JP2012015442A - Back surface protective sheet and solar cell using it - Google Patents

Abstract

[PROBLEMS] To protect the solar cell and improve the power generation efficiency, solve the problem of easily causing a wiring short circuit, and protect the back surface that can release the water vapor and the gas generated inside once to the outside. A sheet and a solar cell using the same are provided.
A back surface protection sheet for protecting a back surface located on the opposite side of a light receiving surface of a solar cell from an external environment. At least the metal layer 8, the light-transmitting protective layer 10 disposed on the light receiving surface 4A side with respect to the metal layer 8, and the outer layer 6 disposed at a position farther from the light receiving surface 4A than the metal layer 8. The metal layer 8 exists in a range of 10% to 95% of the total area of the back surface protection sheet.
[Selection] Figure 2

Description

  The present invention has a structure for deflecting light in a specific direction by diffraction, scattering, diffusion, refraction, or reflection of light, and allows the reuse of light that would otherwise be lost The present invention relates to a protective sheet and a solar cell using the same.

  In recent years, various efforts have been made to suppress carbon dioxide emissions while interest from various countries both inside and outside Japan has increased. Increasing fossil fuel consumption leads to an increase in atmospheric carbon dioxide, and the greenhouse effect raises the Earth's temperature, significantly affecting the global environment. Various studies have been conducted on alternative energy to fossil fuels, but there are growing expectations for power generation using sunlight, which is a clean energy source.

In a solar cell used for power generation by sunlight, a semiconductor having a pn junction is generally used as a photoelectric conversion unit that directly converts light energy into electricity, and silicon is generally used as a semiconductor constituting the pn junction. Is the most commonly used. Note that the above-described silicon generally used for solar cells is classified into a crystalline type and an amorphous type.
On these photoelectric conversion units, a glass substrate such as transparent tempered glass is generally provided as a sealing substrate for protecting the photoelectric conversion units from air and impurities.

  Note that in this specification, a solar cell is obtained by encapsulating at least one cell including such a photoelectric conversion portion with a sealing material and packaging it.

A solar cell is configured by connecting small-sized cells with a plurality of electrodes. In silicon crystal solar cells, there is some space between adjacent cells. Moreover, in order to prevent erosion of rainwater or the like at the end portion of the solar cell, a blank portion where no cell is arranged is provided from several millimeters to several tens of millimeters. Since there are no cells in these gaps and margins, even if light is applied to these areas, power generation is not achieved and loss occurs.
Conventionally, the following measures have been proposed for such a loss of light that pours into the gaps and margins of cells.

  For example, in a crystalline solar cell, the back surface protection sheet placed on the back surface is used as a light reflecting material, so that the light is returned to the cell side again, and is totally reflected by the front glass plate, etc. Some re-enter the surface to increase efficiency.

  Furthermore, there is a structure that increases the efficiency by providing a concavo-convex structure on the back surface protection sheet placed on the back surface, making it easy to scatter the light reflected on the concavo-convex structure and improving the probability of guiding it to the light receiving surface of the cell (Patent Document) 1 and 2). Furthermore, there is also a configuration in which light is scattered by forming irregularities on the back surface protection sheet on the back surface, and further, the efficiency is improved by using a cell in which both surfaces of the cell are light receiving surfaces (see Patent Document 3).

  In addition, the present inventors have found that it is possible to further increase the efficiency by providing the back surface protective sheet with a concavo-convex structure having a specific shape and providing a metal film on the concavo-convex structure.

  On the other hand, as can be seen from the structure of the solar cell, a back surface protection sheet is used on the back surface to fulfill the protection function of the module. This back surface protection sheet is usually a plastic sheet or a laminate for the purpose of protecting contents. Generally, heat conduction is poor. For this reason, the heat generated inside the solar cell module is hardly dissipated to the outside, and it has been accumulated inside to increase the internal temperature.

  In patent document 4, the back surface protection sheet for solar cells has a heat resistance, weather resistance, moisture proof, and other required functions, and is formed by laminating an inexpensive heat and weather resistant plastic film made of a polyester resin. A heat- and weather-resistant plastic film comprising a polyester resin having an intrinsic viscosity of 0.6 (dl / g) or more and a cyclic trimer content of 0.5% by mass or less. It has been proposed that the foil be sandwiched from both sides. One of the reasons for using metal foil for the back sheet for solar cells is that the content protection property, particularly the barrier property of water vapor and oxygen, is excellent. At the same time, the effect of dissipating heat generated inside the module to the outside due to high thermal conductivity can be expected.

  However, such metals often have electrical conductivity, which can cause troubles such as wiring shorts. In addition, since the metal film has a feature that it is difficult to pass water vapor, it is useful for protecting the inside. However, when viewed from the long term, there is a problem that it is difficult to discharge the water vapor that has once entered the inside to the outside or to release the gas generated inside to the outside.

Japanese Utility Model Publication No. 62-101247 JP-A-10-284747 Japanese Patent No. 3670835 JP 2002-134770 A

As described above, it is possible to improve the power generation efficiency by forming the structure on the back surface protection sheet of the solar cell and providing the metal reflective film. Moreover, by using a metal in a back surface protection sheet, heat dissipation can be improved and, as a result, it becomes possible to improve power generation efficiency.
However, since these metals have electrical conductivity, there is a problem that wiring short-circuit is likely to occur.

  Further, when a metal is used as described above, there is a problem that water vapor that has once entered the inside is difficult to be released to the outside, and gas generated inside is difficult to be released.

  In the present invention, it was made paying attention to the above points, and while solving the problem of easily causing a wiring short-circuit while protecting the solar cell and improving the power generation efficiency, An object of the present invention is to provide a back surface protection sheet capable of releasing gas generated inside to the outside and a solar cell using the same.

  In order to solve the above problems, the back surface protection sheet according to claim 1 of the present invention is a back surface protection sheet for protecting the back surface located on the side opposite to the light receiving surface in the solar cell from the external environment, At least a metal layer, a light-transmitting protective layer disposed closer to the light receiving surface than the metal layer, and an outer layer disposed at a position farther from the light receiving surface than the metal layer, and The metal layer is present in the range of 10% or more and 95% or less with respect to the total area of the back surface protection sheet.

  By forming the metal layer on a part of the back surface protection sheet, it is possible to increase the power generation efficiency with the improvement of the light utilization efficiency and the heat dissipation. Further, by forming the metal layer partially without forming it on the entire surface of the back surface protection sheet, it is possible to prevent a short circuit of the wiring and to protect the solar cell from water vapor and gas generated inside.

  As for the short circuit of the wiring, the most likely short circuit is a part where the wiring is passed outside the back surface protection sheet. When the metal layer is formed on the back surface protection sheet, the wiring and the metal layer may come into contact with each other, and the wiring may be short-circuited. Therefore, in the back surface protective sheet, it is desirable that there is a region where the metal layer is not formed in the vicinity of the portion where the wiring is passed to the outside. As a region through which the wiring is passed to the outside, it is sufficient that there is a gap of several mm around the region where the wiring to be passed through to the outside exists. Although the area depends on the size of the solar cell, there is no problem if it is about 1 to 2% with respect to the back protective sheet. On the other hand, there is no problem if the metal layer is not formed in an area of about 5% in order to release the water vapor that has entered the inside or the gas generated inside to the outside and protect the inside. Therefore, if the area where the metal layer is present on the entire back surface protection sheet is 95%, the wiring can be sufficiently passed, and the solar cell can be protected by water vapor or gas generated inside. On the other hand, considering the improvement of light utilization efficiency, at least 10% of the back surface protection sheet needs to be filled with the metal layer.

  The back surface protective sheet according to claim 2 of the present invention is characterized in that at least a part of the metal layer is formed in a halftone dot shape.

  By forming a part of the metal layer in a halftone dot shape, portions that are halftone dots are not energized. Therefore, it is possible to prevent the wiring from being short-circuited by using the metal layer at the place where the wiring needs to pass as a halftone dot. In addition, by arranging the metal layer in a dot pattern, even if there is a wiring where a metal layer is required to improve the light utilization efficiency, the light utilization efficiency is reduced due to the absence of the metal layer. It becomes possible to suppress.

  The invention according to claim 3 of the present invention is a back surface protection sheet for protecting the back surface located on the side opposite to the light receiving surface in the solar cell from the external environment, and one surface is a light incident surface. A light-transmitting protective layer whose other surface is a light emitting surface, and a reflection for reflecting the light emitted from the light emitting surface provided on the light emitting surface side of the protective layer toward the protective layer A structural layer; an outer layer provided on the back surface side opposite to the light emitting surface of the reflective structural layer to protect the reflective structural layer; and at least on at least one of the front surface and the back surface of the reflective structural layer At least a light reflection uneven portion formed of the metal layer, and the metal layer forming the light reflection uneven portion is in a range of 10% to 95% of the area of the back protective sheet. Features that exist in To.

  By providing the back surface protective sheet with a reflective structure layer and using a metal layer for at least a part of the light reflection uneven portion in the reflective structure layer, light can be efficiently incident on the cells of the solar battery. Also, when the metal layer is present in an area of 10% to 95% with respect to the back protective sheet, on the other hand, water vapor that has once entered the inside or gas generated inside is released to the outside. And the light utilization efficiency is improved.

  Moreover, as for the back surface protection sheet which concerns on Claim 4 of this invention, the shape of the said light reflection uneven | corrugated | grooved part made the shape which attached the radius to the vertex of the facet shape, the cone shape, the facet shape, the radius of the cone shape. It is characterized by comprising a shape or any one of these inverse shapes.

  The prism shapes such as the facet shape and the cone shape as described above have good reflectivity. For example, an aspherical lens having a high aspect ratio has a scattering property, but light is absorbed by the structure, which may cause a decrease in retroreflectance. Further, the shape with the rounded corners of the facet shape and the shape with the rounded corners of the conical shape can prevent scratches in the manufacturing process while maintaining good reflectivity.

  Further, in the back surface protective sheet according to claim 5 of the present invention, the shape of the light reflection uneven portion is composed of a plurality of convex portions and a plurality of concave portions, and the apex angle of the convex portions is 111 ° or more, 137 It is characterized by being in the range below °.

  By setting the apex angle in the above angle range, when the refractive index of the sealing resin and glass used in the solar cell is about 1.5, total reflection is performed at the interface between the glass and air, and the reflected light is reflected. It is possible to prevent the light from entering the concavo-convex structure. On the other hand, when the apex angle exceeds 137 °, total reflection is less likely to occur at the glass / air interface, so that the light incident on the reflective back surface protective sheet enters the cell by total reflection at the glass / air interface. There is a high possibility that the re-condensing efficiency for re-incident is reduced. In addition, when the angle is less than 111 °, there is a high possibility that a part of the light reflected by the concavo-convex structure collides within the concavo-convex structure, and the possibility that the re-condensing efficiency decreases.

  Moreover, as for the back surface protection sheet which concerns on Claim 6 of this invention, the said light reflection uneven | corrugated | grooved part is provided with the metal layer which consists of a metal film which has light reflectivity on the uneven | corrugated shape provided in the said reflection structure layer. It is characterized by comprising.

By forming the reflective structure layer as described above, the light reflective concavo-convex portion (concave structure) can be mass-produced by, for example, extrusion molding, embossing using a plate on which the concavo-convex structure is formed, UV molding, and the like. Thus, the same uneven structure can be formed. as a result,
It is possible to stably produce the reflective structure layer.

  Moreover, the solar cell which concerns on Claim 7 of this invention provided the back surface protection sheet of any one of Claims 1-6 on the back surface.

  By using the back surface protective sheet according to any one of claims 1 to 6, it is possible to prevent a wiring short circuit of the solar cell. In addition, the solar cell can be protected from water vapor and gas generated inside.

  A solar cell according to claim 8 of the present invention receives light from a light receiving surface disposed in the filling layer, a front plate through which light is incident, a filling layer that transmits light transmitted through the front plate, and the filling layer. A cell in which an electromotive force is generated and a back surface protective sheet according to any one of claims 3 to 6, wherein the region where the metal layer of the back surface protective sheet is not formed is defined as the cell. The back surface protection sheet is arranged so as to exist only immediately below the region where the slab exists.

  The use efficiency of light can be improved by using any one of the back surface protection sheets according to claims 3 to 6. However, if the region where the metal layer is not formed is formed other than directly under the cell, the light utilization efficiency is somewhat reduced. Therefore, by causing the region where the metal layer is not formed to exist only directly below the cell, it is possible to prevent a wiring short without reducing the light utilization efficiency. Moreover, it becomes possible to protect the solar cell from water vapor and gas generated inside.

  In the present invention, the solar cell is protected and has a metal layer formed of an electric conductor, and the metal layer is not formed on the entire surface of the back surface protection sheet but is partially present. As a result, it is possible to provide a back surface protection sheet and a solar cell that have resistance to wiring shorts, water vapor, and gas generated inside while improving power generation efficiency.

It is a side view which shows an example of a structure of the solar cell which concerns on this Embodiment. It is a side view which shows an example of a structure of the back surface protection sheet which concerns on this Embodiment. It is a perspective view which shows an example of the light reflection uneven | corrugated part which concerns on this Embodiment. It is explanatory drawing which shows apex angle (theta) in the light reflection uneven | corrugated part which concerns on this Embodiment. It is the figure which looked at the back surface protection sheet which concerns on a present Example from the upper part. It is a side view which shows the implementation structure of evaluation of the back surface protection sheet which concerns on a present Example.

Next, embodiments of the present invention will be described with reference to the drawings.
First, the solar cell according to this embodiment will be described. FIG. 1 is a schematic view according to one aspect of the solar cell of the present invention.

(Solar cell)
The solar cell is configured by laminating a front plate 2, a filling layer 3, and a back surface protective sheet 5 in order from the light receiving side on which the light beam 1 (also referred to as external light) is incident. Cell 4 is arranged. The surface on the light receiving side of the light beam 1 of the cell 4 is the light receiving surface 4A.

  The light beam 1 indicates sunlight or artificial light such as room light. The front plate 2 receives the external light 1 and is made of a general transparent material having a high light transmittance. Specifically, a resin sheet such as tempered glass or PEN (polyethylene naphthalate) is used as the front plate 2. The thickness of the front plate 2 is about 5 mm for tempered glass and several tens to several hundreds μm for a resin sheet.

  The light 1 incident on the front plate 2 enters the filling layer 3. The filling layer 3 has a role of sealing the cells 4, and a material having a high light transmittance is used to transmit the external light 1 incident from the front plate 2. For example, EVA (ethylene vinyl acetate) having flame retardancy is widely used as the filling layer 3.

  A part of the light 1 incident on the filling layer 3 enters the cell 4. The cell 4 has a function of converting light incident on the light receiving portion into electricity due to the photoelectric effect, and is a single crystal silicon type, a polycrystalline silicon type, a thin film silicon type, or a CIGS (Cu • In • Ga • Se compound) system. There are many types such as thin film type. A plurality of the cells 4 are connected by electrodes to form a solar cell.

  The light 1 transmitted through the filling layer 3 is incident on the back surface protective sheet 5 disposed on the back surface of the solar cell. The back surface protection sheet 5 has a function of reflecting incident light toward the light receiving surface 4 </ b> A by the reflection structure layer 11 described later. The reflected light is further reflected at the interface between the front plate 2 and the atmosphere, etc., irradiated to the light receiving surface 4A of the cell 4 and photoelectrically converted, thereby improving the light utilization efficiency.

(Back protection sheet)
FIG. 2 is a side view showing an example of the configuration of the back surface protection sheet 5 of the solar cell according to the present embodiment. The back surface protective sheet 5 is configured by laminating an outer layer 6, an intermediate layer 7, a metal layer 8, a structural layer 9, and a transparent protective layer 10 in this order from the side away from the light receiving surface 4 </ b> A.

  In this embodiment, the reflective structural layer 11 is constituted by the structural layer 9 and the metal layer 8. Moreover, the metal layer 8 is not formed on the entire surface of the back surface protection sheet 5 in a top view, and there is a region where the metal layer 8 is not formed in part.

  The structural layer 9 is a reflective structural layer that is provided on the light emitting surface side (the lower surface in FIG. 2) of the protective layer 10 and reflects the light emitted from the light emitting surface toward the protective layer 10. . In FIG. 2, a concavo-convex structure is formed on the lower surface side of both surfaces of the structural layer 9 as described later, and a metal layer 8 is formed as a metal film on the concavo-convex structure of the structural layer 9. However, the metal layer 8 is not formed on the entire surface of the concavo-convex structure, and is formed only in the range of 10% to 95%.

Although FIG. 2 illustrates an example in which the concavo-convex structure is provided on the lower surface side, the concavo-convex structure may be formed on the upper surface side (side closer to the light receiving surface 4A) or both surfaces of the structural layer 9. Further, the uneven structure may be formed by changing the thickness of the metal layer 8 itself without forming the uneven structure in the structure layer 9.
By adopting such a configuration, it becomes possible to efficiently make the light incident on the back surface protective sheet 5 incident on the cell and improve the power generation efficiency.

  In addition, the shape of the concavo-convex portion may be a facet shape, a cone shape, a shape with a rounded corner at the apex of the facet shape, a shape with a rounded corner at the apex of the conical shape, or any of the reverse shapes. . The shape of the concavo-convex part is preferably composed of a plurality of convex parts and a plurality of concave parts, and the apex angle θ of the convex part is preferably in the range of 111 ° to 137 °.

(Outer layer)
The outer layer 6 is provided on the outer side (a position away from the light receiving surface 4 </ b> A) from the reflective structure layer 11 when the back surface protection sheet 5 is disposed in the solar cell. The outer layer 6 protects the reflective structure layer 11.

  In view of being installed outdoors, the outer layer 6 preferably has water resistance and weather resistance such as durability against ultraviolet rays. Examples of the material for the outer layer 6 include polyethylene resins such as polyethylene terephthalate resin (PET resin), polypropylene resins, methacrylic resins, polymethylpentene resins, cyclic polyolefin resins, polystyrene resins, and acrylonitrile- (poly) styrene. Copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polyvinyl chloride resin, fluorine resin, poly (meth) acrylic resin, polycarbonate resin, polyester resin, polyamide resin , Polyimide resin, polyamideimide resin, polyarylphthalate resin, silicone resin, polysulfone resin, polyphenylene sulfide resin, polyethersulfone resin, reethylene naphthalate resin, polyether resin De resins, Epokishin resins, polyurethane resins, acetal resins, cellulose resins and the like.

Among the above-mentioned resins, polyimide resins, polycarbonate resins, polyester resins, fluorine resins, and polylactic acid resins are preferable as those having high heat resistance, strength, weather resistance, durability, gas barrier properties against water vapor and the like. .
Examples of the polyester-based resin include polyethylene terephthalate and polyethylene naphthalate. Among these polyester-based resins, polyethylene terephthalate is particularly preferable because it has a good balance between various functions such as heat resistance and weather resistance, and price.

  Examples of the fluororesin include polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA) made of a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP). ), Copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether and hexafluoropropylene (EPE), copolymer of tetrafluoroethylene and ethylene or propylene (ETFE), polychlorotrifluoroethylene resin (PCTFE), ethylene and chlorotrifluoroethylene Copolymer (ECTFE), vinylidene fluoride resin (PVDF), vinyl fluoride resin (PVF), and the like. Among these fluororesins, polyvinyl fluoride resin (PVF) and a copolymer of tetrafluoroethylene and ethylene or propylene (ETFE) which are excellent in strength, heat resistance, weather resistance and the like are particularly preferable.

  Examples of the above-mentioned cyclic polyolefin-based resin include polymerizing cyclic dienes such as a) cyclopentadiene (and derivatives thereof), dicyclopentadiene (and derivatives thereof), cyclohexadiene (and derivatives thereof), norbornadiene (and derivatives thereof), and the like. And b) a copolymer obtained by copolymerizing the cyclic diene with one or more olefinic monomers such as ethylene, propylene, 4-methyl-1-pentene, styrene, butadiene, and isoprene. It is done. Among these cyclic polyolefin resins, cyclopentadiene (and derivatives thereof), dicyclopentadiene (and derivatives thereof) or norbornadiene (and derivatives thereof) such as polymers having excellent strength, heat resistance, and weather resistance are particularly preferred. preferable.

  In addition, as a formation material of the outer layer 6, the above-mentioned synthetic resin can be used 1 type or in mixture of 2 or more types. In addition, various additives and the like can be mixed in the forming material of the outer layer 6 for the purpose of improving and modifying processability, heat resistance, weather resistance, mechanical properties, dimensional stability, and the like. Examples of the additive include a lubricant, a crosslinking agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a filler, a reinforcing fiber, a reinforcing agent, an antistatic agent, a flame retardant, a flame retardant, a foaming agent, and an antifungal agent. And pigments. The method for forming the outer layer 6 is not particularly limited, and known methods such as an extrusion method, a cast forming method, a T-die method, a cutting method, and an inflation method are employed.

  The outer layer 6 may contain an ultraviolet stabilizer or a polymer having an ultraviolet stabilizing group bonded to a molecular chain. By this ultraviolet stabilizer or ultraviolet stabilizer, radicals generated by ultraviolet rays, active oxygen, and the like are inactivated, and the ultraviolet stability, weather resistance, and the like of the back protective sheet 5 can be improved. As the UV stabilizer or UV stabilizer, a hindered amine UV stabilizer or a hindered amine UV stabilizer having high stability to UV is preferably used.

(Middle layer)
The intermediate layer 7 desirably has good adhesion to two layers in contact with the intermediate layer 7 and is used to supplement various properties such as durability and cushioning properties. Examples of the material for the intermediate layer 7 include polyurethane resins, silicone resins, polyimide resins, epoxy resins, polyethylene resins, polypropylene resins, polymethylpentene resins, cyclic polyolefin resins, and acrylonitrile- (poly). Polystyrene resins such as styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polyvinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyamideimide resin, Examples include polyaryl phthalate resins, polysulfone resins, polyphenylene sulfide resins, polyether sulfone resins, reethylene naphthalate resins, polyether imide resins, acetal resins, and cellulose resins. The polymer may be used alone or in combination.

  By providing the intermediate layer 7, it is possible to compensate for performance that is insufficient with only the other layers. For example, a silicone resin is used to improve durability, cushioning properties, and the like. Particularly in the case of a solar cell for outdoor use, the heat rise of the solar cell during sunshine is remarkable, and the back surface protection sheet made of a resin material is warped, which may cause an unexpected failure of the solar cell. In addition, a metal layer may be used to have a high barrier property that is important for maintaining high power generation efficiency. The thickness of the intermediate layer 7 is desirably 3 μm or more and 10 μm or less from the viewpoint of adhesion and cost.

(Structure layer)
The material forming the structural layer 9 is desirably highly permeable when the structural layer 9 is positioned closer to the permeable protective layer 10 than the metal layer 8. Examples of the material used for the structural layer 9 include a polymer composition and a metal. Further, when a polymer composition is used for the structural layer 9, in addition to the polymer composition, for example, a curing agent, a plasticizer, a dispersant, various leveling agents, an ultraviolet absorber, an antioxidant, a viscosity modifier, a lubricant, a light A stabilizer and the like may be appropriately blended.

  The above-mentioned polymer composition is not particularly limited. For example, poly (meth) acrylic resin, polyurethane resin, fluorine resin, silicone resin, polyimide resin, epoxy resin, polyethylene resin, polypropylene Resin, methacrylic resin, polymethylpentene resin, cyclic polyolefin resin, acrylonitrile- (poly) styrene copolymer (AS resin), polystyrene resin such as acrylonitrile-butadiene-styrene copolymer (ABS resin), Polyvinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyamideimide resin, polyaryl phthalate resin, polysulfone resin, polyphenylene sulfide resin, polyether sulfone resin, reethylene naphthalene DOO-based resins, polyether imide resins, acetal resins, cellulose resins and the like, can be used as a mixture of these polymers alone or in combination.

  Examples of the polyol that is a raw material for the polyurethane resin include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, a polyester polyol obtained under conditions of excess hydroxyl group, and the like. These can be used alone or in admixture of two or more.

  Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, homoallyl alcohol, Keihi Hydroxyl-containing unsaturated monomers such as alcohol and crotonyl alcohol, (b) for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4-bis (hydroxymethyl) cyclohexane, phenylglycidyl Dihydric alcohols or epoxy compounds such as ether, glycidyl decanoate, Plaxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.) and, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, Tonsan, and the like hydroxyl group-containing unsaturated monomers obtained by reaction of an unsaturated carboxylic acid such as itaconic acid. One or more selected from these hydroxyl group-containing unsaturated monomers can be polymerized to produce a polyol.

  The polyols described above are ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, N-butyl methacrylate, tert-butyl methacrylate, ethyl hexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyl toluene, 1-methyl styrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, stearin Vinyl acid, allyl acetate, diallyl adipate, diallyl itaconate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N-butyl One or more ethylenically unsaturated monomers selected from xymethyl acrylamide, diacetone acrylamide, ethylene, propylene, isoprene and the like, and a hydroxyl group-containing non-functional group selected from the above (a) and (b) It can also be produced by polymerizing a saturated monomer.

  The number average molecular weight of a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer is from 1,000 to 500,000, preferably from 5,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.

  The polyester polyol obtained under the condition of excess hydroxyl group is (c), for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl. Glycol, hexamethylene glycol, decamethylene glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, hexanetriol, glycerin, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis (hydroxymethyl) Polyhydric alcohols such as cyclohexane, hydroquinone bis (hydroxyethyl ether), tris (hydroxyethyl) isosinurate, xylylene glycol, and (d) maleic acid, for example. A polybasic acid such as fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimetic acid, terephthalic acid, phthalic acid, isophthalic acid, and other polyvalent acids such as propanediol, hexanediol, polyethylene glycol, trimethylolpropane, etc. It can be produced by reacting under conditions where the number of hydroxyl groups in the alcohol is greater than the number of carboxyl groups in the polybasic acid.

  The number average molecular weight of the polyester polyol obtained under the above hydroxyl group-excess conditions is 500 or more and 300,000 or less, preferably 2000 or more and 100,000 or less. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.

  The polyol used as the polymer material of the polymer composition is obtained by polymerizing the above-described polyester polyol and a monomer component containing the above-mentioned hydroxyl group-containing unsaturated monomer, and is a (meth) acryl unit. Etc. are preferred. When such a polyester polyol or acrylic polyol is used as a polymer material, the weather resistance is high, and yellowing of the structural layer 9 can be suppressed. In addition, any one of this polyester polyol and acrylic polyol may be used, and both may be used.

  The number of hydroxyl groups in the above-described polyester polyol and acrylic polyol is not particularly limited as long as it is 2 or more per molecule, but if the hydroxyl value in the solid content is 10 or less, the number of crosslinking points decreases, and the solvent resistance Film properties such as heat resistance, water resistance, heat resistance and surface hardness tend to decrease.

  Further, by adding a filler to the material forming the structural layer 9, it is possible to impart scattering properties and reduce the influence of the re-condensing efficiency due to the incident angle of external light. Moreover, it becomes possible to improve heat resistance by containing a filler.

  When a filler is mixed in the material forming the structural layer 9, it is desirable to select a material having a refractive index that can improve the heat resistance of the structural layer 9 and is suitable for the required scattering properties. The inorganic material constituting the filler is not particularly limited, and an inorganic oxide is preferable. As the inorganic oxide, metal oxides such as silicon oxide and zinc sulfide can be used, but metal oxides such as titanium oxide and aluminum oxide are particularly desirable. Silicon oxide hollow particles can also be used. Of these, titanium oxide is preferable because of its high refractive index and easy dispersibility. The shape of the filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scale shape, and a crushed shape, and is not particularly limited.

  The average particle diameter of the filler is preferably in the range of 0.1 μm to 30 μm. If the average particle diameter is smaller than 0.1 μm, light is not sufficiently reflected. Further, if the average particle size is larger than 30 μm, the moldability is poor.

  As a minimum of the compounding quantity with respect to 100 parts of polymer compositions of a filler, 30 parts is preferable in conversion of solid content. On the other hand, the upper limit of the amount of the filler described above is preferably 100 parts. This is because if the blending amount of the filler is less than 30 parts, light cannot be sufficiently reflected. On the contrary, if the blending amount exceeds the above range, the moldability is poor.

  As the above-mentioned filler, a material having an organic polymer fixed on its surface may be used. Thus, by using the filler fixed to the organic polymer, the dispersibility in the polymer composition and the affinity with the polymer composition can be improved. The organic polymer is not particularly limited with respect to its molecular weight, shape, composition, presence or absence of a functional group, and any organic polymer can be used. Moreover, about the shape of an organic polymer, the thing of arbitrary shapes, such as a linear form, a branched form, and a crosslinked structure, can be used.

  Specific resins constituting the above-mentioned organic polymer include, for example, (meth) acrylic resin, polystyrene, polyvinyl acetate, polyolefin such as polyethylene and polypropylene, polyester such as polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, and the like. And a resin partially modified with a functional group such as an amino group, an epoxy group, a hydroxyl group, or a carboxyl group. Among them, those having an organic polymer containing a (meth) acryl unit such as a (meth) acrylic resin, a (meth) acrylic-styrene resin, and a (meth) acrylic-polyester resin have a film forming ability. Is preferred. On the other hand, a resin having compatibility with the above-described polymer composition is preferable, and therefore, a resin having the same composition as the material forming the structural layer 9 is most preferable.

  As a material for forming the structural layer 9 described above, a polyol having a cycloalkyl group is preferable. By introducing a cycloalkyl group into the polyol as the polymer composition, the hydrophobicity of the polymer composition, such as water repellency and water resistance, is increased, and the structure layer 9 is flexible and dimensionally stable under high temperature and high humidity conditions. Sex etc. are improved. Further, the basic properties of the coating layer such as weather resistance, hardness, feeling of holding, and solvent resistance of the structural layer 9 are improved. Furthermore, the affinity with the filler having the organic polymer fixed on the surface and the dispersibility of the filler are further improved.

Moreover, it is good to contain isocyanate as a hardening | curing agent in a polymer composition. Thus, by containing an isocyanate hardening | curing agent in a polymer composition, it becomes a much stronger crosslinked structure and the film physical property of the structure layer 9 improves further. As this isocyanate, the same substance as the above-mentioned polyfunctional isocyanate compound is used. Of these, aliphatic isocyanates that prevent yellowing of the coating are preferred.
The filler may contain an organic polymer inside. Thereby, moderate softness and toughness can be imparted to the inorganic material that is the core of the filler.

  An organic polymer containing an alkoxy group may be used as the organic polymer, and the content is not particularly limited, but is preferably 0.01 mmol or more and 50 mmol or less per 1 g of filler. The alkoxy group can improve the affinity with the polymer composition and the dispersibility in the polymer composition.

  The above-described alkoxy group represents an RO group bonded to a metal element that forms a fine particle skeleton. R is an alkyl group which may be substituted, and the RO groups in the fine particles may be the same or different. Specific examples of R include methyl, ethyl, n-propyl, isopropyl, n-butyl and the like. The same metal alkoxy group as the metal constituting the filler is preferably used. When the filler is colloidal silica, it is preferable to use an alkoxy group having silicon as a metal.

The content of the organic polymer in the filler to which the organic polymer is fixed is not particularly limited, but is preferably 0.5% by mass or more and 50% by mass or less based on the filler.
Further, the light reflection uneven portion 11A formed from the structural layer 9 and the metal layer 8 is a structure for reflecting incident light in a specific direction, and as a shape that can be suitably reflected, A faceted shape such as a V-shaped groove or a polygonal pyramid shape, a conical shape, a shape with a rounded corner at the apex of the facet shape, a shape with a rounded corner at the apex of the conical shape, and a reverse type thereof.

As a method for forming the structural layer 9, a plastic raw material is fed into a heating cylinder with a screw or a plunger, heated and fluidized, passed through a die at the tip to give a shape, and cooled and solidified with water or air. There is an extrusion method to make long products.
Further, as another method for forming the structural layer 9, for example, a concave / convex pattern is drawn on a resin or the like by an electron beam, or a concave / convex pattern is formed by cutting or the like, and the concave / convex pattern thus formed is converted into a metal plate by electroforming. An uneven pattern can be replicated in large quantities by producing an original by, for example, raising the pattern and transferring the pattern from the original by an embossing method. Further, instead of transferring by the embossing method, the pattern may be transferred by a molding method using an ultraviolet curable resin.

(Metal layer)
The metal layer 8 is a layer made of metal and having a function of reflecting incident light. The material used for the metal layer 8 is not particularly limited as long as it has reflectivity and can be deposited. For example, aluminum (Al), gold (Au), silver (Ag), copper (Cu) , Platinum (Pt), nickel (Ni), tin (Sn), chromium (Cr), zirconium (Zr) and other metals, and alloys thereof. From the viewpoint of reflectivity, aluminum and silver that exhibit good reflectivity in the ultraviolet, visible, and near infrared regions are desirable. Also desirable are gold and copper, which exhibit good reflectivity in the visible to near infrared region. From the viewpoint of corrosion resistance, stable aluminum, gold, platinum, nickel, chromium, and zirconium are desirable. From the viewpoint of cost, aluminum and copper are desirable.

  The metal layer 8 is formed by evaporating metal along the structural layer 9. The vapor deposition means for the metal layer 8 is not particularly limited as long as the metal can be deposited without causing deterioration such as shrinkage and yellowing on the structural layer 9. Examples of the vapor deposition method include (a) vacuum vapor deposition. Physical vapor deposition (Physical Vapor Deposition method; PVD method) such as sputtering, ion plating, ion cluster beam, etc., (b) plasma chemical vapor deposition, thermal chemical vapor deposition, photochemical vapor A chemical vapor deposition method (Chemical Vapor Deposition method; CVD method) such as a phase growth method may be employed. Among these vapor deposition methods, a vacuum vapor deposition method and an ion plating method that can form a high-quality light reflecting layer with high productivity are preferable.

At this time, a region where the metal layer 8 is not formed is formed as viewed from the incident direction of light. As a result, it is possible to improve the problem that the water vapor that has once entered the inside and the gas that has been generated inside due to the gas barrier property of the metal layer 8 are not released to the outside.
As a method of creating a region where the metal layer 8 is not formed, a method of performing deposition after masking the structural layer 9 or forming a protective layer in a region where the metal layer 8 is to be left after the metal layer 8 is formed. Then, there is a method of removing the metal layer 8 with an alkali or the like.

  Here, the metal layer 8 may have a single layer structure or a multilayer structure of two or more layers. Thus, by making the metal layer 8 into a multilayer structure, as a result of reducing the thermal burden applied during vapor deposition, the deterioration of the structural layer 9 is reduced, and the adhesion between the structural layer 9 and the metal layer 8 is further improved. Can be improved. The vapor deposition conditions in the above physical vapor deposition method and chemical vapor deposition method are appropriately designed according to the resin type of the structural layer 9, the thickness of the metal layer 8, and the like.

In addition, by forming the metal layer 8 in a dot pattern, even when there is a wiring in a place where the metal layer is necessary to improve the light utilization efficiency, the light utilization efficiency is reduced due to the absence of the metal layer. It is desirable because
In addition, as described above, there is some space between adjacent cells of the solar battery. Moreover, in order to prevent erosion of rainwater or the like at the end portion of the solar cell, a blank portion where no cell is arranged is provided from several millimeters to several tens of millimeters. From the viewpoint of improving the light utilization efficiency, it is desirable that the metal layer 8 sufficiently fill this blank portion. Assuming that the cell size is about 156 mm square and the gap is about 5 mm, it is desirable that at least 10% of the metal layer 8 is provided.

  As a minimum of the thickness of the metal layer 8, 10 nm is preferable and 20 nm is especially preferable. On the other hand, the upper limit of the thickness of the metal layer 8 is preferably 200 nm, and particularly preferably 100 nm. If the thickness of the metal layer 8 is less than 10 nm, the light incident on the metal layer 8 cannot be sufficiently reflected. Further, even if the thickness is 20 nm or more, the light reflected by the metal layer 8 does not increase. On the other hand, if the thickness of the metal layer 8 exceeds the upper limit of 200 nm, cracks that can be visually confirmed occur in the metal layer 8, and cracks that cannot be visually confirmed occur if the thickness is 100 nm or less.

  Moreover, as the thickness of the base on which the metal layer 8 is formed, it is desirable that the thickness of the thinnest portion is 100 μm or more. When the thickness is less than 100 μm, the base material is easily bent, and the reflective film is easily cracked. In this example, since the permeable protective layer 10 and the structural layer 9 serve as a base on which the metal layer 8 is formed, the total thickness of both is desirably 100 μm or more.

(Metal layer topcoat treatment)
Further, the outer surface of the metal layer 8 is preferably subjected to a top coat treatment. Thus, by performing a topcoat process on the outer surface of the metal layer 8, the metal layer 8 is sealed and protected, and it becomes possible to suppress deterioration over time.

  Examples of the topcoat agent used in the above-described topcoat treatment include a polyester topcoat agent, a polyamide topcoat agent, a polyurethane topcoat agent, an epoxy topcoat agent, a phenol topcoat agent, and a (meth) acrylic top. Examples thereof include a coating agent, a polyvinyl acetate top coating agent, a polyolefin top coating agent such as polyethylene aly polypropylene, and a cellulose top coating agent. Among such topcoat agents, polyester-based topcoat agents that have high adhesive strength with the metal layer 8 and contribute to surface protection of the metal layer 8, sealing of defects, and the like are particularly preferable.

The coating amount (in terms of solid content) of the above-mentioned topcoat agent is preferably 3 g / m ² or more and 7 g / m ² or less. If the coating amount of the topcoat agent is less than 3 g / m ² , the effect of sealing and protecting the metal layer 8 may be reduced. On the other hand, even if the coating amount of the top coat agent exceeds 7 g / m ² above, the sealing and protective effect of the metal layer 8 does not increase so much, but the thickness of the back surface protective sheet 5 increases. .

  In addition, in the above-mentioned top coat agent, various additives such as a silane coupling agent for improving tight adhesion, an ultraviolet absorber for improving weather resistance and the like, an inorganic filler for improving heat resistance and the like Can be mixed as appropriate. The mixing amount of the additive is preferably 0.1% by mass or more and 10% by mass or less in view of the balance between the effect expression of the additive and the function inhibition of the topcoat agent. When the above-mentioned additive is less than 0.1% by mass, sufficient adhesion, weather resistance and heat resistance cannot be obtained, and when it is more than 10% by mass, the function of the topcoat agent is inhibited.

  When the metal layer 8 is used in the back surface protection sheet 5, the surface of the structural layer 9, which is the deposition target surface of the metal layer 8, may be subjected to a surface treatment in order to improve the tight adhesion and the like. Examples of such surface treatment include (a) corona discharge treatment, ozone treatment, low temperature plasma treatment using oxygen gas or nitrogen gas, glow discharge treatment, oxidation treatment using chemicals, and (b) primer. Examples of the coating treatment include undercoating, anchor coating, vapor deposition anchor coating, and the like. Among these surface treatments, a corona discharge treatment and an anchor coat treatment that improve the adhesive strength with the structural layer 9 and contribute to the formation of a dense and uniform metal layer 8 are preferable.

  Examples of the anchor coating agent used in the above-described anchor coating treatment include a polyester anchor coating agent, a polyamide anchor coating agent, a polyurethane anchor coating agent, an epoxy anchor coating agent, a phenol anchor coating agent, and a (meth) acrylic anchor. Examples thereof include a coating agent, a polyvinyl acetate anchor coating agent, a polyolefin anchor coating agent such as polyethylene aly polypropylene, and a cellulose anchor coating agent. Among these anchor coating agents, polyester anchor coating agents that can further improve the adhesive strength of the metal layer 8 are particularly preferable.

The coating amount (in terms of solid content) of the above-described anchor coating agent is preferably 1 g / m ² or more and 3 g / m ² or less. When the coating amount of the anchor coating agent is less than 1 g / m ^{2, the} effect of improving the adhesion of the metal layer 8 is reduced. On the other hand, when the coating amount of the anchor coating agent is more than 3 g / m ² , the strength, durability and the like of the back surface protection sheet 5 may be lowered.

  In the above-mentioned anchor coating agent, various additives such as a silane coupling agent for improving tight adhesion, an anti-blocking agent for preventing blocking, and an ultraviolet absorber for improving weather resistance, etc. It can mix suitably.

(Protective layer)
The permeable protective layer 10 is preferably excellent in heat resistance, moisture resistance, electrical characteristics (particularly the overall withstand voltage), and mechanical characteristics. Specific examples include a fluororesin film, a fluororesin coating film, and PET for electrical insulation. The thickness of the permeable protective layer 10 is preferably in the range of 180 μm to 350 μm from the viewpoint of electrical insulation and cost.

(Preparation example of back protection sheet)
As an example of a method for producing the back surface protection sheet 5 as shown in FIG. 2, there is the following method, that is, a structural layer 9 having a concavo-convex structure by a UV molding method using a metal plate on the transparent protective layer 10. And a metal layer 8 is formed thereon by mask vapor deposition or the like. The portion where the metal layer 8 is formed on the concavo-convex structure becomes the light reflecting concavo-convex portion 11A. Further, the metal layer 8 and the outer layer 6 are bonded using the intermediate layer 7.

  As described above, the back surface protective sheet 5 of the present embodiment includes the light-transmissive protective layer 10, the reflective structure layer 11 having the metal layer 8 formed of metal, and the reflective structure layer 11. And an outer layer 6 to be protected.

(Example of light reflection unevenness)
FIG. 3 is a perspective view showing an example of the light reflection uneven portion 11A.
The light reflection uneven portion 11A is provided on at least one surface of the structural layer 9 and has a function of dimming the light beam 1. Depending on the type and installation location of the solar cell, a structure in which pyramid types as shown in FIG. 3 (a) are arranged in two directions, a structure in which V-groove types as shown in FIG. 3 (b) are arranged in one direction, An example of an effective shape is a structure in which conical shapes shown in 3 (c) are arranged in two directions.

Moreover, it is sunlight which becomes a light source of a solar cell mainly. Since sunlight is approximated to a light source located at infinity from the solar cell, the sunlight is incident on the solar cell as parallel light on the roof, roof, or the like where the solar cell is installed. However, it is not all parallel light, but there is also scattered light that is reflected by the surrounding objects, but most of the light is incident as parallel light. For the dimming of parallel light, a prism shape having a flat surface is effective as the shape of the light reflection uneven portion.
In addition, the V-groove type and the pyramid type have an advantage that they are easy to manufacture as compared with spherical and aspherical shapes such as microlenses.

FIG. 4 is a side view showing an apex angle of an example of the light reflection uneven portion 11A according to the present embodiment.
The apex angle θ of the light reflecting concavo-convex portion 11A indicates an angle between lines L1 and L2 that are respectively parallel to regions formed linearly on two opposing side surfaces that form the light reflecting concavo-convex portion 11A. The same applies to a shape with a rounded apex as shown in FIG.

  In other words, the shape of the light reflection uneven portion 11A includes a plurality of convex portions and a plurality of concave portions, and the apex angle θ of the convex portions is preferably included in the range of 111 ° or more and 137 ° or less. .

Next, examples of the present invention will be described.
In this embodiment, the configuration of the back surface protection sheet is as shown in FIG. Further, as shown in FIGS. 5A and 5B as seen from the light incident direction (a top view), there is a region where the metal layer 8 is not formed on a part of the back surface protection sheet 5. In addition, a back protective sheet in which the height of the light reflection uneven portion 11A was about 58 μm and the average interval between adjacent convex portions was 200 μm.
And the measurement regarding re-condensing efficiency was performed about the back surface protection sheet.

(Measuring method)
FIG. 6 shows a schematic diagram of the measuring method.
Assuming noon sunlight as a light source, parallel light having an incident angle of about 0 degrees was adopted as a measurement light source. Moreover, the power meter 14 was used for the measurement of re-condensing efficiency. Assuming the configuration of the solar cell, as shown in FIG. 6, the back surface protection sheet 5, the power meter 14, and the glass 13 were sequentially laminated. Moreover, in order to match | combine a refractive index between each layer, it immersed using glycerin 15. FIG.

In this example, the reflective structure layer 11 was produced by using a UV curable acrylic resin with a PET film as the transparent protective layer 10 as a molding substrate, and aluminum was deposited as the metal layer 8. Further, a PET film was used for the outer layer 6.
Regarding the sample produced as described above, light was incident from the transparent protective layer side and measured. The results are shown in Table 1.

For comparison, black paper assuming no reflection and white PET assuming a current back surface protection sheet were measured as similar protection sheets, and measurement was performed under the same conditions.
At this time, as an example, FIG. 5A in which a region where the metal layer 8 does not exist is formed only directly under the region where the power meter 14 is present, and the metal is present only under the region where the power meter 14 is present. Two types of FIG. 5B in which the layer 8 exists were produced.

As can be seen from Table 1, the measurement result of the back surface protection sheet of this example confirmed that the re-condensing efficiency was improved in all samples compared to black paper.
However, in FIG. 5 (a), the re-condensing efficiency is improved as compared with white PET, whereas in FIG. 5 (b), the value is almost the same as that of black paper. . Therefore, it was confirmed that better power generation efficiency can be obtained when the metal layer 8 is present only directly under the region where the power meter 14 as a power generation source is present.

In this embodiment, the configuration is such that the intermediate layer 7 and the outer layer 6 are removed from the configuration shown in FIG. 2, and as shown in FIGS. 5 (a), 5 (b), and 5 (c), a part of the back surface protective sheet 5 is used. This is an example when there is a region where the metal layer 8 is not formed.
A tester was brought into contact with the metal layer 8 in the three types of samples shown in FIGS. In the samples of FIGS. 5 (a) and 5 (b), it was confirmed that energization was performed only when the testers were brought into contact with each other where the metal layer 8 was formed. On the other hand, it was confirmed that the sample of FIG. 5C was not energized unless contact was made between the same points of the metal layer 8 in the form of a halftone dot.

  Therefore, with respect to FIGS. 5A and 5B, there is a possibility of a wiring short by passing the wiring through a region where the metal layer 8 does not exist, and with respect to FIG. It was confirmed that it could be suppressed.

Moreover, Example 3 is an Example which has the structure shown in FIG. 2 and has a region where the metal layer 8 is not formed on a part of the back surface protection sheet 5 as shown in FIG. 5A. .
Measurement of water vapor transmission rate using the JIS K 0208 cup method for samples in which the region where the metal layer is formed is 100%, 95%, 74%, 62%, 32%, and 0% of the entire structure. Carried out.

In this embodiment, the reflective structure layer 11 is made of a PET film having a thickness of 250 μm, which is a transparent protective layer 10, using a UV curable acrylic resin as a molding substrate, and the metal layer 8 is deposited with aluminum by 100 nm. did. Further, a PET film having a thickness of 50 μm was used for the outer layer 6.
The measurement results of water vapor permeability are shown in Table 2.

As can be seen from Table 2, when the metal layer 8 is 100% of the whole, the value of water vapor permeability is 0.9 (g / m ² · d), whereas the metal layer 8 is not formed. For the 0% sample, it was 5 (g / m ² · d).

On the other hand, regarding the sample in which the metal layer is partially formed, even if the metal layer 8 accounts for 95% of the whole, a value of 4.3 (g / m ² · d) is shown. If the area occupied by the metal layer 8 is 95%, the ability to release the water vapor present inside is comparable to the case where the metal layer 8 is not formed. It was confirmed.

1 light beam (external light)
2 Front plate 3 Filling layer 4 Cell 4A Light receiving surface 5 Back surface protection sheet 6 Outer layer 7 Intermediate layer 8 Metal layer 9 Structure layer 10 Protective layer 11 Reflective structure layer 11A Light reflection uneven portion θ Vertical angle

Claims (8)

A back surface protection sheet for protecting the back surface located on the opposite side of the light receiving surface of the solar cell from the external environment,
At least a metal layer, a light-transmitting protective layer disposed closer to the light receiving surface than the metal layer, and an outer layer disposed at a position farther from the light receiving surface than the metal layer,
The said metal layer exists in the range of 10 to 95% of area with respect to the total area of a back surface protection sheet, The back surface protection sheet characterized by the above-mentioned.   The back surface protection sheet according to claim 1, wherein at least a part of the metal layer is formed in a halftone dot shape. A back surface protection sheet for protecting the back surface located on the opposite side of the light receiving surface of the solar cell from the external environment,
A light-transmitting protective layer in which one surface is a light incident surface and the other surface is a light exit surface;
A reflective structure layer provided on the light emitting surface side of the protective layer for reflecting the light emitted from the light emitting surface toward the protective layer;
An outer layer that is provided on the back surface side opposite to the light emitting surface in the reflective structure layer and protects the reflective structure layer;
A light reflection uneven portion formed of the metal layer on at least a part of at least one of the front surface and the back surface of the reflective structure layer,
The metal layer forming the light reflection uneven portion is present in an area range of 10% to 95% with respect to the area of the back protective sheet. Back protection sheet.   The shape of the light reflection uneven portion is a facet shape, a conical shape, a shape with a rounded corner at the apex of the facet shape, a shape with a rounded corner at the apex of the conical shape, or a reverse shape thereof. The back surface protection sheet according to claim 3.   The shape of the light reflection uneven portion is composed of a plurality of convex portions and a plurality of concave portions, and the apex angle of the convex portions is in a range of 111 ° or more and 137 ° or less. 4. The back surface protective sheet according to 4.   The said light reflection uneven | corrugated | grooved part is comprised by providing the metal layer which consists of a metal film which has light reflectivity on the uneven | corrugated shape provided in the said reflection structure layer, The 3-5 characterized by the above-mentioned. The back surface protection sheet according to any one of the above.   A solar cell comprising the back surface protective sheet according to any one of claims 1 to 6 provided on the back surface. A front plate for incident light;
A filling layer that transmits light transmitted through the front plate;
A cell that is arranged in the filling layer and generates electromotive force by receiving light from the light receiving surface;
The back surface protective sheet according to any one of claims 3 to 6,
A solar cell, wherein the back surface protection sheet is arranged so that a region of the back surface protection sheet where the metal layer is not formed is present only immediately below the region where the cells are present.

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