S.S. Shinde

Optoelectronic properties of sprayed transparent and conducting indium doped zinc oxide thin films

Indium doped zinc oxide (IZO) thin films are grown onto Corning glass substrates using the spray pyrolysis technique. The effect of doping concentration on the structural, electrical and optical properties of IZO thin films is studied. X-ray diffraction studies show a change in preferential orientation from the (0 0 2) to the (1 0 1) crystal planes with increase in indium doping concentration. Scanning electron microscopy studies show polycrystalline morphology of the films. Based on the Hall-effect measurements and analysis, impurity scattering is found to be the dominant mechanism determining the diminished mobility in ZnO thin films having higher indium concentration. The addition of indium also induces a drastic decrease in the electrical resistivity of films; the lowest resistivity (4.03 × 10−5 Ω cm) being observed for the film deposited with 3 at% indium doping. The effect of annealing on the film properties has been reported. Films deposited with 3 at% In concentration have relatively low resistivity with 90% transmittance at 550 nm and the highest value of figure of merit 7.9 × 10−2 Ω−1.

Physical properties of sprayed antimony doped tin oxide thin films: The role of thickness

Transparent conducting antimony doped tin oxide (Sb:SnO2) thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution. The structural, morphological, X-ray photoelectron spectroscopy, optical, photoluminescence and electrical properties of these films have been studied. It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the (211) and (112) planes. Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity. The compositional analysis and electronic behaviour of Sb:SnO2 thin films were studied using X-ray photoelectron spectroscopy. The binding energy of Sn3d5/2 for all samples shows the Sn4+ bonding state from SnO2. An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb5+ ions. The film deposited with 20 cc solution shows 70 % transmittance at 550 nm leading to the highest figure of merit (2.11 × 10−3Ω−1). The resistivity and carrier concentration vary over 1.22 × 10−3 to 0.89 × 10−3Ωcm and 5.19 × 1020 to 8.52 × 1020 cm−3, respectively.

Physical properties of spray deposited CdTe thin films: PEC performance

p-CdTe thin films were prepared by spray pyrolysis under different ambient conditions and character- ized using photoelectrochemical (PEC), X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive analysis by X-ray (EDAX), and optical transmission studies. The different preparative parameters viz solution pH, solution quantity, substrate temperature and solution concentration have been optimized by the PEC technique in order to get good-quality photosensitive material. XRD analysis shows the polycrystalline nature of the film, hav- ing cubic structure with strong (111) orientation. Micrographs reveal that grains are uniformly distributed over the surface of the substrate indicating the well-defined growth of polycrystalline CdTe thin film. The EDAX study for the sample deposited at optimized preparative parameters shows the nearly stoichiometric Cd : Te ratio. Optical absorption shows the presence of direct transition with band gap energy of 1.5 eV. Deposited films exhibit the highest photocurrent of 2.3 mA, a photovoltage of 462 mV, a 0.48 fill factor and 3.4% efficiency for the optimized preparative parameters.

Oxidative degradation of acid orange 7 using Ag-doped zinc oxide thin films

Ag-doped ZnO thin films with preferred c-axis orientation along (002) have been prepared by spray pyrolysis technique in aqueous medium on to the corning glass substrates. The effect of Ag-doping on to the photoelectrochemical, structural, morphological, optical, luminescence, electrical and thermal properties has been investigated. XRD and Raman study indicates that the films have hexagonal (wurtzite) crystal structure. The effect of Ag loading on the photocatalytic activity of Ag-doped ZnO in the degradation of azo dye is studied and results are compared with pure ZnO. The results show that the rate of degradation of azo dye over Ag-doped ZnO is much higher as compared to pure ZnO. Ag doping in ZnO is highly effective and can significantly enhance the photocatalytic degradation and mineralization of azo dye. The enhancement of photocatalytic activity of Ag-doped ZnO thin films is mainly due to their smaller crystallite size and capability for reducing the electron-hole pair recombination. Kinetic parameters have been investigated in terms of a first order rate equation. The rate constant (-k) for this heterogeneous photocatalysis is evaluated as a function of the initial concentration of original species. Substantial reduction in azo dye is achieved as analyzed from COD and TOC studies.

Hydroxyl radical's role in the remediation of wastewater.

The photocatalytic degradation of wastewater with ZnO based photocatalysts under solar illumination has been investigated. Advanced oxidation processes such as photoelectrocatalysis, sonolysis and H(2)O(2) treatment show promise in eliminating the dangers of exposure to wastewater and the products of their natural breakdown. A basic understanding of the mechanistic details involved in the oxidative transformations remains the key for improving the effectiveness of the advanced oxidation processes. The role of hydroxyl radical in the breakdown of the wastewater is elucidated through determining the degradation rates, analyzing transformation intermediates and studies using computational chemistry methods. In order to realize a complete mineralization of wastewater COD, BOD and TOC analysis has been carried out.

Photocatalytic activity of sea water using TiO2 catalyst under solar light

Wastewater is generally released into the rivers and streams in developing countries. Industrial wastewater usually contains highly toxic pollutants, cyanides, chlorinated compounds. Ultraviolet (UV) radiation from sunlight also decomposes organic compounds by oxidation process. However, the process is less effective due to large amount of toxic effluent entering in the main stream of water. The solar radiation can effectively be applied to accelerate the process by using suitable catalyst for economically cleaning the water sources. This paper describes the photocatalytic degradation of the sea water using novel approach of photoelectrochemical (PEC) reactor module consisting of nine photoelectrochemical cells equipped with spray deposited TiO₂ catalysts under solar light. The resulted water samples were studied for physicochemical and bacteriological analysis. The complete mineralization of degraded sample was confirmed by total organic carbon (TOC) analysis, COD measurement and estimation of the formation of inorganic ions such as NH₄(+), NO₃⁻, Cl⁻ and SO²⁻₄. Microbiological examinations are performed to determine the bacterial analysis. This implies that photoelectrocatalysis could be a promising way for improving water quality in developing countries with low cost and clean energy reliable resource.

Structural and optoelectronic properties of sprayed Sb:SnO2 thin films: Effects of substrate temperature and nozzle-to-substrate distance

The influence of substrate temperature and nozzle-to-substrate distance (NSD) on the structural, morphological, optical and electrical properties of Sb:SnO2 thin films prepared by chemical spray pyrolysis has been analyzed. The structural, morphological, optical and electrical properties were characterized by using XRD, SEM, UV-visible spectrophotometry and Hall effect measurement techniques. It was seen that the films are polycrystalline, having a tetragonal crystal structure with strong orientation along the (200) reflection. The pyramidal crystallites formed due to coalescence were observed from SEM images. The values of highest conductivity, optical transmittance and figure of merit of about 1449(Ω·cm)−1, 70 %and 5.2 × 10−3 □/Ω, respectively, were observed for a typical film deposited using optimal conditions (substrate temperature = 500 °C and NSD = 30 cm).

Photoelectrocatalytic activity of spray deposited ZnO thin films against E. coli Davis

Abstract Zinc oxide (ZnO) thin films have been deposited onto fluorine doped tin oxide coated glass substrates by economical chemical spray pyrolysis technique. Films were deposited using various quantities of solution from 50 to 200 cc (substrate temperature 400°C, solution concentration 0·2M) in order to achieve different thicknesses. The films were characterised by X-ray diffraction, SEM, AFM and optical absorption techniques. The films exhibit a hexagonal wurtzite crystal structure with preferred (002) orientation. Morphological study showed a smooth and nanocrystalline surface of ZnO films. Direct optical band gap energy of ZnO thin films is found to be 3·24 eV. The average transmission is of the order of 87% in the visible region. The photoelectrocatalytic response of the film against Escherichia coli Davis is studied using a specially designed photoelectrochemical (PEC) reactor module. Thickness and UV light dependent photoelectrocatalytic bactericidal properties of ZnO thin films have been investigated. It shows that biased 1·1 μm thick ZnO thin films with 2 mW cm−2 UV light intensity give better bactericidal response compared to others. The relative percentage of killing of bacteria is 19·81% due to UV illumination, 52·71% due to UV illumination and passing over ZnO surface and 95·03% due to UV illumination and passing through PEC reactor with ZnO thin film after 2·5 h. It can be concluded that the ZnO thin film with photochemical reactor can be used in a water purifier to get bacteria free drinking water.