Antireflective Thin Films Research Articles

Atmospheric pressure chemical vapor deposition of high silica SiO2–TiO2 antireflective thin films for glass based solar panels

The atmospheric pressure chemical vapor deposition (APCVD) of SiO2–TiO2 thin films on glass by employing a [[(tBuO)3SiO]2–Ti(OiPr)2] single-source precursor, which can be prepared from commercially available materials, results in antireflective thin films with high silica SiO2 : TiO2 ratio (i.e. SiO2 > 1) on float glass under industrially relevant manufacturing conditions.

Microstructure Analysis and Properties of Anti-Reflection Thin Films for Spherical Silicon Solar Cells

Structure and properties of anti-reflection thin films of spherical silicon solar cells were investigated and discussed. Conversion efficiencies of spherical Si solar cells coated with F-doped SnO2 anti-reflection films were improved by annealing. Optical absorption and fluorescence of the solar cells increased after annealing. Lattice constants of F-doped SnO2 anti-reflection layers, which were investigated by X-ray diffraction, decreased after annealing. A mechanism of atomic diffusion of F in SnO2 was discussed. The present work indicated a guideline for spherical silicon solar cells with higher efficiencies.

Surface Characterization of Antireflective Thin Films

Surface Characterization of Antireflective Thin Films

High quality antireflective ZnS thin films prepared by chemical bath deposition

Zinc sulfide (ZnS) thin films for antireflective applications were deposited on glass substrates by chemical bath deposition (CBD). Chemical analysis of the soluble species permits to predict the optimal pH conditions to obtain high quality ZnS films. For the CBD, the ZnCl2, NH4NO3, and CS(NH2)2 were fixed components, whereas the KOH concentration was varied from 0.8 to 1.4 M. Groups of samples with deposition times from 60 to 120 min were prepared in a bath with magnetic agitation and heated at 90 °C. ZnS films obtained from optimal KOH concentrations of 0.9 M and 1.0 M exhibited high transparency, homogeneity, adherence, and crystalline. The ZnS films presented a band gap energy of 3.84 eV, an atomic Zn:S stoichiometry ratio of 49:51, a transmittance above 85% in the 300–800 nm wavelength range, and a reflectance below 25% in the UV–Vis range. X-ray diffraction analysis revealed a cubic structure in the (111) orientation for the films. The thickness of the films was tuned between 60 nm and 135 nm by controlling the deposition time and KOH concentration. The incorporation of the CBD-ZnS films into ITO/ZnS/CdS/CdTe and glass/Mo/ZnS heterostructures as antireflective layer confirms their high optical quality.

Porous SiO_2/MgF_2 broadband antireflection coatings for superstrate-type silicon-based tandem cells

The purpose of this study is to reduce the glass substrate reflectivity over a wide spectral range (400-1200 nm) without having high reflectivity in the near-infrared region. After making porous SiO₂/MgF₂ double-layer antireflection (DLAR) thin film structure, the superstrate-type silicon-based tandem cells are added. In comparison to having only silicon-based tandem solar cells, the short-circuit current density has improved by 6.82% when porous SiO₂/MgF₂ DLAR thin film is applied to silicon-based tandem solar cells. This study has demonstrated that porous SiO₂/MgF₂ DLAR thin film structure provides antireflection properties over a broad spectral range (400-1200 nm) without having high reflectivity at near-infrared wavelengths.

Antireflective sol–gel TiO2 thin films for single crystal silicon and textured polycrystal silicon

In this paper, antireflective TiO2 thin films have been prepared on single crystal silicon, and textured polycrystal silicon by sol–gel route using the dip-coating technique. The thickness and the refractive index of the films have been optimised to obtain low reflexion in the visible region, by controlling both the concentration of the titanium isopropoxide (Ti(iOPr)4), and the annealing temperature. We showed that the use of a TiO2 single layer with a thickness of 64.5 nm, heat-treated at 450 or 300 °C, reduces the reflection on single crystal silicon at a level lower than 3% over the broadband spectral ranges 670–830 nm and 790–1010 nm, respectively. In order to broaden the spectral minimum reflectance as much as possible, we have proposed to texture polycrystal silicon wafers, and to coat these wafers by a TiO2 single layer with a thickness of 73.4 nm. In this case, the reflectance has been reduced from 27 to 13% in the spectral range 460–1000 nm.

Synthesis of Neutral / Hydrosol and Its Application as Antireflective Self-Cleaning Thin Film

A neutral SiO2/TiO2composite hydrosol was prepared by a coprecipitation-peptization method using titanium tetrachloride and silicon dioxide hydrosol as precursors. It is not only an antireflective self-cleaning coating material but also an environmental-benign material. Even heated at 700°C for 5 minutes in the tempering process, the as-prepared SiO2/TiO2thin film still demonstrated antireflection and photocatalytic self-cleaning effect. The SiO2/TiO2thin film increased near 2% of transmittance; however, the TiO2thin film decreased 5% of transmittance at least. In addition to antireflection, the SiO2/TiO2thin film decomposed the surface coated oleic acid under ultraviolet light and showed superhydrophilicity under dark for two days. The SiO2/TiO2thin film also showed good photocatalytic degradation of methylene blue. With these antireflection, persistent superhydrophilicity, and photocatalytic self-cleaning effects, this prepared neutral SiO2/TiO2hydrosol would be a good coating material for tempered glass and other building materials.

Development of Nanostructured Antireflection Coatings for EO/IR Sensor and Solar Cell Applications

Electro-optical/infrared (EO/IR) sensors and photovoltaic power sources are being developed for a variety of defense and commercial applications. One of the critical technologies that will enhance both EO/IR sensor and photovoltaic module performance is the development of high quality nanostructure-based antireflection coatings. In this paper, we review our work on advanced antireflection structures that have been designed by using a genetic algorithm and fabricated by using oblique angle deposition. The antireflection coatings are designed for the wavelength range of 250 nm to 2500 nm and an incidence angle between 00 and 400. These nanostructured antireflection coatings are shown to enhance the optical transmission through transparent windows over a wide band of interest and minimize broadband reflection losses to less than one percent, a substantial improvement over conventional thin-film antireflection coating technologies.

A study of the optical properties and adhesion of zinc sulfide anti-reflection thin film coated on a germanium substrate

To conduct this study, zinc sulfide (ZnS) thin films deposited on germanium (Ge) substrates were prepared by an evaporation method. The effects of deposition rate and annealing on the optical properties and adhesion of the ZnS thin films were investigated. The transmission intensity and the X-ray diffraction (XRD) pattern of the samples showed that the transmittance of the samples decreases by increasing the evaporation rates. However, with the increase of the annealing temperature, crystallinity of the thin films improves which, in turn, results in the enhancement of the transmission intensity in a far infrared region. The maximum grain size was obtained at the annealing temperature of 225°C. Our experimental results also show that evaporation rate and annealing influences the adhesion of ZnS thin films to Ge substrates.

Ultraviolet antireflection coatings for use in silicon detector design

We report on the development of coatings for a charged-coupled device (CCD) detector optimized for use in a fixed dispersion UV spectrograph. Because of the rapidly changing index of refraction of Si, single layer broadband antireflection (AR) coatings are not suitable to increase quantum efficiency at all wavelengths of interest. Instead, we describe a creative solution that provides excellent performance over UV wavelengths. We describe progress in the development of a coated CCD detector with theoretical quantum efficiencies (QEs) of greater than 60% at wavelengths from 120 to 300 nm. This high efficiency may be reached by coating a backside-illuminated, thinned, delta-doped CCD with a series of thin film AR coatings. The materials tested include MgF(2) (optimized for highest performance from 120-150 nm), SiO(2) (150-180 nm), Al(2)O(3) (180-240 nm), MgO (200-250 nm), and HfO(2) (240-300 nm). A variety of deposition techniques were tested and a selection of coatings that minimized reflectance on a Si test wafer were applied to functional devices. We also discuss future uses and improvements, including graded and multilayer coatings.

Near-field distribution of broadband antireflective nanostructure arrays

Broadband antireflection (AR) nanostructure arrays patterned directly into a bulk substrate, behaving as the expected performance of high laser induced damage threshold (LIDT), is proposed for the application of laser-transmitting optical elements. These regular periodic arrays known as “moth-eye” structure exhibit particularly noteworthy AR property over a wide spectrum and over a large field of view in addition to overcome efficiently the disadvantages of multilayer AR thin-film. Furthermore, the near-field distribution in nanostructure arrays with respect to the period, the groove depth and incident angle, respectively, was numerically simulated using a rigorous Fourier modal method (FMM). It is interesting that the maximum value of the normalized electric field intensity is obviously distributed inside the air layer upon the nanostructure for the periodicity of 100nm, which has significant potential to reach to ultra high LIDT for the application of short-pulse high-power laser system. Besides, the variation of the near-field distribution inside the nanostructure arrays exhibits critically dependent on the period of surface structure, but the effect caused by the discrepancy in groove depth and incident angle is unimportant.

Design and fabrication of antireflective nanoparticulate thin films with superhydrophilic self-cleaning properties on glass substrate

Design and fabrication of transparent and superhydrophilic self-cleaning thin films on glass substrate by 7 nm TiO 2/22 nm SiO 2 all-nanoparticle coatings via aqueous electrostatic layer-by-layer assembly processing were demonstrated in this work. Stable and conformal structure of multibilayer (TiO 2/SiO 2) x with x up to 120 was shown to exhibit antireflective, superhydrophilic, and self-cleaning multifunctional properties. This was achieved by using appropriate periodic calcinations rather than only once calcination of the assembled nanoparticulate thin films. Average refractive index of 1.30 ± 0.03 at 633 nm and average bilayer thickness of 20.18 nm were determined for the as-fabricated nanoparticulate thin films. Furthermore, average transmittance values higher than 93.5% were exhibited by all the nanoparticulate thin films and the experimental results were only at the very most of 2% lower than those predicted by the theory. The self-cleaning properties of the nanoparticulate thin films were revealed by the decomposition of two model contaminants under UV illumination. The experimental results showed that the photocatalytic decomposition rates are increased with the increase of bilayer number of the nanoparticulate thin film.

Chemical Purification of ZnO Nanoparticles by Dialyzing Treatments and Their Use in Fabricating Luminescent Antireflective Nanocomposite Thin Films

ZnO nanoparticles were prepared by a chemical solution method using the reaction between Zn(CH3COO)2·2H2O and LiOH·H2O in an ethanol solvent. A dialyzing treatment of the resultant chemically impure nanoparticles was introduced in the present work, aiming at increasing their chemical purity in terms of adsorbed species. The progress of dialysis was monitored with electrical conductivity of dialysate. X-ray diffraction analysis and Fourier transform infrared spectroscopy were employed to check the chemical purity of the ZnO nanoparticles after the dialyzing treatment. Furthermore, the dialyzed ZnO nanoparticles were utilized to fabricate ZnO/SiO2 nanocomposite thin films by a sol−gel method with a dip-coating technique. Stable coating solutions were obtained only with the dialyzed ZnO nanoparticles, which also indicated their chemical purity. The nanocomposite thin films exhibited a unique optical property with antireflection against visible light and photoluminescence under irradiation with ultraviolet light.

Control of Structure and Film Thickness Using Spray Layer-by-Layer Method: Application to Double-Layer Anti-Reflection Film

The recently developed practice of spraying solutions onto a substrate to fabricate thin films via layer-by layer (LBL) method has been further investigated and extended. We successfully fabricated double-layer anti-reflection (AR) thin films with high- and low-refractive-index layers by the spray layer-by-layer (spray-LBL) method. For the deposition of a high-refractive-index layer, layers of poly(diallyldimethylammonium chloride) (PDDA) and titanium(IV) bis(ammoniumlactato) dihydroxide (TALH) were alternatively assembled. The average thickness of (PDDA/TALH) was determined to be 7 nm and the refractive index was n=1.76 at 550 nm. Poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) layers were assembled on the high-refractive-index layer for the deposition of the low-refractive-index layer. The average thickness of (PAH/PAA) was determined to be 14 nm and the refractive index was n=1.48 at 550 nm. This AR thin film showed the maximum transmittance (94.5%) and the minimum reflection (0.5%) at approximately 550 nm in wavelength.

Nanostructured thin films for anti-reflection applications

Anti-reflection (AR) thin films composed of ordered arrays of tapered nanostructures on the surface of PMMA and silicon, through the hot-embossing nanoimprint of polymer using molds prepared from e-beam lithography and hydrothermally grown ZnO nanorod arrays. The use of PMMA and ZnO nanorod thin films allows the formation of anti-reflection structures on a curved or flat surface to effectively suppress the reflectance of the incident light. It provides a simple and low-cost means for large-scale use in the production of AR layers for improving optical and optoelectronic device performance, such as solar cells and photodetectors. A drastic reduction in the reflectivity of the AR layer over a broad spectral range was demonstrated. In addition, the great improvement on the light harvest efficiency of the solar cells by over 30% using the nanostructured AR layer was validated.

Antireflective and Radiation Resistant ZnO Thin Films for the Efficiency Enhancement of GaAs Photovoltaics

In this paper, zinc oxide (ZnO) thin films as an antireflective (AR) coating layer have been successfully fabricated on GaAs solar cells by the sol–gel method. ZnO films were prepared chemically by spin coating the gel with an aqueous solution of zinc acetate and ethanolamine. The current–voltage measurements of the solar cells confirmed the increase of the short-circuit current induced by the AR effect. The open-circuit voltage and fill factor were also improved by the surface passivation. As a result, the conversion efficiency of the cells without an AR coating (8.2%) was significantly enhanced to 13.6%. The results indicate that the chemical deposition of ZnO was effective for the AR coating of GaAs solar cells. Additionally, we demonstrate that the cells coated with radiation resistant ZnO films exhibit less efficiency decay than the devices without such treatment. Under the maximum proton fluence of , the conversion efficiency decay was reduced to 69.8%, while the solar cells without ZnO films showed an efficiency decay of 83.1%.

Nanocone SiGe antireflective thin films fabricated by ultrahigh-vacuum chemical vapor deposition with in situ annealing

In this study, we fabricated nanocone-presenting SiGe antireflection layers using only ultrahigh-vacuum chemical vapor deposition. In situ thermal annealing was adopted to cause SiGe clustering, yielding a characteristic nanocone array on the SiGe surface. Atomic force microscopy indicated that the SiGe nanocones had uniform height and distribution. Spectrophotometric measurements revealed that annealing at 900 °C yielded SiGe thin films possessing superior antireflective properties relative to those of the as-grown SiGe sample. We attribute this decrease in reflectance to the presence of the nanostructured cones. Prior to heat treatment, the mean reflectance of ultraviolet rays (wavelength < 400 nm) of the SiGe thin film was ca. 61.7%; it reduced significantly to less than 28.5% when the SiGe thin film was annealed at 900 °C. Thus, the drop in reflectance of the SiGe thin film after thermal treatment exceeded 33%.

백색 OLED의 발광효율 향상을 위한 Dielectric Layer 설계에 관한 연구

We have optimized the device structure by using the dielectric layer such as anti-reflection thin film to improve the emitting efficiency of white organic light emitting device (WOLED). Basically, dielectric layer with anti-reflection characteristics can enhance the emitting efficiency of WOLED by compensating the refractive index of organic layer, ITO, and Glass. Here, WOLED was designed and optimized by Macleod simulator. The refractive index of 1.74 was calculated for Dielectric layer and was selected as <TEX>$TiO_2$</TEX>. The optimal thicknesses of <TEX>$TiO_2$</TEX> and ITO were 119.3 and 166.6 nm, respectively, at the wavelength of 600 nm. The transmittance of ITO was measured with the thickness variation of dielectric layer and ITO in Organic layer/ITO/Dielectric layer structure. The transmittance of ITO was 95.17% and thicknesses of <TEX>$TiO_2$</TEX> and ITO were 119.3 and 166.6 nm, respectively. This result, calculated and measured values were coincided.

Effect of thermal conductivity on the efficiency of single crystal silicon solar cell coated with an anti-reflective thin film

This paper presents the working of a single crystal silicon solar cell coated with a zinc oxide thin film. Single crystalline silicon is the absorber of incident solar radiation, while the zinc oxide film – an optically black film, offers optical improvement. Thermal conductivity measurements were made using the transient line heat source (TLHS) method, where the heat source is placed against the inner and outer surfaces of the solar cell to provide heating and to sense the temperature changes at the same time. In the temperature range 297–360 K, values of thermal conductivities for the silicon material, zinc oxide and the surrounding air at atmospheric pressure were found to be 0.884–1.26 × 10 3 Wm −1 K −1. By comparing the calculation results for the highest and lowest values of thermal conductivities, against the solar cell output, the value of collection efficiency for photo-generated carriers in the cell is seen to be varied. At moderate values of thermal conductivity – corresponding to mid temperatures, the cell output power and hence efficiency is observed to be high.

Influence of Deposition Method on Refractive Index of SiO2and TiO2Thin Films for Anti-reflective Multilayers

Anti-Reflective (AR) thin film coatings of SiO₂ (n=1.48) and TiO₂ (n=2.17) were deposited by ion-beam assisted deposition (IBAD) with End-Hall ion source and conventional electron beam (e-beam) evaporation to investigate the effect of deposition method on the refractive indicies (n) of the films. Green-light generation using a GaAs laser diode was achieved via excitation of the second harmonic. The latter resulted from the transmission of the fundamental guided-mode wave of 1064 nm through periodically poled LiNbO₃. Large differences in the refractive indicies of each of the layers in the multilayer coating may improve AR performance. IBAD of SiO₂ reduced its refractive index from 1.45 to 1.34 at 1064 nm. Conversely, e-beam evaporation of TiO₂ increased its refractive index from 1.80 to 2.11. In addition, no fluctuations in absorption at the wavelength of 1064 nm were found. The results suggest that films prepared by different deposition methods can increase the effectiveness of multilayer AR coatings.