Effect of post annealing treatment on electrochromic properties of spray deposited niobium oxide thin films

Niobium oxide thin films were deposited on the glass and fluorine doped tin oxide (FTO) coated glass substrates using simple and inexpensive spray pyrolysis technique. During deposition of the films various process parameters like nozzle to substrate distance, spray rate, concentration of sprayed solution were optimized to obtain well adherent and transparent films. The films prepared were further annealed and effect of post annealing on the structural, morphological, optical and electrochromic properties was studied. Structural and morphological characterizations of the films were carried out using scanning electron microscopy, atomic force microscopy and X-ray diffraction techniques. Electrochemical properties of the niobium oxide thin films were studied by using cyclic-voltammetry, chronoamperometry and chronocoulometry.     

Electrochromism in spray deposited iridium oxide thin films

Electrochromic iridium oxide thin films were deposited onto fluorine doped tin oxide coated glass substrates from an aqueous iridium chloride solution by pneumatic spray pyrolysis technique. The as-deposited samples were X-ray amorphous. The electrochromic properties of thin films were studied in an aqueous electrolyte (0.5N H₂SO₄) using cyclic voltammetry (CV), chronoamperometry (CA) and spectrophotometry. Iridium oxide films show pronounced anodic electrochromism owing to Ir⁺⁴ ↔ Ir⁺³ intervalency charge transition. The reversibility of cyclic process in Ir oxide films is found to be higher, which increases with increasing number of colour-bleach cycles.     

YSZ thin films deposited by spin-coating for IT-SOFCs

Dense and crack-free yttria stabilized zirconia (YSZ) thin films were fabricated using a spin-coating technique for intermediate temperature solid oxide fuel cells (IT-SOFCs). The film thickness was greatly affected by spinning speed and coating cycles. The morphology of the films was investigated with scanning electron microscope. With cathodes consisting of yttria-stabilized bismuth oxide and sliver, anodes of samaria-doped ceria and nickel, the supported YSZ films were characterized as electrolytes for single cells with humidified hydrogen as fuel and stationary air as oxidant. Open circuit voltage was 1.08 V at 700 °C, close to the theoretical value and power density was 535 mW/cm² at 750 °C and 400 mW/cm² at 700 °C. Impedance analysis indicates that the performances of the SOFCs are determined essentially by the interfacial resistances, suggesting that optimizing the electrode materials are especially important for IT-SOFCs.     

Spray deposited titanium oxide thin films as passive counter electrodes

Titanium dioxide (TiO₂) thin films were deposited from methanolic solution onto fluorine doped tin oxide coated conducting glass substrates by spray pyrolysis technique. The electrochemical properties of TiO₂ thin films were investigated using cyclic voltammetry, chronoamperometry, chronocoulometry and iono-optical studies, in 0.1N H₂SO₄ electrolyte. Performance of the films deposited at three different substrate temperatures, viz. 350, 400 and 450 °C is discussed in view of their utilization in electrochromic devices, as counter electrode. The magnitude of charge storage capacity, Q/t (4.75-6.13 × 10⁻³ mC/(cm² nm)) and colouration efficiency (3.2-4.3 cm²/mC) of TiO₂ rank these films among the promising counter electrodes in electrochromic devices.     

Enhanced photoelectrochemical performance of Ag–ZnO thin films synthesized by spray pyrolysis technique

Silver doped zinc oxide (Ag–ZnO) thin films were deposited on glass and tin doped indium oxide (ITO) coated glass substrates by using pneumatic spray pyrolysis technique (SPT) at 450 °C from aqueous solutions of zinc acetate and silver nitrate precursors. The effect of silver doping on structural, morphological and optical properties of films was studied. The XRD spectra of the Ag–ZnO films indicate the polycrystalline nature having hexagonal crystal structure. SEM micrographs show the uniform distribution of spherical grains of about 80–90 nm grain size for the pure ZnO thin films. The Ag nanoparticles are clearly visualized in SEM images of Ag–ZnO samples. The optical band gap energy decreases as the percentage of silver doping increases. Surface Plasmon Resonance (SPR) related phenomena are observed and correlated to the optical properties of Ag–ZnO thin films. The overall photoelectrochemical (PEC) performance of the samples was investigated and discussed. Moreover, the samples are more photoactive as compare to the pure ZnO sample and the sample ZnOAg₁₅ shows the highest current. The photocurrent increases upto 249 μA cm⁻² and 303 μA cm⁻² in visible light and in UV illumination, respectively, and then decreases as the Ag doping increases into the film.     

Characterization of spray pyrolytically deposited high mobility praseodymium doped CdO thin films

Praseodymium (Pr) doped CdO thin films with high transparency and high mobility were deposited, using a homemade spray pyrolysis setup, on micro-slide glass substrates preheated at 300 °C. Polycrystalline nature and Cd-O bond vibration of deposited films were confirmed by X-ray diffraction, micro-Raman and Fourier transform infrared spectroscopy analyses. The oxidation state of Cd²⁺, O²⁻, and Pr³⁺ was confirmed by X-ray photoelectron spectroscopy analysis. The highest average particle size (92 nm-FESEM) and high RMS (13.48 nm-AFM) values are obtained for 0.50 wt% Pr doped CdO thin film. The optical band gap is varied between 2.38 eV and 2.52 eV, depending on the Pr doping concentration. Photoluminescence spectra revealed that Pr doped CdO thin film exhibits strong green emission at 582 nm. High mobility (82 cm²/V s), high charge carrier concentration (2.19×10²⁰ cm⁻³) and high transmittance (83%) were observed for 0.50 wt% Pr doped CdO film. A high figure of merit (9.79×10⁻³ Ω⁻¹) was obtained for 0.50 wt% Pr doped CdO thin films. The mechanism behind the above results is discussed in detail in this paper.     

Structural, optical, electrical and photovoltaic electrochemical characterization of spray deposited NiWO4 thin films

The preparation of nickel tungstate (NiWO₄) thin film by spray pyrolysis (SP) with ammonical solution is presented. The phase and surface morphology characterizations have been carried out by X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, respectively. The study of optical absorption spectrum in the wavelength range 350-850 nm shows the presence of direct as well as indirect band gaps in the material, respectively found to be 2.28 and 2.00 eV. The thin film material shows semiconducting behaviour and highly resistive at room temperature as evident from its dc electrical conductivity measurements obtained by the Two Point Probe method in the temperature range 310-500 K. The thin films deposited on fluorine doped tin oxide (FTO) coated conducting glass substrates are used as photoanode in photovoltaic electrochemical (PVEC) cell. The PVEC cell configuration is: NiWO₄|Ce⁴⁺, Ce³⁺|Pt; 0.1 M in 0.1N H₂SO₄. The PVEC characterization reveals the fill factor and power conversion efficiency to be 0.47 and 0.78%, respectively. The flat band potential is found to be −0.32 V (SCE).     

Electrophoretically deposited thin film electrolyte for solid oxide fuel cell

Abstract

Thin films of 8 mol% yttria stabilised zirconia (YSZ) electrolyte have been deposited on non-conducting porous NiO–YSZ anode substrates using electrophoretic deposition (EPD) technique. Deposition of such oxide particulates on non-conducting substrates is made possible by placing a conducting steel plate on the reverse side of the presintered porous substrates. Thickness of the substrates, onto which the deposition has been carried out, varied in the range 0·5–2·0 mm. Dense and uniform YSZ thin films (thickness: 5–20 μm) are obtained after being cofired at 1400°C for 6 h. The thickness of the deposited films is seemed to be increased with increasing porous substrate thickness. Solid oxide fuel cell (SOFC) performance is measured at 800°C using coupon cells with various anode thicknesses. While a peak power density of 1·41 W cm^?2 for the cells with minimum anode thickness of 0·5 mm is achieved, the cell performance decreases with anode thickness.     

Photoluminescence and third-order nonlinear optical limiting properties of Sn1-xNdxO2 thin films deposited via spray pyrolysis

In the present work, spray pyrolysis method was adopted to synthesis nano thin films of Sn_1-xNd_xO₂ (x = 0.01 to 0.1) possessing tetragonal structure with (1 1 0) plane orientation. Nd doping reduced the overall crystallinity of the films, however Sn_0.92Nd_0.08O₂ film showed crystallite size of 18.7 nm, similar to that of the pure film. The morphology changed to distinct grains at lower doping concentration, beyond which a fibrous nature evolved but again changed to smaller grains with further increase in the doping. The oxidation states of the constituent elements were confirmed using XPS. The transmittance of the films reduced due to incorporation of Nd ions. A decrease in the energy band gap was also noticed in the films following dopant addition. The PL emissions corresponding to the Nd ion transitions was found in the NIR region resulting from internal 4f-shell transitions of Nd³⁺ ions. Other defect related emissions like the one from oxygen vacancies also showed up in the UV and visible wavelength regions, which were responsible for a near white light emission. The third-order optical nonlinearity of the films was confirmed using the Z-scan technique. All the Sn_1-xNd_xO₂ films till 8 at. % of doping showed reverse saturable absorption. The highest and lowest nonlinear absorption coefficient was exhibited by Sn_0.92Nd_0.08O₂ and Sn_0.98Nd_0.02O₂ films, respectively. Depending on the Nd concentration, the films either showed self-focusing or self-defocusing behavior and influenced the nonlinear refractive indices of the films. The least optical limiting values among the doped films was obtained in the range of 1.73 kJ/cm² for Sn_0.92Nd_0.08O₂ films.     

Effect of structural defects,surface roughness on sensing properties of Al doped ZnO thin films deposited by chemical spray pyrolysis technique

In this article, the gas sensing properties of Al-doped ZnO thin films have been reported where the nanocrystalline ZnO based thin films were well deposited by a simple and inexpensive ‘chemical spray pyrolysis (CSP)’ technique. Films have been found to be uniform, pinhole free and well adherent to the substrate. The morphology, structures, and surface roughness of the deposited Al-doped ZnO thin films were studied by various types of characterization techniques. In addition, the authors have observed that the sensor response and selectivity towards CO gas is improved by the Al doping at a low operating temperature. XRD results showed that the obtained films are nanocrystalline in nature with hexagonal wurtzite phase. Further, the annealed films were used for detection of CO in the air and maximum response was observed at 175 °C. The improvement in sensor response of Al-doped ZnO thin films to CO gas attributed to the defect chemistry, crystallite size and surface roughness.     

Characterization of core-shell structured Ni@GDC anode materials synthesized by ultrasonic spray pyrolysis for solid oxide fuel cells

Core-shell structured NiO@GDC powders with NiO cores and GDC shells were synthesized by ultrasonic spray pyrolysis (USP) with a four-zone furnace. The morphology of the as-synthesized powders can be modified by controlling parameters such as the precursor pH, carrier gas flow rate, and zone temperature. At high carrier gas flow rates, the as-synthesized core-shell structured NiO@GDC powders have raisin-like morphology with a rough surface; this is due to fast gas exhaustion and insufficient particle ordering. The core-shell structured Ni@GDC anode showed considerable electrochemical performance enhancement compared to the conventionally-mixed Ni-GDC anode. The polarization resistance (R_p) of conventionally-mixed Ni-GDC anodes increases gradually as a function of the operation time. Alternatively, the core-shell structured Ni@GDC anode synthesized by USP does not exhibit any significant performance degradation, even after 500 h of operation. This is the case because the rigid GDC ceramic shell in the core-shell structured Ni@GDC may restrain Ni aggregation.     

Realization of Eu-doped p-SnO2 thin film by spray pyrolysis deposition

We report the fabrication of p-SnO₂ thin films by spray pyrolysis deposition using europium (Eu) as an acceptor. Structural and chemical investigations verified that Eu³⁺ ions were successfully incorporated into the SnO₂ crystal by substituting the Sn⁴⁺ sites in the lattice. Even though the undoped SnO₂ thin film showed n-type properties with a charge carrier concentration of −2.343 × 10¹⁸ cm⁻³, SnO₂ showed p-type properties as the Eu was incorporated. In addition, the charge carrier concentration of the Eu-doped SnO₂ increased to 9.121 × 10¹⁹ cm⁻³ as the molar content of the Eu source was increased to 0.2 mM. The optical transmittance was not degraded by the Eu doping and was maintained between 70 and 80% in the visible wavelength spectral range, while the optical band gap of the Eu-doped SnO₂ increased due to the Burstein-Moss effect. The thin film field-effect transistor fabricated by using the Eu-doped SnO₂ showed the typical gate-modulated drain current characteristic of a p-channel transistor with depletion mode. These results demonstrated the effectiveness of Eu as a dopant for p-SnO₂.     

Effect of precursor concentration on structural,morphological and opto-electric properties of ZnO thin films prepared by spray pyrolysis

Sprayed ZnO films were grown on glass substrate at 400 °C using zinc chloride as precursor with different molar concentrations varying from 0.05 to 0.2 M. X-ray diffraction patterns reveal that ZnO films are polycrystalline with hexagonal wurtzite structure with preferred orientation in (002) plane. Optical measurements show that transmittance reaches a maximum value of 95% in the visible region for ZnO films prepared from precursor with 0.05 M concentration. The films obtained from the precursor with 0.1 M concentration have the highest electrical conductivity and photocurrent values.     

Characterization of luminescent SrAl2O4 films doped with terbium and europium ions deposited by ultrasonic spray pyrolysis technique

SrAl₂O₄, SrAl₂O₄:Tb³⁺ and SrAl₂O₄:Eu³⁺:Eu²⁺ films were synthesized by means of the ultrasonic spray pyrolysis technique. These samples, characterized by X-Ray Diffraction, showed the monoclinic phase of the strontium aluminate. Images of the surface morphology of these films were obtained by SEM and the chemical composition was measured by EDS and XPS. The photoluminescence and cathodoluminescence characteristics of the films were studied as a function of the terbium and europium concentrations. The optimal PL emission intensities were reached at 8?at% for terbium doped films and 6?at% for europium doped samples. The CL emission spectra for europium doped films showed the typical bands of Eu³⁺ ions and also a broadband centered at 525?nm which is attributed to Eu²⁺ ions. XPS measurements confirm the presence of Eu³⁺ and Eu²⁺ in europium doped SrAl₂O₄ films, without having been subjected to a reducing atmosphere. Chromatic diagrams exhibited green color for SrAl₂O₄:Tb³⁺ films, red and yellow colors for SrAl₂O₄:Eu³⁺:Eu²⁺ films. The PL decay curves were also obtained: the averaged decay time was 2.7?ms for SrAl₂O₄:Tb³⁺ films and 1.9?ms for SrAl₂O₄:Eu³⁺ films. Similar results were obtained by the stretched exponential model.     

BaZr0.1Co0.4Fe0.4Y0.1O3-SDC composite as quasi-symmetrical electrode for proton conducting solid oxide fuel cells

Symmetric solid oxide fuel cells (SSOFCs) with the identical anode and cathode electrocatalysts show promise to reduce material and system cost while increasing the cell lifespan. In this work, BaZr_0.1Co_0.4Fe_0.4Y_0.1O₃ (BZCFY) oxide perovskite is proposed as a symmetric electrode for SSOFCs based on proton conducting electrolyte, with targets of reducing temperature and high-performance application. Active oxygen ionic conductor and catalyst, SDC, is composited to improve the cell performance and electrode durability. Those materials show good chemical compatibility while BZCFY is decomposed to alloy and mixed oxide composite, which significantly affects electrode activity. SDC-BZCFY composite gives an electrode polarization resistance of 1.35–13.7 Ω cm² and 0.32–1.59 Ω cm² for hydrogen oxidation reaction and oxygen reduction reaction on the proton conducting electrolyte, BZCY, at the temperature range of 700–550 °C, respectively. Moreover, it displays an excellent oxygen reduction kinetics with an impressive activation energy of 0.91 eV. The polarization resistances are significantly reduced in the fuel cell condition owning to the electrochemical promotion effect under open-circuit condition. Quasi-SSOFCs with BZCY electrolyte in a thickness of 480 μm and electrode thickness of 25 μm give a peak power density of 114.8 and 74.3 mW cm⁻² at 650 and 600 °C, respectively. In addition, SSOFC also displays acceptable durability under constant voltage operational condition for 25 h. This work highlights alternative active electrode material for symmetric solid oxide fuel cells for low temperature operation.     

Effect of thermo-physical properties of Zn precursors on ZnO thin films grown by ultrasonic spray

In the present work we have investigated temperature and precursor solution concentration influences on the density, viscosity and surface tension of zinc aqueous solutions. Three zinc salt solution sources, namely acetate, nitrate and chloride, have been investigated. The study was carried out at different concentrations ranged from 0.02 to 0.20 mol/l and solution temperatures varied from 20 to 60 °C. The measurements results show, for the whole studied salt sources, a linear increase in density, surface tension and viscosity with salt concentration. While an inverse behavior of these properties is observed with increasing solution temperature. Zinc acetate has the lower surface tension and viscosity, while zinc chloride has the largest ones. Droplets Weber, Reynolds numbers and surface enthalpy formation have been estimated from solution properties measurements. Ultimately a correlation between the used salts, concentrations and the obtained ZnO thin films morphologies and structures is addressed. Solution viscosity and surface tension are key parameters controlling the films growth and morphology. At fixed substrate temperature, films with smooth surface can be produced by reducing the surface tension and the viscosity of the starting solution.     

Dispersive optical constants and electrical properties of nanocrystalline CuInS2 thin films prepared by chemical spray pyrolysis

Nanocrystalline CuInS₂ thin films were deposited on borosilicate glass substrates via chemical spray pyrolysis method. The structural, morphological, optical, and electrical properties were studied as a function of increasing annealing temperature from 250 to 350 ̊C. XRD analysis showed mixed phases at lower temperatures with the preferred orientation shifting towards the (112) chalcopyrite CuInS₂ plane at higher substrate temperature. The crystallite size increased slightly between 13 and 18 nm with increase in annealing temperature. The optical band gap was determined on basis of Tauc extrapolation method and the Wemple–Di-Domenico single oscillator model. Possible structural and quantum confinement effect may have resulted in relatively larger band gaps of 1.67–2.04 eV, relative to the bulk value of 1.5 eV. The presence of Cu_xS in the as-deposited and wurtzite peaks after annealing at 350 ^̊C play a role in influencing the optical and electrical properties of CuInS₂ thin films.     

Enhanced sintering behavior of LSGM electrolyte and its performance for solid oxide fuel cells deposited by vacuum cold spray

How to obtain dense La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) electrolyte at low sintering temperature (<1300 °C) is a challenge to improve solid oxide fuel cell (SOFC) performance at intermediate operation temperature. In this study, a double-layer design method for vacuum cold spray (VCS) prepared-LSGM electrolyte assisted with two-step sintering at a low temperature was proposed. The sintering behavior of VCS deposited LSGM layers at 1200 °C was investigated. The LSGM layers became denser in most regions except the appearance of some cracks. Subsequently, the effect of a second LSGM layer on the sintered top layer was studied to block cracks. Results showed that the co-sintered layer with a thickness of approximately 5 μm presented a maximum open circuit voltage of ∼0.956 V at 650 °C and a maximum power density of 592 mW/cm² at 750 °C. Result indicates that the sintering assisted VCS is a promising method to prepare the LSGM electrolyte applied in intermediate temperature SOFCs.     

Effect of doping concentration on the properties of aluminium doped zinc oxide thin films prepared by spray pyrolysis for transparent electrode applications

Zinc oxide possesses many interesting properties, such as modifiable conductivity, wide band gap, high excitonic binding energy, piezo-electric polarisation and cathodoluminiscence. In this study transparent conducting aluminium doped zinc oxide (ZnO:Al) thin films were deposited on float glass substrates by tailor made spray pyrolysis with adaptation for measuring the actual temperature of the substrate surface during deposition. The films were characterised and the effect of aluminium doping concentration [Al/Zn] on their optical, electrical and structural properties was investigated as a function of aluminium doping between 0 and 10 at.%. There was widening of optical band gap with increasing doping concentration. ZnO:Al films with low resistivity of 2.8 × 10⁻² Ω cm and high transmittance of over 85% at 550 nm which are crucial for opto-electrical applications were obtained at a doping ratio of 2 at.%.     

Correlation between yttria stabilized zirconia particle size and morphological properties of NiO–YSZ films prepared by spray coating process

A systematic approach was taken to investigate the morphology of NiO–yttria stabilized zirconia (YSZ) films deposited by a spray coating process. The final morphological aspects of anode films were influenced by the particle size of YSZ powders and the milling time of the slurries used for film deposition. YSZ powders with average particle size of 17 and 52 nm were obtained from powders calcined at 800 and 1000 °C, respectively. The results obtained by rheological studies pointed out that slurries prepared from YSZ powders calcinated at 1000 °C and milling time of 20 h had more stability. All slurries presented thixotropic and pseudoplastic behaviors.