Nanocrystalline porous nitrogen doped titanium dioxide (TiO2) thin films were prepared by DC magnetron sputtering. Films were deposited in a plasma of argon, oxygen, and nitrogen, with varying nitrogen contents. The films were characterized by X-ray diffraction, scanning electron microscopy, and optical- and photoelectrochemical (PEC) measurements. These studies showed that the films were porous and displaying rough surfaces with sharp, protruding nodules having a crystal structure varying from rutile to anatase depending on the nitrogen content. All nitrogen doped films showed visible light absorption in the wavelength range from 400 to 535 nm. The PEC properties of the thin film electrodes were determined on as-deposited as well as dye-sensitized films. The nitrogen doped TiO2 generated an incident photon-to-current efficiency response in good agreement with the optical spectra. The PEC measurements on dye-sensitized films showed that the electron-transfer properties in the conduction band were similar to those of undoped TiO2. It was also experimentally confirmed that the states introduced by nitrogen lie close to the valence band edge. For the best nitrogen doped TiO2 electrodes, the photoinduced current due to visible light and at moderate bias was increased around 200 times compared to the behavior of pure TiO2 electrodes. There is an optimum in introduced nitrogen where the response is highest.

Films of nitrogen-doped TiO2 were made by reactive DC magnetron sputtering in a mixture of argon, oxygen, and nitrogen. The nitrogen gas ratio Φ was varied in the 0 < Φ < 0.025 range during the depositions, resulting in TiO2 - x N x films with 0 ≤ x ≤ 0.022 as determined by X-ray photoelectron spectroscopy. Structural and morphological properties of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning and transmission electron microscopy. Films prepared without nitrogen had a rutile structure, while the nitrogen-doped films were either rutile or anatase depending on Φ being below or above ∼0.007. Deposition rate, effective grain size, root-mean-square roughness, morphology, and optical absorption were also found to depend on Φ. The films were photoelectrochemically active, as reported in an earlier papers of ours [J. Phys. Chem. B 2003, 107, 5709−5716 and J. Phys. Chem. B 2004, 108, 5995−6003].

Nanostructured mesoporous titanium dioxide (TiO2) particles with high specific surface area and average crystallite domain sizes within 2 nm and 30 nm have been prepared via the sol-gel and hydrothermal procedures. The characteristics of produced nanoparticles have been tested using X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR), and Raman Spectroscopy as a function of temperature for their microstructural, porosity, morphological, structural and absorption properties. The as-synthesized TiO2 nanostructures were attempted as catalysts in Rhodamine B and Sudan III dyes' photocatalytic decomposition in a batch reactor with the assistance of Ultra Violet (UV) light. The results show that for catalysts calcined at 300 °C, ∼100 % decomposition of Sudan III dye was observed when Hydrothermal based catalyst was used whiles ∼94 % decomposition of Rhodamine B dye was observed using the sol-gel based catalysts. These synthesized TiO2 nanoparticles have promising potential applications in the light aided decomposition of a wide range of dye pollutants.

This is an author produced version of a paper published in Journal of Electroanalytical Chemistry. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. AbstractThin TiO 2 (anatase) films were prepared by reactive DC magnetron sputtering and characterized in detail. Specifically, they were tested as compact blocking underlayers in dye-sensitized solar cells. Elastic recoil detection analysis and optical measurement showed some porosity in the sputtered films, but electrochemical measurements demonstrated good blocking characteristics. This suggests the presence of small voids rather than pinholes in the deposited films. In the case of an iodide/iodine redox couple, thin underlayers (~20 nm) improved the fill factor without affecting other properties of 1 the cell. In case of a ferrocene / ferrocenium-based electrolyte, the presence of underlayers was necessary to obtain functional dye-sensitized solar cells.

Temperature‐dependent electrical characterization of a highly structured TiO2/In(OH)x Sy /Pb(OH)x Sy /PEDOT:PSS eta solar cell has been carried out. The transport mechanism in this type of solar cell has been investigated. A schematic energy band diagram which explains the photoelectrical properties of the device has been proposed. The solar cell has been characterized in the temperature range 200–320 K at illumination intensities between 0.05 mW/cm2 and 100 mW/cm2. The diode ideality factor A under illumination has been found to vary between 1.2 and 1.6, whereas in the dark 6.9 ≤ A ≤ 10.1. The device has been found to undergo a thermally activated recombination under illumination, while tunnelling enhanced recombination has been established to dominate the current in the dark. The solar cell efficiency shows a logarithmic dependence on illumination in the whole temperature range investigated, achieving its maximum at an illumination of ∼45 mW/cm2. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Dye sensitized solar cells based on annealed titanium dioxide films prepared by oblique reactive DC magnetron sputtering have been investigated in detail. Electron transport and recombination were studied using intensity-modulated photocurrent and photovoltage spectroscopy. Electron transport time as well as lifetime were found to increase upon lowering of the light intensity and to increase upon increasing the thickness of the TiO 2 film. The properties are very similar to those observed for solar cells based on colloidal TiO 2 films despite the morphologies being very different. In all cases, films are composed of a porous assembly of TiO 2 nanocrystals. Grain boundaries with associated trap and/or energy barriers may explain the observed transport properties.

The influence of concentration of anthocyanins in dye sensitized solar cells (DSSC) has been investigated, with focus on how concentration influence electron transport. The influence on electron transport was then linked to solar cell performance. Anthocyanins were extracted from fresh flowers of Acanthus pubscenes using methanol acidified with 0.5% trifluoracetic acid, concentrated using a rotary evaporator and partitioned against ethyl acetate. Concentration of the anthocyanins was determined using Keracyanin Chloride as a standard. DSSC were fabricated using Titanium dioxide as anode, anthocyanins as sensitizers and Platinum as counter electrode material. Titanium dioxide was deposited on Fluorine doped Tin oxide glass substrate using slot coating method. Platinum was deposited on FTO glass substrate using a brush previously dipped in plastisol precursor, and annealed at 0 C for 20 min to activate Platinum. Dye sensitized solar cells were assembled using anthocyanins at varying concentrations. Performance parameters of the solar cells were measured using a solar simulator which was fitted with digital source meter. Electron transport parameters were studied using electrochemical impedance spectroscopy (EIS). Open circuit voltage, short circuit current and fill factor were observed to increase with concentration of anthocyanins. The increase in solar cell performance was attributed to increase in charge density which led more charges being available for transported to solar cell contacts. The increased charge resulted in a negative shift in Fermi level of electrons in the conduction band of TiO 2 . The shift in Fermi level resulted into an increase in open circuit voltage and the overall solar cell performance. EIS studies revealed increase in recombination resistance with concentration of anthocyanins. The increase in recombination resistance was found to be related to increase in electron density, and hence the shift in the Fermi level of electrons in the conduction band of TiO 2 .