TiO2 Sintering Research Articles

Nanoporous TiO2 electrode grown by laser ablation of titanium in air at atmospheric pressure and room temperature

Recently, fabrication of the nanoporous TiO2 photoelectrode on metal foils by means of sputtering of the Ti film on preheated metal substrate followed by the TiO2 deposition (doctor blade technique) and sintering represents the frequently applied technique. This is despite the relatively complicated procedure and number of parameters to be controlled in order to fabricate films of required properties. In this work an approach is applied and discussed in which the nanoporous TiO2 electrode is fabricated under conditions similar to pulsed laser deposition but with the deposit formed directly on the ablated target at atmospheric pressure and room temperature. The titanium dioxide thin film is grown by ablation of the Ti foil with the nanosecond UV laser (266nm) at fluence up to 1.5J/cm2. The rutile–anatase phase transformation takes place during this one-step process and no thermal pre-and post-treatment of the deposit is needed. In samples produced in air, the presence of mixed phases of the non-stoichiometric anatase (>70%), rutile and negligible amount of TiN is consistently confirmed by the X-ray diffraction, energy-dispersive X-ray and Raman spectra. For applications of the reported films as electrode material in the third generation photovoltaic cells, the use of industrial lasers could significantly improve the process efficiency.

Effect of titania addition on the properties of freeze-cast alumina samples

This work investigated the behavior of TiO2-containing α-Al2O3 samples prepared by the freeze-casting technique. Camphene and liquid nitrogen were used as the solvent and cooling fluid, respectively. Camphene resulted in the formation of dendritic pores, in the direction of the freeze-casting cold front during sample preparation. The formation of β-Al2TiO5 phase occurred at 1300°C, and became more evident as the sintering temperatures reached 1500°C. The TiO2 loading did not affect the sample porosity at a given temperature, but it was detrimental in the case of mechanical properties under certain conditions. For instance, the flexural strength slightly improved with increasing the TiO2 loading and sintering temperature from 1100 to 1300°C. This effect was attributed to the occurrence of a more effective sintering of alumina. However, as the heat treatment temperature was raised from 1300 to 1500°C, the flexural strength did not increase as a function of the TiO2 loading, even though the densification occurred with loss of porosity. The loss of mechanical strength was found to be associated with the formation of microcracks which stemmed from the formation of β-Al2TiO5 phase for TiO2 loadings in excess of 4wt% at these high sintering temperatures.

Effect of Nano-Silver Ink Composition and Drying Behavior on Its Adhesion on Glass Substrate

The adhesion of silver colloids to a glass substrate was investigated in this study. The silver colloids first added nano-TiO2 particle by varying solid content and changed pH to 10 to make sure the solution dispersion well. The adhesion of silver colloids to the glass substrate after sintering was then measured according to both ASTM D4541 and ASTM 3359 standards. The results indicated that adhesion increased proportionally with TiO2 solid content; however, this enhancement effect was lessened when the solid content was above 8wt%. Sintering temperature was also beneficial in increasing adhesion to the substrate; however, the electrical resistance of the silver colloids after sintering increased with degree of solid content. This implied that TiO2 solid content simultaneously made adhesion and electrical resistance increased. Consequently, values of TiO2 solid content and sintering temperature were optimal when adhesion and electrical resistivity were balanced. Ultimately, using commercial software Origin to fit the TiO2 solid content and sintering temperature to get the optimum value of adhesion and electrical resistivity.

Structural and Optical Properties of Ti4+ Doped Sintered ZnAl2O4 Ceramics

The sintering characteristics, phase composition, microstructure and optical properties of 1:1 ZnAl2O4 spinel doped with Ti4+ from 1.125 to 4.5 mole-% synthesized through coprecipitation were investigated in this study. Effective densification was achieved at a low sintering temperature, 1350°C after 1 h. Powder XRD patterns revealed that, besides ZnAl2O4 spinel and rutile as major crystalline phases, minor Zn2Ti3O8 phase was present in the sintered system, with its extent depending on the TiO2 content and sintering temperature. SEM micrographs demonstrated a coherent and uniformly distributed fine-grained microstructure in the fracture surfaces of the sintered Ti4+ doped ZnAl2O4 spinel ceramics body. The Tauc plot of Ti4+ doped ZnAl2O4 spinel exhibited a leftward shift of the band gap from 3.79 to 3.48 eV with increase of Ti4+ content from 0 to 4.5 mole-%. Ti4+ was observed to function as a normal grain growth accelerator during ZnAl2O4 sintering. This was probably due to enhanced grain boundary diffusion.

TiO2두께 및 소성온도에 따른 염료감응 태양전지 특성에 관한 연구

In this thesis, it is investigated the characteristics of Dye Sensitized Solar Cell (DSSC) according to variation of TiO2 thickness (6, 12, 18, and 24 ㎛) and three distinct TiO₂ sintering temperatures (350, 450 and 550℃) by XRD, SEM, I-V and UV-Vis spectrophotometer. According to sintering temperature, TiO₂ was transformed into the anatase structure at 350℃, rutile structure at 550℃ and further into the two structure at 450℃. With increasing thickness up to 18 ㎛ and sintering temperature up to 450℃, respectively, the irradiance rate increased in the range of 9 ∼26 percent and 2.80∼5.10 percent. Whereas a further increase to 24 ㎛ and 550℃, the irradiance rate decrease in the range of 4∼11 percent and 30∼47 percent. The conversion efficiency increased in the range of 2.80∼5.01 and 3.03∼5.01 with increasing thickness up to 18㎛ and sintering temperature up to 450℃. By contrast, increase to 24 ㎛ and 550℃, the conversion efficiency decreased in the range of 3.31∼5.01 and 2.80∼3.89, respectively. The DSSC that thickness of TiO₂ were 18 ㎛ and sintered at 450℃ exhibited the most excellent characteristics, in which open-circuit voltage, short-circuit current, Fill Factor and conversion efficiency are 0.69 V, 11.4 ㎃/㎠, 0.64 and 5.01%, respectively.

Preparation of microfiltration membrane supports using coarse alumina grains coated by nano TiO2 as raw materials

To increase the mixing uniformity of coarse alumina grains with a small amount of nano TiO2 particles, TiO2 particles were prepared on the surface of coarse Al2O3 grains by in-situ hydrolysis of TiCl4. The coated coarse Al2O3 powder was used to prepare microfiltration membranes supports. The effects of TiO2 content and sintering temperatures on the bending strength, porosity and pore size distribution of the obtained supports were studied. The results show that the melted nano TiO2 grains locate mainly at the neck of Al2O3 grains, which increases the bending strength of the support by increases the neck area. However, the bending strength is weakened if the TiO2 content is excessive. No aggregated nano TiO2 grainsare found. The resulting supports sintered at 1650 °C for 2 h yields a bending strength of 55.4 MPa, a porosity of 38% with a mean pore size of 8.0 μm.

Influences of Gd2Ti2O7 sintering aid on the densification, ionic conductivity and thermal expansion of Gd0.1Ce0.9O1.95 electrolyte for solid oxide fuel cells

The effects of Gd2Ti2O7 (GT) as sintering aid on the densification, electrical properties and thermal expansion of Gd0.1Ce0.9O1.95 (GDC) are examined. Samples added with TiO2 sintering aid are also tested for comparison. It is found that by sintering at a moderate temperature of 1400 °C for 5 h, the relative density of the GT-added GDC can reach over 97% as the molar ratio of GT/GDC reaches 0.02 or higher. XRD analysis indicates that GT does not react with GDC, while TiO2 reacts with Gd in GDC to form GT. The ionic conductivities of the GT-added and the TiO2-added GDC are analyzed by AC impedance spectroscopy at 500–700 °C. The result shows that although the ionic conductivity of the GT-added GDC decreases as the GT/GDC molar ratio increases up to 0.05, it is still higher than that of 8YSZ and much higher than that of the GDC added with an equivalent amount of TiO2. It is also found that the thermal expansion coefficient of GDC decreases as the amount of GT increases. These results show that GT is an excellent sintering aid for GDC, and the optimal molar ratio of GT/GDC is 0.02 in terms of densification and ionic conductivity.

Effect of pore size/distribution in TiO2 films on agarose gel electrolyte-based dye-sensitized solar cells

This study develops a simple method to change the distribution of the pore size in a TiO2 layer, using polyethylene glycol (PEG), while maintaining nearly the same surface area and porosity to clarify how large pores affect the performance of dye-sensitized solar cells (DSSCs). Specifically, a heating step at 100 °C for a specific duration is added prior to PEG removal and TiO2 sintering at 400 °C. This process transforms the role of the PEG from a surfactant to a pore generator (porogen) and forms larger pores, depending on the loading and aggregation time for the PEG to gain larger pores. The effect of larger pores in TiO2 films under 30 % PEG loading, on the performance of an agarose gel electrolyte-based DSSC, was further investigated using the ionic liquid, 1-allyl-3-ethylimidazolium iodide (AEII). The I–V characteristic and the electrochemical impedance spectroscopy analysis show that larger pores readily improve redox couple diffusion in a TiO2 porous electrode and modify the interface between electrolyte and TiO2. Using the optimized TiO2 film with larger pores (30 % PEG loading, 100 °C/60 min), an efficiency of 7.43 % is achieved for the agarose gel electrolyte-based DSSC, which represents a 26.1 % improvement over TiO2 without the addition of PEG.

Plasmonic enhanced dye-sensitized solar cells with self-assembly gold-TiO2@core–shell nanoislands

Decorating TiO2 photoanode of dye-sensitized solar cell (DSSC) with silver or gold nanoparticles has been shown to be an effective approach for enhancing device performance via the plasmonic effects. Here, we show for the first time that the same approach can be adopted simultaneously for both the photoanode and the counter-electrode of a DSSC but operates with different enhancement mechanism. In this work, the plasmonic nanostructure is synthesized by physical vapor deposition of ultra-thin gold films onto the electrodes followed by thermal annealing at a recommended TiO2 sintering temperature to form self-assembly gold nanoislands. Protective TiO2 nanoshells were formed by hydrolysis of titanium isopropoxide (TIP) precursor over the gold nanoislands. By varying the initial gold film thickness, gold nanoislands of controllable dimensions are distributed uniformly over the electrode surfaces. It was found that the optimized core–shell nanoislands nearly doubles the short circuit photocurrent density from 9.4mA/cm2 to 17.5mA/cm2, and has little impact on the open circuit voltage, resulting in a substantial uplift of the energy conversion efficiency.

Dye-sensitized solar cells with nanoporous TiO2 photoanodes sintered by N2 and air atmospheric pressure plasma jets with/without air-quenching

We investigate dye-sensitized solar cells (DSSCs) with TiO2 photoanodes sintered by N2 and air atmospheric pressure plasma jets (APPJs) with/without air-quenching. Air-quenching reduces the APPJ temperature from ∼500 °C to ∼300 °C; however, it accelerates the removal of organic solvents and the TiO2 sintering process. N2 APPJ with air-quenching and air APPJ with/without air-quenching can complete the sintering process in an ultra-short time (30 s); the assembled cells show efficiencies comparable to those of cells fabricated using conventional furnace process. The presence of excited nitrogen plasmas and oxygen gas is critical to the rapid sintering process of nanoporous TiO2 photoanodes at a lower temperature (∼300 °C). This air-quenched APPJ may be applied to the sintering process on lower-melting-point flexible substrate, which facilitates the future application to roll-to-roll process.

Nickel substrate covered with a Sn-based protection bi-layer as a photoanode substrate for dye-sensitized solar cells

Ni is a metallic substrate commonly used in microelectronic and opto-electronic devices due to its high stability, cost-efficiency and flexibility. Up to now, Ni has not yet been used as the substrate for the photoanode in dye-sensitized solar cell (DSSC) because the formation of p-type Ni oxide hinders the electron transfer from n-type TiO2 mesoporous film to Ni substrate. In this paper, a Sn-based protection bi-layer coating on the Ni foil successfully turns Ni into a good photoanode substrate in DSSC. A Sn layer is initially electroplated onto the Ni surface to prevent its oxidation. The Sn layer is then transformed into a bi-layer of SnO2 and Ni–Sn intermetallic compound after high-temperature TiO2 sintering. Unlike the p-type Ni oxide layer, the top n-type SnO2 layer enables the electron transfer from the TiO2 mesoporous film to the conductive Ni substrate because its energy level of conduction band well matches that of TiO2. In addition, the interfacial Ni–Sn intermetallic compound is a good electrical conductor which facilitates the electron transfer. By carefully controlling the plating current density and time, a 1.2-μm-thick Sn layer with a smooth surface morphology is formed and is recognized as the best protection layer over the Ni substrate. The energy conversion efficiency of the resultant DSSC achieves 4.422% with a short-circuit current density of 10mA/cm2, an open-circuit voltage of 0.643V, and fill factor of 0.689 under AM 1.5 back-side illumination.

Surface Metallization of Polyimide as a Photoanode Substrate for Rear-Illuminated Dye-Sensitized Solar Cells

Plastic film is promising as a photoanode substrate of dye-sensitized solar cell (DSSC) for flexible applications, while a low-temperature sintering process is generally adopted for the TiO2 mesoporous film due to unstable thermal property of general plastics. This study demonstrates that typical high-temperature TiO2 sintering can be adopted for preparing the photoanode when using a surface-metallized polyimide (PI) film. A Sn/Ni bi-layer is formed on a PI film via a chemical process as the conductive layer. The Sn/Ni-coated PI photoanode can withstand high-temperature TiO2 sintering at a peak temperature of 430°C for 30 min without significant visual deformation due to high thermal stability of PI and strength reinforcement caused by surface metallization. The DSSC employing the Sn/Ni-coated PI film as the photoanode substrate reaches an energy conversion efficiency of 3.44% under 1 sun rear-side illumination.

Preparation of Nano-ZnFe<sub>2</sub>O<sub>4</sub> Doped TiO<sub>2</sub> Photocatalytic Films on Porous Hayddites

Applied nano-ZnFe2O4/TiO2 photocatlytic films are prepared by template sol-gel method on porous haydites. The effects of ZnFe2O4-doping on TiO2 crystallization, sintering temperature, light absorption and photocatalysis are mainly studied, simultaneously, effect of template, amphiphilic block copolymer P(styrene-b-acrylic acid) (PS-b-PAA) on the phtocatalytic activity of ZnFe2O4/TiO2 films are also studied. The results show that right amount of ZnFe2O4-doping reduces TiO2 sintering temperature and particle size, and increases TiO2 absorbency in ultraviolet region, and a right amount of template (PS-b-PAA) forms orient arranged ZnFe2O4/TiO2 films with the high photocatalytic activity and decomposes fully methyl orange in water after light irradiating 2h.

Evaluation of Microwave Plasma Sintering for the Fabrication of Dye Sensitized Solar Cell (DSSC) Electrodes

Dye-sensitized solar cells (DSSCs) have demonstrated considerable potential due to their solar energy conversion efficiency and their fabrication from relatively low cost materials. Titanium dioxide (TiO2) nanoparticles are widely used in the fabrication of the DSSC electrodes. There is a considerable energy requirement however required for the sintering of the TiO2 particles during the fabrication of the mesoporous electrodes. This study investigates the use of microwave (MW) plasma treatments as a rapid, energy efficient processing technique for the sintering of the metal oxide particles. A comparison is made with conventional furnace treatments for the sintering of TiO2 nanoparticles (Degussa P25), deposited onto fluorine doped tin oxide (FTO) coated glass substrates. Subsequent to the TiO2 sintering, ruthenium based dye (N719) adsorption studies were carried out for coatings heated using both sintering techniques. Based on UV/Vis absorption spectra measurements of 5 mins plasma and 30 mins furnace sintering, it was observed that both sintering techniques exhibited similar levels of dye adsorption. A decrease in the level of dye adsorption was observed for the TiO2 coatings sintered for longer periods (up to 10 mins in this study). This change with longer plasma treatment times was associated with rutile grain growth and a decrease in surface roughness, possibly due to a densification of the mesoporous structure. The effect of TiO2 coating plasma treatment times on the conversion efficiency of the dye sensitised electrodes was also evaluated. Plasma treatments of 5 mins were found to yield the highest conversion efficiency of 6.4%.

Raster Scanning Laser and UV Processing of nanocrystalline TiO2 Films for Sintering in Dye Solar Cells: Device Performance, Throughput and Embodied Energy

ABSTRACTA crucial step in Dye Solar Cell (DSC) fabrication is the sintering of the TiO2 layer which needs to guarantee good electromechanical bonding between nanoparticles whilst maintaining sufficiently large porosity to yield performing devices. The standard procedure for TiO2 sintering requires firing in an oven at ∼ 500°C. An alternative procedure consists in utilizing laser scanning processing which has the advantageous potential of being noncontact, local, low cost, rapid, selective, automated and scalable. We analyzed and optimised a laser process for the sintering of the TiO2 layers in dye solar cells analyzing temperature profiles, throughput and the embodied energy. The development of electronic and photovoltaic devices on plastic substrates is of considerable interest due to the advantages they bring in terms of flexibility and easy processing for lightweight, low-cost large-area applications. An alternative sintering procedure compatible with flexible substrates and large area processing consists in utilizing a UV lamp. We subjected TiO2 pastes deposited on conductive transparent substrates to UV irradiation. Fully plastic devices fabricated through this method showed efficiencies of 4%.

Dye-Sensitized Solar Cell with Photoanode Made with Polystyrene-Ball-Embedded TiO2 Pastes

We report the effect of varying the concentration of polystyrene (PS) balls embedded in TiO2 paste during the fabrication of TiO2 photoanodes on the performance of dye-sensitized solar cells (DSSCs). We fabricated porous photoanodes using TiO2 pastes mixed with various concentrations of PS balls in aqueous solution. During the TiO2 sintering processes, the PS evaporated, leaving behind large cavities (>1 µm) in the photoanodes. These cavities enhance the scattering of light, leading to improved absorption of light by N3 dyes. DSSC efficiency increases with the increase in PS ball concentration during TiO2 fabrication. As with classical devices, TiCl4 treatment of TiO2 and the use of a compact TiO2 layer both improve the cell efficiency of DSSC devices with our large-cavity TiO2 photoanodes.

Ultrafast TiO2 Sintering of Metal Mounted Dye-Sensitized Solar Cells

A primary challenge to the industrial uptake of Dye-sensitized solar cells on metals is the ability to speed up process steps to facilitate rapid roll to roll production. One critical step is the sintering of the TiO2 layer typically taking up to one hour at 500°. Here, an ultrafast near infrared (NIR) heating method is presented which directly heats metal substrates to very high temperatures. NIR is used to heat 1mm thick titanium metal coupons onto which 1cm2 commercial TiO2 pastes have been deposited within 12.5 seconds giving assembled dye-sensitized solar cell efficiencies which are equivalent or better in terms of efficiency to cells prepared using a convection oven for 30 minutes.

Ultrafast near infrared sintering of TiO2 layers on metal substrates for dye‐sensitized solar cells

AbstractA limiting step to roll‐to‐roll production of dye‐sensitized solar cells on metals is TiO2 sintering (10–30 min). Near infrared (NIR) heating is a novel process innovation which directly heats titanium substrates giving rapid binder removal and sintering. NIR heating (for 12.5 s) at varying power gave titanium temperatures of 545, 685 and 817°C yielding cells with efficiencies of 2.9, 2.8 and 2.5%. Identical cells prepared in a conventional oven (1800 s) at 500, 600 and 800°C gave 2.9, 2.6 and 0.2% efficiency. NIR sintering is ultrafast and has a wide process window making it ideal for rapid manufacturing on metals. Copyright © 2010 John Wiley & Sons, Ltd.

Ultrafast TiO2 Sintering of Metal Mounted Dye Sensitized Solar Cells

not Available.

Rapid Fabrication of a Smooth Hollow-Spheres Array

Abstract A smooth TiO2 hollow-spheres array, a kind of inverse opals, was prepared in a wide area (> 1 × 5 cm) in a short time (less than 1 min excluding sintering) using a spin-coating technique. A two-dimensional colloidal crystal was used as a template. The TiO2 sintering process, especially the rate of the temperature increase, was important to copy the periodicity of the colloidal crystal structure. The electron diffraction image taken by the transmission electron microscopy observation showed that the hollow-spheres arrays have anatase-type crystal structure.