CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010
S. Kim
Abstract Currently, the use of fuel cell electrodes containing Pt catalysts has been limited due to technological problems in this system, primarily the system's high cost. The improvement of Pt catalyst use has been achieved by changes in the Pt immobilization method. In this study, we have studied Pt immobilization on carbon nanofiber composites using the photodeposition method. First, we prepared the carbon nanofibers, which were homogeneously embedded TiO2 using the electrospinning technology. These TiO2 -embedded carbon nanofiber composites (TiO2/CNFs) were then immersed in a Pt precursor solution and irradiated with UV light. The obtained Pt-deposited TiO2/CNFs contained Pt that was immobilized on the carbon nanofibers, and the Pt particle size was 2-5 nm. The XPS spectra showed that the amount of Pt increased with an increasing UV irradiation time. The current densities and total charge also increased with an increase in the UV irradiation time, possibly due to an increase of active specific area by finely dispersed Pt nanoparticles. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Photoelectrical properties of crystalline titanium dioxide thin films after thermo-annealing

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007
R. Sathyamoorthy
Abstract This paper reports the photoelectrical properties of sol gel derived titanium dioxide (TiO2) thin films annealed at different temperatures (425-900°C). The structure of the as-grown film was found to be amorphous and it transforms to crystalline upon annealing. The trap levels are studied by thermally stimulated current (TSC) measurements. A single trap level with activation energy of 1.5 eV was identified. The steady state and transient photocurrent was measured and the results are discussed on the basis of structural transformation. The photocurrent was found to be maximum for the films annealed at 425°C and further it decreases with annealing at higher temperatures. The photoconduction parameters such as carrier lifetime, lifetime decay constant and photosensitivity were calculated and the results are discussed as a function of annealing temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Growth and optical characterization of cerium and lead-doped Bi12TiO20 sillenite single crystals

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005
J. F. Carvalho
Abstract Bi12TiO20 (BTO) single crystals doped with PbO and CeO2 were grown by the Top Seeded Solution Growth (TSSG) technique from the liquid phase with nominal compositions of 10Bi2O3 : (1,x)TiO2 : x PbO and 10Bi2O3 : (1,x)TiO2 : xCeO2 with x = 0.25 and 0.10. No growth-related difficulties were encountered other than those typical of sillenite crystals. Samples with good optical quality were obtained and were characterized by optical absorption, dark current, spectral photocurrent dependence, optical activity and electro-optic coefficient measurements. A comparison is made of the results of the optical measurements of doped and undoped BTO crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Particle size of powders under hydrothermal conditions

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2003
Wen-Jun Li
Abstract Various non-oxide (CuI, AgI, AgCl, PbS, CuS and ZnS) and oxide (ZnO, TiO2, SnO2, CeO2 and ZrO2) powders were prepared under hydrothermal conditions to investigate the effects of temperature, pH and precursors on the particle size of powders. It was found that the particle sizes of PbS, CuS and ZnS powders were much smaller than that of CuI, AgI and AgCl powders prepared under the same conditions. The particle sizes of TiO2, SnO2, CeO2 and ZrO2 powders are much smaller than that of ZnO powders prepared under the same conditions. It is concluded that the solution conditions have a certain effect on the particle size of powders under the hydrothermal conditions. The particle size of powders increased with the rising of temperature. Additional factors affecting the particle size were uncovered through studying the nucleation mechanism. The particle size was mainly related to the Madelung constant and the electric charge number of ions. Powders with smaller particle size resulted from systems that possessed the larger Madelung constant and ionic charge number. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Direct Electron Transfer and Electrocatalysis of Hemoglobin on Chitosan-TiO2 Nanorods-Glass Carbon Electrode

ELECTROANALYSIS, Issue 20 2008
Xiaoling Xiao
Abstract The direct electron transfer between hemoglobin (Hb) and the glassy carbon electrode (GC) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and TiO2 nanorods (TiO2 -NRs). TiO2 -NRs greatly promote the electron transfer between Hb and GC, which contribute to the higher redox peaks. UV-vis spectra result indicated the Hb entrapped in the composite film well keep its native structure. The immobilized Hb remains its bioelectrocatalytical activity to the reduction of H2O2 with a lower detection limit. A novel, sensitive, reproducible and stable electrochemical biosensing platform of H2O2 based on Hb-TiO2 -CHT electrode is explored. [source]

Performance of Impedimetric Biosensors Based on Anodically Formed Ti/TiO2 Electrodes

ELECTROANALYSIS, Issue 20 2005
Aikaterini
Abstract The advantages and limitations of impedimetric sensors based on Ti/TiO2 architectures are described. Titanium dioxide (titania) was potentiostatically formed onto titanium electrodes of 2,mm diameter, at 10 and 30,V in 1,M H2SO4. The thickness of the titania layers was ellipsometrically determined to be 30 and 86,nm respectively and they are highly insulating with charge-transfer resistances in the M, range, as they were measured with electrochemical impedance spectroscopy under specific experimental conditions. Low voltage anodization (<10,V) results to amorphous TiO2, whereas at higher applied voltages (>25,V), anatase is the predominant form. SEM images are indicative of quite smooth, compact coatings without any severe cracks. [source]

Immobilization and Electrochemistry of Negatively Charged Proteins on Modified Nanocrystalline Metal Oxide Electrodes

ELECTROANALYSIS, Issue 12 2005
Emmanuel Topoglidis
Abstract The immobilization of two acidic, low isoelectric point proteins, green fluorescence protein and ferredoxin (FRD) is investigated on nanocrystalline, mesoporous TiO2 and SnO2 electrodes. Modification of these electrodes with a cationic polypeptide (poly- L -lysine) or an aminosilane prior to protein immobilization is found to enhance protein binding at least ten fold, attributed to more favorable protein/electrode electrostatic interactions. Cyclic voltammetry studies of FRD-modified SnO2 electrodes indicate reversible protein electrochemistry with a midpoint potential of ,0.59,V (vs. Ag/AgCl) and an interfacial electron transfer rate constant of 0.45,s,1. [source]

Titanium dioxide nanoparticles-coated column for capillary electrochromatographic separation of oligopeptides

ELECTROPHORESIS, Issue 21 2005
Yi-Ling Hsieh
Abstract A novel column made through the condensation reaction of TiO2 nanoparticles (TiO2,NPs) with silanol groups of the fused-silica capillary is described. EOF measurements under various buffer constitutions were used to monitor the completion of reactions. The results indicated that the EOF was dependent on the interactions between buffers and the bonded TiO2,NPs. With formate/Tris buffer, EOF reversal at pH below,5 and cathodic EOF at pH above,5 were indicated. The pI of the bonded TiO2,NPs was found at ,ph,5. Only cathodic EOF was illustrated by substituting the mobile phase with either glutamate or phosphate buffer. It was elucidated that both glutamate and phosphate buffer yield a negative charge layer on the surface of TiO2,NPs attributable to the formation of a titanium complex. The CEC performance of the column was tested with angiotensin-type oligopeptides. Some parameters that would affect the retention behavior were investigated. The interactions between the bonded phases and the analytes were explicated by epitomized acid,base functional groups of the oligopepetides and the speciation of the surface oxide in different pH ranges. The average separation efficiencies of 3.1×104,plates/m is readily achieved with a column of 70,cm (50,cm)×50,,m,ID under an applied voltage of 15,kV, phosphate buffer (pH,6.0, 40,mM), and UV detection at 214,nm. [source]

Photocatalytic degradation of organic dyes in the presence of titanium dioxide under UV and solar light: Effect of operational parameters

ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2005
Feryal Akbal
The photocatalytic degradation of methylene blue and methyl orange have been studied in the presence of titanium dioxide powder illuminated with a 300-W UV lamp. The effect of hydrogen peroxide on the degradation process was also determined. It was found that the color removal efficiency was affected by the concentration of dye, amount of TiO2 added, and the pH of the solution. The degradation of dyes obeys first-order kinetics, with the apparent first-order rate constant increasing with decreasing dye concentration. The rate constants were evaluated as a function of the concentration of dye, amount of TiO2, and pH. © 2005 American Institute of Chemical Engineers Environ Prog, 2005 [source]

Silicon-Assisted Direct Covalent Grafting on Metal Oxide Surfaces: Synthesis and Characterization of Carboxylate N,N,-Ligands on TiO2

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2010
Henri Arzoumanian
Abstract The easy covalent bonding of an OH-bearing molecule onto a metal oxide surface can be done by transesterifying a trimethylsilylated hydroxy function with the surface OH groups. This results in the grafting of the organic molecule directly on the matrix, accompanied by the formation of trimethylsilanol, which can easily be eliminated as volatile hexamethyldisiloxane and water. This was accomplished on a TiO2 matrix with three carboxylic acids: acetic, isonicotinic, and 2,2,-bipyridyl-4,4,-dicarboxylic acids. The N,N,-immobilized ligand was then used for a dioxidomolybdenum entity and tested as such at room temperature and under atmospheric pressure O2 oxidation of ethylbenzene. All intermediates and grafted species were fully characterized by 13CMAS NMR spectroscopy, and thermogravimetric and elemental analysis. [source]

From Single-Molecule Precursors to Coupled Ag2S/TiO2 Nanocomposites

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2008
Márcia C. Neves
Abstract A single-source approach using mild temperatures was applied to prepare morphological well-defined and coupled TiO2/metal,sulfide nanocomposites. Metal N -alkyldithiocarbamates were used as the precursors to the metal,sulfide nanophases and, in particular, Ag2S nanostructures were investigated in more detail. These were observed as nano-islands at the surface of TiO2 (anatase) particles, which were used as substrates. To explain the formation of these nanocomposite particulates, a tentative mechanism has been proposed which involves the controlled release of sulfide ions from an intermediate coordination compound. Because the growth of the metal sulfide can be controlled at the surface of a photoactive substrate, we anticipate the potential of this synthetic method to chemical design reasonable amounts of semiconductor-sensitized TiO2, such as Ag2S/TiO2 nanocomposites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Thermal Shock Performance of Fine Grained Al2O3 Ceramics With TiO2 and ZrO2 Additions for Refractory Applications,

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Christos G. Aneziris
Abstract Due to zirconia and titania additions carbon-free fine grained alumina ceramics are produced with superior thermal shock performance. The decomposition of Al2TiO5 in the alumina doped matrix dominates during thermal shock attack and leads to higher strengths in comparison to the as sintered samples after thermal shock. EDX, EBSD, and XRD investigations describe the phase evolution before and after quenching the samples from 950 to 1200,°C in water, respectively. [source]

Fractal Approach to Hierarchically Evolved Laser Processed CaP Coatings

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Anil Kumar Kurella
This paper discusses a fractal approach to understand nature inspired laser surface engineered coatings. Via a laser surface engineering process a multi-scale CaTiO3 coating was synthesized on Ti alloy surface. At faster laser processing speeds star like CaTiO3 features evolved inside rings rich in calcium phosphate and TiO2. The porosity developed through the distribution of these particles results in a multi-scale distribution. Fractal analysis revealed that such laser processed surfaces had consistent fractal dimension over multiple length scales. This multi-scale and multi-phase surface microstructure contributed to enhanced biomimetic precipitation. [source]

Influence of TiO2 Nanoparticles Incorporated into Elastomeric Polyesters on their Biocompatibility In Vitro and In Vivo

ADVANCED ENGINEERING MATERIALS, Issue 11 2009
Miroslawa El-Fray
Abstract Fibroblasts proliferation and apoptosis as well as tissue response after implantation of elastomers containing nanocrystalline TiO2 were investigated in the present in vitro and in vivo study. Materials investigated were soft poly(aliphatic/aromatic-ester) multiblock thermoplastic elastomers with poly(ethylene terephthalate) (PET) hard segments and dimerized linoleic acid (DLA) soft segments, respectively, containing 0.2,wt% TiO2 nanoparticles. An investigation of the influence of TiO2 nanoparticles incorporated into polymeric material on in vitro biocompatibility revealed enhanced cell proliferation and diminished number of necrotic and apoptotic cells as compared to nanoparticles-free polymer. Implantation tests indicated that the observed tissue changes were similar to those observed with medical-grade silicone elastomer, no evidence of contact necrosis being observed. The unchanged morphology of rat liver hepatocytes and the lack of parenchymal necrosis also indicated that exposure to the material containing TiO2 nanoparticles, did not cause any cytotoxic reactions. The present study, thus, showed that elastomeric polyester containing TiO2 nanoparticles are interesting biomimetic constructs for improved tissue regeneration. [source]

Predicting Spray Processing Parameters from Required Coating Structural Attributes by Artificial Intelligence,

ADVANCED ENGINEERING MATERIALS, Issue 7 2006
A.-F. Kanta
Predicting processing parameters to manufacture a coating with the required structural attributes is of prime interest to reduce the associate development costs. Such an approach permits, among other advantages, to select the most appropriate scheme among several possible to implement. This paper intends to present such an approach. The specific case of predicting plasma spray process parameters to manufacture a grey alumina (Al2O3 -TiO2, 13% by wt.) coating was considered. [source]

Synthesis and Low Cycle Fatigue Behavior of In-situ Al-based Composite Reinforced with Submicron TiB2 and TiC Particulates,

ADVANCED ENGINEERING MATERIALS, Issue 12 2004
S.C. Tjong
Low cycle fatigue behavior of in-situ aluminum based composite reinforced with submicron TiB2 and TiC particulates was investigated. This novel composite was prepared from the TiO2 -Al-B-C system via reactive hot pressing. The incorporation of carbon into such a system induces the formation of TiC particulate at the expense of brittle Al3Ti phase. The influence of submicron particulate formation on the tensile and fatigue properties of the composite is discussed. [source]

Low-Temperature and High-Strain Rate Superplastic Zirconia

ADVANCED ENGINEERING MATERIALS, Issue 3 2003
Y. Sakka
A superplastic ceramic with a strain rate comparable to metals based on 3% Y2O3 -doped tetragonal zirconia (3YTZ) was synthesized at relatively low temperature, based on the doping with MgO and TiO2. The desirable material properties result from both a refined preparation procedure for the zirconia, and from enhanced cation lattice diffusion due to the MgO and TiO2 doping. [source]

Capacitors with an Equivalent Oxide Thickness of <0.5 nm for Nanoscale Electronic Semiconductor Memory

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010
Seong 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]

Antireflective Nanoparticle Arrays Enhance the Efficiency of Silicon Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010
Dehui Wan
Abstract In this study, the phenomenon of light trapping in Si solar cells coated with metal (Au) and dielectric (TiO2, SiO2) nanoparticles (NPs) is systematically investigated. In contrast to previous reports, herein it is proposed that the photocurrent enhancement of solar cells should be attributed to the limited antireflection ability of the Au NP arrays. In other words, the Au NP arrays might not enhance the absorption of the active layer in cells when no light is reflected from the air,substrate interface. Therefore, the Au NPs are replaced with dielectric NPs, which possess lower extinction coefficients, and then the antireflection property of the TiO2 NP arrays is optimized. A simple, rapid, and cheap solution-based method is used to prepare close-packed TiO2 NP films on Si solar cells; these devices exhibit a uniform and remarkable increase (ca. 30%) in their photocurrents. To the best of the authors' knowledge, this uniform photocurrent enhancement is greater than those obtained from previously reported metal and dielectric NP,enhanced Si wafer-based solar cells. [source]

Enhanced Photocatalytic Activity using Layer-by-Layer Electrospun Constructs for Water Remediation

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2010
Jung Ah Lee
Abstract Endocrine disruptors such as bisphenol A (BPA) are environmental pollutants that interfere with the body's endocrine system because of their structural similarity to natural and synthetic hormones. Due to their strong oxidizing potential to decompose such organic pollutants, colloidal metal oxide photocatalysts have attracted increasing attention for water detoxification. However, achieving both long-term physical stability and high efficiency simultaneously with such photocatalytic systems poses many challenges. Here a layer-by-layer (LbL) deposition approach is reported for immobilizing TiO2 nanoparticles (NPs) on a porous support while maintaining a high catalytic efficiency for photochemical decomposition of BPA. Anatase TiO2 NPs ,7,nm in diameter self-assemble in consecutive layers with positively charged polyhedral oligomeric silsesquioxanes on a high surface area, porous electrospun polymer fiber mesh. The TiO2 LbL nanofibers decompose approximately 2.2,mg BPA per mg of TiO2 in 40,h of illumination (AM 1.5G illumination), maintaining first-order kinetics with a rate constant (k) of 0.15,h,1 for over 40,h. Although the colloidal TiO2 NPs initially show significantly higher photocatalytic activity (k,,,0.84,h,1), the rate constant drops to k,,,0.07,h,1 after 4,h of operation, seemingly due to particle agglomeration. In the BPA solution treated with the multilayered TiO2 nanofibers for 40,h, the estrogenic activity, based on human breast cancer cell proliferation, is significantly lower than that in the BPA solution treated with colloidal TiO2 NPs under the same conditions. This study demonstrates that water-based, electrostatic LbL deposition effectively immobilizes and stabilizes TiO2 NPs on electrospun polymer nanofibers for efficient extended photochemical water remediation. [source]

Solar Cells by Design: Photoelectrochemistry of TiO2 Nanorod Arrays Decorated with CdSe

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Jin Ho Bang
Abstract One-dimensional (1D) nanostructures of TiO2 are grown directly on transparent, conductive glass substrate using hydrothermal/solvothermal methods. When employed as a photoanode in photoelectrochemical cells, the vertically aligned TiO2 nanorod array exhibits slower charge recombination at electrolyte interface as compared to mesoscopic TiO2 particulate film. Electrochemical deposition of CdSe onto TiO2 nanorod array is carried out to extend absorption into visible light region. The role of CdSe-sensitized, 1D rutile TiO2 architecture in the solar cell design is discussed. [source]

Control of Solid-State Dye-Sensitized Solar Cell Performance by Block-Copolymer-Directed TiO2 Synthesis

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010
Pablo Docampo
Abstract Hybrid dye-sensitized solar cells are typically composed of mesoporous titania (TiO2), light-harvesting dyes, and organic molecular hole-transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study, TiO2 is synthesized in a well-defined morphological confinement that arises from the self-assembly of a diblock copolymer,poly(isoprene- b -ethylene oxide) (PI- b -PEO). The crystallization environment, tuned by the inorganic (TiO2 mass) to organic (polymer) ratio, is shown to be a decisive factor in determining the distribution of sub-bandgap electronic states and the associated electronic function in solid-state dye-sensitized solar cells. Interestingly, the tuning of the sub-bandgap states does not appear to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub-bandgap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub-bandgap states is critical for efficient photo-induced electron transfer and charge separation. [source]

Light-Driven Titanium-Dioxide-Based Reversible Microfireworks and Micromotor/Micropump Systems

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2010
Yiying Hong
Abstract Titanium dioxide (TiO2) possesses high photocatalytic activity, which can be utilized to power the autonomous motion of microscale objects. This paper presents the first examples of TiO2 micromotors and micropumps. UV-induced TiO2 reversible microfireworks phenomenon was observed and diffusiophoresis has been proposed as a possible mechanism. [source]

Stem Cell Aligned Growth Induced by CeO2 Nanoparticles in PLGA Scaffolds with Improved Bioactivity for Regenerative Medicine

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2010
Corrado Mandoli
Abstract Hybrid 2D polymeric,ceramic biosupports are fabricated by mixing a nanostructured CeO2 powder with 85:15 poly(D,L -lactic- co -glycolic acid) (PLGA)/dichloromethane solutions at specific concentrations, followed by solvent casting onto pre-patterned molds. The mold patterning allows the orientation of ceramic nanoparticles into parallel lines within the composite scaffold. The ability of the produced films to host and address cell growth is evaluated after 1, 3, and 6 days of culturing with murine derived cardiac and mesenchymal stem cells (CSCs and MSCs), and compared with PLGA films without ceramics and loaded with nanostructured TiO2. Aligned cell growth is observed only for scaffolds that incorporate oriented ceramic nanoparticles, attributed to the nanoceramic ability to modulate the roughness pitch, thus improving cell sensitivity towards the host surface features. Better CSC and MSC proliferative activity is observed for CeO2 composites with respect to either TiO2 -added or unfilled PLGA films. This evidence may be related to the nanostructured CeO2 antioxidative properties. [source]

Dual-Function Scattering Layer of Submicrometer-Sized Mesoporous TiO2 Beads for High-Efficiency Dye-Sensitized Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2010
Fuzhi 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]

Improved-Performance Dye-Sensitized Solar Cells Using Nb-Doped TiO2 Electrodes: Efficient Electron Injection and Transfer

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Xujie Lü
Abstract Well-crystallized Nb-doped anatase TiO2 nanoparticles are prepared by a novel synthetic route and successfully used as the photoanode of dye-sensitized solar cells (DSSCs). The homogenous distribution of Nb in the TiO2 lattice is confirmed by scanning transmission electron microscopy (STEM) elemental mapping and line-scanning analyses. After Nb doping, the conductivity of the TiO2 powder increases, and its flat-band potential (Vfb) has a positive shift. The energy-conversion efficiency of a cell based on 5.0,mol% Nb-doped TiO2 is significantly better, by about 18.2%, compared to that of a cell based on undoped TiO2. The as-prepared Nb-doped TiO2 material is proven in detail to be a better photoanode material than pure TiO2, and this new synthetic approach using a water-soluble precursor provides a simple and versatile way to prepare excellent photoanode materials. [source]

p,n-Junction-Based Flexible Dye-Sensitized Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010
Liping Heng
Abstract In this paper, a new type of flexible working electrode, TiO2/CuI/Cu, is reported, in which the p,n junction of TiO2,CuI is introduced into dye-sensitized solar cells (DSSCs) for the first time. The devices give a high conversion efficiency of up to 4.73% under 1 sun illumination. The excellent performance is ascribed to the existence of the p,n junction, which forms a single directional pathway for electron transport which benefits the charge separation, and improves the efficiency of the flexible solar cells as a result. [source]

Conformal Nano-Sized Inorganic Coatings on Mesoporous TiO2 Films for Low-Temperature Dye-Sensitized Solar Cell Fabrication

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010
Larissa 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]

Electric Field-Directed Convective Assembly of Ellipsoidal Colloidal Particles to Create Optically and Mechanically Anisotropic Thin Films

ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
Manish Mittal
Abstract A method of simultaneous field- and flow-directed assembly of anisotropic titania (TiO2) nanoparticle films from a colloidal suspension is presented. Titania particles are oriented by an alternating (ac) electric field as they simultaneously advect towards a drying front due to evaporation of the solvent. At high field frequencies (,,>,,25,kHz) and field strengths (E,>,300,V cm,1), the particles orient with their major axis along the field direction. As the front recedes, a uniform film with thicknesses of 1,10,µm is deposited on the substrate. The films exhibit a large birefringence (,n,,,0.15) and high packing fraction (,,=,0.75,±,0.08), due to the orientation of the particles. When the frequency is lowered, the particle orientation undergoes a parallel,random,perpendicular transition with respect to the field direction. The orientation dependence on field frequency and strength is explained by the polarizability of ellipsoidal particles using an interfacial polarization model. Particle orientation in the films also leads to anisotropic mechanical properties, which are manifested in their cracking patterns. In all, it is demonstrated that the field-directed assembly of anisotropic particles provides a powerful means for tailoring nanoparticle film properties in situ during the deposition process. [source]

Molecular Design of Unsymmetrical Squaraine Dyes for High Efficiency Conversion of Low Energy Photons into Electrons Using TiO2 Nanocrystalline Films

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009
Thomas Geiger
Abstract An optimized unsymmetrical squaraine dye 5-carboxy-2-[[3-[(2,3-dihydro-1, 1-dimethyl-3-ethyl-1H -benzo[e]indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-dimethyl-1-octyl-3H -indolium (SQ02) with carboxylic acid as anchoring group is synthesized for dye-sensitized solar cells (DSCs). Although the , -framework of SQ02 is insignificantly extended compared to its antecessor squaraine dye SQ01, photophysical measurements show that the new sensitizer has a much higher overall conversion efficiency , of 5.40% which is improved by 20% when compared to SQ01. UV-vis spectroscopy, cyclic voltammetry and time dependent density functional theory calculations are accomplished to rationalize the higher conversion efficiency of SQ02. A smaller optical band gap including a higher molar absorption coefficient leads to improved light harvesting of the solar cell and a broadened photocurrent spectrum. Furthermore, all excited state orbitals relevant for the ,,,* transition in SQ02 are delocalized over the carboxylic acid anchoring group, ensuring a strong electronic coupling to the conduction band of TiO2 and hence a fast electron transfer. [source]