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The development of a rapid-forming in-situ sprayable hydrogel with the functions of tumor treatment and wound healing is essential for eliminating residual tumor tissue and promoting wound healing caused by surgical resection. On account of its semiconductor properties, β-FeSi2 (FS) was widely explored as a thermoelectric material. In this work, FS was first applied as a bioactive material for the application of tissue engineering. Excitedly, we found that FS could be used as a novel antitumor agent. It exhibited excellent photothermal performance, and the released Fe ions could generate •OH under the acidic conditions and excessive H2O2 in the tumor microenvironment. Moreover, the sprayable β-FeSi2-incorporated sodium alginate (FS/SA) hydrogel was prepared as an instant gelation after spraying in situ, contributing to timely tumor-induced skin wound healing and efficiently suppressing tumors through photothermal and chemodynamic therapy (PTT and CDT). Furthermore, the released bioactive Fe and Si ions could promote the migration and differentiation of endothelial cells and the pro-angiogenesis of skin wounds. Accordingly, such sprayable hydrogel played an effective role in emergency wound treatment with the advantage of convenience and portability. Overall, with incorporation of FS into the sprayable FS/SA hydrogel, the composite hydrogel possessed dual functions of tumor therapy and skin wound healing.

As a low-cost substitute that uses no expensive rare-earth elements for the high-efficiency Cu(In,Ga)(S,Se)2 solar cell, the Cu2 ZnSn(S,Se)4 (CZTSSe) solar cell has borrowed optimization strategies used for its predecessor to improve its device performance, including a profiled band gap and surface inversion. Indeed, there have been few reports of constructing CZTSSe absorber layers with surface inversion to improve efficiency. Here, a strategy that designs the CZTSSe absorber to attain surface modification by using n-type Ag2 ZnSnS4 is demonstrated. It has been discovered that Ag plays two major roles in the kesterite thin film devices: surface inversion and front gradient distribution. It has not only an excellent carrier transport effect and reduced probability of electron-hole recombination but also results in increased carrier separation by increasing the width of the depletion region, leading to much improved VOC and JSC . Finally, a champion CZTSSe solar cell renders efficiency as high as 12.55%, one of the highest for its type, with the open-circuit voltage deficit reduced to as low as 0.306 V (63.2% Shockley-Queisser limit). The band engineering for surface modification of the absorber and high efficiency achieved here shine a new light on the future of the CZTSSe solar cell.

Recently, a deformable and ductile inorganic semiconductor Ag2S has attracted intense attention due to its potential application in self-powered wearable and hetero-shaped electronics. However, the thermoelectric figure of merit (zT) of Ag2S is greatly limited by its extremely low carrier concentration. In this study, via doping I into Ag2S-based materials, we tune the carrier concentration into the optimal range as well as suppressing the lattice thermal conductivity. A maximum zT value of 0.26 is achieved for Ag2S0.7Se0.295I0.005 at 300 K, about three times higher than the matrix compound. More importantly, doping I has little effect on the ductility and deformability of Ag2S-based materials. Our study shows that I-doped Ag2S-based materials are good candidates for developing flexible thermoelectric technologies.

Rationalizing the underlying mechanism that correlates phonon transport with structural complexity is crucial for the development of materials with ultralow thermal conductivity. Herein, we investigated the abnormal thermal transport and lattice dynamics in Ag9FeS6-xTex argyrodite-type compounds via a combination of properties characterization, model analysis, and theoretical calculations. Our results show that the ordered α-phase and disordered β-phase of Ag9FeS6-xTex exhibit distinct temperature dependency of lattice thermal conductivity κL. Specifically, the κL of ordered α-phase shows a crystalline characteristic with a pronounced Umklapp peak observed at ∼10 K, while the κL of disordered β-phase monotonously increases in the whole temperature range without a peak or plateau. Such different thermal transport behavior is a result of different contributions to the reduction of κL from the structural disorder and the low-lying multi-Einstein oscillators, both of which are associated with the weakly bonded Ag+ ions. The knowledge depicted here provides fundamental insights into the extraordinary thermal transports in materials with structural disorder and/or weak chemical bonds.

Recently, one-dimensional van der Waals crystal Ta4SiTe4 has been reported as a promising low-temperature thermoelectric material. Extraordinarily high power factor has been reported for the one-dimensional Ta4SiTe4 single whisker and two-dimensional (PVDF)/Ta4SiTe4 composite film, but the thermoelectric properties of three-dimensional Ta4SiTe4 polycrystalline bulks have been rarely investigated. In this study, we prepared a series of phosphorus (P)-doped Ta4SiTe4 polycrystalline bulks by using the high-temperature synthesis and cold press method. Their electrical and thermal transport properties along the directions parallel and perpendicular to the pressure were systematically investigated. Upon doping P at the Si-sites to increase the carrier concentration, the electrical conductivity is enhanced while the intrinsic excitation is suppressed, resulting in significantly improved power factor approaching the theoretically optimal value. All Ta4Si1-xPxTe4 bulks possess low lattice thermal conductivities with the values below 1.2 Wm−1K−1. The weak van der Waals interaction among the [Si2Ta8Te8]n chains results in the appearance of low-lying optical modes and introduces additional scattering to phonons. A peak thermoelectric figure of merit value of 0.18 is obtained at 300 K for polycrystalline Ta4Si0·995P0·005Te4, about double that of pristine polycrystalline Ta4SiTe4.

Recently, the electronegative elements (e.g., S, Se, Cl, and Br) filled skutterudites have attracted great attention in thermoelectric community. Via doping of some electron donors at the Sb sites, these electronegative elements can be filled into the voids of CoSb3 forming thermodynamically stable compounds, which greatly extends the scope of filled skutterudites. In this study, we show that doping appropriate elements at the Co sites can also stabilize the electronegative elements in the voids of CoSb3. A series of SyPdxCo4-xSb12 compounds were successfully fabricated by a traditional solid state reaction method combined with a spark plasma sintering technique. The phase composition and electrical and thermal transport properties were systematically characterized, and the related mechanisms were deeply discussed. It is found that the charge compensation between Pd doping and S filling is the main reason for the formation of thermodynamically stable SyPdxCo4-xSb12 compounds. Filling S element in the voids of CoSb3 provides additional holes to reduce the carrier concentration while scarcely affecting the carrier mobility. However, doping Pd at the Co sites not only changes the carrier scattering mechanism but also deteriorates the carrier mobility. Low lattice thermal conductivities are observed in these SyPdxCo4-xSb12 compounds, which are attributed to the low resonant frequency of the S element. Finally, a maximal figure of merit of 0.85 is obtained for S0.05Pd0.25Co3.75Sb12 at 700 K.

Mosaic-crystal microstructure is one of the optimal strategies for decoupling and balancing thermal and electrical transport properties in thermoelectric materials. Herein, we successfully achieve the desired nanoscale mosaic structures in triple-component Cu2−yS1/3Se1/3Te1/3 solid solutions using Cu2S, Cu2Se, and Cu2Te matrix compounds. They are solved in hexagonal structures with space group R3̅m by means of single crystal structural solution and Rietveld refinement. Electron backscatter diffraction measurements show that all the samples are polycrystalline compounds with the grain size in the range of micrometers. However, transmission electron microscopic study reveals that these microscale grains are quasi-single crystals consist of a variety of 10–30 nm mosaic grains. Each mosaic grain is a perfect crystal but titled or rotated with respect to others by a very small angle. In this case, excellent electrical transports are maintained but exceptional low thermal conductivity is achieved throughout the whole temperature range, which is attributed to the combined phonon scatterings by point defects, liquid-like copper ions, and lattice strains or interfaces of mosaic nanograins. Combining all these favorable factors, remarkably high thermoelectric performance is achieved in Cu1.98S1/3Se1/3Te1/3 with a maximum zT of 1.9 at 1000 K.

Recently, many novel superionic thermoelectric materials have been discovered along the concept of “phonon-liquid electron-crystal” (PLEC). Among them, Cu 2- x Se-based liquid-like materials are typical examples. In this study, a series of copper-deficient Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials were synthesized and used to study the role of Cu vacancies on the electrical and thermal transport properties. The X-ray photoelectron spectroscopy (XPS) measurements suggest that the valence states of Cu and Se are independent on the Cu/Se atomic ratio. With increasing the content of Cu vacancies, the hole concentration is monotonously increased, leading to the improved electrical conductivity and reduced Seebeck coefficient. Based on the single parabolic band model analysis, it is found that changing the content of Cu vacancies does not obviously modify the material's electronic band structure and effective mass. Due to the presence of highly mobile Cu ions inside the crystal structure, the lattice thermal conductivities of all Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials are very low with values around 0.39 W m −1 K −1 at 500 K. Because of the significantly reduced Seebeck coefficient and increased electronic thermal conductivity, the thermoelectric figure of merit zTs are decreased when increasing x from 0.05 to 0.25. At 750 K, a maximum zT of 0.46 is obtained in Cu 1.95 Se among all Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials.

Superionic thermoelectric materials have been shown to have high figure-of-merits, leading to expectations for efficient high-temperature thermoelectric generators. These compounds exhibit extremely high cation diffusivity, comparable to that of a liquid, which is believed to be associated with the low thermal conductivity that makes superionic materials good for thermoelectrics. However, the superionic behavior causes cation migration that leads to device deterioration, being the main obstacle for practical applications. It has been reported that lithium doping in superionic Cu_(2−x)Se leads to suppression of the Cu ion diffusivity, but whether the material will retain the promising thermoelectric properties had not yet been investigated. Here, we report a maximum zT>1.4 from Li_(0.09)Cu_(1.9)Se, which is higher than what we find in the undoped samples. The high temperature effective weighted mobility of the doped sample is found higher than Cu_(2−x)Se, while the lattice thermal conductivity remains similar. We find signatures of suppressed bipolar conduction due to an enlarged band gap. Our findings set forth a possible route for tuning the stability of superionic thermoelectric materials.

In recent decades, by continuously enhancing the figure of merit ZT of various thermoelectric (TE) materials, solid state TE technology has matured and is on the verge of making an impact in real industrial settings as a promising approach to harvest waste industrial heat and convert it to useful electricity. Nevertheless, actual TE module development has remained stagnant with rather poor efficiencies. This has raised an urgent need to design rational module structures that rely on complex parameter optimization and utilization of efficient integration technologies that minimize energy losses during bonding of various interfaces. Here, we demonstrate a three-dimensional numerical analysis model of a segmented TE power-generating device, which takes into account the temperature-dependent materials' properties and various parasitic losses. The model generates an optimized design with predictive performance to realize maximum conversion efficiency. Combined with the developed bonding schemes and assembly techniques, the segmented modules consisting of Bi2Te3-based alloys and CoSb3-based filled skutterudites were successfully fabricated with a record-high efficiency of up to 12% when operating under a temperature difference of 541 °C. The rational structure design based on the numerical analysis model and the extremely low thermal and electrical losses enable the heat-to-electricity conversion efficiency to reach up to 96.9% of the theoretical efficiency based on the TE materials themselves. These findings highlight the importance of the optimization strategy for TE power generation devices based on the TE materials' intrinsic properties and demonstrate that realistic high temperature TE modules with predictive high efficiency and high power density can be fabricated, which provides a useful guide to achieve a high conversion efficiency in large-scale TE applications.

Bi2Te3-based alloys are the most well-known thermoelectric materials for room-temperature applications. However, the maximum ZT values of Bi2Te3-based materials are usually achieved near room temperature. The ZT values dramatically drop above 400 K because of the intrinsic thermal excitation in Bi2Te3-based materials, which seriously restricts their applications as thermoelectric power generators. In this study, by doping a tiny amount of Ag into Bi0.5Sb1.5Te3, we successfully suppressed the intrinsic excitation in p-type Bi2Te3-based materials and shifted the ZT peak temperature to high temperatures. Eventually, due to the enhanced power factor and greatly depressed bipolar thermal conductivity at high temperature, a maximum ZT of 1.25 at 400 K was obtained in Ag0.002Bi0.5Sb1.498Te3, and an average ZT value of approximately 1.03 was achieved between 300 and 600 K. The theoretical energy conversion efficiency of the TE module fabricated with Ag0.002Bi0.5Sb1.498Te3 achieves a maximum value of 11.0% when ΔT = 300 K, which makes p-type Bi2Te3-based devices attractive for applications in TE power generation.

We report a ternary argyrodite-type Ag9GaSe6 compound as a promising thermoelectric material in a moderate temperature range. Due to high carrier mobility and ultralow lattice thermal conductivity, a maximum ZT of 1.1 was obtained with stoichiometric Ag9GaSe6 at 800 K. Via introducing slight Se-deficiency to optimize the carrier concentration, the maximum ZT is further enhanced to 1.3.

Here, by utilizing the special interaction between metal Cu and multi-walled carbon nanotubes (CNTs), we have successfully realized the in situ growth of Cu2Se on the surface of CNTs and then fabricated a series of Cu2Se/CNT hybrid materials. Due to the high degree of homogeneously dispersed molecular CNTs inside the Cu2Se matrix, a record-high thermoelectric figure of merit zT of 2.4 at 1000 K has been achieved.

As a successful invasive cyanobacterial species, Raphidiopsis raciborskii is distributed globally and shows a tendency to replace Microcystis aeruginosa in many subtropical and temperate waters, but the ecological traits that contribute to its invasiveness are still unclear. In this study, we found that R. raciborskii occurred in 149 sites in 42 lakes in eastern and central China and coexisted with M. aeruginosa at most sites. Based on field results, a combination of invasion and competition experiments using a biomass gradient to evaluate the invasiveness and competitiveness of R. raciborskii compared with M. aeruginosa was conducted. In invasive groups, both R. raciborskii and M. aeruginosa were shown to have positive specific growth rates, indicating that R. raciborskii could coexist with M. aeruginosa. Furthermore, R. raciborskii was shown to grow faster from invasion while M. aeruginosa reduced growth for invasion. In competitive groups, R. raciborskii reached a higher maximum biomass and grew longer than M. aeruginosa. The specific growth rate of R. raciborskii was not inhibited by M. aeruginosa biomass, whereas the growth of M. aeruginosa was inhibited by R. raciborskii biomass. It was shown during the whole experiment that R. raciborskii tended to replace M. aeruginosa to become dominant owing to its faster growth rate and the eventual decline in growth of M. aeruginosa. With an increase in biomass of M. aeruginosa, the vegetative cell size and filament length of R. raciborskii gradually increased. This study has demonstrated that the inherent invasive traits of R. raciborskii, size differences, niche differences, and relative fitness differences between R. raciborskii and M. aeruginosa are crucial reasons for the invasive success of R. raciborskii. Our results revealed the invasiveness and domination of R. raciborskii from a new perspective.

Intel software-guard extensions (SGX) allows applications to run in a trusted space (enclave), which provides a highly secure primitive for the running codes and data. Most state-of-the-art attacks on SGX either exploit software vulnerabilities in the enclave or utilize side channels. In this study, we propose the first fault injection attack to break SGX by using voltage-induced hardware faults. This attack is completely controlled by software. It does not require the availability of any software vulnerability. Our proposed attack targets multi-core processors where dynamic voltage and frequency scaling (DVFS) is equipped, which covers most of the commercial processors including those by Intel and ARM. We follow the basic principle for frequency and voltage based fault injection attacks which adjust the frequency or voltage levels deliberately to create hardware faults. We have demonstrated that the software-controlled voltage glitches are effective to fault ARM processors in the previous work. However, to the best of our knowledge, this is the first realization of such attacks on SGX. More specifically, we develop a kernel module to schedule frequency and voltage for Intel processors through their model-specific registers (MSR). We firstly utilize the module to furnish the processor a transient low voltage with controlled timing to inject a temporal fault into the target location of the program running on SGX. Then we perform differential fault analysis on the outputs before and after the injection of faults. This allows us to obtain the SGX-protected confidential data such as encryption keys, with which we can access program and data in the enclave or run any application in the enclave. For demonstration, we successfully deploy the proposed attack to extract the key of an AES executed in the SGX enclave.

Liquid‐like materials are one family of promising thermoelectric materials discovered in the past years due to their advantanges of ultrahigh thermoelectric figure of merit (zT), low cost, and environmental friendliness. However, their practial applications are greatly limited by the low service stability from the Cu/Ag metal deposition under large current and/or temperature gradient. Both high zT for high efficiency and large critical voltage for good stability are required for liquid‐like materials, but they are usually strongly correlated and hard to be tuned individually. Herein, based on the thermodynamic analysis, it is shown that such a correlation can be decoupled through doping immobile ions into the liquid‐like sublattice. Taking Cu2− δS as an example, doping immobile Fe ions in Cu1.90S scarcely degrades the initial large critical voltage, but significantly enhances the zT to 1.5 at 1000 K by tuning the carrier concentration to the optimal range. Combining the low‐cost and environmentally friendly features, these Fe‐doped Cu2− δS‐based compounds show great potential in civil applications. This study sheds light on the realization of both good stability and high performance for many other liquid‐like thermoelectric materials that have not been considered for real applications before., Herein, the correlation between thermoelectric figure of merit and critical voltage is revealed and the thermodynamic analysis suggests that it can be decoupled through doping immobile ions into the liquid‐like sublattice. Along this direction, a new approach to design and fabricate liquid‐like materials with both high thermoelectric performance and good stability is proposed and well demonstrated in Cu2− δS‐based liquid‐like materials.

Most of the state-of-the-art thermoelectric (TE) materials exhibit high crystal symmetry, multiple valleys near the Fermi level, heavy constituent elements with small electronegativity differences, or complex crystal structure. Typically, such general features have been well observed in those well-known TE materials such as Bi

β-FeSi

Ag

Liquid-like binary Cu

Flexible thermoelectrics, including flexible thermoelectric materials and devices, can directly convert the heat from human body into useful electricity, providing a promising solution for uninterrupted power to wearables. In the past decade, flexible thermoelectrics has achieved notable progress. Various kinds of flexible thermoelectric materials have been developed and some of them have been fabricated into flexible thermoelectric devices, showing the ability to generate nW‐level or even μW‐level electricity. Herein, the basic design principles and typical configurations of flexible thermoelectric devices, as well as the requirements on thermoelectric materials to achieve high performance flexible thermoelectric devices, are first introduced. Then, the recent progress achieved in flexible thermoelectric devices based on organics materials, traditional inorganic materials, other organic/inorganic composites/hybrids, and plastic deformable inorganic semiconductors, respectively, are summarized. Finally, an outlook on the future development of flexible thermoelectrics is briefly given. This study sheds light on the further development of flexible thermoelectrics.

Recently, defective three-quarter Heusler compounds MCo1.5Sn (M = Ti, Zr, and Hf) have been reported with interesting crystal structure differing from the traditional half-Heusler and full-Heusler compounds. These defective compounds are metallic ferromagnets, but the detailed correlation between magnetic and electrical transport properties is still unclear. In this study, we dope Cu in ZrCo1.5Sn to dilute the magnetic Co atoms with the purpose of clarifying how the magnetism influences the electrical transport properties in the defective three-quarter Heusler compounds. Significantly lowered ferromagnetic transition temperature and decreased saturated magnetic moment are observed in Cu-doped ZrCo1.5Sn due to the diluted Co atoms. Likewise, in the ferromagnetic phase, the dominant carrier scattering mechanism is changed from spin fluctuation scattering to magnetic impurity scattering. The doped Cu atoms introduce non-bonding states below the valence band maximum, resulting in the appearance of a narrow bandgap around 0.1 eV. Correspondingly, the electric transport behavior in the paramagnetic phase shows a semiconducting character with a negative temperature dependence of resistivity. This study provides further understanding to the correlation between magnetic properties and electrical transport properties in defective Heusler-based compounds.

High-efficiency thermoelectric (TE) technology is determined by the performance of TE materials. Doping is a routine approach in TEs to achieve optimized electrical properties and lowered thermal conductivity. However, how to choose appropriate dopants with desirable solution content to realize high TE figure-of-merit (zT) is very tough work. In this study, via the use of large mass and strain field fluctuations as indicators for low lattice thermal conductivity, the combination of (Mg, Bi) in GeTe is screened as very effective dopants for potentially high zTs. In experiments, a series of (Mg, Bi) co-doped GeTe compounds are prepared and the electrical and thermal transport properties are systematically investigated. Ultralow lattice thermal conductivity, about 0.3 W m-1 K-1 at 600 K, is obtained in Ge0.9 Mg0.04 Bi0.06 Te due to the introduced large mass and strain field fluctuations by (Mg, Bi) co-doping. In addition, (Mg, Bi) co-doping can introduce extra electrons for optimal carrier concentration and diminish the energy offset at the top of the valence band for high density-of-states effective mass. Via these synthetic effects, a superhigh zT of ≈2.5 at 700 K is achieved for Ge0.9 Mg0.04 Bi0.06 Te. This study sheds light on the rational design of effective dopants in other TE materials.

Hetero-shaped thermoelectric (TE) generators (TEGs) can power the sensors used in safety monitoring systems of undersea oil pipelines, but their development is greatly limited by the lack of materials with both good shape-conformable ability and high TE performance. In this work, a new ductile inorganic TE material, Ag20 S7 Te3 , with high TE performance is reported. At 300-600 K, Ag20 S7 Te3 crystallizes in a body-centered cubic structure, in which S and Te atoms randomly occupy the (0, 0, 1) site. Due to the smaller generalized stacking fault energy in the ( 10 1 ¯ )[010] slip system, Ag20 S7 Te3 shows better ductility than Ag2 S, yielding excellent shape-conformability. The high carrier mobility and low lattice thermal conductivity observed in Ag20 S7 Te3 result in a maximum dimensionless figure of merit (zT) of 0.80 at 600 K, which is comparable with the best commercial Bi2 Te3 -based alloys. The prototype TEG consisting of 10 Ag20 S7 Te3 strips displays an open-circuit voltage of 69.2 mV and a maximum power output of 17.1 µW under the temperature difference of 70 K. This study creates a new route toward hetero-shaped TEG.

Ag2Se and CuAgSe have been recently reported as promising thermoelectric materials at room temperature. The traditional melting–annealing–sintering processes are used to grow Ag2Se and CuAgSe materials with the disadvantages of high costs of energy and time. In this work, phase-pure polycrystalline Ag2Se and CuAgSe compounds were synthesized from raw elemental powders directly by manual mixing followed by spark plasma sintering (MM-SPS) in a few minutes. The influence of SPS heating rate on the phase composition, microstructure, and thermoelectric properties, including Seebeck coefficient, electrical conductivity, and thermal conductivity, were investigated. The zTs of 0.8 at 390 K and 0.6 at 450 K are obtained for Ag2Se and CuAgSe, respectively, which is comparable with the values in the materials prepared by the traditional method. Furthermore, this ultrafast sample synthesis can significantly save material synthesis time and thus has the obvious advantage for large-scale production.

Thermoelectric technology has the ability to realize direct conversion between heat and electricity. Compared to the traditional refrigeration and energy generation technologies, thermoelectric technology has the advantages of having no moving parts, quiet, and long term stability. Thus, thermoelectric technology offers a great potential for the use in many cooling and power generating applications to help combat the global energy dilemma. Research on copper (Cu)-based materials has a long history in the thermoelectric field and it has become a topic which is very popular recently. In this review, the main progresses and achievements in Cu-based thermoelectric materials are summarized. Commencing with the history of Cu-based thermoelectric materials, we will introduce several typical kinds of high performance Cu-based thermoelectric materials, termed as diamond-like compounds, superionic conductors, tetrahedrites Cu12Sb4S13, and oxyselenide BiCuSeO. Then, new thermoelectric phenomenon and mechanisms discovered in these Cu-based materials and the strategies for the optimization of thermoelectric performance are also discussed. Finally, the challenges for commercial applications by using these Cu-based thermoelectric materials are discussed. We believed that the progresses in Cu-based materials will promote the use of thermoelectric technology to play a positive role in future energy solutions.

By suppressing intrinsic excitation in p-type Bi2Te3-based materials, we report maximum and average zT values of up to 1.4 and 1.2 between 100 and 300 °C, respectively. Thermoelectric modules based on these high performance materials show energy conversion efficiencies of up to 6.0% under a temperature gradient of 217 K, and are greatly superior to current Bi2Te3-based modules.

A pseudocubic structure approach has been proposed recently to screen and design good thermoelectric materials via realizing overlapped band edges for excellent electrical transport properties. A diamond-like compound is a typical example agreeing with the concept of the pseudocubic structure by tuning its lattice distortion parameter to unity. However, besides the band structure, optimized carrier concentration and reduced lattice thermal conductivity are also required for a high thermoelectric figure of merit (zT). In this work, taking CuGaTe2 as an example, we have successfully demonstrated that Cu-deficiency can effectively tune carrier concentrations and In-alloying at Ga sites can effectively lower lattice thermal conductivity. By combining these two strategies, the electrical and thermal transports can be separately optimized in CuGaTe2-based pseudocubic diamond-like compounds, leading to much enhanced zTs, about 24% improvement for Cu0.99In0.6Ga0.4Te2 at 800 K. Furthermore, the average zTs from 300 K to 800 K are improved by 87% compared with that of the CuGaTe2 matrix. This study provides a promising way to optimize the TE performance in pseudocubic diamond-like compounds by simultaneously tuning electrical and thermal transport.

A series of rare-earth filled skutterudites are successfully fabricated by using a non-equilibrium synthesis approach involving super-cooling and high pressure sintering. The filler filling fractions are significantly improved to realize optimum carrier concentrations and hugely suppressed lattice thermal conductivity, thereby leading to significantly enhanced zT.

Heusler-based compounds are a class of important inorganic materials with potential applications in spintronics, solar cells, thermoelectrics, optoelectronics, and so on. Previous studies mainly focus on half-Heusler compounds or full-Heusler compounds. In this work, a class of MCo1.5Sn (M = Ti, Zr, and Hf) compounds, which are named as three-quarter Heusler compounds, has been synthesized. Their formation mechanism, crystal structure, and physical properties have been systematically investigated. Both the high-angle annular dark field images and X-ray refinement confirm that their crystal structures can be viewed as the ordered half-Heusler sublattice with the four empty tetrahedral holes being disorderedly occupied by two extra Co atoms. Electronic structure calculations and experimental results reveal that these compounds are metallic ferromagnets. The magnetic ordering below the Curie temperature greatly affects the electrical transports due to the scattering by spin fluctuations. The three-quarter Heusler compounds have ultralow lattice thermal conductivities compared with other typical Heusler-based compounds due to the partial occupation of Co at the 4d sites. This work enriches the investigation on the Heusler-based compounds.

In this paper, we propose a Na2S soaking process (used as post-treatment process for the precursor films) for the non-vacuum prepared Cu2ZnSn(S,Se)4 (CZTSSe) films. The CZTSSe film prepared without this process show triple-layer structure in which fine-grain layer and obvious layer-boundaries exist. By soaking the precursor film in Na2S aqueous solution with suitable concentration, the fine-grain layer in the triple-layer structure is substituted by a small-grain layer and the layer-boundaries become continuous. We find the quantum efficiencies of the solar cells in long wavelength region are improved by the Na2S soaking. Therefore, the short-circuit currents of the solar cells are significantly increased. By using the Na2S soaking process, CZTSSe solar cells with the best efficiency of 11.5% have been prepared.

Chalcopyrite compounds are promising high efficient thermoelectric materials. However, the relatively high lattice thermal conductivity at modest temperatures limits their performance. Here, we investigate the lattice dynamics in a polycrystalline CuInTe2 with a combined experimental and computational approach. The phonon dispersion and density of states are computed using the density functional theory. Raman scattering is performed to investigate the phonon dynamical properties. Together with the bulk modulus from X-ray diffraction, the mode-Gruneisen parameters are determined. The low energy B 1 1 and E2 modes characterize the weak anharmonicity, thus responsible for the high lattice thermal conductivity. Meanwhile, B 1 1 and E2 modes display energy redshift under pressure. The softening and enhanced anharmonicity of these modes naturally result in the reduction of the thermal conductivity. Our study suggests that pressure is a routine to reduce the phonon heat conduction at modest temperatures in chalcopyrites.

Discovering new high-performance thermoelectric (TE) materials is an eternal pursuit in TE community. Searching materials with heavy average atomic mass to realize intrinsically low lattice thermal conductivity is an effective strategy to discover novel promising TE materials. In this article, by using high-throughput screening, Cu3ErTe3 with heavy average atomic mass is screened out of the 27,782 entries with band gaps in the Materials Informatics Platform as a potential high-performance TE material. In experiment, a series of phase pure Cu3ErTe3-based samples are synthesized. Being consistent with the predication, Cu3ErTe3 has a low speed of sound of 2151 m s−1 and an intrinsically low lattice thermal conductivity of 1.2 W m−1 K−1 at 300 K. Meanwhile, the moderate band gap of Cu3ErTe3 enables decent electrical transport properties. Finally, a peak figure of merit around unit at 900 K is achieved for Ag-alloyed Cu3ErTe3. Beyond the present Cu3LnTe3 (Ln = rare earth metal) compounds, other compounds predicated by the high-throughput screening, such as Cu3La3Bi4, Cu3Ln7Te12 (Ln = Tb, Dy, Ho, and Er), Cu2HfTe3, and Cu3Nd3Sb4, might also possess excellent TE performance. This work opens a door to a large family of new potential high-performance TE materials that have not been investigated for TEs.

The microstructure of MoS2 films is crucial important for its photoelectrical properties, which has significant impact on its application in the field of photovoltaic devices. In this paper, a set of MoS2 thin films with varied thickness was prepared by magnetron sputtering. The influence of the MoS2 microstructure on its optical and electrical properties and, especially, the MoS2/p-Si solar cells photovoltaic performance was investigated in terms of thin films growth. The results reveal that, as the thickness increases, the microstructure of the MoS2 films evolves from amorphous to microcrystalline with the in-plane E2g1 and out-of-plane A1g Raman modes enhancing and the parallel (002) growth orientation increasing. The films electrical conductivity significantly improves owing to the enhanced MoS2 crystallinity. When the thickness is 10 nm, the small ordered MoS2 crystal clusters gradient distribute from the surface to the bulk in the films, contributing to the stress release in the amorphous precursor. Simultaneously, the optical band gap of the MoS2 films shows a maximum of 1.3 eV, due to the less band tail states in the films at the initial phase transition. The optimized optical-electrical properties of the MoS2 films lead to the reducing defects recombination and the enhanced carrier transportation at MoS2/p-Si interface, which promotes the rectification behavior of the pn-junction up to 102. Besides, the significant improvement of the photo-response in MoS2/p-Si heterojunction is obtained, especially in short wavelength range. Correspondingly, the photovoltaic characteristics (Voc, Jsc and FF) of the MoS2/p-Si solar cells increase, and thus an enhancement of the cells conversion efficiency is achieved with 10-nm MoS2 layer.

Thermal conductivity is a very basic property that determines how fast a material conducts heat, which plays an important and sometimes a dominant role in many fields. However, because materials with phase transitions have been widely used recently, understanding and measuring temperature-dependent thermal conductivity during phase transitions are important and sometimes even questionable. Here, the thermal transport equation is corrected by including heat absorption due to phase transitions to reveal how a phase transition affects the measured thermal conductivity. In addition to the enhanced heat capacity that is well known, it is found that thermal diffusivity can be abnormally lowered from the true value, which is also dependent on the speed of phase transitions. The extraction of the true thermal conductivity requires removing the contributions from both altered heat capacity and thermal diffusivity during phase transitions, which is well demonstrated in four selected kinds of phase transition materials (Cu2 Se, Cu2 S, Ag2 S, and Ag2 Se) in experiment. This study also explains the lowered abnormal thermal diffusivity during phase transitions in other materials and thus provides a novel strategy to engineer thermal conductivity for various applications.

Currently, the application of thermoelectric power generators based on Bi

Many superionic mixed ionic–electronic conductors with a liquid-like sublattice have been identified as high efficiency thermoelectric materials, but their applications are limited due to the possibility of decomposition when subjected to high electronic currents and large temperature gradients. Here, through systematically investigating electromigration in copper sulfide/selenide thermoelectric materials, we reveal the mechanism for atom migration and deposition based on a critical chemical potential difference. Then, a strategy for stable use is proposed: constructing a series of electronically conducting, but ion-blocking barriers to reset the chemical potential of such conductors to keep it below the threshold for decomposition, even if it is used with high electric currents and/or large temperature differences. This strategy not only opens the possibility of using such conductors in thermoelectric applications, but may also provide approaches to engineer perovskite photovoltaic materials and the experimental methods may be applicable to understanding dendrite growth in lithium ion batteries., Mixed ionic–electronic conductors are limited by material decomposition. Here the authors reveal the mechanism for atom migration and deposition in Cu2–δ(S,Se) materials based on a critical chemical potential difference and propose electronically conducting, ion-blocking interfaces to enhance stability.

A novel quaternary Cu

Binary Cu2Se and Cu2Te have gained great attention recently because of their interesting and abnormal physical properties, such as ultralow thermal conductivity, high carrier mobility, large effective mass of carriers and excellent thermoelectric performance. In this study, we find that these two compounds are completely miscible throughout the studied composition range. The trigonal structure of Cu2Se is maintained when the Te content x is 0.2, but a new trigonal structure is formed when the Te content x is between 0.3 and 0.7. The carrier concentration is greatly improved when increasing the Te content in Cu2Se1-xTex solid solutions, resulting in a much reduced electrical resistivity and Seebeck coefficient in the whole temperature range as compared with those of binary Cu2Se. The total thermal conductivity is inversely increased due to the contribution from enhanced carrier thermal conductivity. As a result, the overall thermoelectric performance of Cu2Se1-xTex solid solutions lies between Cu2Se and Cu2Te. We also find that the quality factor of Cu2Se1-xTex is higher than those of most typical thermoelectric materials. Thus the thermoelectric performance can be further improved if the intrinsically high hole carrier concentrations can be reduced in Cu2Se1-xTex.

The influence of MeV β-rays irradiation on the thermoelectric performance of n-type filled skutterudite material has been investigated using an electron accelerator. Using a Monte-Carlo simulation base on Fluka code, the deposited energy in the sample material from the irradiation is estimated, which shows a large power deposited around 50 W/mm. Nevertheless, the thermoelectric performances of the filled skutterudite samples are compared before and after irradiations. It indicates that the thermoelectric material will not be easily jeopardized by ‘light’ irradiations with energy lower than MeV range.

Short carbon fiber-reinforced p-type skutterudite CeFe 4 Sb 12 composites were fabricated by a melting-annealing process combined with spark plasma sintering, the effect of carbon fibers on the thermoelectric and mechanical properties were investigated, and the relationship between the microstructure and the mechanical properties of the composites were elucidated. The results indicate that the carbon fibers were well distributed throughout the matrix and were in intimate contact with the CeFe 4 Sb 12 grains without interlayers. Both the flexural strength and the fracture toughness of CeFe 4 Sb 12 were enhanced with the addition of the carbon fibers. Considering the tradeoff between the thermoelectric and mechanical properties, the optimal carbon fiber content was found to be 1 vol.%. The flexural strength of the composite containing 1 vol.% fiber was improved by 53%, whereas the fracture toughness and ZT value remained nearly unchanged.

The ternary selenide CuAgSe shows great potential as a new promising thermoelectric material due to its superior carrier mobility and low lattice thermal conductivity. In this study, we doped Te at Se-sites and systematically studied the effect of Te-doping on the thermoelectric properties of the low-temperature CuAgSe phase (β-CuAgSe). It is found that the Te doping limit in β-CuAgSe is around 0.15. The longitudinal resistivity and Hall resistivity measurements under a magnetic field suggest that Te-doping exerts little effect on the band structure and the low-mobility carriers (holes) contribute weakly to the electrical transport in all Te-doped samples. Thus, the p–n transition and accompanying abrupt Seebeck coefficient decrease at elevated temperatures, which are quite common in non-stoichiometric β-CuAgSe samples, were not observed in Te-doped samples. Although the electrical conductivity of Te-doped samples is reduced due to the decreased carrier concentration and mobility, the significantly decreased thermal conductivity ensures that the Te-doped samples still maintain a similar or slightly higher thermoelectric figure of merit (zT) as compared with that of the stoichiometric β-CuAgSe. The maximum zT around 0.7 at 450 K is obtained in CuAgSe0.95Te0.05.

CuAgSe is a narrow band gap semiconducting material with superior carrier mobility and low lattice thermal conductivity, which are important and useful for high thermoelectric performance. However, its electrical and thermal transport properties are greatly affected by ionic deficiencies or compositional non-stoichiometry, which lead to a low thermoelectric figure of merit near room temperature. In this work, we systematically studied the compound defects in CuAgSe by tuning its starting chemical composition. We found that its phase purity is very sensitive to nominal chemical compositions. Only a small amount of Ag deficiency is allowed in CuAgSe to maintain phase purity, while the other non-stoichiometric compositions lead to impurity phases. Thermoelectric properties are weakly affected by these compound defects or impurity phases at 300 K, but greatly change at high temperatures. A single type carrier conduction is observed in CuAgSe, but a noticeable two-type carrier conduction is observed in the non-stoichiometric samples. This leads to an evident n to p conduction transition. Consequently, zT values in CuAgSe continuously increase to 0.6 at 450 K while the non-stoichiometric samples display considerably low values due to the contribution from both electrons and holes. The high zT value in n-type CuAgSe suggests that it is a promising thermoelectric material near room temperature.

Diamond‐like compounds are a promising class of thermoelectric materials, very suitable for real applications. However, almost all high‐performance diamond‐like thermoelectric materials are p‐type semiconductors. The lack of high‐performance n‐type diamond‐like thermoelectric materials greatly restricts the fabrication of diamond‐like material‐based modules and their real applications. In this work, it is revealed that n‐type AgInSe2 diamond‐like compound has intrinsically high thermoelectric performance with a figure of merit (zT) of 1.1 at 900 K, comparable to the best p‐type diamond‐like thermoelectric materials reported before. Such high zT is mainly due to the ultralow lattice thermal conductivity, which is fundamentally limited by the low‐frequency Ag‐Se “cluster vibrations,” as confirmed by ab initio lattice dynamic calculations. Doping Cd at Ag sites significantly improves the thermoelectric performance in the low and medium temperature ranges. By using such high‐performance n‐type AgInSe2‐based compounds, the diamond‐like thermoelectric module has been fabricated for the first time. An output power of 0.06 W under a temperature difference of 520 K between the two ends of the module is obtained. This work opens a new window for the applications using the diamond‐like thermoelectric materials.