Frosted Glass Research Articles

A study of the annual performance of bifacial photovoltaic modules in the case of vertical facade integration

AbstractDespite the apparent benefits of bifacial modules, their application still suffers from a lack of visibility on the performance gain that they can actually provide. In this work, we consider the specific application of vertically oriented bifacial modules, notably for facade integration. We have developed a methodology to evaluate the annual electrical performance of bifacial modules based on three tools. First, a double illumination characterization setup is used in a solar simulator for comparing module architectures. Then, a reduced scale outdoor test bench allows us to evaluate bifacial module performance in a variety of configurations. Finally, a ray‐tracing model validated with short‐term outdoor data leads to the determination of the annual performance gain. This methodology allowed us to find optimal performance according to the most important parameters of application and module. Specifically, a module architecture using half‐cut cells, a parallel cell interconnection, and textured glasses have been analyzed with respect to their influence on the resistive losses which increase in dual side illumination as well as to their influence on the effect of non‐ uniform and diffuse irradiance on the backside of the module. This work enabled us to give directions for innovative full‐size module architectures.

High‐Strength Frosted Glass by Ion Exchange of Float Glass with a Potassium Water Glass Film

Frosted glasses with increased strength were prepared by ion exchange process. Float glass samples with a size of approximately 7 × 7 cm2 were spray‐coated with potassium water glass. After drying, the samples were thermally treated at 405°C for 20 h. This led to ion exchange of the sodium ions of the float glass for the potassium ions of the water glass layer. The remaining coating was not removed from the glass. At the interface coating/glass, a diffusion layer with a high potassium concentration is formed. The penetration depth is around 18 μm. The strength of the glass increased from 180 MPa for an uncoated glass to 290 MPa for the ion‐exchanged glass (measured with a double ring test). The glasses showed intense light scattering due to the remaining scratch‐resistant coating.

Optimization of surface morphology and scattering properties of TCO/AIT textured glass front electrode for thin film solar cells

Aluminium induced texture (AIT) method has been used for obtaining highly textured glass substrate suitable for silicon based thin film solar cell technology. Wet etch step parameters of AIT process have been varied and effect of different etchants and different etching times on morphological and optical properties has been analyzed. The resulting morphology features (shape, size distribution, inclination angle) have been optimized in order to obtain the best scattering properties. ZnO:Ga (GZO) films have been deposited by sputtering technique on AIT-processed glass. Two different ZnO surface morphologies have been obtained, strongly depending on the underlying glass substrate morphology induced by different etching times. Very rough and porous texture (σrms∼150nm) was obtained on glass etched 2min showing cauliflower-like structure, whereas a softer texture (σrms∼78nm) was obtained on glass etched 7min giving wider and smoother U-shaped craters. The effect of different glass textures on optical confinement has been tested in amorphous silicon based p-i-n devices. Devices fabricated on GZO/high textured glass showed a quantum efficiency enhancement due to both an effective light trapping phenomenon and an effective anti-reflective optical behaviour. Short etching time produce smaller cavities (<1μm) with deep U-shape characterized by high roughness, high inclination angle and low autocorrelation length. This surface morphology promoted a large light scattering phenomenon, as evidenced by haze value and by angular resolved scattering (ARS) behaviour, into a large range of diffraction angles, giving high probability of effective light trapping inside a PV device.

How does frosted glass become transparent?—the answer

In my article (Temiz 2015 Phys. Educ. 50 509) I asked how we can see the other side of the frosted paper. Here I answer the questions posed.

Impact of Cell Texturing Quality on Cell to Module Losses

This work is related to a detailed study on the influence of the quality of solar cell texturing on the electrical performance after encapsulation. The effect of texturing on cells front side reflectance was studied for alkaline texturing on Cz wafer materials and processes, acidic textured Cz wafers as well as polished Cz wafers and correlated to the electrical characteristics after encapsulation. The electrical performance on module level was studied indoor at STC (standard test conditions) with varying incident light angles and outdoor during one year of outdoor exposure at a location in southern Germany. To consider for optical effects of glass surface on module performance solar glass with various deep surface texture resp. a flat surface (float glass) were processed and characterized. We show that the degree of texturing hence the front side cell reflection has a small influence on the electrical performance after encapsulation with no measurable incident light angle dependency. Furthermore do we show that even for various textured glasses the cell texturing has no effect on the module performance, neither at STC nor at varying incident light angles. The annual electrical yield study revealed even a better performance for the acidic textured cell modules if compared to the alkaline (hence well textured) cell modules.

Light scattering effect of ITO:Zr/AZO films deposited on periodic textured glass surface morphologies for silicon thin film solar cells

Various SF6/Ar plasma-textured periodic glass surface morphologies for high transmittance, haze ratio and low sheet resistance of ITO:Zr films are reported. The SF6/Ar plasma-textured glass surface morphologies were changed from low aspect ratio to high aspect ratio with the increase in RF power from 500 to 600 W. The micro- and nano-size features of textured glass surface morphologies enhanced the haze ratio in visible as well as NIR wavelength region. Micro-size textured features also influenced the sheet resistance and electrical characteristics of ITO:Zr films due to step coverage. The ITO:Zr/AZO bilayer was used as front TCO electrode for p-i-n amorphous silicon thin film solar cells with current density–voltage characteristics as: V oc = 875 mV, FF = 70.90 %, J sc = 11.31 mA/cm2, η = 7.02 %.

Improving object recognition with the ℓ-channel

We augment a new channel called the ℓ-channel to conventional RGB images, and propose its application in multiple classification and recognition tasks. The new RGB-ℓ image records the same scene using the color and frosted light channel, which are simultaneously captured using a binocular camera with a low-cost frosted glass placed in front of one of the cameras. Due to the light scattering property of the frosted glass, the acquired frosted light channel is imprecise. In this paper we propose a novel optimization that is guided by the RGB channel to refine the ℓ-channel to preserve edges due to scene radiance. Extensive experimental results have demonstrated the effectiveness of our RGB-ℓ images, where significant improvements are reported in a variety of scene classification and object recognition tasks.

How does frosted glass become transparent—the question

How is the other side of frosted glass seen? In other words, how does frosted glass become transparent?

Thin-film a-Si:H solar cells processed on aluminum-induced texture (AIT) glass superstrates: prediction of light absorption enhancement.

Light scattering superstrates are important for thin-film a-Si:H solar cells. In this work, aluminum-induced texture (AIT) glass, covered with nonetched Al-doped ZnO (AZO), is investigated as an alternative to the commonly used planar glass with texture-etched AZO superstrate. Four different AIT glasses with different surface roughnesses and different lateral feature sizes are investigated for their effects on light trapping in a-Si:H solar cells. For comparison, two reference superstrates are investigated as well: planar glass covered with nonetched AZO and planar glass covered with texture-etched AZO. Single-junction a-Si:H solar cells are deposited onto each superstrate, and the scattering properties (haze and angular resolved scattering) as well as the solar cell characteristics (current-voltage and external quantum efficiency) are measured and compared. The results indicate that AIT glass superstrates with nonetched AZO provide similar, or even superior, light trapping than the standard reference superstrate, which is demonstrated by a higher short-circuit current Jsc and a higher external quantum efficiency. Using the trapped light fraction δ, a quantity based on the integrated light scattering at the AZO/a-Si:H interface, we show that Jsc linearly increases with δ in the scattering regime of the samples, regardless of the type of superstrate used.

SF6/Ar plasma textured periodic glass surface morphologies with high transmittance and haze ratio of ITO:Zr films for amorphous silicon thin film solar cells

We report various SF6/Ar plasma textured periodic glass surface morphologies with high transmittance, haze ratio, and root mean square (rms) roughness of ITO:Zr films for amorphous silicon thin film solar cells (a-Si TFSCs). SF6/Ar plasma textured glass surface morphologies contain micro- and nano-textured features that help to scatter the light in visible and near infra-red (NIR) wavelength regions. We designed the textured glass surface morphologies with big square craters to smaller pyramids for various glass etching times from 30 to 75 min. Magnetron sputtered ITO:Zr (∼210 nm) films were deposited on textured glass surface morphologies and showed higher transmittance and haze ratio of 88.48% and 77.61%, respectively, in the visible-NIR (400–1100 nm) wavelength region. The sheet resistance and resistivity of ITO:Zr films decreased with the increase of etching time, due to high rms roughness and better step coverage. A passivation AZO (30 nm) layer was added to the ITO:Zr films, due to its better stability against hydrogen plasma exposure. The ITO:Zr/AZO films were employed as a front TCO layer and the current density–voltage (J–V) characteristics of a-Si TFSCs increased by light scattering effect, without any reduction in either the open circuit voltage (VOC) or the fill factor (FF). Relative to flat glass substrate, JSC and the efficiency of a-Si TFSCs were enhanced by 7.51% and 19.39%, respectively, for textured glass surface morphology.

A Simple Statistical Model for Transmissivity Characteristics Curve for Fluid Flow Through Rough-Walled Fractures

The fracture transmissivity characteristics curve (Witherspoon et al. in Water Resour. Res. 16(6):1016–1024, 1980) is found to deviate from cubic law as aperture decreases and still have residual transmissivity when aperture is very small. The existing models can partly explain the deviation from cubic law (e.g., Sisavath et al. in PAGEOPH 160:1009–1022, 2003), or the residual transmissivity due to irreducible flow (e.g., Nolte et al. in PAGEOPH 131(1/2):111–138, 1989). In order to predict the transmissivity curve with both the above characteristics, in this study, a simple statistical model is employed with the following assumptions: (1) fracture boundaries are assumed parallel flat at global scale, but with normally distributed aperture variations at local scale (like frosted glasses); and (2) in this case, the flow field is assumed regular with straight head-contours and flow-lines. Then the equivalent transmissivity can be approximated as a series of parallel-connected local transmissivities. The transmissivity curve can be fitted very well with both the above characteristics. It is suggested that the reason for the deviation from cubic low is possibly due to the variations of local apertures which induce redistribution of hydraulic gradients, and the residual foot is because of residual open apertures or micro-fractures in the fracture surfaces.

Automatic measurement of spectral bidirectional transmittance distribution function on translucent optical materials

A measurement platform of spectral bidirectional transmittance distribution function (BTDF) with a full three dimensional spatial coverage is developed based on a fiber spectrometer, a tungsten–halogen lamp and a 3D mechanical rotation angle system. The measurement software and the control software are integrated to realize the automatic measurement. The measurement equipment has a broad spectral coverage, a large angle range, a wide dynamic response and a short acquisition time. The measured spectral range is 380–760nm with 0.04nm spectral resolution. The measured angle range is 0–80° in zenith angle and 0–360° in azimuth angle with 0.01° angle resolution. The dynamic range is 107 and the minimal integration time is 1ms. The measurement of spectral BTDF on translucent frosted glass is performed and a large amount of measured data is obtained with the measurement error no more than 3.28%. It provides a reliable description facility for spectral and spatial transmission characteristics of the translucent materials.

High-haze and wide-spectrum hydrogenated MGZO TCO films on micro-textured glass substrates for thin-film solar cells

High-haze and wide-spectrum hydrogenated Mg and Ga co-doped ZnO (HMGZO) transparent conductive oxide films on ‘U-shaped’ micro-textured glass are developed using magnetron sputtering. The wet-chemically etched glass substrates with large crater-like features obtained via a frosting method exhibit strong light-scattering capability in a wide wavelength range (~350–1100nm). The morphological, structural, optical and electrical properties of HMGZO films on textured and flat glass are investigated in detail. The HMGZO thin films deposited on textured glasses show conformal growth and have a polycrystalline hexagonal wurtzite phase with a c-axis preferred orientation, which is similar to that of films deposited on flat glass. The electrical resistivity of HMGZO films decreases from 9.74×10−4 to 7.67×10−4Ωcm and the optical band gap Eg is in the range from 3.76 to 3.72eV as the deposition time is increased from 25 to 40min. The HMGZO films with textured glass substrate exhibit stronger light-scattering capability compared with films with flat glass substrate. Finally, an a-Si solar cell deposited on textured glass shows a higher conversion efficiency and short-circuit current density than that deposited on flat glass, as a result of effectively improved light scattering. ZnO-TCO films on low-cost chemically etched glass substrates are promising candidates as front electrodes for thin-film solar cells.

Light Scattering and Current Enhancement for Microcrystalline Silicon Thin-Film Solar Cells on Aluminium-Induced Texture Glass Superstrates with Double Texture

Microcrystalline silicon (μc-Si:H) thin-film solar cells are processed on glass superstrates having both micro- and nanoscale surface textures. The microscale texture is realised at the glass surface, using the aluminium-induced texturing (AIT) method, which is an industrially feasible process enabling a wide range of surface feature sizes (i.e., 700 nm–3 μm) of the textured glass. The nanoscale texture is made by conventional acid etching of the sputter-deposited transparent conductive oxide (TCO). The influence of the resulting “double texture” on the optical scattering is investigated by means of atomic force microscopy (AFM) (studying the surface topology), haze measurements (studying scattering into air), and short-circuit current enhancement measurements (studying scattering into silicon). A predicted enhanced optical scattering efficiency is experimentally proven by a short-circuit current enhancementΔIscof up to 1.6 mA/cm2(7.7% relative increase) compared to solar cells fabricated on a standard superstrate, that is, planar glass covered with nanotextured TCO. Enhancing the autocorrelation length (or feature size) of the AIT superstrates might have the large potential to improve theμc-Si:H thin-film solar cell efficiency, by reducing the shunting probability of the device while maintaining a high optical scattering performance.

Modulated surface textured glass as substrate for high efficiency microcrystalline silicon solar cells

In this paper, we investigate three different procedures for making modulated surface textures (MST) on glass substrates and show the application of these substrates to microcrystalline silicon solar cells. MST substrates have broader surface angle distribution (AD) than a single textured glass substrate and this distribution peaks at higher angles. Therefore, (i) the haze in reflection of MST substrates covered with an Ag layer is over 99% in the wavelength range above 350nm, which is higher than in the case of a single textured glass substrate; (ii) more reflected light is scattered into higher angles, resulting in a broader reflective angular intensity distribution (AID) in air. These properties lead to a higher Jsc for n-i-p microcrystalline silicon solar cells deposited on the MST substrates compared to cells deposited on single textured glass substrate. A solar cell deposited on a MST glass substrate with smoother peaks shows the highest electrical performance (Voc×FF value), because of a lower density of defective regions. The best cell achieved in this work has an active-area efficiency of 10.49%, with a Voc of 0.532V, a Jsc of 26.36mA/cm2, and a FF of 74.8% for a 3-μm thick absorber layer.

A novel way of texturing glass for microcrystalline silicon thin film solar cells application

AbstractIn this paper, we present a novel way of texturing glass facilitated by ZnO:Al thin film as sacrificial layer for thin film silicon solar cell application. We name this technique zinc oxide‐induced texturing (ZIT). The texturing of glass was achieved by wet etching of ZnO:Al covered glass with HF and HNO3 as etchants. We investigated the influence of the ZnO:Al layer sputtering condition, the layer thickness, and the etchant composition on the surface morphology of the textured glass. We demonstrate that we are able to control the roughness of the ZIT glass over a wide roughness range, ranging from 20 to 400 nm. Highly efficient microcrystalline silicon n‐i‐p solar cells were deposited on ZIT glass. The influence of the substrate morphology on the solar cell performance is also discussed. The highest efficiency for a single junction n‐i‐p microcrystalline silicon solar cell obtained in this work is 10.64% (Active area). Copyright © 2014 John Wiley &amp; Sons, Ltd.

Laser textured substrates for light in-coupling in thin-film solar cells

In this work, we investigate the use of a picosecond (ps) laser used for monolithic connection to texture three commercially available and frequently used multicomponent glasses, Corning EAGLE XG®, Schott BOROFLOAT® 33 and Saint-Gobain SGG DIAMANT®. The results show that the ablated crater profile and degree of texturing are glass composition dependent. This might be attributed to the different laser-induced electron collision times and recombination rates, and thus the critical electron density evolution leading to ablation. The surface texture is altered from periodic to random with decreasing scribing speed. The transmission of the textured substrates gradually decreases, whereas the multireflection on the surface increases as a consequence of the topological and morphological changes. The angular resolved measurements illustrate that the textured glass substrates scatter the light toward greater angles, which is necessary to increase the effective optical path in the absorber layer. Simulation results show that textured glass increases the absorption in the absorber material and the slightly modified refractive index region around the crater does not counteract the light in-coupling effect. The results suggest that these substrates can be used in various photovoltaic technologies and show potential for the application of alternative front contacts, such as carbon nanotubes.

Effect of wet textured glass surface morphology on the haze ratio and aspect ratio for amorphous silicon thin film solar cells

The impact of controlling the aspect ratio variation on glass substrate for a p-i-n a-Si:H solar cell was investigated and reported. Compared to a flat glass substrate (Corning Eagle XG), we demonstrate an increase of haze ratio from 1% to 79.1%, and an increment in the aspect ratio from 0.1 to 1.16, which is an increase to a high slope angle, using wet chemical etching. Optical transmittance measurements show a major improvement of from 92% to 96% for a wavelength of between 300 and 1100 nm, compared to the reference flat glass. A p-i-n a-Si:H solar cell was simulated using Advanced Semiconductor Analysis simulation based on these haze ratio and aspect ratio results, and yielded an increase in short-circuit current density (Jsc) from 15.38 to 18.74 mA/cm2, as the aspect ratio was increased from 0.1 to 0.84.

Mechanical properties of composites made from locally manufactured carbon fabrics and the composites produced from air-textured glass yarns

Composite materials have a wide range of applications in structural components because of their high strength-to-weight and stiffness-to-weight ratios. However, the most crucial and common life-restricting crack growth mode in laminated composites i.e. delamination is of great concern. Air jet texturing was selected to provide a small amount of bulk to the glass yarn. The purpose was to provide more surface contact between the fibres and resin and also to increase the adhesion between the neighbouring layers. These were expected to enhance the resistance to delamination in the woven glass composites. The development and characterisation of core-and-effect textured glass yarns was presented in the previous paper. This paper describes the comparison of the mechanical properties of composites produced from air-textured glass yarns and the composites made from locally manufactured carbon fabrics. The tensile, flexure and inter-laminar shear strength (ILSS) were compared and it was observed that although glass fibres are inferior to carbon fibres in terms of mechanical properties however, the flexure strength and ILSS of glass based composites increases after texturing and were found closer to the properties of carbon based composites.

Nanosized patterned protective glass exhibiting high transmittance and self-cleaning effects for photovoltaic systems

As a result of the rising concerns surrounding environmental pollution, green energy technologies are beginning to replace conventional power generation technology based on fossil fuels. In particular, photovoltaic systems which convert solar energy into electricity without generating carbon dioxide have been widely used around the world as a result of their conversion energy being exceptionally high. In this investigation, we fabricated anti-reflection and light-scattering patterns on the protective glass of solar cell modules. The path length and quantity of incident light reaching the solar cell module could be increased by incorporating anti-reflection and light-scattering patterns. These patterns were fabricated on the surface of the protective glass using nanoimprint lithography (NIL) and inductively coupled plasma (ICP) processes. The amount of light reflected off the patterned protective glass decreased by up to 4% when the fabricated anti-reflection patterns were implemented. Additionally, the surface of the patterned glass was superhydrophobic as a result of the self-assembled monolayer (SAM) coating employed in this study. The lithium ion battery comprised of the solar module using patterned glass as a protective layer could be charged approximately 14% higher than the lithium ion battery comprised of the solar module using conventional textured glass as a protective layer.