Materials properties of electrodeposited SnS0.5Se0.5 films and characterization of photoelectrochemical solar cells

Thin films of tin sulfoselenide (SnS_0.5Se_0.5) have been electrodeposited from an aqueous solution on tin oxide coated glass substrates by potentiostatic technique. XRD pattern of SnS_0.5Se_0.5 films showed polycrystalline nature and orthorhombic structure. The presence of Sn, S, and Se of the films were confirmed by XPS analysis. All films showed an indirect band gap. Surface morphological studies were carried out using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analyses. Mott-Schottky plots have been drawn (in the dark condition) to evaluate the semiconductor parameters which confirmed the p-type nature of the films. The photoelectrochemical behavior of the SnS_0.5Se_0.5 films was studied in the electrolyte containing 0.1 M (FeCl₂/FeCl₃) + 0.05 M H₂SO₄ and the results are reported.     

Effect of TiCl4 treatment on the photoelectrochemical properties of LaTiO2N electrodes for water splitting under visible light

A lanthanum titanium oxynitride (LaTiO₂N) electrode was studied as a visible-light driven photoelectrode for water splitting. The electrode was prepared by casting a LaTiO₂N powder on a fluorine-doped tin oxide glass substrate, followed by calcination under dinitrogen. The as-prepared electrode exhibited an anodic photocurrent based on water oxidation under visible-light irradiation (λ > 420 nm) in an electrolyte (Na₂SO₄) solution. This current was increased by post-treatment with titanium(IV) chloride (TiCl₄) solution. Scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the titanium species introduced by the post-treatment were titanium oxide, and that they were embedded within LaTiO₂N particles. Resistance measurements of LaTiO₂N electrodes suggested that the increase in the electrode photocurrent after TiCl₄ treatment was due to the improvement of inter-particle electron transfer in the LaTiO₂N thin film.     

Facile conversion of bulk metal surface to metal oxide single-crystalline nanostructures by microwave irradiation: Formation of pure or Cr-doped hematite nanostructure arrays

We report a method for converting the surfaces of bulk metal substrates (pure iron or stainless steel) to metal oxide (hematite or Cr-doped hematite) nanostructures using microwave irradiation. When microwave radiation (2.45 GHz, single-mode) was applied to a metal substrate under the flow of a gas mixture containing O₂ and Ar, metal oxide nanostructures formed and entirely covered the substrate. The nanostructures were single crystalline, and the atomic ratios of the substrate metals were preserved in the nanostructures. When a pure iron sheet was used as a substrate, hematite nanowires (1000 W microwave radiation) or nanosheets (1800 W microwave radiation) formed on the surface of the substrate. When a SUS410 sheet was used as a substrate, slightly curved rod-like nanostructures were synthesized. The oxidation states of Fe and Cr in these nanorods were Fe³⁺ and Cr³⁺. Quantitative analyses revealed an average Fe/Cr atomic ratio of 9.2, nearly identical to the ratio of the metals in the SUS410 substrate.     

Titanium dioxide thin films prepared by electrolysis from aqueous solution of titanium-lactic acid complex for dye-sensitized solar cells

Titanium oxide (TiO_x) thin films were prepared on transparent conducting substrate (fluorine-doped tin oxide) by cathodic electrolysis of a solution containing a titanium bis(ammonium lactato)dihydroxide and an ammonium nitrate at 323 K. Post-deposition treatment: calcination at 723 K or hot-water treatment at > 363 K promoted the growth of an anatase type crystalline phase in the TiO₂ thin film, as evidenced by X-ray diffraction and X-ray photoelectron spectroscopy. The calcined films were used as electrodes of a dye-sensitized solar cells and the cells' energy conversion efficiency was comparable to that obtained with commercially available TiO₂ nanoparticle electrodes.     

Sputtering deposition of amorphous cadmium stannate as transparent conducting oxide

In this work we studied deposition conditions by RF sputtering of ternary oxides of Cd and Sn, starting from Cd₂SnO₄ target and varying substrate temperature, sputtering power and deposition gas (from inert Ar to oxidizing 50% Ar-50% O₂ atmosphere). The aim of this study was to obtain thin films for use as Transparent Conducting Oxide (TCO). TCOs are oxides that couples low sheet resistance and high transparency that find application in many fields like solar cells, light emitting diodes and transparent thin film transistors.Thin films functional properties were characterised by means of sheet resistance and transmittance measurements in the visible region, and film composition and structure were investigated by total reflection X ray fluorescence and glancing incidence X ray diffraction. Morphology was studied by Atomic Force Microscopy and Scanning Electron Microscope and showed very smooth surface suitable for solar cells application. Composition and phase analysis allowed us to discuss possible correlation of film structure with functional properties. Deposition in inert atmosphere at 400 °C substrate temperature was selected for its low sheet resistance and high transparency that are comparable to the ones of commercial TCOs like indium tin oxide or SnO₂: F. The thin film obtained in these conditions was amorphous, and it crystallized into CdSnO₃ ilmenite phase when annealed at 700 °C; segregation of Sn₃O₄ was also observed. Since sheet resistance of thin films increases after annealing treatments, amorphous thin film was selected for future applications.     

Development and characterization of fluorine tin oxide electrodes modified with high area porous thin films containing gold nanoparticles

Different electrode materials are prepared using fluoride doped tin oxide (FTO) electrodes modified with high area porous thin films of metal oxides containing gold nanoparticles. Three different metal oxides (TiO₂, MgO and SnO₂) have been assayed to this end. The effect of the metal oxide nature and gold loading on the structure and performance of the modified electrodes was examined by Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy and electrochemical techniques. XRD measurements reveal that MgO electrodes present the smallest gold nanoparticles after the sintering step however, the electrochemical response of these electrodes shows important problems of mass transport derived from the high porosity of these materials (Brunauer Emmett Teller area of 125 m²/g). The excellent sintering properties of titania nanoparticles result in robust films attached to the FTO electrodes which allow more reliable and reproducible results from an electroanalytical point of view.     

Structural and magnetic properties of phase controlled iron oxide rods

Iron oxide rods are synthesized by thermal decomposition of iron (II) acetate at 700 °C. The X-ray powder diffraction measurement confirms the hematite (α-Fe₂O₃) phase of iron oxide. We observed that the Morin transition depends on applied magnetic field and shift towards lower temperature with increase in applied magnetic field. The Morin temperature at applied field of 500 and 2000 Oe is observed to be 261.1 and 260.3 K respectively. Magnetization versus magnetic field measurements confirms the antiferromagnetic behavior below Morin transition and weak ferromagnetic behavior above Morin transition.     

Solid-phase reaction synthesis of mesostructured tungsten disulfide material with a high specific surface area

A mesostructured tungsten disulfide (WS₂) material was prepared through a solid-phase reaction utilizing ammonium tetrathiotungstate as the precursor and n-octadecylamine as the template. The as-synthesized WS₂ material was characterized by X-ray powder Diffraction (XRD), Low-temperature N₂ Adsorption (BET method), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The characterization results indicate that the WS₂ material has the typical mesopore structure (3.7 nm) with a high specific surface area (145.9 m²/g), and large pore volume (0.18 cm³/g). This approach is novel, green and convenient. The plausible mechanism for the formation of the mesostructured WS₂ material is discussed herein.     

Evaluation of different deposition conditions on thin films deposited by electrostatic spray deposition using a uniformity test

Copper indium disulphide films were produced by electrostatic spray deposition using a water/alcohol solution of copper chloride (CuCl₂), indium chloride (InCl₃) and thiourea (CS(NH₂)₂) sprayed onto SnO₂:F coated glass substrates. The influence of various deposition parameters, namely substrate temperature (380-450 °C), applied voltage (12-18 kV), solution concentration (0.21-0.49 M), flow rate (25-200 μl/min) and needle-substrate distance (40-70 mm) were investigated. particle image velocimetry measurements were made of the spray cone and correlated with the film uniformity. The film uniformity was measured using an optically based test developed in-house. Results show that the highest concentrated spray solution and lowest deposition temperature produce non-uniform films. In contrast, a needle-substrate distance of 50 mm, and the lowest applied voltage and flow rate resulted in the most uniform films.     

Catalytic activity and magnetic properties of barium hexaferrite prepared from barite ore

Barium hexaferrite (BaFe₁₂O₁₉) has traditionally been used in permanent magnets and more recently used for high density magnetic recording. The classical ceramic method for the preparation of barium hexaferrite consists of firing mixture of chemical grade iron oxide and barium carbonate at high temperature. In this paper a mixture of chemical grade hematite, barium oxide and predetermined mixtures of iron oxide ore and barite ore containing variable amounts of coke were used to prepare barium hexaferrite (BaFe₁₂O₁₉) as a permanent magnetic material. The mixtures were mixed in a ball mill and fired for 20 h in a tube furnace at different temperatures (1100, 1150, 1200 and 1250 °C). XRD, magnetic properties, porosity measurements and catalytic activity were used for characterization of the produced ferrite. The results of experiments showed that the optimum conditions for the preparation of barium hexaferrite are found at 1200 °C for the mixture of chemical grade hematite and barium oxide. It was also found that the barium hexaferrite can be prepared from the iron and barite ores at 1200 °C. The addition of coke enhanced the yield of barium hexaferrite and improved its physicochemical properties. Samples prepared from ores with coke% = 0 show the most acidic active sites, they show a higher catalytic activity towards H₂O₂ decomposition. With addition of coke the catalytic activity decreases due to the poisoning effect of carbon on the available active site.     

New transparent conductive films: FTO coated ITO

New transparent conductive films, fluorine doped tin oxide (FTO) films coated on indium-tin-oxide (ITO) films, were developed. These transparent conductive films were prepared by the spray pyrolysis deposition method at a substrate temperature of 350 °C in ITO and 400 °C in FTO. For ITO deposition, an ethanol solution of indium(III) chloride, InCl₃·4H₂O, and tin(II) chloride, SnCl₂·2H₂O [Sn/(In+Sn), 5 at.%] was sprayed on a Corning #7059 glass substrate (100×100×1.1 mm³). After the deposition, FTO films were consecutively deposited for protecting oxidation of ITO films. FTO deposition was carried out by an ethanol solution of tin(IV) chloride, SnCl₄·5H₂O within the saturated water solution of NH₄F. These new transparent conductive films achieved the lowest resistivity of 1.4×10⁻⁴ Ω cm and the optical transmittance of more than 80% in the visible range of the spectrum. The electrical resistance of these new transparent conductive films increased by less than 10% even when exposed to high temperatures of 300-600 °C for 1 h in the air.     

Transparent nanoporous tin-oxide film electrode fabricated by anodization

A transparent nanoporous tin oxide film electrode was fabricated by anodizing a tin film on a fluorine-doped tin oxide (FTO) film electrode. The resulting anodized nanoporous tin oxide (ANPTO) film has columnar-type pore channels with around 50 nm in diameter and is optically transparent. Electrochemical measurements with Fe(CN)₆³⁻ as a redox probe clearly revealed that the ANPTO film could be used for a working electrode with a large internal surface area. Moreover, it was found that ANPTO film had a wider anodic potential window (> ca. 2.0 V) than conventional metal oxide electrodes, such as FTO and indium tin oxide film electrodes (> ca. 1.3 V). The wide anodic potential window improves applicability of a transparent metal oxide electrode for various electrochemical oxidation reactions, which are often interfered by oxygen evolution in water. These results conclude that the ANPTO film can be used as an advanced transparent nanoporous film electrode.     

Titanium and zirconium hard coatings on glass substrates prepared by the sol-gel method

In this work innovative antiscratch sol-gel coating films deposited on a soda-lime glass substrate are examined. Sol-gel coatings of different composition (TiO₂, TiO₂/B₂O₃, ZrO₂ and ZrO₂/B₂O₃) were prepared starting from Titanium, Zirconium and Boron alkoxides and from boron oxide. Coatings were obtained at room temperature and at atmospheric pressure by dip-coating using common soda lime silicate glass slides as substrates. Densification was carried out at 550 °C for 2 h in air. The morphology of the coatings has been studied by Atomic Force Microscopy, Scanning Electron Microscopy, and with a profilometer. Roughness grows with thickness and with boron addition. The mechanical properties of the films were evaluated by micro scratch at fixed and variable load. The scratch hardness numbers of ZrO₂ and ZrO₂/B₂O₃ coatings reach 6 GPa (glass value = 1.9 GPa), whereas the best value for the critical load is 16.7 N (glass value = 9 N).     

Thin film deposition and characterization of pure and iron-doped electron-beam evaporated tungsten oxide for gas sensors

Pure tungsten oxide (WO₃) and iron-doped (10 at.%) tungsten oxide (WO₃:Fe) nanostructured thin films were prepared using a dual crucible Electron Beam Evaporation (EBE) technique. The films were deposited at room temperature under high vacuum onto glass as well as alumina substrates and post-heat treated at 300 °C for 1 h. Using Raman spectroscopy the as-deposited WO₃ and WO₃:Fe films were found to be amorphous, however their crystallinity increased after annealing. The estimated surface roughness of the films was similar (of the order of 3 nm) to that determined using Atomic Force Microscopy (AFM). As observed by AFM, the WO₃:Fe film appeared to have a more compact surface as compared to the more porous WO₃ film. X-ray photoelectron spectroscopy analysis showed that the elemental stoichiometry of the tungsten oxide films was consistent with WO₃. A slight difference in optical band gap energies was found between the as-deposited WO₃ (3.22 eV) and WO₃:Fe (3.12 eV) films. The differences in the band gap energies of the annealed films were significantly higher, having values of 3.12 eV and 2.61 eV for the WO₃ and WO₃:Fe films respectively. The heat treated films were investigated for gas sensing applications using noise spectroscopy. It was found that doping of Fe to WO₃ produced gas selectivity but a reduced gas sensitivity as compared to the WO₃ sensor.     

Surface treatment of TiO2 films for dye-sensitized solar cells using atmospheric-pressure non-equilibrium DC pulse discharge plasma jet

In this paper, we report the utilization of the DC pulse discharge plasma jet technique as a means for the preparation of titanium oxide (TiO₂) films on fluorine dope tin oxide (FTO) coated glass substrates used for dye-sensitized solar cells (DSCs). The TiO₂ film made on these experimental bases exhibited the BET specific surface area of 95 m²/g, the pore volume of 0.3 cm²/g and the TEM particle size of ∼25 nm. The DSCs made by the TiO₂ film exhibited an energy conversion efficiency of 5.7% at 100 mW/cm² light intensity. Consequently, we believe that the optimization between the specific surface area and photocurrent density of TiO₂ film was achieved by the plasma surface treatment which also contributed to the improvement of energy conversion efficiency of DSCs.     

Structural and functional properties of Al:ZnO thin films grown by Pulsed Laser Deposition at room temperature

Current research on transparent conductive oxides (TCOs) is focusing on indium-free TCOs, such as Al-doped ZnO (AZO), as an alternative to indium-tin oxide. In this work, AZO thin films were grown by Pulsed Laser Deposition at room temperature in oxygen atmosphere. The O₂ pressure was varied from 0.01 Pa to 10 Pa, highlighting the effects of defect formation and oxygen vacancies on the film properties. Structural properties were characterized by X-ray diffraction and Scanning Electron Microscopy, while functional properties were characterized by measurement of electrical conductivity, Hall mobility, carrier density and optical transmission. At an optimal deposition pressure of 2 Pa, optical transparency in the visible range and minimum resistivity (4.5 ? 10^− 4 Ω cm) were found, comparable to state-of-the-art TCOs. Mean value of visible transparency was shown to increase with increasing pressure, up to 88% at a deposition pressure of 10 Pa.     

Elaboration of heterojunction solar cells by the deposit of tin oxide thin films on silicon by APCVD

We present in this paper the experimental results concerning the deposition of tin oxide SnO₂ on silicon substrate by the technique of Atmospheric Pressure Chemical Vapour Deposition (APCVD). The obtained Si-SnO₂ heterostructure is used for photovoltaic application. The properties of tin oxide thin films deposited by APCVD technique depends on three parameters which are the deposition temperature, the deposition time and the oxygen pressure. We have obtained the optimal value of each parameter by the measurement of the open-circuit voltage of the obtained Si-SnO₂ heterostructure. So, at the temperature of 490 °C during 12 min of deposition time under oxygen pressure of 1 bar we have obtained tin oxide thin layers exhibiting the best optoelectronic and morphology characteristics. These thin films are polycrystalline and present a resistivity of 1.3 · 10^− 3 Ω cm and a refractive index of 1.72. The Si-SnO₂ heterojunction solar cell that has an area of 2 × 1.5 cm² is characterised by the current-voltage I(V) measurement. It gives an open circuit voltage of 0.45 V and a short circuit current of 74 mA.     

Plastic substrate with gas barrier layer and transparent conductive oxide thin film for flexible displays

A novel plastic substrate for flexible displays was developed. The substrate consisted of a polycarbonate (PC) base film coated with a gas barrier layer and a transparent conductive thin film. PC with ultra-low intrinsic birefringence and high temperature dimensional stability was developed for the base film. The retardation of the PC base film was less than 1 nm at a wavelength of 550 nm (film thickness, 120 µm). Even at 180 °C, the elastic modulus was 2 GPa, and thermal shrinkage was less than 0.01%. The surface roughness of the PC base film was less than 0.5 nm. A silicon oxide (SiO_x) gas barrier layer was deposited on the PC base film by a roll-to-roll DC magnetron reactive sputtering method. The water vapor transmission rate of the SiO_x film was less than 0.05 g/m²/day at 40 °C and 100% relative humidity (RH), and the permeation of oxygen was less than 0.5 cc/m² day atm at 40 °C and 90% RH. As the transparent conductive thin film, amorphous indium zinc oxide was deposited on the SiO_x by sputtering. The transmittance was 87% and the resistivity was 3.5 × 10^− 4 ohm cm.     

Sputter deposition of semicrystalline tin dioxide films

Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO₂ crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda-lime glass (SLG), Mo-coated soda-lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8 mΩ cm and 800 mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3 × 10¹⁸ cm^− 3 to 3 × 10²⁰ cm^− 3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7 cm²/V s and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1-3 cm²/V s range can be obtained even in semicrystalline films. Initial deposition rates range from 4 nm/min at low sputtering power to 11 nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%.     

Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads

Superparamagnetic magnetite nanoparticles were obtained starting from a mixture of iron(II) and iron(III) solutions in a preset total iron concentration from 0.04 to 0.8 mol l⁻¹ with ammonia at 25 and 70 °C. The regeneration of cellulose from viscose produces micrometrical spherical cellulose beads in which synthetic magnetite were embedded. The characterization of cellulose-magnetite beads by X-ray diffraction, Scanning and Transmission Electron Microscopy and magnetic measurement is reported. X-ray diffraction patterns indicate that the higher is the total iron concentration and temperature the higher is the crystal size of the magnetite obtained. Transmission Electron Microscopy studies of cellulose-magnetite beads revealed the distribution of magnetite nanoparticles inside pores of hundred nanometers. Magnetite as well as the cellulose-magnetite composites exhibit superparamagnetic characteristics. Field cooling and zero field cooling magnetic susceptibility measurements confirm the superparamagnetic behaviour and the blocking temperature for the magnetite with a mean size of 12.5 nm, which is 200 K.