JP2004179335A - Solar cell element and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize the formation of solder bridges or solder balls in coating an electrode with solder and to ensure stable output of power generation. <P>SOLUTION: A solar cell element is provided, having an arrangement wherein a surface of a semiconductor substrate 1 having semiconductor junctions is formed with a grid-like surface electrode 5 consisting of finger electrodes 5a and bus bar electrodes 5b having substantially the same length as that of one side of the semiconductor substrate 1, and a back of the semiconductor substrate 1 is formed with a back electrode, and both of the surface and the back electrodes are coated with solder 7. In the arrangement, a cut portion 9 is provided to the solder at approximately the central position of each of the finger electrodes 5a. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solar cell element and a method for manufacturing the same, and more particularly, to a solar cell element in which a surface electrode is composed of a finger electrode and a bus bar electrode and a method for manufacturing the same.
[0002]
[Prior Art and Problems to be Solved by the Invention]
FIG. 4 shows a conventional solar cell element. In FIG. 4, 1 is a semiconductor substrate showing one conductivity type (for example, P type), 2 is a diffusion layer having another conductivity type in which phosphorus atoms are diffused at a high concentration on the surface portion of the semiconductor substrate 1, and 3 is an antireflection The film 4 is a BSF layer in which one conductivity type impurity is diffused at a high concentration, 5 is a front electrode, and 6 is a back electrode. The surface electrode 5 includes a plurality of finger electrodes 5a and a bus bar electrode 5b interconnecting the plurality of finger electrodes 5a.
[0003]
FIG. 5 shows the structure of a surface electrode of a conventional solar cell element. In FIG. 5, 12 indicates a solar cell element, 5a indicates a finger electrode, and 5b indicates a bus bar electrode. A bus bar electrode 5a is provided on the surface of the solar cell element 12, and a plurality of finger electrodes 5b are provided perpendicular to the bus bar electrode 5a. The electrode pattern of this type of solar cell is designed so that the pitch of the finger electrodes 5b is determined by the sheet resistance of the diffusion layer 3 (see FIG. 4) and the wiring resistance is minimized. Coated.
[0004]
FIG. 6A is a diagram for explaining a method of coating the solder 7. Reference numeral 13 denotes a solder bath, and 14 denotes molten solder. At this time, according to the pattern shown in FIG. 5, a pattern portion closed by the two bus bar portions 5a and the finger portions 5b is formed, and there is a possibility that a solder film may be formed on this portion. If the solder film does not repel after the solar cell element 12 is lifted from the solder tank 13, a solder bridge is formed and the space between the adjacent finger electrodes 5a is covered with the solder film, and the light receiving area decreases. On the other hand, when the solder film has popped, a solder ball is formed on the surface electrode 5 by the solder having no place to go. These solder films and solder balls impair the appearance and lower the yield when modularized.
[0005]
Conventionally, as a solution to these problems, when the solar cell element 12 is pulled up from the solder tank 13, there is a method in which hot air is sent by a heater so that the solder film is peeled off, or the pulled up solar cell element 12 is heated (for example, See Patent Document 1.).
[0006]
Further, in order to improve the wettability between the solder and the semiconductor substrate 1, the solder temperature is raised more than necessary or the solder temperature is slowly raised from the solder bath 13.
[0007]
However, if the solar cell element 12 is heated more than necessary at the time of solder dipping or pulling up, a problem that the adhesion strength between the surface electrode 5 and the semiconductor substrate 1 is reduced is caused.
[0008]
In order to solve this problem, when coating the surface electrode 5 with the solder 7, a resist film (not shown) is applied to a part of the surface electrode 5 and coated with the solder 7 (for example, Patent Document 2). According to this method, for example, a solder resist made of, for example, an organic cured resin is applied to the middle of the bus bar electrode 5b where the finger electrode 5a intersects and covered with the solder 7, so that the surface electrode 5 having a closed pattern is formed. However, when the solder 7 is coated, a film of the solder 7 is not formed, so that generation of solder balls can be prevented. Further, since the immersion time in the solder bath 13 is shortened, the adhesion strength between the semiconductor substrate 1 and the surface electrode 5 is improved.
[0009]
However, according to this method, there is a problem that the amount of the solder 7 coated on the bus bar electrode 5b becomes larger than before, and there is a problem that the surplus solder 7 becomes a solder ball in a later process. Was.
[0010]
Further, in order to solve this problem, as shown in FIG. 7, a substantially center of the finger electrode 5a is cut, and as shown in FIG. There is also a method of dipping (for example, see Patent Document 3). 7A is a view when the solar cell element 12 is viewed from the light receiving surface side, FIG. 7B is an enlarged view of a portion A in FIG. 7A, and FIG. 7C is a view in FIG. It is sectional drawing. According to this method, there is no closed pattern because the finger electrode 5a is cut at substantially the center, and no film of the solder 7 is formed when the solder 7 is coated. Can be. Further, it is possible to suppress the problem that the amount of the solder 7 coated on the bus bar electrode 5b increases.
[0011]
However, according to this method, as shown in FIG. 7, since the finger electrode 5a is cut at the substantially central portion 11, a portion of the finger electrode 5a between the two bus bar electrodes 5b is cut off or a high resistance portion occurs. Then, there is a problem that a portion not connected to the bus bar electrode 5b is generated, which causes a significant decrease in output.
[0012]
The present invention has been made in view of the problems of such a conventional method, and when coating an electrode with solder, minimizes the occurrence of solder bridges and solder balls and secures stable power generation output. It is an object of the present invention to provide a solar cell element and a method for manufacturing the same.
[0013]
[Patent Document 1]
JP-A-3-145166 [Patent Document 2]
JP 2002-43596 A [Patent Document 3]
JP-A-11-298019
[Means for Solving the Problems]
In order to achieve the above object, in the solar cell element according to claim 1, a finger electrode and a bus bar electrode having substantially the same length as one side of the semiconductor substrate are provided on the front surface side of the semiconductor substrate having the semiconductor junction. In a solar cell element in which a back electrode is formed on the back side of the semiconductor substrate and the electrodes on both the front and back sides are covered with solder, a solder electrode is formed substantially at the center of the finger electrode. A cutting portion is provided.
[0015]
In the method for manufacturing a solar cell element according to the second aspect, finger electrodes and bus bar electrodes having substantially the same length as one side of the semiconductor substrate are provided in a grid on the front surface side of the semiconductor substrate having the semiconductor junction. In the method of manufacturing a solar cell element in which a front electrode is formed, a back electrode is formed on the back surface of the semiconductor substrate, and the electrodes on both front and back surfaces are coated with solder, a solder resist is applied to a substantially central portion of the finger electrode. The other part is covered with solder.
[0016]
In the method for manufacturing a solar cell element, it is preferable that the semiconductor substrate is immersed in a solder bath to cover the finger electrodes with the solder.
[0017]
In the method for manufacturing a solar cell element, it is preferable that the bus bar electrode is immersed in the solder tank with the vertical direction.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing a method for manufacturing a solar cell element according to the present invention. First, the semiconductor substrate 1 is prepared. This semiconductor substrate 1 is made of single crystal or polycrystalline silicon. This silicon substrate 1 is a substrate containing about 1 × 10 ¹⁶ to 1 × 10 ¹⁸ atoms / cm ³ of one conductivity type semiconductor impurity such as boron (B) and having a specific resistance of about 1.5 Ωcm. In the case of a single crystal silicon substrate, it is formed by a pulling method or the like, and in the case of a polycrystalline silicon substrate, it is formed by a casting method or the like. A polycrystalline silicon substrate can be mass-produced and is more advantageous than a single crystal silicon substrate in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced into a thickness of about 300 to 500 μm, and cut into a size of about 15 cm × 15 cm to obtain a semiconductor substrate 1.
[0019]
Next, the silicon substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ) or the like, so that the surface of the silicon substrate 1 has phosphorus atoms of 1 × 10 ¹⁶ to 1 × 10 ^18. A diffusion layer 2 having another conductivity type is formed by diffusing atoms / cm ³ (see FIG. 1B). The diffusion layer 2 is formed at a depth of about 0.2 to 0.5 μm, and is formed so that the sheet resistance becomes 40Ω / □ or more. The diffusion layer 2 in the other portion is etched while leaving only the diffusion layer 2 on one main surface side of the silicon substrate 1 (FIG. 1C).
[0020]
Next, an antireflection film 3 is formed on one main surface side of the silicon substrate 1. The antireflection film 3 is made of, for example, a silicon nitride film, and is formed by a plasma CVD method using a mixed gas of silane and ammonia. The anti-reflection film 3 is provided to prevent light from being reflected on the surface of the silicon substrate 1 and to effectively take light into the silicon substrate 1. On the other main surface side, a BSF layer 4 is formed by diffusing a high-concentration one-conductivity-type semiconductor impurity (see FIG. 1D).
[0021]
Then, a portion corresponding to the surface electrode 5 of the anti-reflection film 3 is etched, and an electrode paste is applied and baked to form the surface electrode 5 (see FIG. 1E). This surface electrode 5 is formed by applying an electrode paste directly on the anti-reflection film 3 and firing it, thereby melting the anti-reflection film 3 under the paste and making a direct contact with the silicon substrate 1 by a so-called fire-through method. Is also good. Also, the back electrode 6 is formed by applying an electrode paste to the back surface and baking the same. This electrode paste is prepared by adding 0.1 to 5 parts by weight of glass frit to silver powder and an organic vehicle with respect to 100 parts by weight of silver, and printing the paste by screen printing. It is baked by baking for about 30 minutes. The glass frit is made of a material containing at least one of PbO, B ₂ O ₃ and SiO ₂ and having a softening point of 500 ° C. or less. After that, solder layers 7 and 8 are formed on the electrode surface in order to secure long-term reliability and connect the solar cell elements to each other with inner leads in a later step (see FIG. 1F).
[0022]
In the solar cell element of the present invention, as shown in FIGS. 2A, 2B, and 2C, a solder cutout 9 is present at a substantially central portion of the finger electrode 5a. 2A is a view when the solar cell element 12 is viewed from the light receiving surface side, FIG. 2B is an enlarged view of a portion A in FIG. 2A, and FIG. 2C is a view in FIG. It is sectional drawing. However, as shown in FIG. 2 (c), since the finger electrodes 5a themselves are connected, even if the finger electrode 5a between the two bus bar electrodes 5b has a broken wire or a high resistance portion due to some reason, the figure is not changed. The same reliability as the solar cell element 12 having the pattern shown in FIG.
[0023]
In order to form such a solder cutout 9, before forming the solder layer 7, a solder resist 10 is first applied to the center of the finger electrode 5a as shown in FIG. The purpose of the solder resist 10 is to prevent the solder 7 from adhering to the applied portion, and a material having poor wettability with the solder 7 is used. Further, in order to prevent melting in a later step, the melting point is desirably 200 ° C. or higher. For example, an organic resin or glass is used. The application pattern may have a width and a length of about 2 mm, for example.
[0024]
Thereafter, as shown in FIG. 6, the surface solder layer 7 is formed by dipping in the molten solder 14 in the solder bath 13. As a result, a solar cell element 12 having a solder cutout 9 substantially at the center of the finger electrode 5a as shown in FIG. 3 is obtained. At this time, the solder resist 10 may be left as shown in FIG. 3, or may be removed after coating the solder 7 as shown in FIG. According to this method, a film of the solder 7 is not formed when the solder 7 is coated, even in the case of the electrode 5 having a closed pattern, as in the related art, so that the generation of solder balls can be prevented.
[0025]
At this time, as shown in FIG. 6A, the solar cell element 12 can be immersed in the solder bath 13 with the finger electrode 5a directed vertically, as shown in FIG. As shown in (b), when the bus bar electrode 5b is immersed in the vertical direction, the effect is more effectively exhibited. Further, as shown in FIG. 6B, by immersing the bus bar electrode 5b in the vertical direction, the solder 7 coated on the bus bar electrode 5b becomes easier to flow, and the amount of solder can be suppressed.
[0026]
【The invention's effect】
As described above in detail, according to the solar cell element of the first aspect, since the cutout portion of the solder is provided at the substantially central portion of the finger electrode, the finger electrode between the two bus bar electrodes is cut off. Even when a high resistance portion occurs, the finger electrodes are connected, and the same reliability as the solar cell element having the electrode pattern in which the finger electrodes and the bus bar electrodes are provided in a lattice pattern can be secured.
[0027]
According to the method of manufacturing a solar cell element of the second aspect, since the solder resist is applied to the substantially central portion of the finger electrode and the other portion is covered with the solder, the finger electrode and the bus bar electrode are formed in a grid pattern. A solar cell element which can ensure the same reliability as the solar cell element of the electrode pattern provided in the above can be easily formed. In this case, when the bus bar electrode is immersed in the vertical direction, the solder coated on the bus bar electrode easily flows and the amount of solder can be suppressed.
[Brief description of the drawings]
FIG. 1 is a view showing a method for forming a solar cell element according to the present invention.
FIGS. 2A and 2B are views showing a solar cell element according to the present invention, wherein FIG. 2A is a view of the solar cell element viewed from the light receiving surface side, FIG. 2B is an enlarged view of part A of FIG. (C) is a sectional view of (b).
3A and 3B are diagrams showing another solar cell element according to the present invention, wherein FIG. 3A is a view of the solar cell element viewed from the light receiving surface side, and FIG. 3B is an enlarged view of a portion A of FIG. FIG. 3C is a cross-sectional view of FIG.
FIG. 4 is a view showing a conventional solar cell.
FIG. 5 shows a structure of a surface electrode of a conventional solar cell element.
6A and 6B are diagrams showing another conventional solar cell element, wherein FIG. 6A is a view of the solar cell element viewed from the light receiving surface side, FIG. 6B is an enlarged view of a portion A of FIG. (C) is a sectional view of (b).
FIG. 7 is a diagram showing a conventional method of coating solder on electrodes of a solar cell element.
[Explanation of symbols]
1: semiconductor substrate, 5a: finger electrode, 5b: bus bar electrode, 5: front surface electrode, 6: back surface electrode, 7: solder, 9: part where solder is cut off

Claims (4)

On the front surface side of the semiconductor substrate having the semiconductor bonding portion, a surface electrode in which finger electrodes having substantially the same length as one side of the semiconductor substrate and bus bar electrodes are provided in a grid pattern is formed. A solar cell element in which a back electrode is formed on the side and the electrodes on both the front and back surfaces are covered with solder, wherein a cutout portion of the solder is provided substantially at the center of the finger electrode. On the front surface side of the semiconductor substrate having the semiconductor bonding portion, a surface electrode in which finger electrodes having substantially the same length as one side of the semiconductor substrate and bus bar electrodes are provided in a grid pattern is formed, and the back surface side of the semiconductor substrate is formed. A method of manufacturing a solar cell element in which a back electrode is formed on the front and back surfaces of the finger electrode, and a solder resist is applied to a substantially central portion of the finger electrode and the other portion is covered with solder. A method for manufacturing a solar cell element. 3. The method according to claim 2, wherein the semiconductor substrate is immersed in a solder bath to cover the finger electrodes with the solder. 4. The method according to claim 3, wherein the busbar electrode is immersed in the solder bath with the vertical direction.

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