JP7509249B2 - Current collector wire fixing film for solar cell module, and solar cell module using same - Google Patents

Description

The present invention relates to a collector wire fixing film for a solar cell module, and a method for manufacturing a solar cell module using the same. More specifically, the present invention relates to a collector wire fixing film used in a solar cell module in which solar cell elements are mounted using a multi-wire method, a solar cell module constructed using the same, and a method for manufacturing the same.

Conventionally, solar cell modules generally have a layer structure similar to that of solar cell module 1 shown in FIG. 1. That is, from the light-receiving surface side, a transparent front substrate 2, a light-receiving surface-side sealing material 31, a plurality of solar cell elements 4, a non-light-receiving surface-side sealing material 32, and a back surface protective sheet 5 are laminated in this order. Furthermore, for the plurality of solar cell elements 4, a conductor is usually connected to the front or back surface of each element to connect the plurality of adjacent solar cell elements and collect the electricity generated by each of these elements. Conventionally, a strip-shaped conductor with a width of about 2 mm to 5 mm, called a "bus bar," has generally been used as such a conductor arranged to electrically connect the solar cell elements.

Conductive wires that electrically connect multiple solar cell elements are an essential component in constructing a solar cell module. However, on the other hand, in the parts of the light-receiving surface of the solar cell element that are covered by these conductive wires, sunlight entering the solar cell element is physically blocked. Minimizing the resulting decrease in light utilization efficiency has come to be recognized as a pressing issue in the race to develop solar cells, where there is strict demand for improved power generation efficiency per unit area.

To solve these problems, a connection configuration between solar cell elements called "multi-wire connection" has begun to be adopted, in which a collector wire made of many thin wires with a diameter of about 100 μm to 200 μm and a nearly circular cross section is used as a conductor to electrically connect the solar cell elements, instead of the ribbon-shaped conductor (bus bar) mentioned above. This "multi-wire connection" is expected to see increased demand in the future as a technology that can improve the power generation efficiency of solar cell modules (see Patent Documents 1 and 2).

When electrically joining solar cell elements with a "multi-wire connection" using many thin wires (current collector wires), it is possible to fix each thin wire (current collector wire) to the solar cell element by soldering or the like. However, as shown in Figure 2, a structure in which many current collector wires 64 are embedded in a resin film ("current collector wire fixing film" 6A, 6B) and adjacent solar cell elements 4A, 4B are electrically connected by this resin film ("current collector wire fixing film") in which the current collector wires 64 are embedded is a more preferable connection structure, and is expected to become the mainstream connection structure for "multi-wire connections" in the future.

The solar cell module equipped with solar cell elements of the "multi-wire connection" type, which is carried out using a "current collector wire fixing film," is manufactured by joining multiple current collector wires 64 to the front or back of the solar cell elements 4A, 4B in a temporary attachment state (as shown in FIG. 7) to the current collector wire fixing films 6A, 6B, as shown in FIG. 2 and FIG. 3.

In the temporary attachment state between the current collector wire fixing film and the current collector wire, an appropriate wire holding force is required so that the current collector wire, which is made up of many thin wires, is stably held without falling off the film during the work before bonding to the solar cell element. However, if the current collector wire is embedded too deeply, the entire current collector wire will be embedded in the wire holding layer, which increases the risk of poor electrical conductivity between the electrode of the solar cell element.

International Publication No. 2004/021455 International Publication No. 2017/076735

The present invention was developed in consideration of the above situation, and aims to provide a "current collector wire fixing film for solar cell modules" that fixes the current collector wire to the solar cell element in a "multi-wire connection" type solar cell module, and that has an objective of providing a "current collector wire fixing film for solar cell modules" that exhibits an appropriate wire holding force while avoiding poor electrical conductivity caused by the entire current collector wire being buried in the wire holding layer.

The inventors discovered that the above problems could be solved by optimizing the complex viscosity of the wire retaining layer in which the current collector wire is embedded within a specific range in a "current collector wire fixing film for solar cell modules," and thus completed the present invention. Specifically, the present invention provides the following:

(1) A current collecting wire fixing film for a solar cell module, comprising a base material layer and a wire holding layer, the base material layer having a resin with a melting point of 200°C or more as a base resin, the wire holding layer having a polyethylene-based resin with a density of 0.870 g/ ^cm3 or more and 0.930 g/cm3 or ^less as a base resin, containing no silane component, and having a complex viscosity at 80°C of 9.0E+5 Pa s or more and 1.0E+7 Pa s or less and a complex viscosity at 160°C of 6.0E+3 Pa s or more and 5.0E+4 Pa s or less.

(2) The current collector wire fixing film according to (1), in which the melting point of the wire holding layer is 105°C or higher and 125°C or lower.

(3) The current collector wire fixing film according to (1) or (2), in which the thickness of the wire holding layer is 25 μm or more and 100 μm or less.

(4) A collector wire fixing film according to any one of (1) to (3), in which the thickness of the substrate layer is 10 μm or more and 25 μm or less.

(5) A solar cell module of a multi-wire connection type, comprising the collector wire fixing film according to any one of (1) to (4), the solar cell module comprising a plurality of solar cell elements, a plurality of collector wires joined to the surfaces of the solar cell elements, and the collector wire fixing film covering the plurality of collector wires and laminated on the surfaces of the solar cell elements.

(6) A method for manufacturing a solar cell module according to (5), comprising: a temporary attachment step of embedding the current collecting wires in the wire holding layer by heat-pressing the current collecting wire fixing film and the current collecting wires at a heating temperature of more than 150°C and less than 200°C; a temporary joining step of temporarily joining the current collecting wires to the solar cell element by heat-pressing the current collecting wire fixing film, which is temporarily attached to the current collecting wires, to the solar cell element at a heating temperature of 105°C or more and 160°C or less; and a module integration step of integrating the solar cell element to which the current collecting wires and the current collecting wire fixing film are temporarily joined and other components by vacuum thermal lamination, in which the thickness of the wire holding layer of the current collecting wire fixing film before the temporary attachment step is 25% or more and 50% or less of the diameter of the current collecting wires.

According to the present invention, it is possible to provide a "current collector wire fixing film for solar cell modules" that fixes the current collector wire to the solar cell element in a "multi-wire connection" type solar cell module, and that can provide an appropriate wire holding force while avoiding poor electrical conductivity caused by the entire current collector wire being buried in the wire holding layer.

FIG. 1 is a cross-sectional view illustrating a typical example of the layer structure of a solar cell module constructed using the current collector wire fixing film of the present invention. FIG. 1 is a perspective view illustrating a connection structure by "multi-wire connection" of solar cell elements electrically connected using the collector wire fixing film for a solar cell module of the present invention. FIG. 3 is a side view of the “multi-wire connection” connection structure of FIG. 2 . 2 is a partially enlarged cross-sectional view of the solar cell module of FIG. 1 , showing a schematic view of how the current collector wire is embedded in the current collector wire fixing film in the solar cell module. FIG. FIG. 2 is a cross-sectional view showing a schematic layer structure of the current collector wire fixing film of the present invention. 7 is a diagram for explaining an embodiment of temporary pressure bonding between the current collector wire fixing film and the current collector wire of the present invention. 6 is a diagram for explaining an embodiment of temporary pressure bonding between the current collector wire fixing film and the current collector wire of the present invention.

The collector wire fixing film of the present invention and the solar cell module using the same are described below. The present invention is not limited to the embodiments described below.

<Current collector wire fixing film>
As shown in FIG. 1 , the current collector wire fixing film 6 of the present invention is a resin film that constitutes the connection structure when a plurality of solar cell elements 4 in a solar cell module 1 are electrically connected to each other by a “multi-wire connection”.

As shown in Figures 2 and 3, the solar cell elements 4 in a "multi-wire connection" type solar cell module 1 are connected to each other by joining multiple current collector wires 64 to the front or back surface of the solar cell elements 4A, 4B while they are embedded in current collector wire fixing films 6A, 6B.

As shown in FIG. 4, in a "multi-wire connection" using the current collector wire fixing film 6, the current collector wire 64 joined to the solar cell element 4B is mostly embedded in the wire holding layer 63 of the current collector wire fixing film 6B, and at the same time, a part of it is exposed from the surface of the current collector wire fixing film 6B so that it can be electrically connected to the solar cell element 4B. Then, electrical connection between each current collector wire 64 and the solar cell element 4B is ensured in the exposed part.

As shown in FIG. 5, the current collector wire fixing film 6 of the present invention is a multilayer film including a base layer 61 that has heat resistance and functions as a substrate for fixing the current collector wire, and a wire holding layer 63 in which the current collector wire 64 is embedded. It is preferable that the base layer 61 and the wire holding layer 63 are bonded with sufficient adhesive strength by an adhesive layer 62.

The total thickness of the current collector wire fixing film 6 having the above layer structure is preferably 70 μm or more and 100 μm or less. Similarly, the thickness of the base material layer 61 is preferably 10 μm or more and 25 μm or less, and more preferably 10 μm or more and 15 μm or less. Similarly, the thickness of the wire holding layer 63 is preferably 25 μm or more and 100 μm or less, and more preferably 45 μm or more and 80 μm or less.

However, the above thickness ranges are based on the assumption that the diameter of the current collector wire 64 in a typical "multi-wire connection" structure is approximately 100 μm or more and 200 μm or less. Therefore, the thickness of the current collector wire fixing film 6 is not necessarily limited to the above thickness range. For example, the thickness of the wire holding layer 63 can be appropriately adjusted according to the diameter of the current collector wire 64 to be embedded, thereby providing the current collector wire fixing film with favorable wire holding performance.

When the current collecting wire 64 is embedded in the wire retaining layer 63 of the current collecting wire fixing film 6 by heat and pressure bonding, as shown in FIG. 7, the thickness of the wire retaining layer 63 increases compared to the state shown in FIG. 6 in accordance with the volume of resin pushed out by the current collecting wire 64. Taking this into account, the preferred thickness of the wire retaining layer 63 of the current collecting wire fixing film 6 in the initial state before use is 25% to 50% of the diameter of the current collecting wire 64 to be used.

The main feature of the current collector wire fixing film 6 having the above-mentioned layer structure is that it has excellent heat resistance and wire holding power that can stably hold the wire in a temporarily attached state while avoiding poor electrical conductivity of the current collector wire 64, by laminating a wire holding layer 63 having a complex viscosity adjusted to a predetermined range at a predetermined temperature to a base layer 61 having excellent heat resistance.

[Base layer]
The base resin of the substrate layer 61 of the current collector wire fixing film 6 is a thermoplastic resin having a melting point of 200° C. or more, preferably a melting point of 250° C. or more. Specific examples of such a thermoplastic resin having excellent heat resistance and usable as the base resin for forming the substrate layer 61 include polyethylene terephthalate (PET) (melting point: 255° C.) and polybutylene terephthalate (PBT) (melting point: 232° C.). Among the above thermoplastic resins, polyethylene terephthalate (PET) is preferably used as the base resin for forming the substrate layer 61 of the current collector wire fixing film 6, because it is a resin having particularly excellent heat resistance while maintaining good economic efficiency and ease of handling during production.

[Wire retention layer]
The wire holding layer 63 of the current collector wire fixing film 6 is formed from a resin composition having a polyethylene-based resin, which has excellent flexibility, as a base resin.

In addition, in the current collector wire fixing film 6, the wire holding layer 63 does not contain a silane component, which is widely used to improve the metal adhesion of various resin films. By optimizing the complex viscosity of the polyethylene resin used as the base resin, it is possible to achieve a desirable wire holding force without using, for example, relatively expensive silane-modified resins. Therefore, in this respect, the current collector wire fixing film 6 is a resin film material that is also highly economical.

In the current collector wire fixing film 6, the complex viscosity of the wire holding layer 63 is optimized at 80°C and 160°C. In this specification, the complex viscosity (Pa·s) is the value measured using a rotational rheometer (MCR301 manufactured by Anton Paar) under the conditions of parallel plate geometry (diameter 8 mm), stress 0.5 N, strain 5%, angular velocity 0.1 (1/s), and heating rate 5°C/min.

The complex viscosity of the wire holding layer 63 at 160°C may be 6.0E+3 Pa·s or more and 5.0E+4 Pa·s or less, and the complex viscosity at 160°C is preferably 8.0E+3 Pa·s or more and 3.0E+4 Pa·s or less. By making the complex viscosity of the wire holding layer 63 at 160°C 6.0E+3 Pa·s or more, when the current collecting wire 64 is temporarily attached to the current collecting wire fixing film 6, the above-mentioned current failure caused by the entire current collecting wire 64 being buried in the wire holding layer 63 can be sufficiently avoided. On the other hand, by making the complex viscosity of the wire holding layer 63 at 160°C 5.0E+4 Pa·s or less, the wire holding layer 63 can exert a good wire holding force during the above-mentioned temporary attachment.

On the other hand, the complex viscosity of the wire holding layer 63 at 80°C may be 9.0E+5 Pa·s or more and 1.0E+7 Pa·s or less, and the complex viscosity is preferably 1.0E+6 Pa·s or more and 7.0E+6 Pa·s or less. By making the complex viscosity of the wire holding layer 63 at 80°C 9.0E+5 Pa·s or more, defects such as the wire moving or detaching during the heating process when the current collector wire fixing film 6 with the current collector wire 64 temporarily attached is heated and pressed to the solar cell element 4 can be prevented. On the other hand, by making the complex viscosity of the wire holding layer 63 at 80°C 1.0E+7 Pa·s or less, the stress load on the solar cell power generation element during the heating process and the cooling process can be reduced.

The temperature inside the solar cell module may reach as high as 80°C during operation in a high-temperature environment. By setting the complex viscosity of the wire holding layer 63 at 80°C to 9.0E+5 Pa·s or more as described above, it is possible to prevent the collector wire 64 from shifting out of position during operation in a high-temperature environment.

The melting point of the wire holding layer 63 is preferably 105°C or higher and 125°C or lower, and more preferably 105°C or higher and 120°C or lower. By making the melting point of the wire holding layer 63 105°C or higher, it is possible to sufficiently avoid the above-mentioned electrical conductivity failure caused by the entire current collecting wire 64 being buried in the wire holding layer 63 when the current collecting wire 64 is temporarily attached to the current collecting wire fixing film 6. On the other hand, by making the melting point of the wire holding layer 63 125°C or lower, it is possible to make the wire holding layer 63 exert a good wire holding force when the current collecting wire 64 is temporarily attached.

In this specification, the melting point of the material resin forming each resin layer refers to the melting point of each resin that can be obtained by measurement using differential scanning calorimetry (DSC). However, when there are multiple valley peaks in the DSC curve, the melting point indicated by the peak with the largest peak area is referred to as the melting point of the resin.

The Vicat softening point of the wire holding layer 63 is preferably 75°C or higher and 100°C or lower, and more preferably 75°C or higher and 90°C or lower. By making the Vicat softening point of the wire holding layer 63 75°C or higher, it is possible to prevent problems such as the wire moving or detaching during the heating process when the current collector wire fixing film 6 with the current collector wire 64 temporarily attached is heated and compressed to the solar cell element 4. On the other hand, by making the melting point of the wire holding layer 63 125°C or lower, it is possible to reduce the stress load on the solar cell power generation element during the heating process and the cooling process.

As described above, a polyethylene-based resin having a density of 0.870 g/cm 3 or more and 0.930 g/cm 3 or less, preferably 0.880 g/cm ³ or more and 0.920 g/cm ³ or less, can be used as a base resin for forming the wire holding layer ⁶³ having an optimized complex viscosity at a ^{predetermined} temperature. Here, the base resin refers to a resin having the largest content ratio among all the resin components in the resin layer, and the content ratio in the resin components is 50% by mass or more, preferably 90% by mass or more. The content ratio of each resin contained in each layer of the current collector wire fixing film 6 can be analyzed from the peak ratio detected by, for example, DSC (differential scanning calorimetry), IR (infrared spectroscopy), or NMR (nuclear magnetic resonance).

It is more preferable that 90% by mass or more and 100% by mass or less of the polyethylene resin forming the wire holding layer 63 is a polyethylene α-olefin copolymer having a density of 0.870 g/ ^cm3 or more and 0.910 g/cm3 or ^less . When 90% by mass or more of the polyethylene resin within the above density range forming the wire holding layer 63 is a polyethylene α-olefin copolymer, the adhesion between the base material layer 61 and the wire holding layer 63 is improved, and thus the durability of the current collecting wire fixing film 6, which is a film with a multilayer structure, is improved.

[Adhesive layer]
In the current collector wire fixing film 6, the base material layer 61 made of a resin with a high melting point that ensures sufficient heat resistance, and the wire holding layer 63 made of a resin with a moderate viscosity that can stably hold the current collector wire 64 in a temporarily attached state are preferably configured to be bonded with sufficient strength via the adhesive layer 62. In addition, the adhesive layer 62 is also required to be transparent. As an adhesive for forming such an adhesive layer 62, various known adhesives used in dry lamination processing of resin films, such as acrylic, polycarbonate, and phenolic adhesives, can be used. For example, in the case where the base material layer 61 is formed of polyethylene terephthalate and the wire holding layer 63 is formed of low-density polyethylene, a polycarbonate adhesive that can particularly easily strengthen the adhesive strength between layers while maintaining good transparency can be particularly preferably used.

[Method of manufacturing the current collector wire fixing film]
The current collector wire fixing film can be produced by a dry lamination method in which a resin film made of a resin composition that forms the base material layer and the wire holding layer is bonded with an adhesive.

In addition, when manufacturing the current collector wire fixing film, one example of a specific means for optimizing the complex viscosity of the wire holding layer 63 within each of the above-mentioned ranges is to select the material resin with attention to the molecular weight of polyethylene or the like used as the base resin for forming the wire holding layer 63. By increasing the molecular weight of the base resin for forming the wire holding layer 63, it is possible to increase the complex viscosity of the wire holding layer 63, and conversely, by decreasing the molecular weight of the same resin, it is possible to decrease the complex viscosity of the wire holding layer 63.

<Solar cell module>
The solar cell module of the present invention is a "multi-wire connection" type solar cell module 1 having the basic structure shown in Fig. 1. This solar cell module 1 is a solar cell module including a "multi-wire connection" structure in which each solar cell element is connected by a plurality of current collecting wires 64. A current collecting wire fixing film 6 is used to stably arrange and electrically connect these multiple current collecting wires 64 on the surface of each solar cell element. The form of formation of the "multi-wire connection" structure in which the current collecting wires 64 are covered by the current collecting wire fixing film 6 in four solar cell elements is as described above.

The light-receiving surface sealing material 31 and the non-light-receiving surface sealing material 32 constituting the "multi-wire connection" type solar cell module 1 are both resin sheets that mainly function to protect the solar cell elements 4 from external impacts. In particular, the light-receiving surface sealing material 31 is required to be a transparent sheet in order to transmit sunlight with a high transmittance. As these sealing materials 3 (31, 32), sealing material sheets with various olefin resins such as polyethylene and ethylene-vinyl acetate copolymer (EVA) as the base resin can be appropriately used. In order to increase the adhesion of the current collector wire fixing film 6 to the wire holding layer 63, sealing material sheets with polyethylene or EVA as the base resin can be appropriately selected according to the resin composition of each of these layers.

As the solar cell element 4, any solar cell element that can be used with "multi-wire connection", such as an amorphous silicon type or a crystalline silicon type, can be used without any particular limitations. For the transparent front substrate 2 and the back protective sheet 5, any conventionally known member for use in a solar cell module can be used without any particular limitations. In addition, the solar cell module of the present invention may further include members other than the above-mentioned members as necessary.

<Method of manufacturing solar cell module>
The solar cell module 1 including the "multi-wire connection" structure is preferably manufactured by a manufacturing method which sequentially performs a "temporary bonding process" in which a plurality of current collecting wires 64 and the current collecting wire fixing film 6 are temporarily bonded together by heating and pressing, a "temporary bonding process" in which the current collecting wire fixing film 6, which is temporarily bonded to the current collecting wires 64, is heated and pressed to a solar cell element 4 to temporarily bond the current collecting wires 64 to the solar cell element 4, and a "module integration process" in which the solar cell element 4 to which the current collecting wires 64 and the current collecting wire fixing film 6 are temporarily bonded is integrated with other components such as the transparent front substrate 2, the light-receiving surface side sealing material 31, the solar cell element 4, the non-light-receiving surface side sealing material 32, and the back protective sheet 5 by vacuum thermal lamination.

(Temporary attachment process)
In this process, the multiple current collecting wires 64 and the current collecting wire fixing film 6 are heated and pressed together at a heating temperature exceeding 150°C and less than 200°C, thereby embedding and temporarily fixing the current collecting wires 64 in the wire retaining layer 63 to form a temporary bond between the multiple current collecting wires 64 and the current collecting wire fixing film 6.

The reason for setting the heating temperature at a temperature exceeding 150°C is to maintain a high level of reliability for the solar cell module, which is expected to be used in a high-temperature environment. During operation of the solar cell, the temperature inside the module can reach a high temperature exceeding 100°C. Therefore, it is essential to use a resin material that can ensure sufficient heat resistance with a safety margin against such high-temperature environments, and as a result, it is essential that the heating temperature during heat processing is also at or above the above temperature. On the other hand, by setting the heating temperature below 200°C, it is possible to prevent the base material layer 61 from melting when heated.

The current collector wire fixing film 6, whose complex viscosity at 160°C is optimized within the above-mentioned range, can exert an appropriate wire holding force while avoiding the risk of poor electrical conductivity due to the entire current collector wire being buried in the wire holding layer when heat-pressed at the above-mentioned heating temperature (more than 150°C and less than 200°C), as the wire holding layer 63 properly wraps around the current collector wire 64. Note that the heating temperature here is synonymous with the maximum surface temperature reached on the side of the wire holding layer 63 of the current collector wire fixing film 6, which is the object to be heated.

It is preferable that the thickness of the wire holding layer 63 of the current collector wire fixing film 6 before the temporary bonding process is set to 25% to 50% of the diameter of the current collector wire 64 to be temporarily bonded. This allows the wire holding layer 63 to be more reliably and appropriately wrapped around the current collector wire 64 during temporary bonding under the above heating conditions.

(Current collecting wire joining process)
In this process, the collector wire fixing film 6 to which the collector wire 64 is temporarily attached is heated and pressed to the solar cell element 4 at a heating temperature of 105°C or higher and 160°C or lower while covering the wire with the film, thereby temporarily joining the collector wire 64 to the solar cell element.

The reason for setting the heating temperature at 105°C or higher is to maintain a high level of reliability for the solar cell module, which is expected to be used in high-temperature environments, as mentioned above. On the other hand, by setting the heating temperature at 160°C or lower, yellowing due to thermal degradation of the resin that makes up each layer when heated can be prevented.

(Module integration process)
In this step, the solar cell element to which the current collector wires and the current collector wire fixing film are temporarily joined is integrated with other components by vacuum thermal lamination.

When performing this vacuum thermal lamination process, the lamination temperature is preferably in the range of 130°C to 170°C. The lamination time is preferably in the range of 5 minutes to 30 minutes, and particularly preferably in the range of 8 minutes to 15 minutes. In this way, when the above layers are heat-pressed into an integral molded body, the resin that forms the wire holding layer 63 by heating further completely wraps around the current collector wire 64, which has a roughly circular cross section, without any gaps, and high adhesion is achieved between the current collector wire fixing film 6 and the current collector wire 64 in the integrated solar cell module, and the current collector wire 64 is supported in an extremely stable manner.

As shown below, the collector wire fixing films of the examples and comparative examples were created to verify the effects of the present invention.

<Creating a film for fixing current collecting wires>
The following resin materials were used to prepare current collector wire fixing films of Examples and Comparative Examples.

In all of the Examples and Comparative Examples, the resin film constituting the base layer was the "polyethylene terephthalate film" shown below, and the resin film constituting the wire holding layer was the "polyethylene films 1 to 9" shown below, which were used for each Example and Comparative Example.

"Polyethylene terephthalate film"
: Melting point 260°C, thickness 12 μm, product name "Lumirror (registered trademark) S10" (manufactured by Toray Industries, Inc.)

"Polyethylene film 1"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.919 g/cm ³ into a film having a thickness of 60 μm. Melting point: 110° C., Vicat softening point: 80° C. Used in Example 1.

"Polyethylene film 2"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.928 g/cm ³ into a film having a thickness of 60 μm. Melting point: 120° C., Vicat softening point: 80° C. Used in Example 2.

"Polyethylene film 3"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.914 g/cm ³ into a film having a thickness of 60 μm. Melting point: 107° C., Vicat softening point: 75° C. Used in Example 3.

"Polyethylene film 4"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.910 g/cm ³ into a film having a thickness of 60 μm. Melting point: 100° C., Vicat softening point: 68° C. Used in Example 4.

"Polyethylene film 5"
: A resin film obtained by forming a low-medium-density polyethylene (MDPE) having a density of 0.932 g/cm ³ into a film having a thickness of 60 μm. Melting point: 132° C., Vicat softening point: 85° C. Used in Example 5.

"Polyethylene film 6"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.918 g/cm ³ into a film having a thickness of 60 μm. Melting point: 100° C., Vicat softening point: 60° C. Used in Comparative Example 1.
"Polyethylene film 7"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.930 g/cm ³ into a film having a thickness of 60 μm. Melting point: 128° C., Vicat softening point: 92° C. Used in Comparative Example 2.
"Polyethylene film 8"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.920 g/cm ³ into a film having a thickness of 60 μm. Melting point: 105° C., Vicat softening point: 65° C. Used in Comparative Example 3.
"Polyethylene film 9"
: A resin film obtained by forming a metallocene-based linear low density polyethylene (M-LLDPE) having a density of 0.922 g/cm ³ into a film having a thickness of 60 μm. Melting point: 105° C., Vicat softening point: 75° C. Used in Comparative Example 4.

The above-mentioned "polyethylene terephthalate film" and any one of "polyethylene films 1 to 9" were bonded by a dry lamination method using a polycarbonate-based adhesive to obtain a multilayer resin film, which was used as the collector wire fixing film for each of the examples and comparative examples.

For each collector wire fixing film, the total thickness of all layers and each layer was 76 μm, including the thickness of the base layer (12 μm), the thickness of the wire holding layer (60 μm), and the thickness of the adhesive layer between the two films (4 μm).

<Test example: complex viscosity>
For each of the above-mentioned polyethylene films used to form the wire retaining layer of each of the current collector wire fixing films in the Examples and Comparative Examples, the complex viscosity at 80°C and 160°C was measured by the method described below. The measurement results were taken as the complex viscosities at 80°C and 160°C of the wire retaining layer of each current collector wire fixing film, and the results are shown in Table 1.
[Complex viscosity test method]
The complex viscosity was measured using a rotational rheometer (MCR301 manufactured by Anton Paar) under the conditions of parallel plate geometry (diameter 8 mm), stress 0.5 N, strain 5%, angular velocity 0.1 (1/s), and heating rate 5° C./min.

Evaluation Example 1: Wire Retention Force
For each of the current collector wire fixing films of the Examples and Comparative Examples, the wire retention force was measured by the following test method and evaluated based on the following evaluation criteria.

[Creating a sample for evaluating wire retention strength]
A "sample for evaluating wire retention strength" was prepared by placing a current collecting wire fixing film (the current collecting wire fixing film of each Example and Comparative Example) on a current collecting wire (nine wires with a diameter of 250 μm arranged at 15 mm intervals) on a hot plate at a temperature of 160° C. and temporarily bonding them by applying a pressure of 100 kPa.

[Wire retention test]
For each of the above wire retention evaluation samples, a "180-degree peel test" was conducted using a peel tester (Tensilon universal testing machine RTF-1150-H) by pulling the tip of each of the nine current collecting wires whose tip portions had been peeled off from the current collecting wire fixing film. The test results were evaluated for initial adhesion according to the following evaluation criteria. The evaluation results are shown in Table 1 as "initial adhesion". The test conditions for the "180-degree peel test" were room temperature and a peel speed of 50 mm/min.
(Evaluation criteria)
A: 5N/15mm or more B: 2N/15mm or more and less than 5N/15mm C: less than 2N/15mm <Evaluation Example 2: Electrical Conduction Stability>
The current-carrying stability of each of the current-collector-wire fixing films of the Examples and Comparative Examples was measured by the following test method and evaluated based on the following evaluation criteria.

[Preparation of sample for evaluating current stability]
A solar cell element was mounted using each of the "wire retention evaluation samples" of the Examples and Comparative Examples, which are laminates in which current collecting wires (nine wires with a diameter of 250 μm arranged at intervals of 15 mm) were temporarily attached to a current collecting wire fixing film (current collecting wire fixing film of each Example and Comparative Example), and the following materials, and integrated by vacuum lamination under the following lamination conditions to prepare a "sample for evaluating current flow stability." The module layer configuration was as shown in Figures 1 and 2.
Transparent front substrate (blue plate glass, 180mm x 180mm, thickness 3.2m)
Light receiving surface side sealing material (low density polyethylene film with density of 0.985 g/ ^cm3 , thickness of 450 μm)
Wire retention strength evaluation sample ("Wire retention strength evaluation sample" for each Example and Comparative Example)
One solar cell element (PVG Solutions solar cell element (Earth ON-194)) was placed. Non-light-receiving surface sealing material (low-density polyethylene film with a density of 0.985 g/ ^cm3 and a thickness of 450 μm)
Back protective sheet (polyethylene terephthalate (PET) film, thickness 188 μm)
Vacuum lamination conditions: (a) Vacuum drawing: 5.0 minutes (b) Pressure (0 kPa to 70 kPa): 1.5 minutes (c) Pressure retention (70 kPa): 10.0 minutes (d) Temperature 150° C.

[Electrical stability test]
An EL (electroluminescence) test was conducted on each of the above-mentioned samples for evaluating electrical stability. The EL (electroluminescence) test is a test in which an electric field is applied to a solar cell element, and electrons and holes that have entered the semiconductor are recombined to emit light, and the light is photographed and analyzed to check for cracks in the cell, disconnections or poor connections in the interconnector, etc.
(Evaluation criteria)
A: The entire surface is strongly illuminated and electricity is confirmed. B: There are areas other than the wire where the light is weak. C: Some areas are not illuminating and electricity is not flowing.

As can be seen from the results in Table 1, it is important for the wire retention of the collector wire fixing film that the complex viscosity at 160°C is within a specific range, but as can be seen from the results of Comparative Example 4, even if the complex viscosity at 160°C is optimized to impart sufficient wire retention, if the complex viscosity at 80°C is too low, as described above, the wire is likely to shift in position during the heating process, resulting in insufficient electrical stability. On the other hand, the results of Comparative Example 3 show that even if the complex viscosity at 80°C is optimized, if the complex viscosity at 160°C is too low, electrical stability cannot be maintained well.

From the above test and evaluation results, it has been confirmed that the current collector wire fixing film of the present invention is a "current collector wire fixing film for solar cell modules" that fixes current collector wires to solar cell elements in "multi-wire connection" type solar cell modules, and is a multi-layer film in which heat resistance is provided by polyethylene terephthalate resin, which has excellent heat resistance, and the wire holding layer is provided by a polyethylene-based resin that is flexible and can contribute to improving molding properties, and further, that the long-term adhesion durability to current collector wires, etc. has been sufficiently improved.

REFERENCE SIGNS LIST 1 Solar cell module 2 Transparent front substrate 3 Sealant 31 Light-receiving surface side sealing material 32 Non-light-receiving surface side sealing material 4 Solar cell element 5 Back surface protective sheet 6 Current collector wire fixing film 61 Base layer 62 Adhesive layer 63 Wire holding layer 64 Current collector wire

Claims (6)

A collector wire fixing film for a solar cell module, comprising:
A base layer;
a wire retention layer;
The base layer has a thermoplastic resin having a melting point of 200° C. or more as a base resin,
The wire retaining layer has a polyethylene resin having a density of 0.870 g/ ^cm3 or more and 0.930 g/ ^cm3 or less as a base resin, and does not contain a silane component,
The complex viscosity at 80°C is 4.0E+6 Pa s or more and 7.0E+6 Pa s or less,
The complex viscosity at 160 ° C. is 8.0E + 3 Pa s or more and 3.0E + 4 Pa s or less.
Current collector wire fixing film. The melting point of the wire holding layer is 105°C or more and 125°C or less.
The current collector wire fixing film according to claim 1 . The thickness of the wire holding layer is 25 μm or more and 100 μm or less.
The current collector wire fixing film according to claim 1 or 2. The thickness of the base layer is 10 μm or more and 25 μm or less.
The current collector wire fixing film according to claim 1 . A solar cell module of a multi-wire connection type comprising the current collector wire fixing film according to any one of claims 1 to 4,
A plurality of solar cell elements;
A plurality of current collecting wires joined to a surface of the solar cell element;
the current collecting wire fixing film covering the plurality of current collecting wires and laminated on the surface of the solar cell element,
Solar cell module. The solar cell elements are connected by a laminate in which a part of the current collector wire is embedded in the current collector wire fixing film.
The solar cell module according to claim 5 .

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