WO2012128439A1 - Transparent substrate for a solar cell having a broadband anti-reflective multilayered coating thereon and method for preparing the same - Google Patents

Transparent substrate for a solar cell having a broadband anti-reflective multilayered coating thereon and method for preparing the same Download PDF

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WO2012128439A1
WO2012128439A1 PCT/KR2011/008478 KR2011008478W WO2012128439A1 WO 2012128439 A1 WO2012128439 A1 WO 2012128439A1 KR 2011008478 W KR2011008478 W KR 2011008478W WO 2012128439 A1 WO2012128439 A1 WO 2012128439A1
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solar cell
refractive layer
reflective
transparent substrate
refractive
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French (fr)
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Han Jong Yoo
Kyung Hwan BAE
Jin Yong Kim
Seong Kun YOON
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KCC Corp
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KCC Corp
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/30—Coatings
    • H10F77/306—Coatings for devices having potential barriers
    • H10F77/311—Coatings for devices having potential barriers for photovoltaic cells
    • H10F77/315—Coatings for devices having potential barriers for photovoltaic cells the coatings being antireflective or having enhancing optical properties
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F10/00—Individual photovoltaic cells, e.g. solar cells
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/30—Coatings
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/542—Dye sensitized solar cells

Definitions

  • the present invention relates to a broadband anti-reflective, transparent substrate for a solar cell having a multilayered coating thereon and a method for preparing the same. More specifically, the present invention relates to a broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate for a solar cell that is a transparent substrate applicable to the solar cell’s outermost surface (solar light-receiving surface) and has a multilayered coating of six (6) or more coating layers that are formed by alternately depositing a high-refractive material layer and a low-refractive material layer sequentially on its surface, whereby it shows a broadband (350 to 1,100 nm wavelength) anti-reflective function and increases the transmittance of light in a near-infrared region as well as a visible light region while it decreases transmittance of light in an infrared region which causes deterioration of the solar cell without contributing to electricity generation of the solar cell, and thus the efficiency of the solar cell can be improved; and a method for preparing
  • Anti-reflective coating technology which began in the fields of picture frame, lens, display device, etc. and has been developed ⁇ is a technology for improving the transmittance of light in a visible light region (i.e., 350 to 780 nm wavelength).
  • Such anti-reflective coatings conventionally comprise layer(s) of a material having a refractive index between that of a substrate (in the case of glass, conventionally 1.5) and that of air (1.0).
  • a transparent substrate for a solar cell such as glass needs to increase the transmittance of light in a near-infrared region (to 1,100 nm) as well as a visible light region because a solar cell absorbs light in a broader wavelength region than a visible light region.
  • the transmittance of light passing through the outermost transparent substrate of the solar cell needs to be improved in the broadband region (350 to 1,100 nm wavelength).
  • a single-layered anti-reflective coating of porous silicon oxide has been formed on the surface of the outermost glass for a solar cell.
  • the pores provided by such a porous silicon oxide perform the role of lowering the refractive index of silicon oxide.
  • such a single-layered coating lacks durability against water.
  • such a porous silicon oxide coating is conventionally formed by a sol-gel method, and it is difficult to obtain a uniform thin film by the spraying or dipping method of coating.
  • a thin layer of porous silicon oxide can be formed on a glass by etching the external surface of the glass with a chemical reagent such as hydrofluoric acid.
  • a chemical reagent such as hydrofluoric acid.
  • this method has problems of low productivity due to long etching time, non-uniformity of the glass surface and use of environmentally harmful reagents such as hydrofluoric acid.
  • the present invention has an object of providing a broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate for a solar cell that is a transparent substrate applicable to the solar cell’s outermost surface and increases the transmittance of light in a near-infrared region as well as a visible light region while it decreases the transmittance of light in an infrared region which causes deterioration of the solar cell without contributing to electricity generation of the solar cell, and thus the efficiency of the solar cell can be improved; and a method for preparing the same.
  • a broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate for a solar cell that is a transparent substrate applicable to the solar cell’s outermost surface and increases the transmittance of light in a near-infrared region as well as a visible light region while it decreases the transmittance of light in an infrared region which causes deterioration of the solar cell without contributing to electricity generation of the solar cell, and thus the efficiency of the solar cell can be improved;
  • the present invention provides a broadband anti-reflective, transparent substrate for a solar cell having multilayered coating thereon, wherein the multilayered coating has six (6) or more coating layers that are formed by alternately depositing a high-refractive layer having a refractive index of from 1.9 to 2.5 and a low-refractive layer having a refractive index of from 1.3 to 1.6 sequentially on a substrate.
  • the other aspect of the present invention provides a method for preparing a broadband anti-reflective, transparent substrate for a solar cell, comprising the steps of: (1) forming a first high-refractive layer having a refractive index of from 1.9 to 2.5 on a substrate; (2) forming a first low-refractive layer having a refractive index of from 1.3 to 1.6 on the first high-refractive layer; (3) forming a second high-refractive layer having a refractive index of from 1.9 to 2.5 on the first low-refractive layer; (4) forming a second low-refractive layer having a refractive index of from 1.3 to 1.6 on the second high-refractive layer; (5) forming a third high-refractive layer having a refractive index of from 1.9 to 2.5 on the second low-refractive layer; and (6) forming a third low-refractive layer having a refractive index of from 1.3 to 1.6 on the third high-refractive layer.
  • Another aspect of the present invention provides a solar cell module having the broadband anti-reflective, transparent substrate for a solar cell of the present invention on its outermost surface.
  • the broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate according to the present invention shows selective light transmittance property between visible light and a near-infrared region, and a long wavelength region including far-infrared rays.
  • the transmittance of light in visible light and a near-infrared region is increased and accordingly the amount of solar energy absorbed in the solar cell is also increased, whereby the cell efficiency can be improved, and at the same time the transmittance of light in a long-wavelength region including far-infrared rays (1,100 to 2,500 nm wavelength) is decreased, whereby the temperature of s solar cell module can be lowered.
  • Such temperature lowering prevents deterioration of the solar cell, through which the lifespan and efficiency of the solar cell can be increased.
  • Figure 1 schematically represents a layer structure of glass having the multilayered coating of six (6) layers thereon according to an embodiment of the present invention.
  • Figure 2 is the transmittance spectra graph of the glasses prepared in the Example and Comparative Examples of the present invention.
  • any transparent materials such as glass substrate and transparent plastic substrates (for example, transparent substrates of polycarbonate [PC] and polymethylmethacrylate [PMMA]) can be used without limitation as long as the anti-reflective multilayered coating of the present invention can be formed thereon.
  • transparent plastic substrates for example, transparent substrates of polycarbonate [PC] and polymethylmethacrylate [PMMA]
  • PMMA polymethylmethacrylate
  • glass substrate is used.
  • glass for example, general glass such as soda-lime glass for construction or automobiles, low-iron patterned glass for solar cell, low-iron float glass, transparent conductive oxide (TCO) glass and the like can be used without limitation. Furthermore, if needed, surface texture-treated glass or tempered or partly tempered glass may be used.
  • the thickness of the transparent substrate There is no particular limitation on the thickness of the transparent substrate. It can be freely selected from a thickness range of from 2 mm to 8 mm according to the purpose of use.
  • the high-refractive layer comprised in the anti-reflective multilayered coating of the present invention has a refractive index of from 1.9 to 2.5. Materials having a refractive index beyond said range cannot be used as a material for the high-refractive layer in the present invention.
  • the high-refractive layer may comprise one or more metal oxides selected from zinc oxides, tin oxides, zirconium oxides, zinc-tin oxides, titanium oxides and niobium oxides.
  • the high-refractive layer may further comprise one or more nitrides selected from silicon nitrides and silicon aluminum nitrides.
  • Each high-refractive layer comprised in the anti-reflective multilayered coating of the present invention may have a thickness properly selected within a range of from 5 to 60 nm.
  • the thicknesses of the high-refractive layers are, sequentially from the substrate, preferably 5 to 40 nm and more preferably 10 to 30 nm for the first high-refractive layer; preferably 5 to 60 nm and more preferably 5 to 50 nm for the second high-refractive layer; and preferably 10 to 40 nm and more preferably 10 to 30 nm for the third high-refractive layer. It is preferable that each high-refractive layer satisfies the above corresponding thickness range.
  • the substantial increase in transmittance of light in the infrared region as well as the visible light region and the broadband anti-reflection effect can be obtained, and accordingly a high-performance, anti-reflective multilayered coating over 350 nm to 1,100 nm wavelength range can be obtained.
  • the low-refractive layer comprised in the anti-reflective multilayered coating of the present invention has a refractive index of from 1.3 to 1.6. Materials having a refractive index beyond said range cannot be used as a material for the low-refractive layer in the present invention.
  • the low-refractive layer may comprise one or more oxides selected from silicon oxides, silicon oxynitrides, silicon oxycarbides and silicon-aluminum mixed oxides.
  • the mixed oxides are advantageous in that durability (particularly, chemical resistance) may be improved as compared with pure silicon oxide (SiO 2 ).
  • the ratio between silicon and aluminum may be properly adjusted to improve durability as expected, without excessively increasing the refractive index of the layer.
  • Each low-refractive layer comprised in the anti-reflective multilayered coating of the present invention may have a thickness properly selected within a range of from 10 to 150 nm.
  • the thicknesses of the low-refractive layers are, sequentially from the substrate, preferably 10 to 70 nm and more preferably 15 to 60 nm for the first low-refractive layer; preferably 10 to 70 nm and more preferably 10 to 60 nm for the second low-refractive layer; and preferably 70 to 150 nm and more preferably 90 to 130 nm for the third low-refractive layer. It is preferable that each low-refractive layer satisfies the above corresponding thickness range.
  • the substantial increase in transmittance of light in the infrared region as well as the visible light region and the broadband anti-reflection effect can be obtained, and accordingly a high-performance, anti-reflective multilayered coating over 350 nm to 1,100 nm wavelength range can be obtained.
  • the anti-reflective multilayered coating having 6 or more layers is formed by alternately depositing said high-refractive layer and said low-refractive layer sequentially on the aforesaid substrate. If the number of layers constituting the anti-reflective multilayered coating is less than 6, there would be a limitation in increasing the transmittance of light up to 1,100 nm.
  • the anti-reflective multilayered coating is formed sequentially on a transparent substrate, having serial layer constitution as follows:
  • a first high-refractive layer having a thickness of from 5 to 40 nm and a refractive index of from 1.9 to 2.5;
  • a first low-refractive layer having a thickness of from 10 to 70 nm and a refractive index of from 1.3 to 1.6;
  • a second high-refractive layer having a thickness of from 5 to 60 nm and a refractive index of from 1.9 to 2.5;
  • a second low-refractive layer having a thickness of from 10 to 70 nm and a refractive index of from 1.3 to 1.6;
  • a third high-refractive layer having a thickness of from 5 to 40 nm and a refractive index of from 1.9 to 2.5;
  • a third low-refractive layer having a thickness of from 70 to 150 nm and a refractive index of from 1.3 to 1.6.
  • the above six-layered coating preferably comprises the following layer materials sequentially from the substrate:
  • silicon aluminum oxide corresponds to aluminum-silicon mixed oxide, and there is no particular limitation on the use amount ratio of aluminum to silicon.
  • the content of aluminum in aluminum-silicon mixed oxide may be properly selected within a range of from 1 to 20% by weight.
  • Solar cells conventionally absorb solar light energy of 350 to 1,100 nm wavelength only and convert it to electricity. Since the light of wavelengths longer than the above range elevates the temperature of a solar cell module and causes deterioration of solar cell, the transmittance of light in the wavelength region longer than 1,100 nm should be lowered in order to maintain the stability of the module for a long term.
  • the anti-reflective multilayered coating structure of 6 or more layers according to the present invention is an optimized one which can achieve the sufficient anti-reflective effect (i.e., solar cell efficiency) and long-term stability of the solar cell module at the same time since it shows selective transmittance property between the visible light and near-infrared region (350 nm to 1,100 nm wavelength) and the long-wavelength region including far-infrared rays, by the interferential interactions between the layers.
  • the multilayered coating of the present invention is a remarkably improved technology in terms of not only the transmittance increase of visible light but also the decreased transmittance of light wavelength longer than 1,100 nm which is harmful to the solar cell module, as compared with prior arts that sought to increase the transmittance of visible light only.
  • the transparent substrate having thereon the anti-reflective multilayered coating according to the present invention preferably shows an average transmittance of 91% or higher at a wavelength range of from 350 to 1,100 nm, preferably up to 8 mm thickness.
  • it preferably shows a transmittance higher than the substrate before the multilayered coating formation at a wavelength range of from 350 to 1,100 nm and shows a transmittance lower than the substrate before the multilayered coating formation at a wavelength range of from 1,100 nm to 2,500 nm.
  • the other aspect of the present invention provides a method for preparing a broadband anti-reflective, transparent substrate for a solar cell, comprising the steps of: (1) forming a first high-refractive layer having a refractive index of from 1.9 to 2.5 on a substrate; (2) forming a first low-refractive layer having a refractive index of from 1.3 to 1.6 on the first high-refractive layer; (3) forming a second high-refractive layer having a refractive index of from 1.9 to 2.5 on the first low-refractive layer; (4) forming a second low-refractive layer having a refractive index of from 1.3 to 1.6 on the second high-refractive layer; (5) forming a third high-refractive layer having a refractive index of from 1.9 to 2.5 on the second low-refractive layer; and (6) forming a third low-refractive layer having a refractive index of from 1.3 to 1.6 on the third high-refractive layer.
  • the method for preparing the multilayer-coated transparent substrate of the present invention may further comprise, after the above step (6), one or more steps of forming a further high-refractive layer and forming thereon a further low-refractive layer.
  • the method of forming the above respective layers sequentially on a transparent substrate there is no special limitation on the method of forming the above respective layers sequentially on a transparent substrate.
  • Conventionally known methods including physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel method, etc. may be utilized.
  • all the layers can be continuously vapor deposited by a magnetron sputtering method. This is particularly suitable for large substrate products.
  • the oxide layer may be vapor deposited by the reaction sputtering of the corresponding metal in the presence of oxygen, and the nitride layer may be vapor deposited in the presence of nitrogen.
  • vapor deposition may be performed by using a silicon target doped with a small amount of metal such as aluminum, in order to give sufficient conductivity to the target.
  • Another aspect of the present invention provides a solar cell module having the broadband anti-reflective, transparent substrate for a solar cell of the present invention on its outermost surface.
  • the broadband anti-reflective, transparent substrate of the present invention is applicable. It can be applied to all solar cells including crystalline silicon, amorphous silicon thin film, dye-sensitized solar cell (DSSC), CIGS (CuInGaSe)-, CdTe- and GaAs- type solar cells.
  • a solar cell module to which the broadband anti-reflective, transparent substrate of the present invention is applied shows at least 3 to 5% of increase in efficiency, as compared with a module without the present broadband anti-reflective, transparent substrate.
  • a six-layered anti-reflective coating was formed with the layer constitution as shown in the following Table 1.
  • the formation of the respective layers was done by using a magnetron sputtering facility. Conditions for the vapor deposition were as follows: 3 to 5 mtorr pressure of atmosphere, 1 kw of power, Ti metal target and Si alloy target.
  • the transmittance of light in a wavelength range of from 350 to 1,100 nm was measured by using a spectrophotometer (Cary500, Varian), and the resulting value was multiplied by the weighting function corresponding to AM1.5 according to ISO 9050 to obtain the average value which is shown in Table 2 below.
  • the transmittance of light in a wavelength range of from 350 to 1,100 nm was measured by using a spectrophotometer (Cary500, Varian), and the resulting value was multiplied by the weighting function corresponding to AM1.5 according to ISO 9050 to obtain the average value which is shown in Table 2 below.
  • an anti-reflective coating mainly comprising porous silica was formed on a low-iron float glass having 3.2 mm thickness.
  • the formation of the porous silica coating layer was done by dispersing nm-sized SiO 2 powder in a solvent well, forming its layer of 120 nm thickness on the glass by spraying, and heat-treating the coated glass at a high temperature (150°C to 200°C).
  • the transmittance of light in a wavelength range of from 350 to 1,100 nm was measured by using a spectrophotometer (Cary500, Varian), and the resulting value was multiplied by the weighting function corresponding to AM1.5 according to ISO 9050 to obtain the average value which is shown in Table 2 below.

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Abstract

The present invention relates to a broadband anti-reflective, transparent substrate for a solar cell, more specifically, a broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate for a solar cell that is a transparent substrate applicable to the solar cell's outermost surface (solar light-receiving surface) and has a multilayered coating of six (6) or more coating layers that are formed by alternately depositing a high-refractive material layer and a low-refractive material layer sequentially on its surface, whereby it shows a broadband (350 to 1,100 nm wavelength) anti-reflective function and increases the transmittance of light in a near-infrared region as well as a visible light region while it decreases transmittance of light in an infrared region which causes deterioration of the solar cell without contributing to electricity generation of the solar cell, and thus the efficiency of the solar cell can be improved; and a method for preparing the same.

Description

TRANSPARENT SUBSTRATE FOR A SOLAR CELL HAVING A BROADBAND ANTI-REFLECTIVE MULTILAYERED COATING THEREON AND METHOD FOR PREPARING THE SAME
The present invention relates to a broadband anti-reflective, transparent substrate for a solar cell having a multilayered coating thereon and a method for preparing the same. More specifically, the present invention relates to a broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate for a solar cell that is a transparent substrate applicable to the solar cell’s outermost surface (solar light-receiving surface) and has a multilayered coating of six (6) or more coating layers that are formed by alternately depositing a high-refractive material layer and a low-refractive material layer sequentially on its surface, whereby it shows a broadband (350 to 1,100 nm wavelength) anti-reflective function and increases the transmittance of light in a near-infrared region as well as a visible light region while it decreases transmittance of light in an infrared region which causes deterioration of the solar cell without contributing to electricity generation of the solar cell, and thus the efficiency of the solar cell can be improved; and a method for preparing the same.
Anti-reflective coating technology―which began in the fields of picture frame, lens, display device, etc. and has been developed―is a technology for improving the transmittance of light in a visible light region (i.e., 350 to 780 nm wavelength). Such anti-reflective coatings conventionally comprise layer(s) of a material having a refractive index between that of a substrate (in the case of glass, conventionally 1.5) and that of air (1.0).
Unlike the conventional technology, a transparent substrate for a solar cell such as glass needs to increase the transmittance of light in a near-infrared region (to 1,100 nm) as well as a visible light region because a solar cell absorbs light in a broader wavelength region than a visible light region. Thus, in order to increase the energy conversion efficiency of a solar cell, the transmittance of light passing through the outermost transparent substrate of the solar cell needs to be improved in the broadband region (350 to 1,100 nm wavelength).
In conventional arts, for the improvement of the transmittance of solar light in such a broadband region, a single-layered anti-reflective coating of porous silicon oxide has been formed on the surface of the outermost glass for a solar cell. The pores provided by such a porous silicon oxide perform the role of lowering the refractive index of silicon oxide. However, such a single-layered coating lacks durability against water. In addition, such a porous silicon oxide coating is conventionally formed by a sol-gel method, and it is difficult to obtain a uniform thin film by the spraying or dipping method of coating.
Alternatively, it is known that a thin layer of porous silicon oxide can be formed on a glass by etching the external surface of the glass with a chemical reagent such as hydrofluoric acid. However, this method has problems of low productivity due to long etching time, non-uniformity of the glass surface and use of environmentally harmful reagents such as hydrofluoric acid.
To resolve the problems of prior arts as explained above, the present invention has an object of providing a broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate for a solar cell that is a transparent substrate applicable to the solar cell’s outermost surface and increases the transmittance of light in a near-infrared region as well as a visible light region while it decreases the transmittance of light in an infrared region which causes deterioration of the solar cell without contributing to electricity generation of the solar cell, and thus the efficiency of the solar cell can be improved; and a method for preparing the same.
To achieve the object as explained above, the present invention provides a broadband anti-reflective, transparent substrate for a solar cell having multilayered coating thereon, wherein the multilayered coating has six (6) or more coating layers that are formed by alternately depositing a high-refractive layer having a refractive index of from 1.9 to 2.5 and a low-refractive layer having a refractive index of from 1.3 to 1.6 sequentially on a substrate.
The other aspect of the present invention provides a method for preparing a broadband anti-reflective, transparent substrate for a solar cell, comprising the steps of: (1) forming a first high-refractive layer having a refractive index of from 1.9 to 2.5 on a substrate; (2) forming a first low-refractive layer having a refractive index of from 1.3 to 1.6 on the first high-refractive layer; (3) forming a second high-refractive layer having a refractive index of from 1.9 to 2.5 on the first low-refractive layer; (4) forming a second low-refractive layer having a refractive index of from 1.3 to 1.6 on the second high-refractive layer; (5) forming a third high-refractive layer having a refractive index of from 1.9 to 2.5 on the second low-refractive layer; and (6) forming a third low-refractive layer having a refractive index of from 1.3 to 1.6 on the third high-refractive layer.
Another aspect of the present invention provides a solar cell module having the broadband anti-reflective, transparent substrate for a solar cell of the present invention on its outermost surface.
The broadband (350 to 1,100 nm wavelength) anti-reflective, transparent substrate according to the present invention shows selective light transmittance property between visible light and a near-infrared region, and a long wavelength region including far-infrared rays. Thus, if it is applied to a solar cell, the transmittance of light in visible light and a near-infrared region is increased and accordingly the amount of solar energy absorbed in the solar cell is also increased, whereby the cell efficiency can be improved, and at the same time the transmittance of light in a long-wavelength region including far-infrared rays (1,100 to 2,500 nm wavelength) is decreased, whereby the temperature of s solar cell module can be lowered. Such temperature lowering prevents deterioration of the solar cell, through which the lifespan and efficiency of the solar cell can be increased.
Figure 1 schematically represents a layer structure of glass having the multilayered coating of six (6) layers thereon according to an embodiment of the present invention.
Figure 2 is the transmittance spectra graph of the glasses prepared in the Example and Comparative Examples of the present invention.
The present invention is explained in detail below.
(1) Transparent substrate
For the transparent substrate on which the anti-reflective multilayered coating of the present invention is formed, any transparent materials such as glass substrate and transparent plastic substrates (for example, transparent substrates of polycarbonate [PC] and polymethylmethacrylate [PMMA]) can be used without limitation as long as the anti-reflective multilayered coating of the present invention can be formed thereon. Preferably, glass substrate is used.
In case of glass, for example, general glass such as soda-lime glass for construction or automobiles, low-iron patterned glass for solar cell, low-iron float glass, transparent conductive oxide (TCO) glass and the like can be used without limitation. Furthermore, if needed, surface texture-treated glass or tempered or partly tempered glass may be used.
There is no particular limitation on the thickness of the transparent substrate. It can be freely selected from a thickness range of from 2 mm to 8 mm according to the purpose of use.
(2) High-refractive layer
The high-refractive layer comprised in the anti-reflective multilayered coating of the present invention has a refractive index of from 1.9 to 2.5. Materials having a refractive index beyond said range cannot be used as a material for the high-refractive layer in the present invention.
The high-refractive layer may comprise one or more metal oxides selected from zinc oxides, tin oxides, zirconium oxides, zinc-tin oxides, titanium oxides and niobium oxides. In addition, the high-refractive layer may further comprise one or more nitrides selected from silicon nitrides and silicon aluminum nitrides.
Each high-refractive layer comprised in the anti-reflective multilayered coating of the present invention may have a thickness properly selected within a range of from 5 to 60 nm. In a multilayered coating of six layers as an embodiment of the present invention, the thicknesses of the high-refractive layers are, sequentially from the substrate, preferably 5 to 40 nm and more preferably 10 to 30 nm for the first high-refractive layer; preferably 5 to 60 nm and more preferably 5 to 50 nm for the second high-refractive layer; and preferably 10 to 40 nm and more preferably 10 to 30 nm for the third high-refractive layer. It is preferable that each high-refractive layer satisfies the above corresponding thickness range. If so, the substantial increase in transmittance of light in the infrared region as well as the visible light region and the broadband anti-reflection effect can be obtained, and accordingly a high-performance, anti-reflective multilayered coating over 350 nm to 1,100 nm wavelength range can be obtained.
(3) Low-refractive layer
The low-refractive layer comprised in the anti-reflective multilayered coating of the present invention has a refractive index of from 1.3 to 1.6. Materials having a refractive index beyond said range cannot be used as a material for the low-refractive layer in the present invention.
The low-refractive layer may comprise one or more oxides selected from silicon oxides, silicon oxynitrides, silicon oxycarbides and silicon-aluminum mixed oxides. The mixed oxides are advantageous in that durability (particularly, chemical resistance) may be improved as compared with pure silicon oxide (SiO2). The ratio between silicon and aluminum may be properly adjusted to improve durability as expected, without excessively increasing the refractive index of the layer.
Each low-refractive layer comprised in the anti-reflective multilayered coating of the present invention may have a thickness properly selected within a range of from 10 to 150 nm. In a multilayered coating of six layers as an embodiment of the present invention, the thicknesses of the low-refractive layers are, sequentially from the substrate, preferably 10 to 70 nm and more preferably 15 to 60 nm for the first low-refractive layer; preferably 10 to 70 nm and more preferably 10 to 60 nm for the second low-refractive layer; and preferably 70 to 150 nm and more preferably 90 to 130 nm for the third low-refractive layer. It is preferable that each low-refractive layer satisfies the above corresponding thickness range. If so, the substantial increase in transmittance of light in the infrared region as well as the visible light region and the broadband anti-reflection effect can be obtained, and accordingly a high-performance, anti-reflective multilayered coating over 350 nm to 1,100 nm wavelength range can be obtained.
(4) Multilayered coating
According to the present invention, the anti-reflective multilayered coating having 6 or more layers (for example, 6 to 8 layers) is formed by alternately depositing said high-refractive layer and said low-refractive layer sequentially on the aforesaid substrate. If the number of layers constituting the anti-reflective multilayered coating is less than 6, there would be a limitation in increasing the transmittance of light up to 1,100 nm.
According to a preferred embodiment of the present invention, in order to increase the transmittance of light in the broadband region, the anti-reflective multilayered coating is formed sequentially on a transparent substrate, having serial layer constitution as follows:
a first high-refractive layer having a thickness of from 5 to 40 nm and a refractive index of from 1.9 to 2.5;
a first low-refractive layer having a thickness of from 10 to 70 nm and a refractive index of from 1.3 to 1.6;
a second high-refractive layer having a thickness of from 5 to 60 nm and a refractive index of from 1.9 to 2.5;
a second low-refractive layer having a thickness of from 10 to 70 nm and a refractive index of from 1.3 to 1.6;
a third high-refractive layer having a thickness of from 5 to 40 nm and a refractive index of from 1.9 to 2.5; and
a third low-refractive layer having a thickness of from 70 to 150 nm and a refractive index of from 1.3 to 1.6.
Furthermore, the above six-layered coating preferably comprises the following layer materials sequentially from the substrate:
- titanium oxide/silicon oxide/titanium oxide/silicon oxide/titanium oxide/silicon oxide; or
- titanium oxide/silicon aluminum oxide/titanium oxide/silicon aluminum oxide/titanium oxide/silicon aluminum oxide
(In this case, silicon aluminum oxide corresponds to aluminum-silicon mixed oxide, and there is no particular limitation on the use amount ratio of aluminum to silicon. For example, the content of aluminum in aluminum-silicon mixed oxide may be properly selected within a range of from 1 to 20% by weight.)
Solar cells conventionally absorb solar light energy of 350 to 1,100 nm wavelength only and convert it to electricity. Since the light of wavelengths longer than the above range elevates the temperature of a solar cell module and causes deterioration of solar cell, the transmittance of light in the wavelength region longer than 1,100 nm should be lowered in order to maintain the stability of the module for a long term. The anti-reflective multilayered coating structure of 6 or more layers according to the present invention is an optimized one which can achieve the sufficient anti-reflective effect (i.e., solar cell efficiency) and long-term stability of the solar cell module at the same time since it shows selective transmittance property between the visible light and near-infrared region (350 nm to 1,100 nm wavelength) and the long-wavelength region including far-infrared rays, by the interferential interactions between the layers. That is, the multilayered coating of the present invention is a remarkably improved technology in terms of not only the transmittance increase of visible light but also the decreased transmittance of light wavelength longer than 1,100 nm which is harmful to the solar cell module, as compared with prior arts that sought to increase the transmittance of visible light only.
The transparent substrate having thereon the anti-reflective multilayered coating according to the present invention preferably shows an average transmittance of 91% or higher at a wavelength range of from 350 to 1,100 nm, preferably up to 8 mm thickness. In addition, it preferably shows a transmittance higher than the substrate before the multilayered coating formation at a wavelength range of from 350 to 1,100 nm and shows a transmittance lower than the substrate before the multilayered coating formation at a wavelength range of from 1,100 nm to 2,500 nm.
(5) Method for preparing the multilayer-coated transparent substrate
The other aspect of the present invention provides a method for preparing a broadband anti-reflective, transparent substrate for a solar cell, comprising the steps of: (1) forming a first high-refractive layer having a refractive index of from 1.9 to 2.5 on a substrate; (2) forming a first low-refractive layer having a refractive index of from 1.3 to 1.6 on the first high-refractive layer; (3) forming a second high-refractive layer having a refractive index of from 1.9 to 2.5 on the first low-refractive layer; (4) forming a second low-refractive layer having a refractive index of from 1.3 to 1.6 on the second high-refractive layer; (5) forming a third high-refractive layer having a refractive index of from 1.9 to 2.5 on the second low-refractive layer; and (6) forming a third low-refractive layer having a refractive index of from 1.3 to 1.6 on the third high-refractive layer.
If necessary, the method for preparing the multilayer-coated transparent substrate of the present invention may further comprise, after the above step (6), one or more steps of forming a further high-refractive layer and forming thereon a further low-refractive layer.
There is no special limitation on the method of forming the above respective layers sequentially on a transparent substrate. Conventionally known methods including physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel method, etc. may be utilized. According to a preferred embodiment of the present invention, all the layers can be continuously vapor deposited by a magnetron sputtering method. This is particularly suitable for large substrate products. The oxide layer may be vapor deposited by the reaction sputtering of the corresponding metal in the presence of oxygen, and the nitride layer may be vapor deposited in the presence of nitrogen. In addition, for forming SiO2 or Si3N4 layer, vapor deposition may be performed by using a silicon target doped with a small amount of metal such as aluminum, in order to give sufficient conductivity to the target.
(6) Solar cell module
Another aspect of the present invention provides a solar cell module having the broadband anti-reflective, transparent substrate for a solar cell of the present invention on its outermost surface.
There is no special limitation on the kind or type of solar cell module to which the broadband anti-reflective, transparent substrate of the present invention is applicable. It can be applied to all solar cells including crystalline silicon, amorphous silicon thin film, dye-sensitized solar cell (DSSC), CIGS (CuInGaSe)-, CdTe- and GaAs- type solar cells.
According to an embodiment of the present invention, a solar cell module to which the broadband anti-reflective, transparent substrate of the present invention is applied shows at least 3 to 5% of increase in efficiency, as compared with a module without the present broadband anti-reflective, transparent substrate.
The present invention is explained in more detail by the following Example and Comparative Examples. However, the protection scope of the present invention is not limited by them.
Example
On a low-iron float glass having 3.2 mm thickness, a six-layered anti-reflective coating was formed with the layer constitution as shown in the following Table 1. The formation of the respective layers was done by using a magnetron sputtering facility. Conditions for the vapor deposition were as follows: 3 to 5 mtorr pressure of atmosphere, 1 kw of power, Ti metal target and Si alloy target.
For the prepared multilayered coating glass, the transmittance of light in a wavelength range of from 350 to 1,100 nm was measured by using a spectrophotometer (Cary500, Varian), and the resulting value was multiplied by the weighting function corresponding to AM1.5 according to ISO 9050 to obtain the average value which is shown in Table 2 below.
Table 1
Figure PCTKR2011008478-appb-T000001
Comparative Example 1
For uncoated (i.e., without an anti-reflective multilayered coating) low-iron float glass having 3.2 mm thickness, the transmittance of light in a wavelength range of from 350 to 1,100 nm was measured by using a spectrophotometer (Cary500, Varian), and the resulting value was multiplied by the weighting function corresponding to AM1.5 according to ISO 9050 to obtain the average value which is shown in Table 2 below.
Comparative Example 2
On a low-iron float glass having 3.2 mm thickness, an anti-reflective coating mainly comprising porous silica was formed. The formation of the porous silica coating layer was done by dispersing nm-sized SiO2 powder in a solvent well, forming its layer of 120 nm thickness on the glass by spraying, and heat-treating the coated glass at a high temperature (150℃ to 200℃).
For the porous silica-coated float glass prepared as such, the transmittance of light in a wavelength range of from 350 to 1,100 nm was measured by using a spectrophotometer (Cary500, Varian), and the resulting value was multiplied by the weighting function corresponding to AM1.5 according to ISO 9050 to obtain the average value which is shown in Table 2 below.
Table 2
Figure PCTKR2011008478-appb-T000002
Furthermore, the transmittance spectra of the glasses prepared in the Example and Comparative Examples 1 and 2 are shown in Figure 2.

Claims (12)

  1. A broadband anti-reflective, transparent substrate for a solar cell having multilayered coating thereon, wherein the multilayered coating has six (6) or more coating layers that are formed by alternately depositing a high-refractive layer having a refractive index of from 1.9 to 2.5 and a low-refractive layer having a refractive index of from 1.3 to 1.6 sequentially on a substrate.
  2. The broadband anti-reflective, transparent substrate for a solar cell according to claim 1, wherein the substrate is glass.
  3. The broadband anti-reflective, transparent substrate for a solar cell according to claim 1, wherein the high-refractive layer comprises one or more metal oxides selected from zinc oxides, tin oxides, zirconium oxides, zinc-tin oxides, titanium oxides and niobium oxides.
  4. The broadband anti-reflective, transparent substrate for a solar cell according to claim 3, wherein the high-refractive layer further comprises one or more nitrides selected from silicon nitrides and silicon aluminum nitrides.
  5. The broadband anti-reflective, transparent substrate for a solar cell according to claim 1, wherein the low-refractive layer comprises one or more oxides selected from silicon oxides, silicon oxynitrides, silicon oxycarbides and silicon-aluminum mixed oxides.
  6. The broadband anti-reflective, transparent substrate for a solar cell according to claim 1, having the following multilayered coating formed sequentially from the substrate:
    a first high-refractive layer having a thickness of from 5 to 40 nm and a refractive index of from 1.9 to 2.5;
    a first low-refractive layer having a thickness of from 10 to 70 nm and a refractive index of from 1.3 to 1.6;
    a second high-refractive layer having a thickness of from 5 to 60 nm and a refractive index of from 1.9 to 2.5;
    a second low-refractive layer having a thickness of from 10 to 70 nm and a refractive index of from 1.3 to 1.6;
    a third high-refractive layer having a thickness of from 5 to 40 nm and a refractive index of from 1.9 to 2.5; and
    a third low-refractive layer having a thickness of from 70 to 150 nm and a refractive index of from 1.3 to 1.6.
  7. The broadband anti-reflective, transparent substrate for a solar cell according to claim 1, showing an average light transmittance of 91% or higher at a wavelength range of from 350 to 1,100 nm.
  8. The broadband anti-reflective, transparent substrate for a solar cell according to claim 1, showing a light transmittance higher than the substrate before the multilayered coating formation at a wavelength range of from 350 nm to 1,100 nm and showing a light transmittance lower than the substrate before the multilayered coating formation at a wavelength range of from 1,100 nm to 2,500 nm.
  9. A method for preparing a broadband anti-reflective, transparent substrate for a solar cell, comprising the steps of:
    (1) forming a first high-refractive layer having a refractive index of from 1.9 to 2.5 on a substrate;
    (2) forming a first low-refractive layer having a refractive index of from 1.3 to 1.6 on the first high-refractive layer;
    (3) forming a second high-refractive layer having a refractive index of from 1.9 to 2.5 on the first low-refractive layer;
    (4) forming a second low-refractive layer having a refractive index of from 1.3 to 1.6 on the second high-refractive layer;
    (5) forming a third high-refractive layer having a refractive index of from 1.9 to 2.5 on the second low-refractive layer; and
    (6) forming a third low-refractive layer having a refractive index of from 1.3 to 1.6 on the third high-refractive layer.
  10. The method for preparing a broadband anti-reflective, transparent substrate for a solar cell according to claim 9, wherein all the layers are continuously vapor deposited by a magnetron sputtering method.
  11. A solar cell module having the broadband anti-reflective, transparent substrate for solar cell according to any one of claims 1 to 8 on its outermost surface.
  12. The solar cell module according to claim 11 which is crystalline silicon, amorphous silicon thin film, dye-sensitized solar cell (DSSC), CIGS (CuInGaSe)-, CdTe- or GaAs- type solar cell.
PCT/KR2011/008478 2011-03-21 2011-11-08 Transparent substrate for a solar cell having a broadband anti-reflective multilayered coating thereon and method for preparing the same Ceased WO2012128439A1 (en)

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