Thin TiO2 Layer Research Articles

Biotemplated Synthesis of TiO2-Coated Gold Nanowire for Perovskite Solar Cells.

Fibrous nanomaterials have been widely employed toward the improvement of photovoltaic devices. Their light-trapping capabilities, owing to their unique structure, provide a direct pathway for carrier transport. This paper reports the improvement of perovskite solar cell (PSC) performance by a well-dispersed TiO2-coated gold nanowire (GNW) in a TiO2 cell layer. We used an artificially designed cage-shaped protein to synthesize a TiO2-coated GNW in aqueous solution under atmospheric pressure. The artificially cage-shaped protein with gold-binding peptides and titanium-compound-biomineralizing peptides can bind GNWs and selectively deposit a thin TiO2 layer on the gold surface. The TiO2-coated GNW incorporated in the photoelectrodes of PSCs increased the external quantum efficiency within the range of 350–750 nm and decreased the internal resistance by 12%. The efficient collection of photogenerated electrons by the nanowires boosted the power conversion efficiency by 33% compared to a typical mesoporous-TiO2-nanoparticle-only electrode.

Effect of atomic-layer-deposited TiO2 on carbon-supported Ni catalysts for electrocatalytic glycerol oxidation in alkaline media

Thin TiO2 layers were deposited onto a carbon-supported Ni catalyst (Ni/C) through atomic layer deposition (ALD) and the resulting TiO2-coated Ni/C (ALD(TiO2)-Ni/C) was utilized for electrochemical glycerol oxidation in alkaline media. X-ray photoelectron spectroscopy analysis demonstrated that the Ni surface phase of ALD(TiO2)-Ni/C mainly consisted of Ni(OH)2 while that of uncoated Ni/C was a mixed phase of NiO and Ni(OH)2. The ALD(TiO2)-Ni/C exhibited electrocatalytic activity at least 2.4 times higher than that of Ni/C. Density functional theory calculations were used to investigate how the modified Ni surface with the TiO2 coating affects the adsorption/desorption of glycerol.

Bactericidal efficiency of UVA-active titanium dioxide thin layers on bacteria from food industry environments

Titanium dioxide (TiO2) thin layers have been deposited on glass substrates using radio frequency magnetron sputtering technique. The photocatalytic activity of the TiO2 thin layers has been investigated by a methylene blue discolouration test and reveals that films with an anatase structure present the highest performance. Bactericidal activity of the anatase-phase TiO2 layer against food-borne bacteria has then been tested by enumeration of the adherent cells, after adhesion and a subsequent UVA illumination. A decrease of the adherent bacteria number equal to −1.2, −2.6 and −2.3 log is reached for Y. enterocolitica, L. monocytogenes and P. fragi, respectively. SEM observations exhibit bacterial cells with damaged walls for all bacteria. Applied on materials present in the food plants, these TiO2 thin layers may be an effective way for the hygienic conception of the equipment to reduce the biofilm formation and thus, to ensure food safety.

Facile preparation of nanocrystalline TiO2 thin films using electrophoretic deposition for enhancing photoelectrochemical water splitting response

Titanium oxide (TiO2) nanocrystalline particles have been successfully deposited on fluorine-doped tin oxide (FTO) glass using an electrophoretic deposition (EPD) with a good uniformity. This study aims to optimize the heat treatment temperature, applied electric field, and deposition time to produce a good uniformity nanocrystalline TiO2 layer coating on FTO glass for better photoelectrochemical water splitting hydrogen generation performance under UV irradiation. In the present study, EPD technique allows controlling of TiO2 nanocrystalline layer characteristics on FTO glass, including smoothness and thickness. Characterisation like FE-SEM revealed that nanocrystalline TiO2 with a 14.6 μm thickness with good uniformity and minimal cracking surface exhibited the highest photocurrent density (2.12 mA/cm2) among samples. Besides, Raman and XRD analyses showed that nanocrystalline TiO2 thin coating form successfully. Based on our experiments, we proposed that the optimum condition to form nanocrystalline TiO2 thin film layer using EPD technique is 30 V, 60 s of deposition and post-annealing of the thin film at 400 °C based on the jp–V characteristic. Under illumination of 100 W UV light, the photoconversion efficiency can be up to 2.49%. In addition, hydrogen production was tested with the production rate is up to 0.45 mL/cm2/h and the photoelectrode can be re-used and remained stable for five cycles continuously.

The use of Carbon Compounds (Carbon Nanotubes and Activated Carbon) in the Improvement of TiO2–Carbon Supercapacitor Performance

Improvement of the performance of titanium oxide (TiO 2 )–carbon supercapacitor was studied by fabricating a double-layer electrode composite consisting of (TiO 2 ), activated carbon (AC), and carbon nanotubes (CNTs). A thin layer of TiO 2 /CNT/AC electrode was coated on an aluminum foil substrate through the addition of a polyvynilidene fluoride adhesive of around 15% of the total weight of the composite. The resultant layer was then made into a double layer, and its conductivity and capacitance were measured using the electrochemical impedance spectroscopy (EIS). Results showed that the supercapacitor performance improved with the addition of CNTs. The highest performance was obtained with a composition of 23.3% TiO 2 , 21.0% CNT, and 4.0% AC with a 1.29 × 10 -2 S/m conductivity and 5.56 F/g capacitance (C) at a frequency of 0.1 Hz.

Growth of TiO2 Thin Films by High Energy Milling Assisted Pulsed Laser Deposition Method

TiO2 thin film can be deposited on the silicon substrate using pulse laser deposition method. To prove homogeneity of grain size on surface, this study uses milling treatment for TiO2 powder before it is deposited. Milling treatment was conducted on samples of commercial TiO2 powder with high energy milling method. The variation of milling time was 0, 1, 3 and 6 hours. Furthermore, the samples were shaped as disc with diameter of 1 cm and used as a target source in growth of thin film. Variations in time for the milling treatment of the TiO2 powder has no effect on the phase change, but rather on the homogeneity of grain size on a thin layer of TiO2. In this study, the optimum milling time to produce a homogeneous grain size of a thin layer of TiO2 for 3 hours.

Very thin thermally stable TiO2 blocking layers with enhanced electron transfer for solar cells

Very thin TiO2 blocking layers (BLs) are important components for achieving high solar power conversion efficiencies (PCEs) in the dye-sensitized solar cells, and particularly perovskite solar cells (PSCs). When reasonably thin, TiO2 BLs prevent recombination of photogenerated charges at the conductive fluorine-doped tin oxide (FTO) glass substrate used in these devices. However, all previous attempts to generate efficient TiO2 BLs have been hampered by an insufficient charge transfer rate at quasi-amorphous TiO2 and very low thermal stability, leading to the loss of blocking properties after thermal calcination. In this work, we report the deposition of homogenous very thin (∼30nm) TiO2 BLs by combining advanced high impulse power magnetron sputtering (HiPIMS) and additional bipolar medium-frequency (MF) magnetron co-sputtering. The as-deposited TiO2 films were shown to provide excellent blocking properties which were preserved even after thermal treatment at 450°C. Moreover, TiO2 BLs thermally treated at 450°C show a well-developed rutile structure and 70 times higher photocurrents compared to the as-deposited layers. This work opens possibilities for the utilization of very thin TiO2 layers in solar cell technologies providing a double mode of action: blocking functionality and efficient electron transport.

Low temperature reactively sputtered crystalline TiO2 thin film as effective blocking layer for perovskite solar cells

A uniform and compact hole blocking layer is necessary for a high performance perovskite solar cells, as it not only serves as an electron collector but also represses the electron recombination by blocking direct contact between the transparent conducting oxide and the perovskite layer. So far, highly performing perovskite solar cells have been achieved using a blocking layer that requires sintering at high temperatures (>450°C). In this study, reactive magnetron sputtering was used to synthesise crystalline anatase TiO2 thin film blocking layer at a moderate temperature (150°C). The influence of block layer thickness on the photovoltaic performance is scrutinised. A high performance of 8.7% power conversion efficiency was obtained for perovskite solar cells with a 76nm thick TiO2 blocking layer. This low temperature synthesis method will extend the choice of substrate to cheap and flexible polymer substrates. The surface plasma treatment prior to the blocking layer deposition was also found to affect the performance of the solar cells.

Studies on the efficiency enhancement of co-sensitized, transparent DSSCs by employment of core-shell-shell gold nanorods

In this article, we present studies concerning the efficiency enhancement of dye-sensitized solar cells (DSSC) containing cocktails of organic donor-π-acceptor (D-π-A) dyes (L0 and L1) and a squaraine sensitizer (SQ2) by means of the localized surface plasmon resonance (LSPR) effect induced by gold nanorods (GNRs) embedded within the semiconductor layer. In view of the potential application of DSSC devices for building integration, dye cocktails were selected to maximize transparency in the 500–600nm region, where human eye sensitivity has its peak. Thus, the chosen organic dyes and the squaraine sensitizer had absorption maxima in the 380–410nm region and above 660nm, respectively. Thanks to their specific asymmetry, GNRs with a 3:1 aspect ratio could enhance organic dye absorption due to their transverse resonance component as well as squaraine absorption in the far-red/near-infrared (NIR) spectral range due to their longitudinal resonance component; furthermore, they were sequentially coated with thin layers of SiO2 and TiO2 in order to make them robust enough to withstand thermal film sintering and minimize charge recombination during the photovoltaic operation. Whereas incorporation of GNRs in the photoanode did not improve the efficiency of cells prepared with the L0/SQ2 dye combination, a significant increase of 23% (from 3.50% to 4.32%), comparable to that observed for Ru-sensitizer N719, was observed in the case of the L1/SQ2 dye cocktail.

Switching characteristics in TiO2/ZnO double layer resistive switching memory device

The uniform and reliable resistive switching characteristics of a ZnO based resistive random access memory device with a thin TiO2 layer are successfully investigated. In this study, the effect of thickness of the TiO2 layer on switching characteristics has been investigated. Compared with different thicknesses of the thin TiO2 layer, the remarkably improved resistive switching parameters such as lower forming voltage and the narrower variation of endurance are achieved for a TiO2 layer of thickness 2 nm. The forming voltages are dependent on the TiO2 thickness which supports the idea that forming process is governed by a dielectric breakdown-like phenomenon. The Ti/TiO2/ZnO/Pt device with the 2 nm TiO2 layer exhibits good DC endurance up to 103 cycles. The non-volatility of data storage is further confirmed by retention test measured at room temperature. It has been observed that both low resistance state and high resistance state do not exhibit any degradation for more than 104 s.

Optimization of charge transfer and transport processes at the CdSe quantum dots/TiO2 nanorod interface by TiO2 interlayer passivation

Surface trap states hinder charge transfer and transport properties in TiO2 nanorods (NRs), limiting its application on optoelectronic devices. Here, we study the interfacial processes between rutile TiO2 NR and CdSe quantum dots (QDs) using TiO2 interlayer passivation treatments. Anatase or rutile TiO2 thin layers were deposited on an NR surface by two wet-chemical deposition treatments. Reduced interfacial charge recombination between NRs and CdSe QDs was observed by electrochemical impedance spectroscopy with the introduction of TiO2 thin film interlayers compared to bare TiO2 NRs. These results can be ascribed to in-gap trap state passivation of the TiO2 NR surface, which led to an increase in open circuit voltage. Moreover, the rutile thin layer was more efficient than anatase to promote a higher photo-excited electron transfer from CdSe QDs to TiO2 NRs due to a large driving force for charge injection, as confirmed by surface photovoltage spectroscopy.

Impact of Film Thickness of Ultrathin Dip-Coated Compact TiO2 Layers on the Performance of Mesoscopic Perovskite Solar Cells.

Uniform and pinhole-free electron-selective TiO2 layers are of utmost importance for efficient perovskite solar cells. Here we used a scalable and low-cost dip-coating method to prepare uniform and ultrathin (5-50 nm) compact TiO2 films on fluorine-doped tin oxide (FTO) glass substrates. The thickness of the film was tuned by changing the TiCl4 precursor concentration. The formed TiO2 follows the texture of the underlying FTO substrates, but at higher TiCl4 concentrations, the surface roughness is substantially decreased. This change occurs at a film thickness close to 20-30 nm. A similar TiCl4 concentration is needed to produce crystalline TiO2 films. Furthermore, below this film thickness, the underlying FTO might be exposed resulting in pinholes in the compact TiO2 layer. When integrated into mesoscopic perovskite solar cells there appears to be a similar critical compact TiO2 layer thickness above which the devices perform more optimally. The power conversion efficiency was improved by more than 50% (from 5.5% to ∼8.6%) when inserting a compact TiO2 layer. Devices without or with very thin compact TiO2 layers display J-V curves with an "s-shaped" feature in the negative voltage range, which could be attributed to immobilized negative ions at the electron-extracting interface. A strong correlation between the magnitude of the s-shaped feature and the exposed FTO seen in the X-ray photoelectron spectroscopy measurements indicates that the s-shape is related to pinholes in the compact TiO2 layer when it is too thin.

Optical and microstructural characterization of amorphous-like Al2O3, SnO2 and TiO2 thin layers deposited using a pulse gas injection magnetron sputtering technique

In this study, thin Al2O3, SnO2 and TiO2 films (37–58nm) were deposited by means of a recently developed pulse gas injection magnetron sputtering method. The deposition rates are in the range from 1.7nm/min (for Al2O3) to 24.4nm/min (for SnO2). Atomic force microscopy measurements show that the thus prepared layers are very smooth. The results obtained using scanning electron microscopy and Raman spectroscopy techniques revealed their amorphous-like nature. Optical properties of the dielectrics were examined by means of spectroscopic ellipsometry and show the red-shift of their band-gap energy and lower values of the refractive index compared to corresponding values determined for dense films and/or bulk materials.The microstructural and optical properties of examined oxides are directly associated with specific growth conditions (the impulse injection of the reactive gas) in the pulse gas injection magnetron sputtering process carried out in the low pressure oxygen plasma.

Selective Deposition of an Ultrathin Pt Layer on a Au-Nanoisland-Modified Si Photocathode for Hydrogen Generation.

Platinum, being the most efficient and stable catalyst, is used in photoelectrochemical (PEC) devices. However, a minimal amount of Pt with maximum catalytic activity is required to be used to minimize the cost of production. In this work, we use an environmentally friendly, cost-effective, and less Pt-consuming method to prepare PEC devices for the hydrogen evolution reaction (HER). The Pt monolayer catalyst is selectively deposited on a Au-nanoisland-supported boron-doped p-type Si (100) photocathode. The PEC device based on the Si photocathode with an ultralow loading of the Pt catalyst exhibits a comparable performance for the HER to that of devices with a thick Pt layer. In addition, we demonstrate that by using a thin TiO2 layer deposited by atomic layer deposition photo-oxidation of the Si photocathode can be blocked resulting in a stable PEC performance.

Urchin-inspired ZnO-TiO2 core-shell as building blocks for dye sensitized solar cells

We applied the core-shell concept to an urchin-inspired ZnO nanowire photoanode building block as a means to increase the electron transport and reduce recombination between nanowire and electrolyte. Dye-sensitized solar cells (DSSCs) were prepared, for the first time, from arrays of urchin-like ZnO nanowire building blocks covered with a thin layer of anatase TiO2 by atomic layer deposition (ALD). An increase in the cell open-circuit voltage (VOC) and an improvement in the conversion efficiency were observed when the urchin-like ZnO building blocks were coated with 10nm thick TiO2 ALD shells in combination with 10μm thick top layer of TiO2 nanoparticles of 15.8nm size. Using urchin-like ZnO nanowires as building blocks can improve the light-scattering and provide a higher surface area with a great control of the nanowire dimensions to increase the dye loading and reduce the electron collection path. The addition of a thin TiO2 blocking layer decreases the recombination of charges in such a high surface area nanostructure.

Structural colour of polyester fabric coated with Ag/TiO2 multilayer films

Silver/titanium dioxide (Ag/TiO2) multilayer films with structural colours on polyester fabric were fabricated using direct current (DC) magnetron sputtering. The bright and variable structural colourations of polyester fabrics coated with an Ag/TiO2 film were investigated with GretagMacbeth Color-Eye 7000A spectrophotometer. The compositions, surface morphologies and microstructure of multilayer films deposited on polyester fabrics were also analysed by X-ray photoelectron spectroscopy, Scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that the structural colours varied with the thickness of TiO2 thin layer in Ag/TiO2 multilayer films. The TiO2 thin layer thicknesses were 42, 65.6, 82, 98.4 and 114.8 nm, and the samples colours became purple, light blue, blue, pink and dark red, respectively. The creation of colours was coincident to film interference principle. XRD analysis revealed that there were four diffraction peaks for Ag/TiO2 multilayer film at 38, 44, 64 and 77° of 2θ, corresponding to (110), (200), (220) and (311) Ag crystal planes and that TiO2 structure in Ag/TiO2 multilayer film was non-crystalline.

Photocatalysis assisting the mechanical polishing of a single-crystal SiC wafer utilizing an anatase TiO2-coated diamond abrasive

This study introduces a new technique for depositing photocatalytic TiO2 thin layers on a nanodiamond (ND) abrasive to polish a single-crystal 6H-SiC wafer with sol-gel tools. A controllable and simple method is utilized to prepare ND/TiO2 composite abrasives by isothermal hydrolysis without conventional post-heating treatment for crystallization. The composites are characterized by X-ray diffraction and transmission electron microscopy. The TiO2 layer appears on the ND surface completely and continuously, and anatase TiO2 can be synthesized directly in this manner. An electrochemical experiment is performed to oxidize NaNO2 utilizing an ND/TiO2 electrode. Results indicate that ND/TiO2 with a hydrolysis reaction time of 18h exhibits the best oxidative activity. The generation of hydroxyl radical (OH) from the ND/TiO2 composite has increased upon exposure to UV irradiation. A comparative polishing experiment revealed that an ultra-smooth surface and a higher MRR were achieved when applying the ND/TiO2 composite abrasives, superior to those of pristine diamond abrasives. This scenario is due to the SiC being oxidized by ·OH and forming a relatively soft SiO2 layer.

Performance of natural-dye-sensitized solar cells by ZnO nanorod and nanowall enhanced photoelectrodes.

In this work, two natural dyes extracted from henna and mallow plants with a maximum absorbance at 665 nm were studied and used as sensitizers in the fabrication of dye-sensitized solar cells (DSSCs). Fourier transform infrared (FTIR) spectra of the extract revealed the presence of anchoring groups and coloring constituents. Two different structures were prepared by chemical bath deposition (CBD) using zinc oxide (ZnO) layers to obtain ZnO nanowall (NW) or nanorod (NR) layers employed as a thin film at the photoanode side of the DSSC. The ZnO layers were annealed at different temperatures under various gas sources. Indeed, the forming gas (FG) (N2/H2 95:5) was found to enhance the conductivity by a factor of 103 compared to nitrogen (N2) or oxygen (O2) annealing gas. The NR width varied between 40 and 100 nm and the length from 500 to 1000 nm, depending on the growth time. The obtained NWs had a length of 850 nm. The properties of the developed ZnO NW and NR layers with different thicknesses and their effect on the photovoltaic parameters were studied. An internal coverage of the ZnO NWs was also applied by the deposition of a thin TiO2 layer by reactive sputtering to improve the cell performance. The application of this layer increased the overall short circuit current Jsc by seven times from 2.45 × 10−3 mA/cm2 to 1.70 × 10−2 mA /cm2.

Influence of internal stress in optical thin films on their failure modes assessed by in situ real-time scratch analysis

In this study we present a new in situ real-time approach to perform and analyze scratch tests of transparent coating/substrates systems. This method allows for the observation of the contact region during the scratching process. As an example, thin TiO2 layers exhibiting stress levels ranging from tensile to compressive were deposited by ion beam assisted evaporation onto plastic substrates. Failure processes obtained using an increasing and a novel decreasing load scratch sequences were then linked to the internal stress in the coatings allowing one to draw a stress management diagram and to evaluate the yield stress of the TiO2 layers. This work enhances the understanding of the optical films’ failure mechanisms, and outlines a new pathway to increase measurement reproducibility.

有機・無機複合薄膜を修飾した水晶振動子センサによるアンモニアおよびホルムアルデヒドの二成分ガス検知

Quartz crystal microbalance (QCM) gas sensors based on the alternate deposition of TiO2 and polymers were developed for the detection of ammonia and formaldehyde odors. For sensitive detection of both analytes, poly(acrylic acid), PAA, and poly(allyamine hydrochloride), PAH, were employed in the film along with TiO2 thin layers that were prepared by the gas-phase surface sol-gel (GSSG) process. The alternate (TiO2/PAA/TiO2/PAH) film-deposited QCM sensor showed linear responses to ammonia in the concentration range 0.5-40 ppm and to formaldehyde in the concentration range 0.3-20 ppm. The sensor response was very fast, stable, and repeatable. The ammonia or formaldehyde binding is based on the acid-base interaction to the free carboxyl or amino groups of PAA or PAH. TiO2 thin layers deposited by the GSSG process played significant roles in preventing the electrostatic interaction of polymer layers and in improving the diffusion of gaseous analytes inside the film.