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.     

Deposition of cupric oxide thin films by spin coating

Abstract

Cupric oxide thin films were deposited onto soda lime glass by spin coating and subsequent annealing of copper nitrate dissolved in a glycerol–water solvent. It was found that the solution consistently gave reproducible films with good adhesion on glass. A range of band gaps were estimated between 0·8 and 1·17 eV, showing that this material has potential as a photoabsorber. Resistivity was successfully reduced from 1·47×10⁵ to 7·02 Ω cm by doping the films with sodium. Dopant concentrations of 1 at-% gave the lowest resistivity, showing that the ideal doping is 1% or less. Film structure was found to improve with an increase in annealing time from 10 min to 1 h, although this did not have any noticeable effect on either the electrical or optical properties of the films.     

CdS films from two different low cost techniques for solar cell applications – a comparative study

Abstract

CdS films with good structural and optical properties were fabricated by employing a simple and inexpensive spray pyrolysis technique using a perfume atomizer. The films were deposited at a relatively low substrate temperature (280°C) compared with conventional spray pyrolysis technique. The microstructure, surface morphology and optical properties of the sprayed CdS films prepared from starting solutions having different S/Cd ratios (1 : 1, 3 : 1and 5 : 1) were investigated and compared with that of the chemical bath deposited films. It was observed that, for the sprayed CdS films, the preferred orientation changes from (002) plane to (101) plane when S/Cd ratio in the starting solution increases, whereas in the case of their chemical bath deposited counterparts only the degree of preferred orientation increases with the increase in S/Cd ratio. The sprayed CdS films showed good visible transmittance (>85%) and wide optical band gap (2·42 eV) suitable for solar cell applications.     

Transparent conductive Sn-doped indium oxide thin films deposited by spray pyrolysis technique

Films of indium oxide doped with tin (ITO) are prepared using the low cost spray pyrolysis technique. The effect of tin doping on the physical properties of In2O3 are studied. In this study the polycrystalline ITO films with the different Sn concentration of 1 to 100-wt% SnCl₂ were prepared on Corning 7059 glass substrate. These films were confirmed to show the high crystallinity by X-ray diffraction technique. Low sheet resistance (25Ω/▪) and high visible transmission (˜82%) were obtained when the films were deposited at the tin concentration of 2-wt%.     

Si doped ZnO thin films for transparent conducting oxides

Abstract

Transparent conductive silicon doped zinc oxide (SZO, 3%Si) thin films are grown by direct current magnetron sputtering on glass substrates at room temperature. Experimental results show that the sputtering time has a significance impact on the growth rate, crystal quality and electrical properties of the films, and have little impact on the optical properties of the films. The growth rate decreases with the sputtering time. The resistivity of ZnO/Si films decreases as the sputtering time increases from 8 to 20 min. However, as the sputtering time increases further, the electrical resistivity increases instead. When other sputtering conditions are kept unchanged, it is found that the optimum sputtering time is 20 min and the achieved lowest resistivity is 4·92×10^?4 Ω cm (sheet resistance?=?11·5 Ω/sq for thickness 427·5 nm). The UV-vis transmission spectrum shows that all film samples present a transmission of above 90·0% in the visible range.     

Electrical and optical properties of Al doped cadmium oxide thin films deposited by radio frequency magnetron sputtering

Cadmium oxide thin films with different percentages of aluminum doping have been synthesized via radio frequency magnetron sputtering technique. Thin films were deposited on glass and silicon substrates with different percentages of aluminum at a substrate temperature of 573 K and pressure of 0.1 mbar in Ar+O₂ atmosphere. The deposited films were characterized by studying their structural, electrical and optical properties. The X-ray diffraction pattern revealed good crystallinity with preferred (1 1 1) orientation in the films. Aluminum doping in CdO thin films were confirmed by X-ray photoelectron spectroscopic studies and actual doping percentages were also measured from it. The optical band gap was found to decrease first and then increase with increasing percentages of aluminum concentrations. The electrical conductivity was found to increase with increase of aluminum doping concentration up to 5% but for higher doping concentration (>5%) the conductivity was found to decrease.     

High near-infrared transparent molybdenum-doped indium oxide thin films for nanocrystalline silicon solar cell applications

Molybdenum-doped indium oxide (IMO) thin films were deposited at 450 °C for varying molybdenum concentrations in the range of 0.5-2 at% by the spray pyrolysis technique. These films confirmed the cubic bixbyite structure of polycrystalline In₂O_3. The preferred growth orientation along the (2 2 2) plane shifts to (4 0 0) on higher Mo doping levels. The films doped with 0.5 at% Mo showed high mobility of 76.9 cm²/(V s). The high visible transmittance extends well into the near-infrared region. A possibility of using the produced IMO films in nanocrystalline (nc) silicon solar cell applications is discussed in this article. The morphological studies showed a change in the microstructure, which is consistent with the change in crystallographic orientation.     

Effects of sputtering pressure on properties of Al doped ZnO thin films dynamically deposited by rf magnetron sputtering

Abstract

Aluminium doped zinc oxide (AZO) films were dynamically deposited by rf magnetron sputtering under various sputtering pressures in the range of 0·3–2·0 Pa. The effect of the Ar sputtering pressure on the structural, electrical and optical properties of the AZO films was systematically investigated by X-ray diffractometry, scanning electron microscope, four-point probe measurement and UV–vis spectrophotometer. As the sputtering pressures decrease, the crystallite sizes of the films became larger, while their deposition rate turns higher. Under the condition of lower sputtering pressures, a decrease in the resistivity was observed due to an increase in carrier concentration. The AZO film deposited at 0·5 Pa in the dynamic mode has shown the lowest resistivity of 9·5×10^?4 Ω cm. This work was performed in a dynamic deposition system in order to produce a large area of AZO films, which is more important in practical fields to improve productivity.     

Electrochromism of sol–gel derived niobium oxide films

Niobium oxide films are promising cathodic electrochromics that in many aspects can compete with the more frequently studied WO₃ films. The films reported herein were prepared using the sol–gel route from a NbCl₅ precursor. The electrochromic properties were pronounced for crystalline films heat-treated at 500°C and exhibited transmittance changes between coloured and bleached states of 60% in the ultraviolet (UV) and 80% in the visible (VIS) and near-infrared (NIR) regions. Improved bleaching and more reversible electrochromism of thick niobium oxide films (thickness (d)>250 nm) were obtained by lithiation.Electrochromic (EC) devices were also prepared by assembling niobium oxide and lithiated niobium oxide films of different thicknesses with a hybrid inorganic/organic Li⁺ ionic conductor (organically modified electrolyte-ormolyte) and a molybdenum and antimony doped tin oxide (SnO₂ : Sb(7%) : Mo(10%) counter electrode films. The EC devices exhibited adequate colouring/bleaching kinetics (<2 min) and colouring/bleaching changes up to 40–50%.     

Structural,optical, and H2 gas sensing analyses of Cr doped CuO thin films grown by ultrasonic spray pyrolysis

Here, a specific metal oxide (CuO) and its impurity (Cr) added composites were grown onto glass substrates as nanostructured thin films by executing ultrasonic spray pyrolysis method. The effects of the varied Cr dopant concentration on the morphological, structural, optical and H₂ gas sensor properties of the synthesized CuO thin films were determined by conducting scanning electron microscopy, X-ray Diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, ultraviolet–visible spectroscopy, and gas detection analyses. The X-Ray Diffraction analysis revealed the presence of CuO crystals with predominant (111) plane and it changed to (002) orientation for the doped samples, where crystallite sizes varied between 32 and 46 nm. The structural studies disclosed that the crystalline structure modified due to the added impurities. The scanning electron microscopy observations unveiled polyhedron-like shape formations of the synthesized nanostructures which also showed clear indications of changed morphology due to the impacts of different Cr doping percentages. Besides, the presence of copper, oxygen, and chromium was confirmed by EDX elemental analysis as well as X-ray photoelectron spectroscopy. The optical examination concluded that absorbance values followed a random trend with respect to the increased impurity contents while bandgap decreased with the increase of doping concentration. And, it was also noted that the luminescent emission peaks decreased in the photoluminescence spectroscopy as a result of introduced impurity levels. Finally, H₂ responsivity was detected for the grown films and found out that the impurity doping notably increased the sensitivity of the gas sensor based on the prepared CuO nanostructures.     

Low cost method to obtain counter electrode for dye sensitised solar cells

Abstract

In this paper, nanoscaled polypyrrole particles were synthesised using I₂ as dopant and oxidant, which were subsequently used to prepare polypyrrole/epoxy resin composition counter electrode for construction of dye sensitised solar cells (DSSCs). The results of photoelectric properties measurement revealed that the open-circuit voltage V _oc was 0·525 V, short circuit current density J _sc was 0·90 mA cm^–2, fill factor FF was 0·45 and overall energy conversion efficiency η was 0·22% respectively. The introduction of polypyrrole/epoxy resin counter electrode decreased the demand of fluorine doped tin oxide (FTO) coated glass substrate of DSSCs, which proposed a novel idea for the development of counter electrodes.     

Effect of alkaline-doping on photoelectrochemical activity of electrodeposited cuprous oxide films

P-type Cu₂O films with alkaline ions (Li⁺, Na⁺ and K⁺) of unintentional dopants on indium tin oxide coated glass substrate are successfully fabricated via a simple electrodeposition method for photoelectrochemical (PEC) hydrogen generation. The SEM and XRD analysis show the as-grown films with the pyramid-like morphology and cubic structure, and the composition of alkaline-doped Cu₂O films are examined using XPS spectroscopy to demonstrate the substitution of alkaline ions in the Cu₂O lattice. The optical analyses, including the absorbance and low-temperature photoluminescence spectra, confirm a bandgap of 2.3 eV and the presence of structural defects in alkaline-doped Cu₂O films. The Mott-Schottky plot shows the flat band potentials of the alkaline-doped Cu₂O films to be approximately ?0.1 V and the hole concentrations in the order of 10¹⁷ cm^?3. Significantly, the Cu₂O:Li film photocathode exhibits a higher photocurrent of ?2.2 mA cm^?2 at a potential of ?0.6 V vs Ag/AgCl which are greater than those of Cu₂O:K and Cu₂O:Na films due to greater preferred orientation degrees along (111) and less structural defects, because the ionic radii of Cu and Li is similar. These results demonstrate the great potential of alkaline doped Cu₂O films in solar-related applications.     

A new catalyst of AlCu@ZnO for hydrogen evolution reaction

Thin films of undoped ZnO, Al-doped ZnO, Cu-doped ZnO, and AlCu@ZnO deposited on indium tin oxide were performed by the sol-gel spin coating method. The prepared ZnO thin films were investigated for their structural and electrical properties after annealing at 500 °C for 1 h. ZnO thin films were characterized by electrochemical impedance spectroscopy, linear sweep voltammetry, scanning electron microscopy, Fourier transform infrared spectroscopy and Mott Schottky. According to the results obtained from the Nyquist diagrams of the ZnO thin films, the resistance value was found to decrease with binary doping and the resistance value was found to be lowest in AlCu@ZnO doped thin film containing 0.01 M Al and 0.1 M Cu. As ZnO thin films go to cathodic potentials, it is seen that the cathodic current value of ZnO with undoped is the lowest. It has been found that only Al and Cu doping showed less cathodic current than double doping.     

Growth of n- and p-type ZnTe semiconductors by intrinsic doping

Using intrinsic doping, n- and p-type ZnTe thin films have been electrodeposited (ED) on glass/fluorine-doped tin oxide (FTO) conducting substrate in aqueous solutions of ZnSO₄·7H₂O and TeO₂. The intrinsic doping was achieved by simply varying the deposition potential. The films have been characterised for their structural, optical, electrical, morphological and compositional properties using X-ray diffraction (XRD), optical absorption, photoelectrochemical (PEC) cell measurements, scanning electron microscopy and energy-dispersive X-ray analysis techniques, respectively. The XRD results reveal that the electroplated films are polycrystalline and have hexagonal crystal structures. Optical absorption measurements have been used for the bandgap determination of as-deposited and heat-treated ZnTe layers. The bandgap of the as-deposited ZnTe films are in the range (1.70–2.60) eV depending on the deposition potential. PEC cell measurements reveal that the ED-ZnTe films have both n- and p-type electrical conductivity. Using the n- and p-type ZnTe layers, a p-n homo-junction diode with device structure of glass/FTO/n-ZnTe/p-ZnTe/Au was fabricated. The fabricated diode showed rectification factor of 10², ideality factor of 2.58 and threshold voltage of ~0.25 V.     

Enhanced efficiency of hematite photoanode for water splitting with the doping of Ge

Ge doped α-Fe₂O₃ nanowires are synthesized through a hydrothermal procedure with GeO₂ as a precursor and investigated as photoanodes for water splitting. The content of Ge in the photoanode rises with the increase of the amount of GeO₂ in the precursor solution. A proper amount of Ge facilities the preferred oriented growth of the (110) plane of α-Fe₂O₃, while excessive Ge hinders the growth of α-Fe₂O₃ crystals. The doping of Ge increases the absorption efficiency and decreases the recombining rate of the photogenerated electrons and holes. Ge also improves the density and transfer rate of the charge carriers in the photoanode. Ge doped α-Fe₂O₃ photoanode exhibits a highest photocurrent density of 0.92 mA cm^?2 at 1.23 V vs. reversible hydrogen electrode under AM 1.5 G simulated sunlight, which is nearly twice of that obtained by pure α-Fe₂O₃ under the same condition.     

Study of optical properties of some sol–gel derived films of ZnO

The optical transmission and reflection data for aluminum doped zinc oxide films have been analyzed. The optical absorption coefficient (α) and hence the refractive index (n), extinction coefficient (k) and the band gap (E_g) have been determined for these films using different methods. The films are prepared by sol–gel technique and are optically transparent. It is observed that the band gap increases with aluminum doping from 3.19 to 3.24 eV, but is less than the bulk ZnO crystal. A qualitative explanation has been put forward for the band gap widening with doping. The width of the band tail states which is connected to localized states in the band gap is least for 1 at% doped aluminum film. The porosity of the films as deduced from the refractive index seems to be of the same order in all the cases, but relatively higher for 1 at% aluminum doped films.     

Optimisation of zinc oxide nanorods for use in dye sensitised solar cells

Abstract

Zinc oxide nanorods were fabricated via a low temperature hydrothermal method on fluorine doped tin oxide (FTO) substrates. The concentrations of hexamethylenetetramine (HMT) and polyethyleneimine (PEI) were optimised to give nanorods with an aspect ratio of ～110. Post-growth thermal annealing and nitrogen plasma treatment led to significant enhancement of the UV emission peak (380 nm) and suppression of the deep level emission peak (600 nm). Although the post-growth treatments did not appear to affect the crystallinity of the ZnO nanorods, the efficiency of dye sensitised solar cells constructed following the post-growth thermal treatments saw a decrease in efficiency.     

Doped tin oxide coated aluminium solar selective reflector surfaces

An experimental study of spectrally selective reflector (SSR) characteristics of pyrolytically deposited fluorine doped tin oxide on aluminium is reported. It is shown that a pyrolytically deposited doped tin oxide layer offers good spectral selectivity to the aluminium surface. High solar reflectance is obtained for wavelengths below 1.1 μm and low solar reflectance for wavelengths above 1.1 μm. The spectral selectivity is highly dependent on the preparation conditions, doping and thickness of the films and spectral selectivity was significantly improved if the aluminium surface was initially anodized. The results demonstrate a potential for producing SSR’s for silicon based solar cell concentrator applications.     

Effect of heat treatment on crystal phase and photocatalytic activity of Tm doped TiO2 nanoparticles

Abstract

Abstract

Tm doped TiO₂ nanoparticles have been synthesised by hydrolysis-precipitation method. The effect of heat treatment on the crystal phase and photocatalytic activity of Tm doped TiO₂ nanoparticles has been studied. The prepared samples were characterised by transmission electron microscopy, X-ray diffraction, Fourier transformed infrared and diffuse reflection spectrum analysis. The results show that Tm³⁺ doping can effectively inhibit the phase transformation from antase to rutile and decrease the crystallite size of nano-TiO₂ particles. There is an optimal Tm doping (1·4?mol.-%) after calcination at 550°C for the photocatalytic activity of methylene blue degradation.     

Oxide ionic conductivity and crystallographic properties of tetragonal type Bi2O3-based solid electrolyte doped with Ho2O3

Abstract

In the present work, the authors have investigated the binary system of (Bi₂O₃)_1–x(Ho₂O₃)_x. For the stabilisation of the tetragonal type solid solution, small amounts of Ho₂O₃ were doped into the monoclinic Bi₂O₃ via solid state reactions in the stoichiometric range 0·01≤x≤0·1. The crystal formula of the formed solid solution was determined as Bi(III)_4–4xHo(II)_4xO_6–2xVo_(2+2x) (where Vo is the oxide ion vacancy) according to the XRD and SEM microprobe results. In the crystal formula, stoichiometric values of x were 0·04≤x≤0·08, 0·03≤x≤0·09, 0·02≤x≤0·09 and 0·04≤x≤0·09 for annealing temperatures at 750, 800, 805 (quench) and 760°C (quench) respectively. The four probe electrical conductivity measurements showed that the studied system had an oxide ionic type electrical conductivity behaviour, which is increased with increasing dopant concentration and temperature. The obtained solid electrolyte system has an oxygen non-stoichiometry characteristic, and it contains O^2– vacancies, which have disordered arrangements in its tetragonal crystal structure. The increase in the amount of Ho₂O₃ doping and temperature causes an increasing degree of the disordering of oxygen vacancies and a decrease in the activation energy E_a.