JP2000090734A - Conductive paste, and solar battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive paste for forming an electrode on a p-type Si semiconductor substrate that can thin an electrode film with securing a desired solar battery characteristic, and provide the solar battery having the electrode formed using the conductive paste. SOLUTION: Aluminum containing organic compound is added to conductive paste formed by mixing aluminum powder, glass frit, and organic vehicle. Mixing ratio of the aluminum powder, the glass frit, the organic vehicle, and the aluminum containing organic compound is set to be aluminum powder: 50.0-75.0 wt.%, glass frit: 0.5-5.0 wt.%, organic vehicle: 20.0-30.0 wt.%, and aluminum containing organic compound: 1.0-15.0 wt.% (Al metal content: 0.01-3.0 wt.%). A back surface electrode is formed on a p-type Si semiconductor substrate by coating and baking this conductive paste.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode for a semiconductor,
In particular, the present invention relates to a conductive paste suitable for use as a p-type Si semiconductor of a crystalline Si solar cell, and a solar cell having electrodes formed using the same.

[0002]

2. Description of the Related Art A solar cell as shown in FIG. 1 is one of electronic parts having electrodes formed on a p-type semiconductor substrate. In this solar cell, a p-type Si semiconductor substrate 1 having a thickness of 300 to 400 μm is used, and an n-type impurity layer of 0.3 to 0.5 μm is provided on the light receiving surface side of the p-type Si semiconductor substrate 1. 2 and antireflection film 3 for improving photoelectric conversion efficiency
Is formed, and a grid electrode 4 for an n-type Si semiconductor is formed so as to penetrate the anti-reflection film 3 and reach the n-type impurity layer 2 of the p-type Si semiconductor substrate 1.

On the back side of the p-type Si semiconductor substrate 1, a back surface electrode 5 is formed on almost the entire surface. The back electrode 5 is usually formed by applying a conductive Al paste containing aluminum powder, glass frit and an organic vehicle to the back surface of the p-type Si semiconductor substrate 1.
It is formed by firing at a temperature higher than the melting point of Al (660 ° C.). When the back electrode 5 is formed, the interface between the back electrode 5 and the p-type Si semiconductor substrate 1 (A
1 / Si interface) on the p-type Si semiconductor substrate 1 side.
The alloy layer 6 is formed, and the recombination of the generated carriers at the back electrode 5 is suppressed. As a result, the BSF effect of improving the collection efficiency of the generated carriers is obtained.

[0004]

SUMMARY OF THE INVENTION
When a conductive Al paste containing an aluminum powder, a glass frit and an organic vehicle is used, the back electrode (Al electrode film) 5 or the Al—Si alloy layer 6 is baked during firing.
And the p-type Si semiconductor substrate 1 (see Table 1).
), The p-type Si semiconductor substrate 1 is normally warped such that the surface on which the back electrode 5 is formed is concave.

[0005]

[Table 1]

When the p-type Si semiconductor substrate is warped as described above, there is a problem that cracks or the like are generated in a process of manufacturing a solar cell and the yield is reduced.

[0007] Further, when the thickness of the p-type Si semiconductor substrate is reduced, the amount of warpage increases, so that the thickness of the p-type Si semiconductor substrate is restricted. There is a problem that becomes.

As a method of reducing the amount of warpage of a p-type Si semiconductor substrate, a method of reducing the thickness of an electrode is known. However, when the thickness of the electrode is reduced, the amount of Al-Si alloy formed decreases. However, there is a problem in that a sufficient BSF effect cannot be obtained, and the solar cell characteristics deteriorate.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides a conductive material for forming an electrode on a p-type Si semiconductor substrate which can reduce the electrode thickness while securing desired solar cell characteristics. It is an object to provide a solar cell including a paste and an electrode formed using the conductive paste.

[0010]

In order to achieve the above object, the conductive paste of the present invention (claim 1) is a p-type conductive paste.
A conductive paste for forming an electrode on an i-semiconductor substrate, comprising aluminum powder, glass frit, an organic vehicle, and an aluminum-containing organic compound.

By mixing aluminum (Al) powder, glass frit and an organic vehicle, and further containing an aluminum (Al) -containing organic compound, the aluminum-containing organic compound is decomposed in the firing step to produce metallic aluminum. However, in order to efficiently react with the p-type Si semiconductor substrate, the electrode and the p-type Si
At the interface with the semiconductor substrate, it is possible to generate an Al-Si alloy necessary for realizing desired characteristics, and it is possible to obtain a sufficient BSF effect. Therefore,
By using the conductive paste of the present invention, it is possible to reduce the thickness of the electrode while securing desired solar cell characteristics, reduce the amount of warpage of the p-type Si semiconductor substrate,
The yield can be improved and the Si
The cost can be reduced by reducing the thickness of the semiconductor substrate.

In the conductive paste of the present invention, the compounding ratio of the aluminum powder, the glass frit, the organic vehicle and the aluminum-containing organic compound is as follows: aluminum powder: 50.0 to 75.0% by weight; glass frit: 0.5 To 5.0% by weight Organic vehicle: 20.0 to 30.0% by weight Aluminum-containing organic compound: 1.0 to 15.0% by weight (in terms of Al metal: 0.01 to 3.0% by weight) It is characterized by.

The mixing ratio of the Al powder is from 50.0 to 75.0.
The range of the weight percent is that when the proportion of the Al powder is less than 50.0 weight percent, the sintering density of the electrode decreases, the resistance of the electrode film increases, and the characteristics deteriorate. %, The printability of the conductive paste is reduced.

Further, the mixing ratio of the glass frit is 0.5
The reason for setting the range to 5.0 wt% is that when the proportion of the glass frit is less than 0.5 wt%, the adhesive strength of the electrode-p-type Si semiconductor substrate decreases, and when the proportion exceeds 5.0 wt%, the electrode-
This is because glass segregates at the interface of the p-type Si semiconductor substrate and inhibits electrical contact.

Further, the mixing ratio of the organic vehicle is 20.
The range of 0 to 30.0% by weight is that when the ratio of the organic vehicle is less than 20.0% by weight, the printability of the conductive paste is lowered, and when the ratio exceeds 30.0% by weight, the sintering density of the electrode is lowered. Is reduced, the resistance of the electrode film is increased, and the characteristics are reduced.

The reason why the compounding ratio of the Al-containing organic compound is in the range of 1.0 to 15.0% by weight is that when the ratio of the Al-containing organic compound is less than 1.0% by weight, a sufficient effect of addition is obtained. In addition, if it exceeds 15.0% by weight, the sintered density of the electrode decreases, and the resistance of the electrode film increases, thereby deteriorating the solar cell characteristics.

Further, in the conductive paste according to the present invention, the aluminum-containing organic compound may be aluminum resinate, aluminum stearate, aluminum oleate, aluminum laurate, aluminum lactate, aluminum acetylacetonate, aluminum triisopropoxide, It is characterized in that it is at least one selected from the group consisting of aluminum butoxide.

The organic compound containing aluminum is not particularly limited, and various organic compounds containing aluminum can be used. Among them, aluminum resinate, aluminum stearate, aluminum oleate, and lauric acid are particularly preferable. By using at least one selected from the group consisting of aluminum, aluminum lactate, aluminum acetylacetonate, aluminum triisopropoxide, and aluminum butoxide, the effects of the present invention can be surely exerted. It can be effective.

Further, a solar cell according to the present invention (claim 4) is characterized by comprising an electrode formed by applying and baking the conductive paste according to any one of claims 1 to 3. .

When the electrode is formed by using the conductive paste according to any one of claims 1 to 3, the thickness of the electrode is reduced while maintaining the solar cell characteristics, and the warpage of the p-type Si semiconductor substrate is reduced. Will be able to do it. That is, the electrode thickness conventionally required to be 50 to 60 μm is reduced without deteriorating the solar cell characteristics (that is, the Al—Si alloy layer formed on the electrode formation surface of the p-type Si semiconductor substrate). (Without reducing the generation amount of silicon), it is possible to reduce the thickness to 20 to 30 μm, to prevent the p-type Si semiconductor substrate from warping, and to improve the yield.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described, and features thereof will be described in more detail.
In this embodiment, a conductive paste used for forming an electrode on a p-type Si semiconductor substrate for a solar cell will be described as an example.

First, aluminum powder 50.0-75.
0 wt%, glass frit 0.5 to 5.0 wt%, organic vehicle 20.0 to 30.0 wt%, and various Al-containing organic compounds in proportions as shown in Table 2. A conductive paste was prepared.

Specifically, a spherical Al powder and a B-Si-Pb-based glass frit having a softening point of 585 ° C. are added to an organic vehicle obtained by dissolving nitrocellulose in terpineol, and then an Al-containing organic compound ( For example, commercially available Al
Resinate R1058 (NE Chemcat Corporation)
And the like, and kneaded sufficiently using a well-known metal roll, to obtain a conductive paste, while taking care not to flatten the Al powder.

The Al powder used in the conductive paste of the present invention has a specific surface area that is too large to prevent the surface oxidation of the Al powder from progressing too much, while reducing the reactivity with the p-type Si semiconductor substrate. From the viewpoint of securing, it is desirable to use a spherical powder such as an atomized powder having an average particle diameter of 5 to 20 μm.

The glass frit used for the conductive paste of the present invention includes B-Si-P
The b-type glass frit is used as a preferable glass frit, but the glass frit is not limited to this, and by firing at a temperature of 650 to 800 ° C,
It is possible to suitably use various types of glass frit exhibiting good adhesion (bonding property) to the p-type Si semiconductor substrate.
In addition, as examples of other preferable glass frit,
B-Si-Bi system, B-Si-Zn system, Si-Bi-P
b type and the like.

As described above, the organic vehicle is not limited to one obtained by dissolving nitrocellulose in terpineol, but may be a fibrous resin such as ethylcellulose or nitrocellulose in which ash does not remain after firing, an acrylic resin, an alkyd resin, or the like. It is possible to use various ones in which at least one selected from the group consisting of terpineol and cellosolve is dissolved in an organic solvent such as terpineol or cellosolve.

The Al-containing organic compound as an additive is selected from aluminum resinate, aluminum stearate, aluminum oleate, aluminum laurate, aluminum lactate, aluminum acetylacetonate, aluminum triisopropoxide, and aluminum butoxide. At least one kind can be used, and other organic compounds containing Al can be used.

These Al-containing organic compounds may be added in powder form. However, when dissolved in an appropriate solvent and added in liquid form, the degree of dispersion in the paste is improved, and the A
This is preferable because the formation of the l-Si alloy layer 6 is promoted and a sufficient BSF effect can be obtained.

By using the conductive paste prepared as described above, a back electrode (Al electrode) is formed on almost the entire back surface of the p-type Si semiconductor substrate to obtain a solar cell as shown in FIG. Manufactured.

The solar cell shown in FIG. 1 has a thickness of 300 to 400 μm as described in the section of the prior art.
0.3 to 0.5 μm on the light-receiving surface side of the type Si semiconductor substrate 1
N-type impurity layer 2 and antireflection film 3 are formed, and
A grid electrode 4 penetrating the antireflection film 3 and reaching the n-type impurity layer 2 is formed, and a back electrode (Al electrode) 5 is formed on almost the entire back surface of the p-type Si semiconductor substrate. Al- at the interface between the substrate and the p-type Si semiconductor substrate 1
It has a structure in which a Si alloy layer 6 is formed.

The procedure for manufacturing this solar cell is as follows. First, a p-type Si semiconductor substrate 1 has a pn junction in which an n-type impurity layer 2 having a predetermined depth is formed on the light-receiving surface side,
Further, a p-type Si semiconductor substrate on which the antireflection film 3 is formed is prepared. Then, on the anti-reflection film 3, the light-receiving surface Ag
The paste is printed on a grid, applied and dried. Subsequently, a conductive paste to which the above-described Al-containing organic compound is added is applied to almost the entire back surface of the p-type Si semiconductor substrate 1 by a screen printing method. Then, after the conductive paste is dried, it is baked at a maximum temperature of 750 ° C. using a near-infrared firing furnace to form the grid electrode 4 and the back electrode 5 on the light receiving surface, thereby forming a solar cell as shown in FIG. Get batteries.

In the solar cell of this embodiment, in order to obtain a sufficient BSF effect, the thickness of the back electrode, which was required to be 50 to 60 μm in the case of the conventional solar cell, is shown in Table 2. As shown in Sample Nos. 1 to 10,
The thickness is 30 μm.

With respect to the solar cell fabricated as described above, when the conventional conductive paste and the conductive paste of the embodiment of the present invention to which an Al-containing organic compound was added were used, Table 2 shows the relationship between the amount of warpage of the p-type Si semiconductor substrate and the solar cell characteristics (FF value).

[0034]

[Table 2]

The warpage of the p-type Si semiconductor substrate 1 is 10 mm
The value of the distance X shown in FIG. 2 when a conductive paste is applied to a substrate of × 37.5 mm × 200 μm (t) and baked. The target value of the amount of warpage that does not cause a problem in the manufacturing process is 60.0 μm or less, and the solar cell characteristic (FF value) is 0.710 or more.

As shown in Table 2, when the back electrode was formed using a conventional conductive paste, the F
In order to obtain an F value, the back electrode (Al electrode) must be 50 μm or more as in Conventional Example 1, and the p-type Si
If the thickness of the back electrode is reduced as in Conventional Example 2 to increase the amount of warpage of the semiconductor substrate and to reduce the amount of warpage, the FF value becomes less than 0.7, and desired solar cell characteristics can be obtained. Can not be done.

On the other hand, when the back electrode is formed by using the conductive paste according to the embodiment of the present invention, even if the thickness of the back electrode is as thin as 20.3 to 26.1 μm, F
It is possible to obtain solar cell characteristics having an F value of 0.710 or more. Further, since the thickness of the back electrode is reduced as described above, the amount of warpage of the p-type Si semiconductor substrate can be reduced, and the yield in the manufacturing process can be improved.

It should be noted that the present invention is not limited to the above-described embodiment, but includes various proportions of the materials constituting the conductive paste, the structure of the solar cell, etc., within the scope of the invention. Applications and modifications are possible.

[0039]

As described above, the conductive paste of the present invention (Claim 1) contains Al powder, glass frit, and an organic vehicle, and further contains an Al-containing organic compound. As a result, the Al-containing organic compound is decomposed to produce metallic aluminum, which reacts efficiently with the p-type Si semiconductor substrate, so that desired solar cell characteristics can be ensured even if the electrode thickness is reduced. As a result, the electrode thickness can be reduced, so that the yield can be improved and the cost can be reduced by reducing the thickness of the p-type Si semiconductor substrate.

Further, as in the conductive paste of the second aspect, the mixing ratio of the aluminum powder, the glass frit, the organic vehicle and the aluminum-containing organic compound is such that the aluminum powder is 50.0 to 75.0% by weight, the glass frit is 0. 5 to 5.0% by weight, organic vehicle 20.0 to
30.0% by weight, aluminum-containing organic compound 1.0 to
By setting the content to 15.0% by weight (in terms of Al metal: 0.01 to 3.0% by weight), it is possible to more reliably reduce the thickness of the electrode while securing desired solar cell characteristics. .

Further, as in the conductive paste according to claim 3, as the Al-containing organic compound, aluminum resinate, aluminum stearate, aluminum oleate, aluminum laurate, aluminum lactate, aluminum acetylacetonate, aluminum triisopropoxide are used. By using at least one selected from the group consisting of aluminum butoxide, the effects of the present invention can be reliably achieved, and the present invention can be made effective.

Further, when the electrode is formed using the conductive paste according to any one of claims 1 to 3 as in the solar cell of the present invention (claim 4), the electrode is formed while ensuring the solar cell characteristics. It becomes possible to reduce the film thickness and reduce the warpage of the p-type Si semiconductor substrate. That is, what conventionally required the electrode film thickness to be 50 to 60 μm is reduced without impairing the solar cell characteristics (that is, the p-type S
The thickness can be reduced to 20 to 30 μm (without reducing the generation amount of the Al—Si alloy layer formed on the electrode formation surface of the i-semiconductor substrate), and the p-type Si semiconductor substrate can be prevented from warping and the yield can be reduced. Can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a solar cell according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the amount of warpage of a p-type Si semiconductor substrate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 p-type Si semiconductor substrate 2 n-type impurity layer 3 anti-reflection film 4 grid electrode 5 back electrode (Al electrode) 6 Al-Si alloy layer

Claims (4)

[Claims] 1. A conductive paste for forming electrodes on a p-type Si semiconductor substrate, said conductive paste comprising aluminum powder, glass frit, an organic vehicle and an aluminum-containing organic compound. 2. The compounding ratio of aluminum powder, glass frit, organic vehicle and aluminum-containing organic compound is as follows: Aluminum powder: 50.0 to 75.0% by weight Glass frit: 0.5 to 5.0% by weight Organic vehicle: The aluminum-containing organic compound: 20.0 to 30.0% by weight: 1.0 to 15.0% by weight (in terms of Al metal: 0.01 to 3.0% by weight). Conductive paste. 3. The aluminum-containing organic compound is at least one selected from the group consisting of aluminum resinate, aluminum stearate, aluminum oleate, aluminum laurate, aluminum lactate, aluminum acetylacetonate, aluminum triisopropoxide, and aluminum butoxide. 3. The conductive paste according to claim 1, wherein the conductive paste is one kind. 4. A solar cell comprising an electrode formed by applying and baking the conductive paste according to claim 1.