Antireflection Research Articles

Comparative Assessment of Optical and Solid-State Characteristics in Antimony-Doped Chalcogenide Thin Films of ZnSe and PbSe to Boost Photovoltaic Performance in Solar Cells

Solar cell efficiency is crucial for maximizing the potential of solar energy as a sustainable power source. This research investigates the optical and solid-state properties of antimony-doped ZnSe and PbSe thin films using the spray pyrolysis technique. The process involves meticulous cleaning of soda-lime glass substrates, deposition of precursors (antimony chloride (SbCl3), lead chloride (PbCl2), hydrated zinc acetate (Zn (CH3COO) •3H2O), and sodium selenosulfide (NaSeSO3) via nebulizer-driven atomization onto heated substrates at a temperature of 80°C, and subsequent annealing at 300°C in a controlled nitrogen atmosphere for 60 minutes, facilitated by a tube furnace. Optical property evaluation through UV-Vis spectrophotometry reveals intriguing trends, such as a decrease in absorbance and an ascending transmittance with elongated wavelengths. Annealed films exhibit peak optical conductivity values around the visible spectrum, and augmented refractive indices correlate with increased wavelengths, further enhanced through annealing. Antimony doping influences band gap energy, making these materials promising for solar cell fabrication. This study underscores the potential of antimony-doped ZnSe and PbSe thin films to enhance solar cell efficiency. The films offer features like enhanced light trapping, lowered band gap energy, and improved charge transport characteristics, making them suitable for various solar cell applications, including antireflection coatings and light-trapping layers. Continued exploration and refinement of these materials are anticipated to lead to novel advancements in solar cell design and manufacturing, contributing to more efficient and impactful energy conversion techniques.

Sol-Gel Spin Coated Transparent Single-TiO2 and SiO2 Thin Film on Glass for Opto-electronic Applications

Great attention has been given on the sol-gel synthesis and spin-coating deposition techniques for the fabrication of various thin films. Because of its simple technique to fabricate dielectric (metal oxide) films using tetraethyl orthosilicate and titanium isopropoxide precursors. In this work, transparent single layer of SiO2 and TiO2 thin film was deposited on a glass substrate and characterized by FTIR, UV-visible spectroscopy, fluorescence and scanning electron microscopy techniques. The single layer thin film was mechanically stable and strong by adhering to glass substrates. The FTIR transmittance spectrum evidenced the existence of Si-O-Si and Ti-O-Ti at ~1100 and 1400 cm-1. The UV-visible absorbance spectra of single layer of SiO2 and TiO2 thin films showed strong absorption at below 00 nm. The excitation wavelength at 380 nm, the fluorescence spectra of both thin films showed the highest emission spectrum in between 733-798 nm. The SEM studies confirmed the smooth surface in both SiO2 and TiO2 layers. Further, it could be useful for various applications such as back reflector in solar cells, anti-reflection coatings, hydrophobic and anti-fogging materials.

RF sputtered metal oxide layers as ARCs to improve photovoltaic performance of commercial monocrystalline solar cell

The rf-sputtered ZnO, MgO and Al2O3 transition metal oxide nano layers were developed as efficient antireflection coatings (ARCs) on commercial monocrystalline silicon (m-Si) photovoltaic cells. Wavelength dependence reflectance measurements show minimal reflectance (i.e., ∼1.3–2.0%) between 350 and 800 nm wavelength regions affirming antireflection behavior of oxide layers. The phase formation studies of these oxide layers display the crystalline phase however the presence of non-crystalline phase is noted in Al2O3 diffractogram pattern. Cross section microstructure characterization carried out using scanning electron microscopy (SEM) to know the ARC layer thickness illustrates MgO, ZnO and Al2O3 layers with coating thickness around 85 nm, 87 nm and 77 nm respectively. Also, the thickness of antireflection coatings computed using wavelength dependent refractive index measurement is consistent with cross section microstructure images. Photon to energy conversion (PEC) of ARC coated device under 1 sun condition display 1.99%, 1.07% and 0.39% improvement in efficiencies compared with commercial m-Si-solar cell endorsing suitability of selected transition metal oxides as efficient ARC materials. The external quantum efficiency (EQE) measurements show notable improvement in efficiency for MgO, ZnO and Al2O3 coated devices reaffirming their usability as efficient ARC materials on commercial m-Si-solar cells.

Anti‐Reflective Graded‐Index Metasurface with Correlated Disorder for Light Management in Planar Silicon Solar Cells

AbstractRecently, many research efforts have been dedicated to improving light coupling into solar cells and reducing optical losses. Promising candidates regarding scalability include direct nano‐structuring of the absorber layer, anti‐reflective (AR) coatings, or combining both, e.g., pyramidal textures with a conformal coating. However, many of these methods are either insufficient or infeasible for application in thin solar cells. Moreover, approaches based on directly texturing the silicon interface simultaneously strongly increase surface recombination, thus degrading the electronic properties of the solar cell. To circumvent these issues, conformal graded‐index metasurfaces with a correlated positional disorder for light trapping in solar cells are proposed and experimentally demonstrated in this contribution. When considered as a part of a prototypical solar cell geometry, a broadband reduction in reflection is observed that results in photocurrent enhancement. The combined consideration of disorder and conformal graded‐index layers outperforms structures containing only one of these components. The computational guidance toward optimized designs promises to adjust the framework to other settings. The possibility for large‐scale fabrication of the samples paves the way toward a future generation of supporting photonic structures in solar cells.

Bichromatic tetraphasic full-field optical coherence microscopy.

Full-field optical coherence microscopy (FF-OCM) is a prevalent technique for backscattering and phase imaging with epi-detection. Traditional methods have two limitations: suboptimal utilization of functional information about the sample and complicated optical design with several moving parts for phase contrast. We report an OCM setup capable of generating dynamic intensity, phase, and pseudo-spectroscopic contrast with single-shot full-field video-rate imaging called bichromatic tetraphasic (BiTe) full-field OCM with no moving parts. BiTe OCM resourcefully uses the phase-shifting properties of anti-reflection (AR) coatings outside the rated bandwidths to create four unique phase shifts, which are detected with two emission filters for spectroscopic contrast. BiTe OCM overcomes the disadvantages of previous FF-OCM setup techniques by capturing both the intensity and phase profiles without any artifacts or speckle noise for imaging scattering samples in three-dimensional (3D). BiTe OCM also utilizes the raw data effectively to generate three complementary contrasts: intensity, phase, and color. We demonstrate BiTe OCM to observe cellular dynamics, image live, and moving micro-animals in 3D, capture the spectroscopic hemodynamics of scattering tissues along with dynamic intensity and phase profiles, and image the microstructure of fall foliage with two different colors. BiTe OCM can maximize the information efficiency of FF-OCM while maintaining overall simplicity in design for quantitative, dynamic, and spectroscopic characterization of biological samples.

Nano-imprint lithography of broad-band and wide-angle antireflective structures for high-power lasers.

We demonstrate efficient anti reflection coatings based on adiabatic index matching obtained via nano-imprint lithography. They exhibit high total transmission, achromaticity (99.5% < T < 99.8% from 390 to 900 nm and 99% < T < 99.5% from 800 to 1600 nm) and wide angular acceptance (T > 99% up to 50 degrees). Our devices show high laser-induced damage thresholds in the sub-picosecond (>5 J/cm2 at 1030 nm, 500 fs), nanosecond (>150 J/cm2 at 1064 nm, 12 ns and >100 J/cm2 at 532 nm, 12 ns) regimes, and low absorption in the CW regime (<1.3 ppm at 1080 nm), close to those of the fused silica substrate.

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.

First-principles study of structural, electronic, mechanical, optical, thermodynamic and thermoelectric properties of ternary ZnSnN2 and ZnMoN2 nitrides

This paper mainly reports structural, electronic, mechanical, optical, thermodynamic and thermoelectric properties of ternary ZnSnN2 and ZnMoN2 nitrides. Calculations are carried-out (using Wien2k software) to examine the properties of ZnSnN2 and ZnMoN2 nitrides. Both nitrides have negative formation energies confirming their structural and thermodynamic stability. Electronic band structure and DOS plots show semiconducting nature of ZnSnN2 (with a direct band gap = 0.23 eV), while semi-metallic behavior of ZnMoN2. Mechanical properties indicate the brittle behavior of both (ZnSnN2 and ZnMoN2) nitrides. Calculated mechanical properties show anisotropic behavior of ZnSnN2 and ZnMoN2 nitrides. Both nitrides show an average reflectivity of about 20–35% (in the visible region) which show their suitability to enhance light absorption in solar panels and also their use for anti-reflective coatings in optical devices. For ZnSnN2 and ZnMoN2 nitrides, thermodynamic properties are also calculated at different pressures (0–100 GPa) and at different temperatures (0–2000 K). Thermoelectric properties are calculated using Boltztrap2 code. High figure-of-merit (ZT = 2.38 of ZnSnN2 at room temperature) reflects its suitability to use in thermoelectric systems. Combination of electronic optical and thermoelectric properties indicate that the ZnSnN2 and ZnMoN2 nitrides have great potential for use in electronic, optical and thermoelectric devices.

Geometric design of antireflective leafhopper brochosomes

In nature, leafhoppers cover their body surfaces with brochosomes as a protective coating. These leafhopper-produced brochosomes are hollow, buckyball-shaped, nanoscopic spheroids with through-holes distributed across their surfaces, representing a class of deployable optical materials that are rare in nature. Despite their discovery in the 1950s, it remains unknown why the sizes of brochosomes and their through-holes consistently fall within the range of hundreds of nanometers across different leafhopper species. Here, we demonstrate that the hierarchical geometries of brochosomes are engineered within a narrow size range with through-hole architecture to significantly reduce light reflection. By utilizing two-photon polymerization three-dimensional printing to fabricate high-fidelity synthetic brochosomes, we investigated the optical form-to-function relationship of brochosomes. Our results show that the diameters of brochosomes are engineered within a specific size range to maximize broadband light scattering, while the secondary through-holes are designed to function as short-wavelength, low-pass filters, further reducing light reflection. These synergistic effects enable brochosomes to achieve a substantial reduction in specular reflection, by up to approximately 80 to 94%, across a broadband wavelength range. Importantly, brochosomes represent a biological example demonstrating short-wavelength, low-pass filter functionality. Furthermore, our results indicate that the geometries of natural brochosomes may have evolved to effectively reduce reflection from ultraviolet to visible light, thereby enabling leafhoppers to evade predators whose vision spectrum encompasses both ultraviolet and visible light. Our findings offer key design insights into a class of deployable bioinspired optical materials with potential applications in omnidirectional antireflection coatings, optical encryption, and multispectral camouflage.

Thermal radiation transferred to the guided modes of optical interference coatings.

An electromagnetic model is developed to predict the thermal radiation which is trapped in a multilayer structure and transferred to its guided modes. The theory is based on the electromagnetic power supplied by the thermal currents given by the fluctuation-dissipation theorem. The source of the radiation is the ambient temperature or that caused by the optical absorption of the component subjected to spatio-temporal illumination. A numerical example is given for a multi-dielectric mirror at thermodynamic equilibrium. It is shown that the thermal radiation transferred to the guided modes of the multilayer can be much larger or lower than the radiation emerging in free space outside the component.

Influence of functional group and their number of atoms on structural, electronic and optical properties of Sc2C MXenes: A DFT study

Two-dimensional (2D) materials MXenes have gained huge consideration due to their unique electronic, optical and mechanical properties for opto-electronics and other devices. In this work, structural, electronic and optical behavior of Sc2C MXenes by attaching different functional groups i.e. O, OH and F with different configurations (i.e varying number of atoms of functional group) is investigated using density functional theory (DFT). After determining the structural stability of all configurations further calculations are carried out. The calculations of band structures and density of states (DOS) show that the following configurations Sc2C, Sc2CO-G1, Sc2CO-G2, Sc2COH-G1, Sc2COH-G2, Sc2CF-G1, Sc2CF-G2, Sc2CF-G3 have metallic character and Sc2CO-G3, Sc2CO-G4, Sc2COH-G3, Sc2COH-G4, Sc2CF-G4 have band gap. It is observed that all the calculated properties are strongly dependent on both the functional group and their attached numbers. Furthermore, optical characteristics like absorption, dielectric function, refractive index, reflectivity, energy loss and conductivity are calculated and discussed. The calculated optical parameters revealed that the studied materials may be useful in anti-reflecting coatings.

Shift of Brewster's angle with two-dimensional materials and structures

The Brewster effect has a number of applications in antireflection coatings, spectroscopy, and polarization optics, but its tunability is still of high demand. In this Letter, we discover a method of Brewster angle control with two-dimensional conducting layers. Namely, we analyze the angular shift of Brewster's angle depending on the surface conductivity of a two-dimensional layer. First, we derive the analytical model with exact conductivity-dependent solution. Then, we investigate the Brewster angle shift in the cases of monolayer graphene and plasmonic metasurface. Finally, we support our analytical results by the full-wave numerical simulations. The results obtained may find a plethora of applications in flat optical and planar photonic devices. Published by the American Physical Society 2024

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&amp;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

Оптимизация оптического поглощения в спинтронных терагерцовых излучателях с использованием брэгговских отражателей

An optimized design of a spintronic terahertz emitter has been developed, based on a bilayer Co/Pt structure with an integrated distributed Bragg reflector. The incorporation of the Bragg mirror between the Co/Pt structure and the silicon substrate enhances optical absorption in the ferromagnetic layer, thereby amplifying spin current generation and, consequently, THz signal. A model was developed for calculating the optical absorption in the ferromagnetic layer of the spintronic emitter, taking into account the parameters of the Bragg mirror (layer thicknesses, period) based on the superlattice structure [TiO2/SiO2]N. This model is grounded on the solution of Maxwell's equations for electromagnetic waves using the COMSOL Multiphysics software. The effect of anti-reflective dielectric coatings on the level of optical absorption in the ferromagnetic layer was also analyzed. The study confirmed that using the optimized Bragg mirror is sufficient for achieving optimal absorption.

Effect of annealing in air on the properties of carbon-rich amorphous silicon carbide films

Thermal stability of thin carbon-rich Si carbide films was studied. Air anneals at the temperatures up to 700 °C were used to model the operation thermal conditions of the films in photoelectronic devices such as solar cells covered by Si carbide antireflection coatings. Si carbide films with different carbon-to-silicon ratios were studied. Annealing in air was shown to lead to consecutive film oxidation and transformation from Si carbides to oxidized Si carbide composites. The oxidized composites demonstrated the changes in thickness, element composition and optical properties as compared to the non-annealed films. At this, the films with higher Si content showed better stability of the optical properties at increased temperatures. During annealing, the increase of the film thickness by Si oxide formation competed with the thickness decrease by formation and evaporation of carbon oxide.

The Effect of the Solution Flow and Electrical Field on the Homogeneity of Large-Scale Electrodeposited ZnO Nanorods.

In this paper, we demonstrate the significant impact of the solution flow and electrical field on the homogeneity of large-scale ZnO nanorod electrodeposition from an aqueous solution containing zinc nitrate and ammonium nitrate, primarily based on the X-ray fluorescence results. The homogeneity can be enhanced by adjusting the counter electrode size and solution flow rate. We have successfully produced relatively uniform nanorod arrays on an 8 × 10 cm2 i-ZnO-coated fluorine-doped tin oxide (FTO) substrate using a compact counter electrode and a vertical stirring setup. The as-grown nanorods exhibit similar surface morphologies and dominant, intense, almost uniform near-band-edge emissions in different regions of the sample. Additionally, the surface reflectance is significantly reduced after depositing the ZnO nanorods, achieving a moth-eye effect through subwavelength structuring. This effect of the nanorod array structure indicates that it can improve the utilization efficiency of light reception or emission in various optoelectronic devices and products. The large-scale preparation of ZnO nanorods is more practical to apply and has an extremely broad application value. Based on the research results, it is feasible to prepare large-scale ZnO nanorods suitable for antireflective coatings and commercial applications by optimizing the electrodeposition conditions.

Systematic Investigation of the Optical Characteristics of GaAs Solar Cells with Antireflection Coatings and Metallic Nanoparticles Using Finite Element Analysis

Systematic Investigation of the Optical Characteristics of GaAs Solar Cells with Antireflection Coatings and Metallic Nanoparticles Using Finite Element Analysis

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.

Optimization design of surface optical characteristics of space solar cells based on transfer matrix method

The antireflection coating (ARC) can improve the photoelectric conversion efficiency of photovoltaic (PV) cells. In this paper, the influence of film thickness and refractive index of single-layer and double-layer ARC on solar light absorption under different spectral conditions is simulated by the transfer matrix method. The optimum values of ARC film thickness and refractive index are obtained. To optimize it at AM 0 (air mass 0) solar irradiance, a 66 nm thick SiN x ARC with a refractive index of 2.0 was used. The PV cell’s maximum power density is 89.87. The maximum power density of the PV cell with double-layer SiN x as ARC is 90.94. This work provides a theoretical basis for the application of ARC in ground PV power generation systems and space solar power systems.

Practical Jsc Limits for SHJ Devices: Insights From Modelling

Modern industrial silicon heterojunction (SHJ) solar cells are increasingly limited by the short-circuit current density (Jsc) and there is a strong interest in understanding how much novel approaches such as window layers, novel transparent conductive oxides (TCOs) and anti-reflection coatings (ARCs) could improve the Jsc of SHJ solar cells. In this work, the practical Jsc limits of SHJ solar cells are determined using a carefully calibrated ray-tracing model, validated using empirical data from in-house solar cells as well as recently published high-efficiency front-and-back contacted (FAB) SHJ solar cells. The model is then further refined to obtain a detailed Jsc loss breakdown of the latest record efficiency FAB SHJ solar cells, for which there are no published Jsc loss breakdowns. Notable advances made in these advanced solar cells with regards to window layers, TCOs and ARCs at the cell level are analysed. Based on the magnitude of impact on the solar cell Jsc, the most critical factors for achieving high-Jsc SHJ solar cells are identified and ranked. Allowing for additional improvements and combining the best approaches identified, an estimate of the practical upper limit of Jsc for FAB SHJ solar cells is determined to be 41.81 mA/cm2. This work serves as a useful reference for the current state of play for Jsc improvements in SHJ solar cells, and highlights practical pathways and issues for improving commercial SHJ solar cells.