Optimization of broadband omnidirectional antireflection coatings for solar cells

Broadband and omnidirectional antireflection coating is generally an effective way to improve solar cell efficiency, because the destructive interference between the reflected and incident light can maximize the light transmission into the absorption layer. In this paper, we report the incident quantum efficiency ηin, not incident energy or power, as the evaluation function by the ant colony algorithm optimization method, which is a swarm-based optimization method. Also, SPCTRL2 is proposed to be incorporated for accurate optimization because the solar irradiance on a receiver plane is dependent on position, season, and time. Cities of Quito, Beijing and Moscow are selected for two-and three-layer antireflective coating optimization over λ = [300,1100] nm and θ = [0°, 90°]. The ηin increases by 0.26%, 1.37% and 4.24% for the above 3 cities, respectively, compared with that calculated by other rigorous optimization algorithms methods, which is further verified by the effect of position and time dependent solar spectrum on the antireflective coating design.

Design of wideband graded-index antireflection coatings at oblique light incidence

We suggest a design method of graded-refractive-index （GRIN） antireflection （AR） coating for s-polarized or p- polarized light at off-normal incidence. The spectrum characteristic of the designed antireflection coating with a quintic effective refractive-index profile for a given state of polarization has been discussed. In addition, the genetic algorithm was used to optimize the refractive index profile of the GRIN antireflection for reducing the mean reflectance of s- and p-polarizations. The average reflectance loss was reduced to only 0.04% by applying optimized GRIN AR coatings onto BK7 glass over the wavelength range from 400 to 800 nm at the incident angle of θo = 70°.

Wide-angle and broadband graded-refractive-index antireflection coatings

The design and fabrication of graded-refractive-index （GRIN） antireflection （AR） coatings with wide-angle and broadband characteristics are demonstrated. The optimization of the graded-index profiles with a genetic algorithm is used in the design of the GRIN AR coatings. The average reflectance over a wavelength range from 400 nm to 800 nm and angles of incidence from 0° to 80° could be reduced to only 0.1% by applying an optimized AR coating onto BK7 glass. The optimization of step-graded GRIN AR coating is then further investigated in detail. A two-layer AR coating was deposited by electron beam evaporation with glancing angle deposition technology, and the positional homogeneity was improved by depositing the film from two opposite directions. The microstructure of the AR coating was investigated by scanning electron microscopy, and the residual reflectances of the coating sample are in agreement with theoretical calculations. The optimized GRIN AR coatings are beneficial to increasing the efficiency of light utilization.

Graded index broadband antireflection coating prepared by glancing angle deposition for a high-power laser system

This paper reports that SiO2 is selected to fabricate broadband antireflection （AR） coatings on fused silica substrate by using glancing angle deposition and physical vapour deposition. Through accurate control of the graded index of the SiO2 layer, transmittance of thc graded broadband AR coating can achieve an average value of 98% across a spectral range of 300-1850 nm. Moreover, a laser-induced damage threshold measurement of the fabricated AR coating is performed by using a one-on-one protocol according to ISOl1254-1, resulting in an average damage threshold of 17.2 J/cm2.

Employing SiO_2 Buffer Layer to Improve Adhesion of the Frequency-doubled Antireflection Coating on LBO

Frequency-doubled antireflection coatings simultaneously effective at 1064 nm and 532 nm were deposited on the lithium triborate （LiB3O5 or LBO） crystals using the electron beam evaporation method. Comparing with the sample without buffer layer, it is found that the adhesion of the sample with buffer layer of SiO2 between coating and LBO substrate is improved significantly from 137.4 mN to greater than 200 mN. And the laser-induced damage threshold is increased by 20% from 15.1 J/cm^2 to 18.6 J/cm^2. The strengthening mechanism of adhesion of the buffer layer of SiO2 is discussed by considering full plastic indentation and shear theory.

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.

Biomimetic Corrugated Silicon Nanocone Arrays for Self-Cleaning Antireflection Coatings

Corrugated silicon nanocone(SiNC)arrays have been fabricated on a silicon wafer by two polystyrene-sphere-monolayer-masked etching steps in order to create high-performance antireflective coatings.The reflectance was reduced from above 35%to less than 0.7%in the range 400-1050 nm,and it remained below 0.5%at incidence angles up to 70°at 632.8 nm for both s-and p-polarized light.The fluorinated corrugated SiNC array surface exhibits superhydrophobic properties with a water contact angle of 164°.

Fabrication of 3D biomimetic composite coating with broadband antireflection, superhydrophilicity, and double p-n heterojunctions

The traditional single material with two-dimensional （2D） biomimetic moth-eye structures is limited by its narrowband antireflection and single functional capability. To overcome these disadvantages, we exploited wet etching and hydrothermal synthesis coupled with chemical oxidation for fabricating a three- dimensional （3D） biomimetic moth-eye coating with ternary materials （polypyrrole nanoparticles, TiO2 nanorods, and Si micropyramids, i.e., PPy/TiOa/Si-p）. This coating reduced the reflectivity to 〈4% at wavelengths ranging from 200 to 2,300 nm and exhibited remarkable superhydrophilidty with a low water contact angle of 1.8°. Moreover, the composite coating had double p-n heterojunctions, allowing the high-efficiency separation of photogenerated carriers. The photo- current density of PPy/TiO2/Si-p was more than three times higher than that of TiO2/Si-p at a positive potential of 1.5 V. The proposed method provides a means to enhance solar energy conversion.

Rapid Fabrication of Bio-inspired Antireflection Film Replicating From Cicada Wings

Inspired by cicada wings,a flexible film with self-cleaning and broadband antireflection properties was fabricated with a rapid,straightforward and cost-effective method.The cicada wing was selected as the original template,and a polymethyl methacrylate (PMMA) negative replica was obtained by evaporation solvent process.The original template was directly peeled off.Subsequently,the polydimethylsiloxane (PDMS) was spread in the as-prepared PMMA negative replica.After curing and peeling processes,the PDMS positive replica was manufactured successfully.The morphologies and performances of cicada wings were perfectly inherited by the PDMS positive replica.What is more,the excellent optical property of cicada wing was investigated experimentally and theoretically.Compared with fiat PDMS film,the average reflectivity of structural PDMS film was reduced from 9% to 3.5% in the wavelength range of 500 nm-900 nm.These excellent antireflection properties of bio-inspired antireflection film can be attributed to the nanostructures which achieve a gradient refractive index between air and the materials,and the mechanism of the antireflection properties was revealed via effective medium theory.Besides,the bio-inspired broadband antireflective film exhibited superhydrophobic property after the surface treatment (a 152.1° water contact angle),and it also displayed satisfactory flexibility.This work provided a universal method to fabricate the exquisite biological structures,realizing the transfer of structure and function.Moreover,the multifunctional antireflection film exhibited the potential value for applications in optical communications,flexible display screens,and anti-dazzle glasses.

Design and preparation of frequency doubling antireflection coating with different thicknesses of interlayer for LiB3O5 crystal

Design and preparation of frequency doubling antireflection coating with different thicknesses of interlayer were investigated for LIB3O5 （LBO） substrate. The design was based on the vector method. The thickness of the inserted SiO2 interlayer could be changed in a wide range for the four-layer design with two zeros at 1064 and 532 nm. The coatings without any interlayer and with 0.1 quarter-wave （λ/4）, 0.3 λ/4, 0.5 λ/4 SiO2 interlayer were deposited respectively on LBO by using electron beam evaporation technique. All the prepared coatings with SiO2 interlayer indicated satisfying optical behavior. This expanded our option for the thickness of an interlayer when coating on LBO substrate. The prepared films with SiO2 interlayer showed better adhesion than that without any interlayer. The thickness of the interlayer affected the adhesion, the adhesion for the coating with 0.5 λ/4 SiO2 interlayer was not as good as the other two.

Study on Antireflection SiO_2 Coatings Fabricated by Layer-by-Layer Deposition

Multifunctional（poly（diallyldimethyl ammonium chloride）/sodium poly（4-styrene sulfonate）） n（（PDDA/PSS） n） thin films were fabricated by layer-by-layer assembled on the glass substrate.The monolayer silica nanoparticles were prepared on the（PDDA/PSS） n films.The SiO 2-polyelectrolyte coatings exhibit antireflection properties with low refractive index（as low as 1.22）.Interestingly,wavelengths of maximum transmittance could be well tailored by simply changing the particle size of SiO 2.A maximum transmittance of 97.03% in the visible spectral range is achieved for the particle size of 100 nm SiO 2 films.The coatings also show excellent mechanical stability and good adhesion to substrates.The easy availability of the raw materials and simplicity of the fabrication method for such films might make them be potentially useful for various applications.

Ag surface plasmon enhanced double-layer antireflection coatings for GaAs solar cells

Surface plasmon enhanced antireflection coatings for GaAs solar cells have been designed theoretically.The reflectance of double-layer antireflection coatings（ARCs） with different suspensions of Ag particles is calcu-lated as a function of the wavelength according to the optical interference matrix and the Mie theory.The mean dielectric concept was adopted in the simulations.A significant reduction of reflectance in the spectral region from 300 to 400 nm was found to be beneficial for the design of ARCs.A new SiO2/Ag-ZnS double-layer coating with better antireflection ability can be achieved if the particle volume fraction in ZnS is 1%-2%.

Optimization of Al_2O_3/SiN_x stacked antireflection structures for N-type surface-passivated crystalline silicon solar cells

In the case of N-type solar cells,the anti-reflection property,as one of the important factors to further improve the energy-conversion efficiency,has been optimized using a stacked Al_2O_3/SiN_x layer.The effect of SiN_x layer thickness on the surface reflection property was systematically studied in terms of both experimental and theoretical measurement.In the stacked Al_2O_3/SiN_x layers,results demonstrated that the surface reflection property can be effectively optimized by adding a SiN_x layer,leading to the improvement in the final photovoltaic characteristic of the N-type solar cells.

Near-field holography enhanced with antireflection coatings--an improved method for fabricating diffraction gratings

Near-field holography（NFH）, with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings（ARCs） simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.

Optimization of the spectral performance of an antireflection coating on a micro-spherical substrate

To improve the optical performance of an antireflection（AR） coating on a micro-spherical substrate, the ray angle of the incidence distribution and the thickness profile are taken into consideration during the optical coating design. For a convex spherical substrate with a radius of curvature of 10 mm and a clear aperture of 10 mm,three strategies are used for the optimization of the spectral performance of a broadband AR coating in the spectral region from 480 to 720 nm. By comparing the calculated residual reflectance and spectral uniformity,the developed method demonstrates its superiority in spectral performance optimization of an AR coating on a micro-spherical substrate.

Tunable narrowband antireflection optical filter with a metasurface

A narrowband tunable antireflection optical filter is proposed and numerically studied. The structure is a metasurface based on plasmonic nanoparticles on an electro-optic film in a three-layer configuration of metaldielectric-metal(MDM) in the visible near-infrared range. By tuning the voltage and thus tuning the refractive index of the dielectric Li Nb O_3, one can shift the wavelength of minimum reflection as desired. The parameters of gold nanoparticles and other elements used for the filter design and refractive index of the dielectric are obtained by the finite-element method(FEM). An analytical theory is presented to explain the FEM simulation results, and they agree well with each other. It is found that the frequency of the plasmonic resonance wave on the metasurface should be equal to that of the Fabry–Perot resonator formed by the MDM to have a good filtering property. Theoretical spectra obtained by FEM simulation show that the structure has extensive potential for the design of tunable narrow-band filters for modulators, displayers, and color extraction for imaging.

Optical property of an antireflection coating fabricated by an optimal spin-coating method with a pH-modified SiO2 nanoparticle solution

An antireflection （AR） coating is fabricated by applying an optimal spin-coating method and a pH-modified SiO2 nanoparticle solution on a cover glass. Because the pH value of the solution will affect the aggregation and dispersion of the SiO2 particles, the transmittance of the AR-treated cover glass will be enhanced under optimal fabricated conditions. The experimental results show that an AR coating fabricated by an SiO2 nano- particle solution of pH 11 enhances the transmittance approximately by 3% and 5% under normal and oblique incident conditions, respectively. Furthermore, the AR-treated cover glass exhibits hydrophobicity and shows a 65% enhancement at a contact angle to bare glass.

Broadband antireflection coatings deposited by magnetron sputtering

IN 1938, antireflection coatings were prepared by Americans. Later, they were successfullygot by Europeans. The antireflection coatings are very important in optical films, and used inmost optical instruments such as photograph eyes, glasses, telescopes and microscopes. Atpresent, the technology of preparing antireflection is perfect. Especially, with the help ofcomputer, multi-antireflection coating can be constructed easily. Resistance heating

A novel trilayer antireflection coating using dip-coating technique

We report a new structure for broadband antireflection coating by dip-coating technique, which has minimal cost and is compatible with large-scale manufacturing. The coatings are prepared by depositing SiO2 sol-gel film on a glass substrate, subsequently depositing SiO2 single-layer particle coating through electrostatic attraction, and depositing a final very thin SiO2 sol-gel film to improve the mechanical strength of the whole coating structure. The refractive index of the structure changes gradually from the top to the substrate. The transmittance of a glass substrate has been experimentally found to be improved in the spectral range of 400-1 400 nm and in the incidence angle range from 0° to at least 45°. The mechanical strength is immensely improved because of the additional thin SiO2 sol-gel layer. The surface texture can be applied to the substrates of different materials and shapes as an add-on coating.

Influence of window layer thickness on double layer antireflection coating for triple junction solar cells

The optimization of a SiO_2/TiO_2,SiO_2/ZnS double layer antireflection coating（ARC）on Ga_（0.5）In_（0.5）P/In_（0.02）Ga_（0.98）As/Ge solar cells for terrestrial application is discussed.The Al_（0.5）In_（0.5）P window layer thickness is also taken into consideration.It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.