Frosted Glass Research Articles

Comparison of Angular Reflectance Losses Between PV Modules With Planar and Textured Glass Under Singapore Outdoor Conditions

Photovoltaic (PV) modules are rated under standard test conditions with normally incident light, whereas under outdoor conditions photons arrive on a PV module surface at all angles. In this study, the angular losses of PV modules with a planar and textured front glass are investigated for the tropical conditions of Singapore. Angular reflectance for both modules is first measured using a goniophotometer. From the measurements, the angular loss factors due to the different radiation components are calculated. Then, the angular losses under Singapore outdoor conditions are determined using three transposition models: Liu and Jordan, Hay and Davies, and Perez et al. Two 60-cell PV modules with a planar and textured glass are fabricated and measured outdoors for validation of the modeling results. Outdoor measurement results show that the PV module with textured glass captures 1.4% extra light compared with the PV module with planar glass for the 6-mo period studied. Next, the annual angular loss, monthly angular loss, and typical meteorological day angular loss for both module structures are studied. For all cases studied, the PV module with textured glass has consistently lower angular losses compared with the PV module with a planar glass.

Thin-film Silicon Solar Cells on Dry Etched Textured Glass

In this work, we report on the development of thin-film silicon solar cells on textured glass substrates. The textured glass substrates are fabricated by ion beam etching using a wet-chemically textured three-dimensional etching mask. The development of transparent and conductive front contact ZnO:Al films on textured glass is presented. The optimum of the front contact layer thickness was found to be 60nm. For this thickness deteriorating reflection maxima are avoided, which occur due to the interferences in the front contact layer. The glass texture is adjusted to achieve better light trapping in the near infrared range. In addition, ITO instead of ZnO:Al film was investigated to surpass the decreased fill factor of solar cells deposited on ZnO:Al thin front contacts.

Growth and Properties of ZnO:Al on Textured Glass for Thin Film Solar Cells

Aluminium induced texturing (AIT) method has been used to texture glass substrates in order to enhance the photon absorption in thin film solar cells. The resultant glass roughness has been analyzed by varying the AIT process parameters and it has been found that the deposition method of Al is a decisive factor in tuning the texture. Two types of textures, a soft (texture E) and a rough texture (texture S), were achieved from the thermally evaporated and sputtered Al layers through AIT process. Aluminium-doped zinc oxide (AZO) layers of different thickness were deposited over both textures and over smooth glass. Haze values above 30% were obtained for texture S + AZO and above 10% for texture E + AZO. The resultant morphologies were free from sharp edges or deep valleys and the transparency and the resistivity values were also good enough to be used as front contact for thin film solar cells. In order to demonstrate the light absorption enhancement in a solar cell device, 200 nm of a-Si:H followed by 300 nm of Ag were grown over the textured and smooth substrates with AZO, and an optical absorption enhancement of 35% for texture E and 53% for texture S was obtained in comparison to the smooth substrate.

Texture‐Etched SnO2 Glasses Applied to Silicon Thin‐Film Solar Cells

Transparent electrodes of tin dioxide (SnO2) on glasses were further wet‐etched in the diluted HCl:Cr solution to obtain larger surface roughness and better light‐scattering characteristic for thin‐film solar cell applications. The process parameters in terms of HCl/Cr mixture ratio, etching temperature, and etching time have been investigated. After etching process, the surface roughness, transmission haze, and sheet resistance of SnO2 glasses were measured. It was found that the etching rate was increased with the additions in etchant concentration of Cr and etching temperature. The optimum texture‐etching parameters were 0.15 wt.% Cr in 49% HCl, temperature of 90°C, and time of 30 sec. Moreover, silicon thin‐film solar cells with the p‐i‐n structure were fabricated on the textured SnO2 glasses using hot‐wire chemical vapor deposition. By optimizing the texture‐etching process, the cell efficiency was increased from 4.04% to 4.39%, resulting from the increment of short‐circuit current density from 14.14 to 15.58 mA/cm2. This improvement in cell performances can be ascribed to the light‐scattering effect induced by surface texturization of SnO2.

Fabrication of photocatalyst panels and the factors determining their activity for water splitting

A photocatalyst panel of Rh2−yCryO3/(Ga1−xZnx)(N1−xOx) exhibiting activity comparable to that of a conventional powder suspension system was developed by spreading the photocatalyst powder onto 5 cm × 5 cm flat frosted glass plates together with micrometer-sized hydrophilic silica particles, which improved the porosity of the photocatalyst layer for more efficient mass diffusion through the photocatalyst layer.

Block Textured a-Si:H Solar Cell

A series of etching experiments on light trapping structure have been carried out by glass etching. The block structure provides long light traveling path and a constant distance between the cathode and anode electrodes regardless of the block height, which results in higher efficiency of the block textured solar cell. In terms of etching profile of the glass substrate, the addition of NH4F resulted in the smooth and clean etching profile, and the steep slope of the block was obtained by optimizing the composition of etching solution. For a higher HF concentration, a more graded slope was obtained and the addition of HNO3and NH4F provided steep slope and clean etching profile. The effects of the block textured glass were verified by a comparison of the solar cell efficiency. For the textured solar cell, the surface was much rougher than that of the plain glass, which also contributes to the improvement of the efficiency. We accomplished block shaped light trapping structure for the first time by wet etching of the glass substrate, which enables the high efficiency thin film solar cell with the aid of the good step coverage deposition.

Optical Absorption Enhancement in Amorphous Silicon Films and Solar Cell Precursors Using the Aluminum-Induced Glass Texturing Method

One of the key issues of thin-film silicon solar cells is their limited optical absorptance due to the thin absorber layer and the low absorption coefficient for near-infrared wavelengths. Texturing of one or more interfaces in the layered structure of these cells is an important technique to scatter light and enhance the optical pathlength. This in turn enhances the optical absorption of the solar radiation in the absorber layer and improves the solar cell efficiency. In this paper we investigate the effects of textured glass superstrate surfaces on the optical absorptance of intrinsic a-Si:H films and a-Si:Hp-i-nthin-film solar cell precursors deposited onto them. The silicon-facing surface of the glass sheets was textured with the aluminium-induced glass texturing method (AIT method). Absorption in both intrinsic silicon films and solar cell precursor structures is found to increase strongly due to the textured glass superstrate. The increased absorption due to the AIT glass opens up the possibility to reduce the absorber layer thickness of a-Si:H solar cells.

Scientific analyses beyond the excavation: studies for a non invasive preliminary approach

Domo is an archaeological site located in the Foreste Casentinesi National Park, near the town of Bibbiena, in the province of Arezzo (Tuscany). Since the ’80, investigations at Domo have revealed a Roman domus with a Roman baths complex. Unfortunately, the rich stratigraphy was almost completely lost during the first excavations. Since 2008 the archaeological site was reopened by Archeodomani s.a.s., a company that deals with promotion of cultural heritage, and it is still under summer excavation campaigns. In the future perspective to try and solve doubts about the site phase sequence of the Roman baths complex, not easy to understand now for several use modifications of the different areas, we developed an analytical method that could allow a large scale investigation limiting the sampling. In this paper, we present the preliminary results obtained for mortar, both from the walls and from the binding of cocciopesto, with XRD (X Ray Diffraction) and ED-XRF (Energy Dispersive X-Ray Fluorescence) analysis on ground samples. XRD analysis was performed at ICVBC-CNR and the diffraction data (Cu–Ka, 1.5418 A) were collected on a J-J Panalytical X’Pert PRO spectrometer. Grounded samples were placed in aluminium sample holder or dusted on frosted glass sample holder, depending on sample amount. XRF measurements were performed at Physics Department of Milan University using a portable EDXRF spectrometer (Assing Lithos 3000) exploiting polychromatic radiation from a Mo anode X-ray tube. Both analyses were performed after preliminary observation of the samples by stereo-microscope and the results obtained through XRF and XRD were compared to get more complete information about samples. Data were also submitted to multivariate analysis (Hierarchical Clustering) to get material classification. The comparison between the classification obtained and archaeological interpretation is still in progress; the collection of analytical data will go on in future excavation campaigns. The complete overview will be part of a project to promote the archaeological site through an online portal.

Analytical solution for haze values of aluminium-induced texture (AIT) glass superstrates for a-Si:H solar cells.

Light scattering at randomly textured interfaces is essential to improve the absorption of thin-film silicon solar cells. Aluminium-induced texture (AIT) glass provides suitable scattering for amorphous silicon (a-Si:H) solar cells. The scattering properties of textured surfaces are usually characterised by two properties: the angularly resolved intensity distribution and the haze. However, we find that the commonly used haze equations cannot accurately describe the experimentally observed spectral dependence of the haze of AIT glass. This is particularly the case for surface morphologies with a large rms roughness and small lateral feature sizes. In this paper we present an improved method for haze calculation, based on the power spectral density (PSD) function of the randomly textured surface. To better reproduce the measured haze characteristics, we suggest two improvements: i) inclusion of the average lateral feature size of the textured surface into the haze calculation, and ii) considering the opening angle of the haze measurement. We show that with these two improvements an accurate prediction of the haze of AIT glass is possible. Furthermore, we use the new equation to define optimum morphology parameters for AIT glass to be used for a-Si:H solar cell applications. The autocorrelation length is identified as the critical parameter. For the investigated a-Si:H solar cells, the optimum autocorrelation length is shown to be 320 nm.

Superstrate type flexible thin-film Si solar cells using flexible glass substrates

We have investigated the flexible thin-film silicon (Si) solar cells fabricated on the flexible glass substrates. The preliminary p–i–n type flexible hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) double-junction solar cell is compared with its counterpart fabricated on the textured F-doped tin oxide-coated glass substrate. Because of the inferior light transmitting and scattering of the SnO2:F front electrode coated by a spray pyrolysis deposition in the long wavelength region, the preliminary flexible solar cell shows a severely limited short-circuit current. Without any back reflector, the initial efficiency of 8.0% and stabilized efficiency of 7.1% are achieved. The initial efficiency of 9.3% was achieved by improving the current matching. The superstrate type thin-film Si photovoltaic technology using flexible transparent substrates has a high potential to minimize the cell-to-module loss through a monolithic series integration using a laser scribe technique.

Efficient light incoupling into silicon thin-film solar cells by anti-reflecting MgO/high-compact-AZO with air-side textured glass

Light incoupling effects have been enhanced at front interfaces of silicon (Si) thin-film solar cells. Firstly, a MgO thin film was introduced at glass substrate/Al-doped ZnO (AZO) interface for anti-reflection effect. We additionally found that the surface morphology of AZO films grown on MgO film after texture-etching is dependent on the compactness of AZO. For high-compact AZO films, the texture-etched MgO/AZO double layer exhibited significantly enhanced light-scattering capability. Secondly, we made textured surfaces at air/glass interface through simple plasma-etching without sacrificial layers or masks by optimizing the etching pressure. The additional air-side texture contributed to further improvement of total light scattering from the MgO/AZO-coated glass substrate. Fabricated microcrystalline Si thin-film solar cells employing the MgO coated glass with air-side surface texture showed decreased cell reflectance and increased quantum efficiency. The Jsc increased from 21.7 to 26.5 mA cm−2 and final efficiency of 9.49% was achieved. Based on our experimental results, the suggested structure, the MgO coating on glass substrate of which air-side surface is texture-etched, can offer a promising approach to improve the light incoupling and efficiency of Si thin-film solar cells.

Ground-based monitoring of UV radiation

High levels of UV radiation (UV-B) from the Sun have harmful effects on agricultural crops, forest ecosystems, humans, and livestock.1 In recent years the level of UV-B reaching Earth’s surface has increased because the protective stratospheric ozone layer has been eroded by man-made chemicals, such as chlorofluorocarbons and methyl bromide.2 Although the rapid decline in ozone concentration is now showing improvement, the US Department of Agriculture (USDA) remains concerned about possible harmful effects of increased UV-B on plants and ecosystems. UV-B levels, however, are not typically monitored at weather stations in the United States. For this reason, the USDA initiated the UV-B Monitoring and Research Program (UVMRP) in 1992.3 This program represents the only active source of complete ground-based UV measurements (since 1996) in the United States.4 The UVMRP network collects ambient ground-level solar radiation data, including UV-B and photosynthetically active radiation, from 37 climatological and three long-term research sites (see Figure 1). Data is downloaded from the network sites every night, and then subjected to automated quality control and calibration processes, so that it is available to researchers in several disciplines on our website the following morning.5 The primary UV instruments at our network’s stations use independent interference filter-photodiode detectors and automated rotating shadow bands to measure the direct-normal, total-horizontal, and diffuse-horizontal UV solar irradiance at seven wavelengths. The diffuser is an integrating cavity, with thin Teflon walls, that protrudes above the top of the detector head and is surrounded by an artificial horizon that improves the angular response of the instrument. Two diaphragms made of frosted WG-280 glass in the integrating cavity act as transmission diffusers. Light that exits the bottom of the diffuser is incident on seven photodiodes with interference filters, which Figure 1. The location of UV-B Monitoring and Research Program (UVMRP) monitoring sites in 2013. The 37 climatological sites are intended for long-term monitoring of different ecoregions across the United States. The three research sites are used for shorter-term and specific studies.

Development of textured ZnO-coated low-cost glass substrate with very high haze ratio for silicon-based thin film solar cells

Zinc oxide (ZnO) films with a very high haze ratio and low resistivity were developed on soda–lime glass substrate by using reactive ion etching (RIE) treatment with carbon tetrafluoride (CF4) to modify the substrate surface morphology before the deposition of ZnO films. We found that the surface morphology of the ZnO films deposited by metal organic chemical vapor deposition (MOCVD) technique could be modified by varying the glass treatment conditions and the gas pressure was a key parameter. With increasing glass-etching pressure, the surface morphology of the ZnO films changed from conventional pyramid-like single texture to greater cauliflower-like double texture, leading to significant increases in root mean square roughness and haze ratio of the films. By employing the developed high-haze ZnO films as a front transparent conductive oxide (TCO) layer in microcrystalline silicon solar cells, an enhancement in the quantum efficiency in the long-wavelength region has been achieved. Experimental results have verified that our unique and original glass etching treatment is a simple and effective technique to improve the light-scattering properties of the ZnO films while preserving their good transparency and electrical properties. Thus, the ZnO films deposited on etched soda–lime glass have a high potential for the use as a front TCO layer in thin-film Si solar cells.

Large scale antireflective glass texturing using grid contacts in anodization methods

Antireflection coatings on glass are highly desirable, since glasses are widely used as a packaging material in the solar industry due to their transparency and durability. In this report, we propose a novel anodizing method using grid line contacts for antireflective nanostructures on a large area glass substrate. The nanoholes on the glass substrate exhibit broadband and omnidirectional antireflective properties, leading to an 11.34% improvement in the short-circuit current and enhanced power conversion efficiency from 7.9% to 8.57%. Moreover, the enhanced optical properties persist for 3 months in an outdoor environment. The proposed anodizing method can be considered as an alternative technique for the fabrication of large area nanostructures.

Improvement in the fracture toughness (Mode I) of laminated glass fabric composites through air-jet texturing

Delamination is the most common failure mode in laminated composites due to the reduced strength in the through-the-thickness direction. Air-jet texturing was used to provide more surface contact between the fibres and the resin by producing bulk and loops in the yarn. The development and characterization of core-and-effect textured glass yarns and the effect of texturing on the mechanical properties of laminated composites were presented in the previous papers. This paper describes the effect of texturing on the inter-laminar fracture toughness (Mode I) of glass laminated composites. The composites of twill weave fabrics were developed from both the textured and non-textured yarn and fracture toughness is tested in warp and weft directions. Significant improvement was observed in the Mode I fracture toughness of the composites after texturing. The bulkier, loopy structure of the textured yarn provided more surface contact between the fibre and the resin and significantly improved the bonding strength.

Visual Form Perception from Age 20 through 80 Years

We measured performance on a battery of visual form perception tasks for adults sampled evenly from each decade of adult life from 20 to 80 years. Measures were included that are considered to reflect processing at early through intermediate stages of the form processing pathways: collinear facilitation, center-surround contrast effects, global shape discrimination of contours of elements embedded in noise elements, and global shape discrimination in texture (Glass patterns). A total of 38 women and 20 men (mainly Caucasian, low refractive error) participated, aged between 20 and 82 years. With advancing age, contrast sensitivity decreased linearly (B = 0.009, t(56) = 8.14, P < 0.001), perceptual surround suppression of low contrast stimuli embedded in higher contrast surrounds increased (B = -0.006, t(56) = -3.32, P < 0.01), and coherence thresholds for detecting form in Glass patterns increased (B = 0.14, t(56) = 2.53, P = 0.02). Performance between tasks was not correlated. Several aspects of form perception alter gradually throughout the adult lifespan, namely context-dependent perception of contrast, and the extraction of global shape from texture. Our results suggested age-dependent differences under natural viewing conditions that are not predictable by standard clinical measures of visual function, and point to changes in neural function that are ongoing throughout adult life.

Light trapping scheme of ICP-RIE glass texturing by SF6/Ar plasma for high haze ratio

Inductive coupled plasma-reactive ion etching (ICP-RIE) offers an anisotropic texturing with superior surface structure of glass substrate. We report light trapping scheme of ICP-RIE glass texturing by SF6/Ar plasma. We observed that surface structure is an important factor to improve the diffused transmittance and haze ratio of textured glass. The presence of metal elements like Al, B, F and Na are responsible for low etching rate (22.66–27.33 nm/min) of textured glass. The total transmittance remains high whereas the diffused transmittance increased with the pattern size due to the variation of surface morphology of glass. Our textured glass substrates showed the high diffused transmittance and haze ratio in the visible-NIR wavelength region. The electrical properties of the ITO films are independent of glass surface structure that may be suitable for high performance of thin film solar cells.

Development of air textured core-and-effect glass yarns for improving the bonding strength of laminated composites

Delamination is the most common failure mode in laminated composites, due to the reduced strength in the through-the-thickness direction. This paper describes the development of core-and-effect textured glass yarns for improving the bonding strength of laminated glass woven fabric composites. Air-jet texturing introduces bulk and loops in the yarn which provides more contact surface between the fibers and the resin. However, the yarn tenacity decreases after texturing because of the reduced alignment of the filaments. The effects of texturing air pressure, yarn overfeed ratio, yarn linear density and core-sheath ratio were studied in this paper. The tenacity of glass yarns decreased significantly after the texturing process. The reduction was smaller for yarns with a higher core linear density. The effects of texturing air pressure on the tenacity were found to be insignificant.

Optimisation of the Back Surface Reflector for Textured Polycrystalline Si Thin Film Solar Cells

The back surface reflector of a solar cell not only enhances back reflection, but also may contribute to further randomising light. In this paper, three different types of back surface reflectors (dielectric/metal bi-layer, pigmented diffuse reflector and Ag nanoparticles) are investigated and compared with one another to determine the optimal for polycrystalline Si (poly-Si) thin film solar cells grown on textured glass superstrates. The optimal dielectric layer material and thickness of an interposed dielectric layer between Si and metal contact is optimised via WVASE simulation for ∼2μm random textured poly-Si thin film solar cells on glass. Experimentally, the Si thin films are deposited on Aluminium Induced Textured (AIT) glass and those with optical absorption close to Lambertian limited absorption are selected for investigation. The experiment confirms the simulation results and finds the best back reflector configuration— 500 nm MgF2+Ag. Theoretically Ag nanoparticles on the rear surface of a cell should induce surface plasmon effects, scattering light obliquely into the Si film. However, this work indicates that Ag nanoparticles degrade Jsc of textured poly-Si thin film solar cells. The reason why Ag nanoparticles do not work on textured poly-Si thin film solar cells needs further investigation.

A novel silver nanoparticle assisted texture as broadband antireflection coating for solar cell applications

To maximise the degree of light incoupling, therefore improving the short circuit current and efficiency of solar cells, a novel subwavelength (SW) structured ‘moth-eye’ antireflection coating (ARC) is formed on the sun-facing side of the glass superstrate. This moth-eye structure in theory can suppress reflection entirely in the 300–1200nm wavelength range. It is produced by fabricating a mask, followed by reactive ion etch. In this paper, we present a novel etch mask, a random Ag nanoparticle array on glass with feature size ranging from ∼50nm to ∼350nm. The subwavelength features can be adjusted by varying the size, shape and distribution of the Ag nanoparticle array, which in turn is tuned by varying as-deposited Ag thickness. The optimal structures reduce reflection loss by a current equivalent of 1.25mA/cm2 for a 3.3mm borosilicate glass (BSG) superstrate, by 1.39mA/cm2 for 1.1mm BSG and enhances Jsc by 3.4% on average for 2.4μm poly-Si thin-film solar cells on 3.3mm BSG.On Si film side of the glass surface, a preliminary modulated texture investigation, consisting of growing SW structure on micron sized aluminium induced textured (AIT) glass reduced reflection loss by ∼7% compared to original AIT samples.