favourable energy and spin transport properties of these alloys show that they are the potential candidates as thermoelectric for heat energy harvesting and spintronic for magneto electronics applications.