Sol Aging Time Research Articles

Design and preparation of superhydrophobic, broadband and double-layer antireflective coatings

As one of the most widely used optical films, antireflective coating (ARC) is widely used in lasers, display screens and solar cells. In this article, the double-layer ARC coating consists of a bottom layer using SiO2-TiO2 composite nanomaterials and a top layer of SiO2 modified with Hexamethyldisilazane (HMDS). The optimal parameters of the double-layer ARC were obtained through the simulation software Macleod. Meanwhile, the aging time of SiO2 sol, the volume fraction of HMDS, the annealing temperature, the dip-coating speed, and the volume fraction of TiO2, which affect the refractive index of the bottom and top layers, were explored in order to match the best parameters. By adjusting the structure of the bottom and top layers, the double-layer broadband ARC coating has a maximum transmittance of 97.6% in the 400-1800 nm spectral range, and an average transmittance of 96.0%. In addition, HMDS was used to modify the SiO2 sol to obtain a double-layer ARC with superhydrophobic properties with a hydrophobic angle of 151.4°. After the high-temperature and high-humidity environment test, the antireflective performance of the double-layer ARC has not changed significantly, demonstrating the broad prospects for application in large outdoor solar photovoltaic power plants. Moreover, this work not only provides a new method for adjusting the refractive index of the coating, but also opens up a new way for the preparation of broadband ARC.

Fabrication, optimization, and performance of a novel double-skinned Al2O3.TiO2 ceramic nanocomposite membrane for forward osmosis application

Abstract In this study, a thin film nanocomposite ceramic membrane with an Al2O3 substrate and TiO2 as the thin film active layer was fabricated via dip coating technique and optimized for application in FO purification of groundwater. The effect of parameters including sol aging, calcination temperature, and dip time was investigated. Based on the results, the least water flux was obtained during 6 h after sol preparation. Furthermore, boosting the synthesis temperature and dip time led to flux reduction. According to the optimization results, 6.75 h sol aging, 17.00 s dip time and a 319 °C calcination temperature, led to the maximal water flux of 168 L/m2 h bar and 48% salt rejection. In addition, by covering the substrate with 10 layers of TiO2, water flux was reduced to 10.82 L/m2 h bar. FO process using MgCl2 solution (2 M) as draw and DI water as feed solutions, resulted in an initial water flux of 17.04 L.m−2 h−1 (LMH). Replacing DI water with a 0.01 M NaCl solution as feed, the initial water flux was decreased to 15.5 LMH. Also, using groundwater as the feed solution with an EC of 1407, 14.1 LMH initial water flux was obtained.

Durable superhydrophilic and antireflective coating for high-performance anti-dust photovoltaic systems

Antireflection coatings have received extensive attention due to their unique ability to reduce the reflection losses of incident light in photovoltaic (PV) systems. In this study, we report a hybrid silica sol coating fabricated via a simple and cost-effective base/acid-catalyzed two-step sol–gel method. The prepared coating exhibits these main properties: high transmittance, superhydrophilic, and anti-dust effect. Experimental conditions to achieve high transmittance were systematically optimized, such as aging time of the base-catalyzed silica sol and dip-coating speed. A transmittance improvement of about 6.35% compared to the bare glass substrate was then obtained. The morphology and film structure were also characterized. The coatings have a closed and dense structure which, combined with their superhydrophilicity, endowed them with excellent anti-dust performance, as well as high mechanical properties, with a pencil hardness of 4H. Furthermore, the coating showed great resistance to high temperature and high humidity as well as high stability to long-time outdoor exposure. The results suggest the good reliability of the prepared coatings for PV solar glass application.

Fabrication of an Organo-Fluoride–Free Hydrophobic Film Using the Sol-Gel Method by Factors Screening and Poly-Acrylic Acid Addition

Improving silica film’s contact angle (CA) using tetraethoxysilane (TEOS) and iso-butyltrimethoxysilane (iso-BTMS) by the sol-gel method without adding organo-fluoride substances is of interest. Five factors, namely type of solvent, molar ratio and amounts of TEOS and iso-BTMS, mixing intensity, sol aging time, and presence and absence of poly-acrylic acid (PAA), were assessed to improve the static water CA of the film and its surface quality. Results revealed that when ethanol was used as the dissolving solvent and after adding initial iso-BTMS and TEOS concentrations of 0.0270 and 0.0194 mol/L (molar ratio = 1.39), respectively, without sonication and adding PAA/TEOS weight ratio of 0.029, then the maximum static CA of the film reached 147°, a nearly super-hydrophobic surface. Under given conditions, long-term film durability was observed, and the added PAA prevented the formation of nonhomogeneous film surfaces caused by the highly clustering aggregation of silanols under high pH conditions.

Effect of solution aging on properties of spin coated zinc oxide thin films

A series of multilayer zinc oxide (ZnO) films were deposited on glass substrate by solution processed spin coating method. The effect of aging time of ZnO sol on the structural and optical properties of the films was studied. The structural characteristics of the samples were analyzed by an X-ray diffractometer (XRD) and Scanning electron microscopy (SEM). The optical properties were studied by a UV–Vis spectrophotometer and a fluorescence spectrometer. The obtained ZnO thin films show very good transmittance with average transmittance of 85% with no fluctuations in the 300–600 nm range of visible spectrum. The band gap increases with the increase in the sol aging time. The enhanced crystalline quality of films and decrease of defects concentration contributed to improve the ultraviolet emission and weaken the visible emissions with prolonging sol aging time.

Development of a wearable infrared shield based on a polyurethane\u2013antimony tin oxide composite fiber

Here, we investigate a wearable-based IR and thermal stealth structure that effectively blocks IR and thermal radiation from a human body or device using a polyurethane–antimony tin oxide (PU–ATO) composite fiber. The aging time of the ATO sol prepared by a sol–gel method, and the concentration of ATO with respect to that of the PU matrix were optimized to prepare PU–ATO composite fibers that simultaneously have an appropriate mechanical strength (strength of ~4 MPa and strain of ~340%) and IR- and thermal radiation-shielding properties with ~98% IR light, as determined by Fourier transform IR spectroscopic studies. The fabricated PU–ATO composite fiber showed stable IR- and thermal radiation-shielding properties even when exposed to ten cycles of repeated temperature changes of −20 and +80 °C and long-term temperature changes for 30 days. In addition, the surface of the PU–ATO composite fiber was rendered hydrophobic to prevent the distortion of the IR and thermal radiation due to the wetting of the PU–ATO composite fiber with absorbed water. The PU–ATO composite fiber-based textile proposed herein can be applied in wearable IR- and thermal radiation-shielding technologies to shield IR signals generated by objects of diverse and complex shapes.

Elaboration of microporous CeO2 thin layers having nanocrystallites network controlled by Pluronic P123: Impact of key experimental parameters

Microporous ceria thin films having nanocrystallites network were synthesized by evaporation-induced self-assembly process, using P123 amphiphilic copolymer as structure-directing agent. The impact of key experimental parameters, i.e., the sol ageing, the relative humidity (RH), the thermal treatment, on the thin layer elaboration were investigated. The results show that the organization of the nanoparticles is possible for a sol ageing time lower than 16 days and that the size of the mesophase within the thin layer increases with the relative humidity fixed during the film deposition. Finally, an increase of the thermal treatment temperature from 300 to 1000 °C leads to the formation of fluorite-like dioxide material coupled with a loss of nanocrystallites organization and porosity due to the increase of the size of the crystallites. This loss of nanocrystallites organization is more drastic in the direction perpendicular to the surface and less pronounced along the surface. Thus, a compromise between the crystallization and the preservation of the porosity needs to be found.

A Study on Effect of Sol Aging Time on Optical Properties of ZnO Thin Films: Spectroscopic Ellipsometry Method

Background: Due to wide band gap and large excitonic binding energy, being inexpensive, abundance in nature and easy synthesis ZnO is a promising candidate in many applications such as solar cells. Experimental: In the current work a series of ZnO thin films were deposited on glass substrates using sol-gel method to investigate the change in optical behavior of the film with sol aging time (asprepared, 8, 16, 24 and 32 hours) and the annealing temperature (300ᵒC and 500ᵒC). The optical properties of thin films were explored using spectroscopic ellipsometry method including the real and imaginary part of refractive index, real and imaginary part of dielectric function and band gap energy of the layers in the 300-900 nanometer wavelength range. Results: It can be deduced from the results that sol aging time and annealing temperature, affect the optical properties of the samples. Using single oscillator energy model of Wemple and Di Domenico parameters such as free charge carrier concentration ratio to effective mass, and plasma frequency, were calculated. Conclusion: The films prepared using 24 h aged solution, had the highest transmittance and the largest band gap energy.

Simple “titanium alkoxide–water–solvent” solutions as titania coating solutions containing no peptizing or chelating agents

Titanium tetraisopropoxide was hydrolyzed in tetrahydrofuran (THF), 1-butanol, or 2-butanol to prepare coating solutions for titania thin films. The compositions of the starting solutions were so simple, Ti(OC3H7i)4:H2O:solvent = 1:(0.5 or 1.0):25 in mole ratios, that they contained no chelating or peptizing agents. In spite of the absence of chelating or peptizing agents, transparent sols were obtained except for the THF solution of H2O/Ti(OC3H7i)4 = 1.0. All the transparent sols showed high stability in viscosity at least over 1 month. Titania thin films were prepared from the sols by spin- or dip-coating on Si(100) substrates via heat treatment at 700 or 900 °C. The stability of such additive-free sols was examined by comparing the thickness, refractive index, crystalline phase, crystallite size, and microstructure between films that were prepared from sols aged for 1, 5, and 30 days at room temperature. The thickness, refractive index, and crystallite size did not change noticeably with sol aging time. The films prepared from the THF-containing sols were anatase irrespective of the sol-aging time and heat treatment temperature. On the other hand, rutile phase was also observed when the films were prepared from 30-day-aged, 1-butanol-, or 2-butanol-containing sols, followed by firing at 900 °C. The films from the 2-butanol-containing sols also exhibited a change in microstructure at such a long sol aging time. These suggest that the 1-butanol- or 2-butanol-containing sols are unstable during aging while the THF-containing sol is stable as coating solution.

Photodegradation of herbicide Metsulfuron-methyl with TiO2 supported on magnetite particles coated with SiO2

Natural watercourses may be significantly contaminated due to the increase of agricultural activities, making it necessary to develop new methodologies for the remediation of agrochemicals, including herbicides. To this effect, photodegradation with TiO2 is a very effective process. However, this semiconductor cannot be easily removed from the treated aqueous medium. Supporting the photocatalyst on different materials facilitates its removal by several methods, including magnetic attraction. According to this goal, this work reports the synthesis of TiO2 photocatalysts supported on SiO2-coated magnetite particles (Fe3O4) by a low-temperature sol-gel process (75 °C). By varying the aging time of the TiO2 sol, materials with different structural properties and combinations of anatase-brookite phases were obtained. Of all the synthesized solids, the one with the highest photocatalytic activity in the degradation of model compounds was the TiO2/SiO2/Fe3O4 catalyst with a 47.4/13.6/39.0 wt % respectively. Under optimal working conditions and at a pH value close to neutrality (conditions in which Metsulfuron-methyl is persistent in an aqueous medium) this catalyst degraded 70% of the herbicide initial concentration in three and a half hours of artificial irradiation with an activity similar to the mass TiO2. The aging time significantly influenced on structural properties of supported TiO2. With its increase, the degree of crystallinity of the samples also increased but its specific surface decreased. The catalyst with higher photoactivity blends the best combination of both factors and is, therefore, a good alternative for the remediation of contaminated effluents with commercial formulations of this herbicide. Also, its magnetic support facilitates its subsequent removal from treated water samples.

(Invited) Impacts of Nanostructures and Interfaces on Perovskite Solar Cell Performance

Organometallic halide perovskite materials have a variety of remarkable optoelectronic properties, such as suitable band gap (1.5eV), high absorption coefficient, long carrier diffusion lengths and lifetimes. All these unique characters pave the way for perovskite-based devices, especially the photovoltaic cells. This presentation will start with the variation of the surface potential, photo-generated voltage, and photocurrent networks of perovskite solar cells (PSCs) with different film topography has been studied by coupling scanning Kelvin probe force microscopy (SKPM) and photoconductive atomic force microscopy (pcAFM). Then a series of TiO2 compact films was prepared by sol-gel method with different sol aging time resulting in change of, thickness, surface roughness and compactness. High roughness of the films benefits the light absorption of perovskite layer and the injection efficiency at interface. The films with better compactness perform better hole blocking effect. The Ag@TiO2 nanoparticles made by polyol solution method are embedded in perovskite films, resulting in an enhanced short-circuit current density due better light absorption and reduced charge recombination. Finally, both excess CH3NH3Cl and thiourea were introduced into the pristine CH3NH3PbI3 precursor for antisolvent precipitation at low temperature and fabricated high quality perovskite films with desired morphology, crystallinity and optical properties. CH3NH3Cl exerted significant impacts on the perovskite crystallization process by controlling the delivery speed of PbI2 from the intermediate phase CH3NH3I2Cl. Further tuning the chemical composition with controlled film growth condition resulted in an average power conversion efficiency above 21% under the standard light illumination condition.

The Effect of pH and Aging Time on the Synthesis of TiO2 – Chitosan Nanocomposites as Photocatalyst by Sol-Gel Method at Room Temperature

The synthesis of TiO2–chitosan nanocomposite photocatalyst using Titanium(IV)-Isopropoxide (TTIP) as precursors and chitosan as host material has been conducted. The synthesis was carried out using sol-gel method at room temperature and aging to grow crystal seeds and generate nanoparticles. The success of forming nano-sized anatase phase TiO2 nanocrystal was strongly influenced by the sol pH system during hydrolysis and the aging time. The effect of sol pH system and aging time to the crystallinity level and particle size were examined using X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Diffuse Reflectance UV-Spectroscopy (DR-UV). The results showed that TiO2 produced in acidic pHs (pH 2-4) tended to have higher crystallinity level than that produced in weakly alkaline (pH > 6), which prone to be amorphous. The longer aging time (> 14 days) also tended to produce the amorphous phase. Furthermore, chitosan as a host material had a notable influence in determining the crystallinity level and particle size of TiO2 in TiO2–chitosan nanocomposite.

Efficient diagnostics of the electronic and optical properties of defective ZnO nanoparticles synthesized using the sol–gel method: experimental and theoretical studies

ZnO nanoparticles were synthesized using the sol–gel method with a variation on the sol aging time and refined structural data were taken to simulate the synthesized sample in a first-principles calculation. The ZnO nanoparticles aged at 36 h and showed profound properties with high crystallinity and good visual fit in a Rietveld analysis. Optical analysis revealed only small variation in energy band gap for all samples, ranging between 3.08–3.12 eV, with the presence of oxygen vacancy defects. In first-principles calculation, several exchange-correlation functionals, including LDA, GGA-PBE, GGA-PBESol, LDA + U, GGA-PBE + U and GGA-PBESol + U, were tested to converge with the lowest optimized lattice deviation. GGA-PBE + U (Ud,Zn = 10 eV and Up,O = 6.1 eV) showed the lowest lattice deviation and reproduced the experimental band gap. The ZnO supercell structure with an oxygen vacancy showed that a defect state appears in the valence band and acts as a deep donor.

The Effects of Aging Time on the Structural and Electrochemical Properties of Composite Coatings on CP-Ti Substrate

TiO2–SiO2 composite films were produced on commercially pure titanium (CP-Ti) substrate by a sol–gel method to investigate the behavior of sol aging time and its potential effects on the structural and electrochemical properties of composite coatings. Anatase-TiO2 and quartz-SiO2 peaks were observed on all composite coated samples according to XRD results. It was observed that the average grain size increased with sol aging time. Also, the average smallest grain size was seen at composite coatings prepared from unaged sol according to the width of the peaks. Electrochemical behavior of coated samples was mainly investigated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) in Simulated Body Fluid (SBF) solution. In corrosion tests, the composite coatings showed better anti-corrosion behavior than that of uncoated samples. In addition, the corrosion properties of the composite films were considerably affected by sol aging time. Corrosion resistance of coatings decreased with increasing aging time and the best result was obtained from composite coatings prepared from unaged sol.

Annealing Temperature Dependence of Optical Properties of Sol-Gel ZnO Thin Films with Different Sol Aging Time

ZnO thin films on glass substrates have been successfully fabricated by sol-gel method for various aging time and annealing temperature. X-ray diffraction (XRD) patterns showed the crystallites at (100), (002) and (101) plane of hexagonal wurtzite structure. Atomic force microscope (AFM) images were used to investigate the surface morphology. The transmittance, energy gap, Urbach energy and photoluminescence (PL) of samples were investigated to explore the effects of annealing temperature on optical properties of ZnO thin films under different sol aging time. The transmittance spectra of thin films aged for 24 hours and 48 hours revealed the enhanced transmittance in visible region as rising annealing temperature, also, the optical band gap of the samples increased and Urbach energy decreased. The photoluminescence (PL) spectra of samples aged for 24 hours and 48 hours were studied and found the increased ultraviolet emission at ~387 nm, and various decreased visible emissions with rising annealing temperature. Nevertheless, the excessive sol aging time for 72 hours deteriorated the optical characteristics of thin films, resulting in that transmittance, energy gap and ultraviolet emission declined, and visible emissions increased with rising annealing temperature. The optical performances of the ZnO films aged for different time have no the same dependence of annealing temperature.

Effects of aging time and annealing temperature on structural and optical properties of sol-gel ZnO thin films

The ZnO thin films have been prepared by sol-gel method at different annealing temperatures and aging time. The structural properties of ZnO thin films were investigated by X-ray diffraction (XRD) patterns and atomic force microscope (AFM) images. The results indicated that the film possess a hexagonal wurtzite structure with preferred orientation along the (002) direction. The crystalline quality of films improved with increasing post-annealing temperature, while gradually worsened with prolonging aging time. The optical properties of ZnO thin films were studied by the ultra-violet transmittance (UV-Vis) and photoluminescence (PL) spectra. The variations of UV-Vis transmittance and energy gap accorded well with the tendency presented in XRD patterns and AFM images. The PL spectra appeared the apparent ultraviolet emission and visible emissions. As the annealing temperature increased, the ultraviolet and visible emissions of films enhanced and decreased respectively. However, as the sol aging time prolonged, the PL emission presented an opposite tendency.

Effects of sol aging on resistive switching behaviors of HfOx resistive memories

This work investigates effects of long-term sol-aging time on sol-gel HfOx resistive random access memories (RRAMs). A nontoxic solvent of ethanol is used to replace toxic 2-methoxyethanol, which is usually used in sol-gel processes. The top electrodes are fabricated by pressing indium balls onto the HfOx surface rather than by using conventional sputtering or evaporation processes. The maximum process temperature is limited to be 100℃. Therefore, influences of plasma and high temperature on HfOx film can be avoided. Under this circumstance, effects of sol aging time on the HfOx films can be more clearly studied. The current conduction mechanisms in low and high electric regions of the HfOx RRAM are found to be dominated by Ohmic conduction and trap-filled space charge limited conduction (TF-SCLC), respectively. When the sol aging time increases, the resistive switching characteristic of the HfOx layer becomes unstable and the transition voltage from Ohmic conduction to TF-SCLC is also increased. This suggests that an exceedingly long aging time will give a HfOx film with more defect states. The XPS results are consistent with FTIR analysis and they can further explain the unstable HfOx resistive switching characteristic induced by sol aging.

Morphological, Structural and Optical Properties of ZnO Thin Films Deposited by Dip Coating Method

Zinc oxide (ZnO) thin films were deposited on glass substrat by dip coating technique. The effects of sol aging time on the deposition of ZnO films was studied by using the field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and optical transmission techniques. The morphology of the films strongly depends on preparation route and deposition technique. It is noteworthy that films deposited from the freshly prepared solution feature indistinct characteristics; had relatively poor crystalline quality and low optical transmittance in the visible region. The increase in sol aging time resulted in a gradual improvement in crystallinity (in terms of peak sharpness and peak intensity) of the hexagonal phase for all diffraction peaks. Effect of sol aging on optical transparency is quite obvious through increased transmission with prolonged sol aging time. Interestingly, 72-168 h sol aging time was found to be optimal to achieve smooth surface morphology, good crystallinity and high optical transmittance which were attributed to an ideal stability of solution. These findings present a better-defined and more versatile procedure for production of clean ZnO sols of readily adjustable nanocrystalline size.

The effect of sol aging time on Structural and Optical properties of sol gel ZnO doped Al

Currently the doped or undoped ZnO semiconductor is of great importance in the field of electronic and optoelectronic devices such as transparent conductors and optical windows of solar cells based on silicon. ZnO thin films are produced by several techniques such as sol-gel method which is a chemical technique usually dependent on solution conditions. However, the sol gel aging time is an important parameter, which can have a significant impact on the properties of thin films. In this work we studied the effect of aging times (0h, 24h, 48h, 72h, 1 week) of the precursor solution on the structural and optical properties of ZnO doped Al (3 at.%). Thin films prepared by spin coating on glass substrates were investigated. The X-ray diffraction (XRD) analysis shows that the ZnO doped Al (3 at.%) exhibit the hexagonal wurtzite structure with a preferential orientation along [002] direction. The shift of (002) peaks towards higher diffraction angles is observed with sol aging time and also, a variation of crystallite sizes and thickness of thin films are shown with increasing sol aging time. All films present an average optical transmittance around 90% in the visible range with some interference fringes indicating a relative smoothness of films. We note an increasing in transmittance level with sol aging time from 0h to 48h. We can conclude that the aging times of the precursor solution influences the structural and optical properties of studied thin films.

Impact of sol aging on TiO2 compact layer and photovoltaic performance of perovskite solar cell

Perovskite solar cells are known to have a power conversion efficiency dependent on subtle variation in chemical composition and crystal and microstructures of materials, processing conditions, and device fabrication procedures and conditions. The present work demonstrates such strong dependence of power conversion efficiency on a TiO2 film made of the same sol with various aging time. A dense and conformal TiO2 film was prepared by sol-gel method, and the influences of its surface morphology and thickness on performance of perovskite solar cells have been investigated. The surface morphology and thickness of the TiO2 film were tuned by adjusting the aging time of sol, resulting in enhanced short-circuit current density and fill factor of the perovskite solar cells due to increased coverage and roughness of perovskite films, light refraction, and effective charge recombination blocking effect, which were verified by means of the light absorption spectra, photoluminescence of perovskite films with and without hole transport layer, cyclic voltammogram, and electrochemical impedance spectra. The cells with a dense and conformal TiO2 compact layer derived from the sol aged for 4 h exhibit a power conversion efficiency of 15.7%, 50% higher than the efficiency based on TiO2 layer derived from 0 h aging sol and 3 times of the efficiency with TiO2 layer made from 8 h aged sol.