Broadband Antireflection Coatings Research Articles

Design of Broadband and Wide-angle HLHL Antireflective Coatings for Triple Junction Solar Cells

Design of Broadband and Wide-angle HLHL Antireflective Coatings for Triple Junction Solar Cells

Plasma-enhanced atomic-layer-deposited HfO2–SiO2 nanolaminates for broadband antireflection coatings

The ever-increasing demand for broadband antireflection (AR) coatings has led to a growing interest in nanolaminates (NLs) with tunable properties. However, achieving excellent optical performance in NLs can be challenging due to multiple interfaces and a rather thin sublayer. In this study, we systematically investigated the factor that deteriorates the optical performance, focusing on the sublayer thickness deviation, sublayer n deviation, and interfacial diffusion, to correct the n-profiles of NLs. A pre-correction strategy for the AR coating design is proposed and experimentally demonstrated via plasma-enhanced atomic layer deposition. The excellent fit of the spectrum demonstrates that the proposed design strategy can benefit structure-sensitive NL-based coatings.

Research on Broadband Antireflection Coat-ings in the Visible and Near-Infrared Spectral Ranges

Research on Broadband Antireflection Coat-ings in the Visible and Near-Infrared Spectral Ranges

Designing multifunctional silica coatings for enhanced broadband antireflection and microfiber contamination sensing

Multifunctional silica coatings find diverse applications in solar energy conversion and pollution monitoring sensors due to their suitability for mass manufacturing. However, the challenge lies in producing robust silica coatings on a large scale with tunable refractive index. This work presents a two-step acid/base catalyzed sol–gel process for synthesizing multifunctional silica coatings with adjustable refractive index. The coatings' porous microstructure allows them to be used as double-layer broadband antireflective coatings and enhances the sensitivity of contamination sensors. The optimized double-layer coatings, designed using computer-aided techniques, demonstrate excellent broadband antireflective performance in the visible regions and high environmental durability. They achieve a maximum transmittance of 99.87% at 591 nm, with an average transmittance of 99.40% in the visible region (400–800 nm) and 98.63% from 400 nm to 1100 nm. Additionally, the coatings exhibit robust abrasion resistance and enhanced surface hydrophobicity with a water contact angle increased from 30° to 126° through HMDS treatment. This work investigated the particle growth mechanism and the relationship between silica nanoparticle microstructure and antireflective coating properties. Furthermore, the coatings' presence of abundant micropores allows successful application onto microfiber contamination sensors, the additional loss increases from 26.40 dB to 37.69 dB over 140 min and decreases to 31.55 dB within one minute, demonstrating rapid adsorption and desorption rates. The work successfully achieves a wide range of adjustable refractive index while maintaining excellent mechanical and optical properties, addressing the traditional trade-off between high porosity and poor mechanical stability. These rationally designed multifunctional silica coatings hold great potential for high-quality broadband antireflection and high sensitivity in microfiber contamination sensing.

Broadband antireflective coatings in the optical communication band deposited by ion-assisted reactive magnetron sputtering

With the rapid development of silicon-based photonics, broadband anti-reflection coatings for the optical communication band are desired. Silica and silicon nitride with tunable refractive index were employed in anti-reflection coatings, which were deposited by ion-assisted reactive magnetron sputtering. The results showed that the average reflectance of 0.74% for single-layer coatings and below 0.12% after optimization for each sub-band. With the insertion layer, the anti-reflection band broadened and covered the optical communication band. Multi-layer coatings’ average reflectance was reduced to within 0.35%, with only 0.19% for four-layer coatings. Both single-layer and multi-layer coatings exhibited impressive deposition quality. For single-layer and multi-layer coatings, no obvious defects were found on the surface and cross-sectional morphology, and the roughness remained within 0.5 nm. In this work, anti-reflection coatings were deposited by ion-assisted reflective magnetron sputtering, featuring broadband low reflectance and high deposition quality, which is suitable for serving optical communication devices such as photodetectors and wide-tunable lasers.

Nanopatterned SiNx Broadband Antireflection Coating for Planar Silicon Solar Cells

Crystalline Si solar cells based on thin wafers, with thicknesses in the range of 5–50 μm, can find applications in a wide range of markets where flexibility and bendability are important. For these cells, avoiding standard macroscopic texture is desirable to increase structural integrity. Herein, a nanopatterned SiN x antireflection (AR) coating that consists of 174 nm‐radius and 118 nm‐high SiN x nanodisks arranged in a square lattice on a thin (59 nm) SiN x layer is introduced. This geometry combines Fabry–Pérot AR and forward scattering by a resonant Mie mode to achieve high transmission into the Si absorber over a broad spectral band. The nanostructured coating is patterned on a commercial interdigitated‐back‐contact (IBC) Si solar cell, experimentally demonstrating a short‐circuit current density (J sc) of 36.9 mA cm−2, 2.3 mA cm−2 higher than for a single‐layer AR coated cell, and an efficiency of 16.3% at a thickness of around 100 μm. It is shown that light incoupling efficiency is comparable to that of pyramidal texturing, while the absorption in the infrared is lower, due to less‐effective light trapping. Overall, nanopatterned SiN x broadband AR coatings are an appealing option for improving light management in ultrathin solar cells and other optoelectronic devices.

Studies on Femtosecond Laser Textured Broadband Anti-reflective Hierarchical a-SiNx:H Thin Films for Photovoltaic Applications

Simple ultrafast laser writing for the fabrication of hierarchical silicon nitride (a-SiNx:H) microstructures is demonstrated as an effective antireflection coating. A wide range of Si-rich to N-rich a-SiNx:H thin films, having varied optical band gap (2.32–5.94 eV) and refractive index (2.8–1.7) of wavelength-ordered (∼λ/4) thickness, are deposited using the plasma-enhanced chemical vapor deposition technique. The high-intensity femtosecond laser (800 nm, 120 fs, 1 kHz) interaction with a-SiNx:H films resulted in diverse nano-/microstructures with systematic width and depth born out of nonlinear light–matter interactions. These experimentally demonstrated the extremely disordered micro–nano structures over a large area of ∼ 1 cm2 that exhibit significant light trapping and absorption capabilities over a broad spectral region of 200–1000 nm. The extensive reduction of reflection losses from 30 to 2.8% from pre- to post-laser texturing is a favorable condition for broadband anti-reflective coatings for enhanced light harvesting from prefabricated photovoltaic devices.

Broadband antireflection coatings with low polarization splitting.

A major problem for optical systems is the polarization splitting occurring at any interface in the event of oblique light. Low-index nanostructured silica layers were produced by overcoating an initial organic structure with silica and subsequent removal of the organic constituents. The nanostructured layers can be tailored to achieve defined low effective refractive indices down to 1.05. They can also be stacked together with homogeneous layers to produce broadband antireflective coatings with very low polarization splitting. Especially thin interlayers that separate the low-index structured layers turned out to be useful to optimize the polarization properties.

Elastic broadband antireflection coatings for flexible optics using multi-layered polymer thin films

A precise and facile fabrication of robust and flexible polymeric thin film multilayers with optical quality is achieved by iCVD.

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO2/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO2 sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO2 and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO2 and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO2/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO2/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO2/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.

Sol–gel-derived bayberry-like SiO2@TiO2 multifunctional antireflective coatings for enhancing photovoltaic power generation

Multifunctional coatings with broadband antireflective, durable, photocatalytic, and self-cleaning properties can enhance photovoltaic (PV) power generation by reducing the cleaning frequency and surface light reflection of PV modules. However, such coatings must be cost-effective and maintain their functional integrity under harsh outdoor environmental conditions. In this study, bayberry-like SiO2 @TiO2 nanoparticles were prepared by a sol–gel method, and their synthesis procedure and SiO2/TiO2 sol volume ratio were optimized based on the refractive index, transmittance distribution, and methylene blue degradation rate. Afterwards, three-layer gradient refractive index broadband antireflective coatings (TGBA) of the optimized SiO2 @TiO2 nanoparticles were simulated theoretically and systematically characterized by various experimental techniques. The average transmittance of TGBA-coated glass was 8.93% (380–1800 nm) higher than that of undipped glass, and the photocatalytic performance of TGBA was verified by studying methylene blue photodegradation. The self-cleaning performance of TGBA was assessed by outdoor exposure, multi-cycle ultraviolet (UV) irradiation, and dark storage. The durability of TGBA was evaluated by conducting hardness measurements, abrasion testing, thermal cycling, and damp heat tests. The external quantum efficiency and J–V curves of TGBA-coated PV mini-modules revealed that their short-circuit current densities and power conversion efficiencies were substantially higher than those of undipped modules. The proposed multifunctional coatings can enhance PV power generation in harsh environments.

Experimental optical and structural properties of ZnS, MgF2, Ta2O5, Al2O3 and TiO2 deposited by electron beam evaporation for optimum anti-reflective coating designs

MgF2, ZnS, Ta2O5, Al2O3 and TiO2 are some of the most common dielectric materials actually used in solar cells as anti-reflective coatings. For such purpose, they have been deposited by electron beam evaporation, which is one of the preferred technique in industrial settings. In this work we aim to understand the relationship between their optical and physical properties and deposition parameters and thicknesses, being spectroscopic ellipsometry the main technique used for such issue. MgF2 and ZnS have demonstrated rather good optical quality except for the thinnest samples. For Ta2O5, O2 flow during growth has been revealed as critical parameter for ensuring the proper composition of the layer. Al2O3 samples showed a very important amount of Al hydroxide, which is detrimental of the optical quality of these layers. TiO2 samples have also contamination problems, in this case due to oxygen species and Ti3+ oxide presence. For all these oxides, optical properties are clearly influenced by layer thickness. The layer optical parameters n and k have been determined as a function of wavelength (300–1800 nm) and validated against experimental reflectance and transmittance data. Finally, the impact that the proper knowledge of n and k values have when designing broad-band anti-reflective coatings for III-V multijunction solar cells is quantified in terms of short-circuit current relative increase.

Machine-learning reinforcement for optimizing multilayered thin films: applications in designing broadband antireflection coatings.

The design and fabrication of nanoscale multilayered thin films play an essential role in regulating the operation efficiency of sensitive optical sensors and filters. In this paper, we introduce a packaged tool that employs flexible electromagnetic calculation software with machine learning in order to find the optimized double-band antireflection coatings in intervals of wavelength from 3 to 5 µm and 8 to 12 µm. Instead of computing or modeling an extremely enormous set of thin film structures, this tool enhanced with machine learning can swiftly predict the optical properties of a given structure with >99.7% accuracy and a substantial reduction in computation costs. Furthermore, the tool includes two learning methods that can infer a global optimal structure or suitable local optimal ones. Specifically, these well-trained models provide the highest accurate double-band average transmission coefficient combined with the lowest number of layers or the thinnest total thickness starting from a reference multilayered structure. Finally, the more sophisticated enhancement method, called the double deep Q-learning network, exhibited the best performance in finding optimal antireflective multilayered structures with the highest double-band average transmission coefficient of about 98.95%.

Performance and durability of thin film solar cells via testing the abrasion resistance of broadband anti-reflection coatings

Reflection from the front glass of solar modules causes over 4% optical loss leading to a significant decrease in module efficiency. Single layer solution gelation (sol-gel) anti-reflective (AR) coatings are effective over a narrow range of wavelengths, whereas reflection losses can be reduced over a broader wavelength when multilayer broadband AR coatings are applied. In this work, three different multilayer AR coatings including 4-layer SiO2/ZrO2, 4-layer SiO2/ITO, and 6-layer SiO2/ZrO2 were deposited using magnetron sputtering. The abrasion resistance is important because the coatings will be subject to regular cleaning cycles. A variety of abraders including Felt pad, CS-10 and CS-8 under different loads are used. The optical performance and durability of these coatings were analyzed using a spectrophotometer, optical microscope, scanning electron microscope, and scanning white light interferometer. No damage was observed after abrasion of the coatings with a felt pad under 1 and 2 N loads. However, there was a slight increase in Weighted Average Reflection. When coatings were tested with CS-10 and CS-8 abraders, coatings with ZrO2 resulted in higher scratch resistance in comparison to coating with ITO. However, all-dielectric broadband AR coatings are more durable and have better optical performance compared to single layer sol-gel coatings.

Gradient refractive index-based broadband antireflective coatings and application in silicon solar modules

Gradient refractive index-based broadband antireflective coatings (ARCs) could potentially improve solar power production by reducing the amount of sunlight reflected from the surface of photovoltaic (PV) modules. In this study, refractive index tunable hybrid SiO2 sols with refractive indices from 1.20 to 1.44 were prepared by adjusting different volume ratios and pH values and mixing acid-catalyzed SiO2 with base-catalyzed SiO2. Based on Essential Macleod simulation, five-layer graded refractive index broadband ARCs (FGBA) (n = 1.10–1.44) were prepared using hybrid sols derived from the sol-gel method as the building blocks. The morphological and structural characteristics of each coating layer were systematically investigated with different characterization methods. The average transmittance of the glass substrate coated with FGBA reached 97.57% (380–1800 nm), much higher than that of soda-lime glass (88.49%), and exhibited excellent broadband transmittance enhancement performance. The hardness performance of FGBA reached 5H, and the water contact angle of the surface at annealed 400 °C was 149°. The FGBA exhibited excellent durability performance in thermal cycling tests and abrasion tests. According to the external quantum efficiency test and I-V and P-V curve results, the short-circuit current density gain was 4.83% and the photoelectric conversion efficiency gain was 5.81% for the mini-silicon cell solar modules dipped with FGBA, compared to the undipped modules. This indicates positive prospects for application in outdoor PV plants. Meanwhile, it proves that ARCs are essential components of PV modules and could provide additional solar gains.

λ/4–λ/4 Double-Layer Broadband Antireflective Coatings with Constant High Transmittance

Antireflective (AR) coatings can suppress the undesired interfacial Fresnel reflections, and they are widely used in optical devices and energy-related instruments. Conventional single-layer AR coatings, which only work at a single wavelength, encounter serious limitations in some practical applications because of their inherent properties. In this paper, λ/4–λ/4 double-layer antireflective (AR) coatings with constant high transmittance in a pre-determined wavelength range was prepared by the sol–gel method via acid-catalyzed and base-catalyzed SiO2 thin films. A double-layer antireflective coating with an almost constant transmittance value of 99.8% in the range of 550–700 nm was obtained, and the transmittance of this coating was higher than 99% in a wider range of 450–850 nm with a fluctuation of less than 1%. The coatings had good environmental stability and maintained constant high transmittance after two weeks of exposure in 50% humidity. The broadband AR coatings may have important applications in fields such as electroluminescent display.

Sol-gel synthesis of TiO2-SiO2 hybrid films with tunable refractive index for broadband antireflective coatings covering the visible range

Sol-gel synthesis of TiO2-SiO2 hybrid films with tunable refractive index for broadband antireflective coatings covering the visible range

Wide-angle broadband antireflection coatings based on boomerang-like alumina nanostructures in visible region

A novel boomerang-like alumina based antireflective coating with ultra-low reflectance has been produced for light incidence angles form 0 up to 45°. Boomerang-like alumina nanostructures have been fabricated on the BK7 glass substrates by dip-coating and surface modification via hot water treatment. To achieve the lowest residual reflectance, the effect of dip-coating rate and hot-water temperature in the treatment process has been investigated and optimized. To further investigate the boomerang-like alumina nanostructure and extract its graded refractive index profile by fitting the measured reflectance spectrum with the simulated one, a simulation based on the finite-difference time-domain (FDTD) method has been performed. The average reflectance measured at normal incidence for double-sided coated BK7 glass substrates is only 0.3% in the visible spectral region. Considering both sides, the average reflectance of the substrate decreased in the spectral range of 400–700 nm down to 0.4% at incidence angles of 45° by applying the boomerang-like alumina antireflection coatings. The optimized single layer boomerang-like alumina coating on the curved aspheric lens exhibited a low average reflectance of less than 0.14% and an average transmittance of above 99.3% at normal incidence. The presented process is a simple and cost-effective route towards broadband and omnidirectional antireflection coatings, which have promising potential to be applied on substrates having large scales with complex geometric shapes.

Facile synthesis of silica composite films with good mechanical property for spectrally broadband antireflection coatings

Recently, antireflection films have been widely used in the glass cover of solar cells because it can improve the solar transmittance obviously and are usually prepared by a facile sol-gel method and subsequent annealing process. However, the annealing process is complicated, leading to a large preparation cost. In order to solve the problem, a facile one-step annealing method under ammonia mixed atmosphere was developed to prepare the silica composite films with good mechanical property for antireflection coatings. The obtained silica composite film exhibited enhanced hardness of H and good solar transmittance increase of 3.74% in the wavelength range from 380 nm to 1100 nm compared with bare glass substrate. This is mainly because that the ethoxy in the films can be further hydrolyzed to hydroxyl in mixed ammonia gas atmosphere to intensify self-condensation reaction of hydroxyl in the film, leading to a reduced distance between particles for enhanced hardness and a decrease in the film thickness to increase solar transmittance. The increase of chemical connection between particles can improve the mechanical property of the film obviously. Therefore, this work can provide a facile way to simultaneously improve the mechanical performance and the visible transmittance of the antireflection film.

Embedding constructed refractive index graded antireflective coating with high abrasion resistance and environmental stability for polycarbonate glass

Polycarbonate (PC) is a durable and transparent optical plastic material commonly used as shatter-resistant alternative to traditional optical glass. Broadband antireflective (AR) coatings with excellent mechanical strength and environmental stability are essential for PC to achieve high light transmission and visual quality. In this work, chloroform vapor treatment was employed to partially embed the silica coating into the PC substrate for adhesion enhancement, which also divided the silica coating layer into bottom and middle layers with different refractive indices. The contact between the silica nanoparticles and the substrate was transformed from “point-contact” to “area-contact”, which enhanced the adhesion between coating and PC substrate. After the deposition of a top layer coating consisted of silica nanoparticles with smaller diameter, a triple-layer refractive index graded AR structure was constructed. Hexamethyldisilazane vapor surface modification was performed to decrease the surface free energy of top coating layer. The triple-layer coating coated PC exhibits superior antireflection property with an average reflectance of only 0.43% over a wide wavelength range of 400–1000 nm. After 100 times of friction or 5 months of exposure to a contaminated environment, the reflectance of coated PC shows barely noticeable difference, indicating its excellent mechanical strength and environmental stability.