Micron-sized Grains Research Articles

Above 600 mV Open-Circuit Voltage BiI3 Solar Cells

Phase-pure BiI3 films obtained by versatile gas-phase iodination of Bi2S3 are investigated as an absorber in photovoltaic devices. This preparation method leads to highly crystalline BiI3 films featuring a rhombohedral phase and a high-degree of stacking order. The films are composed of micrometer-sized flat grains distributed homogeneously across the F-doped SnO2 (FTO) substrate, exhibiting an indirect band gap transition at 1.72 eV. High-level calculations based on G0W0 approximation are used to rationalize the electronic structure of BiI3, confirming the band gap value estimated experimentally. The films show p-type conductivity with an acceptor density on the order of 1015 cm–3. Solar cells with the architecture glass/FTO/TiO2/BiI3/F8/Au, where F8 is poly(9,9-di-n-octylfluorenyl-2,7-diyl), display a record open-circuit voltage above 600 mV and overall power conversion efficiency of 1.2% under AM 1.5G illumination. The large open-circuit potential is rationalized in terms of carrier lifetimes longer th...

Catching drifting pebbles

Context.Coagulation theory predicts that micron-sized dust grains grow into pebbles, which drift inward towards the star when they reach sizes of mm−cm. When they cross the orbit of a planet, a fraction of these drifting pebbles will be accreted. In the pebble accretion mechanism, the combined effects of the planet’s gravitational attraction and gas drag greatly increase the accretion rate.Aims.We calculate the pebble accretion efficiencyε2D– the probability that a pebble is accreted by the planet – in the 2D limit (pebbles reside in the midplane). In particular, we investigate the dependence ofε2Don the planet eccentricity and its implications for planet formation models.Methods.We conduct N-body simulations to calculate the pebble accretion efficiency in both the local frame and the global frame. With the global method we investigate the pebble accretion efficiency when the planet is on an eccentric orbit.Results.We find that the local and the global methods generally give consistent results. However, the global method becomes more accurate when the planet is more massive than a few Earth masses or when the aerodynamic size (Stokes number) of the pebble is larger than 1. The efficiency increases with the planet’s eccentricity once the relative velocity between the pebble and the planet is determined by the planet’s eccentric velocity. At high eccentricities, however, the relative velocity becomes too high for pebble accretion. The efficiency then drops significantly and the accretion enters the ballistic regime. We present general expressions forε2D. Applying the obtained formula to the formation of a secondary planet, in resonance with an already-formed giant planet, we find that the embryo grows quickly due to its higher eccentricity.Conclusions.The maximumε2Dfor a planet on an eccentric orbit is several times higher than for a planet on a circular orbit, but this increase gives the planet an important headstart and boosts its following mass growth. The recipe forε2Dthat we have obtained is designed to be implemented into N-body codes to simulate the growth and evolution of planetary systems.

Quantifying the grain boundary segregation strengthening induced by post-ECAP aging in an Al-5Cu alloy

Hardening on annealing (HOA) has been frequently observed in nanostructured metals and alloys. For nanostructured materials obtained by severe plastic deformation (SPD), HOA has been attributed to the reduction of dislocation sources within grains and grain boundary relaxation during annealing. In the present work, it is shown that when a bimodal grain structured (a mixture of micron-sized and ultrafine grains) Al-5Cu alloy prepared by equal channel angular pressing (ECAP) was subjected to post-ECAP natural and artificial aging treatments, the alloy shows a completely different precipitation behavior with an accelerated precipitation kinetics. No coherent θ'' or semi-coherent θ' precipitates form in the bulk of grains, while a large fraction of stable incoherent θ precipitates form along high angle boundaries. After artificial aging at low temperatures for a short time, a significant improvement of both ultimate tensile strength and uniform elongation was achieved without sacrificing the yield strength. A systematic microstructure characterization by EBSD, TEM and APT has been carried out to investigate the evolution of grain size, dislocation density and solid solution level of Cu as well as the precipitation of Al-Cu precipitates during natural and artificial aging treatments. A quantitative evaluation of different supposed strengthening mechanisms revealed that the segregation of Cu elements at grain boundaries plays a more important role than grain boundary relaxation and the dislocation source-limited strengthening to compensate the yield strength reduction caused by the decrease in dislocation density and solute content of Cu in solid solution.

Lunar dust lofting due to surface electric field and charging within Micro-cavities between dust grains above the terminator region

It has been suggested that lunar dust grains can be transported by the electrostatic forces above the lunar terminator and produce the lunar horizon glow (LHG) by forward-scattering of sunlight. In addition, the recent experiments have shown that dust grains can be lofted in the vacuum chamber due to charging within micro-cavities by absorbing the emitted secondary electrons under the electron beam current (Wang et al., 2016; Schwan et al., 2017). In this study, the required charge within micro-cavities in order to separate dust particles from the lunar surface are estimated by using the surface electric field and the forces of gravity and contact. In addition, the maximum heights for dust grains are calculated by initial vertical launching velocity from the surface and the acceleration within the electron sheath against the gravity. The following calculations are performed for the particles with 0.1, 1 and 5 μm radius, and the variation of ambient plasma conditions are studied throughout solar wind data of CME passages on 8–13 February 1997, 1–3 May 1998 and 8–12 March 2012. Current balance method is used to estimate the surface potential, electric field and Debye length to investigate how the lunar dust particles are mobilized under the various conditions. First, strong negative surface potentials can be observed during the post-shock plasma passages, and it produces stronger electrostatic forces acting on the lofted dust particles. Second, submicron-sized dust particles are launched from the surface less frequently than the larger size grains due to the charging time. The height predictions of the dust grains with 5 μm radius are similar to the LHG observations of Surveyor mission, and the results suggest that the heights of micron-sized dust grains are controlled by the initial vertical launching velocity more than the surface electric field, unlike the smaller sized particles. Finally, strong electrostatic forces are not sufficient solely to loft the dust particles to higher altitudes since a charged dust requires accelerating for a proper time and distance in the electron sheath.

Rapid mechanochemical synthesis of nanostructured mohite Cu2SnS3 (CTS)

Rapid solvent-free mechanochemical synthesis of CTS nanocrystals from elemental precursors is reported herein. The process is completed in 15 min, proceeding through immediate formation of CuS in a self-sustaining manner and its subsequent reaction with Sn and residual sulfur. The reaction progress was monitored by pressure and temperature changes in the milling vessel, X-ray diffraction, Soxhlet analysis, grain size analysis and electric resistivity measurements. The relationship between the consumption of metallic precursors, grain size and electrical resistivity is provided. The final product was nanocrystalline with crystallite size below 10 nm, as confirmed by both X-ray diffraction and transmission electron microscopy. The nanocrystals are agglomerated into micrometer-sized grains. It exhibits poor porous properties with the specific surface area value of 2.5 m2/g. The X-ray photoelectron spectroscopy has shown that the surface is significantly oxidized, due to milling in air. The optical properties of the prepared CTS nanocrystals are interesting for photovoltaic applications.

Preparation of magnetic Fe-Co alloy using texture controlled technique

Microstructure and texture controlled 48Fe-52Co at% alloy was prepared by repeated cold-rolling and recrystallization through heat treatment at temperatures below order-disorder phase transformation using Fe and Co foils. Furthermore, distortion of controlled texture orientated cubic crystal structured 48Fe-52Co at% alloy along the 〈0 0 1〉 direction was attempted by introducing nitrogen interstitially through plasma nitriding. The textural analysis suggested that the microstructure is composed of micron-sized grains randomly aligned along rolling direction (RD). Furthermore, from the results of orientation distribution function (ODF), the dominance γ-fiber was confirmed in as-rolled samples. However, in recrystallized sample, the intensity of rotated-cube orientation increased while the presence of γ-fiber decreased. Furthermore, a complete rotated-cube orientation was realized in nitrided texture. The appearance of the prominent X-ray diffraction peak (2 0 0) in all samples indicated the presence of rotated-cube orientation. However, the FWHM of (2 0 0) peak of the nitrided sample was broader than the rest. This was attributed to the diffusion of nitrogen into the matrix during plasma nitriding and internal nitriding was confirmed from the EDX analysis. However, further investigation is necessary to understand the behavior of nitrogen.Magnetic properties of as-rolled 48Fe-52Co at% alloy inferred from in-plane magnetic hysteresis loops was similar Fe foil. Furthermore, magnetic properties of recrystallized and nitrided 48Fe-52Co at% alloy were different from Fe-Co particles or crushed bulk Fe-Co alloy prepared by arc melting. However, the internal diffusion of nitrogen was not adequate enough to bring about a considerable change in the magnetic properties. We believe that considerable crystal distortion to induce change in the magnetic properties can be exerted by introducing interstitial carbon and the addition of third or fourth elements.

Ultrafast Imaging of Carrier Transport across Grain Boundaries in Hybrid Perovskite Thin Films

For optoelectronic devices based on polycrystalline semiconducting thin films, carrier transport across grain boundaries is an important process in defining efficiency. Here we employ transient absorption microscopy (TAM) to directly measure carrier transport within and across the boundaries in hybrid organic–inorganic perovskite thin films for solar cell applications with 50 nm spatial precision and 300 fs temporal resolution. By selectively imaging sub-bandgap states, our results show that lateral carrier transport is slowed down by these states at the grain boundaries. However, the long carrier lifetimes allow for efficient transport across the grain boundaries. The carrier diffusion constant is reduced by about a factor of 2 for micron-sized grain samples by the grain boundaries. For grain sizes on the order of ∼200 nm, carrier transport over multiple grains has been observed within a time window of 5 ns. These observations explain both the shortened photoluminescence lifetimes at the boundaries as we...

Two-stage processed CuSbS2 thin films for photovoltaics: Effect of Cu/Sb ratio

In recent years, CuSbS2 has attracted significant research interest because of its direct optical band gap of 1.5 eV, high optical absorption coefficient, p-type electrical conductivity, and composition involving earth-abundant and non-toxic precursor elements. We prepared CuSbS2 thin films by annealing chemically grown Sb2S3 and sputter deposited Cu (Sb2S3/Cu) stacks in a graphite box, and studied the effect of the Cu/Sb ratio on the growth and properties of these films by varying the thickness of Cu while keeping the thickness of Sb2S3 constant. The Cu/Sb ratio significantly impacted the phase purity, grain growth, and morphology of the CuSbS2 films. The CuSbS2 films prepared with a Cu/Sb ratio of 0.78 showed some unreacted Sb2S3 and nonuniform grain growth. Upon increasing the Cu/Sb ratio from 0.85 to 0.97, the Sb2S3 phase was consumed completely, and phase-pure CuSbS2 with homogeneous grain formation was obtained. These films exhibited an orthorhombic crystal structure with the (410) preferred orientation. Further increase in the Cu/Sb ratio from 1.28 to 1.52 resulted in a change in the growth direction along the (200) plane and the formation of several micron-sized grains with a compact morphology and Cu3SbS4 secondary phase. The direct optical band gap of the films decreased from 1.52 to 1.48 eV when Cu/Sb ratio was increased from 0.91 to 1.28. The films exhibited p-type electrical conductivity and their electrical resistivity decreased with increasing Cu/Sb ratio. From this investigation it was clear that deviation in the Cu/Sb ratio from the stoichiometric proportion leads to inhomogeneous grain growth of CuSbS2 films, which affect the performance of devices using these films.

Subgrain-controlled grain growth in the laser-melted 316 L promoting strength at high temperatures.

Stainless steel 316 L prepared by laser melting consisted of a hierarchical austenitic microstructure with micrometre-sized (10–25 µm) grains containing fine 1 µm subgrains with a cellular structure. At high-temperature thermal treatments (greater than or equal to 1100°C), merging and growth of the 1 µm subgrains into bigger subgrains restricted the rapid grain growth and microstructure coarsening. Partial phase transformation of austenite to ferrite at temperatures greater than or equal to 1100°C, in combination with gradual and steady growth of subgrains inside the micrometre-sized grains and nucleation of the sigma phase, has promoted the tensile strength of stainless steel 316 L to 300 MPa at 1100°C compared with that of conventionally made 316 L counterparts (approx. 40 MPa). The grain growth mechanism of the laser-melted microstructure can change the application criteria for 316 L and expand the application fields for 316 L.

Stabilization of cubic Li7La3Hf2O12 by Al-doping

In this paper we report on the stabilization of cubic Li7La3Hf2O12 by Al3+ doping and present a detailed crystal structure study and lithium ion conductivity measurements of the obtained compound. Polycrystalline Al-doped Li7La3Hf2O12 was prepared by a modified solid state method. The compound consists of micrometer size grains encapsulated by a glassy phase, which helps preventing the volatilization of lithium during annealing. Al-doped Li7La3Hf2O12 crystallizes in the garnet-related structure with a cubic unit cell (sp. gr. Ia3¯d (230)). A structural refinement using X-ray and neutron powder diffraction data showed that the Al3+ ions occupy only tetrahedral Li+ sites in the structure. The presence of overextended leading edges of the peaks on the XRD and NPD data is described by the introduction of an additional phase with rhombohedral distortion that occurs through a stretching of the cubic phase along the body diagonal. The activation energy as well as the total conductivity at room temperature are close to values obtained for un-doped cubic Li7La3Zr2O12 and Li7La3Hf2O12 garnets, which make Al-doped Li7La3Hf2O12 a potential candidate for the application as solid electrolyte in solid-state rechargeable lithium-ion batteries.

Microstructural and compositional effects of transition metal carbide additions on dispersion-strengthened tungsten fabricated via spark plasma sintering

Tungsten is the plasma-facing material of choice for the divertor region in ITER as it has favorable properties under ion irradiation. However, tungsten is a very brittle material whose fabrication is complicated by its high melting point and low recrystallization temperature. Spark plasma sintering is a powder consolidation technique that can rapidly compact tungsten powder to high relative densities while preserving fine grain sizes. Dispersing fine transition metal carbide particles within the tungsten matrix has been proposed to enhance the ductility of tungsten by re-arranging the impurity distribution. Tungsten samples consolidated with 0.5–10 wt% zirconium carbide, titanium carbide, or tantalum carbide have been fabricated via spark plasma sintering to >90% relative density. Consolidated samples have transition metal-rich dispersoids uniformly distributed at grain boundaries and within the micron-sized tungsten grains. The presence of the dispersed second phase particles successfully refined the final grain size, as the average grain size decreased from 11 μm for the pure W samples to ~1 μm for the samples with 10 wt% second phase. Correspondingly, the hardness as measured via Vickers hardness rises as the grain size decreases and volume fraction of the second phase increases. XRD and XPS analyses show that formation of tungsten carbide and transition metal oxide complexes alter the impurity distribution and material performance.

Effects of concurrent strain induced martensite formation on tensile and texture properties of 304L stainless steel of varying grain size distribution

Ultrafine grained austenitic stainless steel, with two different types of grain size distributions, was studied for tensile deformation behavior. Tensile deformed specimens were analyzed by electron backscatter diffraction using scanning electron microscope. It was found from this study that uni-modal grained stainless steel (SS) having a larger fraction of submicron grains exhibited early fracture, which is attributed to the development of extensive strain localization. On the other hand, the microstructure of SS having bimodal grain size distribution showed a good combination of strength and ductility. EBSD analysis of the deformed region of these two samples revealed the presence of a distinct transition zone between undeformed or less deformed and extensively sheared regions. Multiple micro shear bands were found to be associated with the transition zone of unimodal type microstructure. The micro shear bands seen in the transition zone of unimodal SS led to the development of strain-induced martensite (SIM), which, in turn, is helpful in delaying the strain localization. However, in bimodal grained SS, the larger fraction of micron size grains undergoes a shape change, with a rotation towards [112] orientation, which results in the formation of a larger fraction of SIM having [112] orientation. The propensity for development of high SIM was found to prevent strain localization in bimodal grained SS.

Ferroelectric domain evolution in gold nanoparticle-modified perovskite barium titanate ceramics by piezoresponse force microscopy

ABSTRACTThis work addresses the domain evolution processes in polycrystalline barium titanate (BaTiO3, BT)-based ceramics containing various amounts of gold nanoparticles (AuNPs) as an additive by using piezoresponse force microscopy (PFM). The obtained PFM images of the AuNPs-modified BT ceramics revealing the change of one spontaneously polarized state to another under various applied direct current (DC) voltage are discussed in terms of their domain topology, PFM phase shift and PFM amplitude. In general, complex microstructures containing almost round-shaped and micron-sized grains, and grain boundary regions are clearly seen in the topographic images of all samples. The obtained results point towards possibility of control the polarization switching of the AuNPs-modified BT ceramics with fined-grains sizes, by a selection of the proper applied DC voltage (VDC). The PFM investigation confirmed good dipole orientation within the AuNPs-modified BT ceramics containing submicron grain size at the elevated external fields and proved the lack of convenient domain switching of the unmodified BT case resulting from their larger grain size.

Listwaenite in the Sartohay ophiolitic mélange (Xinjiang, China): A genetic model based on petrology, U-Pb chronology and trace element geochemistry

Listwaenite lenses in the Sartohay ophiolitic mélange (Xinjiang, China) were formed via reactions between serpentinite and metasomatic fluids. First, serpentinite changed into talc schist via the reaction of serpentine + CO2 → talc + magnesite + H2O. Second, talc schist changed into listwaenite via the reaction of talc + CO2 → magnesite + quartz + H2O. Magnetite was progressively destroyed during transformation from serpentinite to talc schist, and completely consumed in listwaenite. Zircon crystals 30–100 μm long, disseminating in talc schist, undeformed listwaenite and mylonitized listwaenite, coexist with talc, quartz and magnesite, while micron-sized zircon grains (<5 μm in length) occur along the shearing foliation in the weakly deformed listwaenite and mylonitized listwaenite. We postulate that these micron-sized zircon crystals may have grown in-situ from medium-temperature hydrothermal fluids. Concentrations of most trace elements including high field strength elements (HFSE) increase from the undeformed, through the weakly deformed, to the mylonitized listwaenite, showing a positive correlation with the degrees of deformation and proportions of micron-size zircon, apatite, rutile and monazite. The large zircon crystals recovered from talc schist, undeformed listwaenite and mylonitized listwaenite yield similar weighted mean U-Pb ages (302.9 ± 6.8 Ma, 299.7 ± 5.5 Ma and 296.5 ± 3.5 Ma), and are thought to represent the age of formation of the talc schist and listwaenite. These ages are indistinguishable within errors and suggest a rapid transformation from talc schist to listwaenite. Some zircon rims in samples of the undeformed listwaenite and mylonitized listwaenite give much younger apparent U-Pb ages (280–277 Ma), which could be interpreted as a recrystallization age reflecting late-stage shearing in the Sartohay ophiolitic mélange.

Microstructure and mechanical properties of intragranular W-Cu/TiC-ZrC composite prepared by reactive melt infiltration at 1300 °C

Newly intragranular W-Cu/TiC-ZrC composites with nano W dispersoids in TiC matrix have been prepared by reactive melt infiltration at 1300 °C for 1 h in vacuum using molten Zr-Cu binary alloys and a (Ti0.75,W0.25)C solid solution powder as raw materials. The as-synthesized composites consist of major phases of W, Cu, TiC and ZrC. With the decrease of Zr content from 66 to 21 at.% in the Zr-Cu infiltrator, the reaction formed W phase in the composite has changed from micron-sized intergranular grains to nano-sized rounded inclusions in TiCy grains. The crystallographic orientation relationship at W and TiC interfaces are detected as:011¯W//111¯TiC&011W//011TiCand411W//424TiC&011¯W//42¯3¯TiC. Nano-sized lamellar structure with both W and Cu rich is detected to have super-lattice structure based on the TiC lattice. The elastic modulus, flexural strength, fracture toughness of the intragranular W-Cu/TiC-ZrC composite infiltrated with Zr14Cu51 melt are 207.5 GPa, 457 MPa and 10.21 MPa∙m1/2, respectively. The intragranular nano W dispersoids and ribbon like precipitates hinder crack propagation via crack deflection and bridging.

Synthesis, Characterization, Optical and Transport Properties of BaSnO&amp;lt;SUB&amp;gt;3&amp;lt;/SUB&amp;gt; Synthesized by Wet Chemical Route

Alkaline earth stannates have renewed attention as potential materials for gas sensing, transparent conducting oxides and ceramic capacitor applications. A noble wet chemical route is chosen to synthesize BaSnO3 powders having micron size grains. Problems related to uneven grains and poor densification in conventional solid state route have been overcome in the present method. X-ray diffraction data confirms the single phase formation without any secondary phase having cubic perovskite structure (S.G. Pm-3m). The estimated lattice parameter is ≈4.11933A and percentage density is ≈90%. The microstructure probed by scanning electron micrograph reveals almost homogeneously distributed particles having random shape with some porosity. Phonon modes in FT-IR and Raman spectra confirm the local symmetry distortion. The DC conductivity at 200°C approaches almost 2 × 10-2 (Ω-cm)-1, which is almost of the same order as that observed in perovskite based electronic conductors. DC and a.c. electrical conductivity of the material follow Mott’s variable range hopping at low temperature and Arrhenius type thermally activated process at elevated temperatures. Evidence of small polar on formation is also verified. Optical band gap estimated from absorption data is ≈2.94 very close to the reported value. Composition prepared through the noble wet chemical route has high electrical conduction and suitable for gas sensing applications.

Micron-sized columnar grains of CH3NH3PbI3 grown by solvent-vapor assisted low-temperature (75 °C) solid-state reaction: The role of non-coordinating solvent-vapor

The preparation of hybrid perovskite films with large columnar grains via low-temperature solid-state reaction remains a big challenge. Conventional solvent annealing using DMF, DMSO and ethanol, etc. fails to work effectively at low temperature (<100 °C). Here, we comprehensively investigated the effects of non-coordinating solvent vapor on the properties of perovskite film, and obtained micron-sized columnar grains (with an average grain size of 1.4 μm) of CH3NH3PbI3 even at a low temperature of 75 °C when annealed with benzyl alcohol vapor. The perovskite solar cells based on benzyl-alcohol-vapor annealing (75 °C), delivered much higher photovoltaic performance, better stability and smaller hysteresis than those based on conventional thermal annealing. Additionally, a champion power conversion efficiency (PCE) of 15.1% was obtained and the average PCE reached 12.2% with a tiny deviation. Finally, the mechanism of solvent annealing with non-coordinating solvent was discussed. Moreover, we revealed that high polarity and high boiling point of the solvent used for generating vapor, was critical to grow micron-sized columnar grains at such a low temperature (75 °C). This work will contribute to understanding the mechanism of grain growth in solvent annealing and improving its facility and effectiveness.

A likely planet-induced gap in the disc around T Cha

Abstract We present high-resolution (0.11 × 0.06 arcsec2) 3 mm ALMA observations of the highly inclined transition disc around the star T Cha. Our continuum image reveals multiple dust structures: an inner disc, a spatially resolved dust gap, and an outer ring. When fitting sky-brightness models to the real component of the 3 mm visibilities, we infer that the inner emission is compact (≤1 au in radius), the gap width is between 18 and 28 au, and the emission from the outer ring peaks at ∼36 au. We compare our ALMA image with previously published 1.6 μm VLT/SPHERE imagery. This comparison reveals that the location of the outer ring is wavelength dependent. More specifically, the peak emission of the 3 mm ring is at a larger radial distance than that of the 1.6 μm ring, suggesting that millimeter-sized grains in the outer disc are located farther away from the central star than micron-sized grains. We discuss different scenarios to explain our findings, including dead zones, star-driven photoevaporation, and planet-disc interactions. We find that the most likely origin of the dust gap is from an embedded planet, and estimate – for a single planet scenario – that T Cha's gap is carved by a 1.2MJup planet.

Effect of martensitic transformation on nano/ultrafine-grained structure in 304 austenitic stainless steel

304 austenitic stainless steel was cold rolled in the range of 20%–80% reductions and then annealed at 700–900 °C for 60 s to obtain nano/ultrafine-grained (NG/UFG) structure. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures. The results showed that with the increase of cold reduction, the content of martensite was increased. The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands. Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands. Samples annealed at 800–960 °C for 60 s were of NG/UFG structure with different percentage of nanocrystalline (60–100 nm) and ultrafine (100–500 nm) grains, submicron size (500–1000 nm) grains and micron size (>1000 nm) grains. The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature. For a certain annealing time during the reversion process, austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains, while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains. The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.

Fabrication of $$\text {Cu}_{2}\text {SnS}_{3}$$ Cu 2 SnS 3 films by annealing chemically deposited SnS–CuS precursors in a graphite box

Monoclinic $$\text {Cu}_{2}\text {SnS}_{3}$$ (CTS) thin films are prepared by annealing chemically deposited SnS–CuS precursors at 520-580 $$^{\circ }\text {C}$$ in a graphite box under atmospheric ( $$\text {N}_{2}+\text {S}_{2}$$ ) pressure, and the effects of annealing temperature and time on the grain growth and morphology of the films are investigated. The films prepared at 520 and 550 $$^{\circ }{\text{C }}$$ show improvement in grain size and the formation of uniform and compact grains with increasing annealing time. The films prepared at 580 $$^{\circ }\text {C}$$ exhibit good grain growth with grain sizes $$\sim 1.0{-}3.0\,\upmu \text {m}$$ ; however, the grain size does not increase with annealing time. Further, annealing time of 120 min at 550 and 580 $$^{\circ }\text {C}$$ leads to material loss. A small amount of $$\text {Cu}_{4}\text {SnS}_{4}$$ is detected in the films. In addition, annealing the films at 550 and 580 $$^{\circ }\text {C}$$ for 90 min with decreased CuS thickness results in a reduction of $$\text {Cu}_{4}\text {SnS}_{4}$$ phase, homogeneous grain growth with grain sizes of $$2.0{-}3.5\,\upmu \text {m}$$ throughout the film thickness, and hole mobilities in the range of $$6.0{-}5.3\,\text {cm}^{2}\,\text {V}^{-1}\,\text {s}^{-1}$$ . These results demonstrate the effectiveness of this annealing approach for producing high quality CTS films with micron-sized grains, which is useful for improving the efficiency of CTS-based thin film solar cells.