Surface Of TiO2 Film Research Articles

Multifunctional molecular bridge enabled interface passivation and strain release for stable and efficient all-inorganic perovskite solar cells

The precise management of the buried interface in n-i-p perovskite solar cells (PSCs) to achieve efficient charge extraction and transport is crucial for improving the photovoltaic performance. Here, a 4-chloro-2,5-dimethoxyaniline (CDA) modifier with multifunctional groups is utilized as a molecular bridge at the TiO2/CsPbBr3 buried interface to enhance the qualities of TiO2 and CsPbBr3 films and the arrangement of interface energy level. The chlorine atom in CDA can heal the oxygen vacancies defects on the TiO2 film surface, thereby improving its electron mobility and conductivity. The –O– and -NH2 groups in CDA play a passivation effect on the ions defects of CsPbBr3 film, and especially the two –O– groups can anchor the lattice Pb atoms of CsPbBr3 perovskite, which effectively reduce the trap states of CsPbBr3 film and release the residual lattice strain. The modification of CDA also improves the wettability and energy level of TiO2 film to optimize CsPbBr3 crystal growth and charge transport, respectively. Consequently, the CsPbBr3 PSCs with CDA molecular bridge free of encapsulation achieve a highly increased power conversion efficiency of 10.85%, in contrast with 8.16% value of the control device. After 720 h of storage at 85 °C and in air environment with 85% relative humidity, the efficiency of the CDA-modified device retains 93.1% of the initial value, demonstrating excellent long-term humidity and thermal stability.

Electronic and Structural Properties of Antibacterial Ag–Ti-Based Surfaces: An Ab Initio Theoretical Study

Coatings with tunable multifunctional features are important for several technological applications. Ti-based materials have been used in diverse applications ranging from metallic diodes in electronic devices up to medical implants. This work uses ab initio calculations to achieve a more fundamental understanding of the structural and electronic properties of β-TiNb and its passive TiO2 film surfaces upon Ag addition, investigating the alterations in the electronic band gap and the stability of the antibacterial coating. We find that Ag’s 4d electrons introduce localized electron states, characterized by bonding features with the favoured Ti first neighbour atoms, approximately −5 eV below the fermi level in both β-TiNb bulk and surface. Ag’s binding energy on β-TiNb(110) depends on the local environment (the lattice site and the type of bonded surface atoms) ranging from −2.70 eV up to −4.21 eV for the adatom on a four-fold Ti site, offering a variety of options for the design of a stable coating or for Ag ion release. In Ti–O terminated anatase and rutile (001) surfaces, surface states are introduced altering the TiO2 band gap. Silver is bonded more strongly, and therefore creates a more stable antibacterial coat on rutile than on anatase. In addition, the Ag coating exhibits enhanced 4d electron states at the highest occupied state on anatase (001),which are extended from −5 eV up to the Fermi level on rutile (001), which might be altered depending on the coat structural features, thus creating systems with tunable electronic band gap that can be used for the design of thin film semiconductors.

Growth of MAPbI3 perovskite films on MWCNT-modified TiO2 thin films for solar cell applications

In this work, we have modified titanium dioxide (TiO2) films by incorporating multi-walled carbon nanotubes (MWCNTs) in TiO2-sol. TiO2 and MWCNT-modified TiO2 thin films have been prepared via solution processing spin coating route. Further, the structural, optical, and surface morphology of methyl ammonium lead iodide (MAPbI3) films have been studied onto pristine TiO2 and MWCNT-modified TiO2 films. We extensively analyze how different MWCNT concentrations impact the TiO2 and perovskite film structure, optoelectronic properties, and surface characteristics. The findings highlight that the MAPbI3 films maintain a tetragonal structure with enhanced crystallinity compact and smooth surface morphology in MWCNT-modified TiO2/MAPbI3 films. Besides this, enhanced optical absorbance in MAPbI3 films have also been observed on perovskite films fabricated onto MWCNT-modified TiO2 films with enlarged grains and a red shift in optical band gap has been observed for MWCNT-modified TiO2 films and MWCNT-modified TiO2/ MAPbI3 films. Further, various critical electrical parameters such as charge carrier concentration, Hall mobility, sheet resistance, and resistivity have been investigated to understand the effects of the incorporation of MWCNT on TiO2 films. The value of carrier concentration enhances from 3.76 × 1024 cm−3 to 6.39 × 1024 cm−3 on incorporation of MWCNT in TiO2 films. Furthermore, an enhancement in crystallinity, optical absorbance, and grain size has been observed in perovskite films fabricated onto TiO2/MWCNT films. Thus, TiO2 modification with MWCNT can tune the optical and charge transport properties of charge-transporting layer TiO2 films for perovskite photovoltaics and other optoelectronic devices.

Effect of laser spot diameter on oxygen bubble behavior in photoelectrochemical water splitting

The detrimental effect caused by the long-term adhesion of bubbles on the gas production efficiency has been the main bottleneck limiting the efficiency improvement of photoelectrochemical water splitting. The evolution of oxygen bubbles on the fixed photoelectrode surface of TiO2 films was observed in-situ using a combination of a synchronized high-speed microscopic camera and an electrochemical workstation. The effect of oxygen bubble evolution on the current during the photoelectrochemical reaction was investigated under different laser spot diameters. When the spot diameter increased 1.68 times from 700 μm to 1176 μm with a laser power of 5 mW, the bubble detachment diameter and growth period increased 2.7 times and 20.2 times, respectively, yet the gas production efficiency decreased by 34.7%. Meanwhile, the peak current caused by the bubble detachment gradually increased. However, the valley current at the nucleation waiting stage of the bubble did not have obvious changes. The model for the gas evolving based on supersaturation was adopted. It illustrated that the concentration gradient of dissolved gas perpendicular to the photoelectrode surface increased with the increase of spot diameter, leading to an increase in the bubble surface tension gradient, and causing the Marangoni force to inhibit the detachment of bubbles. A force balance model was developed to evaluate the Marangoni forces and the buoyancy forces. The growth rate of the Marangoni force was found to be proportional to the spot diameter. Therefore, reducing the laser spot diameter is a means to effectively remove the bubbles from the photoelectrode surface.

The effects of radio frequency atmospheric pressure plasma and thermal treatment on the hydrogenation of TiO2 thin film

The effects of radio frequency (RF) atmospheric pressure (AP) He/H2 plasma and thermal treatment on the hydrogenation of TiO2 thin films were investigated and compared in this work. The color of the original TiO2 film changes from white to black after being hydrogenated in He/H2 plasma at 160 W (gas temperature ∼381 °C) within 5 min, while the color of the thermally treated TiO2 film did not change significantly even in pure H2 or He/H2 atmosphere with higher temperature (470 °C) and longer time (30 min). This indicated that a more effective hydrogenation reaction happened through RF AP He/H2 plasma treatment than through pure H2 or He/H2 thermal treatment. The color change of TiO2 film was measured based on the Commission Internationale d’Eclairage L*a*b* color space system. Hydrogenated TiO2 film displayed improved visible light absorption with increased plasma power. The morphology of the cauliflower-like nanoparticles of the TiO2 film surface remained unchanged after plasma processing. X-ray photoelectron spectroscopy results showed that the contents of Ti3+ species and Ti–OH bonds in the plasma-hydrogenated black TiO2 increased compared with those in the thermally treated TiO2. X-ray diffraction (XRD) patterns and Raman spectra indicated that plasma would destroy the crystal structure of the TiO2 surface layer, while thermal annealing would increase the overall crystallinity. The different trends of XRD and Raman spectra results suggested that plasma modification on the TiO2 surface layer is more drastic than on its inner layer, which was also consistent with transmission electron microscopy results. Optical emission spectra results suggest that numerous active species were generated during RF AP He/H2 plasma processing, while there were no peaks detected from thermal processing. A possible mechanism for the TiO2 hydrogenation process by plasma has been proposed. Numerous active species were generated in the bulk plasma region, accelerated in the sheath region, and bumped toward the TiO2 film, which will react with the TiO2 surface to form OVs and disordered layers. This leads to the tailoring of the band gap of black TiO2 and causes its light absorption to extend into the visible region.

Fabrication of Ag/TiO2 membrane on Ti substrate with integral structure for catalytic reduction of 4-nitrophenol

In this work, Ag/TiO2 monolithic membrane catalyst was successfully fabricated on alpha-titanium plate by using a facile two-step method. Firstly, a layer of anatase TiO2 film with nanosheet morphology was formed by the hydrothermal reaction in combination with calcination. After photo-deposition in AgNO3 solution under the ultraviolet irradiation, Ag nanoparticles in metallic state were then deposited on the surface of the as-prepared Ti-based TiO2 film. The catalytic performance of the Ag/TiO2 membrane in the presence of NaBH4 was evaluated by taking p-nitrophenol (4-NP) as a pollutant model. The results indicated that the Ag/TiO2 as a monolithic membrane catalyst exhibited excellent catalytic ability and high stability towards 4-NP degradation. During six consecutive recycling runs, the degradation rates of 4-NP were maintained above 73%, with slight difference. This study shows that the monolithic membrane catalyst Ag/TiO2 is a promising material for the degradation of 4-NP owe to its high activity and easy recovery.

Bifunctional Passivation through Fluoride Treatment for Highly Efficient and Stable Perovskite Solar Cells

AbstractDue to the low formation energy, surface defects are more likely to form on the surface of TiO2 films, resulting in a decline in the efficiency and stability of perovskite solar cells (PSCs). Additionally, defects on the bottom surface of the perovskite layer in contact with TiO2 play a key role in Voc (open circuit voltage) loss and the PSC degradation process. Therefore, to improve the efficiency and stability of PSCs, it is critical to develop a reproducible and low‐cost method for passivating the defects on both the TiO2 surface and on the bottom surface of the perovskite layer. In this work, fluoride is utilized as a bifacial contact passivation agent for decreasing the number of defects on the TiO2 surface and the bottom surface of the perovskite layer. PSC efficiency can be significantly increased from 21.3% to 23.7% with fluoride passivation. In addition, the long‐term stability of PSCs, especially light irradiation stability, can be markedly improved. The passivation effects of fluoride treatment on TiO2 films are studied by theoretical calculation and experimental characterization. This work provides a thorough understanding of the TiO2/perovskite interface and demonstrates an approach for improving the efficiency and stability of PSCs.

A general guide for adsorption of cadmium sulfide (CdS) quantum dots by successive ionic layer adsorption and reaction (SILAR) for efficient CdS-sensitized photoelectrochemical cells

Using CdS quantum dots grown on the surface of mesoscopic TiO2 film through SILAR deposition as a model semiconductor-sensitizer, common but not well understood parameters in the deposition process such as precursor compound & its concentration, solvent, and dipping time of the substrate electrode are systematically checked for suggesting a general guideline to make efficient CdS-sensitized mesoporous TiO2 electrode for photovoltaic and photocatalytic applications. Among many variables, the electrostatic interaction between intrinsic (+)-charge of metal cation (Cd2+) and induced (−)-charge of TiO2 surface, which is generated by the degree of solution’s pH above the point of zero charge (pzc) of TiO2, is observed to be the most critical for controlling the extent of CdS adsorption by taking absorbance and TEM images after a defined SILAR process. The acetate salt is the best one for faster and more adsorption of as-grown CdS due to its role of increasing the pH value in solution as a weak base. The highest pH of ∼ 9.5 obtained by adding a weak base, triethanolamine (TEA) to any Cd2+-dissolved solution induces the most adsorption of CdS within the least cycle optimized for better photovoltaic conversions efficiency and photoelectrochemical H2 evolution than those from any other conditions.

Laser-Induced Chemical Liquid-Phase Deposition Plasmonic Gold Nanoparticles on Porous TiO2 Film with Great Photoelectrochemical Performance

This paper considers the photoelectrochemical characteristics of a composite porous TiO2 thin film with deposited plasmonic gold nanoparticles. The deposition of gold nanoparticles was carried out by the laser-induced chemical liquid-phase deposition (LCLD) method. The structural characteristics of the composite have been studied; it has been shown that the porous TiO2 film has a lattice related to the tetragonal system and is in the anatase phase. Gold nanoparticles form on the surface of a porous TiO2 film. A complex of photoelectrochemical measurements was carried out. It was shown that the deposition of plasmonic gold nanoparticles led to a significant increase in the photocurrent density by ~820%. The proposed concept is aimed at testing the method of forming a uniform layer of plasmonic gold nanoparticles on a porous TiO2 film, studying their photocatalytic properties for further scaling, and obtaining large area Au/TiO2/FTO photoelectrodes, including in the roll-to-roll process.

First principle and experimental investigations of monodispersed Au plasmonic nanoparticles on TiO2

Plasmonic nanostructures play an important part in improving the light absorption of semiconductors that are feasible for photovoltaic and other optical devices. In this context, we have synthesized TiO2 thin films with monodispersed Au nanoparticles. These metallic nanoparticles act as plasmonic structures over the smooth semiconductor surface thereby enhancing their properties. X-ray diffraction was done to confirm the formation of the rutile phase while electron microscope images reveal the presence of Au nanoparticles over the entire surface of TiO2 film. Electronic properties were performed to determine a direct bandgap of 2.8 eV which was reduced significantly to 0.3 eV. Thermoelectric calculations were performed to explore the various temeperature dependent physical properties. Optical properties were also enhanced as high values of optical absorption and refractive index were obtained for TiO2 thin film with monodispersed Au nanoparticles.

Preparation of nanoscale inorganic CsPbIxBr3-x perovskite photosensitizers on the surface of mesoporous TiO2 film for solid-state sensitized solar cells

Metal chalcogenide quantum dot (QD)-like all-inorganic nanoscale perovskite photosensitizers of CsPbIxBr3-x were prepared on the surface of mesoscopic TiO2 film by a direct two-step spin-coating of lead and cesium halide precursors for application into solid-state dye-sensitized solar cells (DSSCs), as confirmed by impedance frequency response analysis. A few nanometer-sized hemisphere-shaped dots of CsPbIxBr3-x perovskites were deposited and distributed separately onto TiO2, which were checked by scanning and transmission electron microscopic (SEM and TEM) techniques. The as-deposited CsPbIxBr3-x perovskites were stable only in the case of including about 20% or more bromide in the composition of halides. When the bromide content increased in the ratio of halides of CsPbIxBr3-x, gradual decrease in lattice spacing and blue-shift of emission peaks were observed in X-ray diffraction (XRD) and photoluminescence (PL) measurements, respectively. These well-defined nano-particulate CsPbIxBr3-x perovskites were incorporated into solid-state DSSCs and tested as a new type of photosensitizers. The initial power conversion efficiency (PCE) of ca. 1.0–3.5% based on relatively thin mesoporous TiO2 film (~1 μm) looks promising with many parameters remaining for possibly more optimization. The best result, 3.79%, was obtained from CsPbI2.2Br0.80 25 days after initial measurement. These CsPbIxBr3-x-sensitized cells displayed a stable record of PCE over ~2 month and no hysteresis behavior in current-voltage traces.

TiO2 surface oxygen vacancy passivation towards mitigated interfacial lattice distortion and efficient perovskite solar cell

It is known that there exist inherent oxygen vacancies which is reported to be negative to PSCs performance on the TiO2 film surface where contacts the gaseous phase while the manufacturing process. In this work, we clarified the role of surface oxygen vacancy on TiO2/perovskite interface structure, which would not only serve as trap states to capture generated electrons, but also cause perovskite crystal distortion and PbI bond broken due to the interfacial interaction, generating additional interfacial defects. In addition, by analyzing the interfacial carrier transport routes, the common reason behind the different carrier loss pathways was ascertained to be the oxygen vacancy. Hence, for reducing oxygen vacancies and its negative impact on the device performance, the surface passivation method with gaseous fluorine was proposed, both the DFT (density functional theory) calculation results and experimental approaches proved that the surface passivation method could effectively reduce the traps states, mitigate interface structure distortion and enhance the interfacial charge transfer. As a consequence, MAPbI3-based PSCs with surface passivation obtained a champion PCE of 20.43%, 7.7% higher than that (18.98%) of control device, and FA0.15MA0.85PbI3-based PSCs with surface passivation obtained a champion PCE of 21.16%, 6.2% higher than that (19.92%) of control device.

Flexible TiO2 nanograss array film decorated with BiOI nanoflakes and its greatly boosted photocatalytic activity

A flexible TiO2 nanograss array film on Ti wire mesh was prepared by a mild chemical reaction. To overcome its shortcoming of almost no absorption of visible light, successive ionic layer adsorption and reaction (SILAR) was executed to decorate the prepared TiO2 film with BiOI. The results of XRD and SEM measurements showed that BiOI nanoflakes formed on the surface of TiO2 film, and the loading amounts of BiOI nanoflakes increased with the increase in SILAR cycles. The XPS results confirmed the heterojunction formation of BiOI-TiO2. The photocurrent measurement suggests that a moderate loading amount of BiOI nanoflakes is beneficial to improve the charge separation efficiency, which is ascribed to the heterojunction formation of BiOI-TiO2. The BiOI-decorated TiO2 film with SILAR cycles of seven showed the most excellent visible-light photocatalytic activity among all the samples. Compared with the bareTiO2 nanograss array film, its visible-light photocatalytic activity increased by 11.7 times. The flexible BiOI-decorated TiO2 nanograss array film with high photocatalytic activity shows great applications in air pollution and the pollution caused by offshore oil spills.

Controlling N and C-atom densities in N2/H2 and N2/CH4 microwave afterglows for selective TiO2 surface nitriding

Radiative states of N2/<5% H2 and N2/<50/00 CH4 HF(microwave) flowing afterglows of microwave plasmas at reduced gas pressures (4–20 Torr) have been analyzed by emission spectroscopy. The N2 1st pos (580 nm), 2nd pos (316 nm), N2+ 1st neg (391.4 nm), NH (336 nm) and CN (386 nm) bands in the pink (early) and the late afterglows were measured and the NO titration was used to determine the concentrations of N-atoms, O-atoms in impurity, N2(X,v > 13) and N2(A) metastable molecules, N2+ ions. Introduction of small percentages of H2 (or CH4) into N2 lead to a size reduction of the early afterglow region which was followed by a late afterglow zone where the N + N recombination is the dominant process. In addition, it also gave an effect of reducing the densities of N atoms (as well as the N2 excited states) in the afterglow regions. At the same time, it introduced other active species such as H (or C) atoms, of which the densities strongly vary depending on the percentage of H2 (or CH4) in the mixture. Such changes in the densities of active species such as N and C atoms in the afterglow region had a strong influence on the incorporation characteristics of N atoms into the surface of TiO2 films introduced into the afterglow region. These results deliver an important meaning in devising process conditions especially for selective nitrogen or carbon doping into a skin-depth layers of oxide materials, which is desired in the case of preparing a few nm-thick functional films for photovoltaic and photocatalytic applications.

Surface morphology change of protective film on collector mirror related to implantation of Sn emitted from laser produced plasma in EUV light source

The change in surface morphology of an amorphous TiO2 protective film coated on a Mo/Si multilayer of an extreme ultraviolet (EUV) light collector mirror has been investigated. After long-time operation of an EUV light source, many pinholes of about 10 nm diameter were observed on the protective TiO2 film surface. Accelerated aging tests with thin film samples that simulated surface conditions on the collector mirror suggest that crystallization of the protective film induced by Sn implantation is the main cause of the formation of the observed pinholes.

Surface, structural and optical properties dependence of Fe-doped TiO2 films deposited onto soda–lime–glass

In this study, pure and Fe doped TiO2 thin films have been prepared via sol-gel method using the tetraethyl-orthotitanate as source of Ti and Fe(III) nitrate as a source of Fe3+ doping. XRD patterns exhibit typical peaks of TiO2 anatase phase. SEM observations confirm the nanometer grain size (below 10 nm) without a defined shape. Optical measurements indicate a transparency in the range 80–100%, it increases with Fe doping level while the energy band gap slightly decreases; 3.36 – 3.28 eV. Wettability test shows a super-hydrophilicity of Fe3+ doped TiO2 thin films and the low contact angle is founded for 0.6%Fe. However, no enhancement in photocatalytic activity of Fe doped TiO2 thin films have been achieved. This may be attributed to sodium diffusion from the substrate. The as-prepared nanostructured Fe-doped TiO2 thin films can be used as potential candidate for self-cleaning due to the super-hydrophilicity character in the visible light.

Specific Features of Photoluminescence of CH3NH3PBI3 Perovskites Synthesized on Nanostructured TiO2 Surface

The influence of nanostructured titania surface on the photoluminescence of organometallic perovskite CH3NH3PbI3 films is studied. It is found that the CH3NH3PbI3 luminescence intensity and lifetime decrease on the TiO2 surface, which testifies to charge transfer from perovskite to titania. Charge transfer occurs most efficiently for perovskite films synthesized on the surface of mesoporous TiO2 films. The time dependence of magnetic effect on the luminescence of CH3NH3PbI3 on mesoporous TiO2 films is related to the recombination luminescence caused by forward and backward electron transfer between perovskite and titania.

Highly sensitive detection of estradiol by a SERS sensor based on TiO2 covered with gold nanoparticles.

We propose the use of gold nanoparticles grown on the surface of nanoporous TiO2 films as surface-enhanced Raman scattering (SERS) sensors for the detection of 17β-estradiol. Gold deposition on top of a TiO2 surface leads to the formation of nanoparticles the plasmonic properties of which fulfil the requirements of a SERS sensor. The morphological and optical properties of the surface were investigated. Specifically, we demonstrate that the TiO2 background pressure during pulsed laser deposition and the annealing conditions offer control over the formation of Au nanoparticles with different sizes, shapes and distributions, yielding a versatile sensor. We have exploited the surface for the detection of 17β-estradiol, an emerging contaminant in environmental waters. We have found a limit of detection of 1 nM with a sensitivity allowing for a dynamic range of five orders of magnitude (up to 100 µM).

Sn-doped TiO2 nanotubular thin film for photocatalytic degradation of methyl orange dye

We fabricated Sn-doped TiO2 nanotubular film via annealing of anodized TiO2 nanotubes grown on F–SnO2 (FTO) glass. Annealing was carried out at 500 °C in ambient air. Anatase crystal structure was achieved with no change in nanotubular morphology in respect to as-anodized amorphous TiO2 nanotubes. The X-ray photoelectron spectroscopy analysis revealed Sn on the surface of TiO2 film, following the thermal treatment, probably caused by the diffusion from FTO glass. Depth profile examination of the film chemical composition was conducted by elastic recoil detection analysis, which showed that in addition to the diffusion of Sn from FTO, diffusion of Ti to FTO concurrently occurred. Thus, a higher concentration of Sn was found at the bottom of the tubes, while a lower concentration was present on the tubes’ surface top. This explains the improved optical response revealed by a diffuse reflectance spectroscopy. The absorption enhancement demonstrated that Sn-doped TiO2 film was efficient in the degradation of methyl orange dye under visible light.

Effects of structure and electronic properties of D-π-A organic dyes on photovoltaic performance of dye-sensitized solar cells

Abstract Herein, we examine the performance of dye-sensitized solar cells containing five D-π-A organic dyes designed by systematic modification of π-bridge size and geometric structure. Each dye has a simple push-pull structure with a triarylamino group as an electron donor, bithiophene-4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M11), 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene-thiophene (M12), thiophene-4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M13), 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene-benzene (M14), and 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M15) units as π-bridges, and cyanoacrylic acid as an electron acceptor/anchor. The extension of the π-bridge linkage favors wide-range absorption but, because of the concomitant molecular volume increase, hinders the efficient adsorption of dyes on the TiO2 film surface. Hence, higher loadings are achieved for smaller dye molecules, resulting in (i) a shift of the TiO2 conduction band edge to more negative values, (ii) a greater photocurrent, and (iii) suppressed charge recombination between the photoanode and the redox couple in the electrolyte. Consequently, under one-sun equivalent illumination (AM 1.5 G, 100 mW/cm2), the highest photovoltage, photocurrent, and conversion efficiency (η = 7.19%) are observed for M15, which has the smallest molecular volume among M series dyes.