High Thermoelectric Properties Research Articles

Obtaining higher manganese silicide films with high thermoelectric properties

This article provides information about the process of obtaining a Mn4Si7 film by magnetron sputtering, its high thermoelectric properties, and the possibility of using the resulting film in instrument-making production. Using the magnetron sputtering method, a thin Mn4Si7 film was obtained, and the composition and structure were studied by a scanning electron microscope. Two-stage cleaning of the silicon surface was used in work. Resistivity was determined by the four-probe method, thermoelectric properties, by the two-probe method. The bandwidth of the Mn4Si7/SiO2 film was measured on a high-precision spectrometer according to the law of light reflection. It is shown that the thermoelectric power of the Mn4Si7 film increases during the transition from the amorphous state to the nanocrystalline one, which is associated with the selective scattering of charge carriers at the boundaries of nanoclusters and Mn4Si7 on SiO2/Si have high speed and high sensitivity. It is shown that this film can be used in thermal detectors radiation waves in the visible and IR ranges.

A ferromagnetic composite of PEDOT:PSS and nitrogen-graphene decorated with copper oxide nanoparticles with high anisotropic thermoelectric properties

PP/CuONG system has been designed for high TE properties. CuONG plays a dual role in increasing S by the dipole and interfacial polarizations and the spin Seebeck coefficient and lowering k by phonons scattering and gaseous (N-/static air) environs.

Durable and stretchable nanocomposite ionogels with high thermoelectric property for low-grade heat harvesting

Durable and stretchable nanocomposite ionogels with high thermoelectric property for low-grade heat harvesting

Broad Temperature Plateau for High Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 by 3D Printing-Driven Defect Engineering

High-energy-conversion Bi2Te3-based thermoelectric generators (TEGs) are needed to ensure that the assembled material has a high value of average figure of merit (ZTave). However, the inferior ZTave of the n-type leg severely restricts the large-scale applications of Bi2Te3-based TEGs. In this study, we achieved and reported a high peak ZT (1.33) of three-dimensional (3D)-printing n-type Bi2Te2.7Se0.3. In addition, a superior ZTave of 1.23 at a temperature ranging from 300 to 500 K was achieved. The high value of ZTave was obtained by synergistically optimizing the electronic- and phonon-transport properties using the 3D-printing-driven defect engineering. The nonequilibrium solidification mechanism facilitated the multiscale defects formed during the 3D-printed process. Among the defects formed, the nanotwins triggered the energy-filtering effect, thus enhancing the Seebeck coefficient at a temperature range of 300-500 K. The effective scattering of wide-frequency phonons by multiscale defects reduced the lattice thermal conductivity close to the theoretical minimum of ∼0.35 W m-1 k-1. Given the advantages of 3D printing in freeform device shapes, we assembled and measured bionic honeycomb-shaped single-leg TEGs, exhibiting a record-high energy conversion efficiency (10.2%). This work demonstrates the great potential of defect engineering driven by selective laser melting 3D-printing technology for the rational design of advanced n-type Bi2Te2.7Se0.3 thermoelectric material.

Stability, Electronic Structures, and Thermoelectric Properties of 2D Janus LiZnX (X = N, P, As)

In the framework of density functional theory, we investigated the structure and mechanical properties of Janus monolayer LiZnX (X = N, P, As). The electronic and phonon transport preferences were calculated on the basis of the Boltzmann transport theory. We discovered that the band gaps of these three single-layers are 0.93–2.17 eV, and they are direct band semiconductors. Also, the monolayers exhibit relatively high electron and hole mobilities of ∼103 cm2·V–1·s–1 and ∼102 cm2·V–1·s–1, respectively. Besides, they possess the high Seebeck coefficient (0.16–1.99 mV·K–1), large conductivity (∼107 Ω–1·m–1), and low lattice thermal conductivity (0.52–3.59 W·m–1·K–1). Hence, all monolayers show high thermoelectric properties, with favorable ZT values of 0.36, 0.78, and 1.22 for p-type doping LiZnN, LiZnP, and LiZnAs at room temperature, even up to 0.48–4.16 at 500 K. In general, the monolayer LiZnX (X = N, P, As) are promising for applications in thermoelectric and microelectronic devices.

High thermoelectric properties of shear-exfoliation-derived TiS2-AgSnSe2 nano-composites via ionized impurity scattering

Liquid-assisted shear exfoliation (LASE) has been proved previously to be a facile approach for micro-texture engineering and TE performance optimization for TiS2. Furtherly in this work, ionized impurity scattering was introduced by incorporating 4 mol% nano-AgSnSe2 via LASE. In a specific temperature range of 373–573 K, Seebeck coefficient increased exceptionally in correspondence to an exceptional variation of electrical conductivity with growing temperature, featuring an ionized impurity scattering characteristic and contributing to a record high power factor of 18.2 μW cm−1 K−2 at 573 K in the LASE-derived nanocomposite. Moreover, lattice thermal conductivity was further reduced because of enhanced phonon scattering due to intercalation, impurity, and enhanced grain boundary density. Ultimately, a highest ZT of 0.78 at 673 K as a renewed record for TiS2-based materials was achieved, demonstrating an improved effectiveness of the combination of LASE and ionized impurity scattering in optimization of TE performance of TiS2-like layered TE materials.

Carbon-based monochalcogenides for efficient solar and heat energy harvesting

A new generation of two-dimensional (2D) material has captivated significant attention in the energy conversion field owing to their promising optoelectronics and thermoelectric applications. The present work involves the systematic investigation of fundamental properties of single-layered 2D carbon-based monochalcogenides (CS, CSe, CTe) with planar, buckled and puckered geometry within the framework of density functional theory (DFT). The structural and lattice dynamics analysis disclose that puckered and buckled configurations are energetically and dynamically stable whereas planar structures depict instability. The anisotropic group velocity of longitudinal acoustic (LA) and transverse acoustic (TA) phonon modes in puckered systems may render the characteristics thermal transport properties. Additionally, for the first time, we scrutinized the thermoelectric and optical properties of these materials. At room temperature, the electron carrier mobilities are 174.698 and 160.830m2V-1s-1 of puckered and buckled CS systems, respectively are highest among all structures. The computed Seebeck coefficient, electrical conductivity and power factor manifests the high thermoelectric transport properties of puckered CS material. Further, the calculated solar parameters demonstrate an exceptionally high-power conversion efficiency of 19.61 % for puckered CTe. Present work indicates that puckered phase of CS and CTe show their potential for the heat and solar energy harvesting devices, respectively.

Ultra-low thermal conductivity through the reduced phonon lifetime by microstructural and Umklapp scattering in Sn1−xMnxSe nanostructures

Tin selenide (SnSe), a layered material with low thermal conductivity high thermoelectric properties, has recently attracted a lot of attention in the field of thermoelectrics. Herein, Sn 1−x Mn x Se is prepared by single-step hydrothermal route and the effect of Mn on the TE properties of SnSe compound were investigated. The formation of orthorhombic crystal structure is confirmed by X-ray diffraction (XRD) pattern. High crystalline nature of the sample and nanoparticles formation is observed in high resolution transmission electron microscopy (HRTEM). Thermal conductivity is obtained in the temperature range from 303 K to 653 K. The effect of Mn substitution leads to low thermal conductivity of 0.204 W/mK at 653 K, due to the shortened phonon lifetime through the various scattering mechanisms. This result demonstrates that the introduction of Mn substitution in SnSe can effectively lift the thermoelectric performance of polycrystalline SnSe via reduced thermal conductivity. ● Mn substituted SnSe samples were synthesized by hydrothermal method followed by cold pressing densification technique. ● Formation of grain boundaries, dislocations and mass fluctuation scattering synergistically reduced the phonon life time. ● Reduced phonon life time resulting in ultra-low thermal conductivity of 0.204 W/mK at 653 K.

High thermoelectric properties of disordered layered Ge1-xSnxTe semiconductors

For layered GeTe based materials, a typical strategy to reduce the thermal conductivity of the lattice is to introduce disorder and increase the lattice anharmonicity of the material, while enhancing the mass/stress field fluctuations of the sample. Due to the Sn doping, the GeTe-based material forms a disordered structure, and the resulting strong phonon scattering leads to a sharp decrease in the lattice thermal conductivity over the entire temperature range. In addition, Sn doping was able to enhance the effective mass of the material, significantly increasing the seebeck coefficient of GeTe, ZT 1.49 at 730 K. Finally, the thermoelectric properties of the GeTe-based materials synthesized by Sn doping are significantly improved.

High thermoelectric properties of P-SiGe/Sr0.9La0.1Ti0.9−xZrxNb0.1O3 composite

SrTiO3 is a high temperature thermoelectric material with calcium titanite structure that is environmentally friendly and affordable, but the high thermal conductivity at high temperatures limits its development, so how to maintain high electrical properties while reducing thermal conductivity is the most important problem facing SrTiO3. SiGe and SrTiO3 are both thermoelectric materials in the intermediate and high temperature region and have a lot of commonalities, and it is likely to obtain high thermoelectric properties through the interfacial effect of both, however, there is not any study on the compound regulation of the two. Therefore, in this study, phosphorus (P)-doped SiGe was compounded with Zr, La and Nb co-doped SrTiO3. 3 mol.%SiGe(C)/97 mol.% Sr[Formula: see text]La[Formula: see text]Ti[Formula: see text]Zr[Formula: see text]Nb[Formula: see text]O3(Zr1Si3(C)) obtained by sintering under carbon reducing atmosphere shows a relatively large power factor of and low thermal conductivity of 2.88 Wm[Formula: see text]K[Formula: see text] at 1000 K, achieve a ZT value to 0.42 at 1000 K. This is at a high level in this study of SrTiO3 composite thermoelectric materials and provides a new idea for the subsequent study of composite modulation.

Controlling the Thermal Stability, Threshold Voltage, and Thermoelectric Properties of Cuprous Sulfide Thermoelectrics.

Cu-ion liquid-like copper sulfide materials have excellent thermoelectric properties, while their applications are limited by their high-temperature decomposition and electric field-driven Cu precipitation issues. In particular, high thermoelectric properties and electric field-driven degradation are difficult to reconcile because liquid-like Cu ions are dominant in low κ and high ZT, while they cause electric field-driven degradation. Here, we control the sintering current and duration time to remove the Cu1.8S phase, thereby inhibiting the thermal decomposition of the copper sulfide samples, and introduce the Fe element into the sample matrix to improve its resistance to electric field-driven degradation. We reveal that the kinetic process of Cu1.8S phase decomposition can be suppressed by increasing the relative density of the sample or covering a layer of dense coating/film on the surface of the sample. However, as long as the Cu1.8S phase is present in the sample, it cannot maintain thermal stability above 450 °C. Furthermore, we find that the Fe element forms a nanogrid spinodal decomposition structure in the sample matrix, which acts as a barrier wall to prevent the long-range diffusion of liquid-like Cu ions and inhibit the electric field-driven degradation. The freely movable liquid-like Cu ions in the grid maintain a strong scattering of phonons in a short range, so the sample possesses low κ and high ZT. Then, a strategy to unify the high thermal decomposition temperature, high threshold voltage, and high thermoelectric performance of copper sulfide thermoelectric materials is proposed: transforming the Cu1.8S phase and introducing a liquid-like Cu ion migration barrier.

High Thermoelectric Properties of Janus WSeS Bilayer Membranes with Different Stacking Modes

High Thermoelectric Properties of Janus WSeS Bilayer Membranes with Different Stacking Modes

Extending the temperature range of high thermoelectric properties of cuprous sulfide materials

Cu-rich cuprous sulfide materials enter the superionic state after high-temperature phase transition and obtain high ZT. In order to improve the average ZT of cuprous sulfide materials, it is necessary to reduce the high-temperature phase transition temperature and extend the temperature range of high ZT. In this study, the sintered Se-alloyed cuprous sulfide blocks were heat treated to vaporize anions, so as to control the relative Cu content of the material. It is found that reducing the Cu content can make the cuprous sulfide material undergo superionic phase transition at lower temperature, so as to extend the high ZT temperature range of the material to the low temperature region and improve the average ZT. Paradoxically, the increase of Cu vacancies will inevitably increase the carrier concentration and carrier thermal conductivity, thereby increasing the total thermal conductivity of the material and reducing ZT. Therefore, only by reasonably controlling the Cu content can we achieve the coordination of low carrier concentration and low superionic phase transition temperature, and improve the average ZT of materials. Based on the experimental results, it is proposed that the effect of increasing the average ZT of cuprous sulfide only by controlling the Cu content is limited. The potential strategies of simultaneously reducing the superionic phase transition temperature and carrier concentration of Cu-rich cuprous sulfide materials to improve their average ZT are prospected.

Unveiling the Role of the Metal Oxide/Sn Perovskite Interface Leading to Low Efficiency of Sn-Perovskite Solar Cells but Providing High Thermoelectric Properties

Tin halide perovskites (THPs) have appealing optoelectronic properties similar to lead halide perovskites (LHPs). However, THPs coated on metal oxide electrodes in normal-structure perovskite solar cells exhibit poor diode rectification, resulting in poor efficiency. This poor photoelectric performance in n–i–p-based THP solar cells is in contrast with LHP solar cells. We report that this deficient performance of THP solar cells is triggered by the defect states of the metal oxide layer. The defect states of the metal oxide can trap the electrons from the THP, leading to the prompt formation of Sn(IV), which will increase the carrier density and lead to poor photoelectric performance. This observation was supported by the ultraviolet-photoelectron spectroscopic measurements of inorganic thin films Al2O3, SnO2, TiO2, ZnO, and ZrO2. However, this self-doping phenomenon resulting in the increase in carrier density can be applied to thermoelectric studies. Using CsSnI3/ZrO2 nanocomposites as thermoelectric active layers, we report a power factor of 186.58 μW/mK2 measured at room temperature, which is better than the 148.61 μW/mK2 of the original CsSnI3 thin film.

Environmentally Tolerant Ionic Hydrogel with High Power Density for Low-Grade Heat Harvesting.

Harvesting low-grade heat by an ionic hydrogel thermoelectric generator (ITEG) into useful electricity is promising to power flexible electronics. However, the poor environmental tolerance of the ionic hydrogel limits its application. Herein, we demonstrate an ITEG with high thermoelectric properties, as well as excellent capabilities of water retention, freezing resistance, and self-regeneration. The obtained ITEG can maintain the original water content at ambient conditions (302 K, 65% relative humidity (RH)) for 7 days and keep unfreezing at a low temperature (253 K). It can even be self-regenerated and recovered to its original state after a water loss in high-temperature conditions. Furthermore, a high ionic Seebeck coefficient of 11.3 mV K-1 and an impressive power density of 167.90 mW m-2 are achieved under a temperature difference of 20 K. A high power density of 60.00 mW m-2 can also be maintained even at 258 K. After drying and regeneration, ITEG-re could even exhibit a higher ionic Seebeck coefficient of 11.8 mV K-1. Successful lighting of light-emitting diodes (LEDs) and charging of capacitors demonstrate the great potential of ITEG to provide continuous energy supply for powering flexible electronics.

Regulating Multiscale Defects to Enhance the Thermoelectric Performance of Ca0.87Ag0.1Dy0.03MnO3 Ceramics.

Achieving high thermoelectric properties of CaMnO3 ceramics is significant for its applications at high temperature. Herein, Ca0.87Ag0.1Dy0.03MnO3 ceramics with plate-like template seeds additives were prepared by using a solid-state reaction method. The multiscale defects, including grain boundaries, oxygen defects, and Ag nanoprecipitations, which were regulated by the different sintering atmospheres, were beneficial for electron transport and phonon scattering. The grain boundaries as coherent interfaces could act as an alternative phonon scattering source. Oxygen vacancies coupled with Ag nanoprecipitations were verified by geometric phase analysis and annular bright-field analysis. The decrement in oxygen vacancies concentration strongly depended on the enriched oxygen environment, which could reduce electrical resistivities. Compared to the sample sintered at Ar atmosphere, a 17.5 times increment in power factor and a 20.1% reduction of the total thermal conductivity were obtained for the sample sintered at O2 atmosphere. As a result, the maximum ZT value of 0.22 was obtained at 500 °C. It is an effective way for improving the thermoelectric performance of oxide-based thermoelectric materials.

High thermoelectric and mechanical performance in the n-type polycrystalline SnSe incorporated with multi-walled carbon nanotubes

• A high ZT of ∼1.0 at 773 K and a high vickers hardness of >50 are simultaneously achieved in n-type SnSe. • MWCNTs act as “bridges” to accelerate the electron transport between n-SnSe grains. • MWCNTs act as phonon scattering centers to suppress the lattice thermal conductivity. • MWCNTs act as “binders” to bond adjacent n-SnSe grains and strengthen the hardness. In this study, we introduce multi-walled carbon nanotubes (MWCNTs) in Pb/I co-doped n-type polycrystal SnSe to simultaneously improve its thermoelectric and mechanical properties for the first time. The introduced MWCNTs act as the “bridges” to accelerate the electron carrier transport between SnSe grains, leading to significantly increased electrical conductivity from 32.6 to 45.7 S cm −1 at 773 K, which contributes to an enhanced power factor of ∼5.0 μW cm −1 K − 2 at this temperature. Although MWCNTs possess high intrinsic thermal conductivities, these MWCNTs, acting as nanoinclusions in the SnSe matrix to form the dense interfaces between SnSe and MWCNTs, provide extra heat-carrying phonon scattering centers, leading to a slightly reduced lattice thermal conductivity of only 0.34 W m − 1 K − 2 at 773 K and in turn, a high ZT of ∼1.0 at this temperature. Furthermore, the introduced MWCNTs can simultaneously act as the “binders” to bond adjacent grains, significantly improving the mechanical properties of SnSe by boosting its Vickers hardness from 39.5 to 50.5. This work indicates that our facile approach can achieve high thermoelectric and mechanical properties in n-type SnSe polycrystals with a considerable potential for applying to thermoelectric devices as n-type elements.

Focusing on the Structural, Electronic, Optic and Elastic Behaviours of RhBiSe Compound by Ab-initio Calculations

Some physical features such as structural, electronic, optic and elastic of RhBiSe compound were investigated theoretically by Density Functional Theory within Generalized Gradient Approximation. The lattice parameter, total ground state energy, bond types and lengths were calculated in the structural features frame. Focusing on the electronic properties has shown that RhBiSe is a semiconductor with an indirect band gap. The density of states and partial density of states were also demonstrated. Fundamental optic features obtained and it is noticed that RhBiSe is very convenient for the optical application areas such as optoelectronic devices. It was also exhibited that RhBiSe is a fragile material. The calculations on elastic features also revealed that RhBiSe is a mechanically stable, elastically anisotropic material with a high thermoelectric conductivity property.

Mechanically Flexible Thermoelectric Hybrid Thin Films by Introduction of PEDOT:PSS in Nanoporous Ca3Co4O9.

Nanoporous Ca3Co4O9 exhibits high thermoelectric properties and low thermal conductivity and can be made mechanically flexible by nanostructural design. To improve the mechanical flexibility with retained thermoelectric properties near room temperature, however, it is desirable to incorporate an organic filler in this nanoporous inorganic matrix material. Here, double-layer nanoporous Ca3Co4O9/PEDOT:PSS thin films were synthesized by spin-coating PEDOT:PSS into the nanopores. The obtained hybrid films exhibit high Seebeck coefficient (∼+130 μV/K) and thermoelectric power factor (0.75 μW cm–1 K–2) at room temperature with no deterioration in electrical properties after cyclic bending tests (98% preservation of electrical conductivity after 1000 cycles bending to a bending radius of 3 mm). Compared with the nanoporous Ca3Co4O9 thin film, the mechanical flexibility of the hybrid film can be effectively improved after hybrid with PEDOT:PSS with only a slight decrease of the thermoelectric properties.

Achieving high thermoelectric properties in PEDOT:PSS/SWCNTs composite films by a combination of dimethyl sulfoxide doping and NaBH4 dedoping

Incorporating single-walled carbon nanotubes (SWCNTs) can effectively optimize the thermoelectric properties of poly(3,4-ethylenedioxithiophene):poly(styrenesulfonate) (PEDOT:PSS). However, the thermoelectric performance of flexible PEDOT:PSS/SWCNTs composites is still undesired due to the contradiction between electrical conductivity (σ) and Seebeck coefficient (S). Here, we adopt dimethyl sulfoxide (DMSO) doping and NaBH4 dedoping to achieve high thermoelectric properties of PEDOT:PSS/SWCNTs composite film by simultaneously improving σ and S. The PEDOT:PSS/SWCNTs composite with 60 wt% SWCNTs exhibits the highest power factor of 411 μW m−1 K−2, originating from high σ of 1718 S cm−1 and high S of 49 μV K−1. The high σ is derived from the improved carrier transport by insulating PSS removal, the transition of PEDOT chains with ordered stacking structures, and the formed three-dimensional conductive network between PEDOT:PSS and SWCNTs. As well, the decreased carrier concentration induced by the reduction of oxidation level of PEDOT:PSS after NaBH4 dedoping leads to a compromise between σ and S. Besides, a home-made thermoelectric device, fabricated using eight pieces of as-prepared PEDOT:PSS/SWCNTs composite films, shows an output power of 391 nW at a temperature difference of 20 K. Our work indicates that the combination of DMSO doping and NaBH4 dedoping can extend to promote the thermoelectric properties of flexible thermoelectric composite films.