Anion/Cation Co-Doping to Improve the Thermoelectric Performance of Sn-Enriched n-Type SnSe Polycrystals with Suppressed Lattice Thermal Conductivity.

Enhancing the thermoelectric performance of n-type polycrystalline SnSe is essential, addressing challenges posed by elevated thermal conductivity and compromised power factor inherent in its intrinsic p-type characteristics. This investigation utilized solid-state reactions and spark plasma sintering techniques for the synthesis of n-type SnSe. A significant improvement in the figure of merit (ZT) is achieved through strategic reduction in Se concentration and optimization of crystal orientation. The co-doping with Br and Ge further improves the material; Br amplifies carrier concentration, enhancing electrical conductivity, while Ge introduces effective phonon scattering centers. In the Br/Ge co-doped SnSe sample, thermal conductivity dropped to 0.38 Wm⁻¹K⁻¹, yielding a remarkable power factor of 662 µW mK- 2 at 773 K, culminating in a ZT of 1.34. This signifies a noteworthy 605% improvement over the pristine sample, underscoring the pivotal role of Ge doping in enhancing n-type material thermoelectric properties. The enhancement is attributed to Br doping introducing additional electronic states near the valence band, and Ge doping modifying the band structure, fostering resonant states near the conduction band. The Br/Ge co-doping further transforms the band structure, influencing electrical conductivity, Seebeck coefficient, and thermal conductivity, advancing the understanding and application of n-type SnSe materials for superior thermoelectric performance.

High-Performance Thermoelectric Flexible Ag2Se-Based Films with Wave-Shaped Buckling via a Thermal Diffusion Method.

Herein, an n-type Ag2Se thermoelectric flexible thin film has been fabricated on a polyimide (PI) substrate via a novel thermal diffusion method, and the thermoelectric performance is well-optimized by adjusting the pressure and temperature of thermal diffusion. All of the Ag2Se films are beneficial to grow (013) preferred orientations, which is conducive to performing a high Seebeck coefficient. By increasing the thermal diffusion temperature, the electrical conductivity can be rationally regulated while maintaining the independence of the Seebeck coefficient, which is mainly attributed to the increased electric mobility. As a result, the fabricated Ag2Se thin film achieves a high power factor of 18.25 µW cm-1 K-2 at room temperature and a maximum value of 21.7 µW cm-1 K-2 at 393 K. Additionally, the thermal diffusion method has resulted in a wave-shaped buckling, which is further verified as a promising structure to realize a larger temperature difference by the simulation results of finite element analysis (FEA). Additionally, this unique surface morphology of the Ag2Se thin film also exhibits outstanding mechanical properties, for which the elasticity modulus is only 0.42 GPa. Finally, a flexible round-shaped module assembled with Sb2Te3 has demonstrated an output power of 166 nW at a temperature difference of 50 K. This work not only introduces a new method of preparing Ag2Se thin films but also offers a convincing strategy of optimizing the microstructure to enhance low-grade heat utilization efficiency.

Effects of Si Substrates with Variable Initial Orientations on the Growth and Thermoelectric Properties of Bi-Sb-Te Thin Films.

For thermoelectric thin film, the substrate plays an important role during the growing process and produces effects on its thermoelectric properties. Some special kinds of substrates provide an optimal combination of influences on both the structure and thermoelectric properties. In this work, Bi-Sb-Te films are deposited on Si substrates with different initial orientations by magnetron sputtering in two ways: with and without a pre-coating process. The preferred orientations of the Bi-Sb-Te films are greatly affected by the substrates, in which the thin film tends to deposit on Si substrate with (100) initial orientation and high (015)-texture, while the (00l)-textured Bi-Sb-Te film easily deposits on Si substrate with (110) initial orientation. The experimental and theoretical calculation results indicate that Bi-Sb-Te film with (00l)-texture presents good electrical conductivity and a higher power factor than that of film with (015)-texture.

Achieving High Thermoelectric Performance of Eco-Friendly SnTe-Based Materials by Selective Alloying and Defect Modulation.

Recently, rock-salt lead-free chalcogenide SnTe-based thermoelectric (TE) materials have been considered an alternative to PbTe because of the nontoxic properties of Sn as compared to Pb. However, high carrier concentration that originated from intrinsic Sn vacancies and relatively high thermal conductivity of pristine SnTe lead to poor TE efficiency, which makes room for improving its TE properties. In this study, we present that the Na incorporation into the SnTe matrix is helpful for modifying the electronic band structure, optimization of carrier concentration, introducing dislocations, and kink planes; benefiting from these synergistic effects obviates the disadvantages of SnTe and makes a significant improvement in TE performance. We reveal that Na favorably impacts the structure of electronic bands by valence, conduction band engineering, leading to a nice enhancement in the Seebeck coefficient, which exhibits the highest power factor value of 37.93 µWcm-1 K-2 at 898 K, representing the best result for the SnTe material system. Moreover, a broader phonon spectrum is introduced by new phonon-scattering centers, scattered by dislocations and kink planes which suppressed lattice thermal conductivity to 0.57 Wm-1 K-1 at 898 K, which is much lower than that of pristine SnTe. Ultimately, a maximum ZT of 1.26 at 898 K is achieved in the Sn1.03Te + 3% Na sample, which is 97% higher than that of the pristine SnTe, suggesting that SnTe-based materials are a robust candidate for TE applications specifically, an ideal alternative of lead chalcogenides for TE power generation at high temperatures.

Novel Thermal Diffusion Temperature Engineering Leading to High Thermoelectric Performance in Bi2 Te3 -Based Flexible Thin-Films.

Flexible Bi2 Te3 -based thermoelectric devices can function as power generators for powering wearable electronics or chip-sensors for internet-of-things. However, the unsatisfied performance of n-type Bi2 Te3 flexible thin films significantly limits their wide application. In this study, a novel thermal diffusion method is employed to fabricate n-type Te-embedded Bi2 Te3 flexible thin films on flexible polyimide substrates, where Te embeddings can be achieved by tuning the thermal diffusion temperature and correspondingly result in an energy filtering effect at the Bi2 Te3 /Te interfaces. The energy filtering effect can lead to a high Seebeck coefficient ≈160 µV K-1 as well as high carrier mobility of ≈200 cm2 V-1 s-1 at room-temperature. Consequently, an ultrahigh room-temperature power factor of 14.65 µW cm-1 K-2 can be observed in the Te-embedded Bi2 Te3 flexible thin films prepared at the diffusion temperature of 623 K. A thermoelectric sensor is also assembled through integrating the n-type Bi2 Te3 flexible thin films with p-type Sb2 Te3 counterparts, which can fast reflect finger-touch status and demonstrate the applicability of as-prepared Te-embedded Bi2 Te3 flexible thin films. This study indicates that the thermal diffusion method is an effective way to fabricate high-performance and applicable flexible Te-embedded Bi2 Te3 -based thin films.

Two-Dimensional Platinum Diselenide: Synthesis, Emerging Applications, and Future Challenges.

In recent years, emerging two-dimensional (2D) platinum diselenide (PtSe2) has quickly attracted the attention of the research community due to its novel physical and chemical properties. For the past few years, increasing research achievements on 2D PtSe2 have been reported toward the fundamental science and various potential applications of PtSe2. In this review, the properties and structure characteristics of 2D PtSe2 are discussed at first. Then, the recent advances in synthesis of PtSe2 as well as their applications are reviewed. At last, potential perspectives in exploring the application of 2D PtSe2 are reviewed.

Thermoelectric Properties of Tin Telluride Quasi Crystal Grown by Vertical Bridgman Method.

Tin telluride (SnTe), with the same rock salt structure and similar band structure of PbTe alloys, was developed as a good thermoelectric material. In this work, SnTe quasi crystal was grown by vertical Bridgman method, with texturing degree achieved at 0.98. Two sets of samples, perpendicular and parallel to the growth direction, were cut to investigate thermoelectric properties. As a result, a carrier concentration (pH) of ~9.5 × 1020 cm-3 was obtained, which may have originated from fully generated Sn vacancies during the long term crystal growth. The relatively high Seebeck coefficient of ~30 µVK-1 and ~40 µVK-1 along the two directions was higher than most pristine SnTe reported in the literature, which leads to the room temperature (PF) for SnTe_IP and SnTe_OP achieved at ~14.0 µWcm-1K-2 and ~7.0 µWcm-1K-2, respectively. Finally, the maximum dimensionless figure of merit (ZT) values were around 0.55 at 873 K.

Effect of Graphene Oxide Nano-Sheets on Structural, Morphological and Photocatalytic Activity of BiFeO3-Based Nanostructures.

Photocatalysts are widely used for the elimination of organic contaminants from waste-water and H2 evaluation by water-splitting. Herein, the nanohybrids of lanthanum (La) and selenium (Se) co-doped bismuth ferrites with graphene oxide were synthesized. A structural analysis from X-ray diffraction confirmed the transition of phases from rhombohedral to the distorted orthorhombic. Scanning electron microscopy (SEM) revealed that the graphene nano-sheets homogenously covered La-Se co-doped bismuth ferrites nanoparticles, particularly the (Bi0.92La0.08Fe0.50Se0.50O3-graphene oxide) LBFSe50-G sample. Moreover, the band-gap nanohybrids of La-Se co-doped bismuth ferrites were estimated from diffuse reflectance spectra (DRS), which showed a variation from 1.84 to 2.09 eV, because the lowering of the band-gap can enhance photocatalytic degradation efficiency. Additionally, the photo-degradation efficiencies increased after the incorporation of graphene nano-sheets onto the La-Se co-doped bismuth ferrite. The maximum degradation efficiency of the LBFSe50-G sample was up to 80%, which may have been due to reduced band-gap and availability of enhanced surface area for incoming photons at the surface of the photocatalyst. Furthermore, photoluminescence spectra confirmed that the graphene oxide provided more electron-capturing sites, which decreased the recombination time of the photo-generated charge carriers. Thus, we can propose that the use of nanohybrids of La-Se co-doped bismuth ferrite with graphene oxide nano-sheets is a promising approach for both water-treatment and water-splitting, with better efficiencies of BiFeO3.

Achieving high thermoelectric performance of Cu1.8S composites with WSe2 nanoparticles.

Polycrystalline p-type Cu1.8S composites with WSe2 nanoparticles were fabricated by the mechanical alloying method combined with the spark plasma sintering technique. The Seebeck coefficient was significantly enhanced by the optimized carrier concentration, while the thermal conductivity was simultaneously decreased due to the refined grain and WSe2 nanoparticles. An enhanced Seebeck coefficient of 110 µV K-1 and a reduced thermal conductivity of 0.68 W m-1 K-1 were obtained for the Cu1.8S + 1 wt% WSe2 sample at 773 K, resulting in a remarkably enhanced peak ZT of 1.22 at 773 K, which is 2.5 times higher than that (0.49 at 773 K) of a pristine Cu1.8S sample. The cheap and environmentally friendly Cu1.8S-based materials with enhanced properties may find promising applications in thermoelectric devices.

Hydrothermal synthesis of SnQ (Q = Te, Se, S) and their thermoelectric properties.

Lead-free IV-VI semiconductors SnQ (Q = Te, Se, S) are deemed as promising thermoelectric (TE) materials. In this work, we designed a hydrothermal route to selectively synthesize single phase SnTe, SnSe and SnS nanopowders. For all three samples, the phase structure were characterized by x-ray diffraction, SnTe particles with octahedron structure and SnSe/SnS particles with plate-like shape were observed by field emission scanning electron microscopy and transmission electron microscopy, the formation mechanism was discussed in detail. Then, SnTe, SnSe and SnS nanopowders were densified by spark plasma sintering for investigating TE properties. It was noticed that SnSe and SnS exhibited remarkably anisotropy in both electrical and thermal properties attributed to the layered crystal structure. The highest ZT values 0.79 at 873 K, 0.21 at 773 K, and 0.13 at 773 K were achieved for SnTe, SnSe and SnS bulk samples, respectively.

Origin of the enhancement in transport properties on polycrystalline SnSe with compositing two-dimensional material MoSe2.

P-type SnSe compositing with 2D MoSe2 materials have been prepared by the solid solution method followed by the spark plasma sintering technique. The total thermal conductivities of SnSe/MoSe2 composites were found to be higher than for pristineSnSe at room temperature; and the disparity between them becomes smaller at higher temperatures, where the low thermal conductivities remained. Both the carrier concentration and the carrier mobility were significantly improved after MoSe2 was introduced into the SnSe matrix along the direction perpendicular to the pressing direction, leading to an extraordinary enhancement in electrical transport performance. The maximum ZT of 0.5 was obtained at 773 K for SnSe + 1.5%MoSe2 along the direction perpendicular to the pressing direction; this value is 1.5 times as large as that of the pristine SnSe.

Enhanced thermoelectric properties of SnSe polycrystals via texture control.

We present in this manuscript that enhanced thermoelectric performance can be achieved in polycrystalline SnSe prepared by hydrothermal reaction and spark plasma sintering (SPS). X-ray diffraction (XRD) patterns revealed strong orientation along the [l 0 0] direction in bulk samples, which was further confirmed by microstructural observation through transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). It was noticed that the texturing degree of bulk samples could be controlled by sintering temperature during the SPS process. The best electrical transport properties were found in the sample which sintered at 450 °C in the direction vertical to the pressing direction, where the highest texturing degree and mass density were achieved. Coupled with the relatively low thermal conductivity, an average ZT of ∼ 0.38, the highest ever reported in pristine polycrystalline SnSe was obtained. This work set up a forceful example that a texture-control approach can be utilized to enhance the thermoelectric performance effectively.

Synthesis and transport property of Cu(1.8)S as a promising thermoelectric compound.

Polycrystalline Cu(1.8)S compounds were fabricated by using a combined process of mechanical alloying and spark plasma sintering. The Cu(1.8)S sample with a second Cu(1.96)S phase and a lot of micro pores shows its maximum ZT value 0.5 at 673 K which is the highest value for p-type sulfide thermoelectric materials so far.