JP2002170972A - Method of manufacturing solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell element with good soldering property and high output. SOLUTION: The manufacturing method of the solar cell element has a paste application process where paste including silver is applied on a reflection preventing film which is applied onto a wafer and prevents the reflection of light, and a burning process where paste is burnt and an electrode is formed. Oxygen gas is supplied so that an oxygen atmosphere can be obtained during the burning process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solar cell element, and more particularly, to a method for manufacturing a solar cell element having high initial characteristics.

[0002]

2. Description of the Related Art A conventional solar cell manufacturing process will be described with reference to FIG. A silicon wafer 1 is used as a solar cell element. As shown in FIG. 9A, the surface of the silicon wafer 1 has a defect layer 11. Therefore, as shown in FIG. 9B, the wafer is etched and removed. Next, as shown in FIG. 9C, a diffusion layer 2 is formed on the light receiving surface side of the silicon wafer 1 on which the wafer etching has been performed in order to form a PN junction. Then, as shown in FIG. 9D, in order to prevent a decrease in output due to recombination of carriers near the back surface of the silicon wafer 1,
The back surface electric field layer 3 is formed on the back surface of the silicon wafer 1.
Further, as shown in FIG. 9E, an antireflection film 6 is formed on the surface of the silicon wafer 1 in order to prevent a decrease in output due to light reflection on the solar cell surface. Then, FIG.
As shown in (f), a paste application step of printing the front electrode paste 40 on the antireflection film 6 and printing the back electrode paste 50 on the back surface field layer 3 is performed. After that, the front electrode paste 40 and the back electrode paste 50 are dried. Next, as shown in FIG. 9G, in a firing step of firing at a high temperature while supplying nitrogen or air, a front paste electrode (front electrode 4) and a back paste electrode (back electrode 5) are formed. Next, as shown in FIG. 9H, a step of laying the solder 12 on the front paste electrode (front electrode 4) and the back paste electrode (back electrode 5) is performed. Thereafter, a lead wire is attached to the electrode on which the solder 12 is provided by soldering, and a solar cell element is formed.

For example, a P-type silicon wafer 1 can be obtained by cutting a polycrystalline silicon ingot manufactured by a casting method. Since there is a defect layer 11 on the surface of the P-type silicon wafer 1, the wafer is etched by being immersed in an alkaline solution such as NaOH or KOH and removed. On the light receiving surface side of the P-type silicon wafer 1, N + diffusion is performed to form a PN junction. The diffusion layer 2 is formed by a gas phase diffusion method using POCl ₃ , a coating diffusion method using P ₂ O ₅ , an ion implantation method of directly doping P ⁺ ions, or the like. Next, in order to prevent a reduction in output due to recombination of carriers near the back surface of the silicon wafer 1, for example, Al
To form a P + back surface electric field layer 3. Further, in order to prevent a decrease in output due to light reflection on the surface of the solar cell, for example, TiO ₂ , SiN, S
forming an anti-reflection film 6 of nO ₂ or the like;
The front electrode 4 is formed so as to penetrate through the
To form

The electrode forming process of a solar cell using a paste will be described in detail. First, a front electrode paste 40 containing Ag as a main component and a back electrode paste 50 are printed. Then, the front electrode paste 40 and the back electrode paste 50 are dried. Next, a front paste electrode (front electrode 4) and a back paste electrode (back electrode 5) are formed by a firing step of performing treatment at a high temperature while supplying nitrogen or air. By this firing step, the front electrode 4 penetrates through the antireflection film 6 and comes into contact with the silicon wafer 1 to be electrically connected. Next, a step of placing the solder 12 on the front paste electrode and the back paste electrode is performed. Thereafter, the output of the solar cell element is measured, and the one with a small output is determined as an output failure. If the output is judged to be non-defective, a lead wire is attached to the soldered electrode by soldering, and a solar cell element is formed.

[0005]

As described above, in the firing step, air is usually supplied and firing is performed at a high temperature.
Oxidation of the surface of the paste electrode causes a problem of poor solderability in a soldering process performed after the firing process. When the solderability is poor, the initial characteristics of the solar cell tend to be low. Further, the deterioration of solderability has made it difficult to attach lead wires even in a process of connecting individual solar cells to form a panel, since there is not enough solder on the electrodes.

Therefore, it has been proposed to supply nitrogen instead of air in the firing step in order to improve the solderability in the soldering step. However, even when air is supplied in the firing step, the solderability in the soldering step is not sufficiently improved.

An object of the present invention is to solve the above-mentioned problem and to provide a high-output solar cell element having good solderability.

[0008]

According to the present invention, there is provided a method for manufacturing a solar cell element, comprising applying a paste containing silver on an antireflection film for preventing reflection of light applied on a wafer. A method for manufacturing a solar cell element, comprising: a step of firing the paste to form an electrode by firing the paste; wherein, during the firing step, an oxygen gas is supplied so as to provide an oxygen atmosphere. This is a method for manufacturing an element.

Further, in the method for manufacturing a solar cell element according to the present invention, the particle diameter of silver contained in the paste is 0.1 to 2 μm in the paste application step. Is the way.

Further, in the method of manufacturing a solar cell element according to the present invention, in the firing step, the amount of oxygen gas to be supplied is from 1 to 3 times per minute with respect to the inner volume of the furnace. This is a method for manufacturing a solar cell element.

Further, the method for manufacturing a solar cell element according to the present invention is a method for manufacturing a solar cell element, wherein in the firing step, the wafer is fired in a conveyor-type firing furnace.

Further, the method for manufacturing a solar cell element according to the present invention is a method for manufacturing a solar cell element, wherein in the firing step, firing is heating by an infrared lamp.

Further, in the method for manufacturing a solar cell element according to the present invention, in the firing step, the oxygen gas supply ports of the oxygen gas supply pipe of the conveyor-type firing furnace are provided on the left and right sides with respect to the traveling direction of the conveyor. A method for manufacturing a solar cell element.

Further, in the method of manufacturing a solar cell element according to the present invention, in the firing step, the oxygen gas in the oxygen gas supply pipe is arranged perpendicular to a conveyor. It is a manufacturing method.

Further, in the method for manufacturing a solar cell element according to the present invention, in the firing step, the speed of the conveyor belt of the conveyor-type firing furnace is 1000 to 2000 m / min.
m, a method for manufacturing a solar cell element.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a solar cell element according to the present invention comprises a paste application step of applying a silver-containing paste on an antireflection film for preventing reflection of light applied on a wafer; A method for manufacturing a solar cell element, comprising: a firing step of firing the paste to form an electrode; wherein an oxygen gas is supplied so as to provide an oxygen atmosphere during the firing step. Is the way.
It is considered that in the baking step, by supplying oxygen gas to form an oxygen gas atmosphere, the paste can easily penetrate the antireflection film. In the firing step, the paste easily penetrates the antireflection film, so that the heating in the firing step can be minimized. Since the heating in the firing step can be minimized, the firing can be completed before the surface of the silver contained in the paste is oxidized and the solder is hardly attached. Note that a silicon wafer can be used as the wafer. In some cases, a defect layer exists on the surface of the silicon wafer. In such a case, the silicon wafer can be subjected to wafer etching to remove the defect layer on the surface of the silicon wafer. In addition, a diffusion layer is formed on the light receiving surface side of the silicon wafer from which the defect layer has been removed to form a PN junction, and an antireflection film for preventing a decrease in output due to light reflection is formed on the diffusion layer. It is possible to form.

In the paste application step, it is preferable that the particle size of silver contained in the paste is 0.1 to 2 μm. The particle size of silver contained in the paste is 0.1 to 2 μm
This is because it is considered that the paste easily penetrates the antireflection film in the baking step, and the silver in the paste sufficiently reaches the silicon surface. The paste can contain 70 to 90% by weight of silver. If the amount is less than 70% by weight, sufficient electric conductivity cannot be obtained. 90% by weight
If the amount is larger than the above, the amount of other additives is small, so that the antireflection film cannot be penetrated.

In the firing step, it is preferable that the amount of oxygen gas to be supplied is from 1 to 3 times per minute with respect to the furnace volume. That is, in the firing step,
It is preferable to supply oxygen gas having a volume equal to or greater than the furnace volume and equal to or less than three times the furnace volume. This is considered to be because the atmosphere in the furnace is sufficiently replaced with oxygen in the firing step, and a substantial oxygen atmosphere is obtained. Here, the substantial oxygen atmosphere means that the oxygen concentration in the furnace is 40 to 90%. Note that even if the supply is more than three times, there is no effect because the inside of the furnace is already in a sufficient oxygen atmosphere.

In the firing step, the wafer can be fired in a conveyor-type firing furnace. A conveyor type baking furnace is a method in which a wafer to be baked is placed on a conveyor moving at a predetermined speed, and the placed wafer is baked by a heat source installed at a constant interval in the furnace. It is a firing furnace to be performed.

When the wafer is fired in a conveyor-type firing furnace, the firing in the firing step can be performed by heating with an infrared lamp. When the baking is performed by heating with an infrared lamp, the wafer placed on the conveyor can be heated uniformly.

In the firing step, the oxygen gas supply ports of the oxygen gas supply pipe of the conveyor-type firing furnace can be provided on the left and right sides with respect to the traveling direction of the conveyor. By providing the oxygen gas supply ports of the oxygen gas supply pipes on the left and right sides with respect to the traveling direction of the conveyor, both the left wall and the right wall in the furnace can be used for the wafer placed on the conveyor. Oxygen gas can be supplied from the oxygen gas supply port. Therefore, the oxygen gas can be uniformly supplied to the wafer placed on the conveyor.

In the firing step, it is possible to arrange the oxygen gas supply pipe perpendicular to the conveyor. By arranging the oxygen gas supply pipe perpendicular to the conveyor, it is possible to supply the oxygen gas from the vertical direction to the wafer placed on the conveyor.

In the firing step, the speed of the conveyor belt of the conveyor-type firing furnace is set to 1000 to 2000 mm / min.
It is possible. If the speed of the conveyor belt is higher than 2000 mm / min, it is difficult to stabilize the firing conditions, and as a result, the output starts to vary among the solar cell elements. On the other hand, if the speed of the conveyor belt is less than 1000 mm per minute, it becomes difficult to obtain a solar cell element having a large output.

FIG. 1 is a sectional view of one embodiment of a solar cell element according to the present invention before solder formation. Since the manufacturing process of the solar cell element is the same except for the electrode baking process, it will be described with reference to FIG.

First, a P-type silicon wafer 1 obtained by cutting a polycrystalline silicon ingot manufactured by a casting method was immersed in a 5% NaOH solution at 80 ° C. for 10 minutes to perform wafer etching. On the light receiving surface side of the silicon wafer 1, P ₂ O ₅ was applied by a coating diffusion method, and then heat treatment was performed at 850 ° C. for 10 minutes, and N + diffusion was performed to form a diffusion layer 2, thereby forming a PN junction. Next, in order to prevent a decrease in output due to recombination of carriers near the back surface of the silicon wafer 1, an Al paste is applied to the back surface of the silicon wafer 1 and then a heat treatment is performed at 700 ° C. for 5 minutes.
+ A back surface electric field layer 3 was formed. Further, a TiO ₂ antireflection film 6 of 800 angstroms was formed on the surface of the silicon wafer 1, a front electrode 4 was formed, and a back electrode 5 was formed on the surface of the silicon wafer 1 in order to prevent a decrease in output due to light reflection on the solar cell surface. . The antireflection film 6 is a SiN film (silicon nitride film)
But it doesn't matter.

First, the front electrode 4 and the back electrode 5 are coated with a paste containing silver as a main component on the silicon wafer 1 by a printing method.
0 is formed. The particle size of silver contained in the paste is 0.
It is desirable that the thickness be 1 to 2 μm. This is considered to be because if the particle size is in this range, the paste easily penetrates the antireflection film in the subsequent baking step, and the silver in the paste sufficiently reaches the silicon surface. If the thickness is 0.1 μm or less or 2 μm or more, good ohmic contact cannot be obtained.

Next, this is treated at about 150 ° C. for about 3 minutes, dried, and fired using a conveyor-type firing furnace as shown in FIG. The heating at this time was performed by an infrared lamp. At this time, the front electrode 4 is formed so as to penetrate the antireflection film 6. FIG. 3 is a cross-sectional view of the conveyor of FIG. 2 as viewed from the traveling direction. In the present embodiment, the gas supply pipe 10 is arranged on the side of the firing furnace, and oxygen gas is supplied from the gas supply pipe 10. That is, the oxygen gas supply ports of the oxygen gas supply pipe 10 of the conveyor-type baking furnace are provided on the left and right sides with respect to the traveling direction of the conveyor. The effect of introducing the oxygen gas is that the electrode paste 40 easily penetrates the antireflection film 6 by setting the oxygen gas atmosphere, so that the heating is minimized, the silver surface is oxidized, and the solder adheres. It is considered that firing can be completed before the state becomes difficult. As shown in FIG. 4, the output of the solar cell element produced at a flow rate of 1 to 3 times or less the internal volume of the firing furnace per minute as shown in FIG. Therefore, the flow rate of the oxygen gas is desirably 1 to 3 times the furnace volume per minute. This is because the atmosphere in the furnace is sufficiently replaced with oxygen,
It is considered that the atmosphere becomes a substantial oxygen atmosphere. FIG.
As shown in (1), the furnace peak temperature during firing is desirably 500 ° C. to 700 ° C. at which the output of the element becomes a large value. Further, the speed of the conveyor is 1000 to 20 as shown in FIG.
00 mm / min is desirable. When the rate was 2000 mm / min or more, the firing conditions became unstable, and output variations began to appear among the devices. 1000 mm / min
Below this, an element with a large output was not obtained.

FIGS. 7 and 8 are cross-sectional views of a firing furnace according to another embodiment of the present invention. The preparation conditions are almost the same, except that the oxygen supply port of the oxygen supply pipe 10 is arranged in the vertical direction (up or down) of the silicon wafer 1. Therefore, oxygen gas is uniformly supplied to the silicon wafer 1, and uniform firing can be performed.

[0029]

(Embodiment 1) FIG. 1 is a sectional view of an embodiment of a solar cell element according to the present invention before solder formation. Since the manufacturing process of the solar cell element is the same except for the electrode baking process, it will be described with reference to FIG.

First, a P-type silicon wafer 1 obtained by cutting a polycrystalline silicon ingot manufactured by a casting method was immersed in a 5% NaOH solution at 80 ° C. for 10 minutes to perform wafer etching. On the light receiving surface side of the silicon wafer 1, P ₂ O ₅ was applied by a coating diffusion method, and then heat treatment was performed at 850 ° C. for 10 minutes, and N + diffusion was performed to form a diffusion layer 2, thereby forming a PN junction. Next, in order to prevent a decrease in output due to recombination of carriers near the back surface of the silicon wafer 1, an Al paste is applied to the back surface of the silicon wafer 1 and then a heat treatment is performed at 700 ° C. for 5 minutes.
+ A back surface electric field layer 3 was formed. Further, a TiO ₂ anti-reflection film 6 of 800 Å was formed on the surface of the silicon wafer 1, a front electrode 4 was formed, and a back electrode 5 was formed on the surface of the silicon wafer 1 in order to prevent a decrease in output due to light reflection on the solar cell surface. .

First, the front electrode 4 and the back electrode 5 are made of silver.
A paste containing 0% by weight is applied on the silicon wafer 1 by a printing method to form a front electrode paste 40 and a back electrode paste 50. The particle size of silver contained in the paste was 1 μm.

Next, this is treated at about 150 ° C. for about 3 minutes, dried, and fired using a conveyor-type firing furnace as shown in FIG. The heating at this time was performed by an infrared lamp. At this time, the front electrode 4 is formed so as to penetrate the antireflection film 6. FIG. 3 is a sectional view of the conveyor of FIG. In this embodiment, a gas supply pipe 10 is arranged on the side of the firing furnace, and oxygen gas is supplied from the gas supply pipe 10. That is, the oxygen gas supply pipes 10 of the conveyor-type firing furnace are provided on the left and right sides with respect to the traveling direction of the conveyor. The gas flow rate of oxygen at the time of this firing was 1,300 liter / minute. Further, as shown in FIG. 5, the peak temperature in the furnace during firing was 600 ° C. Further, the speed of the conveyor was 1500 mm / min.

Embodiment 2 FIGS. 7 and 8 are sectional views of a firing furnace according to Embodiment 2 of the present invention. The production conditions are almost the same, but differ in that the oxygen supply pipe 10 is arranged in the vertical direction (above or below) of the silicon wafer 1. As a result, oxygen gas is uniformly supplied to the silicon wafer 1, and uniform firing can be performed.

It should be understood that the embodiments and examples disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0035]

When the soldering step was carried out using the solar cell element shown in FIG. 1 prepared according to Examples 1 and 2, the solderability was good and the initial characteristics of the solar cell were not reduced. . Also, in the process of connecting individual solar cells to form a panel, it was confirmed that the solder was sufficiently provided on the electrodes, and that the attachment of the lead wires was good.

[Brief description of the drawings]

FIG. 1 is a sectional view of a solar cell element according to the present invention.

FIG. 2 is a conveyor-type firing furnace used in the present invention.

FIG. 3 is a cross-sectional view as viewed from a traveling direction of a conveyor.

FIG. 4 is a diagram showing a relationship between a gas flow rate of oxygen and an element output.

FIG. 5 is a view showing a relationship between a peak temperature in a furnace during firing and an element output.

FIG. 6 is a diagram showing a relationship between a conveyor speed and element output during firing.

FIG. 7 is a cross-sectional view of another conveyor-type firing furnace used in the present invention as viewed from a traveling direction of a conveyor.

FIG. 8 is a cross-sectional view as seen from the traveling direction of the conveyor of another conveyor-type firing furnace used in the present invention.

FIG. 9 is an explanatory view illustrating a manufacturing process of a conventional solar cell element.

[Explanation of symbols]

1 silicon wafer, 2 diffusion layers formed in the silicon wafer, 3 electric field layers formed in the silicon wafer,
4 front electrode, 5 back electrode, 6 anti-reflection film, 7 heating zone of firing furnace, 8 infrared lamp, 9 conveyor, 10
Gas supply piping, 11 defective layers, 12 solder, 40 front electrode paste, 50 back electrode paste.

Claims (8)

[Claims] A paste application step of applying a silver-containing paste on an antireflection film for preventing reflection of light applied on a wafer; a baking step of baking the paste to form an electrode; A method of manufacturing a solar cell element, comprising: supplying an oxygen gas during the firing step so as to provide an oxygen atmosphere. 2. The method for manufacturing a solar cell element according to claim 1, wherein in the paste application step, the particle size of silver contained in the paste is 0.1 to 2 μm. 3. The method for manufacturing a solar cell element according to claim 1, wherein in the firing step, the amount of oxygen gas supplied is from 1 to 3 times per minute with respect to the furnace volume. . 4. The method according to claim 1, wherein in the firing step, the wafer is fired in a conveyor-type firing furnace. 5. The method according to claim 4, wherein in the firing step, the firing is heating by an infrared lamp. 6. The baking step according to claim 4, wherein the oxygen gas supply ports of the oxygen gas supply pipe of the conveyor type baking furnace are provided on the left and right sides with respect to the traveling direction of the conveyor. A method for manufacturing a solar cell element. 7. The method according to claim 4, wherein in the firing step, the oxygen gas supply pipe is arranged perpendicular to a conveyor. 8. In the firing step, the speed of the conveyor belt of the conveyor-type firing furnace is 1000 to 2 / min.
The method for producing a solar cell element according to claim 4, wherein the thickness is 000 mm.