Poor Thermoelectric Performance Research Articles

Synergetic Optimization via Indium and Rare Metal Yttrium Co-doping in GeTe Results in High Power Factor and Excellent Thermal Performance.

Excess intrinsic Ge vacancies in GeTe materials lead to excessively high hole concentration and high thermal conductivity, producing poor thermoelectric performance. Here, synergistic control and optimization of the thermoelectric transport properties and microstructure of GeTe-based materials were achieved through co-doping with In and rare earth element Y, resulting in a significant enhancement of thermoelectric performance. The Ge0.94In0.03Y0.03Te sample reached a ZTmax of 1.84 at 773 K, representing an increase of around 91% compared to the GeTe matrix. The experimental results indicate that the doping of In optimizes the band structure by introducing resonant levels and increasing the degeneracy of the valence band. Y doping introduces in situ nanoscale secondary phases and lattice distortions due to defect generation, enhancing phonon scattering and significantly reducing the κlat. This work elaborates on how co-doping with In and Y achieves the optimization of the thermoelectric performance of GeTe-based materials. While the electrical transmission characteristics are improved, the thermal conductivity is significantly reduced. For the Ge0.94In0.03Y0.03Te sample, κlat decreased to ∼0.56 W m-1 K-1 at 573 K, resulting in a ZTave of ∼0.99 over the entire temperature range, representing over 140% improvement compared to undoped GeTe. This improvement is significantly higher compared with other works on GeTe and PbTe.

High-power-density hybrid planar-type silicon thermoelectric generator with phononic nanostructures

Energy harvesting is essential for the internet-of-things networks where a tremendous number of sensors require power. Thermoelectric generators (TEGs), especially those based on silicon (Si), are a promising source of clean and sustainable energy for these sensors. Although large thermoelectric figure of merit has been reported for nanostructured Si material, however, nanostructuring has not been effectively used in device applications, and the reported performance of hybrid planar-type Si TEGs never exceeded normalized powers of 0.1μWcm−2K−2 due to the poor thermoelectric performance of Si and the suboptimal design of the devices. Here, we report a hybrid planar-type Si TEG with a normalized power of 1.3μWcm−2K−2 around room temperature. The increase in thermoelectric performance of Si by nanostructuring based on the phonon-glass electron-crystal concept and optimized three-dimensional heat-guiding structures resulted in a record-high power density. The improvement of power generation by a factor of 10 makes the once-a-day sensing applications realistic in a practical environment for the first time. In-field testing demonstrated that our Si TEG functions as a sufficient energy harvester. This demonstration paves the way for energy harvesting with a low-environmental load and cost-effective material with high throughput, a necessary condition for energy-autonomous sensor nodes for the trillion sensors universe.

Electronic transport and the thermoelectric properties of donor-doped SrTiO3

Strontium titanate (SrTiO3) is widely recognised as an environmentally-benign perovskite material with potential for thermoelectric applications. In this work we employ a systematic modelling approach to study the electronic structure and thermoelectric power factor (PF) of pure SrTiO3 and donor-doped Sr(Ti0.875M0.125)O3 (M = Cr, Mo, W, V, Nb, Ta). We find that the carrier concentration required to optimise the PF of SrTiO3 is on the order of 1021 cm−3, in line with experimental studies. Substitution at the Ti (B) site with 12.5 mol% Nb or Ta is predicted to yield the best PF among the six Group V/VI dopants examined, balancing the Seebeck coefficient and electrical conductivity, and doping with the more abundant Nb would likely give the best price/performance ratio. Although W doping can significantly improve the electrical conductivity, this is at the expense of a reduced Seebeck coefficient. The first-row elements V and Cr have a significantly different impact on the electrical properties compared to the other dopants, forming resonant levels or creating hole carriers and leading to poor thermoelectric performance compared to the second- and third-row dopants. However, the reduction in the bandgap due obtained with these dopants may make the materials suitable for other applications such as photovoltaics or photocatalysis. Our modelling reveals the critical carrier concentrations and best B-site dopants for optimising the electrical properties of SrTiO3, and our predictions are supported by good agreement with available experimental data. The work therefore highlights avenues for maximising the thermoelectric properties of this archetypal oxide material.

Suppressed lattice thermal conductivity in porous compounds for high-performance thermoelectric applications

Traditional zinc blende semiconductor materials of groups II–VI and III–V exhibit excellent electrical properties, yet suffer from oversized lattice thermal conductivity, causing poor thermoelectric performance. Herein, we have explored an alternative metastable phase of those materials, namely, porous phase. Compared with the stable zinc blende structure, which has simple crystal structure with nearly isotropic bonding feature, porous compounds exhibit complex bonding hierarchy and softened acoustic phonon modes with strong anharmonicity, reducing the lattice thermal conductivity by nearly two orders of magnitude. As an outstanding representative of porous compound family, the suppressed thermal conductivity [∼0.76 W/(m K) at room temperature] combined with enhanced Seebeck coefficient makes porous MgTe a high-performance thermoelectric material with figure of merit above unity at n-type doping and high temperature. This work highlights the important role of intrinsic porosity in design of high-performance thermoelectric materials with low lattice thermal conductivity.

Dual‐Site Doping and Low‐Angle Grain Boundaries Lead to High Thermoelectric Performance in N‐Type Bi2S3

AbstractBismuth sulfide (Bi2S3) is a promising thermoelectric material with earth‐abundant, low‐cost, and environment‐friendly constituents. However, it shows poor thermoelectric performance due to its extremely low electrical conductivity derived from the low electron concentration. Here, a high‐performance Bi2S3‐based material is reported to benefit from the Fermi level tuning by Ag and Cl co‐doping and defect engineering by introducing dense low‐angle grain boundaries. Both Ag and Cl act as donors in Bi2S3, upshifting the Fermi level. This increases the electron concentration without degrading the electron mobility, thereby obtaining improved electrical conductivity. The electron localization function (ELF) contour map indicates that interstitial Ag causes electron delocalization, showing higher electron mobility in Bi2S3. More importantly, dense low‐angle grain boundaries block phonon propagation, yielding an ultralow lattice thermal conductivity of 0.30 W m−1 K−1. Consequently, a record ZT value of ≈0.9 at 676 K is achieved in the Bi2Ag0.01S3‐0.5%BiCl3 sample.

Magnetism, electrical and thermal transport in R2Ni5C3 (R = La-Nd, Sm, Gd, Tb)

Ternary carbides R2Ni5C3 (R = La-Nd, Sm, Gd, Tb) are the only representatives of the family of interstitial carbides (i.e., compounds with the composition RxTyCz, where T is a transition metal and 2 ≤ (x + y)/z ≤ 4). The crystal structures (space group P4/mbm) of Sm2Ni5C3 [a = 8.26131(7) Å, c = 3.89090(4) Å, RB = 3.2 %, Rp = 1.3 %] and Gd2Ni5C3 [a = 8.24683(4) Å, c = 3.85398(2) Å, RB = 3.9 %, Rp = 3.6 %] are refined for the first time. They are considered to be built by distorted [R8]-cubes incorporating [CNi6]-octahedra condensed with [C2R8]-trigonal bi-prisms. The structural units are characteristic of the CaTiO3- and AlB2-prototypes, respectively. Temperature dependencies of the magnetic susceptibility, specific heat, electrical resistivity, thermal conductivity, and thermopower in the range 1.8 K (2 K) – 300 K are studied. R2Ni5C3 with R = Nd, Sm, Gd, order antiferromagnetically at TN = 3.4, 6.6, and 22.2 K, respectively. The nature of magnetic transitions in Ce2Ni5C3 at Tmag = 2.3 K and Tb2Ni5C3 at 29.4 K requires further clarification. No magnetic orderings for La2Ni5C3 (Pauli paramagnetic) and Pr2Ni5C3 (Curie-Weiss/van Vleck paramagnetic) are detected. Relatively high electrical resistivities and thermal conductivities, together with the small absolute values of Seebeck coefficients, result in poor thermoelectric performance of the R2Ni5C3 carbides. The calculated electronic structure for La2Ni5C3 indicated a rather low density of states at the Fermi level as well as its extreme sensitivity to any doping. The stabilization of the R2Ni5C3 interstitial carbides up to R = Tb is discussed assuming the rigid-band approach as well as the analysis of selected Ni-C interatomic distances.

The origin of shifted fermi level and improved thermoelectric performance of monolayer BiCuSeO under pressures

The layered BiCuSeO has been widely investigated because of high thermoelectric (TE) performance. However, there is few reports about the TE property of two-dimensional (2D) BiCuSeO so far. In this work, it is found that the Fermi level passes through the conduction band of [Bi2O2]2+ layer and the valence band of [Cu2Se2]2- layer simultaneously. Therefore, there is no band gap appeared for monolayer BiCuSeO, which would lead to very poor TE performance. First-principles calculation shows that negative hydrostatic pressure could weaken the intra-layer bonding and enhance the inter-layer coupling. Thus, the Fermi level would gradually get out of conduction and valence bands along with the increased pressure. To improve the TE performance of monolayer BiCuSeO, negative hydrostatic pressures are applied and successfully increased its band gap values from 0 eV to 0.85 eV. At the same time, an obvious band convergence near conduction band minimum (CBM) is found under the −2.22 GPa pressure. Besides, the band convergence near the Fermi level under negative pressure will greatly improve the TE performance of n- and p-type monolayer BiCuSeO.

Synthesis and Thermoelectric Properties of La-doped n-type Mg3SbBi Materials

Mg3Sb2-based materials are very promising for thermoelectric applications at low temperatures, and are strong candidates to replace n-type Bi2Te3 for cooling and power generation. Substituting Sb atoms with chalcogen elements (S, Se, Te) is a typical method of n-type doping, while doping the Mg site with Group 3 elements (Y, Sc) and Lanthanides has also been studied. Unique advantages have been recently reported. In this study, a La-containing compound, LaSb, was used to fabricate n-type Mg3SbBi. The thermoelectric properties of polycrystalline Mg3LaxSbBi (0 ≤ <i>x</i> ≤ 0.02) were investigated after synthesis by sequential processes of arc melting, ball milling, and spark plasma sintering. Undoped Mg3SbBi is p-type with poor thermoelectric performance, and switched to n-type with La doping. The electron concentration of Mg3LaxSbBi increased linearly with La content <i>x</i>, reaching up to 9.4 × 10<sup>19</sup> cm<sup>-3</sup> at <i>x</i> = 0.02. The power factor and the figure of merit were also maximized in Mg3La0.02SbBi, reaching 1.8 mW m<sup>-1</sup>K<sup>-2</sup> (573 K) and 0.89 (623 K), respectively. The lattice thermal conductivity decreased with increasing La content above ~500 K, and the minimum value of 0.73 W m<sup>-1</sup>K<sup>-1</sup> was obtained in Mg3La0.02SbBi. This study shows that La doping using LaSb provides a reliable method for n-type doping of Mg3Sb2-based materials.

Metal Complex Molecular Junctions as Thermoelectric Devices.

Single-molecule junctions and self-assembled monolayer junctions are attractive architectures for thermoelectric devices. However, given the poor thermoelectric performance of organic molecules investigated so far, molecules characterized by high conductance and Seebeck coefficient values are desired to be explored. Metal complexes are promising possible active components of high-performance thermoelectric devices given that metal-ligand combinations and functions can be made to vary to modulate the transmission functions, thus strongly influencing conductance and Seebeck coefficient. In this concept article are described recent studies wherein thermoelectric measurements were conducted on metal complex junctions. Furthermore, the potential for the use of the junctions in thermoelectric devices is discussed.

A new ternary molybdenum phospho-silicide Mo3Si2P: Phase equilibria, structural, electronic, transport and thermal properties

Here we report the successful preparation and systematical characterization of a novel molybdenum compound Mo3Si2P. As the first genuine ternary molybdenum phospho-silicide, it augments the Mo–Si–P family and may be served as an innovative archetype to develop exotic electronic states. The phase-equilibrium relation of Mo–Si–P system was studied, which defines the phase-stability region of Mo3Si2P, and a phase diagram that makes reviews on the abundant material and electronic physics in the system was established. Mo3Si2P crystallizes in a non-centrosymmetric orthorhombic structure (space group: Ama2) that appears as alternately stacking flat (Mo1)3P3 sheets and buckled (Mo2)3Si3 double-layers along the a-axis direction. The Bloch-Grüneisen-Mott model is employed to describe the T-dependent multiband metallic-conduction which is principally governed by electrons at high temperatures. The thermal-conductivity components of charge carrier and lattice vibration were extracted from κtotal by following the extended Wiedemann-Franz law. Poor thermoelectric performance is evidenced by very low thermoelectric power factor and figure-of-merit that are ascribed to small Seebeck coefficient and high thermal conductivity. Sommerfeld coefficient (γ) and Wilson ratio (RW) demonstrate that the electron correlation is extremely weak. First-principles calculations predict significant contribution from Mo-4 dx2−y2 orbital electrons to the Fermi surface of Mo3Si2P which shows different band fillings from Mo3Ge2P where dz2 electrons take the maximal occupation. Electron-phonon coupling parameter λep was calculated as 0.74, which reveals a medium interaction strength.

Electrical property enhancement and lattice thermal conductivity reduction of n-type Mg3Sb1.5Bi0.5-based Zintl compound by In&Se co-doping

Mg3Sb1.5Bi0.5-based Zintl compounds have attracted extensive attention as potential thermoelectric materials due to their earth-abundant elements. However, pure and intrinsic Mg3Sb1.5Bi0.5 manifests a poor thermoelectric performance because of its low electrical conductivity of about 3 × 102 S/m at room temperature. In this work, In and Se co-doping was carried out to optimize the thermoelectric performance of n-type Mg3Sb1.5Bi0.5-based material. The experimental results revealed that the carrier concentration and mobility of Mg3Sb1.5Bi0.5 significantly increased after In and Se co-doping, leading to an improvement of power factor. Simultaneously, lattice thermal conductivity was significantly reduced due to the large mass difference between In and Mg. A maximum zT of 1.64 at 723 K was obtained for the Mg3.17In0.03Sb1.5Bi0.49Se0.01 sample. And an average zT value of about 1.1 between 300 and 723 K was achieved, which insures its possible application at medium temperature range as a non-toxic and low-cost TE material.

Synergistic Optimization of Thermoelectric Performance in SnSe2 through co-doping: Anionic Vacancy Formation and Band Engineering

SnSe2 is a layered crystal structure material that is abundant in the Earth's crust and considered non-toxic. However, its thermoelectric properties are anisotropic due to the differences in its interlayer and intralayer electrical and thermal transport properties. The intrinsically poor thermoelectric performance of SnSe2 can be attributed to its lower electrical transport properties in its pristine condition. To address this, we developed a method involving combined mechanical alloying (MA) and spark plasma sintering (SPS) to synthesize n-type Sn-rich Cu-Br co-doped SnSe2 polycrystals. Optimization of Sn enrichment facilitated superior material selection for subsequent doping. The resulting substitutional doping induced a substantial rise in carrier concentration, leading to improved thermoelectric performance. Notably, the power factor displayed a significant increase, reaching approximately 795 µWm-1K-2 at 765 K through Cu-Br co-doping. Furthermore, density functional theory (DFT) analysis elucidated a reduced bandgap and increased degeneracy within the electronic band structure and density of states, affirming the enhancement of thermoelectric properties in Cu-Br co-doped Sn-rich SnSe2 polycrystals. Finally, a maximum figure of merit (ZT) value of 0.46 was achieved at 765 K for the Sn0.985Cu0.015Se1.92Br0.03 sample, perpendicular to the SPS pressing direction, which was nearly threefold higher than the pure SnSe1.95. This compelling outcome highlights the improved thermoelectric performance of the co-doped SnSe2 polycrystals.

Thermoelectric Properties of Cu-added Polycrystalline Bi2O2Se Oxyselenide

Bi2O2Se oxyselenide has been actively studied as a potentialn-type thermoelectric material because of its intrinsically low thermal conductivity and high Seebeck coefficient (S). However, Bi2O2Se has very low electrical conductivity (σ), resulting in relatively poor thermoelectric performance. Herein, we investigate the effect of Cu addition on the electrical and thermal transport ofn-type polycrystalline Bi2O2Se. A series of CuxBi2O2Se (x = 0, 0.0025, 0.005, and 0.0075) polycrystalline samples were synthesized by a conventional solidstate reaction. Tetragonal Bi2O2Se was successfully synthesized, and its lattice parameters gradually decreased with the addition of Cu. Further, σ decreased and the magnitude of S increased with increasing Cu content, according to the trade-off relationship between these parameters. Consequently, a maximum power factor of 0.106 mW m-1 K-2 was achieved for the sample with x = 0.0025 at 300 K, owing to the increase in the magnitude of S. The Hall carrier concentration decreased exponentially with the addition of Cu, which is mainly attributed to the possible enlargement of the band gap of the Cu-added samples. The lattice thermal conductivity decreased with increasing x, which was attributed to point-defect phonon scattering via Cu addition. Therefore, a maximumzT of 0.222 was obtained at 790 K for the Cu0.0025Bi2O2Se (x = 0.0025) sample, which was approximately 8% higher than that of the pristine Bi2O2Se sample.

High Thermoelectric Performance in AgBiSe2-Incorporated n-Type Bi2Te2.69Se0.33Cl0.03.

Bismuth telluride-based (Bi2Te3) alloys have long been considered the best thermoelectric (TE) materials at room temperature. However, the n-type Bi2Te3 alloys always exhibit poor thermoelectric performance than their p-type counterpart, which severely limits the energy conversion efficiency of thermoelectric devices. Here, we demonstrate that incorporating AgBiSe2 can concurrently regulate the electrical and thermal transport properties as well as improve the mechanical performance of n-type Bi2Te2.69Se0.33Cl0.03 for high thermoelectric performance. Among these, AgBiSe2 effectively enhanced the Seebeck coefficients of n-type Bi2Te2.69Se0.33Cl0.03 due to the reduced carrier concentration and reduced the thermal conductivity of n-type Bi2Te2.69Se0.33Cl0.03 owing to the enhanced phonon scattering by AgBiSe2 as well as its low thermal conductivity nature. Consequently, the simultaneous optimization of electrical and thermal transport properties enables us to achieve a maximum ZT of ∼1.21 (at ∼353 K) and an average ZTave of ∼1.07 (300-433 K) for 3.5 wt % AgBiSe2-incorporated Bi2Te2.69Se0.33Cl0.03, which are ∼25.62 and ∼23.36% larger than those of Bi2Te2.69Se0.33Cl0.03, respectively. This work proves that the incorporation of AgBiSe2 is an efficient way to improve the thermoelectric performance of bismuth telluride-based materials.

Enhanced Thermoelectric Efficiency through Li-Induced Phonon Softening in CuGaTe2

Thermoelectric materials convert thermal energy into electrical energy and can be a solution for the global climate crisis. For advanced thermoelectric applications, the conversion efficiency has to be high, motivating the search for materials with a high average thermoelectric figure of merit. To achieve such large thermoelectric figures of merit, the electronic properties must be maximized, and the thermal transport must be minimized over a wide temperature range. The chalcopyrite CuGaTe2 exhibits promising electronic properties but suffers from poor thermoelectric performance due to its high lattice thermal conductivity. In the present study, we perform compressive sensing lattice dynamics (CSLD) and ShengBTE calculations, which suggest that the high room temperature lattice thermal conductivity is a result of high longitudinal group velocities. To effectively reduce the thermal conductivity, we introduce lithium into three variants of CuGaTe2: pristine, Sb-doped, and Ag-doped. All compositions exhibited a significant reduction in the lattice thermal conductivity with the inclusion of lithium without any compromise to the electronic properties. By comparing the elastic moduli, we demonstrate that the reduction in the lattice thermal conductivity is to some extent the result of phonon softening. The low thermal conductivity and high power factor in Cu0.90Li0.05Ag0.05GaTe2 lead to a 56% increase in the average zT compared to the pristine sample. Due to the low cost of lithium, this approach can be adapted to chalcopyrite compounds and other thermoelectric systems to develop sustainable and affordable applications for waste heat recovery.

First-principles investigation of the significant anisotropy and ultrahigh thermoelectric efficiency of a novel two-dimensional Ga2I2S2 at room temperature

Two-dimensional (2D) thermoelectric (TE) materials have been widely developed; however, some 2D materials exhibit isotropic phonon, electron transport properties, and poor TE performance, which limit their application scope. Thus, exploring excellent anisotropic and ultrahigh-performance TE materials are very warranted. Herein, we first investigate the phonon thermal and TE properties of a novel 2D-connectivity ternary compound named Ga2I2S2. This paper comprehensively studies the phonon dispersion, phonon anharmonicity, lattice thermal conductivity, electronic structure, carrier mobility, Seebeck coefficient, electrical conductivity, and the dimensionless figure of merit (ZT) versus carrier concentration for 2D Ga2I2S2. We conclude that the in-plane lattice thermal conductivities of Ga2I2S2 at room temperature (300 K) are found to be 1.55 W mK−1 in the X-axis direction (xx-direction) and 3.82 W mK−1 in the Y-axis direction (yy-direction), which means its anisotropy ratio reaches 1.46. Simultaneously, the TE performance of p-type and n-type doping 2D Ga2I2S2 also shows significant anisotropy, giving rise to the ZT peak values of p-type doping in xx- and yy-directions being 0.81 and 1.99, respectively, and those of n-type doping reach ultrahigh values of 7.12 and 2.89 at 300 K, which are obviously higher than the reported values for p-type and n-type doping ternary compound Sn2BiX (ZT∼ 1.70 and ∼2.45 at 300 K) (2020 Nano Energy 67 104283). This work demonstrates that 2D Ga2I2S2 has high anisotropic TE conversion efficiency and can also be used as a new potential room-temperature TE material.

Rattling-like scattering behavior in ALiSb (A = Ca, Sr, Eu, Yb) Zintl phases with low thermal conductivity

In this report, for the first time TiNiSi-type Zintl phases with the nominal formulae of ALiSb (A = Ca, Sr, Eu, Yb) were systematically investigated on their thermoelectric properties. The results indicated that ALiSb Zintl phases possessed intrinsically low lattice thermal conductivity despite the simple structure. In combination of thorough crystallographic and theoretical investigation, rattling-like scattering behavior originating from the Li atoms was suggested. As a result, the pristine ALiSb materials featured decent zT values of 0.4–0.7 at 823 K. With the electrical and thermal transport properties further optimized by configuring the solid solutions such as Sr0.8Eu0.2LiSb, the material approached a maximum zT up to 1.2 at the same temperature. These breakthroughs are distinct from the previous knowledge that low thermal conductivity in Zintl phases is usually realized through complex crystal structures, and for compounds with simple structures such as the TiNiSi type it is common to have poor thermoelectric performance. Owing to such a rattling-like scattering behavior, now light-element containing Zintl phases can be a promising resource for thermoelectric considerations as well. The mechanism is surely interesting and worth of in-depth investigation.

Tuning the carrier scattering mechanism to improve the thermoelectric performance of p-type Mg3Sb1.5Bi0.5-based material by Ge doping

P-type Mg3Sb2-based Zintl compounds remain largely unexplored due to their inferior ZT values compared with n-type counterparts. The intrinsic p-type Mg3Sb1.5Bi0.5 manifests relatively poor thermoelectric performance because of its low electrical conductivity of about 3 × 102 S/m at room temperature. In this work, Ge is doped on the Bi site of Mg3Sb1.5Bi0.5, where the carrier scattering mechanism changes from ionized impurity scattering to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼1.8 to ∼24 cm2 V−1/s is obtained, thus leading to a notably enhanced electrical conductivity of 2.2 × 104 S/m from 2.9 × 102 S/m. A simultaneous reduction in lattice thermal conductivity is also achieved. Collectively, a maximum ZT value of 0.5 is obtained at 723 K in Mg3Sb1.5Bi0.47Ge0.03 with a carrier concentration of 5.02 × 1019/cm3.

Super-structured defects modulation for synergistically optimizing thermoelectric property in SnTe-based materials

Among the intriguing p-type thermoelectric IV-VI compounds, SnTe is an important alternative to both PbTe and GeTe for free of toxicity of Pb and scarcity of Ge. However, pristine SnTe has poor thermoelectric performance because of its intrinsic high hole concentration, big energy difference between L and Σ bands and high lattice thermal conductivity. In this work, In and Cd co-doping SnTe material, which combines the effect of resonant level and band convergence together, was obtained by self-propagating high-temperature synthesis (SHS) and plasma activated sintering (PAS). The generated Te vacancies are regularly arranged to form super-structured defects in the subsequent constrained hot compressing process, which include regular array of atomic defects and nanoscale precipitates. As a result, the hole concentration of the compressed SnTe-based material is reduced due to the donor doping effect of Te vacancies, and the hole mobility is remarkably improved to 372.94 cm2V−1s−1 and 66.19 cm2V−1s−1 at room temperature for the SnTe and In0.01Cd0.02Sn0.97Te material with compressibility of 35%, respectively. These atomic and nanoscale super-structured defects not only ensure superior electrical transport properties, but also bring much stronger scattering effect on phonons, thus leading to extremely low lattice thermal conductivity of 1.2 Wm−1K−1 at 888 K for the 35% compressed In0.01Cd0.02Sn0.97Te material. With synergistically optimized carrier and phonon transport behavior through resonant level engineering, band convergence engineering and super-structured defects engineering, a peak ZT value of 0.8 is achieved in In0.01Cd0.02Sn0.97Te material with compressibility of 35%. This work provides an effective strategy to realize the decoupling of electron and phonon scattering through Te vacancy-based super-structured defects modulation, and makes up an important part of multiscale microstructure tailoring for thermoelectric materials.

Two-dimensional electronic structure for high thermoelectric performance in halide perovskite Cs2Au(I)Au(III)I6.

Pb- or Sn-based halide perovskites usually exhibit poor thermoelectric performance, arising from their low electrical conductivity or oxidation state instability. It is highly desired to search for new halide perovskites with good thermoelectric properties. In this work, the thermally stable mixed-valence halide perovskite Cs2Au(I)Au(III)I6 is revealed to be a highly promising thermoelectric material with high in-plane power factor and ultralow lattice thermal conductivity using first-principles calculations. The high in-plane power factor is achieved due to the novel two-dimensional electronic structure near the Fermi level driven by the weak interaction between AuI-5d and I-p orbitals. In addition, the small group velocities and short phonon lifetimes give rise to ultralow lattice thermal conductivity in Cs2Au(I)Au(III)I6. These excellent electronic and thermal properties lead to a high ZT value, which is close to 1 at 300 K and ∼4 at 800 K. Our results suggest that the 2D electronic structure from the weak interaction between d and p crystal orbitals is a promising route to design high-efficiency halide double perovskite thermoelectric materials.