COVER GLASS FOR SOLAR CELL, SOLAR CELL MODULE PROVIDED WITH COVER GLASS FOR SOLAR CELL, AND TRANSPARENT PROTECTIVE FILM

Abstract

A provided cover glass for a solar cell panel has excellent transparency, and minimal incidence so-called glass surface turbidity due to reactions with components contained in a glass substrate. The cover glass for the solar cell panel comprises: the glass substrate including a surface; and a transparent protective film containing zinc telluride for coating the surface. Particularly, in the cover glass for the solar cell panel, the transparent protective film is preferably formed by bonding the zinc telluride with silica binders. Such a transparent protective film has excellent transparency, and reactions of the contained zinc telluride inhibit the surface of the glass substrate, which is a base of the solar cell, from becoming turbid.

Claims

1. A cover glass for a solar cell, the cover glass comprising: a glass substrate including a surface; and a transparent protective film containing zinc telluride for coating the surface, wherein: the transparent protective film is formed by coating a coating liquid containing zinc telluride on a surface of a glass substrate; and a pH of the coating liquid is not less than nine.

2. The cover glass as defined in claim 1, wherein said transparent protective film is formed by bonding the zinc telluride with silica binders.

3. The cover glass as defined in claim 1, wherein said transparent protective film contains titanium oxide.

4. The cover glass as defined in claim 1, wherein said transparent protective film has thickness of 20-1200 nanometers.

5. The cover glass as defined in claim 1, wherein said glass substrate contains elements belonging to at least one of alkali metal and alkaline earth metal.

6. A solar cell module, including the cover glass as defined in claim 1.

7. A transparent protective film containing zinc telluride, wherein: the transparent protective film is formed by coating a coating liquid containing zinc telluride on a surface of a glass substrate; and a pH of the coating liquid is not less than nine.

8. The transparent protective film as defined in claim 7, containing the zinc telluride of 0.1-20 wt % based on total 100 wt % of the coating liquid.

9. The transparent protective film as defined in claim 7, further containing silica binders of 0.1-20 wt % in terms of SiO.sub.2 based on the total 100 wt % of the coating liquid.

10. The transparent protective film as defined in claim 7, further containing titanium oxide of 0.1-20 wt % based on the total 100 wt % of the coating liquid.

11. The transparent protective film as defined in claim 7, further containing: iodine of 0.1-10 wt %; and silver compounds of 0.1-10 wt % based on the total 100 wt % of the coating liquid.

12. The transparent protective film as defined in claim 7, wherein mixed solvent containing ethanol of 20-40 wt % and water of 40-80 wt % is used.

13. (canceled)

14. The cover glass as defined in claim 1, wherein the glass substrate is a cover glass of a solar cell.

15. The transparent protective film as defined in claim 7, wherein the glass substrate is a cover glass of a solar cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a cross-section mimetic diagram of a solar cell module; and

[0039] FIG. 2 is a cross-section mimetic diagram of cover glass for a solar cell according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, the present invention will now be described in detail showing examples thereof. The present invention is never limited to the examples. Arbitrary change from the examples may be carried out within the scope and/or the aspects of the present invention.

[0041] [1. Cover Glass for Solar Cell]

[0042] Cover glass for a solar cell according to the present invention is provided with: a glass substrate including a surface; and a transparent protective film containing zinc telluride, the transparent protective film coating the surface. That is, the surface of the glass substrate of the cover glass for the solar cell according to the present invention is coated by the transparent protective film containing the zinc telluride. As shown in FIG. 1, the cover glass for the solar cell is a protection member protecting the solar cell in a solar cell module. As shown in FIG. 2, the cover glass for the solar cell according to the present invention (hereinafter, may by called the cover glass according to the present invention) possesses a structure that the surface of the glass substrate is coated by the transparent protective film. In FIG. 2, the transparent protective film is formed only on an upper surface of the glass substrate. Alternatively, the transparent protective film may be formed on both of the upper surface and a lower surface of the glass substrate. Hereafter, details of the cover glass according to the present invention will now be explained.

[0043] (Glass Substrate)

[0044] A generally used glass substrate can be employed as cover glass for a solar cell. Such a glass substrate has transmittance for transmitting sun light. More concretely, soda-lime silicate glass, alumino-silicate glass, barium borosilicate glass, borosilicate glass, or the like is suitable for constituting the glass substrate. These kinds of glass may contain at least one of potassium (K), and sodium (Na), or the like belonging to alkali metal and calcium (Ca), Magnesium (Mg), or the like belonging to alkaline earth metal within a range contained in process for producing it. Glass for constituting the glass substrate may be functional glass, such as colored glass and laminated glass.

[0045] Glass substantially containing neither alkali metal element nor alkaline earth metal element may be employed as the glass substrate. Since a transparent protective film, details of which will be discussed later, exists in the cover glass according to the present invention, so-called glass surface turbidity caused by reactions between acid gas (e.g. CO2 in the air, or the like) and at least one of alkali metal elements and alkaline earth metal elements is inhibited. Even if the glass substrate contains at least one of alkali metal elements and alkaline earth metal elements, deterioration, especially caused by so-called glass surface turbidity, hardly occurs. For this reason, the glass substrate contains at least one of alkali metal elements and alkaline earth metal elements may be suitably employed as the cover glass according to the present invention.

[0046] Thickness of the glass substrate is determined considering mechanical strength needed as the cover glass and transmittance of sun light. Size (area) of the glass substrate is determined corresponding to that of a target solar cell module.

[0047] (Transparent Protective Film)

[0048] In the cover glass according to the present invention, a transparent protective film (hereinafter, may be called the transparent protective film according to the present invention) contains zinc telluride (ZnTe) as an essential constituent, and coats the glass substrate. The transparent protective film according to the present invention has excellent transparency of sun light, and can inhibit deterioration (especially, so-called glass surface turbidity) of the glass substrate. In a case where zinc telluride is not contained therein, effects of the inhibition cannot be recognized.

[0049] Containing zinc telluride enables to modulate ultraviolet light included in irradiated sun light into visible light of a band near 600 nanometers, thereby improving power-generating efficiency.

[0050] At this time, it is not completely clear why forming the transparent protective film according to the present invention enables to inhibit so-called glass surface turbidity. It is supposed, however, that zinc telluride of conductive oxide acts on free electrons in the glass of an insulator to restrain reactions between acid gas (e.g. CO.sub.2) and at least one of alkali metal (e.g. sodium, calcium, or the like) and alkaline earth metal contained in the glass, thereby inhibiting so-called glass surface turbidity caused by the reactions.

[0051] Particle size of zinc telluride is determined in a range of 0.1-500 micrometers, in which effects of the present invention can be obtained.

[0052] The transparent protective film according to the present invention is preferably formed by bonding zinc telluride with silica binders. The transparent protective film according to the present invention may be formed only with zinc telluride. Binders are usually contained therein so as to increase mechanical strength. As the binders, those with excellent transparency are selected, and both of inorganic binders and organic binders can be chosen. Particularly, silica binders, which have excellent transparency, high light resistance, and enough mechanical strength, are preferably used for the binders.

[0053] The ratio between the zinc telluride and the silica binders in the transparent protective film is determined within a range where effects of the present invention are not spoiled. Normally, the silica binders have 10-50 wt % in terms of SiO.sub.2 based on weight 100% of the zinc telluride.

[0054] Since the cover glass according to the present invention is provided with the transparent protective film, heat reflection effects are also expected. Due to the effects, it is possible to prevent the temperature of the panel from rising too high. Accordingly, loss of power-generating efficiency caused by overheating of the solar cell module is also controlled.

[0055] The transparent protective film according to the present invention preferably further contains titanium oxide. As the titanium oxide, both of an anatase crystal type and a rutile crystal type can be used. Yellow sand, ash, dust, dirt or the like may be adhered on the surface of the cover glass for a solar cell, which is normally used outdoors, to form attachment. Therefore, transmittance of sun light is reduced, and chemical reactions, such as oxidation of the attachment and/or carbonization by resolution may cause deterioration of the glass. When the transparent protective film according to the present invention contains titanium oxide, the attachment can be removed due to photocatalyst effect of the contained titanium oxide, thereby restraining the reduction of transmittance of sun light and the deterioration of the glass. In this specification, the photocatalyst effect includes the titanium oxide's function of making something into a super-hydrophilic state. The attachment on the surface can be easily removed by washing with water (including rain water) according to the function. The titanium oxide modulates ultraviolet into a visible light band. Containing the titanium oxide in the transparent protective film according to the present invention enables to improve power-generating efficiency thereof.

[0056] A ratio of the titanium oxide in the transparent protective film may be determined in a range where the transparent protective film performs the photocatalyst effect. If the ratio of the contained titanium oxide is too large, strength of the transparent protective film may be not enough and the above effect caused by zinc telluride may become weak. The ratio is normally 1-40 wt % based on the total weight 100% of the transparent protective film.

[0057] As long as not spoiling the effects of the present invention, the transparent protective film may further contain another kind of well-known wavelength conversion material so as to modulate ultraviolet into the visible light band.

[0058] The transparent protective film according to the present invention preferably contains silver ions (Ag+). The silver ions can reinforce action of visible light.

[0059] As long as not spoiling the effects of the present invention of restraining so-called glass surface turbidity, the thickness of the transparent protective film is not limited. The thickness is preferably, however, 20-1200 nanometers so as to make the wavelength conversion function effective. Herein, the thickness of the transparent protective film can be measured utilizing a film thickness-measuring instrument (e.g. F20 system of Filmetrics, Inc.).

[0060] [2. Method for Forming Transparent Protective Film]

[0061] As long as not spoiling the above-mentioned act, the transparent protective film according to the present invention may be formed according to any method, such as a dry film-forming method (e.g. a vapor deposition method, a spattering method, or the like), a wet film-forming method of coating liquid on a surface to form the film. Herein, the dry film-forming method needs expensive equipment, such as vacuum equipment. The wet film-forming method is preferable, since the film can be produced by low cost.

[0062] (Coating Liquid for Transparent Protective Film)

[0063] Coating liquid (hereinafter simply called coating liquid according to the present invention or merely called coating liquid) suitable for the transparent protective film according to the present invention will now be explained. The coating liquid assumes the wet film-forming method.

[0064] The coating liquid for the transparent protective film according to the present invention contains zinc telluride, and a pH thereof is not less than nine. The contained zinc telluride in the coating liquid preferably has 0.1-20 wt % based on total 100 wt % of the coating liquid.

[0065] Such composition provides excellent applicability on a surface of a glass substrate, and one time application thereof enables to form a uniform transparent protective film on the surface of the glass substrate. Two or more times application may be performed in order to make the transparent protective film thicker.

[0066] Solvent of the coating liquid according to the present invention is aqueous solvent having a pH not less than nine. Herein, the aqueous solvent means not less than 40 wt % based on total weight of the solvent is composed of water. If a pH of the solvent of the coating liquid is smaller than nine, applicability of the coating liquid falls and a uniform film cannot be formed. The solvent of the coating liquid is preferably mixed solvent containing ethanol of 20-40 wt % and water of 40-80 wt % in order to improve the applicability of the coating liquid, thereby forming a film of high quality.

[0067] The coating liquid preferably contains binder components. Containing the binder components enables to reinforce strength of the formed transparent protective film, and to improve adhesiveness with the glass substrate. Both of inorganic binders with high transparency and organic binders may be selected for the binders. Silica binders are preferably employed, since the silica binders have excellent transparency, high light resistance, and enough mechanical strength. The preferable ratio of the silica binders is 0.1-20 wt % in terms of SiO.sub.2 based the total weight 100 wt % of the coating liquid.

[0068] In addition to the above components (the zinc telluride, the binders, and the solvent), the coating liquid according to the present invention preferably further contains titanium oxide of 0.1-20 wt % based on the total 100 wt % of the coating liquid so as to improve wavelength conversion properties of the formed transparent protective film and to add photocatalyst effects to the same.

[0069] The coating liquid according to the present invention preferably further contains iodine of 0.1-10 wt % and silver compounds of 0.1-10 wt %, since effects of further improving the wavelength conversion properties are expected. An as long as capable of ionizing, any kinds of silver compounds may be employed. Silver chloride (AgCl) can be given as a preferable example.

[0070] Components other than the above-mentioned components may be mixed into the coating liquid according to the present invention as long as not spoiling the effects of the present invention. Components for improving characteristics of the coating liquid such as surfactant or the like can be given as an example of the components to be mixed.

[0071] The coating liquid according to the present invention can be manufactured by mixing components constituting thereof. Mixing order is arbitrary. For example, first, prior to the other necessary components, two or three components may be mixed, and second, the remainder of the necessary components may be further mixed thereto. Alternatively, all of the necessary components may be mixed at once.

[0072] The transparent protective film according to the present invention can be suitably manufactured by:

[0073] applying the coating liquid according to the present invention on a surface of the glass substrate; and

[0074] curing the applied coating liquid.

[0075] Details of the glass substrate, which is a target to be applied, are as above-discussed.

[0076] There is no special limitation with respect to a method for applying the coating liquid on the surface of the glass substrate. Any of well-known wet film-forming methods can be adapted for the method. More concretely, a spin coat method, a slit die-coating method, a spray coat method, a dip-coating method, a roll-coating method, a screen printing method, a capillary coat method, a bar coater method, or the like are given as the well-known methods. Thickness of the coating liquid is controllable by respectively adjusting consistencies and amounts of the components contained in the coating liquid.

[0077] Curing the coating liquid applied on the surface of the glass substrate enables to preferably manufacture the transparent protective film according to the present invention. There is no limitation with respect to a method for curing the applied coating liquid as long as the formed transparent protective film has sufficient transparency and enough mechanical strength. The method is normally performed by heating the applied coating liquid. Heating atmosphere is not limited. However, air atmosphere is normally used.

[0078] Since the coating liquid according to the present invention can be cured by heating at relatively low temperature, suitable curing temperature is usually about 10-100 centigrade degrees. Curing time is time for the transparent protective film to fully harden, and is suitably determined considering composition of the coating liquid and thickness of the transparent protective film to be formed.

[0079] Thus, the glass substrate possessing a surface covered by the transparent protective film can be employed as the cover glass for a solar cell according to the present invention. The transparent protective film formed with the coating liquid according to the present invention can be also employed as a transparent protective film for glass for automobile, a lighting apparatus, a liquid crystal display, or the like other than the cover glass for the solar cell.

[0080] [3. Solar Cell Module]

[0081] The solar cell module according to the present invention comprises the above-mentioned cover glass for the solar cell. Elements other than the cover glass are not limited but the same elements as well-known solar cell modules can be used. FIG. 1 is an example of a structure of the solar cell module. The solar cell module according to the present invention may include wired electrodes, extraction electrodes, or the like in addition to elements shown in FIG. 1.

[0082] Especially material of cell portions in the solar cell module is not limited. For example, silicone based material, such as single crystal silicon, polycrystalline silicon, and amorphous silicone, and CIS type compound semiconductor material including a light-absorbing layer of P-type semiconductor and a PN hetero junction may be given. Composition of the transparent protective film according to the present invention is determined considering absorption wave length of the material of the cell portions.

EXAMPLES

[0083] Hereafter, details of the present invention will now be explained showing Examples. The present invention, however, is not limited to the following Examples as long as the scope of the present invention is not changed.

[0084] A used reagent and composition of a glass substrate are as follows:

[0085] Reagent

[0086] Powder of zinc telluride (II) (made by Kojundo Chemical Laboratory Co., Ltd.)

[0087] Titanium oxide (IV) (rutile type) (made by Wako Pure Chemical Industries, Ltd.)

[0088] Glass Substrate

[0089] (Composition)

[0090] SiO.sub.2: 70-72 wt %;

[0091] Na.sub.2O: 13-15 wt %;

[0092] CaO: 8-12 wt %;

[0093] MgO: 1-4 wt %;

[0094] Al.sub.2O.sub.3: 1-2 wt %; and

[0095] Fe.sub.2O.sub.3: 0.07-0.15 wt %.

Example 1

[0096] (1) Manufacturing Coating Liquid

[0097] The coating liquid 1 concerning Example 1 was produced according to the following procedures. First, sodium hydroxide was added to pure water, and then the added water was prepared so as to have a pH of 12.5. Next, 2 g of zinc telluride powder was added to 370 milliliters of water prepared to have a pH of 12.5. The added water was fully mixed so as to become uniform, and then Solution A was obtained. 4 g of titanium-oxide powder was added to 390 milliliters of pure-water, and the added water was fully mixed so as to become uniform, and the Solution B was obtained. 1 g of silver chloride and 4 g of iodine was added to 270 milliliters of ethanol, and the added ethanol was fully mixed so as to become uniform, and then Solution C was obtained. The Solution A and the Solution B were respectively added to 275 milliliters of the Solution C, the Solution A, B and C was fully mixed so as to become uniform, and then coating liquid 1 was prepared. The composition of the obtained coating liquid 1 is as follows.

[0098] Zinc telluride: 0.2 wt %;

[0099] Titanium oxide: 0.4 wt %;

[0100] Silver chloride: 0.1 wt %;

[0101] Ethanol: 35 wt %; and

[0102] Water: 60 wt %.

[0103] (2) Manufacturing Cover Glass for Solar Cell

[0104] Forming the transparent protective film on the glass substrate was performed according the following procedures. The coating liquid 1 was applied on a glass substrate (600900 mm, thickness: 3 mm), and the applied coating liquid was dried. Thereby, cover glass for a solar cell of Example 1 whose surface of the glass substrate has been coated with the transparent protective film was obtained. The thickness of the transparent protective film measured with a film thickness-measuring instrument (F20 system of Filmetrics, Inc.) was 60 nanometers

[0105] (3) Evaluation

[0106] The cover glass for the solar cell of Example 1 was arranged to coat a light-receiving face of a silicon solar cell, and power-generating efficiency was evaluated. A first result thereof was 107%. Herein, the power-generating efficiency is a relative value assuming that a clear glass substrate (comparative example) on which the transparent protective film is not formed has 100% of generation efficiency.

Example 2

[0107] (1) Manufacturing Coating Liquid 2

[0108] 1000 g of coating liquid 1 and 2000 g of ceramic based resin was mixed to obtain Coating liquid 2. The ceramic based resin contains silica as binder components.

[0109] (2) Manufacturing of Cover Glass for Solar Cell

[0110] Not Coating liquid 1 but Coating liquid 2 was used to obtain the cover glass for the solar cell of Example 2 whose surface of the glass substrate has been coated with the transparent protective film was obtained.

[0111] (3) Evaluation

[0112] Similar to Example 1, except for using the cover glass for the solar cell of Example 2 instead of the cover glass for the solar cell of Example 1, power-generating efficiency was evaluated. A second result thereof was 107%.

INDUSTRIAL APPLICABILITY

[0113] The present invention provides the cover glass for solar cell panels has excellent transparency, and minimal incidence so-called glass surface turbidity caused by reactions with components contained in a glass substrate. The cover glass is good at removing substances adhered on the surface, and can also prevent from rising temperature of the panel. Even if the cover glass has been used for a long time, it is possible to control decline of power-generating efficiency. The present invention has such advantage in industrial fields.