Starting with the first published works on the electrochemical deposition of thermoelectric (TE) V–VI compounds in the early nineties, these past two decades have seen a steady increase in scientific interest and publications on this topic. This is hardly surprising, as TE devices offer unique opportunities for power generation in virtually any environment (“energy harvesting”) or demanding cooling applications through the Peltier effect. This review first provides an overview of the advances in the electrodeposition of n- and p-type thin films based on Bi2(Te, Se)3 and (Bi, Sb)2Te3, the currently best-known TE materials for room temperature applications. The overview includes information about the electrolyte and the deposition conditions as well as the achieved composition, thickness, morphology, and TE properties of the deposited films. Additionally, we present the state-of-the-art and recent developments in electroplating-based fabrication processes for microscale TE devices.

Thermoelectric generation is one of the strongest candidates for recovering the waste heat from industry and transportation. Some of oxides and silicides are considered to be promising thermoelectric materials because of their high oxidation resistance. Several types of modules using p-type Ca3Co4O9/n-type CaMnO3 and p-type MnSi1.75/n-type Mn3Si4Al2 have been prepared and shown around 4 kW/m2 of maximum power density. The present study described the challenging enhancement of the thermoelectric figure of merit ZT of both oxide and silicide compounds. Introduction of secondary phases and low bulk density using a partial melting method is found to be effective for reducing phonon thermal conductivity in the promising Bi2Sr2Co2Ox. The grain size and distribution of the secondary phases can be controlled by optimizing the parameters of the partial melting method. On the other hand, detailed crystallographic structure of a new n-type Mn3Si4Al2 is clarified and leads to the enhancement of the ZT values by elemental substitution.

Double-filled high Fe content skutterudites, BaxYbyFe3CoSb12 (x + y = 1), were synthesized to investigate their high temperature transport properties. Both their phase and stoichiometry were characterized by powder x-ray diffraction and energy dispersive spectroscopy. The Seebeck coefficient, S, and electrical resistivity, ρ, increase with increasing temperature for all specimens over the entire measured temperature range. The thermal conductivity for the two low Ba content specimens decreases with increasing temperature up to 550 K at which point it increases with temperature due to bipolar diffusion. Bipolar diffusion becomes negligible with increasing Ba content. Due to this low bipolar diffusion, the ZT values of the higher Ba content specimens increase linearly with temperature, with the highest ZT value obtained for Ba0.9Yb0.1Fe3CoSb12.

We theoretically investigated the structural and thermoelectric properties of Mg2Si with Al and Sb (Na and B) as n-type (p-type) impurities. Supercell calculations involving relaxation of the atomic positions using an ab initio pseudo-potential method were performed. The formation energies, Eform,i, for the i = Mg, Si, and 4b sites, and consequently, the energetically preferred sites occupied by the impurities, were discussed. The calculated Eform,i were used to estimate the impurity-site occupancy probabilities, pi(T), based on the canonical distribution in the equilibrium state, i.e., pi(T) ∝ exp(−Eform,i/kBT) (Boltzmann constant: kB, temperature: T), and the resultant effects on the carrier concentration. Next, an all-electron full-potential linearized augmented-plane-wave calculation was performed based on the optimized structures, and the temperature dependence of the thermoelectromotive force (the Seebeck coefficient) was evaluated using the Boltzmann transport equation. The calculated and experimental results for n-type doped systems were compared.

We present the results of a mixed-space approach, based on first-principles calculations, to investigate phonon dispersions and thermal properties of Mg2Si and Mg2Sn, including the bulk modulus, Grüneisen parameter, heat capacity, and Debye temperature. It is shown that good agreements are obtained between the calculated results and available experimental data for both phonon dispersions and thermal properties. The phonon dispersions are accurately calculated compared with experimental data due to the high-quality description of LO–TO splitting and transverse acoustic branches along the Γ-K-X symmetry line. We also calculate the heat capacity CP and Debye temperature of Mg2Si1−xSnx alloys (x = 0.375, 0.5, 0.625, 0.875). The CP values at high temperature range from 0.5 to 0.7 J/g/K and ΘD values at room temperature from 332 to 384 K as the Sn content decreases from 0.875 to 0.375.

Semisolid powder processing (SPP) was used to fabricate n-type bismuth telluride-based polycrystalline bulk materials with improved thermoelectric properties. The minimum lattice thermal conductivity and the maximum ZT value of the SPP sample obtained in this study are 0.163 W m−1 K−1 at 383 K and 0.89 at 423 K, respectively. This ZT value exhibited a significant enhancement of 65.7 and 101.3% compared with the hot-pressing and the die-casting counterparts, respectively. The reduction of the lattice thermal conductivity is mainly due to the nanoscale grains and the mesoscale pores induced by the SPP. The grain boundaries and the interfaces brought by the porosities could scatter the phonons with mean free paths extensively from 300 nm to 1 μm. The remarkable enhancement of the ZT value and the convenient fabricating process suggest that the SPP is a promising method for mass production of high-performance bismuth telluride-based polycrystalline bulk materials.

Highly textured, ultrafine grain pure Bi2Te3 has been obtained by applying large-strain high-pressure torsion (HPT) to hot-pressed (HP) coarse grain material. Its thermal conductivity is significantly smaller than the conductivity of HP Bi2Te3, and its crystallographic texture and mechanical properties significantly improved. The mechanical properties of both, coarse grain and ultrafine grain, samples have been assessed by compression tests of 2 µm diameter micropillars machined by focused ion beam. The micropillars built from coarse grain samples are single crystalline, those built from ultrafine grain materials are an order of magnitude larger than their grain size. The test results put in evidence the elastic and plastic anisotropy of Bi2Te3 and the significant strengthening and toughening effect of ultrafine grain refining. For instance, after an equivalent strain of about 100, the Vickers hardness (in kg mm−2) increases from 60 to 120. Simultaneously, about a 40% reduction of the thermal conductivity has been measured, and a very strong basal texture is developed normal to the torsion axis. Such combination of properties looks very promising for simultaneously enhancing the thermoelectric figure of merit and the mechanical reliability of Bi2Te3-based alloys through HPT processing.

Phase change materials are identified for their ability to rapidly alternate between the amorphous and crystalline phases and have large contrast in the optical/electrical properties of the respective phases. The materials are not only primarily used in memory storage applications, but also recently they have been identified as potential thermoelectric materials [D. Lencer et al., Adv. Mater.23, 2030–2058 (2011)]. Many of the phase change materials studied today can be found on the pseudo-binary (GeTe)1−x(Sb2Te3)x tie-line. While many compounds on this tie-line have been recognized as thermoelectric materials, here we focus on Ge4SbTe5, a single phase compound just off of the (GeTe)1−x(Sb2Te3)x tie-line, which forms in a stable rocksalt crystal structure at room temperature. We find that stoichiometric and undoped Ge4SbTe5 exhibits a thermal conductivity of ∼1.2 W/m K at high temperature and a large Seebeck coefficient of ∼250 μV/K. The resistivity decreases dramatically at 623 K due to a structural phase transition which leads to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. In a more general sense, the work presents evidence that phase change materials can potentially provide a new route to highly efficient thermoelectric materials for power generation at high temperature.

The (3 + 1)-dimensional crystal structure of the Nowotny chimney–ladder compound Rh17Ge22 was revealed using powder x-ray diffraction technique. As in the case of the higher manganese silicide MnSiγ (known as Mn11Si19, etc.), this germanide consists of two tetragonal subsystems of [Rh] and [Ge] with an irrational c-axis ratio γ = cRh/cGe, and hence the structural formula can be represented as RhGeγ. As expected from first-principles calculations of the approximate structure and the valence electron count, n-type (negative Seebeck coefficient) conduction was experimentally confirmed over the whole temperature range of 333–984 K. Although the absolute value of the Seebeck coefficient was limited to |S| ≤ 53 μV/K, a high electrical conductivity (σ = 4.8 × 103 S/cm) yielded a reasonable power factor of S2σ ∼ 1 mW/K2 m above 600 K. A maximum dimensionless figure-of-merit of ∼0.1 at 900 K was expected using thermal conductivity data of a sintered pellet.

The peculiarities of the Seebeck coefficient and power factor are studied in porous thermoelectric materials with spherical hollow pores of varying diameter from nanometer to micrometer length scales. The pores are assumed to be randomly dispersed throughout the matrix material. The influence of trap centers situated at pore interfaces on the power factor is investigated. Using the model based on gamma distribution of the pore sizes, the analytical expression is obtained for the power factor at the arbitrary level of the Fermi energy. Limiting cases of nondegenerate and degenerately doped porous semiconductors are examined as well. The results are compared with calculations for a multilayer composite in which each layer contains pores of a single length-scale. It is shown that the presence of hollow pores with multiscale hierarchical disorder leads to more considerable enhancement in the thermopower over its value in the bulk. Necessary conditions for the enhancement of the power factor are found.

Over the last decade, the inclusion of nanofeatures has been demonstrated extensively for improving the performance of thermoelectric materials. The continued approach is to nanofeaturing these materials in a smart manner tailoring their electronic and thermal response. This research provides a computational tool for predicting all parameters in the thermoelectric figure of merit for a Si/Ge superlattice structure as a function of doping and layer thickness. The approach involves coupling a nonequilibrium Green's function electronic and thermal transport model. The phonon description is communicated between the two models to facilitate spatially resolved multiphonon frequency electron–phonon scattering. Findings support the consideration of multiple phonon frequency scattering to accurately predict ZT values. An extrema in ZT as function of both doping and geometry were predicted. Furthermore, the optimal superlattice design was determined to be a Si(2 nm)/Ge(7 nm) with a donor concentration on the order of 1019 cm−3 for operation at 300 K.

We report a cost-effective, surfactant-free, and scalable synthesis technique for lead telluride (PbTe) nanocubes by a chemical precipitation method. The high-resolution transmission electron microscopy studies indicated the evolution of nucleation centers (spherical) into nanocubes with the addition of the Pb and Te atoms. The spark plasma sintered PbTe nanocubes exhibited an enhanced Seebeck coefficient, S > +400 µV, higher than the reported values of the bulk PbTe over an extended temperature range of 300–425 K, and a moderate electrical conductivity, σ ∼ 8000 S/m at 300 K. A significant reduction in the lattice thermal conductivity was observed due to effective phonon scattering from the presence of numerous interfaces introduced by nanostructuring. The resulting figure-of-merit (ZT) ∼ 0.45 at 300 K is higher than the reported values at this temperature in other PbTe nanostructures. Moreover, a moderate thermoelectric compatibility factor makes the PbTe nanocubes a potential candidate for green energy generation.

Thermoelectric converters based on silicon nanostructures offer exciting opportunities for higher efficiency, lower cost, ease of manufacturing, and integration into circuits. This paper considers phonon transport in a broad range of nanostructured materials made from Si, Ge, and their alloys. Our model based on the phonon Boltzmann transport equation captures the lattice thermal transport in silicon–germanium (SiGe) nanostructures, including thin films, superlattices (SLs), and nanocomposites. In nanocomposites, the model captures the grain structure using a Voronoi tessellation to mimic the grains and their size distribution. Our results show thermal conductivity in SiGe nanostructures below their bulk counterparts and reaching almost to the amorphous limit of thermal conductivity. We also demonstrate that thermal transport in SiGe nanostructures is tuneable by sample size (thin films), period thickness (SLs), and grain size (nanocomposites) through boundary scattering. Our results are relevant to the design of nanostructured SiGe alloys for thermoelectric applications.

A possible approach to raise the efficiency of single-junction solar cells is to couple them with thermoelectric generators (TEGs). It was shown that TEG contribution to the output power is basically ruled by the characteristics of the photovoltaic (PV) material. In this study, we present a quantitative model that correlates the efficiency of the hybrid thermoelectric–photovoltaic (HTEPV) device with the energy gap and the working temperature of the solar cell. Two HTEPV structures are discussed, one capable only to recover the heat released by relaxation of hot electron–hole pairs; and a second one also capturing the low–energy part of the solar spectrum. We show that in the second case the increase of the conversion efficiency could justify the effort needed to add a TEG stage to the PV device. HTEPV constructions are also shown to enable the use of wide-gap materials that are not currently considered in PV applications.

The Seebeck coefficient is an important parameter of thermoelectric materials, which is routinely measured by commercial or home-made equipment based on different methods. However, due to various temperature offsets in the measurement, the determination of temperature gradient can be inaccurate, leading to a large uncertainty in Seebeck coefficient. To elucidate the influence of the inaccurate temperature gradient on the determination of Seebeck coefficient, an error analysis has been performed on a commercial system. Several potential factors that may affect the establishment of temperature gradient were discussed in detail. A comparison between the single point method and the slope method was made to verify which is more accurate to calculate the Seebeck coefficient from the raw measurement data. It is suggested that the slope method is more preferable and the single point method can also be accurate enough when a relatively large temperature gradient is adopted.