Showing papers on "Seebeck coefficient published in 2018"

3D charge and 2D phonon transports leading to high out-of-plane ZT in n-type SnSe crystals

Abstract: Thermoelectric technology enables the harvest of waste heat and its direct conversion into electricity. The conversion efficiency is determined by the materials figure of merit ZT . Here we show a maximum ZT of ~2.8 ± 0.5 at 773 kelvin in n-type tin selenide (SnSe) crystals out of plane. The thermal conductivity in layered SnSe crystals is the lowest in the out-of-plane direction [two-dimensional (2D) phonon transport]. We doped SnSe with bromine to make n-type SnSe crystals with the overlapping interlayer charge density (3D charge transport). A continuous phase transition increases the symmetry and diverges two converged conduction bands. These two factors improve carrier mobility, while preserving a large Seebeck coefficient. Our findings can be applied in 2D layered materials and provide a new strategy to enhance out-of-plane electrical transport properties without degrading thermal properties.

Plasmon induced thermoelectric effect in graphene

Abstract: Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.

Grain boundary dominated charge transport in Mg3Sb2-based compounds

Abstract: Thermally activated mobility near room temperature is a signature of detrimental scattering that limits the efficiency and figure-of-merit zT in thermoelectric semiconductors. This effect has been observed dramatically in Mg3Sb2-based compounds, but also to a lesser extent in other thermoelectric compounds. Processing samples differently or adding impurities such that this effect is less noticeable produces materials with a higher zT. Experiments suggest that the behavior is related to grain boundaries, but impurity scattering has also been proposed. However, conventional models using Matthissen's rule are not able to explain the dramatic change in the temperature dependency of conductivity or drift mobility which is observed in Mg3Sb2-based compounds. We find that it is essential to consider the grain boundary region as an effectively separate phase rather than a scattering center, taking into account the weaker screening in semiconductors compared with classical metals. By modeling a grain boundary phase with a band offset, we successfully reproduce the experimentally observed conductivity versus temperature and thermopower versus conductivity relations, which indicate an improved description of transport. The model shows good agreement with measured grain size dependencies of conductivity, opening up avenues for quantitatively engineering materials with similar behavior. Model estimates predict room for >60% improvement in the room temperature zT of Mg3.2Sb1.5Bi0.49Te0.01 if the grain boundary resistance could be eliminated.

Aqueous thermogalvanic cells with a high Seebeck coefficient for low-grade heat harvest.

Abstract: Thermogalvanic cells offer a cheap, flexible and scalable route for directly converting heat into electricity. However, achieving a high output voltage and power performance simultaneously from low-grade thermal energy remains challenging. Here, we introduce strong chaotropic cations (guanidinium) and highly soluble amide derivatives (urea) into aqueous ferri/ferrocyanide ([Fe(CN)6]4−/[Fe(CN)6]3−) electrolytes to significantly boost their thermopowers. The corresponding Seebeck coefficient and temperature-insensitive power density simultaneously increase from 1.4 to 4.2 mV K−1 and from 0.4 to 1.1 mW K−2 m−2, respectively. The results reveal that guanidinium and urea synergistically enlarge the entropy difference of the redox couple and significantly increase the Seebeck effect. As a demonstration, we design a prototype module that generates a high open-circuit voltage of 3.4 V at a small temperature difference of 18 K. This thermogalvanic cell system, which features high Seebeck coefficient and low cost, holds promise for the efficient harvest of low-grade thermal energy. Achieving high thermopower in liquid-state thermogalvanic cells is vital to realize a low-cost technology solution for thermal-to-electrical energy conversion. Here, the authors present aqueous thermogalvanic cells based on modified electrolyte with enhanced Seebeck coefficient and thermopower.

Recent Development of Thermoelectric Polymers and Composites.

Abstract: Thermoelectric materials can be used as the active materials in thermoelectric generators and as Peltier coolers for direct energy conversion between heat and electricity. Apart from inorganic thermoelectric materials, thermoelectric polymers have been receiving great attention due to their unique advantages including low cost, high mechanical flexibility, light weight, low or no toxicity, and intrinsically low thermal conductivity. The power factor of thermoelectric polymers has been continuously rising, and the highest ZT value is more than 0.25 at room temperature. The power factor can be further improved by forming composites with nanomaterials. This article provides a review of recent developments on thermoelectric polymers and polymer composites. It focuses on the relationship between thermoelectric properties and the materials structure, including chemical structure, microstructure, dopants, and doping levels. Their thermoelectric properties can be further improved to be comparable to inorganic counterparts in the near future.

Thermoelectric Properties of Poly(3-hexylthiophene) (P3HT) Doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) by Vapor-Phase Infiltration

Abstract: Doping of thin films of semiconducting polymers provides control of their electrical conductivity and thermopower. The electrical conductivity of semiconducting polymers rises nonlinearly with the carrier concentration, and there is a lack of understanding of the detailed factors that lead to this behavior. We report a study of the morphological effects of doping on the electrical conductivity of poly(3-hexylthiophene) (P3HT) thin films doped with small molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Resonant soft X-ray scattering shows that the morphology of films of P3HT is not strongly changed by infiltration of F4TCNQ from the vapor phase. We show that the local ordering of P3HT, the texture and form factor of crystallites, and the long-range connectivity of crystalline domains contribute to the electrical conductivity in thin films. The thermopower of films of P3HT doped with F4TCNQ from the vapor phase is not strongly enhanced relative to films doped from solution, but the el...

Phase-transition temperature suppression to achieve cubic GeTe and high thermoelectric performance by Bi and Mn codoping

Abstract: Germanium telluride (GeTe)-based materials, which display intriguing functionalities, have been intensively studied from both fundamental and technological perspectives. As a thermoelectric material, though, the phase transition in GeTe from a rhombohedral structure to a cubic structure at ∼700 K is a major obstacle impeding applications for energy harvesting. In this work, we discovered that the phase-transition temperature can be suppressed to below 300 K by a simple Bi and Mn codoping, resulting in the high performance of cubic GeTe from 300 to 773 K. Bi doping on the Ge site was found to reduce the hole concentration and thus to enhance the thermoelectric properties. Mn alloying on the Ge site simultaneously increased the hole effective mass and the Seebeck coefficient through modification of the valence bands. With the Bi and Mn codoping, the lattice thermal conductivity was also largely reduced due to the strong point-defect scattering for phonons, resulting in a peak thermoelectric figure of merit (ZT) of ∼1.5 at 773 K and an average ZT of ∼1.1 from 300 to 773 K in cubic Ge0.81Mn0.15Bi0.04Te. Our results open the door for further studies of this exciting material for thermoelectric and other applications.

N-Type Organic Thermoelectrics of Donor-Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States.

Abstract: It is demonstrated that the n-type thermoelectric performance of donor-acceptor (D-A) copolymers can be enhanced by a factor of >1000 by tailoring the density of states (DOS) The DOS distribution is tailored by embedding sp(2)-nitrogen atoms into the donor moiety of the D-A backbone Consequently, an electrical conductivity of 18 S cm(-1) and a power factor of 45 mu W m(-1) K-2 are achieved Interestingly, an unusual sign switching (from negative to positive) of the Seebeck coefficient of the unmodified D-A copolymer at moderately high dopant loading is observed A direct measurement of the DOS shows that the DOS distributions become less broad upon modifying the backbone in both pristine and doped states Additionally, doping-induced charge transfer complexes (CTC) states, which are energetically located below the neutral band, are observed in DOS of the doped unmodified D-A copolymer It is proposed that charge transport through these CTC states is responsible for the positive Seebeck coefficients in this n-doped system This is supported by numerical simulation and temperature dependence of Seebeck coefficient The work provides a unique insight into the fundamental understanding of molecular doping and sheds light on designing efficient n-type OTE materials from a perspective of tailoring the DOS

Thermoelectric SnTe with Band Convergence, Dense Dislocations, and Interstitials through Sn Self-Compensation and Mn Alloying.

Abstract: SnTe is known as an eco-friendly analogue of PbTe without toxic elements. However, the application potentials of pure SnTe are limited because of its high hole carrier concentration derived from intrinsic Sn vacancies, which lead to a high electrical thermal conductivity and low Seebeck coefficient. In this study, Sn self-compensation and Mn alloying could significantly improve the Seebeck coefficients in the whole temperature range through simultaneous carrier concentration optimization and band engineering, thereby leading to a large improvement of the power factors. Combining precipitates and atomic-scale interstitials due to Mn alloying with dense dislocations induced by long time annealing, the lattice thermal conductivity is drastically reduced. As a result, an enhanced figure of merit (ZT) of 1.35 is achieved for the composition of Sn0.94 Mn0.09 Te at 873 K and the ZTave from 300 to 873 K is boosted to 0.78, which is of great significance for practical application. Hitherto, the ZTmax and ZTave of this work are the highest values among all single-element-doped SnTe systems.

Large thermoelectric power factor from crystal symmetry-protected non-bonding orbital in half-Heuslers.

Abstract: Modern society relies on high charge mobility for efficient energy production and fast information technologies. The power factor of a material-the combination of electrical conductivity and Seebeck coefficient-measures its ability to extract electrical power from temperature differences. Recent advancements in thermoelectric materials have achieved enhanced Seebeck coefficient by manipulating the electronic band structure. However, this approach generally applies at relatively low conductivities, preventing the realization of exceptionally high-power factors. In contrast, half-Heusler semiconductors have been shown to break through that barrier in a way that could not be explained. Here, we show that symmetry-protected orbital interactions can steer electron-acoustic phonon interactions towards high mobility. This high-mobility regime enables large power factors in half-Heuslers, well above the maximum measured values. We anticipate that our understanding will spark new routes to search for better thermoelectric materials, and to discover high electron mobility semiconductors for electronic and photonic applications.

Peltier cooling in molecular junctions

Abstract: The study of thermoelectricity in molecular junctions is of fundamental interest for the development of various technologies including cooling (refrigeration) and heat-to-electricity conversion 1-4 . Recent experimental progress in probing the thermopower (Seebeck effect) of molecular junctions 5-9 has enabled studies of the relationship between thermoelectricity and molecular structure 10,11 . However, observations of Peltier cooling in molecular junctions-a critical step for establishing molecular-based refrigeration-have remained inaccessible. Here, we report direct experimental observations of Peltier cooling in molecular junctions. By integrating conducting-probe atomic force microscopy 12,13 with custom-fabricated picowatt-resolution calorimetric microdevices, we created an experimental platform that enables the unified characterization of electrical, thermoelectric and energy dissipation characteristics of molecular junctions. Using this platform, we studied gold junctions with prototypical molecules (Au-biphenyl-4,4'-dithiol-Au, Au-terphenyl-4,4''-dithiol-Au and Au-4,4'-bipyridine-Au) and revealed the relationship between heating or cooling and charge transmission characteristics. Our experimental conclusions are supported by self-energy-corrected density functional theory calculations. We expect these advances to stimulate studies of both thermal and thermoelectric transport in molecular junctions where the possibility of extraordinarily efficient energy conversion has been theoretically predicted 2-4,14 .

Enhancement of average thermoelectric figure of merit by increasing the grain-size of Mg3.2Sb1.5Bi0.49Te0.01

Abstract: Zintl compound n-type Mg3(Sb,Bi)2 was recently found to exhibit excellent thermoelectric figure of merit zT (∼1.5 at around 700 K). To improve the thermoelectric performance in the whole temperature range of operation from room temperature to 720 K, we investigated how the grain size of sintered samples influences electronic and thermal transport. By increasing the average grain size from 1.0 μm to 7.8 μm, the Hall mobility below 500 K was significantly improved, possibly due to suppression of grain boundary scattering. We also confirmed that the thermal conductivity did not change by increasing the grain size. Consequently, the sample with larger grains exhibited enhanced average zT. The calculated efficiency of thermoelectric power generation reaches 14.5% (ΔT = 420 K), which is quite high for a polycrystalline pristine material.

Highly Conductive Hydrogel Polymer Fibers toward Promising Wearable Thermoelectric Energy Harvesting

Abstract: The requirement of a portable electron is functioning as a driving force for a wearable energy instrument. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), as one of the most promising organic electron materials, has been widely studied in energy conversion devices. However, the efforts for PEDOT:PSS fibers are insufficient to boost the development of wearable thermoelectric energy harvesting. Here, a highly conductive p-type PEDOT:PSS fiber was produced by gelation process, which was 3 orders of magnitude higher than that of previous hydrogel fibers. Surprisingly, a post-treatment with organic solvents such as ethylene glycol and dimethyl sulfoxide tripled their electrical conductivity with an only 5% decreased Seebeck coefficient, consequently leading to an optimized thermoelectric power factor. Furthermore, we assembled a p-n-type thermoelectric device connecting five pairs of p-type PEDOT:PSS fibers and n-type carbon nanotube fibers. This fiber-based device displayed an acceptable output voltage of 20.7 mV and a power density of 481.2 μW·cm-2 with a temperature difference of ∼60 K, which might pave the way for the development of organic thermoelectric fibers for wearable energy harvesting.

Multifunctional structural design of graphene thermoelectrics by Bayesian optimization.

Abstract: Materials development often confronts a dilemma as it needs to satisfy multifunctional, often conflicting, demands. For example, thermoelectric conversion requires high electrical conductivity, a high Seebeck coefficient, and low thermal conductivity, despite the fact that these three properties are normally closely correlated. Nanostructuring techniques have been shown to break the correlations to some extent; however, optimal design has been a major challenge due to the extraordinarily large degrees of freedom in the structures. By taking graphene nanoribbons (GNRs) as a representative thermoelectric material, we carried out structural optimization by alternating multifunctional (phonon and electron) transport calculations and Bayesian optimization to resolve the trade-off. As a result, we have achieved multifunctional structural optimization with an efficiency more than five times that achieved by random search. The obtained GNRs with optimized antidots significantly enhance the thermoelectric figure of merit by up to 11 times that of the pristine GNR. Knowledge of the optimal structure further provides new physical insights that independent tuning of electron and phonon transport properties can be realized by making use of zigzag edge states and aperiodic nanostructuring. The demonstrated optimization framework is also useful for other multifunctional problems in various applications.

Enhanced thermoelectric performance of Bi-Sb-Te/Sb2O3 nanocomposites by energy filtering effect

Abstract: Engineering of thermoelectric materials through hybridization with nanoparticles has been proved effective to boost their thermoelectric efficiency by providing the means to decouple thermal and electrical transport phenomena. Here, we report the synthesis of p-type Bi0.5Sb1.5Te3/X wt% Sb2O3 (X = 0, 1, 2, 4, 6) nanocomposites, in which the Sb2O3 nanoparticles are dispersed mainly at the grain boundaries of the Bi0.5Sb1.5Te3 matrix. It is shown that incorporation of up to 4 wt% Sb2O3 into the matrix results in simultaneous enhancement of the Seebeck coefficient (by filtering of low energy charge carriers) and decline of thermal conductivity (mainly by charge carrier scattering at the interfaces), both of which contribute to improving the thermoelectric figure of merit to a maximum of 1.51 at 350 K. Moreover, the nanocomposites with 2, 4, and 6 wt% Sb2O3 demonstrate ZT > 1.0 up to 450 K, making them commercially appealing for thermoelectric applications in a wide temperature range. Furthermore, it is shown that Bi0.5Sb1.5Te3/4 wt% Sb2O3 samples exhibit excellent thermal and chemical stability in ambient atmosphere and 300–475 K temperature range over a 24 month period.

The influence of surface functionalization on thermal transport and thermoelectric properties of MXene monolayers

Abstract: The newest members of a two-dimensional material family, involving transition metal carbides and nitrides (called MXenes), have garnered increasing attention due to their tunable electronic and thermal properties depending on the chemical composition and functionalization. This flexibility can be exploited to fabricate efficient electrochemical energy storage (batteries) and energy conversion (thermoelectric) devices. In this study, we calculated the Seebeck coefficients and lattice thermal conductivity values of oxygen terminated M2CO2 (where M = Ti, Zr, Hf, Sc) monolayer MXene crystals in two different functionalization configurations (model-II (MD-II) and model-III (MD-III)), using density functional theory and Boltzmann transport theory. We estimated the thermoelectric figure-of-merit, zT, of these materials by two different approaches, as well. First of all, we found that the structural model (i.e. adsorption site of oxygen atom on the surface of MXene) has a paramount impact on the electronic and thermoelectric properties of MXene crystals, which can be exploited to engineer the thermoelectric properties of these materials. The lattice thermal conductivity κl, Seebeck coefficient and zT values may vary by 40% depending on the structural model. The MD-III configuration always has the larger band gap, Seebeck coefficient and zT, and smaller κl as compared to the MD-II structure due to a larger band gap, highly flat valence band and reduced crystal symmetry in the former. The MD-III configuration of Ti2CO2 and Zr2CO2 has the lowest κl as compared to the same configuration of Hf2CO2 and Sc2CO2. Among all the considered structures, the MD-II configuration of Hf2CO2 has the highest κl, and Ti2CO2 and Zr2CO2 in the MD-III configuration have the lowest κl. For instance, while the band gap of the MD-II configuration of Ti2CO2 is 0.26 eV, it becomes 0.69 eV in MD-III. The zTmax value may reach up to 1.1 depending on the structural model of MXene.

Metal oxides for thermoelectric power generation and beyond

Abstract: Metal oxides are widely used in many applications such as thermoelectric, solar cells, sensors, transistors, and optoelectronic devices due to their outstanding mechanical, chemical, electrical, and optical properties. For instance, their high Seebeck coefficient, high thermal stability, and earth abundancy make them suitable for thermoelectric power generation, particularly at a high-temperature regime. In this article, we review the recent advances of developing high electrical properties of metal oxides and their applications in thermoelectric, solar cells, sensors, and other optoelectronic devices. The materials examined include both narrow-band-gap (e.g., Na x CoO2, Ca3Co4O9, BiCuSeO, CaMnO3, SrTiO3) and wide-band-gap materials (e.g., ZnO-based, SnO2-based, In2O3-based). Unlike previous review articles, the focus of this study is on identifying an effective doping mechanism of different metal oxides to reach a high power factor. Effective dopants and doping strategies to achieve high carrier concentration and high electrical conductivities are highlighted in this review to enable the advanced applications of metal oxides in thermoelectric power generation and beyond.

High Thermoelectric Performance in Two-Dimensional Tellurium: An Ab Initio Study

Abstract: In 2016, bulk tellurium was experimentally observed as a remarkable thermoelectric material. Recently, two-dimensional (2D) tellurium, called tellurene, has been synthesized and has exhibited unexpected electronic properties compared with the 2D MoS2. They have also been fabricated into air-stable and highly efficient field-effect transistors. There are two stable 2D tellurene phases. One (β-Te) has been confirmed with an ultralow lattice thermal conductivity (κL). However, the study of the transport properties of the other more stable phase, α-Te, is still lacking. Here, we report the thermoelectric performance and phonon properties of α-Te using Boltzmann transport theory and first-principles calculations. A maximum ZT value of 0.83 is achieved under a reasonable hole concentration, suggesting that the monolayer α-Te is a potential competitor in the thermoelectric field.

Enhancement of thermoelectric performance of PEDOT:PSS films by post-treatment with a superacid

Abstract: Several methods such as the addition of a polar solvent, an acid as well as various post-treatments have been used to improve the thermoelectric performance of conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films. This paper reports a method using a superacid, trifluoromethanesulfonic acid, in methanol to treat PEDO:PSS films to improve their thermoelectric performance. Treatment of PEDOT:PSS films with this superacid in methanol leads to a significant increase in electrical conductivity from 0.7 to 2980 S cm−1 together with a moderate increase in Seebeck coefficient from 17.6 to 21.9 μV K−1, giving a power factor of 142 μW m−1 K−2, one of the highest values reported in the literature for conductive polymers. The figure of merit (ZT) value is estimated to be 0.19 under optimized conditions. The enhancement of thermoelectric performance, particularly the increase in both electrical conductivity and Seebeck coefficient, is due to the removal of the insulating component and polymer chain realignment giving in turn a denser packing of the conductive PEDOT polymer chains. This post-treatment method would offer an alternative way to improve the thermoelectric performance.

Impact of Ni content on the thermoelectric properties of half-Heusler TiNiSn

Abstract: From phase boundary mapping, we find that the thermoelectric TiNiSn half-Heusler phase shows a narrow solubility range on the Ti–Ni–Sn phase diagram primarily in the range of excess Ni that can be approximated as TiNi1+xSn, where x is temperature dependent with 0 ≤ x ≤ 0.06 at 1223 K. Four phase boundary compositions with different Ni contents associated with four three-phase regions are identified. We characterize the thermoelectric properties of these stable compositions and find significant difference between Ni-rich and Ni-poor phase boundary compositions of TiNiSn, which amounts up to 41%, 58%, and 25% difference in the Seebeck coefficient, lattice thermal conductivity, and thermoelectric figure of merit respectively. This explains the large discrepancy of literature data on the thermoelectric properties of TiNiSn within a unified phase diagram framework. We demonstrate that Ni-rich TiNiSn results in a narrower band gap using the Goldsmid formula, which we interpret to be due to the formation of an impurity band from interstitial Ni in the forbidden gap as previously suggested. Interstitial Ni atoms scatter both electrons and phonons, with the latter effect being much stronger, thus a lower lattice thermal conductivity compensates for the decrease in electron mobility leading to a high zT value of 0.6 at 850 K for intrinsic Ni-rich TiNiSn. With Sb doping, the carrier concentration in these stable boundary compositions can be tuned but the distinct features in their transport properties remain unchanged. A maximum zT value of 0.6 was also achieved at 850 K for intrinsic Ni-poor TiNiSn upon Sb doping.

Development of Perovskite-Type Materials for Thermoelectric Application.

Abstract: Oxide perovskite materials have a long history of being investigated for thermoelectric applications. Compared to the state-of-the-art tin and lead chalcogenides, these perovskite compounds have advantages of low toxicity, eco-friendliness, and high elemental abundance. However, because of low electrical conductivity and high thermal conductivity, the total thermoelectric performance of oxide perovskites is relatively poor. Variety of methods were used to enhance the TE properties of oxide perovskite materials, such as doping, inducing oxygen vacancy, embedding crystal imperfection, and so on. Recently, hybrid perovskite materials started to draw attention for thermoelectric application. Due to the low thermal conductivity and high Seebeck coefficient feature of hybrid perovskites materials, they can be promising thermoelectric materials and hold the potential for the application of wearable energy generators and cooling devices. This mini-review will build a bridge between oxide perovskites and burgeoning hybrid halide perovskites in the research of thermoelectric properties with an aim to further enhance the relevant performance of perovskite-type materials.

High-Performance n-Type PbSe-Cu2Se Thermoelectrics through Conduction Band Engineering and Phonon Softening.

Abstract: From a structural and economic perspective, tellurium-free PbSe can be an attractive alternative to its more expensive isostructural analogue of PbTe for intermediate temperature power generation. Here we report that PbSe0.998Br0.002-2%Cu2Se exhibits record high peak ZT 1.8 at 723 K and average ZT 1.1 between 300 and 823 K to date for all previously reported n- and p-type PbSe-based materials as well as tellurium-free n-type polycrystalline materials. These even rival the highest reported values for n-type PbTe-based materials. Cu2Se doping not only enhance charge transport properties but also depress thermal conductivity of n-type PbSe. It flattens the edge of the conduction band of PbSe, increases the effective mass of charge carriers, and enlarges the energy band gap, which collectively improve the Seebeck coefficient markedly. This is the first example of manipulating the electronic conduction band to enhance the thermoelectric properties of n-type PbSe. Concurrently, Cu2Se increases the carrier conce...

Recent progress towards high performance of tin chalcogenide thermoelectric materials

Abstract: Thermoelectric materials have been extensively studied for decades to help resolve the global energy shortage and environmental problems. Many efforts have been focused on the improvement of the figure of merit (ZT) for highly efficient power generation. Lead telluride is one of the materials with high ZT, but lead toxicity is always a concern, which has inspired research on lead-free tin chalcogenides. ZT values as high as ∼2.6 at 923 K for SnSe single crystals and ∼1.6 at 923 K for Sn0.86Mn0.14Te(Cu2Te)0.05-5 atm% Sn were recently reported, attracting extensive attention for potential applications. In this review, we present the progress in SnTe, SnSe, and SnS, mainly discussing the effective tuning of the electron and phonon transport based on the intrinsic properties, along with the challenges for further optimization and applications. For SnTe, successful strategies, including resonant doping, band convergence, defect engineering, etc., are discussed. For SnSe, we focus on the analysis of the intrinsic low thermal conductivity due to strong anharmonicity and a high Seebeck coefficient because of the multi-valley bands. For SnS, high performance is expected considering its similar band structure and crystal structure to SnSe.