Resin film for current collector sheets, current collector sheets, solar cell elements with current collector sheets, and solar cells

Abstract

The present invention provides a resin film for current collector sheets that exhibits excellent adhesion to wires, excellent wire embedding properties, and excellent thermal dimensional stability, as well as a current collector sheet using the same, and a solar cell element with a current collector sheet. [Solution] A resin film for current collector sheets comprising a base layer 1, an adhesive layer 2, and a polyethylene resin layer 3 in this order, wherein the base layer contains polyethylene terephthalate resin, the melt mass flow rate of the polyethylene resin layer at 190°C is 4 g / 10 min or more and 8 g / 10 min or less, and the heat shrinkage rate when held at 150°C for 10 minutes is 2.0% or less.

Description

[Technical Field]

[0001] This disclosure relates to a film for current collector sheets, a current collector sheet, a solar cell element with a current collector sheet, and a solar cell. [Background technology]

[0002] In recent years, global warming, caused by carbon dioxide, has become a worldwide problem. In response to this issue, solar cells, which utilize solar energy as an environmentally friendly and clean energy source, are attracting attention, and active research and development are underway.

[0003] Solar cells are used, for example, in the form of modules that connect multiple solar cell elements. Conventionally, a method of connecting solar cell elements has been used that involves using a strip-shaped wire, approximately 2mm to 5mm wide, called a busbar. However, with this busbar connection method, a problem arises in the solar cell module: sunlight is physically blocked in the area where the busbar is placed, reducing the amount of sunlight incident on the solar cell elements.

[0004] In response to this, in recent years, a method called multi-wire connection has begun to be adopted, which connects solar cell elements using wires (thin wire-like conductors) with a diameter of approximately 150 μm to 300 μm. In multi-wire connection, one method for fixing the wires to the solar cell elements is to embed the wires in a heat-weldable resin film to form a current collector sheet, and then fix the current collector sheet to the solar cell elements by heat-pressing it (Patent Documents 1 and 2). The resin film used for the current collector sheet is also called a connecting film. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2004 / 021455 [Patent Document 2] International Publication No. 2017 / 076735 [Patent Document 3] Japanese Patent Publication No. 2020-174060 [Overview of the project] [Problems that the invention aims to solve]

[0006] In multi-wire connections, when embedding wires in a heat-sealable resin film to create a current collector sheet, it is necessary that the wires are stably held in the resin film to prevent them from coming loose before the current collector sheet is heat-pressed onto the solar cell element. Furthermore, when heat-pressing the current collector sheet onto the solar cell element, the resin film must wrap around the wires to secure them to the solar cell element. Therefore, the resin film of the current collector sheet used in multi-wire connections requires both adhesion to the wires and the ability to embed the wires.

[0007] For example, Patent Document 3 discloses a technology for fixing current collector wires for a solar cell module having a base layer and a wire holding layer, which allows for adequate wire holding force while avoiding poor current conduction caused by the entire wire becoming embedded in the wire holding layer, by optimizing the complex viscosity of the wire holding layer to a specific range.

[0008] However, depending on the wire material, the adhesion of the resin film to the wire may not be sufficient, and there is still room for improvement.

[0009] Furthermore, in multi-wire connections, when the solar cell elements with current collector sheets and other components are heat-sealed together to form a solar cell module, the resin film shrinks due to heat, causing the wires to shift relative to the solar cell elements. When the wires shift, the electrical conductivity between the solar cell elements and the wires becomes insufficient, reducing reliability.

[0010] This disclosure has been made in view of the above circumstances, and its main purpose is to provide a resin film for current collector sheets that has excellent adhesion to wires and wire embedding properties, as well as excellent thermal dimensional stability, and a current collector sheet using the same, a solar cell element with a current collector sheet, and a solar cell. [Means for solving the problem]

[0011] One embodiment of the present disclosure provides a resin film for current collector sheets used in current collector sheets of solar cells, comprising a base layer, an adhesive layer, and a polyethylene resin layer in that order, wherein the base layer contains polyethylene terephthalate resin, the melt mass flow rate (MFR) of the polyethylene resin layer at 190°C is 4 g / 10 min or more and 8 g / 10 min or less, and the thermal shrinkage rate when held at 150°C for 10 minutes is 2.0% or less.

[0012] Another embodiment of the present disclosure provides a current collector sheet for use in a solar cell, comprising the above-described resin film for current collector sheets and a wire disposed on the side of the polyethylene resin layer of the resin film for current collector sheets.

[0013] Another embodiment of the present disclosure provides a solar cell element with a current collector sheet, comprising the current collector sheet described above and a solar cell element disposed on the side of the polyethylene resin layer of the current collector sheet and electrically connected to the wire.

[0014] Another embodiment of the present disclosure provides a solar cell comprising, in this order, a transparent substrate, a first encapsulant, a solar cell element with the current collector sheet described above, a second encapsulant, and a counter substrate. [Effects of the Invention]

[0015] The resin film for current collector sheets in this disclosure exhibits excellent adhesion to wires, excellent wire embedding properties, and excellent thermal dimensional stability. [Brief explanation of the drawing]

[0016] [Figure 1] It is a schematic cross-sectional view illustrating a resin film for a current collecting sheet in the present disclosure. [Figure 2] It is a schematic plan view and cross-sectional view illustrating a current collecting sheet in the present disclosure. [Figure 3] It is a schematic perspective view and cross-sectional view illustrating a solar cell element with a current collecting sheet in the present disclosure. [Figure 4] It is a schematic cross-sectional view illustrating a current collecting sheet in the present disclosure. [Figure 5] It is a schematic cross-sectional view illustrating a solar cell element with a current collecting sheet in the present disclosure. [Figure 6] It is a schematic cross-sectional view illustrating a solar cell in the present disclosure.

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings and the like. However, the present disclosure can be implemented in many different modes and is not to be construed as being limited to the description of the embodiments exemplified below. Also, for the purpose of making the description clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual form, but this is merely an example and does not limit the interpretation of the present disclosure. Further, in this specification and each figure, elements that are the same as those described above with respect to the previously presented figures may be denoted by the same reference numerals, and detailed description may be omitted as appropriate.

[0018] In this specification, when describing a configuration in which one member is placed on top of another member, unless otherwise specified, the terms "on top" or "below" include both cases: when the other member is placed directly above or below the other member so as to be in contact with it, and when the other member is placed above or below the other member via yet another member. Similarly, when describing a configuration in this specification in which one member is placed on the surface of another member, unless otherwise specified, the terms "on the surface" or "on the side of the surface" include both cases: when the other member is placed directly above or below the other member so as to be in contact with it, and when the other member is placed above or below the other member via yet another member.

[0019] Furthermore, in this specification, terms such as "film," "sheet," and "substrate" are not distinguished from each other based on differences in terminology.

[0020] The resin film for current collector sheets, current collector sheets, solar cell elements with current collector sheets, and solar cells described herein will be explained in detail below.

[0021] A. Resin film for current collection sheets The resin film for current collector sheets in this disclosure is a resin film for current collector sheets used in solar cells, and comprises a base layer, an adhesive layer, and a polyethylene resin layer in that order, wherein the base layer contains polyethylene terephthalate resin, the melt mass flow rate (MFR) of the polyethylene resin layer at 190°C is 4 g / 10 min or more and 8 g / 10 min or less, and the thermal shrinkage rate when held at 150°C for 10 minutes is 2.0% or less.

[0022] The resin film for current collector sheets in this disclosure will be described with reference to the figures. Figure 1 is a schematic cross-sectional view illustrating the resin film for current collector sheets in this disclosure. As shown in Figure 1, the resin film for current collector sheets 10 has, in this order, a base layer 1 containing polyethylene terephthalate resin, an adhesive layer 2, and a polyethylene resin layer 3. The melt mass flow rate (MFR) of the polyethylene resin layer 3 is within a predetermined range. Furthermore, the thermal shrinkage rate when the resin film for current collector sheets 10 is held at 150°C for 10 minutes is less than or equal to a predetermined value.

[0023] Figures 2(a) and 2(b) are schematic plan and cross-sectional views illustrating a current collector sheet having a resin film for current collector sheets according to this disclosure. Figure 2(b) is a cross-sectional view taken along line AA in Figure 2(a). As shown in Figures 2(a) and 2(b), the current collector sheet 20 has a resin film for current collector sheets 10 and wires 11 arranged on the side of the polyethylene resin layer 3 of the resin film for current collector sheets 10. Thus, the resin film for current collector sheets 10 is used to support the wires 11. Figure 2(a) shows a schematic plan view of the current collector sheet as seen from the polyethylene resin layer side of the resin film for current collector sheets.

[0024] Figures 3(a) to 3(c) are schematic perspective views and cross-sectional views illustrating a solar cell element with a current collector sheet having a resin film for current collector sheets in this disclosure. Figure 3(b) is a cross-sectional view along line AA of Figure 3(a), and Figure 3(c) is a cross-sectional view along line BB of Figure 3(a). As shown in Figures 3(a) to 3(c), the solar cell element with a current collector sheet 30 has a current collector sheet 10 and a solar cell element 31 which is arranged on the side of the polyethylene resin layer 3 of the current collector sheet 10 and electrically connected to a wire 11. Thus, the resin film for current collector sheets 10 is used to fix the wire 11 which is electrically connected to the solar cell element 31. Figures 3(a) to 3(c) show an example in which the current collector sheet 20 has two resin films for current collector sheets 10, and a solar cell element 31 is arranged on each resin film for current collector sheets 10.

[0025] In this disclosure, the base layer contains polyethylene terephthalate resin. The polyethylene terephthalate resin contained in the base layer has a melting point of approximately 260°C and high heat resistance. Furthermore, when formed into a film, polyethylene terephthalate resin provides good rigidity. Therefore, the base layer containing polyethylene terephthalate resin can impart rigidity to the resin film for the current collector sheet. Thus, 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 resin film for the current collector sheet can sufficiently press the wire against the solar cell element during thermocompression bonding. In addition, in this disclosure, by having the MFR of the polyethylene resin layer within a predetermined range, the adhesion of the polyethylene resin layer to the wire and the embedding ability of the wire can be improved. Therefore, in a current collector sheet having a resin film for the current collector sheet, the resin film for the current collector sheet can securely fix the wire to the solar cell element.

[0026] Furthermore, when solar cells with current-collecting sheets are used in solar cells, the resin film for the current-collecting sheet allows the wires to be securely fixed to the solar cell elements, thereby suppressing a decrease in power generation efficiency due to poor wire adhesion.

[0027] Furthermore, in solar cells, by ensuring that the MFR of the polyethylene resin layer is within a predetermined range, good adhesion of the polyethylene resin layer to the solar cell element can be achieved.

[0028] Furthermore, as described above, in this disclosure, the resin film for the current collector sheet can have rigidity because the base layer contains polyethylene terephthalate resin. Therefore, thermal shrinkage of the resin film for the current collector sheet can be suppressed. Also, as described above, by having the MFR of the polyethylene resin layer within a predetermined range, the adhesion of the polyethylene resin layer to the wire, the embedding of the wire, and the adhesion to the solar cell element can be improved. Therefore, even when the thickness of the polyethylene resin layer is relatively thin, adhesion to the wire, the embedding of the wire, and the 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 is small. Therefore, having the MFR of the polyethylene resin layer within a predetermined range can also contribute to suppressing thermal shrinkage of the resin film for the current collector sheet. Furthermore, since the resin film for the current collector sheet in this disclosure has a predetermined thermal shrinkage rate, thermal dimensional stability can be improved. 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, misalignment of the wire relative to the solar cell element during the heating process can be suppressed. Furthermore, when manufacturing solar cells using solar cell elements with current collector sheets, misalignment of the wires relative to the solar cell elements during the heating process can be suppressed. Moreover, even when the solar cell reaches high temperatures in the operating environment, misalignment of the wires relative to the solar cell elements can be suppressed. Therefore, the reliability of the solar cell can be improved.

[0029] Furthermore, since the resin film for current collector sheets in this disclosure has excellent thermal dimensional stability, when manufacturing a solar cell element with a current collector sheet using a current collector sheet having the resin film for current collector sheets, and when manufacturing a solar cell using a solar cell element with a current collector sheet, thermal shrinkage of the resin film for current collector sheets during the heating process can be suppressed, and curl deformation can be suppressed.

[0030] The following describes the various components of the resin film for current collector sheets in this disclosure.

[0031] I. Composition of resin film for current collector sheet The resin film for current collector sheets in this disclosure comprises a base layer, an adhesive layer, and a polyethylene resin layer in that order.

[0032] 1. Polyethylene resin layer In this disclosure, the polyethylene resin layer is a component that supports the wire when a resin film for current collection sheets is used as the current collection sheet.

[0033] (1) Characteristics of the polyethylene resin layer The melt mass flow rate (MFR) of the polyethylene resin layer at 190°C is preferably 4 g / 10 min or more and 8 g / 10 min or less, and more preferably 6 g / 10 min or more and 8 g / 10 min or less. Having the MFR of the polyethylene resin layer within this range improves adhesion to the wire and wire embedding. In particular, an MFR of 6 g / 10 min or more allows for a polyethylene resin layer with excellent adhesion to the wire and wire embedding, regardless of the wire material.

[0034] 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.

[0035] The MFR of the polyethylene resin layer can be adjusted, for example, by the molecular weight of the polyethylene resin contained in the polyethylene resin layer.

[0036] Furthermore, the melting point of the polyethylene resin layer is not particularly limited as long as it exhibits the desired heat-welding properties. The melting point of the polyethylene resin layer is preferably, for example, 100°C or higher and 120°C or lower, and more preferably 105°C or higher and 110°C or lower. If the melting point of the polyethylene resin layer is too high, it will be necessary to increase the heating temperature when pressing the current collector sheet to the solar cell element, which may increase manufacturing costs or degrade the solar cell element. On the other hand, if the melting point of the polyethylene resin layer is too low, the polyethylene resin layer may melt in the operating environment of the solar cell, making it difficult to fix the wires.

[0037] 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). If two or more melting point peaks are present, the higher temperature peak can be used as the melting point.

[0038] (2) Polyethylene resin layer material (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 very low-density polyethylene (VLDPE). The polyethylene resin may be used alone or in combination of two or more types. Among these, low-density polyethylene (LDPE) is preferred due to its good flexibility and processability.

[0039] The density of polyethylene resin is not particularly limited, for example, 0.890 g / cm³. 3 More than 0.930g / cm 3 Preferably, it is 0.900 g / cm³. 3 More than 0.925g / cm 3The following is more preferable: By having the density of the polyethylene resin within the above range, the flexibility and processability of the polyethylene resin layer can be improved, and the adhesion to the wire and the ability to embed the wire can be enhanced.

[0040] Here, the density of polyethylene resin can be measured, for example, by the pycnometer method in accordance with JIS K7112.

[0041] The polyethylene resin layer may contain only polyethylene resin as its resin component, or it may contain polyethylene resin in addition to other resins. In the latter case, it is preferable that the polyethylene resin layer contains polyethylene resin as its main component. Note that "containing polyethylene resin as its main component" means that polyethylene resin accounts for the largest proportion of all resin components.

[0042] The proportion of polyethylene resin to the total resin components in the polyethylene resin layer is, for example, 50% by mass or more, may be 60% by mass or more, or 70% by mass or more. Furthermore, the proportion of polyethylene resin is, for example, 99% by mass or less, may be 95% by mass or less, or 90% by mass or less. The proportion of polyethylene resin may also be 100% by mass.

[0043] (b) Adhesion enhancer The polyethylene resin layer in this disclosure may contain an adhesion improver. The adhesion improver is a component that improves adhesion to wires and to solar cell elements.

[0044] Examples of adhesion improvers include silane-modified resins and silane coupling agents.

[0045] (i) Silane-modified resin Examples of silane-modified resins include silane-modified polyolefin resins. Silane-modified polyolefin resins are copolymers of α-olefins and ethylenically unsaturated silane compounds. 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 more preferably a graft copolymer in which polyolefin is the main chain and ethylenically unsaturated silane compounds are polymerized as side chains. Such graft copolymers have a higher degree of freedom for the silanol groups that contribute to adhesion, and thus can further improve adhesion to wires and to solar cell elements.

[0046] Examples of α-olefins that constitute silane-modified polyolefin resins include ethylene, propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. α-olefins may be used individually or in combination of two or more. Among these, polyethylene is preferred. In other words, the silane-modified polyolefin resin is preferably a silane-modified polyethylene resin. This is because silane-modified polyethylene resin has good compatibility with the polyethylene resin contained in the polyethylene resin layer.

[0047] Furthermore, the silane-modified polyethylene resin is preferably a resin obtained by graft polymerization of linear low-density polyethylene (LLDPE) as the main chain and an ethylenically unsaturated silane compound as the side chain.

[0048] Examples of the ethylenically unsaturated silane compounds mentioned above include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane, vinyltriphenoxysilane, vinyltribenzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane. The ethylenically unsaturated silane compounds may be used individually or in combination of two or more.

[0049] Silane-modified polyolefin resin can be obtained, for example, by the manufacturing method described in Japanese Patent Publication No. 2003-46105.

[0050] Silane-modified resins may be used individually or in combination of two or more types.

[0051] 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.

[0052] (ii) Silane coupling agent As the silane coupling agent, a silane coupling agent commonly used as a encapsulant for solar cells can be used. The silane coupling agent may be used alone or in combination of two or more types.

[0053] 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.

[0054] (c) Other ingredients The polyethylene resin layer may contain additives such as antioxidants, antiblocking agents, and lubricants, as needed.

[0055] Here, the proportion of each resin component contained in each layer of the current collector sheet resin film can be analyzed, for example, from the peak ratio detected by scanning calorimetry (DSC), infrared spectroscopy (IR), nuclear magnetic resonance (NMR), etc.

[0056] (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 collection sheets is used as the current collection sheet, and can be appropriately selected according to the thickness of the wire. The thickness of the polyethylene resin layer is preferably greater than the thickness of the base material layer described later. This improves the adhesion to the wire and the embedding of the wire. Specifically, the thickness of the polyethylene resin layer is preferably 40 μm to 100 μm, and more preferably 45 μm to 80 μm. By having the polyethylene resin layer thickness within the above range, the adhesion to the wire and the embedding of the wire can be improved.

[0057] The side of the polyethylene resin layer opposite the adhesive layer may be surface-treated. That is, the polyethylene resin layer may have a surface-treated surface on the side opposite the adhesive layer. This can improve adhesion to the wire and to the solar cell element.

[0058] The surface treatment is not particularly limited as long as it can improve adhesion to the wire and to the solar cell elements, and examples include corona treatment, plasma treatment, ultraviolet treatment, electron beam treatment, and flame treatment. Among these, corona treatment is preferred in terms of processing costs and reducing damage to the polyethylene resin layer.

[0059] 2.Base material layer The base layer in this disclosure contains polyethylene terephthalate resin. The base layer is a component that imparts rigidity to the resin film for the current collector sheet.

[0060] The base layer may contain various additives as needed.

[0061] The thickness of the base layer is not particularly limited and can be appropriately selected depending on the size and application of the solar cell in which the current collector sheet resin film is used. As mentioned above, it is preferable that the thickness of the base layer be 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, and more preferably 12 μm or more and 25 μm or less. If the base layer is too thin, sufficient rigidity may not be achieved. Conversely, if the base layer is too thick, the rigidity may become too high, potentially reducing the ability of the resin film for the current collector sheet to follow the wire.

[0062] The base layer is preferably annealed. This improves thermal dimensional stability. This makes it easier to adjust the thermal shrinkage rate of the resin film for the current collector sheet, described later, to be within a predetermined range. Therefore, when manufacturing a solar cell with a current collector sheet using a current collector sheet having a resin film for the current collector sheet, misalignment of the wires relative to the solar cell elements during the heating process for fixing the wires to the solar cell elements can be suppressed. Also, when manufacturing a solar cell using a solar cell with a current collector sheet, misalignment of the wires relative to the solar cell elements during the heating process for integrating each component can be suppressed. Furthermore, even when the solar cell reaches high temperatures in the operating environment of the solar cell, misalignment of the wires relative to the solar cell elements can be suppressed. As a result, the reliability of the solar cell can be improved.

[0063] The annealing temperature of the substrate layer is preferably, for example, between 120°C and 250°C.

[0064] 3.Adhesive layer The adhesive layer in this disclosure is a component that is placed between the substrate layer and the polyethylene resin layer and is used to bond the substrate layer and the polyethylene resin layer together.

[0065] The adhesive used in the bonding layer is not particularly limited as long as it is transparent and capable of bonding the above-mentioned base material layer and polyethylene resin layer, and examples include adhesives commonly used for laminating films. Examples of adhesives include urethane adhesives, acrylic adhesives, polycarbonate adhesives, and phenolic adhesives. The adhesive may also be, for example, a dry laminating adhesive or an anchor coating agent for extrusion laminating.

[0066] Furthermore, it is preferable that the adhesive has heat and moisture resistance. This can suppress the decrease in adhesive strength due to hydrolysis. For example, it is preferable that the resin component constituting the adhesive does not have ester bonds. Specifically, in the case of a urethane-based adhesive, it is preferable that the main component is polycarbonate polyurethane resin.

[0067] The thickness of the adhesive layer is not particularly limited as long as it is transparent and capable of bonding the substrate layer and the polyethylene resin layer, but is preferably, for example, 0.1 μm or more and 10 μm or less.

[0068] 4. Others The thickness of the resin film for the current collector sheet in this disclosure is not particularly limited and can be appropriately selected according to the thickness of the wire used in the current collector sheet. For example, the thickness of the resin film for the current collector sheet may be 50 μm or more and 300 μm or less. If the resin film for the 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 resin film for the current collector sheet is too thick, the transparency may decrease.

[0069] II. Physical properties of resin film for current collection sheets 1. Thermal shrinkage rate In the resin film for current collector sheets in this disclosure, the thermal shrinkage rate when held at 150°C for 10 minutes is 2.0% or less, preferably 1.5% or less, and more preferably 1.0% or less. By having the thermal shrinkage rate of the resin film for current collector sheets within the above range, thermal dimensional stability can be improved. As a result, when manufacturing a solar cell with a current collector sheet using a current collector sheet having the resin film for current collector sheets, misalignment of the wires relative to the solar cell elements during the heating process for fixing the wires to the solar cell elements can be suppressed. Furthermore, when manufacturing a solar cell using a solar cell with a current collector sheet, misalignment of the wires relative to the solar cell elements during the heating process for integrating each component can be suppressed. Moreover, even when the solar cell reaches high temperatures in the operating environment of the solar cell, misalignment of the wires relative to the solar cell elements can be suppressed. As a result, the reliability of the solar cell can be improved.

[0070] In particular, as will be described later, if the wire is coated with Bi-Sn or Sn-In-Ag-Bi solder, the melting point of these solders is relatively high, which tends to increase the heating temperature in the heating process described above. Therefore, in the above case, it is more preferable that the thermal shrinkage rate of the resin film for the current collector sheet is small, and specifically, it is more preferable that it be 1.0% or less.

[0071] On the other hand, the lower limit of the thermal shrinkage rate mentioned above is sufficient if it is 0% or greater.

[0072] Here, the thermal shrinkage rate of the resin film for current collection sheets mentioned above refers to the larger of the thermal shrinkage rate in the MD direction and the thermal shrinkage rate in the TD direction. In other words, in the resin film for current collection sheets, the larger of the thermal shrinkage rate in the MD direction and the thermal shrinkage rate in the TD direction falls within the above range.

[0073] The MD direction of the resin film for current collection sheets is usually the longitudinal direction of the resin film. The TD direction of the resin film for current collection sheets is usually the short direction of the resin film.

[0074] Furthermore, the thermal shrinkage rate of the resin film for the current collector sheet can be measured, for example, by a method compliant with ASTM D1204.

[0075] One method for controlling the thermal shrinkage rate of resin films for current collector sheets is to adjust the thermal shrinkage rate of the base layer. As mentioned above, methods for adjusting the thermal shrinkage rate of the base layer include, for example, annealing the base layer, adjusting the crystallinity of the polyethylene terephthalate resin contained in the base layer, and adjusting the molding method and molding conditions when forming the polyethylene terephthalate resin into a film. As an example of adjusting the molding method, one method is to apply a relaxation treatment to alleviate stress and strain during molding. As for molding conditions, for example, the stretch ratio can be used.

[0076] 2. Light transmittance at wavelengths between 400 nm and 1200 nm The light transmittance of the resin film for current collector sheets in this disclosure at wavelengths of 400 nm to 1200 nm is not particularly limited, as long as it transmits enough sunlight to enable the solar cell element to generate electricity. The light transmittance of the resin film for current collector sheets at wavelengths of 400 nm to 1200 nm is preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. By having the above light transmittance within the above range, the light utilization efficiency of the solar cell element can be increased.

[0077] Here, the light transmittance in the wavelength range of 400 nm to 1200 nm is the average value of the light transmittance in the wavelength range of 400 nm to 1200 nm. The light transmittance in the wavelength range of 400 nm to 1200 nm can be measured in accordance with JIS K7361 1. Specifically, the light transmittance in the wavelength range of 400 nm to 1200 nm can be measured using the HM150 haze meter manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0078] 3. Hayes The transparency of the resin film for current collector sheets in this disclosure is not particularly limited, as long as it allows sunlight to pass through to a degree that enables the solar cell element to generate electricity. The transparency of the resin film for current collector sheets can be evaluated, for example, by haze. The haze of the resin film for current collector sheets is, for example, 1% to 40%, may be 5% to 30%, or 10% to 20%.

[0079] Here, haze is measured in accordance with JIS K7136. Haze can be measured using, for example, a haze meter HM150 manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0080] When measuring the haze of the resin film for current collector sheets, a sample for measurement will be prepared and used for measurement. The sample for measurement will be prepared by the following method. First, the resin film for current collector sheets will be cut to 50 mm x 50 mm to prepare a test piece. Next, the ETFE (tetrafluoroethylene-ethylene copolymer) film, the test piece, and the ETFE film will be laminated in this order, and vacuum lamination will be performed under the conditions of a set temperature of 165°C, vacuuming for 2 minutes, pressing for 2.5 minutes, and a pressure of 100 kPa. This is to eliminate fine irregularities on the surface of the resin film for current collector sheets during the film formation stage. Subsequently, the ETFE film will be removed from both sides of the test piece to prepare a sample for measurement.

[0081] III. Method for manufacturing resin film for current collector sheets The method for manufacturing a resin film for current collector sheets in this disclosure is not particularly limited as long as a resin film for current collector sheets having a base layer, an adhesive layer, and a polyethylene resin layer in that order can be obtained. For example, examples include a method of using a film-like base layer and a polyethylene resin layer and laminating the base layer and the polyethylene resin layer via a dry laminating adhesive by a dry lamination method, or a method of using a film-like base layer and laminating the base layer and the polyethylene resin layer via an extrusion laminating anchor coating agent by an extrusion lamination method.

[0082] As a method for forming the film-like substrate layer and the polyethylene resin layer, for example, a method can be used in which a resin composition for forming each layer is prepared and the resin composition is melt-molded. As the melt-molding method, a known molding method can be used, for example, injection molding, extrusion molding, hollow molding, compression molding, rotational molding, etc. The molding temperature is, for example, above the melting point of the resin composition. The upper limit of the molding temperature is appropriately adjusted depending on the type of resin composition.

[0083] B. Current collection sheet The current collector sheet in this disclosure is a current collector sheet used in a solar cell, and comprises the above-mentioned resin film for current collector sheets and wires arranged on the side of the polyethylene resin layer of the resin film for current collector sheets.

[0084] Figures 2(a) and 2(b) are schematic plan and cross-sectional views illustrating the current collector sheet in this disclosure, with Figure 2(b) being a cross-sectional view taken along line AA in Figure 2(a). As shown in Figures 2(a) and 2(b), the current collector sheet 20 comprises a current collector sheet resin film 10 and wires 11 arranged on the side of the polyethylene resin layer 3 of the current collector sheet resin film 10. Figure 2(a) shows a schematic plan view of the current collector sheet as seen from the polyethylene resin layer side of the current collector sheet resin film.

[0085] In the current collector sheet described herein, the resin film for current collector sheets allows the wires to be securely fixed to the solar cell elements. Furthermore, the resin film for current collector sheets can suppress wire displacement due to heat. Therefore, when the current collector sheet is used in a solar cell, the power generation efficiency can be improved and reliability can be enhanced.

[0086] I. Configuration of the current collection sheet The current collector sheet in this disclosure comprises a resin film for current collector sheets and a wire.

[0087] 1. Resin film for current collection sheets The resin film for the current collection sheet is a component that supports the wire. Furthermore, the resin film for the current collection sheet is a component that fixes the wire to the solar cell element.

[0088] The resin film for the current collection sheet can be the same as described in "A. Resin Film for Current Collection Sheet" above, so the explanation is omitted here.

[0089] As described later, if the current collection sheet has multiple resin films for current collection sheets, at least one of the resin films for current collection sheets should be the resin film for current collection sheets described above. In this case, the current collection sheet may have other resin films for current collection sheets besides the resin film for current collection sheets described above. In particular, it is preferable that all of the multiple resin films for current collection sheets that the current collection sheet has are the resin films for current collection sheets described above.

[0090] 2. Wire The wire is positioned on the side of the polyethylene resin layer of the current collector sheet resin film. The wire is used, for example, to connect solar cell elements in a solar cell module. It is also used, for example, to collect electricity generated by a solar cell element in a single-cell solar cell. The wire is typically positioned to connect to the electrodes of the solar cell element.

[0091] The cross-sectional shape of a wire is typically circular, such as a perfect circle or an ellipse, but is not limited to these.

[0092] The thickness of the wire, that is, the size of the wire's cross-section, is not particularly limited as long as it does not obstruct the incidence of sunlight onto the solar cell element; for example, it can be between 100 μm and 300 μm. The size of a wire's cross-section refers to, for example, the diameter if the cross-section is circular, the major axis if it is elliptical, and the length of the longest diagonal if it is polygonal.

[0093] The wire material is not particularly limited as long as it exhibits the desired conductivity, and can be the same as the wire material used for current collector sheets in general solar cell elements. For example, metallic materials such as copper (Cu) and silver (Ag) can be used as the wire material. The wire may also have, for example, a core portion and a skin portion located on the outside of the core portion. In this case, for example, the above-mentioned metallic material can be used as the material for the core portion. Solder can be used as the material for the skin portion.

[0094] The melting point of the solder is preferably between 70°C and 140°C, and more preferably between 80°C and 135°C. If the melting point of the solder is too high, it may degrade the substrate layer and polyethylene resin layer when connecting wires to the solar cell element.

[0095] Examples of such solders include Sn-In and Bi-Sn types.

[0096] For example, Bi-Sn solder has a higher melting point compared to Sn-In and In-Bi solders. Therefore, when using Bi-Sn solder, the heating temperature in the heating process when manufacturing solar cell elements with current collectors using current collector sheets, and the heating temperature in the heating process when manufacturing solar cells using solar cell elements with current collector sheets, tend to be higher. Consequently, in the above cases, poor wire adhesion and wire misalignment are likely to occur. Therefore, this disclosure is particularly effective in the above cases.

[0097] II. Structure of current collection sheets In the current collector sheet described herein, it is sufficient that at least one wire is arranged on a single resin film for the current collector sheet. From the viewpoint of improving the conductivity of the current collector sheet, it is preferable that multiple wires are arranged on a single resin film for the current collector sheet.

[0098] When a current collector sheet has multiple wires, the arrangement of the wires in a plan view is not particularly limited and can be the same as the arrangement of wires in known current collector sheets. For example, as shown in Figure 2(a), the wires 11 may be arranged in a line, or, although not shown, the wires may be arranged in a grid.

[0099] Furthermore, in the current collection sheet, the wire is positioned on the side of the polyethylene resin layer of the resin film for the current collection sheet. For example, as shown in Figure 2(b), it is preferable that the wire 11 is positioned such that a portion of the wire 11 is embedded in the polyethylene resin layer 3 of the resin film 10 for the current collection sheet, and a portion of the wire 11 is exposed. This allows the wire to be securely fixed.

[0100] Furthermore, as shown in Figure 2(b), the wire 11 may be embedded in the polyethylene resin layer 3 so as not to contact the base layer 1, or as shown in Figure 4, the wire 11 may be embedded in the polyethylene resin layer 3 so as to contact the base layer 1. When the wire is embedded in the polyethylene resin layer so as to contact the base layer, the thickness of the current collector sheet can be reduced, thus enabling the solar cell using the current collector sheet to be made thinner.

[0101] The degree to which the wires are embedded, i.e., the degree to which the wires are exposed, is not particularly limited and can be appropriately selected depending on the material and thickness of the polyethylene resin layer, the thickness of the wires, and the form of the solar cell element on which the current collector sheet is placed.

[0102] In a current collector sheet, for example, the same wire may be arranged on multiple current collector resin films. For example, Figure 5 shows an example in which the same wire 11 is arranged on two current collector resin films 10A and 10B. Also, as shown in Figure 5, adjacent current collector resin films 10A and 10B may be arranged so that the sides facing the polyethylene resin layer 3 are in opposite plane directions. That is, the side of one current collector resin film 10A facing the polyethylene resin layer 3 and the side of the other current collector resin film 10B facing the base material layer 1 may be in the same plane direction. By having the above structure, the current collector sheet 20 can be made capable of arranging two solar cell elements 31 in series, as shown in Figure 3(a). Although not shown, adjacent current collector resin films may be arranged so that the sides facing the polyethylene resin layer are in the same plane direction.

[0103] III. Manufacturing method of current collector sheets The method for manufacturing a current collector sheet in this disclosure is not particularly limited as long as it allows for the wire to be embedded to a certain extent in the surface side of the polyethylene resin layer of the current collector sheet resin film, and known methods can be used. For example, a method can be given in which a wire is placed on the surface side of the polyethylene resin layer of the current collector sheet resin film, and the wire is heated to melt a portion of the polyethylene resin in the polyethylene resin layer and embed the wire.

[0104] C. Solar cell element with current collector sheet The solar cell element with a current collector sheet in this disclosure comprises the current collector sheet described above, and a solar cell element disposed on the side of the polyethylene resin layer of the current collector sheet and electrically connected to a wire.

[0105] Figures 3(a) to 3(c) are schematic perspective views and cross-sectional views illustrating a solar cell element with a current collector sheet in this disclosure, where Figure 3(b) is a cross-sectional view along line AA of Figure 3(a), and Figure 3(c) is a cross-sectional view along line BB of Figure 3(a). As shown in Figures 3(a) to 3(c), the solar cell element with a current collector sheet 30 includes a current collector sheet 10 and a solar cell element 31 arranged on the side of the polyethylene resin layer 3 of the current collector sheet 10 and electrically connected to a wire 11. Figures 3(a) to 3(c) show an example in which the current collector sheet 20 has two resin films 10 for current collector sheets, and a solar cell element 31 is arranged on each resin film 10 for current collector sheets.

[0106] In the solar cell element with a current collector sheet described in this disclosure, the current collector sheet allows the wires to be securely fixed to the solar cell element by the resin film for the current collector sheet. Furthermore, the resin film for the current collector sheet can suppress wire displacement due to heat. Therefore, when a solar cell element with a current collector sheet is used in a solar cell, the power generation efficiency can be improved and reliability can be enhanced.

[0107] I. Configuration of a solar cell with a current collector sheet The solar cell element with a current collector sheet in this disclosure comprises a current collector sheet and a solar cell element.

[0108] 1. Current collection sheet The current collection sheet can be the same as described in "B. Current Collection Sheet" above, so the explanation here will be omitted.

[0109] If a solar cell element with current collector sheets has multiple current collector sheets, at least one of them should be the current collector sheet described above. In this case, the solar cell element with current collector sheets may also have other current collector sheets besides the current collector sheet described above. In particular, it is preferable that all of the current collector sheets are the current collector sheet described above.

[0110] 2. Solar cell element Solar cell elements can be similar to those used in general solar cells. Examples of solar cell elements include monocrystalline silicon solar cell elements, polycrystalline silicon solar cell elements, amorphous silicon solar cell elements, compound semiconductor solar cell elements, dye-sensitized solar cell elements, quantum dot solar cell elements, and organic thin-film solar cell elements. The size and shape of the solar cell elements can be appropriately selected according to the application of the solar cell.

[0111] II. Structure of a solar cell with a current collector sheet Solar cell elements with current collector sheets typically have a laminated structure in which the current collector sheet and the solar cell element are stacked.

[0112] When a solar cell element with a current collector sheet is viewed with respect to the placement surface of the current collector sheet of the solar cell element, for example, as shown in Figure 3(c), the direction D perpendicular to the placement surface is such that L In this laminated structure, the thickness of the resin film 10 for the current collector sheet, that is, the distance from the surface of the solar cell element 31 on which the current collector sheet 20 is placed to the surface of the base layer 1 opposite to the solar cell element 31, is preferably such that the region where the wire 11 is placed is thicker (longer distance) than other regions. By using such a laminated structure, the base layer 1 can effectively press the wire 11 towards the solar cell element 31, preventing problems such as poor contact between the wire 11 and the solar cell element 31.

[0113] In this case, the direction D is perpendicular to the placement surface. L The maximum distance y of wire 11, that is, the maximum distance y of wire 11 from the surface on which the current collector sheet 20 of the solar cell element 31 is placed, and the perpendicular direction D with respect to the placement surface. L The minimum distance x of the current collector sheet resin film 10, that is, the ratio x / y of the minimum distance x from the surface on which the current collector sheet 20 of the solar cell element 31 is arranged to the surface of the substrate layer 1 opposite to the solar cell element 31, is preferably 2 / 3 or less, and more preferably 1 / 2 or less.

[0114] The lower limit of the above ratio x / y is a value that is appropriately adjusted according to the thickness of the polyethylene resin layer and the thickness of the wire, but for example, it is 1 / 20 or more. As long as the above ratio x / y is within the above range, the wire can be securely fixed to the solar cell element using the resin film for current collection sheets.

[0115] The above ratio x / y can be controlled by adjusting the wire thickness (diameter, etc.) and the thickness of the polyethylene resin layer. Furthermore, as will be described later, the above ratio x / y can also be controlled by adjusting the pressure applied when heat-pressing the current collector sheet to the solar cell element.

[0116] Furthermore, as shown in Figure 3(c), for example, in a cross-sectional view of the solar cell element 30 with a current collector sheet, it is preferable that the distance from the surface of the solar cell element 31 on the current collector sheet 20 side to the surface of the substrate layer 1 opposite to the solar cell element 31 gradually decreases from the position of the maximum distance y to the position of the minimum distance x.

[0117] Furthermore, when multiple wires are arranged, for example, as shown in Figure 3(c), in a cross-sectional view of the solar cell element 30 with a current collector sheet, it is preferable that the portion between adjacent wires 11 is the shortest distance from the surface on which the current collector sheet 20 of the solar cell element 31 is located to the surface of the base layer 1 opposite to the solar cell element 31. This creates a recess between the wires, resulting in a structure where the current collector sheet has an uneven shape, thus increasing the area of ​​the surface of the base layer opposite to the solar cell element. As a result, 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 increases, thereby improving adhesion to the encapsulant.

[0118] Furthermore, in solar cell elements with current collector sheets, as described in section "B. Current Collector Sheet" above, the wire 11 may be embedded in the polyethylene resin layer 3 so as to contact the base material layer 1, for example, as shown in Figure 3(c). This makes it possible to reduce the thickness of the solar cell element with a current collector sheet, thereby making the solar cell thinner.

[0119] A solar cell element with a current collector sheet only needs to have at least one solar cell element and a current collector sheet connected to at least one of the positive and negative electrodes of the solar cell element. For example, it may be a solar cell element with a current collector sheet that constitutes a single-cell type solar cell, in which a current collector sheet is placed on each of the positive and negative electrodes of a single solar cell element. Alternatively, for example, a solar cell element with a current collector sheet may be a solar cell element that constitutes a solar cell module type solar cell (solar cell module) in which multiple solar cells are connected in parallel or in series using current collector sheets.

[0120] Other The method for manufacturing a solar cell element with a current collector sheet in this disclosure is not particularly limited as long as it is a method that can be obtained in which the wires of the current collector sheet are electrically connected to and fixed to the solar cell element. For example, a manufacturing method can be given which includes a temporary bonding step of temporarily bonding the current collector sheet to the solar cell element, and a fixing step of electrically connecting and fixing the wires of the current collector sheet to the solar cell element by thermocompression bonding the temporarily bonded current collector sheet to the solar cell element. Known methods can be used for the temporary bonding method and the thermocompression bonding method, for example, the vacuum thermal lamination method. Furthermore, the fixing step may be performed simultaneously with the integration step of laminating and integrating the various components of the solar cell, as described in section "D. Solar Cell" below.

[0121] Solar cell elements with current collector sheets are typically used as components of a solar cell. If a solar cell element with a current collector sheet comprises, for example, one solar cell element and a current collector sheet connected to only one of the electrodes (either the positive or negative electrode) of the solar cell element, then the solar cell element with a current collector sheet can be used, for example, as part of the single-cell type solar cell described above, or as part of a solar cell module.

[0122] D. Solar cells The solar cell in this disclosure comprises a transparent substrate, a first encapsulant, the solar cell element with the current collector sheet described above, a second encapsulant, and a counter substrate, in this order.

[0123] Figure 6 is a schematic cross-sectional view illustrating a solar cell in this disclosure. As shown in Figure 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.

[0124] The solar cell in this disclosure may be a solar cell module having a plurality of solar cell elements with current collector sheets.

[0125] In the solar cell described herein, by having a solar cell element with a current collector sheet as described above, the wires can be securely fixed to the solar cell element by the resin film for the current collector sheet. Furthermore, the resin film for the current collector sheet can suppress wire displacement due to heat. Therefore, power generation efficiency can be improved and reliability can be enhanced.

[0126] I. Solar cell composition The solar cell in this disclosure comprises, in this order, a transparent substrate, a first encapsulant, a solar cell element with a current collector sheet, a second encapsulant, and a counter substrate.

[0127] 1. Solar cell element with current collection sheet The explanation for solar cell elements with current collector sheets is the same as described in section "C. Solar cell elements with current collector sheets" above, so the explanation is omitted here.

[0128] 2. Transparent substrate and opposing substrate The transparent substrate, along with the opposing substrate, is a component that protects the solar cell elements. Typically, the transparent substrate is placed on the light-receiving side of the solar cell and functions as a front protective plate on that side. The transparency of the transparent substrate is not particularly limited, as long as it does not hinder the power generation of the solar cell elements. Since the transparent substrate can be the same as that used in general solar cells, a detailed explanation is omitted here.

[0129] The opposing substrate, together with the transparent substrate, is a component that protects the solar cell element. The opposing substrate may or may not be transparent. If the opposing substrate is transparent, both sides of the solar cell can be used as light-receiving surfaces. The transparent substrate described above can be used as the opposing substrate. Alternatively, a back-side protective sheet for solar cells can be used as the opposing substrate.

[0130] 3. First sealing material and second sealing material The first encapsulant and the second encapsulant are components that encapsulate the solar cell element. The first encapsulant is usually placed on the light-receiving side of the solar cell.

[0131] The first encapsulant and the second encapsulant contain a thermoplastic resin. The thermoplastic resin used in the first encapsulant and the second encapsulant can be the same as the thermoplastic resin used in general solar cell encapsulants. For example, encapsulants mainly composed of various olefin resins such as polyethylene resin and ethylene-vinyl acetate copolymer (EVA) can be used. Note that "mainly composed of these resins" means that these resins make up the largest proportion of all resin components.

[0132] The first encapsulant typically contains an ultraviolet absorber. This can suppress the deterioration of the substrate layer containing polyethylene terephthalate resin due to ultraviolet light, such as yellowing, cracking, and fracture.

[0133] If the opposing substrate is transparent, the second encapsulant typically contains an ultraviolet absorber, similar to the first encapsulant.

[0134] The ultraviolet absorber can be the same as the ultraviolet absorber used in the encapsulating material of a typical solar cell.

[0135] The thickness of the first and second encapsulants is selected appropriately according to the type and size of the solar cell.

[0136] II. Manufacturing Methods for Solar Cells The method for manufacturing a solar cell in this disclosure can be the same as that for manufacturing a general solar cell. As an example, a manufacturing method can be cited which includes a laminate formation step of forming a laminate by stacking a transparent substrate, a first encapsulant, a solar cell element with a current collector sheet, a second encapsulant, and a counter substrate in that order, and an integration step of integrating the laminate to form a solar cell by heating and pressurizing it.

[0137] The heating and pressurizing processes are not particularly limited and can be the same as those performed during the general manufacture of solar cells. For example, vacuum thermal lamination is preferred. The conditions for the vacuum thermal lamination are not particularly limited and can be appropriately selected depending on the size of the solar cell, the type of each component, etc. The lamination temperature is preferably, for example, 130°C to 170°C. Furthermore, 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.

[0138] III.Applications Examples of applications for solar cells in this disclosure include various applications such as solar cells for electronic devices and large-scale solar cells for outdoor installation.

[0139] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0140] [Example 1] A 12 μm thick polyethylene terephthalate (PET) film (DuPont "LBD") was used as the base layer. A two-component adhesive (anchor coating agent) consisting of a polycarbonate-based main component (Rock Paint "KT-0035") and an isocyanate-based curing agent (Rock Paint "H-039Z2") was used. The polyethylene resin used had a density of 0.92 g / cm³.3 High-pressure low-density polyethylene (LDPE) with a melting point of 106°C and an MFR (190°C) of 7 g / 10 min was used.

[0141] On one side of the base material layer, 0.1 g / m of the above adhesive was applied as an anchor agent. 2 The above polyethylene resin was extruded with a thickness of 60 μm to form a polyethylene resin layer. Further, a corona treatment was performed on the surface of the polyethylene resin layer opposite to the base material layer. As a result, 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.

[0142] [Example 2] A resin film for a current collector sheet was produced in the same manner as in Example 1, except that the base material layer was subjected to an annealing treatment at 200°C for 10 seconds.

[0143] [Comparative Example 1] As the base material layer, a PET film with a thickness of 12 μm was used. Also, as the adhesive (anchor coat agent), a urethane-based adhesive was used. 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 min was used.

[0144] A resin film for a current collector sheet was produced in the same manner as in Example 1.

[0145] [Comparative Example 2] As the base material layer, a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., "E5104") with a thickness of 12 μm was used. Also, as the adhesive (anchor coat agent), a two-component adhesive composed of a polycarbonate-based main agent (manufactured by Rock Paint Co., Ltd., "KT-0035") and an isocyanate-based curing agent (manufactured by Rock Paint Co., Ltd., "H-039Z2") was used. Further, as the polyethylene resin layer, 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 105°C, and an MFR (190°C) of 2 g / 10 min was used.

[0146] A resin film for current collector sheets was obtained by bonding a base material layer and a polyethylene resin layer with an adhesive using a dry lamination method.

[0147] [Comparative Example 3] The polyethylene resin layer has a density of 0.915 g / cm³. 3 A resin film for current collector sheets was prepared in the same manner as in Comparative Example 2, except that a polyethylene film containing metallocene-based linear low-density polyethylene (M-LLDPE) with a melting point of 110°C and an MFR (190°C) of 2 g / 10 min was used.

[0148] [Comparative Example 4] A resin film for current collector sheets was prepared in the same manner as in Example 1, except that the thickness of the polyethylene resin layer was set to 70 μm.

[0149] [evaluation] (1) Thermal shrinkage The thermal shrinkage rates of the resin film for current collector sheets in the MD and TD directions were measured in accordance with ASTM D1204. The measurement conditions were 150°C for 10 minutes.

[0150] (2) Light transmittance at wavelengths between 400 nm and 1200 nm The light transmittance of the resin film for current collector sheets at wavelengths between 400 nm and 1200 nm was measured using a HM150 haze meter manufactured by Murakami Color Technology Laboratory Co., Ltd., in accordance with JIS K7361 1.

[0151] (3) Hayes A resin film for current collector sheets was cut to 50 mm x 50 mm to prepare a test specimen. Next, the ETFE (tetrafluoroethylene-ethylene copolymer) film, the test specimen, and the ETFE film were laminated in this order, and vacuum lamination was performed under the conditions of a set temperature of 165°C, vacuum evacuation for 2 minutes, pressing for 2.5 minutes, and a pressure of 100 kPa. Subsequently, the ETFE film was removed from both sides of the test specimen to obtain a sample for measurement. The haze of the sample was then measured using a haze meter HM150 manufactured by Murakami Color Technology Laboratory Co., Ltd., in accordance with JIS K7136.

[0152] (4) Wire adhesion Wire A, coated with SnIn-based solder, and wire B, coated with SnBi-based solder, were used as the wires. The diameters of wires A and B were 250 μm each. A current collector sheet resin film was cut to 100 mm × 100 mm to prepare a test specimen. Next, an ETFE (tetrafluoroethylene-ethylene copolymer) film was placed on the substrate layer side of the test specimen. On the polyethylene resin layer side of the test specimen, five wires A and five wires B were placed at 10 mm intervals, and then the ETFE film was placed in order. Then, lamination was performed using a hot roll laminator under the 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 specimen to obtain evaluation samples. The wires of the evaluation samples were then bent 180 degrees and peeled off the current collector sheet resin film under the condition of a tensile speed of 300 mm / min, and the peel strength of the current collector wires from the current collector sheet resin film was measured. Wire adhesion was evaluated according to the following criteria. "N / wire" indicates the peel strength when a single wire is peeled off. A: The peel strength is greater than 0.1 N / wire. B: The wire adheres tightly to the resin film for the current collection sheet, but the peel strength is 0.1 N / wire or less. C: The wire does not adhere to the resin film for the current collection sheet and peels off naturally.

[0153] (5) Module reliability First, a current collector sheet was obtained by fixing wires to a resin film for current collector sheets, using the same method as for preparing evaluation samples in the wire adhesion evaluation described above. In this case, a total of 18 wires were placed at 8 mm intervals on the polyethylene resin layer side of the test piece. For samples that received a wire adhesion evaluation of "C", the wire adhesion was ensured by raising the set temperature of the thermal roll laminator to 130°C.

[0154] A 3.2 mm thick white tempered glass board was used as the transparent substrate, a 470 μm thick ethylene-vinyl acetate copolymer (EVA) sheet (Fast Cure EVA, manufactured by Takiron CI Co., Ltd.) was used as the first and second encapsulants, an N-type silicon cell was used as the solar cell element, and an aluminum layer-containing backsheet (VAPE-CW, manufactured by Dai Nippon 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 were laminated together, and vacuum lamination was performed under the conditions of a set temperature of 150°C, vacuuming for 5 minutes, pressing for 7.5 minutes, and a pressure of 100 kPa. When laminating each component, the current collector sheet was positioned so that the wire side of the current collector sheet faced the solar cell element side. Furthermore, as illustrated in Figure 3(b), an evaluation module was fabricated as a solar cell module in which four solar cells were joined in series by arranging the current collection sheets 20 above and below the solar cell elements 31.

[0155] The evaluation modules underwent high-temperature and high-humidity testing (85°C, 85%RH, 2000 hours) and temperature cycling testing (-40°C⇔90°C, 200 cycles, 1 cycle = 6 hours). The photovoltaic output was measured before and after each test, and the output degradation rate was determined. Module reliability was evaluated according to the following criteria. A: The rate of output reduction after both tests is less than 5%. B: The power output reduction rate after at least one of the tests is 5% or more but less than 10%. C: The output reduction rate after at least one of the tests is 10% or more.

[0156] [Table 1]

[0157] Table 1 confirms that when the MFR of the polyethylene resin layer in the current collector sheet resin film is within a predetermined range, and the heat shrinkage rate of the current collector sheet resin film is within a predetermined range, wire adhesion and module reliability are good.

[0158] Furthermore, in Comparative Examples 1 and 4, the output decreased after the temperature cycling test. This is because a high thermal shrinkage rate of the resin film for the current collector sheet leads to high residual stress after module lamination.

[0159] Furthermore, when the PET film used as the base layer in Example 1 and Comparative Example 4 was measured for its thermal shrinkage rate in the same way as the resin film for current collector sheets, the thermal shrinkage rate in the MD direction was 1.4%, and the thermal shrinkage rate in the TD direction was 0.3%. This suggests that even if the thermal shrinkage rate of the base layer itself is 2.0% or less, the overall thermal shrinkage rate of the resin film for current collector sheets is not necessarily 2.0% or less.

[0160] This disclosure provides the following [1] to

[11] . [1] A resin film for current collector sheets used in current collector sheets for solar cells, It has a base layer, an adhesive layer, and a polyethylene resin layer in this order. The above substrate layer contains polyethylene terephthalate resin, The melt mass flow rate of the polyethylene resin layer at 190°C is 4 g / 10 min or more and 8 g / 10 min or less. A resin film for current collector sheets, having a heat shrinkage rate of 2.0% or less when held at 150°C for 10 minutes. [2] The resin film for current collector sheets according to [1], wherein the melting point of the polyethylene resin layer is 100°C or higher and 120°C or lower. [3] A resin film for current collector sheets according to [1] or [2], wherein the thickness of the polyethylene resin layer is greater than the thickness of the base material layer. [4] A resin film for current collector sheets according to any one of [1] to [3], wherein the thickness of the polyethylene resin layer is 40 μm or more and 100 μm or less. [5] A resin film for current collector sheets according to any one of [1] to [4], wherein the thickness of the base material layer is 12 μm or more and 38 μm or less. [6] A resin film for current collector sheets according to any one of [1] to [5], wherein the thickness of the adhesive layer is 0.1 μm or more and 10 μm or less. [7] A resin film for current collector sheets according to any one of [1] to [6], wherein the base material layer has a surface treatment on the side opposite to the adhesive layer. [8] A current collector sheet used in solar cells, A resin film for current collection sheets as described in any of [1] to [7], A wire arranged on the surface side of the polyethylene resin layer of the resin film for current collection sheet, A current collector sheet. The current collection sheet described in [9][8], A solar cell element is arranged on the side of the polyethylene resin layer of the current collector sheet and electrically connected to the wire, A solar cell element with a current collector sheet.

[10] A solar cell comprising, in this order, a transparent substrate, a first encapsulant, a solar cell element with a current collector sheet as described in [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 solar cell elements with current collecting sheets. [Explanation of Symbols]

[0161] 1 … Base material layer 2 … Adhesive layer 3. Polyethylene resin layer 10, 10A, 10B… Resin film for current collection sheets 11… Wire 20... Current collection sheet 30… Solar cell element with current collection sheet 31… Solar cell 40… Solar cells 41… Transparent substrate 42 … First sealing material 43… Second sealing material 44 ... Opposite circuit board

Claims

[Claim 1] A resin film for current collector sheets used in current collector sheets for solar cells, It has a base layer, an adhesive layer, and a polyethylene resin layer in this order. The aforementioned substrate layer contains polyethylene terephthalate resin, The melt mass flow rate of the polyethylene resin layer at 190°C is 4 g / 10 min or more and 8 g / 10 min or less. A resin film for current collector sheets, having a heat shrinkage rate of 2.0% or less when held at 150°C for 10 minutes.

Images