Antireflection Properties Research Articles

Quintic refractive index profile-based funnel-shaped silicon antireflective structures for enhanced photodetector performance

Antireflection, vital in optoelectronics devices such as solar cells and photodetectors, reduces light reflection and increases absorption. Antireflective structures (ARS), a primary method by which to realize this effect, control the refractive index (RI) profile based on their shape. The antireflection efficiency depends on the refractive index profile, with the quintic RI profile being recognized as ideal for superior antireflection. However, fabricating nano-sized structures with a desired shape, particularly in silicon with a quintic RI profile, has been a challenge. In this study, we introduce a funnel-shaped silicon (Si) ARS with a quintic RI profile. Its antireflective properties are demonstrated through reflectance measurements and by an application to a photodetector surface. Compared to the film Si and cone-shaped ARS types, which are common structures to achieve antireflection, the funnel-shaped ARS showed reflectance of 4.24% at 760 nm, whereas those of the film Si and cone-shaped ARS were 32.8% and 10.6%, respectively. Photodetectors with the funnel-shaped ARS showed responsivity of 0.077 A/W at 950 nm, which is 19.54 times higher than that with the film Si and 2.45 times higher than that with the cone-shaped ARS.

Sub-bandgap photo-response of black silicon fabricated by femtosecond laser irradiation under water

Here we propose a method to fabricate black Si without the need for any chalcogenide doping, accomplished by femtosecond (fs) laser irradiation in a liquid environment, aiming to fabricate the infrared detector and investigating their optoelectronic performance. Multi-scale laser-induced periodical surface structures (LIPSSs), containing micron sized grooves decorated with low spatial frequency ripples on the surface, can be clearly observed by SEM and 3D confocal microscope. The generated black Si demonstrates superior absorption capabilities across a broad wavelength range of 200-2500 nm, achieving an average absorptance of up to 71%. This represents a notable enhancement in comparison to untreated Si, which exhibits an average absorption rate of no more than 20% across the entire detectable spectrum. A metal-semiconductor-metal (MSM) type photodetector was fabricated based on this black Si, demonstrating remarkable optoelectronic properties, specifically, it attains a responsivity of 50.2 mA/W@10 V and an external quantum efficiency (EQE) of 4.02% at a wavelength of 1550 nm, significantly outperforming the unprocessed Si by more than five orders of magnitude. The great enhancement in infrared absorption as well as the optoelectronic performance can be ascribed to the synergistic effect of the multi-scale LIPSSs and the generated intermediate energy levels. On one hand, the multi-scale structures contribute to an anti-reflection and light trapping property; on the other hand, the defects levels generated through fs laser ablation process under water may narrow the band gap of the Si. The results therefore underscore the remarkable potential of black Si processed by fs laser under water for the application of photodetection, especially in the near-infrared band.

Aluminum-doped zinc oxide thickness controllable wavelengths in visible light and high responsivity devices using interrupted flow atomic layer deposition

In this study, we develop a highly sensitive visible light photodetector that utilizes a thin-film structure composed of low-cost aluminum-doped zinc oxide (AZO) and n-type silicon. The AZO thickness can be adequately controlled to fit the different wavelengths of interest for photodetectors in the visible light range using interrupted flow atomic layer deposition (ALD). This in situ aluminum doping method ensures a uniform aluminum distribution within the AZO thin films and effectively increases the internal film reflections and photoresponsivity. The Schottky interface with n-type silicon is created by degenerated AZO due to the lower Fermi level, and visible light can effectively penetrate the underlying depletion zone. Optical simulation of the high conductivity of AZO indicated that the optimal thickness was 54.6, 65.8, and 91.7 nm for devices illuminated with 450 nm blue, 525 nm green and 700 nm red light, respectively. Hall effect measurements confirmed that the AZO film can achieve a low resistivity of 5 × 10–4 Ω-cm and high carrier concentration of 3 × 1020 cm−3 at a suitable precursor ratio. Additionally, AZO films offer multifunctionality by providing optical antireflective properties and forming Schottky junctions with n-type silicon to enable photoelectric conversion. This multifunctional role of AZO was experimentally validated through electrical, optical, and optical-to-electrical experiments, which showed that the optimized device can reach an optical responsivity of approximately 10.7 AW−1 at specific visible light wavelengths. The significant photoelectrical conversion efficiency and simple thin-film structure design facilitate future applications in light intensity measurement, such as in colorimetry or fluorometry.

Enhanced Durability and Antireflective Performance of Ag-Based Transparent Conductors Achieved via Controlled N-Doping.

Ag-based transparent conductors (TCs) are often proposed as an alternative to ITO coatings. However, while their performance has been widely demonstrated, their environmental durability is frequently overlooked or addressed with the use of highly specific encapsulating layers. In this work, the durability and antireflective performance of Ag-based TCs are simultaneously enhanced. To do so, a transfer matrix modeling approach is used to determine the general requirements for high performance antireflective properties as a function of Ag thickness and dielectric refractive indices, offering more widely applicable insight into stack optimization. Coating durability is investigated as a function of the Ag microstructure, which is modified by altering the N2 concentration used for doping of the Ag layer and the selection of the seed layer. Increasing N2 concentration during Ag deposition was found to decrease grain size and durability of Ag coatings deposited on Si3N4 whereas all coatings on ZnO(Al) showed higher stability. Significantly higher durability is found when specifically combining intermediate N2 concentrations in the sputtering gas mixture (Ag(N):5%, compared to 0% and 50%) and a ZnO(Al) seed layer, and a mechanism accounting for this increased durability is proposed. The addition of NiCrNx protective coatings increases the system durability without altering these trends. These findings are combined to fabricate a highly performant Ag-based TC (TV = 89.2%, RVFS = 0.23%, 21.4 Ω), which shows minimal property changes following corrosion testing by immersion in a heated and highly concentrated aqueous NaCl solution (200 g/L, 50 °C).

Effect of deposition rate on anti-reflection and wettability properties of RF magnetron sputtering SiCON thin film

Effect of deposition rate on anti-reflection and wettability properties of RF magnetron sputtering SiCON thin film

Broadband high-contrast-grating-type waveplates for the terahertz range

The high-contrast-grating waveplates utilizing high contrast between silicon and air refractive indexes were developed in order to perform as a quarter wave and a half wave plate in the selected THz frequency range. The waveplates possessed anti-reflective properties due to the specific inclination of the walls both in parallel and in perpendicular direction to grating axis, efficiently suppressing the reflection losses caused by air-dielectric interface for both transverse magnetic and transverse electric polarizations. Moreover, significant reduction of the transmittance gap was achieved between both polarizations while mitigating overall Fabry-Perot effect. Validation of the concepts was carried out by measuring transmission amplitude and phase spectra of the fabricated samples in a broadband of THz time-domain spectroscopy and vector-network-analysis systems considering also some real applications.

Solar‐Driven Hydrogen Evolution with Superior Efficiency by a Low‐Cost, Large‐Scale Synergetic Hybrid of 1D‐Si Nanowires/0D‐Au Nanoparticles/2D‐MoS2 Nanofilms

The technology of semiconductor photocatalystshas become an important research area. 2D molybdenum disulfide (MoS2) is recognized as a promising catalyst for photoelectrocatalytic and photocatalytic (PC) hydrogen evolution reaction (HER). However, owing to its 2D nature of low optical cross‐section, the effective light absorption needs to be further boosted. Herein, we dramatically amplify the light‐matter interaction by hybridizing these photocatalysts with plasmonic materials that present strong electromagnetic field confinement and with nanowires that offer efficient light management. Such a system is designed in the heterostructure of silicon nanowires (SiNW)/ gold nanoparticles (AuNP)/ MoS2 nanofilms (SiNW/AuNP/MoS2), which demonstrates excellent PC HER. The absorption frequency of 2D‐MoS2, the resonance frequency of the 0D‐AuNP, and the antireflection frequency of 1D‐SiNW match with the visible range, enabling this heterostructure to effectively utilize solar energy. Additionally, an optimal MoS2 nanofilm that is a mixture of 1 T and 2 H phases was prepared with high reproducibility using facile pyrolysis. Moreover, the SiNW substrate validates high antireflection properties, achieving 95% visible light absorption. In addition, SiNW forms a p–n junction with the MoS2 to facilitate charge separation. The synergetic hybrid of 1D‐SiNW/0D‐AuNP/2D‐MoS2 nanofilms exhibits the highest hydrogen generation rate of 246 mmol g−1 h−1.

Minimizing annual reflection loss in fixed-tilt photovoltaic modules using graded refractive index (GRIN) anti-reflective glass

This study evaluates the performance of graded refractive index (GRIN) anti-reflective (AR) structures on photovoltaic (PV) modules across twenty global locations and compares them with conventional thin film AR coatings and bare glass. Optimized glass nanocones were chosen to represent the GRIN structures. Electrodynamic simulations were conducted to assess reflection properties at multiple angles of incidence. GRIN AR structures dramatically reduce total solar-integrated reflection to 0.2% at normal incidence, compared to 3.8% for bare glass and 0.8% for optimized thin film AR coatings, and maintained low reflection across a range of incident angles, demonstrating only 0.7% reflection at 60 degrees compared to significantly higher values for other surfaces. Detailed hourly simulations for twenty global locations revealed that GRIN AR coatings substantially reduce annual reflection loss to just 0.86±0.19% and increase expected annual energy output by up to 11.15±1.00% compared to bare glass at optimal tilt angles. The benefits of GRIN AR coatings are more substantial at sub-optimal panel orientations such as horizontal or vertical due to its broad angle AR properties. These findings highlight the potential of GRIN AR technology to approach the theoretical limit where front surface reflection loss is completely eliminated and enhance solar power conversion efficiencies. Additionally, a generalized model to approximate annual reflection loss for various materials is presented. This research encourages further exploration into GRIN AR coatings to optimize power conversion efficiencies and reduce reflection in PV modules.

New Coating Paradigm to Boost Performance and Durability of Solar Receivers

The development of renewable energy sources is nowadays of enormous importance, not only for the climate change fight but also for the security of the energy supply. The latest geopolitical unfortunate events in Europe have highlighted our energy dependency on foreign fossil fuels. In this context, solar technologies are already playing an essential role in shifting towards neutral carbon economies, ensuring a reliable energy supply. In this regard, dispatchability provided by CSP plants is key to pave the way towards energy transition. It is worth noting that the long-term durability and performance of solar components in arid regions are crucial to increase the reliability and performance of CSP plants while reducing O&M costs. In this work, an innovative approach based on nano-structuring the solar receiver tube glass is presented, which provides improved anti-reflective (AR) and anti-soiling (AS) properties, also showing good durability with respect to abrasion. Spectral transmittance improvement, soiling rate decrease, and durability measurements are presented for nano-structured glasses, comparing with current state of the art glass performance. The achieved experimental results suggest that the new structured glasses would be good candidates for CSP applications

Optical Analysis of Perovskite III-V Nanowires Interpenetrated Tandem Solar Cells.

Multi-junction photovoltaics approaches are being explored to mitigate thermalization losses that occur in the absorption of high-energy photons. However, the design of tandem cells faces challenges such as light reflection and parasitic absorption. Nanostructures have emerged as promising solutions due to their anti-reflection properties, which enhances light absorption. III-V nanowires (NWs) solar cells can achieve strong power conversion efficiencies, offering the advantage of potentially integrating tunnel diodes within the same fabrication process. Metal halide perovskites (MHPs) have gained attention for their optoelectronic attributes and cost-effectiveness. Notably, both material classes allow for tunable bandgaps. This study explores the integration of MHPs with III-V NWs solar cells in both two-terminal and three-terminal configurations. Our primary focus lies in the optical analysis of a tandem design using III-V semiconductor nanowire arrays in combination with perovskites, highlighting their potential for tandem applications. The space offered by the compact footprint of NW arrays is used in an interpenetrated tandem structure. We systematically optimize the bottom cell, addressing reflectivity and parasitic absorption, and extend to a full tandem structure, considering experimentally feasible thicknesses. Simulation of a three-terminal structure highlights a potential increase in efficiency, decoupling the operating points of the subcells. The two-terminal analysis underscores the benefits of nanowires in reducing reflection and achieving a higher matched current between the top and the bottom cells. This research provides significant insights into NW tandem solar cell optics, enhancing our understanding of their potential to improve photovoltaic performance.

Low-temperature preparation of nanostructured porous sol-gel anti-reflective coating for near-infrared wavelengths

Anti-reflective coatings are crucial in minimizing reflection between different optical media at the interfaces. This study aims to develop an anti-reflective layer for the near-infrared region using a sol-gel coating method combined with a low-temperature plasma-jet-assisted surfactant extraction. For the deposition of the sol-gel layer on glass and polycarbonate substrates, dip-coating and spray-coating techniques were used. Surfactant removal was carried out using a plasma-jet and solvent exchange. Some of the samples were also annealed at 450 °C. The samples were characterized through light transmission measurements, haze percentage determination, 3D laser scanning microscopy, scanning electron microscopy, profilometry, Fourier transform Infrared spectroscopy, ellipsometry and atomic force microscopy. The results showed that the anti-reflective coating layer treated with a plasma-jet and solvent exchange at room temperature demonstrated broadband anti-reflective properties with high transmission in near-infrared regions (up to 7.6% relative improvements in transmission for two sides). Annealing, performed only on the glass substrate, also showed the maximum relative improvement in transmission up to 8% for two sides. Moreover, in the case of polymer-based substrates, a low-temperature process is essential, which is implemented successfully by a plasma-jet method. These findings highlight the effectiveness of the proposed method for fabricating anti-reflective layers on both glass and polycarbonate substrates, offering potential applications in various industries, e.g. where either low-temperature fabrication or cost-cutting, quick and “simple” production methods play a major role for the feasibility of products as in mass markets.

Organic inorganic hybrid solar cell with photoactive hole transporting CuSbS2 nanoflakes

An easy-to-process, low-cost and environmentally benign organic inorganic hybrid solar cell (HSC) based on textured silicon (t-Si) is fabricated. The heterojunction solid state cell is composed of n-type t-Si having a micro-pyramidal surface with good anti-reflection properties, coated with a p-type layer of CuSbS2 nanoflakes dispersed in a polymer matrix of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The large hole density (2.7 × 1015 /cm3), high photoconductivity (5.37 mS cm−1), mono-dispersity of nanoflakes (50–80 nm), increased recombination resistance and a broad band absorption, with a band gap of ∼ 0.85 eV render CuSbS2 nanoflakes to be an ideal photo-absorber cum hole transport material for a highly scalable all solid-state HSC. Besides these attributes, the thermodynamically aligned energy levels of t-Si and CuSbS2 nanoflakes enable one-directional pathways for transfer and transport of electrons and holes to their respective contacts, yielding a high-power conversion efficiency (PCE) of 8.5 % under AM 1.5, 1 sun irradiance along with an average external quantum efficiency of 60 % superior by 39.2 % relative to its analogue devoid of CuSbS2. The effect of alkali texturization on the photovoltaic performance of the cells is also delineated by comparison with planar (pl)-Si based cells. The long-term stability of the In-Ga/t-Si/PEDOT:PSS + CuSbS2/Ag cell under intermittent illumination and storage over eight weeks confirmed from the nominal drop in PCE by ∼ 22 % demonstrates the efficacy of this affordable wet-chemistry approach for developing robust Si based HSC contrasting with the classical and expensive inorganic p-n junction crystalline Si solar cell.

Enhancing anti-reflective properties of electronic glass through two-step chemical etching

With the rapid growth of the electronic display industry, aluminosilicate glass has emerged as a replacement for traditional soda lime silica glass as the cover plate of various display devices because of its excellent physical and chemical properties. High transmittance and low reflectivity are the inevitable requirements of its application. However, few studies have been reported about the antireflection of aluminosilicate glass. In this study, a two-step etching method was employed to treat both sides of the alkali-aluminosilicate glass to obtain surface antireflection. Analytical methods such as EPMA, AFM, and UV spectrophotometry were utilized to evaluate the effect of the etching process and resultant surface microstructure on the optical properties of the glass. Furthermore, comparative research was conducted to distinguish the etching reaction differences between alkali-aluminosilicate glass and other glass compositions like soda-lime glass and high-boron-silicon glass. The results demonstrated that the controlled two-step etching process created a micro-porous surface structure, with a gradient refractive index. Subsequent to the secondary etching, the glass exhibits an impressive average transmittance of 98.88% within the visible light spectrum (380–780 nm). Moreover, identical etchant across different composition glasses leads to discernible differences in transmittance.

Fabrication of Superhydrophobic Nanostructures on Glass Surfaces Using Hydrogen Fluoride Gas.

Water-repellent glass surfaces have become increasingly important to ensure clear visibility in outdoor cameras, sensors, and automotive windows. In this study, we investigated a process for the formation of nanoscale structures on a glass surface using chemical reactions with hydrogen fluoride gas. Using this approach, nanostructures with superhydrophobicity, superhydrophilicity, and antireflective properties were formed on glass surfaces with minimal processing time. This mask-free method, working at atmospheric pressure, can be efficiently integrated within the float process, a mainstream manufacturing technique for flat glass, to introduce nanostructures onto the glass surface. Notably, after treatment with (1-H, 1-H, 2-H, 2-H-tridecafluorooctyl)trimethoxysilane (FAS-13), a typical hydrophobic agent, the resulting surface exhibited a maximum water contact angle of 162°. Owing to its low reflectivity and superhydrophobicity, this surface is anticipated to find applications in not only the design of architectural window glass and vehicle windows but also the development of solar panels and sensor cover glass for autonomous vehicles.

Wide-Spectrum Antireflective Properties of Germanium by Femtosecond Laser Raster-Type In Situ Repetitive Direct Writing Technique

A femtosecond laser raster-type in situ repetitive direct writing technique was used for the fabrication of anti-reflective microhole structures in Germanium (Ge) in the visible near-infrared range (300–1800 nm). This technique builds a layer of microstructured arrays on the surface of Ge, enabling Ge to exhibit excellent anti-reflective properties. The large-area micro-nanostructures of Ge were fabricated using femtosecond laser raster-type in situ repetitive direct writing. Ge microstructures are characterized by their structural regularity, high processing efficiency, high reproducibility, and excellent anti-reflective properties. Experimental test results showed that the average reflectance of the Ge microporous structure surface in the range of 300–1800 nm was 2.25% (the average reflectance of flat Ge was 41.5%), and the lowest reflectance was ~1.6%. This microstructure fabrication drastically reduced the optical loss of Ge, thus enhancing the photothermal utilization of Ge. The many nanoburrs and voids in the Ge microporous structure provided excellent hydrophobicity, with a hydrophobicity angle of up to 133 ± 2° (the hydrophobicity angle of flat Ge was 70 ± 2°). The high hydrophobicity angle allows for strong and effective self-cleaning performance. The femtosecond laser raster-type in situ repeatable direct writing technology has many desirable properties, including simplicity, high accuracy, flexibility, and repeatability, that make it one of the preferred choices for advanced manufacturing. The Ge micro-nanostructured arrays with excellent optical anti-reflective properties and hydrophobicity have become an attractive alternative to the current photo-thermal absorbers. It is expected to be used in many applications such as solar panels, photovoltaic sensors, and other optoelectronic devices.

Flexible Antireflection Coatings with Enhanced Durability and Antifogging Properties.

Antireflection coatings (ARCs) enhance optical clarity and improve light transmission by reducing glare and reflections. The application of conventional ARCs in flexible devices, however, is impeded by their lack of durability, particularly under bending deformation. We develop ARCs that withstand delamination and fracture, remaining intact even after 1000 bending cycles with a 5 cm bending radius. We fabricate integrated ARCs (iARCs) on a poly(methyl methacrylate) (PMMA) substrate by inducing free polymers to infiltrate the interstices of a disordered assembly of hollow silica nanochains and nanospheres. The polydispersity of PMMA creates a refractive index gradient, yielding a broadband antireflection capability. The nanochain-based iARCs are superior to the nanosphere-based coatings in both antireflection properties and mechanical durability, owing to the lower packing density and mechanical interlocking of the nanochains, respectively. Additionally, these nanochain iARCs display antifogging properties stemming from their superhydrophilicity. While our demonstrations are based on PMMA as a model substrate, this methodology is potentially extendable to other polymers, enhancing the iARC's applicability across various practical applications, including flexible and wearable devices.

Optimizing broadband antireflection with Au micropatterns: a combined FDTD simulation andtwo-beam LIL approach.

Broadband antireflection (AR) is highly significant in a wide range of optical applications, and using a gold (Au) micropattern presents a viable method for controlling the behavior of light propagation. This study investigates a novel, to the best of our knowledge, methodology to achieve broadband AR properties in Au micropatterns. It employed the three-dimensional finite-difference time-domain (FDTD) method to simulate and optimize the design of micropatterns. In contrast, the fabrication of Au micropatterns was carried out using two-beam laser interference lithography (LIL). The fabricated Au micropatterns were characterized by a scanning electron microscope (SEM) and spectroscope to validate their antireflection and transmission properties and evaluate their performance at various wavelengths. The optimized Au micropatterns had a high transmittance rating of 96.2%. In addition, the device exhibits a broad-spectrum antireflective property, covering wavelengths ranging from 400 to 1100nm. The simulation data and experimentally derived results show comparable patterns. These structures can potentially be employed in many optical devices, such as solar cells and photodetectors, whereby achieving optimal device performance reduced reflection and enhanced light absorption.

Multifunctional capabilities of radio frequency sputtered GO-TiO2 nanocomposite ultra-thin films

The work presents the successful synthesis of ultra-thin Graphene Oxide-Titanium (GOT) nanocomposite films using radio frequency sputtering. It was employed a thorough characterization encompassing structural, optical, and morphological aspects, with a focus on practical applications such as photocatalysis, anti-corrosion, anti-reflective properties, and superhydrophobicity (PAAS). Notably, the GOT film exhibited outstanding photocatalytic efficiency, achieving a significant 96% photodegradation rate, and offering promise for environmental remediation. Additionally, it demonstrated excellent visible-light-induced photocatalytic disinfection against E. coli K12 contamination. Furthermore, the film displayed notable corrosion resistance, a fivefold improvement over pristine surfaces, and excellent anti-reflective properties with 98% transmittance in the visible light range, making it suitable for advanced optical devices with multifunctional benefits.

Formation of Tubular Aluminum Oxides by Local Electrochemical Anodization in Organic Electrolytes and Their Anti-Reflection Properties

Research has been carried out on the formation of tubular aluminum oxides by local electrochemical anodization in aqueous solutions of organic acids such as formic, citric, tartaric, malic and others. Self-ordered nanostructures formed this way can be used in the manufacture of various optical devices. Tubular aluminum oxides formed by local electrochemical anodization in organic acids have a high concentration of anionic complexes containing carbon atoms over 10 at.%. Studies of reflection spectra showed effective anti-reflection properties of films with a specular reflection coefficient of 0.7–1.4 %.

Infrared-reflective ultrathin-metal-film-based transparent electrode with ultralow optical loss for high efficiency in solar cells

In this work we study in-depth the antireflection and filtering properties of ultrathin-metal-film-based transparent electrodes (MTEs) integrated in thin-film solar cells. Based on numerical optimization of the MTE design and the experimental characterization of thin-film perovskite solar cell (PSC) samples, we show that reflection in the visible spectrum can be strongly suppressed, in contrast to common belief (due to the compact metal layer). The optical loss of the optimized electrode (~ 2.9%), composed of a low-resistivity metal and an insulator, is significantly lower than that of a conventional transparent conductive oxide (TCO ~ 6.3%), thanks to the very high transmission of visible light within the cell (> 91%) and low thickness (< 70 nm), whereas the reflection of infrared light (~ 70%) improves by > 370%. To assess the application potentials, integrated current density > 25 mA/cm2, power conversion efficiency > 20%, combined with vastly reduced device heat load by 177.1 W/m2 was achieved in state-of-the-art PSCs. Our study aims to set the basis for a novel interpretation of composite electrodes/structures, such as TCO–metal–TCO, dielectric–metal–dielectric or insulator–metal–insulator, and hyperbolic metamaterials, in high-efficiency optoelectronic devices, such as solar cells, semi-transparent, and concentrated systems, and other electro-optical components including smart windows, light-emitting diodes, and displays.