JP7500457B2 - Solar Cell Module - Google Patents

Description

The present invention relates to a solar cell module.

A solar cell module is constructed by sealing solar cells with a sealing material (see, for example, the descriptions in Patent Documents 1 and 2).

JP 2009-40951 A JP 2008-205448 A

There is room for improvement in the durability of solar cell modules in high temperature and high humidity environments.

A solar cell module according to one embodiment of the present disclosure includes a solar cell, a sealing material located on the solar cell , and a light-transmitting substrate located on the sealing material, the sealing material including a main agent, an acid acceptor as a first additive, and an isocyanurate component as a second additive, and a surface layer portion of the sealing material near the light-transmitting substrate and an inner layer portion of the sealing material away from the light-transmitting substrate are measured by FT-IR analysis to calculate a first value obtained by dividing an area showing a peak derived from the second additive located in the surface layer portion by an area showing a peak derived from the main agent, and a second value obtained by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more.

Moreover, a solar cell module according to an embodiment of the present disclosure includes a solar cell, a sealing material located on the solar cell , and a light-transmitting substrate located on the sealing material, the sealing material including a main agent, a metal hydroxide as a first additive, and an isocyanurate component as a second additive, and a surface layer portion of the sealing material near the light-transmitting substrate and an inner layer portion of the sealing material distant from the light-transmitting substrate are measured by FT-IR analysis to calculate a first value obtained by dividing an area showing a peak derived from the second additive located on the surface layer portion by an area showing a peak derived from the main agent, and a second value obtained by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more.

Moreover, a solar cell module according to an embodiment of the present disclosure includes a solar cell, a sealing material located on the solar cell , and a light-transmitting substrate located on the sealing material, the sealing material including a main agent, a metal oxide as a first additive, and an isocyanurate component as a second additive, and a surface layer portion of the sealing material near the light-transmitting substrate and an inner layer portion of the sealing material distant from the light-transmitting substrate are measured by FT-IR analysis to calculate a first value obtained by dividing an area showing a peak derived from the second additive located on the surface layer portion by an area showing a peak derived from the main agent, and a second value obtained by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more.

Furthermore, a solar cell module according to an embodiment of the present disclosure includes a solar cell, a sealing material located on the solar cell , and a light-transmitting substrate located on the sealing material, the sealing material including a main agent, a carbonate as a first additive, and an isocyanurate component as a second additive, and an FT-IR analysis is performed to measure a surface layer portion of the sealing material near the light-transmitting substrate and an inner layer portion of the sealing material distant from the light-transmitting substrate, to calculate a first value obtained by dividing an area showing a peak derived from the second additive located on the surface layer portion by an area showing a peak derived from the main agent, and a second value obtained by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more.

The solar cell module of one embodiment is resistant to deterioration even when installed in a high-temperature, high-humidity environment.

FIG. 1 is a drawing showing a schematic diagram of an example of a solar cell module according to one embodiment of the present disclosure, in which FIG. 1(a) is a plan view of the solar cell module seen from the light receiving surface side, and FIG. 1(b) is a cross-sectional view taken along line A-A in FIG. 1(a). FIG. 2 is an exploded perspective view of a solar cell module according to one embodiment of the present disclosure, in which FIG. 2(a) is a perspective view showing a solar cell group formed by connecting a plurality of solar cells with an interconnector and connection wiring, and FIG. 2(b) is an exploded perspective view illustrating the stacked state of a module stack consisting of a translucent substrate, a first sealing material, a solar cell group, a second sealing material, and a rear surface protective material. 3A and 3B are diagrams showing the lamination process of a solar cell module manufacturing method according to one embodiment of the present disclosure, in which FIG. 3A is a schematic diagram showing the placement of a module stack in a laminator, and FIG. 3B is a schematic diagram showing the application of pressure to the module stack in the laminator. FIG. 4 is a diagram showing the relationship between time and temperature in the crosslinking step in the method for producing a solar cell module according to the present disclosure. FIG. 5 is a diagram showing, using a structural formula, how the sealing material peels off from the light-transmitting substrate in the solar cell module. FIG. 6 is a model diagram showing FT-IR imaging of an isocyanurate component measured using an FT-IR device in an embodiment of the solar cell module of the present disclosure.

In general, a sealing material containing an ethylene-vinyl acetate copolymer as a main agent is used in a solar cell module. The ethylene-vinyl acetate copolymer has a drawback in that the acetic acid generated by hydrolysis corrodes and damages the solar cell. Specifically, the acetic acid generated by hydrolysis may corrode the contact glass layer between the electrode of the solar cell and the semiconductor silicon. Therefore, a solar cell module using an ethylene-vinyl acetate copolymer may cause insulation failure when used in a high-temperature environment, and the power generation performance of the solar cell module may be reduced. Therefore, a technology is known in which an acid acceptor (Mg(OH)2) is added to the sealing material to neutralize the acetic acid, thereby reducing the corrosion damage of the contact glass layer between the electrode of the solar cell and the semiconductor silicon (see Patent Document 1). In addition, a technology is known in which a crosslinking assistant such as triallyl isocyanurate is added to the sealing material to increase the volume resistivity of the sealing material, suppress the occurrence of insulation failure, and reduce the decrease in the power generation performance of the solar cell module (see Patent Document 2).

However, when a solar cell module is installed in a high-temperature and high-humidity environment where moisture and heat stress are relatively strong, it is known that the encapsulant containing an acid acceptor generates hydroxide ions (OH-) when the acid acceptor is ionized in the presence of moisture. If there is an excess of these hydroxide ions (OH-), the bonds of the polymers that make up the encapsulant are broken (basic hydrolysis reaction). This reduces the adhesive strength of the encapsulant. Therefore, if the breakage of the polymer bonds occurs near the adhesive interface between the transparent substrate of the solar cell module and the encapsulant, the adhesive strength is reduced, and there is a risk that the encapsulant will peel off from the transparent substrate.

In the future, when solar cell modules are installed in hot and humid environments such as tropical and subtropical regions such as Southeast Asia and India, solar cell modules that are less susceptible to the above-mentioned peeling will be required.

The inventors of the present disclosure have therefore created a technology for a solar cell module whose adhesive strength is less likely to decrease in a hot and humid environment. Below, an example of an embodiment of a solar cell module according to one aspect of the present disclosure will be described in detail with reference to the drawings. Note that the drawings are schematic, and therefore the dimensional ratios and positional relationships of each component in the drawings are not necessarily accurate.

<<Solar cell module configuration>>
A solar cell module X according to an embodiment of the present disclosure will be described with reference to Fig. 1 and Fig. 2. Hereinafter, in the normal direction to the main surface of the solar cell module X, the side that mainly receives light will be referred to as the light-receiving surface side, and the side behind the light-receiving surface side will be referred to as the back surface side.

The solar cell module X according to one embodiment of the present disclosure is constructed by stacking a translucent substrate 1, a first sealing material 2a, solar cells 3 electrically connected to each other by an interconnector 5 and a connection wiring 6, a second sealing material 2b, and a back surface protection material 4 in sequence.

The solar cell module X has, for example, a terminal box 7 on the outside of the back surface protective material 4 for extracting the power generated by the solar cell 3 to the outside. The solar cell module X may also have, for example, a frame 8 that protects the outer periphery of the solar cell module X.

In one embodiment of the solar cell module X of the present disclosure, a plurality of solar cells 3 are electrically connected to each other via interconnectors 5 and connection wiring 6 to form a solar cell group 11. In other configurations, a single large-area solar cell may be used instead of the solar cell group 11.

Next, we will explain each component that makes up the solar cell module X of this embodiment.

<Light-transmitting substrate>
The light-transmitting substrate 1 can protect the light-receiving surface side of the solar cell 3 from water, for example. The light-transmitting substrate 1 may have light-transmitting properties for light of a specific range of wavelengths. The specific range of wavelengths may be, for example, the wavelength of light that the solar cell 3 can convert photoelectrically. The material of such a light-transmitting substrate 1 may be, for example, a hard substrate having light-transmitting properties. The hard substrate having light-transmitting properties may be, for example, glass or a transparent synthetic resin. As the glass, for example, blue plate glass (soda-lime glass), white plate glass obtained by removing iron from blue plate glass, or hard glass may be used. In addition, as the transparent synthetic resin, a transparent polycarbonate resin or a transparent acrylic resin may be used. The light-transmitting substrate 1 has a light-receiving surface into which light is mainly incident, and a back surface to which the first sealing material 2a is bonded. The shape of the light-transmitting substrate 1 is not limited to a flat plate shape, and may have a curved shape according to the application. The thickness of such a light-transmitting substrate 1 may be, for example, about 3 mm in the case of glass, and may be, for example, about 5 mm in the case of synthetic resin.

<Sealing material>
The sealing material 2 includes a first sealing material 2a and a second sealing material 2b. Hereinafter, the first sealing material 2a and the second sealing material 2b are collectively referred to as the sealing material 2. The first sealing material 2a is located between the light-transmitting substrate 1 and the solar cell group 11, and the second sealing material 2b is located between the solar cell group 11 and the back surface protection material 4. The first sealing material 2a protects the light-receiving surface side of the solar cell group 11, and the second sealing material 2b protects the back surface side of the solar cell group 11. The first sealing material 2a is in contact with the second sealing material 2b, and bonds the light-transmitting substrate 1 and the solar cell group 11. The second sealing material 2b bonds the solar cell group 11 and the back surface protection material 4.

The first sealing material 2a and the second sealing material 2b are stacked with the solar cell group 11 and other members, and are heated and pressed under reduced pressure by a laminating device, so that they are fused and integrated with the solar cell group 11 and other members. The first sealing material 2a has translucency for light of a specific wavelength. Therefore, light irradiated to the light receiving surface side of the solar cell module X can be transmitted through the translucent substrate 1 and the first sealing material 2a and enter the solar cell group 11. The second sealing material 2b may have translucency for light of a specific wavelength, or may not have translucency for light of a specific wavelength. When the second sealing material 2b does not have translucency for light of a specific wavelength, for example, the second sealing material 2b may have a pigment. In other words, the second sealing material 2b may be colored. For such first sealing material 2a and second sealing material 2b, for example, a sheet-like member having flexibility can be adopted. In addition, the first sealing material 2a and the second sealing material 2b may have different thicknesses. The first sealing material 2a and the second sealing material 2b may have a thickness of, for example, about 0.4 to 1 mm.

In the following description, the interface formed by bonding the light-transmitting substrate 1 and the first seal 2a is referred to as the adhesive interface 10, the portion of the first seal 2a near the adhesive interface 10 is referred to as the adhesive portion 2a1 or surface layer portion 2a1, and the portion farther from the light-transmitting substrate 1 than the adhesive portion 2a1 is referred to as the inner layer portion 2a2.

<Sealant Composition>
The encapsulant 2 includes a base material, a first additive, a second additive, and a third additive. Each component of the encapsulant 2 will be described in detail below.

(Base material: ethylene-vinyl acetate copolymer)
The main component of the sealing material 2 may be, for example, an ethylene-vinyl acetate copolymer. Here, the term "mainly made of ethylene-vinyl acetate copolymer" means that the sealing material 2 contains 50 parts by weight or more and 100 parts by weight or less of ethylene-vinyl acetate copolymer in 100 parts by weight of all components. The flexibility of the sealing material 2 can be increased by using ethylene-vinyl acetate copolymer as the main component. This protects the solar cell 3 from load and impact applied to the solar cell module X. The melting point of such an ethylene-vinyl acetate copolymer may be around 60°C. The content of the ethylene-vinyl acetate copolymer in the sealing material 2 may be, for example, 70 parts by weight or more and 99.5 parts by weight or less, or may be, for example, 90 parts by weight or more and 99 parts by weight or less.

(First additive: acid acceptor)
The first additive is an acid acceptor. The acid acceptor may contain, for example, one or more of a metal hydroxide, a metal oxide, and a carbonate. The metal hydroxide may be, for example, magnesium hydroxide, calcium hydroxide, barium hydroxide, aluminum hydroxide, iron hydroxide, etc. The metal oxide may be, for example, magnesium oxide, calcium oxide, aluminum oxide, zinc oxide, etc., and the carbonate may be, for example, magnesium carbonate, calcium carbonate, barium carbonate, etc. For example, by using magnesium hydroxide as the metal hydroxide, magnesium oxide as the metal oxide, and calcium carbonate as the carbonate, it is possible to make it difficult for rust to occur on the conductors and electrodes inside the solar cell module. Since the sealing material 2 has the first additive, the first additive can neutralize acetic acid generated by hydrolysis or the like from the ethylene-vinyl acetate copolymer in the solar cell module X. As a result, the solar cell module X can be reduced in occurrence of corrosion damage caused by acid. When the content of the main agent is 100 parts by weight, the content of the acid acceptor may be, for example, 0.05 to 2 parts by weight.

(Second Additive: Isocyanurate Component)
The second additive is a crosslinking aid. The crosslinking aid may have, for example, a radical polymerizable group as a functional group. For example, a trifunctional isocyanurate-based crosslinking aid may be used as the crosslinking aid. Such a crosslinking aid is referred to as an isocyanurate component in this disclosure. The isocyanurate component may be, for example, triallyl isocyanurate, tris[(meth)acryloyloxyethyl]isocyanurate, or the like. The crosslinking temperature of the second additive may be, for example, higher than the melting point of the ethylene-vinyl acetate copolymer, which is the main agent. More specifically, the crosslinking temperature of the second additive may be, for example, around 170°C.

It is known that the isocyanurate component has a low degree of freedom of deformation after crosslinking due to the nitrogen in its composition. Therefore, while the isocyanurate component can reduce the water permeability of the sealing material 2, there is a risk of reducing the flexibility of the sealing material 2 as the amount of the isocyanurate component added to the sealing material 2 increases. For this reason, when the content of the main agent is 100 parts by weight, the content of the isocyanurate component may be, for example, 0.2 to 3 parts by weight. This allows the sealing material 2 to protect the solar cell 3 from load and impact while maintaining the flexibility of the sealing material 2.

(Third Additive: (Meth)Acrylate Component)
The third additive is a (meth)acrylate component. In the present disclosure, the term "(meth)acrylate component" refers to at least one of an acrylate and a methacrylate.

The (meth)acrylate component may be, for example, a polyfunctional acrylate crosslinking aid. In other words, a polyfunctional acrylate crosslinking aid is a polyfunctional acrylate compound that is a monomer having multiple acryloyl groups in the molecule. More specifically, the polyfunctional acrylate crosslinking aid may be, for example, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc.

The crosslinking temperature of the third additive may be higher than the melting point of the ethylene-vinyl acetate copolymer, which is the main component, and lower than the crosslinking temperature of the isocyanurate component, which is the second additive. More specifically, the crosslinking temperature of the third additive may be, for example, around 125°C.

The (meth)acrylate component is a material that does not easily dissolve in ethylene-vinyl acetate copolymer. Therefore, when the content of the main agent is 100 parts by weight, the content of the (meth)acrylate component may be, for example, 0.2 to 1.0 parts by weight. This makes it easier to dissolve the (meth)acrylate component, which is the third additive, in the sealing material 2.

The compounding ratio of the second additive to the third additive can be, for example, in the range of 10:90 to 90:10.

(Other additives)
The composition of the present disclosure is not limited to the above-mentioned main agent, first additive, second additive, and third additive. That is, various physical properties, such as mechanical strength, adhesiveness, optical properties such as transparency, heat resistance, light resistance, crosslinking speed, etc., may be improved or adjusted within the range that does not impair the effects of the present disclosure. Therefore, the composition of the present disclosure may contain various additives such as adhesion improvers (silane coupling agents, etc.), plasticizers, ultraviolet absorbers, light stabilizers, anti-aging agents, acryloxy group-containing compounds, methacryloxy group-containing compounds, and/or epoxy group-containing compounds, as necessary.

<Solar cell group>
The solar cell group 11 has a function of converting incident sunlight into electricity. The solar cell group 11 in this embodiment is formed by electrically connecting a plurality of solar cells 3 with an interconnector 5 and a connection wiring 6. As the solar cell 3, a crystalline solar cell or a thin-film solar cell can be adopted. In the example of FIG. 1 and FIG. 2, a crystalline solar cell 3 is adopted as the solar cell 3. In the case of the crystalline solar cell 3, for example, a solar cell having a substrate of monocrystalline or polycrystalline semiconductor silicon having a thickness of about 0.1 to 0.4 mm can be used. A pn junction is formed inside such a solar cell 3. Then, electrodes are provided on the light-receiving surface and the back surface of the solar cell 3, respectively, and further, an anti-reflection film may be provided on the light-receiving surface of the solar cell 3. The size of the solar cell 3 is about 150 to 220 mm square if it is a crystalline solar cell 3. Such solar cells 3 are electrically connected in series or in parallel by the interconnector 5 and the connection wiring 6 to constitute the solar cell group 11.

<Back surface protection material>
The back surface protective material 4 is positioned in a state facing the light-transmitting substrate 1. A solar cell group 11 sealed with a sealing material 2 is positioned in the region between the light-transmitting substrate 1 and the back surface protective material 4. Therefore, the back surface protective material 4 can protect the back surface side of the solar cell group 11. In addition, the back surface protective material 4 can reduce the intrusion of moisture from the back surface side into the solar cell 3, the first sealing material 2a, and the second sealing material 2b. The back surface protective material 4 may be translucent for light of a specific wavelength range, for example, or may not be translucent for light of a specific wavelength range.

For example, a plate-shaped member or a flexible sheet-shaped member is used as the back surface protective material 4. For example, the same material as the light-transmitting substrate 1 may be used as the back surface protective material 4, and specifically, a polyethylene terephthalate (PET) sheet, a polyethylene naphthalate (PEN) sheet, a polyvinyl fluoride (PVF) sheet, a laminate of these, a weather-resistant fluorine-based resin sheet sandwiched between aluminum foil, or a polyethylene terephthalate (PET) sheet vapor-deposited with alumina or silica may be used.

<Interconnector and connection wiring>
The interconnector 5 and the connection wiring 6 have the function of electrically connecting the solar cell 3 to each other. There are no particular limitations on the shape, material, etc. of such interconnector 5 and connection wiring 6, but for example, a strip of copper foil with a thickness of about 0.1 mm and a width of about 1 mm to 6 mm may be entirely solder-coated, cut to a predetermined length, and soldered onto the electrodes of the solar cell 3.

<Terminal box>
The terminal box 7 can, for example, extract to the outside the output obtained by the solar cell 3. As the terminal box 7, for example, one having a box body made of modified polyphenylene ether (modified PPE) resin or polyphenylene oxide (PPO) resin, a terminal plate disposed within the box body, and an output cable that leads out electric power to the outside of the box body is adopted.

<Frame>
Frame 8 may be made of aluminum alloy or plastic and have a fitting portion that is shaped to sandwich the light-receiving surface side of light-transmitting substrate 1 and the back surface side of back surface protection material 4 .

<<Solar cell module manufacturing method>>
Next, a method for manufacturing the solar cell module X according to the present disclosure will be described with reference to Fig. 2 to Fig. 4. The method for manufacturing the solar cell module X includes a preparation step, a lamination step, and a cross-linking step, in that order.

<Preparation process>
2, a solar cell group 11 is formed by integrating solar cells 3 with interconnectors 5 and connection wiring 6. Then, a first sealing material 2a, the solar cell group 11, a second sealing material 2b, and a rear surface protection material 4 are stacked in this order on a light-transmitting substrate 1 to form a module laminate 9.

<Lamination process>
As shown in FIG. 3( a ), the module stack 9 is placed on the heating plate 22 in the lower housing 21 a of the laminator 20 with the light-transmitting substrate 1 facing downward, and the upper housing 21 b is lowered toward the lower housing 21 a to close the housing 21 .

Next, as shown in FIG. 3(b), the module stack 9 is heated and pressurized to a temperature equal to or higher than the melting point temperature of the first sealing material 2a and the second sealing material 2b. More specifically, the module stack 9 is heated for about 10 to 15 minutes in a reduced pressure atmosphere of about 50 to 400 Pa at a temperature equal to or higher than the melting point of the main agent of the first sealing material 2a and the second sealing material 2b and lower than the heat generation peak temperature indicated by the polymerization reaction of the second additive and the third additive (for example, about 95°C to 105°C), while the entire module stack 9 is pressed as uniformly as possible with the diaphragm 23 at about 10 to 100 KPa, thereby softening the first sealing material 2a and the second sealing material 2b and bonding them to other members to integrate the members constituting the module stack 9. The heat generation peak temperature indicated by the polymerization reaction of the crosslinking auxiliary can be obtained, for example, by differential scanning calorimetry (DSC).

<Crosslinking step>
After the above lamination process, the pressure inside the housing 21 of the laminator 20 is returned to atmospheric pressure. The laminated module stack 9 is transferred to a crosslinking furnace and heated until the degree of crosslinking of the sealing material 2 reaches at least 80%. The crosslinking furnace heats the module stack 9 to crosslink the sealing material 2, and a conventionally known heating device such as a hot air heating furnace or an infrared heating furnace can be used. The laminator 20 may be used as a substitute for a crosslinking furnace by continuing to increase the temperature inside the laminator 20.

The rate of the crosslinking reaction of the crosslinking aid is temperature dependent, with the reaction proceeding faster at higher temperatures. In addition, the temperature range in which the crosslinking reaction proceeds varies depending on the type of crosslinking aid. Therefore, by controlling the temperature and time in the crosslinking process, it is possible to more efficiently adjust the concentration distribution of the second additive after crosslinking.

This method is explained below.

The crosslinking reaction of the second additive, the isocyanurate component, begins at a temperature of approximately 150°C to 155°C, and the crosslinking reaction is most intense at a temperature of approximately 165°C to 175°C.

The crosslinking initiation temperature of the third additive, the (meth)acrylate component, is approximately 105°C to 110°C, and the temperature at which the crosslinking reaction occurs most rapidly is approximately 120°C to 130°C.

In the following description, the temperature range of 150° C. to 155° C. to which the module laminate 9 is heated in the crosslinking step is also referred to as the initiation temperature of the crosslinking reaction of the isocyanurate component, and 105° C.
The temperature in the range of 100° C. to 110° C. is also referred to as the crosslinking initiation temperature of the (meth)acrylate component.

The temperature at which the second additive starts crosslinking is the temperature at which heat begins to be generated by the polymerization reaction of the second additive in a graph showing the relationship between temperature and heat obtained from differential scanning calorimetry (DSC). The temperature at which the crosslinking reaction of the second additive occurs most strongly is the temperature at which the amount of heat generated by the polymerization reaction of the second additive is the largest in a graph showing the relationship between temperature and heat obtained from differential scanning calorimetry (DSC). In other words, the temperature at which the crosslinking reaction of the second additive occurs most strongly is the peak temperature at which the amount of heat generated by the heat generated by the polymerization reaction of the second additive reaches a peak.

The temperature at which the third additive begins to crosslink is the temperature at which heat begins to be generated by the polymerization reaction of the third additive in a graph showing the relationship between temperature and heat obtained from differential scanning calorimetry (DSC). The temperature at which the crosslinking reaction of the third additive occurs most strongly is the temperature at which the amount of heat generated by the polymerization reaction of the third additive is the largest in a graph showing the relationship between temperature and heat obtained from differential scanning calorimetry (DSC). In other words, the temperature at which the crosslinking reaction of the third additive occurs most strongly is the peak temperature at which the amount of heat generated by the polymerization reaction of the third additive reaches a peak.

The cross-linking process consists of the first half, middle half, and last half, as described below.

The first half is a process of heating to the crosslinking initiation temperature of the (meth)acrylate component, which is the third additive. Since the first sealing material 2a and the second sealing material 2b are heated to a temperature higher than the melting point of the ethylene-vinyl acetate copolymer, which is the main agent, the polymers of the second additive and the third additive become mobile in the sealing material 2. The heating rate in the first half is higher than the heating rates in the middle and latter half, which will be described later. For example, the heating rate in the first half may be 0.6 to 1.0°C/sec. The temperature in the first half of the crosslinking process is lower than the temperature at which the polymerization reaction of the isocyanurate component, which is the second additive, and the (meth)acrylate component, which is the third additive, begins. Therefore, by increasing the heating rate in the first half, the time required for the crosslinking process can be shortened without affecting the crosslinking of the second additive and the third additive.

The intermediate portion is a process of increasing the temperature from the crosslinking initiation temperature of the (meth)acrylate component, which is the third additive, to the crosslinking initiation temperature of the isocyanurate component, which is the second additive. In the intermediate portion, the (meth)acrylate component, which is the third additive, starts a crosslinking reaction, and a crosslinked network structure formed by the crosslinking of the (meth)acrylate component, which is the third additive, is formed accordingly. This makes it difficult for the second additive (isocyanurate) to move. The temperature increase rate of such an intermediate portion may be smaller than the temperature increase rate of the first half portion and larger than the temperature increase rate of the second half portion described below. In other words, the temperature increase rate in the temperature range between the crosslinking initiation temperature of the second additive and the crosslinking initiation temperature of the third additive in the crosslinking process may be smaller than the temperature increase rate of the first half portion. By increasing the temperature increase rate of the intermediate portion larger than the second half rate, the crosslinked network structure of the (meth)acrylate component, which is the third additive, is formed at an earlier stage than the isocyanurate component, which is the second additive, starts to move due to crosslinking shrinkage, and the movement of the second additive can be reduced. Specifically, for example, the heating rate in the middle part may be about 0.2 to 0.4°C/sec, and the heating time may be about 110 to 220 seconds.

The latter half is a process of heating in the range of 155°C or more, which is the crosslinking initiation temperature of the isocyanurate component, the second additive. Through the latter half, the crosslinking of the second additive and the third additive proceeds further, and the degree of crosslinking of the sealing material 2 can be increased to 80% or more. In the latter half, the isocyanurate component, the second additive, starts crosslinking and starts linking multiple molecules by chemical covalent bonds. The crosslinking reaction at this time causes a phenomenon called crosslinking shrinkage, in which the distance between the molecules constituting the isocyanurate component, the second additive, tends to decrease. When this phenomenon occurs, the molecules constituting the isocyanurate component, the second additive, tend to be drawn and gathered from the interface between the first sealing material 2a and the light-transmitting substrate 1 toward the inside of the first sealing material 2a, so that the concentration becomes low in the surface layer 2a1 of the first sealing material 2a and the concentration becomes high in the inner layer 2a2. A similar phenomenon also occurs between the second sealing material 2b and the back surface protection material 4. That is, the molecules constituting the isocyanurate component have a low concentration in the surface layer of the second sealing material 2b that contacts the interface between the two materials, and a high concentration in the inner layer portion away from the interface.

However, as described above, the (meth)acrylate component, which is the third additive, starts crosslinking first to form a crosslinked network structure, so that the molecules of the isocyanurate component, which is the second additive, are less likely to move. This makes it possible to reduce the concentration decrease of the isocyanurate component, which is the second additive, in the surface layer portion 2a1 of the first sealing material 2a that contacts the adhesive interface 10 between the first sealing material 2a and the light-transmitting substrate 1. Similarly, it is possible to reduce the concentration decrease of the isocyanurate component, which is the second additive, in the surface layer portion of the second sealing material 2b that contacts the adhesive interface 10 between the second sealing material 2b and the back surface protective material 4.

The heating rate in the latter half of the process may be set lower than that in the former half and the middle part. By setting a lower heating rate, the temperature of the module stack 9 can be gradually brought closer to that of the heating plate 22 over time, which makes it difficult for the sealing material 2 to locally foam due to an excessively high temperature of the heating plate 22. Specifically, the heating rate in the latter half of the process may be set to 0.05 to 0.1°C/sec. Also, in order to sufficiently polymerize the isocyanurate component as the second additive and the (meth)acrylate component as the third additive to increase the degree of cross-linking of the sealing material 2, the heating time in the latter half of the process may be set longer than that in the middle part. Specifically, the heating time may be set to, for example, 200 seconds or more.

If there is a difference in the rate of temperature rise in the first, middle, and second half sections, it is advisable to compare the rates of temperature rise in the first, middle, and second half sections by taking the average rate of temperature rise in the first, middle, and second half sections.

<Action and Effects>
According to this embodiment, it is possible to provide a solar cell module X that reduces the decrease in adhesive strength of the sealing material 2 caused by moist heat and has improved reliability. The operation and effects of this embodiment will be described below.

When the solar cell module has a sealing material 2 whose main component is an ethylene-vinyl acetate copolymer, there is a risk that the acetic acid generated by hydrolysis of the sealing material 2 may corrode the solar cell group 11. Therefore, in order to neutralize the acetic acid generated from the sealing material 2 or to reduce the increase in the generation of acetic acid itself, a first additive that functions as an acid acceptor is added.

However, when the first additive is added, there is a risk that hydroxide ions generated from the first additive due to excessive moist heat may easily deteriorate the adhesive strength between the light-transmitting substrate 1 and the first sealing material 2a, and may also deteriorate the adhesive strength between the second sealing material 2b and the back surface protection material 4.

As such, in addition to measures to reduce the possibility of corrosion caused by the generation of acetic acid from the sealing material 2, measures are also needed to reduce deterioration caused by the acid acceptor in the sealing material 2 itself.

The mechanism by which the adhesive strength of the sealing material 2 deteriorates due to the acid acceptor and the countermeasures for this will be explained in detail below.

First, regarding humidity stress, the vicinity of the adhesive interface 10 between the adherend, the transparent substrate 1, and the adhesive, the sealant 2, i.e., the surface layer of the sealant 2, is a portion that is more susceptible to moisture penetration than other portions. When moisture penetrates, the metal hydroxide (magnesium hydroxide, etc.) that is the first additive obtains moisture, ionizes, and generates hydroxide ions (OH-), which then bind the transparent substrate 1 and the first additive.
The surface layer of the sealing material 2 in the vicinity of the adhesive interface 10 of the sealing material 2a is in a basic condition. Then, at the position of line B-B shown in Fig. 5, hydroxide ions generated from the metal hydroxide cut the ester bond in the first sealing material 2a by a basic hydrolysis reaction. When the ester bond is cut, the adhesive portion (surface layer) 2a1 between the first sealing material 2a and the light-transmitting substrate 1 deteriorates, and moisture becomes more likely to penetrate through the adhesive interface 10. As a result, the deterioration of the adhesive portion (surface layer) 2a1 progresses further, and the adhesive strength decreases.

Next, the mechanism of deterioration of the sealing material 2 caused by temperature difference stress will be explained. Since the adhesive interface 10 between the light-transmitting substrate 1 and the first sealing material 2a is a connection part of materials with different thermal expansion coefficients, thermal stress is repeatedly generated at the adhesive interface 10 due to temperature changes in the natural environment. As a result, the adhesive part 2a1 of the first sealing material 2a repeatedly undergoes shear deformation. Looking at it more microscopically, the first sealing material 2a has a three-dimensional mesh-like molecular structure in which chain polymers are polymerized and bonded together by crosslinking. And, the adhesive part (surface layer) 2a1 of the first sealing material 2a is repeatedly subjected to mechanical stress associated with shear deformation, which causes fatigue deterioration (bond scission) of the adhesive molecules (silane coupling agent, etc.), and the adhesive strength of the first sealing material 2a to the light-transmitting substrate 1 decreases.

Next, we will explain how to prevent deterioration of the adhesive strength between the light-transmitting substrate 1 and the sealing material 2 in the solar cell module X.

The first sealing material 2a of the solar cell module X has an isocyanurate component as a second additive. The crosslinked structure formed by the isocyanurate component after crosslinking has a molecular structure with low degree of freedom of deformation (rigid) and high crosslinking density because the isocyanurate component has nitrogen atoms in its molecular chain, and has the advantage of being able to reduce moisture penetration. Reducing moisture penetration reduces the scission of ester bonds accompanying hydrolysis in the first sealing material 2a, which leads to reduced deterioration of adhesive strength.

However, since the crosslinked structure formed by the isocyanurate component is rigid and highly brittle, if the amount of the isocyanurate component added to the sealing material is excessively increased, the rigidity of the entire sealing material increases, and the deformation resistance of the first sealing material 2a increases. That is, the viscous effect in viscoelasticity decreases, and the consumption of shear stress (shear momentum) in the entire sealing material 2 when stress is applied to the sealing material 2 decreases. Then, when the solar cell module X is exposed to a temperature change (temperature difference stress), the thermal stress generated at the adhesive interface 10 between the translucent substrate 1 and the first sealing material 2a increases, and the transfer rate of the thermal stress to the adhesive interface 10 increases. As a result, the adhesive portion 2a1 is easily deteriorated and peeled off. In this way, if the amount of the isocyanurate component added, which is the second additive, is simply increased, the storage modulus becomes too high in exchange for reducing the deterioration of the adhesive strength caused by the hydrolysis of the first sealing material 2a, and the viscous properties become insufficient, which may impair durability against temperature changes.

Furthermore, since the isocyanurate component as the second additive has the property of shrinking during crosslinking, the isocyanurate component has the property of easily moving in the softened base material from the adhesive portion (surface portion) 2a1 of the first sealing material 2a toward the inner layer side 2a2. Therefore, it may be difficult to obtain the effect of adding the isocyanurate component to the first sealing material 2a.

Therefore, in order to utilize the advantages of the isocyanurate component while reducing its disadvantages, it is important to intentionally arrange the distribution of the isocyanurate component in the first sealing material 2a in a region that is useful for reducing deterioration of the adhesive strength. Therefore, in the solar cell module X, a large number of crosslinked structures of the isocyanurate component are arranged in the adhesive portion (surface layer portion) 2a1 of the first sealing material 2a near the adhesive interface 10 between the light-transmitting substrate 1 and the first sealing material 2a, thereby reducing deterioration of the adhesive strength between the light-transmitting substrate 1 and the first sealing material 2a.

Specifically, by utilizing the property of the (meth)acrylate component, which is the third additive, crosslinking at a lower temperature than the isocyanurate component, which is the second additive, it is possible to induce the crosslinked structure of the isocyanurate component, which is the second additive, to be formed more in the adhesive portion (surface portion) 2a1 that contacts the adhesive interface 10. Since the (meth)acrylate component, which is the third additive, has the property of crosslinking at a lower temperature than the isocyanurate component, which is the second additive, when the solar cell module X is heated in the crosslinking process, the (meth)acrylate component polymerizes at an earlier timing than the isocyanurate component to form a crosslinked network structure.

On the other hand, the isocyanurate component has the property of causing crosslinking shrinkage during crosslinking. Therefore, if there is no factor that inhibits the movement of the isocyanurate component in the first sealing material 2a, the isocyanurate component will move from the adhesive portion (surface layer) 2a1 side of the first sealing material 2a to the inner layer portion 2a2 side during crosslinking. However, as described above, the (meth)acrylate component crosslinks before the isocyanurate component to form a crosslinked network structure. Therefore, if the crosslinked network structure formed by the (meth)acrylate component is formed sufficiently densely in advance in the first sealing material 2a, the possibility of the crosslinked network structure of the (meth)acrylate component moving due to the crosslinking shrinkage of the isocyanurate component can be reduced.

As a result, the isocyanurate component remains in large amounts in the adhesive portion (surface portion) 2a1 that contacts the adhesive interface 10, and crosslinks when the temperature is subsequently increased, forming a high-density crosslinked structure in the adhesive portion (surface portion) 2a1 that contacts the adhesive interface 10 between the light-transmitting substrate 1 and the first sealing material 2a.

As a result, a crosslinked network structure of many isocyanurate components can be formed in the adhesive portion (surface portion) 2a1 that contacts the adhesive interface 10 between the light-transmitting substrate 1 and the first sealing material 2a without adding an excessive amount of the isocyanurate component, which is rigid and highly brittle, to the first sealing material 2a, thereby achieving the effect of reducing the penetration of moisture into the first sealing material 2a.

However, if the amount of (meth)acrylate component is insufficient, it is not possible to form a crosslinked structure of a sufficient amount of isocyanurate component near the interface with the glass, but conversely, if the amount of (meth)acrylate component is excessive, the (meth)acrylate component becomes saturated and cannot dissolve in the base material, making it difficult to mold the first sealing material 2a into a sheet. For this reason, it is important to add an amount of (meth)acrylate component that is not saturated and that allows the isocyanurate component to be placed in the desired position during the heating process during crosslinking. Note that the above explanation was given using the example between the translucent substrate 1 and the first sealing material 2a, but the same can be said for the relationship between the second sealing material 2b and the back surface protection material 4.

In addition, the above description has focused on the hydroxide ions that are generated when a metal hydroxide is used as the first additive, but the effects of the present invention can also be obtained favorably when a metal oxide or carbonate is used as the first additive, since the intrusion of water into the sealing material 2 can be suppressed.

The present disclosure will be explained using examples. The present disclosure is not limited to the following examples.

Example 1
The solar cell module X of Example 1 was manufactured by the above-mentioned method using the following members (1) to (6).
(1) Light-transmitting substrate 1: White tempered glass (2) Sealing material 2
(2.1) Base of encapsulant: Ethylene-vinyl acetate copolymer 100 parts by weight (2.2) First additive of encapsulant: Magnesium hydroxide 0.1 parts by weight (2.3) Second additive of encapsulant: Triallyl isocyanurate 2 parts by weight (2.4) Third additive of encapsulant: Trimethylolpropane tri(meth)acrylate 0.32 parts by weight (3) Solar cell: Crystalline silicon solar cell (4) Back surface protective material: Polyethylene terephthalate resin film (5) Interconnector: Solder-coated copper foil (6) Connection wiring: Solder-coated copper foil

(Examples 2, 3, 4, 5, 6, 7 and Comparative Example 1)
Solar cell modules X of Examples 2, 3, 4, 5, 6, 7, and Comparative Example 1 were manufactured in the same manner as in Example 1, except that the amounts of the second additive and the third additive in the encapsulant 2 were blended as shown in Table 1. The solar cell modules X manufactured in each Example and Comparative Example 1 were evaluated as follows, and the results are shown in Tables 2 and 3.

<Accelerated test method>
For each of the examples and Comparative Example 1, in order to reproduce a solar cell module X equivalent to a state in which it is used in a hot and humid natural environment and deteriorates over time, an accelerated test was performed in which high temperature and high humidity stress was applied to the solar cell module X. Specifically, the accelerated test was performed by changing the stress conditions to a more severe level (temperature 95°C, relative humidity 95%) with reference to the moisture resistance test (temperature 85°C, relative humidity 85%) of JIS-C-8917 (environmental test method and durability test method for crystalline solar cell module). The time for which the solar cell module X was put into the accelerated test was set to four types, 0 hours, 50 hours, 100 hours, and 200 hours, in consideration of the state of the solar cell module actually installed in a natural environment.

<Method for evaluating the rate of adhesion strength retention>
Next, a method for evaluating the adhesive strength of the sealing material 2 to the light-transmitting substrate 1 after the accelerated test will be described. First, a method for preparing a sample will be described. Using a cutter knife or the like, an incision is made from the rear surface protective material 4 side of the solar cell module X to a depth that reaches the light-transmitting substrate 1. With the sealing material 2 adhered to the light-transmitting substrate 1, a strip of the sealing material 2 is cut out with a sample width of 10 mm. Next, a part of the sealing material 2 at one end side of the slice is peeled off from the light-transmitting substrate 1 and processed to become a gripping margin for a jig of a tensile tester, thereby preparing a sample.

Next, the method of measuring the adhesive strength will be described. Using a tensile tester (Tensilon universal testing machine) under conditions of a sample width of 10 mm, a peel angle of 90 degrees (T-shaped peel), and a peel speed of 10 mm/min, a chart of the load change was taken, and the maximum value (maximum adhesive strength) on the chart was read. Then, in order to express the adhesive strength maintenance rate for each Example and Comparative Example 1, the initial maximum adhesive strength of Comparative Example 1 and each Example, and the maximum adhesive strength after 50 hours, 100 hours, and 200 hours of accelerated testing in Comparative Example 1 and each Example were divided by the initial maximum adhesive strength of Comparative Example 1 to normalize and obtain the adhesive strength maintenance rate. Note that, in the above, the initial value of the maximum adhesive strength means the maximum adhesive strength when the accelerated test is started for 0 hours, i.e., before the accelerated test is started.

<Method for evaluating encapsulant properties>
Evaluation method 1. Method for evaluating the concentration distribution of isocyanurate component For the first sealing material 2a of the solar cell module X produced in each Example and Comparative Example 1, the ratio of the concentration of the isocyanurate component within a range of up to 50 μm away from the adhesive interface 10 with the light-transmitting substrate 1 to the concentration of the isocyanurate component within a range of 200 to 300 μm away from the adhesive interface 10 was calculated by the following method. Hereinafter, the portion of the first sealing material 2a within a range of up to 50 μm away from the adhesive interface 10 between the light-transmitting substrate 1 and the first sealing material 2a will also be referred to as a surface layer portion 2a1, and the portion of the first sealing material 2a within a range of 200 to 300 μm away from the adhesive interface 10 will also be referred to as an inner layer portion 2a2.

We will explain how to prepare the samples.

First, the solar cell module X is disassembled from the back surface protective material side 4 to expose the sealing material 2. For example, if the back surface protective material 4 is a resin sheet, it may be cut open, and if the back surface protective material 4 is glass, it may be removed by crushing, etc. The adhesive portion 2a1 between the light-transmitting substrate 1 and the first sealing material 2a is peeled off from the light-transmitting substrate 1 and sampled. One example of a sampling method is to process the sealing material 2 into thin slices using a blade as a sample. Other cross-sectional sample preparation devices such as a microtome, an FIB device (focused ion beam device), or a CP device (cross-section polisher device) may also be used. The method of preparing the sample is not limited to the method of preparing it from the disassembled solar cell module X, and may be prepared, for example, by the same method as the above-mentioned cross-sectional processing method after the light-transmitting substrate 1, sealing material 2, solar cell 3, and back surface protective material 4 obtained as members are subjected to the above-mentioned lamination process and cross-linking process. At this time, the solar cell 3 may be omitted. In addition, a film material with release properties may be used instead of the back surface protective material 4.

Next, we will explain how to evaluate the concentration distribution of isocyanurate components.

The index relating to the concentration of the isocyanurate component, which is the second additive, can be obtained by measuring with an ATR method (attenuated total reflection measurement method) using an FT-IR device (Fourier transform infrared spectrophotometer). Specifically, imaging measurement is performed with the FT-IR device on a cross section in a direction perpendicular to the main surface (the surface in contact with the light-transmitting substrate 1) of the first sealing material 2a. At this time, if the measurement range is too narrow, the measured values are likely to vary, so it is preferable to measure a cross section having a width of 400 μm or more in a direction parallel to the main surface of the first sealing material 2a.

The measurement conditions are as follows:

Light source: Special ceramics Detector: Two-dimensional detector Purge: Nitrogen gas Detection pixel size: 8 μm/pixel Resolution: 4 cm ^-1
Measurement wavelength range: 3900 cm ^-1 to 750 cm ^-1
Number of integration times: 16 times As a result of measurement using an FT-IR device, it is possible to obtain an imaging image showing a signal intensity proportional to the density of the isocyanurate component, as shown in Figure 6. In Figure 6, the strength of the signal intensity is represented by the density of black dots. In addition, the light-transmitting substrate shown in Figure 1 is removed during FT-IR measurement.

In addition, in the measurement by the FT-IR device, a prism is pressed against the sample, but since the state of contact between the prism and the sample affects the measured value of the peak intensity, and the measured value itself (absolute value) contains errors, the measured value was properly standardized for evaluation. In other words, the peak at a wavelength of about 1690 cm -1, which is thought to be derived from the isocyanurate component, the second additive, was set as the peak of interest, and the peak at a wavelength of about 1370 cm ^-1 , which is attributable to the CH bending vibration of the ethylene-vinyl ^acetate copolymer, the main agent, was set as the reference peak for standardization for evaluation.

Specifically, for the surface layer portion 2a1, a first peak area value derived from the isocyanurate component (near 1690 cm ^-1 ) and a second peak area value derived from the CH group of the ethylene-vinyl acetate copolymer (near 1370 cm ^- 1) are derived. Then, the first peak area value is divided by the second peak area value to calculate a first peak area ratio (first value) that evaluates the peak area of the isocyanurate component on the surface layer side. The first peak area ratio is proportional to the abundance ratio of the isocyanurate component in the sealing material surface layer portion 2a1.

In the same manner, the third peak area value derived from isocyanurate (near 1690 cm ^-1 ) and the fourth peak area value derived from EVA CH group (near 1370 cm ^-1 ) are derived for the inner layer portion 2a2. The third peak area value is then divided by the fourth peak area value to calculate a second peak area ratio (second value) that evaluates the peak area of the isocyanurate component on the inner layer side. The second peak area ratio is proportional to the proportion of the isocyanurate component in the encapsulant inner layer portion 2a2.

Then, the intensity ratio between the surface layer 2a2 and the inner layer 2a2, which represents the concentration distribution (concentration ratio) of the isocyanurate component in the surface layer 2a1 and the inner layer 2a2, was calculated by dividing the first peak area ratio by the second peak area ratio.

The peak area was calculated by integrating the area enclosed by the baseline and the peak for the IR spectrum obtained by measurement using an FT-IR device.

More specifically, the area values of the first peak and the third peak derived from the isocyanurate component (near 1690 cm ^-1 ) were obtained by integrating the area surrounded by the baseline and the peak derived from the isocyanurate component, which is a line connecting the left end of the waveform of the isocyanurate component at wavenumber 1713 cm ^-1 and the right end at wavenumber 1671 ^cm -1.

Next, the area values of the second peak and the fourth peak derived from the CH group of the ethylene-vinyl acetate copolymer (near 1370 cm ^{- 1} ) were determined by integrating the region surrounded by the baseline and the peak derived from the CH group of the ethylene-vinyl acetate copolymer, with the line connecting the left end of the waveform derived from the CH group of the ethylene-vinyl acetate copolymer wave number 1394 cm ^-1 and the right end of the waveform derived from the CH group of the ethylene-vinyl acetate copolymer being the baseline. The results of the measurement by the above "Evaluation method 1. Method for evaluating the concentration distribution of the isocyanurate component" are shown in the column of 1st value/2nd value in Table 2.

Evaluation Method 2. Measurement of Mechanical Properties For the first encapsulant 2a of the solar cell modules X produced in each Example and Comparative Example, the storage modulus was measured by the following method in order to evaluate the difference in the mechanical properties of the encapsulant, which correlates with the difference in the ease of deterioration of the peel strength.

First, we will explain how to prepare the samples.

The solar cell module X is cut into pieces measuring approximately 10 mm x 10 mm using a cutting tool such as a blade or grinder. Next, the cross section is processed using a Cryo-CP (Cross Section Polisher) to create a sample.

The method of preparing the sample is not limited to the method of preparing it from a disassembled solar cell module X. For example, the translucent substrate 1, the sealing material 2, the solar cell 3, and the back surface protection material 4 obtained as components may be processed to a size of about 10 mm x 10 mm after undergoing the lamination process and cross-linking process described above, and then the sample may be prepared in the same manner as the cross-sectional processing described above.

Next, we will explain the measurement method.

The storage modulus can be obtained by measuring the cross section of the above-mentioned sample using the nanoindentation method, for example, using a nanoindenter device such as the one described below.

The measurement conditions are as follows:

Indenter used: Berkovich (triangular pyramid type)
Measurement method: Dynamic measurement Measurement temperature: Room temperature (20-25°C)
Indentation depth setting: approx. 900-1000 nm
Frequency: 100Hz
Sample size: 10 mm x 10 mm
The measured value of the storage modulus was taken by taking the same measurement five or more times at different positions in a section 200 μm from the adhesive interface 10 in the inner layer portion 2 a 2 toward the solar cell 3 and averaging the measurements.

The results of the measurements made using the above "Evaluation method 2. Mechanical property measurements" are shown in the storage modulus column of Table 2.

Evaluation method 3. Loss factor measurement For the first encapsulant 2a of the solar cell module X produced in each Example and Comparative Example, the loss factor was measured by the following method in order to evaluate the difference in mechanical properties of the encapsulant, which correlates with the difference in the ease of deterioration of the peel strength.

First, the method for preparing the sample is the same as in 1. Mechanical property measurement.

The solar cell module X is cut into pieces measuring approximately 10 mm x 10 mm using a cutting tool such as a blade or grinder. Next, the cross section is processed using a Cryo-CP (Cross Section Polisher) to create a sample.

The method of preparing the sample is not limited to the method of preparing it from a disassembled solar cell module X. For example, the translucent substrate 1, the sealing material 2, the solar cell 3, and the back surface protection material 4 obtained as components may be processed to a size of about 10 mm x 10 mm after undergoing the lamination process and cross-linking process described above, and then the sample may be prepared in the same manner as the cross-sectional processing described above.

The measurement method is the same as Evaluation Method 2: Mechanical property measurement.

The loss factor can be obtained by measuring the cross section of the above-mentioned sample using the nanoindentation method, for example, using a nanoindenter device such as the one shown below.

The measurement conditions are as follows:

Indenter used: Berkovich (triangular pyramid type)
Measurement method: Dynamic measurement Measurement temperature: Room temperature (20-25°C)
Indentation depth setting: approx. 900-1000 nm
Frequency: 100Hz
Sample size: 10 mm x 10 mm
The loss factor was measured by taking the same measurement five or more times at different positions over a 200 μm area from adhesive interface 10 included in inner layer portion 2 a 2 closer to solar cell 3 and averaging the measurements.

The results of the measurement in the above "Evaluation method 3. Loss factor measurement" are shown in the loss factor column of Table 2.

Evaluation Method 4: Relaxation Time Measurement For the first sealing material 2a of the solar cell modules X produced in Example 2 and Comparative Example 1, relaxation time was measured by the following method in order to evaluate the difference in the crosslinked structure in the first sealing material 2a, which correlates with the difference in the ease of deterioration of the peel strength.

First, we will explain how to prepare the samples.

Using a cutting tool such as a blade or grinder, a piece of the first sealing material 2a was cut out from the solar cell module X. The piece of the first sealing material 2a was then filled into a tube with a diameter of about 10 mm for a measuring device to prepare a sample.

Next, we will explain the measurement method.

The relaxation time is obtained as the _T2 relaxation time by analyzing the decay curve measured by the CPMG method using, for example, a TD-NMR (pulse nuclear magnetic resonance) apparatus as described below for the above sample. The measurement conditions are as follows.

Measurement method: CPMG method ( _T2 )
Measurement nuclear frequency: 19.95 MHz ( ^1H nuclear)
Pulse width: Comparative Example 1 2.34 μsec (90° pulse)
Example 2 2.18 μsec (90° pulse)
Pulse repetition time: 4 sec
Temperature: 150°C
Measurements were performed after the sample was allowed to stabilize by placing it in the instrument's probe for 20 minutes.

The amount of crosslinked structures in the first sealing material 2a can be evaluated by the _T2 relaxation time obtained by analyzing the attenuation curve obtained as a result of the measurement. For example, the shorter the _T2 relaxation time in the sample, the lower the molecular mobility in the sample. And the lower the molecular mobility in the sample, the more crosslinked structures there are in the sample, i.e., the higher the crosslink density.

In extracting the _T2 relaxation time from the decay curve, which is the measurement result, a waveform separation analysis method was applied, which assumes three components with different relaxation times, and the relaxation times for each of the three components and the abundance ratios of the three components were obtained.

The results of the measurements made using the above "Evaluation method 4. Relaxation time measurement" are shown in Table 3.

<Adhesive strength evaluation results>
Comparative Example 1, Example 1, Example 2, and Example 3 in Table 2 show the results when the amount of the second additive was kept constant at 2 parts by weight, and the amount of the third additive was changed.
In Examples 6 and 7, the amount of the third additive was kept constant at 0.64 parts by weight, and the amount of the second additive was varied.

As shown in Table 2, Comparative Example 1 is a solar cell module in which the strength ratio of the surface layer 2a1 to the inner layer 2a2, which represents the concentration of the second additive (isocyanurate component) in the surface layer 2a1 and the inner layer 2a2 in the sealing material 2, is less than 0.95. The initial value of the maximum adhesive strength of each example is significantly higher than the initial value of the adhesive strength of Comparative Example 1.

In Comparative Example 1, the adhesive strength maintenance rate after 50 hours, 100 hours, and 200 hours is lower than the adhesive strength maintenance rate of each of the Examples.

Next, each example is a solar cell module in which the strength ratio of the surface layer 2a1 to the inner layer 2a2, which indicates the concentration of the isocyanurate component in the surface layer 2a1 and the inner layer 2a2 in the sealing material 2, is 0.95 or more. In each of these examples, the adhesion strength retention rate was 0.637 or more after 50 hours, 0.252 or more after 100 hours, and 0.053 or more after 200 hours, and it was found that the adhesion strength could be maintained at a higher level than in Comparative Example 1.

This makes it clear that a concentration distribution ratio of the isocyanurate component of 0.95 or more can significantly reduce the deterioration of adhesive strength.

In addition, it was found that when the deterioration of adhesive strength can be reduced, the strength ratio (first value/second value) of the surface layer 2a1 and the inner layer 2a2 of the isocyanurate component as the second additive falls within the range of at least 0.95 to 1.1.

Comparing Example 7 with Examples 1 to 6, the strength ratio of the surface layer 2a1 to the inner layer 2a2 in Example 7 is 0.95 or more, but the maintenance rate of the adhesive strength after 50 hours, 100 hours, and 200 hours is less than half that of Examples 1 to 6. This is because the storage modulus exceeds the appropriate range (does not fall within 0.036 GPa or less). In other words, it is believed that the proportion of viscous components that make up the viscoelastic properties of the sealing material 2 has decreased, making it easier for large shear stresses to occur at the adhesive interface.

As shown in Table 2, when the loss factor was measured for the inner layer of Comparative Example 1 and each Example, it was found that the inner layer of Examples 1 to 6, which has a high adhesive strength retention rate, had a loss factor of less than 0.13.

Furthermore, when comparing Example 7 shown in Table 2 with Examples 1 to 6, it is clear that by setting the amount of the isocyanurate component, which is the second additive, to 2.5 parts by weight or less, the maintenance rate of adhesive strength can be further increased compared to when the amount of the second additive is set to a range of more than 2.5 parts by weight, as shown in Example 7.

Furthermore, as shown in Table 3, when the _T2 relaxation times based on the decay curves measured by the CMPG method using a TD-NMR apparatus (pulse nuclear magnetic resonance apparatus) for Comparative Example 1 and Example 2 were compared, the following became clear.

Although the details of the molecular structural attribution of components 1, 2, and 3 are unknown, a comparison between Example 2 and Comparative Example 1 revealed that, among the _T2 relaxation times of the three components, the _T2 relaxation time of component 1, which is the component with the highest abundance ratio, is shorter in Example 2.

Considering that the measurement environment (temperature conditions) is an environment in which the ethylene-vinyl acetate copolymer, which is the main agent before crosslinking, melts, this is considered to be due to the difference in the amount of the (meth)acrylate component added as the third additive. That is, it is considered that the _T2 relaxation time is shorter in Example 2 because the amount of the (meth)acrylate component added is greater than that in Comparative Example 1. A shorter _T2 relaxation time indicates lower molecular mobility. And lower molecular mobility indicates more crosslinked structures, i.e., higher crosslink density. From this, it is considered that Example 2 has more crosslinked structures of the (meth)acrylate component as the third additive than Comparative Example 1, i.e., has a higher crosslink density.

Similarly, in Examples 1, 3, 4, 5, and 6, the amount of the (meth)acrylate component added as the second additive is greater than in Comparative Example 1, and therefore it is believed that the crosslinked structure of the (meth)acrylate component is greater than in Comparative Example 1. For this reason, it is presumed that the _T2 relaxation time of component 1 in Examples 1, 3, 4, 5, and 6 is less than 2.08 [msec], which is the _T2 relaxation time of component 1 in Comparative Example 1, similar to Example 2.

In other words, for Example 1 and Examples 2 to 6, Component 1, which is the component with the highest abundance ratio among the three components based on the attenuation curves obtained by the CPMG method using a TD-NMR device,
The _T2 relaxation time of is estimated to be at least less than 2.08 msec.

X: solar cell module 1: light-transmitting substrate 2: sealing material 2a: first sealing material 2a1: adhesive portion (surface layer portion)
2a2: inner layer portion 2b: second sealing material 3: solar cell 4: back surface protective material 5: interconnector 6: connection wiring 7: terminal box 8: frame 9: module stack 10: adhesive interface 11: solar cell group 20: lamination device 21: housing 21a: lower housing 21b: upper housing 22: heating plate 23: diaphragm

Claims (7)

A solar cell;
An encapsulant positioned over the solar cell ;
a light-transmitting substrate located on the sealing material;
The sealing material has a base material, an acid acceptor as a first additive, and an isocyanurate component as a second additive,
a surface layer portion of the encapsulant near the light-transmitting substrate and an inner layer portion of the encapsulant away from the light-transmitting substrate are measured by FT-IR analysis, and a first value is calculated by dividing an area showing a peak derived from the second additive located in the surface layer portion by an area showing a peak derived from the main agent, and a second value is calculated by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more. A solar cell;
An encapsulant positioned over the solar cell ;
a light-transmitting substrate located on the sealing material;
The sealing material has a base material, a metal hydroxide as a first additive, and an isocyanurate component as a second additive,
a surface layer portion of the encapsulant near the light-transmitting substrate and an inner layer portion of the encapsulant away from the light-transmitting substrate are measured by FT-IR analysis, and a first value is calculated by dividing an area showing a peak derived from the second additive located in the surface layer portion by an area showing a peak derived from the main agent, and a second value is calculated by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more. A solar cell;
An encapsulant positioned over the solar cell ;
a light-transmitting substrate located on the sealing material;
The sealing material has a base material, a metal oxide as a first additive, and an isocyanurate component as a second additive,
a surface layer portion of the encapsulant near the light-transmitting substrate and an inner layer portion of the encapsulant away from the light-transmitting substrate are measured by FT-IR analysis, and a first value is calculated by dividing an area showing a peak derived from the second additive located in the surface layer portion by an area showing a peak derived from the main agent, and a second value is calculated by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more. A solar cell;
An encapsulant positioned over the solar cell ;
a light-transmitting substrate located on the sealing material;
The sealing material has a base material, a carbonate as a first additive, and an isocyanurate component as a second additive,
a surface layer portion of the encapsulant near the light-transmitting substrate and an inner layer portion of the encapsulant away from the light-transmitting substrate are measured by FT-IR analysis, and a first value is calculated by dividing an area showing a peak derived from the second additive located in the surface layer portion by an area showing a peak derived from the main agent, and a second value is calculated by dividing an area showing a peak derived from the second additive located in the inner layer portion by an area showing a peak derived from the main agent, and the value obtained by dividing the first value by the second value is 0.95 or more. 5. The solar cell module according to claim 1, wherein the sealing material has a storage modulus of 0.036 GPa or less. The solar cell module according to any one of claims 1 to 5, wherein the loss coefficient of the inner layer is less than 0.13. The solar cell module according to any one of claims 1 to 6, wherein when the concentration of the second additive is less than 2.5 parts by weight, the value obtained by dividing the first value by the second value is 0.95 or more and 1.1 or less.

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