Antireflection Properties Research Articles

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.

Design of multilayer planar film structures for near-perfect absorption in the visible to near-infrared.

In this work, a near-perfect broadband absorber, consisting of Fe, MgF2, Fe, TiO2 and MgF2 planar film, is proposed and investigated through simulations and experiments. The Fe material is first applied in the multilayer film structure, and it is proved to be more favorable for achieving broadband absorption. MgF2 and TiO2 are chosen as anti-reflection coatings to decrease unwanted reflections. The proposed absorber is optimized by employing a hybrid numerical method combining the transfer matrix method (TMM) and the genetic algorithm (GA). Under normal incidence conditions, the average absorption of the absorber is 97.6% in the range of 400 to 1400 nm. The finite difference time domain (FDTD) method and phase analysis reveal that the anti-reflection property and the Fabry-Perot resonance result in broadband absorption performance. Furthermore, when an additional Fe-MgF2 layer is inserted on the bottom Fe layer, an average absorption of 97.9% in the range of 400 to 2000 nm can be achieved. Our approach could be of vital significance for numerous applications involving solar energy.

Modified polymer nanopillars array for enhanced light trapping on large area

ABSTRACT Electroless plating is used to enhance the strength of anodised aluminium oxide (AAO) which can be further utilised as a mould to fabricate the structures on large area of polymer for anti-reflection properties. Nanopillars of high aspect ratio are fabricated on polymer (polystyrene) sheet by hot embossing process which has ensured repeatability with precision and high throughput. The height of nanopillars matches the depth of the mould cavity. The enhanced light trapping performance is attributed to the high aspect ratio nanopillars with cup-shaped top surface.

Effect of Au film mask on antiwetting and antireflection properties of nanostructural polymer by plasma nanotexturing

Capacitively coupled radiofrequency plasma nanotexturing assisted by an Au film mask is carried out to fabricate the fluorocarbon-film decorated nanowires bundles from the semicrystalline polyethylene (PE) and amorphous PolyMethyl methacrylate (PMMA) subatrates. The spacing distance and height of the nanowires in a bundle on the PE and PMMA substrates are adjusted by the thickness of Au film mask. The complete rebound phenomenon occurs when the droplets impact with a high speed on the nanowire bundles. The nanowire bundles exhibit an improved superhydrophobicity. The narrow spacing distance between the nanowires is beneficial to the antiwetting of superhydrophobic surface. The low reflectivity of the nanowire bundles is also obtained with an incident light wavelength from 400 to 2000 nm. The antireflection property of the nanowire bundles is caused by the high height of nanowires in a bundle. The nanowire bundles on the PE and PMMA substrates prepared by the plasma nanotexturing assisted by the Au film mask have the excellent antiwetting and antireflection properties.

Properties of PEDOT:PSS on Black Silicon and Hybrid Textured Surfaces

This work investigates properties of Poly (3,4-ethylenedioxythiophene)–poly (styrene sulfonate) (PEDOT:PSS) on black silicon (nanotextured) and hybrid textured (nanotextured/microtextured) surfaces. The black silicon (b-Si) surface is fabricated using two-step metal-assisted chemical etching (MACE) process on crystalline silicon (c-Si) while the hybrid textures are fabricated using two-step MACE process on microscale pyramids. With PEDOT:PSS, weighted average reflection (WAR) reduces from 9.2% to 7.7% for b-Si and from 7.2% to 5.2% for hybrid textures. This is due to the anti-reflective (AR) property of the polymer. Electrical characterizations of the PEDOT:PSS layer reveal higher sheet resistance (Rs), lower hole concentration (nh) and improved mobility (μh) with the presence of the surface textures on c-Si, in comparison to the results from planar c-Si reference.

Anti-Reflective Zeolite Coating for Implantable Bioelectronic Devices.

Since sunlight is one of the most easily available and clean energy supplies, solar cell development and the improvement of its conversion efficiency represent a highly interesting topic. Superficial light reflection is one of the limiting factors of the photovoltaic cells (PV) efficiency. To this end, interfacial layer with anti-reflective properties reduces this phenomenon, improving the energy potentially available for transduction. Nanoporous materials, because of the correlation between the refractive index and the porosity, allow low reflection, improving light transmission through the coating. In this work, anti-reflective coatings (ARCs) deposited on commercial PV cells, which were fabricated using two different Linde Type A (LTA) zeolites (type 3A and 4A), have been investigated. The proposed technique allows an easier deposition of a zeolite-based mixture, avoiding the use of chemicals and elevated temperature calcination processes. Results using radiation in the range 470–610 nm evidenced substantial enhancement of the fill factor, with maximum achieved values of over 40%. At 590 and 610 nm, which are the most interesting bands for implantable devices, FF is improved, with a maximum of 22% and 10%, respectively. ARCs differences are mostly related to the morphology of the zeolite powder used, which resulted in thicker and rougher coatings using zeolite 3A. The proposed approach allows a simple and reliable deposition technique, which can be of interest for implantable medical devices.

Diamond-Like Carbon Film Deposited via Electrochemical Route for Antireflection Applications in Photovoltaic

Diamond-like carbon (DLC) is widely studied for various applications such as optoelectronics, energy, aerospace, and medicine. It’s hard, chemically inert, and optically transparent. Due to its superior antireflection properties, DLC films are more suited for photovoltaic technology. Here in this work, we report a facile, high speed, and low-cost method of DLC film development from an aqueous solution via electrodeposition. The effect of applied voltage and solution concentration on the properties of DLC film was analyzed. The morphology, shape, and uniformity of the DLCs were analyzed with optical and electron microscopies. The presence of C-H, C-C, and C=C bonds in the DLC films was confirmed from FTIR and Raman spectroscopies. Whereas the optical behavior was analyzed with a UV-Vis-NIR spectrophotometer. The DLC films were deposited at 2.7 V, 4V, 6V, 8V, and 10V, and it was shown that for a fixed electrolyte concentration and electrode spacing, the applied voltage can be adjusted to obtain varying deposition rates. Likewise, the solution concentration was varied in the 2 vol.% to 10 vol.%, and it was demonstrated that by increasing the solution concentration the deposition rate increases. The increase in the deposition rate was evidenced by an increase in the deposition current as well as the roughness of the films. It was noticed that smaller-sized, well-defined, and more uniform DLC films were obtained at lower concentrations and low voltage levels. The band gap was varied between 2.91ev to 3.39ev. It was clearly shown that reflection reduced remarkably after depositing DLC film on the substrate surface. This work demonstrates that DLC film has a potential to utilized as an antireflection layer in photovoltaic application.

Taguchi method and Box-Behnken design approach for process parameter optimization of magnetite (Fe3O4) coating developed on stainless steel 410 grade by hot alkaline treatment

The blackening of materials is widely used in the automobile industry, defense applications, aerospace applications, and solar applications. Methods such as electroless chemical process, conversion coating, physical vapor deposition, chemical vapor deposition, and diamond-like carbon are some of the commonly employed techniques to produce black coatings on various metals. Hot aqueous alkaline treatment is a chemical conversion coating process. In this study, hot alkaline treatment is used to blacken surgical equipment made of stainless steel 410, which is a novel approach. The effect of process variables such as immersion time, salt solution temperature, and wt% of sodium dichromate on the anti-reflective property of ferrous ferric oxide (magnetite, Fe3O4) coating has been optimized using the Taguchi method and response surface methodology. The experiments were designed using a Taguchi orthogonal array and a Box-Behnken design. The influences of coating parameters on average percentage reflectance were quantified by the signal-to-noise ratio, main effect plot, analysis of variance, and two-dimensional and three-dimensional plots. The comparison of experimental and confirmatory tests shows that both procedures optimized the parameters successfully. The lowest average percentage reflectance value of 8.013% was obtained at 56.976 min immersion time, 124.998°C salt solution temperature, and 348.689 g/l wt% of sodium dichromate in the composition by Box-Behnken design methodology.

Dual-functional antireflection and down-shifting coating for Si solar cells

It is important for Si solar cells to make full use of sunlight by minimizing spectral mismatch and reducing light reflection. Herein, ZnO nanoparticles coating, which has a dual function of antireflection and down-shifting, was prepared on Si substrate by the sol-gel method. The obtained ZnO coating has a uniform structure, low roughness, and good mechanical robustness. The ZnO coating on Si substrate has a remarkable antireflection enhancement effect, with an average reflectance was 10.83% at the 400 ~ 1100 nm band, which was 19.43% lower than that of the uncoated Si substrate. Moreover, ZnO nanoparticles coatings can absorb light before 400 nm and convert it to about 527 nm, showing an apparent down-shifting effect. The photocurrent of the coated solar cells was significantly improved, with an average photocurrent increase of 21% at 300–800 nm. The coatings prepared herein with both antireflection and down-shifting luminescence properties are important for improving the photovoltaic conversion efficiency of solar cells.

Reducing Optical Reflection Loss for Perovskite Solar Cells Via Printable Mesoporous SiO2 Antireflection Coatings

AbstractThe power conversion efficiency (PCE) of single‐junction perovskite solar cells (PSCs) is being rapidly promoted towards their theoretical limit, with a certified value of 25.7%. Reducing optical loss will further contribute to PCE improvement. Here, the optical loss including reflection loss, absorption loss, and transmission loss in printable mesoscopic perovskite solar cells (p‐MPSCs) is analyzed. A printable mesoporous SiO2 antireflection coating for improving the transmittance of the fluorine‐doped tin oxide (FTO) glass substrate by reducing optical reflection at the air/glass interface is reported. With modulated porosity and thickness, the mesoporous SiO2 film constructs a graded refractive index interface and increases the transmittance of FTO glass by ≈2%–4% in the spectral range of 350–800 nm at normal incident angle with the highest transmittance improved from 85% to 89%. The SiO2 coating also exhibits wide‐angle and broadband antireflection properties. The coatings successfully help p‐MPSCs obtain about an average 3% enhancement in the short‐circuit current density (JSC) and PCE. This study demonstrates the necessity of optical management for efficient solar cells and provides a cost‐effective and scalable antireflection coating for the future realistic application of PSCs.

Germany: Orion – carbon black

Glass samples have been processed by a single-step self-masking RIE (Reactive Ion Etching) process to obtain random subwavelength structures (SWSs), which mimic anti-reflective and anti-soiling patterns present in nature. The SWSs fabricated on glass provide an excellent broadband omnidirectional anti-reflective (AR) property (¡1% absolute reflectance) in the spectral region (300–1200) nm due to the graded refractive index that these SWS produce in the air–glass interface, reducing the reflectance. Moreover, these SWSs increase the roughness of the glass surface enhancing its wettability and anti-soiling properties. In order to quantify the performance improvement of photovoltaic devices when using these structured glasses as front cover, commercial PERC (Passivated Emitter and Rear Contact) solar cells have been laminated with these structured glasses using the standard configuration (glass/EVA/Solar Cell/EVA/backsheet) and their electrical parameters such as I–V curve, spectral response, and IAM (Incidence Angle Modifier) factor have characterized.

Anti-Reflective superhydrophobic coatings with excellent durable and Self-cleaning properties for solar cells

Photovoltaic modules are long-term exposed outdoors, and the surfaces are easily covered by dust, which seriously affects the power generation efficiency and increases the workload of maintenance. An anti-reflective and superhydrophobic coating with excellent durable and self-cleaning properties was proposed to improve this problem. The prepared coating has multiple structures to improve the durability. Firstly, the coating consists of a double-layer film structure, and the bottom layer is connected to the substrate through covalent bonding to improve the adhesion of the coatings; secondly, the hydrophobic silica particles in the top layer can be embedded in the pore structure of the bottom layer to improve the connection strength between the top and bottom layers; thirdly, hydrophobic silica particles in the top layer are fixed in a three-dimensional mesh structure formed by long-chain silica, which can improve the mechanical stability of the coatings. In addition, the preparation conditions of the hydrophobic particulate silica sols and the ratio of long-chain silica sol in the top layer solution can be adjusted to control the durable, anti-reflective, and superhydrophobic properties of the coatings. The experimental results indicate that the transmittance of the coated glass is increased by 5 % compared to the bare glass, and the coating has 6H pencil hardness test grade and 5B tape adhesion test grade. The maximum output power of the coated PV modules can be increased by 5.67 %. After simulating dust accumulation and rainfall, the power of coated and uncoated photovoltaic modules can be restored to 96.6 % and 83.0 % respectively, indicating that the prepared coating also has excellent self-cleaning ability.

Mg2Si is the new black: Introducing a black silicide with >95% average absorption at 200–1800 nm wavelengths

Textured silicon surface structures, in particular black silicon (b-Si), open up possibilities for Si-based solar cells and photodetectors to be extremely thin and highly sensitive owing to perfect light-trapping and antireflection properties. However, near-infrared (NIR) performance of bare b-Si is limited by Si band gap of 1.12 eV. This work reports a simple method to increase NIR absorption of b-Si by in vacuo silicidation with magnesium. Obtained Mg2Si/b-Si heterostructure has a complex geometry where b-Si nanocones are covered by Mg2Si shells and crowned with flake-like Mg2Si hexagons. After growth optimization, Mg2Si cover atop b-Si resulted in 5-fold lower total reflectivity (3.7%) and optical absorption to be no lower than 88% over 200–1800 nm spectral range. More importantly, Mg2Si/b-Si heterostructure is more adjusted to match AM-1.5 solar spectrum with theoretically higher photogenerated current density. The maximal advantage is demonstrated in the NIR region compared to bare b-Si in full accordance with one‘s expectations about NIR-sensitive narrow band gap (0.75 eV) semiconductor with high absorption coefficient, which is Mg2Si. Results of optical simulation confirmed the superiority of Mg2Si/b-Si NIR performance. Therefore, this new wide-band optical absorber called black silicide proved rather competitive alongside state-of-the-art approaches to extend b-Si spectral blackness.

Femtosecond Laser Processing Technology for Anti-Reflection Surfaces of Hard Materials.

The anti-reflection properties of hard material surfaces are of great significance in the fields of infrared imaging, optoelectronic devices, and aerospace. Femtosecond laser processing has drawn a lot of attentions in the field of optics as an innovative, efficient, and green micro-nano processing method. The anti-reflection surface prepared on hard materials by femtosecond laser processing technology has good anti-reflection properties under a broad spectrum with all angles, effectively suppresses reflection, and improves light transmittance/absorption. In this review, the recent advances on femtosecond laser processing of anti-reflection surfaces on hard materials are summarized. The principle of anti-reflection structure and the selection of anti-reflection materials in different applications are elaborated upon. Finally, the limitations and challenges of the current anti-reflection surface are discussed, and the future development trend of the anti-reflection surface are prospected.

Highly Water-Repellent and Anti-Reflective Glass Based on a Hierarchical Nanoporous Layer

Optically anti-reflective and water-repellent glass is required for solar cell covers to improve power-generation efficiency due to transparency improvement and dirt removal. Research has been conducted in recent years on technologies that do not use fluorine materials. In this study, we focused on the anti-reflective properties and microstructure of hierarchical nanoporous layer (HNL) glass and used it as a substrate. As a result, we have achieved both strong anti-reflectivity and high water repellency on HNL glass by coating polydimethylsiloxane (PDMS) using baking and thermal chemical vapor deposition (CVD). The surfaces showed a significantly higher sliding velocity of water droplets than the PDMS-treated material on the flat glass plate. They also showed such water repellency that the droplets bounced off the surface.

Characterization of Calcium Phosphate Chitosan Nanocomposite as Plant Growth Promoter

In this study, calcium phosphate-chitosan nanocomposite (CaP-CS NC) was prepared by a convenient and affordable co-precipitation method, and the prepared NC was tested for agriculture application. Physico-chemicals analyses of the CaP-CS NC were conducted by X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-Vis) instruments to determine the structural characteristics, surface topology, chemical composition, function group, and optical properties. The XRD pattern of CaP-CS NC revealed that the average crystallite size was 43 nm. The SEM images showed agglomeration of the CaP-CS NC with a rod-like shape. The EDS spectrum of the CaP-CS NC indicated the presence of Ca, P, O, and N elements. FTIR displayed vibrational peaks for the active functional group such as carboxylic (C=O), amines (N-H), hydroxyl (O-H), and alkyne (C-H). Furthermore, the spectrum of CaP-CS NC showed the bending mode of phosphates at 588.37 cm-1 and 508.45 cm-1. The UV-Vis-NIR spectrum of the prepared nanocomposite indicates the anti-reflection properties, which might be useful in solar cell applications to increase the efficiency of the solar cell. In addition, the prepared CaP-CS NC was tested for the plant growth stimulator properties at the lab scale level, wherein it exhibited substantial growth. Accordingly, the current study suggests that the prepared CaP-CS NC could be used as a plant growth promoter.

Tunable antireflective characteristics enabled by small yellow leafhopper-inspired soccer ball-shaped structure arrays

BackgroundNowadays, tunable antireflective characteristics have attracted considerable attention due to growing demands in next-generation optical energy-related fields. MethodBioinspired by the distinctive structural geometry on small yellow leafhopper wings, this study reports reversibly switchable antireflective characteristics enabled by ambient-temperature shape memory polymer-based soccer ball-shaped structure arrays with multilayer porous structures underneath. Significant findsThe resulting structures behave a broadband omnidirectional antireflection performance, where the average reflectance in the visible spectrum can even be reduced by 22% for an incident angle of 75º. Interestingly, the structures can be instantaneously deformed or recovered through applying external stimuli in ambient environments. The antireflective property switches associated with the shape memory transitions deliver vast opportunities in developing smart optical devices. Moreover, the structure-shape effect and reversibility on the antireflective properties are systematically assessed in the research.

Fabrication of Robust, Anti-reflective, Transparent Superhydrophobic Coatings with a Micropatterned Multilayer Structure.

Transparent superhydrophobic coatings with mechanical stability, self-cleaning function, and anti-reflective property have drawn much attention due to the great potential in a variety of real-world applications. In this work, we develop an ingenious approach to construct micropatterned transparent superhydrophobic coatings with a multilayer structure (water contact angle ∼153.6°, sliding angle ∼3.2°). A micropatterned ultraviolet-cured resist frame facilitates durability, while the modified silica nanoparticles, which are housed within the micro-cavities and bonded by an epoxy-based adhesive, impart superhydrophobicity. The micropatterned multilayer surface could endure sandpaper abrasion while maintaining satisfactory hydrophobicity. The prepared surfaces also retain the excellent water repellency after water jet impact, acid submerging, and mechanical bending, suggesting that they are sustainable in the case of adverse conditions and can be integrated with objects with non-flat geometries. Further, the superhydrophobic coatings exhibit an anti-reflection property while preserving high transparency. Taken together, we envision that the design strategies here can offer a practicable route to produce transparent superhydrophobic coatings for diverse outdoor applications.

Fabrication of moth-eye patterned TiO2 active layers for high energy efficiency and current density of dye-sensitized solar cells

Past two decades have shown the unprecedentedly rapid emergence of dye-sensitized solar cells (DSSCs) that are efficient, inexpensive, and eco-friendly. However, structural studies of the internal solar cells have not made much progress because of the high cost and complexity of the fabrication. In this study, therefore, we designed and fabricated a moth-eye patterned TiO2 layer as a working electrode using a soft lithography method with polystyrene (PS) monolayer, and the moth-eye patterned TiO2 active layers were constructed using a polydimethylsiloxane (PDMS) stamp via inverse honeycomb patterning having various PS beads of 400, 800, 1200 and 1600 nm. For the 1600 nm patterned stamp, Jsc is higher for moth-eye patterned TiO2 (13.63 mA/cm2) than that for flat TiO2 (11.09 mA/cm2), which results in a higher power efficiency of 7.66% rather than 6.40%. This result found an increment of around 23% in current density and 20% in energy conversion efficiency, mainly because of greater light-harvesting effect by its structural anti-reflective property.

High Anti-Reflection Large-Scale Cup-Shaped Nano-Pillar Arrays via Thin Film Anodic Aluminum Oxide Replication.

Surface anti-reflection (AR) with nanometer-scaled texture has shown excellent light trapping performance involving optical devices. In this work, we developed a simple and lithography-free structure replication process to obtain large scale surface cup-shaped nano-pillar (CSNP) arrays for the first time. A method of depositing was used for pattern transfer based on PMMA pre-coated through-hole anodic aluminum oxide (AAO) thin film (~500 nm), and eventually, the uniformity of the transferred nanostructures was guaranteed. From the spectrum (250 nm~2000 nm) dependent measurements, the CSNP nanostructured Si showed excellent AR performance when compared with that of the single-polished Si. Moreover, the CSNP was found to be polarization insensitive and less dependent on incidence angles (≤80°) over the whole spectrum. To further prove the excellent antireflective properties of the CSNP structure, thin film solar cell models were built and studied. The maximum value of Jph for CSNP solar cells shows obvious improvement comparing with that of the cylinder, cone and parabola structured ones. Specifically, in comparison with the optimized Si3N4 thin film solar cell, an increment of 54.64% has been achieved for the CSNP thin film solar cell.