Thermoelectric Figure Of Merit Research Articles

Copper-Enriched Nanostructured Conductive Thermoelectric Copper(I) Iodide Films Obtained by Chemical Solution Deposition on Flexible Substrates

The objects of our research are flexible thin-film thermoelectric materials with nanostructured CuI layers 0.5–1.0 μm thick, fabricated by the chemical solution method Successive Ionic Layer Adsorption and Reaction (SILAR) on flexible polyethylene terephthalate and polyimide substrates. These cubic γ-CuI films differ from films obtained by other chemical solution methods, such as spin-coating, sputtering, and inject printing, in their low resistivity due to acceptor impurities of sulfur and oxygen introduced into CuI from aqueous precursor solutions during SILAR deposition. Energy barriers at the boundaries of 18–22 nm CuI nanograins and a large number of charge carriers inside the nanograins determine the transport properties in the temperature interval 295–340 K characterized by transitions from semiconductor to metallic behavior with increasing temperature, which are typical of nanostructured degenerate semiconductors. Due to the resistivity of about 0.8 mΩ· m at 310 K and the Seebeck coefficient 101 μV/K, the thermoelectric power factor of the CuI film 1.0 μm thick on the polyimide substrate is 12.3 μW/(m · K2), which corresponds to modern thin-film p-type thermoelectric materials. It confirms the suitability of CuI films obtained by the SILAR method for the fabrication of promising inexpensive non-toxic flexible thermoelectric materials.

Mesoscopic combinatorial design of anisotropic graphitic carbon with ordered porous frameworks for thermoelectric conversion

The incorporation of carbon materials can effectively enhance the performance of thermoelectric materials. By optimizing the thermoelectric properties of the carbon scaffold, it is possible to further improve the thermoelectric performance of the prepared carbon-based composites. To elevate the thermoelectric performance of the carbon scaffold, this work introduces a novel mesoscopic design strategy, utilizing natural flake graphite to create a three-dimensional ordered porous framework. Highly controllable anisotropic conductivity and thermal conductivity of the porous graphite skeleton were achieved, by combining sizable sodium chlorine templates (37.5–250 μm) with a natural flake graphite matrix (50–150 μm). A porous graphite with high electrical conductivity and low thermal conductivity along the vertical axis was obtained by carefully regulating the parameters. The sample demonstrated exceptional thermoelectric conversion performance, achieving a thermoelectric power factor of 12.2 μW m−1 K−2 and a figure of merit value of 28.3 × 10−4. Furthermore, the thermoelectric property of the samples could be greatly improved by adding a small amount of ferric chloride, with a thermoelectric power factor reaching 41.9 × 10−4 and a thermoelectric figure of merit reaching 81.4 μW m−1 K−2. This work provides an effective scheme for the mesoscopic regulation of porous graphite carbon structures and offers a new strategy for enhancing the performance of thermoelectric generators.

Structural and thermoelectric properties of doped Bi2Te3 crystalline alloys

Bulk alloys of Bi2Te3 doped with various amounts of Se, Sb and Na were synthesized by simple melting. Structural and morphological properties have been checked using x-ray diffraction (XRD) and scanning electron microscope (SEM) observations. XRD and SEM investigations revealed that the obtained samples are of high crystallinity with the structural characteristics of the Bi2Te3 phase. Electrical and thermoelectric properties of the prepared samples were investigated over the temperature range 283–473 K. Seebeck coefficient and electrical and thermal conductivities were measured and studied as functions of temperature between 283 K and 473 K. The power factor (PF) was calculated and examined against the temperature increasing, as well. The thermoelectric figure of merit (ZT) was estimated from the materials power factor and thermal conductivity. The Sb-doped alloy exhibited the largest power factor, recorded at 285.23 µW/m.K2 at 430 K. On the other side, the Sb-doped and the Na-doped Bi2Te3 showed increased ZT than that of the pristine alloy. The maximum ZT was recorded at 1.97 for the highest Sb-doped Bi1.94Sb0.06Te3 sample, observed at 430 K. It is believed that the increased number of grain boundaries besides the decreased grain size are main reasons behind the high observed ZT in this work, especially because the phonon scattering on grain boundaries results in reducing the lattice part of the thermal conductivity.

Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration.

Metal-semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe2) nanophase within the nanocrystalline ternary skutterudite (Co(Ge1.22Sb0.22)Te1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase's role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ∼ 1.30) is attained with CGST-7 wt. % CoTe2 nanocomposite film at 655 K compared to that of pristine CGST.

A Novel Application of a Parabolic Trough Collector for Solar Cooking, Thermal Storage and Thermoelectric Energy Harvesting

The work here involves designing a solar solution for safe cooking and low-power generation intended for application in rural communities. A system was developed that combines Concentrated Solar Power (CSP) and Thermoelectric Generator (TEG) technologies. The CSP provides heat for clean cooking, and the excess heat is harvested by the TEG and converted into electrical power. A storage tank was integrated into the system, storing excess energy and serving as the medium for indirect cooking and supplying the heat required by the TEG. The Parabolic Trough Collector, having a resulting average thermal efficiency value of 21%, provided the useful energy to store over 4.25kWh of heat in the tank during the initial testing of the system. The TEG developed has four Peltier modules and attained 23W - over 80% of their rated power and a maximum conversion efficiency of 4.14% at a temperature difference of 220°C between the cold and hot surfaces of the generator. During the experiment, the TEG operation was limited to only four hours before subjecting a no-load test to assess the total energy storable from the system. The initial results from the test carried out here show the potential of the hybrid system in storing energy in the tank for an extended period and simultaneous operation of the TEG. Excess energy stored can be utilised further in providing the heat required for cooking or further electrical power generation.

Preparation of High-Performance Mn-Doped SnTe Materials at High Pressure and High Temperature.

SnTe is an environmentally friendly medium-temperature thermoelectric material, but its inherent low power factor (PF) and high lattice thermal conductivity severely limit its application. In this study, based on the fact that Mn doping can induce band convergence, the high-pressure and high-temperature (HPHT) synthesis method was used to optimize the sample preparation and shorten the synthesis cycle to 30 min. The results show that the Sn0.93Mn0.10Te sample achieves the maximum PF value of 34.00 μW cm-1 K-2 at 775 K and PFave value of 21.36 μW cm-1 K-2 between 300-875 K. Microstructure analysis shows that the high-pressure synthesis method introduces abundant grain boundaries, various grain sizes, multiple defects, and pore structures into the sample. These microscopic crystal structures can effectively scatter phonons and lower the lattice thermal conductivity. The modification of these micromorphologies results in the Sn0.92Mn0.11Te sample attaining a minimum lattice thermal conductivity of 0.45 W m-1 K-1 at 625 K. The thermoelectric figure of merit (zT) of sample Sn0.92Mn0.11Te reaches a maximum value of 1.1 at 775 K, and the zTave reaches 0.63 in the range of 300-875 K. This study indicates that the synergistic effect of Mn element doping and microstructure modification can effectively optimize the thermoelectric transport performance of SnTe materials.

Structure, Opto-electronic and Thermoelectric Properties of Tetra One Type Structured Compounds AFMgY (A = Ca–Ba and Y = P, As) for Solar Cell and Thermoelectric Applications

Structure, Opto-electronic and Thermoelectric Properties of Tetra One Type Structured Compounds AFMgY (A = Ca–Ba and Y = P, As) for Solar Cell and Thermoelectric Applications

N-DMBI Doping of Carbon Nanotube Yarns for Achieving High n-Type Thermoelectric Power Factor and Figure of Merit.

The application of carbon nanotube (CNT) yarns as thermoelectric materials for harvesting energy from low-grade waste heat including that generated by the human body, is attracting considerable attention. However, the lack of efficient n-type CNT yarns hinders their practical implementation in thermoelectric devices. This study reports efficient n-doping of CNT yarns, employing 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzimidazole-2-yl) phenyl) dimethylamine (N-DMBI) in alternative to conventional n-dopants, with o-dichlorobenzene emerging as the optimal solvent. The small molecular size of N-DMBI enables highly efficient doping within a remarkably short duration (10s) while ensuring prolonged stability in air and at high temperature (150°C). Furthermore, Joule annealing of the yarns significantly improves the n-doping efficiency. Consequently, thermoelectric power factors (PFs) of 2800, 2390, and 1534µWm-1K-2 are achieved at 200, 150, and 30°C, respectively. The intercalation of N-DMBI molecules significantly suppresses the thermal conductivity, resulting in the high figure of merit (ZT) of 1.69×10-2 at 100°C. Additionally, a π-type thermoelectric module is successfully demonstrated incorporating both p- and n-doped CNT yarns. This study offers an efficient doping strategy for achieving CNT yarns with high thermoelectric performance, contributing to the realization of lightweight and mechanically flexible CNT-based thermoelectric devices.

Modeling Temperature-Dependent Thermoelectric Performance of Magnesium-Based Compounds for Energy Conversion Efficiency Enhancement Using Intelligent Computational Methods

Eco-friendly magnesium-based thermoelectric materials have recently attracted significant attention in green refrigeration technology and wasted heat recovery applications due to their cost effectiveness, non-toxicity, and earth abundance. The energy conversion efficiency of these thermoelectric materials is controlled by a dimensionless thermoelectric figure of merit (TFM), which depends on thermal and electrical conductivity. The independent tuning of the electrical and thermal properties of these materials for TFM enhancement is challenging. The improvement in the TFM of magnesium thermoelectric materials through scattering and structural engineering is experimentally challenging, especially if multiple elements are to be incorporated at different concentrations and at different doping sites. This work models the TFM of magnesium-based thermoelectric materials with the aid of single-hidden-layer extreme learning machine (ELM) and hybrid genetic-algorithm-based support vector regression (GSVR) algorithms using operating absolute temperature, elemental ionic radii, and elemental concentration as descriptors. The developed TFM-G-GSVR model (with a Gaussian mapping function) outperforms the TFM-S-ELM model (with a sine activation function) using magnesium-based thermoelectric testing samples with improvements of 17.06%, 72%, and 73.03% based on correlation coefficient (CC), root mean square error (RMSE), and mean absolute error (MAE) assessment metrics, respectively. The developed TFM-P-GSVR (with a polynomial mapping function) also outperforms TFM-S-ELM during the testing stage, with improvements of 14.59%, 55.31%, and 62.86% using CC, RMSE, and MAE assessment metrics, respectively. Also, the developed TFM-G-ELM model (with a sigmoid activation function) shows superiority over the TFM-S-ELM model with improvements of 14.69%, 79.52%, and 83.82% for CC, RMSE, and MAE assessment yardsticks, respectively. The dependence of some selected magnesium-based thermoelectric materials on temperature and dopant concentration on TFM was investigated using the developed model, and the predicted patterns align excellently with the reported values. This unique performance demonstrated that the developed intelligent models can strengthen room-temperature magnesium-based thermoelectric materials for industrial and technological applications in addressing the global energy crisis.

Line Edge Roughness Effects on the Thermoelectric Properties of Armchair Black Phosphorene Nanoribbons

AbstractThis study delves into the thermoelectric properties of armchair black phosphorene nanoribbons while considering the presence of line edge roughness. Employing the tight‐binding method in conjunction with non‐equilibrium Green's function techniques and Landauer formulas, the impact of various parameters on thermoelectric performance is explored. These findings reveal that the electrical conductivity and, consequently, the power factor exhibits an increasing trend with expanding ribbon length and width. This behavior can be attributed to heightened collision rates, particularly in narrow ribbons, induced by line edge roughness as length increases. Remarkably, the Seebeck coefficient at the Fermi energy corresponding to the maximum power factor remains nearly constant across different widths, lengths, temperatures, and transport regimes. Furthermore, the thermoelectric figure of merit (ZT) demonstrates a positive correlation with both ribbon length and width. In narrow widths and lengths ≈1000 nm, the power factor and figure of merit exhibit an upward trend with ribbon width. However, with further increases in ribbon width, the influence of line edge roughness on thermal conductivity diminishes. Consequently, the figure of merit decreases due to the rise in thermal conductivity. Notably, the thermoelectric figure of merit is higher for short and narrow ribbons and long and wider ribbons.

Enhancing thermoelectric performance of single-walled carbon nanotube films by poly(styrene sulfonate acid) dispersing and sequential base treatment

Despite single-walled carbon nanotubes (SWCNTs) have attracted great interest for thermoelectric (TE) conversion, the strong van der Waals forces between SWCNTs cause them to aggregate into bundles with poor dispersibility, which dramatically deteriorates the charge carrier transport, and thereby induces low electrical conductivity and TE power factor. Herein, we report a facile and efficient approach to enhance TE performance of SWCNTs via the addition of poly(styrene sulfonic acid) (PSSH) and sequential base treatment. PSSH is served as a dispersant and dopant to improve the dispersibility of SWCNTs and facilitate charge carrier conduction, contributing to high electrical conductivity of 3749 ± 122 S cm−1 and power factor of 117.7 ± 3.4 μW m−1 K−2 for 20 wt% PSSH/SWCNT composite film. Further base treatment induces partial removal of insulative PSSH and de-doping effect of SWCNTs, which decreases the barriers between adjacent nanotubes junctions and modulates charge carrier transport to synergistically optimize the electrical conductivity and Seebeck coefficient. With fine-tuning base treatment temperature, the PSSH/SWCNT composite film reaches highest power factor of 160.6 ± 7.9 μW m−1 K−2, higher than pristine SWCNTs of 70.2 ± 4.4 μW m−1 K−2. This work demonstrates the feasibility of this approach to boost the TE properties of SWCNTs, exhibiting potential application for high performance renewable energy harvesting.

Ultrahigh power factor and excellent solar efficiency in two-dimensional hexagonal group-IV–V nanomaterials

The mesmerizing physical properties of two-dimensional (2D) nanomaterials have resulted in their enormous potential for high-power solar energy conversion and long-term stability devices. The present work systematically investigated the fundamental properties of monolayered 2D group-IV–V materials using a combined approach of first-principles calculations and Boltzmann transport theory, specifically the thermoelectric and optical properties, for the first time. The structural and lattice dynamics analysis disclosed the energetic, dynamical, and mechanical stabilities of 17 out of 25 considered materials. The electronic properties’ calculation shows that all the stable materials exhibit a semiconducting nature. Additionally, the energy–momentum relation in a few systems reveals the quartic Mexican-hat-like dispersion in their valence band edges. Owing to the larger depth of Mexican-hat dispersion and the larger height of density step function modes, the hole carrier mobilities of SnN (761.43 m2/Vs), GeN (422.80 m2/Vs), and SiN (108.90 m2/Vs) materials were found to be significantly higher than their electron mobilities at room temperature. The achieved high Seebeck coefficient and electrical conductivity at room temperature result in excellent thermoelectric power factors for GeN (3190 mW/mK2), SiN (1473 mW/mK2), and CAs (774 mW/mK2) materials, manifesting their potential for thermoelectric devices. Further, the calculated optical and solar parameters demonstrate an exceptionally high value (27.25%) of theoretical limits of power conversion efficiency for the SnBi material, making it a suitable candidate as a light-absorbing material in solar cell devices. The present theoretical work filters out the potential 2D group-IV–V materials for solar and heat energy-harvesting devices.

New thermoelectric semiconductors Pb5Sb12+xBi6−xSe32 with ultralow thermal conductivity

Five new semiconductors Pb5Sb12+xBi6−xSe32 (x = 0, 1, 2, 3, and 4) have been synthesized for the first time, which adopt pavonite-type structure and crystallize in monoclinic C2/m space group. The crystal structure is composed of two different types of polyhedral slabs. Slab-I is a galena-like structure motif that forms with [MSe6] (M = Pb, Sb, and Bi) octahedra and slab-II contains one octahedral [MSe6] block and paired squared pyramids [MSe5]. Pb5Sb12+xBi6−xSe32 exhibits n-type semiconductor behaviors and the remarkable Seebeck coefficient from −64.1 μV K−1 for x = 0 sample to −242 μV K−1 for x = 4 sample at 300 K. Moreover, the Pb5Sb12Bi6Se32 has the highest carrier concentration of 1.35 × 1020 cm−3 in pavonite-type materials. The complex compositions, mixed occupancies of the cations, and quasi-two-dimensional structure lead to the low lattice thermal conductivity (κlat) less than 0.48 W m−1 K−1 from 300 to 723 K, at which Pb5Sb16Bi2Se32 especially shows the ultralow value of 0.25 W m−1 K−1. As a result, the thermoelectric figure of merit, ZT ∼0.34 at 723 K, is obtained for the intrinsic Pb5Sb12Bi6Se32.

First-principles investigation of structural, electronic and thermoelectric properties of SmMg2X2 (X = P, As, Sb, Bi) zintl compounds

Structure complexity, adequate electronic character and congenital lower thermal conductivity of zintl phases result in designing thermoelectrics of tremendous efficiency. Such qualities of zintl phases embolden us to present a detailed study of SmMg2X2 (X = P, As, Sb, Bi) zintl compounds by first principles. The structural characteristics fit well with the existing data. Electronic properties of titled compounds are scrutinized by adopting PBE-GGA, TB-mBJ and hybrid (YS-PBE0) potentials. The band structure calculations through TB-mBJ and hybrid (YS-PBE0) proclaim the semiconducting behavior of compounds and there is a shrinkage of band gap by changing X anion from P to Bi. The density of states (DOS) calculation reveals that there is a major contribution of Sm-f states and Mg atom in valence band while in conduction band, the prominent role is offered by Sm-d states and p states of X anion. Similarly, the temperature-dependent thermoelectric properties are scrutinized by using BoltzTraP2 code embedded within WIEN2k software for with and without spin–orbit coupling (SOC) and also through hybrid (YS-PBE0) functional. SOC, but even more hybrid functional, has been shown to have a significant effect on the transport behavior. Optimized values of carriers’ concentration are achieved which subsidize thermoelectric parameters like power factor (PF), Seebeck coefficient ([Formula: see text] and thermoelectric figure of merit (ZT) at elevated temperature. The compounds show excellent thermoelectric performance in the studied temperature range.

All-Automated Fabrication of Freestanding and Scalable Photo-Thermoelectric Devices with High Performance.

Flexible photo-thermoelectric (PTE) devices have great application prospects in the fields of solar energy conversion, ultrabroadband light detection, etc. A suitable manufacturing process to avoid the substrate effects as well as to create a narrow transition area between p-n modules for high-performance freestanding flexible PTE devices is highly desired. Herein, an automated laser fabrication (ALF) method is reported to construct the PTE devices with rylene-diimide-doped n-type single-walled carbon nanotube (SWCNT) films. Thewet-compressing approach is developed to improve the thermoelectric power factors and figure of merit (ZT) of the SWCNT hybrid films. Then, the films are cut and patterned automatically to make PTE devices with various structures by the proposed ALF method. The freestanding PTE device with a narrow transition area of ≈2-3 µm between the p and n modules exhibits a high-power density of 0.32 µW cm-2 under the light of 200 mW cm-2, which is among the highest level for freestanding-film-based PTE devices. The results pave the way for the automatic production process of PTE devices for green power generation and ultrabroadband light detection.

Maximum power and the corresponding efficiency for a Carnot-like thermoelectric cycle based on fluctuation theorem.

Here, we investigate the maximum power and efficiency of thermoelectric generators through devising a set of protocols for the isothermal and adiabatic processes of thermoelectricity to build a Carnot-like thermoelectric cycle, with the analysis based on fluctuation theorem. The Carnot efficiency can be readily obtained for the quasistatic thermoelectric cycle with vanishing power. The maximum power-efficiency pair of the finite-time thermoelectric cycle is derived, which is found to have the identical form to that of Brownian motors characterized by the stochastic thermodynamics. However, it is of significant discrepancy compared to the linear-irreversible and endoreversible-thermodynamics based formulations. The distinction with the linear-irreversible-thermodynamics case could result from the difference in the definitions of Peltier and Seebeck coefficients in the thermoelectric cycle. As for the endoreversible thermodynamics, we argue the applicability of endoreversibility could be questionable for analyzing the Carnot-like thermoelectric cycle, due to the incompatibility of the endoreversible hypothesis that attributes the irreversibility to finite heat transfer with thermal reservoirs, though the distinction in the mathematical expressions can vanish with the assumption that the ratio of thermoelectric power factors at the high and low temperatures (γ) is equal to the square root of the temperature ratio, γ=sqrt[T_{L}/T_{H}] (this condition could significantly deviate from the practical case). Last, utilizing our models as a concise tool to evaluate the maximum power-efficiency pairs of realistic thermoelectric material, we present a case study on the n-type silicon.

Exceptional Thermoelectric Performance of Cu2(Zn,Fe,Cd)SnS4 Thin Films.

High-quality Cu2(Zn,Fe,Cd)SnS4 (CZFCTS) thin films based on the parent CZTS were prepared by aerosol-assisted chemical vapor deposition (AACVD). Substitution of Zn by Fe and Cd significantly improved the electrical transport properties, and monophasic CZFCTS thin films exhibited a maximum power factor (PF) of ∼0.22 μW cm-1 K-2 at 575 K. The quality and performance of the CZFCTS thin films were further improved by postdeposition annealing. CZFCTS thin films annealed for 24 h showed a significantly enhanced maximum PF of ∼2.4 μW cm-1 K-2 at 575 K. This is higher than all reported values for single-phase quaternary sulfide (Cu2BSnS4, B = Mn, Fe, Co, Ni) thin films and even exceeds the PF for most polycrystalline bulk materials of these sulfides. Density functional theory (DFT) calculations were performed to understand the impact of Cd and Fe substitution on the electronic properties of CZTS. It was predicted that CZFCTS would have a smaller band gap than CZTS and a higher density of states (DoS) near the Fermi level. The thermal conductivity and thermoelectric figure of merit (zT) of the CZFCTS thin films have been evaluated, yielding an estimated maximum zT range of 0.18-0.69 at 550 K. The simple processing route and improved thermoelectric performance make CZFCTS thin films extremely promising for thermoelectric energy generation.

Prediction of thermoelectric-figure-of-merit based on autoencoder and light gradient boosting machine

The evaluation of thermoelectric materials relies significantly on the thermoelectric figure of merit, ZT, which serves as a crucial parameter in assessing their properties. The accurate prediction of ZT values can be accomplished by utilizing machine learning models to learn material characteristics. However, factors such as the size of the dataset, model hyperparameters, and data quality can all impact the accuracy of machine learning. In contrast to previous research where high-dimensional features were simply discarded to transform them into low-dimensional ones, deep learning models such as autoencoder can extract more effective information. Therefore, in this article, the combination of autoencoders and the Light Gradient Boosting Machine (LightGBM) is employed to learn the chemical characteristics and ZT values of various materials. The reliability of the model was confirmed by achieving an R2 score of 0.94 during tenfold cross-validation. 130 000 materials were predicted and screened, the temperature dependence of the screened materials was studied in depth, and 13 materials with high ZT values were identified. Four of the 13 most promising candidates identified are existing thermoelectric materials, while nine are ideal candidates for future experimental studies and validation. This work utilizes autoencoders for extensive prediction and screening of promising materials, providing an effective approach for handling high-dimensional material data.

Computational identification of 2D TlPt2X3 (X = S, Se, Te) for thermoelectric and photocatalytic applications

Thermoelectric (TE) device can convert heat into electricity, and suitable photocatalyst can split water to produce hydrogen, which makes them have great potential in the field of clean energy and environmental protection. In this paper, we investigated three 2D materials, TlPt2X3 (X = S, Se, Te), which are indirect semiconductors with band-gaps of 2.11 eV, 1.85 eV, and 1.14 eV, respectively. The three single-layers show moderate mobilities (102 – 103 cm2/Vs), large Seebeck coefficients (0.66 – 1.86 mV/K), and high TE power factor (13.73 – 25.20 mW/K2m) at 300 K. Besides, due to the weak bonding and “Rattling” vibrations caused by Tl atoms, the single-layers have strong phonon–phonon scattering, and thus possess low lattice thermal conductivities of 2.34 – 4.46 W/mK. As a result, they can deliver high TE figure-of-merit of 0.53/0.63/0.52 at 300 K, and rise even further to 2.72/3.05/2.38 at 700 K. They also have appropriate REDOX potential, which satisfy the band structure requirement for overall water splitting. Also, the three single-layers also have strong absorption coefficient of ∼ 105 cm−1 in vision-ultraviolet region, which can efficiently carry out photocatalytic water splitting to produce H2. Ultimately, 2D TlPt2X3 are suitable candidates for both TE and photocatalytic applications.

Multiple conduction bands with strong valley anisotropy yielding ultrahigh thermoelectric power factors in n-type elemental Ge

Materials with high power factors are of great importance for thermoelectric power generation. However, currently most state-of-the-art thermoelectric compounds with excellent ZT values mainly benefit from thermal conductivity reduction. Herein, we report an ultrahigh power factor of 64.8 μWcm−1K−2 at 673 K in phosphorus-doped n-type elemental Ge. This is achieved because of the presence of multiple conduction bands with strong valley anisotropy that ensures both large band degeneracy and high electron mobility. By contrast, for the gallium-doped p-type Ge whose electrical properties are governed by one valence band, the optimized power factor is only 26.2 μWcm−1K−2, far less than that of Ge1-xPx. Consequently, a decent ZT of ∼0.5 at 873 K is achieved for n-type elemental Ge. Our work highlights the importance of multi-valley electronic structure and band anisotropy in optimizing thermoelectric performance.