Sulfurized Thin Films Research Articles

Impact on Structural and Optical Properties of CZTS Thin Films with Solvents and Ge Incorporation

This report demonstrates nontoxic colloidal nitrate route CZTS (Cu2ZnSnS4) synthesis at room temperature, along with their band grading due to incorporation of Ge as cost of Sn (3%). The parent CZTS, CZGTS (Cu2ZnGeSnS4), and their polyvinyl alcohol (PVA), dimethyl sulfoxide (DMSO) solvent containing solutions doctor blade-coated thin film structural and optical properties are discussed. Their sulfurized thin films thickness have been achieved ±2 μ. It has noticed that addition of Ge in CZTS alloy affects the grain sizes, crystallographic structure, Raman spectral peak shift toward the higher wave number side. The addition of PVA and DMSO is also substantially contributed in their physical property modification by demonstrating the gradual improvement in grain sizes and compactness. Moreover, the gradual changes have also appeared in their X-ray diffractometer (XRD) and Raman spectroscopic results. The optical energy band gaps of the CZTS, CZGTS, and their PVA, DMSO mixed alloyed thin films are obtained in between 1.27 eV to 1.57 eV and 1.58 eV to 1.83 eV.

Gas Permeation of Sulfur Thin-Films and Potential as a Barrier Material.

Elemental sulfur was formed into poly(ether sulfone)-supported thin-films (ca. 10 µm) via a melt-casting process. Observed permeabilities of C2H4, CO2, H2, He, and N2 through the sulphur thin-films were <1 barrer. The sulfur thin-films were observed to age over a period of ca. 15 days, related to the reversion of polymerized sulfur to the S8 allotrope. This structural conversion was observed to correlate with an increase in the permeability of all gases.

Growth of Cu2ZnSnS4 absorber layer on flexible metallic substrates for thin film solar cell applications

In this work, Cu2ZnSnS4 (CZTS) absorber layers were fabricated using a two-stage process. Sequentially deposited Cu–Zn–Sn thin film layers on metallic foils were annealed in an Ar+S2(g) atmosphere. We aimed to investigate the role of flexible titanium and molybdenum foil substrates in the growth mechanism of CZTS thin films. The Raman spectra and X-ray photoelectron spectroscopy analyses of the sulfurized thin films revealed that, except for the presence of Sn-based secondary phases, nearly pure CZTS thin films were obtained. Additionally, the intense and sharp X-ray diffraction peak from the (112) plane provided evidence of good crystallinity. Electron dispersive spectroscopy analysis indicated sufficient sulfur content but poor Zn atomic weight percentage in the films. Absorption and band-gap energy analyses were carried out to confirm the suitability of CZTS thin films as the absorber layer in solar cell applications. Hall effect measurements showed the p-type semiconductor behavior of the CZTS samples. Moreover, the back contact behavior of these metallic flexible substrates was investigated and compared. We detected formation of cracks in the CZTS layer on the molybdenum foils, which indicates the incompatibility of molybdenum's thermal expansion coefficient with the CZTS structure. We demonstrated the application of the magnetron sputtering technique for the fabrication of CZTS thin films on titanium foils having lightweight, flexible properties and suitable for roll-to-roll manufacturing for high throughput fabrication. Titanium foils are also cost competitive compared to molybdenum foils.

Control of gallium incorporation in sol–gel derived CuIn(1−x)GaxS2 thin films for photovoltaic applications

In this paper, we report the elaboration of Cu(In,Ga)S2 chalcopyrite thin films via a sol–gel process. To reach this aim, solutions containing copper, indium and gallium complexes were prepared. These solutions were thereafter spin-coated onto the soda lime glass substrates and calcined, leading to metallic oxides thin films. Expected chalcopyrite films were finally obtained by sulfurization of oxides layers using a sulfur atmosphere at 500°C. The rate of gallium incorporation was studied both at the solutions synthesis step and at the thin films sulfurization process. Elemental and X-ray diffraction (XRD) analyses have shown the efficiency of monoethanolamine used as a complexing agent for the preparation of CuIn(1−x)GaxS2 thin layers. Moreover, the replacement of diethanolamine by monoethanolamine has permitted the substitution of indium by isovalent gallium from x=0 to x=0.4 and prevented the precipitation of copper derivatives. XRD analyses of sulfurized thin films CuIn(1−x)GaxS2, clearly indicated that the increasing rate of gallium induced a shift of XRD peaks, revealing an evolution of the lattice parameter in the chalcopyrite structure. These results were confirmed by Raman analyses. Moreover, the optical band gap was also found to be linearly dependent upon the gallium rate incorporated within the thin films: it varies from 1.47eV for x=0 to 1.63eV for x=0.4.

Correlation between soft annealing conditions and structural, microstructural, morphological, and optical properties of CuInS2 thin films prepared by sulfurization of stacked precursor

CuInS2 (CIS) thin films were prepared by sulfurization of In/Cu stacked precursor films. Prior to sulfurization the stacked metallic precursors were subjected to the soft annealing in Ar atmosphere at different time (10, 30, and 60min) and temperature (100°C and 300°C). The effect of soft annealing condition on the structural, morphological and optical properties of CIS films was investigated. X-ray diffraction, Raman, and X-ray photoelectron spectroscopy studies showed that the sulfurized thin films exhibited a CIS tetragonal structure with minor secondary phases such as Cu2−xS and CuIn5S8. The secondary phases were minimized by introducing soft annealed process in the CIS thin films. Void free CIS microstructures have been observed for soft annealed CIS films. The band gap energy of CIS films were increased from 1.37 to 1.5eV depending on the soft annealing conditions.

Effect of Sulfurization Temperature on the Properties of Cu2ZnSn(S,Se)4 Thin Films

(CZTSSe) thin films were prepared by sulfurization of evaporated precursor thin films. Precursor was prepared using evaporation method at room temperature. The sulfurization was carried out in a graphite box with S powder at different temperatures. The temperatures were varied in a four step process from to . The effects of the sulfurization temperature on the micro-structural, morphological, and compositional properties of the CZTSSe thin films were investigated using X-ray diffraction (XRD), Raman spectra, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The XRD and Raman results showed that the sulfurized thin films had a single kesterite crystal CZTSSe. From the FE-SEM and TEM results, the (MoSSe) interfacial layers of the sulfurized CZTS thin films were observed and their thickness was seen to increase with increasing sulfurization temperature. The microstructures of the CZTSSe thin films were strongly related to the sulfurization temperatures. The voids in the CZTSSe thin films increased with the increasing sulfurization temperature.

Crystallization behaviour of co-sputtered Cu2ZnSnS4 precursor prepared by sequential sulfurization processes

Cu2ZnSnS4 (CZTS) thin films were prepared by the sequential sulfurization of a co-sputtered precursor with a multitarget (Cu, ZnS, and SnS2) sputtering system. In order to investigate the crystallization behaviour of the thin films, the precursors were sulfurized in a tube furnace at different temperatures for different time durations. The Raman spectra of the sulfurized thin films showed that their crystallinity gradually improved with an increase in the sulfurization temperature and duration. However, transmission electron microscopy revealed an unexpected result—the precursor thin films were not completely transformed to the CZTS phase and showed the presence of uncrystallized material when sulfurized at 250–400 °C for 60 min and at 500 °C for 30 min. Thus, the crystallization of the co-sputtered precursor thin films showed a strong dependence on the sulfurization temperature and duration. The crystallization mechanism of the precursor thin films was understood on the basis of these results and has been described in this paper. The understanding of this mechanism may improve the standard preparation method for high-quality CZTS absorber layers.

Study on the effects of different sulfur vaporization temperature on the properties of CuInS2 thin films

CuInS2 (CIS) absorber thin films were prepared by sulfurization of In/Cu metallic stacked precursor. The precursor thin films were sulfurized using a commercial furnace system in the S2 (s)+Ar atmosphere at 425°C for 1h. Effects of different S vapor temperature from 150 to 400°C on the structural, morphological, compositional and optical properties of CIS thin films were investigated. X-ray diffraction and Raman studies showed that the sulfurized thin films with S vaporization temperature below 300°C exhibited CIS tetragonal structure with secondary phases such as CuxSy, CuIn5S8, and InxSy. The sulfurized thin films with S vaporization temperature over 350°C showed a single CIS tetragonal structure. Compositional ratio of CIS thin films showed that Cu/In and S/(Cu+In) ratio in the CIS thin films with S vaporization temperature over 350°C were 1.0–1.2 and 0.9–1.1, respectively, while compositional ratio deviated from stoichiometry when the sulfurized thin films below S vaporization temperature of 350°C. Optical study showed that the band gap energy and the absorption coefficient of CIS thin films were estimated from 1.18eV to 1.5eV and over 104cm−1, respectively.

Effects of Cu/In compositional ratio on the characteristics of CuInS2 absorber layers prepared by sulfurization of metallic precursors

This paper investigates the effects of the Cu/In compositional ratio on morphological, structural and optical properties of CuInS2 (CIS) absorber layers formed by sulfurization of In/Cu stacked precursors. In/Cu stacked precursors were prepared on Mo-coated soda-lime glass substrates by DC magnetron sputtering method. The Cu/In compositional ratio in the precursor thin film was varied from 0.55 to 1.44. The as-deposited stacked precursor thin films were sulfurized using a tubular furnace annealing system in a mixture of N2 (95%) + H2S (5%) atmosphere at 450°C for 1 hour. X-ray diffraction patterns and Raman spectra results showed that the sulfurized thin films contained both tetragonal CIS and a Cu-based secondary phase, except for the film with a Cu/In compositional ratio of 0.55. Field emission-scanning electron microscopy study showed that the microstructure of the sulfurized CIS thin films became denser with increasing Cu/In compositional ratio. Optical properties of the CIS thin films showed that all the CIS thin films had a good absorption coefficient over 104 cm−1 in the visible region. The direct band gap energy of the sulfurized CIS thin films decreased from 1.39 eV to 1.08 eV with increasing Cu/In compositional ratio. These results demonstrated the effect of the Cu/In compositional ratio on the properties of the CIS thin films and the consequent importance of precisely controlling the metal ratio in the precursor film in order to control the properties of absorber layers in thin film solar cells.

Electrochemical layer by layer growth and characterization of copper sulfur thin films on Ag(1 1 1)

Copper sulfide (CuS) thin films were grown on a single crystal Ag(1 1 1) substrate by Electrochemical Atomic Layer Deposition (ECALD) method, i.e., by alternated surface limited deposition of copper and sulfur. A detailed investigation of deposition of Cu on S allowed to find the best conditions for copper deposition. The electrochemical characterization of deposits obtained with different deposition cycles suggests a 1:1 stoichiometric ratio between Cu and S corresponding to Cu monosulfide. The compositional analysis was performed by X-rays Photoelectron Spectroscopy (XPS), and the morphological was investigated by Atomic Force Microscopy (AFM) for deposits formed with 20 ECALD cycles.

Nickel sulfur thin films deposited by ECALE: Electrochemical, XPS and AFM characterization

This paper reports on a study of the electrodeposition of nickel sulfide thin films on Ag(1 1 1) by the Electrochemical Atomic Layer Epitaxy (ECALE) technique. The multilayer growth of nickel sulfide has been studied by cyclic and stripping voltammetry. The composition of the films was studied by XPS analysis and the morphology was studied by Atomic Force Microscopy (AFM). The phenomenological observation of the hydrogen evolution reaction (HER) suggests the presence of electrocatalytic properties of the thin films obtained.

Influence of RF power on the structure of ZnS thin films grown by sulfurizing RF sputter deposited ZnO

ZnS thin films with a c-axis preferred orientation have been prepared by sulfurizing the RF reactive sputter deposited ZnO thin films at 500 °C in sulfur vapor. These thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible transmission spectra and Auger electron spectroscopy (AES). It is found that the degree of c-axis orientations of ZnO and ZnS thin films increases with enhancing RF power. Also, the sulfurized thin films have markedly greater grains than the as-deposited films, mainly due to recrystallization of ZnS in sulfur vapor. The grain size for the ZnS films increases from ∼200 to ∼500 nm with enhancing RF power from 80 to 120 W. A reason for this is that in the case of the greater RF power, high compactness of the films will be very beneficial to the grain growth. Additionally, the excess sulfur can be absorbed on the grain surface of the ZnS film produced by 22 h sulfidation. This will cause the great broadening of absorption edge in the optical transmittance.

Incorporation of sulfur into hydrogenated amorphous carbon films

Amorphous hydrogenated carbon–sulfur thin films (a-C:H:S) were deposited from CH 4/H 2S gas mixtures by capacitively-coupled radio-frequency PECVD. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to probe the composition of the films. XPS showed that the sulfur atomic percentage within a film was proportional to the fraction of H 2S in the H 2S/CH 4 gas mixture, and that films had been deposited with a sulfur content of up to 27 at.%. SIMS showed that the distribution of C and S was homogeneous throughout the films. Ex situ variable angle spectroscopic ellipsometry was used to evaluate the band gap energy variation by three different methods. Values of the E04 band gap for these films were between 1.5 and 2.5 eV, with refractive index values of between 1.8 and 2.1. Laser Raman spectroscopy (514.5 nm) suggested that the addition of sulfur increases the clustering of aromatic six-membered rings.