Polycrystalline SnSe Research Articles

Enhanced thermoelectric performance of AgCuTe-doped polycrystalline SnSe by lattice plainification

Abstract Polycrystalline SnSe, renowned for its environmental sustainability, holds promise as a significant thermoelectric material, attracting considerable research attention. This study focuses on the thermoelectric properties of p-type polycrystalline SnSe doped with silver copper telluride (AgCuTe). Our experimental results conclusively show that the decomposition products of AgCuTe not only fill Sn vacancies but also act as acceptors, thereby introducing additional hole carriers. This leads to a notable improvement in both carrier mobility and concentration. Importantly, the thermal conductivity of the doped samples remains largely unchanged, as the lattice flattening strategy significantly boosts electrical performance without affecting lattice thermal conductivity. Ultimately, the doped sample Sn0.97Se-0.5%AgCuTe resulted in a power factor of 6.2 mW/mK and a peak ZT value of 1.4 at 798 K, representing a 109% improvement in ZT value. All samples exhibits superior stability and reproducibility, emphasizing its reliability for practical applications.

Boosting thermoelectric performance of polycrystalline SnSe by controlled in-situ Ag2Se precipitates in grain boundaries

Boundary engineering has proven effective in enhancing the thermoelectric performance of materials. SnSe, known for its low thermal conductivity, has garnered significant interest; however, its application is hindered by poor electrical conductivity. Herein, the Ag8GeSe6 is introduced into the p-type polycrystalline SnSe matrix to optimize the thermoelectric performance, and the in-situ Ag2Se precipitates are formed in grain boundaries, which play dual roles, acting as an electron attraction center for improving hole concentration and a phonon scattering center for reducing lattice thermal conductivity. It effectively decouples the thermal and electrical transport properties to optimize the thermoelectric performance. Importantly, the amount of Ag2Se can be controlled by adjusting the amount of Ag8GeSe6 added to the SnSe matrix. The introduction of Ag8GeSe6 enhances electrical conductivity due to the increased hole carrier caused by the introduced Ag+ and the formed electron attraction center (in-situ Ag2Se precipitates). Based on the DFT calculations, the band gap of the Ag8GeSe6-doped samples is considerably decreased, facilitating carrier transport. As a result, the electrical transport properties increase to 808 μW m−1 K−2 at 823 K for SnSe + 0.5 wt% Ag8GeSe6. In addition, in-situ Ag2Se precipitates in grain boundaries strongly enhance phonon scattering, causing a decrease in lattice thermal conductivity. Furthermore, the presence of defects contributes to a reduction in lattice thermal conductivity. Specifically, the thermal conductivity of SnSe + 1.0 wt% Ag8GeSe6 decreases to 0.29 W m−1 K−1 at 823 K. Consequently, SnSe + 0.5 wt% Ag8GeSe6 obtains a high ZT value of 1.7 at 823 K and maintains a high average ZT value of 0.57 over the temperature range of 323−773 K. Additionally, the mechanical properties of Ag8GeSe6-doped also show an improvement. These advancements can be applied to energy supply applications during deep space exploration.

Influence of Sputtering Power on the Properties of Magnetron Sputtered Tin Selenide Films.

The ecofriendly tin selenide (SnSe) is expected to find multiple applications in optoelectronic, photovoltaic, and thermoelectric systems. This work is focused on the thermoelectric properties of thin films. SnSe single crystals exhibit excellent thermoelectric properties, but it is not so in the case of polycrystalline bulk materials. The investigations were motivated by the fact that nanostructuring may lead to an improvement in thermoelectric efficiency, which is evaluated through a dimensionless figure of merit, ZT = S2 σ T/λ, where S is the Seebeck coefficient (V/K), σ is the electrical conductivity (S/m), λ is the thermal conductivity (W/mK), and T is the absolute temperature (K). The main objective of this work was to obtain SnSe films via magnetron sputtering of a single target. Instead of common radiofrequency (RF) magnetron sputtering with a high voltage alternating current (AC) power source, a modified direct current (DC) power supply was employed. This technique in the classical version is not suitable for sputtering targets with relatively low thermal and electrical conductivity, such as SnSe. The proposed solution enabled stable sputtering of this target without detrimental cracking and arcing and resulted in high-quality polycrystalline SnSe films with unprecedented high values of ZT equal to 0.5 at a relatively low temperature of 530 K. All parameters included in ZT were measured in one setup, i.e., Linseis Thin Film Analyzer (TFA). The SnSe films were deposited at sputtering powers of 120, 140, and 170 W. They had the same orthorhombic structure, as determined by X-ray diffraction (XRD), but the thickness and microstructure examined by scanning electron microscopy (SEM) were dependent on the sputtering power. It was demonstrated that thermoelectric efficiency improved with increasing sputtering power and stable values were attained after two heating-cooling cycles. This research additionally provides further insights into the DC sputtering process and opens up new possibilities for magnetron sputtering technology.

Divacancy and resonance level enables high thermoelectric performance in n-type SnSe polycrystals

N-type polycrystalline SnSe is considered as a highly promising candidates for thermoelectric applications due to facile processing, machinability, and scalability. However, existing efforts do not enable a peak ZT value exceeding 2.0 in n-type polycrystalline SnSe. Here, we realized a significant ZT enhancement by leveraging the synergistic effects of divacancy defect and introducing resonance level into the conduction band. The resonance level and increased density of states resulting from tungsten boost the Seebeck coefficient. The combination of the enhanced electrical conductivity (achieved by increasing carrier concentration through WCl6 doping and Se vacancies) and large Seebeck coefficient lead to a high power factor. Microstructural analyses reveal that the co-existence of divacancy defects (Se vacancies and Sn vacancies) and endotaxial W- and Cl-rich nanoprecipitates scatter phonons effectively, resulting in ultralow lattice conductivity. Ultimately, a record-high peak ZT of 2.2 at 773 K is achieved in n-type SnSe0.92 + 0.03WCl6.

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 0.38Wm⁻¹K⁻¹, yielding a remarkable power factor of 662µWmK- 2 at 773K, 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.

Enhancing thermoelectric performance of solution-processed polycrystalline SnSe with PbSe nanocrystals

There is a growing interest in cost-effective polycrystalline SnSe-based thermoelectric (TE) materials, which are able to replace the high performance but mechanically fragile and costly single-crystalline SnSe. In this study, we present a low-temperature solution-based approach to produce SnSe-PbSe nanocomposites with outstanding TE performance. Our method involves combining surfactant-free SnSe particles with oleate-capped PbSe nanocrystals in specific ratios, followed by thermal annealing and consolidation using spark plasma sintering. These nanocomposites are characterized by distinct compositional and structural properties that significantly impact their transport properties. In particular, the addition of oleate-capped PbSe nanocrystals results in: i) a reduction in the electrostatically adsorbed Na at the surface of the SnSe particles; ii) a reduction of Sn vacancies due to alloying with Pb; iii) an increase in grain boundary density; and iv) the formation of PbSnSe secondary phases. Notably, the SnSe-2.5 %PbSe nanocomposites demonstrate a 30 % decrease in thermal conductivity compared to that of the SnSe matrix. This reduction contributes to a maximum figure of merit (zT) of 1.75 at 788 K with a high average zT value of ca. 1.2 in the medium temperature range of 573–773 K. These values represent one of the highest reported in polycrystalline SnSe materials, showcasing the potential of our fabricated SnSe-PbSe nanocomposites for cost-effective TE applications.

Achieving High Isotropic Figure of Merit in Cd and in Codoped Polycrystalline SnSe.

Here, we combined Cd and In codoping with a simple hydrothermal synthesis method to prepare SnSe powders composed of nanorod-like flowers. After spark plasma sintering, its internal grains inherited well the morphological features of the precursor, and the multiscale microstructure included nanorod-shaped grains, high-density dislocations, and stacking faults, as well as abundant nanoprecipitates, resulting in an ultralow thermal conductivity of 0.15 W m-1 K-1 for the synthesized material. At the same time, Cd and In synergistically regulated the electrical conductivity and Seebeck coefficient of SnSe, leading to an enhanced power factor. Among them, Sn0.94Cd0.03In0.03Se achieved a peak ZT of 1.50 parallel to the pressing direction, representing an 87.5% improvement compared with pure SnSe. Notably, the material possesses isotropic ZT values parallel and perpendicular to the pressing direction, overcoming the characteristic anisotropy in thermal performance observed in previous polycrystalline SnSe-based materials. Our results provide a new strategy for optimizing the performance of thermoelectric materials through structural engineering.

Metavalent Bonding in Cubic SnSe Alloys Improves Thermoelectric Properties over a Broad Temperature Range

AbstractMonocrystalline SnSe is one of the most promising thermoelectric materials with outstanding performance and a high abundance of constituting elements. However, polycrystalline SnSe, which is more robust for applications, only shows large figure‐of‐merit (zT) values in its high‐symmetry phase. Stabilizing the high‐symmetry phase at low temperatures can thus enhance the average zT value over a broad temperature range. In this work, the high‐symmetry rock‐salt SnSe phase is successfully obtained by alloying SnSe with AgVVI2 compounds (V = Sb, Bi; VI = Se, Te). These cubic SnSe phases show a unique portfolio of properties including a high optical dielectric constant, a large maximum of optical absorption, a large Born effective charge, and abnormal bond‐breaking behavior in laser‐assisted atom probe tomography. All of these characteristics are indicative of metavalent bonding. In contrast, the Pnma phase of SnSe employs covalent bonding. The enhanced symmetry at low temperatures is realized by tailoring chemical bonding. Concomitantly, zT near room temperature is increased by a factor of more than 10 from the pristine Pnma SnSe to Fmm SnSe alloys. This provides insights into the enhancement of the thermoelectric performance of SnSe and other chalcogenides over a broad temperature range by manipulating the chemical bonds.

High thermoelectric properties in polycrystalline SnSe materials realized by rare earth halide Co-doping

SnSe materials have garnered significant interest due to the intrinsic low thermal conductivity. However, its limited electrical conductivity hinders their practical implementation. This study achieved a high ZT value of 1.40 at 773 K in the samples of n-type polycrystalline SnSe0.95 + x wt% SmCl3 + y wt% ErCl3 (x = 0, 0.75, 1.0, 1.25, and 1.5; y = 0, 0.0675, 0.125, and 0.25) since (SmCl3, ErCl3) co-doping decoupled the electrical-thermal transport properties. First, the released electron carrier concentration due to SmCl3 doping enhanced the electrical transport properties. The SnSe0.95 + 1.25 wt% SmCl3 sample exhibited a high power factor of 563 μWm−1K−2 at 773 K. Then, the lattice thermal conductivity markedly decreased with further ErCl3 doping due to the high-density dislocations and coherent boundary, resulting in effective the phonon scattering. Additionally, the special microtopography was conducive to the decreased lattice thermal conductivity. Therefore, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample achieved a low lattice thermal conductivity value of 0.28 Wm−1K−1 at 773 K. Simultaneously, the (SmCl3, ErCl3) co-doped samples maintained the electrical transport properties than the SmCl3-doped samples. Consequently, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample obtained a peak ZT value of 1.40 at 773 K and a competitive average ZT value of 0.37 from 323 to 773 K, and a theoretically calculated conversion efficiency reached 7.2%, which can be applied in the deep space for power generation. This strategy can be utilized to optimize the thermoelectric performance of other thermoelectrical material systems.

Enhancing Electrical Transport Performance of Polycrystalline Tin Selenide by Doping Different Elements

In the face of ever‐evolving energy and environmental challenges, tin selenide (SnSe) has garnered significant attention due to its outstanding thermoelectric performance. The article focuses on the research of easily accessible and highly practical polycrystalline SnSe thermoelectric materials, providing an overview of their crystal structure, band structure, and electrical transport performance. Compared with previous studies, this research classifies elements based on their own properties, mainly dividing them into alkali metals, transition metals, main group metals, halogens, and rare earth (Re) elements. The study systematically summarizes the experimental results of doping SnSe with these elements and analyzes the mechanisms by which different elements enhance the electrical transport performance and thermoelectric figure of merit of polycrystalline SnSe. The enhanced mechanism is mainly achieved by increasing the conductivity and Seebeck coefficient. Finally, a systematic analysis is conducted to identify the factors that improve electrical transport performance, and strategies for enhancing the electrical transport and thermoelectric properties of polycrystalline SnSe through precise doping techniques are discussed, with a prospect for their application in the future.

Simultaneously engineering electronic and phonon band structures for high-performance n-type polycrystalline SnSe

Simultaneously engineering electronic and phonon band structures for high-performance n-type polycrystalline SnSe

CdSe Quantum Dots Enable High Thermoelectric Performance in Solution-Processed Polycrystalline SnSe.

Here, a high peakZTof ≈2.0 is reported in solution-processed polycrystalline Ge and Cd codoped SnSe. Microstructural characterization reveals that CdSe quantum dots are successfully introduced by solution process method. Ultraviolet photoelectron spectroscopy evinces that CdSe quantum dots enhance the density of states in the electronic structure of SnSe, which leads to a large Seebeck coefficient. It is found that Ge and Cd codoping simultaneously optimizes carrier concentration and improves electrical conductivity. The enhanced Seebeck coefficient and optimization of carrier concentration lead to marked increase in power factor. CdSe quantum dots combined with strong lattice strain give rise to strong phonon scattering, leading to an ultralow lattice thermal conductivity. Consequently, high thermoelectric performance is realized in solution-processed polycrystalline SnSe by designing quantum dot structures and introducing lattice strain. This work provides a new route for designing prospective thermoelectric materials by microstructural manipulation in solution chemistry.

Cold Sintering Mediated Engineering of Polycrystalline SnSe with High Thermoelectric Efficiency.

Despite the attractive thermoelectric properties in single crystals, the fabrication of high-performance polycrystalline SnSe by a cost-effective strategy remains challenging. In this study, we prepare the undoped SnSe ceramic with remarkable thermoelectric efficiency by the combination of a cold sintering process (CSP) and thermal annealing. The high sintering pressure during CSP induces not only highly oriented grains but also a high concentration of lattice dislocations and stacking faults, which leads to large lattice strain that can shorten the phonon relaxation time. Meanwhile, the thermal annealing breaks the highly resistive SnOx layers at grain boundaries, which improves the electrical conductivity and power factor. In addition, the grain growth during annealing further turns the broken SnOx layers into nanoparticles, which further lowers the thermal conductivity by enhanced scattering. As a result, a peak ZT of 1.3 at 890 K and a high average ZT of 0.69 are achieved in the polycrystalline SnSe, suggesting great potential in mid-temperature power generation. This work may pave the way for the mass production of SnSe-based ceramics for thermoelectric devices.

Simultaneously Enhanced Thermoelectric and Mechanical Performance in SnSe-Based Nanocomposites Produced via Sintering SnSe and KCu7S4 Nanomaterials.

Both thermoelectric and mechanical properties are important to the practical applications of thermoelectric materials. Herein, we develop a strategy for alloying KCu7S4 to improve the dimensionless figure of merit (zT), compressive strength, and Vickers hardness of polycrystalline SnSe. Through chemical synthesis and particle mixing in solutions, powders with SnSe nanoparticles and KCu7S4 nanowires are produced, and the subsequent spark plasma sintering triggers the reaction between the two chalcogenides, resulting in the formation of Cu2SnSe3 nanoparticles and substitution of Cu and S in the SnSe matrix. The composition tuning and secondary phase formation effectively enhance the power factor and diminish the lattice thermal conductivity, leading to a maximum zT of 1.13 at 823 K for the optimal sample, which is improved by 135% over that of SnSe. Simultaneously, the compressive strength and hardness are also enhanced, as exemplified by a high compressive strength of 135 MPa that is enhanced by ∼81% compared to that of SnSe. The current study demonstrates effective composite and composition design toward enhanced thermoelectric and mechanical performance in polycrystalline SnSe.

Modulating structures to decouple thermoelectric transport leads to high performance in polycrystalline SnSe

Introducing AgInSe2 modifies the crystal and band structures to facilitate electrical transport of SnSe, and Ge alloying further depresses phonon transport. The effective phonon-electron decoupling leads to an ultrahigh ZT ∼ 1.6 at 773 K.

Facile Synthesis and Enhancement of Thermoelectric Performance with Voltage Generation of Bulk Polycrystalline SnSe by Zn Doping

Facile Synthesis and Enhancement of Thermoelectric Performance with Voltage Generation of Bulk Polycrystalline SnSe by Zn Doping

High thermoelectric properties realized in polycrystalline (Ag, Ga) Co-doped SnSe via two-steps point defects modulation

Tin selenide materials have attracted much attention due to the intrinsic low thermal conductivity. However, the further application of SnSe materials is limited due to the poor electrical conductivity. Herein, a two-step doping process is employed on p-type polycrystalline SnSe materials to enhance the thermoelectric properties. It is found that the Sn0·98Ag0.01Ga0.01Se sample achieves a high ZT value of 1.53 at 823 K and a quite competitive ZTave value of 1.04 from 673 to 823 K. This is attributed to the associations of point defects, AgSn′, GaSn·, and Ga0, and nano-precipitates, SnGa4Se7, Ag9GaSe6 and AgGa1+δ. In those defects, AgSn′ acts as an accepter, which can conduce to enhancing the hole carrier concentration. Ga element doping astonishingly play dual-roles, in that it both faultlessly maintains the electrical transport properties and effectively decreases the thermal conductivity through the associations with the point defects, GaSn·, and Ga0, and nano-precipitates, SnGa4Se7, Ag9GaSe6 and AgGa1+δ. The method paves the way for achieving high thermoelectric properties in SnSe materials by the point defects engineering and nano-precipitates.

Filtering low‐energy carriers to enhance thermoelectric performance of Cd‐doped SnSe via incorporation of MXene sheets

AbstractSnSe‐based materials have attracted widespread attention in thermoelectrics due to their outstanding thermoelectric performance. However, the pristine and unmodified polycrystalline SnSe reveals poor electrical properties. Doping and constructing nanostructured composite architectures to produce energy filtering effect proved to be an effective method to strengthen thermoelectric performance. In this study, Ti3C2/Sn0.98Cd0.02Se composites are successfully fabricated by the solvothermal method combined with the electrostatic self‐assembly method and spark plasma sintering. The phase interface introduced by incorporating Ti3C2 into Sn0.98Cd0.02Se can effectively filter low‐energy carriers due to its generation of energy barriers, thereby the Seebeck coefficient of x wt% Ti3C2/Sn0.98Cd0.02Se x = (0.05, 0.5, 1) samples is better than that of the pristine Sn0.98Cd0.02Se over the whole temperature range. Meanwhile, high conductivity was also obtained in 1 wt% Ti3C2/Sn0.98Cd0.02Se sample so that the high power factor of 3.31 μWcm−1K−2 was acquired at 773 K. Ultimately, a peak ZT value of 0.41 was obtained at 773 K, compared with pristine Sn0.98Cd0.02Se, and the thermoelectric performance improved by 24%. This study offers an available approach to efficiently enhance the thermoelectric properties of polycrystalline SnSe‐based materials.

Electrodeposition of SnSe thin film using an organophosphorus [(Me2)3N3PSe] precursor for photovoltaic application

One prevalent class of thin films concerns SnSe (tin selenide), which is the primary focus of this research, with the aim of discovering cost-effective coatings for photovoltaic applications. The electrodeposition method was employed to successfully synthesize tin selenide thin films on glass substrates (ITO and FTO) utilizing the novel organophosphorus precursor [(Me2)3N3PSe]. Notably, this precursor has not been utilized in prior literature. Initial cyclic voltammetry (CV) analyses were performed to thoroughly investigate the electrochemical behavior of the tin and selenium redox systems within the electrolyte. The CV outcomes yielded crucial insights, guiding the establishment of a defined potential range (− 1.1 to − 1.2 V vs. SCE) for effective SnSe film electrodeposition. Films deposited within this potential range exhibited characteristic needle-shaped polycrystalline SnSe structures. Comprehensive analyses of the thin films’ structural, microstructural, and morphological characteristics were conducted, employing X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS). The crystallites’ size was determined using the Debye–Scherrer formula. Moreover, a systematic exploration of the impact of deposition potential and substrate type on various film properties was undertaken. The results from XRD and Raman spectroscopy confirmed the formation of an orthorhombic single-phase SnSe under different deposition potentials. SEM/EDS analysis revealed uniform element distribution for deposition potentials of − 1.1 V and − 1 V on ITO and FTO substrates, respectively. The investigation further extended to the optical properties of films on glass substrates (ITO and FTO). Optical data showed a direct optical band gap (Eg) ranging from 1.25 to 2.24 eV for ITO and 1.46 to 2.87 eV for FTO across a wide spectra range. These optical traits, significantly influenced by deposition potential and substrate type, hold promise. Particularly, SnSe thin films deposited on ITO substrates at − 1.1 V displayed distinct advantages for potential photovoltaic applications compared to samples on FTO substrates.Graphical

The improvement of thermoelectric properties of SnSe by alkali metal doping

Selenium selenide (SnSe) has attracted widespread attention because of its environmental friendliness and ultra-low lattice thermal conductivity. Single-crystal SnSe has been discovered to exhibit a high ZT value, but its mechanical qualities are weak and its manufacturing process is complicated, rendering it unsuitable for commercial usage. Polycrystalline SnSe is facile to synthesis; however, due to its weakened electrical performance, it has a poor thermoelectric property. In this study, polycrystalline SnSe samples are prepared using hydrothermal synthesis combined with vacuum sintering, and their thermoelectric properties are modulated using alkali metal element doping.