SnS Thin Films Research Articles

Reduced graphene oxide layer on nanostructured SnS thin films for improved visible light photoelectrochemical activity

The deposition of reduced graphene oxide over layer on the SnS thin films had been shown to be an effective tool to improve its photoelectrochemical response. Pure phase SnS thin films were prepared using simple and inexpensive thermal evaporation method on ITO glass substrate followed by the deposition of reduced graphene oxide (rGO) layer by drop cast method. Samples were characterized using X-ray diffraction, Raman, scanning electron microscopy, UV–Visible absorption spectroscopy and their photoelectrochemical activity has been investigated. The results show the formation of pure phase SnS having orthorhombic crystal structure with optical band gap of 2.0 eV, rGO layer enhances the absorption in visible region. Maximum photocurrent density exhibited by SnS/0.1 wt% rGO was observed to be 1.1 mA/cm2 as compared to pristine SnS (0.3 mA/cm2) at 0.95V Ag/AgCl with enhanced photostability up to 1 h. Graphene oxide over layer acts as protecting layer for SnS in the electrolyte and plays a promising role in enhancing the charge carriers separation at the interface on account of being an electron reservoir to accept the photoexcited electrons. This work highlights the role of rGO and SnS interface on the photoelectrochemical water splitting.

NBu2Sn(SnBu)2 and nBu3SnEnBu (E = S or Se) – effective single source precursors for the CVD of SnS and SnSe thermoelectric thin films

LPCVD with the title compounds produces S-deficient SnS, or stoichiometric, semiconducting, resistive SnS or SnSe films with large positive Seebeck coefficients and an SnSe power factor of 0.4 μW cm−1 K−2 at 425 K.

Physical properties of photo assisted chemically synthesized Cu-doped tin sulphide porous thin films

Undoped and Cu-doped films exhibited hexagonal SnS2 structure with different preferred orientations. The doped films cover almost all the surface uniformly with agglomerated bigger crystallites. As prepared films were highly resistive and became conducting on doping. Both films were found to be Sn-rich and the doped films confirmed the presence of copper through EDAX analyzer. There was a considerable redshift in the absorption threshold from the bulk for Cu-doped SnS2 thin films. All the films were highly reflecting in the infrared region and the reflectivity of the films decreased with doping concentration. Conducting tin sulphide nanostructures are highly applicable in dye sensitized solar cells.

From thin films to shaped platelets: effects of temperature gradient on SnS synthesis

In this work, we studied the synthesis and properties of SnS thin films and platelets obtained by vapor phase deposition under controlled pressure. Two morphological types are obtained in the same process depending on the absolute temperature and the temperature gradient inside the reactor. The growth of isolated platelets is favored by a small temperature gradient between the sublimation and deposition regions of the deposition chamber. Films are formed when there is a large temperature gradient. Raman spectroscopy and energy dispersive spectroscopy analysis were used to identify the phase of the synthesized samples, and polarized Raman spectroscopy and X-ray diffraction analysis helped us confirm the crystallographic orientation of the isolated platelets. We have carried out studies on the crystallographic shape and orientation of orthorhombic isolated platelets using optical microscopy, scanning electron microscopy and surface energies of the crystalline planes of SnS.

Tuning the properties of RF sputtered tin sulphide thin films and enhanced performance in RF sputtered SnS thin films hetero-junction solar cell devices

Abstract Tin sulphide (SnS) thin films were grown using the RF sputtering techniques. The working pressures (WP) were tuned between 0.70 and 4.00 Pa at fixed RF power of 100 W and deposition time of 2 min. X-ray diffractometry studies indicate that the films crystallized in the orthorhombic crystal structure and were single phase. The crystallite size increased up to a critical working pressure of 1.33 Pa and decreased thereafter with increased WP. Scanning electron microscopy (SEM) indicates that the films exhibit columnar grain structures. Energy dispersive spectroscopy indicates that the films are slightly Sn-rich. Transmittance and reflectance plots exhibits interference pattern, an indication that the films were of uniform thickness. Analysis from the optical data gives optical absorption coefficient (α) > 104 cm−1, and direct energy bandgap that exhibits relative decrease with the deposition conditions. Electrical studies from Hall effect measurements indicates that the films possess p-type electrical conductivity, and carrier concentration of 1016 cm−3 for films grown at WP of 1.33 Pa. The RF sputtered SnS thin films grown on Mo-substrates served as absorber layers to fabricate thin film hetero-junction solar cell devices in the substrate configuration with a cadmium sulphide (CdS) window partner. The best device yielded a short circuit current density of 25.94 mA/cm2, open circuit voltage of 0.087 V and an enhanced solar conversion efficiency of 0.60%. A world record value for RF-sputtered SnS/CdS based hetero-junction thin film solar cell devices.

(Invited) SnS2 Thin Film and Powder for Artificial Photosynthesis

Solar photoreduction of CO2 to produce value added hydrocarbons is highly desirable to tackle environmental and energy issues. [1-2] Despite the great improvement in the efficiency and cost of solar cells, the efficiency in artificial photosynthesis is much lower than the >15% of solar cells. Recent progress in 2D chalcogenides with tunable bandgap and layer numbers offers great opportunity for the investigation in this field. In this work, thin film and powder SnS2 have been synthesized for the study. Hydrothermal synthesis of carbon-containing SnS2 exhibits a highly active photocatalytic conversion of CO2 to selective hydrocarbons under visible-light irradiation. Overall, the carbon doping in the SnS2 nanostructure plays a key role and significantly enhance the visible light photocatalytic activity with a photochemical quantum efficiency above 0.7%. [3-4] Meanwhile, Thin film SnS2 has been grown for the mechanism study. By carbon-ion implantation of the thin film, we observed enhanced CO2 reduction under solar illumination. Other FTIR, Raman, NMR, BET, SECM, and synchrotron based facilities including APXPS and XAS have been used to investigate this issue.1. Shown, H.C. Hsu, Y.C. Chang, C.H. Lin, P.K. Roy, A. Ganguly, C.H. Wang, J.K. Chang, C.I. Wu, L.C. Chen, K.H. Chen, Nano Letters 14, 6097-6103 (2014).2. Billo, F.Y. Fu, P. Raghunath, I. Shown, W.F. Chen, H.T. Lien, T.H. Shen, J.F. Lee, M. C. Lin, J.S. Hwang, C.H. Lee, L.C. Chen, and K.H. Chen, Small 14, 1702928 (2018).3. Shown, S. Samireddi, Y.C. Chang, R. Putikam, P.H. Chang, A. Sabbah, F.Y. Fu, W.F. Chen, C.I. Wu, T.Y. Yu, P.W. Chung, M.C. Lin, L.C. Chen, and K.H. Chen, Nature Comm. 9, 169 (2018).4. T. Billo, I. Shown, A.K. Anbalagan, T.A. Effendi, A. Sabbah, F.Y. Fu, C.M. Chu, W.Y. Woon, R.S. Chen, C.H. Lee, K.H. Chen, L.C. Chen, Nano Energy 72, 104717 (2020).

Graded bandgap nanostructured SnS-based photocells

Tin sulfide SnS, SnS2 thin films have been fabricated and investigated for solar cell application as prospective inexpensive and environmentally safe material. Today, SnSx-based single bandgap and tandem solar cell designs demonstrate promising results as environment-friendly and cheap alternative to common Si, CdTe, CIGS cells. To enhance further the solar spectrum utilization, the graded bandgap structures are preffered. The chemical deposition of tin sulfide films presents a low-cost and scalable processing for thin-film solar cells mass production. In the paper, the successive ionic layer adsorption and reaction (SILAR) technique was used to produce SnSx layers, including successive cyclic dipping into Na2S and SnCl2 + NaCl + triethanolamine solutions. The XRD measurements reveal the SnS, SnS2 layers formation with nanograins micromorphology. The optical transmission measurements show the variable bandgap values depending, presumably, on the nanograins size. In this study, we propose and analyse, using SCAPS code simulation, a simple graded bandgap heterostructure solar cell structure based on nanostructured bandgap-engineered SnS/SnS2 active layers showing conversion efficiency up to ~ 14% for non-graded and ~ 16% for graded bandgap heterostructure.

Effect of precursor concentration and post-annealing temperature on (040) oriented tin sulfide thin films deposited on SLG/Mo substrates by spin coating

SnS is a layered material that crystallizes in an orthorhombic structure. This hinders the formation of a dense, pinhole-free morphology. The present study demonstrated the deposition of SnS thin films on soda-lime glass (SLG) and SLG/Mo substrates by spin-coating approach. The developed films were subsequently applied for the fabrication of a thin-film solar cell. The effect of the annealing temperature on the structural, optical, and morphological properties of the deposited SnS films was analyzed. The precursor concentrations and the annealing temperature played a critical role in determining the phase composition and morphological characteristics of the SnS thin films. TFSC with SLG/Mo/SnS/CdS/i-ZnO/AZO/Al configuration was fabricated using the optimal precursor ratio, i.e., Sn:S = 1:1.2, and this device showed a photoconversion efficiency of 0.076%. The reasons for the poor performance of the device were addressed in detail, and the scope for future research to optimize the device performance was elucidated.

Secondary Crystalline Phases Influence on Optical Properties in Off-Stoichiometric Cu2S-ZnS-SnS2 Thin Films.

Cu2ZnSnS4 (CZTS) is an economically and environmentally friendly alternative to other toxic and expensive materials used for photovoltaics, however, the variation in the composition during synthesis is often followed by the occurrence of the secondary binary and ternary crystalline phases. These phases produce changes in the optical absorption edge important in cell efficiency. We explore here the secondary phases that emerge in a combinatorial Cu2S–ZnS–SnS2 thin films library. Thin films with a composition gradient were prepared by simultaneous magnetron sputtering from three binary chalcogenide targets (Cu2S, SnS2 and ZnS). Then, the samples were crystallized by sulfurization annealing at 450 °C under argon flow. Their composition was measured by energy dispersive X-ray spectroscopy (EDX), whereas the structural and optical properties were investigated by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and optical transmission measurements. As already known, we found that annealing in a sulfur environment is beneficial, increasing the crystallinity of the samples. Raman spectroscopy revealed the presence of CZTS in all the samples from the library. Secondary crystalline phases such as SnS2, ZnS and Cu–S are also formed in the samples depending on their proximity to the binary chalcogenide targets. The formation of ZnS or Cu–S strongly correlates with the Zn/Sn and Cu/Zn ratio of the total sample composition. The presence of these phases produces a variation in the bandgap between 1.41 eV and 1.68 eV. This study reveals that as we go further away from CZTS in the composition space, in the quasi-ternary Cu2S–ZnS–SnS2 diagram, secondary crystalline phases arise and increase in number, whereas the bandgap takes values outside the optimum range for photovoltaic applications.

Optical, electrical and electronic properties of SnS thin films deposited by sol gel spin coating technique for photovoltaic applications

In the current study, thin films of tin sulfide (SnS) were grown by sol–gel spin-coating technique deposited on glass substrates. The obtained thin films were characterized using X-ray diffraction (XRD), photoluminescence (PL) and UV–Vis spectrometer and the four point technique, respectively. The effect of annealing temperature on the SnS properties has been studied. The XRD results reveal that the films annealed at 500 °C have good crystalline quality with orthorhombic phase. Fourier-transform infrared spectroscopy (FTIR) spectra shows the Sn–S bond. The photoluminescence spectra showed two categories of band emission. The optical parameters (α, e, n, k, Eg, and σop) were determined using UV–Vis spectroscopy. Moreover, the obtained results were compared to the theatricals results obtained with density functional theory (DFT) method using ab-initio approach. The optical and the electrical properties of the SnS Layers annealed at 400 °C and 500 °C offer the best possibility for their utilization in photovoltaic applications.

Effect of substrate temperature on the optoelectronic properties of chemically sprayed SnS thin films

Tin Sulphide (SnS) thin films were deposited on glass substrate through chemical spray pyrolysis (CSP). Precursor solution was prepared by mixing stannous chloride and thiourea in the ratio 1:4. Influence of substrate temperature was studied. Pure SnS phase was obtained for an optimised deposition temperature of 280 °C. Substrate above and below 280 °C resulted in the formation of other phases such as SnS2, Sn2S3. Structural, electrical and optical properties of the films were determined using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) and UV–VIS-NIR spectrophotometer. The XRD pattern of the film at the optimized condition exhibited polycrystalline orthorhombic structure of SnS with preferential orientation along (1 1 1) plane. The prepared thin films have optical absorption coefficient >104 cm−1in the wavelength rage of 400–800 nm. Phase purity was determined by Raman analysis, which confirmed the formation of single phase SnS film. In this study we could optimise deposition temperature to get SnS with single phase, avoiding unwanted phases like Sn2S3, SnS2 and Sn3S4.

Improving the Efficiency of SnS Thin Film Solar Cells by Adjusting the Mg/(Mg+Zn) Ratio of Secondary Buffer Layer ZnMgO Thin Film

In the recent years, thin film solar cells (TFSCs) have emerged as a viable replacement for crystalline silicon solar cells and offer a variety of choices, particularly in terms of synthesis processes and substrates (rigid or flexible, metal or insulator). Among the thin-film absorber materials, SnS has great potential for the manufacturing of low-cost TFSCs due to its suitable optical and electrical properties, non-toxic nature, and earth abundancy. However, the efficiency of SnS-based solar cells is found to be in the range of 1 ~ 4 % and remains far below those of CdTe-, CIGS-, and CZTSSe-based TFSCs. Aside from the improvement in the physical properties of absorber layer, enormous efforts have been focused on the development of suitable buffer layer for SnS-based solar cells. Herein, we investigate the device performance of SnS-based TFSCs by introducing double buffer layers, in which CdS is applied as first buffer layer and ZnMgO films is employed as second buffer layer. The effect of the composition ratio (Mg/(Mg+Zn)) of RF sputtered ZnMgO films on the device performance is studied. The structural and optical properties of ZnMgO films with various Mg/(Mg+Zn) ratios are also analyzed systemically. The fabricated SnS-based TFSCs with device structure of SLG/Mo/SnS/CdS/ZnMgO/AZO/Al exhibit a highest cell efficiency of 1.84 % along with open-circuit voltage of 0.302 V, short-circuit current density of 13.55 mA cm−2, and fill factor of 0.45 with an optimum Mg/(Mg + Zn) ratio of 0.02.

Photovoltaic Properties and Surface Analysis of Mixed (SnS2)x (CdS)1-x Thin Films by X-ray Photoelectron Spectroscopy (XPS)

Mixed thin films (SnS2)x(CdS)1-x with various x compositions (x=1, 0.8, 0.2, 0) have been synthesized by spray pyrolysis technique at a substrate temperature of 350°C. Cadmium chloride (CdCl2), Tin chloride (SnCl2), and thiourea (SC(NH2)2) were used as starting chemicals at different compositions. The chemical binding state of the deposited thin films was studied by X-ray photoelectron spectroscopy (XPS). XPS studies indicate the formation of the single phase of CdS and SnS2 thin films and mixed-phase (SnS2)x (CdS)1-x for x=0.8 and x=0.2. Four components of oxygen change in chemical states which are different in BE have been distinguished and studied in the O 1s spectrum. The optical expected absorption capacity and photocurrent (jph) depend on x concentration.

Quantitative analysis of Ag-doped SnS thin films for solar cell applications

This work reports the changes in the properties of Ag-doped SnS thin films (SnS:Ag), and CdS/SnS solar cells with an Ag dopant concentration in the absorber varied from 0 to 6 wt.% in steps of 3 wt.% prepared by the nebulizer-assisted spray pyrolysis method (NSP). X-ray diffraction (XRD) studies confirm the SnS:Ag (3 wt.%) thin film has a higher crystallite size than the undoped and SnS:Ag (6 wt.%) thin film. An atomic force microscope (AFM) image shows SnS:Ag (3 wt.%) film possesses larger-sized grains than other samples. The energy-dispersive X-ray analysis (EDS) confirms the presence of the constituent elements in the SnS:Ag thin films. PL analysis revealed the films possess the band edge as well as the other defect-related emissions of SnS. The Ag doping facilitates the tunability in absorption and decreases in optical bandgap for the SnS:Ag (3 wt.%) film. Hall measurements provide the low resistivity of 3.31 Ωcm, the high charge carrier concentration of 1.56 × 1017 cm−3, and high mobility of 12.1 cm2 V−1 s−1 for 3 wt.% Ag-doped SnS film. The better photovoltaic conversion efficiency of 0.285% was observed for the device prepared with SnS:Ag (3 wt.%) thin film compared to other samples due to enhanced absorption, optimum bandgap, and better electrical properties.

SnS nanocrystalline thin films for n-CdS/p-SnS solar cell devices

Tin sulfide (SnS) thin films were galvanostatically electrodeposited on glass/Indium-Tin Oxide (ITO)/Cadmium Sulfide (CdS) substrates from a non-aqueous solution. The effect of different DL-tartaric acid concentrations and various annealing environments (vacuum, air and argon) on the electrical and physical properties, secondary phase formation and performance of the solar cells were investigated in this study. From X-ray diffraction (XRD) and Raman spectra, nanocrystalline SnS thin films with orthorhombic structure were produced with some secondary phases of SnS2 and Sn2S3 which decreased by annealing in air and Ar atmospheres. Cyclic voltammetry studies showed that the films have good electrochemical properties and photoluminescence analysis indicates that the samples have a direct band gab energy about 1.55 eV. Chemical composition and morphological structure of the nanoparticles were identified using energy dispersive X-ray analysis and scanning electron microscopy, respectively. The current–voltage (I–V) characteristics (under dark) and capacitance–voltage (C–V) relations for the fabricated devices (glass/ITO/n-CdS/p-SnS/Mo), for the SnS thin film annealed under Ar environment, exhibited a rectifying behavior with a saturation current and carrier concentration of ~ 10−6 A and 1016 cm−3, respectively. The illuminated cell have an efficiency of 4.35%, which was investigated with an illumination intensity of 100 mW/cm2 and the output parameters; short circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF) are 13.6 mA/cm2, 1000 mV and 0.32, respectively.

Growth of Large Single Crystals of n-Type SnS from Halogen-Added Sn Flux

We report the growth of large Cl-doped and Br-doped SnS single crystals from a molten Sn-based flux. Compared with the small and lamellar undoped SnS crystals, the addition of SnCl2 or SnBr2 halogen sources in the flux substantially enhanced lateral growth along the (100)-plane and vertical growth. The maximum size of the obtained single crystals reached a diameter and thickness of 16 mm and 0.7 mm for the Cl-doped SnS and 24 mm and 1.0 mm for the Br-doped SnS, respectively. The X-ray rocking curves and the X-ray back-reflection Laue patterns indicated a high crystal quality. The obtained crystals were further characterized via electrical measurements, including electrical conductivity and Hall measurements, optical absorption spectroscopy, and X-ray and ultraviolet photoelectron spectroscopies. Both the Cl-doped and Br-doped SnS single crystals exhibited degenerate n-type conductivity with a high electrical conductivity of 11.1 S cm–1 for Cl-doped SnS and 18.9 S cm–1 for Br-doped SnS along the (100)-plane at 300 K. Furthermore, the photoelectron spectroscopy results also indicated n-type conductivity. The large single crystals of n-type SnS obtained in this work would enable the fabrication of p-n homojunction SnS solar cells via the deposition of p-type SnS thin films.

Comparative study of binary cadmium sulfide (CdS) and tin disulfide (SnS2) thin buffer layers

Binary compound tin disulfide (SnS2) and cadmium sulfide (CdS) are the potential candidates used as a buffer layer for copper indium gallium selenide (CIGS) and copper zinc tin sulfide (CZTS) thin-film device. Herein, both compounds have been successfully prepared through simple hydrothermal (HD) and chemical bath deposition (CBD) techniques, respectively. The prepared samples were characterized by different available techniques like X-ray diffraction (XRD), atomic force microscopy (AFM), surface electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmittance electrons microscopy (TEM), UV–Visible spectroscopy and photoelectrochemical (PEC) analysis. The XRD analysis confirms the polycrystalline nature of the prepared thin films. AFM analysis showed that the SnS2 display better roughness (60 nm), grain size (75 nm) than CdS roughness (23 nm), grain size (41 nm) thin films. SEM and EDS studies revealed near stoichiometry behavior of elemental composition of the films. The optical absorption spectrum showed the direct bandgap of CdS 2.45 eV and 2.20 eV for SnS2 thin films. The PEC analysis revealed that the SnS2 thin films exhibit two times higher photoresponse (140 µA) as compare to CdS (80 µA) thin films. The SnS2 high photocurrent could be attributed to the small band gap and increase in grain size which can trap more incident light. Based on the results the SnS2 used as a buffer layer can be a good choice for an efficient photovoltaic device.

Influence of the Temperature Ramping Rate on the Performance of Vapor Transport Deposited SnS Thin-Film Solar Cells

The effect of the temperature ramping rate of vapor transport deposition (VTD) on the morphology, crystallinity and orientation of SnS-absorber layers and their impact on SnS/CdS heterojunction thi...

Argon vs. air atmosphere in close spaced vapor transport deposited tin sulfide thin films

The fundamental understanding and tailoring of material properties play a fundamental role on the performance of tin (II) sulfide (SnS)-based photovoltaic devices. In this regard, this work reports on the deposition of single-phase, p-type SnS thin films synthesized by close spaced vapor transport (CSVT) and the impact of employing argon (Ar) and bare vacuum (air) atmospheres on CSVT-SnS thin film properties is presented and compared for the first time. The analysis of film properties was performed by structural, directional, morphological, topographical, along with thermoelectric and optoelectronic characterizations of the samples. It is demonstrated that by changing the CSVT annealing atmosphere, the SnS grains change their orientation from perpendicular (respect to substrate) in Ar to parallel in a bare vacuumed (air) conditions. Furthermore, Hall measurements show that the hole concentration are mostly the same but that hole mobility depends, in turn, on the direction of preferred orientation of the SnS crystals. This translates into a twice higher lateral conductivity on the air- respect to the argon-SnS thin films. In this way, the different atmospheric exhibit a profound impact on the physical, morphological and structurally orientated properties of the SnS grains. These results demonstrate that photovoltaic grade p-type SnS films can be deposited in air without the need of an inert gas atmosphere which opens the way to a cost reduction in the fabrication of SnS-based photovoltaic devices.

STRUCTURAL, OPTICAL AND MORPHOLOGICAL INVESTIGATIONS OF Fe-DOPED SnS THIN FILMS

SnS could have novel applications in optoelectronics including solar cell devices, sensors, batteries and also in biomedical sciences. Fe-doped SnS thin films were prepared on glass substrates using chemical spray pyrolysis (CSP) method. Pure and Fe-doped SnS thin films were deposited onto microscopic glass substrates using the spray pyrolysis technique. The precursors of SnCl2·2H2O (0.1 M) and thiourea (0.1 M) were dissolved separately in a solution containing deionised water and isopropyl alcohol in proper ratio. Equal volumes of these two solutions were mixed together and sprayed onto the microscopic glass substrates at a substrate temperature of 450⁰C. Fe was doped with SnS thin films using FeCl3 (5 at.%, 7 at.%, 9 at.%, and 11 at.%) as the dopant source. Structural, optical, vibrational, structural, morphological properties were studied.