JP2009088152A - Solar battery module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery module whose module output degradation is suppressed by suppressing warpage stress due to the bonding of solar battery elements to a tab wire, cracking in the elements or the separation of electrodes. <P>SOLUTION: The tab wire 30 to which the plurality of solar battery elements 1 are connected into a module form and collector electrodes 12 on the solar battery elements are electrically connected to each other using conductive adhesive 20 formed of a resin containing a conductive material 26. The conductive material 26 is rod-shaped, and so it has an area contacting the collector electrodes 12 and the tab wire 30, larger than spherical one, thus improving adhesive strength. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solar cell module in which collector electrodes of a plurality of solar cell elements are connected by a conductive connector.

  In recent years, solar cells are expected as a new energy source that does not emit carbon dioxide, which causes global warming.

  When a solar cell is installed in a building or house and used as a power source, it is often used in the form of a solar cell module in which a plurality of solar cell elements are connected in series or in parallel in order to increase the output to several hundred watts.

  Conventionally, in the modularization of solar cell elements, electrical connection was made by soldering a conductive connection body (tab wiring) such as copper foil to a collecting electrode provided in a plurality of solar cell elements ( For example, Patent Document 1).

  Currently, lead-free solder is being used due to concerns about the impact on the natural environment. However, lead-free solder has a higher melting point than conventional solder, and the heating temperature for bonding increases, so There was a risk of damaging the material constituting the periphery to be attached and reducing the yield in manufacturing.

  Also, in the soldered solar cell element, due to the difference between the thermal expansion coefficient of the base material and the thermal expansion coefficient of the core material of the tab wiring, the junction between the collector electrode and the tab wiring in the course of the temperature cycle in use. There was a problem that the stress was concentrated, causing cracking and warping of the element.

  Further, in the joining by soldering, the flux residue is present in the alloy layer formed at the joining interface between the collector electrode and the tab wiring, which becomes a resistance component, which causes a decrease in module output.

  From such a background, it has been studied to use a conductive adhesive as an alternative to solder for connecting the collector electrode and the tab wiring.

  FIG. 11 is a plan view showing a part of a conventional solar cell module. In the figure, a conductive adhesive 20 is applied as an adhesive layer on the collector electrode 12 of the solar cell element 1, and a tab wiring 30 is attached thereon. The conductive adhesive 20 is obtained by adding a spherical conductive material 24 (such as nickel particles) to a non-conductive adhesive resin 22 (such as an epoxy resin). In FIG. 11, the conductive material 24 is schematically shown and does not accurately represent actual dimensions and shapes.

  FIG. 12 is a partial cross-sectional view of the tab wiring attachment portion. The tab wiring 30 in which the copper foil 30 a is coated with tin 30 b and the collector electrode 12 on the photoelectric conversion layer 10 are thermocompression bonded via the conductive adhesive 20. Is done. The tab wiring 30 and the collector electrode 12 are electrically connected by contacting the nickel particles 24 in the epoxy resin 22 by thermocompression bonding.

If the temperature of thermocompression bonding is 200 ° C. or less, productivity can be improved because processing can be performed at a temperature lower than that by joining by soldering. In addition, since the concentration of stress on the joint can be avoided by using a resin material, the output of the module can be prevented from being reduced due to peeling of the tab wiring, etc., and at the same time, the output of the module can be reduced due to the flux residue at the solder joint interface. Therefore, the reliability of the module can be improved.
JP 2005-217148 A

However, since the collector electrode on the solar cell element is formed by printing and curing a conductive paste containing metal particles by screen printing or the like, the surface has many irregularities.
As shown in FIG. 12, in the conventional conductive adhesive using a spherical conductive material, the conductive material 24 makes electrical connection by contacting both the collector electrode 12 and the tab wiring 30 on the solar cell element 10. However, depending on the interval and depth of the unevenness on the surface of the collector electrode 12, the conductive material 24 is buried in the recess, and a large number of particles that do not adhere to the tab wiring 30 and contribute to electrical conduction are generated. There is a problem that the electrical connection between the collector electrode 12 and the tab wiring 30 is not sufficient and the output of the solar cell module is lowered.

  Therefore, in the present invention, in view of the above-described problems, a conductive adhesive is used that provides sufficient electrical connection between the collector electrode of the solar cell element and the tab wiring by adding a rod-shaped conductive material into the resin. Provided solar cell module.

  The present invention is a solar cell module in which electrodes of a plurality of solar cell elements are electrically connected to each other by a connection body, and the electrodes and the connection body are connected by an adhesive layer made of a resin including a plurality of rod-shaped conductive materials. It is characterized by.

  Further, the rod-shaped conductive material in the adhesive layer has a major axis larger than the average interval of the irregularities formed on the surface of the electrode.

  Furthermore, the rod-shaped conductive material in the adhesive layer is 2 to 20 vol. It is characterized by being included.

  According to the present invention, since the conductive material in the adhesive layer for connecting the collector electrode of the solar cell element and the tab wiring is rod-shaped, it is in line contact with the collector electrode and the tab wiring, and the conventional spherical conductive material Compared with the point contact, the contact area becomes large.

  Since the long diameter of the rod-shaped conductive material existing in the adhesive layer is larger than the average interval of the unevenness on the collector electrode surface, the conductive material exists across the convex part on the collector electrode surface, so the collector electrode and the tab wiring are securely Can connect. Even if one end of the conductive material fits into the recess, the other end reaches the tab wiring, so that a sufficient electrical connection can be obtained between the collector electrode and the tab wiring.

  Further, by using a conductive adhesive, the temperature required for joining becomes lower than that in the case of soldering, and the material constituting the periphery of the solder is damaged, and the manufacturing yield is hardly lowered.

  Furthermore, by using a resin material as the binder for the conductive adhesive, it is possible to alleviate the stress concentration caused by the large difference in thermal expansion coefficient between the solar cell element and the core material of the tab wiring. Can be prevented and reliability can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a solar cell element 1 constituting a solar cell module according to an embodiment of the present invention, and FIG. 2 shows a cross-sectional view of the I-I ′ portion in FIG. 1.

  The solar cell element 1 includes a substrate 10 on which a photoelectric conversion layer that generates a photogenerated carrier by light incidence is formed, and a pair of positive and negative collector electrodes 12 and 14 for taking out the photogenerated carrier generated in the photoelectric conversion layer.

  The pair of positive and negative collector electrodes 12 and 14 are usually provided on the light receiving surface and the back surface of the photoelectric conversion layer, respectively. In this case, of the pair of collector electrodes 12 and 14, the collector electrode 12 provided on the light receiving surface side of the photoelectric conversion layer is a plurality of layers disposed over almost the entire light receiving surface in order to minimize the area that blocks incident light. The narrow finger portion 12a and the wide bus bar portion 12b that intersects the finger portion 12a and is connected to the tab wiring. The finger part 12a is an electrode for collecting photogenerated carriers generated in the photoelectric conversion layer. For example, line-shaped electrodes having a width of about 100 μm are arranged every 2 mm. The bus bar portion 12b is an electrode for collecting photogenerated carriers collected by the plurality of finger portions 12a, and is formed in a line shape so as to intersect with all the finger portions 12a with a width of about 1 mm, for example. The bus bar portions 12b are appropriately set in an appropriate number in consideration of the size and resistance of the solar cell element 1.

  Further, the other collector electrode 14 provided on the back side does not need to consider incident light, and may be formed so as to cover almost the entire surface of the photoelectric conversion layer. You may form in a shape.

The collector electrode 12 is formed by printing and curing a thermosetting conductive paste using epoxy resin as a binder and silver particles as a filler by screen printing or the like. Or you may form by baking an electrically conductive paste.
The collector electrodes 12 and 14 are formed with irregularities with an average interval of 20 μm on the surface due to the influence of screen printing mesh and the like.

  In the composition of the conductive paste, in addition to silver, the conductive filler may be one kind of metal particles selected from copper, nickel, gold, tin, aluminum or the like, or an alloy or a mixture thereof.

  Furthermore, as a filler shape, a flaky shape and a spherical shape can be mixed, or a mixture of different sizes can be devised to increase electrical conductivity.

  The binder resin is mainly intended to adhere a conductive material, and is required to be excellent in moisture resistance and heat resistance in order to maintain reliability. Examples of the resin satisfying these include an acrylic resin, a polyimide resin, a phenol resin, a urethane resin, a silicon resin, and the like, in addition to an epoxy resin, at least one selected from these, or a mixture or copolymerization of these resins. Can be applied. The ratio of the binder resin to the conductive filler is 70 wt. % Or more is preferable.

  As shown in FIG. 2, in the solar cell element 1, a p-type amorphous silicon layer 10c is formed on the upper surface of an n-type single crystal silicon substrate 10a via an i-type amorphous silicon layer 10b, and i is also formed on the lower surface. An n-type amorphous silicon layer 10f is formed via a type amorphous silicon layer 10e, and ITO films 10d and 10g are formed as transparent conductive films.

  On the ITO film 10d on the light receiving surface side, the collector electrode 12 including the finger portions 12a and the bus bar portions 12b is formed as described above. Similarly, a collecting electrode 14 including finger portions 14a and bus bar portions 14b is formed on the back side.

  In the above embodiment, the ITO film is used as the transparent conductive film, but another transparent conductive film such as a ZnO film may be used.

  As shown in FIG. 3, the solar cell element 1 is connected to the tab wiring 30 by a conductive adhesive at the bus bar portion 12b, and a solar cell module is configured by connecting a plurality of solar cell elements similarly.

  FIG. 4 is a cross-sectional view taken along the line II-II ′ in FIG.

  In FIG. 4, the tab wiring 30 includes a conductive adhesive that connects the bus bar portion 12 b of the collector electrode 12 on the light receiving surface side of the solar cell element and the bus bar portion 14 b of the collector electrode 14 on the back surface side of another adjacent solar cell element. By using the connection 20, a plurality of solar cell elements are connected in series.

  As shown in FIG. 5, the conductive adhesive 20 includes a plurality of rod-shaped conductive materials 26, which will be described in detail later, in an adhesive resin 22 such as an epoxy thermosetting resin. Alternatively, the rod-shaped conductive material 26 is in contact with both 14 and the tab wiring 30 to electrically connect them. In order to achieve both sufficient adhesive force and electrical connection, it is preferable that the ratio of the surface area at which the bar-shaped conductive material 26 sandwiched therebetween is in contact with the tab wiring 30 is 20 to 80%. In FIG. 5, the rod-shaped conductive material 26 is schematically shown and does not accurately represent actual dimensions and shapes.

  As the rod-like conductive material 26 to be contained in the conductive adhesive 20, at least one metal selected from nickel, silver, copper, gold, tin, aluminum or the like, or an alloy or a mixture thereof can be applied. Furthermore, in order to improve electrical conductivity, the surface of the conductive material may be provided with irregularities so as to increase the surface area.

  FIG. 6 shows a state in which the tab wiring 30 and the collector electrode 12 are bonded via the conductive adhesive 20 in the section taken along the line III-III ′ in FIG.

  As shown in FIG. 6, the tab wiring 30 in which the periphery of the copper foil 30 a is coated with tin 30 b is electrically connected by a rod-shaped conductive material 26 included in the adhesive resin 22.

  The rod-shaped conductive material 26 is, for example, a metal powder such as nickel, but may be a gap spacer having a current-carrying function in which a minute core material such as a monofilament is plated with nickel, or a hollow shape. There may be. Assuming that the maximum length of the rod-shaped conductive material 26 is the long diameter, the rod-shaped conductive material 26 is made so that the long diameter is larger than the average interval of the irregularities formed on the surface of the collector electrode 12. Here, a rod-shaped conductive material 26 having a major axis of 30 μm is used with respect to an average interval of unevenness of 20 μm. Further, the rod-like conductive material 26 is not limited to a material having a major axis of 30 μm, but may be a material in which the conductive material is mixed in a certain ratio.

  As the conductive adhesive 20, in order to achieve both the adhesive property of the adhesive resin 22 and the electrical conductivity of the rod-shaped conductive material 26, the conductive material 26 is contained in the resin 22 in an amount of 2 to 20 vol. % Addition is preferable. This is because, when a large amount of conductive material is added, the original physical properties of the resin are impaired.

  As shown in FIG. 7, the rod-like conductive material 28 may be a rod-like rod having a non-constant width such as a cylinder, and shapes such as a needle shape and a fiber shape are also included in the rod shape. Moreover, even if it is columnar, it does not necessarily need to be a cylinder, and what has arbitrary cross-sectional shapes, such as a triangular prism and a quadratic prism, is applicable, and these may be mixed. A shape having a major axis as described above is collectively referred to as a rod shape.

  The tab wiring 30 is made of tin-plated copper foil, but the core material of the tab wiring may be made of a material such as silver, gold, tin, nickel, aluminum, or an alloy thereof in addition to copper. good.

  The solar cell element groups connected by the tab wiring 30 are laminated with glass and a back film, and a sealing material is filled therebetween. Furthermore, after attaching a terminal box and a metal frame, it is used as a solar cell module.

  Regarding the selection of the resin to be used as the conductive adhesive, the resin that coats the periphery of the collector electrode that intersects the tab wiring is a material used for the tab wiring in order to relieve stress caused by expansion and contraction of the tab wiring due to the temperature cycle. It is preferable that the material be more flexible, and at the same time, it is preferable to use a thermosetting resin material in consideration of bonding with the tab wiring. In addition, since it is required to have excellent moisture resistance and heat resistance for maintaining reliability, in addition to epoxy resin, at least one selected from acrylic resin, polyimide resin, phenol resin, urethane resin, silicon resin, etc. Alternatively, it is preferable to use a mixture or copolymerization of these resins.

  Below, the manufacture example of the solar cell module concerning this embodiment is demonstrated using FIG. 2, FIG.

(Step 1: Formation of photoelectric conversion layer)
An n-type single crystal silicon substrate 10a having a resistivity of about 1 Ω · cm from which impurities have been removed and a thickness of about 300 μm is prepared. Using an RF plasma CVD method, an i-type amorphous silicon layer 10b having a thickness of about 5 nm and a p-type amorphous silicon layer 10c having a thickness of about 5 nm are formed on the upper surface of the n-type single crystal silicon substrate 10a. They were formed in this order. The specific formation conditions of the i-type amorphous silicon layer 10b and the p-type amorphous silicon layer 10c by RF plasma CVD are as follows: a frequency of about 13.65 MHz, a formation temperature of about 100 to 250 ° C., and a reaction stress of about 26. .6 to 80.0 Pa, RF power was about 10 to 100 W.

  Next, an i-type amorphous silicon layer 10e having a thickness of about 5 nm and an n-type amorphous silicon layer 10f having a thickness of about 5 nm were formed in this order on the lower surface of the n-type single crystal silicon substrate 10a. . The i-type amorphous silicon layer 10e and the n-type amorphous silicon layer 10f were formed by the same processes as the i-type amorphous silicon layer 10b and the p-type amorphous silicon layer 10c, respectively.

Next, ITO films 10d and 10g having a thickness of about 100 nm were formed on the p-type amorphous silicon layer 10c and the n-type amorphous silicon layer 10f by magnetron sputtering, respectively. The specific formation conditions of the ITO films 10d and 10g are a formation temperature of about 50 to 250 ° C., an Ar gas flow rate of about 200 sccm, an O ₂ gas flow rate of about 50 sccm, a power of about 0.5 to 3 kW, and a magnetic field strength of about 500 to 3000 Gauss. there were.

(Process 2: Collector electrode formation)
The collector electrodes 12 and 14 were formed by printing a thermosetting conductive paste on the ITO films 10d and 10g by a screen printing method, followed by thermosetting. As a procedure, first, printing on the light-receiving surface side, heating at 150 ° C. for 10 minutes and pre-curing, then printing on the back side, heating at 150 ° C. for 10 minutes, pre-curing, then heating at 200 ° C. for 1 hour By doing so, the silver paste was completely cured. As a result, collector electrodes 12 and 14 including a plurality of finger portions 12a and 14a and bus bar portions 12b and 14b formed to extend in parallel with each other at a predetermined interval were formed. The finger portions 12a, 14a and the bus bar portions 12b, 14b may be formed integrally, or the bus bar portions 12b, 14b may be formed after the finger portions 12a, 14a are formed.

  Here, the collector electrode is printed to have a film thickness of 35 μm, and the resistance of the formed electrode is 10 to 20 μΩcm. The interval between the irregularities on the surface of the collector electrode is 20 μm on average.

(Process 3: Attaching the tab)
The conductive adhesive 20 has an epoxy resin as a binder and nickel particles as a conductive material. Is applied to the bus bar portions 12b and 14b of the collector electrodes 12 and 14 by using a dispenser so that the line width is 1.3 mm and the thickness is about 30 μm, and the tab wiring having a width of 1.5 mm is provided thereon. 30 is arranged. A plurality of solar cell elements are connected by heating at 200 ° C. for 1 hour while pressurizing at 2 MPa. By curing while applying pressure, the conductive material in the conductive adhesive can be sandwiched between the tab wiring 30 and the collector electrodes 12 and 14, so that good electrical conductivity is obtained. In addition, the conductive adhesive 20 is stretched by thermocompression bonding and is expanded to almost the same width as the tab wiring 30.

(Process 4: modularization)
A plurality of solar cell element groups connected by the tab wiring 30 were placed after placing a sealing material made of an EVA sheet on the glass serving as the surface protective material. Further, an EVA sheet was placed thereon, and then a back film having a three-layer structure of PET / aluminum foil / PET was disposed. These are vacuum-bonded and then temporarily bonded by thermocompression bonding at 150 ° C. for 10 minutes, and then completely cured by heating at 150 ° C. for 1 hour. A terminal box and a metal frame were attached to the solar cell module.

(Solar cell module using solar cell element without bus bar)
In the embodiment described above, the collector electrodes 12 and 14 are composed of the finger portions 12a and 14a and the bus bar portions 12b and 14b. The invention may be applied.

  A case where the present invention is applied to a bus barless solar cell element will be described below.

  The configuration of the photoelectric conversion layer 10 of the solar cell element 1 and the method of forming the collector electrodes 12 and 14 are the same as those of the solar cell element having the bus bar portion.

  In the case of a bus barless solar cell element, collector electrodes 12 are formed at almost equal intervals on the light receiving surface side of the photoelectric conversion layer as shown in FIG. 8, and the conductive adhesive 20 as shown in FIGS. 9 and 10. The collector electrode 12 and the tab wiring 30 are connected so as to cross each other. In FIG. 9, the rod-like conductive material 26 is schematically shown and does not accurately represent actual dimensions and shapes.

(Comparative Example 1)
As a solar cell module according to the comparative example, a solar cell element having a bus bar portion was used, and a conductive adhesive was made to contain spherical nickel as a conductive material, and the diameter of the conductive material was 10 μm.

Example 1
As a solar cell module according to an embodiment of the present invention, a solar cell element having a bus bar portion is used, and a conductive adhesive contains cylindrical nickel as a conductive material, and the short diameter of the conductive material is 15 μm and the long diameter is 30 μm. Produced.

(Example 2)
As a solar cell module according to an example of the present invention, a bus barless solar cell element was used, and a conductive adhesive was made to contain columnar nickel as a conductive material, and the conductive material was made with a short diameter of 15 μm and a long diameter of 30 μm. .

(Evaluation methods)
About the solar cell module in the comparative example 1 and Example 1, 400 cycles of the temperature cycle test (JIS C8917) were respectively performed, the output of the solar cell module before and after the test was measured, and the output reduction rate was compared. The output of the solar cell module was measured under light irradiation of AM 1.5 and 100 mW / cm ² .

(Experimental result)
Table 1 shows the normalized output decrease rate in each comparative example and example. The output reduction rate is calculated from the formula (1-output after test / output before test), and the relative output reduction rate is displayed with the output reduction rate in Comparative Example 1 being 1.00. Moreover, about the conversion light rate, the value which normalized the comparative example as 1.000 about the initial value is shown.

実施例と比較例との対比により、以下のことが分かった。すなわち、集電極１２、１４とタブ配線３０を接続する導電性接着剤２０中の導電材に、集電極表面の凹凸の平均間隔よりも大きい長径を有する棒状のものを用いることで、従来の球状のものよりも出力低下が少なく、太陽電池モジュールとしての信頼性が向上できたことが分かった。また、本発明はバスバー部を有する太陽電池素子だけでなく、バスバーレスの太陽電池素子を用いた太陽電池モジュールにも有効であることが分かった。

The following was found by comparing the Examples and Comparative Examples. In other words, the conductive material in the conductive adhesive 20 that connects the collector electrodes 12, 14 and the tab wiring 30 is a rod-shaped member having a major axis larger than the average interval of the irregularities on the collector electrode surface, so that a conventional spherical shape is used. It was found that the output reduction was less than that of the solar cell module and the reliability as a solar cell module could be improved. Moreover, it turned out that this invention is effective not only for the solar cell element which has a bus-bar part but the solar cell module using a bus-bar-less solar cell element.

  In the embodiment of the present invention, a substantially intrinsic amorphous silicon layer is sandwiched between the single crystal silicon substrate and the amorphous silicon layer, defects at the interface are reduced, and the heterojunction interface is reduced. Although the description has been made using the solar cell element having a structure with improved characteristics, the same applies to a normal crystal system, a thin film system, a compound semiconductor system, a dye sensitization system, and an organic system solar cell.

  In the present embodiment, the conductive adhesive 20 as an adhesive layer is applied to the collector electrodes 12 and 14, but a film-like conductive adhesive may be disposed on the collector electrode.

  Furthermore, the conductive adhesive 20 in the present invention only needs to include a rod-shaped conductive material, and may include other shapes of conductive materials such as a granular conductive material in addition to the rod-shaped conductive material.

  As described above, the present invention is not particularly limited to the embodiments shown in the drawings, and includes various embodiments that are not described. Therefore, the present invention is limited only by the invention specifying matters according to the scope of claims reasonable from this disclosure.

It is a top view of the solar cell element by embodiment of this invention. It is sectional drawing of the solar cell element by embodiment shown in FIG. It is a top view at the time of connecting a solar cell element in series with a tab wiring as an example used for a solar cell module. It is sectional drawing of the solar cell element group shown in FIG. It is a figure which shows a part of solar cell module by the 1st Embodiment of this invention. It is a fragmentary sectional view of the solar cell element by the 1st Embodiment of this invention. It is a fragmentary sectional view of the solar cell element by other embodiments of the present invention. It is a top view of the solar cell element by the 2nd Embodiment of this invention. It is a figure which shows a part of solar cell module by the 2nd Embodiment of this invention. It is sectional drawing of the solar cell element group shown in FIG. It is a top view which shows a part of conventional solar cell module. It is a fragmentary sectional view of the conventional solar cell element shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell element 10 Photoelectric conversion layers 12 and 14 Collector electrode 20 Conductive adhesive 22 Adhesive resin 24 Spherical conductive material 26 and 28 Rod-shaped conductive material 30 Tab wiring

Claims (3)

  A solar cell module in which electrodes of a plurality of solar cell elements are electrically connected to each other by a connecting body, wherein the electrodes and the connecting body are connected by an adhesive layer made of a resin including a plurality of rod-shaped conductive materials. A solar cell module characterized by that.   2. The solar cell module according to claim 1, wherein the rod-shaped conductive material in the adhesive layer has a major axis that is larger than an average interval of irregularities formed on the surface of the electrode. The rod-shaped conductive material in the adhesive layer is 2 to 20 vol. % Is contained, The solar cell module of Claim 1 or 2.

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