JP6053567B2 - Conductive adhesive film for connecting ribbon wire to solar cell surface electrode - Google Patents

Description

  The present invention relates to a conductive adhesive film for connecting a ribbon wire to a surface electrode formed on a solar cell, and more particularly, a ribbon wire connected to the surface electrode and a ribbon connected to a back electrode of the solar cell. The present invention relates to a conductive adhesive film for connecting a ribbon line to a solar cell surface electrode with little reduction in conversion efficiency when converting light energy such as sunlight received by a solar cell into electric energy between wires.

  Conventionally, as a thermosetting adhesive film that is cured by heating to connect a semiconductor element and a substrate, an adhesive film that can sufficiently suppress warping of the substrate and has excellent connection reliability is used. An adhesive film, which is a conventional circuit connection material, has been proposed (Patent Document 1). Also, as an anisotropic conductive adhesive for connecting and electrically connecting substrates and electronic parts with electrodes, circuits, etc., without impairing basic properties such as adhesiveness, conduction / insulation performance, etc. An anisotropic conductive adhesive that can suppress thermal expansion under high temperature and high humidity conditions and improve connection stability has been proposed.

JP 2007-91959 A Japanese Patent Laid-Open No. 2010-100900

  The adhesive film shown in Patent Document 1 is an adhesive film made of a curable resin composition, has a glass transition temperature after curing of 65 to 110 ° C., and an elastic modulus at 40 ° C. after curing of 1500 MPa or less. And the elastic modulus at 100 ° C. after curing is 10 MPa or more. Further, the anisotropic conductive adhesive of Patent Document 2 has an epoxy resin, a phenoxy resin, a curing agent, an inorganic filler, and conductive particles as essential components, and the glass transition temperature (Tg) of the phenoxy resin is 66 ° C. or higher and 100 ° C. It is characterized by the following.

  However, these adhesive films and anisotropic conductive adhesives are intended only to connect a semiconductor element and a substrate, and to connect a substrate or an electronic component provided with electrodes, circuits, etc. Thus, it was not intended to connect the ribbon wire to the surface electrode formed in the solar cell. For this reason, when these adhesive films or anisotropic conductive adhesives are used to connect the ribbon wire to the surface electrode of the solar cell, light energy such as sunlight received by the solar cell is converted into electric energy. There is a problem that the conversion efficiency at the time of conversion greatly decreases with time and the adhesive strength may be insufficient.

  The problem to be solved by the present invention is that there is little or almost no decrease in the conversion efficiency with time when converting light energy such as sunlight received by the solar cell into electric energy, and it has sufficient adhesive strength. An object of the present invention is to provide a conductive adhesive film for connecting a ribbon wire to a solar cell surface electrode.

The invention described in claim 1 is a conductive adhesive film used for connecting a ribbon wire to a surface electrode of a solar battery cell, and is a potential of phenoxy resin, epoxy resin, silane coupling agent, and epoxy resin. A conductive adhesive film for connecting a ribbon wire to a solar cell surface electrode, characterized by comprising a conductive curing agent and a conductive filler and having a glass transition temperature after curing of 182 ° C. or higher and 190 ° C. or lower. is there.

The invention according to claim 2, phenoxy resin comprises at least fluorene skeleton-containing phenoxy resin, epoxy resin solar cell surface electrode of claim 1, wherein it is a tetrafunctional epoxy resin di naphthalene skeleton-containing It is an electroconductive adhesive film for connecting a ribbon wire to.

The invention described in claim 3 is characterized in that the silane coupling agent is epoxy silane, and the conductive material for connecting the ribbon wire to the solar cell surface electrode according to any one of claims 1 to 2. Adhesive film.

The invention relating to the conductive adhesive film for connecting a ribbon wire to a solar cell surface electrode according to claim 1 and claim 2 converts light energy such as sunlight received by the solar cell into electrical energy. There is almost no decrease in the conversion efficiency with time, and there is an effect of having a sufficient adhesive strength even after time.

  The present invention will be described in detail below.

The invention relating to the conductive adhesive film for connecting the ribbon wire to the solar cell surface electrode according to claim 1 includes a phenoxy resin, an epoxy resin, a silane coupling agent, an epoxy resin latent curing agent, and a conductive material. A conductive adhesive film composed of a conductive filler, containing an antifoaming agent, a leveling agent, a thixotropic agent, a diluent, a tackifier, and a flame retardant, if necessary, and a glass transition temperature after curing of 182 ° C. or higher 190 It is below ℃. If the glass transition temperature is less than 182 ° C , there is a slight decrease in the conversion efficiency over time when converting light energy such as sunlight received by the solar cell into electrical energy, and if it exceeds 190 ° C, the adhesive strength over time Decrease rate increases.

Although the phenoxy resin phenoxy resin is not particularly limited, a weight average molecular weight of 20,000 to 100,000 is preferable. The weight average molecular weight here is measured by the GPC method. By using these phenoxy resins, the composition before film formation according to the present invention can be dissolved in an organic solvent and can be easily formed into a film by a cast coating method, a melt extrusion method or the like. In addition to the phenoxy resin, the conductive adhesive film of the invention of the present application contains the following epoxy resin, and further contains a latent curing agent for the epoxy resin. Functions as a curable resin. As a commercial product of phenoxy resin, there is Epotot YP-50 (trade name, pellet-like solid, weight average molecular weight: 60000-80000, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.).

The phenoxy resin contains a fluorene skeleton-containing phenoxy resin in addition to the phenoxy resin, or a fluorene skeleton-containing phenoxy resin is used instead of the phenoxy resin, and a difunctionalene skeleton-containing tetrafunctional epoxy resin is used as the epoxy resin. By using it, the glass transition temperature after hardening can be made into 182 degreeC-190 degrees C or less. As a commercially available fluorene skeleton-containing phenoxy resin, there is Epototo FX-293 (trade name, solid, weight average molecular weight: about 45000, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.).

Epoxy resin When the phenoxy resin contains at least a fluorene skeleton-containing phenoxy resin, a difunctional phthalene-containing tetrafunctional epoxy resin can be used. It can be 182 degreeC or more and 190 degrees C or less. A commercially available tetrafunctional epoxy resin containing a dinaphthalene skeleton is EPICLON HP4710 (trade name, solid, tetrafunctional epoxy resin, epoxy equivalent; 160-180, manufactured by DIC Corporation).

 The compounding quantity of the epoxy resin used for the invention which concerns on this application is 1 weight part or more and less than 300 weight part with respect to 100 weight part of phenoxy resins, More preferably, it is 10 weight part or more and less than 200 weight part. If it is less than 1 part by weight, the adhesive strength is insufficient, and if it is 300 parts by weight or more, film formation becomes difficult. If it is less than 10 parts by weight, the adhesive strength tends to be insufficient, and if it is 200 parts by weight or more, film formation tends to be difficult.

Silane coupling agent Examples of the silane coupling agent include 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltrimethyl having an epoxy group. Epoxy silanes such as ethoxysilane and epoxy silanes such as 3-glycidoxypropyl monomethyldimethoxysilane can be used. Commercially available products include DYNASYLAN G as 3-glycidoxypropyltrimethoxysilane.
There is LYMO (trade name, 3.7 mPa · s / 20 ° C., manufactured by EVONIK). The amount is from 0.1 parts by weight to less than 30 parts by weight, more preferably from 1 part by weight to less than 15 parts by weight, based on 100 parts by weight of the phenoxy resin. If it is less than 0.1 parts by weight, the adhesive strength is insufficient, and if it is 30 parts by weight or more, curing is insufficient. Further, if it is less than 1 part by weight, the adhesive strength tends to be insufficient, and if it is 15 parts by weight or more, curing tends to be insufficient.

Epoxy resin latent curing agent Epoxy resin latent curing agent can be selected from imidazole, hydrazide, modified polyamine, boron trifluoride amine complex, guanamine, melamine, and urea. It is desirable to consist of at least one. As an imidazole-based commercial product, there is Curazole 2MZ-H (solid, imidazole-based, manufactured by Shikoku Kasei Co., Ltd.). In addition, the latent curing agent may be microencapsulated by coating with a polymer material such as polyurethane, polyurea, polyester, etc. As a commercial product of the microencapsulated latent curing agent, NovaCure HX-3941HP (trade name, 35% microencapsulated latent curing agent, 15% bisphenol A type liquid epoxy resin, 50% bisphenol F type liquid epoxy resin, manufactured by Asahi Kasei E-Materials). NovaCure HX-3941HP is obtained by dispersing a microencapsulated latent curing agent in a liquid epoxy resin. The blending amount of the latent curing agent is 1 part by weight or more and less than 200 parts by weight, more preferably 10 parts by weight or more and less than 100 parts by weight with respect to 100 parts by weight of the phenoxy resin. If it is less than 1 part by weight, curing is insufficient, and if it is more than 200 parts by weight, the storage stability is deteriorated. Further, if it is less than 10 parts by weight, curing tends to be insufficient, and if it is 100 parts by weight or more, storage stability tends to be poor.

Conductive filler In the present invention, metal particles such as gold, silver, nickel, copper, zinc and tin, and conductive fillers obtained by applying gold plating and nickel plating to the metal particles can be used. As a commercial item, there is nickel powder 4SP10 (trade name, powdered solid, average particle diameter 7 μm, manufactured by NOVAMENT). The blending amount is 0.1 part by weight or more and less than 300 parts by weight, more preferably 1 part by weight or more and less than 200 parts by weight with respect to 100 parts by weight of the phenoxy resin. If the amount is less than 0.1 parts by weight, conduction failure is caused. If the amount is 300 parts by weight or more, the aggregation of the conductive filler increases and the production becomes impossible. Further, if it is less than 1 part by weight, there is a tendency for poor conduction, and if it is 200 parts by weight or more, aggregation of the conductive filler tends to increase during stirring. The average particle size of the conductive filler measured by particle size distribution measurement is desirably 1 μm or more and less than 20 μm, and more preferably 5 μm or more and less than 15 μm. If it is less than 1 μm, conduction failure occurs, and if it is 20 μm or more, it becomes impossible to manufacture. Further, if it is less than 5 μm, there is a tendency for poor conduction, and if it is 15 μm or more, it tends to be difficult to manufacture. Here, the average particle size means the particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method.

  The conductive film according to the present application is desirably formed to a thickness of 100% to 500% with respect to the average particle diameter of the conductive filler to be blended. As a result, when the conductive adhesive film of the present invention is used to heat and pressurize the ribbon wire to connect to the solar cell surface electrode, the melt flow of the film is easily performed, and the conductive adhesion can be performed in a short time. Can be formed.

Hereinafter, the conductive adhesive film according to the present application will be specifically described with reference to Examples, Reference Examples, and Comparative Examples.

Reference Example 1 to Reference Example 7 and Example 1 to Example 2
Epototo YP50 (trade name, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) as the phenoxy resin, Epototo FX-293 (trade name, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) as the phthalene skeleton-containing epoxy resin , EPICLON HP-4032 (trade name, manufactured by DIC Corporation) as cresol novolac type epoxy resin A, EPICLON N730A (trade name, manufactured by DIC Corporation) and EPICLON N-770 (cresol novolak type epoxy resin B) EPALLOY 8370 (trade name, high-viscosity liquid, epoxy equivalent; 205-215, CVC Thermoset Specialia), trade name, solid, epoxy equivalent; 183 to 193, manufactured by DIC Corporation) as cresol novolac type epoxy resin C IES) as a trifunctional or higher functional epoxy group-containing epoxy resin, EPALLOY 9000 (trade name, manufactured by CVC Thermoset Specialties) as a dinaphthalene skeleton-containing tetrafunctional epoxy resin, EPICLONP 4710 (trade name, manufactured by DIC Corporation) ) And 75 parts by weight of ethyl acetate are added to the prescribed parts by weight shown in Table 1, respectively, to prepare a 40 wt% ethyl acetate solution (Table 1 does not indicate the number of blended ethyl acetate).

8 parts by weight of nickel powder 4SP10 (trade name, manufactured by NOVAMENT) having an average particle diameter of 7 μm is added to the solution as a conductive filler. Next, as a latent curing agent for the epoxy resin, 40 parts by weight of liquid epoxy resin NovaCure HX-3941HP (trade name, manufactured by Asahi Kasei E-Materials) containing a microcapsule type latent curing agent, and 3-glycidoxypropyltrimethoxysilane 2 parts by weight of DYNASYLAN GLYMO (trade name, manufactured by EVONIC) is added and stirred uniformly to obtain a mixed solution before film formation. The mixed solution is uniformly applied to PET film NP38SA (trade name, manufactured by Panac Co., Ltd.) with a film applicator SA-204 (manufactured by Sheen Co., Ltd.) to about 40 to 50 μm, and then dried at 80 ° C. for 5 minutes to obtain ethyl acetate. Is volatilized out of the coating film. With a film thickness measuring device DIGIMICRO (manufactured by NIKON), it was confirmed that the thickness of the conductive adhesive film formed on the PET film was 20 to 25 μm, and Reference Examples 1 to 7 and Examples 1 to The conductive adhesive film of Example 2 was obtained.

Comparative Example 1 and Comparative Example 2
EP828 (trade name, epoxy equivalent: 184) is used as a bisphenol A type liquid epoxy resin in place of the epoxy resin blended in Reference Examples 1 to 7 and Examples 1 to 2 in the blending shown in Table 1. -194 g / eq, manufactured by Mitsubishi Chemical) or Adeka Resin EP-4010 (trade name, epoxy equivalent: 350 g / eq, manufactured by ADEKA) as an EO-modified epoxy resin, and Comparative Example 1 and Comparative Example by the same method 2 conductive adhesive films were obtained.

Evaluation items and evaluation methods

Glass-transition temperature
The conductive adhesive films of Reference Example 1 to Reference Example 7, Example 1 to Example 2, and Comparative Example 1 and Comparative Example 2 are cut into 50 mm × 50 mm, and heat-treated for 10 minutes in a 200 ° C. constant temperature layer. The film after the heat treatment was further cut into a width of 40 mm × 5 mm and used as a sample. The obtained sample was subjected to a tensile test using a dynamic viscoelasticity measuring device Q800 (manufactured by TA Instruments) from room temperature to 220 ° C. under the conditions of a heating rate of 3 ° C./min and a frequency of 1 Hz, and a storage elastic modulus. The loss elastic modulus was obtained, and the temperature at the maximum point of TanΔ obtained was defined as the glass transition temperature.

Initial shear strength and post-heating shear strength
The conductive adhesive films of Reference Examples 1 to 7, Example 1 to Example 2, Comparative Example 1 and Comparative Example 2 are made of surface electrodes (material: Ag) formed on solar cells (125 mm × 125 mm). Paste, cut to the width of 2 mm x 125 mm and pasted on the surface electrode as a 1 mm x 120 mm adhesive conductive film for bonding, and ribbon wire (material: solder-plated copper, manufactured by Hitachi Cable, NoWarp, (1.5mm wide x 100mm long x about 0.25mm thick) is placed on a pressure bonding device (Osaki Engineering Co., Ltd., CT-400) and heated and pressurized at 180 ° C, 1Mpa, 10 seconds, Adhere the surface electrode and ribbon wire with a conductive adhesive film to make a solar cell test specimen with a ribbon wire for shear strength measurement. The ribbon wire and solar cell of the solar cell test specimen with a ribbon wire for measuring shear strength are 5 mm in an Instron tensile tester 5500R (manufactured by Instron) so that a shear stress is applied to the conductive adhesive film portion. Tensile per minute, the shear strength (MPa) was measured, and the measured value was taken as the initial shear strength. The measurement was performed at 23 ° C.

  Similarly, after preparing a solar cell test specimen with a ribbon wire for measuring shear strength, the test specimen was left at 125 ° C. for 1000 hours, and then the shear strength (MPa) was measured at 23 ° C. in the same manner. Was the shear strength after heating.

Initial conversion efficiency and post-heat cycle conversion efficiency and conversion efficiency decrease rate
The conductive adhesive films of Reference Examples 1 to 7, Example 1 to Example 2, Comparative Example 1 and Comparative Example 2 are made of surface electrodes (material: Ag) formed on solar cells (125 mm × 125 mm). Paste, cut to the width of 2 mm x 125 mm and pasted on the surface electrode as a 1 mm x 120 mm adhesive conductive film for bonding, and ribbon wire (material: solder-plated copper, manufactured by Hitachi Cable, NoWarp, (1.5mm wide x 100mm long x about 0.25mm thick) is placed on a pressure bonding device (Osaki Engineering Co., Ltd., CT-400) and heated and pressurized at 180 ° C, 1Mpa, 10 seconds, The surface electrode and the ribbon wire are bonded with a conductive adhesive film. The ribbon wire is soldered to the back surface silver electrode of the solar battery cell to obtain a solar battery cell specimen with a ribbon wire for measuring conversion efficiency. The conversion efficiency Pmax when converting the light energy into the electrical energy using the solar simulator for solar cell evaluation (product name, manufactured by Wacom Denso Co., Ltd.) in an atmosphere of 23 ° C. immediately after the preparation of the test body. (W) was measured and the conversion efficiency was defined as the initial conversion efficiency.

  Next, the same specimen was placed at −40 ° C. for 30 minutes and then immediately placed at 120 ° C. for 30 minutes as one cycle. This was repeated 200 cycles, and then a solar cell evaluation apparatus solar simulator was used in an atmosphere at 23 ° C. Thus, the conversion efficiency Pmax (W) at the time of converting light energy into electric energy was measured, and the conversion efficiency was defined as the conversion efficiency after heat cycle. The% conversion efficiency after the heat cycle relative to the initial conversion efficiency was calculated as the conversion efficiency reduction rate%.

Evaluation results The evaluation results are shown in Table 2.

Summary
Becomes 88.8% ～96.8% decrease rate of Reference Example 1 to Reference Example 5 the conversion efficiency, it is determined that the glass transition temperature conversion efficiency is below 97% 88% less than 120 ° C. or higher 165 ° C. . In Reference 6 to Reference 7 and Examples 1 to 2 , the conversion efficiency decrease rate is 97.1% to 99.8%. When the glass transition temperature is 165 ° C. or higher and 190 ° C. or lower, the conversion efficiency is 97% or higher and 99.99. It is judged to be 8% or less.

The shear strength is 0.59 MPa or more in Reference Examples 1 to 7 and Examples 1 to 2, and the ratio of the shear strength after heating to the initial shear strength is 80% or more, and the adhesive strength is sufficient.

Claims (3)

A conductive adhesive film used to connect a ribbon wire to the surface electrode of a solar battery cell, comprising a phenoxy resin, an epoxy resin, a silane coupling agent, an epoxy resin latent curing agent, and a conductive filler A conductive adhesive film for connecting a ribbon wire to a solar cell surface electrode, wherein the glass transition temperature after curing is 182 ° C. or higher and 190 ° C. or lower.   The conductive material for connecting a ribbon wire to a solar cell surface electrode according to claim 1, wherein the phenoxy resin includes at least a fluorene skeleton-containing phenoxy resin, and the epoxy resin is a dinaphthalene skeleton-containing tetrafunctional epoxy resin. Adhesive film. The conductive adhesive film for connecting a ribbon wire to the solar cell surface electrode according to claim 1, wherein the silane coupling agent is epoxy silane.