Preparation of CuInSe2 films by an electrophoretic deposition technique

Films of CuInSe₂ with a thickness of about 10 μm have been prepared by an electrophoretic method from a suspension containing CuInSe₂ powder, acetone, alcohol and tetramethylammonium hydroxide. The as-deposited films were soft; however, the quality was improved after a heat treatment at temperatures above 700 °C.     

Electrochromic effect in WO3 thin films prepared by spray pyrolysis

Polycrystalline WO₃ thin films were produced by spray pyrolysis on corning glass or ITO coated glass substrates. The optical, electrical and structural properties of these films were studied as a function of preparation conditions in their colored state. The transmittance value decreased from 80% to 5% when the films were colored. This was accompanied by an increase of the reflectivity in the NIR region. In addition, the electrical conductivity varied with heat treatment temperature. The change in electrical conductivity indicates that WO₃ films exhibit a semiconducting behavior in their colored state. Furthermore, a change in the structure of the films from monoclinic to cubic was observed upon coloration. The electrochemical behavior was investigated in 1 M H₂SO₄/H₂O solution using a three-electrode cell.     

Effect of doping and heat treatment on the photoluminescence of CdS films deposited by spray pyrolysis

Large area thin films of n-type CdS were prepared by spray pyrolysis technique. The films were n-type doped by having [In/Cd] ion concentration ratio of 10⁻⁶, 10⁻⁵, 10⁻⁴, 10⁻³, and 10⁻² in the sprayed solution. These films were heat treated in N₂ atmosphere at 450°C for 1 h. The as-deposited undoped, doped, and heat treated were analyzed by photoluminescence (PL) at 5 K sample temperature. In general, the spectra displayed three main emission regions (green, yellow and red) with more than one band in each. The emission intensity is found to decrease with doping and the relative intensity of the bands is found to depend on the doping concentration level. The red band is only present in doped samples and its relative intensity is found to increase with doping. The effect of heat treatment in N₂ on the as-deposited undoped and the doped (10⁻⁴) samples on the relative intensity of the observed bands were compared and discussed. The results are compared with the electrical and morphological results and correlated with the probable changes in the concentration of shallow and deep radiative native defects and structural changes. These allow for better prediction of suitable doping and treatment conditions for good quality films.     

Fabrication of three-dimensional nanoporous nickel films with tunable nanoporosity and their excellent electrocatalytic activities for hydrogen evolution reaction

Three-dimensional (3D) nanoporous nickel films were fabricated by a novel and facile method. The fabrication process involved the heat treatment of the electrodeposited zinc layer on nickel substrate and the subsequent electrochemical dealloying. The mutual diffusion of Ni and Zn during the heat treatment resulted in the formation of the Ni₂Zn₁₁ alloy surface film. The 3D nanoporous nickel films with open pores and interconnected ligaments were obtained by the electrochemical dealloying of relatively active zinc from the alloy surface film. As the electrodeposited zinc amount increased, the thickness, pore diameter and pore density of the nanoporous nickel films became larger. In our experimental range, the thickest nanoporous nickel film presented a thickness of 8 μm and an average pore diameter of 700 nm. The as-prepared 3D nanoporous nickel films exhibited much higher electrocatalytic activity for hydrogen evolution reaction (HER) than smooth nickel foil, and their electrocatalytic activities for HER enhanced with increase in the porosity and thickness. It was concluded that the enhanced electrocatalytic activity and excellent electrochemical stability for HER of the as-prepared 3D nanoporous nickel films can be ascribed to their unique nanostructured characteristics.     

The sol-gel route: A versatile process for up-scaling the fabrication of gas-tight thin electrolyte layers

Sol-gel routes are often investigated and adapted to prepare, by suitable chemical modifications, submicronic powders and derived materials with controlled morphology, which cannot be obtained by conventional solid state chemistry paths. Wet chemistry methods provide attractive alternative routes because mixing of species occurs at the atomic scale. In this paper, ultrafine powders were prepared by a novel synthesis method based on the sol-gel process and were dispersed into suspensions before processing. This paper presents new developments for the preparation of functional materials like yttria-stabilized-zirconia (YSZ, 8% Y₂O₃) used as electrolyte for solid oxide fuel cells. YSZ thick films were coated onto porous Ni-YSZ substrates using a suspension with an optimized formulation deposited by either a dip-coating or a spin-coating process. The suspension composition is based on YSZ particles encapsulated by a zirconium alkoxide which was added with an alkoxide derived colloidal sol. The in situ growth of these colloids increases significantly the layer density after an appropriated heat treatment. The derived films were continuous, homogeneous and around 20 μm thick. The possible up-scaling of this process has been also considered and the suitable processing parameters were defined in order to obtain, at an industrial scale, homogeneous, crack-free, thick and adherent films after heat treatment at 1400 °C.     

Temperature effect on the electrical properties of pyrolytic MnO2 thin films prepared from Mn(C2H3O2)2·4H2O

Spray deposited MnO₂ thin films onto glass substrate were subjected to a post-deposition heat treatment and the effects of temperature on electrical transport properties were studied in details. The heating and cooling cycles of the samples are reversible after successive heat-treatments in air and vacuum. The films were polycrystalline in structure and the oxygen chemisorption–desorption process was found to play an important role in controlling the electronic properties. Various grain-boundary and energy band parameters were calculated by taking conventional extrinsic semiconductor theory and grain boundary trapping models into account. The samples were non-degenerate n-type semiconductors. The transport properties are interpreted in terms of Seto's model which was proposed for polycrystalline semiconducting films. The inter-crystallite boundaries of the thin films play an important role in the transport properties.     

Electrochromic properties of one-dimensional tungsten oxide nanobundles

In this study, one-dimensional (1D) tungsten oxide nanobundles (TNB) were synthesized via a simple solvothermal method. The phase of 1D tungsten oxide was W₁₈O₄₉, and the diameter and length of the building units (nanowires) were about 7 and 800 nm, respectively. TNB films were fabricated by the Langmuir–Blodgett (LB) method. The locally arranged domains of the long nanobundles form the LB films, but it is difficult for them to align perfectly owing to the inter-nanobundle interaction and dispersion problems. The electrochromic (EC) property of the TNB LB films was characterized by electrochemical potential cycling tests and in situ transmittance measurement. The deposition condition of the LB films influenced their EC property. The heat treatment and surface pressure of the TNB LB films plays an important role in the response time and transmittance of the TNBs.     

Stability of SnO2 thin films used for photovoltaic devices

Conducting films of SnO₂, prepared by RF Sputtering, were studied for their stability following a heat treatment at 200°C in air. Auger Spectroscopy was used to analyze the surface and bulk compositions both before and after the tests. The results so obtained, indicated that the main changes in the film took place in the first 400 Å. This was viewed as seriously limiting the efficiency of solar cells employing transparent windown on the front surface.     

Electrochromic characterization of Co(OH)2 thin film prepared by sol–gel process

Electrochemical, spectroscopic and structural measurements were used to characterize the electrochromic behavior and stability of sol–gel deposited Co(OH)₂ thin films. These films were prepared from polymeric solutions containing cobalt methoxyethoxide precursor by spin coating technique. The as-deposited films are amorphous and show crystalline structure after heat treatment at 450°C. Sol–gel-deposited cobalt hydroxide films show reversible electrochromic response in 1 M LiClO₄/ propylene carbonate solution beyond 500 cycles. The structural and chemical properties of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Spectral transmittance change was T_p=29.9–60.2% for cobalt hydroxide films. It is argued that reversible lithium insertion capacity, good cyclic reversibility of Co(OH)₂ films make them suitable as counterelectrode layers in the electrochromic devices.     

Structural and optical properties of CuInTe2 films prepared by thermal vacuum evaporation from a single source

The CuInTe₂ thin films were prepared by thermal vacuum evaporation from a single source. The effects of heat treatment on both structural an optical properties of CuInTe₂ films were studied. X-ray diffraction studies reveal that the films prepared by the present method showed formation of single phase CuInTe₂ at heating treatment temperature higher than 300°C. The calculated lattice constants for CuInTe₂ films annealed at 300°C were found to be and . The value of the grain size obtained in these films was of the order of 50 nm. The value of optical energy gap (0.97 eV) and the dispersive refractive index n(λ) for CuInTe₂ film annealed at 300°C were evaluated by optical absorption measurement.     

Electrochromic properties of heat-treated thin films of CeO2–TiO2–ZrO2 prepared by sol–gel route

CeO₂–TiO₂–ZrO₂ thin films were prepared using the sol–gel process and deposited on glass and ITO-coated glass substrates via dip-coating technique. The samples were heat treated between 100 and 500 °C. The heat treatment effects on the electrochromic performances of the films were determined by means of cyclic voltammetry measurements. The structural behavior of the film was characterized by atomic force microscopy and X-ray diffraction. Refractive index, extinction coefficient, and thickness of the films were determined in the 350–1000 nm wavelength, using nkd spectrophotometry analysis.Heat treatment temperature affects the electrochromic, optical, and structural properties of the film. The charge density of the samples increased from 8.8 to 14.8 mC/cm², with increasing heat-treatment temperatures from 100 to 500 °C. It was determined that the highest ratio between anodic and cathodic charge takes place with increase of temperature up to 500 °C.     

Reaction kinetics study of CdTe thin films during CdCl2 heat treatment

In order to investigate the effect of CdCl₂ heat treatment on the physical properties of CdTe thin films grown by a sputtering method, the CdTe thin films were coated with CdCl₂. The recrystallization, grain growth, randomization, and reaction kinetics were investigated by monitoring the phase transition of CdCl₂-heat-treated CdTe specimens during temperature ramp annealing or isothermal soaking by using in-situ time-resolved high-temperature X-ray diffraction. The results of annealing show that the recrystallizations of CdTe (1 1 1) and other planes do not occur simultaneously, but sequentially in terms of temperature. The results of isothermal soaking imply that the Avrami diffusion-controlled reaction model fits well with the experimental data. This proves that the CdCl₂ diffusion process is the dominant factor in the CdTe recrystallization mechanism.     

Effects of annealing on the properties of SnSe films

Tin selenide thin films were deposited potentiostatically from an unstirred aqueous solution containing Sn-EDTA and Na₂SeO₃ onto indium-doped tin oxide glass substrates. The difference in the structural and compositional properties of the film before and after heat treatment in a nitrogen atmosphere were studied. The as-grown and treated films were characterised using various techniques such as X-ray diffractometry, scanning electron microscopy and energy-dispersive X-ray analysis. Photoactivity of the samples was studied using linear sweep voltammetry. An annealing temperature of 150°C was found to be the optimum temperature.     

Electrodeposited cuprous oxide on indium tin oxide for solar applications

Semiconducting cuprous oxide films were prepared by electrodeposition onto commercial conducting glass coated with indium tin oxide deposited by spraying technique. The cuprous oxide (Cu₂O) films were deposited using a galvanostatic method from an alkaline CuSO₄ bath containing lactic acid and sodium hydroxide at a temperature of 60°C. The film's thickness was about 4–6 μm. This paper includes discussion for Cu₂O films fabrication, scanning electron microscopy and X-ray diffractometry studies, optical properties and experimental results of solar cells. The values of the open circuit voltage V_oc of 340 mV and the short circuit current density I_sc of 245 μA/cm² for ITO/Cu₂O solar cell were obtained by depositing graphite paste on the rear of the Cu₂O layer. It should be stressed that these cells exhibited photovoltaic properties after heat treatment of the films for 3 h at 130°C. An electrodeposited layer of Cu₂O offers wider possibilites for application and production of low cost cells, both in metal–semiconductor and hetero-junction cell structures, hence the need to improve the photovoltaic properties of the cells.     

Heat treatment effects on the optical properties of Sol–gel Ta2O5 thin films

In this work optical properties of Ta₂O₅ thin films with respect to heat treatment temperature were investigated. Ta₂O₅ thin films were prepared by sol–gel process using dip-coated method with a constant speed of 107 mm/min. Optical properties have been calculated from optical transmission measurements as a function of heat treatment temperature. The refractive indices and absorption coefficients were affected by heat treatment. The refractive index at λ=550 nm increased from 1.84 to 2.04 and absorption coefficient increased from 241 to 5668 cm⁻¹ when heat treatment temperature increased from 100°C to 500°C. The thickness of the film decreased from 272 to 190 nm and their optical band gap decreased from 3.68±0.09 eV to 3.51±0.08 eV for the film heated from 100°C to 500°C.     

Effect of TiO2 mixtures on the optical, structural and electrochromic properties of Nb2O5 thin films

Metal oxide films are important for various optical devices and especially for solar energy materials. TiO₂-mixed Nb₂O₅ thin films have been produced by sol–gel dip-coating method. Several parameters such as heat treatment, thickness, and mixture percentages are studied for the effect of the optical, structural and electrochromic properties of the materials. Optical parameters of the films were calculated through transmission and reflection measurement by a refractive index, extinction coefficient and thickness analyzer. Structural, electrochromic and surface analyses of the films were done by X-ray diffractometer, potentiostat/galvanostat and atomic force microscope systems.     

Substrate temperature effect on transparent heat reflecting nanocrystalline ITO films prepared by electron beam evaporation

In this study, indium tin oxide (ITO) thin films were preparedon glass substrate by electron beam evaporation technique and then were annealed in air atmosphere at 350 °C for 30 min. Increasing substrate temperature (T_s) from 25 to 380°°C reduced sheet resistance of ITO thin films from 150(Ω/□) to 14(Ω/□). The UV-visible-near IR transmittance and reflectance spectra were also confirmed that the substrate temperature has significant effect on the properties of heat reflecting thin films. High transparency (83%) over the visible wavelength region of spectrum and (over 90%) reflectance in near-IR region were obtained at T_s = 300° C. Plasma wavelength, carrier concentrations (n_e) and refractive index of the layer were also calculated. The allowed direct band gap at the temperature range 100–300° C was estimated to be in the range 3.71–3.89 eV. Band gap widening due to increase in substrate temperature was observed and is explained on the basis of Burstein-Moss shift. XRD patterns showed that the films were polycrystalline. High quality crystalline thin films with grain size of about 40 nm were obtained.     

Optical properties of electrodeposited CdTe thin films

The absorption coefficient spectra of the elctrodeposited CdTe thin films were analyzed and compared with that of the single crystal. Pinhole-free thin films facilitated the analysis of the high-energy regions of the absorption coefficient spectra. The various allowed direct and indirect transitions were detected successively by subtracting the extrapolated values of the lower-energy transitions. The effect of heat treatment on the optical transitions were analyzed with films annealed at 300°C in air, argon and CdCl₂.The direct band gap of the electrodeposited films decreased with increasing film thickness and approaches the value of the single crystal. The films annealed at different environments show slightly lower value for the band gap. Annealing in argon caused significant change in the optical transition spectra.     

Effects of surface modification on the PEC performance of electrochemically deposited n-CdTe films

CdTe thin films were electrodeposited on Ni substrates from aqueous solutions containing CdSO₄, TeO₂ and H₂SO₄ with an interchangeable rotating disk electrode. The variations in the composition of the CdTe films with cathodic potentials and heat treatment temperatures were studied by the polarographic method. The deposition and annealing parameters had been optimized to yield a good photoelectrochemical performance. After surface modification, the conversion efficiencies were 0.61% and 5.3% for the cells p-CdTe/SnCl₂ (sat.), 0.2M HCl/C and n-CdTe/1 M Na₂S, 1 M S, 1 M NaOH/C, respectively.     

The effects of various annealing regimes on the microstructure and physical properties of ITO (In2O3:Sn) thin films deposited by electron beam evaporation for solar energy applications

The goal of this study has been to investigate the influence of various post-deposition heat treatments on the microstructure, electrical and optical properties of In₂O₃:Sn (ITO) thin films deposited by electron beam evaporation. We have shown that electron beam evaporated ITO thin films deposited onto substrates kept upto 150 °C, have poor electrical properties and low optical transmission in the visible range, due to their amorphous structure. As the microstructure changes from amorphous to polycrystalline it was observed that the film resistivity decreases and it is simultaneously related to an improvement in the optical transmission. From comparisons of several annealing processes it has been observed that oxygen plays an important role in doping as well as the presence of Sn in the target material. Furthermore we have shown that high quality ITO thin films can be reproducibly prepared with optical transmission being enhanced by an annealing in air and the electrical characteristics being improved by a further annealing in a reducing atmosphere. Superior electrical and optical properties could be correlated with annealed films that exhibited a cubic bixbyte structure and large crystallite dimensions larger than 50 nm.