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TiO2 Films (tio2 + film)
Kinds of TiO2 Films Selected AbstractsEffects of TiO2 Film on the Performance of Dye-sensitized Solar Cells Based on Ionic Liquid ElectrolyteCHINESE JOURNAL OF CHEMISTRY, Issue 12 2005Xu Pan Abstract Photo correlation spectroscopy was used to measure the particle size distribution of TiO2 films. Other parameters, such as porosity, BET surface area, average pore size, crystallite size D101, distribution of pore size etc. were also measured. The effects of these parameters on the ionic liquid based dye-sensitized solar cells (DSC) were studied. It was concluded that the particle size distribution of nanocrystalline TiO2 played an important role on the performance of DSC. The narrow particle size distribution of nanocrystalline TiO2 increased the efficiency of DSC, while the wide distribution decreased the efficiency of DSC. From the result above, it was also concluded that the photo correlation spectroscopy was a good method to identify the performance of TiO2 films. Based on electrochemical impedance spectroscopy, we found that the particle size distribution could affect the electronic contact between the TiO2 layers as well. The narrow particle size distribution made the electronic contact between TiO2 layers better than the wide particle size distribution of the TiO2 films, and then better the electronic contact, higher the efficiency of the DSC. [source] Dye-Sensitized Solar Cells Based on a Novel Fluorescent Dye with a Pyridine Ring and a Pyridinium Dye with the Pyridinium Ring Forming Strong Interactions with Nanocrystalline TiO2 FilmsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2010Yousuke Ooyama Abstract As new-type donor,acceptor ,-conjugated dyes capable of forming a strong interaction between the electron-acceptor moiety of the sensitizers and a TiO2 surface, fluorescent dye OH11 and pyridinum dye OH12 with a pyridine and pyridinium ring as the electron-accepting group, respectively, have been designed and synthesized as photosensitizers for use in dye-sensitized solar cells (DSSCs). The fluorescent dye OH11 exhibits an absorption band at around 410 nm and a fluorescence band at around 530 nm. On the other hand, the pyridinum dye OH12 shows an absorption maximum at around 560 nm, assigned to a strong intramolecular charge-transfer excitation from the dibutylamino group to the pyridinium ring. The short-circuit photocurrent densities of the DSSCs prepared by using OH11 and OH12 are 4.33 and 1.74mA cm,2, and the solar energy-to-electricity conversion yields are 1.33 and 0.51,%, respectively, under simulated solar light [AM (air mass) 1.5, 100 mW,cm,2]. The open-circuit photovoltage for OH11 (525 mV) is higher than that of OH12 (444 mV). The effects of the configuration of the dyes on the TiO2 surface and of their chemical structures on the photovoltaic performances are discussed on the basis of semi-empirical molecular orbital calculations (AM1 and INDO/S), spectral analyses and cyclic voltammetry. [source] Conformal Nano-Sized Inorganic Coatings on Mesoporous TiO2 Films for Low-Temperature Dye-Sensitized Solar Cell FabricationADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Larissa Grinis Abstract Here, a new method based on sol,gel electrophoretic deposition to produce uniform high-quality inorganic conformal coatings on mesoporous nano-particulate films is presented. This novel sol preparation method allows for very fine control of the coating properties, thus inducing new adjustable functionalities to these electrodes. It is shown that the deposition of an amorphous TiO2 and/or MgO shell onto photoanodes used in dye-sensitized solar cells (DSSCs) improves their light-to-electric-power conversion efficiency without the need for sintering. It is proposed that the amorphous TiO2 coating improves the electronic inter-particle connection and passivates the surface states. The insulating MgO coating further reduces the electron transfer from the conduction band into the electrolyte while the electron injection from the excited dye state remains unperturbed for thin coatings. Using a low-temperature method for DSSC production on plastic substrates, a maximum efficiency of 6.2% applying pressure together with an optimized TiO2 coating is achieved. For systems that cannot be pressed a conversion efficiency of 5.1% is achieved using a double shell TiO2/MgO coating. [source] Low-Temperature Atomic Layer-Deposited TiO2 Films with Low PhotoactivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009Xinhua Liang Atomic layer deposition (ALD) has been successfully utilized for the conformal and uniform deposition of ultrathin titanium dioxide (TiO2) films on high-density polyethylene (HDPE) particles. The deposition was carried out by alternating reactions of titanium tetraisopropoxide and H2O2 (50 wt% in H2O) at 77°C in a fluidized bed reactor. X-ray photoelectron spectroscopy confirmed the deposition of TiO2 and scanning transmission electron microscopy showed the conformal TiO2 films deposited on polymer particle surfaces. The TiO2 ALD process yielded a growth rate of 0.15 nm/cycle at 77°C. The results of inductively coupled plasma atomic emission spectroscopy suggested that there was a nucleation period, which showed the reaction mechanism of TiO2 ALD on HDPE particles without chemical functional groups. TiO2 ALD films deposited at such a low temperature had an amorphous structure and showed a much weaker photoactivity intensity than common pigment-grade anatase TiO2 particles. [source] Dual-Function Scattering Layer of Submicrometer-Sized Mesoporous TiO2 Beads for High-Efficiency Dye-Sensitized Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Fuzhi Huang Abstract Submicrometer-sized (830,±,40,nm) mesoporous TiO2 beads are used to form a scattering layer on top of a transparent, 6-µm-thick, nanocrystalline TiO2 film. According to the Mie theory, the large beads scatter light in the region of 600,800,nm. In addition, the mesoporous structure offers a high surface area, 89.1,m2 g,1, which allows high dye loading. The dual functions of light scattering and electrode participation make the mesoporous TiO2 beads superior candidates for the scattering layer in dye-sensitized solar cells. A high efficiency of 8.84% was achieved with the mesoporous beads as a scattering layer, compared with an efficiency of 7.87% for the electrode with the scattering layer of 400-nm TiO2 of similar thickness. [source] Highly Efficient Quantum-Dot-Sensitized Solar Cell Based on Co-Sensitization of CdS/CdSeADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Yuh-Lang Lee Abstract Cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots (QDs) are sequentially assembled onto a nanocrystalline TiO2 film to prepare a CdS/CdSe co-sensitized photoelectrode for QD-sensitized solar cell application. The results show that CdS and CdSe QDs have a complementary effect in the light harvest and the performance of a QDs co-sensitized solar cell is strongly dependent on the order of CdS and CdSe respected to the TiO2. In the cascade structure of TiO2/CdS/CdSe electrode, the re-organization of energy levels between CdS and CdSe forms a stepwise structure of band-edge levels which is advantageous to the electron injection and hole-recovery of CdS and CdSe QDs. An energy conversion efficiency of 4.22% is achieved using a TiO2/CdS/CdSe/ZnS electrode, under the illumination of one sun (AM1.5,100,mW cm,2). This efficiency is relatively higher than other QD-sensitized solar cells previously reported in the literature. [source] Dye-Sensitized Back-Contact Solar CellsADVANCED MATERIALS, Issue 38 2010Dongchuan Fu Dye-sensitized back-contact solar cells are fabricated on back plates comprising a patterned FTO glass substrate, a selectively deposited Pt coating, a protective ZrO2 coating covering the Pt layers and a screen printed TiO2 film. Such devices show a solar energy conversion efficiency of 3.64% under AM 1.5 sunlight and a peak incident photon to electron conversion efficiency of 54%. [source] Structure, electrical and optical properties of (PVA/LiAsF6) polymer composite electrolyte filmsPOLYMER ENGINEERING & SCIENCE, Issue 5 2010Madhu Mohan Varishetty In this work, Li+ ion conducting polymer composite electrolyte films (PECs) were prepared based on poly (vinyl alcohol) (PVA), lithium hexafluoro arsenate (LiAsF6), and ceramic filler TiO2 using solution cast technique. The XRD and FTIR spectra were used to determine the complexation of the PVA polymer with LiAsF6 salt. The ionic conductivities of the (PVA + LiAsF6) and (PVA + LiAsF6 + TiO2) films have been determined by the A.C. impedance measurements in the temperature range 320,440 K. The maximum conductivity was found to be 5.10 × 10,4 S cm,1 for PVA:LiAsF6 (75:25) + 5 wt% TiO2 polymer composite film at 320 K. The calculation of Li+ ion transference number was carried out by the combination of A.C. impedance and D.C. polarization methods and is found to be 0.52 for PVA:LiAsF6 (75:25) + 5 wt% TiO2 film. Optical properties such as direct energy gap, indirect energy gap, and optical absorption edge values were investigated in pure PVA and salt complexed PVA films from their optical absorption spectra in the wavelength range of 200,600 nm. The absorption edge was found at 5.76 eV for undoped film, while it is observed at 4.87 and 4.70 eV for 20 and 25 wt% LiAsF6 doped films, respectively. The direct band gaps for these undoped and salt doped PVA films were found to be 5.40, 5.12, and 4.87 eV, respectively, whereas the indirect band gaps were determined as 4.75, 4.45, and 4.30 eV. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] The Influence of Charge Transport and Recombination on the Performance of Dye-Sensitized Solar CellsCHEMPHYSCHEM, Issue 1 2009Mingkui Wang Dr. Abstract Electrochemical impedance spectroscopy (EIS) and transient voltage decay measurements are applied to compare the performance of dye sensitized solar cells (DSCs) using organic electrolytes, ionic liquids and organic-hole conductors as hole transport materials (HTM). Nano-crystalline titania films sensitized by the same heteroleptic ruthenium complex NaRu(4-carboxylic acid-4,-carboxylate) (4,4,-dinonyl-2,2,-bipyridyl)(NCS)2,, coded Z-907Na are employed as working electrodes. The influence of the nature of the HTM on the photovoltaic figures of merit, that is, the open circuit voltage, short circuit photocurrent and fill factor is evaluated. In order to derive the electron lifetime, as well as the electron diffusion coefficient and charge collection efficiency, EIS measurements are performed in the dark and under illumination corresponding to realistic photovoltaic operating conditions of these mesoscopic solar cells. A theoretical model is established to interpret the frequency response off the impedance under open circuit conditions, which is conceptually similar to photovoltage transient decay measurements. Important information on factors that govern the dynamics of electron transport within the nanocrystalline TiO2 film and charge recombination across the dye sensitized heterojunction is obtained. [source] Ordered Mesoporous Thin Films of Rutile TiO2 Nanocrystals Mixed with Amorphous Ta2O5CHEMPHYSCHEM, Issue 5 2008Jin-Ming Wu Dr. Abstract Ordered mesoporous thin films of composites of rutile TiO2 nanocrystals with amorphous Ta2O5 are fabricated by evaporation-induced self-assembly followed by subsequent heat treatment beyond 780,°C. Incorporation of selected amounts of Ta2O5 (20 mol,%) in the mesoporous TiO2 film, together with the unique mesoporous structure itself, increased the onset of crystallization temperature which is high enough to ensure the crystallization of amorphous titania to rutile. The ordered mesoporous structure benefits from a block-copolymer template, which stabilizes the mesostructure of the amorphous mixed oxides before crystallization. The surface and in-depth composition analysis by X-ray photoelectron spectroscopy suggests a homogeneous intermixing of the two oxides in the thin film. A detailed X-ray absorption fine structure measurement on the composite film containing 20 mol,% Ta2O5 and heated to 800,°C confirms the amorphous nature of the Ta2O5 phase. Photocatalytic activity evaluation suggests that the rutile nanocrystals in the synthesized ordered mesoporous thin film possess good ability to assist the photodegradation of rhodamine B in water under illumination by UV light. [source] Electropolymerization and Electrochromic Properties of Poly(3-bromothiophene) Films on a Transparent Nano-mesoporous TiO2 SurfaceCHINESE JOURNAL OF CHEMISTRY, Issue 11 2008He XU A novel method for electrodeposition of poly(3-bromothiophene) film onto nano- and mesoporous TiO2 film was developed. The PBrT/TiO2 exhibited excellent electrochromic properties with good coloration efficiency and high chromatic contrast, which could be a commercially promising electrochromic material. [source] Effect of annealing on the structural, electrical and optical properties of nanostructured TiO2 thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2009S. Sankar Abstract Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO2 films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV-Visible spectroscopy and electrical studies. X-ray diffraction studies showed that the as-deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator-Wemple and Didomenico model. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tungsten Oxide and Tungsten Oxide-Titania Thin Films Prepared by Aerosol-Assisted Deposition , Use of Preformed Solid NanoparticlesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2007Uzma Qureshi Abstract Aerosol-assisted deposition (AAD) was used to deposit films of WO3 from a suspension of solid nanoparticulate WO3 in toluene. Titania films were deposited by the aerosol-assisted chemical vapour deposition of [Ti(OiPr)4] in the presence of WO3 nanoparticles. The WO3 and TiO2 films exhibited photoactivity and photoinduced superhydrophilicity, further the titania films showed very unusual highly crenulated microstructures. These microstructures could not be obtained by sol-gel, atmospheric pressure chemical vapour deposition or evaporation routes. Furthermore, the microstructures could not be obtained from [Ti(OiPr)4] in the absence of nanoparticulate WO3. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Capacitors with an Equivalent Oxide Thickness of <0.5 nm for Nanoscale Electronic Semiconductor MemoryADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Seong Keun Kim Abstract The recent progress in the metal-insulator-metal (MIM) capacitor technology is reviewed in terms of the materials and processes mostly for dynamic random access memory (DRAM) applications. As TiN/ZrO2 -Al2O3 -ZrO2/TiN (ZAZ) type DRAM capacitors approach their technical limits, there has been renewed interest in the perovskite SrTiO3, which has a dielectric constant of >100, even at a thickness ,10 nm. However, there are many technical challenges to overcome before this type of MIM capacitor can be used in mass-production compatible processes despite the large advancements in atomic layer deposition (ALD) technology over the past decade. In the mean time, rutile structure TiO2 and Al-doped TiO2 films might find space to fill the gap between ZAZ and SrTiO3 MIM capacitors due to their exceptionally high dielectric constant among binary oxides. Achieving a uniform and dense rutile structure is the key technology for the TiO2 -based dielectrics, which depends on having a dense, uniform and smooth RuO2 layer as bottom electrode. Although the Ru (and RuO2) layers grown by ALD using metal-organic precursors are promising, recent technological breakthroughs using the RuO4 precursor made a thin, uniform, and denser Ru and RuO2 layer on a TiN electrode. A minimum equivalent oxide thickness as small as 0.45 nm with a low enough leakage current was confirmed, even in laboratory scale experiments. The bulk dielectric constant of ALD SrTiO3 films, grown at 370 °C, was ,150 even with thicknesses ,15 nm. The recent development of novel group II precursors made it possible to increase the growth rate largely while leaving the electrical properties of the ALD SrTiO3 film intact. This is an important advancement toward the commercial applications of these MIM capacitors to DRAM as well as to other fields, where an extremely high capacitor density and three-dimensional structures are necessary. [source] PbS and CdS Quantum Dot-Sensitized Solid-State Solar Cells: "Old Concepts, New Results"ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009HyoJoong Lee Abstract Lead sulfide (PbS) and cadmium sulfide (CdS) quantum dots (QDs) are prepared over mesoporous TiO2 films by a successive ionic layer adsorption and reaction (SILAR) process. These QDs are exploited as a sensitizer in solid-state solar cells with 2,2,,7,7,-tetrakis(N,N -di- p -methoxyphenylamine)-9,9,-spirobifluorene (spiro-OMeTAD) as a hole conductor. High-resolution transmission electron microscopy (TEM) images reveal that PbS QDs of around 3,nm in size are distributed homogeneously over the TiO2 surface and are well separated from each other if prepared under common SILAR deposition conditions. The pore size of the TiO2 films and the deposition medium are found to be very critical in determining the overall performance of the solid-state QD cells. By incorporating promising inorganic QDs (PbS) and an organic hole conductor spiro-OMeTAD into the solid-state cells, it is possible to attain an efficiency of over 1% for PbS-sensitized solid-state cells after some optimizations. The optimized deposition cycle of the SILAR process for PbS QDs has also been confirmed by transient spectroscopic studies on the hole generation of spiro-OMeTAD. In addition, it is established that the PbS QD layer plays a role in mediating the interfacial recombination between the spiro-OMeTAD+ cation and the TiO2 conduction band electron, and that the lifetime of these species can change by around 2 orders of magnitude by varying the number of SILAR cycles used. When a near infrared (NIR)-absorbing zinc carboxyphthalocyanine dye (TT1) is added on top of the PbS-sensitized electrode to obtain a panchromatic response, two signals from each component are observed, which results in an improved efficiency. In particular, when a CdS-sensitized electrode is first prepared, and then co-sensitized with a squarine dye (SQ1), the resulting color change is clearly an addition of each component and the overall efficiencies are also added in a more synergistic way than those in PbS/TT1-modified cells because of favorable charge-transfer energetics. [source] Pore-Filling of Spiro-OMeTAD in Solid-State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 15 2009I-Kang Ding Abstract In this paper, the pore filling of spiro-OMeTAD (2,2,,7,7,-tetrakis-(N,N -di- p -methoxyphenylamine)9,9,-spirobifluorene) in mesoporous TiO2 films is quantified for the first time using XPS depth profiling and UV,Vis absorption spectroscopy. It is shown that spiro-OMeTAD can penetrate the entire depth of the film, and its concentration is constant throughout the film. We determine that in a 2.5-µm-thick film, the volume of the pores is 60,65% filled. The pores become less filled when thicker films are used. Such filling fraction is much higher than the solution concentration because the excess solution on top of the film can act as a reservoir during the spin coating process. Lastly, we demonstrate that by using a lower spin coating speed and higher spiro-OMeTAD solution concentration, we can increase the filling fraction and consequently the efficiency of the device. [source] A High-Light-Harvesting-Efficiency Coumarin Dye for Stable Dye-Sensitized Solar Cells,ADVANCED MATERIALS, Issue 8 2007Z.-S. Wang A new coumarin dye (see figure) for use in dye-sensitized solar cells (DSSCs) is reported. It exhibits near-unity light harvesting efficiency and incident photon-to-electron conversion efficiency (see figure) over a wide spectral region in 6,,m transparent TiO2 films. DSSCs based on this metal-free organic dye show long-term stability and power-conversion efficiencies of around 6,% under continuous light-soaking stress for up to 1000,h. [source] A 4,% Efficient Dye-Sensitized Solar Cell Fabricated from Cathodically Electrosynthesized Composite Titania Films,ADVANCED MATERIALS, Issue 21 2003J. Yamamoto Cathodically electrosynthesized TiO2 films (see Figure) containing occluded Degussa P-25 titania particles can yield short-circuit current densities as high as 10.5 mA,cm,2, an open-circuit photovoltage of 690 mV, a fill factor of 57.3,%, and a photovoltaic efficiency of 4.13,% under simulated air mass 1.5 (100 mW,cm,2) sunlight in a dye-sensitized solar cell device. [source] Rigorous modeling of UV absorption by TiO2 films in a photocatalytic reactorAICHE JOURNAL, Issue 7 2000Z. Zhang The radiation absorption profiles on the surfaces of TiO2 films in a corrugated-plate photocatalytic reactor were modeled based on first principles. A new term, the local-area-specific rate of energy absorption (LASREA), was adopted to describe the catalyst surface radiation in heterogeneous photoreactors. The LASREA and the energy absorption efficiency were both quite sensitive to the dimensions of the corrugated plates. Due to the multiple photon reflections between the opposing surfaces, corrugated plates possess a superior capability for recapturing longer wavelength photons that would otherwise be reflected out of some reactor designs. This results in higher energy absorption efficiency and more uniform LASREA on the catalyst films. Compared to a flat plate, corrugations are predicted to enhance the energy absorption efficiency by up to 50% for UV-A fluorescent-lamp-powered systems and more than 100% for solar-powered systems. [source] Preparation of Crystalline-Oriented Titania Photoelectrodes on ITO Glasses from a 2-Propanol,2,4-Pentanedione Solvent by Electrophoretic Deposition in a Strong Magnetic FieldJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009Mamiko Kawakita Crystal-oriented and crack-free thin TiO2 films with a good interfacial adhesion on indium,tin oxide glass substrates for photoelectrodes of dye-sensitized solar cells were fabricated by the constant voltage electrophoretic deposition (EPD) method in a strong magnetic field of 12 T generated by a superconducting magnet. A binder-free suspension for the EPD was prepared by dispersing TiO2 in a mixture of 2-propanol and 2,4-pentanedione (acetylacetone). The electrical conductivity, sedimentation rate, and the electrophoretic mobility were measured at varying ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO2 films were characterized by X-ray diffraction and scanning electron microscopic analyses. [source] Low-Temperature Atomic Layer-Deposited TiO2 Films with Low PhotoactivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009Xinhua Liang Atomic layer deposition (ALD) has been successfully utilized for the conformal and uniform deposition of ultrathin titanium dioxide (TiO2) films on high-density polyethylene (HDPE) particles. The deposition was carried out by alternating reactions of titanium tetraisopropoxide and H2O2 (50 wt% in H2O) at 77°C in a fluidized bed reactor. X-ray photoelectron spectroscopy confirmed the deposition of TiO2 and scanning transmission electron microscopy showed the conformal TiO2 films deposited on polymer particle surfaces. The TiO2 ALD process yielded a growth rate of 0.15 nm/cycle at 77°C. The results of inductively coupled plasma atomic emission spectroscopy suggested that there was a nucleation period, which showed the reaction mechanism of TiO2 ALD on HDPE particles without chemical functional groups. TiO2 ALD films deposited at such a low temperature had an amorphous structure and showed a much weaker photoactivity intensity than common pigment-grade anatase TiO2 particles. [source] Influence of Dipolar Fields on the Photochemical Reactivity of Thin Titania Films on BaTiO3 SubstratesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Nina V. Burbure The photochemical properties of TiO2 films supported on BaTiO3 were investigated to test the hypothesis that dipolar fields from a ferroelectric substrate would affect the reactivity of the supported film. Photochemical reaction products were formed on the TiO2 surface in patterns that correspond to the underlying domain structure of BaTiO3. As the film thickness increases from 10 to 100 nm, the titania more effectively screens the ferroelectric field, and the pattern of reaction products is obscured. It is concluded that dipolar fields from the ferroelectric substrate influence charge carrier transport in the film and spatially localize the reaction products. [source] Transparent Anatase Nanocomposite Films by the Sol,Gel Process at Low TemperaturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Atsunori Matsuda We have successfully prepared transparent anatase nanocomposite films on various types of substrates, including organic polymers, using the sol,gel method at temperatures <100°C under ambient pressure. This novel process is based on the findings that (i) anatase nanocrystals are uniquely formed in sol,gel-derived SiO2,TiO2 films that have been subjected to a hot-water treatment, and (ii) the addition of an organic polymer such as poly(ethylene glycol) in the films accelerates the formation of anatase nanocrystals. The film coating on the substrates is a promising candidate for use as a photocatalyst to decompose environmental pollutants and harmful microorganisms. [source] Effect of the substrate temperature on the properties of the RF sputtered TiO2 thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2010I. Ben Mbarek Abstract Titanium dioxide (TiO2) thin films were deposited by RF magnetron sputtering on glass and silicon substrates at different substrate temperatures (20, 100, 200 and 300 °C). The structural and morphological characteristics of the films were investigated by X ray Diffractometry (XRD) and Atomic Force Microscopy (AFM) while the optical properties of the films were studied by optical spectroscopy. It was shown that at room temperature, TiO2 films grown on glass were amorphous following the substrate structure. At higher temperatures, XRD detected only a nanocrystalline rutile TiO2 structure. This indicated that the transition temperature toward the most stable TiO2 phase was obtained from 100 °C and the crystallinity was enhanced at higher growth temperature. For TiO2 films grown on Si substrates, only a nanocrystalline anatase TiO2 structure was obtained at room temperature. At higher temperatures, we noticed the appearance of other secondary phases related to rutile, anatase and brookite structures. From AFM images, we noticed that at room temperature, the films were porous. With increasing the temperature, the structure of the films became crystallized showing a columnar structure. Film growth and structural properties were discussed in terms of the Thornton model. From optical analysis, the films were transparent with an indirect band gap and a refraction index which reached 3.09 eV and 2.7, respectively. The reflectance and transmittance spectra showed, not only that there was a little translation from UVB to UVA and near-visible range, but also a decrease of reflection with a temperature increase indicating that the films could be used as anti-reflection coatings. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Titanium dioxide thin films deposited by the sol-gel technique starting from titanium oxy-acetyl acetonate: gas sensing and photocatalyst applicationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2010A. Maldonado Abstract Titanium dioxide (TiO2) thin films were deposited onto sodocalcic glass plates by the sol-gel technique, starting from a non-alkoxide route, namely, titanium oxy-acetyl acetonate as Ti precursor. Film thickness effect on both the gas sensing and photocatalytic degradation performance was studied. The as-deposited films were annealed in air at 400 °C. All the X-ray spectra of the films show a very broad-peak centered in a 2, angle around 30°. In the case of the thinnest films the surface morphology is uniform and very smooth, whereas for the thickest films the corresponding surface is covered by grains with a rod-like shape with a length on the order of 140 nm. The films were tested both for two straightforward applications: ultraviolet assisted-degradation of methylene blue dissolved in water, at different times, as well as gas sensor in a controlled propane (C3H8) atmosphere. As the film thickness increases, the degradation of methylene blue (MB) also increases. The thickest TiO2 thin films after being exposed by 5 hours to the catalytic degradation, promoted by ultraviolet illumination, showed a final MB solution degradation in the order of 48%. This reult can be associated with the increase in the effective exposed area of the TiO2 thin films. On the other hand, the exposition of the films to a controlled propane atmosphere produced a significant change in the surface electrical resistance of the films at operating temperatures of 200 °C and above. In fact, in the case of the thickest TiO2 films, a dramatic electrical resistance change of non-exposed and propane exposed , 560 to 0.7 M, ,, was registered. The results show that TiO2 films deposited by an economical deposition technique, as is the case of the sol-gel technique, could have an important potential in industrial applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and spectroscopic study of the Fe doped TiO2 thin films for applications in photocatalysisPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009N. R. Mathews Abstract In this work we are presenting the results of structural and optical investigations of TiO2 and Fe doped TiO2 films using XRD, XPS, UV-VIS transmittance spectroscopy, and the application of these films in photocatalysis is demonstrated. Fe-doped TiO2 films were prepared by sol-gel method. The concentration of Fe utilized for doping ranged from 0.5 to 4% by atomic weight. For lower concentrations of Fe the transformation from amorphous-to-polycrystalline occurred at 400 °C. However, as the Fe concentration was increased to 4% this transformation occurred only after annealing at 600 °C. The average grain size for 4% Fe doped sample was in the range of 13 nm. In the case of pure TiO2 the XPS analysis showed only the presence of Ti 4+, where the 4% Fe doped film showed the presence of two species of Ti atoms; one of unperturbed Ti atoms and another of negatively charged surface of Ti atoms due to the interaction with Fe atoms in the anatase lattice of TiO2. The optical band gap was found to decrease with Fe concentration. The resistivity was found to decrease by one order after doping. The 4% Fe doped TiO2 films showed an increased photocatalytic activity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] CVD of Thin Titanium Dioxide Films Using Hexanuclear Titanium Oxo Carboxylate Isopropoxides,CHEMICAL VAPOR DEPOSITION, Issue 10 2005P. Piszczek TiO2 films can deposited at 400,600,°C on Si(111), carbon fiber (see Figure), and activated carbon grain substrates via thermal inducted CVD using [Ti6O6(OiPr)6(OOCR)6] (R = tBu (1), CH2tBu (2)) as precursors. Deposition of layers with a low content of impurities (lower than 2%) can be achieved using Ar/H2O as a carrier gas. The structure and surface morphology of films change with increasing temperature from large grain layers of anatase (TD,=,440,460,°C), to close-packed crystals of rutile (TD,=,580,600,°C). [source] Novel Zinc Porphyrin Sensitizers for Dye-Sensitized Solar Cells: Synthesis and Spectral, Electrochemical, and Photovoltaic PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Cheng-Wei Lee Abstract Novel meso - or ,-derivatized porphyrins with a carboxyl group have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSCs). The position and nature of a bridge connecting the porphyrin ring and carboxylic acid group show significant influences on the spectral, electrochemical, and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins with a phenylethynyl bridge show that both Soret and Q,bands are red-shifted with respect to those of porphyrin 6. This phenomenon is more pronounced for porphyrins 3 and 4, which have a ,-conjugated electron-donating group at the meso position opposite the anchoring group. Upon introduction of an ethynylene group at the meso position, the potential at the first oxidation alters only slightly whereas that for the first reduction is significantly shifted to the positive, thus indicating a decreased HOMO,LUMO gap. Quantum-chemical (DFT) results support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrin 5, which exhibits the best photovoltaic performance among all the porphyrins under investigation. From a comparison of the cell performance based on the same TiO2 films, the devices made of porphyrin 5 coadsorbed with chenodeoxycholic acid (CDCA) on TiO2 in ratios [5]/[CDCA]=1:1 and 1:2 have efficiencies of power conversion similar to that of an N3 -based DSSC, which makes this green dye a promising candidate for colorful DSSC applications. [source] Effects of TiO2 Film on the Performance of Dye-sensitized Solar Cells Based on Ionic Liquid ElectrolyteCHINESE JOURNAL OF CHEMISTRY, Issue 12 2005Xu Pan Abstract Photo correlation spectroscopy was used to measure the particle size distribution of TiO2 films. Other parameters, such as porosity, BET surface area, average pore size, crystallite size D101, distribution of pore size etc. were also measured. The effects of these parameters on the ionic liquid based dye-sensitized solar cells (DSC) were studied. It was concluded that the particle size distribution of nanocrystalline TiO2 played an important role on the performance of DSC. The narrow particle size distribution of nanocrystalline TiO2 increased the efficiency of DSC, while the wide distribution decreased the efficiency of DSC. From the result above, it was also concluded that the photo correlation spectroscopy was a good method to identify the performance of TiO2 films. Based on electrochemical impedance spectroscopy, we found that the particle size distribution could affect the electronic contact between the TiO2 layers as well. The narrow particle size distribution made the electronic contact between TiO2 layers better than the wide particle size distribution of the TiO2 films, and then better the electronic contact, higher the efficiency of the DSC. [source] | ||||||||||||||||