SnS Thin Films Research Articles

The effect of in-situ and post deposition annealing towards the structural optimization studies of RF sputtered SnS and Sn2S3 thin films for solar cell application

Optimization studies towards the formation of single phase orthorhombic SnS and Sn2S3 thin films are independently achieved using SnS target in RF magnetron sputtering by varying the RF power, in-situ and post-deposition vacuum annealing temperature. Micro structural analyses confirmed the role of in-situ annealing at 400 °C for the columnar growth formation of single phase SnS nanostructures which is an important aspect towards the fabrication of SnS based thin film solar cells with improved efficiency. Further, SnS to Sn2S3 phase transition is observed at 500 °C. The observed variations in the optical properties such as band edge shift, direct energy band gap (Eg), absorption coefficient (α), extinction coefficient (K) and refractive index (n) of the films are correlated with the structural and morphological analysis. Electrical studies along with band gap measurement further confirmed the transition from p-type SnS phase having a band gap value of 1.55 eV with resistivity as 1280 Ω cm to n-type Sn2S3 with band gap value of 1.06 eV and resistivity of 0.864 Ω cm.

Enhancement in photovoltaic properties of Nd:SnS films prepared by low-cost NSP method

The inner transition metal (ITM) neodymium (Nd)-doped tin sulfide (Nd:SnS) thin films with various Nd concentrations were coated by nebulizer spray pyrolysis (NSP) technique at 350 °C. All the coated films were analyzed for their structural, optical and photoelectrical properties. X-ray diffractometer (XRD) study showed (111) direction as the highly preferred orientation with orthorhombic crystal structure for all the films. The intensity of the peaks was found to increase until 5 at% Nd doping and then reduced for higher (7 at% Nd) doping concentration. Atomic force microscopic (AFM) images of the films proclaimed an increase in the surface and line roughness of the films by increasing Nd concentrations. Optical analysis on the films showed a variation in energy gap from 2.05 to 1.69 eV when the doping concentration increased from 0 at% to 7 at%. At 5 at% Nd doping, the photoluminescence (PL) spectra displayed a single strong emission peak at 723.1 nm with enhanced intensity corresponding to near-band-edge emission. All the SnS thin films exhibited p-type behavior with the lowest resistivity of ~ 4.311 Ω·cm and high carrier concentrations of ~ 1.441 × 1017 cm−3 for 5 at% Nd doping level as observed from Hall effect studies. Furthermore, fluorine-doped tin oxide (FTO)/n-CdS/p-Nd:SnS hetero-junction solar cells were prepared and the current–voltage curve in dark and light condition was obtained for the device. An efficiency of 0.135% was observed for the solar cell fabricated with 5 at% Nd-doped SnS thin film.

Effect of sulfurization temperature on the efficiency of SnS solar cells fabricated by sulfurization of sputtered tin precursor layers using effusion cell evaporation

Earth-abundant tin monosulfide (SnS) thin films have attracted considerable interest for eco-friendly and low-cost thin film solar cells. However, less attention has been paid on the fabrication of SnS solar cell by the industrial processes. In view of that the current study aimed to fabricate the SnS solar cells via two-stage (sputtering + sulfurization) industrial process. For the preparation of SnS thin films, first tin metallic precursor layers were deposited by DC sputtering and then sulfurized using the rapid thermal effusion cell evaporation process. The effect of sulfurization temperature on the physical properties of SnS thin films and the efficiency of SnS solar cells was examined. Formation of the single phase SnS thin films was confirmed when the tin metallic precursor layers sulfurized in the range of 450–470 °C, whereas secondary phases of Sn, SnS2, and Sn2S3 were noticed at the sulfurization temperature lower than 450 °C and re-evaporation of deposited SnS thin films was observed at the sulfurization temperature higher than 470 °C. Solar cell fabricated with SnS absorber sulfurized at a temperature of 470 °C showed the conversion efficiency of ∼ 2.3%. The causes for lower efficiency of these solar cells were recombination in the SnS absorber and non-uniform compositional distribution of Cd, S and Sn as a function of depth in the CdS/SnS/Mo structure.

Investigation on nebulizer spray coated Nd-doped SnS2 thin films for solar cell window layer application

Economic nebulizer spray pyrolysis (NSP) technique has been employed to deposit Neodymium (Nd) doped Tin disulfide (SnS2) thin films at 325 °C by varying the doping concentration of Nd (0%, 2%, 4% and 6%). The impact of Nd concentration on crystalline structure, morphology and opto-electronic properties of films were studied using X-ray diffraction (XRD), FT-Raman spectrophotometer, atomic force microscope (AFM), energy-dispersive X-ray spectroscope, scanning electron microscope (SEM), UV–Visible spectrometer and Hall Effect measurements. Structural parameters such as lattice constants, texture orientation factor, micro strain, dislocation density and crystallite size were estimated using XRD data. The SEM and AFM images of films displayed an exceptional morphology. The surface roughness of the films was found to increase with the increase of dopant concentration. Optical analysis done on the films revealed variation in band gap from 2.75 to 2.92 eV as the Nd doping concentration is increased from 2 to 6%. SnS2 thin film exhibited n-type conductivity as, confirmed from Hall Effect studies. The resistivity and concentration of the carrier in the film were found to be 4.17 × 10−2 Ω cm and 4.06 × 1017 cm−3 respectively which were then correlated to the deposition parameters. Furthermore, FTO/n-Nd-SnS2/p-SnS hetero-junction based solar cells were prepared and their current voltage curve in dark condition was obtained.

Nebulizer spray assisted chemical vapour deposited (NACVD) tin disulfide (SnS2) thin films for solar cell window layer applications

The prospective nontoxic Tin disulfide (SnS2) thin films have been fabricated through nebulizer spray assisted chemical vapour deposition (NACVD) method by varying carrier gas pressure as 0.05, 0.1 and 0.15 Pa at 325 °C temperature on soda lime glass substrates. Exceedingly single crystalline phase SnS2 film coated uniformly on the substrate was observed from structural and morphological analysis. Optical studies of the fabricated films reveal a decrement of band gap from 2.85 eV to 2.65 eV as pressure of carrier gas increased from 0.05 Pa to 0.15 Pa. The emitted photoluminescent (PL) intensity was strong at about 561 nm which is related to the near band edge (NBE) emission of SnS2. Hall analysis showed the value of conductivity and carrier concentration of SnS2 in the range of 6.84 × 10−5 to 1.34 × 10−3 Ω−1 cm−1 and 2.47 × 1013 to 7.18 × 1013 cm−3, respectively. This study confirms that a superior device quality SnS2 thin film can be fabricated and can be used as a nontoxic window layer through low cost NACVD method by optimizing the carrier gas flow rate and other factors such as temperature of the substrate and precursor concentration. A good interface between the window and absorber layers minimizes the recombination and aids to increase the efficiency of a photovoltaic cell structure.

Chemical Spray Pyrolysis pure and Transition Metal doped Structural, Morphological and Optical properties of SnS Thin Films

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Dual-wavelength mode-locked erbium-doped fiber laser based on tin disulfide thin film as saturable absorber

The use of tin disulfide (SnS2) as a candidate material for saturable absorption in nonlinear optical devices is investigated in this article. A dual-wavelength soliton mode-locked fiber laser is demonstrated using a fabricated SnS2 thin film as a saturable absorber within an erbium-doped fiber laser cavity. The laser generates two peaks centered at 1536.7 and 1562.6 nm, with a pulse width of 5.3 ps. The experimental results indicate that the SnS2 thin film has the required absorption characteristics to realize good mode-locked operation. Thus, we confirm that SnS2 has great potential to be used in multiwavelength ultrafast fiber laser applications.

Investigating the light harvesting capacity of sulfur ion concentration dependent SnS2 thin films synthesized by self-assembled arrested precipitation technique

In the present report, we have successfully synthesized sulfur ion concentration dependent SnS2 thin films using energy efficient, low cost and self-assembled arrested precipitation technique (APT). The influence of sulfur ion concentration on the crystallinity, optical tuning, surface morphology and photoconversion efficiency of SnS2 thin films was studied thoroughly. Optical absorption studies confirm a red shift in the absorption edge, which asserts its application as photoactive material. X-ray diffraction (XRD) and Raman studies confirmed the SnS2 thin film corresponds to the hexagonal crystal phase with preferential orientation along (001) plane, further the compositional analysis was verified by Energy dispersive x-ray (EDS) and x-ray photoelectron spectroscopy (XPS) studies. SEM images clearly highlight the transformation of surface morphology from nanospheres to compact interconnected nanograins with an increase in sulfur ion concentration; also HRTEM image confirms the formation of aggregated nanograins. Moreover, the diffraction rings in the SAED pattern suggest the hexagonal SnS2 structure which corroborates well with the XRD data. SnS2 as photoanode exhibits good photoelectrochemical (PEC) performance in I-/I3- redox electrolyte. Synthesized SnS2 thin films showed a significant enhancement in photocurrent conversion efficiency (0.09%) among reported values. Thus, sulfur ion concentration variation has the ability to alter the PEC performance of SnS2. Electrochemical Impedance Spectroscopy (EIS) study was used to analyze the charge transfer resistance (Rct) through the film. Finally, the improved PEC performance highlights the application of SnS2 photoanode in PEC cell.

Influence of deposition techniques on quality and photodetection properties of tin disulfide (SnS2) thin films

Tin disulfide (SnS2) is one of the potential candidates for optoelectronics because of its chemical and environmental stability accompanied by favourable characteristics. Herein, the SnS2 thin films are deposited by different techniques; chemical bath deposition (CBD), dip coating (DC) and spin coating (SC). The energy dispersive analysis of x-ray confirms the stoichiometry of the films deposited by these techniques. The x-ray diffraction showed hexagonal lattice structure of thin films. The morphology is studied by transmission electron, scanning electron and optical microscopy. The selected area electron diffraction exhibited ring patterns, confirming the polycrystalline nature of the deposited thin films. The atomic force microscopy showed presence of globular grains, hills and valleys on surfaces of thin films. The absorption spectra analysis showed the thin film possess direct optical bandgap of 2.39 eV for CBD, 2.50 eV for DC and 2.75 eV for SC. Raman spectra of the as-deposited SnS2 thin films showed occurrence of A1g phonon mode at 314 cm−1. The electrical transport properties assessment depicts the n-type semiconducting nature of deposited thin films. The as-deposited thin films showed good pulsed photoresponse for white light illumination intensities of 80 mW/cm2 and 120 mW/cm2.

Structural and microstructural study of SnS thin film semiconductor of 0.2<t≤ 0.4 μm thickness for application in a field effect transistor

SnS semiconductor thin film of 0.20, 0.25, 0.30, 0.35, 0.40 μm were deposited using aerosol assisted chemical vapour deposition (AACV) on glass substrates and were investigated for use in a field effect transistor. Profilometry, X-ray diffraction, Scanning electron microscope and Energy dispersive X-ray spectroscopy were used to characterise the structural and microstructural properties of the SnS semiconductor. The SnS thin film was found to initially consist of a single crystal at thickness of 0.20 to 0.25μm after which it becomes polycrystalline with an orthorhombic crystal structure consisting of Sn and S elements whose composition varied with increase in thickness. The SnS film of 0.4 μm thickness shows a more uniform grain distribution and growth with a crystal size of 60.57 nm and grain size of 130.31 nm signifying an optimum for the as deposited SnS films as the larger grains reduces the number of grain boundaries and charge trap density hence allowing charge carriers to move freely in the lattice thereby causing a reduction in resistivity, increase in conductivity of the films and enhanced energy band gap which are essentially parameters for a semiconductor material for application in a field effect transistor. Â

Optimization of absorber layer for band gap energy moderation of nanostructured SnS thin films

In the present work, band gap energy moderated nanostructured Sn1−xZnxS thin film solar cell devices are investigated in details in order to optimize the number of their layers, which can enhance their efficiency. Sn1−xZnxS nanostructures were synthesized by simple and cost-effective co-precipitation method and were primarily characterized for the study of their structural and phase purification as well as morphological and optical properties. Structural results confirmed the formation of polycrystalline orthorhombic and hexagonal phase of SnS and ZnS nanostructures, respectively. Morphological studies showed that increasing the Zn concentrations changed the morphology of samples from the rod- to spherical- and hexagonal-like particles. Electrical characterization also presented the highest carrier concentration and conductivity conversion in the Sn1/2Zn1/2S sample. Photovoltaic devices were deposited using the ethyl cellulose as a green binder on the transparent substrates and TiO2 buffer layers. Photovoltaic characterization showed that a sample moderated from low-to-high values of band gap energy and with four layers has better efficiency (3.17%) because of factors such as having a wide broadband range of band gap energy in absorber layer, increase in carrier lifetimes, presence of minor carriers in output current, and an increase in carrier concentration of the moderated layers. This paper also investigates and compares our results with the literature and gives some suggestions for coping with the problems involved in having a high number of layers in the fabricated devices.

Characterization of evaporated tin sulfide and its application for hybrid solar cell

Tin sulfide (SnS) is a promising absorber material for photovoltaic cells, because of its optimum band gap, strong optical absorption, simple phase composition, earth-abundant and nontoxic constituents. However, this material is largely unexploited to date with only a handful of studies reporting SnS for photovoltaic application. We present systematic preparation of SnS thin films through thermal evaporation route and characterize phase composition of these films. We have observed that the films grown at the substrate temperature of 250 °C exhibit a single SnS phase, which could be alternative light absorber materials for photovoltaic devices fabrication. Hence, a solar conversion efficiency of 1.47% was obtained at standard one sun illumination using a planar device consisting of FTO/TiO2/SnS/P3HT/Au. The present findings offer novel directions for achieving high-efficiency solid-state solar cells by hybridization of inorganic-organic light harvesters and hole transporters.

Controlled thickness of a chemical-bath-deposited CdS buffer layer for a SnS thin film solar cell with more than 3% efficiency

Tin monosulfide (SnS) is considered a promising earth-abundant absorber material for thin film solar cells (TFSCs) with a theoretical power conversion efficiency (PCE) as high as 30%. However, the maximum PCE reported thus far is just 4.36%. This inferior device performance is attributed to low values of open-circuit voltage. In addition to the dense and pinhole-free surface morphology of the phase-pure p-type SnS thin film absorber, a controlled growth of the n-type buffer layer is a prerequisite for enhanced device performance. In this study, we explore the manner in which the thickness of a chemical-bath-deposited n-type CdS buffer layer influences the performance of SnS/CdS TFSCs. The thickness of the buffer layer was adjusted by varying the deposition time from 15 to 25 min, which resulted in thicknesses of 30–80 nm. Initially, the performance parameters of the TFSCs improved with the buffer layer thickness, but later deteriorated with thicker CdS layers. The highest PCE achieved was 3.05% at an optimized CdS buffer layer thickness of approximately 42 nm. This performance was accompanied by a significant decrease in reverse saturation current and shunt conductance, as evidenced by the current density–voltage characteristics under dark conditions.

Tuning optoelectronic properties of SnS thin films by a kinetically controllable low temperature microwave hydrothermal method

In the polycrystalline SnS semiconductor films, the crystallite size and stoichiometry play a central role in dictating their optoelectronic properties. Most strategies to tailoring these parameters require long-time deposition methods and post-deposition thermal annealing at high temperature under inert atmosphere or sulfur vapor. Here, we report a different strategy of tuning optoelectronic properties of SnS films by controlling the kinetical parameters in a microwave-hydrothermal solution method at low temperatures (50–60 °C). The interaction between microwave radiation and the highly polar thioacetamide (TA, sulfur source) enhances local temperature in the reaction solution and permits a rapid formation of orthorhombic SnS crystallites on glass substrates. For as-deposited SnS films, a lineal dependence is observed of the film thickness, crystallite size and electrical conductivity on the TA concentration. In addition, the microstrain, Sn/S ratio and optical band gap of the films decrease with the concentration of TA, leading to the optimal values for stoichiometry and optical properties of SnS films. The ability to synthesize highly crystalline SnS thin films at high growth rates and low temperatures opens up possibilities to the fabrication of SnS-based optoelectronic devices on plastic substrates.

Template-free electrodeposition of SnS nanotubes and their photoelectrochemical properties

In this paper, SnS nanotubes are firstly prepared in acidic solution by template free electrodeposition method at room temperature. The morphological evolution and photoelectrochemical properties of SnS nanotubes are investigated. X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS) and Raman spectra measurements examine the phase purities of deposited SnS thin films. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations indicate morphological properties of SnS nanotubes. The band-gap of SnS nanotubes is confirmed by UV–Vis-NIR diffuse reflection spectra. The photoelectrochemical measurements show that the photocurrent density of FTO/SnS nanotubes is about 31 μA/cm2 and maximum IPCE value of SnS nanotubes is 7.4%.

Postdeposition Processing of SnS Thin Films and Solar Cells: Prospective Strategy To Obtain Large, Sintered, and Doped SnS Grains by Recrystallization in the Presence of a Metal Halide Flux.

Postdeposition treatments (PDTs) are common technological approaches to achieve high-efficiency chalcogenide solar cells. For SnS, a promising solar cell material, most PDT strategies to control the SnS properties are overwhelmingly based on an annealing in sulfur-containing ambient atmosphere that is described by condensed-state reactions and vapor-phase transport. In this work, a systematic study of the impact of PDTs in a N2 atmosphere, ampules at temperatures between 400 and 600 °C, and a SnCl2 treatment at 250-500 °C on the properties of SnS films and SnS/CdS solar cells prepared by close-spaced sublimation is reported. The ampule and N2 annealing conditions do not affect the grain size of the SnS layers but significantly impact the concentration of intrinsic point defects, carrier density, and mobility. Annealing at 500-600 °C strongly enhances the hole concentration and decreases the carrier mobility, having detrimental impacts on the device performance. SnCl2 treatment promotes grain growth, sintering, and doping by mass transport through the melted phase; it adjusts the hole density and improves the carrier mobility in the SnS layers. SnS/CdS solar cells with an efficiency of 2.8% are achieved in the SnCl2 treatment step, opening new possibilities to further improve the performance of SnS-based devices.

Formation of SnSSe thin films by heat treatment of SnS thin films in S/Se atmosphere

In the present work we have deposited ternary SnS-Se thin films by thermal treatment of SnS in S/Se atmosphere. The effect of annealing conditions on the formation of ternary phase was studied and the optimum condition was identified. The structural, morphological and optoelectronic studies were analyzed by techniques such as X-ray diffraction (XRD), Raman spectroscopy, AFM and photo-response. The best results were found for samples treated under S/Se atmosphere at a temperature of 500 °C during 15 min. The XRD results showed good crystallinity. The formation of SnS-Se compound is confirmed by Raman measurements which illustrated the contribution of three peaks reported at 137, 200 and 299.5 cm−1. The morphology of the film was analyzed by the AFM technique and the results were compared with SnS thin films obtaining a slight increase in the roughness of the ternary films and a similar grain size. XPS analyses confirmed the presence of Sn, S and Se elements on the surface of the film. The bandgap of the films was calculated from the optical transmittance in the visible spectrum, showing direct transitions for SnS and SnSSe at 1.3 eV and 1.12 eV respectively. As a fundamental part of this work, SnSSe thin films showed response to light with higher photosensitivity values, in comparison to SnS films without treatment.

Effect of carrier gas pressure on structural, optical and photovoltaic properties of tin sulphide thin films prepared by nebulizer spray pyrolysis method

Tin sulphide (SnS) thin films deposited using nebulizer spray pyrolysis technique by changing pressure (0.1, 0.15, 0.2 and 0.25 Pascal) at $$350^{\circ }\hbox {C}$$ and their characterization are reported. The influence of carrier gas pressure on structural, morphological, optical and electrical properties of the film are determined using X-ray diffraction (XRD), energy-dispersive X-ray, atomic force microscopy, UV–Vis spectrophotometry and Hall effect measurement. Structural parameters such as pole density, orientation factor, crystallite size, micro strain and dislocation density were analysed using XRD data. The scanning electron microscopy studies display superior morphology and surface roughness of the films which were found to increase with pressure. Optical studies on the films revealed a variation in band gap from 1.78 to 1.66 eV for were the raise of pressure from 0.1 to 0.2 Pa. A single strong emission peak at about 825 nm is observed in photoluminescence spectra with enhanced intensity which may be attributed to near band edge emission. Grown SnS thin film exhibits p-type conductivity, which was confirmed from the Hall effect measurement. The low resistivity and higher carrier concentration are found to be $$0.235\,\Omega \,\hbox {cm}$$ and $$5.04\times 10^{18}\,\hbox {cm}^{-3}$$ , respectively. These properties were then correlated with the deposition parameters. Furthermore, to study the photovoltaic properties of SnS thin films, a heterojunction solar cell FTO/n-CdS/p-SnS/Al was fabricated showing conversion efficiency of 0.16%.

Influence of Al doping concentration on the opto-electronic chattels of SnS thin films readied by NSP

Herein, we limelight the key features of SnS thin films coated by spray pyrolysis process with different Al doping concentrations. The SnS thin films coated with different Al concentration (0, 2, 4, 6 at wt%) were characterized by various techniques. Structural parameters studied by XRD data revealed that all the prepared films were orthorhombic crystal structure with (111) as a preferential direction. Raman spectroscopy showed the presence of Ag, B1g, B2g, and B3g vibration modes at their corresponding wave numbers. Concentration dependent granular change of Al:SnS films were shown by AFM images. The presence of Sn, S and Al element without any other impurities was confirmed through EDAX picture. UV studies revealed the shrinkage of band gap from 1.97 to 1.72 eV on increasing the Al doping concentration from 0% to 4 at wt%. Room temperature PL showed a high intense red shift, as emission observed at 722 nm for 4% of Al doped SnS thin film. Hall measurements exhibited p-type conducting nature of undoped and Al doped SnS films. The films showed a lowest resistivity of 2.695×10−1 Ω cm for 4 at wt% Al doping concentration. 0.093% efficiency was obtained for the solar cell device fabricated by 4 at wt% of Al doped SnS thin film.

Investigations on Fe doped SnS thin films by nebulizer spray pyrolysis technique for solar cell applications

Undoped and different concentrations of iron (Fe) doped tin sulphide (SnS) thin films were coated by nebulizer spray pyrolysis method with the substrate temperature of 350 °C. Polycrystalline nature of orthorhombic crystal structured pure and Fe doped SnS (Fe:SnS) thin films confirmed by X-ray diffraction (XRD) patterns. Structural studies further explored the preferential orientation of (201) plane for undoped SnS and their shifts to (400) and (111) directions for Fe:SnS at 6 and 10 wt.% of Fe concentration, respectively. The versatile route of structural modification has obviously demonstrated due to inclusion of Fe doping in SnS. Raman spectra further confirmed the structural variation of Fe:SnS. Topological variations obviously explained by atomic force microscopy images for pure and Fe:SnS. Optical results evidently claimed the deterioration of band gap values from 1.96 to 1.58 eV due to increase of Fe doping concentrations from 0 to 10 wt.%, respectively. Luminescence spectra showed a strong emission peak centered at 772 nm and low resistivity 3.32 × 10−2 Ω cm with the high carrier concentration for 8 wt.% of Fe concentration using prepared Fe:SnS film. The fabricated solar cell device with n-CdS exposed the 0.18% of efficiency for p-Fe:SnS prepared using 8 wt.% Fe concentration.