Isotropic Thermoelectric Performance of Layer-Structured n-Type Bi2Te2.7Se0.3 by Cu Doping

Triple Synergistic Modulation via Sn Doping in Tetrahedrites: Electronic Structure, DOS, and Scattering Engineering for a High Thermoelectric Performance

Achieving a high power factor and low lattice thermal conductivity is crucial for improving the thermoelectric performance. The eco-friendly Cu12Sb4S13 tetrahedrite inherently exhibits a high power factor (∼10-14 μW cm-1 K-2) and low thermal conductivity (0.5-1.00 W m-1 K-1), but these properties also impose significant limitations for further performance enhancement. To overcome these challenges, researchers have explored strategies such as codoping/synergistic element doping and nanocomposites. In this work, we demonstrate that Sn doping at the Sb site in Cu12Sb4S13 (without the use of nanocomposites) enables the synergistic modulation of both the electronic and thermal properties. The Sn doping increases the hole concentration and enhances the density of states (DOS), leading to a marked improvement in the power factor (at 750 K), 12 μW cm-1 K-2 for x = 0 to 16 μW cm-1 K-2 for x = 0.04. Simultaneously, Sn doping induces strong phonon scattering, which lowers thermal conductivity by ∼69% (at 750 K). This synergistic modulation of the electronic structure, DOS, and scattering mechanisms results in a significant enhancement in the thermoelectric performance. The optimized Cu12Sb3.96Sn0.04S13 sample exhibits an exceptional figure of merit (ZT) of 1.26 at 750 K, representing a 126% increase compared to pristine Cu12Sb4S13. These findings demonstrate the effectiveness of Sn doping in simultaneously optimizing the electrical and thermal properties of Cu12Sb4S13 through the synergistic modulation of the electronic structure, density of states, and phonon scattering mechanisms.

Lattice plainification and band engineering lead to high thermoelectric cooling and power generation in n-type Bi2Te3 with mass production

Thermoelectrics can mutually convert between thermal and electrical energy, ensuring its utilization in both power generation and solid-state cooling. Bi2Te3 exhibits promising room-temperature performance, making it the sole commercially available thermoelectrics to date. Guided by the lattice plainification strategy, we introduce trace amounts of Cu into n-type Bi2(Te, Se)3 (BTS) to occupy Bi vacancies, thereby simultaneously weakening defect scattering and modulating the electronic bands. Meanwhile, the interstitial Cu can bond with the BTS matrix to form extra electron transport pathways. The multiple occupations of Cu substantially boost carrier mobility and electrical performance. Consequently, the BTS + 0.2%Cu achieves a room-temperature ZT of ∼1.3 with an average ZT ave of ∼1.2 at 300-523 K. Moreover, the kilogram-scale ingot designed for mass production also exhibits high uniformity. Finally, we fabricate a full-scale device that achieves an excellent conversion efficiency of ∼6.4% and a high cooling ΔT max of ∼70.1 K, both of which outperform commercial devices.

Thermoelectric Cooling-Oriented Large Power Factor Realized in N-Type Bi2Te3 Via Deformation Potential Modulation and Giant Deformation

Thermoelectric refrigeration, utilizing Peltier effect, has great potential in all-solid-state active cooling field near room temperature. The performance of a thermoelectric cooling device is highly determined by the power factor of consisting materials besides the figure of merit. In this work, it is demonstrated that successive addition of Cu and Nd can realize non-trivial modulation of deformation potential in n-type room temperature thermoelectric material Bi2Te2.7Se0.3 and result in a significant increment of electron mobility and remarkably enhanced power factor. Following giant hot deformation process improves grain texturing and strengthens inter-layer interaction in Bi2Te2.7Se0.3 lattice, further pushing the power factor to ≈47 µW cm-1 K-2 at 300 K and maximal figure of merit ZTmax to ≈1.34 at 423 K with average ZTave of ≈1.27 at 300-473 K. Moreover, robust compressive strength is enhanced to ≈146.6 MPa. The corresponding finite element simulations demonstrate large temperature differences ΔT of ≈70 K and a maximal coefficient of performance COP ≈ 10.6 (hot end temperature at 300 K), which can be achieved in a ten-pair thermoelectric cooling virtual module. The strategies and results as shown in this work can further advance the application of n-type Bi2Te3 for thermoelectric cooling.

Broad-Temperature Thermoelectric Figure of Merit Enhancement in Unconventional n-Type Bi2Te2.3Se0.7 Alloys

Bi2Te2.7Se0.3-based alloys are conventional n-type thermoelectric materials for solid-state cooling and heat harvest near room temperature; high thermoelectric performance over a wide temperature range and superior mechanical properties are essential for their use in practical thermoelectric devices. In this work, we demonstrated that decent thermoelectric performance can also be realized in an unconventional composite with a nominal composition of Bi2Te2.3Se0.7 since the emergence of a Bi2Te2Se phase with Se ordered occupation could induce an enlargement of the electronic band gap. Follow-up Cu/Na codoping could generate a dynamic optimization of carrier concentration, significantly broadening the temperature range of high thermoelectric performance. Further B incorporation and annealing treatment resulted in obvious grain refinement and stacking fault structures, which help pushing the ultimate maximal figure of merit up to ∼1.3 at 423 K with an average value of ∼1.2 at 300-573 K. This work might provide insights for further research on bismuth tellurides and other thermoelectric materials.

Interstitials in Thermoelectrics

Defect structure is pivotal in advancing thermoelectric performance with interstitials being widely recognized for their remarkable roles in optimizing both phonon and electron transport properties. Diverse interstitial atoms are identified in previous works according to their distinct roles and can be classified into rattling interstitial, decoupling interstitial, interlayer interstitial, dynamic interstitial, and liquid interstitial. Specifically, rattling interstitial can cause phonon resonance in cage compound to scatter phonon transport; decoupling interstitial can contribute to phonon blocking and electron transport due to their significantly different mean free paths; interlayer interstitial can facilitate out-of-layer electron transport in layered compounds; dynamic interstitial can tune temperature-dependent carrier density and optimize electrical transport properties at wide temperatures; liquid interstitial could improve the carrier mobility at homogeneous dispersion state. All of these interstitials have positive impact on thermoelectric performance by adjusting transport parameters. This perspective therefore intends to provide a thorough overview of advances in interstitial strategy and highlight their significance for optimizing thermoelectric parameters. Finally, the profound potential for extending interstitial strategy to various other thermoelectric systems is discussed and some future directions in thermoelectric material are also outlined.

Realizing high-efficiency thermoelectric module by suppressing donor-like effect and improving preferred orientation in n-type Bi2(Te, Se)3

Thermoelectric materials have a wide range of application because they can be directly used in refrigeration and power generation. And the Bi2Te3 stand out because of its excellent thermoelectric performance and are used in commercial thermoelectric devices. However, n-type Bi2Te3 has seriously hindered the development of Bi2Te3-based thermoelectric devices due to its weak mechanical properties and inferior thermoelectric performance. Therefore, it is urgent to develop a high-performance n-type Bi2Te3 polycrystalline. In this work, we employed interstitial Cu and the hot deformation process to optimize the thermoelectric properties of Bi2Te2.7Se0.3, and a high-performance thermoelectric module was fabricated based on this material. Our combined theoretical and experimental effort indicates that the interstitial Cu reduce the defect density in the matrix and suppresses the donor-like effect, leading to a lattice plainification effect in the material. In addition, the two-step hot deformation process significantly improves the preferred orientation of the material and boosts the mobility. As a result, a maximum ZT of 1.27 at 373 K and a remarkable high ZTave of 1.22 across the temperature range of 300-425 K are obtained. The thermoelectric generator (TEG, 7-pair) and thermoelectric cooling (TEC, 127-pair) modules were fabricated with our n-type textured Cu0.01Bi2Te2.7Se0.3 coupled with commercial p-type Bi2Te3. The TEC module demonstrates superior cooling efficiency compared with the commercial Bi2Te3 device, achieving a ΔT of 65 and 83.4 K when the hot end temperature at 300 and 350 K, respectively. In addition, the TEG module attains an impressive conversion efficiency of 6.5% at a ΔT of 225 K, which is almost the highest value among the reported Bi2Te3-based TEG modules.

Advancing Thermoelectric Performance of Bi2Te3 below 400 K

Thermoelectric cooling devices utilizing Bi2Te3-based alloys have seen increased utilization in recent years. However, their thermoelectric performance remains inadequate within the operational temperature range (≤400 K), with limited research addressing this issue. In this study, we successfully modulated the carrier concentration of the sample through Te content reduction, consequently lowering the peak temperature of the zT value from 400 to 300 K. This led to a substantial enhancement in thermoelectric performance at room temperature (≤400 K). Furthermore, by doping with La, the electrical transport properties have been further optimized, and the lattice thermal conductivity has been effectively reduced at the same time; the average zT value was ultimately elevated from 0.69 to 0.9 within the temperature range of 300-400 K. These findings hold significant promise for enhancing the efficacy of existing thermoelectric cooling devices based on Bi2Te3-based alloys.

Cu2Te Incorporation-Induced High Average Thermoelectric Performance in p-Type Bi2Te3 Alloys

p-Type (Bi, Sb)₂Te₃ alloys are attractive materials for near-room-temperature thermoelectric applications due to their high atomic masses and large spin-orbit interactions. However, their narrow band gaps originating from spin-orbit interactions lead to bipolar excitation, thereby limiting average thermoelectrics within a local temperature region (300-400 K). Here, we introduce Cu₂Te into the Bi_0.3Sb_1.7Te₃ (BST) lattice to implement high thermoelectrics over a wide temperature range. The carrier concentration is synergistically modulated via Cu substitution and the evolution of intrinsic point defects (antisites and vacancies). Furthermore, the chain effect caused by Cu₂Te incorporation in BST is reflected in the improvement of the weighted mobility μ_W, thereby enhancing the power factor in the whole temperature range. Extrinsic and intrinsic defects due to the incorporation of Cu₂Te lead to a significant reduction in the lattice thermal conductivity κ_L, which is further demonstrated by Raman spectroscopy. Combining κ_L and μ_W, the quantity factor B increases from 0.5 to 1 with increasing Cu₂Te content due to not only the reduction of κ_L but also a significant improvement in electrical properties. Eventually, a peak figure of merit (zT) of ∼1.15 at 423 K is achieved in BST-Cu₂Te samples, and an average figure of merit (zT_ave) of ∼1.12 (350-500 K) surpasses other excellent p-type Bi₂Te₃-based thermoelectrics. Such a synergistic effect can facilitate near-room-temperature thermoelectric applications of Bi₂Te₃-based alloys and provide chances for the technology space in thermoelectrics.

Enhancing thermoelectric performance of n-type Bi2Te2.7Se0.3 through incorporation of Ag9AlSe6 inclusions

Bi2Te2.7Se0.3 (BTS) is the best commercial n-type thermoelectric alloy near room temperatures. However, as compared to its p-type counterpart its figure of merit (ZT) and the energy conversion efficiency is...