Enhancement Of Thermoelectric Efficiency Research Articles

Unlocking the Potential of Porous Bi2Te3-Based Thermoelectrics Using Precise Interface Engineering through Atomic Layer Deposition.

Porous thermoelectric materials offer exciting prospects for improving the thermoelectric performance by significantly reducing the thermal conductivity. Nevertheless, porous structures are affected by issues, including restricted enhancements in performance attributed to decreased electronic conductivity and degraded mechanical strength. This study introduces an innovative strategy for overcoming these challenges using porous Bi0.4Sb1.6Te3 (BST) by combining porous structuring and interface engineering via atomic layer deposition (ALD). Porous BST powder was produced by selectively dissolving KCl in a milled mixture of BST and KCl; the interfaces were engineered by coating ZnO films through ALD. This novel architecture remarkably reduced the thermal conductivity owing to the presence of several nanopores and ZnO/BST heterointerfaces, promoting efficient phonon scattering. Additionally, the ZnO coating mitigated the high resistivity associated with the porous structure, resulting in an improved power factor. Consequently, the ZnO-coated porous BST demonstrated a remarkable enhancement in thermoelectric efficiency, with a maximum zT of approximately 1.53 in the temperature range of 333-353 K, and a zT of 1.44 at 298 K. Furthermore, this approach plays a significant role in enhancing the mechanical strength, effectively mitigating a critical limitation of porous structures. These findings open new avenues for the development of advanced porous thermoelectric materials and highlight their potential for precise interface engineering through the ALD.

Performance boost of an integrated photovoltaic-thermal and solar thermal collectors using minichannel heat sink: Energy, exergy, and environmental analysis

This case study investigates the enhancement of thermo-electric efficiency of an integrated photovoltaic-thermal and solar thermal collectors through the utilization of a minichannel heat sink. The integration of a photovoltaic-thermal collector and a solar thermal collector forms a cohesive system designed to minimize heat loss and streamline the external connection process. The energy, exergy, and environmental analysis of the integrated system are numerically investigated and compared by four solar systems including a photovoltaic module, solar thermal collector, photovoltaic-thermal collector, and simple channel-based integrated system. The results of energy analysis show that among the five investigated systems, the maximum electrical and thermal power is obtained using minichannel-based integrated systems, which are 0.8 % and 55.8 % higher than those of photovoltaic-thermal systems, respectively. By using minichannels instead of the simple channel, the electrical and thermal exergy of the integrated system increases by 0.80 % and 7.16 %, respectively. The greater effect of the solar radiation on the systems’ performance than other operating parameters is found from the results so the total power of the minichannel-based integrated systems increases by 245.39 W, by increasing the radiation rate from 700 W/m2 to 1100 W/m2. The annual CO2 mitigation of the integrated system, in term of energy, is 11.54 tCO2/annum, which is 81.5 % and 56.8 % more than photovoltaic module and solar thermal collector, respectively.

The Effect of Width-Mismatch of Modulated Nanowaveguides on the Thermoelectric Efficiency.

Width-modulated nanowaveguides are promising for thermoelectric efficiency enhancement because electron and phonon transport properties can be geometrically tuned for improved performance. The shape of the modulation profile drastically affects the transport properties. Optimization of the width modulation for simultaneous maximum thermoelectric transport and minimum thermal transport is challenging because of the interconnected electron and phonon transport properties. We addressed this problem by analysing the effect of each characteristic dimension of a single rectangular modulation unit on electron and phonon transport. We identified distinct behaviours for electrons and phonons. We reveal that whereas phonon thermal conductance decreases with increasing width-mismatch, the electron thermoelectric power factor shows a non-monotonic dependence. It is pointed out that optimal width-mismatch that maximizes thermoelectric efficiency is mainly determined by electron transport and should be identified by maximizing the thermoelectric power. Our work points to a new strategy of optimizing geometry-modulated metamaterials for maximum thermoelectric efficiency.

Biaxial Tensile Strain-Induced Enhancement of Thermoelectric Efficiency of α-Phase Se2Te and SeTe2 Monolayers.

Thermoelectric (TE) materials can convert waste heat into electrical energy, which has attracted great interest in recent years. In this paper, the effect of biaxial-tensile strain on the electronic properties, lattice thermal conductivity, and thermoelectric performance of α-phase Se2Te and SeTe2 monolayers are calculated based on density-functional theory and the semiclassical Boltzmann theory. The calculated results show that the tensile strain reduces the bandgap because the bond length between atoms enlarges. Moreover, the tensile strain strengthens the scatting rate while it weakens the group velocity and softens the phonon model, leading to lower lattice thermal conductivity kl. Simultaneously, combined with the weakened kl, the tensile strain can also effectively modulate the electronic transport coefficients, such as the electronic conductivity, Seebeck coefficient, and electronic thermal conductivity, to greatly enhance the ZT value. In particular, the maximum n-type doping ZT under 1% and 3% strain increases up to six and five times higher than the corresponding ZT without strain for the Se2Te and SeTe2 monolayers, respectively. Our calculations indicated that the tensile strain can effectively enhance the thermoelectric efficiency of Se2Te and SeTe2 monolayers and they have great potential as TE materials.

Enhancement of Thermoelectric Efficiency and Optical Properties of Hydrogen Absorption in SiC:Mn Nanotube

Enhancement of Thermoelectric Efficiency and Optical Properties of Hydrogen Absorption in SiC:Mn Nanotube

Dimensional Crossover and Enhanced Thermoelectric Efficiency Due to Broken Symmetry in Graphene Antidot Lattices

Graphene antidot lattices (GALs) are two-dimensional (2D) monolayers with periodically placed holes in otherwise pristine graphene. We investigate the electronic properties of symmetric and asymmetric GAL structures having hexagonal holes, and show that anisotropic 2D GALs can display a dimensional crossover such that effectively one-dimensional (1D) electronic structures can be realized in two-dimensions around the charge neutrality point. We investigate the transport and thermoelectric properties of these 2D GALs by using non-equilibrium Green function (NEGF) method. Dimensional crossover manifests itself as transmission plateaus, a characteristic feature of 1D systems, and enhancement of thermoelectric efficiency, where thermoelectric figure of merit, $zT$, can be as high as 0.9 at room temperature. We also study the transport properties in the presence of Anderson disorder and find that mean free paths of effectively 1D electrons of anisotropic configuration are much longer than their isotropic counterparts. We further argue that dimensional crossover due to broken symmetry and enhancement of thermoelectric efficiency can be nanostructuring strategy virtually for all 2D materials.

Electrical and mechanical properties and thermoelectric efficiency enhancement of monolayer and bilayer Si2BN: A first-principle study

In this article density functional calculations were utilized to determine the characteristics and the enhancement of thermoelectric efficiency of monolayer Si2BN (Si2BNmono) in the presence and absence of biaxial strain. Furthermore, we studied the structural stability and thermoelectric and electronic properties of eight various stacking of the bilayer Si2BN (Si2BNbi). Metallic behavior was observed as a result of the band structure of Si2BNmono and Si2BNbi. This issue prompted an emphasis on the metallic characteristics comprising electrical conductivity per relaxation time (σ/τ) and Work Function (WF). By comparing the σ/τ and WF between the graphene and Si2BN, it is concluded that σ/τgheraphene is less than σ/τSi2BN and WFSi2BN is close to WFgraphene. Finally, the highest figure of merit (ZT) for Si2BNmono without strain and with + 10% strain on the Fermi energy were 0.15 and 0.16, respectively. Moreover, it was 0.76 for the A1B2 stacking of Si2BNbi for energy below the Fermi level.

Enhanced thermoelectric efficiency in nanocrystalline bismuth telluride nanotubes

We report on the thermal and thermoelectric properties of individual nanocrystalline Bi2 Te3 nanotubes synthesized by the solution phase method using 3ω method and a microfabricated testbench. Measurements show that the nanotubes offer improved ZT compared to bulk Bi2Te3 near room temperature due to an enhanced Seebeck coefficient and suppressed thermal conductivity. This improvement in ZT originates from the nanocrystalline nature and low dimensionality of the nanotubes. Domain boundary filtering of low-energy electrons provides an enhanced Seebeck coefficient. The scattering of phonons at the surface of the nanotube leads to suppressed thermal conductivity. These have been theoretically analyzed using the Boltzmann equation based on the relaxation time approximation and Landauer approach. This work clearly demonstrates the possibility of achieving enhancement in thermoelectric efficiency by combining nanocrystalline and low-dimensional systems.

Role of polarization electric field on thermal conductivity of GaN/In0.9Ga0.1N/GaN superlattices

Enhancement in thermoelectric efficiency of GaN/In0.9Ga0.1N/GaN superlattice (SL) needs higher electrical conductivity (σ) and Seebeck coefficient (S); but lower thermal conductivity (k). Both S and σ are improved due to the presence of polarization electric field (PEF) of this SL. In this work, the role of PEF on k of SL has been investigated and found that cross-plane and in-plane k are reduced due to PEF upto a certain temperature. Both cross-plane and in-plane thermal conductivities in the presence of PEF show cross over temperature termed as transition temperature(Tc ). It is noted the Tc for cross-plane and in-plane thermal conductivity of GaN/In0.9Ga0.1N superlattice (SL) are 510K and 530K, respectively which depends on In contents. Thus, the preferred value of S, σ and k of GaN/In0.9Ga0.1N SL can be achieved as per requirement by changing In content; making it suitable for TE module for maximum power production at room temperature and above.

Enhancement of thermoelectric efficiency in granular Co-Cu thin films from spin-dependent scattering

In contrast to traditional concepts that eliminate magnetic impurities to achieve larger thermoelectric efficiencies, we report an enhanced thermoelectric efficiency for Cu through doping with the magnetic impurity Co. With doping concentrations from 15% to 30%, the amplitude of the Seebeck coefficient increases from 1.90 μV/K up to 16.3 μV/K, which greatly enhances the thermoelectric efficiency (i.e., power factor). Measuring the magnetoresistance and magnetothermoelectric powers at different temperatures indicates that the enhancement of thermoelectric efficiency is a result of spin-dependent scattering from Co nanoparticles, which are less sensitive to the superparamagnetic transitions. Our finding illustrates a path for the use of nanomagnets to develop potential thermoelectric materials.

Large Enhancement of Thermoelectric Efficiency Due to a Pressure-Induced Lifshitz Transition in SnSe.

The Lifshitz transition, a change in Fermi surface topology, is likely to greatly influence exotic correlated phenomena in solids, such as high-temperature superconductivity and complex magnetism. However, since the observation of Fermi surfaces is generally difficult in the strongly correlated systems, a direct link between the Lifshitz transition and quantum phenomena has been elusive so far. Here, we report a marked impact of the pressure-induced Lifshitz transition on thermoelectric performance for SnSe, a promising thermoelectric material without a strong electron correlation. By applying pressure up to 1.6GPa, we have observed a large enhancement of the thermoelectric power factor by more than 100% over a wide temperature range (10-300K). Furthermore, the high carrier mobility enables the detection of quantum oscillations of resistivity, revealing the emergence of new Fermi pockets at ∼0.86 GPa. The observed thermoelectric properties linked to the multivalley band structure are quantitatively reproduced by first-principles calculations, providing novel insight into designing the SnSe-related materials for potential valleytronic as well as thermoelectric applications.

Ultralow thermal conductivity and low charge carrier scattering potential in Zn1-xCdxSb solid solutions for thermoelectric application

Zinc Antimonide (ZnSb) is a promising p-type thermoelectric (TE) material for mid-temperature (room temperature to 673 K) power generation application due to its high TE conversion efficiency and low cost. Here we show that further improvements of the TE efficiency of ZnSb is possible by reduction of the lattice thermal conductivity (κL). This is achieved by forming a solid solution between ZnSb and CdSb which enhance the phonon scattering due to the mass disorder/strain effect. Compositions of Zn1-xCdxSb (x = 0, 0.25, 0.375 and 0.5) have been synthesized by melting, rapid compaction followed by annealing. The formation of the solid solution is confirmed from X-ray Diffraction (XRD) measurements and the calculated lattice parameters indicate an expected increase with Cd content. Thermoelectric properties have been measured between room temperature and 673 K. It is observed that the lattice thermal conductivity (κL) is significantly reduced by this alloying. At room temperature ∼50% reduction is achieved for x = 0.5 composition, while at elevated temperatures (523 K) a κL value 0.62 W m−1 K−1 is obtained for x = 0.375 composition. The reduction in κL is attributed to the additional contribution to the phonon scattering by mass/strain disorder based on fitting the room temperature κL data with the Klemens-Callaway model. A significant contribution to the lowering of κL in the solid solutions is found to be due to the anharmonic nature of the bonding. The effect of alloying on the electrical properties have been further investigated and results indicate low alloy scattering (U) potential ∼0.3 eV in the solid solutions. The possible origin of such low U values is further an indicator of the muti-center, anharmonic nature of bonding in this system. Thus, the ultra-low lattice thermal conductivity coupled with low alloy scattering potential make Zn1-xCdxSb ideal candidates for further enhancement in thermoelectric efficiency.

Anisotropic thermoelectric properties of Bi1.9Lu0.1Te2.7Se0.3 textured via spark plasma sintering

Spark plasma sintering method was applied to prepare bulk n-type Bi1.9Lu0.1Te2.7Se0.3 samples highly textured along the 001 direction parallel to the pressing direction. The texture development is confirmed by X-ray diffraction analysis and scanning electron microscopy. The grains in the textured samples form ordered lamellar structure and lamellar sheets lie in plane perpendicular to the pressing direction. The average grain size measured along the pressing direction is much less as compared to the average grain size measured in the perpendicular direction (∼50 nm against ∼400 nm). A strong anisotropy in the transport properties measured along directions parallel and perpendicular to the pressing direction within the 290 ÷ 650 K interval was found. The specific electrical resistivity increases and the thermal conductivity decreases for the parallel orientation as compared to these properties for the perpendicular orientation. The Seebeck coefficient for both orientations is almost equal. Increase of the electrical resistivity is stronger than decrease of the thermal conductivity resulting in almost three-fold enhancement of the thermoelectric figure-of-merit coefficient for the perpendicular orientation (∼0.68 against ∼0.24 at ∼420 K). The texturing effect can be attributed to (i) recovery of crystal structure anisotropy typical for the single crystal Bi2Te3-based alloys and (ii) grain boundary scattering of electrons and phonons. An onset of intrinsic conductivity observed above Td ≈ 410 K results in appearance of maxima in the temperature dependences of the specific electrical resistivity, the Seebeck coefficient and the thermoelectric figure-of-merit coefficient and minimum in the temperature dependence of the total thermal conductivity. The intrinsic conductivity is harmful for the thermoelectric efficiency enhancement since thermal excitation of the electron-hole pairs reduces the Seebeck coefficient and increases the thermal conductivity.

The Smaller the Better: Hosting Trivalent Rare-Earth Guests in Cu–P Clathrate Cages

Summary The most striking difference between the trivalent rare-earth cations and their alkali and alkaline-earth peers is the presence of localized 4 f electrons. Placing trivalent rare-earth cations inside fullerene molecules or in between blocks of intermetallics has given rise to a plethora of fascinating properties and materials. A long-sought-after yet undiscovered material is a semiconducting compound with rare-earth cations situated inside the oversized polyhedral cages of a three-dimensional framework. In this work, we present a synthesis of unconventional clathrates, Ba 8−x R x Cu 16 P 30 , with the smallest pentagonal dodecahedral cages encapsulating La 3+ and Ce 3+ . Their composition and crystal structure were unambiguously determined by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances hole mobility and reduces hole concentration, resulting in a drastic (700%) increase in the thermoelectric performance.

Thermal conductivity engineering in width-modulated silicon nanowires and thermoelectric efficiency enhancement

Width-modulated nanowires have been proposed as efficient thermoelectric materials. Here, the electron and phonon transport properties and the thermoelectric efficiency are discussed for dimensions above the quantum confinement regime. The thermal conductivity decreases dramatically in the presence of thin constrictions due to their ballistic thermal resistance. It shows a scaling behavior upon the width-modulation rate that allows for thermal conductivity engineering. The electron conductivity also decreases due to enhanced boundary scattering by the constrictions. The effect of boundary scattering is weaker for electrons than for phonons and the overall thermoelectric efficiency is enhanced. A ZT enhancement by a factor of 20–30 is predicted for width-modulated nanowires compared to bulk silicon. Our findings indicate that width-modulated nanostructures are promising for developing silicon nanostructures with high thermoelectric efficiency.

Mechanisms of thermoelectric efficiency enhancement in Lu-doped Bi2Te3

The LuxBi2−xTe3 thermoelectrics with x = 0, 0.05, 0.1 and 0.2 have been prepared by microwave-solvothermal method and spark plasma sintering. All the compositions are semiconductors of n-type conductivity. It was found that electron concentration increases and electron mobility decreases with x increasing. The Lu doping results in remarkable increase of the thermoelectric figure-of-merit from ∼0.4 for undoped Bi2Te3 up to ∼0.9 for Bi1.9Lu0.1Te3. Enhancing the thermoelectric efficiency at the doping is originated from: (i) increase of the electron concentration since the Lu atoms behave as donors in the Bi2Te3 lattice that decreases the specific electrical resistance, (ii) increase of the Seebeck coefficient via increase of the density-of-states effective mass for conduction band, (iii) decrease of the total thermal conductivity via forming the point defects like antisite defects and Lu atoms substituting for the Bi sites. Formation of narrow non-parabolic impurity band lying near the Fermi energy with sharp density of states is believed to be responsible for increasing the density-of-states effective mass and decreasing the electron contribution to the total thermal conductivity.

Enhancement of thermoelectric efficiency in Bi2Te3 via rare earth element doping

The Bi2Te3, Bi1.9Lu0.1Te3 and Bi1.9Tm0.1Te3 thermoelectrics of n-type conductivity were prepared by microwave-solvothermal method and spark plasma sintering. At the Lu and Tm doping, the Seebeck coefficient increases, while the specific electrical conductivity and total thermal conductivity decreases resulting in thermoelectric efficiency enhancement of Bi2Te3. It is believed that the thermoelectric efficiency can enhance mainly due to formation of narrow impurity Lu or Tm band with high and sharp density of states near the Fermi level. Both increase of the density-of-states effective mass of electrons and decrease of electronic contribution to the total thermal conductivity take place in this case.

Limited thermal transport in rippled graphene induced by bi-axial strain for thermoelectric applications

Among efforts made to improve thermoelectric efficiency, the use of structurally modified graphene nanomaterials as thermoelectric matter are one of the promising strategies owing to their fascinating physical and electrical properties, and these materials are anticipated to be less thermally conductive than regular graphene structures, as a result of an additional phonon scattering introduced at the modified surfaces. In this study, we explore the thermal conductivity behaviors of strain-induced rippled graphene sheets by varying the ripple amplitude, periodicity, and dimensions of the structure. We introduce a technique which enables creation of a graphene sheet with evenly distributed ripples in molecular dynamics simulation, and the Green-Kubo linear response theory is used to calculate the thermal conductivity of the structures of interest. The results reveal the reduction of thermal conductivity with the greater degree of strain, the smaller system dimension, and the shorter ripple wavelength, which, in turn, could lead to the thermoelectric efficiency enhancement. This work has significance in that it presents the capability of generating repeated and controllable patterns in molecular dynamics, and so, it enables the atomic-level transport study in the regularly patterned two-dimensional surface or in any structures with a specified degree of strain.

Large enhancement in thermoelectric efficiency of quantum dot junctions due to increase of level degeneracy

It is theoretically demonstrated that the figure of merit ($ZT$) of quantum dot (QD) junctions can be significantly enhanced when the degree of degeneracy of the energy levels involved in electron transport is increased. The theory is based on the the Green-function approach in the Coulomb blockade regime by including all correlation functions resulting from electron-electron interactions associated with the degenerate levels ($L$). We found that electrical conductance ($G_e$) as well as electron thermal conductance ($\kappa_e$) are highly dependent on the level degeneracy ($L$), whereas the Seebeck coefficient ($S$) is not. Therefore, the large enhancement of $ZT$ is mainly attributed to the increase of $G_e$ when the phonon thermal conductance ($\kappa_{ph}$) dominates the heat transport of QD junction system. In the serially coupled double-QD case, we also obtain a large enhancement of $ZT$ arising from higher $L$. Unlike $G_e$ and $\kappa_e$, $S$ is found almost independent on electron inter-dot hopping strength.

Enhancement of thermoelectric efficiency by quantum interference effects in trilayer silicene flakes

In recent years, the enhancement of thermoelectric efficiencies has been accomplished in nanoscale systems by making use of quantum effects. We exploit the presence of quantum interference phenomena such as bound states in the continuum and Fano antiresonances in trilayer silicene flakes to produce sharp changes in the electronic transmission of the system. By applying symmetric gate voltages the thermoelectric properties can be tuned and, for particular flake lengths, a great enhancement of the figure of merit can be achieved. We show that the most favorable configurations are those in which the electronic transmission is dominated by the coupling of bound states to the continuum, tuned by an external gate.