Antimony Chalcogenides Research Articles

On the Stability of Operation of Antimony Sulfide Selenide Thin Film Solar Cells Under Solar Radiation

Operational stability of FTO/CdS/Sb2S1.08Se1.92/C‐Ag thin film solar cells under solar radiation is presented. These solar cells are produced on fluorine‐doped SnO2 (FTO) by thermal evaporation of Sb2S3 and Sb2Se3 powders. Thin film of Sb2S1.08Se1.92 (300 nm) shows a bandgap of 1.45 eV. Its electrical conductivity is 10−7 Ω−1 cm−1 (dark) and 10−5 Ω−1 cm−1 under illumination. Thin film of CdS (120 nm) for the solar cell is obtained on FTO by chemical deposition. Antimony chalcogenide film is deposited on FTO/CdS substrates maintained at 425 °C via thermal evaporation from a mixture of Sb2S3 and Sb2Se3 powders. Subsequently, graphite paint and silver paint electrodes of area 0.49–0.64 cm2 are applied on it. Efficiency of conversion (η) is 5.9 % for the best solar cell and 5.6% on an average for eight cells. Open circuit voltage (Voc) of the cell is 0.453 V; short circuit current density (Jsc), 24.7 mA cm−2; and fill factor, 0.53. For solar cells placed under the sun over 5 days in the exterior with exposure of 24 kWh m−2, η dropped to 5%. Under 30 suns, Voc of 0.54 V and Jsc of 130 mA cm−2 are recorded. The cells remained functional.

Fabrication of Bi2Te3 films on the surface of silica optical fibres by MOCVD

Crystalline 2D bismuth and antimony chalcogenides, as well as graphene, can successively operate as saturable absorbers in various schemes of passively mode-locked fibre lasers. An attractive benefit of these saturable absorbers is their power to effectively operate at different wavelengths in the wideband from 1 to 2 microns. However, the problem is how to provide a reliable interaction between light in a fibre and the absorber. The main disadvantage of a standard solution to the problem essentially is to use exfoliated flakes dissolved in a coupling agent, which deposits additional heat that negatively affects the absorber. In the present research, thin crystalline films of a narrow-band semiconductor Bi2Te3 were deposited directly on silica optical fibres by means of metal-organic chemical vapour deposition (MOCVD). A ZnTe buffer layer was deposited first in a single growth run, providing the necessary condition for better adhesion of bismuth telluride film to the silica surface. Two types of fibre coatings were prepared and tested: the coating upon the cleaved end of the fibre and the one upon the lateral surface of the light-guiding fibre core. In the latter case, prior to deposition a fibre section of about 1 cm in length was uniformly thinned via chemical etching to a diameter of about 20 microns. Reflection and transmission of the growing films were monitored in situ during the deposition.

Efficient Double Buffer Layer Sb2 (SexS1–x)3 Thin Film Solar Cell Via Single Source Evaporation

Sb2(SexS1–x)3 has been proven a very promising light absorbing material for photovoltaic applications due to its high stability, tunable band gap, non‐toxic element, and high extinction coefficient. For Sb2(SexS1–x)3 alloy film deposition, the authors develop a single source based rapid‐thermal‐evaporation (RTE) method instead of the traditional in‐situ sulfurization or double source co‐evaporation based RTE method. The absorber band gap can be precisely tuned from 1.1 to 1.7 eV by simply varying the molar ratio of Sb2Se3 and Sb2S3 source powder. From the systematical composition screening, FTO/CdS/Sb2(Se0.68S0.32)3/Au devices show higher power conversion efficiency (PCE ∼ 4.17%) when compared with other absorber compositions based devices. In order to achieve thinner ETL layers and simultaneously avoid pinholes led by rough FTO surface, we introduce for the first time double buffer layer in the Sb2(Se0.68S0.32)3 device system which could further improve the device efficiency from 4.17% to 5.73%. The double buffer layer ZnO/CdS helped to form graded energy band alignment, suppress charge recombination and efficiently extract electrons. The devices obtained higher Jsc and Voc supported by various physical characterization analyses. The facile single source deposition method, efficient double buffer layer device structure and notable PCE are expected to pronouncedly promote antimony chalcogenide device development.

Research Update: Emerging chalcostibite absorbers for thin-film solar cells

Copper antimony chalcogenides CuSbCh2 (Ch=S, Se) are an emerging family of absorbers studied for thin-film solar cells. These non-toxic and Earth-abundant materials show a layered low-dimensional chalcostibite crystal structure, leading to interesting optoelectronic properties for applications in photovoltaic (PV) devices. This research update describes the CuSbCh2 crystallographic structures, synthesis methods, competing phases, band structures, optoelectronic properties, point defects, carrier dynamics, and interface band offsets, based on experimental and theoretical data. Correlations between these absorber properties and PV device performance are discussed, and opportunities for further increase in the efficiency of the chalcostibite PV devices are highlighted.

High‐throughput method to deposit continuous composition spread Sb2(SexS1 − x)3thin film for photovoltaic application

AbstractSb2(SexS1 − x)3alloy materials with tunable bandgaps combining the advantages of Sb2S3and Sb2Se3showed high potential in low cost, non‐toxicity, and high stability solar cells. The composition dependence of device performance becomes indispensable to study. However, traditional approaches often implement 1 composition at a time, which easily lead to long period and systematic errors. The present work developed a high‐throughput experimental method, close‐space dual‐plane‐source evaporation (CDE) method, to successfully deposit continuous composition spread Sb2(SexS1 − x)3library at 1 time. On the surface of the obtained film, thexvalue of Se content evolved from 0.09 to 0.84 by a series of complementary characterizations. At depth direction, the alloy film kept high crystallinity and composition consistency. Solar cell arrays (19 × 6) were fabricated to investigate the relationship between compositions and performances. As the increase of Se content, the conversion efficiency first increased from 1.8% to 5.6% and then decreased to 5%. The Vocand Jscdemonstrated an opposite evolution trend. The champion device with the composition of Sb2(Se0.68S0.32)3achieved the Vocand Jsctrade‐off exceeding the performances of Sb2S3(2.43%) and Sb2Se3(4.97%) devices. Cryogenic and transient characterizations were utilized to investigate the distinct performance evolution mechanism. There existed shallow defect levels in Se‐rich alloys and deep defects in sulfur‐rich ones. The widely tuned absorber compositions combined with distinct defect characters induced to the large variation of device performance. The present continuous composition spread Sb2(SexS1 − x)3film and their CDE fabrication technique were expected to efficiently screen materials and promote the development of antimony chalcogenide solar cells.

Facile synthesis and thermal analysis of antimony telluride nanostructures

Fabrication of nano-sized thermoelectric (TE) semiconductors like Antimony chalcogenides and study of their properties is a growing interest among the inorganic thermoelectric (TE) materials, which leads to the increase in the efficiency of energy conversion. The demand for fabricating high performance Thermoelectric (TE) materials in large quantity is very high. A facile synthesis was carried out for nanostructures of Sb2Te3 material trough chemical precipitation and solvo-thermal route. Both these chemical synthesis routes are not complicated and are suitable for expeditious way of synthesizing Nano crystallites, but have their own advantages. The structural and morphological studies of the prepared nanostructure material were carried out by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The thermal studies were carried by Non destructive Thermal Analysis. Measurements of the thermal conductivity of the prepared nanostructured powders indicate that these synthesized Sb2Te3 material can be tuned to enhance the thermoelectric (TE) behavior as they possess considerably low thermal conductivity than that of bulk Sb2Te3.

Density of State Calculations for Tl3SbS3 and SbTeI

Based on the full-potential linearized augmented plane waves method (FL-LAPW) with local density approximation (LDA), the partials and totals densities of state of Tl3SbS3 and SbT eI are calculated in order to find the semiconductor character via direct or indirect gap. Tl3SbS3 and SbTeI present the most important candidates of the antimony chalcogenides family. Their densities of states curves bring out characteristic features in the valence band a core like peak, at environ 13.00 eV below the valence band maximum, originating mainly from S 3s and I 5s states respectively, and a three-peak structure at the top of the valence band from S 3p and I 5p states hybridized with Sb 5p and Te 5p states. Our results give a good agreement with other theoretical calculations and experimental data.

Effect of melt-spun powder additions on the thermoelectric properties of bismuth and antimony chalcogenides

We have studied the thermoelectric properties of p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.4Se0.6 solid solutions prepared by vacuum hot pressing of mixtures of powders differing in particle size composition. The powders were prepared by mechanically grinding ingots and by ultrarapid melt cooling (melt spinning). Fracture surfaces of samples were examined by scanning electron microscopy. The samples consisted of large, layered particles of the major component (up to hundreds of microns in size) and small flakes (a few to tens of microns in size) of the component prepared by melt spinning. The microstructure of the materials was examined under an optical microscope. On grain boundaries in the p-type materials, we observed telluriumbased eutectic precipitates in the form of a white phase. In some of the n-type samples, the Bi2Te2.4Se0.6 solid solution was found to undergo ordering, resulting in the formation of the ternary compound Bi2Te2Se. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the materials were measured in the temperature range 100–700 K. The addition of 40 wt % powder prepared by melt spinning to hot-pressed p-type samples was shown to have no effect on their thermoelectric figure of merit (ZT)max, which was 1.0 at 350 K. On the addition of 20 wt % powder prepared by melt spinning, we obtained (ZT)max = 1.1 at 550 K in a hot-pressed n-type sample.

Antimony selenide nanostructures: morphology control through modulation of ligand chemistry and variation of the precursor ratio

Nanocrystalline antimony chalcogenides belong to a class of materials that offer significant potential for photovoltaics, display and lighting applications. However, a lack of synthetic methodologies that allow facile solution-based access to these nanomaterials currently restricts their practical use. Herein, a new synthetic route for the controlled preparation of antimony selenide nanostructures through colloidal chemistry is reported. A collection of nanostructures ranging from nanorods and nanocrystals to hollow spheres was successfully synthesized through the reported methodology, for which the morphological control during the particle formation was accomplished through both modulation of ligand chemistry for passivating the nanocrystal surface and accurate adjustment of the precursor ratio.

Recent progress in copper antimony chalcogenides thin films and photovoltaic devices

In recent years, owing its advantages such as high material utilization and low energy consumption during manufacturing, strong low light performance and high energy output during operation, and easy integration with buildings, thin film solar cell has become a very competitive technology for photovoltaic application. Particularly, copper antimony chalcogenides (Cu-Sb-S/Se) have attracted tremendous research attention as the promising absorber candidates because of the advantages of low cost, high stability and nontoxic composition, large absorption coefficient and appropriate band gap. In the Cu-Sb-S/Se system, there are four kinds of stoichiometric ratio phases with Cu:Sb:S/Se of 1:1:2, 3:1:3; 3:1:4 and 12:4:13. Among them, CuSbS2 and CuSbSe2 have appropriate bandgaps of ~1.5 and ~1.1eV, large absorption coefficient of ~105cm - 1, which is larger than CuInSe2, and low grain growth temperature (about 300–400°C). Theoretical calculations indicate that CuSbS2 and CuSbSe2 solar cells have higher theoretical maximum efficiency than CuInSe2, and the majority defects are shallow defects. Various approaches have been explored to fabricate CuSbS2 and CuSbSe2 thin films, including direct thermal evaporation, post-annealing after chemical bath deposition, spray pyrolysis, electrodeposition, magnetron sputtering and so on. In the last few years, several groups have reported thin film solar cells based on CuSbS2 and CuSbSe2, including our groups’ work. We prepared prototype CuSbS2 and CuSbSe2 solar cells employing the conventional substrate structure of glass/FTO/CuSbS2/CuSbSe2/CdS/ZnO/ZnO:Al/Au with conversion efficiencies of 0.5% for CuSbS2 solar cell( V OC=0.44V, J SC=3.65mA/cm2, FF=31%, area=0.45cm2) and 1.32% for CuSbSe2 solar cell ( V OC=0.274V, J SC=11.84mA/cm2, FF=40.51%, area=0.19cm2). Former research obtained a high quality CuSbS2 film through sulfurizing Cu-Sb precursor in H2S atmosphere, and the devices achieved a remarkable efficiency of 3.13% ( V OC=0.49V, J SC=14.73mA/cm2, FF=44%). NREL scientists studied CuSbM2 solar cells in-depth and prepared high efficiency CuSbSe2 devices of 3.5% with an three-stage self-regulated growth approach (glass/Mo/CuSbSe2/CdS/ZnO/ ZnO:Al/Al; V OC=0.35V, J SC=22.82mA/cm2, FF=44%). Specifically, high-throughput combinatorial method, using the natural compound nonuniformity caused by magnetron sputtering of CuS2 and Sb2Se3 targets, was used to optimize the phase purity, thickness of absorbers, carrier concentration and so on. This research revealed that the weak carrier collection related to the low mobility and short charge carrier lifetime were the main problems of CuSbSe2 solar cells. So it is crucial to optimize the absorber fabrication process to obtain a high quality film with benign defects properties. Besides, improving the back contact of devices and selecting a suitable buffer layer to replace CdS are also important. In summary, this paper reviews the research progress of copper antimony chalcogenide photovoltaics in recent years with special emphasis on the crystal structure, photoelectric properties, preparation methods and advancement in solar cells. The development tendency and the direction for future work are also summarized and prospected.

Crystallization and mechanical properties of solid solutions between bismuth and antimony chalcogenides

Using scanning electron microscopy, we have studied how the conditions of preparation of granules of Sb2Te3–Bi2Te3 and Bi2Te3–Bi2Se3 solid solutions through melt solidification in a liquid influence their morphology, fractographs of fracture surfaces of samples prepared by hot-pressing the granules, and the contents of the major components in the samples. The granules are rounded (solidification in water and liquid nitrogen) or platelike (solidification in water under an excess pressure and in liquid-nitrogen-cooled ethanol) in shape. Fracture surfaces of hot-pressed samples prepared from granules comminuted in a ball mill have a uniform, fine microstructure, with faceted grains several microns in size. Characteristically, samples prepared from granules comminuted in a cutting mill have transgranular layered fractures, with layers up to hundreds of microns in thickness. The mechanical properties of the samples (ultimate strength and relative elongation) have been studied using compression tests at temperatures of 300 and 620 K. The samples experience brittle fracture. Their compression strength σc is 55 ± 12 MPa. With increasing temperature, σc varies only slightly, but at 620 K the samples become more plastic and their relative elongation eb increases by a factor of 2–4. The ultimate strength of hot-pressed samples prepared by uniaxial compression is 20% higher than that of samples prepared by biaxial compression.

Mechanical properties of (Bi,Sb)2Te3 solid solutions obtained by directional crystallization and spark plasma sintering

We have studied the temperature dependence of the mechanical strength at uniaxial compression for solid solutions based on bismuth and antimony chalcogenides, which were prepared by three methods: (i) vertical zone melting (VZM), (ii) hot extrusion, and (iii) spark plasma sintering (SPS). In the samples of solid solutions obtained by VZM and extrusion, a brittle–ductile transition was observed in a wised temperature interval of 200–350°C. In nanostructured SPS samples, transition from brittle to plastic fracture was observed within 170–200°C. The room-temperature strength of nanostructured samples was eight to nine times as large as that of VZM samples, and the stress–strain curves of these materials were significantly different. At a temperature of about 300°C, the strength of nanostructured solid solutions decreases to nearly zero.

A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4.

Recent progress in the field of topological states of matter has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators (TIs; refs,,,), followed by closely related ternary compounds and predictions of several weak TIs (refs,,). However, both the conceptual richness of Z2 classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z2 topological insulator is theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide Bi4I4. The electronic structure of β-Bi4I4, characterized by Z2 invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements performed on the (001) surface reveal a highly anisotropic band-crossing feature located at the point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoreticalprediction.

On Improvement of Thermoelectric Properties of Bulk Bi-Sb-Te Nanostructures

Fabrication of bulk nanostructures based on bismuth and antimony chalcogenides, including ball milling and subsequent hot pressing or spark plasma sintering, are discussed. Sets of samples of different compositions were obtained using different technological conditions (pressure, sintering temperature). Structure and mechanical properties of consolidated samples were investigated. Thermoelectric parameters were measured using direct methods and Harman technique; measurement errors in the thermoelectric properties were determined. The thermal conductivity of bulk nanostructures based on Bi-Sb-Te was calculated taking into account real phonon spectrum and anisotropy; conditions that promoted the minimizing of thermal conductivity were determined.

Interplay between spin–orbit coupling and crystal-field effect in topological insulators

Band inversion, one of the key signatures of time-reversal invariant topological insulators (TIs), arises mostly due to the spin–orbit (SO) coupling. Here, based on ab initio density-functional calculations, we report a theoretical investigation of the SO-driven band inversion in isostructural bismuth and antimony chalcogenide TIs from the viewpoint of its interplay with the crystal-field effect. We calculate the SO-induced energy shift of states in the top valence and bottom conduction manifolds and reproduce this behavior using a simple one-atom model adjusted to incorporate the crystal-field effect. The crystal-field splitting is shown to compete with the SO coupling, that is, stronger crystal-field splitting leads to weaker SO band shift. We further show how both these effects can be controlled by changing the chemical composition, whereas the crystal-field splitting can be tuned by means of uniaxial strain. These results provide a practical guidance to the rational design of novel TIs as well as to controlling the properties of existing materials.

Synthesis, Crystal, and Electronic Structure of Ba3Sb2Q7 (Q = S, Se)

AbstractTwo new barium antimony chalcogenides, Ba3Sb2S7 and Ba3Sb2Se7, were synthesized from elements by high‐temperature solid‐state reactions. The crystal structures were determined by means of single‐crystal X‐ray diffraction. Both compounds are isostructural and crystallize in a new structure type in the monoclinic space group C2/c (No. = 15) with unit cell parameters of a = 18.305(2)/18.904(5) Å, b = 12.202(1)/12.651(3) Å, c = 13.117(1)/13.554(3) Å, and β = 110.134(1)/109.839(4)° for Ba3Sb2S7/Ba3Sb2Se7, respectively. The crystal structures are comprised of Ba cations, trigonal‐pyramidal [SbQ3]3–, and [SbQ4]3– units (Q = S, Se). In the SbQ4 unit, one vertex is a Q2 dumbbell instead of a single Q atom. Quantum‐chemical calculations show that the sulfur‐containing compound is an indirect semiconductor with a high density of states below the Fermi level. ELF analysis shows highly polarized Sb–S bonds and unusual torus‐shaped ELF distributions around the terminal sulfur atom of the S2 dumbbell. According to UV/Vis measurements Ba3Sb2S7 is an indirect semiconductor with a bandgap of 2.1 eV.

Synthesis of Nanostructured Antimony Telluride for Thermoelectric Applications

ABSTRACTThermoelectric (TE) materials have been studied during past decades since they can generate electricity directly from waste heat. Antimony chalcogenides (Sb2M3, M = S, Se, Te) are well known as one of the promising candidates among the inorganic TE materials. We report on the synthesis of Sb2Te3 nanoparticle via thermolysis method. A systematic study was done to investigate the effect of reaction time and ratio between the precursors as well as the method of cooling on the morphology and composition of obtained nanoparticles. The ratio between precursors was varied to study the effect on the morphology. Furthermore, the high purity phase Sb2Te3 was obtained by a rapid cooling process.

The electronic structure of the antimony chalcogenide series: Prospects for optoelectronic applications

In this study, density functional theory is used to evaluate the electronic structure of the antimony chalcogenide series. Analysis of the electronic density of states and charge density shows that asymmetric density, or ‘lone pairs’, forms on the SbIII cations in the distorted oxide, sulphide and selenide materials. The asymmetric density progressively weakens down the series, due to the increase in energy of valence p states from O to Te, and is absent for Sb2Te3. The fundamental and optical band gaps were calculated and Sb2O3, Sb2S3 and Sb2Se3 have indirect band gaps, while Sb2Te3 was calculated to have a direct band gap at Γ. The band gaps are also seen to reduce from Sb2O3 to Sb2Te3. The optical band gap for Sb2O3 makes it a candidate as a transparent conducting oxide, while Sb2S3 and Sb2Se3 have suitable band gaps for thin film solar cell absorbers.

High Efficiency Solar Cells As Fabricated by Sb2S3-Modified TiO2 Nanofibrous Networks

High-efficiency hybrid solar cells (HSCs) based on electrospun titanium dioxide (TiO2) nanofibers plus poly(3-hexylthiophene) (P3HT) are fabricated by means of both the pretreatment using tetrahydrofuran (THF) vapor and the surface modification using n-type antimony chalcogenide (Sb2S3) on the TiO2 nanofibrous networks. It is revealed that the THF pretreatment not only reinforces the interfacial physical contact but also suppresses the interfacial recombination. The Sb2S3 modification improves the light absorption and charge transfer. Given that the active layer of the HSCs is as thin as 300 nm, it is demonstrated that the power conversion efficiency (PCE) is enhanced over 175%, exhibiting a PCE of 2.32%.

Thermoelectric properties of nanocrystalline solid solutions of bismuth and antimony chalcogenides

The samples structure of solid solutions of p- and n-type bismuth and antimony chalcogenides obtained in the form of rods 1.6 mm in diameter by hot extrusion have been studied. These rods are found to consists of nanocrystallites 8–60 nm in size. In p-type samples, nanocrystallites aggregated into spherical crystallites 50–100 nm in diameter, whereas nanocrystallites in n-type samples formed disoriented fibers with a transverse cross section of several ten nanometers to several micrometers and a length of a few micrometers to several dozen micrometers. The presence of nanocrystallites of this size in the sample structure reduces the thermal conductivity of bismuth and antimony chalcogenides by 10% but barely changes their resistivity and thermoelectric power. The thermoelectric efficiencies of the p- and n-type chalcogenides are 3.27 × 10−3 and 2.78 × 10−3 K−1, respectively.