Morphology Of TiO2 Films Research Articles

Microstructure and optical and electrical properties of TiO 2 nanotube thin films prepared by spin‐coating method

Titanium dioxide nanotubes prepared by hydrothermal method and the TiO2 films and TiO2 nanotube film were prepared by spin-coating method. The TiO2 nanotube film and a part of TiO2 film were annealed at 150°C for 1 h, while the another part of TiO2 film was annealed at 500°C. The high-resolution transmission electron microscopy analysis indicated that the TiO2 nanotubes prepared by hydrothermal method have been crystallised and the lattice plane indices corresponded to anatase {200}, and the TiO2 nanotube grown along the 〈100〉 direction. The atomic force microscopy results show that the surface morphology of the TiO2 film annealed at 150°C was smooth and uniform (0.62 nm in roughness) compared to the surface morphology of TiO2 film annealed at 500°C (roughness is 2.41 nm). For the TiO2 nanotube film, the nanotube fragments were uniformly dispersed in the base and the complete films have been prepared and the roughness was reached to 6.4 nm. The optical properties showed that the visible light transmittance of the TiO2 nanotube film was larger (larger than 95%) than the TiO2 film. The electrical properties showed that square resistance of TiO2 nanotube film was smaller than that of TiO2 film.

Enhancing the efficiency of dye-sensitized solar cells by hydrothermal post-treatment in acidic environment

Dye-sensitized solar cell (DSSC) have been extensively studied due to its low production cost and simple production process. In this research, DSSC with improved performance is acquired by modification of TiO2 layer through hydrothermal post-treatment with different hydrochloric acid (HCl) concentrations to obtain various particles and pore sizes. Qualitative and quantitative characterizations of the TiO2 film were conducted using thickness measurement, scanning electron microscope (SEM), and X-ray diffraction (XRD), while the solar cell performances were characterized using current-voltage (I-V) measurement under 0.5 Sun. When hydrothermally treated with 1 mol/L HCl at 180 °C for 3 h, the DSSC showed the most optimum photo-electricity conversion performance of 3.60%, which improved the efficiency of the non-treated DSSC by a factor of 1.2. As the HCl concentration increased, the treated TiO2 film became thinner with smaller particle size and denser structure. It was suspected that the modification in the TiO2 film morphology has led to better light absorption, which consequently resulted in the improvement of DSSC performance.

The effect of solution flow rate and substrate temperature on structural and optical properties of TiO2 films deposited by spray pyrolysis technique

Titanium dioxide thin films have been deposited on glass substrate at various solution flow rates by spray pyrolysis technique with substrate temperatures between 350°C–550°C. Samples were characterized for structural, morphological and optical properties by X-ray diffraction (XRD), scanning electron microscope (SEM) and UV–visible spectrometry. The XRD analysis of deposited TiO2 films exhibited nanocrystalline nature and preferentially oriented along [101] direction. The UV–visible transmittance results show that all thin films were transparent with an average transmittance higher than 70% in the visible region. Due to nanosized grains, the optical band gaps of the TiO2 thin films (3.35–3.68eV) were larger than the bulk TiO2 (3.2eV). The SEM analysis revealed that thickness and morphology of TiO2 films can be adjusted by rate of solution flow and substrate temperature. It seems that the process of spray pyrolysis provides an easy way to prepare either homogeneous thin and thick films.

PH-dependent structure and wettability of TiO2-based wood surface

TiO2 thin films with different wettability were fabricated on the wood surfaces by a simple low-temperature hydrothermal method with the precursor solution pH adjusted by hydrochloric acid/sodium hydroxide. The morphologies of TiO2 films have been changed from sphere species to filmy ones by adjusting pH of precursor solution. The TiO2 films synthesized at the precursor solution pH of 1~10 were mainly primary existed in anatase phase without other structure, and the TiO2-treated wood surfaces presented different wettability with the water contact angles ranged from 9.6° to 132.7°, when the precursor solution pH were controlled to the range of 1~14. Such a wood surface with the desirable wettability shows great potential, as it may be selectively used in the various environments with different humidity.

Poly(ethylene-co-acrylic acid)-g-poly(ethylene glycol) graft copolymer templated synthesis of mesoporous TiO2 thin films for quasi-solid-state dye sensitized solar cells

An amphiphilic graft copolymer, poly(ethylene-co-acrylic acid)-graft-poly(ethylene glycol) (PEAA-g-PEG), consisting of a PEAA backbone and PEG side chains was synthesized via an esterification reaction. 1H nuclear magnetic resonance and Fourier-transformed infrared analysis demonstrated esterification between carboxylic acid of PEAA and hydroxyl group of PEG. Small angle X-ray scattering results revealed that the crystalline domain spacing of PEAA increased from 11.3 to 12.8nm upon using a more polar solvent with a higher affinity for poly(acrylic acid), while the crystalline domain spacing of PEAA disappeared with PEG grafting, indicating structural change to an amorphous state. Mesoporous TiO2 thin films were synthesized via a sol–gel reaction using PEAA-g-PEG graft copolymer as a structure-directing agent. The hydrophilically-preformed TiO2 nanoparticles were selectively confined in the hydrophilic PEG domains of the graft copolymer, and mesoporous TiO2 thin films were formed, as confirmed by scanning electron microscopy. The morphology of TiO2 films was tunable by varying the concentrations of polymer solutions and the amount of preformed TiO2. A quasi-solid-state dye-sensitized solar cell fabricated with PEAA-g-PEG templated TiO2 film exhibited an energy conversion efficiency of 3.8% at 100mW/cm2, which was greater than that of commercially-available paste (2.6%) at a similar film thickness (3μm). The improved performance was due to the larger surface area for high dye loading and organized structure with good interconnectivity.

Structural and Optical Properties of TiO<sub>2</sub> Thin Films Prepared by Thermal Oxidation of Ti Thin Films

Titanium dioxide (TiO2) films were prepared by thermal oxidation from Ti films. The Ti films were deposited on glass and silicon (100) wafer substrate by dc magnetron sputtering and subsequent with thermal oxidation process. The crystal structure and morphology of TiO2 films were estimated by using X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The optical property of TiO2 films was determined by UV-Visible spectrophotometer. The influences of annealing temperature between 200 to 500°C in air for 1 hour on the structure and optical properties of TiO2 films were investigated. The increasing of annealing temperature was directly affected the phase transition from Ti to TiO2. The optical and structural properties of TiO2 films are the best exhibited with increasing the annealing temperature at 500 °C.

Fabrication of Flexible Dye-Sensitized Solar Cells by Pressurization-Transfer Technique

In this study, the flexible dye-sensitized solar cell is fabricated by pressurization-transfer technique, which involves assembling TiO2 films on ITO/PEN flexible substrates via high temperature sintering. During the experiment, we change not only the film thickness and structure of TiO2 but also the dye of working electrodes. The surface morphology of TiO2 films are examined by field emission scanning electron microscopy (FE-SEM). The analyses of UV-Vis show that N3 dye could be adsorbed on the TiO2 thin films, and the TiO2 thin film with scattering layer has better absorption than that of without scattering layer. The current-voltage of the DSSC is illuminated by the solar simulator whose incident light intensity was 1000 W/m2. These results indicate that the best efficiency of flexible dye-sensitized solar cell with high-temperature sintering TiO2 film and scattering layer is 6.13%.

Utilization of Size-Controlled Squid Ink Particles as Enhancer for the Porosity of Titania Electrode in Dye-Sensitized Solar Cell

TiO2 films were prepared using a paste mixture of titania and size-controlled squid ink particles that was used to manufacture macroporous electrodes in a dye-sensitized solar cell (DSSC). The sintering procedure at 450 °C decomposed the ink particles, thereby increasing the porosity of the structure in the films. An increase in the proportion of ink particles in the paste formulation increased the surface roughness of the films. The ink particles in the paste consequently enhanced the film porosity. The TiO2 films prepared using a paste mixture consisting of 30% ink particles had the roughest surface, but its DSSC had the lowest photoelectric conversion efficiency. Thus, this study revealed the effects of the paste composition on the TiO2 film morphology and DSSC performance.

Structure and Morphology of Sol-Gel Nanocrystalline TiO<sub>2</sub> Films Coated on Glass Substrates

The Ce3+-doped and undoped nanocrystalline TiO2 films were prepared on glass substrates surface by sol-gel dip coating technique. The crystal structure and surface morphology of TiO2 films were characterized by means of X-ray diffractometer (XRD), transmission electron microscopy (TEM) and atomic force microscope (AFM). The results indicated that the Ce3+-doped TiO2 films were solely composed of the anatase phase whereas in the undoped films small amount of the rutile phase of TiO2 were present. The average crystallite size of the undoped TiO2 films was about 30nm and was decreased with Ce3+-doping in the TiO2 films. Moreover, the grains distributed more uniform and the surface roughness was smaller in the Ce3+-doped TiO2 films than in the undoped one. The action mechanism of Ce3+-doping inhibits the crystallization of the rutile phase and decreases the anatase granularity of TiO2 films is associated with its physicochemical properties, as well as ionic diffusion and valance change of Ce3+ to Ce4+ in the sintering process.

Stress of Tio2 Thin Films Produced by Different Deposition Techniques

ABSTRACTStress in thin films has been measured very precisely (< 10 MPa) by analysing the curvature of quartz glass substrates before and after film deposition by means of a ZYGO Mark IV interferometer system. TiO2 films of approximately 100 nm thickness were prepared by reactive evaporation (RE), reactive ion plating (IP), plasma impulse chemical vapor deposition (PICVD) and spin coating (SC). Large variations in stress are found for different coating techniques and deposition conditions. This can be correlated to differences in optical properties, film density and crystalline structure. Relaxation effects and the influence of thermal treatment are also studied. The crystallization of amorphous TiO2 during heat treatment is accompanied by significant changes in film stress. The crystal size and morphology of TiO2 films after heat treatment strongly depend on the deposition technique and process conditions.