JP2023178632A - Resin film for power collection sheet, power collection sheet, solar battery element with power collection sheet, and solar battery - Google Patents

Abstract

To provide a resin film for a power collection sheet that has an excellent adhesion property to a wire, an excellent embeddability of a wire, and an excellent thermal dimension stability, and to provide a power collection sheet, a solar battery element with a power collection sheet, and a solar battery that include the resin film.SOLUTION: Provided is a resin film for a power collection sheet that is used for a power collection sheet of a solar battery and that has a base material layer, an adhesive layer, and a polyethylene resin layer in this order. The base material layer contains a polyethylene terephthalate resin. A melt mass flow rate at 190°C of the polyethylene resin layer is 4 g/10 min to 8 g/10 min. A thermal shrinkage at the time when held for 10 minutes at 150°C is equal to or less than 2.0%.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a film for a current collector sheet, a current collector sheet, a solar cell element with a current collector sheet, and a solar cell.

In recent years, global warming caused by carbon dioxide has become a worldwide problem. In response to this problem, solar cells that utilize sunlight energy are attracting attention as an environmentally friendly and clean energy source, and active research and development is underway.

A solar cell is used, for example, in the form of a module in which a plurality of solar cell elements are connected. As a method of connecting solar cell elements to each other, for example, a method of connecting solar cell elements to each other using a strip-shaped conducting wire with a width of about 2 mm to 5 mm, which is called a buspar, has been conventionally used. In the case of the connection method using buspars, the problem is that sunlight is physically blocked in the area where the buspars are placed in the solar cell module, reducing the amount of sunlight incident on the solar electronic elements. be.

In contrast, in recent years, a method called multi-wire connection has begun to be adopted, in which solar cell elements are connected to each other using wires (thin conductive wires) having a diameter of approximately 150 μm or more and 300 μm or less, for example. In the multi-wire connection, a method for fixing the wires to the solar cell element is, for example, by embedding the wires in a thermofusible resin film to make a current collecting sheet, and then thermocompression bonding the current collecting sheet to the solar cell element. Examples include fixing methods (Patent Documents 1 and 2). The resin film used for the current collector sheet is also called a connecting film.

International Publication No. 2004/021455 International Publication No. 2017/076735 JP2020-174060A

In multi-wire connection, when wires are embedded in a heat-fusible resin film to form a current collector sheet, before thermocompression bonding the current collector sheet to the solar cell element, make sure that the wires do not come off the resin film. The wire needs to be stably held in the resin film. Furthermore, when thermocompression bonding the current collector sheet to the solar cell element, it is necessary for the resin film to wrap around the wire and fix the wire to the solar cell element. Therefore, the resin film of the current collector sheet used for multi-wire connections is required to have good adhesion to the wires and embeddability of the wires.

For example, in Patent Document 3, in a current collecting wire fixing film for a solar cell module having a base material layer and a wire holding layer, the entire wire is fixed by optimizing the complex viscosity of the wire holding layer to a specific range. A technique has been disclosed that can exert a suitable wire holding force while avoiding poor conduction due to being buried in the layer.

However, depending on the material of the wire, the adhesion of the resin film to the wire may not be sufficient, and there is still room for improvement.

In addition, in multi-wire connections, when the solar cell element with a current collector sheet and other components are integrated by thermocompression bonding to form a solar cell module, the resin film shrinks due to heat, and the wires are connected to the solar cell element. There is a problem that the position of the image may be shifted. When the wires are misaligned, electrical conduction between the solar cell element and the wires becomes insufficient, resulting in decreased reliability.

The present disclosure has been made in view of the above-mentioned circumstances, and provides a resin film for a current collector sheet that has excellent adhesion to wires, embedding of wires, and excellent thermal dimensional stability, and a current collector sheet using the same. The main purpose of the present invention is to provide a solar cell element with a current collecting sheet and a solar cell.

One embodiment of the present disclosure is a resin film for a current collector sheet used for a current collector sheet of a solar cell, which includes a base material layer, an adhesive layer, and a polyethylene resin layer in this order, The layer contains a polyethylene terephthalate resin, the melt mass flow rate (MFR) at 190°C of the polyethylene resin layer is 4 g/10 minutes or more and 8 g/10 minutes or less, and heat shrinkage when held at 150° C. for 10 minutes. Provided is a resin film for a current collector sheet having a ratio of 2.0% or less.

Another embodiment of the present disclosure is a current collector sheet used for a solar cell, which includes the above resin film for current collector sheet and the polyethylene resin layer disposed on the surface side of the polyethylene resin layer of the resin film for current collector sheet. A current collecting sheet having a wire is provided.

Another embodiment of the present disclosure is a current collector comprising the above-described current collector sheet and a solar cell element disposed on the surface side of the polyethylene resin layer of the current collector sheet and electrically connected to the wire. A solar cell element with a sheet is provided.

Another embodiment of the present disclosure provides a solar cell having a transparent substrate, a first encapsulant, the above-described solar cell element with a current collector sheet, a second encapsulant, and a counter substrate in this order. provide.

The resin film for a current collector sheet according to the present disclosure has excellent adhesion to wires, excellent wire embedding properties, and excellent thermal dimensional stability.

FIG. 1 is a schematic cross-sectional view illustrating a resin film for a current collector sheet in the present disclosure. FIG. 1 is a schematic plan view and a cross-sectional view illustrating a current collecting sheet according to the present disclosure. FIG. 1 is a schematic perspective view and a cross-sectional view illustrating a solar cell element with a current collector sheet according to the present disclosure. FIG. 1 is a schematic cross-sectional view illustrating a current collector sheet in the present disclosure. FIG. 1 is a schematic cross-sectional view illustrating a solar cell element with a current collector sheet according to the present disclosure. FIG. 1 is a schematic cross-sectional view illustrating a solar cell according to the present disclosure.

Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different ways, and should not be construed as being limited to the description of the embodiments exemplified below. Further, in order to make the explanation clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual form, but this is just an example and does not limit the interpretation of the present disclosure. It's not something you do. In addition, in this specification and each figure, the same elements as those described above with respect to the previously shown figures are denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

In this specification, when expressing a mode in which another member is placed on top of a certain member, when it is simply expressed as "above" or "below", unless otherwise specified, it means that the member is in contact with a certain member. This includes both cases in which another member is placed directly above or below a certain member, and cases in which another member is placed above or below a certain member via another member. In addition, in this specification, when expressing a mode in which another member is arranged on the surface of a certain member, when it is simply expressed as "on the surface" or "on the surface side", unless otherwise specified, This includes both a case in which another member is placed directly above or directly below a certain member, and a case in which another member is placed above or below a certain member via another member.

Further, in this specification, terms such as "film", "sheet", "substrate", etc. are not distinguished from each other based on the difference in designation.

Hereinafter, the resin film for a current collecting sheet, the current collecting sheet, the solar cell element with a current collecting sheet, and the solar cell in the present disclosure will be described in detail.

A. Resin film for current collector sheet The resin film for current collector sheet in the present disclosure is a resin film for current collector sheet used for a current collector sheet of a solar cell, and includes a base material layer, an adhesive layer, a polyethylene resin layer, in this order, the base layer contains a polyethylene terephthalate resin, the polyethylene resin layer has a melt mass flow rate (MFR) at 190°C of 4 g/10 minutes or more and 8 g/10 minutes or less, and 150°C The heat shrinkage rate when held for 10 minutes is 2.0% or less.

A resin film for a current collector sheet in the present disclosure will be explained using figures. FIG. 1 is a schematic cross-sectional view illustrating a resin film for a current collector sheet according to the present disclosure. As shown in FIG. 1, the resin film 10 for current collector sheet has a base material layer 1 containing polyethylene terephthalate resin, an adhesive layer 2, and a polyethylene resin layer 3 in this order. The melt mass flow rate (MFR) of the polyethylene resin layer 3 is within a predetermined range. Moreover, the heat shrinkage rate of the resin film 10 for current collector sheet when held at 150° C. for 10 minutes is below a predetermined value.

FIGS. 2A and 2B are a schematic plan view and a cross-sectional view illustrating a current collector sheet having a resin film for a current collector sheet according to the present disclosure. FIG. 2(b) is a cross-sectional view taken along the line AA in FIG. 2(a). As shown in FIGS. 2A and 2B, the current collector sheet 20 includes a resin film 10 for a current collector sheet, and a wire 11 disposed on the surface side of the polyethylene resin layer 3 of the resin film 10 for a current collector sheet. and has. In this way, the resin film 10 for current collector sheet is used to support the wire 11. Note that FIG. 2(a) shows a schematic plan view of the current collecting sheet viewed from the polyethylene resin layer side of the resin film for current collecting sheet.

FIGS. 3(a) to 3(c) are a schematic perspective view and a cross-sectional view illustrating a solar cell element with a current collecting sheet including a current collecting sheet having a resin film for a current collecting sheet according to the present disclosure. FIG. 3(b) is a cross-sectional view taken along line AA in FIG. 3(a), and FIG. 3(c) is a cross-sectional view taken along line BB in FIG. 3(a). As shown in FIGS. 3(a) to 3(c), the solar cell element 30 with a current collector sheet is arranged on the surface side of the current collector sheet 10 and the polyethylene resin layer 3 of the current collector sheet 10, and is connected to the wire 11 and It has a solar cell element 31 which is connected to the solar cell element 31. In this way, the resin film 10 for current collector sheet is used to fix the wire 11 electrically connected to the solar cell element 31. In addition, in FIGS. 3(a) to 3(c), the current collecting sheet 20 has two resin films 10 for current collecting sheets, and a solar cell element 31 is arranged on each resin film 10 for current collecting sheets. An example is shown.

In the present disclosure, the base layer contains polyethylene terephthalate resin. Here, the polyethylene terephthalate resin contained in the base material layer has a melting point of about 260° C. and has high heat resistance. Furthermore, polyethylene terephthalate resin provides good rigidity when molded into a film. Therefore, the base material layer containing the polyethylene terephthalate resin can impart rigidity to the resin film for the current collector sheet. Therefore, when manufacturing a solar cell element with a current collector sheet using a current collector sheet having a resin film for the current collector sheet, the wire is sufficiently pressed against the solar cell element by the resin film for the current collector sheet during thermocompression bonding. be able to. Further, in the present disclosure, since the MFR of the polyethylene resin layer is within a predetermined range, the adhesion of the polyethylene resin layer to the wire and the embeddability of the wire can be improved. Therefore, in the current collector sheet having the resin film for the current collector sheet, the wire can be well fixed to the solar electronic element by the resin film for the current collector sheet.

In addition, when a solar cell element with a current collector sheet is used in a solar cell, the wire can be well fixed to the solar electronic element by the resin film for the current collector sheet, resulting in a decrease in power generation efficiency due to poor adhesion of the wire. can be suppressed.

Furthermore, in a solar cell, when the MFR of the polyethylene resin layer is within a predetermined range, the adhesion of the polyethylene resin layer to the solar cell element can also be improved.

Furthermore, in the present disclosure, as described above, the resin film for a current collector sheet can have rigidity because the base layer contains a polyethylene terephthalate resin. Therefore, thermal shrinkage of the resin film for current collector sheet can be suppressed. Furthermore, as described above, by setting the MFR of the polyethylene resin layer within a predetermined range, it is possible to improve the adhesion of the polyethylene resin layer to the wire, the embeddability of the wire, and the adhesion to the solar cell element. Therefore, even if the thickness of the polyethylene resin layer is relatively thin, adhesion to the wire, embeddability of the wire, and adhesion to the solar cell element can be ensured. When the thickness of the polyethylene resin layer is thin, the thermal shrinkage of the resin film for the current collector sheet becomes small. Therefore, the fact that the MFR of the polyethylene resin layer is within a predetermined range can also contribute to suppressing thermal shrinkage of the resin film for current collector sheet. Furthermore, since the resin film for a current collector sheet in the present disclosure has a predetermined thermal shrinkage rate, thermal dimensional stability can be improved. Therefore, when manufacturing a solar cell element with a current collecting sheet using a current collecting sheet having a resin film for current collecting sheet, it is possible to suppress the positional shift of the wire with respect to the solar cell element during the heating process. Moreover, when manufacturing a solar cell using a solar cell element with a current collector sheet, it is possible to suppress misalignment of the wire with respect to the solar cell element during the heating process. Furthermore, even if the solar cell reaches a high temperature in the environment in which the solar cell is used, it is possible to suppress misalignment of the wire relative to the solar cell element. Therefore, the reliability of the solar cell can be improved.

In addition, since the resin film for a current collector sheet in the present disclosure has excellent thermal dimensional stability, it can be used when manufacturing a solar cell element with a current collector sheet using a current collector sheet having the resin film for a current collector sheet. When manufacturing a solar cell using a solar cell element with an electric sheet, thermal shrinkage of the resin film for the current collector sheet during the heating process can be suppressed, and curl deformation can be suppressed.

Hereinafter, each structure of the resin film for current collector sheet in the present disclosure will be explained.

I. Configuration of resin film for current collector sheet The resin film for current collector sheet in the present disclosure has a base material layer, an adhesive layer, and a polyethylene resin layer in this order.

1. Polyethylene Resin Layer The polyethylene resin layer in the present disclosure is a member that supports the wire when the resin film for current collector sheet is used as the current collector sheet.

(1) Characteristics of polyethylene resin layer The melt mass flow rate (MFR) of the polyethylene resin layer at 190°C is preferably 4 g/10 minutes or more and 8 g/10 minutes or less, and 6 g/10 minutes or more and 8 g/10 minutes. It is more preferable that it is below. When the MFR of the polyethylene resin layer is within the above range, the adhesion to the wire and the embeddability of the wire can be improved. In particular, when the MFR of the polyethylene resin layer is 6 g/10 minutes or more, the polyethylene resin layer can have excellent adhesion to the wire and excellent wire embedding properties, regardless of the material of the wire.

Note that the MFR of the polyethylene resin layer refers to the MFR of the polyethylene resin composition that constitutes the polyethylene resin layer. Here, the melt mass flow rate (MFR) of the polyethylene resin layer can be measured in accordance with JIS K7210-1. The measurement conditions are a temperature of 190° C. and a load of 2.16 kg.

The MFR of the polyethylene resin layer can be adjusted, for example, by adjusting the molecular weight of the polyethylene resin contained in the polyethylene resin layer.

Further, the melting point of the polyethylene resin layer is not particularly limited as long as it can exhibit desired thermal weldability. The melting point of the polyethylene resin layer is, for example, preferably 100°C or higher and 120°C or lower, more preferably 105°C or higher and 110°C or lower. If the melting point of the polyethylene resin layer is too high, it is necessary to increase the heating temperature when press-bonding the current collector sheet to the solar cell element, which may increase manufacturing costs or cause the solar cell element to deteriorate. There is. On the other hand, if the melting point of the polyethylene resin layer is too low, the polyethylene resin layer may melt in the usage environment of the solar cell, making it difficult to fix the wire.

Here, the melting point of the polyethylene resin layer can be determined by differential scanning calorimetry (DSC) in accordance with JIS K7121 (method for measuring transition temperature of plastics). In addition, in that case, when two or more melting point peaks exist, the higher temperature can be set as the melting point.

(2) Material of polyethylene resin layer (a) Polyethylene resin The polyethylene resin layer contains polyethylene resin. The polyethylene resin is not particularly limited as long as it is possible to obtain a polyethylene resin layer that satisfies the above-mentioned MFR. Examples of polyethylene resins include high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene-based linear low-density polyethylene (M-LLDPE), and ultra-low density polyethylene ( VLDPE), etc. One type of polyethylene resin may be used alone, or two or more types may be used in combination. Among these, low density polyethylene (LDPE) is preferred because of its good flexibility and workability.

The density of the polyethylene resin is not particularly limited, and for example, it is preferably 0.890 g/cm ³ or more and 0.930 g/cm ³ or less, and 0.900 g/cm ³ or more and 0.925 g/cm ³ or less. is more preferable. When the density of the polyethylene resin is within the above range, the flexibility and processability of the polyethylene resin layer can be improved, and the adhesion to the wire and the embeddability of the wire can be improved.

Here, the density of the polyethylene resin can be measured, for example, by a pycnometer method based on JIS K7112.

The polyethylene resin layer may contain only polyethylene resin as a resin component, or may further contain a resin other than polyethylene resin in addition to polyethylene resin. In the latter case, the polyethylene resin layer preferably contains polyethylene resin as a main component. Note that the expression that the polyethylene resin layer contains polyethylene resin as a main component means that the proportion of polyethylene resin is the highest among all resin components.

The ratio of the polyethylene resin to all resin components in the polyethylene resin layer is, for example, 50% by mass or more, may be 60% by mass or more, or may be 70% by mass or more. Further, the proportion of the polyethylene resin may be, for example, 99% by mass or less, 95% by mass or less, or 90% by mass or less. Note that the proportion of the polyethylene resin may be 100% by mass.

(b) Adhesiveness Improver The polyethylene resin layer in the present disclosure may contain an adhesiveness improver. The adhesion improver is a component that improves the adhesion to wires and the adhesion to solar cell elements.

Examples of the adhesion improver include silane-modified resins and silane coupling agents.

(i) Silane-modified resin Examples of the silane-modified resin include silane-modified polyolefin resins. The silane-modified polyolefin resin is a copolymer of an α-olefin and an ethylenically unsaturated silane compound. The copolymer may be, for example, a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer. Among these, the copolymer is preferably a graft copolymer, and is preferably a graft copolymer in which a main chain is a polyolefin and an ethylenically unsaturated silane compound is polymerized as a side chain. In such a graft copolymer, the degree of freedom of the silanol groups that contribute to adhesion is increased, so that the adhesion to the wire and the adhesion to the solar cell element can be further improved.

Examples of the α-olefin constituting the silane-modified polyolefin resin include ethylene, propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, -heptene, 1-octene, 1-nonene, 1-decene, etc. One type of α-olefin may be used alone, or two or more types may be used in combination. Among them, polyethylene is preferred. That is, the silane-modified polyolefin resin is preferably a silane-modified polyethylene resin. This is because the silane-modified polyethylene resin has good compatibility with the polyethylene resin contained in the polyethylene resin layer.

The silane-modified polyethylene resin is preferably a resin obtained by graft polymerizing linear low-density polyethylene (LLDPE) as a main chain and an ethylenically unsaturated silane compound as a side chain.

Examples of the ethylenically unsaturated silane compound include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane, vinyltriphenoxysilane, vinyl Tribenzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane can be mentioned. One type of ethylenically unsaturated silane compound may be used alone, or two or more types may be used in combination.

The silane-modified polyolefin resin can be obtained, for example, by the manufacturing method described in JP-A No. 2003-46105.

The silane-modified resins may be used alone or in combination of two or more.

The content of the silane-modified resin in the polyethylene resin layer is not particularly limited, and may be, for example, 25% by mass or less, or 15% by mass or less.

(ii) Silane coupling agent As the silane coupling agent, a silane coupling agent used in general solar cell encapsulants can be used. The silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent in the polyethylene resin layer is not particularly limited, and may be, for example, 5% by mass or less.

(c) Other components The polyethylene resin layer may contain additives such as an antioxidant, an anti-blocking agent, and a lubricant, if necessary.

Here, the proportion of each resin component contained in each layer of the resin film for current collector sheet is detected by, for example, differential scanning calorimetry (DSC), infrared spectroscopy (IR), or nuclear magnetic resonance (NMR). It can be analyzed from the peak ratio etc.

(3) Others The thickness of the polyethylene resin layer is not particularly limited as long as it can support the wire when the resin film for current collector sheet is used as the current collector sheet, and can be appropriately selected depending on the thickness of the wire. The thickness of the polyethylene resin layer is preferably thicker than the thickness of the base material layer described below. Thereby, the adhesion to the wire and the embeddability of the wire can be improved. Specifically, the thickness of the polyethylene resin layer is preferably 40 μm or more and 100 μm or less, more preferably 45 μm or more and 80 μm or less. When the thickness of the polyethylene resin layer is within the above range, the adhesion to the wire and the embeddability of the wire can be improved.

The surface of the polyethylene resin layer opposite to the adhesive layer may be surface-treated. That is, the polyethylene resin layer may have a surface treatment portion on the opposite side to the adhesive layer. Thereby, the adhesion to the wire and the adhesion to the solar cell element can be improved.

The surface treatment is not particularly limited as long as it can improve adhesion to wires and solar cell elements, and examples include corona treatment, plasma treatment, ultraviolet treatment, electron beam treatment, flame treatment, etc. Can be mentioned. Among these, corona treatment is preferred from the viewpoint of processing cost and damage reduction to the polyethylene resin layer.

2. Base Material Layer The base material layer in the present disclosure contains polyethylene terephthalate resin. The base material layer is a member that provides rigidity to the resin film for current collector sheet.

The base material layer can contain various additives as necessary.

The thickness of the base material layer is not particularly limited, and can be appropriately selected depending on the size and purpose of the solar cell in which the resin film for current collector sheet is used. As mentioned above, the thickness of the base material layer is preferably thinner than the thickness of the polyethylene resin layer. Specifically, the thickness of the base layer is preferably 12 μm or more and 38 μm or less, more preferably 12 μm or more and 25 μm or less. If the thickness of the base material layer is too thin, sufficient rigidity may not be obtained. Moreover, if the thickness of the base material layer is too thick, the rigidity will become too high, and there is a possibility that the followability of the resin film for the current collector sheet to the wire will decrease.

The base material layer is preferably subjected to an annealing treatment. Thermal dimensional stability can be improved. This makes it easier to adjust the heat shrinkage rate of the resin film for current collector sheet, which will be described later, within a predetermined range. Therefore, when manufacturing a solar cell with a current collecting sheet using a current collecting sheet having a resin film for current collecting sheet, the position of the wire relative to the solar cell element during the heating process for fixing the wire to the solar cell element Misalignment can be suppressed. Moreover, when manufacturing a solar cell using a solar cell with a current collector sheet, it is possible to suppress misalignment of the wire with respect to the solar cell element during the heating process for integrating each member. Furthermore, even if the solar cell reaches a high temperature in the environment in which the solar cell is used, it is possible to suppress misalignment of the wire relative to the solar cell element. As a result, the reliability of the solar cell can be improved.

The temperature of the annealing treatment of the base material layer is preferably, for example, 120° C. or more and 250° C. or less.

3. Adhesive Layer The adhesive layer in the present disclosure is a member that is disposed between the base layer and the polyethylene resin layer and serves to bond the base layer and the polyethylene resin layer.

The adhesive used for the adhesive layer is not particularly limited as long as it is transparent and capable of bonding the base material layer and the polyethylene resin layer, and general film adhesives can be used. Adhesives used for bonding can be mentioned. Examples of the adhesive include urethane adhesive, acrylic adhesive, polycarbonate adhesive, and phenol adhesive. Further, the adhesive may be, for example, an adhesive for dry lamination or an anchor coating agent for extrusion lamination.

Moreover, it is preferable that the adhesive has heat and humidity resistance. Decrease in adhesive strength due to hydrolysis can be suppressed. For example, it is preferable that the resin component constituting the adhesive does not have an ester bond. Specifically, in the case of a urethane adhesive, it is preferable that the main ingredient is a polycarbonate polyurethane resin.

The thickness of the adhesive layer is not particularly limited as long as it has transparency and can bond the base material layer and the polyethylene resin layer, and is preferably, for example, 0.1 μm or more and 10 μm or less.

4. Others The thickness of the resin film for a current collector sheet in the present disclosure is not particularly limited, and can be appropriately selected depending on the thickness of the wire used in the current collector sheet. The thickness of the resin film for the current collector sheet may be, for example, 50 μm or more and 300 μm or less. If the thickness of the resin film for current collector sheet is too thin, it may become difficult to fix the wire to the solar cell element. On the other hand, if the thickness of the resin film for the current collector sheet is too thick, the transparency may decrease.

II. Physical properties of resin film for current collector sheet 1. Heat Shrinkage Rate In the resin film for current collector sheet according to the present disclosure, the heat shrinkage rate when held at 150°C for 10 minutes is 2.0% or less, preferably 1.5% or less, and more preferably It is 1.0% or less. When the heat shrinkage rate of the resin film for current collector sheet is within the above range, thermal dimensional stability can be improved. As a result, when manufacturing a solar cell with a current collecting sheet using a current collecting sheet having a resin film for current collecting sheet, the wire is attached to the solar cell element during the heating process for fixing the wire to the solar cell element. Positional shift can be suppressed. Moreover, when manufacturing a solar cell using a solar cell with a current collector sheet, it is possible to suppress misalignment of the wire with respect to the solar cell element during the heating process for integrating each member. Furthermore, even if the solar cell reaches a high temperature in the environment in which the solar cell is used, it is possible to suppress misalignment of the wire relative to the solar cell element. As a result, the reliability of the solar cell can be improved.

In particular, as will be described later, when the wire is coated with Bi-Sn solder or Sn-In-Ag-Bi solder, the melting points of these solders are relatively high. The heating temperature in the heating process tends to be higher. Therefore, in the above case, the heat shrinkage rate of the resin film for current collector sheet is more preferably small, and specifically, it is more preferably 1.0% or less.

On the other hand, the lower limit of the heat shrinkage rate may be 0% or more.

Here, the heat shrinkage rate of the resin film for current collector sheet refers to the larger heat shrinkage rate of the heat shrinkage rate in the MD direction and the heat shrinkage rate in the TD direction. That is, in the resin film for a current collector sheet, the larger heat shrinkage rate of the heat shrinkage rate in the MD direction and the heat shrinkage rate in the TD direction falls within the above range.

Note that the MD direction of the resin film for current collector sheet is usually the longitudinal direction of the resin film for current collector sheet. Moreover, the TD direction of the resin film for current collector sheet is usually the transverse direction of the resin film for current collector sheet.

Moreover, the thermal shrinkage rate of the resin film for current collector sheet can be measured, for example, by a method based on ASTM D1204.

Examples of methods for controlling the heat shrinkage rate of the resin film for current collector sheet include a method of adjusting the heat shrinkage rate of the base material layer. As mentioned above, methods for adjusting the heat shrinkage rate of the base material layer include, for example, a method of annealing the base material layer, a method of adjusting the crystallinity of the polyethylene terephthalate resin contained in the base material layer, and a method of adjusting the crystallinity of the polyethylene terephthalate resin contained in the base material layer. Examples include a method of adjusting the molding method and molding conditions when molding the terephthalate resin into a film. Examples of methods for adjusting the molding method include a method of performing a relaxation treatment to relieve stress and strain during molding. Furthermore, examples of the molding conditions include the stretching ratio and the like.

2. Light transmittance at a wavelength of 400 nm or more and 1200 nm or less The light transmittance of the resin film for a current collector sheet in the present disclosure at a wavelength of 400 nm or more and 1200 nm or less is such that sunlight can be transmitted through the solar cell element to the extent that it can generate electricity. There are no particular limitations. The light transmittance of the resin film for current collector sheet at a wavelength of 400 nm or more and 1200 nm or less is, for example, preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. When the light transmittance is within the above range, the light utilization efficiency of the solar cell element can be increased.

Here, the light transmittance at a wavelength of 400 nm or more and 1200 nm or less is an average value of the light transmittance at a wavelength of 400 nm or more and 1200 nm or less. The light transmittance at a wavelength of 400 nm or more and 1200 nm or less can be measured in accordance with JIS K7361 1. Specifically, the light transmittance at a wavelength of 400 nm or more and 1200 nm or less can be measured using a haze meter HM150 manufactured by Murakami Color Research Institute.

3. Haze The transparency of the resin film for a current collector sheet in the present disclosure is not particularly limited as long as it can transmit sunlight to the extent that the solar cell element can generate electricity. The transparency of the resin film for current collector sheet can be evaluated by, for example, haze. The haze of the resin film for the current collector sheet is, for example, 1% or more and 40% or less, may be 5% or more and 30% or less, or may be 10% or more and 20% or less.

Here, haze is measured in accordance with JIS K7136. Haze can be measured using, for example, a haze meter HM150 manufactured by Murakami Color Research Institute.

In addition, when measuring the haze of the resin film for a current collector sheet, a sample for measurement is produced and used for measurement. The sample for measurement is prepared by the following method. First, a resin film for a current collector sheet is cut into a size of 50 mm x 50 mm to prepare a test piece. Next, the ETFE (tetrafluoroethylene-ethylene copolymer) film, the test piece, and the ETFE film were laminated in this order, and vacuum laminated at a set temperature of 165°C, vacuuming for 2 minutes, pressing for 2.5 minutes, and pressure of 100 kPa. I do. This is to eliminate minute irregularities on the surface of the resin film for current collector sheet at the film forming stage. Subsequently, the ETFE film is removed from both sides of the test piece to prepare a measurement sample.

III. Method for manufacturing a resin film for current collector sheet The method for manufacturing a resin film for current collector sheet in the present disclosure is particularly suitable if a resin film for current collector sheet having a base material layer, an adhesive layer, and a polyethylene resin layer in this order can be obtained. Not limited. For example, a dry lamination method using a film-like base material layer and a polyethylene resin layer, a method in which the base material layer and a polyethylene resin layer are laminated via a dry laminating adhesive, a method using a film-like base material layer, and an extrusion method. Examples of the lamination method include a method in which a base material layer and a polyethylene resin layer are extruded and laminated via an anchor coating agent for lamination.

Examples of the method for forming the film-like base material layer and polyethylene resin layer include a method of preparing a resin composition for forming each layer and melt-molding the resin composition. As the melt molding method, a known molding method can be used, and examples thereof include injection molding, extrusion molding, blow molding, compression molding, and rotational molding. The temperature during molding is, for example, higher than the melting point of the resin composition. The upper limit of the temperature during molding is appropriately adjusted depending on the type of resin composition.

B. Current collector sheet The current collector sheet in the present disclosure is a current collector sheet used for a solar cell, and is composed of the above-mentioned resin film for current collector sheet and the polyethylene resin layer disposed on the surface side of the resin film for current collector sheet. It has a wire.

2(a) and 2(b) are a schematic plan view and a cross-sectional view illustrating a current collecting sheet according to the present disclosure, and FIG. 2(b) is a cross-sectional view taken along the line AA in FIG. 2(a). As shown in FIGS. 2A and 2B, the current collector sheet 20 includes a resin film 10 for a current collector sheet, and a wire 11 disposed on the surface side of the polyethylene resin layer 3 of the resin film 10 for a current collector sheet. and has. Note that FIG. 2(a) shows a schematic plan view of the current collecting sheet viewed from the polyethylene resin layer side of the resin film for current collecting sheet.

In the current collecting sheet according to the present disclosure, by having the above resin film for current collecting sheet, the wire can be satisfactorily fixed to the solar cell element by the resin film for current collecting sheet. Moreover, the resin film for the current collector sheet can suppress the displacement of the wire due to heat. Therefore, when the current collecting sheet is used in a solar cell, power generation efficiency can be improved and reliability can be improved.

I. Configuration of current collector sheet The current collector sheet in the present disclosure includes a resin film for current collector sheet and a wire.

1. Resin film for current collector sheet The resin film for current collector sheet is a member that supports the wire. Moreover, the resin film for current collector sheet is a member that fixes the wire to the solar cell element.

Regarding the resin film for current collector sheet, the content can be the same as that explained in "A. Resin film for current collector sheet" mentioned above, so the description here will be omitted.

As described later, when the current collecting sheet has a plurality of resin films for current collecting sheets, at least one resin film for current collecting sheets may be the above-mentioned resin film for current collecting sheets. In this case, the current collector sheet may have a resin film for current collector sheet other than the above-mentioned resin film for current collector sheet. Among these, it is preferable that all of the plurality of current collector sheet resin films included in the current collector sheet are the above-mentioned current collector sheet resin films.

2. Wire The wire is arranged on the surface side of the polyethylene resin layer of the resin film for current collector sheet. Wires are used, for example, in solar cell modules to connect solar cell elements to each other. Further, the wire is used, for example, in a single cell type solar cell to collect electricity generated in a solar cell element. The wire is usually arranged to connect with the electrode of the solar cell element.

The cross-sectional shape of the wire is typically circular, such as a perfect circle or an ellipse, but is not limited thereto.

The thickness of the wire, that is, the size of the cross section of the wire, is not particularly limited as long as it does not prevent sunlight from entering the solar cell element, and is, for example, 100 μm or more and 300 μm or less. The cross-sectional size of the wire is, for example, the diameter when the cross-section is circular, the major axis when the cross-section is elliptical, and the maximum diagonal length when the cross-section is polygonal.

The material of the wire is not particularly limited as long as it can exhibit desired conductivity, and may be the same as the material of the wire used in current collector sheets of general solar cell elements. As the material of the wire, for example, metal materials such as copper (Cu) and silver (Ag) can be used. Further, the wire may have, for example, a core portion and a skin portion disposed on the outside of the core portion. In this case, as the material of the core part, for example, the above metal materials can be used. Furthermore, solder can be used as the material for the skin portion.

The melting point of the solder is, for example, preferably 70°C or more and 140°C or less, more preferably 80°C or more and 135°C or less. If the melting point of the solder is too high, there is a possibility that the base material layer and the polyethylene resin layer described above will deteriorate when connecting wires to the solar cell element.

Examples of such solder include Sn--In based solder, Bi--Sn based solder, and the like.

For example, compared to Sn--In-based solder and In--Bi-based solder, Bi--Sn-based solder has a higher melting point. Therefore, when using Bi-Sn solder, the heating temperature in the heating process when manufacturing a solar cell element with a current collector sheet and the solar cell element with a current collector sheet must be adjusted. The heating temperature in the heating process when manufacturing solar cells tends to be higher. Therefore, in the above case, poor adhesion of the wires and misalignment of the wires are likely to occur. Therefore, the present disclosure is particularly effective in the above case.

II. Structure of Current Collecting Sheet In the current collecting sheet according to the present disclosure, at least one wire may be disposed in one resin film for current collecting sheet. From the viewpoint of increasing the conductivity of the current collector sheet, it is preferable that a plurality of wires are arranged for one resin film for current collector sheet.

When the current collector sheet has a plurality of wires, the arrangement of the wires in plan view is not particularly limited, and may be the same as the arrangement of the wires in known current collector sheets. For example, as shown in FIG. 2(a), the wires 11 may be arranged in a line, or, although not shown, the wires may be arranged in a grid.

Moreover, in the current collector sheet, the wire is arranged on the surface side of the polyethylene resin layer of the resin film for current collector sheet. For example, as shown in FIG. 2(b), the wire 11 is arranged so that a part of the wire 11 is embedded in the polyethylene resin layer 3 of the resin film 10 for current collector sheet, and a part of the wire 11 is exposed. Preferably. Wires can be fixed well.

Further, for example, as shown in FIG. 2(b), the wire 11 may be embedded in the polyethylene resin layer 3 so as not to contact the base material layer 1, and as shown in FIG. It may be embedded in the polyethylene resin layer 3 so as to be in contact with the layer 1 . When the wire is embedded in the polyethylene resin layer so as to be in contact with the base material layer, the thickness of the current collector sheet can be reduced, so that the solar cell using the current collector sheet can be made thinner.

The degree of embedding of the wires, that is, the degree of exposure of the wires, is not particularly limited and depends on the material and thickness of the polyethylene resin layer, the thickness of the wires, and the form of the solar cell element in which the current collector sheet is arranged. You can choose as appropriate.

In the current collecting sheet, for example, the same wire may be arranged on a plurality of resin films for current collecting sheets. For example, FIG. 5 shows an example in which the same wire 11 is arranged for two resin films 10A and 10B for current collector sheets. Moreover, as shown in FIG. 5, adjacent resin films 10A and 10B for current collector sheets may be arranged so that the surfaces on the polyethylene resin layer 3 side are in opposite surface directions. That is, the surface of one resin film for current collector sheet 10A on the polyethylene resin layer 3 side and the surface of the other resin film for current collector sheet 10B on the base material layer 1 side are arranged in the same surface direction. Good too. By having the current collector sheet having the above structure, the current collector sheet 20 can be made into a current collector sheet 20 in which two solar cell elements 31 can be arranged in series, as shown in FIG. 3(a), for example. Although not shown, adjacent resin films for current collector sheets may be arranged so that their surfaces facing the polyethylene resin layer are in the same surface direction.

III. Method for manufacturing current collector sheet The method for manufacturing the current collector sheet in the present disclosure is not particularly limited as long as it is a method that can embed wires to the surface side of the polyethylene resin layer of the resin film for current collector sheet to the extent that they can be fixed. , a known method can be used. One example is a method in which a wire is placed on the side of the polyethylene resin layer of a resin film for a current collector sheet, and by heating the wire, a part of the polyethylene resin in the polyethylene resin layer is melted and the wire is embedded. be able to.

C. Solar cell element with a current collector sheet The solar cell element with a current collector sheet in the present disclosure includes the above-mentioned current collector sheet, and a solar cell arranged on the surface side of the polyethylene resin layer of the current collector sheet and electrically connected to a wire. It has an element.

3(a) to 3(c) are a schematic perspective view and a cross-sectional view illustrating a solar cell element with a current collecting sheet according to the present disclosure, and FIG. 3(b) is a cross-sectional view taken along the line AA in FIG. 3(a). FIG. 3(c) is a sectional view taken along line BB in FIG. 3(a). As shown in FIGS. 3(a) to 3(c), the solar cell element 30 with a current collector sheet is arranged on the surface side of the current collector sheet 10 and the polyethylene resin layer 3 of the current collector sheet 10, and is connected to the wire 11 and It has a solar cell element 31 which is connected to the solar cell element 31. 3(a) to (c) are examples in which the current collecting sheet 20 has two resin films 10 for current collecting sheets, and solar cell elements 31 are arranged on each resin film 10 for current collecting sheets. It shows.

In the solar cell element with a current collecting sheet according to the present disclosure, by having the above-mentioned current collecting sheet, the wire can be satisfactorily fixed to the solar cell element by the resin film for the current collecting sheet. Moreover, the resin film for the current collector sheet can suppress the displacement of the wire due to heat. Therefore, when a solar cell element with a current collector sheet is used in a solar cell, power generation efficiency can be improved and reliability can be improved.

I. Configuration of solar cell element with current collector sheet The solar cell element with current collector sheet in the present disclosure includes a current collector sheet and a solar cell element.

1. Current Collector Sheet The current collector sheet can be the same as that explained in "B. Current Collector Sheet" above, so the description here will be omitted.

When the solar cell element with a current collecting sheet has a plurality of current collecting sheets, at least one current collecting sheet may be the above current collecting sheet. In this case, the solar cell element with a current collecting sheet may have a current collecting sheet other than the above-mentioned current collecting sheet. Among these, it is preferable that all the current collecting sheets are the above-mentioned current collecting sheets.

2. Solar Cell Element The solar cell element can be similar to elements used in general solar cells. Examples of the solar cell element include a single crystal silicon solar cell element, a polycrystalline silicon solar cell element, an amorphous silicon solar cell element, a compound semiconductor solar cell element, a dye-sensitized solar cell element, and a quantum dot solar cell element. Examples include battery elements, organic thin film type solar cell elements, and the like. The size, form, etc. of the solar cell element can be appropriately selected depending on the use of the solar cell.

II. Structure of a solar cell element with a current collector sheet A solar cell element with a current collector sheet usually has a laminated structure in which a current collector sheet and a solar cell element are laminated.

When the solar cell element with a current collector sheet is viewed from the arrangement surface of the current collector sheet of the solar cell element, for example, as shown in _FIG . The thickness of the resin film 10, that is, the distance from the surface of the solar cell element 31 on which the current collector sheet 20 is arranged to the surface of the base material layer 1 on the opposite side to the solar cell element 31, is determined by the distance on which the wire 11 is arranged. It is preferable that the region is thicker (distance is larger) than other regions. With such a laminated structure, the base material layer 1 can effectively press the wire 11 toward the solar cell element 31 side, and problems such as poor contact of the wire 11 with the solar cell element 31 can be prevented.

In this case, the maximum distance y of the wire 11 in the direction D _L perpendicular to the arrangement surface, that is, the maximum distance y of the wire 11 from the surface on which the current collector sheet 20 of the solar cell element 31 is arranged, and the maximum distance y of the wire 11 in the direction D L perpendicular to the arrangement surface. The minimum distance x of the current collector sheet resin film 10 of _L , that is, the distance from the surface of the solar cell element 31 on which the current collector sheet 20 is arranged to the surface of the base material layer 1 on the opposite side from the solar cell element 31 The ratio x/y to the minimum distance x is, for example, preferably 2/3 or less, more preferably 1/2 or less.

Note that the lower limit of the ratio x/y is a value that is appropriately adjusted depending on the thickness of the polyethylene resin layer and the thickness of the wire, and is, for example, 1/20 or more. When the ratio x/y is within the above range, the wire can be well fixed to the solar cell element using the resin film for current collector sheet.

The ratio x/y can be controlled by adjusting the thickness (diameter, etc.) of the wire and the thickness of the polyethylene resin layer. Further, as will be described later, the ratio x/y can also be controlled by adjusting the pressure when thermocompression bonding the current collector sheet to the solar cell element.

Further, as shown in FIG. 3C, for example, in a cross-sectional view of the solar cell element 30 with a current collector sheet, the solar cell element 31 is It is preferable that the distance from the surface on the current collector sheet 20 side to the surface of the base material layer 1 on the opposite side to the solar cell element 31 gradually decreases.

In addition, when a plurality of wires are arranged, for example, as shown in FIG. It is preferable that the distance from the surface on which the sheet 20 is disposed to the surface of the base layer 1 opposite to the solar cell element 31 is disposed at the minimum distance. Since depressions are formed between the wires and the current collector sheet has an uneven structure, the area of the surface of the base material layer opposite to the solar cell element becomes large. Thereby, in a solar cell having a solar cell element with a current collector sheet, the contact area between the base layer and the encapsulant described later becomes large, so that adhesion to the encapsulant can be improved.

In addition, in the solar cell element with a current collector sheet, as described in the above section "B. Current collector sheet", the wire 11 comes into contact with the base material layer 1, for example, as shown in FIG. 3(c). It may be embedded in the polyethylene resin layer 3 as shown in FIG. Thereby, the thickness of the solar cell element with the current collecting sheet can be reduced, so that the solar cell can be made thinner.

A solar cell element with a current collector sheet may include at least one solar cell element and a current collector sheet connected to at least one of a positive electrode and a negative electrode of the solar cell element. For example, it may be a solar cell element with a current collecting sheet that constitutes a single cell type solar cell, in which a current collecting sheet is placed on each of the positive electrode and the negative electrode of one solar cell element. For example, a solar cell element with a current collector sheet is a solar cell with a current collector sheet that constitutes a solar cell module type solar cell (solar cell module) in which multiple solar cell elements are connected in parallel or in series using a current collector sheet. It may also be a solar cell element.

III. Others The method for manufacturing a solar cell element with a current collector sheet in the present disclosure is not particularly limited as long as it is a method that can obtain a structure in which the wires of the current collector sheet are electrically connected and fixed to the solar cell element. For example, by temporarily adhering a current collector sheet to a solar cell element, and by thermocompression bonding the temporarily adhered current collector sheet to the solar cell element, the wires of the current collector sheet can be electrically connected to the solar cell element. An example of a manufacturing method includes a fixing step of physically connecting and fixing. As for the temporary bonding method and the thermocompression bonding method, known methods can be used, such as a vacuum thermal lamination method. Further, the fixing step may be performed at the same time as the unifying step of laminating and integrating each member of the solar cell, for example, as described in the section "D. Solar Cell" below.

A solar cell element with a current collector sheet is normally used as a member constituting a solar cell. In addition, when a solar cell element with a current collector sheet has, for example, one solar cell element and a current collector sheet connected to only one electrode of the positive electrode or the negative electrode of the solar cell element, the solar cell element with a current collector sheet The solar cell element can be used, for example, as a part of the above-mentioned single-cell type solar cell, or as a part of the solar cell element with a current collector sheet that constitutes the above-mentioned solar cell module.

D. Solar Cell The solar cell according to the present disclosure includes a transparent substrate, a first sealing material, the above-described solar cell element with a current collecting sheet, a second sealing material, and a counter substrate in this order.

FIG. 6 is a schematic cross-sectional view illustrating a solar cell according to the present disclosure. As shown in FIG. 6, the solar cell 40 includes a transparent substrate 41, a first encapsulant 42, a solar cell element 30 with a current collector sheet, a second encapsulant 43, and a counter substrate 44.

The solar cell in the present disclosure may be a solar cell module having a plurality of solar cell elements with current collector sheets.

In the solar cell according to the present disclosure, by having the solar cell element with the above-mentioned current collector sheet, the wire can be well fixed to the solar cell element by the resin film for the current collector sheet. Moreover, the resin film for the current collector sheet can suppress the displacement of the wire due to heat. Therefore, power generation efficiency can be improved and reliability can be improved.

I. Configuration of Solar Cell The solar cell in the present disclosure includes, in this order, a transparent substrate, a first sealing material, a solar cell element with a current collector sheet, a second sealing material, and a counter substrate.

1. Solar cell element with current collector sheet Regarding the solar cell element with current collector sheet, the content can be the same as that explained in the above section "C. Solar cell element with current collector sheet", so the explanation here is Omitted.

2. Transparent Substrate and Counter Substrate The transparent substrate is a member that protects the solar cell element together with the counter substrate. Further, the transparent substrate is usually arranged on the light-receiving surface side of the solar cell, and functions as a front protection plate on the light-receiving surface side. The transparency of the transparent substrate is not particularly limited as long as it does not inhibit the power generation of the solar cell element. The transparent substrate can be the same as the transparent substrate used in general solar cells, so the explanation here will be omitted.

The counter substrate is a member that protects the solar cell element together with the transparent substrate. The counter substrate may or may not have transparency. When the counter substrate has transparency, both surfaces of the solar cell can be used as sunlight receiving surfaces. As the counter substrate, the above-mentioned transparent substrate can be used. Further, as the counter substrate, a back protection sheet for solar cells can also be used.

3. First Encapsulant and Second Encapsulant The first encapsulant and the second encapsulant are members that seal the solar cell element. The first sealing material is usually placed on the light-receiving surface side of the solar cell.

The first sealing material and the second sealing member contain thermoplastic resin. The thermoplastic resin used for the first encapsulant and the second encapsulant may be similar to thermoplastic resins used for encapsulants of general solar cells, such as polyethylene resin, ethylene- Encapsulants containing various olefin resins such as vinyl acetate copolymer (EVA) as a main component can be used. In addition, when these resins are the main components, it means that the ratio of these resins is the largest among all resin components.

The first sealing material usually contains an ultraviolet absorber. Deterioration of the base material layer containing polyethylene terephthalate resin caused by ultraviolet rays, such as yellowing, cracking, and breakage, can be suppressed.

When the counter substrate has transparency, the second sealing material usually contains an ultraviolet absorber like the first sealing material.

The ultraviolet absorber can be the same as the ultraviolet absorber used in general solar cell encapsulants.

The thicknesses of the first encapsulant and the second encapsulant are appropriately selected depending on the type and size of the solar cell.

II. Method for Manufacturing a Solar Cell A method for manufacturing a solar cell in the present disclosure can be similar to a method for manufacturing a general solar cell. As an example, a laminate forming step of forming a laminate in which a transparent substrate, a first encapsulant, a solar cell element with a current collector sheet, a second encapsulant, and a counter substrate are laminated in this order, and heating the laminate. and a step of integrating them into a solar cell by pressure treatment.

The heating and pressurizing treatments are not particularly limited, and can be similar to treatments performed during the manufacture of general solar cells. For example, a vacuum thermal lamination method is preferred. The conditions for the vacuum thermal lamination method are not particularly limited, and can be appropriately selected depending on the size of the solar cell, the type of each member, etc. The lamination temperature is preferably, for example, 130°C or higher and 170°C or lower. Further, the lamination time is preferably, for example, 5 minutes or more and 30 minutes or less, and more preferably 8 minutes or more and 15 minutes or less.

III. Applications Applications of the solar cell in the present disclosure include various applications such as solar cells for electronic devices and large solar cells for outdoor installation.

Note that the present disclosure is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present disclosure and provides similar effects is the present invention. within the technical scope of the disclosure.

[Example 1]
A polyethylene terephthalate (PET) film ("LBD" manufactured by DuPont) with a thickness of 12 μm was used as the base material layer. In addition, as an adhesive (anchor coating agent), a two-component type consisting of a polycarbonate-based main agent ("KT-0035" manufactured by Rock Paint Co., Ltd.) and an isocyanate-based curing agent ("H-039Z2" manufactured by Rock Paint Co., Ltd.) is used. Glue was used. Further, as the polyethylene resin, high-pressure low density polyethylene (LDPE) having a density of 0.92 g/cm ³ , a melting point of 106° C., and an MFR (190° C.) of 7 g/10 minutes was used.

On one side of the base layer, 0.1 g/m ² of the adhesive was applied as an anchor agent, and the polyethylene resin was extruded to a thickness of 60 μm to form a polyethylene resin layer. Furthermore, the surface of the polyethylene resin layer opposite to the base material layer was subjected to corona treatment. Thereby, a resin film for a current collector sheet having a base material layer, an adhesive layer, and a polyethylene resin layer in this order was obtained.

[Example 2]
A resin film for a current collector sheet was produced in the same manner as in Example 1, except that the base layer was annealed at 200° C. for 10 seconds.

[Comparative example 1]
A PET film with a thickness of 12 μm was used as the base layer. In addition, a urethane adhesive was used as the adhesive (anchor coating agent). Further, as the polyethylene resin, linear low density polyethylene (LLDPE) with a melting point of 109° C. and an MFR (190° C.) of 5.7 g/10 minutes was used.

A resin film for a current collector sheet was produced in the same manner as in Example 1.

[Comparative example 2]
A 12 μm thick polyethylene terephthalate (PET) film (“E5104” manufactured by Toyobo Co., Ltd.) was used as the base material layer. In addition, as an adhesive (anchor coating agent), a two-component type consisting of a polycarbonate-based main agent ("KT-0035" manufactured by Rock Paint Co., Ltd.) and an isocyanate-based curing agent ("H-039Z2" manufactured by Rock Paint Co., Ltd.) is used. Glue was used. Further, as the polyethylene resin layer, a polyethylene film containing metallocene linear low density polyethylene (M-LLDPE) having a density of 0.915 g/cm ³ , a melting point of 105° C., and an MFR (190° C.) of 2 g/10 minutes was used.

A resin film for a current collector sheet was obtained by bonding the base material layer and the polyethylene resin layer together via an adhesive using a dry lamination method.

[Comparative example 3]
Except that a polyethylene film containing metallocene-based linear low-density polyethylene (M-LLDPE) with a density of 0.915 g/cm ³ , a melting point of 110°C, and an MFR (190°C) of 2 g/10 min was used as the polyethylene resin layer. A resin film for a current collector sheet was produced in the same manner as in Comparative Example 2.

[Comparative example 4]
A resin film for a current collector sheet was produced in the same manner as in Example 1 except that the thickness of the polyethylene resin layer was 70 μm.

[evaluation]
(1) Heat shrinkage rate The heat shrinkage rate of the resin film for current collector sheet in the MD direction and the TD direction was measured in accordance with ASTM D1204. The measurement conditions were 150°C and 10 minutes.

(2) Light transmittance at wavelengths of 400 nm or more and 1200 nm or less The light transmittance of the resin film for current collector sheet at wavelengths of 400 nm or more and 1200 nm or less was measured using a haze meter manufactured by Murakami Color Research Institute Co., Ltd. in accordance with JIS K7361 1. Measured using HM150.

(3) Haze A test piece was prepared by cutting a resin film for a current collector sheet into a size of 50 mm x 50 mm. Next, the ETFE (tetrafluoroethylene-ethylene copolymer) film, the test piece, and the ETFE film were laminated in this order, and vacuum laminated at a set temperature of 165°C, vacuuming for 2 minutes, pressing for 2.5 minutes, and pressure of 100 kPa. I did it. Subsequently, the ETFE film was removed from both sides of the test piece to obtain a measurement sample. Then, the haze of the measurement sample was measured in accordance with JIS K7136 using a haze meter HM150 manufactured by Murakami Color Research Institute.

(4) Wire Adhesion Wire A coated with SnIn-based solder and Wire B coated with SnBi-based solder were used as wires. The diameters of wire A and wire B were each 250 μm. A test piece was prepared by cutting the resin film for current collector sheet into a size of 100 mm x 100 mm. Next, an ETFE (tetrafluoroethylene-ethylene copolymer) film was placed on the surface of the test piece on the base layer side. Further, on the polyethylene resin layer side surface of the test piece, five wires A and five wires B each at a pitch of 10 mm and an ETFE film were arranged in this order. Thereafter, lamination was performed using a hot roll laminator under conditions of a set temperature of 120° C. and a press pressure of 0.1 MPa. Subsequently, the ETFE film was removed from both sides of the test piece to obtain a sample for evaluation. Then, the wire of the evaluation sample was bent 180 degrees and peeled from the resin film for current collector sheet under conditions of a tensile speed of 300 mm/min, and the peel strength of the current collector wire from the resin film for current collector sheet was measured. Wire adhesion was evaluated based on the following criteria. Note that "N/wire" indicates the peel strength when one wire is peeled off.
A: Peel strength is more than 0.1 N/wire.
B: The wire adheres closely to the resin film for current collector sheet, but the peel strength is 0.1 N/wire or less.
C: The wire did not adhere to the resin film for current collector sheet and naturally peeled off.

(5) Module Reliability First, a current collector sheet in which wires were fixed to a resin film for a current collector sheet was obtained in the same manner as the method for preparing the evaluation sample in the wire adhesion evaluation described above. At this time, a total of 18 wires were arranged at a pitch of 8 mm on the surface of the test piece on the polyethylene resin layer side. Note that for the samples whose wire adhesion was evaluated as "C", wire adhesion was ensured by increasing the set temperature of the hot roll laminator to 130°C.

A white tempered glass sheet with a thickness of 3.2 mm was used as the transparent substrate, and an ethylene-vinyl acetate copolymer (EVA) sheet with a thickness of 470 μm (manufactured by Takiron CI Co., Ltd., Fast Cure EVA) was used, an N-type silicon cell was used as the solar cell element, and an aluminum layer-containing backsheet (VAPE-CW, manufactured by Dainippon Printing Co., Ltd.) was used as the counter substrate. Next, the transparent substrate, the first encapsulant, the current collector sheet, the solar cell element, the current collector sheet, the second encapsulant, and the counter substrate are laminated, and the temperature is set to 150°C and vacuum is applied. Vacuum lamination was performed under the conditions of 5 minutes, pressing 7.5 minutes, and pressure 100 kPa. In addition, when laminating each member, the current collecting sheet was arranged so that the surface on the wire side of the current collecting sheet faced the solar cell element side. At this time, as illustrated in FIG. 3(b), by arranging the current collector sheets 20 above and below the solar cell elements 31, a solar cell module in which four solar cell elements are connected in series can be used for evaluation. A module was created.

A high temperature and high humidity test (85°C, 85% RH, 2000 hours) and a temperature cycle test (-40°C⇔90°C, 200 cycles, 1 cycle = 6 hours) were conducted on the evaluation module. The photovoltaic output before and after each test was measured, and the output reduction rate was determined. Module reliability was evaluated based on the following criteria.
A: The output reduction rate after both tests is less than 5%.
B: The output reduction rate after at least one test is 5% or more and less than 10%.
C: The output reduction rate after at least one test is 10% or more.

From Table 1, when the MFR of the polyethylene resin layer in the resin film for current collector sheet is within a predetermined range and the heat shrinkage rate of the resin film for current collector sheet is within a predetermined range, wire adhesion and module It was confirmed that reliability was good.

Furthermore, in Comparative Examples 1 and 4, the output decreased after the temperature cycle test. This is because if the resin film for the current collector sheet has a high thermal shrinkage rate, the residual stress after module lamination will increase.

In addition, when the heat shrinkage rate of the PET film alone used as the base layer in Example 1 and Comparative Example 4 was measured in the same manner as the resin film for current collector sheet, the heat shrinkage rate in the MD direction was 1.4%. , the heat shrinkage rate in the TD direction was 0.3%. This suggests that even if the heat shrinkage rate of the base layer itself is 2.0% or less, the heat shrinkage rate of the entire resin film for current collector sheet is not necessarily 2.0% or less. .

The present disclosure provides the following [1] to [11].
[1] A resin film for a current collector sheet used in a current collector sheet of a solar cell,
It has a base material layer, an adhesive layer, and a polyethylene resin layer in this order,
The base layer contains polyethylene terephthalate resin,
The polyethylene resin layer has a melt mass flow rate at 190° C. of 4 g/10 minutes or more and 8 g/10 minutes or less,
A resin film for a current collector sheet, which has a heat shrinkage rate of 2.0% or less when held at 150°C for 10 minutes.
[2] The resin film for a current collector sheet according to [1], wherein the polyethylene resin layer has a melting point of 100°C or more and 120°C or less.
[3] The resin film for a current collector sheet according to [1] or [2], wherein the polyethylene resin layer is thicker than the base layer.
[4] The resin film for a current collector sheet according to any one of [1] to [3], wherein the polyethylene resin layer has a thickness of 40 μm or more and 100 μm or less.
[5] The resin film for a current collector sheet according to any one of [1] to [4], wherein the base layer has a thickness of 12 μm or more and 38 μm or less.
[6] The resin film for a current collector sheet according to any one of [1] to [5], wherein the adhesive layer has a thickness of 0.1 μm or more and 10 μm or less.
[7] The resin film for a current collector sheet according to any one of [1] to [6], wherein the base layer has a surface-treated portion on a surface opposite to the adhesive layer.
[8] A current collector sheet used for solar cells,
The resin film for current collector sheet according to any one of [1] to [7],
A wire arranged on the surface side of the polyethylene resin layer of the resin film for current collector sheet;
A current collecting sheet having.
[9] The current collector sheet according to [8],
a solar cell element arranged on the surface side of the polyethylene resin layer of the current collector sheet and electrically connected to the wire;
A solar cell element with a current collecting sheet.
[10] A solar cell comprising, in this order, a transparent substrate, a first encapsulant, the solar cell element with a current collector sheet according to [9], a second encapsulant, and a counter substrate.
[11] The solar cell according to [10], wherein the solar cell is a solar cell module having a plurality of the solar cell elements with the current collector sheet.

1... Base material layer 2... Adhesive layer 3... Polyethylene resin layer 10, 10A, 10B... Resin film for current collector sheet 11... Wire 20... Current collector sheet 30... Solar cell element with current collector sheet 31... Solar cell element 40... Solar cell 41...Transparent substrate 42...First sealing material 43...Second sealing material 44...Counter substrate

Claims (11)

A resin film for a current collector sheet used for a current collector sheet of a solar cell,
It has a base material layer, an adhesive layer, and a polyethylene resin layer in this order,
The base material layer contains polyethylene terephthalate resin,
The polyethylene resin layer has a melt mass flow rate at 190° C. of 4 g/10 minutes or more and 8 g/10 minutes or less,
A resin film for a current collector sheet, which has a heat shrinkage rate of 2.0% or less when held at 150°C for 10 minutes. The resin film for a current collector sheet according to claim 1, wherein the polyethylene resin layer has a melting point of 100°C or more and 120°C or less. The resin film for a current collector sheet according to claim 1 or 2, wherein the polyethylene resin layer is thicker than the base layer. The resin film for a current collector sheet according to claim 1 or 2, wherein the polyethylene resin layer has a thickness of 40 μm or more and 100 μm or less. The resin film for a current collector sheet according to claim 1 or 2, wherein the base layer has a thickness of 12 μm or more and 38 μm or less. The resin film for a current collector sheet according to claim 1 or 2, wherein the adhesive layer has a thickness of 0.1 μm or more and 10 μm or less. The resin film for a current collector sheet according to claim 1 or 2, wherein the base layer has a surface treatment portion on a surface opposite to the adhesive layer. A current collector sheet used for solar cells,
The resin film for a current collector sheet according to claim 1 or 2,
a wire disposed on the surface side of the polyethylene resin layer of the resin film for current collector sheet;
A current collecting sheet having. The current collector sheet according to claim 8,
a solar cell element arranged on the surface side of the polyethylene resin layer of the current collector sheet and electrically connected to the wire;
A solar cell element with a current collecting sheet. A solar cell comprising, in this order, a transparent substrate, a first encapsulant, the solar cell element with a current collector sheet according to claim 9, a second encapsulant, and a counter substrate. The solar cell according to claim 10, wherein the solar cell is a solar cell module having a plurality of solar cell elements with a current collector sheet.

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