WO2017090056A1

WO2017090056A1 - Solar module with selective colored coating

Info

Publication number: WO2017090056A1
Application number: PCT/IN2016/050275
Authority: WO
Inventors: Anishkumar SOMAN; Aldrin Antony
Original assignee: Indian Institute Of Technology Bombay
Priority date: 2015-11-24
Filing date: 2016-08-17
Publication date: 2017-06-01
Also published as: WO2017090056A4

Abstract

Embodiments herein describe a solar module including an element positioned on a solar cell. One or more reflective colored coating layer(s) is deposited on the element or the solar cell. The reflective colored coating layer can selectively reflect a desired wavelength of light and can provide the required color on the solar cell or the solar module without altering the structure or manufacturing process of the solar cell.

Description

SOLAR MODULE WITH SELECTIVE COLORED COATING FIELD OF INVENTION

[0001] The present embodiments relate to a solar cell, and more particularly to a solar module including one or more reflective colored coating layers. The present application is based on, and claims priority from an Indian Application Number 4410/MUM/2015 filed on 24^th November, 2015, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF INVENTION

[0002] A crystalline silicon solar cell technology is a most matured one in photovoltaic s, and a solar cell is generally installed in a rooftop or land spaces. Conventional silicon solar cells have a typical blue color because of Anti-Reflection Coating (ARC) on it. This limits the application of the solar cell or a solar module for integration into architectural designs which not only requires an alternate energy source but also expects it to "blend-in" in its environment. In order to be integrated into architectural structures for Building Integrated Photovoltaic' s (BIPV), it is imperative that the conventional solar cells which generally look dark blue or black can have colors which increase the aesthetics of the solar modules.

[0003] In the conventional system and method, the colored solar cells are fabricated by using a multi-layer ARC included in the solar cells. In another conventional system and method, the colored solar cells are fabricated by changing the thickness of a single layer ARC. In yet another conventional system and method, the colors are modulated for industrial textured multi-crystalline solar cells by multi-layer ARCs. However, all these methods are process-dependent and altering the thickness of the ARC requires optimization of the solar cell fabrication steps for contact formation. [0004] The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.

OBJECT OF INVENTION

[0005] The principal object of the embodiments herein describes a solar module including one or more reflective colored coating layer(s).

SUMMARY

[0006] The embodiments herein disclose a solar module including a plurality of solar cells and an element positioned on the solar cell. One or more reflective colored coating layer(s) is deposited on the element or the solar cell.

[0007] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES

[0008] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which: [0009] FIGS. 1 to 3 are schematic of a solar module including one or more reflective colored coating layer(s), according to embodiments as disclosed herein;

[0010] FIG. 4 is a photograph showing a proof of concept of a colored coating on 5 cm x 5 cm glass placed over 156 cm crystalline silicon solar cells, according to embodiments as disclosed herein;

[0011] FIGS. 5a and 5bare graphs showing reflectance of Red- Green-Blue (RGB) colors on a glass and reflectance of white color on the glass respectively, according to embodiments as disclosed herein;

[0012] FIG. 6 is a graph showing transmittance of R,G,B and white coating on a glass according to the embodiments as disclosed herein;

[0013] FIG. 7 is a graph showing absorbance of R,G,B and white coating on a glass according to embodiments as disclosed herein;

[0014] FIG. 8 is a graph showing an External Quantum Efficiency (EQE) of different colored solar cells, according to embodiments as disclosed herein;

[0015] FIG. 9 is a graph showing current density versus voltage (J- V) of different colored solar cells, according to embodiments as disclosed herein; and

[0016] FIG. lOis a chromaticity diagram of different colored reflectors, according to an embodiment as disclosed herein.

DETAILED DESCRIPTION OF INVENTION

[0017] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well- known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, refers to a nonexclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0018] Embodiments herein achieve a solar module including a plurality of solar cells and an element positioned on a solar cell. One or more reflective colored coating layer(s) is/are deposited on the element or the solar cells.

[0019] In an embodiment, the refractive index of the one or more reflective colored coating layer(s) is in a predefined range.

[0020] In an embodiment, the predefined range is below 2.5

[0021] In an embodiment, the reflective coating layers are placed alternatively.

[0022] In an embodiment, the reflective coating layers are made of different material.

[0023] In an embodiment, the element is a glass.

[0024] In an embodiment, the element is a polymeric sheet. [0025] In an embodiment, the reflective colored coating layer is a selective reflector optical coating (SROC) layer.

[0026] In an embodiment, the reflective colored coating layer is a selective reflector.

[0027] In an embodiment, the reflective colored coating layer is a

Selectively Modulated Aesthetic Reflector Technology (SMART) coating layer.

[0028] Unlike the conventional systems and methods, the proposed solar cell includes an element in which reflective colored coating layer is deposited on the element. The reflective colored coating layer can selectively reflect a desired wavelength range of light and can provide the required color for the solar cell or a solar module without altering the structure or manufacturing process of the solar cell.

[0029] The SMART layer can be coated on the glass or on the polymeric sheet to stick over the conventional solar modules or even on the solar cell itself, which can help to provide aesthetic value for the conventional solar cell or conventional solar module.

[0030] The proposed mechanism can directly be used by a glass manufacturing company for producing the colored glass for a Building Integrated Photovoltaics (BIPV) application. It can also be used by architects and developers for designing colored building. The proposed mechanism can be a process independent, so that it can be applied to any type of solar cell or solar modules. The proposed solar cells can have considerable efficiencies to be commercially viable.

[0031] The proposed mechanism can be used to integrate the reflective colored coating layer along with the traditional solar cell or the traditional module as BIPV building material. Though the SMART layer will decrease the efficiency of the solar module, the application of the aesthetic integration in the buildings increases the possibility for large scale installation of solar modules onto the buildings and can help in increasing the energy generation. The BIPV can prove to be economically viable in urban areas, since tall buildings offer large surface for energy generation as compared to rooftop installations and a Photovoltaic (PV) module can replace the traditional glass facades. In spite of the reflection or absorption losses due to this multilayer SMART layer, the proposed reflective colored coating layer could provide around 60% efficiency of standard silicon solar cell for the white colored solar cells/modules and nearly 80% efficiency of standard cell for the Red-Green-Blue (RGB) colored cells/modules.

[0032] Further, the BIPV doesn't require mounting systems that are used for roof top installations and the additional cost incurred for the building material can be recovered from the energy payback of the mounting system. The proposed mechanism provides the colored coatings to aesthetically integrate the solar modules into building facades, windows, roof tops, etc.

[0033] The proposed colored solar cell or colored solar module can be realized by using a SMART coating layer between the encapsulation material and the glass. This type of SMART layers coated glass can be commercially made by the glass manufacturer. The SMART coatings can also be done on the polymeric substrates to stick to the solar modules. It could also be used for making colored stick-on sheets or tiles to cover solar modules or solar cells.

[0034] Referring now to the drawing, and more particularly to FIGS. 1 through 10, there are shown preferred embodiments.

[0035] FIGS. 1 to 3 are schematic of a solar modulelOO including one or more reflective colored coating layer(s) 106, according to embodiments as disclosed herein. As shown in the FIG. l, the solar module 100 includes a solar cell 102, an element 104, and one or more reflective colored coating layer(s) 106. The solar modulelOO includes the element 104 positioned on the solar cell 102. One or more reflective colored coating layer(s) 106 is deposited on the element 104. The element 104 can be, for example but not limited to, a glass, a polymeric sheet, or the like.

[0036] In an embodiment, the refractive index of the one or more reflective colored coating layer(s) 106 is in a predefined range. In an embodiment, the predefined range is below 2.5.

[0037] In an embodiment, the reflective coating layers 106 are placed alternatively. The reflective coating layers 106 are made of different material. The materials can be, for example but not limited to, a silicon oxynitride (SiON), a silicon nitride (SiN), combination of transparent dielectric or transparent conducting oxides or the like.

[0038] In an embodiment, as shown in the FIG.2, the solar module200 includes the solar cell 102and one or more reflective colored coating layer(s) 106. One or more reflective colored coating layer(s) 106 is directly placed on the solar cell 102.

[0039] In an embodiment, as shown in the FIG.3, the solar cell 102is provided with the reflective colored coating layers 106, a glass, and an Ethylene Vinyl Acetate (EVA). The EVA is a transparent layer. The reflective colored coating layer(s) 106is deposited on the glass. In the proposed solar cell 102, the reflective colored coating layers 106 are formed by depositing alternate layers of dielectrics namely silicon oxynitride (SiON) and silicon nitride (SiN) by a Plasma Enhanced Chemical Vapor Deposition(PECVD) technique. The silicon oxynitride has a thickness range of 50nm to 100 nm, and the silicon nitride has a thickness range of 40 nm to 70 nm. The silicon oxynitride and silicon nitride included in the reflective colored coating layers 106 are deposited at a low substrate temperature of less than 200 °C. [0040] In an embodiment, in order to obtain individual red, green and blue colors, the proposed solar module 100 utilizes 4 bi-layers of SiON and SiN.

[0041] In an embodiment, in order to obtain the white color, the proposed solar module 100 is provided by fabricating a modulated structure out of the red, green and blue coatings consisting of 12 bi-layers of SiON and SiN. The SiN is a stable material which is currently used as ARC for a crystalline silicon (c-Si) solar cell. The SiON has a high temperature stability and better chemically inert behavior. The SiON/SiN layer stack is in an inner side of the glass, therefore the solar cell 102is protected from direct exposure to air and moisture.

[0042] In an embodiment, the reflective colored coating layer 106 is a Selectively Modulated Aesthetic Reflector Technology (SMART) layer. The SMART layer includes a 4 bi-layer of SiON/SiN. The first layer on the glass is the SiON, and a second layer on the glass is the SiN. The refractive index of the SiON (ni) is less than the refractive index of the SiN (n₂). The range of ni is betweenl.5 to 1.8 and that of n₂ is betweenl.9 to 2.1. The structures of the solar module 100 are designed in such a way that the solar cell 102show similar performance whether it is coated on an outer side of the glass or an inner side of the glass. In order to verify it's functionality on the solar cell 102, External Quantum Efficiency (EQE) and Lighted Current Density v/s Voltage (J-V) of the solar cells 102placed below the SMART layer having multi-layers on the outer side of the glass as well as inner side of the glass are measured and obtained identical and repeatable results of EQE and J-V for both sides.

[0043] In an embodiment, the reflective colored coating layer 106 is a selective reflector. The selective reflector can selectively reflect the desired wavelength of light and can give the solar cell 102or the solar module lOOthe required color without altering the structure or manufacturing process mechanism of the solar cell 102.

[0044] In an embodiment, the reflective colored coating layer 106 is a Selectively Modulated Aesthetic Reflector Technology (SMART) layer. The SMART layer can be coated on the glass or on the polymeric sheet to stick over the solar cell 102 or the solar module lOOor even on the solar cell 102itself, which can help to provide aesthetic value for the conventional solar cell 102.

[0045] In an embodiment, the reflective colored coating layer 106 is a SMART coating layer. The element 104with the SMART coating layer can be used as a cover element for the solar cell 102or the solar module 100.

[0046] In an example, the glass with the SMART coating layer can be used as a cover glass for the solar cell 102 or the solar module 100.

[0047] In an embodiment, the selective reflector optical coating depositing process has been developed by depositing multi-layers of dielectric coatings by the PECVD at a low temperature of less than 200 °C and is realized by a Physical Vapor Deposition (PVD) technique, a Chemical Vapor Deposition (CVD) technique, or the like. The dielectric coating layer is made of a material. The material can be, for example but not limited to, an oxide, nitride, oxynitrides, transition metal oxides or transparent conducting oxides material. Since the coating layer is deposited at a low temperature of less than 200°C, the coating layer can also be deposited over polymeric sheets which could then be integrated with the solar module 100.

[0048] FIG. 4 is a photograph illustrating a proof of concept of the colored coating on 5 cm x 5 cm glass placed over 156 cm crystalline silicon solar cells, according to embodiments as disclosed herein. [0049] FIGS. 5a and 5b are graphs showing reflectance of Red- Green-Blue (RGB) colors on the glass and reflectance of the white color on the glass respectively, according to embodiments as disclosed herein. The SMART layer works on the principle of selectively reflecting a particular wavelength range of light as shown from the reflectance data in the FIGS. 5a and 5b. In Table-1, visible spectrum refers to 390 nm to 700 nm whereas the active absorption of photons in the silicon solar cell is in the wavelength range of 300 nm to 1200 nm. For the primary color coatings (i.e., RGB color coatings), the integrated reflectance is ~ 30% in the visible spectrum which equates to a reflection loss of 18-24% in the spectral range for the silicon solar cells. For white coating, the reflection loss increases to 50% in visible spectrum and 30% in the spectral range for the silicon solar cells. The reflective colored coating layers 106 are designed in such a way that it only gives its peculiar color of appearance when the reflective colored coating layer 106is placed on the solar cell 102and appear normally transparent in air.

Table 1: Integrated reflectance in visible and in the spectral range for the silicon (Si) solar cells

[0050] FIG. 6 is a graph showing transmittance of RGB and white coating on the glass according to the embodiments as disclosed herein. The representative transmittances of the SMART layer are given in the FIG. 6 and that can be observed from the Table-2 that the primary colored coatings have a high transmittance of around 70% in the visible spectrum and white coating has a transmittance of ~ 45% in the visible spectrum. It is important to note that the RGB colored SMART coating has a high transmittance of 80-90% in a Near-Infrared Region (NIR) of 700 to 1200 nm in the silicon solar cell spectrum whereas the white coating has a transmittance of -80% in the same NIR wavelength range (700 to 1200 nm).

Table 2: Integrated transmittance in visible and spectral range for the silicon (Si) solar cells

[0051] FIG. 7 is a graph showing absorbance of RGB and white coating on the glass according to embodiments as disclosed herein. The material (i.e., SiON/SiN) has negligible absorption losses in the required range of 400 nm to 1200 nm which can be verified from the absorption graph in the FIG. 7.

[0052] FIG. 8 is a graph showing an External Quantum Efficiency (EQE) of different colored solar cells, according to embodiments as disclosed herein. The SMART layer is integrated with the conventional silicon (Si) solar cell having the ARC on a top portion along with a silver grid and an aluminum back contact. The EQE of the solar cells are measured from 300 to 1200 nm to understand the spectral response for the photon absorption and is shown in the FIG. 8. The short circuit current density (J_sc) from the EQE decreases by a minimum of ~ 17% for the blue colored solar cell and by a maximum of ~ 39% for the white colored solar cells. The reference solar cell has a calculated J_sc of 38 mA/cm as seen in the Table-3. The proposed solar cell 102obtains the exactly same values of EQE and calculated J_sc for the SMART layer on the outer side of the glass or the inner side of the glass which demonstrates the proof of concept of using the same coating as an external or internal part of the solar cell 102.

Table 3: Calculated J_sc from EQE plot

[0053] FIG. 9 is a graph showing current density versus voltage (J-

V) of different colored solar cells, according to embodiments as disclosed herein. The J-V curves under standard 1 sun illumination of the solar cells with different SMART coatings layer are shown in the FIG. 9. It can be observed that the cells have considerable performance in spite of the reflection losses providing a good tradeoff between efficiency and optical losses. The standard reference cell has an efficiency of 15% and the white solar cell has an efficiency of 9% which amounts to 60% effective efficiency of the reference cell in spite of 50% losses in visible light reflection. The primary colored solar cells have an even better performance of 11-12% efficiency which amounts to -80% efficiency of the reference cell without any coating. A detailed record of the current-voltage (I-V) parameters can be seen in the Table-4. Thus, the SMART layer seems viable for large area applications which emphasizes on aesthetic appearance as well. Sample Open Short circuit Fill factor Efficiency Relative name circuit current density (FF) (%) (%) efficiency voltage (Jsc) (%)

(Voc) [mA/cm2]

[mV]

Blue Solar 575.8 28.3 75.7 12.3 81 cell

Green 574.1 27.1 75.7 11.8 78 Solar cell

Red Solar 571.1 24.6 75.4 10.6 70 cell

White 566.9 21.0 75.3 8.9 59 Solar cell

Reference 580.9 34.1 76 15.1 100 Solar cell

Table 4: 1-V parameters of different colored solar cells

[0054] FIG. 10 is a chromaticity diagram of different colored reflectors, according to an embodiment as disclosed herein. The colors of the different SMART layer have been verified by the 1931 International Commission on Illumination (CIE) standards. The (x,y) values and the chromaticity diagrams of R,G,B and white coatings are given in the Table-5 and FIG. 10 respectively along with the co-ordinates of a commercially available white diffuser (Spectralon© coating) for comparison.

Reflector Color CIE (x,y) co-ordinates

Blue (0.20, 0.17)

Green (0.25, 0.38)

Red (0.39, 0.32)

White (0.27, 0.29)

Commercial white diffuser (0.33, 0.33)

Table 5: The CIE co-ordinates for R, G, B & white SMART with respect to a white diffuser

[0055] Though the above description is described using the reflective colored coating layer 106 but, it is to be understood that other embodiments are not limited thereon. A person having ordinary skill in the art can quick identify that other methods which includes colored as well as white solar cells having considerable efficiencies can be used for the SMART coatings for the colored aesthetic photovoltaic modules without departing from the scope of the invention.

[0056] Although the FIGS. 3-10 are explained in context of solar cell 102, it is to be understood to a person of ordinary skill in the art to describe the FIGS. 3-10 with respect to the solar module 200.

[0057] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

STATEMENT OF CLAIMS We claim:

1. A solar module comprising:

a plurality of solar cells;

an element positioned on the solar cell; and

at least one reflective colored coating layer deposited on one of the solar cell and the element.

2. The solar module as claimed in claim 1, wherein refractive index of the at least one reflective colored coating layer is in a predefined range.

3. The solar module as claimed in claim 2, wherein the predefined range is below 2.5.

4. The solar module as claimed in claim 1, wherein the reflective coating layers are placed alternatively and the reflective coating layers are made of different material.

5. The solar module as claimed in claim 1, wherein the element is one of a glass, and a polymeric sheet.

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