Moth-eye Structure Research Articles

Fabrication of perovskite solar cell with high short-circuit current density (JSC) using moth-eye structure of SiOX

The performance of solar cells is determined by three factors: the open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF). The VOC and FF are determined by the material bandgap and the series/shunt resistance, respectively. However, JSC is determined by the amount of incident light in addition to the bandgap of the material. In this study, a moth-eye pattern was formed on a glass surface via direct printing to increase the amount of incident light and thus increase JSC. The moth-eye pattern is a typical antireflection pattern that reduces the reflection by gradually increasing the refractive index. A flat perovskite solar cell (F-PSC) and a moth-eye patterned perovskite solar cell (M-PSC) had JSC values of 23.70 and 25.50 mA/cm2, respectively. The power-conversion efficiencies of the F-PSC and M-PSC were 19.81% and 21.77%, respectively.

Transfer durability of high aspect ratio moth-eye structure on glassy carbon mold using release agent

The moth-eye structure is an anti-reflection structure that is expected to effective over a wide range of wavelengths and angles of incident light. In addition, since the moth-eye structure is a single layer, it can be easily replicated using ultraviolet nanoimprint lithography (UV-NIL). However the moth-eye structure is fragile, because it has a lot of small sharp needles, and it has been reported that the durability decreases as the aspect ratio increases. The moth-eye structure exhibits anti-reflection function even with a low aspect ratio, but in this study, a fragile moth-eye structure with a high aspect ratio was used to facilitate evaluation of the releasability. In this experiment, a glassy carbon mold with high aspect ratio was release treated using a newly developed release agent. Furthermore, using the “partial-filling method” led to a dramatic improvement in the durability when compared to the conventional method using repeated cycles of the UV-NIL machine.

Moth-eye shaped on-demand broadband and switchable perfect absorbers based on vanadium dioxide

Two biomimetic, moth-eye structure, perfect absorbers in the visible and near infrared regions are introduced and investigated. The moth-eye structure is made up of vanadium oxide (VO2), which is a phase change material that changes from an insulator state to a metallic state at around 85 °C. The VO2 structure sits on top of a sapphire (Al2O3) dielectric spacer layer, above a gold (Au) back reflector. Two perfect absorbers are designed, one with perfect absorption over an ultra-broadband range between 400 and 1,600 nm, for both the insulating and metallic phases, while the second can switch between being a perfect absorber or not in the range 1,000 and 1,600 nm. The absorption profiles and electric and magnetic fields are examined and discussed to provide insight into how absorbers function in the four different situations.

Newly Developed Broadband Antireflective Nanostructures by Coating a Low-Index MgF2 Film onto a SiO2 Moth-Eye Nanopattern.

A newly developed nanopatterned broadband antireflective (AR) coating was fabricated on the front side of a glass/indium tin oxide/perovskite solar cell (PSC) by depositing a single interference layer onto a two-dimensional (2D)-patterned moth-eye-like nanostructure. The optimized developed AR nanostructure was simulated in a finite-difference time domain analysis. To realize the simulated developed AR nanostructure, we controlled the SiO2 moth-eye structure with various diameters and heights and a MgF2 single layer with varying thicknesses by sequentially performing nanosphere lithography, reactive ion etching, and electron-beam evaporation. Optimization of the developed AR nanostructure, which has a 100 nm-thick MgF2 film coated onto the SiO2 moth-eye-like nanostructure (diameter 165 nm and height 400 nm), minimizes the reflection loss throughout the visible range. As a result, the short-circuit current density (JSC) of the newly AR-coated PSC increases by 11.80%, while the open-circuit voltage (VOC) remains nearly constant. Therefore, the power conversion efficiency of the newly developed AR-decorated PSC increases by 12.50%, from 18.21% for a control sample to 20.48% for the optimum AR-coated sample. These results indicate that the newly developed MgF2/SiO2 AR nanostructure can provide an advanced platform technology that reduces the Fresnel loss and therefore increases the possibility of the commercialization of glass-based PSCs.

Improvement of sensitivity of Si based infrared detector using moth eye structure

Improvement of sensitivity of Si based infrared detector using moth eye structure

Combined 'moth-eye' structured and graded index-layer anti-reflecting coating for high index glasses.

We present a hybrid antireflective coating (ARC) providing a complete continuous graded refractive index (GRIN) transition from a high-index substrate down to ambient air. The ARC comprises a first GRIN layer of dense silicon-oxy-nitride with a varying, height adjusted material composition. Secondly, a layer of quasi-periodic nanopillars imitating AR-"moth-eye structure" is added to the dense GRIN layer. Demonstrated on a high index glass with a refractive index of ne=1.73 the hybrid GRIN-ARC is applicable to a broad material selection and allows to eliminate any step-like transition up to a refractive index of the substrate of ∼2.0. The ARC offers antireflective properties for large incidence angles and over an extremely broad spectrum ranging from 400 nm up to 2.5 µm. Compared to the sole substrate, the hybrid GRIN-ARC results in an increase of transmittance of more than 10% in the maximum, and more than 6% in the peripheral regions of the spectrum.

Biomimetic Moth-eye Anti-reflective Poly-(methyl methacrylate) Nanostructural Coating

This study reports a simple imprinting method for the fabrication of biomimetic moth-eye antireflective polymethyl methacrylate (PMMA) nanostructures on the surface of the substrate. The antireflection structured silicon was obtained by Reactive Ion Etching (RIE) method. By using the antireflection structured silicon substrate as the imprinting stamp, the biomimetic moth-eye polymer structures showed tapered holes, whose depth and periodicity were around 780 nm and 580 nm, respectively. The reflectance of the resulting PMMA structures was reduced from 10% to less than 1% in the wavelength range from 300 nm to 1600 nm. This simple methodology can be scaled up via self-loading and nanoimprinting, which may have a promising application in optoelectronic devices and solar cells.

Optical performances of antireflective moth-eye structures. Comparison with standard vacuum antireflection coatings for application to outdoor lighting LEDs

Protection windows or lenses for outdoor white LED lighting generate high optical losses. Moth-eye structures elaborated by plasma etching offers a simple and low cost way for conferring broadband antireflective properties to protection optics. In this study, we optimized this technology and compared it to “standard” antireflective coatings elaborated by electron-beam evaporation: MgF2 single layer and broadband SiO2/ZrO2 multilayers.First glass substrates have been treated in order to compare nominal antireflective performances of these three vacuum technologies. Reactive ion etching process was then optimized for maximising transmission in normal and angular incidence in the wavelength range of white LEDs (400–750 nm). Best results with moth-eye structure were achieved on glass substrate etched on both sides: we measured 97,5% of white LED light transmission comparatively to 92% with untreated substrate. In a second time, the influence on antireflective properties of different ageing conditions generated during outdoor normative tests have been studied. Spectrophotometry and surface energy measurement highlighted the degradation of MgF2 coating under high humidity ageing conditions: we noticed a decrease of 1% of antireflective performance. Only moth-eye structures gave high environmental stability as they kept their white LED light transmission after ageing tests. In a third time, we introduced a novel comparison approach for such “technological study”: These three antireflective vacuum solutions were confronted from an economical and environmental impact point of view. Moth-eye structures elaborated by plasma etching offer a simple and low cost technology. Nevertheless, the use of greenhouse gas in this reactive ion etching process could be problematic for a large-scale industrialization.

Ultra-broadband all-dielectric metamaterial thermal emitter for passive radiative cooling.

Passive radiative cooling, which pumps heat to outer space via thermal radiation, has been a promising energy free technology to maintain the earth surface temperature. Nighttime radiative cooling technology is quite mature, while daytime radiative cooling still poses many challenges due to the requirement of minimization of incident solar absorption and maximization of the mid-infrared emissivity in the atmospheric transparency windows. However, the mid-infrared emissivity efficiency of natural materials is usually poor, providing a low cooling efficiency and the realization of a high performance daytime radiative cooler is still quite challenge. In this work, we design and numerically investigate a three dimensional (3D) all-dielectric pyramidal multilayer metamaterial (PMM), which not only avoids the problem of high absorptivity loss of metal materials to solar, but also provide extremely high infrared absorptivity due to the attenuation effect of moth-eye structure and the electromagnetic resonant absorption in the metamaterial, achieving the purpose of both extremely low solar spectrum absorption and strong infrared emissivity within the atmospheric windows under the direct sunlight. Eventually, our designed cooler presents the potential to achieve a net radiative cooling power exceeding 156 W/m2 at ambient temperature of 300 K under direct solar irradiation, leading to a temperature reduction of 42.4°C. At nighttime, the net cooling power is more than 199 W/m2 at ambient temperature, resulting in a temperature reduction of 58.5°C. Even considering the non-radiative heat exchange conditions, this metamaterial cooler can still cool down 9.6°C at the daytime and 12.3°C at the nighttime respectively. Therefore, this work further promotes the development of all-dielectric metamaterial based passive radiative coolers and is of great significance for energy conservation.

Mechanically robust antireflective moth-eye structures with a tailored coating of dielectric materials

Bioinspired moth-eye surface provides broadband antireflection features, which significantly enhance performances in optical components/devices. However, their practical uses are strictly limited due to poor mechanical stability of nano-patterns. In this study, we artificially engineered moth-eye structures on polycarbonate substrate through a thin-film coating of mechanically stable dielectric materials (i.e., Al2O3, Cr2O3, ZrO2, and TiO2 etc). The geometry of Al2O3-coated moth-eye surface is designed by considering the effective medium theory and confirmed by calculation of diffraction efficiency based on a rigorous coupled-wave analysis method. The tailored Al2O3-coating on moth eye surface exhibit the improved hardness while maintaining high optical transmittance.

Terahertz broadband anti-reflection moth-eye structures fabricated by femtosecond laser processing

Anti-reflection (AR) coatings aiming at the reduction of Fresnel reflection losses has come into demand in the terahertz (THz) region. Implementation of such a coating in practice is a difficult task, partially because the broad spectrum of the THz signal is difficult to control. Here, we propose and demonstrate a moth-eye AR structure capable of suppressing reflection losses in the range of 0.3 to 2.5 THz for high-resistivity silicon, resulting in a maximum transmission of 91%. The structure comprises of pyramid-like structures with a height of about 100 μm created on the material surface by femtosecond laser processing. We demonstrate experimentally and theoretically that such micromachining considerably increases transmittance of the silicon in the spectral range of 0.3–2.5 THz. We also demonstrate experimentally that such a structure allows one to improve performance of the THz source based on the LiNbO3 crystal.

Nanoimprinting reflow modified moth-eye structures in chalcogenide glass for enhanced broadband antireflection in the mid-infrared.

We report on the progress towards developing a new method for fabricating more efficient, broadband antireflective (AR) moth-eye structures in As2Se3 via a direct nanoimprinting technique. Thermal reflow is used during mold fabrication to reshape a conventional deep-ultraviolet lithography in order to promote a pattern transfer of "secant ogive"-like moth-eye structures. Once replicated, structures modified by reflow displayed greater AR efficiency compared to structures replicated by a conventional mold, achieving the highest spectrum-averaged transmittance improvement of 12.36% from 3.3 to 12 μm.

Fabrication of hierarchical moth-eye structures with durable superhydrophobic property for ultra-broadband visual and mid-infrared applications.

Multifunctional antireflective coatings have practical applications as important optical components in many fields, particularly for optical devices and imaging systems. However, a good antireflection application in the visible region is often unsatisfactory for mid-infrared devices, and the difficulty in obtaining multiple capabilities simultaneously is one of the main factors limiting their applications. In this work, hierarchical moth-eye structures with superhydrophobicity were fabricated via inductively coupled plasma reactive ion etching (ICP-RIE) using nanodisk-array masks, which were formed by three-beam laser interference lithography (LIL), for improving the ultra-broadband optical properties. The uniform antireflection efficiency, which was close to 1% reflectivity covering over the visible and mid-infrared wavelength range, was exhibited by the moth-eye structures with high-quality pillar arrays. Additionally, irregular nanostructures were tailored onto the top of the pillars to generate hierarchical moth-eye structures for simultaneously obtaining both the superhydrophobic and anticorrosive properties. The fabricated antireflective structures, with the features of self-cleaning and durability, have the advantage of being for long-term use in harsh environments.

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.

A large-area fabrication of moth-eye patterned Au/TiO2 gap-plasmon structure and its application to plasmonic solar water splitting

TiO2 is promising candidate for solar water splitting material. To enhance the insufficient absorption range of TiO2, TiO2 decorated with Au nanoparticles(AuNPs) structure have been studied intensively. This plasmonic approach can extend absorption range to visible light, but its incident photon-to-current conversion efficiency is still insufficient. Therefore, it is important to amplify surface plasmon resonance, obtained by using AuNPs. At the same time, for application to next-generation energy device, the way to improve this plasmonic effect needs to be available to large area fabrication, high reproducibility, low cost and so on. In this study, we successfully fabricated a three-dimensional (3D) moth-eye AuNP/TiO2/Au hierarchical structure for water splitting via direct printing method and deposition process. The proposed structure can effectively intensify the light–matter interaction owing to two mechanisms: Photonic mode light trapping attributed by moth-eye structure and enhanced surface plasmon resonance by gap-plasmon structure. Moth-eye structure, densely packed subwavelength-nanocone array, was easily fabricated by direct printing method. Using this moth-eye structure as a template, we effectively fabricated 3D moth-eye patterned gap-plasmon structure on 5 × 5 cm2. Compared with the two-dimensional (2D) AuNP/TiO2/Au absorber, the 3D moth-eye type absorber has higher absorption in entire 300–800 nm range. In accordance with this result, the 3D moth-eye absorber provides a photocurrent density of approximately 52.82 μA cm−2, which is approximately 2.3 times higher than that of the flat 2D TiO2/Au thin film (22.96 μA cm−2). Notably, it exhibits extraordinary enhancement of the photocurrent density—from 1.5 to 22.51 μA cm−2—in the visible range (≥420 nm).

Moth-eye Structured Polydimethylsiloxane Films for High-Efficiency Perovskite Solar Cells

HighlightsMoth-eye structured polydimethylsiloxane (PDMS) films with different sizes were fabricated to improve the efficiency of perovskite solar cells.The PDMS with 300-nm moth-eye films significantly reduced light reflection at the front of the glass and therefore enhanced the solar cell efficiency of ~ 21%.The PDMS with 1000-nm moth-eye films exhibited beautiful coloration.

Evaluation of Scratch Durability of Moth-eye Structures Made of High Hardness Ultraviolet Curable Resin

Evaluation of Scratch Durability of Moth-eye Structures Made of High Hardness Ultraviolet Curable Resin

One-pod preparation of anodic porous alumina molds with tapered holes for moth-eye structures by nanoimprinting

An anodic porous alumina mold with tapered holes was formed by a one-pod preparation process. In this process, one-pod of a mixed solution containing oxalic acid and phosphoric acid was used for both anodization and pore widening. The anodization proceeded during the on state of the applied voltage, while the pore widening proceeded during the off state. The shape of the tapered holes in anodic porous alumina could be controlled by adjusting the program composed of on and off periods. Moth-eye structures were formed by nanoimprinting using the obtained molds. These moth-eye structures effectively suppressed the reflection of incident light.

Shape optimization of a moth-eye structure for omnidirectional and broadband antireflection

The shape optimization method was proposed to acquire omnidirectional and broadband antireflection properties of a moth-eye structure. Demonstrated by a poly(methyl methacrylate) substrate used for packaging material of solar cells, an average transmittance up to 0.936 has been achieved over the AM1.5 spectrum and incident angle from 0 to 90 degrees, showing a better antireflection performance compared with the most widely used shapes with conical, sinusoidal and parabolic profiles. The improvement is attributed to the optimized effective refractive index profile, leading to a smaller reflection in large incidence angles. The method can be applied to solar cells for higher light management efficiency.

Does a nano-scale nipple array (moth-eye structure) suppress the settlement of ascidian larvae?

AbstractIn some metazoans, the body surface is entirely or partly covered with an array of nipples about 100 nm or less in height. This structure, a nipple array, is sometimes called the moth-eye structure because it serves as an anti-reflection property on the compound eyes of a night moth. The nipple array is supposed to be a multifunctional structure since this structure occurs in various species across different taxa. Here, we hypothesize that the nipple array may prevent the settlement of epibionts that are often a nuisance and potentially cause serious problems for the host. Using a synthetic film that imitates the nipple array, we tested the substrate selection within ascidian larval settlement. The results indicate that the nipple array has anti-fouling properties, since more larvae settled on the flat surface than the nipple array (P < 0.01, paired t-test). The present results demonstrated that the nipple array potentially serves an anti-fouling function on the body surface, which should be important especially for sessile organisms.