Thermoelectric Semiconductor Research Articles

Origins of three‐dimensional charge and two‐dimensional phonon transports in Pnma phase PbSnSe2 thermoelectric crystal

AbstractRecently, PbSnSe2 alloy was found to exhibit a large hysteresis effect on transport properties, demonstrating its significant potential for thermoelectric applications. Using ab initio approaches, we studied the carrier transport properties of PbSnSe2 crystal, which is a special case of the alloy with the shortest‐range order. A peak power factor of 134.2 μW cm−1 K−2 was found along the cross‐plane direction in the n‐type PbSnSe2 at a doping concentration of 7 × 1020 cm−3 at 700 K. This high power factor originates from delocalized p electrons between intra‐plane Pb–Se pairs and between cross‐plane Sn–Se pairs that can build up transport channels for conducting electrons, leading to a high electrical conductivity of 5.9 × 105 S m−1. Introducing Pb atoms into Pnma phase SnSe can decrease the phonon group velocities and enhance the phonon–phonon scatterings, leading to a low thermal conductivity of 0.53 W m−1 K−1 at 700 K along the cross‐plane direction. The calculated peak ZT of ~3 along the cross‐plane direction at an n‐type doping concentration of around 5 × 1019 cm−3, which represents a theoretical upper limit for an idealized PbSnSe2 crystal. This work interprets the origins of three‐dimensional charge and two‐dimensional phonon transport behavior in PbSnSe2 and demonstrates that such crystals are promising high‐performance thermoelectric semiconductors.

Towards a new chalcopyrite high-performance thermoelectric semiconductor Cu3InSnSe5 by entropy engineering

A new semiconductor Cu3InSnSe5 is introduced by entropy driven alloying equimolar ratio CuInSe2 and Cu2SnSe3. Cu3InSnSe5 is a p-type semiconductor (Eg ∼0.41 eV) and crystallizes in the chalcopyrite structure with I4_2 m space group. Our density functional theory calculations show that Cu3InSnSe5 exhibits an electronic band structure with multiple valance band peaks, rendering a large density of state effective mass m* of 1.8 me. Therefore, Cu3InSnSe5 has a high power factor of 7.59 μW cm−1 K−2 at 773 K. In addition, Cu3InSnSe5 also has a low lattice thermal conductivity (0.34 W m−1 K−1 at 773 K) owing to its severe lattice distortion arose by entropy enhancement. As a result, the figure of merit reaches as high as 1.08 at 773 K for Cu3InSnSe5. Furthermore, electronic band engineering is adopted to enhance the carrier concentration and m* of Cu3InSnSe5 via the substitution of In for Sn, resulting in ∼28% enhancement in power factor, ∼21% increment in ZT (1.31 at 773 K), and ∼10% enhancement in average ZT (∼ 0.67 at 473 – 773 K) for Cu3In1.01Sn0.99Se5 compared with Cu3InSnSe5 itself. Our work shows Cu3InSnSe5 should be a promising candidate for thermoelectric power generation at medium temperature.

Improve description of electronic structure of layer material Bi2O2Te: A DFT+ U + V calculation

The conventional first-principles density-functional theory (DFT) predicts a negative bandgap of the thermoelectric semiconductor Bi2O2Te, which needs to be corrected. To enable a higher-level precise calculation, in this report, we include the self-consistent on-site [Formula: see text] and inter-site [Formula: see text] interactions in our studies, the so-called [Formula: see text] method, and demonstrate that it significantly improves the description of excited states of Bi2O2Te. The on-site interactions of Te-p and O-p play an essential role and substantially improve the band gap of Bi2O2Te. Inter-site interaction between Bi-s, Bi-p, and O-p within the [Bi2O2] layer and between the intercalated Te layer and the [Bi2O2] layer further increases the band gap. Thermoelectric coefficient calculations show a significant Seebeck coefficient and the power factor in p-type doping, which originates from the intercalated Te layer.

Stacking fault-induced strengthening mechanism in thermoelectric semiconductor Bi2Te3

Stacking fault-induced strengthening mechanism in thermoelectric semiconductor Bi2Te3

A Novel Method to Analyze the Relationship between Thermoelectric Coefficient and Energy Disorder of Any Density of States in an Organic Semiconductor.

In this work, a unified method is proposed for analyzing the relationship between the Seebeck coefficient and the energy disorder of organic semiconductors at any multi-parameter density of states (DOS) to study carrier transport in disordered thermoelectric organic semiconductors and the physical meaning of improved DOS parameters. By introducing the Gibbs entropy, a new multi-parameter DOS and traditional Gaussian DOS are used to verify this method, and the simulated result of this method can well fit the experiment data obtained on three organic devices. In particular, the impact of DOS parameters on the Gibbs entropy can also influence the impact of the energy disorder on the Seebeck coefficient.

Current Control System for the Peltier Element in a Thermoelectric Cooling Device for Cooling the Human Head

. Thermoelectric semiconductor devices have been widely introduced in various sectors of the national economy. Methods of local thermal exposure are widely used in medical practice in the treatment and prevention of various diseases, such as mechanical injuries and diseases of joints and muscles, pain in the gastrointestinal tract, cholelithiasis and kidney stone disease, neuroses, arthrosis and arthritis, pharyngitis, tonsillitis, chronic fatigue, etc. At the same time, the thermal effect has a significant impact on the energy balance of the body. Under the influence of heat, blood and lymphatic vessels expand, improving blood circulation in many internal organs. The presence of such a device in medicine requires the creation of thermostats capable of influencing a local biophysical object using the Peltier element. This article discusses the development of a mathematical model for human head cooling devices using Peltier elements

Atomic simulation of crystal orientation and workpiece composition effect on nano-scratching of SiGe alloy

Silicon–germanium (SiGe) alloy is a new semiconductor material of great interest in thermoelectric devices, optoelectronic devices, infrared detectors, and semiconductor industry. In the present work, molecular dynamics simulation was conducted to investigate the deformation behavior in nano-scratching of SiGe alloy. The effect of scratching direction and Ge composition on material removal mechanism was discussed, aiming to understand the nanoscale deformation mechanism of SiGe alloy. The simulation results indicate that the machining direction and Ge composition have significant influences on the atomic flow and chip formation during nano-scratching. Besides, less subsurface damage and elastic recovery are observed when scratching along the (011)[100] direction with higher Ge composition. The highest crystal purity of the machined surface is achieved when scratching on the Si60Ge40 workpiece. Furthermore, the Ge composition has a significant influence on the workpiece temperature due to the variation of the thermal conductivity of the workpiece. This work could enrich the understanding of the deformation mechanism of SiGe alloy during nanoscale machining and open a potential to improve the machining performance of multicomponent semiconductor materials.

Long-distance transport of hot carriers due to acoustic phonon bottleneck in PbSe with room-temperature sensitive mid-infrared sensing

In the optoelectronic conversion process of semiconductors, the photo-excited carriers with energy higher than energy band edge, i.e., hot carriers, have always fast (picoseconds scale) dissipated within 100 nanometers distance through lattice scattering. Specifically, the hot carriers relaxation accounts for more than 60% energy loss in narrow bandgap semiconductor. Herein, we observe an ultralong transport of hot carriers (558 nm) by local light excitation in single-crystalline thermoelectric semiconductor PbSe via the time-resolved reflectivity dynamics. The ultraweak phonon emission of PbSe results in a long-distance thermalized carriers transport due to acoustic phonon bottleneck. Furthermore, the hot carriers effect gives rise to a self-driven (zero bias), fast (900 ns), and sensitive (D* = 1.1 × 1010 cm Hz1/2 W−1 at 3.3 μm) mid-infrared detection and imaging at room temperature. Our discovery provides an insight into optoelectronic conversion mechanism of narrow bandgap thermoelectric semiconductors with intriguing optoelectronic applications.

Dynamic Phase Transition Leading to Extraordinary Plastic Deformability of Thermoelectric SnSe2 Single Crystal

AbstractPlastic/ductile inorganic van der Waals (vdW) thermoelectric semiconductors offer transformative advantages for high‐performance flexible thermoelectric devices, which can displace the self‐charge system of wearable electronics. However, the chemical origin of their plasticity remains unclear. Here, it is reported that the exceptionally large plastic strain of the bulk SnSe2 crystal results from its polytype conversion under an external force. The SnSe2 single crystal consists of a large‐period polytype with 18R low‐symmetry structure rather than the trigonal and hexagonal‐phase that are frequently observed in the polycrystalline specimen. In situ applied pressure to the specimen drives a phase transition from low to high‐symmetry, that is, from 18R to 4H, and finally to 2H‐SnSe2. First principle calculations corroborate that the dynamic phase transition is a pressure‐activated process and only 15 MPa pressure erases their energy gaps, consistent with experimentally measured strain–stress curves. This dynamic phase transition results in superior and near isotropic plasticity along the direction parallel and perpendicular to the cleavage plane.

Nano cone ITO thin films prepared by pulsed laser deposition for surface measurement of high-temperature components

Semiconductor thin-film thermocouples (TFTCs) are widely used for temperature measurement of aero-engine components due to their large output and fast response. As a thermoelectric material, indium tin oxide (ITO) makes the device have very good thermoelectric merit because of its low resistivity, which is very suitable for the preparation of thin-film thermocouples. In this study, Pt-ITO thin-film thermocouple was fabricated on alumina ceramic substrate by pulsed laser deposition (PLD), and the microstructure and electrical properties of TFTCs prepared under different deposition conditions and annealing conditions were investigated. The results show that the ITO thin films prepared by PLD have a new type of nano cone structure and the resistivity of ITO thin films was only 2.76 × 10−4 Ω·cm when the substrate temperature was 600 °C. The Pt-ITO thin-film thermocouples can stable work for at 25–1300 °C and work in a short time at 1400 °C, and the average Seebeck coefficient is more than 50 µV/°C at 1300 °C. The response time of the prepared TFTC tested by pulsed laser is no more than 435 μs. These results provide an important basis for a potential application prospect of Pt-ITO TFTCs in the field of high-temperature measurement. It is further confirmed that the preparation of superior thermoelectric semiconductor materials by PLD is a promising method.

Engineering twin boundaries for enhancing strength and ductility of thermoelectric semiconductor PbTe

Twin boundary engineering is a potential strategy for achieving robust mechanical properties of materials. Our previous molecular dynamics simulations indicated that the nanotwin could significantly enhance the ductility of thermoelectric (TE) semiconductors PbTe due to coherent twin boundary (CTB) migration accompanied by the ‘catching bond’ at room temperature. To further improve the mechanical strength or ductility of PbTe, we investigated the role of the shear direction, the CTB orientation and the temperature on mechanical properties of nanotwinned PbTe. Under the shear stress along [11̅0] loading direction, the partial dislocations with a/6 [12̅1] and a/6 [21̅1̅] Burgers vectors are preferentially activated on (111) twin plane with higher yield strength and ultimate shear strength than that of the (111)[112̅] slip system. The nanotwinned PbTe with CTB orientation ranging from 125° to 161° has both higher fracture strain and larger ultimate shear strength than 0° CTB orientation. This is attributed to the motion of the twinning partial dislocation significantly enhancing the ductility while the blocking of dislocations by CTBs further improving the shear strength and deformability of PbTe. Moreover, the low temperature (below 100 K) energetically enables the partial dislocation to nucleate and glide on the strong Te-CTB plane, which induces successive CTB migration along Pb- and Te-CTB planes, resulting in enhanced ductility of nanotwinned PbTe.

Dense dislocations induced ductile SnTe thermoelectric semiconductor over a wide range of temperatures

Dense dislocations induced ductile SnTe thermoelectric semiconductor over a wide range of temperatures

Effect of carrier doping on the electronic states of earth-abundant Fe–Al–Si thermoelectric materials

Fe–Al–Si-based thermoelectric (FAST) materials are non-toxic and low-cost materials that can be used for autonomous power supplies to drive internet-of-things wireless sensor devices. The conduction type can be controlled by changing the Al/Si ratio, which is suitable for fabricating reliable thermoelectric power-generation modules consisting of materials with similar thermal expansion coefficients. In this work, we evaluated the electronic structures of p- and n-type FAST materials with relatively large absolute values of the Seebeck coefficient by photoemission spectroscopy to obtain deeper insight into controlling the p-n characteristics of FAST materials. The core-level spectra suggested that the FAST materials have a covalent bonding nature. The chemical-potential shift should be the dominant factor of the core-level shift, which is consistent with the expected behavior of carrier doping of thermoelectric semiconductors, that is, rigid-band-like behavior. The size of the core-level shift of ∼0.15 eV is close to the band gap of ∼0.18 eV obtained from transport measurements. The observed electronic structure can qualitatively explain the experimental results.

A Review of Nanocrystalline Film Thermoelectrics on Lead Chalcogenide Semiconductors: Progress and Application

Submicron-structured films of thermoelectric materials, exhibiting an improved thermoelectric figure of merit, are reviewed, including methods of fabrication and characterization. The review emphasizes the beneficial role of the grain boundaries in polycrystalline films. The enhanced Seebeck coefficient of lead chalcogenide films is attributed to a potential relief that is built along the grain boundaries. It scatters charge carriers with low energy and does not affect carriers with higher energy. The model that accounts for the thermoelectric properties of the films is described and assessed experimentally. The application of a flexible thermoelectric device (module) based on the nanocrystalline film thermoelectric semiconductors as high sensitivity radiation detectors is suggested.

Ni atomic disorder in ZrNiSn revealed by scanning transmission electron microscopy

Atomic disorders and defects in thermoelectric semiconductors can significantly affect their electronic and phonon transport. In this work, we report the studies of Ni atomic disorder in ZrNiSn by scanning transmission electron microscopy. Three different ZrNiSn polycrystalline and single-crystalline samples were synthesized under different processes from thermodynamically non-equilibrium conditions to more equilibrium ones, as demonstrated by characterizing their phase structure and transport properties. Atomic-resolution high-angle annular-dark-field scanning transmission electron microscopy was employed to study the Ni atomic disorder. The polycrystalline sample prepared by levitation melting exhibited a strong local composition fluctuation, while the sample after further long-term annealing and the single crystal exhibited a more uniform distribution of Ni at the 4c and 4d sites. These results reveal the evolution of Ni atomic disorder in different samples that were prepared under different thermodynamic conditions, which will be helpful to understand the Ni atomic disorder and its relationship with thermoelectric transport in the representative half-Heusler system ZrNiSn.

Toughening Thermoelectric Materials: From Mechanisms to Applications.

With the tendency of thermoelectric semiconductor devices towards miniaturization, integration, and flexibility, there is an urgent need to develop high-performance thermoelectric materials. Compared with the continuously enhanced thermoelectric properties of thermoelectric materials, the understanding of toughening mechanisms lags behind. Recent advances in thermoelectric materials with novel crystal structures show intrinsic ductility. In addition, some promising toughening strategies provide new opportunities for further improving the mechanical strength and ductility of thermoelectric materials. The synergistic mechanisms between microstructure-mechanical performances are expected to show a large set of potential applications in flexible thermoelectric devices. This review explores enlightening research into recent intrinsically ductile thermoelectric materials and promising toughening strategies of thermoelectric materials to elucidate their applications in the field of flexible thermoelectric devices.

High-performance non-Fermi-liquid metallic thermoelectric materials

Searching for high-performance thermoelectric (TE) materials in the paradigm of narrow-bandgap semiconductors is hampered by a bottleneck. Here we report on the discovery of metallic compounds, TiFexCu2x−1Sb and TiFe1.33Sb, showing the thermopower exceeding many TE semiconductors and the dimensionless figure of merits zTs comparable with the state-of-the-art TE materials. A quasi-linear temperature (T) dependent electrical resistivity in 2–700 K and the logarithmic T-dependent electronic specific heat at low temperature coexist with the high thermopower, highlighting the strong intercoupling of the non-Fermi-liquid (NFL) quantum critical behavior of electrons with TE transports. Electronic structure analysis reveals a competition between the antiferromagnetic (AFM) ordering and Kondo-like spin compensation as well as a parallel two-channel Kondo effect. The T-dependent magnetic susceptibility agrees with the quantum critical scenario of strong local correlation. Our work demonstrates the correlation among high TE performance, NFL quantum criticality, and magnetic fluctuation, which opens up directions for future research.

Highly deformable Ag2Te1-xSex-based thermoelectric compounds

Thermoelectric semiconductors are crucial for many critical applications, but are also universally fragile, which greatly limits the development of room temperature flexible thermoelectric devices. Herein, an extraordinary deformability at room temperature and high thermoelectric performance are simultaneously realized in wide composition of Ag2Te1-xSex (x = 0–0.2) compounds with monoclinic structure. An average compressive strain rate of 24% at room temperature is attained for the pristine Ag2Te compound. Moreover, a tensile strain rate of 43% is measured at room temperature using the in-situ transmission electron microscopy. First Principles calculations and in-situ transmission electron microscope tensile test results indicate that the Ag2Te compound is inclined to slip along the (−102) [010] plane under external forces due to a larger ratio between the cleavage energy (Ec) and the slip energy barrier. The slipping process generates high concentrations of dislocations, deformations, and amorphous structures, which together dissipate the externally applied load energy, yielding superior deformability. Meanwhile, the maximum dimensionless figure of merit ZT of 0.61 is obtained at 380 K. This study demonstrates that Ag2Te-based compounds are promising for the fabrication of flexible thermoelectric devices in applications, such as wearable, room temperature electronic gadgets.

Flexible thermoelectrics: From energy harvesting to human–machine interaction

Thermoelectrics is the simplest technology applicable for direct energy conversion between heat and electricity. After over 60 years of fruitful research efforts, recent boom in flexible electronics has promoted the rapid development of flexible thermoelectrics with rising performances, discovery of new materials and concepts, unconventional device configuration, and emerging applications not possible for traditional thermoelectric (TE) semiconductors. In this Perspective, we first overview representative flexible TE materials, then discuss recent breakthroughs for flexible TE devices assembled from various types of TE materials employing different technical routes. They exhibit promising power generation and sensing performances, and aim for applications in wearable electronics, such as the power supply harvesting heat from body for low-power electronics, temperature sensors for tactile e-skin, and newly emerged application as a thermo-haptic device in an extended reality system.

Pressure induced bands convergence and strength enhancement in thermoelectric semiconductor β-InSe

The semiconductor InSe possesses an exceptional ductility at room temperature, but its weak electronic transport properties leads to the low thermoelectric properties, limiting its applications in flexible thermoelectric devices. In this work, we applied first principles to find that the hydrostatic pressure can remarkably improve the thermoelectric and mechanical properties of β-InSe. The multiple conduction bands convergence is observed at the hydrostatic pressure of 5 GPa, resulting in a maximum zT value of 0.235 at 300 K, which is 170 % higher than the intrinsic zT value of 0.087. The point defect calculations suggest that In0.96Pb0.04Se or InSe0.96Cl0.04 could obtain the optimal carrier concentration of 7.65 × 1019 cm−3 with the highest zT value. In addition, we find that the (001)/<110>slip system of InSe exhibits the lowest ideal shear strength of 0.68 GPa, due to the weak interlayered van der Waals SeSe bonds. While the hydrostatic pressure can reduce the bond lengths and strengthen the van der Waals SeSe bonds. At 5 GPa, a maximum stretching force constant of van der Waals SeSe bond is obtained, giving rise to a maximum shear ideal strength of 1.45 GPa, which is 113 % higher than that without pressure. This hydrostatic pressure induced strain engineering strategy provides a theoretical guidance to synthesize high-performance thermoelectric β-InSe with robust mechanical properties.