JP2009302458A - Solar cell and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell capable of preventing breakage of the solar cell itself in packing and transport processes. <P>SOLUTION: This solar cell is provided with a semiconductor substrate having a p-n junction, and an aluminum electrode formed on the back face of the semiconductor substrate. The the aluminum electrode is characterized in that a ten-point average height Rz of the front face thereof is larger than 15 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solar cell and a manufacturing method thereof.

  A conventional solar cell 10 will be described with reference to FIGS. FIGS. 7A to 7C are a plan view (light-receiving surface view), a side view, and a back view showing the structure of a conventional solar cell, respectively.

  The solar cell 10 is electrically connected to the semiconductor substrate 1 through the semiconductor substrate 1 having a pn junction, the antireflection film 3 formed on the light receiving surface side of the semiconductor substrate 1, and the antireflection film 3. The light receiving surface connecting bus bar electrode 5 and the light receiving surface collecting electrode 7 are formed, and the aluminum electrode 9 and the back surface connecting bus bar electrode 11 formed on the back surface side of the semiconductor substrate 1 are provided.

The solar cell 10 can be produced by the following method.
First, the antireflection film 3 is formed on the light receiving surface side of the semiconductor substrate 1 on which the pn junction is formed.
Next, a silver paste for the backside connection bus bar electrode 11 is screen-printed on the back side of the semiconductor substrate 1 and dried at about 150 to 200 ° C. Further, an aluminum paste for the aluminum electrode 9 is screen-printed so as to partially overlap the silver paste, and dried at about 150 to 200 ° C. Next, a silver paste is screen-printed to form the light-receiving surface connecting bus bar electrode 5 and the light-receiving surface current collecting electrode 7, dried at about 150 to 200 ° C., and then fired at about 700 to 750 ° C.
Thus, the light receiving surface connecting bus bar electrode 5 and the light receiving surface collecting electrode 7 are formed on the light receiving surface side of the semiconductor substrate 1, and the back surface connecting bus bar electrode 11 and the aluminum electrode 9 are formed on the back surface side of the semiconductor substrate 1. The production of the solar cell 10 is completed.

  As shown in FIG. 8, the solar cell 10 manufactured in this way is transported to a packaging process by belt conveyance in a state where a plurality of solar cells 10 are stacked, and the plurality of solar cells 10 are joined together by a shrink film 13. Packaging. The packaged product is packed in a storage container and transported.

By the way, when the solar cell 10 is packaged by the above method, the stacked solar cells 10 are displaced as shown in FIG. 9 and are packaged in that state. It may cause cracking.
This invention is made | formed in view of such a situation, and provides the solar cell which can suppress the crack of the solar cell in a packing and a conveyance process.

  The solar cell of the present invention comprises a semiconductor substrate having a pn junction and an aluminum electrode provided on the back surface of the semiconductor substrate, and the aluminum electrode has a ten-point average height Rz of greater than 15 on the surface. Features.

As a result of intensive studies on the cause of the deviation of the stacked solar cells, the present inventors have found that the surface of the aluminum electrode formed by the conventional method is flat and free of irregularities, which is likely to cause deviation. I found it. And it discovered that generation | occurrence | production of shift | offset | difference can be suppressed by making 10-point average height Rz of the aluminum electrode surface larger than 15 micrometers, and came to completion of this invention.
According to this invention, since the shift | offset | difference of the laminated | stacked solar cell can be suppressed, the crack of the solar cell in a packing and a conveyance process can be suppressed.
Hereinafter, embodiments of the present invention will be exemplified.

  The occupation area ratio of the aluminum electrode on the back surface of the semiconductor substrate may be 50% or more.

The present invention comprises a step of screen printing an aluminum paste on the back surface of a semiconductor substrate having a pn junction and firing to form an aluminum electrode, the screen printing having a structure in which warp and weft are plain woven. A method for producing a solar cell is provided, wherein the warp yarn and the weft yarn have substantially the same wire diameter, and the weft yarn has a strength higher than that of the warp yarn. According to this method, it is easy to set the ten-point average height Rz of the aluminum electrode surface to a value larger than 15 μm.
The strength ratio of the weft to the warp may be 1.1 or more.
The warp yarn may have a strength of 500 to 1500 N / mm ² , a wire diameter of 15 to 45 μm, and the screen printing plate may have an aperture ratio of 30 to 70%.
In the screen printing, the distance between the semiconductor substrate and the screen printing plate is 1 to 5 mm, the squeegee printing pressure is 0.05 to 0.5 MPa, the squeegee angle is 45 to 75 degrees, and the squeegee speed is 20 to 100 mm / second. The viscosity of the aluminum paste at room temperature at a shear rate of 50 rpm may be 10 to 100 Pa · s.
The embodiments illustrated here can be combined with each other.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The contents shown in the drawings and the following description are examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

1. Configuration of Solar Cell A solar cell 10 according to an embodiment of the present invention will be described with reference to FIGS. 1A to 1C are a plan view (light-receiving surface view), a side view, and a back view showing the structure of the solar cell of this embodiment, respectively.

  The solar cell 10 of this embodiment includes a semiconductor substrate 1 having a pn junction and an aluminum electrode 9 provided on the back surface of the semiconductor substrate 1, and the aluminum electrode 9 has a 10-point average height Rz of 15 μm on the surface. Greater than. Further, the solar cell 10 includes an antireflection film 3 formed on the light receiving surface side of the semiconductor substrate 1 and a light receiving surface connection formed so as to penetrate the antireflection film 3 and be electrically connected to the semiconductor substrate 1. At least one of the bus bar electrode 5 and the light receiving surface collecting electrode 7 and the back surface connecting bus bar electrode 11 formed on the back surface side of the semiconductor substrate 1 is optionally provided.

  The solar cell 10 is characterized in that the ten-point average height Rz of the surface of the aluminum electrode 9 is larger than 15 μm. In the conventional solar cell 10, the surface of the aluminum electrode 9 is not uneven and the surface is flat. Therefore, when the solar cells 10 are stacked, the frictional force acting between the adjacent solar cells 10 is small, and the solar cell 10 is misaligned. In this embodiment, the ten-point average height Rz of the surface of the aluminum electrode 9 is larger than 15 μm. Therefore, when the solar cells 10 are stacked, a large frictional force acts between the adjacent solar cells 10 and the solar The deviation of the battery 10 is suppressed.

  The ten-point average height Rz of the surface of the aluminum electrode 9 is preferably large from the viewpoint of preventing displacement, but if it is too large, partial peeling of the aluminum electrode 9 tends to occur, and therefore it is preferably 60 μm or less. Specifically, the ten-point average height Rz is, for example, 15.1, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 40, 50, 60 μm. The ten-point average height Rz may be within a range between any two of the numerical values exemplified here, or may be any one or more.

  The occupation area ratio of the aluminum electrode 9 on the back surface of the semiconductor substrate 1 (area of the aluminum electrode 9 / area of the back surface of the semiconductor substrate 1) is not particularly limited, but is preferably 50% or more. This is because the greater the occupied area ratio, the more remarkable the effect of suppressing displacement. Specifically, the occupation area ratio is, for example, 50, 60, 70, 80, 85, 90, 95, 99%. This occupation area ratio may be within a range between any two of the numerical values exemplified here, or may be any one or more.

2. Hereinafter, the manufacturing method of the solar cell 10 of one Embodiment of this invention is demonstrated.
The method for manufacturing the solar cell 10 according to the present embodiment includes a step of screen printing an aluminum paste on the back surface of the semiconductor substrate 1 having a pn junction and baking to form an aluminum electrode 9, wherein the screen printing includes warp and It is performed using a screen printing plate having a structure in which wefts are plain woven. The warp yarns and weft yarns have substantially the same wire diameter, and the weft yarns are stronger than the warp yarns. In the method of this embodiment, at least one of the steps of forming the antireflection film 3, the light receiving surface connecting bus bar electrode 5, the light receiving surface collecting electrode 7 and the back surface connecting bus bar electrode 11 is arbitrarily performed. Prepare.
Hereinafter, each step will be described in detail.

(1) Manufacturing process of semiconductor substrate having pn junction The semiconductor substrate 1 having a pn junction is manufactured by, for example, forming an n-type layer on a p-type semiconductor substrate or forming a p-type layer on an n-type semiconductor substrate. can do. The type of semiconductor is not particularly limited, and for example, single crystal or polycrystalline silicon. The substrate surface may be etched before or after forming the pn junction. Thereby, it is possible to remove a damaged layer generated at the time of cutting from the ingot, or to form a fine concavo-convex structure to reduce the reflectance.

Hereinafter, an example of a specific method for manufacturing the semiconductor substrate 1 having a pn junction will be described in detail.
First, a p-type silicon substrate is obtained by cutting a polycrystalline p-type silicon ingot using a wire saw or the like. A damage layer is formed on the surface of the p-type silicon substrate by a wire saw or the like. Note that single crystal silicon can also be used as the p-type silicon substrate.
Next, for example, the damaged layer is removed by etching using an acid solution made of hydrofluoric acid, water, and nitric acid, and irregularities having large steps are formed on the light receiving surface and the back surface of the p-type silicon substrate. When single crystal silicon is used as the p-type silicon substrate, unevenness may be formed by performing anisotropic etching using an alkaline solution obtained by adding isopropyl alcohol to KOH (potassium hydroxide) or NaOH. it can.
Next, for the purpose of separating the pn junction, a mask material made of a solution containing, for example, silicon and titanium is applied to the peripheral edge of the back surface of the p-type silicon substrate by a spin coater.
Then, a dopant liquid containing, for example, P ₂ O ₅ (phosphorus pentoxide) as a diffusion source is applied to the light receiving surface side of the p-type silicon substrate by a spin coater. Subsequently, the p-type silicon substrate is heated to about 800 to 900 ° C. in a diffusion furnace, so that the n-type dopant is diffused into the main surface to be the light-receiving surface of the p-type silicon substrate. An n-type impurity diffusion layer which is an impurity diffusion layer is formed on the light receiving surface side. At this time, a mask film in which TiO ₂ (titanium oxide) and SiO ₂ (silicon oxide) produced by heating the mask material are mixed is formed in the area where the mask material is applied on the back surface of the p-type silicon substrate. At the same time, a PSG (phosphorus silicate glass) layer generated by heating the dopant liquid is formed.
Then, the mask film and the PSG layer are removed by immersing the p-type silicon substrate in hydrofluoric acid.
Through the above steps, the semiconductor substrate 1 having a pn junction is manufactured.

(2) Antireflection Film Formation Step Next, the antireflection film 3 is formed on the light receiving surface side of the semiconductor substrate 1. The antireflection film 3 is made of, for example, a silicon nitride film having a thickness of 70 nm to 100 nm, and can be formed by using, for example, a plasma CVD method. The antireflection film 3 is formed for the purpose of preventing the reflection of sunlight and the passivation of the semiconductor substrate 1.

(3) Electrode formation process Next, a silver paste and an aluminum paste are formed on the back surface side of the semiconductor substrate 1, and a silver paste is screen-printed, dried and fired on the light receiving surface side to form an electrode to manufacture the solar battery cell 10. To complete. By this step, the aluminum electrode 9 and the back surface connecting bus bar electrode 11 are formed on the back surface side, and the light receiving surface connecting bus bar electrode 5 and the light receiving surface current collecting electrode 7 are formed on the light receiving surface side.

  In this embodiment, the screen printing plate used for screen printing of the aluminum paste has a structure in which warp and weft are plain woven, and the warp and the weft have substantially the same wire diameter, Stronger than warp. By performing screen printing using such a screen printing plate, the ten-point average height Rz of the surface of the aluminum electrode 9 can be made larger than 15 μm. Details of this screen printing will be described later.

Hereinafter, an example of a specific method of the electrode forming process will be described in detail.
First, a silver paste is printed at a position where the back surface connection bus bar electrode 11 on the back surface of the semiconductor substrate 1 is formed by screen printing, and is dried at about 150 to 200 ° C. Next, the aluminum paste is screen-printed at a position where the back surface collecting aluminum electrode 9 is formed so as to partially overlap the silver paste, and dried at about 150 to 200 ° C. Next, a silver paste is screen-printed at a position where the light receiving surface connecting bus bar electrode 5 and the light receiving surface collecting electrode 7 are formed, and dried at about 150 to 200 ° C.

  Next, baking is performed at about 700 to 750 ° C. By this firing, the aluminum electrode 9 and the back surface connecting bus bar electrode 11 are formed on the back surface side, and the light receiving surface connecting bus bar electrode 5 and the light receiving surface current collecting electrode 7 are formed on the light receiving surface side.

  During firing, the silver paste on the light receiving surface fires through the antireflection film 3 and makes ohmic contact with the n-type diffusion layer of the semiconductor substrate 1. Further, a eutectic reaction occurs between the aluminum paste on the back surface and the semiconductor substrate 1 during firing, and a p-type impurity diffusion layer containing a large amount of p-type impurity aluminum is formed on the back surface side of the semiconductor substrate 1. Is done. An alloy layer of aluminum and silicon is formed between the aluminum electrode 9 and the p-type impurity diffusion layer.

3. Screen printing of aluminum paste Hereinafter, screen printing of aluminum paste will be described in detail.

(1) Outline of Screen Printing First, an outline of screen printing will be described.
As shown in FIG. 2, the screen printing of the aluminum paste is performed by arranging the screen printing plate 17 so as to face the back surface of the semiconductor substrate 1, placing the aluminum paste 9a on the screen printing plate 17, and applying the aluminum paste 9a to the squeegee. The aluminum paste 9a can be adhered onto the semiconductor substrate 1 by being extruded through the opening of the screen printing plate 17 using 21. The screen printing plate 17 is fixed with a plate frame 23. FIG. 2 shows the case where the aluminum paste 9a is printed on the semiconductor substrate 1 on which the silver paste 11a for forming the back surface connecting bus bar electrode 11 is already printed, but the silver paste 11a is not printed. The aluminum paste 9a can also be printed on the semiconductor substrate 1.

  Although the distance of the screen printing plate 17 and the semiconductor substrate 1 is not specifically limited, For example, it is 1-5 mm. Specifically, this distance is, for example, 1, 1.5, 2, 2.5, 3, 4, 5 mm. This distance may be within a range between any two of the numerical values exemplified here.

  Although the pressure (printing pressure of the squeegee 21) which the squeegee 21 applies with respect to the screen printing plate 17 is not specifically limited, For example, it is 0.05-0.5 MPa. Specifically, this pressure is, for example, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, or 0.5 MPa. This pressure may be within a range between any two of the numerical values exemplified herein.

  Although the angle of the squeegee 21 with respect to the screen printing plate 17 is not specifically limited, For example, it is 45 to 75 degrees. Specifically, this angle is 45, 50, 55, 60, 65, or 70 degrees, for example. This angle may be within a range between any two of the numerical values exemplified here.

  The moving speed of the squeegee 21 is not particularly limited, but is, for example, 20 to 100 mm / second. Specifically, this speed is, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100 mm / sec. This speed may be within a range between any two of the numerical values exemplified herein.

  The viscosity (room temperature, shear rate 50 rpm) of the aluminum paste 9a is not particularly limited, but is, for example, 10 to 100 Pa · s. Specifically, the viscosity is, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 Pa · s. This viscosity may be within a range between any two of the numerical values exemplified herein.

(2) Screen Printing Plate Next, the screen printing plate 17 will be described in detail with reference to FIGS. 3A is a plan view showing the configuration of the screen printing plate 17, FIG. 3B is a cross-sectional view taken along the line II in FIG. 3A, and FIG. It is II-II sectional drawing in 3 (a).

The screen printing plate 17 has a structure in which warp yarns 17a and weft yarns 17b are plain woven. The warp yarn 17a and the weft yarn 17b have substantially the same wire diameter, and the weft yarn 17b has a higher strength (N / mm ² ) than the warp yarn 17a. The difference in strength comes from, for example, the difference in the type of wire.

  Since the strength of the weft 17b is greater than the strength of the warp 17a, when the warp 17a and the weft 17b abut, the warp 17a is strongly pressed by the weft 17b, and the position of the warp 17a changes greatly. For this reason, the waviness of the warp yarn 17a becomes larger than the waviness of the weft yarn 17b, and as a result, the thickness D of the screen printing plate 17 becomes thicker than when the warp yarn 17a and the weft yarn 17b have the same strength. When such a screen printing plate 17 is used, the unevenness of the surface of the aluminum electrode 9 tends to be large, and the ten-point average height Rz of the surface of the aluminum electrode 9 is likely to be larger than 15 μm.

  By the way, in the case of the conventional screen printing plate 17 in which the strengths of the warp yarn 17a and the weft yarn 17b are equal, as shown in FIGS. The thickness D of the printing plate 17 is almost twice the wire diameter. Therefore, the thickness D of the screen printing plate 17 of the present embodiment is larger than twice the wire diameter, and preferably 2.2 to 3 times the wire diameter. Specifically, the thickness D is, for example, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 times the wire diameter. . This magnification may be within a range between any two of the numerical values exemplified here.

  The strength ratio of the weft yarn 17b to the warp yarn 17a is, for example, 1.1 or more, and preferably 1.1 to 2. This is because if the difference in strength between the warp yarns 17a and the weft yarns 17b is too large, the warp yarns may be caught during squeezing, resulting in resistance, and it may be difficult to perform smooth printing. Specifically, the intensity ratio is 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, for example. This intensity ratio may be within a range between any two of the numerical values exemplified here.

The strength of the warp 17a is not particularly limited, but is, for example, 500 to 1500 N / mm ² . Specifically, the strength is, for example, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500 N / mm ² . This intensity may be within a range between any two of the numerical values exemplified herein.

  Although the wire diameter of the warp 17a is not specifically limited, For example, it is 15-45 micrometers. Specifically, the intensity is, for example, 15, 20, 25, 30, 35, 40, or 45 μm. This wire diameter may be within a range between any two of the numerical values exemplified here.

  Although the aperture ratio of the screen printing plate 17 is not specifically limited, For example, it is 30 to 70%. Specifically, the aperture ratio is, for example, 30, 35, 40, 45, 50, 55, 60, 65, 70%. This aperture ratio may be within a range between any two of the numerical values exemplified here.

4). Effect Demonstration Experiment Hereinafter, an experiment demonstrating the effect of the present invention will be described.

4-1. Production of Solar Cell A solar cell having a structure as shown in FIGS. 1A to 1C was produced by the following method.
First, an n-type impurity diffusion layer was formed on the light-receiving surface side of a p-type silicon substrate having a thickness of 156 × 156 mm and a thickness of 200 μm to obtain a semiconductor substrate 1 having a pn junction. Next, an antireflection film 3 made of silicon nitride having a thickness of about 80 nm was formed on the light receiving surface side of the semiconductor substrate 1. Next, the silver paste was printed in the position which forms the back surface connection bus-bar electrode 11 of the back surface of the semiconductor substrate 1, and was dried at about 180 degreeC. Next, the aluminum paste was screen-printed at a position where the back surface collecting aluminum electrode 9 was formed so as to partially overlap the silver paste, and dried at about 180 ° C. Next, a silver paste was screen-printed at a position where the light receiving surface connecting bus bar electrode 5 and the light receiving surface collecting electrode 7 were formed, and dried at about 180 ° C. Next, by baking at about 750 ° C., the aluminum electrode 9 and the back surface connecting bus bar electrode 11 are formed on the back surface side, and the light receiving surface connecting bus bar electrode 5 and the light receiving surface current collecting electrode 7 are formed on the light receiving surface side. And the solar cell was produced.

As shown in FIG. 2, the screen printing of the aluminum paste is performed by arranging the screen printing plate 17 so as to face the back surface of the semiconductor substrate 1, placing the aluminum paste 9a on the screen printing plate 17, and applying the aluminum paste 9a to the squeegee. The aluminum paste 9a was adhered onto the semiconductor substrate 1 by extruding from the screen printing plate 17 using 21.
In Examples 1-2 and Comparative Examples 1-2, screen printing was performed under the conditions shown in Tables 1 and 2. Screen printing was performed using a screen printer (manufactured by Neurong Seimitsu Kogyo, model: LS-150). Moreover, as the aluminum paste 9a, one having a viscosity at room temperature at a shear rate of 50 rpm of 35 to 60 Pa · s was used. The viscosity of the aluminum paste 9a was measured using a Brookfield viscometer.
In the screen printing plate A, the strength of the weft 17b is greater than the strength of the warp 17a, whereas in the screen printing plate B, the strength of the warp 17a and the weft 17b is the same. In the screen printing plate A, the strength of the weft 17b was increased by using a high-tensile wire as the weft 17b.

4-2. Measurement of Ten-Point Average Height Rz of Aluminum Electrode Surface Next, the aluminum electrode 9 surface shape of the solar cells of Examples 1-2 and Comparative Examples 1-2 was measured. This measurement was performed using a laser displacement meter. The graph of the surface shape of the aluminum electrode 9 of the solar cell of Example 1 and Comparative Example 1 obtained by this measurement is shown in FIGS. Table 10 shows the ten-point average height Rz of the surface of the aluminum electrode 9. The ten-point average height Rz was measured according to JIS standards.

Referring to FIGS. 5 and 6, it can be seen that the surface of the aluminum electrode 9 of the solar cell of Example 1 has larger irregularities than those of Comparative Example 1.
In Table 3, when Example 1 and Comparative Example 1 are compared, and Example 2 and Comparative Example 2 are respectively compared, by using screen printing plate A instead of screen printing plate B, the ten-point average height Rz is doubled. It turns out that it was able to do it above. This result shows that the ten-point average height Rz of the surface of the aluminum electrode 9 can be easily made larger than 15 μm by using the screen printing plate 17 in which the strength of the weft yarn 17b is larger than that of the warp yarn 17a. ing.

4-3. Next, the deviation of the stacked solar cells was evaluated.
Specifically, this evaluation was performed after preparing 30 stacked solar cells 10 of Example 1 and Comparative Example 1 and packing them with a shrink film 13 as shown in FIG. This was done by counting the number of misaligned solar cells.
As a result, the number of deviations was 3 out of 450 (0.7%) in the solar cell of Example 1, and 9 out of 450 (2.0%) in the solar cell of Comparative Example 1. . This result indicates that the deviation of the solar cell can be suppressed by making the ten-point average height Rz of the surface of the aluminum electrode 9 larger than 15 μm as in Example 1.

1A to 1C are a plan view (light-receiving surface view), a side view, and a back view, respectively, showing the structure of a solar cell according to an embodiment of the present invention. It is a side view corresponding to FIG.1 (b) for demonstrating the method of the screen printing of the aluminum paste in the manufacturing method of the solar cell of one Embodiment of this invention. Fig.3 (a) is a top view which shows the structure of the screen printing plate used with the manufacturing method of the solar cell of one Embodiment of this invention, FIG.3 (b) is I- in FIG.3 (a). It is I sectional drawing, FIG.3 (c) is II-II sectional drawing in Fig.3 (a). 4A is a plan view showing a configuration of a conventional screen printing plate, FIG. 4B is a cross-sectional view taken along the line II in FIG. 4A, and FIG. It is II-II sectional drawing in Fig.4 (a). The graph of the surface shape of the aluminum electrode 9 of the solar cell of Example 1 in the effect verification experiment of this invention is shown. The graph of the surface shape of the aluminum electrode 9 of the solar cell of the comparative example 1 in the effect verification experiment of this invention is shown. FIGS. 7A to 7C are a plan view (light-receiving surface view), a side view, and a back view showing the structure of a conventional solar cell, respectively. It is a perspective view which shows the state which wrapped what wrapped the conventional solar cell with the shrink film. FIG. 9 is a perspective view showing a state in which the solar cell has shifted in FIG. 8.

Explanation of symbols

1: Semiconductor substrate 3: Antireflection film 5: Bus bar electrode for light receiving surface connection 7: Electrode for collecting light receiving surface 9: Aluminum electrode 9a: Aluminum paste 10: Solar cell 11: Bus bar electrode for back surface connection 11a: Silver paste 13: Shrink film 17: Screen printing plate 17a: Warp yarn 17b: Weft yarn 21: Squeegee 23: Plate frame

Claims (5)

a semiconductor substrate having a pn junction, and an aluminum electrode provided on the back surface of the semiconductor substrate,
The aluminum electrode has a ten-point average height Rz of a surface larger than 15 μm. The solar cell according to claim 1, wherein an area ratio of the aluminum electrode on the back surface of the semiconductor substrate is 50% or more. a step of screen-printing an aluminum paste on the back surface of a semiconductor substrate having a pn junction and baking to form an aluminum electrode;
The screen printing is performed using a screen printing plate having a structure in which warp and weft are plain woven. The warp and the weft have substantially the same wire diameter, and the weft is stronger than the warp. A method for manufacturing a solar cell. The method according to claim 3, wherein a strength ratio of the weft to the warp is 1.1 or more. In the screen printing, the distance between the semiconductor substrate and the screen printing plate is 1 to 5 mm, the squeegee printing pressure is 0.05 to 0.5 MPa, the squeegee angle is 45 to 75 degrees, and the squeegee speed is 20 to 100 mm / second. The method according to claim 3 or 4, wherein the viscosity is 10 to 100 Pa · s at room temperature at a shear rate of 50 rpm.

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