JP5304444B2 - Solar cell back sheet and solar cell module using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell back sheet capable of improving light utilization efficiency by controlling a reflection angle, and excelling in an electric insulation property, and to provide a solar cell module using the same. <P>SOLUTION: This solar cell back sheet 14 arranged on the back side of a solar cell module is composed by sequentially laminating, from the front side, at least a translucent insulation layer 144, a metal foil 142 with an uneven structure 143 shaped on the front side and a weather-resistant layer 141, and formed so that each apex part of the uneven structure 143 includes a curvature. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention is a solar cell back sheet that is arranged on the back surface of the solar cell module and can effectively utilize the light that is originally incident on the back sheet without entering the solar cell, and the solar cell module, The present invention relates to a solar cell module using a solar cell back sheet.

  In recent years, the widespread use of solar panels has increased greatly, from relatively small ones mounted on small electronic devices such as calculators to large areas used for solar panels installed in houses for home use and large-scale power generation facilities The use of solar cell power generation systems and power supplies for artificial satellites has been promoted in various fields (see, for example, Patent Document 1).

This solar cell converts incident light energy into electric energy, and the main one of the solar cells is classified into crystalline silicon type, amorphous silicon type, organic compound type, etc., depending on the type of material used. Among these, most of those currently on the market are crystalline silicon solar cells, which are further classified into single crystal type and polycrystalline type.
The single-crystal silicon solar cell has the advantage that it is easy to increase the efficiency because the quality of the substrate is good, but has the disadvantage that the manufacturing cost of the substrate is high. On the other hand, although the polycrystalline silicon solar cell has the disadvantage that it is difficult to increase the efficiency because the quality of the substrate is inferior, it has the advantage that it can be manufactured at a low cost, and is currently the mainstream.

Various studies have been conducted on the improvement of the efficiency of such polycrystalline silicon solar cells.
As an example, a texture structure is formed on the surface of a silicon substrate used in a solar cell, thereby reducing the reflection of sunlight on the surface of the silicon substrate and improving the conversion efficiency.

  In single crystal silicon, the reflection of sunlight is reduced by forming fine pyramids or inverted pyramids by anisotropic etching such as an alkaline solution. This anisotropic etching utilizes the fact that the etching rate of single crystal silicon differs between the Si (100) crystal orientation plane and the Si (111) crystal orientation plane. (For example, refer to Patent Document 2).

  However, when such anisotropic etching is applied to polycrystalline silicon, the etching with alkaline aqueous solution depends on the crystal plane orientation, so the pyramid structure in polycrystalline silicon cannot be formed uniformly, and the entire silicon substrate There is a problem that the reflectance cannot be effectively reduced.

  In order to solve such problems, a method of forming fine protrusions on the surface of the polycrystalline silicon substrate by the reactive ion etching method has been proposed as a method of forming a texture on the polycrystalline silicon substrate. (For example, see Patent Document 3). According to this technique, the fine protrusions are uniformly formed without being influenced by the surface orientation of the irregular crystal in the polycrystalline silicon, so that the reflectance is more effective particularly in the solar cell using the polycrystalline silicon. Can be reduced.

  It is also known that the conversion efficiency can be further improved by combining a surface antireflection film. That is, since crystalline silicon has a large refractive index of 6.00 to 3.50 in the wavelength region of 400 nm to 1100 nm, there is a reflection loss of about 54% in the short wavelength region and about 34% in the long wavelength region. In order to reduce this reflection loss, a surface antireflection film can be formed from transparent materials having different refractive indexes, thereby improving the conversion efficiency.

  Further, studies have been made to increase the light receiving area by miniaturizing the electrodes formed on the silicon substrate and improve the conversion efficiency by taking in a large amount of sunlight (for example, see Patent Document 4).

  Due to the progress of the high efficiency technology as described above, conversion efficiency of about 18% has been achieved at the research level recently even in polycrystalline silicon solar cells, and the theoretical limit of conversion efficiency in polycrystalline silicon solar cells (20 ~ 30%).

Therefore, among the sunlight incident from the front of the solar cell module in order to increase the light utilization efficiency, the sunlight incident on the back sheet without being incident on the solar cell that performs energy conversion in the solar cell module is reused. Attempts have been made.
As described above, the sunlight that does not enter the solar battery cell but enters the back sheet exists because gaps are formed between the solar battery modules in the solar battery module in order to reduce the leakage current. Based on that. So, on the back side of the solar cell module, a solar cell back sheet provided with a reflective material is arranged, and the sunlight leaking from the gap between the solar cells is reflected to re-enter the solar cells to improve the light utilization efficiency. Improvement is achieved (for example, refer to Patent Document 5).

  Attempts have also been made to make the surface of the reflective material uneven. By making the surface of the reflective material uneven, it is possible to further improve the light utilization efficiency. At this time, it is possible to use a specular reflector such as aluminum in addition to the above-mentioned scattering reflector as the reflector, but there has been a problem of a decrease in electrical insulation due to the conductor having an uneven structure. . (For example, patent document 6).

JP 2001-295437 A JP 62-35582 A Japanese Patent Publication No. 60-27195 JP 2000-332279 A Japanese Patent Application Laid-Open No. 11-307791 Japanese Patent Laid-Open No. 10-284747

  By the way, in the solar cell back surface sheet as described above, a scattering reflector is generally used as a reflector. When such a scattering reflector is used, light loss due to scattering occurs, and light cannot be efficiently reflected toward the solar battery cell. Therefore, if the reflection angle by the reflecting material can be set appropriately, the amount of light incident on the solar cell can be increased, and the light utilization efficiency can be improved.

  Here, in order to appropriately set the reflection angle, it is desirable to form the concavo-convex structure with a specular reflector such as a metal. However, there is a problem that the discharge breakdown is likely to occur due to the charge concentration when the metal convex portion exists.

  The present invention has been made in view of such problems, and it is possible to improve the light utilization efficiency by appropriately setting the reflection angle, and the solar cell back surface is also excellent in electrical insulation. It aims at providing a sheet | seat and a solar cell module using the same.

In order to solve the above problems, the present invention proposes the following means.
That is, the solar cell back sheet according to the present invention is a solar cell back surface disposed on the back side of a solar cell module in which a translucent front plate is laminated on the front side of a sealing material encapsulating solar cells inside. A sheet comprising at least a light-transmissive insulating layer in order from the front side, a metal foil having a concavo-convex structure formed on the front side, and a weathering layer, and the top of the concavo-convex structure having a curvature. And the bottom and height of the unit structure of the concavo-convex structure so that the light reflected by the concavo-convex structure is totally reflected at the interface between the translucent front plate and the atmosphere and enters the light receiving surface of the solar cell. Is set to a range of 0.15 to 0.35, and the curvature radius r of the top of the concavo-convex structure is 0.01 Pt or more when the pitch of the top of the concavo-convex structure is Pt. Is set to a range of 0.1 Pt or less, Light insulating layer is characterized by having a breakdown voltage greater than or equal to 3 kV.

According to the solar cell back surface sheet having such a feature, since the concavo-convex structure is formed on the front surface of the metal foil, light incident from the front surface side can be reflected in a specific direction. Accordingly, the reflected light re-enters the solar cell module main body, whereby the light use efficiency can be improved.
Here, when the aspect ratio of the unit structure of the concavo-convex structure is larger than 0.35, the moldability when embossing the concavo-convex structure is lowered. On the other hand, if the aspect ratio is smaller than 0.15, the effect of improving the light utilization efficiency is weakened. In view of this point, in the present invention, since the aspect ratio is set in the above range, the light utilization efficiency can be improved while maintaining the formability during embossing.
In addition, it is possible to prevent discharge breakdown due to charge concentration that occurs when metal protrusions exist.
Furthermore, it is possible to prevent the occurrence of short circuits and leakage due to long-term use.

The solar cell backsheet according to the present invention is characterized in that the concavo-convex structure is any one of a substantially prism shape, a substantially polygonal pyramid shape, or an inverted shape of these shapes.
This makes it possible to improve the light utilization efficiency by reliably making the light incident from the front side re-enter the solar battery cell.

  The back sheet of the solar cell according to the present invention is characterized in that the top pitch of the concavo-convex structure is set in a range of 10 μm or more and 30 μm or less.

  When the pitch is larger than 30 μm, the height of the structure increases as the pitch increases, and thus problems such as bubbles tend to occur when the light-transmitting insulating layer and the adhesive layer are bonded together. It becomes easy and is not preferable. In addition, it is necessary to increase the thickness of the adhesive layer, which makes it difficult to form the adhesive layer, and increases the cost. On the other hand, when the pitch is 10 μm or less, light can be diffracted when the light is reflected by the concavo-convex structure. Since the diffracted light becomes light that is spread by spectroscopy, it is difficult to control, and it is not preferable for reflection in a specific direction. Furthermore, it is not preferable because the time for cutting the mold is long, the tact is reduced, and the production efficiency is deteriorated. Based on this, in the present invention, the pitch is set in the range of 10 μm or more and 30 μm or less, so the above inconvenience can be solved.

  The solar cell backsheet according to the present invention is characterized in that the thickness of the metal foil is set in a range of 10 μm to 100 μm.

  When the thickness of the metal foil is smaller than the lower limit of 10 μm, handling becomes difficult in a process such as bonding, and the possibility of occurrence of defects such as wrinkles increases. On the other hand, if the thickness of the metal foil exceeds the upper limit of 100 μm, the flexibility of the metal foil is lowered, which is not preferable because it causes cracks and breaks in the bonding process and the embossing process. Based on this, in the present invention, the thickness of the metal foil is set in the range of 10 μm or more and 100 μm or less, and thus the above inconvenience can be solved.

  The solar cell module according to the present invention is characterized in that any one of the solar cell back sheets is disposed on the back surface of the solar cell module.

  According to the solar cell module having such a feature, the concave and convex structure having a curvature at the top is formed on the front surface of the metal foil of the solar cell back sheet, so that light incident on the solar cell back sheet from the front side is specified. It can reflect toward the direction. Therefore, when the reflected light reenters the solar battery cell, the light use efficiency can be improved. In addition, it is possible to prevent discharge breakdown due to charge concentration that is likely to occur due to the presence of the metal convex portion. Therefore, it is possible to improve electrical insulation.

  According to the solar cell back sheet and the solar cell module according to the present invention, the concave and convex structure having the curvature at the top is formed on the front surface of the metal foil of the solar cell back sheet, so that the solar cell back sheet enters the solar cell back sheet from the front side. Light can be reflected in a specific direction. Thereby, it becomes possible to improve the utilization efficiency of the light in a solar cell module and to increase electric power generation amount. In addition, it is possible to prevent discharge breakdown due to charge concentration that is likely to occur due to the presence of the metal convex portion. Thereby, sufficient electrical insulation can be obtained.

It is a longitudinal cross-sectional view which shows schematic structure of the solar cell module of embodiment. It is a longitudinal cross-sectional view which shows schematic structure of the back surface sheet of embodiment. It is a perspective view which shows the example of an uneven structure. It is a longitudinal cross-sectional view which shows the example of the unit structure of an uneven structure. It is a longitudinal cross-sectional view which shows schematic structure of the solar cell module containing an electrode. It is a figure explaining a mode when discharge arises in a cathode from the uneven structure shape | molded by metal foil. It is a longitudinal cross-sectional view explaining the effect | action of the back surface sheet in a solar cell module. It is a longitudinal cross-sectional view which shows schematic structure of the back surface sheet of a 1st structural example. It is a longitudinal cross-sectional view which shows schematic structure of the back surface sheet of a 2nd structural example. It is a longitudinal cross-sectional view which shows schematic structure of the back surface sheet of a 3rd structural example.

  Hereinafter, embodiments of a solar cell back sheet and a solar cell module according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing a schematic configuration of the solar cell module of the embodiment. As shown in FIG. 1, the solar cell module 1 is configured by laminating a front plate 11, a sealing material 13, solar cells 12 and a back sheet (solar cell back sheet) 14, It is a device that generates electricity by receiving light from the light source L. In addition, as the light source L, the artificial illumination of the sun or a room lamp is normally employ | adopted.
Moreover, the said solar cell module 1 is integrally molded by laminating | stacking the said front plate 11, the sealing material 13, the photovoltaic cell 12, and the back surface sheet | seat 14 by laminating with a vacuum laminator.

The front plate 11 is disposed on the forefront of the solar cell module 1 and protects the solar cells 12 from impact, dirt, moisture intrusion, and the like. The front plate 11 is made of a transparent material having a high transmittance. There is no.
As shown in FIG. 1, among the light emitted from the light source L, the light H0 perpendicularly incident on the incident surface 110 of the front plate 11 is incident on the front plate 11 and then transmitted through the front plate 11 to be sealed. Incident on the material 13. The normal line NG of the incident surface 110 is, for example, a direction parallel to the normal line N of the plane P when the front plate 11 is placed on the plane P parallel to the horizontal plane. The light H0 incident perpendicularly to the incident surface 110 indicates the light H0 incident on the front plate 11 parallel to the normal line NG, that is, the light H0 incident on the solar cell module 1.

  The front plate 11 is made of glass such as tempered glass or sapphire glass, or a resin sheet such as PC (polycarbonate) or PEN (polyethylene naphthalate). Further, the thickness of the front plate 11 is about 3 to 5 mm for tempered glass and about 5 mm for a resin sheet.

  The light emitted from the front plate 11 enters the sealing material 13. The sealing material 13 has a sheet shape with a thickness of about 0.4 to 1 mm, and a plurality of solar cells 12 are fixed therein. The light H0 incident on the front plate 11 passes through the sealing material 13 and becomes light H1 incident on the solar battery cell 12, and a part of the light H1 passes through the sealing material 13 and enters the back sheet 14. It becomes light H1.

  The sealing material 13 is made of a material having a high light transmittance so as to transmit the incident light H0, and further has a heat resistance, a high temperature resistance, a high humidity resistance, a weather resistance and other durability and electrical insulation properties. Is preferred. As a material that satisfies this condition, for example, a thermoplastic synthetic resin material mainly composed of EVA (ethylene vinyl acetate copolymer) or PVB (polyvinyl butyral) having a vinyl acetate content of 20 to 30% is used. Is done.

  The solar cell 12 has a function of converting light incident on the light receiving surface J into electricity by photoelectric effect, and is a single crystal silicon type, a polycrystalline silicon type, an amorphous silicon type, CISG (Cu · In · Ga · Se). There are many types such as compound) thin film type. A plurality of solar cells 12 are connected by electrodes (not shown) to form a module.

  In the present embodiment, the light H <b> 1 that has entered the solar battery cell 12 from the sealing material 13 is converted into electricity by the solar battery cell 12. In general, light obliquely incident on the incident surface 110 has a higher ratio of reflection on the incident surface 110 and less light incident on the solar cells 12 than the vertically incident light H0. That is, there is little light available for power generation. Therefore, power generation can be performed most efficiently when the incident light H0 is incident on the incident surface 110 perpendicularly.

  FIG. 2 is a longitudinal sectional view illustrating a schematic configuration of the back sheet 14 of the embodiment. The back sheet 14 has a function of reflecting the light transmitted through the solar cells 12 itself and the light H1 transmitted through the sealing material 13 without entering the solar cells 12, and in order from the back side, the weather resistant layer 141. The metal foil 142 and the translucent insulating layer 144 are laminated. In other words, the back sheet 14 is configured by laminating at least the light-transmissive insulating layer 144, the metal foil 142, and the weather resistant layer 141 in order from the front side.

  The weather resistant layer 141 is required to have long-term weather resistance such as heat resistance, high temperature resistance, high humidity resistance, and flame resistance. In order to satisfy these requirements, a fluororesin film such as PVF (polyvinyl fluoride), a fluororesin coating film, or a heat-resistant PET film such as a low oligomer PET (polyethylene terephthalate) film is generally used. In addition, you may use the PEN film etc. which are excellent in heat resistance. The material of the weather resistant layer 141 is not limited to the above, and any material that satisfies the long-term weather resistance standard value can be used as appropriate.

  The weather resistant layer 141 may be a single layer or a multilayer. In the case of a single layer, any of the above materials can be selected according to the required characteristics. PVF is suitable because it is particularly excellent in long-term weather resistance. A heat-resistant PET film such as a low-oligomer PET film is suitable because it is inexpensive and has excellent long-term weather resistance.

Examples of this weather-resistant layer 141 having a multilayer structure include a PET film laminated with a fluororesin film such as PVF (poly, fluoride, vinyl), or a PET film with a fluororesin coating such as PVF. And the like.
Fluororesin such as PVF is very excellent in long-term weather resistance, and even if a single layer exhibits sufficient performance, it is necessary to increase the thickness to obtain sufficient strength with a single layer, which is a factor of high cost It becomes. Therefore, it is preferable to have a multilayer structure in combination with a base material that ensures strength. In particular, when forming a fluororesin coating film, it is better to form a coating film once on the PET film and then bond it to the metal foil 142 than to form the coating film directly on the metal foil 142. From the viewpoint of.

  The layer structure of the weather resistant layer 141 is not limited to the above, and can be changed as appropriate according to the required characteristics.

The metal foil 142 has a sheet shape arranged on the front side of the weather resistant layer 141, and a concavo-convex structure 143 is formed on the front surface of the metal foil 142. The uneven structure 143 forms an uneven reflection layer.
That is, the metal foil 142 has a function of reflecting light incident on the concavo-convex structure 143 in a predetermined direction. In order to provide such a reflection function, it is desirable that the reflection surface of the uneven structure 143 is a specular reflection surface. Therefore, it is preferable to use the metal foil 142.

  The material of the metal foil 142 is not particularly limited. For example, it is possible to use a single metal or alloy of a highly malleable metal such as aluminum, gold, silver, copper, or platinum as a foil. It is particularly preferable to use an aluminum foil that has a high reflectivity and hardly undergoes alteration due to oxidation or the like and is inexpensive.

  In addition, when the metal foil 142 is configured using an aluminum foil, the metal foil 142 has a high water vapor barrier property and an oxygen barrier property, and has a function as a water vapor barrier layer in addition to a function of reflecting light. Is preferred.

  An example of a method for forming the concavo-convex structure 143 on the metal foil 142 is an embossing method using a mold. The mold to be used can be obtained by cutting a metal plate with a cutting tool, electroforming of a mother die obtained by cutting with a cutting tool, drawing or etching with an electron beam, or the like. The mold formed by such a process has an inverted structure with an uneven structure on the surface. For example, by cutting a metal plate with a cutting tool having a tip shape having a curvature, a mold in which an inverted structure of the concavo-convex structure 143 having a curvature is formed on a desired top portion is obtained. At this time, there is a problem that the shape reproducibility is difficult if the tip of the tool is sharp, and the tip of the tool is easily chipped. However, if the tip has a curvature, the shape is highly reproducible and the tool is not chipped. Such a problem is less likely to occur, which is preferable. By pressing this metal mold against the metal foil 142, a metal foil 142 having a concave-convex structure 143 having a curvature at a desired top is obtained. At this time, if the shape of the concave portion of the mold corresponding to the top of the concavo-convex structure 143 is sharp, it is difficult to reproduce the shape, but if the shape has a curvature, the structure can be shaped with good reproducibility, which is preferable. is there. The mold may be plate-shaped or roll-shaped, but is preferably a roll-shaped mold. If it is a roll-shaped metal mold | die, continuous embossing is possible and it is suitable as a preparation method of a back surface sheet which requires a large area.

   As shown in FIGS. 3A and 3B, the concavo-convex structure 143 has a substantially prism shape (a) having a curvature at the top, a substantially polygonal pyramid shape (b) having a curvature at the top, or a reverse type of these shapes. It is desirable to have any shape.

Further, in these structures, it is desirable that the aspect ratio of the base X and the height Y of the unit structure as shown in FIG. 4 is 0.35 or less. When the aspect ratio of the unit structure is larger than 0.35, the formability when embossing the concavo-convex structure 143 is lowered. If the unit structure has an aspect ratio of 0.35 or less, it can be formed into a designed shape.
The aspect ratio of the unit structure is desirably 0.15 or more. When the aspect ratio is smaller than 0.15, the effect of improving the light utilization efficiency is weakened. The reason for this will be described later.

  The concavo-convex structure 143 may have a periodic structure in which a plurality of convex portions constituting the concavo-convex structure 143 are arranged at a constant pitch, or may be an amorphous structure in which the pitch is random.

When the uneven structure 143 has a periodic structure, the pitch of the protrusions is desirably 30 μm or less.
If the pitch is larger than 30 μm, the height of the structure increases as the pitch increases, causing problems such as air bubbles entering when pasting the light-transmitting insulating layer 144 through the adhesive layer. This is not preferable. In addition, it is necessary to increase the thickness of the adhesive layer, which makes it difficult to form the adhesive layer, and increases the cost. In this respect, if the pitch is 30 μm or less, there is a low possibility that problems such as bubbles occur at the time of bonding, and this is preferable from the viewpoint of moldability and cost.

Moreover, when the uneven structure 143 has a periodic structure, the pitch of the protrusions is desirably 10 μm or more.
When the pitch is 10 μm or less, light can be diffracted when light is reflected by the uneven structure 143. Since the diffracted light is dispersed and spread, it is difficult to control and is not preferable for reflecting in a specific direction. Furthermore, it is not preferable because the time for cutting the mold is long, the tact is reduced, and the production efficiency is deteriorated. In this respect, if the pitch is 10 μm or more, the light can be accurately reflected in a specific direction, which is further preferable from the viewpoint of power generation efficiency.

  On the other hand, the lower limit of the thickness of the metal foil 142 is preferably 10 μm, and the upper limit is preferably 100 μm. When the thickness of the metal foil 142 is smaller than the lower limit of 10 μm, handling becomes difficult in a process such as bonding, and the possibility of occurrence of defects such as wrinkles increases. On the other hand, when the thickness of the metal foil 142 exceeds the upper limit of 100 μm, the flexibility of the metal foil 142 is lowered, which is not preferable because it causes cracks and breaks in the bonding process and the embossing process.

  In addition, as another method for forming the reflective layer such as the concavo-convex structure 143, for example, there is a method of providing a metal vapor deposition layer on a resin film having a concavo-convex structure. It is not preferable because pinholes are likely to occur and cause performance degradation. Moreover, since a metal vapor deposition layer is thin compared with the metal foil 142 and is inferior to long-term weather resistance, it is unpreferable. Furthermore, since the long-term weather resistance is inferior, the reflectance is lowered by long-term use, and the effect of improving the light utilization efficiency may be reduced. Furthermore, the concavo-convex structure formed of a resin material is not preferable because it may be deformed by heat when a module is manufactured by thermal lamination.

  Further, as another method for forming a reflective layer such as the concavo-convex structure 143, for example, a method of coating a resin containing metal particles or flakes on a resin film having a concavo-convex structure may be mentioned. The method is not preferred because the specular reflectivity is inferior and the effect of improving light utilization efficiency is small. Further, similar to the method of providing the metal vapor deposition layer, the concavo-convex structure formed of a resin material may be deformed by heat when a module is manufactured by thermal lamination, which is not preferable.

  The method of directly forming the concavo-convex structure 143 on the metal foil 142 as in this embodiment is highly effective in improving the light utilization efficiency because of its high specular reflectivity, and is excellent in long-term weather resistance. Almost no decrease in reflectance occurs. Therefore, there is an advantage that there is a low possibility that the effect of improving the light utilization efficiency is reduced. Furthermore, it is preferable in that the uneven structure is less likely to be deformed by heat when the solar cell module 1 is manufactured by thermal lamination, is inexpensive, has a simple process, and also functions as a water vapor barrier layer.

The translucent insulating layer 144 is disposed on the front side of the metal foil 142 and is made of a material having electrical insulation.
Here, one of the important performances required for the solar cell back sheet 14 is electrical insulation. This electrical insulation is an indispensable performance for preventing a short circuit or leakage during long-term use since the solar cell module 1 includes electrodes therein. Moreover, in the solar cell module 1, it is calculated | required that especially the surface by the side of the photovoltaic cell 12 is electrically insulating.

FIG. 5A shows the configuration of the solar cell module 1. The solar battery cell 12 has an electrode 22c for taking out the generated electric power.
Usually, the solar battery cell 12 is in the vicinity of the center of the filling layer 13 and is away from the metal foil 142, so that current leakage due to short-circuiting of the electrode 22c does not occur.
However, since the solar cell is sealed with the softened filler, it may come into contact with the metal foil 142 as shown in FIG. At this time, the electrode 22c is short-circuited through the metal foil 142, and current leaks.
In order to prevent this short circuit, the above-mentioned short circuit can be prevented by disposing the insulating layer 144 on the metal foil 142 as shown in FIG.

  One of the numerical standards indicating the electrical insulation is a dielectric breakdown voltage. This breakdown voltage is an index that the insulation state is broken when a voltage higher than the breakdown voltage is applied, and it can be said that a higher breakdown voltage is more electrically stable.

In general, a plastic film for electrical insulation, or a fluororesin film such as PVF, or a fluororesin coating film is disposed on the front side of the backsheet 14. For example, according to Reference 1 (“Photovoltaic power generation system constituent material” (Industry Research Committee)), the approximate breakdown voltage (kV) of various plastic films for electrical insulation (25 μm) is PET (polyethylene terephthalate). 6.5, PEN (polyethylene naphthalate) 7.5, PVC (stretched hard vinyl chloride) 4.0, PC (polycarbonate) 5.0, OPP (stretched polypropylene) 6.0, PE (polyethylene) 4.0, TAC (Triacetate) 3.0 and PI (polyimide) 7.0. All of these satisfy the dielectric breakdown voltage as an insulating material (reference JISC2318 / biaxially oriented polyethylene terephthalate film for electricity).
The dielectric breakdown voltage of a DuPont tedlar, which is a typical PVF (poly, fluoride, vinyl) product, is about 3.0 kV.
As one of the insulation performances of solar cell modules, it is determined that there is no abnormality such as dielectric breakdown even when a DC voltage of twice the maximum system voltage +1000 V is applied for 1 minute (reference JISC8918 / crystalline solar cell) module). The maximum system voltage is usually 600-1000V.
From the above, it is desirable that the average value of the dielectric breakdown voltage is 3 kV or more, and the above-mentioned various materials satisfy this standard (reference JISC2151 / electric plastic film test method 17.2.2 flat plate electrode method). When the dielectric breakdown voltage is smaller than 3 kV, the possibility of short circuit or leakage due to long-term use increases.

The translucent insulating layer 144 in the present embodiment is composed of a resin film made of any of the various materials described above. The material used for the translucent insulating layer 144 is preferably a transparent or translucent material, and preferably has fewer elements that cause light scattering.
Here, the light incident on the back sheet 14 is reflected by the uneven structure 143 on the metal foil 142 after passing through the translucent insulating layer 144, passes through the translucent insulating layer 144 again, and is transmitted from the back sheet 14. It becomes reflected light. Therefore, if the transparency is high and there are few scattering elements, the efficiency when the light incident on the back sheet 14 becomes reflected light becomes high.

  Further, the material used for forming the light-transmitting insulating layer 144 is not limited to the above, and any material that satisfies the reference value of the dielectric breakdown voltage can be used as appropriate. For example, it is possible to employ a synthetic resin film mainly composed of EVA, PVB or the like. The use of these resins is preferable because the adhesion with the sealing material 13 is improved.

The light-transmitting insulating layer 144 may be a single layer or a multilayer. In the case of a single layer, any of the above materials can be selected according to the required characteristics.
As a constitution method in the case of a multilayer, for example, a method of bonding a fluororesin film such as PVF to a PET film, a method of forming a fluororesin coating film such as PVF on a PET film, and EVA or PVB as a main component on a PET film And a method of attaching a synthetic resin film to be bonded.
A fluororesin such as PVF is preferable because it satisfies the electrical insulation standard and improves the adhesion to the sealing material 13. However, to obtain sufficient strength with a single layer, it is necessary to increase the thickness, which causes a high cost. Therefore, it is preferable to have a multilayer structure in combination with a base material that ensures strength. In particular, when a fluororesin coating film is formed, the method of forming the coating film once on the PET film and then bonding the metal foil 142 to the metal foil 142 rather than directly forming the coating film on the metal foil 142 has a good adhesion and workability. From the viewpoint of.

  Further, any of the above materials, for example, a multilayer structure in which two layers of PET films are bonded together may be used. In order to increase the insulation, it is known that the multilayer structure covers the insulation defects and has higher reliability than the single-sheet structure. Therefore, the insulating property can be further improved in the multilayer structure in which two layers are bonded to each other than the single layer of PET film.

  Note that the layer structure of the light-transmitting insulating layer 144 is not limited to the above, and can be changed as appropriate according to required characteristics.

  The back sheet 14 made of the above members is formed by bonding a weather-resistant layer 141, a metal foil 142, and a translucent insulating layer 144 through an adhesive layer (not shown in FIG. 2). As the adhesive to be used, a thermoplastic resin is preferable, and a simple substance or a copolymer such as an acrylic resin, a urethane resin, an epoxy resin, a polyester resin, and a vinyl resin can be used alone or in combination. However, the present invention is not limited to this. These adhesives are applied by known application means such as a gravure printing method, a screen printing method, and a nozzle coater method.

  When the thickness of the insulating layer 144 is insufficient, as shown in FIG. 5C, the insulating layer breaks down and current leaks between the electrode 22c and the metal foil 142 due to the discharge d.

となる。なお、等電位線ＰＩが密集する層Ｉｃは、凹凸構造１４３の頂部１４３ｔのピッチＰｔの半分となる。
また、絶縁破壊電圧は、３ｋＶ以上あれば、通常の太陽電池モジュールの使用で絶縁破壊が起こらないため、上述の絶縁層１４４の総厚Ｉｔ、凹凸構造１４３の頂部１４３ｔのピッチＰｔは以下の式を満たす必要がある。

Further, FIG. 6 shows a state where discharge occurs from the concavo-convex structure 143 formed on the metal foil 142 to the cathode 22c.
As shown in FIG. 6A, when the metal foil 142 has the concavo-convex structure 143, a layer Ic where the equipotential lines PI are densely formed can be formed. This layer is susceptible to discharge. Therefore, in order to obtain sufficient insulation, it is necessary that the total thickness It of the insulating layer 144 minus Ic has a sufficient thickness.
In the layer Ic where the equipotential lines PI are densely packed, the dielectric breakdown occurs at a lower voltage than the entire insulating layer 144 breaks down. Therefore, the dielectric breakdown voltage Dv of the insulating layer 144 is obtained by multiplying the total thickness It of the above-described insulating layer 144 by the thickness Ie obtained by subtracting the above-mentioned layer Ic where the equipotential lines PI are concentrated and the dielectric strength Ds per unit thickness. It becomes. When the breakdown voltage Dv is expressed by an equation,

It becomes. It should be noted that the layer Ic where the equipotential lines PI are dense is half the pitch Pt of the top 143t of the concavo-convex structure 143.
In addition, if the dielectric breakdown voltage is 3 kV or higher, dielectric breakdown does not occur when a normal solar cell module is used. Therefore, the total thickness It of the insulating layer 144 and the pitch Pt of the top portion 143t of the concavo-convex structure 143 are as follows: It is necessary to satisfy.

  Further, when the top portion 143t is pointed, as shown in FIG. 6A, a discharge breakdown occurs from the metal foil 142 even at a low voltage due to the charge concentration Ec, and the translucent insulating layer 144 discharges in the translucent insulating layer 144. Blackening occurs in the layer 144. When blackened, the amount of light transmitted through the light-transmitting insulating layer 144 falls, and the light absorbed without being reflected by the metal foil 142 increases, so that the solar battery cell 12 has a curvature as shown in FIG. 6B. Those are preferred. The larger the radius r of the circle Pc inscribed in the top portion 143t, the more the charge concentration can be prevented. However, if the radius r is larger than 10% of the pitch Pt of the top portion 143t, a large amount of light is scattered and the power generation efficiency of the solar cell module 1 is reduced. End up. For this reason, the radius r is preferably 10% or less. In addition, if the radius r is too small, charge concentration occurs. Therefore, the radius r is preferably 1% or more of the pitch Pt of the top portion 143t.

Next, a mechanism for improving the light utilization efficiency by the back sheet 14 will be described with reference to FIG.
FIG. 7 shows a process in which light incident on the back sheet 14 is reflected by the metal foil 142 having the concavo-convex structure 143 and is incident on the light receiving surface J of the solar battery cell 12. In FIG. 7, a prism structure is employed as the uneven structure 143.

  As shown in FIG. 7, a metal foil 142 with a concavo-convex structure 143 is provided on the front side of the back sheet 14. Of the light incident from the incident surface 110 of the solar cell module 1, the light H <b> 1 transmitted through the solar cell module 1 and incident on the back sheet 14 is reflected by the concavo-convex structure 143. The reflected light H2 is reflected again at the interface such as between the front plate 11 and the atmosphere, and becomes light H3 incident on the light receiving surface J of the solar battery cell 12, and is photoelectrically converted. Therefore, if the light H3 incident on the light receiving surface J of the solar battery cell 12 increases, the amount of photoelectric conversion increases, and the improvement of the light utilization efficiency can be expected.

  In this respect, in the present embodiment, since the concavo-convex structure 143 is formed on the front surface of the metal foil 142, light incident from the front surface side can be reflected in a specific direction. When the reflected light is incident again, the light H3 incident on the light receiving surface J of the solar battery cell 12 increases. Therefore, it is possible to improve the light utilization efficiency and increase the amount of power generation.

FIG. 7C shows the relationship between the apex angle θ and the reflection angle α (incident angle α) of the prisms constituting the concavo-convex structure 143. As shown in FIG. 7C, when light enters perpendicularly to the incident surface 110, the following relationship is established between the apex angle θ and the reflection angle α.

The light H2 reflected by the uneven structure 143 is reflected at the interface between the front plate 11 and the atmosphere. At this time, the incident angle of the incident light H2 is 2α.
Here, when 2α is greater than or equal to the critical angle φ, total reflection is performed at the interface between the front plate and the atmosphere, and therefore, the incident light H2 has very little loss and becomes reflected light H3 (see FIG. 7A).
On the other hand, when 2α is smaller than the critical angle φ, transmitted light H4 is generated in addition to the reflected light H3 (see FIG. 7B). When the transmitted light H4 is generated, the amount of the reflected light H3 is reduced and the amount of the light H3 incident on the light receiving surface J of the solar battery cell 12 is reduced. Therefore, the incident angle 2α of the incident light H2 is greater than or equal to the critical angle φ. It is desirable to become.

The critical angle φ is determined by the refractive index n1 of the front plate 11 and the refractive index n2 of the atmosphere, and the following relational expression is established.

  For example, when glass such as tempered glass is used for the front plate 11, the refractive index n1 is about 1.5 and the atmospheric refractive index n2 is about 1.0, so the critical angle φ is about 42 °. .

  From the above, in order to effectively use the reflected light H2 from the reflective layer 143, 2α needs to be equal to or larger than the critical angle φ. As described above, when the critical angle φ is 42 °, the reflective layer 143 Is required to have a reflection angle α of 21 ° or more.

  Here, the values of the apex angle θ and the reflection angle α at the reflection layer 143 with respect to the aspect ratio between the base X and the height Y of the prism when the concavo-convex structure 143 is a prism structure are shown in Table 1 below. As described above, in order to effectively use the reflected light H2 from the reflective layer 143, the reflection angle α needs to be 21 ° or more, and therefore it is necessary to set the prism aspect ratio to 0.2 or more. is there.

  In the above, the case where the incident angle to the incident surface 110 of the front plate 11 is 0 ° has been considered, but actually, the incident angle of incident light is various. Therefore, if the aspect ratio is 0.15 or more, that is, the difference between the incident angle 2α and the critical angle φ of the light H2 incident on the interface between the front plate 11 and the atmosphere is within about 10 °, the incident angle of the light is different. Finally, light incident on the light receiving surface J is generated. However, when the aspect ratio is less than 0.15, the incident angle 2α of the light H2 incident on the interface between the front plate 11 and the atmosphere becomes nearly 10 ° smaller than the critical angle φ, and the total reflected light is reduced. Therefore, the aspect ratio is preferably at least 0.15 or more. Thereby, the utilization efficiency of light can be kept large.

  As described above, when the aspect ratio of the prism is 0.35 or more, the formability deteriorates, and therefore the aspect ratio is desirably 0.35 or less. Therefore, the aspect ratio in the present embodiment is. It is set to 0.15 or more and 0.35 or less.

As mentioned above, although embodiment in this invention was described in detail, unless it deviates from the technical idea of this invention, it is not limited to these, A some design change etc. are possible.
For example, the back sheet 20 of the first configuration example may have a layer configuration shown in FIG.
In the back sheet 20, a heat resistant PET film is used as the weather resistant layer 141. On the weather resistant layer 141, an aluminum foil is disposed as a metal foil 142 having a concavo-convex structure 143 formed through an adhesive layer 145. Further, a light-transmitting insulating layer 144 made of a PET film is formed on the metal foil 142 with an adhesive layer 145 interposed therebetween.

Further, the back sheet 30 of the second configuration example may have a layer configuration shown in FIG.
In this back sheet 30, the weather resistant layer 141 is comprised by laminating | stacking the heat resistant PET film 412 on the PVF layer 411 for obtaining long-term weather resistance. On the weather resistant layer 141, an aluminum foil is disposed as a metal foil 142 having a concavo-convex structure 143 formed through an adhesive layer 145. Furthermore, a translucent insulating layer 144 made of a PET film is formed on the metal foil 142 with an adhesive layer 145 interposed therebetween.

And as a back surface sheet 40 of a 3rd structural example, the thing of the layer structure shown in FIG. 10 may be sufficient.
In the back sheet 40, the weather resistant layer 141 is configured by laminating a heat resistant PET film 412 on a PVF layer 411 for obtaining long-term weather resistance. On the weather resistant layer 141, an aluminum foil is disposed as a metal foil 142 having a concavo-convex structure 143 formed through an adhesive layer 145. A translucent insulating layer 144 is formed on the metal foil 142 with an adhesive layer 145 interposed therebetween. The translucent insulating layer 144 is made of a PET film 441 and an EVA film 442.

  In the back sheets 20, 30, and 40 of the first to third configuration examples, similarly to the back sheet 14 of the embodiment, since the concavo-convex structure 143 is formed on the metal foil 142, light is emitted toward the front side. It can be reflected efficiently. Therefore, it is possible to increase the power generation amount by improving the light use efficiency of the solar cell module 1.

  In addition, in the back sheet 14, 20, 30, 40 of the said embodiment and the 1st-3rd structural example, when employ | adopting a prism structure as the uneven structure 143, the longitudinal direction of the prism which is a unit structure is made into the photovoltaic cell 12. It is preferable to incline with respect to light because the light utilization efficiency can be further improved.

  Further, the backsheets 14, 20, 30, and 40 are not limited to use in the solar cell module 1, but are optically desired to improve light utilization efficiency such as improvement in light utilization efficiency of light emitting elements such as LED lighting and EL elements. Diversion to elements and display members is possible.

  Next, comparative examples and examples will be described.

(Comparative Example 1)
As Comparative Example 1, the back sheet 20 of the first configuration example shown in FIG. 8, that is, a weather resistant layer 141 made of a heat-resistant PET film, and a metal foil 142 made of aluminum formed with an uneven structure 143, 25 insulating properties The back sheet 20 which bonded the translucent insulating layer 144 which consists of PET films with the contact bonding layer 145 was produced, and the test which confirms the improvement of light utilization efficiency, and the dielectric breakdown test were done.
The uneven structure 143 in the back sheet 20 has a prism structure, an aspect ratio of 0.2, a pitch of 15 μm, and the top has no curvature.
Moreover, the thickness of the translucent insulating layer in the said back surface sheet 20 was 25 micrometers.

  Using the back sheet 20 of Comparative Example 1, the solar cell module 1 was produced. For comparison, a solar cell module was produced using white PET (Toray Lumirror E20) which is a scattering reflector instead of the back sheet 20.

In the solar cell module 1 of the comparative example 1 and the solar cell module for comparison, an optical sensor was disposed at a location corresponding to the solar battery cell 12 and the amount of power generated when light was irradiated from the front side was measured.
As a result, the power generation amount in the solar cell module 1 of Comparative Example 1 when the power generation amount in the comparative solar cell module was 1 was 1.12. Thereby, when the metal foil 142 in which the uneven structure 143 was shaped was used for the back surface sheet 20, it was confirmed that the light use efficiency of the solar cell module 1 could be improved.

In addition, when the dielectric breakdown test was performed on the solar cell module of Comparative Example 1, dielectric breakdown occurred at 3 kV or less.
Accordingly, it was confirmed that the electrical insulating property is low when the top of the concavo-convex structure 143 has a structure having no curvature.

(Comparative Example 2)
As Comparative Example 2, the back sheet 20 of the first configuration example shown in FIG. 8, that is, a weather resistant layer 141 made of a heat resistant PET film, a metal foil 142 made of aluminum formed with a concavo-convex structure 143, an insulating PET A back sheet 20 in which a translucent insulating layer 144 made of a film was bonded with an adhesive layer 145 was manufactured, and a test for confirming improvement in light utilization efficiency and a dielectric breakdown test were performed.
The uneven structure 143 in the back sheet 20 is a prism structure, and has an aspect ratio of 0.2, a pitch of 30 μm, and a curvature radius of the top of 1.5 μm.
Moreover, the thickness of the translucent insulating layer in the said back surface sheet 20 was 25 micrometers.

  Using the back sheet 20 of Comparative Example 2, a solar cell module 2 was produced.

In the solar cell module 1 of the comparative example 2 and the solar cell module for reference, an optical sensor was arranged at a location corresponding to the solar cell 12, and the amount of power generation was measured when light was irradiated from the front side.
As a result, the power generation amount in the solar cell module 1 of Comparative Example 2 when the power generation amount in the reference solar cell module was 1 was 1.12. Thereby, even if the uneven structure 143 has a shape having a curvature at the top portion 143t, it was confirmed that the light utilization efficiency of the solar cell module 1 did not decrease.

  Further, when the dielectric breakdown test was performed by increasing the voltage to 3 kV in the solar cell module of Comparative Example 2, no phenomenon of blackening in the translucent insulating layer 144 was observed. However, the insulation state was broken and leak current was generated.

Example 1
As Example 1, the back sheet 20 of the first configuration example shown in FIG. 8, that is, the weather resistant layer 141 made of a heat resistant PET film, the metal foil 142 made of aluminum in which the concavo-convex structure 143 was shaped, the insulating PET A back sheet 20 in which a translucent insulating layer 144 made of a film was bonded with an adhesive layer 145 was manufactured, and a test for confirming improvement in light utilization efficiency and a dielectric breakdown test were performed.
The concave-convex structure 143 in the back sheet 20 has a prism structure, an aspect ratio of 0.2, a pitch of 15 μm, and a curvature radius of the top portion of 0.75 μm.
Moreover, the thickness of the translucent insulating layer in the said back surface sheet 20 was 25 micrometers.

  Using the back sheet 20 of Example 1, a solar cell module 2 was produced. Moreover, the solar cell module 1 of Example 1 was used as a comparative example.

In the solar cell module 1 of Example 1 and the reference solar cell module, an optical sensor was arranged at a location corresponding to the solar battery cell 12, and the amount of power generated when light was irradiated from the front side was measured.
As a result, the power generation amount in the solar cell module 1 of Example 1 when the power generation amount in the reference solar cell module was set to 1 was 1.12. Thereby, even if the uneven structure 143 has a shape having a curvature at the top portion 143t, it was confirmed that the light utilization efficiency of the solar cell module 1 did not decrease.

In addition, when the dielectric breakdown test was performed on the solar cell module of Example 1, no dielectric breakdown occurred even when the voltage was increased to 3 kV.
Thereby, it has been confirmed that the electrical insulation is improved by the curvature of the concavo-convex structure 143 at the top 143t.

1 Solar cell module 11 Front plate (translucent front plate)
12 solar cell 13 sealing material 14 back sheet (solar cell back sheet)
20 Back sheet (Solar cell back sheet)
22c Electrode 30 Back sheet (Solar cell back sheet)
40 Back sheet (Solar cell back sheet)
DESCRIPTION OF SYMBOLS 110 Incident surface 141 Weather resistant layer 142 Metal foil 143 Uneven structure 143t Uneven structure top 144 Translucent insulating layer 145 Adhesive layer 411 Weather resistant layer layer 412 Weather resistant layer layer 441 Translucent insulating layer layer 442 Layer constituting light-transmitting insulating layer F Light source direction J Light receiving surface N Normal line NG Front plate normal line H0 Light incident perpendicular to solar cell module H1 Light incident on reflective layer H2 Reflected light H3 Reused Light L
X Base of concavo-convex structure Y Height of concavo-convex structure d Discharge PI from electrode Equipotential line Dv Dielectric breakdown voltage It Total thickness of translucent insulating layer Ic Layer where isopotential lines are dense Ie Total thickness of translucent insulating layer Thickness obtained by subtracting layers with dense equipotential lines Ds Dielectric strength Ec per unit thickness Charge concentration Pc Circle Pt inscribed in top part Pitch of top part of concavo-convex structure θ Top angle of prism α Reflection β Transmission angle φ Critical angle

Claims (5)

A solar cell back sheet disposed on the back side of a solar cell module in which a translucent front plate is laminated on the front side of a sealing material encapsulating solar cells inside,
At least a translucent insulating layer in order from the front side, a metal foil having a concavo-convex structure formed on the front side, and a weathering layer are sequentially laminated,
The top of the concavo-convex structure has a curvature;
The aspect ratio between the bottom and the height of the unit structure of the concavo-convex structure so that the light reflected by the concavo-convex structure is totally reflected at the interface between the translucent front plate and the atmosphere and enters the light receiving surface of the solar cell. Is set in the range of 0.15 to 0.35 ,
The radius of curvature r of the top of the concavo-convex structure is set in the range of 0.01 Pt or more and 0.1 Pt or less, where Pt is the pitch of the top of the concavo-convex structure,
The said translucent insulating layer has a dielectric breakdown voltage of 3 kV or more, The solar cell back surface sheet characterized by the above-mentioned .   The solar cell backsheet according to claim 1, wherein the concavo-convex structure is formed by arranging a plurality of substantially prism shapes, substantially polygonal pyramid shapes, or inverted shapes of these shapes. 3. The solar cell backsheet according to claim 1, wherein the pitch of the top of the concavo-convex structure is set in a range of 10 μm to 30 μm. The thickness of the said metal foil is set to the range of 10 micrometers or more and 100 micrometers or less, The solar cell back surface sheet of any one of Claim 1 to 3 characterized by the above-mentioned. A solar cell module comprising the solar cell backsheet according to any one of claims 1 to 4 disposed on a back surface of the solar cell module.

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