SiO2 Antireflective Coatings Research Articles

Damage regularity and multifractal analysis of sol-gel reflection coating of KDP crystal under low UV irradiation flux.

This study employed multifractal analysis to investigate the changes in surface morphology of SiO2 anti-reflective coatings prepared on KDP substrates using the sol-gel method, under various conditions of ultraviolet (UV) irradiance. The coatings were successfully fabricated, and the chemical structure of the SiO2 sol was comprehensively characterized using Solid-State Nuclear Magnetic Resonance (SSNMR) technology. Under low UV irradiance (4 J/cm2), repeated experiments revealed a crack-induced mechanism of surface fatigue damage. Utilizing Scanning Electron Microscopy (SEM), the study discovered the induction effect of initial crack defects in UV-damaged coatings and established a damage model. Furthermore, Atomic Force Microscopy (AFM) was used to acquire images of the coatings' surface morphology at different damage levels, which were analyzed using the multifractal spectrum f(α). This analysis confirmed the multifractal nature of the coatings both before and after damage. This study identified significant effects of UV irradiation on the width of the multifractal spectrum and Δf, indicating that the SiO2 anti-reflective coatings exhibit multifractal characteristics under various damage states. The coatings displayed a pattern of decreasing and then increasing singularity spectrum width, height distribution unevenness, and surface roughness with increasing damage. This study demonstrates that multifractal analysis is an effective tool for describing the complexity of the surface morphology of sol-gel-derived anti-reflective coatings for the first time and for validating their multifractal properties across different stages of UV damage. HIGHLIGHTS: Damage dynamic process of KDP crystal sol-gel coating was described by SEM&AFM; The crack propagation mechanism of sol-gel coating under UV radiation is proposed; The damage evolution of sol-gel coating was described by multifractal analysis.

Effects of the thermal treatments on the optical properties of SiO2 anti-reflective coatings on sapphire windows

The SiO2 films were deposited on sapphire substrates using radio frequency (RF) magnetron sputtering to enhance the mid-wave infrared (IR) transmittance. The effects of thermal treatments by annealing and in-situ heating on the SiO2 films were investigated. After annealing at 600 °C, the surface morphology, microstructure, chemical states, and optical constants were investigated. No obvious microcracks or delamination were observed on the film surfaces, indicating excellent adhesion to the sapphire substrates. With an increase in the annealing time, gradual oxidation of Si atoms within the SiO2 thin films occurred, resulting in the release of OH groups and evaporation of moisture. The refractive index exhibited slight changes, while the extinction coefficient showed a significant reduction, thus the transmittance was improved. According to the in-situ heating tests from the annealed samples, it revealed a slight increase in average transmittance with prolonged annealing time. Finally, we assessed the performance of the annealed samples by rapid heat shock to 600 °C at a very short time, which demonstrated outstanding optical performance and heat-resistant properties. The present work supports the feasibility of applying the SiO2 films under harsh high-temperature environments.

In Situ Generating YVO4:Eu3+,Bi3+ Downshifting Phosphors in SiO2 Antireflection Coating for Efficiency Enhancement and Ultraviolet Stability of Silicon Solar Cells

Herein, a solid strategy to prepare bifunctional SiO2 coatings (BSCs) with both antireflection and luminescence downshifting properties by in situ generating YVO4:Eu3+,Bi3+ phosphors in SiO2 antireflection coatings (ARCs) is reported. Namely, a self‐prepared precursor solution of the downshifting phosphors is added to a mixture of commercial SiO2 sol solution and ethanol to uniformly coat the surface of quartz glass; therefore, a novel composite porous SiO2 coating containing in situ generated YVO4:Eu3+,Bi3+ phosphors (labeled SiO2@YVO4:Eu3+,Bi3+ coating) is formed on the glass surface after annealing. The SiO2@YVO4:Eu3+,Bi3+ BSCs can effectively convert ultraviolet (UV) region photons to visible photons that are well absorbed by silicon solar cells and have better transmittance than pure SiO2 ARC. As proof‐of‐concept applications, the as‐prepared optimal SiO2@YVO4:Eu3+,Bi3+ coating can effectively improve the photoelectric conversion efficiency (PCE) of tunnel oxide passivated contact solar cells by 0.18%abs and decrease the UV‐induced degradation value of the PCE of silicon heterojunction solar cells by 0.62%abs compared to the pure SiO2 ARC. The results demonstrate that in situ generating luminescence downshifting phosphors in the SiO2 ARC of photovoltaic glass is a promising way to improve the PCE and UV stability of silicon solar cells.

High luminous transmittance and solar modulation of VO2-based smart windows with SiO2 anti-reflection coatings

High luminous transmittance and solar modulation of VO2-based smart windows with SiO2 anti-reflection coatings

Post-treatment of 351 nm SiO2 antireflective coatings for high power laser systems prepared by the sol-gel method

Different post-treatment processes involving the use of ammonia and hexamethyldisilazane (HMDS) were explored for application to 351 nm third harmonic generation SiO2 antireflective (3ωSiO2 AR) coatings for high power laser systems prepared by the sol-gel method. According to experimental analysis, the 3ωSiO2 AR coatings that were successively post-treated with ammonia and HMDS at 150°C for 48 h and again heat-treated at 180°C for 2 h (N/H 150 + 180 AR) were relatively better. There were relatively fewer changes in the optical properties of the N/H 150 + 180 AR coating under a humid and polluted environment, and the increase in defect density was slow in high humidity environments. The laser-induced damage threshold of the N/H 150 + 180 AR coating reached 15.83 J/cm2 (355 nm, 6.8 ns), a value that meets the basic requirements of high power laser systems.

Surface free energy and microstructure dependent environmental stability of sol–gel SiO2 antireflective coatings: Effect of combined vapor phase surface treatment

Environmental stability is of great interest for sol–gel porous antireflective (AR) coatings. In this work, sol–gel silica AR coatings with excellent environmental stability were prepared via ammonia vapor treatment (AVT) combined with organosilane (hexamethyldisilazane (HMDS) or hexadecyltrimethoxysilane (HTMS)) vapor treatment. The surface free energy (SFE) of the coatings treated with different approaches was estimated through Owens–Wendt method combined with Wenzel equation from the contact angles of water, glycerol and diiodomethane. Scanning electron microscope and Fourier transform infrared spectroscopy were employed to study the surface morphology and chemical composition of the silica coatings treated with different methods. The silica coatings treated by combined vapor phase method possess the SFE of 24.11 mJ·m−2 for N-HD-SiO2 and 34.18 mJ·m−2 for N-HT-SiO2. After being placed in a 90%RH humid environment for 2 months, the peak transmittance of BK7 glasses coated with N-HD-SiO2 and N-HT-SiO2 only decreases by 0.58% and 0.95%, respectively. Meanwhile, N-HD-SiO2 and N-HT-SiO2 coated BK7 glasses also show quite stable optical transmittance after exposure to a vacuum oil environment for 2 months. The mechanism of the combined vapor phase surface treatment is discussed based on the combination analysis of surface morphology, chemical composition and SFE of the coatings.

Omnidirectional SiO2 AR Coatings

It is of great importance to develop antireflective (AR) coatings and techniques because improved optical performance has been progressively prerequisite for wide-ranging applications such as flat panel displays, optoelectronic devices or solar cells. Natural surroundings inspire researchers considerably to impersonate in order to provoke analogous characteristics via artificial approaches, which provide the opportunity for emerging techniques and development in material engineering. Herein, SiO2 antireflective (AR) coatings comprised of two layers were fabricated using a physical vapour deposition method via glancing angle. The top layer fabricated at an oblique angle of 80° and the bottom layer close to the substrate was deposited at a deposition angle of 0°. The experimental outcomes demonstrate that there is a slight influence on the refractive index of thin films by changing the morphology of nanostructures keeping deposition angles the same. The top layer shows a periodic arrangement of SiO2 nanostructures while the bottom stratum represents a SiO2 compact dense layer. The assembled bilayer SiO2 AR coating retains omnidirectional AR efficiency and tunability at a preferred wavelength range displaying <1% reflectance. Moreover, the fabricated omnidirectional SiO2 AR coatings have thermal stability up to 300 °C. These SiO2 AR coatings also possess negative temperature resistivity to withstand different cold storage conditions. Hence, the flexible and environmental adaptive SiO2 AR coating offers an intriguing route for imminent research in optics.

Enhanced visible transmittance and reduced transition temperature for VO2 thin films modulated by index-tunable SiO2 anti-reflection coatings.

The low visible transmission is one of the bottleneck problems for the application of vanadium dioxide films since the high refractive index (RI) of VO2 films results in strong reflection in the visible wavelength. To address this problem, in this paper, high-purity VO2 films were deposited on fused silica by DC reactive magnetron sputtering at low temperature of 320 °C. Silica sol–gel coatings with tunable refractive index (RI) coated onto VO2 films have been fabricated to enhance visible transmittance with the potential application in the field of smart windows. SiO2 coatings with tunable RI (1.16–1.42 at λ = 700 nm) were prepared by sol–gel dip-coating technique. The double structure SiO2/VO2 films were characterized through several techniques, including X-ray diffraction, UV-VIS-NIR spectrophotometry and scanning electron microscopy. Compared with the single-layer VO2 film (ΔTsol of 6.25% and Tlum of 38.58%), the three kinds of SiO2/VO2 bilayer films had higher Tlum (41.93–50.44%) and larger ΔTsol (8.15–8.51%) simultaneously due to significantly decreased reflectance. Moreover, the crystallization properties of VO2 films are essentially unchanged by applying a SiO2 top layer, while the phase transition temperature and thermal hysteresis width of sample S116 are lower than those of pure VO2 film. The presented RI-tunable SiO2 coatings, can regulate optical properties continuously for various VO2 substrates, paving the way for practical applications of VO2 films in the field of smart windows or others.

Preparation of SiO2 anti-reflection coatings by sol-gel method

Antireflection coating for photovoltaic glass is very important for enhancing its optical transmittance, and ensuring a high light absorption and efficiency of PV modules. In this paper, a SiO2 coating with an excellent antireflection effect was realised with the sol-gel method, which is low cost and easily controlled. In our experiments, a silica (SiO2) sol was prepared by a sol-gel process and then the SiO2 coating was deposited on clean glass substrates by dip coating. The coatings were then annealed at 450°C for 1 hour to increase the quality. Using an optimized type of catalyst and film thickness, the optical transmittance of the coated soda-lime glass could be increased by more than 5%. In addition, the influence of a catalyst (PF127) on the refractive index of the coating was evaluated. The experimental results showed that catalyst PF127 and a suitable heat treatment generate pores in the film which reduce the refractive index. The optimized single-layer SiO2 coatings on soda-lime glass substrates exhibited an average transmittance of 95% in the 300 to 1300 nm wavelength range.

Preparation and stress evolution of sol–gel SiO2 antireflective coatings for small-size anisotropic lithium triborate crystals

Lithium triborate (LiB3O5, LBO) crystal is now one of the most useful nonlinear optical materials for frequency conversion of high power lasers. The use of the crystal, however, has been hampered by the unavailability of antireflective (AR) coatings with high laser damage resistance. In this work, a “point contact” dip-coating method is developed to prepare sol–gel SiO2 AR coatings on small-size LBO crystals. Using this approach, we obtain a homogenous coating surface on an 8 mm×8 mm×3 mm LBO crystal. The stress measurements show that the stresses in sol–gel SiO2 coatings vary with the time of natural drying, which is beyond our expectation. The anisotropic Young’s modulus of the LBO crystal and the different evolution tendency of the stress in the different SiO2 coating layers are found to be responsible for the crack of the double-layer AR coatings on anisotropic LBO crystal. Meanwhile, the resulting coatings on LBO crystal achieve a LIDT of over 15 J/cm2 (532 nm, 3ns) and the coated LBO is expected to have a transmittance of over 99% at 800 nm.

Study on low-refractive-index sol-gel SiO2 antireflective coatings

A study on low-refractive-index SiO2 antireflective (AR) coatings by a sol-gel method is reported. Variations in the properties of the coatings are related to the molar ratios of ammonia to deionized water being changed in the process of preparing the sols. From the performance test results, the optimal ratio of the reactants necessary to prepare low-refractive-index SiO2 AR coatings is determined. Of all the SiO2 AR coatings, the lowest recorded refractive index is 1.16 at a wavelength of 700 nm. The largest water contact angle is 121.2°, and the peak transmittance is 99.95% at a wavelength of 908 nm. Furthermore, the sol used to deposit the film with the lowest refractive index is stable because of the narrow size distribution of its constituent particles.

Novel-type nanostructured SiO2 antireflection coatings and their application in Cu(In,Ga)Se2 solar cells

Broadband antireflection coatings (ARCs) are a considerable way to sufficiently harvest more solar light into the solar cells due to dramatically reducing the reflection losses at the surface of substrate. Novel structures consisting of continuous SiO2 film and monodispersed SiO2 nanospeheres (NSs) array are proposed to fabricate ARCs according to mimicking the moth-eye-like nanostructure with a periodic sub-wavelength protuberance. Three distinct architectures of coatings based on SiO2 film and SiO2 NSs were successfully obtained by sol–gel dip-coating and electrostatic self-assembly technique, and the structural, morphological and optical properties of the coatings were investigated. Antireflection functionality of the coatings is achieved over the solar spectrum, and the solar transmittance of the substrate in visible region is increased by 7.02% on average with maximum of 8.21% by introducing coating of SiO2 NSs/SiO2 film. The power conversion efficiency of Cu(In,Ga)Se2 solar cells is clearly increased from 11.66% to 12.59% by using with as-prepared ARCs. The novel-type nanostructured ARCs are promising materials in both optical and photovoltaic applications.

Efficiency Enhancement of Cu(In,Ga)Se2 Solar Cells by Applying SiO2–PEG/PVP Antireflection Coatings

An effective approach was presented to enhance photoelectric conversion efficiency of Cu(In,Ga)Se2 (CIGS) solar cells by using modified SiO2 antireflection coatings (ARCs) to harvest more incident sunlight. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) used as additives were introduced into silica sols to prepare SiO2–PEG and SiO2–PVP coatings in the sol–gel dip-coating process, respectively. The different effects of PEG and PVP additives on SiO2 coatings were analyzed and the antireflection performance of SiO2–PEG and SiO2–PVP coatings was investigated. The transmittance over 97% ranging from 450 nm to 700 nm with a maximum transmittance over 99.40% at about 550 nm was achieved for both SiO2–PEG2000A and SiO2–PVP0.5 coatings. The relative efficiencies of CIGS solar cells coated with SiO2–PEG2000A and SiO2–PVP0.5 ARCs were increased by 7.27% and 8.33%, respectively. The modified SiO2 ARCs possessed the advantages of the low manufacturing cost, good adhesion, superior antireflective performance and the feasible method for large area fabrication.

Combined SiO2 antireflective coatings with MOCVD-ZnO:B to improve light absorption in thin-film solar cells

Boron-doped zinc oxide (ZnO:B or BZO) thin films prepared by metal organic chemical vapor deposition (MOCVD) are widely used as the front contact in thin-film solar cells. However, because reflection at the air/glass interface reduces the absorption of incident light, the short circuit current densities, as well as the efficiencies of the cells are deteriorated. To solve this problem, we proposed the combination of silicon dioxide (SiO2) antireflective (AR) coatings prepared by a sol–gel dip-coating method, with MOCVD-BZO films as the new substrate of the cell. The novel structure of the substrate obtained is: SiO2 AR coatings/glass/BZO. An improvement in the optical properties of the new substrate was achieved by destructive interference of the AR coatings at the coatings/air interface. Appling this novel substrate in amorphous silicon solar cells resulted in significant improvement of both the external quantum efficiency and the performance of the cell.

多孔性二氧化硅减反膜胶体规律性研究

多孔性二氧化硅减反膜胶体规律性研究

Design, preparation, and durability of TiO2/SiO2 and ZrO2/SiO2 double-layer antireflective coatings in crystalline silicon solar modules

This paper reports the use of a combination of numerical calculations and experimental work to establish the optimum photovoltaic transmittance (Tpv) and durability of the quarter wave, the quarter-half wave, and the non-quarter wave double-layer TiO2–SiO2 and ZrO2–SiO2 antireflective coatings (ARCs) on solar glass towards practical photovoltaic applications. Numerical calculations based on 4×4 propagation matrix method indicated that the non-quarter wave double-layer ARCs exhibited higher Tpv values than those of the quarter wave and the quarter-half wave ARCs. Such calculated values are in good agreement with the experimental Tpv values. For examples, the Tpv values for the non-quarter wave double-layer TiO2–SiO2 and ZrO2–SiO2 ARCs prepared by sol–gel reached 94.4±0.1% and 94.3±0.1%, respectively. In terms of the coating durability, the non-quarter wave double-layer coatings with a dense and thicker TiO2 or ZrO2 barrier layer on solar glass exhibited less than 1% reduction in Tpv after 96h highly-accelerated temperature and humidity stress test (HAST), as compared with the standard single-layer porous SiO2 used in industry which tested in the same HAST conditions to be greater than (15.4%) after 48h. Single crystalline Si modules encapsulated by the non-quarter wave TiO2–SiO2 or ZrO2–SiO2 AR-coated glass are more durable, with only less than 10% degradation in efficiency after 48h HAST, as compared with Si modules encapsulated by single-layer porous SiO2 AR-coated glass which have signification loss in efficiency (circa. 21.8%).

Porous SiO2 anti-reflective coatings on large-area substrates by electrospinning and their application to solar modules

Fabrication of large-area anti-reflective coatings (ARCs) on glass substrates by using a cost-efficient and simple approach, especially for applications in photovoltaics, remains a challenge. This study proposes electrospinning as a technique to fabricate porous SiO2 ARCs on large-area glass substrates (20×20cm2). The existing electrospinning setup is modified to enable large-area glass coatings and electrospinning process parameters are optimized to achieve sub-wavelength ARCs. The post-sintered SiO2 ARC is thoroughly characterized for the film morphology and optical properties. The transmittance for one-side and both-sides coated glass is found to be 94.3% and 96% respectively. The anti-reflective glass is incorporated in solar modules to determine the increase in short circuit current. The increase in short-circuit current is found to be 3%. Electrospinning as a fabrication technique has potential in offering a cost effective solution for synthesizing ARCs on large-area substrates for photovoltaic applications.

The stability of sol–gel silica coatings in vacuum with organic contaminants

Sol–gel SiO2 antireflective coatings were prepared with different post-treatments, and their performance in a vacuum environment with intentionally induced organic contaminants were studied in detail. The pores of the silica coating can be filled with contaminants, which can increase the refractive index of the film and also absorb or scatter the light and therefore reduce the transmittance. Heat treatment at low temperature can insure against the possible volatilization of the components of the coating, but does not prevent the adsorption of organic contaminants and the degeneration of the transmittance. If an ammonia and hexamethyldisilazane (HMDS) vapor treatment is adopted before heat treatment, the optical stability can be greatly enhanced by reducing the adsorption of contaminants. The increased resistance to contamination is due to changes in the coating’s structure and composition, including a reduction of the specific surface area and surface polarity as a result of ammonia treatment and HMDS treatment, respectively.

Two solutions of the three-dimensional problem of limit waves on the surface of a ponderable fluid

An effective approach was presented to enhance photoelectric conversion efficiency of Cu(In,Ga)Se2 (CIGS) solar cells by using modified SiO2 antireflection coatings (ARCs) to harvest more incident sunlight. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) used as additives were introduced into silica sols to prepare SiO2–PEG and SiO2–PVP coatings in the sol–gel dip-coating process, respectively. The different effects of PEG and PVP additives on SiO2 coatings were analyzed and the antireflection performance of SiO2–PEG and SiO2–PVP coatings was investigated. The transmittance over 97% ranging from 450 nm to 700 nm with a maximum transmittance over 99.40% at about 550 nm was achieved for both SiO2–PEG2000A and SiO2–PVP0.5 coatings. The relative efficiencies of CIGS solar cells coated with SiO2–PEG2000A and SiO2–PVP0.5 ARCs were increased by 7.27% and 8.33%, respectively. The modified SiO2 ARCs possessed the advantages of the low manufacturing cost, good adhesion, superior antireflective performance and the feasible method for large area fabrication.

Ni-Al2O3 cermet solar absorbers by RF planar magnetron sputtering for high temperature applications

Ni-Al2O3 cermet films were sputtered from a hot pressed Ni-Al2O3 composite target, in a RF planar magnetron sputtering system. Coatings of various thickness were deposited on different substrates and their absorptance (α) and emittance (ε) were obtained in the solar and thermal infrared regions, respectively, to evaluate their use as spectrally selective surfaces. Films were also deposited on different substrates with SiO2 anti-reflection coatings and an α of 0.88 to 0.92 and ε of 0.07 to 0.33 were obtained. Films of about 700 Å thick deposited on molybdenum-coated nickel-plated stainless steel substrates with 600 Å SiO2 AR coating and annealed at 550°C in air for six hours have best selective properties with α=0.91 and ε=0.07. These coatings are stable up to 500°C in air for more than 1000 h. ESCA and Auger depth profilings were done to estimate the composition and its variation with depth.