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Bi2Te3‐based thin films are attracting increasing attention due to their considerable wearability and flexibility feature. However, the relatively low performance compared to their bulk counterparts limits their development and wider application. In this work, synergistic texturing and Bi/Sb‐Te antisite doping are used to achieve a high room‐temperature ZT of ≈1.5 in p‐type Bi0.5Sb1.5Te3 thin films by a magnetron sputtering method. Structural characterization confirms that carefully tuning the deposition temperature can strengthen the texture of as‐prepared polycrystalline Bi0.5Sb1.5Te3 thin films, leading to significantly enhanced carrier mobility and electrical conductivity. Simultaneously, rational engineering of the deposition temperature can induce antisite doping between Bi/Sb and Te, which can reduce the carrier concentration and make it closer to the optimized level. In turn, a high power factor of 45.3 µW cm−1 K−2 and a maximized ZT of ≈1.5 at room temperature are obtained. This high power factor and ZT are highly competitive to other state‐of‐the‐art p‐type thin‐film‐based thermoelectric materials, showing great potentials for practical applications. [ABSTRACT FROM AUTHOR]

Thin-film solar thermoelectric generators show much promise in effective use of solar energy as a power supply for microscale devices. In this paper, we fabricated a flexible thin-film solar thermoelectric generator on the polyimide substrate using simple mask-assisted deposition process. The p-type Bi 0.5 Sb 1.5 Te 3 and n-type Bi 2 Te 2.7 Se 0.3 thermoelectric films with special hierarchical nanostructure were prepared, resulting in substantial improvement in the electrical conductivity. The solar thermoelectric generator with the hierarchical Bi–Te thin films is able to generate 220 mV of the output voltage and 80 μW of the maximum power for a temperature difference of 100 K. We also analyzed the optimized design for the solar thermoelectric generator. By employing a package for the thermoelectric legs and a perforated structure, the heat flow was restricted along the thermoelectric legs and a larger temperature difference was achieved. A fast electrical response to the on–off simulated solar light irradiation was also observed, indicating light sensing feature of the fabricated thin-film solar thermoelectric generator. Our results revealed that a remarkably enhanced output power has been achieved in the flexible thin-film solar thermoelectric generator due to the introduction of the improved thermoelectric films and the optimized thermal design. [ABSTRACT FROM AUTHOR]

Thin-film STEGs (solar thermoelectric generators) show promise in effective use of solar energy as a power supply for wireless sensors and microscale devices. This paper reports a simulation procedure that aims to identify desirable heat flow and temperature distribution to improve the performance of thin-film STEGs. The temperature distribution, heat flux, and voltage of a thin-film STEG are simulated using the finite element method, resulting in an optimal design of the substrate, heat conductive layer, and thermoelectric legs of thin-film STEGs. The effect of air convection on the STEG's performance is also studied. Based on the simulation, a thin-film STEG was designed and fabricated, which exhibits an open-circuit voltage of 22 mV. In addition, the experimental results demonstrate that the measured temperature distribution is in good agreement with the simulated result. To minimize the heat loss from the passive region of the device, an improved design was created in an attempt to confine the heat flow within the thermoelectric legs. This improved design resulted in a 21.4% increase of the output voltage. [ABSTRACT FROM AUTHOR]

In this paper, it was found that layered and columnar structure can favorably influence the carrier and phonon transport properties of films. The n-Bi2Te2.7Se0.3 columnar film with layered structure was successfully achieved by simple magnetron co-sputtering method at 400 °C deposition temperature, due to the more sufficient growth along the in-plane direction induced by the enhanced mobility of deposited atoms. The layered nanostructure is clear with each layer <25 nm in the columnar film. The properties of the Bi2Te2.7Se0.3 columnar film with layered structure were greatly enhanced in comparison with those of the columnar and the ordinary films synthesized respectively at 350 °C and 250 °C deposition temperature. The layered Bi2Te2.7Se0.3 columnar film with a thermoelectric dimensionless figure-of-merit ZT = 1.27 was obtained at room temperature. The layered column structure was the main reason for the properties enhancement observed in the Bi2Te2.7Se0.3 film. Introduction of such uniquely layered and columnar structure into thermoelectric films is therefore a very promising approach. [ABSTRACT FROM AUTHOR]

Abstract: Preferential growth transformation from (015) plane to (00l) plane of the bismuth antimony tellurium (Bi0.5Sb1.5Te3) film has been achieved through a facile post-annealing process with enhanced thermoelectric performance. The Bi0.5Sb1.5Te3 film with preferential growth of (015) crystal plane was obtained via dc magnetron sputtering, and the Stranski–Krastanov model has been used to explain its growth mechanism. Preferential growth transformation from (015) plane to (00l) plane occurred after a post-annealing process. The driving force of this phenomenon is the natural tendency to reduce the total interfacial energy of the system, and the migration and coalescence of atoms along the in-plane direction form the layered structure. Moreover, the carrier concentration of Bi0.5Sb1.5Te3 films is optimized to ~019/cm3 in the film with preferential growth of (00l) plan. Hence, a synchronous increase of electrical conductivity and Seebeck coefficient is obtained due to the greatly enhanced carrier mobility and optimized carrier concentration. Therefore, the Bi0.5Sb1.5Te3 film with the preferential growth of (00l) plane possesses power factor of 48.2μW/cmK2 which is three times higher than that of the film with the preferential growth of (015) plane. Our study has provided a facile strategy to induce preferential growth transformation in Bi0.5Sb1.5Te3 films and meanwhile largely enhanced the thermoelectric performance. [Copyright &y& Elsevier]

In this paper, uniquely (0 1 5)-preferential growth plane and alternating stress field can favorably influence the carrier and phonon transport properties of multilayered films. The p-type Bi1.5Sb0.5Te3 multilayered film has been successfully fabricated by a simple thermal co-evaporation technique. The composition, microstructure, and in-plane thermoelectric (TE) properties of films have been characterized and measured, respectively. The measurement results show that the multilayered Bi1.5Sb0.5Te3 film is (0 1 5)-preferential growth. The multilayered structure film is composed of the (0 1 5)-oriented and the ordinary nanolayers. The properties of the multilayered Bi1.5Sb0.5Te3 film has been significantly enhanced in comparison with those of the highly (0 1 5)-oriented and the ordinary Bi1.5Sb0.5Te3 films. The multilayered Bi1.5Sb0.5Te3 film with a TE dimensionless figure-of-merit ZT = 1.28 was obtained at room temperature. The transport mechanism of multilayered structure is proposed and investigated. The internal strain field and (0 1 5)-preferential growth plane are the main reasons for the properties enhancement observed in the multilayered Bi1.5Sb0.5Te3 film. Introduction of such uniquely (0 1 5)-preferential growth plane and alternating stress field into TE films is therefore a very promising approach. [ABSTRACT FROM AUTHOR]

Layer-by-layer assembly of nanostructured Bi 0.5Sb 1.5Te 3 thin films were prepared by a simple magnetron sputtering method. X-ray diffraction investigations revealed that all the thin films were well crystallized with preferred orientation along (00 l) direction. Scanning electron microscopy images indicated that nanostructure of the condensed films was stacked by tens of parallel repeating layers. Meanwhile, the particular thicknesses of layers could be controlled in the range of 20–140 nm by adjusting the deposition time. The electrical conductivity and power factor were significantly increased compared with those of ordinary thin films, while the maximum power factor reached 53 μW cm −1 K −2 when the layer thickness was 40 nm. The multi-layered materials are promising candidates for miniaturized modules with their unique properties. [ABSTRACT FROM AUTHOR]

The p-type antimony telluride (SbTe) pillar arrays with unique hierarchical architecture have been self-assembled in large scale by a simple vacuum thermal evaporation technique. The composition and the microstructure of the films are studied by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. The results show that the hierarchical film with multi-scale and multi-dimensional structure is well-oriented pillar arrays perpendicular to the substrate. A large number of nanowires (NWs) are assembled into a submicro/micro-scaled pillar, while antisite defects and dislocations as well as other defects are found in the one-dimensional NWs. The growth mechanism of such nanostructure is proposed and investigated. The thermoelectric (TE) properties, i.e., electrical conductivity (σ), Seebeck coefficient ( S), and thermal conductivity ( κ) of the films are measured. The properties of the hierarchical SbTe film have been greatly enhanced in comparison with those of the ordinary SbTe films. A TE dimensionless figure-of-merit ZT = 0.88 in the novel hierarchical SbTe film is obtained at room temperature. [ABSTRACT FROM AUTHOR]

Preferential growth of different crystal planes in layered BiTe thin films with each layer <40 nm has been achieved by a simple magnetron co-sputtering method. The preferential growth of (015) plane or (001) was achieved at special depositing conditions due to the more sufficient growth along the in-plane direction induced by the enhanced diffusion of atoms and lower deposition rate. The BiTe film with preferential growth of (001) plane possesses about two times higher electrical conductivity and Seebeck coefficient as compared to the film with preferential growth of (015) plane, due to the greatly enhanced carrier mobility. Furthermore, the thermal conductivity has been suppressed due to more phonon scattering at grain boundaries, compared with ordinary BiTe alloys and films. [ABSTRACT FROM AUTHOR]

Abstract: Oriented n-type bismuth telluride thin films with various layered nanostructures have been fabricated by radio-frequency (RF) magnetron sputtering. The crystal structures and microstructures of the films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The transport properties including carrier concentration, mobility, Seebeck coefficient and in-plane electrical conductivity were measured, which showed strong microstructure-dependent behaviors. The relationship between morphologies and transport properties of the films was explored. The optimal morphology and transport properties of films were obtained at the substrate temperature of 350°C under the pressure of 1.0Pa with oriented layered structure. Based on these results, a formation mechanism of these nanostructures is proposed and discussed. The interfaces and grain boundaries formed in these layered structures are beneficial to the reduction in thermal conductivity, which could result in potential TE films with high ZT value. [Copyright &y& Elsevier]

Anisotropic Bi2Te3‐based thermoelectric materials have drawn extensive interest in the past decades. Here, n‐type Bi2Te2.7Se0.3 films with superhigh figure of merit are developed through anisotropy control via tuning an external electric field and deposition anisotropy. It is found that the angle of interplanar grain boundaries between (0 1 5) and (0 1 11) planes can be tuned by the applied external electric field, which leads to the strengthened anisotropy of electron mobility and simultaneously maintains low lattice thermal conductivity. Dominated by the unique change in the anisotropy of both lattice thermal conductivity and electron mobility, a record‐high zT value of ≈1.6 at room temperature can be achieved in the as‐deposited n‐type Bi2Te2.7Se0.3 film under 20 V external electric field. This work indicates that the electric field–induced deposition anisotropy control can be used to develop high‐performance Bi2Te3‐based thermoelectric films. [ABSTRACT FROM AUTHOR]

The interface stability is of great significance for maintaining the high output performance of thin‐film thermoelectric devices. Here, it is demonstrated that by introducing a Ti layer and controlling its thickness, the interface stability relating to element diffusion, contact resistance, and mechanical strength can be regulated at Bi2Te3/Cu interfaces. After heat treatment, the multilayer interface with a thickness of 270 nm for the Ti layer has a stable structure that can suppress element diffusion, maintain a low specific contact resistivity (7.49 × 10−6 Ω cm2) and obtain an excellent critical load (58.1 mN). These characteristics are achieved because the Ti film with a thickness of 270 nm can keep multilayer interface stable, maintain the interface as effective junctions, and alleviate stress release. Due to the diffusion of Cu, the Cu‐Te compounds are formatted and Cu diffusion into Bi2Te3 is generated in the interfaces. Meanwhile, the results show that the Cu diffusion into Bi2Te3 has a greater impact on contact resistance than p‐CuTe in the interface. The work provides a general method for maintaining the reliability and stability of multilayer interfaces in thin‐film thermoelectric devices. [ABSTRACT FROM AUTHOR]

Preparation of high performance flexible thermoelectric thin films would promote applications of flexible thermoelectric device. In this work, antimony telluride (Sb 2 Te 3 ) thin films were directly deposited on polyimide substrate. The crystalline structures and morphologies of the thin films were analyzed, and the mechanism of crystal growth influenced by sputtering pressure was discussed. We also investigated the effects of microstructure on their thermoelectric properties, where Hall effect measurement was conducted to provide further insight into the enhancement of thermoelectric properties. The mean free path of the carrier was calculated on the basis of carrier concentration and mobility. Our results showed that with (015) crystal preferential orientation, the electrical conductivity and Seebeck coefficient of Sb 2 Te 3 thin films were simultaneously increased, and a maximum power factor of 6.0 μW cm −1 K −2 was achieved, which was increased by 75% compared with the ordinary thin film. Meanwhile, due to the reduced lattice thermal conductivity and increased power factor, the estimated figure of merit (ZT) value was largely enhanced to 0.42. [ABSTRACT FROM AUTHOR]

Abstract: Oriented thermoelectric (TE) p-Sb2Te3 and n-Bi2Te3 thin films with special nanostructures have been synthesized by a simple vacuum thermal evaporation technique. The composition and microstructure of the films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), presenting a well preferential crystal growth with dense slender columnar grains grown perpendicular to the substrate, and energy dispersive X-ray spectrum (EDX) indicating the compositions distribution in the films. The electric transport properties, i.e., conductivity and Seebeck coefficient, and the thermal transportation of the oriented films show optimized properties. Prototype devices were built up by p and n elements in series and parallel circuits. The largest output power and cooling could be achieved in Sb2Te3 parallel device with P max =6.51μW at ΔT =106K, and cooling of 4.1K at 2V. The 24-pair p–n couples series device could output maximum voltage of 313mV at ΔT =102K. The power generation and the cooling of the devices show times enhanced TE performances than those consisting of common films. The results proved that introducing nanostructures into films is an effective choice to obtain high-efficient micro TE device. [Copyright &y& Elsevier]

Abstract: Highly ()-oriented pure Bi2Te3 films with in-plane layered grown columnar nanostructure have been fabricated by a simple magnetron co-sputtering method. Compared with ordinary Bi2Te3 film and bulk materials, the electrical conductivity and Seebeck coefficient of such films have been greatly increased simultaneously due to raised carrier mobility and electron scattering parameter, while the thermal conductivity has been decreased due to phonon scattering by grain boundaries between columnar grains and interfaces between each layers. The power factor has reached as large as 33.7 μW cm−1 K−2, and the out-of-plane thermal conductivity is reduced to 0.86 W m−1 K−1. Our results confirm that tailoring nanoscale structures inside thermoelectric films effectively enhances their performances. [Copyright &y& Elsevier]

Abstract Highly oriented Bi 2-x Sb x Te 3 (x = 0, 0.7, 1.1, 1.5, 2) ternary nanocrystalline films were fabricated using vacuum thermal evaporation method. Microstructures and morphologies indicate that Bi 2-x Sb x Te 3 films have pure rhombohedral phase with well-ordered nanopillars array. Bi, Sb and Te atoms uniformly distributed throughtout films with no precipitation. Electrical conductivity of Bi 2-x Sb x Te 3 films transforms from n-type to p-type when x > 1.1. Metal-insulator transition was observed due to the incorporation of Sb in Bi 2 Te 3. Bi 2-x Sb x Te 3 film with x = 1.5 exhibits optimized electrical properties with maximum electrical conductivity σ of 2.95 × 105 S m−1 at T = 300 K, which is approximately ten times higher than that of the undoped Bi 2 Te 3 film, and three times higher than previous report for Bi 0.5 Sb 1.5 Te 3 films and bulk materials. The maximum power factor PF of Bi 0.5 Sb 1.5 Te 3 nanopillars array film is about 3.83 μW cm−1 K−2 at T = 475 K. Highly oriented (Bi,Sb) 2 Te 3 nanocrystalline films with tuned electronic transport properties have potentials in thermoelectric devices. [ABSTRACT FROM AUTHOR]

SnTe, an ideal lead-free substitute of PbTe, recently has attracted much attention for thermoelectric heat to electricity generation. Previous reports mainly focused on band engineering and all-scale phonon scattering for enhancing the thermoelectric performance of bulk SnTe. Herein, we adopt strategy of interface engineering to design oriented nanopillar structure in SnTe film via one-step thermal evaporation method. The analysis of the electrical and thermal properties illustrates that the SnTe film with highly oriented growth shows enhanced thermoelectric performance. The excellent properties are mainly attributed to the special nanopillar structure, which may facilitate the electrons' transport while significantly scatter the phonons. The maximum power factor of 19.8 μW cm −1 K −2 and the thermal conductivity of 3.54 W m −1 K −1 are obtained. This work provides a promising approach to enhance the thermoelectric performance of SnTe film, which can be easily extended to other thermoelectric films. [ABSTRACT FROM AUTHOR]

In this study, the phosphorus doped silicon nanocrystals embedded in silicon-rich SiN x :H thin films were fabricated using a radio frequency plasma enhanced chemical vapor deposition technique, from a SiH 4 , pH 3 , H 2 and NH 3 mixture. The effects of nitrogen incorporation on the microstructure and photoelectric properties of the nc-Si:H film were systematically investigated. Raman and transmission electron microscope observation revealed the fact that nitrogen incorporation inhibited the growth of Si nanocrystals, and their sizes and densities of them could be adjusted by varying the incorporation flow ratio NH 3 /(SiH 4 + H 2 + pH 3 ). The reduction of refractive index and improvement of conductivity of the prepared films were observed with increasing nitrogen impurity, and a maximal conductivity was obtained when the flow ratio was 0.02. In addition, the P-doped nc-SiN x :H film was used as an n-type layer for the amorphous silicon thin film solar cells to optimize its efficiency, and the solar cell with high fill factor (0.624) and efficiency (9.26%) has been obtained when the flow ratio was 0.02. As a result, the P-doped nc-SiN x :H film with proper nitrogen incorporation was able to efficiently improve the performance of the thin film solar cells. [ABSTRACT FROM AUTHOR]

We successfully fabricated hetero-junction (H-J) devices from P-doped silicon-rich SiN x embedded with Si nanoparticles on a p-type crystalline Si substrate at low temperature. High-resolution transmission electron microscopy (HRTEM) analysis indicates that the thin films contain nano-crystallites. The H-J devices showed a good rectification ratio at room temperature. Three distinct regions of temperature dependent J-V characteristics curve can be identified, where different current density variations are indicated. In the low voltage range, the current across the interface of H-J follows an ohmic behavior. In the intermediate range of voltage, the current transport mechanism shows a transition from the phosphorus diffusion to tunneling dominant due to the silicon nanoparticle size and interface of HJ device changed, while the space-charge-limited current (SCLC) dominates the conduction mechanism in the high voltage range and the density of trapping states also affects the electron transport proceeding. At last, the proper size of silicon nanoparticle can reduces the interface charge density of H-J, which is confirmed via the numerical C-V matching technique and we propose a new energy band diagram to fit the HJ device embedded by the silicon nanoparticles. [ABSTRACT FROM AUTHOR]