Sprayed ZnO Thin Films Research Articles

Influence of optical properties of ZnO thin-films deposited by spray pyrolysis and RF magnetron sputtering on the output performance of silicon solar cell

ZnO thin-films were deposited by spray pyrolysis and RF magnetron sputtering techniques. The optical reflection of these thin-films is measured using UV-Vis spectrophotometer. The measured optical reflection data is used in PC-1D simulation software to study the output performance of commercial silicon wafer-based solar cell. As far as optical performance is concerned it could be demonstrated that the sprayed ZnO thin-film under laboratory conditions show equivalent performance compared to sputtered ZnO thin-film. The influence of optical properties of 65 nm thick zinc oxide thin-films deposited by vacuum and non-vacuum techniques on quantum efficiency and IV characteristics of commercial silicon-wafer based solar cell is studied and reported here.

Photoelectrocatrocatalytic hydrolysis of starch by using sprayed ZnO thin films

Thin films of zinc oxide have been deposited onto glass/FTO substrates at optimized 400 °C by using a chemical spray pyrolysis technique. Deposited films are character photocatalytic activity by using XRD, an SEM, a UV-vis spectrophotometer, and a PEC single-cell reactor. Films are polycrystalline and have a hexagonal (wurtzite) crystal structure with c-axis (002) orientation growth perpendicular to the substrate surface. The observed direct band gap is about 3.22 eV for typical films prepared at 400 °C. The photocatalytic activity of starch with a ZnO photocatalyst has been studied by using a novel photoelectrocatalytic process.

Influence of Fe doping on the structural, optical and acetone sensing properties of sprayed ZnO thin films

The ZnO thin films (undoped and Fe-doped) deposited by chemical spray pyrolysis technique have been analyzed by X-ray powder diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results show that all the films possess hexagonal wurtzite structure of zinc oxide having crystallite sizes in the range 15–36nm. On 1at% Fe doping, the surface roughness of the film increases which favors the adsorption of atmospheric oxygen on the film surface and thereby increase in the gas response. Optical studies reveal that the band gap decreases due to creation of some defect energy states below the conduction band edge, arising out of the lattice disorder in the doped films. The refractive index of the films decreases on Fe doping and follows the Cauchy relation of normal dispersion. Among all the films examined, the 1at% Fe-doped film exhibits the maximum response (~72%) at 300°C for 100ppm concentration of acetone in air.

Ni-Doping Effect on the Structural and Optical Properties of Sprayed ZnO Thin Films

Nickel-doped ZnO thin films with different Ni contents (0 - 15%) were deposited on glass substrate at 350°C by a spray pyrolysis technique. 0.1 M solutions of zinc acetate and nickel sulphate were used as the precursors with air as the carrier gas. The effect of Ni-doping on the structural and optical properties of the layers was evaluated using appropriate techniques. The X-ray diffraction studies revealed that nickel atoms were successively incorporated into ZnO host matrix without forming any detectable secondary phase. All the grown films were polycrystalline with the (002) plane as the preferred orientation and the peak position shifted towards higher diffraction angle with the increase of doping content in the films. The films had hexagonal shaped grains and the evaluated grain size varied in the range of 20 - 48 nm. The optical studies revealed a decrease of transmittance with the increase of Ni-doping content in the films and the evaluated energy band gap was found to be direct that decreased from 3.32 eV to 3.05 eV.

Influence of tin doping onto structural, morphological, optoelectronic and impedance properties of sprayed ZnO thin films

Tin doped zinc oxide thin films are synthesized by simple chemical spray pyrolysis onto glass substrates using zinc acetate and stannic chloride precursors in an aqueous medium. The influence of tin doping onto photoelectrochemical, structural, morphological, optical, electrical and impedance properties have been investigated. Structural analysis confirms the hexagonal (wurtzite) structure of deposited films with crystal reorientation effect. SEM micrographs depict the films are rough, adherent and homogeneous with varying grain size (average grain size ∼100–300nm). Contact angle measurement shows that the films are hydrophilic in nature. Valence states of constituent elements in ZnO host lattice are analyzed by X-ray photoelectron spectroscopy. Direct band gap of the films decreases with tin doping up to 3.19eV. The highest electrical conductivity (0.95Ω−1cm−1 and carrier concentration (8.94×1017cm−3) and lowest mobility (6.64cm2V−1s−1) is observed at 1.5at.% tin doping. We studied interparticle interactions like grains, grain boundary effects using complex impedance spectroscopy.

The Effect of Growth Temperatures on Structural, Morphological and Optical Properties of Sprayed ZnO Thin Films

The Effect of Growth Temperatures on Structural, Morphological and Optical Properties of Sprayed ZnO Thin Films

Photocatalytic degradation of toluene using sprayed N-doped ZnO thin films in aqueous suspension

Thin films of N-doped ZnO are synthesized via spray pyrolysis technique in aqueous medium using zinc acetate and ammonium acetate as precursors. Influence of N doping onto photochemical, structural, morphological, optical and thermal properties have been investigated. Structural analysis depicts hexagonal (wurtzite) crystal structure. The effect of N doping on the photocatalytic activity of N-doped ZnO in the degradation of toluene is studied and results are compared with pure ZnO. The results show that the rate of degradation of toluene over N-doped ZnO is higher as compared to that of pure ZnO and increases with increasing N doping up to 10at.% and then decreases. The enhancement of photocatalytic activity of N-doped ZnO thin films is mainly due to their capability for reducing the electron hole pair recombination. The photocatalytic mineralization of toluene in aqueous solution has been studied by measuring COD and TOC. Possible reaction mechanism pathways during toluene degradation over N-doped ZnO has been proposed.

Enhancement of electrical conductivity in sprayed ZnO thin film through zero-energyprocess

Conductivity enhancement in spray pyrolysed ZnO thin film was achieved through post-deposition cooling. We present a comparison between the effect of cooling after the deposition of thin films by two different processes namely “regular cooling” and “inversion cooling”. X-ray photoelectron spectroscopy studies proved that zinc to oxygen ratio enhanced after the “inversion” process. It was observed that the process of “inversion” has caused dramatic improvement in the conductivity of ZnO thin film. The resistivity of the film decreased to 5×10 −2 Ω cm with the inversion process. The films exhibited luminescence in two regions:“near band edge emission” (NBE; ∼380 nm) and “blue–green emission” (∼503 nm). The relationship between blue–green emission and oxygen concentration in the sprayed ZnO thin film was discussed.

Study of ytterbium doping effects on structural, mechanical and opto-thermal properties of sprayed ZnO thin films using the Boubaker Polynomials Expansion Scheme (BPES)

In this work, ZnO thin films have been grown on glass substrates by using a solution of propanol (C 3H 8O), water (H 2O) and zinc acetate (Z n (CH 3CO 2) 2) in acidified medium (pH 5). The obtained films were n doped with ytterbium (Yb) at the rates of 100, 200 and 300 ppm. The structural features of the doped films were investigated using XRD, atomic force microscopy and scanning electronic microscopy techniques. XRD analysis shows a strong (0 0 2) X-ray diffraction line for increasing Yb-doping amounts. This c-axis preferential orientation of ZnO crystallites is naturally required to use this oxide as transparent conductor in optoelectronic applications. Atomic force microscopy (AFM) analysis shows an enhancement in the surface roughness of the doped ZnO:Yb thin films. Optical measurements were performed in 300–1800 nm domain via transmittance T( λ) and reflectance R( λ) spectra. Conjoint optical and thermal properties were deduced from the optical measurements in reference to the Amlouk–Boubaker opto-thermal expansivity ψ AB. Optically relevant ytterbium doping effects have been discussed. Finally, mechanical measurements have been carried out using Vickers standard disposal. The results confirmed the structural and functional changes that several recent studies attributed to ytterbium doping.

Effects of substrate temperature on sprayed ZnO thin films optical and morphological properties in terms of Amlouk–Boubaker opto-thermal expansivity ψAB

In this study, ZnO thin films have been grown using spray pyrolysis technique on glass substrates under various substrate temperature (400, 420, 440, 460, 480 and 500 °C). The Precursors were Propan-2-ol C 3H 8O and zinc acetate zinc Zn(CH 3CO 2) 2 in acidified medium (acetic acid CH 3CO 2H, pH = 5). XRD analyses yielded a strong (0 0 2) X-ray diffraction line for low substrate temperatures (400–420 °C). This c-axis preferential orientation was not observed for substrate temperature beyond 440 °C. Atomic Force Microscopy (AFM) analyses monitored clusters with variable shapes (pyramidal for high temperatures and rounded concentrated ones for temperatures below 440 °C). Finally, the optical measurements were carried out via transmittance T(λ) and reflectance R(λ) spectra inside 250–2500 nm domain. Thanks to optical measurements, the conjoint optical and thermal properties were deduced using the Amlouk–Boubaker opto-thermal expansively ψ AB.

Development and characterization of a sprayed ZnO thin film‐based NO 2 sensor

NO2 is one of the most harmful gases nowadays. A NO2 sensor based on sprayed ZnO thin film is reported in this work. Indium additive is used to improve the sensor performance, i.e. on the sensor response as well as on the sensor impedance, is studied. It was demonstrated that by adding 3 wt% of indium acetate to the spraying solution it is possible to enhance the film gas-response to 5 ppm of NO2 at 275 °C. At the same time the electrical resistance of the ZnO thin films significantly decreases in this case as a result of an effective doping process. Furthermore, the dependence of the electrical resistance on temperature in several gas atmospheres was also studied. The surface roughness was measured by atomic force microscopy (AFM). It was observed that doping increases the surface roughness and this fact plays an important role in the sensitization mechanism. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Sprayed ZnO thin films for ethanol sensors

The electrical characteristics of ZnO thin films prepared by spray pyrolysis, have been studied for ethanol sensors. The sensitivities of the films are measured at various temperatures and concentrations of ethanol. It is observed that the sensitivity increases with increasing working temperature. At higher ethanol concentrations, the sensitivity increases more rapidly with increasing temperature. Further, the films show fast response and recovery times at higher working temperatures. The sensing mechanism of the films towards ethanol vapour has been explained.

Improved performance of 2-imidazolin-5-one as sensitizer at nanocrystalline ZnO thin film electrode in acetonitrile solution

The photosensitizing behaviour of 2-imidazolin-5-one, which was studied earlier at sprayed ZnO thin film electrodes, has been reinvestigated at nanocrystalline ZnO thin film electrodes prepared by the sol-gel method. By using semiconductor electrodes in the form of nanocrystalline thin films, all PEC cell parameters such as dye-sensitized photovoltage, photocurrent and IPCE were found to be higher as compared to those obtained with the use of sprayed thin film electrodes. Thus, through this investigation it has clearly been demonstrated that the same dye can perform better on nanocrystalline than sprayed thin film electrodes of the same semiconducting material.

Flow rate and interface roughness of zinc oxide thin films deposited by spray pyrolysis technique

The interface growth and topology of sprayed ZnO thin films are examined here using the spatial scaling approach to the film surface in relation with the effect of a spraying deposition flow rate, f, ranging between 1 and 8 mil min−1. This thermally activated process is performed at the optimal temperature of the material (T=723 K). Two different growth mechanisms are identified, each of them characteristic of a particular f region. These related regions are separated from each other at a critical growth rate value of fc=5 mil min−1. The mechanism evolved below fc leads to a Hurst exponent α=0.4 typical of simple ballistic deposition growth modes. The morphology evolution in this f region corresponds to smoothing of the film surface with an increase of the flow rate. The growth kinetic exponent n=0.9 obtained in this region could be assigned to the elimination of some groove. Beyond fc, the spraying process engenders duplicate roughness exponents. The first value relative to the lowest scan lengths increases with f from α1=0.40 until unity. The second one, always evaluated at α2=0.16, is free of the f value. The growth kinetic exponent obtained in this f region, n=1.6, confirms a change of the growth mechanism, the last probably linked to incorporation of Zn particles at the growing film surface.

A binary mixture of dyes (2-imidazolin-5-oneand Rose Bengal) for photosensitization of n-ZnO thin film electrodes in aqueous and acetonitrile media

Two well characterized photosensitizers, namely, 4-m- methoxy-p-hydroxy benzylidene-2-m-methoxy- p-hydroxystyryl-1-phenyl-2-imidazolin-5-one (subsequently referred to as 2-imidazolin-5-one) and Rose Bengal, have been used together to sensitize sprayed ZnO thin film electrodes in aqueous and acetonitrile media. Through current–potential curves and action spectra (iphoto/λ), it has been confirmed that both dyes, when present together, contribute additively to the sensitized photocurrent. The quantum efficiencies of the dye- sensitized photocurrent at 480 and 555nm wavelengths (λmax of 2-imidazolin-5-one and Rose Bengal, respectively) were found to be 3.5 and 4.4%, respectively, in aqueous solution, while in acetonitrile medium the corresponding values were 4 and 6.5%.

Characterization of [Fe(o-phen) 3][Ni(CS 3) 2] as a photosensitizer for wide-band gap semiconductor (ZnO) electrodes in acetonitrile media

A newly synthesized transition metal complex tris-1,110-ortho-phenanthroline iron (II) bis-thiocarbonato nickelate (II), [ [Fe(o-phen) 3][Ni(CS 3) 2], has been studied for its photosensitizing properties at n-ZnO semiconductor electrodes prepared by spray pyrolysis and sol-gel techniques. The absorption spectrum of this inorganic complex in acetonitrile solution exhibits a strong peak at 462 nm and a shoulder at 510 nm wavelength of light. From cyclic voltammetric studies it has been found that this compound can undergo reversible, one-electron transfer oxidation with formal redox potential E 0 = 0.985 V vs. SSCE in acetonitrile medium. The sensitization of the photocurrent at the ZnO electrode by the test dye was controlled by determining current-potential curves and action spectrum. As compared with sprayed ZnO thin films, particulate films prepared by sol-gel technique were found to give better performance.

Spectral sensitization of a sprayed ZnO thin film electrode by a new synthetic dye (2-imidazolin-5-one) in acetonitrile medium

A new tailor-made organic dye, namely 4-m-methoxy-p-hydroxybenzylidene-2-m-methoxy-p-hydroxystyryl-1-phenyl-2-imidazolin-5-one (subsequently referred to as 2-imidazolin-5-one) has been studied as a photosensitizer for its application in a photoelectrochemical cell. Highly n-doped polycrystalline thin ZnO films prepared by the spray pyrolysis method were used as photoelectrodes and hydroquinone as the supersensitizer for such investigations. The absorption spectrum of the adsorbed dye on a dry ZnO electrode was found to be drastically modified compared with that of dye in solution and this has been attributed to the strong interaction between dye and ZnO surface and the formation of J-aggregates due to intermolecular hydrogen bonding. The cyclic voltammogram of the dye at the platinum electrode exhibited a quasi-reversible anodic peak with formal redox potential EDD+/0=1.24 V versus SSCE. The flat band potential of the ZnO electrode in dye containing acetonitrile solution, Vfb=-0.62 V versus SSCE, was determined from the Mott-Schottky plots. The transient technique was used to monitor the response of a dye-coated ZnO electrode to monochromatic light. The photocurrent response of a dye-coated ZnO electrode was found to be extended well into the visible region. The incident photon to current conversion efficiency (IPCE) was found to be 3.4% at the excitation wavelength (480 nm) of the dye.

Extension of the spectral response of sprayed ZnO thin film electrodes induced by nickel and cobalt doping

In this work the influence of the dopants Ni and Ni+Co on the photoresponse of sprayed ZnO thin film electrodes in acetonitrile solution was studied. In the case of an Ni-doped ZnO electrode, the photocurrent spectrum showed the extension up to a wavelength of light of 580 nm, while the (Ni+Co)-doped electrode exhibited an extension up to around 700 nm. These extensions are attributed to the dopant energy bands lying in the bandgap region of ZnO.