An investigation into the effect of rate of stirring of bath electrolyte on the properties of electrodeposited CdTe thin film semiconductors

Electrodeposition (ED) has been recognized as a low cost and scalable technique available for fabrication of CdS/CdTe solar cells. Photovoltaic activity of these electrodeposited semiconductor materials drastically depends on the ED growth parameters namely; electrodeposition potential, concentrations and ratios of concentrations of precursors used to prepare the bath electrolyte, pH of the electrolyte, deposition temperature and rate of stirring of the electrolyte. In order to grow thin films with good photovoltaic properties, it is essential to maintain these variables at their optimum ranges of values during electrodepositions. Hence, this study was conducted to investigate the dependence of the properties of electrodeposited CdTe thin film material on the rate of stirring of the bath electrolyte. The CdTe material was grown on glass/FTO (2?×?3 cm²) and glass/FTO/CdS (2?×?3 cm²) surfaces in bath electrolytes containing 1.0 mol/L CdSO₄ and 1.0 mmol/L TeO₂ solutions at different rates of stirring within the range of 0–350 rpm while keeping the values of pH of the electrolyte, deposition temperature and cathodic deposition potential with respect to the saturated calomel electrode at 2.3, 65 °C and 650 mV respectively. After the heat treatment at 400 °C in air atmosphere, the deposited samples with a good visual appearance were selected and evaluated based on their morphological, elemental, structural, optical and electrical properties in order to identify the optimum range of rate of stirring for electrodeposition of CdTe thin film semiconductors. Results revealed that, rates of stirring in the range of 60–85 rpm in a 100 mL volume of electrolyte containing the substrate and the counter electrodes in the center of the bath with a separation of 2.0 cm between them can electrodeposit CdTe layers exhibiting required levels of morphological, structural, optical and electrical properties on both glass/FTO and glass/FTO/CdS surfaces.     

Structural and optical characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure

This article presents the deposition and characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure. The growth of CdS and CdHgTe thin films on FTO-coated conducting glass substrates have been performed by chemical bath deposition (CBD) and electrodeposition methods, respectively. The deposition conditions have been optimized for getting better quality layers of CdS and CdHgTe. The grown layers of both CdS and CdHgTe have been characterized by photoelectrochemical cell (PEC) measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectrophotometer. Annealing effect of the deposited films has also been investigated. Finally the fabrication of CdHgTe/CdS structure has been performed and investigated by I–V characteristics. PEC, XRD, SEM and UV–vis spectrophotometer studies reveal that chemically deposited CdS layers are n-type with band gap values vary from 2.29 to 2.41 eV and cubic with (111) preferential orientation, and have spherical grain distributed over the surface. However, electrodeposited CdHgTe layers are p-type with band gap values varying from 1.50 to 1.53 eV and cubic with highly oriented CdHgTe crystallites with the (111) planes parallel to the substrate, and have uniform distribution of granular grains over the surface. The fabricated CdHgTe/CdS structure gave an open-circuit photovoltage and a short-circuit photocurrent of 510 mV and 13 mA/cm² respectively, under AM 1.5 illumination.     

Effect of the substrate temperature on the structural, optical and electrical properties of spray-deposited CdS:B films

Boron doped CdS films have been deposited by spray pyrolysis method onto glass substrate temperature in the range of 350–450 °C. And the effect of substrate temperature (T _s) on the structural, electrical and optical properties of the films were studied. The structural properties of boron doped CdS films have been investigated by (XRD) X-ray diffraction techniques. The X-ray diffraction spectra showed that boron doped CdS films are polycrystalline and have a hexagonal (wurtzite) structure. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of substrate temperature. The substrate temperature is directly related with the shift detected in the band gap values derived from optical of parameters and the direct band gap values were found to be in the region of 2.08–2.44 eV. The electrical studies showed that the film deposited at the substrate temperature 400 °C had high carrier concentration and Hall mobility and minimum resistivity. This resistivity value decreased with increase in temperature up to 400 °C indicating the semiconducting nature of B- doped CdS films. The lattice parameter, grain size, microstrain and dislocation densities were calculated and correlated with the substrate temperature (T _s ).     

Performance evaluation of galvanostatically deposited nickel oxide electrode for electrochemical supercapacitors

Nanostructured nickel oxide (NiO) electrode has been prepared using electrochemical work station operated on galvanostatic mode in supercapacitor application. Crystalline cubic structure and nanoplate-type of morphology of synthesized NiO electrode was confirmed from X-ray diffraction and scanning electron microscopy analysis respectively. The wettability study was tested by contact angle measurement, which reveals hydrophilic nature of NiO electrode with contact angle of 59°. The presence of nickel and oxygen characteristic bands in EDAX and XPS spectrum has corroborated the NiO formation. The supercapacitive properties of NiO electrode were tested by cyclic voltammogram (CV) in 1 M aqueous Na₂SO₄, KOH, NaOH electrolytes within the potential range of ??1.1 to 0.9 V, 0 to 0.4 V and ??1.2 to 0.4 respectively. The CV study demonstrates maximum specific capacitance of 481.16 Fg^??1 for 1 M Na₂SO₄. The obtained specific power, specific energy and coulombic efficiency values of NiO electrode are 19.48 kW kg^??1, 60.12 Whkg^??1, and 92.31%, respectively. In the meantime it exhibited excellent cycle life time with 92.3% specific capacitance kept after 1000 cycles. These results imply that NiO electrode is promising candidate for upcoming thin film supercapacitors and other microelectronic constructions.     

Synthesis,thermodynamic and magnetic properties of pure hexagonal close packed nickel

A novel and fast technique for the synthesis of pure hexagonal close packed (HCP) nickel is demonstrated. The HCP nickel was electrodeposited from NiCl₂-1-ethyl-3-methylimidazolium chloride (NiCl₂-EmimCl) ionic liquid at 160 °C. X-ray diffraction confirmed the formation of pure phase. A phase transformation from HCP nickel to face centered cubic (FCC) nickel was observed at 422.6 °C and the enthalpy of transformation was found to be 16.72 J g⁻¹. The phase transformation resulted in the release of hydrogen which makes HCP nickel a potential hydrogen storage material. The electrodeposited nickel showed ferromagnetic properties and the magnetic coercivity was found to be 43 Oe.     

Effect of Ga doping concentrations,substrate temperatures and working pressures on the electrical and optical properties of ZnO thin films

We fabricated Ga-doped ZnO (GZO) thin films on glass substrate by RF magnetron sputtering method with different conditions of Ga₂O₃ concentration, substrate temperature and working pressure. Next we investigated the electrical, optical and structural properties of the GZO thin films. At a substrate temperature of 300 °C, a working pressure of 1 mTorr, and a Ga₂O₃ concentration of 3 wt%, the GZO thin films showed the lowest resistivity of 3.16 × 10^?4 Ω cm, a carrier concentration of 7.64 × 10²⁰ cm^?3 and a Hall mobility of 25.8 cm²/Vs. Moreover, the GZO thin films exhibited the highest (002) orientation under the same conditions and the full width at half maximum of X-ray peak was 0.34°. All GZO thin films showed the optical transmittance of more than 80 % in the visible range regardless of working conditions. The Burstein–Moss effect was observed by the change of doping concentration of Ga₂O₃. The GZO thin films were fabricated to have the good electrical and optical properties through optimizing doping concentration of Ga₂O₃, substrate temperature, working pressure. Therefore, we confirmed the possibility of application of GZO thin film as transparent conductive oxide used in flat panel display and solar cell.     

Cu content dependence of Cu<Subscript>2</Subscript>Zn(SnGe)Se<Subscript>4</Subscript> solar cells prepared by using sequential thermal evaporation technique of Cu/Sn/Cu/Zn/Ge stacked layers

The doping of Cu₂ZnSnSe₄ semiconductor with Ge element has demonstrated improvements to kesterite solar cell efficiency. However, the impact of different Cu concentrations on Cu₂ZnSnGeSe₄/CdS solar cell performance has been poorly studied. In this work, Cu₂ZnSnGeSe₄ thin films with different Cu contents were synthesized by selenization of sequential thermal evaporation precursors. Solar cells based on kesterite-type Cu₂ZnSnGeSe₄ (CZTGSe) were fabricated and the influence of the Cu thickness on the chemical composition and morphology of the layers and electro-optical properties of solar cells was studied. The stacking process was performed at room substrate temperature. Efficiency values in the range of 2.0–6.8% are reported as a function of Cu concentration. The highest efficiency of 6.8%, was achieved for solar cell with glass/Mo/CZTGSe/CdS/i-ZnO/ITO structure using the stacking of Cu (3 nm)/Sn (248 nm)/Cu (112 nm)/Zn (174 nm)/Ge (20 nm).     

Influence of pulse reversal on the performance of pulse electrodeposited copper indium sulphide solar cells

This paper reports for the first time influence of pulse reversal on the properties and performance of pulse electrodeposited CuInS₂ films. The films exhibited single phase chalcopyrite structure. The intensity of the X-ray diffraction peaks become sharp and increase in intensity with increase of pulse reversal time. The crystallite size increases with pulse reversal time. Resistivity of the films decreases from 2.0 to 0.05 Ω cm with increase of pulse reversal time. The mobility and carrier density increase with pulse reversal time. Solar cells fabricated with Mo/CuInS₂/CdS/Ag have yielded reasonable photo outputs.     

Chemical adsorption of NiO nanostructures on nickel foam-graphene for supercapacitor applications

Few-layer graphene was synthesized on a nickel foam template by chemical vapor deposition. The resulting three-dimensional (3D) graphene was loaded with nickel oxide nanostructures using the successive ionic layer adsorption and reaction technique. The composites were characterized and investigated as electrode material for supercapacitors. Raman spectroscopy measurements on the sample revealed that the 3D graphene consisted of mostly few layers, while X-ray diffractometry and scanning electron microscopy revealed the presence of nickel oxide. The electrochemical properties were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and potentiostatic charge–discharge in aqueous KOH electrolyte. The novelty of this study is the use of the 3D porous cell structure of the nickel foam which allows for the growth of highly conductive graphene and subsequently provides support for uniform adsorption of the NiO onto the graphene. The NF-G/NiO electrode material showed excellent properties as a pseudocapacitive device with a high-specific capacitance value of 783 F g^?1 at a scan rate of 2 mV s^?1. The device also exhibited excellent cycle stability, with 84 % retention of the initial capacitance after 1000 cycles. The results demonstrate that composites made using 3D graphene are versatile and show considerable promise as electrode materials for supercapacitor applications.     

Effect of substrate temperature on structural, morphological and optical properties of crystalline titanium dioxide films prepared by DC reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films have been deposited with various substrate temperatures by dc reactive magnetron sputtering method onto glass substrate. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. Chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) analysis of the films revealed that they have polycrystalline tetragonal structure with strong (101) texture. The surface morphological study revealed the crystalline nature of the films at higher substrate temperatures. The TiO₂ films show the main bands in the range 400–700 cm^?1, which are attributed to Ti–O stretching and Ti–O–Ti bridging. The transmittance spectra of the TiO₂ thin film measured with various substrate temperatures ranged from 75 to 90 % in the visible light region. The optical band gap values of the films are increasing from 3.44 to 4.0 eV at growth temperature from 100 to 400 °C. The structural and optical properties of the films improved with the increase in the deposition temperature.     

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Antimony telluride (Sb₂Te₃) thin films were deposited on silicon substrates at room temperature (300 K) by radio frequency magnetron sputtering method. The effects of annealing in N₂ atmosphere on their thermoelectric properties were investigated. The microstructure and composition of these films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. Both of the Seebeck coefficient and Hall coefficient measurement showed that the prepared Sb₂Te₃ thin films were p-type semiconductor materials. By optimizing the annealing temperature, the power factor achieved a maximum value of 18.02 μW cm^?1 K^?2 when the annealing temperature was increased to 523 K for 6 h with a maximum electrical conductivity (1.17 × 10³ S/cm) and moderate Seebeck coefficient (123.9 μV/K).     

Hydrothermal Synthesis,Structural and Electrical Properties of Antimony (Sb3+) Substituted Nickel Ferrites

Antimony (Sb³⁺) doped nickel ferrites have been synthesized by hydrothermal route using an autoclave at 160 ^°C for 12 hours. Pure spinel phase NiSb _x Fe_2?x O₄ (x=0.0 to 0.1) with step increment of 0.035 has been prepared by sintering the precursor samples at 500 ^°C. Structural studies have been performed using X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Lattice parameter and X-ray density found to increase with increase in the antimony concentration. Average crystallite size lies in the range of 14 to 24 nm?±?2 nm. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) have been used to characterize the morphology and sizes of nanoparticles. Electrical properties were analyzed by measuring DC-electrical resistivity, complex dielectric permittivity, AC conductivity and complex electrical modulus analysis. DC resistivity of nickel ferrites decreases due to the substitution of antimony from 6.7×10⁸ to 3.4×10⁷ Ω-cm. Dielectric permittivity and losses were studied in the frequency range of 20 Hz–5 MHz and found to increase due to addition of Sb³⁺ in nickel nanoferrites at room temperature. High dielectric permittivity and conductivity made this material a compatible option for single-layered and multilayered chip inductors.     

Raman,photoluminescence analysis on Cu(InAl)Se2 thin films and the fabrication of Cu(InAl)Se2 based thin film solar cells

Cu(InAl)Se₂ (CIAS) thin films have been prepared by chemical bath deposition technique. Thickness of the prepared films has been measured by gravimetric technique. The structure, composition and optical transition as well as bandgap have been estimated by X-ray diffraction, energy dispersive X-ray analysis and spectrophotometer analysis. Raman analysis has been made on the prepared CIAS thin films to assign the fundamental lattice mode and to confirm the films crystallinity and stoichiometry. PL analysis has been carried out to find the effective mass of holes and electron, dielectric constant, the involved defects and their activation energy. Cu(InAl)Se₂-based solar cells with different types of buffer layers such as CdS, CdS:Cu, CdS:In were fabricated. The current and voltage were measured using an optical power meter and an electrometer and the fabricated solar cells were illuminated using 100 mW/cm² white light under AM1 conditions.     

Enhanced photovoltaic performance of solar cell based on front-side illuminated CdSe/CdS double-sensitized TiO2 nanotube arrays electrode

Free-standing TiO₂ nanotube (NT) arrays have been prepared by a two-step anodization method. These translucent TiO₂ NT arrays can be transferred to the fluorine-doped tin oxide glass substrates to form front-side illuminated TiO₂ NT electrodes. The TiO₂ NT electrodes were double-sensitized by CdSe/CdS quantum dots (QDs) through successive ionic layer adsorption and reaction (SILAR) process. The absorption range of the TiO₂ NT electrode was extended from ~380 to 700 nm after sensitization with CdSe/CdS QDs. The SILAR cycles were investigated to find out the best combination of CdS and CdSe QDs for photovoltaic performance. The power conversion efficiency of 2.42 % was achieved by the CdSe(10)/CdS(8)/TiO₂ NT solar cell. A further improved efficiency of 2.57 % was obtained with two cycles of ZnS overlayer on the CdSe(10)/CdS(8)/TiO₂ NT electrode, which is 45.19 % higher than that of back-side illuminated solar cell. Furthermore, the ZnS(2)/CdSe(10)/CdS(8)/TiO₂ NT solar cell possesses a higher stability than CdSe(10)/CdS(8)/TiO₂ NT solar cell during the same period. The better photovoltaic performance of the ZnS(2)/CdSe(10)/CdS(8)/TiO₂ NT solar cell has demonstrated the promising value to design quantum dots-sensitized solar cells with double-sensitized front-side illuminated TiO₂ NT arrays strategy.     

Effect of the substrate temperature on the properties of spray-deposited SnO2:F thin films

The effect of the substrate temperature on the properties of spray-deposited SnO₂:F thin films is investigated. X-ray diffraction patterns show that the crystallinity of the films is enhanced with the increasing of substrate temperature. Comparing the SEM images, both the particle size and density are increased at a higher deposition temperature. The lowest sheet resistance of 8.43 Ω/□ is obtained at the substrate temperature of 350 °C. In addition, the average optical transmittance of the three films reaches up to 85 % in the visible range. The absorption coefficient is the lowest at 350 °C. The band gap increases from 3.36 to 3.61 eV while the electrical resistivity of SnO₂:F thin films decreases from 8.51 × 10^?3 to 9.86 × 10^?4 Ω cm as elevating the substrate temperature from 250 to 350 °C.     

Chemical deposition of CdS films: structure,RBS, PIXE,optical and photoelectrochemical solar cell studies

CdS semiconductor films have been chemically prepared from a basic solution containing CdSO₄, thiourea and NH₄OH. X-ray diffraction studies have revealed the presence of polycrystalline mixed cubic and hexagonal phases of CdS in the deposit. The surface topography has been identified by SEM analysis and found to be non-uniform and spongy. Rutherford Backscattering Spectrometry (RBS) analysis gave the Cd to S ratio as 1.016 whereas that of Proton Induced X-ray Emission (PIXE) analysis gave the Cd to S ratio as 0.905. The band gap of the CdS film has been estimated from optical absorption studies and found to be 2.46 eV. The CdS/S^2–, S₂ ^2– interface has been characterized in order to identify the charge transfer process. Finally, Photoelectrochemical Solar Cells (PESCs) have been fabricated with cell configuration Ti/CdS/S^2–, S₂ ^2–/Pt and the results have been discussed.     

Characterization of In<Subscript>1 − x</Subscript>Cd<Subscript>x</Subscript>S,In<Subscript>2</Subscript>S<Subscript>3</Subscript> and CdS thin films grown by SILAR method

Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit In_1???xCd_xS, In₂S₃ and CdS thin films on glass substrate at room temperature. The crystal structure and crystal size of the thin films were characterized by X-ray diffraction (XRD) method. Scanning Electron Microscopy (SEM) was used to determine morphology and composition of the films. Optical and electrical properties of these films have been investigated as a function of temperature. The photoluminescence measurements were carried out at room temperature and absorption measurements were carried out in the temperature range 10–320 K with a step of 10 K. The band gap energies for CdS, In_0.8Cd_0.2S, In_0.6Cd_0.4S, In_0.4Cd_0.6S, In_0.2Cd_0.8S and In₂S₃ thin films were found as 2.22 eV, 2.56 eV, 2.52 eV, 2.46 eV, 2.38 eV, and 2.72 eV, respectively. The refractive indices (n), optical static and high frequency dielectric constants (\({\in }_{0}\), \({\in }_{{\infty}}\)) values have been calculated by using the energy bandgap values. The electrical resistivity of CdS, Cd_0.5In_0.5S and In₂S₃ thin films have been determined using a ‘dc’ two probe method, in the temperature range of 300–450 K. The electrical resistivity values have been calculated at 300 K.     

Thin film solar cells based on the ternary compound Cu2SnS3

Alongside with Cu₂ZnSnS₄ and SnS, the p-type semiconductor Cu₂SnS₃ also consists of only Earth abundant and low-cost elements and shows comparable opto-electronic properties, with respect to Cu₂ZnSnS₄ and SnS, making it a promising candidate for photovoltaic applications of the future. In this work, the ternary compound has been produced via the annealing of an electrodeposited precursor in a sulfur and tin sulfide environment. The obtained absorber layer has been structurally investigated by X-ray diffraction and results indicate the crystal structure to be monoclinic. Its optical properties have been measured via photoluminescence, where an asymmetric peak at 0.95 eV has been found. The evaluation of the photoluminescence spectrum indicates a band gap of 0.93 eV which agrees well with the results from the external quantum efficiency. Furthermore, this semiconductor layer has been processed into a photovoltaic device with a power conversion efficiency of 0.54%, a short circuit current of 17.1 mA/cm², an open circuit voltage of 104 mV hampered by a small shunt resistance, a fill factor of 30.4%, and a maximal external quantum efficiency of just less than 60%. In addition, the potential of this Cu₂SnS₃ absorber layer for photovoltaic applications is discussed.     

Super-capacitive performance depending on different crystal structures of MnO2 in graphene/MnO2 composites for supercapacitors

In the present study, we synthesize nanoneedle structures of MnO₂/graphene nanocomposites (N-RGO/MnO₂) and birnessite-type MnO₂/graphene nanocomposites (B-RGO/MnO₂). The morphologies and microstructures of as-prepared composites are characterized by X-ray diffractometry, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Our characterizations indicate that nanoneedle structures of MnO₂ and birnessite-type MnO₂ are successfully formed on graphene surfaces. Capacitive properties of the N-RGO/MnO₂ and B-RGO/MnO₂ electrodes are measured using cyclic voltammetry, galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy in a three-electrode experimental setup using a 1 M Na₂SO₄ aqueous solution as the electrolyte. The N-RGO/MnO₂ electrode displays a specific capacitance as high as 327.5 F g^?1 at 10 mV s^?1, which is higher than that of a B-RGO/MnO₂ electrode (248.5 F g^?1). It is believed that the nanoneedle structure of MnO₂ shows excellent electrochemical properties than birnessite-type MnO₂ for the electrode materials for supercapacitors.     

Application of ultra-thin CdS film as buffer layer in non-doped blue organic light-emitting diodes

The device inserted 0.5 nm thick cadmium sulfide (CdS) as buffer layer, prepared by vacuum thermal evaporation method, has been studied on the non-doped blue organic light-emitting diode. Compared to the device without ultra-thin CdS film, the maximum luminance of the device with ultra-thin CdS film was 11,370 cd/m² at 11 V, and the maximum current efficiency reached 3.10 cd/A, increased 1.5 times and 1.2 times, respectively. In the optimized devices with the structure of ITO/MoO₃ (10 nm)/TPABBI (35 nm)/Bphen (40 nm)/CdS (0, 0.1, 0.3 and 0.5 nm)/LiF (0.5 nm)/Al (100 nm), the effects of CdS layer on the photoelectric performance of the devices were investigated in detail. When the CdS thickness was 0.3 nm, the maximum luminance was 13,590 cd/m² at 9 V and the turn on voltage was only 3 V. The maximum current efficiency of 3.42 cd/A was obtained. It is indicated that the simple structure of the device with inserted ultra-thin CdS film, cheap and stable inorganic photoelectric material, may be a promising way to fabricate hybrid organic–inorganic LEDs with high performances.