Cobalt Sulfide Thin Films Research Articles

Substrate Temperature Effect on the Structural, Optical and Morphological Proprties of Cobalt Sulfide Thin Films Deposited Using Spray Pyrolisis

Abstract Thin films of cobalt sulfide were grown on glass substrates at four different temperatures (250 °C, 300 °C, 350 °C and 400 °C) using spray-pyrolysis technique. The precursor solutions were prepared using cobalt chloride and thiourea. The effect of deposition temperature on the structural, morphological, and optical properties of cobalt sulfide thin films was investigated using different experimental techniques such as X-ray diffraction (XRD), and UV-visible spectrophotometry, Fourier Transform Infrared Spectroscopy (FT-IR) and four-probe method. The XRD analysis showed that crystallite size varies from 9.76 to 14.11 nm with increasing the deposition temperature. UV-visible data analysis shows a decrease in the band gap energies with increasing temperature (1.82 eV for 250 °C, 1.76 eV for 300 °C, 1.72 eV for 350 °C, and 1.65 eV for 400 °C). The analysis of the chemical composition by FTIR confirmed the presence of Co, S elements. On the other hand, the electrical conductivity of the cobalt sulfide thin films increased owing to the increase in the crystallite size and reduction of defects density.

Retracted] Studying the Effect of Metallic Precursor Concentration on the Structural, Optical, and Morphological Properties of Zinc Sulfide Thin Films in Photovoltaic Cell Applications

Thin films of zinc sulfide (ZnS) with different concentrations of zinc acetate have been made by chemical bath deposition technique in acidic medium (pH = 5) on glass substrate using zinc acetate and sodium sulfide as sources of Zn+2 ion and S−2 ion, respectively, and ethylenediaminetetraacetate as complexing agents and sulfuric acid to adjust pH value at a constant deposition temperature of 85°C, and the deposition time of 90 minutes was used. The effect of the concentration of metallic precursor on the structural, morphological, and optical properties of chemical bath deposited zinc sulfide thin films was investigated in this study. The XRD result confirmed mixed phases of crystalline and amorphous structure dominating other phases, which is witnessed by larger crystallite size than other phases. It reveals that the thin films had hexagonal structure at the medium concentration with preferred orientation along (111) plane, and at lower and higher concentration, it showed that film has an amorphous structure in nature. The crystallinity of all the phases significantly enlarged with increasing the zinc precursor concentration. The SEM micrographs showed high‐pitched edged irregular‐shaped grains covering the substrate with pinholes and bangs. The optical properties investigated by the UV‐VIS spectrometer specified a decrease in the optical bandgap of the films between 3.5 eV and 2.6 eV as the zinc acetate concentration in the solution increased from 0.1 to 0.2 M. It showed that the zinc sulfide had high absorption in the UV radiation. The main finding of this paper is that metallic precursor concentration has a significant role in the optical, morphological, and microstructural properties of the cobalt sulfide thin films, which are most suitable for photovoltaic applications.

Cobalt Sulfide as Photoelectrode of Photoelectrochemical Hydrogen Generation from Water

This study aimed to synthesize and characterize cobalt sulfide deposited on FTO by hydrothermal method and investigate its photoelectrochemical (PEC) water splitting performance. Cobalt sulfide thin films were produced by annealing at two different temperatures, namely, 400 and 500 °C. X-ray diffraction (XRD) and Fourier transform Raman spectroscopy were used to characterize the phase structure. Scanning electron microscopy was used to observe the morphology. Ultraviolet-visible spectroscopy and linear sweep voltammetry analyses were used to determine the thin-film band gap and evaluate the PEC water splitting performance, respectively. From the XRD and Raman analyses, all the samples produced consisted of mixed phases of Co3S4 and Co9S8. However, each sample contained different percentage phases. The sample annealed at 400 °C contained more Co9S8, whereas that annealed at 500 °C contained comparable amounts of Co3S4 and Co9S8. The morphologies of pre-annealed samples showed vertical flakes with diameters around 200-250 nm and flake thickness around 25-50 nm. When the temperature was increased from pre-annealing temperature to 400 and 500 °C, several flakes were destructed and formed spherical-like clusters. The Tauc plot from absorption analysis showed that the samples annealed at 400 and 500 °C produced similar band gaps at ~2.0 eV. The PEC performance analysis results show that annealing at 400 °C produced the highest photocurrent density of 10 μA/cm2 at a potential of -0.7 V.

The Effect of Deposition Cycles on Intrinsic and Electrochemical Properties Ofmetallic Cobalt Sulfide By Simple Chemical Route

Cobalt Sulfide Thin Film Was Synthesized on Glass and Steel Substrates Via Chemical Route. Thestructure, Surface Morphology, and Optical Characterization of the Deposited Thin Films Indicated a Strong Relationship between the Number of Deposition Cycles and Intrinsic Properties. the Scanning Electron Microscope(SEM) Showed a Uniform Morphology with Randomly Oriented Nano-Grains of Cobalt Sulfide Film at Varying Deposition Cycles. the XRD Spectra Revealed That the Films Became Amorphous As the Number of Deposition Cycles Increased. the Crystalline Films Had a Hexagonal Structure of Average Crystallite Size of 27.55 Nm. the Optical Transmission Spectra of the Films Gave a Direct Band Gap Energy Which Varied between 1.90 Ev and 2.20 Ev with an Average Value of the Optical Conductivity Was 1.77 1017 S ̶ 1. the Electrochemical Energy Storage Behavior of the Electrodes Was Evaluated Using Cyclic Voltammetery (CV), Galvanostatic Charge-Discharge (GCD) Technique and Electrochemical Impedance Spectroscopy (EIS) in a Neutral Electrolyte of 0.1M Solution of Na2SO4 Performed on Films Deposited on a Steel Substrate. a Specific Capacity of 298.4 Mah/g at a Scan Rate of 20 Mv/s Was Obtained at 30 Deposition Cycles. the SILAR Deposited Cos Thin Film Electrodes Is a Promising Material for Both Energy Storage and Optoelectronics Application Based on the Electrochemical Properties Obtained. the Material Showed about 80% Charge Capacity Retention after 1000 Cycles.

Characterization of Cobalt Sulfide Thin Films Synthesized from Acidic Chemical Baths

Cobalt sulfide thin films were synthesized from acidic chemical baths by varying the deposition time. The powder X‐ray diffraction studies indicated that there are hexagonal CoS, face‐centered cubic Co3S4, and cubic Co9S8 phases of cobalt sulfide. The crystallite size of the hexagonal CoS phase decreased from 52.8 nm to 22.5 nm and that of the cubic Co9S8 phase increased from 11 nm to 60 nm as the deposition time increased from 2 hrs to 3.5 hrs. The scanning electron microscopic images revealed crack and pinhole free thin films with uniform and smooth background and few large polygonal grains on the surface. The band gap of the cobalt sulfide thin films decreased from 1.75 eV to 1.3 eV as the deposition time increased from 2 hrs to 3.5 hrs. The photoluminescence (PL) spectra of the films confirmed the emission of ultraviolet, violet, and blue lights. The intense PL emission of violet light at 384 nm had red shifted with increasing deposition time that could be resulted from the increase in the average crystallite size. The FTIR spectra of the films indicated the presence of OH, C‐O‐H, C‐O, double sulfide, and Co‐S groups. As the deposition time increased, the electrical resistivity of the cobalt sulfide thin films decreased due to the increase in both the crystallite size and the films’ thickness.

The effect of deposition cycles on intrinsic and electrochemical properties of metallic cobalt sulfide by Simple chemical route

In this paper, cobalt sulfide thin film was synthesized on glass and steel substrates via chemical route. The structure, surface morphology, and optical characterization of the deposited thin films indicated a strong relationship between the number of deposition cycles and intrinsic properties. The scanning electron microscope (SEM) showed a uniform morphology with randomly oriented nano-grains of cobalt sulfide film at varying deposition cycles. The XRD spectra revealed that the films became amorphous as the number of deposition cycles increased. The crystalline films had a hexagonal structure of average crystallite size of 27.55 nm. The optical transmission spectra of the films gave a direct band gap energy which varied between 1.90 eV and 2.20 eV with an average value of the optical conductivity was 1.77 1017 S̶ 1. The electrochemical energy storage behavior of the electrodes was evaluated using cyclic voltammetery (CV), galvanostatic charge-discharge (GCD) technique and electrochemical impedance spectroscopy (EIS) in a neutral electrolyte of 0.1 M solution of Na2SO4 performed on films deposited on a steel substrate. A specific capacity of 298.4 mAh/g at a scan rate of 20 mV/s was obtained at 30 deposition cycles. The SILAR deposited CoS thin film electrodes is a promising material for both energy storage and optoelectronics application based on the electrochemical properties obtained. The material showed about 80% charge capacity retention after 1000 cycles.

Synthesis and physiognomic study of copper sulfide doped cobalt sulfide

Cobalt sulfide thin films have been efficaciously fabricated by physical vapour deposition technique (PVD). Diethyldithiocarbamato metal complexes of the overall formula [M(S2CN(Et)2)n] (M=Co,Cu) have been manufactured and used as precursors for the deposition of pure and copper sulfide doped cobalt sulfide thin films on glass substrate. X-ray diffraction and Fourier transform infrared analysis of thin films confirmed the cubic and spherical sheet like structures. UV–vis studies revealed that absorption peak shifted from higher to lower wavelength with the reduction in transmittance and reflectance. While the scanning electron micrographs confirmed the cubic metal sulfide particles with the band gap calculated as 2.4–2.0 eV in metal sulfide thin films. These complexes are the first in their class to be used as single source precursors to deposit CuxCo1−xS2 thin films.

Cobalt sulfide thin films for electrocatalytic oxygen evolution reaction and supercapacitor applications

Nanocrystalline cobalt sulfide thin film electrodes have been deposited on stainless steel substrate using binder-free chemical bath deposition (CBD) method and electrochemical study is performed in 1 M KOH electrolyte. Linear sweep voltammetry (LSV) curve shows that cobalt sulfide thin film electrode requires 300 mV overpotential (ƞ) to reach the current density of 10 mA cm−2. Also, it exhibits Tafel slope of 57 mV decade−1 with stable catalytic activity over 14 h. Along with good electrocatalytic oxygen evolution performance, in supercapacitive study it shows specific capacitance of 252.39 F g−1 at a scan rate of 5 mV s−1. The stability test indicates that cobalt sulfide electrode is stable for 1000 cyclic voltammetry (CV) cycles.

Effect of pretreatment on catalytic activity of cobalt sulfide thin film for oxygen evolution reaction

Cobalt sulfide thin films have been successfully synthesized on stainless steel substrate using chemical bath deposition (CBD) method. The as prepared cobalt sulfide thin film is pretreated anodically at constant current density of 10 mA cm−2 for 14 h and its physical and structural properties are studied. The electrochemical study in 1 M KOH shows enhancement in catalytic activity after treatment. The linear sweep voltammetry study shows decrease in overpotential from 300 mV to 270 mV after anodic constant current treatment, making cobalt sulfide catalytically more active.

One-step facile route to copper cobalt sulfide electrodes for supercapacitors with high-rate long-cycle life performance

The impressive electrochemical energy storage performance of Earth-abundant ternary copper cobalt sulfide (CCS) thin film electrodes that are prepared on stainless steel substrates via a simple and cost-effective hydrothermal process is demonstrated. The optimized CCS electrode shows a high specific capacitance of ∼516 F/g at a current density of 10 A/g, a good rate capability of ∼72% at a high current density of 50 A/g, and a good cycling retention of ∼66% with a coulombic efficiency of ∼99% after 10,000 charge-discharge cycles. The CCS electrode exhibits a high energy density of ∼35.2 Wh/kg at a power density of ∼6.6 kW/kg. The excellent electrochemical supercapacitor properties of the CCS electrode are a result of a synergetic effect between the uniform full coverage, robust adhesion, and desired chemical composition. A low charge transfer resistance, resulting from the large electrochemically active surface area (ECSA) and good diffusion, significantly contributes to the enhanced electrochemical supercapacitor performance. This excellent CCS electrode material has the potential to become a low-cost and long-cycle life electrode for the next-generation high-power-capacity supercapacitors.

Cobalt sulfide counter electrode using hydrothermal method for quantum dot-sensitized solar cells

Chalcogenides are potential alternatives to platinum (Pt) based counter electrode (CE). This study reports cobalt sulfide (CoS2) thin films as robust, high-performance, economical, earth-abundant CE for quantum dot-sensitized solar cells (QDSSCs). CoS2 thin film has been deposited on a fluorine-doped tin oxide substrate by a hydro thermal method using 3-mercapto propionic acid and used as an efficient CE for polysulfide redox reactions in quantum dot-sensitized solar cells (QDSSCs). CdS/CdSe-sensitized QDSSCs exploiting CoS2 CE improved short-circuit photocurrent density and fill factor. We attained 2.27% solar light-to-electricity conversion efficiency, a value higher than reaped with Pt CE (1.73%). Electrochemical measurements testified that CoS2 reveals high electro-catalytic activity towards polysulfide reduction, thus accelerating QDSSCs performance. CoS2 also showed stability at a working state for over 10h, resulting in highly reproducible performance, which is a serious challenge for solar cell.

A high performance cobalt sulfide counter electrode for dye-sensitized solar cells

A cobalt sulfide (CoS) thin film is deposited on fluorine doped SnO2 (FTO) glass by repetitive electrophoretic deposition (EPD) and ion exchange deposition (IED), then the thin film is treated with sodium borohydride or/and sulfuric acid solution. The film is used as the counter electrode of dye-sensitized solar cells (DSSCs), and is characterized by field emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and Tafel measurements. The results show that the CoS counter electrode has a honeycomb-like morphology with large specific surface area, good catalytic activity for reduction of I3−, lower charge-transfer and series resistances, which result in the better electrochemical property of CoS counter electrodes. Under a simulated solar light irradiation of 100mWcm−2, the DSSC based on the CoS counter electrode achieves a power conversion efficiency of 7.72%, thus, synthesized CoS can serve as an efficient Pt-free counter electrode material for DSSCs.

Deposition of cobalt and nickel sulfide thin films from thio- and alkylthio-urea complexes as precursors via the aerosol assisted chemical vapour deposition technique

We report the synthesis of Co(II) and Ni(II) thiourea and alkylthiourea complexes by reacting the metal salts (CoCl2 and NiCl2) with the thiourea, phenylthiourea and dicyclohexylthiourea ligands in a 1:2 ratio. The complexes, [CoCl2(CS(NH2)2)2] (I), [CoCl2(CSNHC6H5NH2)2 (II) and [CoCI2(SC(NHC6H11)2)2] (III), [NiCl2(CS(NH2)2)2] (IV), [NiCl2(CSNHC6H5NH2)2] (V) and [NiCl2(SC(NHC6H11)2)2] (VI) were characterized by C, H, N analysis and Fourier transform infrared spectroscopy. Thermogravimetric analysis shows that all complexes undergo a two step decomposition process except for [NiCl2(CSNHC6H5NH2)2] (V) which decomposes in a single step. The complexes were used as single-source precursors for the deposition of cobalt sulfide and nickel sulfide thin films by aerosol assisted chemical vapor deposition at temperatures between 350 an 500°C. The crystallinity of the films was determined by X-ray diffraction and their morphology was determined by scanning electron microscopy. The morphology of the cobalt sulfide thin films varies from randomly oriented platelets, to granulated spheres and cubes as the precursor and deposition conditions are changed. For nickel sulfide, the [NiCl2(CS(NH2)2)2] (IV) complex gave rods whereas the [NiCl2(CSNHC6H5NH2)2] (V) produced spherical particles.

Cobalt sulfide thin film as an efficient counter electrode for dye-sensitized solar cells

The power conversion efficiency of dye sensitized solar cells (DSSCs) was improved using a nano rose petal like structured cobalt sulfide (CoS2) counter electrode (CE) with an iodine triiodide (I−/I3−) electrolyte. The CoS2 nano rose petals like structure with a mean film thickness of 280nm prepared using a solution containing 0.1M cobalt chloride, 0.8M urea and 0.8M thioacetamide by inexpensive chemical bath deposition at 80°C for 3h resulted in an improved fill factor, short circuit current and open circuit voltage compared to the Pt electrodes. Tafel polarization and electrochemical impedance spectroscopy showed that CoS2 electrode has smaller charge transfer resistance than Pt electrodes. DSSC fabricated with the CoS2 CE achieved a power conversion efficiency of 5.32% under 1 sunlight illumination (100 mW cm−2, AM 1.5 G), which surpassed that of the device based on Pt (5.02%).

Cathodic Electrodeposition of Cobalt Sulfide Thin Films for Dye-Sensitized Solar Cells and Supercapacitors

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Cobalt sulfide thin films for counter electrodes of dye-sensitized solar cells with cobalt complex based electrolytes

Recently, a cobalt complex based electrolyte such as [Co(bpy)3]2+/3+ was suggested to replace the conventional I3−/I− system because of its potential to provide high open circuit potential and power conversion efficiency in dye-sensitized solar cells (DSSCs). Here, a cobalt sulfide thin film was synthesized by electrochemical deposition and used for a counter electrode. A DSSC with the cobalt sulfide counter electrode exhibits Jsc=7.228mA/cm2, which is 13% higher than that with Pt (Jsc=6.443mA/cm2), thereby achieving an enhanced power conversion efficiency. Electrochemical impedance spectroscopy measurements indicate that the reduced Warburg diffusion impedance and faster adsorption of [Co(bpy)3]3+ facilitate the reduction of the cobalt complex.

Electrodeposition of polymer encapsulated cobalt sulfide thin films: search for a frequency switching material

Polymer encapsulated nanostructure cobalt sulfide (CoS) thin films have been synthesized electrochemically at pH 6.5, using cobalt nitrate (Co(NO3)2, 6H2O), thioacetamide (CH3C(S)NH2, TAA) and poly vinyl pyrolidone (PVP) as the capping agent. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive analysis of X-rays (EDAX) techniques were used to characterize the CoS thin films. The attachment between PVP and CoS is envisaged by Fourier transform infrared spectroscopy (FTIR). Frequency switching study reveals that the encapsulated material could be used as frequency switching material. The nanostructure films exhibit light induced frequency switching under 1 Sun illumination and generate a frequency ∼50Hz. Encapsulation with PVP causes surface modification that reduces surface states and barrier height. As a result, the width of depletion region decreases and exciton related emission increases by the reduction of nonradiative recombination process.

Pulse electrodeposition of CoS on MWCNT/Ti as a high performance counter electrode for a Pt-free dye-sensitized solar cell

Because of the large specific surface area and superior electrical conductivity of multi-wall carbon nanotubes (MWCNTs) and the high electrocatalytic activity of cobalt sulfide (CoS), CoS/MWCNT hybrid films are deposited onto Ti foil substrates by sequential electrophoresis and pulse potentiostatic electrodeposition. Field-emission scanning electron microscopy observes that the surface of the MWCNTs is wrapped with a nano-honeycomb CoS thin film of ∼55 nm in thickness. Cyclic voltammograms, electrochemical impedance spectroscopy, and Tafel polarization characterization indicate that the CoS/MWCNT/Ti counter electrode (CE) has better electrocatalytic activity for I3− reduction than Pt CE. Under full sunlight illumination (100 mW cm−2, AM 1.5 G), the dye-sensitized solar cell based on the CoS/MWCNT/Ti CE achieves a power conversion efficiency of 8.05%, which exceeds that of the device based on Pt/Ti CE (6.39%).

Pulse-Reversal Deposition of Cobalt Sulfide Thin Film as a Counter Electrode for Dye-Sensitized Solar Cells

In this study, cobalt sulfide (CoS) thin film was electrochemically deposited on a transparent conducting glass substrate in a neutral aqueous by means of a simple pulse-reversal (PR) deposition technique, and employed as a counter electrode (CE) for dye-sensitized solar cells (DSCs) for the first time. Initially, extensive electrochemical measurements were conducted to investigate the deposition mechanism for the proposed PR deposition mode and determine the suitable pulse potentials. When compared to the conventional potentiostatic (PS) deposition mode, the proposed PR deposition mode can facilitate the formation of single-component CoS with granular morphology. Moreover, the effects of the parameters in the PR mode, including duty cycle and pulse frequency, on the electrocatalytic activity for I3− reduction were investigated. After the optimization, the CoSPR CE at duty cycle of 0.1 and pulse frequency of 1/30 Hz showed the most excellent electrocatalytic activity for I3− reduction among all electrodeposited-CoS CEs. The DSC with the CoSPR CE exhibits an impressive cell efficiency of 5.48%, which is much better than that of the DSC with CoSPS CE (2.13%) and comparable to that of the DSC using Pt CE (5.50%).

Selective Deposition of Cobalt Sulfide Nanostructured Thin Films from Single-Source Precursors

The cobalt(III) complexes of 1,1,5,5-tetramethyl- and 1,1,5,5-tetraethyl-2,4-dithiobiuret and the cobalt(II) complex of 1,1,5,5-tetra-iso-propyl-2-thiobiuret have been synthesized. The single-crystal X-ray structure of the thiocyanide (1) and cobalt tetrachlorate (2) salts of the parent cyclized ligand, together with complexes [Co{N(SCNMe2)2}3] (3), [Co{N(SCNEt2)2}3] (4) and [Co{N(SOCNiPr2)2}2] (5) have been determined. The thermal decomposition of 3, 4, and 5 was studied. The complexes were used as single source precursors for the deposition of cobalt sulfide thin films by aerosol assisted chemical vapor deposition (AACVD). The X-ray diffraction (XRD) of the deposited films showed hexagonal Co1−xS from complexes (3) and (4) whereas complex (5) gave a mixture of cubic and hexagonal Co4S3. The morphology of films was characterized by scanning electron microscope (SEM) and showed rod like crystallites from 3, granular crystallites from 4 and stalagmitic structures from 5. Transmission electron microscopy (TEM) of the samples obtained from thin films from 3 and 4 show that the films are composed of hexagonal nanoplates with nanocubes from 5. Magnetic measurements showed the para or ferro-magnetic behavior from crystallites. The mechanism for decomposition of precursors to the cobalt sulfide was studied by pyrolysis gas chromatography (Py-GC-MS).