JP2002353475A - Solar battery element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a cell cracking by concentrating stresses caused by a difference in the coefficient of thermal expansion by overlapping a collecting electrode part and an electrode leadout part or that the cell is cracked by solder stacking. SOLUTION: Different conductive regions are formed on one principal surface side and the other principal surface side of a semiconductor wafer, a surface electrode is formed on one principal surface side, and a rear surface electrode composed of the band-shaped electrode leadout part and the collecting electrode part formed on the part except for this electrode leadout part is formed on the other principal surface side. In such a solar battery, the peripheral edge part of the electrode leadout part of the rear surface electrode is provided close to the collecting electrode part, so as not to overlap with the collecting electrode part and the collecting electrode part is connected striding the electrode leadout part at a plurality of spots in the lengthwise direction of the electrode leadout part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell device.

[0002]

2. Description of the Related Art A typical manufacturing process of a conventional solar cell device is shown in FIG. First,
As shown in FIG. 3A, a P-type semiconductor substrate 1 is prepared. Then, as shown in FIG. 3B, the semiconductor substrate 1 is heat-treated in an N-type impurity atmosphere to diffuse the N-type impurity to a certain depth over the entire surface near the surface of the semiconductor substrate 1 so as to exhibit N-type. The diffusion layer 2 is formed. Next, as shown in FIG. 3C, an antireflection film 3 is formed on the surface of the semiconductor substrate 1 by a plasma CVD method or the like. Further, a V-shaped groove is formed at an end on the back surface side of the semiconductor substrate 1 to physically separate the diffusion layer 2.

Next, a silver paste is screen-printed on the front surface, and an aluminum paste and a silver paste are screen-printed on the back surface and fired.
A solar cell having a front surface electrode 4 and a back surface electrode 5 as shown in FIG.

As shown in FIG. 4, the back electrode 5 is formed by applying a silver paste to a region of the back surface of the semiconductor substrate 1 where an electrode extraction portion 5a is to be formed, drying the silver paste, and then forming a silver paste on the periphery of the silver paste in the region 5a. A simultaneous firing method in which an aluminum paste is applied to a region to be the current collecting electrode portion 5b so as to overlap and is dried, and the silver paste and the aluminum paste are simultaneously fired to simultaneously form the electrode extraction portion 5a and the current collecting electrode portion 5b. (One-step firing) is used (for example, Japanese Patent Application Laid-Open No. 5-326).
990 and Japanese Patent Publication No. 6-509910).

[0005] The solar cell element manufactured in this manner is generally used by boosting the voltage by connecting a plurality of elements in series using a wiring member (not shown). Since soldering is required to connect these multiple elements,
Wiring materials are coated with solder. However, since the aluminum of the current collecting electrode portion 5b has poor solder wettability and is difficult to be solder coated, the electrode extraction portion 5a is formed of silver having good solder wettability, and a wiring material is soldered thereto. I have.

As described above, by forming the electrode extraction portion from silver having a lower electric resistivity than aluminum, it is possible to prevent the fill factor of the solar cell from being reduced and to improve the workability.

In the structure of the back electrode 5 as described above, an aluminum paste serving as a current collecting electrode portion 5b and an electrode extracting portion 5 are formed on the back surface of the semiconductor substrate 1 made of silicon or the like.
The silver paste to be a is formed by co-firing. However, since materials such as silicon, aluminum, and silver have different coefficients of thermal expansion, the current collecting electrode portion 5b made of aluminum and the electrode extraction portion 5a made of silver are different. There has been a problem that stress concentration due to residual stress occurs at the interface, the crack strength of the semiconductor substrate 1 is reduced, and cell cracks occur.

To solve this problem, Japanese Patent Laid-Open Publication No. 2000-13
Japanese Patent No. 3826 discloses a method in which a silver paste serving as an electrode extraction portion 5a is coated on an aluminum paste serving as a current collecting electrode portion 5b, and a gap is provided between the electrode paste and the aluminum paste serving as a current collecting electrode portion 5b. A method of applying a silver paste to be 5a is shown.

However, in the method of applying a silver paste for forming the electrode take-out portion 5a from above the aluminum paste for forming the current collecting electrode portion 5b, the silver for forming the electrode take-out portion 5a for soldering the wiring material for connecting the cells to each other is provided. There is a problem that the electrode strength of the paste portion is weak. In addition, the collecting electrode portion 5b
In the method of applying a silver paste that becomes the electrode extraction portion 5a with a gap between the aluminum paste and the aluminum paste, there is a problem that the fill factor is reduced.

Further, when soldering is carried out by immersion for the purpose of cost reduction, there is a problem that the solder pile on the lower side of the pull-up becomes large and cell cracks occur at the time of work in a later step.

In view of the above problems, the present invention concentrates stress caused by a difference in the coefficient of thermal expansion on an overlapping portion between a current collecting electrode portion and an electrode take-out portion to cause cell cracking, or cell cracking due to solder pile. It is an object of the present invention to provide a solar cell element that eliminates the problem.

[0012]

In order to achieve the above object, in the solar cell according to the first aspect, different conductive regions are formed on one main surface side of the semiconductor substrate and another main surface side, and the one main surface is formed. A solar cell with a front surface electrode formed on the side and a back electrode composed of a strip-shaped electrode extraction portion on the other main surface side and a current collecting electrode portion formed in a portion other than this electrode extraction portion,
A peripheral portion of an electrode extraction portion of the back electrode is provided near the current collection electrode portion so as not to overlap with the current collection electrode portion, and the current collection electrode portion is provided at a plurality of positions in a longitudinal direction of the electrode extraction portion. To connect over the electrode take-out part.

In the conventional solar cell element, since the collecting electrode portion is overlapped on the peripheral portion of the electrode extracting portion of the back electrode, the thin portion of the electrode extracting portion and the end portion of the collecting electrode portion overlap. However, the peripheral portion of the electrode extracting portion and the end of the current collecting electrode portion are formed so as not to overlap with each other, and the current collecting electrode portion is connected across the electrode extracting portion at a plurality of locations in the longitudinal direction of the electrode extracting portion. By doing so, the current collecting electrode portion is formed in the thick portion of the electrode extraction portion, and the stress is dispersed because the electrodes are not continuously stacked. Thereby, the concentration of stress is reduced, and the problematic cell crack does not occur.

Further, since the electrode take-out portion is divided by the current collecting electrode portion, the portion to which the solder is applied is subdivided, and the solder pile is made uniform. As a result, it is possible to prevent cell cracking in a later step due to a difference in solder height.

In the above-mentioned solar cell element, it is desirable that the electrode extraction portion of the back electrode is divided into a plurality of pieces.

In the above solar cell element, the electrode extraction portions of the front electrode and the back electrode are mainly composed of silver, and the current collecting electrode part of the back electrode is mainly composed of aluminum. Is desirable.

With this configuration, it is possible to optimize the efficiency of the solar cell and reduce the amount of solder.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. A P-type semiconductor substrate 1 is prepared as shown in FIG. Then, as shown in FIG.
An N-type impurity is diffused to a certain depth over the entire surface near the surface of the semiconductor substrate 1 by performing a heat treatment or the like in a type impurity atmosphere to form an N-type diffusion layer 2. Next, as shown in FIG. 1C, an antireflection film 3 is formed on the surface of the semiconductor substrate 1 by a plasma CVD apparatus or the like. Further, a V-shaped groove is formed at the end on the back surface side of the semiconductor substrate 1 to physically separate the diffusion layer 2.

Next, a silver paste is screen-printed on the front surface of the semiconductor substrate 1, and a silver paste and an aluminum paste are screen-printed on the back surface and fired, so that the surface electrode 4 as shown in FIG. A solar cell having the back electrode 5 can be obtained. Conventionally, the silver paste is applied from the top of the semiconductor substrate 1 on which the aluminum paste is applied, whereas the present invention applies the aluminum paste from the top of the semiconductor substrate 1 on which the silver paste is applied.

FIG. 2 shows the structure of the back electrode 5. FIG.
In the solar cell element shown in (a), the electrode extraction portions 5a of the back electrode 5 are provided in two places in parallel over substantially the entire width on the rear surface side of the semiconductor substrate 1, and are collected so as not to overlap the peripheral edge of the electrode extraction portion 5a. This is provided with an electrode part 5b. The electrode extraction portion 5a may be provided so as not to overlap the current collecting electrode portion 5b in the vertical direction, and the end portions may be in contact. Further, at a plurality of positions in the length direction of the electrode extraction portion 5a, the current collecting electrode portion 5b is connected so as to straddle the electrode extraction portion 5a. This is because the electrons collected by the current collecting electrode portion 5b are supplied to the electrode extracting portion 5a, and the exposed portion of the electrode extracting portion 5a is subdivided to reduce the solder pile.

The electrode extraction portion 5a has a thickness of, for example, 0.0
5 to 1 mm, a width of 1 to 10 mm, and a length of about 145 mm.
It is formed at a pitch of 5 mm. If the pitch is reduced, the width must be reduced. Conversely, if the pitch is increased, the width must be increased.

As shown in FIG. 2B, the back electrode 5 may be formed such that a constant gap 6 is formed between the periphery of the electrode extraction portion 5a and the collecting electrode portion 5b. With such a configuration, the stress at the boundary between the electrode extraction portion 5a and the current collecting electrode portion 5b can be further reduced.

The electrode extraction section 5a and the current collecting electrode section 5b
In order to reduce the stress concentration, it is better to keep the gap as wide as possible, but in order to enhance the BSF effect obtained simultaneously with the aluminum electrode,
It is better to provide b as close as possible so that b has as large an area as possible. Therefore, the electrode extraction portion 5a and the current collecting electrode portion 5b are provided at a distance of about 3 mm from a position where the end portion of the current collecting electrode portion 5b is abutted so as not to overlap the peripheral portion of the electrode extraction portion 5a. You may.

Further, as shown in FIG. 2 (c), the back electrode 5 may have a plurality of electrode extraction portions 5a formed in the longitudinal direction. When a plurality of electrode extraction portions 5a are formed in the longitudinal direction in this way, when soldering a wiring member (not shown) to the electrode extraction portions 5a, the plurality of electrode extraction portions 5a are formed.
a, a solder pool can be formed between them, and the wiring material can be stably soldered to the extraction electrode portion 5a.

Then, the front surface electrode 4 and the back surface electrode 5 are formed simultaneously by firing the semiconductor substrate 1 in a firing furnace such as a belt furnace. The front electrode 4 and the back electrode 5
The semiconductor substrate 1 on which is formed is immersed in a solder bath, and the electrode extraction portions 5a of the front surface electrode 4 and the back surface electrode 5 are coated with solder to form a solder layer.

It should be noted that the present invention is not limited to the above embodiment, and that many changes can be made within the scope of the present invention. For example, a metal paste based on gallium or indium may be used instead of the aluminum paste, or boron may be applied. Further, a metal paste based on copper, gold, or platinum may be used instead of the silver paste.

[0027]

Examples of the present invention will be described below. FIG. 1 (a)
As shown in FIG.
A P-type silicon substrate having a specific resistance of 1.5 Ω · cm was prepared. Then, as shown in FIG. 1 (b), phosphorus oxychloride (POCl ₃ ) was used as a diffusion source by a thermal diffusion method to a depth of 0.5 μm.
m N-type diffusion layers were formed.

Next, an antireflection film made of silicon nitride is formed on the front surface by plasma CVD at a thickness of 800 °, and the back surface is sprayed with an injection nozzle at an angle of 80 ° to the semiconductor substrate. Is directly injected, and FIG. 1 (c)
As shown in FIG.

Finally, a silver paste and an aluminum paste are screen-printed on the back surface in the pattern shown in FIGS. 2A, 2B and 2C, and a silver paste is screen-printed on the front surface and fired at 700 ° C. After forming the collector electrode, the substrate was immersed in a solder bath at 200 ° C. and pulled up to coat the surface of the collector electrode with solder, thereby manufacturing a solar cell.

Table 1 shows the cracking rates of the solar cells obtained by the method of the present invention and the solar cells obtained by the conventional method.

[0031]

[Table 1]

The solar cell of the present invention has a crack occurrence rate of 3 to 1
4%, which is much lower than the conventional 27%.

Table 2 shows the results of a bending test for measuring the breaking strength up to the occurrence of cracks.

[0034]

[Table 2]

In the solar cell of the present invention, the breaking strength is 0.7
It is 5 to 1.06 Kg, which is much higher than the conventional 0.38 Kg. The effect of the present invention can be understood from the test results.

[0036]

As described above in detail, according to the present invention, the peripheral portion of the electrode extraction portion of the back electrode is provided close to the current collecting electrode portion so as not to overlap with the current collecting electrode portion. Since the collecting electrode portion is connected across the electrode extracting portion at a plurality of locations in the longitudinal direction of the electrode extracting portion, stress concentration at the boundary between the aluminum electrode and the silver electrode, which has conventionally been a problem, can be eliminated, The crack strength can be increased to prevent the occurrence of cracks, and a high-quality cell can be obtained. In addition, even when the solder is applied by the immersion method, the problem that the solder height is partially increased does not occur, and the occurrence of the cell crack in the subsequent process is suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for manufacturing a solar cell element according to the present invention.

FIG. 2 is a diagram showing a back electrode of the solar cell element according to the present invention.

FIG. 3 is a view illustrating a conventional method for manufacturing a solar cell element.

FIG. 4 is a diagram showing a back electrode of a conventional solar cell.

[Explanation of symbols]

1; semiconductor substrate, 2; n-type diffusion layer, 3; antireflection film,
4; front surface electrode, 5; back surface electrode, 5a; electrode extraction portion, 5
b; aluminum electrode

Claims (3)

[Claims] 1. A semiconductor device according to claim 1, wherein a conductive region is formed on one main surface side of the semiconductor substrate and another conductive region is formed on another main surface side to form a surface electrode on one main surface side and a strip-shaped electrode extraction portion on the other main surface side. And a current collecting electrode portion formed in a portion other than the electrode extracting portion, in a solar cell, in which the peripheral portion of the electrode extracting portion of the rear electrode does not overlap with the current collecting electrode portion. A solar cell element, wherein the solar cell element is provided close to the current collecting electrode portion, and the current collecting electrode portion is connected across the electrode extracting portion at a plurality of locations in the longitudinal direction of the electrode extracting portion. 2. The solar cell element according to claim 1, wherein an electrode extraction portion of the back electrode is divided into a plurality of pieces. 3. The electrode extraction portion of the front surface electrode and the back surface electrode is mainly composed of silver, and the current collecting electrode portion of the back surface electrode is mainly composed of aluminum. The solar cell element according to claim 1 or 2.