Broadband Antireflection Coatings Research Articles

Superhydrophilic antifogging broadband antireflective coatings with worm-like nanostructures fabricated by one dip-coating method and calcination

In this work, superhydrophilic antifogging antireflective coatings were prepared by the dip-coating of polyacrylate/polypropylsilsesquioxane core-shell nanocomposite particles’ sols followed by calcination at 500 °C for 4 h. The results showed that the transmittance of all the coatings in the band of 350–1000 nm was significantly higher than that of pure glass substrate, showing excellent broadband and antireflection performance. In particular, the maximum transmittance of the coatings with 8.0 g of propyltrimethoxysilane (PTMS-8) was 99.1% at the wavelength of 546 nm, and the average transmittance of the coatings reached 98.0% in the wavelength range of 400–700 nm and was enhanced by 9.3% compared to that of the bare glass substrate. Furthermore, the contact angle of the coatings decreased with the increase in the surface bumps structures of the coatings, and the minimum contact angle of the surface of the coatings with 10.0 g of propyltrimethoxysilane (PTMS-10) reached nearly zero within 0.5 s when the bumps evolved into a worm-like nanostructure, showing excellent superhydrophilic and antifogging properties. It was concluded that both roughness and special worm-like nanostructures give rise to the superhydrophilicity of the coatings.

Preparation of superhydrophilic silicate coating by sol–gel for double-wavelength broadband antireflective coatings

In the process of realizing double-wavelength broadband antireflection (AR) coatings, it is very important to control the refractive index in a wide range, but at present, many methods of adjusting the refractive index are too complex or expensive. Here, a simple and inexpensive sol–gel route is proposed to prepare the superhydrophilic silica (SiO2) thin films having ultra-low refractive indices by the SiO2 particles surface corrosion with hydrofluoric acid (HF) in sol; this treatment effectively reduces the refractive index of the coating from 1.22 to 1.11. The formation mechanism of the coatings with ultra-low refractive index was discussed in detail. The corrosion of HF on the particles surface significantly improves the hydrophilicity of the coating, and reduces the water contact angle of the coating from 27° to 2°. The bottom layer is prepared by mixing the acid–base complex silica sol. When the refractive indices of the bottom and top layers were set as 1.29 and 1.13, the double-layer double-wavelength AR coating with excellent optical properties has the transmittance of 99.95% and 100.00% at 532 and 1064 nm, respectively.

A novel and facile method to fabrication of broadband and semi-omnidirectional antireflective coatings with bowl-like pit structure

In the current work, excellent optical antireflective coatings with various surface morphologies are prepared combining with emulsion polymerization, sol-gel process and dip-coating technique. Among these antireflective coatings, bowl-like pit structure antireflective coatings show broadband and semi-omnidirectional antireflective properties. The mean transmittance of this kind of coatings reaches 99.5% and increases 7.2% compared with that of bare glass in the range of wavelength from 400 nm to 700 nm and the maximum transmittance is 99.8% when the incident angle is 0°. The mean transmittance of the coatings still keeps 97.7% and increases 6.7% compared with that of bare glass in the range of wavelength from 400 nm to 700 nm and the maximum transmittance is 98.5% when the incident angle is 30°. The coatings still show antireflective properties in a degree even the incident angle increases to 60°. The corresponding mechanism is also provided. More importantly, the whole process is simple, solvents free, low-cost and appropriate for large-scale production.

Single compound in-situ synthesis of core-shell CaF2 nanoparticles based broad band antireflective coatings for solar energy conversion

A unique in-situ synthesis approach of formation-deformation-reformation routes lead to high crystalline core-shell Calcium Fluoride (CaF2) nanoparticles. They were tuned by the solvothermal process to achieve superior antireflection property (>95%) in the broadband region (400–1500 nm) after fabricating films by a dip coating method. These nanoparticles capped by cetyltrimethylammonium bromide (CTAB), to increase the porosity in single layer antireflective (AR) film to reduce the refractive index. This efficient antireflection layer with glass implemented on the c-Si solar cell to measure the efficiency and found out to be an improved performance (>5.7% net enhancement) compared to uncoated glass. In addition, the AR coatings exhibited a good mechanical strength which gives us the direction of future development for practical applications like highly transparent window coatings, optical and solar energy conversion applications.

Hybrid Nanostructured Antireflection Coating by Self-Assembled Nanosphere Lithography

Broadband antireflection (AR) coatings are essential elements for improving the photocurrent generation of photovoltaic modules or the enhancement of visibility in optical devices. In this paper, we report a hybrid nanostructured antireflection coating combination that is a clean and efficient method for fabricating a nanostructured antireflection coating (ARC). A multilayer thin-film was introduced between the ARC and substrate to solve the significant problem of preparing nanostructured ARCs on different substrates. In this way, we rebuilt a gradient refractive index structure and optimize the antireflective property by simply adjusting the moth-eye structure and multilayers. Subwavelength-structured cone arrays were directly patterned using a self-assembled single-layer polystyrene (PS) nanosphere array as an etching mask. Nanostructure coatings exhibited excellent broadband and wide-angle antireflective properties. The bottom-up preparation process and hybrid structural combination have the potential to significantly enhance the broadband and wide-angle antireflective properties for a number of optical systems that require high transparency, which is promising for reducing the manufacturing cost of nanostructured AR coatings.

Broadband antireflection coatings for visible and infrared ranges

Antireflection coatings are critical elements for space applications as they will influence the overall performances of optical systems. They are among the most classical elements that are produced with optical coatings but remain a challenge when high performances are required. In this paper, we present some recent results based on thin film technology for the production of antireflection coatings dedicated to visible, near-IR and mid-IR spectral ranges. We first present a theoretical and experimental study of broadband antireflection coatings for (400–1100)-nm spectral range. We then show antireflection coatings covering the (1.5–15)-µm range. Experimental demonstrations and limitations are presented.

Super-hydrophilic broadband anti-reflective coating with high weather stability for solar and optical applications

The development of Broadband Antireflective Coatings (B-ARC) plays a vital role in the accomplishment of more competitive architectural glasses for renewable solar energy applications. In this respect, coatings that provide dual properties like high transmittance and easy-to-clean property, along with weather & UV stabilities could mean an added value to such architectural glasses especially for Solar Photovoltaic (PV) and Concentrated Solar Thermal (CST) applications. Herein we report the design and preparation of novel hybrid B-ARC with other functional properties like super-hydrophilic (easy-to-clean/antifogging property), weather and UV stability developed by using a facile sol-gel process. Film-thickness and morphology were optimized by varying the synthesis parameters, coating thickness and curing temperatures; to achieve dual characteristics for the coating. The developed broadband anti-reflective coating shows an average solar transmittance of 98.1% in the visible region (400–800 nm) and 96.6% in the active solar region (300–1500 nm). It is noteworthy that B-ARC generated by this method shows super-hydrophilic property with high weather and UV stabilities (withstand 100 h in high accelerated weather test).

Hydrophobic and spectrally broadband antireflective methyl-silylated silica coatings with high performance stability for concentrated solar applications

An efficient and environment-friendly process, consisting of acid-catalyzed sol-gel process combined with evaporation induced self-assembly, was conducted to build antireflective (AR) layer stacks for concentrated solar applications. Considering the external factors that may alter the optical properties of the system when operating outdoors, such as soiling, harsh climate conditions and alkali ions diffusion from glass, several stack configurations were proposed. Particularly, the effect of a methyl-silylating post-treatment, the presence of the inner layer and the optimization of sintering temperature have been devised in order to minimize soiling adherence and alkali diffusion from the glass substrate and to assure the required robustness to comply with the durability requirements. The assessment consisted of (i) an analysis of the optical transmittance, reflectance and refractive index and (ii) hydrophobicity and effect of water absorption on the external porous coatings in relation to the results of accelerated aging tests following photovoltaics standards. The main goal was to achieve the most rational design, based on a proper trade-off between cost efficiency, processability, optical properties and reliability during real life operation.

Wide-Angle Broadband Antireflection Coatings Prepared by Atomic Layer Deposition.

A novel broadband antireflective coating with ultra-low residual reflectance for light incidence angles from 0° up to 60° is presented. The system consists of an interference multilayer coating made by atomic layer deposition (ALD) combined with a low- n nanoporous SiO2 top-layer obtained by wet-chemical etching of an atomically mixed SiO2/Al2O3 ALD composite. The average residual reflectance measured at normal incidence for double-sided coated B270 glass substrates is only 0.5% in a broad spectral range from 400 to 1100 nm. The average reflectance of the substrate considering both front and rear sides decreased in the visible spectral range of 420-680 nm from 9.9 and 15.8 to 0.4 and 1.8% at an oblique angle of incidence (AOI) of 45° and 60°, respectively, by applying the hybrid ALD antireflection coatings. The measured average transmittance reaches 99.5% at AOI 6° in the 400-950 nm spectral range. Measurements three weeks after preparation show only a small reduction of the average transmittance to 99.3% in this spectral range spanning 550 nm. Ten months later, the average transmittance is still 99.0%, whereby the sample handling might have also affected the performance. The hybrid ALD system shows excellent conformal AR performance on a strongly curved B270 aspheric lens with a diameter of 50 mm and a height of 25 mm. The presented process is a promising route toward omnidirectional AR coatings on complex 3D optics, which are increasingly important for consumer and high-performance optical systems.

Broadband antireflective and superhydrophobic coatings for solar cells

High-performance, broadband antireflective (AR) and superhydrophobic coatings are fabricated on glass through deposition of silica nanoparticles with spin coating method, followed by calcination and hydrophobic modification. Silica particles with unique porous structures not only increase the roughness of the coating, but also enhance the transmittance of the glass. The coated glass has displayed a large transmittance of 99% at wavelength of 580 nm, an absolute transmittance increase by 6% or more in the wavelength range of 480–900 nm, and an excellent hydrophobicity with a water contact angle (WCA) of 147° and a sliding angle < 10°. As a result, this coating effectively improves the short-circuit current density from 13.27 to 14.17 mA/cm2 and the conversion efficiency from 6.03 to 6.64% for dye-sensitized solar cells (DSSCs), with a 10.12% improvement. This work thus has shown a promising approach to enhance the performance of solar cells with broadband antireflective coating surfaces.

Moth-eye-like antireflection coatings based on close-packed solid/hollow silica nanospheres

Broadband antireflection coatings (ARCs) attract increasing attentions due to the effective reduction of reflection between the interface of air and substrates over a broad range of wavelengths. Moth-eye-like array ARCs with high antireflection performance have been successfully fabricated via a facile and low-cost sol–gel method using solid silica nanospheres (SSNSs) and hollow silica nanospheres (HSNSs). The composite of SSNSs and HSNSs was closely arranged on the glass substrate to firstly construct the close-packed solid/hollow silica nanospheres (c-S/HSNSs) array, in which HSNSs were used to regulate the refractive index and many triangular grooves among adjacent nanospheres were formed. Then moth-eye-like array structure was obtained by locating the nanospheres on the groove positions in c-S/HSNSs array. The transmittance of glass substrates with moth-eye-like array structure has been increased from 91.0% to 99.0%, with an average solar transmittance of 97.8%. The reflection of glass substrates with moth-eye-like array structure was prominently reduced in wide-angle incidence, and the minimum reflectance changed from 0.17% to 1.34% within 8 to 60°. The moth-eye-like array structure exhibits the high antireflection performance and excellent thermal stability and is promising in photovoltaic modules, optical lenses, and other outdoor applications.

λ/4-λ/2 Double-layer Broadband Antireflective Coatings with Superhydrophilicity and Photocatalysis

λ/4-λ/2 Double-layer Broadband Antireflective Coatings with Superhydrophilicity and Photocatalysis

Fabrication and properties of broadband antireflective coatings on inert perfluoropolymer films treated by inductively coupled oxygen plasma

Fluorinated ethylene propylene (FEP) film is an attractive candidate for mitigating target debris in high-power laser systems due to its remarkable advantages such as low cost, low absorption, and high damage threshold. However, the inert surface with bad wettability presents an enormous challenge to realize optical antireflection. In this Letter, we experimentally demonstrate that broadband antireflection of FEP film can be achieved through combining oxygen plasma treatment and solgel coating techniques. By optimizing the plasma treating time and withdrawal rate during the coating process, the treated FEP film has 4.7% enhanced transmittance compared to the untreated sample. In this case, transmittance over 99% with wide wave bands ranging from 600 to 950nm is achieved. The mechanism of broadband antireflection was revealed by investigating the fluorocarbon groups on the FEP surface. The applicable wave band of antireflective FEP film can be designed at will by changing plasma-treating conditions, which could open up a new avenue in the field of laser debris mitigation.

Process study about silica anti-reflection coatings prepared by sol–gel method for cadmium telluride solar cells

Silica (SiO2) thin films with different refractive indexes as the anti-reflection coating for cadmium telluride (CdTe) solar cells were prepared by sol–gel method in this paper. In order to obtain the preparation process of SiO2 films with suitable refractive index, the different hydrolysis processes relied on the acid-base environment as well as the ratio of reactants was studied, respectively. It mainly includes that (I) the gel growth model in hydrogen or hydroxide ion environment provided by hydrochloric and ammonia. (II) The ratio of solvent, precursor and catalyst under base catalysis. (III) The weight and amount of polyethylene glycol molecular which is an additive agent to increase the porosity of sol film under acid catalysis. Based on the results above, a monolayer SiO2 coating with optimized refractive index was applied onto the glass substrate of CdTe solar cell, and the quantum efficiency has been enhanced at the band of 400–800 nm. After that, multilayer SiO2 coatings with high–low refractive indexes were designed according to the Fresnel theory to achieve wider spectrum (390–870 nm) enhancement. The broadband anti-reflection coatings (BARCs) were deposited on CdTe solar cell. The results were not consistent with expectations, which required further study about process matching between BARCs and device manufacture.

Pushing the Limits of Broadband and High-Frequency Metamaterial Silicon Antireflection Coatings

Broadband refractive optics realized from high index materials provide compelling design solutions for the next generation of observatories for the Cosmic Microwave Background (CMB), and for sub-millimeter astronomy. In this paper, work is presented which extends the state of the art in silicon lenses with metamaterial antireflection (AR) coatings towards larger bandwidth and higher frequency operation. Examples presented include octave bandwidth coatings with less than $0.5\%$ reflection, a prototype 4:1 bandwidth coating, and a coating optimized for 1.4 THz. For these coatings the detailed design, fabrication and testing processes are described as well as the inherent performance trade offs.

Design and fabrication of PbTe/BaF2 hydrophobic high-efficiency broad-band antireflection coating on Ge substrate in long-wave infrared region

Hydrophobic high efficiency broad-band antireflection (BBAR) coating in long-wave infrared (LWIR) region (7.5–11 µm) was designed and fabricated on germanium substrate by PVD technique. The multi-layer coating materials used in the design were Lead Telluride (PbTe) as high index material and Barium Fluoride (BaF2) as low index material. Hydrophobic high-efficiency BBAR coating with an average water contact angle of 102° was obtained only by the intrinsic surface roughness of BaF2 layer and without any surface treatment. AFM and FTIR spectrophotometer were used to investigate the surface topography and average reflection of the multi-layer coating, respectively. The average roughness obtained about 13 nm. The average reflection of the hydrophobic high-efficiency BBAR coating was 0.72% in the wavelength range from 7.5 to 11 µm that leads to eliminate Narcissus effect. Infrared optical windows and domes, having hydrophobic BBAR coatings, can effectively be applicable to humid or marine environments.

Preparation of broadband antireflective coatings with ultra-low refractive index layer by sol-gel method

In this paper, a novel long-time refluxing process has been applied for ultra-low refractive index antireflective coatings preparation. Coating with refractive index of 1.12 was obtained. Double layer antireflective coatings with refractive index of 1.12 for the top layer and that of 1.30–1.40 for the bottom layer have been fabricated on soda-lime glasses. By adjusting the preparation parameters, the numerical difference between peak and valley transmittance value gradually reduced, i.e. the broadband antireflective coatings were prepared. The light transmittance of double layer antireflective coatings achieved to 99.04%, while the average transmittance attained to 95.49% in 300–1200 nm wavelength.

Fabrication of robust, self-cleaning, broadband TiO2[sbnd]SiO2 double-layer antireflective coatings with closed-pore structure through a surface sol-gel process

Multifunctional antireflective (AR) coatings are widely used in fields of optical devices, flat-panel displays, windows and solar cell devices. In this paper, silica (SiO2) and titanium dioxide (TiO2) nanomaterials were used as building blocks to construct multifunctional AR coatings. The surface of the SiO2 coating derived from SiO2 nanoparticles consists of a large number of nanopores, and its refractive index is tuned conveniently from 1.19 to 1.45 by controlled incorporation of TiO2 into these nanopores through a surface sol-gel process. By tuning the coating structure, substrates with double-layer TiO2SiO2 coatings presented a maxium transmittance of 98.4% and average transmittance as high as 97.7% over the visible and near infrared region. The nanocomposite TiO2SiO2 coatings demonstrated a good hydrophilicity, favorable robustness and high photocatalytic activity. In addition, the double-layer TiO2SiO2 coatings had a long-term durability after accelerated-aging test, while the porous SiO2 coatings with a great of open nanopores showed a severe decrease. This double-layer TiO2SiO2 coatings have the benefit of designing, fabricating, and developing multifunctional AR coatings with broadband transmittance, high photocatalytic activity and high environmental stability, which makes them extremely appealing for applications in lenses, solar photovoltaic cells, etc.. Moreover, this work not only provides an alternative way to tune the refractive indices of AR coatings, but also opens up a new avenue towards broadband AR coatings.

Preparation and stability study of broadband anti-reflection coatings and application research for CdTe solar cell

Reflection loss is essential factor to limit the efficiency of all of photovoltaic devices. Glass substrate that with no trapping mechanism to reduce the reflection of light as most CdTe commercial thin film solar cells are manufactured. The absorption band gap of CdTe devices is 387–850 nm, to minimize the losses, a broadband anti-reflection coating that its transmittance must as high as possible at 390–850 nm is designed with TFCALC modeling software and deposited with sol-gel method and dip-coatings technique on both sides of the glass substrate. See from the transmittance spectrum of broadband anti-reflection coatings (BARCs) is more than 98% at the band of 390–870 nm which is the same as the band gap of CdTe photovoltaic cells and its maximum transmittance is 99.70%. In addition to matched band and high transmittance, the durability of BARCs is crucial for applying on CdTe devices. It presents that BARCs that uses trimethyl chlorosilane (TMCS) to optimize the hydrophilic of the surface of BARCs is relatively stable from the examination of Contact angle and Environmental include damp heat, ultraviolet radiation and light-tact. The BARCs can well apply on CdTe modules that the optical property of BARCs is not affected by the preparation process of CdTe solar cell with simulation.

Broadband multilayer anti-reflection coating for mid-infrared range from 7 μm to 12 μm.

We describe a design concept for broadband anti-reflection coatings for the mid-infrared that allows thinner film thickness and characterize its properties in the mid-infrared range from 7μm to 12μm. Two demonstrator coatings comprising zinc sulfide, yttrium fluoride, and germanium, all of which are deposited by electron beam evaporation on indium phosphide substrates, are optimized for the 7-12μm and the 10-12μm ranges. They exhibit less than 1.0% reflection over the target wavelength ranges with notably thin coating thickness.