JP2010123719A - Solar cell backside sheet and solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical reuse sheet having an uneven shape optimum for improving light utilization efficiency, and to provide a solar cell module using the same. <P>SOLUTION: In the solar cell module having at least a light transmissive front plate, a solar cell, a sealing material and a backside sheet, the backside sheet includes a base material, an uneven structure, a reflection layer and a top coat layer which are formed on the surface of the base material, and the top coat layer, the reflection layer, the uneven structure and the base material are stacked in this order from the front surface side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a back sheet that is formed with a concavo-convex structure having a reflective layer, reflects light by the structure, and can effectively utilize light that is originally lost, and a solar cell module using the back sheet.

  In recent years, the widespread use of solar cell modules has expanded greatly, from relatively small ones mounted on small electronic devices such as calculators to large areas used for solar cell modules installed in homes 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).

  In the solar cell, the amount of power generation increases mainly in proportion to the area irradiated with light. Therefore, in order to improve the power generation efficiency, in addition to improving the manufacturing technology such as the sealing technology and the film forming technology, how to increase the aperture ratio of the solar cell module, that is, the ratio of the power generating area to the total area Is an important issue.

In particular, single crystal silicon or polycrystalline silicon has a problem that the cost of the silicon is high. Also, the cost for pasting it is added.
In view of this, the amount of silicon that is a constituent member of a solar cell is small, and a thin-film silicon solar cell that can be formed by a technique such as CVD has been used.

  However, the light absorption rate of the above-mentioned is particularly low because infrared light is likely to pass through thin-film silicon solar cells. Therefore, in order to increase the light utilization efficiency, the incident light is intentionally scattered to increase the light transmission efficiency by increasing the distance through which the thin-film silicon solar cells are transmitted.

  In general, there are two types of amorphous silicon solar cells. First, a transparent conductive film such as SnO2 or ITO is formed on a light-transmitting substrate such as glass, and an amorphous semiconductor (Si) p-layer, i-layer, and n-layer are stacked in this order. It is of the structure which consists of. The other is an amorphous semiconductor (Si) n-layer, i-layer, and p-layer stacked in this order on a metal substrate electrode to form a photoelectric conversion active layer, and a transparent conductive film is further formed thereon. It has a laminated structure.

  In particular, in the former structure, in order to form amorphous semiconductors in the order of pin layers, the translucent insulating substrate can also serve as a solar cell surface cover glass, and resistance to SnO 2 or the like. A plasma transparent conductive film has been developed, and an amorphous semiconductor photoelectric conversion active layer can be formed thereon by a plasma CVD method.

The amorphous semi-light-guided conversion active layer can be formed by using a plasma CVD method by glow discharge decomposition of a source gas or a vapor phase growth method by a photo-CVD method. There is also an advantage that a thin film can be formed.

  Since an amorphous Si solar cell can be formed at a relatively low temperature of about 100 ° C. to 200 ° C., it is possible to use substrates of various materials as a substrate for forming the amorphous Si solar cell. However, glass substrates and stainless steel substrates are commonly used.

  In addition, the amorphous Si solar cell has a silicon light absorption layer thickness of about 500 nm when the conversion efficiency for replacing light with an electric machine is maximized. Therefore, in order to improve the conversion efficiency of the light absorption layer, Increasing the amount of light absorption within the film thickness is an important point. Therefore, the optical path length of light in the light absorption layer is increased by forming a transparent conductive film with unevenness on the surface of the glass substrate or forming a metal film with unevenness on the surface of the stainless steel substrate. It has been performed conventionally.

  In the case of the solar cell in which the optical path length in the light absorption layer is increased by such a method, the light is compared with the case where the amorphous Si solar cell is formed on a flat substrate having no irregularities on the surface. The utilization efficiency of is significantly improved.

  By the way, as a general method for forming irregularities on the surface of a glass substrate, there is a method of forming a SnO 2 film as a transparent electrode by atmospheric pressure CVD. In addition, as a method of forming irregularities on a metal substrate such as stainless steel, a method of adjusting the formation conditions when Ag is formed by a vapor deposition method or a sputtering method, or performing a heat treatment after the formation of Ag is used. It was done.

  This thin film solar cell has a transparent conductive film, a hydrogenated amorphous silicon carbide (a-SiCH) p layer, a hydrogenated amorphous silicon (a-SiH) i layer, a hydrogenated amorphous silicon (a —SiH) n layer, transparent conductive film, and back electrode are sequentially formed. Then, as described above, a concavo-convex shape is formed on the surface of the transparent conductive film, whereby each layer formed on the top has a concavo-convex structure.

  Moreover, when forming semiconductor elements, such as a thin film solar cell, on a flexible substrate or a lightweight substrate, the polyimide resin with high heat resistance has been used. A method for forming irregularities in such a resin is disclosed in Patent Document 2 and the like.

  Further, Patent Document 3 discloses a patent that retroreflects light by the periodic structure of the V-groove to increase the light utilization efficiency, and that the V-groove apex angle is desirably 50 to 90 degrees. There is a description. Further, there is a description that the pitch of the period of the V groove is preferably 10 μm to 20 μm.

Further, if the arrangement interval of the solar battery cells 30 is narrowed, a leak current is generated, so that a region between adjacent solar battery cells 30 is required. As shown in FIG. 17, among the light H0 incident on the solar cell module 200, the light H1 incident on this region is reflected on the back surface material 300 by disposing the back surface material 300 on the back surface of the solar cell module 200. What is reused as H2 (Patent Document 4) is known. However, sufficient power generation efficiency has not been obtained yet.
JP 2001-295437 A Japanese Laid-Open Patent Publication No. 4-61285 JP 11-274533 A Japanese Patent Application Laid-Open No. 11-307791

  As described above, the conventional solar cell module has many requests to increase the power generation efficiency per unit area, but it is not yet sufficient because there is light that causes loss.

  The present invention has been made in view of such problems, and a back sheet that can improve light use efficiency by reusing light that would otherwise be lost, and a sun using the back sheet An object is to provide a battery module.

  In order to achieve the above object, the present invention takes the following measures.

The invention of claim 1
In a solar cell module having at least a translucent front plate, solar cells, a sealing material, and a back sheet,
The back sheet is composed of a base material, a concavo-convex structure formed on the surface of the base material, a reflective layer, and a top coat layer,
It is a solar cell back surface sheet | seat characterized by laminating | stacking in order of a topcoat layer, a reflection layer, an uneven structure, and a base material from the front side.
The invention of claim 2
The solar cell backsheet according to claim 1, wherein the reflective layer is a metal layer or a dielectric layer composed of one layer or multiple layers.
The invention of claim 3
3. The solar cell backsheet according to claim 1, wherein the topcoat layer has electrical insulation and has a dielectric breakdown voltage of 3 KV or more.
The invention of claim 4
The solar cell backsheet according to any one of claims 1 to 3, wherein the topcoat layer has antioxidant properties.
The invention of claim 5
5. The solar cell backsheet according to claim 1, wherein a thickness of the topcoat layer is equal to or greater than a height of the concavo-convex structure.
The invention of claim 6
6. The back surface of a solar cell according to claim 1, wherein the concavo-convex structure is any one of a prism, a polygonal pyramid shape, a cylindrical lens, a microlens, or an inverse shape thereof. It is a sheet.
The invention of claim 7
7. The aspect ratio between the bottom and the height of the unit structure of the concavo-convex structure having a periodic structure composed of repeated concavo-convex is 0.15 to 0.4. It is a solar cell back surface sheet of description.
The invention of claim 8
8. The aspect ratio of the base to the height of the unit structure of the concavo-convex structure having a periodic structure formed by repeating the concavo-convex is 0.2 or more and 0.35 or less. It is a solar cell back surface sheet of description.
The invention of claim 9
The solar cell backsheet according to any one of claims 1 to 8, wherein a pitch of the concavo-convex structure having a periodic structure composed of repeated concavo-convex is 25 µm or more and 300 µm or less.
The invention of claim 10
10. The solar cell backsheet according to claim 1, wherein a pitch of the concavo-convex structure composed of a periodic structure composed of repeated concavo-convex is 50 μm or more and 200 μm or less.
The invention of claim 11
It is a solar cell module using the solar cell back surface sheet of any one of Claims 1 thru | or 10.

 The present invention can improve the light utilization efficiency by reusing light that is originally lost by the above-described means, and can provide a solar cell module with good power generation efficiency.

First, the solar cell back surface sheet | seat which concerns on this invention, and a solar cell module using the same are demonstrated.
FIG. 1 is a cross-sectional view showing a uniform state of a solar cell module 1 using the solar cell backsheet of the present invention. The solar cell module 1 according to the present invention includes a front plate 11, solar cells 12, a sealing material 13, and a back sheet 14.

The front plate 11 transmits light from the light source L such as sunlight and illumination light, and protects the solar battery cell 12 from impact, dirt, moisture intrusion, etc., and is made of a transparent material having high transmittance. Become. The light H0 that the light of the light source L is incident on the incident surface 110 perpendicularly from the sunlight / illumination light side is incident on the front plate 11, then passes through the front plate 11 and enters the sealing material 21.
The normal line NG of the incident surface 110 is a direction parallel to the normal line N of the plane P when the front plate 11 is placed on the plane P in the most stable state. The light that is perpendicularly incident on the incident surface 110 is light that is incident on the solar cell module 1 in parallel with the normal line NG.

  The material of the front plate 11 is glass such as tempered glass or sapphire glass, or a resin sheet such as PC (polycarbonate) or PEN (polyethylene naphthalate). The thickness of the front plate 11 is about 3 to 6 mm for tempered glass, and 100 μm to 3000 μm for a resin sheet.

  The light emitted from the front plate 11 enters the sealing material 12. The sealing material 12 fixes the solar battery cell 13. The light H0 incident on the front plate 11 is transmitted through the sealing material 12, becomes light H10 incident on the solar battery cell 13, and part of the light H0 is incident on the rear sheet 14. The sealing material 12 is made of a material having a high light transmittance so as to transmit the incident light H0. EVA (ethylene vinyl acetate) having excellent durability such as heat resistance, high temperature resistance, high humidity resistance, and weather resistance. ) Is widely used.

The solar cell 13 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, polycrystalline silicon type, amorphous silicon type, CISG (Cu · In · Ga · Se). There are many types such as compound) thin film type. A plurality of solar cells 13 are connected by electrodes to form a module. The light H <b> 10 that has entered the solar battery cell 13 from the sealing material 12 is converted into electricity by the solar battery cell 13.
Usually, the light incident obliquely with respect to the incident surface 110 is reflected at the incident surface 110 more than the vertically incident light H0, and the amount of light incident on the solar cells 13 is small, that is, it can be used for power generation. There is little light.
Therefore, the efficiency is highest when the incident light H0 is incident on the incident surface 110 perpendicularly.

The back sheet 14 has a function of reflecting light that has passed through the solar battery cell 13 itself and light H1 that has not entered the solar battery cell 13 and has entered the back battery sheet.
An uneven structure 142 having a reflective layer 143 is provided on the front side of the back sheet 14. The light H <b> 1 incident on the back sheet 14 is reflected by the reflective layer 143. The reflected light H2 is reflected again at the interface such as between the front plate 11 and the atmosphere, and becomes photoelectrically converted into light H3 incident on the light receiving surface J of the solar battery cell 13. Thereby, there is an effect that the light use efficiency is improved as compared with the configuration in which the back sheet 14 does not have the uneven structure having the reflective layer.

FIG. 2 is a cross-sectional view showing a uniform state of the back sheet 14 of the present invention. The back sheet 14 according to the present invention includes a base material 141, a concavo-convex structure 142, a reflective layer 143, and a topcoat layer 144.

In addition to polyethylene terephthalate, polycarbonate, and acrylic resin, materials used for the substrate 141 include polyester resin, methacrylic resin, polymethylpentene resin, polyolefin resin, and transparent polyimide having both heat resistance and transparency. , Fluorine resin, polylactic acid resin, silicone, polysulfone resin, polyethylene naphthalate resin, polyetherimide resin, epoxy resin, and the like.

The substrate 141 may be a single layer or a multilayer, and has a multilayer structure for imparting various performances such as long-term weather resistance such as heat resistance, high temperature resistance, high humidity resistance, and flame resistance, and water vapor barrier properties. Is desirable.

For example, the outermost layer is a fluororesin film such as PVF (poly, fluoride, vinyl), etc. that has excellent long-term weather resistance, a heat-resistant PET film such as a fluororesin coating film, or a low-oligomer PET film, or a PEN film that is excellent in heat resistance It is desirable to arrange etc.

For example, it is desirable to arrange an aluminum thin film excellent in water vapor barrier property, a silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) vapor deposition film, etc. as the intermediate layer.

Which combination to use depends on the required performance, so it is desirable to design appropriately according to the required performance.
For example, when importance is attached to long-term weather resistance, it is preferable to use a fluororesin film such as PVF as the outermost layer. However, when cost is important, a heat-resistant PET film may be used. In recent years, the heat resistance of PET films has been improved and sufficient long-term weather resistance can be obtained.
In addition, when a crystal system such as single crystal silicon or polycrystalline silicon is used as a solar battery cell, silica or alumina deposited film can be used. However, when a thin film system using amorphous silicon is used, it is inferior in heat and moisture resistance. Therefore, it is desirable to use an aluminum thin film that is more excellent in water vapor barrier properties.

The uneven structure 142 is formed on the front surface side of the substrate 141. You may form directly on the surface of the base material 141 (FIG. 2 (a)), and you may provide and form another layer (FIG.2 (b)).

  Examples of the method for directly forming the concavo-convex structure 142 on the substrate 141 include a pressing method using a mold, a casting method, an extrusion molding method, and an injection molding method. In these methods, it is possible to form an uneven structure simultaneously with sheet formation.

In addition, as a method for forming the concavo-convex structure 142 by providing another layer on the base material 141, a thermosetting resin, an ultraviolet curable resin, an electron beam curable resin, or the like is applied to the concavo-convex forming surface of a flat stamper or a roll stamper. Alternatively, there is a method of injecting, placing the base material 141 thereon, and releasing the mold from the stamper after the curing process. These methods have the advantage that the moldability is good because the viscosity of the resin used can be lowered.

  The resin used in the above-described production method is not particularly limited. For example, poly (meth) acrylic resin, polyurethane resin, fluorine resin, silicone resin, polyimide resin, epoxy resin, polyethylene resin , Polystyrene resins such as polypropylene resins, methacrylic resins, polymethylpentene resins, cyclic polyolefin resins, acrylonitrile- (poly) styrene copolymers (AS resins), acrylonitrile-butadiene-styrene copolymers (ABS resins), etc. Resin, polyvinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyamideimide resin, polyaryl phthalate resin, polysulfone resin, polyphenylene sulfide resin, polyethersulfone resin, polyethylene naphtha Over preparative resin, polyether imide resin, acetal resin, cellulose resin and the like, may be used by mixing these resins singly or in combination.

  In addition to the above resins, various additions such as scattering reflectors, curing agents, plasticizers, dispersants, various leveling agents, ultraviolet absorbers, antioxidants, viscosity modifiers, lubricants, light stabilizers, etc. An agent may be appropriately blended.

  The mold used for these forming methods can be obtained by a method of cutting a metal plate with a cutting tool, or by electroforming a mother die obtained by drawing or etching with an electron beam.

  It is desirable that the concavo-convex structure 142 has a prism shape, a polygonal pyramid shape, a cylindrical lens, a microlens, or any of the inverse shapes thereof as shown in FIGS.

In these structures, the aspect ratio of the base X and the height Y of the unit structure as shown in FIG. 4 is desirably 0.4 or less, and more desirably 0.35 or less. When the aspect ratio of the above-described structure is larger than 0.4, the resin tends to remain at the tip portion of the mold when the concavo-convex structure 142 is molded, and the moldability is poor. If the aspect ratio of the above-described structure is 0.35 or less, the possibility that the resin remains in the mold is reduced, and the resin can be molded into the shape as designed.

In addition, the aspect ratio of the above structure is desirably 0.15 or more, and more desirably 0.2 or more. When the aspect ratio of the above structure is smaller than 0.2, the effect of improving the light utilization efficiency is weakened. When the aspect ratio of the above-described structure is smaller than 0.15, the effect of improving the light utilization efficiency is further weakened. The reason for this will be described later in detail.

The uneven structure 142 may have a periodic structure or may be indefinite. At this time, the pitch of the period of the concavo-convex structure 142 is desirably 300 μm or less, and more desirably 200 μm or less. When the pitch of the period of the above-described structure is larger than 300 μm, the moldability is poor because the resin does not sufficiently enter the mold of the concavo-convex tip when the concavo-convex structure 142 is molded. If the pitch of the period of the above-mentioned structure is 200 μm or less, even a resin having a relatively high viscosity can be molded. In addition, if the pitch of the period of the above-described structure is too small, it is difficult to produce a mold. Therefore, it is preferably 25 μm or more, and more preferably 50 μm or more. If the pitch of the period of the above-mentioned structure is smaller than 25 μm, it takes a long time to cut the mold and the tact time decreases, resulting in poor production efficiency. If the pitch of the period of the above-described structure is smaller than 50 μm, the resin does not enter the groove well when forming the concavo-convex structure 142, and it is difficult to produce the shape of the concavo-convex tip portion according to the mold. Further, when the pitch of the period of the above structure is smaller than 25 μm, light may be diffracted when light is reflected by the structure. Diffracted light is not preferable because it is difficult to control because it becomes diffused light.

The reflective layer 143 is formed, for example, by vapor-depositing a metal such as aluminum or silver so as to have a layer shape following the unevenness of the uneven structure 142. The deposition means for the reflective layer 4 is not particularly limited as long as a metal can be deposited without causing deterioration such as shrinkage and yellowing in the concavo-convex structure 142. (a) Vacuum deposition method, sputtering method, ion plating Chemical vapor deposition (physical vapor deposition method; PVD method), (b) plasma chemical vapor deposition, thermal chemical vapor deposition, photochemical vapor deposition, etc. A growth method (Chemical Vapor Deposition method; CVD method) is employed. Among these vapor deposition methods, a vacuum vapor deposition method and an ion plating method that can form a high-quality reflective layer 143 with high productivity are preferable.

The metal used for the reflective layer 143 is not particularly limited as long as it has a metallic luster and can be deposited. For example, aluminum (Al), silver (Ag) nickel (Ni), tin (Sn), Zirconium (Zr) etc. are mentioned. Among these, aluminum or silver is preferable because it has high reflectivity and the dense reflective layer 143 can be formed relatively easily (FIG. 5A).

  The material used for the reflective layer 143 is not limited to a metal, and a high refractive index material h such as zinc sulfide (ZnS) may be used (FIG. 5B). In this case, although the reflectance is inferior to that of metal, a relatively high reflectance can be obtained, and the reflective layer can be transparent or translucent. Good.

Note that the reflective layer 143 may have a single-layer structure made of the above-described metal or high refractive material, or may have a multilayer structure of two or more layers. For example, as shown in FIG. 5C, a dielectric multilayer obtained by multilayer deposition of a high refractive index material h such as zinc sulfide (ZnS) and a low refractive index material l such as magnesium fluoride (MgF). A membrane may be employed. Since the dielectric multilayer film can control the reflectance and wavelength distribution of reflected light by changing the film thickness and the number of layers, the characteristics of the reflected light are optimized according to the type of solar cell. It becomes possible.

  The lower limit of the thickness of the reflective layer 143 is preferably 10 nm, and particularly preferably 20 nm. On the other hand, the upper limit of the thickness of the reflective layer 4 is preferably 200 nm, and particularly preferably 100 nm. If the thickness of the reflective layer 143 is smaller than the lower limit of 10 nm, light incident on the reflective layer 143 cannot be sufficiently reflected. Even if the thickness is 20 nm or more, the light reflected by the reflective layer 143 does not increase significantly. On the other hand, when the thickness of the reflective layer 143 exceeds the upper limit of 200 nm, cracks that can be visually confirmed occur in the reflective layer 143, and cracks that cannot be visually confirmed occur if the thickness is 100 nm or less.

  The top coat layer 144 is preferably a material having electrical insulation.

One of the important performances required for the solar cell back sheet is electrical insulation. Since electrical insulation is a module that includes an electrode inside the solar cell, it is a necessary performance to prevent leakage during long-term use. In particular, the cell-side surface must be electrically insulating. It has been.

One of numerical standards indicating electrical insulation is a breakdown voltage. The 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 the higher breakdown voltage is electrically stable.

In general, a plastic film for electrical insulation, or a fluororesin film such as PVF (poly, fluoride, vinyl) or a fluororesin coating film is disposed on the cell side surface (innermost inner surface) of the back sheet.
For example, according to Reference 1 (“Photovoltaic power generation system constituent material” (Industry Research Committee)), the approximate value of the dielectric 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 electrical use).
The dielectric breakdown voltage of a DuPont Tedlar, which is a typical PVF (poly, fluoride, vinyl) product, is about 3.0 KV.
These various materials, particularly PET and PVF for electrical insulation, have been used for solar cell back sheets as electrical insulation materials, and have been confirmed to satisfy the required performance.
From the above, it is desirable that the dielectric breakdown voltage is 3.0 KV or more. When the dielectric breakdown voltage is 2.0 KV or less, the possibility of leakage due to long-term use increases.

The above-described electrically insulating topcoat layer 144 is obtained by applying the above-described various materials on the reflective layer 143. At this time, the material used is preferably a transparent or translucent material.
In addition, the material to be used is not limited to the above, and any material that satisfies the reference value of the dielectric breakdown voltage can be used as appropriate.

  Further, when the reflective layer 143 is a metal layer, it is desirable that the top coat layer 144 further has an antioxidant property. This is because the surface of metals such as aluminum and silver is likely to be oxidized, and if the topcoat layer has antioxidant properties, it is possible to suppress deterioration over time.

Examples of the above-described antioxidant topcoat layer include polyester topcoat agents, polyamide topcoat agents, polyurethane topcoat agents, epoxy topcoat agents, phenolic topcoat agents, and (meth) acrylic topcoat agents. Polyvinyl acetate-based topcoat agents, polyolefin-based topcoat agents such as polyethylene aly polypropylene, cellulose-based topcoat agents, and the like can be used, and can be obtained by applying these various materials onto the reflective layer 143. At this time, the material used is preferably a transparent or translucent material. Among these, a polyester-based topcoat agent that has high adhesive strength with the reflective layer 143 and contributes to surface protection of the reflective layer 143, sealing of defects, and the like is particularly preferable.
In addition, the material to be used is not limited to the above, and any material that satisfies the reference value of the dielectric breakdown voltage can be used as appropriate.

  The coating amount (in terms of solid content) of the above antioxidant topcoat agent is preferably 3 g / m 2 or more and 7 g / m 2 or less. When the coating amount of the top coat agent is smaller than 3 g / m 2, the effect of sealing and protecting the reflective layer 143 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 reflective layer 143 does not increase so much.

  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 amount of the additive to be mixed is preferably 0.1% by weight or more and 10% by weight or less from the balance between the effect expression of the additive and the function inhibition of the topcoat agent. If the above-mentioned additive is less than 0.1% by weight, close adhesion, weather resistance and heat resistance cannot be sufficiently obtained, and if it is more than 10% by weight, the function of the topcoat agent is inhibited.

The top coat layer 144 may be a single layer or a multilayer. For example, in the case where the antioxidant property is not required, a single-layer structure made of only an electrically insulating material can be used (FIG. 6A). In addition, a single layer structure can also be used when a single material has both electrical insulation and antioxidant properties (FIG. 6A).
For example, a multi-layer structure may be used when electrical insulation and antioxidant properties are provided by different materials. In this case, the antioxidant layer o and the electrically insulating layer e are preferably laminated in this order on the reflective layer 143 (FIG. 6B).
For example, it is good also as a multilayer structure which bonds the above-mentioned electrically insulating plastic film f through the contact bonding layer a (FIG.6 (c)). Among them, an electrically insulating PET film that is excellent in heat resistance, moisture resistance, mechanical strength, and the like that are simultaneously required and advantageous in terms of cost is particularly preferable.
Furthermore, for example, a multilayer structure in which an electrically insulating PET film f is bonded with an adhesive a after first providing a layer having an antioxidant property o may be employed.
Since these materials use different materials and have different structures depending on required characteristics, it is desirable to design them appropriately according to the required characteristics.

  The thickness of the top coat layer 144 is desirably equal to or greater than the height of the concavo-convex structure 142 including the reflective layer 143 as a whole in order to protect the concavo-convex structure 142 and the reflective layer 143 (FIG. 7A). If the thickness of the top coat layer is thinner than the height of the concavo-convex structure, the concavo-convex structure is likely to be damaged in the back sheet manufacturing process and subsequent processes such as modularization. Since light is generated, it is not preferable. Moreover, when modularizing, there is a high possibility that bubbles are generated at the interface between the back sheet and the sealing material, which is undesirable from the standpoint of resistance (FIGS. 7B and 7C).

In FIG. 8, the example of a laminated constitution of the back surface sheet 14 is shown.
The substrate 141 includes a heat resistant PET film 411, a silica vapor deposition layer 412 for obtaining a water vapor barrier property, and a PET film 413 for protecting the silica vapor deposition layer. A resin layer that forms the concavo-convex structure 142 is disposed on the substrate 141. On the concavo-convex structure 142, a reflective layer 143 made of an aluminum vapor deposition layer is formed. On the reflective layer 143, a top coat layer 144 made of a coating layer 441 for obtaining antioxidant properties and a resin layer 443 for obtaining electrical insulation is disposed.

In FIG. 9, the example of another layer structure of the back surface sheet 14 is shown.
The substrate 141 includes a PVF layer 411 for obtaining long-term weather resistance, a heat-resistant PET film 412, an adhesive layer 413, an aluminum foil layer 414 for obtaining high water vapor barrier properties, an adhesive layer 415, and an uneven structure 142 on the surface. It consists of a molded PET film 416. A reflective layer 143 made of aluminum is formed on the concavo-convex structure 142 on the substrate 141. On the reflective layer 143, a top coat layer 144 made of a coating layer 441 for obtaining antioxidant properties, an adhesive layer 442, and an electrically insulating PET film 443 for obtaining electrical insulation is disposed.

In FIG. 10, the example of another layer structure of the back surface sheet 14 is shown.
The base material 141 protects the PVF layer 411 for obtaining long-term weather resistance, the heat-resistant PET film 412, the silica vapor deposition layer 413 for obtaining the water vapor barrier property, and the silica vapor deposition layer, and the uneven structure 142 is integrally formed on the surface. PET film 414 formed. A reflective layer 143 made of aluminum is formed on the concavo-convex structure 142 on the substrate 141. On the reflective layer 143, a top coat layer 144 is disposed which includes a coat layer 441 for obtaining antioxidant properties and a PVF layer 442 for further enhancing long-term weather resistance and obtaining electrical insulation.

In FIG. 11, the example of another layer structure of the back surface sheet 14 is shown.
The substrate 141 includes a PVF layer 411 for obtaining long-term weather resistance, a heat-resistant PET film 412, a silica vapor deposition layer 413 for obtaining a water vapor barrier property, a PET film 414 for protecting the silica vapor deposition layer, and further strengthening long-term weather resistance. And a PET film 417 in which a concavo-convex structure 142 is integrally formed on the surface. A reflective layer 143 made of aluminum is formed on the concavo-convex structure 142 on the substrate 141. On the reflective layer 143, a top coat layer 144 made of a coating layer 441 for obtaining antioxidant properties, an adhesive layer 442, and an electrically insulating PET film 443 for obtaining electrical insulation is disposed.

The layer configuration of the back sheet 14 is not limited to the illustrated layer configuration, and various modifications can be made according to required characteristics other than the illustrated layer configuration.

Next, a mechanism for improving the light utilization efficiency by the back sheet 14 will be described.

FIG. 12 is a schematic view showing a mechanism in which light incident on the back sheet 14 is reflected by the concavo-convex structure 142 having the reflective layer 143 and is incident on the light receiving surface J of the solar battery cell 12 (details of the layer configuration are shown in FIG. 12). Not shown). Here, a prism is adopted as the concavo-convex structure.
An uneven structure 142 having a reflective layer 143 is provided on the front side of the back sheet 14. The light H <b> 1 incident on the back sheet 14 is reflected by the reflective layer 143. The reflected light H2 is reflected again at the interface such as between the front plate 11 and the atmosphere, and becomes photoelectrically converted into light H3 incident on the light receiving surface J of the solar battery cell 13. If the light H3 incident on the light receiving surface J of the solar battery cell 13 increases, the amount of photoelectric conversion increases, and the light use efficiency can be improved.

FIG. 12C shows the relationship between the apex angle θ of the prism and the reflection angle α (incident angle α). Here, when light is incident perpendicular 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 reflective layer 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.
At this time, when 2α is equal to or larger than the critical angle φ, the light is totally reflected at the interface between the front plate and the atmosphere, so that the incident light H2 is very little loss and becomes reflected light H3 (FIG. 11A). 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 (FIG. 11B). Since the amount of reflected light H3 decreases due to the generation of transmitted light H4, that is, the amount of light H3 incident on the light receiving surface J of the solar battery cell 12 decreases, the incident angle 2α of the incident light H2 becomes greater than or equal to the critical angle φ. It is desirable.

In this case, the critical angle φ is determined by the refractive index n ₁ of the front plate 11 and the refractive index n _{2 of the} atmosphere, and the following relationship is established.

For example, in the case of using a glass such as tempered glass on the front plate 11, the refractive index n ₁ is about 1.5, the refractive index n ₂ of the atmosphere is about 1.0, the critical angle φ is approximately 42 ° It becomes.
In order to effectively use the reflected light H2 from the reflective layer 143, it is desirable that 2α is equal to or greater than the critical angle φ, that is, when the critical angle φ is 42 °, the reflective angle α at the reflective layer 143 is 21 °. The above is desirable.

Here, approximate 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 are shown in Table 1 below.

Considering the above, it is desirable that the aspect ratio of the prism is 0.2 or more.
However, although the case where the incident angle to the incident surface 110 of the front plate 11 is 0 ° has been considered so far, 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 0.15 or less, the incident angle 2α of the light H2 incident on the interface between the front plate 11 and the atmosphere is nearly 10 ° smaller than the critical angle φ, and the total reflected light is reduced.

  As described above, when the aspect ratio of the prism is 0.4 or more, the moldability deteriorates. Therefore, the aspect ratio is desirably 0.4 or less, and if the aspect ratio is 0.35 or less, the moldability is further improved. In order to improve, it is more desirably 0.35 or less.

As shown in FIG. 13, the substrate 141 is composed of a PET film, the concavo-convex structure 142 is composed of an ultraviolet curable resin, the reflective layer 143 is an aluminum vapor deposition layer, the adhesive layer 441, and the topcoat layer 144 is composed of a PET film 442. The back sheet 14 was produced, and the effect of improving the light utilization efficiency was confirmed. At this time, a prism having an aspect ratio of 0.2 and a pitch of 200 μm was adopted as the concavo-convex structure 142.
In the positional relationship as shown in FIG. 12, when the light amount was measured by arranging a photosensor in the portion corresponding to the solar battery cell 12, assuming that the light amount when there is no uneven structure and no reflective layer is 1, the back sheet shown in FIG. 13. The amount of light when using was 1.3 in relative ratio. Thereby, when the uneven structure 142 which has the reflection layer 143 was provided in the front side of the back sheet, it has confirmed that the light utilization efficiency of a solar cell module could be improved.

  Moreover, when the back sheet 14 (not shown) of the structure which excluded the top coat layer 144 from the back sheet 14 shown in FIG. 13 was produced and the same measurement was performed, the same result as the case where the top coat layer 144 exists is obtained. Obtained. Thereby, it was confirmed that the topcoat layer 144 does not hinder the improvement of light utilization efficiency.

  Further, the back sheet 14 of the present invention is not limited to use in a solar cell module, but an optical element or a display member that is desired to improve light utilization efficiency such as improvement of light utilization efficiency of light emitting elements such as LED lighting and EL elements. Diversion to is possible.

Sectional drawing which shows the solar cell back surface sheet and solar cell module of this invention roughly Sectional drawing which shows the solar cell back surface sheet of this invention roughly The perspective view which shows the example of the uneven structure of the solar cell back surface sheet of this invention Sectional drawing which shows the example of the uneven structure of the solar cell back surface sheet of this invention Sectional drawing which shows the example of the reflection layer of the solar cell back surface sheet of this invention Sectional drawing which shows the example of the topcoat layer of the solar cell back surface sheet | seat of this invention Sectional drawing which shows the example of the topcoat layer of the solar cell back surface sheet | seat of this invention Sectional drawing which shows the example of the layer structure of the solar cell back surface sheet of this invention Sectional drawing which shows the example of the layer structure of the solar cell back surface sheet of this invention Sectional drawing which shows the example of the layer structure of the solar cell back surface sheet of this invention Sectional drawing which shows the example of the layer structure of the solar cell back surface sheet of this invention Sectional drawing which shows the solar cell back surface sheet of this invention roughly Sectional drawing which shows the example of the layer structure of the solar cell back surface sheet of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solar cell module, 11 ... Front plate, 12 ... Solar cell, 13 ... Sealing material, 14 ... Back surface sheet, 141 ... Base material, 142 ... Uneven structure, 143 ... Reflective layer, 144 ... Topcoat layer, 110 ... incident surface, F ... light source direction, J ... light-receiving surface, N ... normal, NG ... normal to front plate 11, H0 ... light incident perpendicular to the solar cell module, H1 ... light incident on the reflective layer, H2 ... reflected light, H3 ... light to be reused, L ... light source, X ... bottom of the concavo-convex structure, Y ... height of the concavo-convex structure, m ... metal reflective layer, h ... high refractive index material, l ... low refractive index material , E ... electrically insulating layer, o ... antioxidant layer, f ... electrically insulating film, a ... adhesive layer, 411, 412, 413, 414, 415, 416, 417 ... layer constituting the substrate 141 , 441, 442, 443 ... layers constituting the top coat layer 144, θ ... Apex angle of prism, alpha ... reflection angle, beta ... transmission angle, phi ... critical angle

Claims (11)

In a solar cell module having at least a translucent front plate, solar cells, a sealing material, and a back sheet,
The back sheet is composed of a base material, a concavo-convex structure formed on the surface of the base material, a reflective layer, and a top coat layer,
A solar cell back sheet comprising a top coat layer, a reflective layer, a concavo-convex structure, and a base material laminated in this order from the front side.   The solar cell backsheet according to claim 1, wherein the reflective layer is a metal layer or a dielectric layer composed of one layer or multiple layers.   The solar cell backsheet according to any one of claims 1 to 2, wherein the topcoat layer has electrical insulation and has a dielectric breakdown voltage of 3 KV or more.   The solar cell backsheet according to any one of claims 1 to 3, wherein the topcoat layer has antioxidant properties.   The solar cell backsheet according to any one of claims 1 to 4, wherein the topcoat layer has a thickness equal to or greater than a height of the uneven structure.   6. The back surface of a solar cell according to claim 1, wherein the concavo-convex structure is any one of a prism, a polygonal pyramid shape, a cylindrical lens, a microlens, or an inverse shape thereof. Sheet.   7. The aspect ratio between the bottom and the height of the unit structure of the concavo-convex structure having a periodic structure composed of repeated concavo-convex is 0.15 to 0.4. The solar cell back surface sheet of description.   8. The aspect ratio of the base to the height of the unit structure of the concavo-convex structure having a periodic structure formed by repeating the concavo-convex is 0.2 or more and 0.35 or less. The solar cell back surface sheet of description.   The solar cell backsheet according to any one of claims 1 to 8, wherein the pitch of the concavo-convex structure comprising a periodic structure composed of repeated concavo-convex is 25 µm or more and 300 µm or less. 10. The solar cell backsheet according to claim 1, wherein a pitch of the concavo-convex structure formed of a periodic structure including repetitions of the concavo-convex is 50 μm or more and 200 μm or less.   A solar cell module comprising the solar cell back sheet according to any one of claims 1 to 10.

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