P-type Sb2Te3 Research Articles

Design and fabrication of tetradymites-based vertically oriented single and multilayer thin-film thermoelectric generators

Tetradymites-based thermoelectric materials and devices have received renewed attention due to their engineering and design flexibility, large scalability, and commercial viability in producing electricity from waste heat for niche applications in small power generation and micro refrigeration. In fact, most commercially available bulk thermoelectric generators (TEGs) are made from tetradymites. In contrast to their bulk counterparts, thin-film vertical TEGs have not been widely adopted. This can be attributable to complexities in design and fabrication methodologies, device measurement challenges, and the hurdle of maintaining a large enough temperature gradient for optimal device performance. In this study, we utilize a facile approach for the design, fabrication, and characterization of tetradymite-based n-type Bi2Te3 and p-type Sb2Te3 single-layer thermoelectric generators, as well as n-type Bi2Te3/Bi2Te2.83Se0.17 and p-type Sb2Te3/Bi0.4Sb1.6Te3 alternating multilayer superlattice TEGs. State-of-the-art characterization techniques were employed to investigate the structural, chemical, and thermoelectric properties of the materials. XRD analysis showed a preferential orientation along the (100) plane with a high intensity peak at 2θ = 25.5°, and XPS spectra exhibited a high-resolution peak at 531.5 eV corresponding to the Bi 4f7/2 core level. The structural data analysis confirmed the dominant metallic phase of the materials as well as their high crystalline nature. Device characterization showed that the multilayer device performed better than the single-layer devices with a recorded voltage, power, and power density of 11 mV, 12 pW, and 15.87 mW/m3 at ΔT = 18 °C, respectively, in comparison to 9.4 mV, 7.8 pW, and 10.31 mW/m3 for the most performing single-layer devices.

Achieving High Thermoelectric Performance in Bi2(Te, Se)3 Thin Film with (00l)-Oriented by Incorporating Tellurization and Selenization Processes.

Flexible thermoelectric (TE) generators have received great attention as a sustainable and reliable option to convert heat from the human body and other ambient sources into electricity. This study provides a synthesis route that involves thermally induced diffusion to introduce Te and Se into Bi, fabricating an n-type Bi-Te-Se flexible thin film on a flexible substrate. This specific synthesis alters the crystal orientation (00l) of the thin film, improving in-plane electrical transportation and optimizing carrier concentration. Consequently, BixTeySe0.42 enhanced both the Seebeck coefficient and electrical conductivity, achieving a power factor of 17.1 μW cm-1 K-2 at room temperature. The TE device assembled with p-type Sb2Te3 exhibited exceptional flexibility with only a 26.2% change in resistance after 1000 times of bending at a radius of about 6 mm. The resistance change was further reduced to 7.5% after the application of a vinyl laurate coating. The fabricated TE device generated an ultrahigh output power of 792 nW with a temperature difference of 30 K.

Deviceization of high-performance and flexible Ag2Se films for electronic skin and servo rotation angle control

Ag2Se shows significant potential for near-room-temperature thermoelectric applications, but its performance and device design are still evolving. In this work, we design a novel flexible Ag2Se thin-film-based thermoelectric device with optimized electrode materials and structure, achieving a high output power density of over 65 W m−2 and a normalized power density up to 3.68 μW cm−2 K−2 at a temperature difference of 42 K. By fine-tuning vapor selenization time, we strengthen the (013) orientation and carrier mobility of Ag2Se films, reducing excessive Ag interstitials and achieving a power factor of over 29 μW cm−1 K−2 at 393 K. A protective layer boosts flexibility of the thin film, retaining 90% performance after 1000 bends at 60°. Coupled with p-type Sb2Te3 thin films and rational simulations, the device shows rapid human motion response and precise servo motor control, highlighting the potential of high-performance Ag2Se thin films in advanced applications.

Self-aligned shadow masking for antimony telluride growth: Novel advancements in single-leg thermoelectric array design

In the present study, a fabrication technique using self-aligned shadow masking was employed to create a state-of-art thermoelectric single-leg array of Antimony telluride (Sb2Te3) thin film via thermal evaporation technique. The thermoelectric (TE) performance of the array was evaluated using an in-house developed measurement setup. The TE characteristics of the developed p-type Sb2Te3 based TEGs with single-leg configurations, having 5-TE legs, exhibits a highest Power factor (PF) of ∼5173 μW/mK2 at RT along with thermoelectric voltage generation of 70 mV. As compared to planar configuration these segmented single-leg array-based TEG of Sb2Te3 exhibit higher efficiency (∼10 %) under a near-ambient temperature gradient. Also, the 3ω-method is utilized to assess the thermal conductivity of fabricated thin films of Sb2Te3, yielding a value of 0.41 Wm⁻1K⁻1. Furthermore, these thermoelectric generators (TEGs) showcase their versatility across various applications, efficiently harnessing near-room temperature waste heat from a range of sources such as tea coasters, the human body, and gas cookstoves into useable energy near room temperature.

Fabrication of Bi2Te3 and Sb2Te3 Thermoelectric Thin Films using Radio Frequency Magnetron Sputtering Technique.

Through various studies on thermoelectric (TE) materials, thin film configuration gives superior advantages over conventional bulk TEs, including adaptability to curved and flexible substrates. Several different thin film deposition methods have been explored, yet magnetron sputtering is still favorable due to its high deposition efficiency and scalability. Therefore, this study aims to fabricate a bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thin film via the radio frequency (RF) magnetron sputtering method. The thin films were deposited on soda lime glass substrates at ambient temperature. The substrates were first washed using water and soap, ultrasonically cleaned with methanol, acetone, ethanol, and deionized water for 10 min, dried with nitrogen gas and hot plate, and finally treated under UV ozone for 10 min to remove residues before the coating process. A sputter target of Bi2Te3 and Sb2Te3 with Argon gas was used, and pre-sputtering was done to clean the target's surface. Then, a few clean substrates were loaded into the sputtering chamber, and the chamber was vacuumed until the pressure reached 2 x 10-5 Torr. The thin films were deposited for 60 min with Argon flow of 4 sccm and RF power at 75 W and 30 W for Bi2Te3 and Sb2Te3, respectively. This method resulted in highly uniform n-type Bi2Te3 and p-type Sb2Te3 thin films.

A facile in-situ reaction method for preparing flexible Sb2Te3 thermoelectric thin films

Inorganic p-type Sb2Te3 flexible thin films (f-TFs) with eco-friendly and high thermoelectric performance have attracted wide research interest and potential for commercial applications. This study employs a facile in-situ reaction method to prepare flexible Sb2Te3 thin films by rationally adjusting the synthesized temperature. The prepared thin films show good crystallinity, which enhances the electrical conductivity of ~1,440 S·cm-1 due to the weakened carrier scattering. Simultaneously, the optimized carrier concentration, through adjusting the synthesis temperature, causes the intermediate Seebeck coefficient. Consequently, a high-power factor (16.0 μW·cm-1·K-2 at 300 K) is achieved for Sb2Te3 f-TFs prepared at 623 K. Besides, the f-TFs also exhibit good flexibility due to the slight change in resistance after bending. This study specifies that the in-situ reaction method is an effective route to prepare Sb2Te3 f-TFs with high thermoelectric performance.

Enhancing Thermoelectric Performance in P-Type Sb2Te3-Based Compounds Through Nb─Ag Co-Doping with Donor-Like Effect.

P-type Sb2Te3 has been recognized as a potential thermoelectric material for applications in low-medium temperature ranges. However, its inherent high carrier concentration and lattice thermal conductivity led to a relatively low ZT value, particularly around room temperature. This study addresses these limitations by leveraging high-energy ball milling and rapid hot-pressing techniques to substantially enhance the Seebeck coefficient and power factor of Sb2Te3, yielding a remarkable ZT value of 0.55 at 323K due to the donor-like effect. Furthermore, the incorporation of Nb─Ag co-doping increases hole concentration, effectively suppressing intrinsic excitations ≈548K while maintaining the favorable power factor. Simultaneously, the lattice thermal conductivity can be significantly reduced upon doping. As a result, the ZT values of Sb2Te3-based materials attain an impressive range of 0.5-0.6 at 323K, representing an almost 100% improvement compared to previous research endeavors. Finally, the ZT value of Sb1.97Nb0.03Ag0.005Te3 escalates to 0.92 at 548K with a record average ZT value (ZTavg) of 0.75 within the temperature range of 323-573K. These achievements hold promising implications for advancing the viability of V-VI commercialized materials for low-medium temperature application.

Improved Thermoelectric Performance of Sb2Te3 Nanosheets by Coating Pt Particles in Wide Medium-Temperature Zone.

The p-type Sb2Te3 alloy, a binary compound belonging to the V2VI3-based materials, has been widely used as a commercial material in the room-temperature zone. However, its low thermoelectric performance hinders its application in the low-medium temperature range. In this study, we prepared Sb2Te3 nanosheets coated with nanometer-sized Pt particles using a combination of solvothermal and photo-reduction methods. Our findings demonstrate that despite the adverse effects on certain properties, the addition of Pt particles to Sb2Te3 significantly improves the thermoelectric properties, primarily due to the enhanced electronic conductivity. The optimal ZT value reached 1.67 at 573 K for Sb2Te3 coated with 0.2 wt% Pt particles, and it remained above 1.0 within the temperature range of 333-573 K. These values represent a 47% and 49% increase, respectively, compared to the pure Sb2Te3 matrix. This enhancement in thermoelectric performance can be attributed to the presence of Pt metal particles, which effectively enhance carrier and phonon transport properties. Additionally, we conducted a Density Functional Theory (DFT) study to gain further insights into the underlying mechanisms. The results revealed that Sb2Te3 doped with Pt exhibited a doping level in the band structure, and a sharp rise in the Density of States (DOS) was observed. This sharp rise can be attributed to the presence of Pt atoms, which lead to enhanced electronic conductivity. In conclusion, our findings demonstrate that the incorporation of nanometer-sized Pt particles effectively improves the carrier and phonon transport properties of the Sb2Te3 alloy. This makes it a promising candidate for medium-temperature thermoelectric applications, as evidenced by the significant enhancement in thermoelectric performance achieved in this study.

Optimized thermoelectric properties of flexible p-type Sb2Te3 thin film prepared by a facile thermal diffusion method

Sb2Te3-based thermoelectric thin film is a competitive candidate for preparing thermoelectric thin film devices, which power the wearable electronic devices and chip-sensor of internet-of-things. In this work, a directed thermal diffusion reaction method was applied to synthesize p-type Sb2Te3 thin films synthesis at polyimide flexible substrate with self-assembled growth. A high power factor of 1.94 mWm−1K−2 with excellent flexibility which is very competitive among similar Sb2Te3 based materials by the control of synthesis condition, especially the chemical composition. Meanwhile, the performance of thermoelectric thin film device is limited by contact resistance. Thus the more systematic study of contact resistance, including choice of electrode material for the device was investigated. The results indicate that Mo/Sb2Te3 have the lowest contact resistivity compared with Al/Sb2Te3 and Ni/Sb2Te3. In addition, the fabricated flexible device with Mo electrode has outstanding thermal stability.

Thickness Dependence of Thermoelectric Properties and Maximum Output Power of Single Planar Sb2Te3 Films.

P-type Sb2Te3 films with different thicknesses were deposited on polyimide substrates via heat treatment-assisted DC magnetron sputtering. The correlations between the thickness variance and the structure, dislocation density, surface morphology, thermoelectric properties and output power are investigated. As a result, it is clear that the film thickness and the heat treatment process during growth are related to the diffusion of deposited atoms on the substrate surface, leading to imperfection defects inside the films. The imperfections inside the films are affected by their properties. This work also presents the thermoelectric efficiency of a planar single leg of the deposited films with various thicknesses. The maximum power factor is 2.73 mW/mK2 obtained with a film thickness of 9.0 µm and an applied temperature of 100 °C. Planar Sb2Te3 produced a maximum output power of 0.032 µW for a temperature difference of 58 K.

Nanostructured Sb2Te3 films composited with Bi2S3 for p–n conduction type conversion

The crystallization of p-type Sb2Te3 material can be tuned deterministically through compositing with n-type Bi2S3. The underlying changes in conduction from p-type to n-type are due to the crystallization changes induced by the composited Bi2S3 and the simultaneous changes in crystalline phase type. Bi2S3 nanoprecipitate formation and crystallization transition could effectively stimulate the p–n conduction transition. Upon annealing, pure Sb2Te3 partially crystallizes from the as-deposited state, which exhibits continuous crystallization during annealing. The formation of the p-type Sb2Te3 phase and the Sb2O3 phase in pure Sb2Te3 films through oxidation is significantly suppressed through compositing with excess Bi2S3. Moreover, the crystallization temperatures of the Sb2Te3–Bi2S3 films exceed 200 ℃, and the Seebeck coefficients and carrier concentrations of the samples are larger than those of pure Sb2Te3. The X-ray diffraction and Raman spectroscopy characterization of the crystalline thin films reveals a local change of the bonding arrangement around Sb atoms during crystallization. Our results suggest that Sb2Te3–Bi2S3 can serve as a promising candidate for thermoelectric applications based on n-type conduction.

High figure of merit of Sb2.18Te3 achieved via modulating stoichiometric ratio with chemical method

Doping an element or more is widely used to regulate thermoelectric materials performance through adjusting electrical and thermal properties. In this work, a series of p-type Sb2(1+x)Te3 nanoflake composites are fabricated and tested. Excessive Sb in Sb2(1+x)Te3 causes high carrier density, which results in much larger electrical conductivity compared with that of pure Sb2Te3. The highest merit ZT of the Sb2.18Te3 composite reaches to 1.22 at 523 K, and the average ZT value in Sb2.18Te3 sample is above 1 obtained from 323 to 523 K, which is a decent ZT value at low–mid temperature zone for doped Sb2Te3-based composites. Self-doping element Sb into Sb2Te3 nanoflakes is an effective strategy that has a significant influence on improving power factor and keeping low thermal conductivity. Sb2(1+x)Te3 nanostructure composites are synthesized by reflux chemical method. Comparing with other methods involving solid solution melting, high-energy ball milling and solvothermal reaction, reflux chemical reaction method is not only a more facile, timesaving and green way to produce nanoscale materials but also can be applied to mass production.

Deposition and Fabrication of Sputtered Bismuth Telluride and Antimony Telluride for Microscale Thermoelectric Energy Harvesters

Thermoelectric (TE) n-type bismuth telluride (Bi2Te3) films and p-type antimony telluride (Sb2Te3) films are grown on SiO2/Si substrates via radio frequency magnetron sputtering. The crystal structures and TE properties are characterized for 1 µm and 10 µm films deposited using different deposition conditions and using various heat treatment conditions. Single-target sputtered deposition of n-type Bi2Te3 films resulted in a Te-deficient off stoichiometric films due to the evaporation of tellurium. Two-target co-sputtered deposition using Bi2Te3 and Te targets at room temperature and subsequent anneal at 250°C yielded a 10 µm n-type film with -102 µV/K for the Seebeck coefficient and 0.7 mW/K2.m for the power factor. Similarly, prepared p-type Sb2Te3 film but using a single sputtering target yielded +110 µV/K and 1.3 mW/K2.m for their Seebeck coefficient and power factor respectively. The fabrication of the micro-scale thermoelectric energy generator (µTEG) using separate n-type and p-type wafers is demonstrated.

Preparation and thermoelectric power properties of highly doped p-type Sb2Te3 thin films

In this study, we provide facile procedures for the growth of p-type Bi-doped Sb 2 Te 3 thin films on ceramic substrates using vacuum thermal evaporation technique. Crystal structure and surface morphology of the prepared films were probed via powder X-ray diffraction (PXRD) and scanning electron microscope (SEM). The thermoelectric power properties were investigated, in terms of electrical conductivity and Seebeck coefficient measurements, over the temperature range from room temperature up to 473 K. The electrical conductivity behavior showed notable transition from metallic behavior to semiconducting as a function of temperature. In addition, Seebeck coefficient measurements confirmed this transition and supported the behavior of the electrical conductivity. Importantly, power factor was estimated based on both the electrical conductivity and Seebeck coefficient values. A maximum value of 227.6 μW/m.K 2 was obtained for the Sb 1.85 Bi 0.15 Te 3 thin film sample at 428 K.

Enhanced thermoelectricity at the ultra-thin film limit

At the ultra-thin film limit, quantum confinement strongly improves the thermoelectric figure of merit in materials such as Sb2Te3 and Bi2Te3. These high quality films have only been realized using well controlled techniques such as molecular beam epitaxy. We report a twofold increase in the Seebeck coefficient for both p-type Sb2Te3 and n-type Bi2Te3 using thermal co-evaporation, an affordable approach. At the thick film limit greater than 100 nm, their Seebeck coefficients are around 100 μV/K, similar to the results obtained in other works. When the films are thinner than 50 nm, the Seebeck coefficient increases to about 500 μV/K. With the Seebeck coefficient ∼1 mV/K and an estimate ZT ∼0.6, this pair of materials presents the first step toward a practical micro-cooler at room temperature.

Interplay between positive magnetoresistance and thermoelectric properties by tuning carrier concentration in Sb2−xSnxTe3 (x ⩽ 0.05) crystals

We report transport properties of Sb2−xSnxTe3 (x ⩽ 0.05) single crystals, where the tuning of the charge carrier densities via Sn doping significantly improves the magnetoresistance (MR) and the thermoelectric (TE) properties. The MR increases significantly at 2 K for x = 0.01, which reduces considerably with further Sn doping at x = 0.05. The MR results below 90 K for x = 0.01 satisfy the semi-classical two-band approach of Kohler’s rule, which does not satisfy the MR results for x = 0.05. At 300 K, the Seebeck coefficient (S) is positive and small for x = 0.01 and it changes the sign with the further increase in Sn doping at x = 0.05 at 300 K. The value of |S| is considerable with an enhancement of the thermoelectric power factor compared to the value for x = 0.01 at 300 K. Analysis of the Hall conductivity indicates the interplay between carrier mobilities and densities, leading to the tuning of MR and TE properties with Sn doping. These results demonstrate that the p-type Sb2Te3 becomes n-type with a suitable doping engineering.

Optimized structure of tubular thermoelectric generators using n-type Bi2Te3 and p-type Sb2Te3 thin films on flexible substrate for energy harvesting

Thermoelectric energy harvesting has garnered considerable interest as a means of power supply in Internet of Things sensors. In this study, tubular thin-film thermoelectric generators (TTTEGs) were developed using flexible thermoelectric films for energy harvesting. The strip-shaped n-type Bi2Te3 and p-type Sb2Te3 thin films were deposited on a polyimide sheet using radio-frequency magnetron sputtering, followed by thermal annealing. After the formation of metal electrodes to connect p-n pairs, the flexible thin-film generator was rolled and placed in a plastic tube. Assuming that the TTTEGs would be partially immersed in hot water in the optimal design, the temperature distributions in the TTTEGs were calculated using computational fluid dynamics. The calculations indicated that a steep temperature gradient occurred near the water surface, which was also observed in an experimental measurement. Therefore, we prepared TTTEGs with different film lengths ranging from 16 to 36 mm while the film width and radius of tube were maintained at 2 mm and 7.5 mm, respectively. The TTTEGs with a film length of 16 mm exhibited the highest thermoelectric performance, i.e., an open-circuit voltage of 122.9 mV and a maximum output power of 306.8 nW, at a temperature difference of 20 K. This trend occurred because the short-film TTTEG effectively utilized the steep temperature gradient and had a small circuit resistance.

Ultrathin MEMS thermoelectric generator with Bi2Te3/(Pt, Au) multilayers and Sb2Te3 legs

Multilayer structure is one of the research focuses of thermoelectric (TE) material in recent years. In this work, n-type 800 nm Bi2Te3/(Pt, Au) multilayers are designed with p-type Sb2Te3 legs to fabricate ultrathin microelectromechanical systems (MEMS) TE devices. The power factor of the annealed Bi2Te3/Pt multilayer reaches 46.5 μW cm−1 K−2 at 303 K, which corresponds to more than a 350% enhancement when compared to pristine Bi2Te3. The annealed Bi2Te3/Au multilayers have a lower power factor than pristine Bi2Te3. The power of the device with Sb2Te3 and Bi2Te3/Pt multilayers measures 20.9 nW at 463 K and the calculated maximum output power reaches 10.5 nW, which is 39.5% higher than the device based on Sb2Te3 and Bi2Te3, and 96.7% higher than the Sb2Te3 and Bi2Te3/Au multilayers one. This work can provide an opportunity to improve TE properties by using multilayer structures and novel ultrathin MEMS TE devices in a wide variety of applications.

Experimental and Computational Analyses of Temperature Distributions in Slope-Type Thin-Film Thermoelectric Generators at Different Slope Angles and Evaluation of Their Thermoelectric Performance

Thin-film thermoelectric generators are not widely used mainly because it is difficult to provide a temperature difference (ΔT) within the generators. To solve this problem, in our previous study, we prepared slope-type thin-film thermoelectric generators (STTEGs) using electrodeposition and transferred processes. A thin-film generator including n-type Bi2Te3 and p-type Sb2Te3 thin films was attached on slope blocks made of polydimethylsiloxane. In this study, the slope angle of STTEGs was optimized based on experimental results and computational analyses using computational fluid dynamics (CFD). With the increase in the slope angle, the ΔT began increasing and became saturated at a slope angle of 58°, and this trend was also confirmed by experimental measurements. When the heat source temperature was set at 65 °C, the ΔT computationally reached 26 K at a slope angle of 58°, and the maximum output power was 46.1 nW. Therefore, we demonstrated that the highest performance of STTEGs with an optimal slope angle can be estimated by combining the experimental results and computational analyses.

Effect of Thermoelectric Leg Thickness in a Planar Thin Film TEC Device on Different Substrates

Recently, mobile application processors (APs) have suffered from thermal issues such as local hot spot generation. Several approaches for chip cooling, such as dynamic thermal management, and heat pipe cooling, have been attempted so far, but, these solutions cannot completely eliminate increasing thermal issues. Therefore, in this study, we fabricated a planar type of thin film thermoelectric cooler (TEC) as an active cooling device for a mobile AP chip. We studied the effect of thickness on a planar thin film TEC device related to Joule heating and demonstrated the Peltier cooling effect on polyimide (PI) and Si substrates. The optimal thicknesses of n-type Bi2Te3 and p-type Sb2Te3 films were evaluated by ANSYS® simulation, and are 5.05 μm and 5.45 μm, respectively. It was shown that heat moves to the TE leg on the PI substrate, while the Si substrate serves as a heat sink according to the IR thermography analysis. The optimal thickness of the TE showed a temperature difference between the cold junction and hot junction up to 1.3 °C.