JP2016143747A - Solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell module using an encapsulant sheet for solar cell module having a sufficient heat resistance, suppressing occurrence of crack in a solar cell element caused by a bus bar, having embeddability, and higher glass adhesiveness.SOLUTION: In an encapsulant sheet, the content of polyethylene having a density of 0.860-0.970 g/cmis 85% or more of the whole encapsulant composition. The encapsulant sheet has a degree of crosslinking which changes in the thickness direction of the encapsulant sheet, and the surface of the encapsulant sheet on the side of higher degree of crosslinking is located on the bus bar side of a solar cell element.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a solar cell module.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. Currently, various types of solar cell modules have been developed and proposed. Generally, a solar cell module has a configuration in which a transparent front substrate made of glass or the like, a solar cell element, and a back surface protection sheet are laminated via a sealing material sheet.

  The sealing material sheet is required to have adhesion and durability with the transparent front substrate, the solar cell element, and the back surface protection sheet, embedding property of the solar cell element, heat resistance, and the like.

  The sealing material sheet is improved in heat resistance of the sealing material sheet by crosslinking the resin composition. However, when the encapsulant sheet is excessively crosslinked, the embedding property of the solar cell element is deteriorated.

  Then, as what combines the embedding property and heat resistance of a solar cell element when manufacturing a solar cell module, an ionizing radiation cross-linking resin is included in the resin constituting the encapsulant sheet, A sealing material sheet having a structure in which the gel fraction is changed along the sheet thickness direction by irradiating ionizing radiation from one surface has been proposed (Patent Document 1).

JP 2011-74261 A

  Although patent document 1 describes the sealing material sheet excellent in the embedding property of a solar cell element, it does not consider about the wiring which connects a photovoltaic cell. On the other hand, when stacking as a solar cell module, a wiring for extracting electricity from the solar cell element called a bus bar is arranged between the solar cell element and the sealing material sheet. Here, when manufacturing a solar cell module, it generally includes a laminating step of laminating solar cell modules, and in the laminating step, the solar cell element and the sealing material sheet are laminated by applying a pressing pressure. However, since the bus bar has a certain thickness, the stress due to press working concentrates on the portion of the solar cell element where the bus bar overlaps. Therefore, there is a problem that cracks occur in the solar cell element portion where the bus bars overlap.

  Moreover, since it is necessary to make a sealing material sheet adhere | attach on a glass substrate simultaneously, high adhesiveness (glass adhesiveness) with a glass substrate is requested | required. For this reason, the surface of the encapsulant sheet on which the solar cell elements are brought into close contact has a characteristic capable of suppressing the occurrence of cracks in the solar cell element caused by the bus bar, and further the solar cell elements on the encapsulant sheet are brought into close contact with each other. Glass adhesion is required on the surface to which the glass substrate that is opposite to the surface to be adhered is adhered.

  This invention is made | formed in view of the above condition, and suppresses generation | occurrence | production of the crack of the solar cell element resulting from a bus bar, although it is a sealing material sheet for solar cell modules which has heat resistance enough. It is an object to provide a solar cell module using a sealing material sheet that is possible and has higher glass adhesion.

  The present inventors conducted sincerity studies in order to solve the above problems. In order to solve the problem that cracks occur in the solar cell element portion where the bus bars overlap, in order to improve the embedding property of the bus bars, the surface of the sealing material sheet having a low degree of crosslinking is arranged on the bus bar side. It is considered that lamination is good. However, the present inventors have surprisingly confirmed that the embedding property of the bus bar is improved by arranging the surface of the sealing material sheet having a high degree of crosslinking on the bus bar side. Therefore, by making the solar cell module configured such that the surface with a high degree of crosslinking of the encapsulant sheet is arranged on the bus bar side, the embedding property of the bus bar is improved, and the solar cell module with higher glass adhesion The present inventors have found that the present invention has been completed. More specifically, the present invention provides the following.

(1) A solar cell module in which a solar cell element, a bus bar that is a wiring for taking out electricity from the solar cell element, and a sealing material sheet are arranged in this order, and the sealing material sheet has a density The polyethylene content of 0.860 g / cm ³ or more and 0.970 g / cm ³ or less is 85% or more in the total encapsulant composition, and the encapsulant sheet extends in the thickness direction of the encapsulant sheet. The degree of cross-linking varies along the solar cell module, and the surface of the encapsulant sheet on the side with the high degree of cross-linking is disposed on the bus bar side.

  (2) The sealing material sheet is irradiated with ionizing radiation from only one side of the front and back surfaces, or is irradiated with ionizing radiation of different intensity from the front and back surfaces (1). The solar cell module described.

  (3) The sealing material sheet is a multilayer sheet including an intermediate layer and outermost layers disposed on both sides thereof, and is provided on one outermost layer of the multilayer sheet on the side opposite to the bus bar side. Is a solar cell module according to (1) or (2), further comprising a silane-modified polyethylene resin.

  (4) The solar cell module according to (3), wherein glass is disposed on a surface opposite to the bus bar side of the sealing material sheet.

  (5) The solar cell module according to any one of (1) to (4), wherein a thickness of the sealing material sheet is 300 μm or more and 600 μm or less.

  (6) The solar cell module according to any one of (1) to (5), wherein the solar cell element has a thickness of 150 μm to 300 μm, and the bus bar has a thickness of 150 μm to 300 μm.

(7) The sealing material sheet is obtained in a thermomechanical analysis (TMA) test under the following conditions, and the relationship between a predetermined temperature range (° C.) and the depth of pressing of the needle into the sealing material sheet (μm). In the TMA curve, the needle is pushed in from the surface with the higher degree of cross-linking of the sealing material sheet, and the gradient P (indentation depth (μm) / temperature of the TMA curve in the predetermined temperature range (° C.). (° C.)), the value of P ₈₀ which is the gradient at 80% of the film thickness of the encapsulant sheet is 1 μm / ° C. to 10 μm / ° C., and 50% of the film thickness of the encapsulant sheet the value of P ₅₀ is the slope of the solar cell module according to any one of claims 1 to 6 or less 13 .mu.m / ° C. or higher 23 .mu.m / ° C..
(TMA test: A 10 mm diameter sealing material sheet is set in the TMA apparatus, the pressure is set to a constant pressure of 20 kPa with a φ1 mm needle, the temperature is raised from room temperature to 150 ° C. at a temperature rising rate of 5 ° C./min, and the needle at that time The indentation depth is measured, provided that when P ₈₀ has an indentation depth of the needle at 150 ° C. of more than 50% and less than 80% of the thickness of the encapsulant sheet, P _{150 °} C. is a gradient at _{150 ° C.} Is used.)

  According to the present invention, the degree of cross-linking of the encapsulant sheet of the solar cell module varies along the thickness direction, and the surface of the encapsulant sheet having the higher degree of cross-linking is disposed on the bus bar side. It is an excellent solar cell module that has sufficient heat resistance and can suppress the occurrence of cracks in the solar cell element due to the bus bar due to its embedding property, and has higher glass adhesion. .

It is a cross-sectional schematic diagram which shows an example of the laminated constitution of the solar cell module of this invention. In the thermomechanical analysis test (TMA) test which concerns on the sealing material sheets 1-3, it is the graph which showed the relationship between temperature (degreeC) and the pushing depth of the needle | hook into a sealing material sheet. In the thermomechanical analysis test (TMA) test concerning the sealing material sheets 1 to 3, the relationship between the temperature (° C.) and the absolute value of the gradient of the TMA curve (indentation depth (μm) / temperature (° C.)) was shown. It is a graph.

  Hereinafter, the solar cell module of the present invention will be described in detail. The present invention is not limited to the embodiments described below.

<Solar cell module>
An embodiment of the solar cell module of the present invention will be described. FIG. 1 is a cross-sectional view showing a layer structure of a solar cell module 10 of the present invention. In the solar cell module 10 of the present invention, the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protection sheet 6 are laminated in order from the incident light receiving surface side. ing. Between the solar cell element 4 and the front sealing material layer 3, a bus bar 7, which is a wiring for taking out electricity from the solar cell element, is disposed. In the present embodiment, the degree of cross-linking of the encapsulant sheet of the front encapsulant layer 3 varies along the thickness direction of the encapsulant sheet of the encapsulant sheet, and the degree of cross-linking of the encapsulant sheet is high. It arrange | positions so that a surface and the bus-bar 7 may contact. With such a configuration, it is possible to suppress the generation of cracks in the solar cell element due to sufficient heat resistance and due to the bus bar. At the same time, the surface with a low degree of crosslinking of the encapsulant sheet is disposed on the transparent front substrate side. The surface with a low degree of crosslinking of the encapsulant sheet has high adhesion to glass or the like. Therefore, it can be set as the outstanding solar cell module whose adhesiveness with the transparent front substrate which is glass etc. is higher.

  Although it will not specifically limit if it is a material which can permeate | transmit sunlight etc. as a transparent front substrate, It is especially preferable to use glass. The transparent front substrate is laminated in contact with the surface of the solar cell element opposite to the bus bar, that is, the surface of the encapsulant sheet having a low degree of crosslinking. Adhesiveness with a transparent front substrate can be made more preferable by contacting and laminating the surface of the encapsulant sheet with a low degree of crosslinking.

  The thickness of the bus bar is preferably 150 μm or more and 300 μm or less. By setting it as such a range, it can have favorable electroconductivity as wiring which takes out electricity from a solar cell element.

  The thickness of the solar cell element is preferably 150 μm or more and 300 μm or less. By setting it as 150 micrometers or more, the risk of the crack generation of a solar cell element can be suppressed. Productivity can be made favorable by setting it as 300 micrometers or less.

<Sealing material sheet>
As for the sealing material sheet used for the solar cell module of this invention, the bridge | crosslinking degree is changing along the thickness direction of a sealing material sheet. The method of crosslinking so that the degree of crosslinking of the encapsulant sheet changes along the thickness direction of the encapsulant sheet is not particularly limited. For example, the method of bridge | crosslinking can be used by irradiating ionizing radiation from only one surface side of the front and back surfaces of a sealing material sheet, or by irradiating ionizing radiation of different intensity | strength from front and back surfaces. In the case of crosslinking by such a method, ionizing radiation was irradiated from only one surface side of the front and back surfaces of the encapsulant sheet so that the surface on the side having a high degree of crosslinking is disposed on the bus bar side. In this case, if ionizing radiation is irradiated on the surface irradiated with ionizing radiation of different intensity from the front and back surfaces, the solar cell element bus bar is placed on the irradiation surface irradiated with strong ionizing radiation. good.

  Here, the degree of cross-linking of the encapsulant sheet refers to the rate of cross-linking of the encapsulant sheet as specified by parameters such as gel fraction and MFR, and the lower the degree of cross-linking, the less cross-linking reaction has occurred. It means that there are many resin component regions. The gel fraction (%) means that 0.1 g of the sealing material is put in a resin mesh, extracted with 60 ° C. toluene for 4 hours, taken out together with the resin mesh, weighed after drying, and compared before and after extraction. The mass% of residual insoluble matter was measured and this was used as the gel fraction. Moreover, MFR (g / 10min) can be calculated | required by measuring by 190 degreeC measured by JIS-K6922-2 and a load of 2.16kg.

The encapsulant sheet used in the solar cell module of the present invention is pressed in from the surface of the encapsulant sheet having a high degree of crosslinking in a thermomechanical analysis test (hereinafter sometimes referred to as a TMA test). Measure the predetermined temperature range (° C.) and the indentation depth (μm) of the needle into the sealing material sheet, and the gradient P (indentation depth (μm) / temperature of the TMA curve in the predetermined temperature range (° C.) (° C.)) and P ₁ (P ₁ = 100 × (P ₁₎ which is the ratio of P ₈₀ which is the gradient at 80% of the film thickness of the encapsulant sheet to P _MAX which is the maximum absolute value of the gradient P. it is preferred values of _{P 80} / P _MAX)) is the sealing material sheet is 30% or less. By setting the value of P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) to such a value, cracks in the solar cell element caused by the bus bar while being a sealing material sheet having sufficient heat resistance It can be set as the sealing material sheet which can suppress generation | occurrence | production of this.

  Here, the TMA test in the present invention means that a sealing material sheet of φ10 mm is set in a TMA apparatus, an indentation pressure of 20 kPa is applied to a needle of φ1 mm, a predetermined temperature range (° C.) at a heating rate of 5 ° C./min, For example, it refers to a test in which the temperature is raised from room temperature to 150 ° C., and the indentation depth of the needle at that time is measured. As a thermomechanical analysis (TMA) apparatus, for example, TMA / SS7100 manufactured by SII Nanotechnology Inc. can be used.

P _MAX in the TMA test is the maximum absolute value of the gradient P (indentation depth (μm) / temperature (° C)) obtained by differentiating the indentation depth (μm) in the TMA curve with temperature (° C). is there. P _MAX is the maximum value of the pushing speed of the needle in the TMA test, and is a parameter indicating the flexibility of the sealing material sheet. An encapsulant sheet having a large P _MAX indicates that the encapsulant sheet has high flexibility in press processing of the laminate. Therefore, in the case of a sealing material sheet having a large P _MAX , the bus bar can be easily embedded in the pressing process of the laminate, and the stress of the pressing process applied to the place where the bus bar and the solar cell element overlap is reduced. Can do. Therefore, the generation | occurrence | production of the crack of the solar cell element resulting from the overlap of a bus bar can be suppressed. Lamination in the laminating process is divided into a vacuuming process and a pressing process, and is performed at a set temperature of about 110 ° C to 150 ° C. The temperature reaches 70 ° C. to 90 ° C. in the evacuation step, and the temperature is raised to the set temperature in the pressing step. Thus general burden on the solar cell element is preferably a temperature at P _MAX for at pressing process starts becomes highest is 70 ° C. to 90 ° C.. The value of P _MAX (indentation depth (μm) / temperature (° C.)) is preferably 10 μm / ° C. to 50 μm / ° C., more preferably 12 μm / ° C. to 35 μm / ° C., and more preferably 15 μm / ° C. More preferably, the temperature is set to 30 ° C./° C. or higher. By setting the value of P _MAX (indentation depth (μm) / temperature (° C.)) to 10 μm / ° C. or more, the generation of cracks in the solar cell element due to the overlapping of the bus bars can be more effectively suppressed. . By setting the value of P _MAX (indentation depth (μm) / temperature (° C.)) to 50 μm / ° C. or less, a sealing material sheet having sufficient heat resistance can be obtained.

The _{P 80} of TMA test, a gradient at 80% of the thickness of the sealing material sheet (indentation depth ([mu] m) / Temperature (° C.)). Here, the gradient at 80% of the film thickness of the encapsulant sheet is the gradient when the needle indentation depth reaches 80% of the film thickness of the encapsulant sheet (indentation depth (μm ) / Temperature (° C.)). P ₈₀ is a parameter indicating the heat resistance of the sealing material sheet. Higher P ₈₀ is smaller sealing material sheet, which means to include many areas highly crosslinked during sealing material sheet. Therefore, it has a high heat resistance as small encapsulant sheet P _80. If less sealing material sheet P ₈₀ is the heat resistance of the sealing material sheet is further improved. The value of P ₈₀ (indentation depth (μm) / temperature (° C.)) is preferably from 1 μm / ° C. to 10 μm / ° C., more preferably from 2 μm / ° C. to 6 μm / ° C. By setting the value of P ₈₀ (indentation depth (μm) / temperature (° C.)) to 10 μm / ° C. or less, a sealing material sheet having sufficient heat resistance can be obtained. By setting the value of P ₈₀ (indentation depth (μm) / temperature (° C.) to 1 μm / ° C. or more, the generation of cracks in the solar cell element due to the overlapping of the bus bars can be more effectively suppressed. . In addition, when P ₈₀ has a pressing depth of the needle at 150 ° C. of more than 50% and less than 80% of the film thickness of the encapsulant sheet, P _{150 ° C.} which is a gradient at _{150 ° C.} is used.

In the TMA test, P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) is P _MAX which is the maximum absolute value of the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve. for, the ratio of the P ₈₀ is the slope at 80% of the thickness of the sealing material sheet. The encapsulant sheet used in the solar cell module of the present invention appropriately adjusts the processing conditions with ionizing radiation, and has both a flexible region excellent in lamination suitability and a region having a high degree of crosslinking excellent in heat resistance. By making P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) 30% or less, more preferably 20% or less, the solar cell resulting from the bus bar while having high heat resistance Generation of cracks in the element can be suppressed.

  In the TMA test, the needle pressing depth at the melting point of the sealing material sheet + 40 ° C. is preferably within 85% of the film thickness of the sealing material sheet, more preferably within 80%, more preferably 75%. More preferably, it is within. The heat resistance of a sealing material sheet | seat can be made more preferable by making the indentation depth of the needle | hook in a TMA test into such a range.

Further, in the TMA test in which a needle was pushed in from the surface on the side with a high degree of cross-linking of the encapsulant sheet, and a predetermined temperature range (° C.) and an indentation depth (μm) of the needle into the encapsulant sheet were measured The gradient P ₅₀ (indentation depth (μm) / temperature (° C.)) at 50% of the film thickness of the material sheet is preferably 13 μm / ° C. or more and 23 μm / ° C. or less. Here, the gradient at 50% of the film thickness of the encapsulant sheet refers to the gradient (indentation depth (μm) / temperature) when the needle indentation depth is 50% of the film thickness of the encapsulant sheet. ° C)). P ₅₀ is a parameter indicating the property narrowing filling of the sealing material sheet. If large sealing material sheet P _50, of narrowing filled encapsulant sheet or irregularities followability is further improved. The value of P ₅₀ (indentation depth (μm) / temperature (° C.)) is preferably 13 μm / ° C. to 23 μm / ° C., more preferably 15 μm / ° C. to 20 μm / ° C. By setting the value of P ₅₀ (indentation depth (μm) / temperature (° C.) to 13 μm / ° C. or more, it is possible to obtain a sealing material sheet having the embedding property of the sealing material sheet, that is, the unevenness following property. . By setting the value of P ₅₀ (indentation depth (μm) / temperature (° C.)) to 23 μm / ° C. or less, sufficient heat resistance can be obtained.

  The thickness of the encapsulant sheet is more preferably 300 μm or more and 600 μm or less. By setting it as such a range, an impact can fully be relieved and it can be set as a highly productive sealing material sheet.

[Encapsulant composition]
The encapsulant sheet contains 85% or more of a polyethylene-based resin having a density of 0.860 g / cm ³ or more and 0.970 g / cm ³ or less in the total encapsulant composition. By including the polyethylene-based resin in such a range, it is possible to reduce decomposition due to long-term use of the encapsulant sheet and to have transparency of the encapsulant sheet. As the polyethylene resin, low density polyethylene (LDPE) can be preferably used, and linear low density polyethylene (LLDPE) or metallocene linear low density polyethylene (M-LLDPE) can be particularly preferably used.

The density of the polyethylene resin is 0.860 g / cm ³ or more and 0.970 g / cm ³ or less, preferably 0.865 g / cm ³ or more and 0.930 g / cm ³ or less. By setting the density of the polyethylene resin within the above range, the transparency of the sealing material can be further improved.

  The polyethylene resin preferably has a melting point of 40 ° C. or higher and 90 ° C. or lower, and more preferably a melting point of 55 ° C. or higher and 80 ° C. or lower.

  Further, the sealing material sheet is preferably a multilayer sheet comprising an intermediate layer and outermost layers disposed on both sides thereof, and further one outermost layer of the multilayer sheet on the side opposite to the bus bar side. Further, it is preferable that a silane-modified polyethylene-based resin is included. The silane-modified polyethylene resin is a resin obtained by graft polymerizing low-density polyethylene (LDPE) serving as a main chain, preferably linear low-density polyethylene (LLDPE) with an ethylenically unsaturated silane compound as a side chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, it can improve the adhesion of the sealing material sheet to other members in the solar cell module. In particular, in the present invention, it is preferable that the outermost layer containing the silane-modified polyethylene resin is disposed so as to be a surface opposite to the bus bar side. By arrange | positioning in this way, adhesiveness with transparent front substrates, such as glass arrange | positioned on the surface on the opposite side to a bus-bar side, can be made more preferable.

  The encapsulant composition for forming the encapsulant sheet may contain a necessary minimum amount of a crosslinking agent, but it is more preferable not to add a crosslinking agent. While adequate crosslinking can proceed by adding a crosslinking agent, a crosslinking agent such as an organic peroxide has been added separately, during the heat laminating process for integration with the solar cell module, This is because the risk of problems such as foaming due to degas increases. When adding a crosslinking agent, a well-known thing can be used and it does not specifically limit, For example, a well-known radical polymerization initiator can be used.

  In addition, the sealing material composition for molding the sealing material sheet may contain other components such as a crosslinking aid, a light stabilizer, an ultraviolet absorber, and a heat stabilizer as necessary. . The other components are preferably in the range of 0.001% by mass to 5% by mass with respect to the total amount of the sealing material composition.

<Method for manufacturing solar cell module>
[Sheet making process]
The encapsulant sheet used in the solar cell module of the present invention can be produced, for example, by undergoing a sheeting step in which each composition is melt-molded to obtain an encapsulant sheet. Molding is performed by various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding, which are usually used in ordinary thermoplastic resins. As an example of the method for forming the encapsulant sheet as the multilayer sheet, a method of forming by co-extrusion using two or more melt-kneading extruders can be given.

[Crosslinking process]
The crosslinking step of the encapsulant sheet used in the solar cell module of the present invention is not particularly limited. For example, the uncrosslinked encapsulant sheet after the sheeting step is crosslinked by ionizing radiation. And the like. A cross-linking step of performing a cross-linking treatment with ionizing radiation on an uncross-linked encapsulant sheet is a solar cell module integration step in which the encapsulant sheet is integrated with other members after completion of the sheeting step. Do before you start. It can be set as the sealing material sheet from which the bridge | crosslinking degree changed along the thickness direction of the sealing material sheet by this bridge | crosslinking process. The crosslinking step may be performed continuously in-line following the sheeting step, or may be performed off-line.

  Regarding the crosslinking treatment by irradiation with ionizing radiation, the individual crosslinking conditions are not particularly limited. Although it can carry out by ionizing radiations, such as an electron beam (EB), an alpha ray, a beta ray, a gamma ray, a neutron beam, it is preferable to use an electron beam especially.

  Moreover, the ionizing radiation can mention the method of irradiating the ionizing radiation of different intensity | strength from only one surface side or front and back of a sealing material sheet. By irradiating ionizing radiation having different intensities from only one side or front and back surfaces of the encapsulant sheet, the degree of crosslinking can be changed along the thickness direction of the encapsulant sheet. By doing so, it is possible to manufacture a sealing material sheet in which the degree of crosslinking changes along the thickness direction of the sealing material sheet.

  When ionizing radiation is irradiated by single-sided irradiation, the acceleration voltage is determined by the thickness of the sheet that is the object to be irradiated, and a thicker sheet requires a larger acceleration voltage. For example, in a sealing material sheet having a thickness of 550 μm, irradiation is performed at 100 kV to 250 kV. When the acceleration voltage is less than 100 kV, crosslinking is insufficient, and the heat resistance of the encapsulant sheet is insufficient. On the other hand, when the acceleration voltage exceeds 250 kV, the inside of the surface has a peak of the maximum dose, and it becomes difficult to produce a sealing material sheet in which the degree of crosslinking changes along the thickness direction of the sealing material sheet. Become. The irradiation dose ranges from 30 kGy to 50 kGy, preferably from 35 kGy to 45 kGy. Irradiation may be in an air atmosphere or a nitrogen atmosphere.

  In addition to performing irradiation with ionizing radiation by single-sided irradiation, ionizing radiation with different intensities may be irradiated from the front and back surfaces. In this case, the surface irradiated with strong ionizing radiation is arranged on the bus bar side. The sealing material sheet used for the solar cell module of the present invention can also be produced by irradiating ionizing radiation having different intensities from the front and back surfaces, as in the case of single-side irradiation.

  When the crosslinking treatment is a general heat treatment, generally, the content of the crosslinking agent is required to be 0.5 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of all components of the sealing material sheet. However, in the case of crosslinking by irradiating with ionizing radiation, the content of the crosslinking agent may be 0, and even if it is contained, it may be less than 0.5 parts by mass. preferable. Thereby, the risk of the productivity fall by gelatinization of the sealing material composition in the sheeting process of a sealing material composition can be reduced.

[Lamination process]
A lamination process is a process of laminating | stacking a sealing material sheet with another member, and integrating a solar cell module. For example, the solar cell module is formed by sequentially laminating a member including a transparent front substrate, a front sealing material layer, a solar cell element having a bus bar, a back sealing material layer, and a back protection sheet, and then integrating them by vacuum suction or the like. Thereafter, the above-mentioned member can be manufactured by thermocompression molding as an integral molded body by a molding method such as a lamination method.

  In the cross-linking step, when ionizing radiation is irradiated from only one side of the front and back surfaces of the encapsulant sheet, the ionizing radiation irradiation surface is irradiated with ionizing radiation of different strength from the front and back surfaces. If the solar cell module is laminated so that the bus bar of the solar cell element is disposed on the irradiation surface irradiated with ionizing radiation, the solar cell module in which the surface on the side with the high degree of crosslinking of the encapsulant sheet is disposed on the bus bar side Can be manufactured.

  In the solar cell module of the present invention, conventionally known materials can be used without particular limitation for the solar cell element and the back surface protective sheet. Moreover, the solar cell module of this invention may also contain members other than the said members, such as a heat dissipation sheet, for example.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

[Sealing material composition for intermediate layer for sealing material sheet]
Metallocene-based linear low density polyethylene (M-LLDPE): Metallocene linear low-density polyethylene 96.5 mass with a density of 0.880 g / cm ³ , a melting point of 60 ° C. and an MFR of 3.5 g / 10 min at 190 ° C. %, Density 0.884 g / cm ³ , MFR at 190 ° C. 1.8 g / 10 min silane-modified polyethylene resin 2.73% by mass, light stabilizer (KEMISTAB 62) 0.0545% by mass, ultraviolet absorber (KEMISORB 12 ) 0.318% by mass, UV absorber (KEMISORB 79) 0.0545% by mass, UV absorber (KEMISORB 202) 0.00636% by mass, crosslinking aid (tricyclodecane dimethanol diacrylate) 0.382% by mass. In order to create a sealing material sheet for the inner layer of the sealing material sheets of Examples and Comparative Examples It was set as the sealing material composition of this.

[Sealant composition for outermost layer for sealant sheet]
Metallocene linear low density polyethylene (M-LLDPE): density 0.885 g / cm ³ , melting point 66 ° C., MFR at 190 ° C. of 18 g / 10 min. Metallocene linear low density polyethylene 86.0% by mass, Silane modification with a metallocene linear low density polyethylene of 96.5% by mass at 190 ° C. of 3.5 g / 10 min, a density of 0.884 g / cm ³ , and an MFR at 190 ° C. of 1.8 g / 10 min. Polyethylene resin 13.6% by mass, light stabilizer (KEMISTAB62) 0.0545% by mass, UV absorber (KEMISORB12) 0.318% by mass, UV absorber (KEMISORB79) 0.0545% by mass, UV absorber (KEMISORB202) It mixes so that it may become 0.00636 mass%, the sealing material sheet | seat for inner layers of the sealing material sheet of an Example and a comparative example It was set as the sealing material composition for producing a process.

<Manufacture of encapsulant sheet for solar cell module>
Each sealing material composition was produced using a 30 mm extruder and a film molding machine having a 200 mm wide T-die to produce an inner layer and an outer layer sealing material sheet at an extrusion temperature of 210 ° C. and a take-off speed of 1.1 m / min. These inner-layer and outer-layer sealing material sheets were laminated to obtain a three-layer solar cell module sealing material sheet (Example and Comparative Example). All of these encapsulant sheets had a thickness of 550 μm, and the outer layer: inner layer: outer layer thickness ratio was 1: 5: 1. Moreover, about the sealing material sheet, an electron beam is applied only to one surface of the sealing material sheet at an acceleration voltage of 195 kV and an illuminance of 40 kGy, respectively, using an electron beam irradiation device (product name EC250 / 15 / 180L, manufactured by Iwasaki Electric Co., Ltd.). Was irradiated to produce a crosslinked encapsulant sheet 1. In addition, when the gel fraction of the encapsulant sheet 1 was measured by the following method, the gel fraction of the encapsulant sheet obtained by collecting portions from the surface on the electron beam irradiation side of the encapsulant sheet to a depth of 100 μm was It was 20%, and the gel fraction of the encapsulant sheet obtained by collecting a portion from the surface opposite to the electron beam irradiation surface of the encapsulant sheet to a depth of 100 μm was 0%. From this result, it was confirmed that the cross-linking degree of the encapsulant sheet 1 changed along the thickness direction of the encapsulant sheet, and the surface on the electron beam irradiation side was a surface having a high degree of crosslinking. In addition, melting | fusing point of the sealing material sheet was 60 degreeC.

  The gel fraction is measured by collecting 0.1 g of each part from the both sides of the encapsulant sheet 1 to a depth of 100 μm, putting it in a resin mesh, extracting it with toluene at 60 ° C. for 4 hours, taking out the resin mesh and drying it. After weighing, it was measured by comparing the mass before and after extraction and measuring the mass% of the remaining insoluble matter.

  Moreover, the sealing material sheet 2 was created similarly to the sealing material sheet 1 except not irradiating an electron beam as the sealing material sheet 2. When the gel fraction on both sides of the encapsulant sheet 2 was measured in the same manner as the encapsulant sheet 1, the gel fraction of the part from the surface to 100 μm on both sides was 0%, and in the thickness direction of the encapsulant sheet It was confirmed that the degree of cross-linking did not change.

  Furthermore, it produced similarly to the sealing material sheet 1 except having irradiated the electron beam on both surfaces of the sealing material sheet as the sealing material sheet 3. FIG. When the gel fraction on both sides of the encapsulant sheet 3 was measured in the same manner as the encapsulant sheet 1, the gel fraction of the part from the surface to 100 μm on both sides was 20%, and in the thickness direction of the encapsulant sheet It was confirmed that the degree of cross-linking did not change.

<TMA test>
A TMA test was performed on the sealing material sheets 1 to 3 manufactured as described above. Specifically, the encapsulant sheet is cut out to φ10 mm, set in a TMA apparatus (TMA / SS7100 manufactured by SII Nanotechnology Co., Ltd.), the encapsulant sheet is heated, and a pressure of 20 kPa is applied from the surface of the encapsulant sheet. Then, a φ1 mm needle was pushed in and the indentation depth was measured. The heating rate was 5 ° C./min, and the temperature was raised from room temperature to 150 ° C. Table 2 shows P ₈₀ which is the gradient of the TMA curve at 80% of the film thickness of the encapsulant sheet (indicated as P _{80 in} Table 2) and P _MAX which is the maximum absolute value of the gradient P of the TMA curve ( In Table 2, P _MAX (denoted as P _MAX ), 100 × (P ₈₀ / P _MAX ), P ₁ (denoted as P _{1 in} Table 1), melting point of resin + sealing material film thickness at 100 ° C. which is 40 ° C. The ratio of the indentation depth of the needle with respect to (indicated as the indentation depth in Table 1) is shown. Table 1 shows the direction in which the needle is pushed in the TMA test (indicated as “measurement direction” in Table 1), and “EB irradiation surface” means that measurement was performed by pushing the needle from the electron beam irradiation surface. The “opposite surface” means that the measurement was performed by pushing the needle from the opposite surface as viewed from the electron beam irradiation surface. In addition, since the sealing material sheet 2 is not irradiated and the sealing material sheet 3 is double-sided irradiation, the special measurement direction is not described.

  FIG. 2 shows a graph showing the relationship between the temperature (° C.) in the TMA test of the sealing material sheet and the pressing depth (μm) of the needles of the sealing material sheets 1 to 3. FIG. 3 is a graph showing the relationship between the temperature (° C.) and the gradient of the TMA curve (indentation depth (μm) / temperature (° C.)) of the sealing material sheets 1 to 3.

From Table 1, both the electron beam irradiation surface (surface with a high degree of crosslinking) of the encapsulant sheet 1 and the surface opposite to the electron beam irradiation surface of the encapsulant sheet 1 (the surface with a low degree of crosslinking) are both. P ₁ was 30% or less. On the other hand, sealing material sheet 2 and the sealing material sheet 3 already crosslinked irradiated with an electron beam from both surfaces of the uncrosslinked not irradiated with an electron beam even P ₁ Any showed 30 percent. Further, the electron beam irradiation surface of the sealing material sheet 1 (the surface of the high degree of cross-linking side) _{is, P 50} showed 13 .mu.m / ° C. or higher 23 .mu.m / ° C. or less. On the other hand, the opposite surface (the surface of the low degree of crosslinking side) of the electron beam irradiation surface of the sealing material sheet 1, and an electron beam are both sealing material sheet 3 of cross-linked, which is irradiated from both sides P ₅₀ 13 .mu.m / less than ° C., sealing material sheet 2 uncrosslinked not irradiated with the electron beam is P ₅₀ was 23 .mu.m / ° C. greater.

<Cell crack test>
Using the sealing material sheet, solar cell modules of Examples and Comparative Examples were created, and a cell crack test was performed. Specifically, 180 mm, 3.2 mm thick white plate semi-tempered glass (manufactured by AGC Fabritech Co., Ltd .: 3KWE33), each sealing material sheet as a light receiving surface side sealing material, 5 mm wide bus bar (thickness 250 μm) ) 3 inch single crystal solar cell elements (thickness 200 μm), non-light-receiving surface side sealing material as each sealing material sheet, and back surface protection sheet (polyethylene terephthalate (PET): thickness 188 μm) Lamination was performed in order, and lamination was performed at a lamination temperature of 110 ° C. to 150 ° C. under vacuum: 5 minutes (0 kPa) and atmospheric pressure press: 7 minutes (100 kPa) to prepare a solar cell module. In addition, the bus bar connected to the solar battery cell is disposed on the light receiving surface side. In Table 2, “the sealing material sheet surface in contact with the bus bar” represents the surface of the light receiving surface side sealing material in contact with the bus bar, and “EB irradiation surface” represents the electron beam irradiation surface. The “opposite surface” means that the opposite surface as viewed from the electron beam irradiation surface is laminated so as to contact the bus bar. And the presence or absence of the crack generation | occurrence | production of the solar cell element of a solar cell module was confirmed by the EL (Electroluminescence) test | inspection. The evaluation results are shown in Table 2 (shown as cell cracks in Table 2). The temperatures listed in Table 2 are lamination temperatures. The evaluation criteria are as follows.

[Evaluation criteria]
○: No crack was confirmed in the solar cell element.
X: A crack was confirmed in the solar cell element.

  From Table 2, the example in which the electron beam irradiation surface (the surface having a high degree of cross-linking) of the encapsulant sheet was laminated so as to be in contact with the bus bar is a crack of the solar cell element in any lamination temperature condition in the cell crack test. Was not confirmed. However, the comparative example in which the surface opposite to the electron beam irradiation surface of the encapsulant sheet (the surface on the side having a low degree of cross-linking) is laminated so as to be in contact with the bus bar is a solar cell element in a cell crack test under a lamination temperature condition of 110 ° Cracks were confirmed. From this, the solar cell module according to the example in which the surface of the encapsulant sheet having the higher degree of cross-linking is disposed on the bus bar side is the surface of the encapsulant sheet having the lower degree of cross-linking disposed on the bus bar side. Compared with the comparative example currently performed, it turns out that generation | occurrence | production of the crack of the solar cell element resulting from a bus bar can be suppressed more.

<Heat resistance test>
Electron beam irradiation surface (surface with a high degree of crosslinking) of sealing material sheet 1, surface opposite to the electron beam irradiation surface (surface with a low degree of crosslinking), sealing material sheet 3, and sealing material sheet About 4, the heat resistance test was done. Specifically, a sealing material sheet cut out to 5 × 7.5 cm is placed vertically on a large-sized glass plate on a large-sized glass plate that has been subjected to graining, and left at 80 ° C. for 12 hours. The moving distance of 5 × 7.5 grain glass after being left was measured and evaluated. The measured values were evaluated according to the following evaluation criteria. The evaluation results (shown as heat resistance in Table 3) are shown in Table 3. The evaluation criteria are as follows.

(Evaluation criteria)
○: Less than 1.5 mm Δ: 1.5 mm or more and less than 2 mm ×: 2 mm or more

  From Table 3, the surface of the encapsulant sheet 1 contacted with the surface glass on the electron beam irradiated surface (the surface on the side having a high degree of crosslinking) and the surface opposite the electron beam irradiated surface on the encapsulant sheet 1 (the surface on the side having a low degree of crosslinking) It can be seen that the grain glass moving distance measured on the face is comparable and superior to the encapsulant sheet 2.

[Glass adhesion test]
Glass adhesion of the sealing material sheet 1 with respect to the electron beam irradiation surface (the surface on the side having a high degree of crosslinking) and the surface opposite to the electron beam irradiation surface (the surface on the side with a low degree of crosslinking) and the sealing material sheets 2 and 3 A test was conducted. Electron beam irradiation surface (surface with a high degree of crosslinking) of the encapsulant sheet 1, surface opposite to the electron beam irradiation surface of the encapsulant sheet 1 (surface with a low degree of crosslinking), encapsulant sheet 2 Each of the encapsulant sheets 3 is brought into close contact with a glass substrate (white plate semi-tempered glass JPT3.2 75 mm × 50 mm × 3.2 mm), heating temperature 150 ° C., vacuum heating (0 kPa) time 5 minutes, atmospheric pressure press (100 kPa) Lamination was performed in 7 minutes to prepare a sample for evaluating adhesion. And in this sample for adhesion evaluation, the sealing material sheet | seat closely_contact | adhered on a glass substrate is cut into 15 mm width, and vertical peeling (50 mm / mm) with a peeling tester (Tensilon universal testing machine RTF-1150-H). min) A test was conducted to measure the glass adhesion strength. The measurement results are shown in Table 4 as “glass initial adhesion strength”.

(Evaluation criteria)
○: 40 N / 15 mm or more Δ: 30 N / 15 mm or more and less than 40 N / 15 mm ×: less than 30 N / 15 mm

Next, the glass adhesion strength maintenance rate after the following dump heat (DH) test was measured for each of the above samples for adhesion evaluation. D. H. The test was performed in accordance with JIS C8917, and the durability test of the sample for evaluation was performed for 500 hours under the conditions of a temperature in the test tank of 85 ° C. and a humidity of 85%. About the sample for evaluation after the test, the glass adhesion strength was measured again by the same test method as described above, and the maintenance ratio (%) of the adhesion strength with respect to the initial glass adhesion strength was calculated. The results are shown in Table 4 as “glass adhesion strength maintenance ratio”.
(Evaluation criteria)
○: 80% or more △: 70% or more and less than 80% ×: less than 70%

  Sealing material sheet 1 The glass adhesion on the surface opposite to the electron beam irradiation surface (the surface on the side having a low degree of crosslinking) is higher than the electron beam irradiation surface of the sealing material sheet 1 (the surface on the side having a high degree of crosslinking). It has become. From this, in the solar cell module in which the surface on the side with a high degree of crosslinking of the encapsulant sheet 1 is arranged on the bus bar side, the surface on the side with a low degree of cross-linking of the encapsulant sheet is arranged on the bus bar side. It turns out that it is a module for solar cells with favorable adhesiveness with the transparent front substrate (glass) arrange | positioned on the opposite side to a bus-bar side compared with a solar cell module.

  From Tables 2 to 4, in the encapsulant sheet in which the degree of cross-linking changed along the thickness direction of the encapsulant sheet, the surface of the encapsulant sheet having the higher degree of cross-linking is disposed on the bus bar side of the solar cell element. The solar cell module has the same heat resistance as the solar cell module with the lower cross-linking surface disposed on the bus bar side of the solar cell element, and has an equivalent or better embedding property. It can be seen that the solar cell module can suppress the occurrence of cracks in the solar cell element due to the bus bar, and is an excellent solar cell module with high adhesion to the glass used for the transparent front substrate.

DESCRIPTION OF SYMBOLS 10 Solar cell module 2 Transparent front substrate 3 Front sealing material layer 4 Solar cell element 5 Back surface sealing material layer 6 Back surface protection sheet 7 Bus bar

Claims (7)

A solar cell module, a bus bar that is a wiring for extracting electricity from the solar cell element, and a sealing material sheet are arranged at least in this order,
The encapsulant sheet has a polyethylene content with a density of 0.860 g / cm ³ or more and 0.970 g / cm ³ or less of 85% or more in the total encapsulant composition,
The degree of cross-linking has changed along the thickness direction of the sealing material sheet,
The solar cell module in which the surface by the side of the said high degree of bridge | crosslinking of the said sealing material sheet is arrange | positioned at the said bus-bar side.   2. The sun according to claim 1, wherein the sealing material sheet is irradiated with ionizing radiation from only one surface side of the front and back surfaces, or is irradiated with ionizing radiation having different intensities from the front and back surfaces. Battery module. The sealing material sheet is a multilayer sheet comprising an intermediate layer and an outermost layer disposed on both sides thereof,
3. The solar cell module according to claim 1, wherein a silane-modified polyethylene resin is further included in one outermost layer of the multilayer sheet that is opposite to the bus bar side.   The solar cell module according to claim 3, wherein glass is disposed on a surface opposite to the bus bar side of the sealing material sheet.   The solar cell module according to any one of claims 1 to 4, wherein a thickness of the sealing material sheet is 300 µm or more and 600 µm or less. The solar cell element has a thickness of 150 μm or more and 300 μm or less,
The solar cell module according to claim 1, wherein the bus bar has a thickness of 150 μm or more and 300 μm or less. The sealing material sheet is
In a TMA curve obtained in a thermomechanical analysis (TMA) test under the following conditions and showing a relationship between a predetermined temperature range (° C.) and the depth of pressing of the needle into the sealing material sheet (μm),
A needle is pushed in from the surface of the sealing material sheet having the higher degree of crosslinking, and the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve in the predetermined temperature range (° C.) is obtained. ,
The value of P ₈₀ which is a gradient at 80% of the film thickness of the encapsulant sheet is 1 μm / ° C. or more and 10 μm / ° C. or less
The value of P ₅₀ is the gradient at 50% of the sealing material sheet having a thickness of solar cell module according to any one of claims 1 to 6 or less 13 .mu.m / ° C. or higher 23 .mu.m / ° C..
(TMA test: A 10 mm diameter sealing material sheet is set in the TMA apparatus, the pressure is set to a constant pressure of 20 kPa with a φ1 mm needle, the temperature is raised from room temperature to 150 ° C. at a temperature rising rate of 5 ° C./min, and the needle at that time The indentation depth is measured, provided that when P ₈₀ has an indentation depth of the needle at 150 ° C. of more than 50% and less than 80% of the thickness of the encapsulant sheet, P _{150 °} C. is a gradient at _{150 ° C.} Is used.)

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