Moth-eye Structure Research Articles

Computational Study of Moth-Eye Structures for Silicon Solar Cells Lights Harvesting Improvement

Abstract Recently Moth-Eye nanostructure is widely used in solar cell light harvesting enhancement, in this computational work, three different designs; rectangular, triangular, and semi-circular structures were introduced as anti-reflect structures placed above a silicon solar cell, anti-reflected nanostructured modeled and optimized for silicon ultra-thin film solar cells using the finite difference time domain method for optical, and Lumerical devise software for electrical properties study. The effect of the geometrical dimension of the three structures was investigated. It is found that light-harvesting and solar cell performance can be enhanced by choosing a suitable structure and dimension for the suggested structure. The optimum efficiency enhancement achieved was by a semi-circular structure with a radius of 200nm from 8.81% to 11.95%.

Optimized two-layer random motheye structures for SiO₂ windows

Optimized two-layer random motheye structures for SiO₂ windows

Enhanced optical properties of BiVO4 photoanode with subwavelength moth-eye structure fabricated via e-beam evaporation and direct printing

Photoelectrochemical (PEC) water splitting, which harnesses solar radiation (an infinite energy source) for clean hydrogen production without carbon-dioxide emissions, is an ideal eco-friendly energy technology. The core reactions in PEC water splitting, involving the oxidation and reduction of water, are driven by electron–hole pairs generated through solar energy absorption. Consequently, the light-absorption efficiency emerges as a critical parameter in PEC devices. Conventional thin-film-type photoanodes, however, grapple with limited absorption due to their high reflectance, hindering absorption and carrier separation efficiency. Conversely, moth-eye-structured photoanodes exhibit an anti-reflection effect stemming from their subwavelength structure, markedly enhancing light-absorption efficiency. In this study, we present the design and fabrication of a densely packed moth-eye-structured bismuth vanadate (BiVO4) (M-BVO) photoanode, which is engineered to possess superior light absorption properties. The photoanode was fabricated via direct printing, electron-beam evaporation, and Vanadium calcination processes. The light absorption of the resulting M-BVO photoanode increased to approximately 92 % within the 300–500 nm wavelength range, with the absorption efficiency (ηabs) surging to 82.9 %. This represents a 23.5 % enhancement compared to its flat BiVO4 counterparts. Impressively, the photocurrent density of M-BVO reached 2.98 mA cm−2 at 1.23 VRHE, 37.6 % higher than that of flat BiVO4. These results indicate that the PEC efficiency can be significantly increased through moth-eye structuring, emphasizing the indispensable role of nanostructure research in the manufacture of high-efficiency photoanodes.

Metamaterial Absorbers with Archimedean Tiling Structures: Toward Response and Absorption of Multiband Electromagnetic Waves.

With the continuous development of electromagnetic wave-absorbing materials, the design of artificial structures for electromagnetic absorbers based on the concept of metamaterials is becoming more abundant. However, in the design process, it is difficult to further broaden the effective absorption band due to the limitation that the traditional single-size structure responds to electromagnetic waves only in specific frequency bands. Therefore, in this paper, based on the moth-eye bionic hexagonal structure absorber with antireflection performance, an Archimedean tiling structure is designed to optimize it, and through the introduction of a variety of primitives with large differences in dimensions, a multifrequency band-response mechanism is achieved to enhance the multireflection mechanism, which can effectively broaden the absorption band and improve the wave absorption performance. Ultimately, the moth-eye bionic structure absorber optimized by (3.4.6.4) can achieve an effective absorption of 10.26 GHz at a thickness of 2 mm. This work presents a new idea for the design work of electromagnetic wave-absorbing metamaterials, which has a broad application prospect in the aerospace, electronic information countermeasures, communication, and detection industries.

Double moth-eye structures to reduce parasitic absorbed and reflected in homojunction perovskite solar cells

Perovskite materials for solar cells have excellent optical performance to achieve over 90% light absorption without trapping structure. However, the perovskite solar cell structure determines the occurrence of light loss, because light needs to pass through the window layer before being effectivity absorbed. In this work, we use a combination of double moth-eye structures in ITO and PDMS films to reduce parasitic absorption and reflection. It is shown that the moth-eye structure can smoothly change the vertical refractive index to reduce the light reflection generated by multiple functional layers. In addition, the moth-eye structure in ITO film can regulate the internal light field distribution, directly affecting parasitic absorption, and reducing the parasitic absorption by 62.98%. After optimization of this double moth-eye structure, the maximum current density obtained is 25.93 mA cm−2, which is 9.78% higher than that of the perovskite solar cell without moth-eye structure.

Optical enhancement in perovskite thin films using moth-eye anti-reflection film

Perovskite solar cells represent an emerging photovoltaic technology. With the latest record efficiencies exceeding 25% coupled with low fabrication cost and tunable transparency, perovskite solar cells demonstrate promising applications as solar windows. For these applications, the perovskite solar cells need to be semi-transparent to allow incident light to pass through the windows while generating electricity. However, semi-transparency compromises light absorption in the solar cells. In this work, optical enhancement in perovskite thin films using moth-eye anti-reflection (AR) film is investigated. Perovskite thin films with different thicknesses are used and the thickness is controlled by varying the spin speeds during the deposition of the perovskite precursor. The optical effects in the perovskite films without and with moth-eye AR film are studied. From the findings, the reflection loss is reduced by maximum of ∼4%, which contributes to a higher light absorption in the perovskite layer, due to the AR effect of the moth-eye structure. These results imply that the moth-eye film can be a promising and facile alternative for developing a highly efficient and semi-transparent perovskite solar cell with a thin absorber layer.

Design of a novel anti-reflective coating with ultra-low reflectance based on resin-anchored hollow silica strategy

The strategy of resin-anchored hollow silica particles (HSPs) offers a tempting option for large-scale fabrication of anti-reflective functional surfaces on flexible plastic substrates. However, attempts to experimentally investigate the structure-performance relationship of such anti-reflective coatings and to further optimize the coating structure require long experimental cycles and significant labor costs. In view of this, the effectiveness of using COMSOL two-dimensional (2D) simulation to solve the problem is validated in conjunction with experimental results. Then three coating structure models are investigated. Finally, a coating with ultra-low reflectance in the entire visible wavelength band (380–780 nm) is designed. The coating has a novel structure consisting of resin-anchored double-layer unequal-size HSPs. It combines two anti-reflective principles, the moth-eye bionic structure and the refractive index adjustment of the film layer. The maximum reflectance of the coating is only 0.32 % over the entire visible wavelength range, and its average reflectance reaches an ultra-low level of 0.14 %. The coating has a wide angle anti-reflective performance. When the angle of incidence is <60°, the reflectance of the coating is <3 %. The results of this study are expected to provide direction for later experimental improvements.

(Digital Presentation) Moth-Eye Structured BiVO4 Photoanode with Improved Optical Properties for Efficient PEC Water Splitting Performance

Photoelectrochemical (PEC) water splitting, wherein infinite solar energy is used to produce hydrogen without CO2 emissions, is an ideal eco-friendly energy technology. The main reactions in PEC water splitting, the oxidation and reduction of water, are caused by the electron–hole pairs generated by solar energy; hence, the light absorption efficiency is a key parameter in PEC devices. In conventional thin-film-type photoanodes, absorption is limited owing to their high reflectance, which hinders their absorption and separation efficiency. Conversely, a moth-eye-structured photoanode exhibits an anti-reflection effect owing to its subwavelength structure, which significantly increases the light absorption efficiency. Hence, in this study, a densely packed moth-eye-structured BiVO4 photoanode with good light absorption properties was designed. It was fabricated via direct printing, e-beam evaporation, and V calcination. The light absorption of M-BVO increased to approximately 92% within the 300–500 nm wavelength range, and the absorption efficiency (ηabs) increased to 82.9%, indicating a 23.5% increase in comparison to that of flat BiVO4. The photocurrent density of M-BVO reached 2.98 mA cm−2 at 1.23 VRHE, which was 37.6% higher than that of flat BiVO4. These results show that the PEC efficiency can be significantly increased through moth-eye structuring, which suggests that research on nanostructures is essential for the manufacture of high-efficiency photoanodes. Figure 1

Highly Effective Index-Matching Antireflective Structures for Polymer Optics

Optical polymers are attractive for lightweight and cost-effective refractive optical components, yet they reflect part of the incident light. Traditional vacuum-deposited antireflective films purely adhere to polymers and suffer from mechanical stresses due to the difference in the thermal expansion coefficients. Alternatively, reflection can be reduced by moth-eye structures; yet, their efficiency strongly depends on their index-matching with the optical substrate, which has not been demonstrated so far. Here, we introduce a new approach to engineering highly effective antireflective structures on the surface of the optical polymer, with an unprecedented ability to reduce the surface reflection from 5 to 0.1%. The structures were produced by high-throughput nanoimprint lithography, and their superior optical performance was achieved due to the precise matching of their index to that of the underlying substrate. We further applied these structures on different polymers and showed that their antireflective effect correlates with index-matching. We demonstrated that these structures could be applied on flat surfaces and curved lenses and produce high surface hydrophobicity. Overall, our work paves the way to an efficient and scalable antireflective solution for polymer optics.

Fabrication of Moth-Eye Structures with Precisely Controlled Shapes by Nanoimprinting Using Anodic Porous Alumina Molds

An anodic porous alumina mold with tapered pores, which can be used to form moth-eye structures, was formed by repetitions of anodization and etching. It was shown that the controllability of the pore shape of the anodic porous alumina mold improved with the number of repetitions of anodization and etching. However, it was found that even when the total anodization time or anodic charge (electrical current × time) was kept constant, the thickness of anodic films was not constant because the total etching time varied. This is because the etching of the anodic porous alumina mold not only increases the pore size but also reduces the thickness of the barrier layer so that pore growth proceeds after the barrier layer is re-formed during re-anodization. Therefore, it was found that if anodization is performed with the additional anodic charge required to re-form the barrier layer, an anodic porous alumina mold with tapered pores and uniform film thickness can be produced even if the etching time is varied. Nanoimprinting using the resulting anodic porous alumina mold was shown to form a moth-eye structure with a reflectance of less than 0.1% over the entire visible light range.

Large-Scale Moth-Eye-Structured Roll Mold Fabrication Using Sputtered Glassy Carbon Layer and Transferred Moth-Eye Film Characterization.

Currently, there is high demand for the development of a highly mass-producible technology for manufacturing moth-eye-structured films with an antireflection function. Conventional moth-eye-structured films have been produced by roll-to-roll (RTR) ultraviolet nanoimprint lithography (UV-NIL) using porous alumina, but the process of manufacturing the roll mold with aluminum is both complicated and time-consuming. To solve this problem, we proposed a sputtering process for forming a thin film of glassy carbon on a roll substrate and fabricated a moth-eye structure through the irradiation of oxygen plasma. A glassy carbon (GC) moth-eye-structure roll mold with a uniform reflectance of less than 0.1% over a length of 1560 mm was fabricated following this method. In addition, a superhydrophobic moth-eye-structured film was produced by RTR UV-NIL using the proposed roll mold, which exhibited a reflectance of 0.1%. In this study, a moth-eye-structure roll using porous alumina was compared with a film transferred from it. The GC moth-eye-structure roll mold was found to be superior in terms of antireflection, water repellency, and productivity. When the proposed large-area GC moth-eye-structured film was applied to window glass, significant anti-reflection and water-repellent functionalities were obtained.

Absorption properties and mechanisms of metallic moth-eye structures

The antireflection and absorption properties of non-metallic moth-eye structures have been intensively studied, however the research on those of metallic moth-eye structures, especially their absorption mechanisms, is far from enough. In this paper, the absorption properties and mechanisms of a metallic Au moth-eye structure are studied in detail. The results show that broadband perfect absorption covering the entire visible to the near infrared range with polarization independence and in a wide incident angle range can be easily realized using a single-layer single-material Au moth-eye structure. As for the absorption mechanism, in the short wavelength range of 300 nm–550 nm, due to the high loss of the Au material, the antireflection effect plays a main role. While in the long wavelength range of 550 nm–1000 nm, the widely accepted absorption mechanisms (the antireflection effect as well as the cascaded multiple plasmonic resonances, and even the combination of them) cannot completely account for the broadband perfect absorption. We found that the adiabatic nanofocusing effect of the plasmonic resonances enabled by the ultra-sharp air grooves plays a key role in the absorption. It is the nanofocusing effect that effectively increases the absorption to nearly 100% in a broad wavelength band. These findings provide a deeper insight into the absorption mechanisms of metallic moth-eye structures and offer an effective guide to explore demanded excellent absorption performance.

A photocatalytic degradation self-cleaning composite membrane for oil-water separation inspired by light-trapping effect of moth-eye

Membrane separation technology with superwetting surfaces is ideal for treating water pollution. However, the fouling problem of membranes limits their practical application in this field. Membranes with self-cleaning property during the separation are the key to solve this problem. In this study, inspired by the light-trapping effect of the moth-eye, a kind of composite membrane with efficient self-cleaning by photocatalytic degradation was proposed. The composite membrane is based on polyvinyl alcohol cross-linked tannic acid (PVA-TA) and its photocatalytic function is achieved by doping magnetic titanium dioxide nanoparticles (MTiO2) as well as MXene. Meanwhile, its surface was constructed by magnetically controlled self-assembly method using MTiO2 to mimic the moth-eye structure. The composite membrane has superhydrophilic/underwater superoleophobic, excellent oil-water separation efficiency (99.85%) and long service life (64 cycles). In addition, due to the light-trapping effect of the bionic moth-eye structure and the redox reaction at the interface of MTiO2-MXene composites under sunlight irradiation, the membrane can achieve efficient and convenient photocatalytic degradation self-cleaning by sunlight irradiation. This study will provide new insights into the self-cleaning method of oil-water separation materials.

Spectrally selective antireflection of nanoimprint lithography-formed 3D spherical structures on film coated with a silver layer

We fabricate moth-eye antireflection (AR) coatings using high-resolution and low-cost UV nanoimprint lithography with polyethylene terphthalate (PET) molds. Several various thicknesses of silver films placed on the moth-eye structure were analyzed for reflectance and transmission. On PET, the conical nanostructured surface arrays had a spatial period length of approximately 250 nm, a diameter of approximately 200 nm, and a height of approximately 160 nm. After them, a silver (Ag) layer of 18 nm is deposited satisfactorily on the PET substrate surface. The never-ending moth-eye formations of the imprinted mold were fabricated by Ni mold electroplating, interference lithography, and replication. We found that an Ag layer of suitable thickness on AR film in the spectrum range that can be seen has high transmittance (Highest value is 72%) while in the infrared spectrum it has high reflectance (At least 60%). For an optical film with a silver coating has been placed on an anti-reflection subwavelength-structured (ASS) surface, such properties, including heat insulation, have obvious applications in windows for homes and vehicles.

Nonequilibrium Self-Assembly of Ultrahigh-Molecular-Weight Block Copolymers into an Asymmetric Nanostructure

Self-assembly of block copolymers (BCPs) provides a unique platform for producing periodic and orderly structured soft materials of nanometer scale. The kinetics of the assembly process defines the accessible range of morphologies and allows for the formation of asymmetric hierarchies. Here, self-assembly of ultrahigh-molecular-weight BCPs with relatively slow molecular chain dynamics is used to fabricate a metastable asymmetric structure. More specifically, a kinetically trapped solvent vapor annealing process is applied to poly(styrene-block-2-vinylpyridine) thin films, wherein the concentration ratio of trichloroethylene to tetrahydrofuran of the mixed solvent vapor gradually increases throughout the annealing process, pushing the system away from equilibrium. Under such a dynamic process, poly(styrene-block-2-vinylpyridine) micelles rearrange into vertical protuberances that mimic moth-eye structures enhancing the light transmission. Sequential infiltration synthesis is used to convert the poly-2-vinylpyridine domain into alumina in order to verify the formation mechanism of the asymmetric protuberances. It is determined that vertically packed and merged micelles are only formed under a gradually built solvent vapor environment.

The Reflectance Characteristics of an Inverse Moth-Eye Structure in a Silicon Substrate Depending on SF6/O2 Plasma Etching Conditions.

The global RE100 campaign is attracting attention worldwide due to climate change caused by global warming, increasingly highlighting the efficiency of renewable energy. Texturing of photovoltaic devices increases the devices’ efficiency by reducing light reflectance at their surfaces. This study introduces the change in light reflectance following the process conditions of plasma etching as a texturing process to increase the efficiency of photovoltaic cells. Isotropic etching was induced through plasma using SF6 gas, and the etch profile was modulated by adding O2 gas to reduce light reflectance. A high etch rate produces high surface roughness, which results in low surface reflectance properties. The inverse moth-eye structure was implemented using a square PR pattern arranged diagonally and showed the minimum reflectance in visible light at a tip spacing of 1 μm. This study can be applied to the development of higher-efficiency optical devices.

Ultrawide-Angle Optical Elements With Enhanced Transmittance Obtained by a Half-Etched Moth-Eye Structure Coating on Infrared Substrates

Ultrawide-Angle Optical Elements With Enhanced Transmittance Obtained by a Half-Etched Moth-Eye Structure Coating on Infrared Substrates

An energy-efficient glass using biomimetic structures with excellent energy saving features in both hot and cold weather

Solar irradiation is the main factor contributing to ultra-high energy demand in buildings, and windows are crucial elements with a significant effect on the energy demand in indoor spaces, affecting the cooling, heating, and artificial lighting requirements. Inspired by hercules beetle utilizing the refractive index difference of spongy multilayer structure for infrared reflection and moth-eye using the continuous refractive index change of microscopic convex structure for anti-reflection, this study proposes a visibly transparent and infrared-reflective energy-efficient glass using biomimetic structures to save energy in buildings, based on the idea of regulating the radiation to match the energy utilization on-demand. The selected materials for the proposed biomimetic energy-efficient (BE) glass are SiO2, Al2O3, and Ag based on the idea of using the difference in refractive index of multilayer media for radiation regulating. The transmissivity and reflectivity of BE glass are examined adopting the finite-difference time-domain (FDTD) method. The numerical analysis results demonstrate that BE glass covered with a cone-shaped biomimetic moth-eye structure and a biomimetic multilayer structure exhibits visible light transmissivity of 82.37%, in addition to an infrared light reflectivity of over 90%, which is higher than that of the currently employed low-E glasses. The proposed BE glass offers excellent energy-saving features in both hot and cold weather and the energy consumption analysis indicates that comparing with conventional common glass, it could save about 20% total electrical consumption (43.5 kWh/m2) per year

Surface nanostructuring of alkali-aluminosilicate Gorilla display glass substrates using a maskless process

This paper reports on the formation of moth-eye nanopillar structures on surfaces of alkali-aluminosilicate Gorilla glass substrates using a self-masking plasma etching method. Surface and cross-section chemical compositions studies were carried out to study the formation of the nanostructures. CF x induced polymers were shown to be the self-masking material during plasma etching. The nanostructures enhance transmission at wavelengths over 525 nm may be utilized for fluid-induced switchable haze. Additional functionalities associated with nanostructures may be realized such as self-cleaning, anti-fogging, and stain-resistance.

Preparation of moth-eye structures on curved surfaces by nanoimprinting using anodic porous alumina molds

Al substrates with smooth curved surfaces were fabricated by peeling off Al foil sputtered on the surface of concaved substrates. Anodic porous alumina with tapered pores on the curved surface was obtained by repeated anodization and etching of the obtained Al substrate. The moth-eye structure was formed on the curved surface by nanoimprinting using the anodic porous alumina as a mold. From the reflectance measurement, it was shown that the reflection of the incident light was suppressed on the curved surface where the moth-eye structure was formed. This process can be used to fabricate moth-eye structures on the surface of substrates of various shapes by changing the substrate used for sputtering and is expected to expand the range of applications for moth-eye structures.