Low Light Reflectivity Research Articles

Towards high-efficiency Al-BSF c-Si solar cell with both superior omnidirectional and electrical performance by modulating the tilt angle of quasi-periodic inverted pyramid arrays

Seeking efficient light trapping structures with both superior omnidirectional and electrical performance is always on the way for increasing electrical energy output of c -Si solar cell over a wide range of light incident angle (θ). Here, tile angle (δ) of quasi-periodic structure arrays is systematically modulated from 35.9° to 72.8° on diamond-wire-sawn (DWS) c -Si by a simple and cost-effective Cu and Ni co-assisted chemical etching way followed by a post treatment. Interestingly, compared with the conventional micro pyramid (MP), the optimized inverted pyramid (IP) like arrays with a δ of 64° possess both lower light reflectance and carrier recombination, leading to a corresponding solar cell with a higher efficiency (∼19.67%) than that of MP based counterpart (∼19.31%). Moreover, during the increase of θ, the external quantum efficiency (EQE) of 64° IP based cell drops much more slowly than that of MP based one by properly adjusting the relative position of the structure arrays and incident light, indicating its omnidirectional property. Simultaneously, a maximum relative enhancement of electrical output power approaching ∼5.8% in the θ range of −90°–90° is achieved on 64° IP based cell compared to the MP based one, the mechanism behind which is further explained by optical simulation. The above finds pave a new way to increase the electrical energy output in a simple and cost-effective way. • Tilt angle control of quasi-periodic IP was achieved by varying Cu and Ni ratio. • 0.36% absolute increase in solar cell efficiency was made based on 64° IP. • ∼5.8% relative increase of output power was achieved on 64° IP based cell. • Mechanism behind omnidirectional performance was explained by optical simulation.

First principle study of optoelectronic and mechanical properties of lead-free double perovskites Cs2SeX6 (X = Cl, Br, I)

The variant double perovskites are considered novel materials for solar cells and optoelectronic applications. Here, we explored electronic, mechanical, and optical characteristics of Cs2SeX6 (X = Cl, Br, I) by density functional theory (DFT) analysis. The tolerance factor between 0.97–1.0 signifies the structural stability of the investigated compounds while thermodynamic and mechanical stabilities were ensured by positive frequencies of phonon dispersion as well as elastic constants. Moreover, the Poisson and Pugh's ratios are explored for brittle and ductile behavior. The Debye and melting temperatures have also been reported through mechanical analysis. The tuning of the bandgap takes place from 3.10 to 2.64 eV and then 1.15 eV by substitution of Cl with Br and I, respectively. The optical spectra show a shift in absorption region from ultraviolet-to-visible. In addition, the low light reflection and optical energy loss range (0.0–3.0 eV) promises potential of the studied potential for solar cells and optoelectronics uses.

Optical composites based on organic polymers and semiconductor pigments

The aim of the work was the development of optical organic-inorganic composite materials with high absorption of light the visible part of the spectrum and high reflection in the near infrared region of the spectrum. Such materials are used in industry and construction as coatings. To create these optical composites, epoxy and epoxy-polyurethane polymer matrices containing inorganic semiconducting particles (CuS, PbS, Fe3O4) were used. Highly dispersive powders of inorganic pigments were used for the preparation of homogeneous composite materials. The wet precipitation method with the application of organic stabilizing additions was applied for the preparation of dispersive CuS and PbS powders. Optical microscopy and X-ray diffraction analysis helped to study the crystal structure and morphology of the obtained semiconductor pigments. PMT-3 device was applied for microhardness measurements of the prepared composite materials. Based on the data of X-ray diffraction analysis, the average crystallite size was calculated using the Scherrer formula. It was found that freshly precipitated CuS and PbS powders consist of nanocrystals with a size of 11–20 nm. Optical microscopy data indicate the formation of aggregates of semiconductor nanocrystals in powders. Experiments have shown that all synthesized composites have low light reflection coefficient (less than 0.06) in the visible part of the spectrum and an increased light reflection coefficient in the near infrared region of the spectrum (0.13–0.15 and more). The results of the study showed that the use of epoxy-polyurethane polymer matrices provides greater microhardness of composite materials, compared to the composites based on epoxy polymers. The highest microhardness values were observed in composite materials based on epoxy-polyurethane polymers containing highly dispersed Fe3O4 particles. Obtained organic-inorganic composites could be used as materials for light-absorbing coatings in different industrial applications.

Bio-inspired spatially variant photonic crystals for self-collimation and beam-steering applications in the near-infrared spectrum

The self-collimation of light through Photonic Crystals (PCs) due to their optical properties and through a special geometric structure offers a new form of beam steering with highly optical control capabilities for a range of different applications. The objective of this work is to understand self-collimation and bending of light beams through bio-inspired Spatially Variant Photonic Crystals (SVPCs) made from dielectric materials such as silicon dioxide and common polymers used in three-dimensional printing like SU-8. Based upon natural PCs found in animals such as butterflies and fish, the PCs developed in this work can be used to manipulate different wavelengths of light for optical communications, multiplexing, and beam-tuning devices for light detection and ranging applications. In this paper, we show the optical properties and potential applications of two different SVPC designs that can control light through a 90-degree bend and optical logic gates. These two-dimensional SVPC designs were optimized for operation in the near-infrared range of approximately 800–1000 nm for the 90-degree bend and 700–1000 nm for the optical logic gate. These SVPCs were shown to provide high transmission through desired regions with low reflection and absorption of light to prove the potential benefits of these structures for future optical systems.

One-dimensional SnO2 nanotube solid-state electrolyte for fast electron transport and high light harvesting in solar energy conversion

We incorporated one-dimensional SnO2 hollow nanotubes (1DTONT) into a quasi-solid-state nanogel polymer electrolyte to produce a highly efficient solid-state electrolyte for solid-state dye-sensitized solar cells (ssDSSCs). The concentration of 1DTONT in the solid-state electrolyte was systematically controlled to understand its effect on solar cell performance and stability. The addition of 1DTONT increases electrolyte viscosity, resulting in a solid-state electrolyte. Although the 1DTONT reduces ion mobility due to enhanced viscosity, its oriented structure with a high aspect ratio increases electron transport. Thus, ssDSSCs incorporated with solid-state 9 wt% 1DTONT electrolyte (ss-9 wt% 1DTONT) display lower charge-transfer resistance than those incorporated with quasi-solid-state nanogel polymer electrolyte. Additionally, 1DTONTs possess light scattering characteristics. Their large particle size distribution (from a few hundred nanometers to a few micrometers) and hollow structure result in multiple scattering opportunities. This feature allows 1DTONTs in solid-state electrolytes to form a thin light-scattering layer (~1 μm) on the TiO2 photoanode. Therefore, ssDSSCs with ss-9 wt% 1DTONT electrolyte exhibit low transmittance and high light reflectance, producing high incident photon-to-current efficiency (IPCE) values over the wavelength range of interest. Overall, ssDSSCs with ss-9 wt% 1DTONT electrolyte exhibit a solar energy conversion efficiency of ~5.8% due to enhanced current density resulting from improved electron transport and light harvesting.

Лазерный монитор с независимой подсветкой для наблюдения процессов высокотемпературного горения нанопорошков металлов

The paper presents a laser monitor with independent illumination and a mirror imaging scheme based on an active medium on copper bromide vapors, which allows visualizing the surface of metal nanopowders during combustion. Independent laser illumination using a second active element based on copper bromide vapors can significantly increase the contrast of images compared to a laser monitor based on a single active element. This feature is advantageous when examining surfaces of materials with low light reflection. The paper also demonstrates the realization of a two-channel pulse generator for pumping active elements on copper bromide vapors based on one high-voltage power supply.

Low reflectance of carbon nanotube and nanoscroll-based thin film coatings: a case study.

Research on carbon material-based thin films with low light reflectance has received significant attention for the development of high absorber coatings for stray light control applications. Herein, we report a method for the successful fabrication of stable thin films comprised of carbon nanotubes (CNTs) and nanoscrolls (CNS) on an aluminium (Al) substrate, which exhibited low reflectance of the order of 2–3% in the visible and near-infrared (NIR) spectral bands. Changes in the structural and chemical composition of pristine single-walled carbon nanotube (SWCNT) samples were analyzed after each processing step. Spectroscopy, microscopy and microstructural studies demonstrated emergence of CNS and multi-walled carbon nanotubes (MWCNTs) due to the sequential chemical processing of the sample. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies revealed the formation of CNS via curling and folding of graphene sheets. Microstructural investigations including SEM and atomic force microscopy (AFM) confirmed the presence of microcavities and pores on the surface of the film. These cavities and pores significantly contribute to the observed low reflectance value of CNTs, CNS compound films by trapping the incident light. Fundamental space environmental simulation tests (SEST) were performed on the coated films, that showed promising results with reflectance values almost unaltered in the visible and NIR spectral bands, demonstrating the durability of these films as potential candidates to be used in extreme space environmental conditions. This study describes the preparation, characterization, and testing of blended CNT and CNS coatings for low-light scattering applications.

Fluorescent proteins for in vivo imaging, where's the biliverdin?

Noninvasive fluorescent imaging requires far-red and near-infrared fluorescent proteins for deeper imaging. Near-infrared light penetrates biological tissue with blood vessels due to low absorbance, scattering, and reflection of light and has a greater signal-to-noise due to less autofluorescence. Far-red and near-infrared fluorescent proteins absorb light >600 nm to expand the color palette for imaging multiple biosensors and noninvasive in vivo imaging. The ideal fluorescent proteins are bright, photobleach minimally, express well in the desired cells, do not oligomerize, and generate or incorporate exogenous fluorophores efficiently. Coral-derived red fluorescent proteins require oxygen for fluorophore formation and release two hydrogen peroxide molecules. New fluorescent proteins based on phytochrome and phycobiliproteins use biliverdin IXα as fluorophores, do not require oxygen for maturation to image anaerobic organisms and tumor core, and do not generate hydrogen peroxide. The small Ultra-Red Fluorescent Protein (smURFP) was evolved from a cyanobacterial phycobiliprotein to covalently attach biliverdin as an exogenous fluorophore. The small Ultra-Red Fluorescent Protein is biophysically as bright as the enhanced green fluorescent protein, is exceptionally photostable, used for biosensor development, and visible in living mice. Novel applications of smURFP include in vitro protein diagnostics with attomolar (10-18 M) sensitivity, encapsulation in viral particles, and fluorescent protein nanoparticles. However, the availability of biliverdin limits the fluorescence of biliverdin-attaching fluorescent proteins; hence, extra biliverdin is needed to enhance brightness. New methods for improved biliverdin bioavailability are necessary to develop improved bright far-red and near-infrared fluorescent proteins for noninvasive imaging in vivo.

Excitation Density Dependent Photoluminescence Studies on Homo-Epitaxial GaN Nanowall Networks Grown by Laser Assisted Molecular Beam Epitaxy.

The optical properties of laser-assisted molecular beam epitaxy grown homo-epitaxialGaN nanowall networks (NWNs) were investigated using power dependent photoluminescence (PL) spectroscopy and compared with homo-epitaxial GaN thin film. The pore size and tip width of GaN NWN sample is ˜120-180 nm and 10-15 nm, respectively. The ultraviolet-visible spectroscopy study shows that the GaN NWNs have low optical light reflection and minimum Fabry-Perot cavity effect than GaN film. The room temperature PL spectroscopy reveals that the GaN NWNs possesses enhanced band gap of 3.51 eV with blue shift of 90 meV than the GaN film (3.42 eV). The excitation density dependent PL spectroscopy measurements reveal that the GaN NWNs nanowall and near band emission (NBE) peak position and its linewidth invariant. The intensity of NBE peak for GaN film and nanowalls varies linearly whereas NBE to defect related yellow luminescence peak intensity ratio shows a non-linear variation on the excitation density. The excitation density in PL measurements plays a key role when the sample quality compared on the basis of PL data.

Fabrication of SiNWs/PEDOT:PSS Heterojunction Solar Cells

Silicon nanowires (SiNWs) are synthesized through a metal-assisted chemical etching (MACE) method using Si(100) substrates and silver (Ag) as a catalyst. Scanning electron microscope (SEM) images confirmed that length of prepared SiNWs was increased when etching time increased. The prepared SiNWs demonstrated considerably low light reflectance at a wavelength range of 200–1100 nm. The photoluminescence (PL) spectra of the grown SiNWs showed a broad emission band peaked at a wavelength of about 750 nm. A solar cell and photodetector based on heterojunction SiNWs/PEDOT:PSS were fabricated using SiNWs that prepared with different etching time and its J–V, sensitivity, and time response were investigated. The conversion efficiency of fabricated solar cell was increased from 0.39% to 0.68% when wire length decreased from 24 µm to 21 µm, respectively. However, the sensitivity of the heterojunction SiNWs/PEDOT:PSS photodetector was decreased from 53774% to 36826% when wire length decreased from 24 µm to 21 µm, respectively.

Bio-inspired hierarchical assembly of Au/ZnO decorated carbonized spinach leaves with enhanced photocatalysis performance

Inspired by the characteristics that plant leaves are beneficial for solar light absorption, we have prepared a bio-inspired hierarchical assembly of carbonized spinach leaves@Au/ZnO (CS@Au/ZnO) for solar energy utilization. CS@Au/ZnO shows a low light reflectance of 5% and a high specific surface area of 311.41 m2/g. CS@Au/ZnO demonstrates higher photocatalytic degradation efficiency: more than 97% of Rhodamine B (RhB) and 61% of ciprofloxacin (CIP) could be degraded in 180 min under the visible light irradiation. In addition, we also tested the photocatalytic H2 production performance of CS@Au/ZnO and the H2 evolution rate is 2.384 mmol g−1 h−1 under simulated solar light. CS@Au/ZnO shows a high cycling stability in recyclable photocatalytic degradation and photocatalytic water splitting. Moreover, CS@Au/ZnO shows a swift and steady photocurrent of about 63.6 μA/cm2, illustrating a high sensitivity to solar light. The enhanced photocatalysis performance of CS@Au/ZnO could be ascribed to the naturally optimized macroporous structure of CS with high conductivity, which could enhance the light harvesting and carrier transport, simultaneously. Moreover, modification of AuNPs can broaden the light response range of ZnONRs and reduce the probability of electron-hole recombination. Due to the wide availability of plant leaves, CS@Au/ZnO assembly has broad application prospects in photocatalytic degradation of organic pollutions, photovoltaic devices, and photocatalytic H2 evolution.

Photoelectrochemical Self-Powered Solar-Blind Photodetectors Based on Ga2O3 Nanorod Array/Electrolyte Solid/Liquid Heterojunctions with a Large Separation Interface of Photogenerated Carriers

Solar-blind photodetectors have been widely developed because of their great potential application in biological analysis, ultraviolet communication, and so on. Photodetectors constructed by vertically aligned nanorod arrays (NRAs), have attracted intensive interest recently owing to the virtues of low light reflectivity and rapid electron transport. However, limited by the insufficient contact between the upper electrode and NRAs because of uneven NRAs, photogenerated carriers cannot be effectively separated and transferred. In this work, a novel photoelectrochemical (PEC) type self-powered solar-blind photodetectors constructed in the form of Ga2O3 NRAs/electrolyte solid/liquid heterojunction with a large photogenerated carrier separation interface has been fabricated, β-Ga2O3 NRAs PEC photodetector shows a photoresponsivity of 3.81 mA/W at a bias voltage of 0 V under the 254 nm light illumination with the light intensity of 2.8 mW/cm2, thus yielding a Iphoto/Idark ratio of 28.97 and an external quantum...

Increased Absorption with Al Nanoparticle at Front Surface of Thin Film Silicon Solar Cell

This article presents an effective structural design arrangement for light trapping in the front surface of a thin film silicon solar cell (TFSC). Front surface light trapping rate is significantly enhanced here by incorporating the Aluminium (Al) nanoparticle arrays into silicon nitride anti-reflection layer. The light trapping capability of these arrays is extensively analyzed via Finite Difference Time Domain (FDTD) method considering the wavelength ranging from 400 to 1100 nm. The outcome indicates that the structural parameters associated with the aluminium nanoparticle arrays like particle radii and separations between adjacent particles, play vital roles in designing the solar cell to achieve better light trapping efficiency. A detailed comparative analysis has justified the effectiveness of this approach while contrasting the results found with commonly used silver nanoparticle arrays at the front surface of the cell. Because of the surface plasmon excitation, lower light reflectance, and significant near field enhancement, aluminium nanoparticle arrays offer broadband light absorption by the cell.

Single-step electrodeposition of superhydrophobic black NiO thin films

Black finished surfaces have extensive applications in many domains, such as optics, solar cells, and aerospace. The single-step electrodeposition of superhydrophobic black NiO films from a dimethyl sulfoxide-based electrolyte is described in this paper. The physicochemical properties of the obtained film were characterized using scanning electron microscopy, X-ray diffraction, and electrochemical tests (electrochemical impedance spectroscopy and potentiodynamic polarization). A rough surface with a low reflection of light was formed after the deposition process that increased the contact angle of water from about 87° (for bare Cu) to 163° (in presence of the black coating), which improved the corrosion resistance of the Cu substrate by about 30%. The formed black NiO film revealed a notably high stability and kept its appearance even after corrosion tests.

In Situ Surface Oxidized Copper Mesh Electrodes for High‐Performance Transparent Electrical Heating and Electromagnetic Interference Shielding

AbstractMetallic mesh is a significant candidate of transparent conductive electrodes (TCEs) to substitute the current state‐of‐the‐art material indium tin oxide for optoelectronic devices. However, there remains a challenge to fabricate stable and good‐visibility metallic mesh with the low‐cost copper (Cu) material. A metallic Cu mesh electrode (on glass) with a high absolute transmittance of ≈82% combined with an adjustable low electrical resistance of ≈0.2 Ω sq−1 and a low total light reflectance of 8.7% is demonstrated here. The Cu mesh TCE shows excellent visibility and good thermal, moisture, and environmental stability that can be used in practical applications. This was achieved by in situ forming an oxidation‐resistive and light‐absorptive capping layer of oxide on the surface of Cu meshes. The electrode was fabricated by UV‐lithography and electroplating, and then directly annealing in the air. To assess the application potentials, transparent electrical heating up to 100 °C under 3 V supply and transparent shielding of radiofrequency with ≈24 dB attenuation in Ku band are achieved. Good photoelectric properties, low‐cost material, and excellent stability imply that this Cu mesh electrode is a striking candidate for low‐cost TCE for efficient optoelectronic devices.

An Innovative Light Trapping Structure Fabrication Method on Diamond‐Wire‐Sawing Multi‐Crystalline Silicon Wafers

AbstractAn innovative fabrication method of light trapping structures on the surface of diamond‐wire‐sawing multi‐crystalline silicon (DWS mc‐Si) is proposed, which may trigger new progress in photovoltaic (PV) industry. A simple pre‐etching step with HNO3/HF solution is used to remove the saw marks of the wafers as well as amorphous silicon layers, and form vermicular micro‐hollows. Then, the HNO3/HF fog formed by ultrasonic vibration etches the silicon surface to fabricate nano‐scale porous structures on the above microstructures. This micro‐nano composite structure (MNCS) surface shows low average light reflectivity (∼5.5%) and relatively higher effective minority carrier lifetime (∼5.2 μs). The innovative method is applied to fabricate the 156 mm × 156 mm DWS mc‐Si solar cells and the conversion efficiency of 18.01% has been obtained, which is 0.93% higher than the cells without MNCS. This method matches well with current PV industrial processes, which shows a promising prospect.

Dependence of Copper Phthalocyanine Photovoltaic Thin Film on the Sizes of Silver Nanoparticles

In this work, silver nanoparticles (AgNPs) were prepared with different particle sizes (6 nm, 11 nm, and 14 nm) using chemical methods. The morphology, distribution, and account sizes have been studying from transmission electron microscope (TEM) images. The change of the surface Plasmon resonance (SPR) bands with the particle sizes clarified from ultraviolet-visible spectra. A thin film from copper phthalocyanine (CuPc) and their doped by AgNPs was done using thermal evaporation technique and spin coater under vacuum. The surface morphology of the films was studied using scanning electron microscope (SEM). Films tested as photovoltaics (PV) cells. It turns out that, the calculated efficiencies were (0.237%, 0.266%, and 0.280%) when the size of AgNPs was (6 nm, 11 nm, and 14 nm) respectively. We concluded that the large size of AgNPs increases the efficiency of CuPc thin films due to the increase of the scattering and low reflection of the incident light at the surface of the thin films.

Wide variation in the structure and physical properties of reactively sputtered (TiZrHf)N coatings under different working pressures

The dependence of the structure of (TiZrHf)N coatings deposited by reactive magnetron sputtering on different working pressures and their mechanical and electro-optical properties were investigated. The increased working pressure contributed to the decreased oxygen contamination. With increased working pressure, the compressive stress was transitioned to tensile one. Compressively stressed coatings consisted of tightly packed columns with a smooth surface. The tensile stressed coatings presented void network structure surrounding the columnar grains with a rough surface. Moreover, the grain size initially increased and subsequently decreased. Accordingly, the (TiZrHf)N coatings deposited at high working pressure were characterized with poor hardness, low electrical conductivity, and low light reflectivity due to the porous structure and high oxygen contamination. In addition, the coating color changed from bright gold to dark gray. In this study, the working pressure was proven a sensitive deposition parameter in controlling the microstructure, mechanical, and electro-optical properties of the coating. The wide structural variation in the (TiZrHf)N coatings allowed a diverse physical performance suitable for a broad range of applications.

High-performance Si/organic hybrid solar cells using a novel cone-shaped Si nanoholes structures and back surface passivation layer

Nanostructured silicon (Si) can provide improved light trapping capacity in Si/organic hybrid solar cells (HSCs) due to its low light reflectance compared with planar Si. However, the poor contact of nanostructured Si/organic interface and serious recombination on the uncovered Si surface can result in an inferior open-circuit voltage (VOC) and fill factor (FF) for HSCs. Here, we have designed and fabricated a novel cone-shaped Si nanoholes (SiNHs) structures to form a superior interface contact between SiNHs and organic layer by using an advanced metal assisted chemical etching method. In addition, a Cs2CO3 layer was also introduced on the Si back surface to reduce the contact resistance as well as to suppress the surface recombination for the HSCs. With such improvements, a power conversion efficiency (PCE) up to 13.5% was achieved for Si/organic hybrid solar cell with the back passivation layer. This work provided a new strategy to improve the junction quality and performance of nanostructured Si/PEDOT:PSS HSCs.

Antifogging abilities of model nanotextures.

Nanometre-scale features with special shapes impart a broad spectrum of unique properties to the surface of insects. These properties are essential for the animal's survival, and include the low light reflectance of moth eyes, the oil repellency of springtail carapaces and the ultra-adhesive nature of palmtree bugs. Antireflective mosquito eyes and cicada wings are also known to exhibit some antifogging and self-cleaning properties. In all cases, the combination of small feature size and optimal shape provides exceptional surface properties. In this work, we investigate the underlying antifogging mechanism in model materials designed to mimic natural systems, and explain the importance of the texture's feature size and shape. While exposure to fog strongly compromises the water-repellency of hydrophobic structures, this failure can be minimized by scaling the texture down to nanosize. This undesired effect even becomes non-measurable if the hydrophobic surface consists of nanocones, which generate antifogging efficiency close to unity and water departure of droplets smaller than 2 μm.