SnS Thin Films Research Articles

Phase control of two-dimensional tin sulfide compounds deposited via atomic layer deposition

Two-dimensional (2D) semiconductor materials are emerging as potential candidates for emerging electronic device applications due to their excellent electrical properties and unique properties such as flexibility and transparency. Among the various potential 2D semiconductor materials, tin sulfide compounds can form polymorphs of different 2D crystals: 2D layered-SnS2 with hexagonal symmetry and 2D layered SnS with orthorhombic symmetry. In addition, since they each have different electrical and optical properties, their controlled growth is important for appropriate target applications. Therefore, we investigated the phase control of tin sulfide compounds deposited via atomic layer deposition according to their deposition temperature and post-annealing conditions. A strategy for controlling the growth of SnS2 or SnS was proposed by investigating phase transition tendencies according to deposition temperature and annealing conditions (temperature, pressure, atmosphere). As a result, it was possible to selectively deposit SnS2 and SnS thin films based on a phase transition study; it was confirmed that SnS2 and SnS thin films exhibited n-type and p-type semiconductor characteristics, respectively.

Study on preparation and characterisation of pure and lithium incorporated SnS thin films for solar cell applications

A ternary transition metal sulfide was synthesized and characterized by the sonochemical approach in this study, namely a Li (Li) and tin sulfide (SnS) thin film incorporating lithium (Li). Lithium incorporated SnS thin films (Li-SnS) were synthesized by equal molar ratios used in the synthesis approach. In these prepared thin films, the crystallite size averaged 5 nm and the thin films were of good crystalline nature. Nanoparticles in the thin film samples have a uniform sphere shape, with clusters forming in a few places, as seen by FE-SEM images. The presence of Li, Sn and S was confirmed through XRF spectral analysis. From the fingerprint region of the FTIR spectra, the presence of Ni, Li, Sn and sulphur was confirmed and no other impurities were detected. The UV absorption analysis was highly indicating the enhanced photon absorption behaviour of the prepared thin film samples due to the incorporation of Li with SnS samples. The efficiencies of the solar cell fabricated with SnS, Li-SnS, were found to be 6.21 and 7.92 %. From the results it is concluded that Li-SnS thin film samples can be a potential candidate for use as an electrode in solar cell applications

Novel low-cost synthesis of crystalline SnI4 thin films via anionic replacement: Effect of iodization time on properties

SnI4 thin films were deposited for the first time via a novel low-cost route employing rapid iodization of SnS thin films at relatively low temperature in atmospheric conditions. This is the first report on SnI4 thin films obtained via anionic replacement of sulfur in SnS thin films. The effect of iodization time on the structure, morphology, optical and electrical properties of SnI4 thin films were studied. X-ray diffraction analysis revealed the formation of SnI4 thin films which crystallized in cubic Pa-3 structure and all samples were preferentially oriented along the (222) plane. The diffraction pattern of SnI4 thin film was subjected to Rietveld refinement and obtained excellent goodness of fit value of 1.19. The formation of SnI4 was further verified using Raman spectroscopy and intense peaks of SnI4 at 43, 56, 101 and 140 cm−1 are reported. X-ray photoelectron spectroscopy analysis was employed for the determination of chemical composition and the presence of tin and iodine in the Sn4+ and I− states were verified throughout the depth of sample using depth profiling analysis. Elemental mapping from the Energy-dispersive X-ray spectroscopy confirmed uniform distribution of elements (tin and iodine). Surface morphology was modified after iodization and the optical bandgap was shifted from 1.7 to 2.7 eV on the transition of as prepared SnS to SnI4. The best condition SnI4 thin films exhibited crystallite size, refractive index and resistivity values of 63 nm, 2.46 and 3.1 × 105 Ω cm, respectively. SnI4 films obtained by the rapid iodization of SnS films can be used as precursor layer in the two-step deposition of lead-free tin iodide perovskite solar cells for better photovoltaic performance. The obtained results validate the key role of iodization time on the properties of SnI4 films.

Characterization of multifunctional solution-processed Sn1-xZnxS nanostructured thin films for photosensitivity and photocatalytic applications

Zinc (Zn) doped/substituted Tin(II) sulfide (SnS) is one of the most important semiconductors for optoelectronic, photocatalytic, and gas-sensing applications. Herein, an ultra-fast, highly efficient and room temperature operated photocatalyst degrading powerful organic dyes under direct exposure to the UV–Vis/Sun-light and photo sensor based on Sn1-xZnxS (x = 0.00–0.20) nanostructured thin films were fabricated for the first time by using facile solution process. Compared to the SnS the crystallite/grain size, absorption, active surface area, absorption/reflectivity intensity, photoluminescence, and electrical conductivity of the Sn1-xZnxS thin films were improved considerably at a certain substitution level of Zn (at. %1) according to XRD, SEM, XPS, Raman, UV–Vis spectroscopy, Photoluminescence (PL), and electrical analysis. Amongst all, the Sn0.99Zn0.01S exhibits the highest photocatalytic efficiency (100% for 25 min) for degradation of MB at pH = 11 under sunlight at room temperature, which is higher than the most reported efficient photocatalyst based on SnS thin films whilst it shows 97% photocatalytic efficiency under the UV–Vis-light (at pH = 4, for 210 min) according to photocatalytic measurements. The observed highest values have been attributed to the synergic effect of pH and the highest crystallite size of the photocatalyst. Moreover, the Sn0.99Zn0.01S film sample also has the highest photosensitivity response (225%) with a decay time of 1.06 s amongst all the SnS and Zn-substituted SnS thin films due to having higher crystallite size and hence having more active crystallite site for the other Zn-substitution levels. These outcomes make the Zn-substituted SnS thin films promising and highly efficient multifunctional materials for photocatalytic, photosensitivity, and optoelectronic applications.

Synthesis and optimization of SnS absorber layer by spin-coating process and Taguchi approach

In this paper, a synthesis of SnS thin films using sol-gel spin coating method and optimization of the parameters influencing the experimental process. Taguchi experiment design with a L9(34) orthogonal array was used to optimize several parameters such as the annealing temperature, annealing time, concentration, and [S]/[Sn] ratio. To perform the necessary tests three levels of each factor were chosen. The analysis of variance (ANOVA) and signal-to-noise (S/N) was used to obtain the good optical properties (optimal band-gap) at the best combination of choosing factors. The obtained results indicate that the most influencing factors in the preparation of SnS thin films are the concentration and the [S]/[Sn] ratio. To confirm the results obtained, the test validation was performed using the optimal conditions. SnS thin films obtained at optimal condition were analyzed using X-Ray diffraction, UV–visible spectrophotometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and four-point probe.

Influence of S/Sn ratio on microstructural, morphological and optical properties of tin monosulfide thin films

Tin monosulfide (SnS) is promising candidate as a photovoltaic material due to its large tuneable physical properties, which can be achieved by altering the synthesis conditions. Synthesis of pure phase SnS with high crystallinity is really a challenging issue for researchers. The present work mainly focuses on synthesis SnS nanoparticles using a direct reaction approach and manipulate their properties by altering S content. The formation of orthorhombic α-SnS nanoparticles with preferential orientations along the (400) direction has been confirmed by X-ray Diffraction (XRD). Energy Dispersive X-ray analysis (EDX) is used to investigate the elemental composition of all synthesised SnS nanoparticles. SnS nanoparticles of different compositions are deposited on glass substrate using thermal evaporation. The crystal structures of deposited SnS thin films are analysed by XRD. Fourier Transform Infrared (FTIR) spectra indicate the Sn–S bond stretching around 580 - 950 cm−1 including a broad peak around 950 - 1450 cm−1. The Raman spectrum of all SnS thin films shows peaks at 136 ± 2, 190 ± 2, and 231 ± 2 cm−1 assigned as Ag mode of SnS. The presence of excess sulphur impacts on the surface morphology of the SnS thin film and is noticeable in FESEM images. UV–Vis–NIR absorbance spectrum revealed that the visible-light absorption of the SnS thin film was significantly high (α ∼105 cm−1). The calculated direct bandgaps of SnS thin films are found to increase (1.63–2.43 eV) with increasing sulphur ratio.

N-type SnS2 thin films spray-coated from transparent molecular ink as a non-toxic buffer layer for solar photovoltaics

This paper reports the effect of solvent evaporation temperature on spray-coated tin disulfide (SnS2) thin films from molecular ink. Thiourea and tin chloride were the key chemical reagents used for the synthesis of SnS2 transparent ink under atmospheric conditions. The structural and compositional properties of SnS2 thin films revealed formation of pristine hexagonal SnS2. The films are smooth, homogeneous resulting in band gaps ranging from 2 to 2.22 eV suited for a Cd-free alternative buffer layer for Cu-based multicomponent solar cells. Thermoelectric power measurement showed that tin disulfide films exhibit n-type conductivity. Activation energy estimated from temperature variation of electrical conductivity measurement varied from 40 to 90 mV. Our results suggest that ink-processed SnS2 can be used as a potential alternative for opto-electronic devices such as thin film solar cell and photodetector devices.

Preparation of high-quality SnS thin films for self-powered photodetectors and solar cells using a low-temperature powder technique

The binary compound tin-sulfide (SnS) is a promising absorber semiconductor for visible photodetectors and solar cells due to its optimum forbidden band gap and high absorption coefficient. It was shown in this study that high quality SnS powder can be prepared by a powder preparation method at relatively low temperatures. The resulting powder was used to deposit SnS layers via thermal evaporation. The SnS layers were then grown on molybdenum coated and uncoated glass substrates. The crystalline structures of the films prepared on molybdenum coated substrates were reported to be enhanced. According to the XRD and Raman measurements, the thin films grown on both substrates did not contain foreign phases such as SnS2 and Sn2S3. The optical investigation of samples revealed a high absorption coefficient that exceeded ∼8 × 104 cm−1 at 700 nm wavelength. Furthermore, the optical and electrical measurements show that SnS thin films exhibit p-type conductivity and can be employed in heterojunction solar cells and self-powered photodetectors with a desired forbidden band gap of ∼1.5 eV. A short circuit current density of ∼1.5 mA/cm2, an open circuit voltage of ∼113 mV, and an efficiency of 0.05% were obtained for the Ag/SnS/CdS/ITO/glass structured solar cell. The on/off current ratio of the prepared self-powered Ag/SnS/CdS/ITO/glass structured photodetector was as high as 28316.76 ± 1588 at zero bias. On the other hand, it was shown that the detectivity of the self-powered photodetector device can be tuned between (1.201 ± 0.011)x108 and (1157.83 ± 2.39)x108 Jones by adjusting the substrate temperature. A responsivity value as high as (15149.47 ± 31.31) μA/W has been achieved at zero bias.

Lead-doped cubic tin sulfide thin films for solar cell applications

Cubic tin sulfide (SnS), an earth-abundant and non-toxic material, is a promising candidate for thin film solar cells. Lead(Pb)-doped (0.0–11.6 atomic percent (at.%)) cubic SnS thin films were prepared via chemical bath deposition to achieve improved structural, optical, and electrical properties. X-ray diffraction studies revealed that the films were polycrystalline and exhibited cubic crystal structure, decreased crystallite size, and increased lattice parameter, strain, and dislocation density on increasing Pb content. Field emission scanning electron microscopy images revealed increased grain size up to 2.5 at.% and decreased grain size beyond 2.5 at.% of Pb content. Optical absorption studies showed a decrease in the band gap from 1.73 to 1.64 eV upon increasing the Pb dopant concentration. Hall measurements revealed an increase in the hole mobility up to 2.5 at.% and decreased mobility beyond the 2.5 at.% of Pb dopant concentration. In conclusion, the prepared cubic SnS films have potential for application in solar cells because of the demonstrated reduced optical band gap and enhanced hole mobility resulting from Pb-doping.

Ultrathin tin sulfide field-effect transistors with subthreshold slope below 60 mV/decade

In this paper, we present for the first time a field-effect-transistor (FET) having a 10 nm thick tin sulfide (SnS) channel fabricated at the wafer scale with high reproducibility. SnS-based FETs are in on-state for increasing positive back-gate voltages up to 6 V, whereas the off-state is attained for negative back-gate voltages not exceeding −6 V, the on/off ratio being in the range 102–103 depending on FET dimensions. The SnS FETs show a subthreshold slope (SS) below 60 mV/decade thanks to the in-plane ferroelectricity of SnS and attaining a minimum value SS = 21 mV/decade. Moreover, the low SS values can be explained by the existence of a negative value of the capacitance of the SnS thin film up to 10 GHz (for any DC bias voltage between 1 and 5 V), with the minimum value being −12.87 pF at 0.1 GHz.

Synthesis of tin monosulfide SnS thin films via spray pyrolysis method based on Taguchi design for solar absorber

In this study, the effect of controlled conditions on the optical properties of tin monosulfide (SnS) thin films was successfully investigated by the chemistry spray pyrolysis deposition method on glass substrates. The Taguchi model is reported to find the most important factor for the deposition process of SnS thin films with orthogonal L9 (34) alignment. We also derive the band gap energy from transmittance data used to determine S/N relation. The selected influencing parameters are: tin-[Sn-] and sulfide-[S] concentrations, deposition substrate temperature (°C) Td and deposition time (min). The results show that the deposited film has a uniform, pure orthorhombic SnS phase and smooth morphology. Energy dispersive X-ray spectroscopy (EDS) utilizes the chemical composition of the prepared layers. In addition, the UV–Vis transmittance spectrum of the obtained film via the optimum conditions showed low transmittance in the visible region. Also, the SnS thin film shows the best gap interstitial energy of 1.52 eV. However, the SnS thin films produced by optimizing the Taguchi model display good optical properties and suggest that SnS thin films may be one of the potential solar cell absorbers in photovoltaic devices.

Effects of annealing on SnS films produced by chemical bath deposition (CBD)

Tin sulfide (SnS) thin films were produced on glass substrates at 65 °C by chemical bath deposition (CBD). Two of the obtained five identical films were annealed in an air atmosphere while the other two were annealed in a nitrogen atmosphere at different temperatures. The effects of annealing (at 150 °C and 250 °C in air and nitrogen atmospheres) on the optical, structural, and electrical properties of the films were investigated by UV-visible spectrophotometer, x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and Hall-effect measurement. The energy band gap of as-deposited SnS thin film was determined to be 1.16 eV, and it was observed to change with annealing. All of the as-deposited and annealed SnS films had orthorhombic structures. The optical phonon modes to orthorhombic SnS phases were determined by Raman shifts. The carrier type of all SnS films was identified as p-type using Hall measurement, and the changing carrier concentration, mobility, and resistivity values of the films were investigated depending on annealing conditions. The p-type SnS film can be used as an alternative material for the absorber layer in p-n heterojunction solar cell applications.

Structural, Optical and Electrical Properties of Nebulizer Spray-Deposited Tin Disulphide Thin Films with Different Substrate Temperatures

The Nebulizer spray pyrolysis technique is used to make tin disulphide thin films at various substrate temperatures. SnS2 thin films structural, electrical and optical properties are investigated. The polycrystalline nature was confirmed by X-ray diffraction (XRD) analysis, which revealed a hexagonal structure with a preferred orientation along the (0 0 2) plane. The full width half maximum value of the Bragg peak is used to calculate the size of SnS2 crystallization. Scanning Electron Microscope (SEM) is used to examine the composition and surface morphology of SnS2 thin films. The wavelength range of 400-1110 nm is used to determine the transmittance and absorption spectra of these films. With increasing substrate temperature, the optical band gap of tin disulphide thin films decreases from 3.17 eV to 2.61 eV. With regard to substrate temperature, the absorption coefficient and activation energy were reduced with SnS2 deposition.

Effect of Ar and H2 mixture gas on SnS thin films deposited by radio frequency (RF) magnetron sputtering

The effect of hydrogen on the deposition of SnS films was investigated using conventional radio frequency (RF) magnetron sputtering. The structure of the deposited SnS films was transformed from amorphous to polycrystalline by increasing the partial pressure of H2 gas. Simultaneously, the H2 supply suppressed the formation of an extra S-rich phase and enabled the Sn/S composition to be controlled by exploiting the reaction between hydrogen and sulfur atoms. By increasing the H2 supply, the Sn/S atomic ratio changed from 0.85 (S-rich) to 1.25 (Sn-rich). As the composition changes as a result of hydrogen supplementation, the carrier concentration of the SnS films decreases with increasing H2 gas supply, which may be due to the increase in the enthalpy of formation of tin vacancies. The incorporation of hydrogen in the films was observed using secondary ion mass spectrometry measurements. The amount of incorporated hydrogen did not strongly depend on the amount of H2 supplied. This suggests that hydrogen may not act as a carrier, but simply serves to modify the Sn/S ratio of SnS films using RF magnetron sputtering.

Effect of SnS thin film thickness on visible light photo detection

In this study, SnS thin films of various thicknesses (500 nm–700 nm) were prepared by the thermal evaporation technique for potential photodetector application. High purity SnS prepared at 1000 °C is used to deposit thin films at room temperature. The prepared SnS thin films were characterized to assess the thickness effect on the crystallite size, morphology, transmittance, band gap, and photo-sensing properties. SnS pure phase confirmed through XRD and Raman spectral analysis. Among the fabricated SnS thin films, the sample having a thickness of 650 nm showed better crystallinity with higher crystallite size and preferred orientation of crystallites. SnS grew plate-like-columnar grain morphology of different widths and thicknesses which is confirmed by FESEM results. The UV–Vis studies showed a minimum band gap value obtained for 650 nm thickness film. The 650 nm thickness SnS films have a highest photo response of 6.72 × 10−1 AW−1, external quantum efficiency (EQE) of 157%, and detectivity of 14.2 × 109 Jones. The transient photo-response analysis showed the 650 nm SnS thin film has a 5.3 s rise and 5.1 s fall duration, which is better suitable for photodetector applications compared to other samples.

Enhanced photosensitivity of Mn-doped p-type SnS thin films

Enhanced photosensitivity of Mn-doped p-type SnS thin films

Photosensitivity properties of Eu-doped SnS2 thin films deposited by cost-effective nebulizer spray pyrolysis technique

Photosensitivity properties of Eu-doped SnS2 thin films deposited by cost-effective nebulizer spray pyrolysis technique

Synthesis and characterization of solution processed p-SnS and n-SnS2 thin films: Effect of starting chemicals

This study represents the investigation of earth-abundant and non-toxic SnS absorber and SnS2 buffer layer materials by using a green solution process. Some physical properties of prepared thin films were investigated for different starting chemicals and molar ratios of Sn/S. Here, by using different starting chemicals such as tin (II) 2-ethylhexanoate and tin (II) chloride dihydrate, we observed that the formation of p-SnS and n-SnS2 phases can be simply controlled. All the SnS films obtained by the tin (II) 2-ethylhexanoate showed p-type conductivity. Moreover, it has been observed that an n-type SnS2 thin film can be produced by using tin (II) chloride dihydrate as the starting chemical instead of tin (II) 2-ethylhexanoate. According to the Hall effect measurement results, the resistivity of the p-type films obtained with both starting chemicals is in the order of 106 Ωcm. The resistivity of films with n-type properties drops to the order of 101 Ωcm. The I–V characteristic of the n-SnS2/p-SnS bilayer exhibits the p-n heterojunction diode characteristic. This study paves the way for solution processed SnS and SnS2 thin films as a potential absorber and buffer layer to be used in photovoltaic devices.

Annealing effect of absorber layer on SnS/CdS heterojunction band alignments

The effect of annealing on the physical properties of an SnS thin film and also on SnS/CdS heterojunction band alignment was studied. Vacuum annealing has greatly improved the crystalline quality of SnS and an average grain size of 1.6 μm was achieved. Sulfur-rich secondary phases observed on the surface of as-grown SnS thin film were eliminated after vacuum annealing, resulting in a decrease of the resistivity and an increase of the carrier concentration of the film. A maximum hole mobility of 17 cm2 V−1 s−1 was obtained for SnS thin films annealed at 400 °C. A transition of SnS/CdS heterojunction from “spike” type to “cliff” type was observed when the vacuum annealed SnS thin film was post-air-annealed at 200 and 250 °C. The band alignment of SnS/CdS heterojunction could be adjustable between “spike” type to “cliff” type via vacuum annealing followed by post-air-annealing.

A novel two-step strategy to fabricate phase-pure SnS photoelectrodes with tunable conductivity: formation mechanism and photoelectrochemical properties

Tin monosulfide (SnS) is a narrow band gap semiconductor for visible-light harvesting, however the easy formation of secondary phases such as Sn2S3 and SnS2 severely restricts its photoelectrochemical (PEC) properties. Herein, we propose a novel two-step strategy to fabricate phase-pure SnS photoelectrodes with tunable conductivity on Ti foil substrate and carefully investigated the formation mechanism and PEC properties. The tunable conductivity is determined by Na2SO4 pretreatment before annealing, which is supported by energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and electron paramagnetic resonance characterizations. Na+ adsorbed to the edge of the precursor SnS2 nanosheets forming a dangling bond adsorption will protect S2− against reaction with the trace oxygen in the chemical vapor deposition system within a certain temperature range (<525 °C), thereby reducing the generation of S vacancies to adjust the S/Sn ratio and further regulate the conductivity type. Moreover, the anodic photocurrent density of SnS thin films was about 0.32 mA cm−2 at 1.23 V vs reversible hydrogen electrode (RHE) with the separation and injection efficiency of 1.22% and 72.78% and a maximum cathodic photocurrent density reaching approximately −0.36 mA cm−2 at 0 V vs RHE with the separation and injection efficiency 1.15% and 5.44% respectively. The method shown in this work provides an effective approach to control the electrical conductivity of SnS thin films with considerable photocurrent response for phase-pure SnS.