Prepared TiO2 Thin Films Research Articles

High-Quality TiO2 Electron Transport Film Prepared via Vacuum Ultraviolet Illumination for MAPbI3 Perovskite Solar Cells.

The electron transport layer (ETL) plays an important role in determining the conversion efficiency and stability of perovskite solar cells (PSCs). Here, TiO2 thin film was prepared by irradiating diisopropoxy diacetylacetone titanium precursor thin film with 172 nm vacuum ultraviolet (VUV) at a low temperature. The prepared TiO2 thin film has higher electron mobility and conductivity. As it is used as an ETL for MAPbI3 PSCs, its band structure is better matched with the perovskite, and at the same time, due to the good interface contact, more uniform perovskite crystals are formed. Most importantly, a large number of hydroxyl radicals were formed during VUV irradiation of the precursor film, which made up for the oxygen defect present on the surface of the TiO2 thin film, and were adsorbed to the film surface. These hydroxyl groups form hydrogen bonds with methylammonium (MA) components on the MAPbI3 buried surface, thus promoting the transfer of photogenerated electrons at the MAPbI3/ETL interface. The power conversion efficiency of PSCs fabricated in air with the ETL prepared by VUV irradiation is 20.46%, which is higher than that of the contrast solar cell based on the sintered ETL (17.96%).

High-Performance MEMS Oxygen Sensors Based on Au/TiO2 Films

High-performance microelectromechanical system (MEMS) oxygen sensors were realized by successful preparation of Au nanofilms over TiO2 thin films through successive sputtering on commercial MEMS microhotplates. Oxygen sensing performance of 3 and 6 nm thick Au over TiO2 thin films were compared with that of pure TiO2 thin films. It was shown that 6 nm thick Au over TiO2 thin films have the best sensitivity toward oxygen. The prepared TiO2 thin films were characterized using SEM, EDS, XPS, and a gas testing instrument. The results show that Au decoration has little influence on the surface morphologies of TiO2 thin films. However, Au decoration has a strong influence on the surface properties of the composite films. The favorable performance of 6 nm Au-doped TiO2 thin films is attributed to factors such as catalytical performance, height of Schottky contact, and number of oxygen vacancies. This work makes contributions to low power consumption and high-performance oxygen sensors for Internet of Things applications.

Photocatalytic Performance of Sol-Gel Prepared TiO2 Thin Films Annealed at Various Temperatures.

Titanium dioxide (TiO2) in the form of thin films has attracted enormous attention for photocatalysis. It combines the fundamental properties of TiO2 as a large bandgap semiconductor with the advantage of thin films, making it competitive with TiO2 powders for recycling and maintenance in photocatalytic applications. There are many aspects affecting the photocatalytic performance of thin film structures, such as the nanocrystalline size, surface morphology, and phase composition. However, the quantification of each influencing aspect needs to be better studied and correlated. Here, we prepared a series of TiO2 thin films using a sol-gel process and spin-coated on p-type, (100)-oriented silicon substrates with a native oxide layer. The as-deposited TiO2 thin films were then annealed at different temperatures from 400 °C to 800 °C for 3 h in an ambient atmosphere. This sample synthesis provided systemic parameter variation regarding the aspects mentioned above. To characterize thin films, several techniques were used. Spectroscopic ellipsometry (SE) was employed for the investigation of the film thickness and the optical properties. The results revealed that an increasing annealing temperature reduced the film thickness with an increase in the refractive index. Atomic force microscopy (AFM) was utilized to examine the surface morphology, revealing an increased surface roughness and grain sizes. X-ray diffractometry (XRD) and UV-Raman spectroscopy were used to study the phase composition and crystallite size. The annealing process initially led to the formation of pure anatase, followed by a transformation from anatase to rutile as the annealing temperature increased. An overall enhancement in crystallinity was also observed. The photocatalytic properties of the thin films were tested using the photocatalytic decomposition of acetone gas in a home-built solid (photocatalyst)-gas (reactant) reactor. The composition of the gas mixture in the reaction chamber was monitored using in situ Fourier transform infrared spectroscopy. Finally, all of the structural and spectroscopic characteristics of the TiO2 thin films were quantified and correlated with their photocatalytic properties using a correlation matrix. This provided a good overview of which film properties affect the photocatalytic efficiency the most.

Preparation of compact TiO2 thin film by artist spray gun-assisted pyrolysis method for lead-free perovskite solar cell

In the present investigation, compact TiO2 thin film was prepared by using an artist spray gun (ASG)-assisted pyrolysis method to use as an electron transport layer (ETL) for perovskite solar cell (PSC). The influence of the distance between the spray gun nozzle and the substrate was studied to get quality TiO2 thin film onto FTO substrate among three different distantly deposited TiO2 thin films. The formation of anatase TiO2 thin film was confirmed by XRD and Raman spectroscopy studies. The bandgap of this thin film was measured by UV–Vis analysis and it was found to be 3.19 eV. The emission spectrum and charge separation of TiO2 thin film were analysed by photoluminescence studies. The emission spectrum of TiO2 thin film exhibited at 380 nm confirmed the indirect transition from the conduction band to the valence band. The FE-SEM image confirmed that the prepared TiO2 thin film was uniformly deposited over the substrate without any pinhole, which shows a good agreement with the Raman mapping analysis. A power conversion efficiency (PCE) of 2.69% has been achieved with Pb-free PSC fabricated from uniformly deposited TiO2 ETL.

Pulsed Laser Deposition of Tio2 Nanostructures for Verify the Linear and Non-Linear Optical Characteristics

The present work aims to achieve pulsed laser deposition ofTiO2 nanostructures and investigate their nonlinear properties using z-scan technique.The second harmonic Q-switched Nd: YAG laser at repetition rate of 1Hz and wavelength of 532 nm with three different laser fluencies in the range of 0.77-1.1 J/cm2 was utilized to irradiate the TiO2 target. The products of laser-induced plasma were characterized by utilizing UV-Vis absorption spectroscopy, x-ray diffraction (XRD), atomic force Microscope (AFM),and Fourier transform infrared (FTIR). A reasonable agreement was found among the data obtained usingX-Ray diffraction, UV-Vis and Raman spectroscopy. The XRD results showed that the prepared TiO2 thin films were all crystallite structure with no impurity peaks of other elements. Also, their peak intensities were increased with increasing the ablating laser fluency. AFM measurements indicated that,during pulsed laser deposition, as the laser fluency was increased, the average diameter of the prepared TiO2 nanoparticles (TiO2 NPs)was decreased from 86 to 57 nm, althoughthe differences were increased with the increase in the laser fluency. The multiphoton absorption was investigated using ultra-fast femtosecond laser with the z-scan method.The impact of thickness of the prepared films on the non-linear absorption coefficient was studied as well.

Multifractal study of TiO2 thin films deposited by MO-CVD method: The role of precursor amount and substrate temperature

Since TiO2 thin film is an important semiconductor with many applications in various fields, in this work we studied surface morphology of TiO2 thin films deposited by metal-organic chemical vapor deposition method using multifractal technique. In order to do this, AFM images of prepared TiO2 thin films were analyzed by multifractal method and the effects of the precursor amount and substrate temperature on multifractality of The TiO2 thin films surface were investigated. Multifractal nature of surface of TiO2 thin films deposited with different amounts of precursor at two different positions of substrate with different temperatures was detected using multifractal analysis of the AFM images. The multifractal spectrum f(α) obtained from AFM images indicated that the Δf and width of spectrum are functions dependent on precursor amount and substrate temperature. The obtained data showed that local fluctuation and hight distribution increase with increasing in temperature of substrate for high amount of precursor. Also, it was observed that the substrate temperature has no effect on width of multifractal spectrum at low amount of precursor. Our results clearly showed that morphological complexity of the TiO2 surface and the effect of the precursor amount and temperature of substrate are satisfactorily described by perform multifractal analysis on AFM images. These results can be used in the design and manufacture of interface layer for application in laptops, planer device, transparent electrode, solar cell, sensors and optical devices.

Fabrication of Al-TiO₂ Thin Film Electrode by Spray Pyrolysis Technique for Urea Sensing.

A simple cost effective Al-TiO₂ thin film electrode was fabricated for urea sensing. Urea is the key end product of nitrogen metabolism in humans. Increased level of urea leads to loss of kidney function. Thus determination of urea is important in analysis of kidney diseases. Al-TiO₂ thin films were deposited with different concentration of Al by Spray pyrolysis technique. The X-ray diffraction (XRD) pattern reveals the anatase phase of the Al-TiO₂ thin films with tetragonal structure. A shift is observed in the XRD peak position compared to as prepared TiO₂ thin film indicates the incorporation of Al ions into Ti ions. The UV-Vis spectroscopy study shows that the absorption increases and the absorption peak shifts towards the visible region for Al-TiO₂ thin films compared with that of the as prepared TiO₂ thin film. The optical band gap values changes with the change in the Al concentration in TiO₂ thin films. The electrochemical analysis for optimized Al-TiO₂ thin film electrode was carried out by cyclic voltammetry (CV) method. CV studies of Al-TiO₂ thin film electrode show the good stability and linearity which is essential to fabricate biosensor. The sensor response to urea is linear with correlation coefficient of 0.944 and the sensitivity is 3.17 μA mM-1 cm-2.

Optimization of Self-Cleaning Thin-Film Layer for Photovoltaic Applications.

To improve the productivity of a photovoltaic (PV) module, TiO₂ thin films of different thicknesses were applied as a self-cleaning layer on soda-lime glass and a Si PV module by spray-coating a TiO₂ solution. The structural, optical, and wettability characteristics of the TiO₂ thin films were investigated with respect to the thickness. Thermogravimetric-differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, contact-angle analysis, ultraviolet-visible spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and a solar simulator were used to analyze the prepared TiO₂ thin films. The optimal thickness was determined to be 100 nm. The TiO₂ thin film exhibited a self-cleaning ability even after post-annealing at 250 °C. After the self-cleaning ability was confirmed, the TiO₂ thin film was applied to the PV module.

Hydrothermally-Grown TiO2 Thin Film-Based Metal–Semiconductor–Metal UV Photodetector

A metal–semiconductor–metal (MSM) ultraviolet photodetector has been fabricated by using hydrothermally-grown TiO2 thin films. Ag paint was used as a contact electrode which showed the good ohmic contact between the metal–semiconductor junctions. The effect of deposition time on the structural, morphological and photodetector properties have been studied. The prepared TiO2 thin films are polycrystalline and show a rutile crystal structure with the preferred orientation along the (110) plane. The MSM UV photodetector was illuminated under a UV lamp with an intensity of 1.8 μW/cm2 and at 5-V bias. The photocurrent of the device increased linearly with the applied voltage. The maximum photocurrent of 3.96 μA was obtained for the film deposited at 5 h and maximum spectral photoresponsivity was 13.29 A/W. The device showed a fast optical switching behavior. The high responsivity and fast photoresponse shows that fabricated TiO2 detectors are good candidates for ultraviolet photodetectors.

Preparation of dye sensitized solar cell (DSSC) using isolated anthocyanin fromfruit sat (melastomamalabathricum l) dicopimented with salicylic acid as dye

A study has been conducted on the use of anthocyanin extract from fruits (Melastomamalabthricum L), which was incubated by the addition of salicylic acid as photosensitizer in DSSC solar cells. The objective of this study was to determine the optimum condition of the extracts of copigmenation which resulted in the optimum efficiency of DSSC solar cells by increasing the absorption ability of anthocyanin pigment photons.The method used is the method of copigmentation. Copigmentation is an anthocyanin reaction with a copigment compound to form a more complex anthocyanin structure with a number of double bonds that can absorb more photons than the original anthocyanin.. The results of dye characterization using UV-Vis and FTIR indicate a wider absorption spectrum and a more complex structure in antigianated anthocyanins when compared without copigmentation. Based on the results of the characterization of the prepared TiO2 thin film, obtained crystal size of TiO2 used ranged from 27.377 to 64.738 nm with a width of200-950 nm photocathode spekrum absorption. Based on the results of the research, it is found that the antiganant extract can be increased by DSSC solar cell efficiency from 0.62% to 1.32% with 24 hours of copigmentation time and 1: 2 concentration of concentration.

Effect of annealing on the photocatalytic activity of chemically prepared TiO2 thin films under visible light

Porous TiO2 thin film was fabricated onto glass substrate using a simplified chemical bath deposition method at moderately low temperature and the effects of thermal annealing on the structural, morphological, optical and photocatalytic properties were investigated. We report here that the as-prepared TiO2 thin films showed the amorphous phase while the little improvement in the crystallinity was observed after annealing. FESEM image of the as-deposited TiO2 thin film shows that the total surface of the substrate uniformly acquired by nearly spherical TiO2 clusters and a significant grain growth takes place and porous structure generates after the thermal annealing at 773 K. The average transmittance of the TiO2 films slightly decreases after annealing thus absorption band edge shifted towards higher wavelength. The decrease in bandgap value from 3.32 eV to 3.08 eV was observed after thermal annealing. The photocatalytic activity of the as-prepared and annealed TiO2 films was evaluated by photodegradation of congo red dye solution. After annealing, the photocatalytic activity of the TiO2 films was found to be increased because of the improvement of crystallization of anatase TiO2 thin films as evident from XRD and FESEM studies. The photocatalytic reaction for both as-deposited and annealed TiO2 thin film follows pseudo-first order kinetics.

Role of point defects in hybrid phase TiO2 for resistive random-access memory (RRAM)

TiO2 thin films based resistive random-access memory was examined for resistive switching behavior. TiO2 thin films were deposited on FTO glass substrate using single step hydro-thermal method with different synthesis parameters. The x-ray Diffraction results confirmed the existence of both anatase and rutile phases (hybrid) in one film and only rutile phase in other film. Morphological studies of prepared TiO2 thin film were carried out using scanning electron microscope. The photo-luminescence results revealed the presence of Ti interstitial defects (Ti+4 & Ti+3) and oxygen vacancies in hybrid phase film. Whereas, Ti interstitial defects were absent in rutile phase film. Current voltage characteristics showed the presence of resistive switching in the hybrid phase film only. The switching characteristics have been attributed to originate from the presence of Ti interstitial defects, facilitating Ag+ ion migration in TiO2 dielectric layer. The observed resistive switching has been explained on the electrochemical metallization (ECM) model.

Comparison of the Physicochemical Properties of TiO2 Thin Films Obtained by Magnetron Sputtering with Continuous and Pulsed Gas Flow

In this paper, a comparison of TiO2 thin films prepared by magnetron sputtering with a continuous and pulsed gas flow was presented. Structural, surface, optical, and mechanical properties of deposited titanium dioxide coatings were analyzed with the use of a wide range of measurement techniques. It was found that thin films deposited with a gas impulse had a nanocrystalline rutile structure instead of fibrous-like anatase obtained with a continuous gas flow. TiO2 thin films deposited with both techniques were transparent in the visible wavelength range, however, a much higher refractive index and packing density were observed for coatings deposited by the pulsed gas technique. The application of a gas impulse improved the hardness and scratch resistance of the prepared TiO2 thin films.

Thickness effect on the optical properties of TiO2-anatase thin films prepared by ultrasonic spray pyrolysis: Experimental and ab initio study

TiO2 thin films with different thicknesses were deposited on glass substrates by using the Ion Layer Gas Reaction (Spray-ILGAR) technique at a substrate temperature of 460°. The effects of deposition time on the morphology and the optical properties of deposited anatase TiO2 thin films are studied. A wide range of characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), Atomic Force Microscopy (AFM) and Ultraviolet–Visible-Near Infrared spectrum were used to characterize prepared TiO2 thin films. The experimental results show that the morphology of deposited thin film changes from sheet like to pyramid like morphology and the optical band gap decreases with increasing the thickness of TiO2 thin films from 3.41 eV to 2.97 eV for thicknesses ranging respectively from 48 nm to 510 nm. XPS measurements revealed oxygen excess, which can be ascribed to the appearance of oxygen vacancy point defects and/or surface adsorption of different species with oxygen element. The ab initio calculations were conducted based on the full-potential linearized augmented plane wave (FP-LAPW) method, to calculate the indirect band gap of different TiO2 thin film thicknesses. The band gap energy calculated using the modified Becker Johnson (mBJ) potential was 3.19 eV for pure bulk TiO2 and 2.98 eV for bulk TiO2 with 8% oxygen vacancy, which is closer to the experimental band gap value of 2.97 eV measured for 510 nm film thickness.

Hydrothermal synthesis of brookite TiO2 nanoparticles for dye-sensitized solar cell

We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO2) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO2 thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO2 sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I2 + 0.1 M KCl) electrolyte at 40 mW cm−2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.

The effect of TiO2 thin film thickness on self-cleaning glass properties

TiO2 is one of semiconductor materials which are widely used as photocatalyst in the form of a thin film. The TiO2 thin film is prepared by using the spin coating sol-gel method. The researcher prepared TiO2 thin film with 3 coating variations and X-Ray Diffraction characterization, UV-Vis Spectrophotometer, Electron Microscopy Scanning, and examined its hydrophilic and anti-fogging properties. The result of X-Ray Diffraction showed that the phase formed is the anatase on 101crystal field. The Electron Microscopy Scanning images showed that TiO2 thin films had a homogeneous surface with the particle sizes as big as 235 nm, 179 nm, and 137 nm. The thickness of each thin film was 2.06μm, 3.33μm, and 5.20μm. The characterization of UV-Vis Spectrophotometer showed that the greatest absorption to the wavelength of visible light was in the thin film’s thickness of 3 coatings with the band-gap determined by using 3.30 eV, 3.33 eV, and 3.33 eV Plot Tuoc. These results indicated that the rate of absorption would be increased by increasing the thickness of film. The increasing thickness of the thin film makes the film hydrophilic able to be used as an anti-fogging substance.

Analysis of the properties of functional titanium dioxide thin films deposited by pulsed DC magnetron sputtering with various O2:Ar ratios

For the purpose of thin film preparation, pulsed DC magnetron sputtering process was performed and various O2:Ar gas ratios were applied during deposition. Structural properties of thin films deposited with various sputtering atmospheres were determined based on the results of the x-ray diffraction method and Raman spectroscopy, which revealed that all coatings were nanocrystalline and had anatase or rutile structure. The surface morphology of the coatings were investigated with the aid of a scanning electron microscopy and atomic force microscopy. Surface properties were evaluated by x-ray photoelectron spectroscopy and wettability measurements. It was revealed that an increase of Ar amount in the sputtering gas atmosphere caused as a result an increase of thin film water contact angle and enhanced ability of the surface to adsorb water molecules and hydroxyl radicals. Optical properties evaluated on the basis of transmission and reflection measurements showed that all coatings were transparent in the visible wavelength range, but had different refractive index, porosity and packing density. The mechanical properties of the obtained coatings were determined on the basis of nanoindentation tests. Prepared TiO2 thin films had different surface, optical and mechanical properties depending on the gas atmosphere during deposition.

Effect of sputtering power on optical properties of prepared TiO2 thin films by thermal oxidation of sputtered Ti layers

In this research, TiO2 thin films prepared via thermal oxidation of Ti layers were deposited by RF-magnetron sputtering method at three different sputtering powers. The effects of sputtering power on structure, surface and optical properties of TiO2 thin films grown on glass substrate were studied by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV–visible spectrophotometer. The results reveal that, the structure of layers is changed from amorphous to crystalline at anatase phase by thermal oxidation of deposited Ti layers and rutile phase is formed when sputtering power is increased. The optical parameters: absorption coefficient, dielectric constants, extinction coefficient, refractive index, optical conductivity and dissipation factor are decreased with increase in sputtering power, but increase in optical band gap is observed. The roughness of thin films surface is affected by changes in sputtering power which is obtained by AFM images.

THz pulse generation using a contact grating device composed of TiO2/SiO2 thin films on LiNbO3 crystal

We developed a new contact grating device for terahertz (THz) pulse generation by optical rectification. The device was made from polycrystalline rutile TiO2 thin film in the grating region and an amorphous SiO2 layer deposited on a Mg-doped LiNbO3 crystal. Our calculations indicated that the TiO2 grating on the SiO2 layer would yield an increase in diffraction efficiency of up to 0.69. The prepared TiO2 thin film had a sufficient laser induced damage threshold (140 GW/cm2) to enable effective THz pulse generation. Using a prototype device, we demonstrated THz pulse generation and investigated the phase-matching conditions experimentally.

Study of COD Removal Efficiency from Synthetic Wastewater by Photocatalytic Process

In this research, we compared the COD removal efficiencies of titanium dioxide (TiO2) thin films coated on the surfaces of borosilicate glass that prepared by three different numbers of coating layer; i) 3 layers ii) 4 layers and iii) 5 layers by sol-gel method. All of the prepared TiO2 thin films consisted of pure anatase crystalline structure with grain sizes in the range 20-250 nm. The calculated optical band gaps of the TiO2 thin films were 3.24. The total apparent surface area per total weight of TiO2 thin films were 4.74, 3.86 and 2.79 m 2 g －1 for 3, 4 and 5 layers coating, respectively. The kinetics of the photodegradation reactions of COD under UVA light source were described by the Langmuir-Hinshelwood (L-H) kinetic model. The specific rates of the photodegradation of TiO2 thin films at 3 layers coating was 1.40×10 －4 min －1 mW －1 , while for the 4 layers coating and the 5 layers coating were 1.50×10 －4 and 4.60×10 －4 min －1 mW －1 , respectively. The photocatalytic performance of COD degradation was higher with smaller grain size, higher surface area and narrow optical band gaps. Moreover, the numbers of coating layer on substrate also have great influence for kinetic of COD removal.