Patent Application
20120240985
1. Field of the Invention
The invention relates a solar cell string and a solar cell module using the same.
2. Description of Related Art
A solar cell converts clean and unlimitedly-supplied sunlight directly into electricity and is therefore expected to be a new energy source.
The output power of a single solar cell is generally about a couple of watts. Thus, when solar cells are used as a power source of a house, a building, or the like, a solar cell module is used in which multiple solar cells are connected to increase the output power of the solar cell module. The solar cell module has a structure in which the solar cells are connected in series and/or in parallel by wiring members electrically connected to electrodes on front and rear surfaces of the solar cells.
In the manufacturing process of the solar cell module, solder is conventionally used to connect the electrodes of the solar cells to the wiring members. Solder is widely used since it is low in cost, has high versatility, and is excellent in connection reliability such as conductivity and fixing strength.
On the other hand, in a solar cell module, a method of connecting wiring members without using solder is also used to reduce effects of heat during the connection of wiring members. For example, there is known a method of connecting solar cells to wiring members by using an adhesive film including a resin adhesive (for example, see Patent Document 1).
The connection of wiring with an adhesive film is performed as follows. First, adhesive films are attached onto electrodes of the solar cells. Then, the wiring members are placed on the adhesive films and the resultant solar cells are heated with the wiring members pressed toward the solar cells. The wiring members are thereby connected to the electrodes of the solar cells by using the resin adhesive.
Such a technique can reduce the effects of temperature change on the solar cells during thermo-compression bonding of wiring members, compared to the case of soldering the wiring members.
In this connection, a type of wiring member used for the connection of wiring with an adhesive film is one including a thin-plate-shaped low-resistance member made of copper or the like and having its surface plated with a conductor such as a eutectic solder. Then, the wiring member is connected with part of an electrode buried into the conductor on the wiring member.
A high-temperature storage test at 170° C. is performed on the aforementioned conventional solar cell module in which the wiring members plated with the eutectic solder are connected to electrodes by using a resin adhesive. As a result of this test, it is found that the adhesion strength of the wiring members is reduced in some cases. The reason of this is not sure but it is conceivable that the adhesion force is reduced by flow of solder which is caused by heat.
Meanwhile, the solar cell modules are also required to be reliable in a high-temperature cycle.
An aspect of the invention provides a solar cell string that comprises multiple solar cells including a photoelectric conversion body configured to generate carriers upon receiving light; an electrode formed on a principle surface of the photoelectric conversion body and configured to collect the carriers; a wiring member electrically connecting the solar cells to each other; and a resin adhesive is disposed between the wiring member and the principle surface of each of the solar cells; wherein the wiring member comprising: a low-resistance body; a conductor including tin or a tin-containing alloy material formed on a periphery of the low-resistance body; and a metal thin film including silver or a silver alloy covering a surface of the conductor.
Embodiments are described in detail with reference to the drawings. Note that the same or corresponding parts are denoted by the same reference numerals and descriptions thereof are omitted to avoid overlapping descriptions. However, the drawings are schematic and proportions of dimensions and the like are different from actual ones. Accordingly, specific dimensions and the like should be determined in consideration of the descriptions below. Moreover, parts where relations and proportions of the dimensions are different among the drawings are included as a matter of course.
A schematic configuration of solar cell module 100 of an embodiment is described with reference to
Solar cell module 100 includes solar cell string 1, light-receiving surface protection member 2, Rear surface protection member 3, and sealing material 4. Solar cell module 100 is formed by sealing solar cell string 1 between light-receiving surface protection member 2 and rear surface protection member 3.
Solar cell string 1 includes solar cells 10, wiring members 11, and resin adhesive 12. Solar cell string 1 is formed by connecting solar cells 10 arranged in a first direction to one another with wiring members 11.
Each of solar cells 10 has a light-receiving surface on which the sunlight falls and a rear surface which is provided on the opposite side of the light-receiving surface. The light-receiving surface and the rear surface are principal surfaces of solar cell 10. Collection electrodes are formed on the light-receiving surface and the rear surface of solar cell 10. A configuration of solar cell 10 is to be described later.
Each of wiring members 11 is connected to the electrode formed on the light-receiving surface of one solar cell 10 and to the electrode formed on the rear surface of another solar cell 10 adjacent to the one solar cell. Solar cells 10, 10 adjacent to each other are thereby electrically connected to each other. As to be described later, wiring member 11 includes: a thin-plate shaped low-resistance body (copper or the like); a conductor (an eutectic solder or the like) formed on a surface of the low resistance body by plating; and a metal thin film covering a surface of the conductor and including silver or a silver alloy.
Resin adhesive 12 is disposed between each of wiring members 11 and correspond one of solar cells 10. In other words, wiring member 11 is connected to solar cell 10 via resin adhesive 12. Resin adhesive 12 preferably cures at a temperature equal to or lower than the melting point of the eutectic solder, i.e. at a temperature of about 200° C. or below. For example, a conductive adhesive film is used as resin adhesive 12. Conductive adhesive film 12 is formed to include at least a resin adhesive component and conductive particles dispersed in the resin adhesive component. The resin adhesive component in which the conductive particles are dispersed is provided on a base film made of polyimide or the like. Resin adhesive component 5b is made of a composition including a thermosetting setting resin. For example, an epoxy resin, a phenoxy resin, an acrylic resin, a polyimide resin, a polyamide resin, and a polycarbonate resin can be used. These thermosetting resins are used alone or in combination of two or more thermosetting resins. One or more thermosetting resins selected from the group consisting of the epoxy resin, the phenoxy resin, and the acrylic resin are preferably used.
Examples of the conductive particles may be metal particles such as gold particles, silver particles, copper particles and nickel particles. Alternatively, gold-plated particles, copper-plated particles, and nickel-plated particles, which are each formed by covering a surface of a conductive or insulative core particle with a conductive layer such as a metal layer, are used as the conductive particles.
Light-receiving surface protection member 2 is disposed on a light-receiving-surface side of sealing material 4 and protects a front surface of solar cell module 100. A translucent glass with water-blocking properties, a translucent plastic, or the like can be used as light-receiving surface protection member 2.
Rear surface protection member 3 is disposed on a rear-surface side of sealing material 4 and protects a back surface of solar cell module 100. A resin film of PET (Polyethylene Terephthalate) or the like, a stacked film having such a structure that Al foil is interposed between resin films, or the like can be used as rear surface protection member 3.
Sealing material 4 seals solar cell string 1 at a position between light-receiving surface protection member 2 and rear surface protection member 3. A translucent resin such as EVA, EEA, PVB, silicon, urethane, acryl, or epoxy can be used as sealing material 4.
Note that an Al (aluminum) frame (not illustrated) can be attached to an outer periphery of solar cell module 100 having the aforementioned configuration.
Next, a configuration of solar cell 10 is described with reference to
As shown in
Photoelectric conversion body 20 generates carriers by receiving the sunlight. Here, the carries refer to positive holes and electrons generated when the sunlight is absorbed by photoelectric conversion body 20. Photoelectric conversion body 20 includes therein an n-type region and a p-type region and a semiconductor junction is formed at an interface between the n-type region and the p-type region. Photoelectric conversion body 20 can be formed by using a semiconductor substrate made of a semiconductor material including a crystalline semiconductor material such as a single crystal Si and a polycrystalline Si, a compound semiconductor material such as GaAs and InP, and the like. A solar cell as follows is used as photoelectric conversion body 20. For example, in the solar cell, an intrinsic amorphous silicon layer is interposed between a single crystal silicon and an amorphous silicon layer, which respectively have conductivity types opposite to each other, to reduce defects in the interface therebetween and improve characteristics of heterojunction interface.
Finger electrodes 30 are electrodes configured to collect the carriers from photoelectric conversion body 20. As shown in
Bus bar electrodes 40 are electrodes configured to collect carriers from finger electrodes 30. As shown in
The number of bus bar electrodes 40 can be set to an appropriate number in consideration of the size of photoelectric conversion body 20 and the like. Solar cell 10 of the embodiment includes two bus bar electrodes 40.
Next, a case where photoelectric conversion body 20 has a so-called HIT structure is described as an example of the configuration of solar cell 10 with reference to
As shown in
p-type amorphous silicon layer 20b is formed on the light-receiving-surface side of n-type single silicon substrate 20d with i-type amorphous silicon layer 20c in between. Translucent conductive film 20a is formed on the light-receiving-surface side of p-type amorphous silicon layer 20b. Meanwhile, n-type amorphous silicon layer 20f is formed on the rear-surface side of n-type single crystal silicon substrate 20d with i-type amorphous silicon layer 20e in between. Translucent conductive film 20g is formed on the rear-surface side of n-type amorphous silicon layer 20f.
Finger electrodes 30 and bus bar electrodes 40 are formed on each of translucent conductive film 20a on the light-receiving-surface side and translucent conductive film 20g on the rear-surface side.
Next, a structure of solar cell string 1 is described with reference to
As shown in
Moreover, wiring members 11 are disposed on resin adhesive 12 along bus bar electrodes 40, respectively. In other words, wiring members 11 are disposed along the first direction on the primary surface of solar cell 10. The width of wiring member 11 is approximately the same as the width of bus bar electrode 40.
Bus bar electrodes 40, resin adhesive 12, and wiring members 11 are sequentially disposed on photoelectric conversion body 20 as described above. Wiring members 11 and bus bar electrodes 40 are electrically connected to each other, respectively.
As shown in
Tin, SnAgCu, SnPb, SnCuNi or the like is used for conductor 11b. In the embodiment, a SnAgCu solder is provided on the periphery of copper foil 11a. Conductor 11b has a thickness of 40 μm at a center portion and the thickness thereof becomes smaller from the center portion toward end portions. Metal thin film 11c is provided by plating the periphery of conductor 11b with silver to a thickness of 1 μm.
Resin adhesive 12 has a thickness of 30 μm before pressure bonding and bus bar electrode 40 has a thickness of 50 μm and a width of 1 mm. Incidentally, the substrate of solar cell 10 has a thickness of 200 μm.
As described above, the thickness of conductor 11b becomes smaller toward the end portions in a direction approximately perpendicular to the primarily surface of solar cell 10. Accordingly, in a cut section approximately perpendicular to the first direction, an outer periphery of wiring member 11 is formed to have a shape protruding toward solar cell 10. As shown in
Resin adhesive 12 is disposed between each wiring member 11 and solar cell 10. Resin adhesive 12 includes particles 13 being conductive. As shown in
Wiring member 11 and bus bar electrode 40 are electrically connected to each other by particles 13 embedded in metal thin film 11c and conductor 11b and particles 13 interposed among metal thin film 11c, conductor 11b, and bus bar electrode 40.
Next, a configuration of wiring member 11 used in the embodiment is further described with reference to
Such a wiring member 11 is formed as follows. A rectangular copper wire having a thickness of 200 μm and a width of 1 mm is prepared and the SnAgCu solder is provided on the rectangular copper wire to have a thickness of 1 μm to 100 μm, preferably about 40 μm, by dip soldering. The solder composition of the dip soldering is set to Sn 96.5 wt %, Ag 3 wt %, Cu 0.5 wt % in standard concentration. Conductor 11b including the SnAgCu solder is provided by dip soldering the rectangular copper wire at a withdrawal speed of 1 m/second. Then, Ni plating as an underlying layer of silver plating is provided on a surface of the SnAgCu solder by electroplating to have a thickness of 0.5 μm. The Ni plating is performed with a temperature and a pH respectively set to 60° C. and 4, by using a plating bath having a composition of 330 g/liter of nickel nitrate (NiSO4.6H2O), 45 g/liter of nickel chloride (NiCl2.6H2O), and boric acid (H3BO3).
Then, sliver plating is performed to a thickness of 0.1 μm to 10 μm, preferably about 1.0 μm and metal thin film 11c is thereby formed. An ammoniacal solution of silver nitrate including aldehyde, glucose, Rochelle salt, and the like as a reducer is used as a plating bath.
Note that when a copper plating (formed to 0.5 μm by electroplating) is formed on the Ni plating by using a copper sulfate aqueous solution, the sliver plating to be formed on the copper plating can be formed better.
By using wiring member 11 formed as described above, reliability in a high-temperature storage test and in a high-temperature cycle can be secured. Conductor 11b made of the aforementioned solder may be made of a metal having a Vickers hardness smaller than 25 Hv or any one of SnAgCu, SnPb, and the like. Moreover, a sliver plating portion may be made of a silver-containing alloy.
Next, a solar cell using the wiring member of the embodiment and a solar cell using a conventional wiring member are prepared to perform reliability test and results thereof are shown.
In the high-temperature storage test, solar cell 10 to which wiring member 11 is connected is stored at 170° C. for 1000 hours and the strength thereof is then measured to be compared with the initial strength. The measurement is performed as follows. As shown in
The prepared samples include: a conventional example using a wiring member in which conductor 11b made of a solder is provided around a copper foil having the same width of 1 mm and the same thickness of 200 μm; the embodiment using a wiring member which is provided with metal thin film 11c by plating the surface of conductor 11b with 1.0 μm of sliver; and a reference example using a wiring member which is provided with sliver plating of 1.0 μm directly on the periphery of the copper foil. The peel strength test is performed by using these samples in such a way that, as shown in
As is apparent from Table 1, the strength after the test is 11.7% of the initial value in the sample using the conventional wiring member in which only the solder is provided, and the strength of the wiring member is drastically reduced. On the other hand, the embodiment has a strength equal to 58.4% of the initial value and the reference example has a strength equal to 59.8% of the initial value. It can be understood from this that the degree of deterioration is improved compared to the conventional example.
Next, for each of the samples described above, wiring members 11 are connected to the front and rear of single solar cell 10 by using resin adhesive 12. Then, the solar cell is sealed between a glass member on a front surface and a rear surface member by using a sealing material to form a module. Thereafter, the sample is subjected to the high-temperature cycle test as follows. The sample is heated at a temperature of 120° C. for 90 minutes and thereafter cooled to −40° C. in 90 minutes. Subsequently, the sample is maintained at −40° C. for 90 minutes and thereafter heated to 120° C. in 90 minutes. Table 2 shows results of comparison between the maximum output power value (Pmax) after 200 cycles of this test and the initial value.
It can be found from Table 2 that the embodiment has the smallest degree of deterioration with respect to the initial value and achieves a value equal to 98.70% of the initial value.
Accordingly, it can be found from Tables 1, 2 that a wiring member which satisfies both tests is the one of the embodiment.
Next, modifications of the wiring member used in the embodiment are described with reference to
In an embodiment shown in
In an embodiment shown in
In an embodiment shown in
Next, a method of manufacturing solar cell module 100 of an embodiment is described.
First, n-type single crystal silicon substrate 20d of 100 mm square is subjected to anisotropic etching by using an alkaline aqueous solution and fine concaves and convexes is thereby formed on a light receiving surface of n-type single crystal silicon substrate 20d. Further, the light-receiving surface of n-type single crystal silicon substrate 20d is cleaned to remove impurities.
Next, i-type amorphous silicon layer 20c and p-type amorphous silicon layer 20b are sequentially stacked on the light-receiving-surface side of n-type single crystal silicon substrate 20d by using the CVD (Chemical Vapor Deposition) method. Similarly, i-type amorphous silicon layer 20e and n-type amorphous silicon layer 20f are sequentially stacked on the rear-surface side of n-type single crystal silicon substrate 20d.
Then, translucent conductive film 20a is formed on the light-receiving-surface side of p-type amorphous silicon layer 20b by using the PVD (Physical Vapor Deposition) method. Similarly, translucent conductive film 20g is formed on the rear-surface side of n-type amorphous silicon layer 20f. Photoelectric conversion body 20 is thus produced.
Subsequently, an epoxy-based thermosetting type silver paste is disposed on the light-receiving surface and the rear surface of photoelectric conversion body 20 in a predetermined pattern by using a printing method such as screen printing and offset printing.
The silver paste is heated under a predetermined conduction to vaporize a solvent and is then further heated to be subjected to main drying. Solar cell 10 is thus produced.
Next, as shown in
Particles 13 are embedded into the conductors by pressing wiring members 11 to solar cell 10.
Solar cell string 1 is thus formed.
Then, a EVA (sealing material 4) sheet, solar cell string 1, another EVA (sealing material 4) sheet, and a PET sheet (rear surface protection member 3) are sequentially stacked on a glass substrate (light-receiving surface protection member 2) to form a stacked body.
Subsequently, the stacked body is temporally compression-bonded by subjecting the stacked body to thermo-compression bonding in a vacuum atmosphere. Thereafter, EVA is completely cured by heating under a predetermined condition. Solar cell module 100 is thus manufactured.
Incidentally, a terminal box, Al frame, and the like can be attached to solar cell module 100.
In each of the embodiments described above, the solar cell including bus bar electrodes 40 with the same width as that of wiring member 11 is described as solar cell 10. However, it is possible to use a solar cell including no bus bar electrodes 40 and a solar cell including bus bar electrodes 40 with a width wider than that of finger electrode 30 but narrower than that of wiring member 11.
Moreover, in the embodiments described above, the conductive resin adhesive including conductive particles is used as the resin adhesive. However, it is possible to use a resin adhesive including no conductive particles. When the resin adhesive including no conductive particles is used, the electrical connection is achieved by bringing a portion of each electrode in direct contact with the surface of a corresponding wiring member. In this case, the wiring member and the electrode are preferably connected to each other with the portion of the electrode buried into the conductor of the wiring member.
As described above, according to the embodiment, a conductor including tin or a tin-containing alloy material is formed on the periphery of the low-resistance body and the surface of the conductor is coated with the metal thin film including silver or a silver alloy. By using a wiring material including the conductor, the embodiment can secure reliability in a high temperature storage test and a high-temperature cycle and to improve reliability of the solar cell module.
It should be understood that the embodiments disclosed herein are exemplary in all points and does not limit the invention. The scope of the invention is defined not by the descriptions of the embodiments but by claims and it is intended that the scope of the invention includes equivalents of claims and all modifications within the scope of claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-196293 | Aug 2009 | JP | national |
This application is a continuation application of International Application No. PCT/JP2010/063809, filed on Aug. 16, 2010, entitled “SOLAR CELL STRING, SOLAR CELL MODULE USING THEREOF”, which claims priority based on Article 8 of Patent Cooperation Treaty from prior Japanese Patent Applications No. 2009-196293, filed on Aug. 19, 2009, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2010/063809 | Aug 2010 | US |
| Child | 13406199 | US |
