JP2004296793A - Solar battery element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery element whose long-term reliability can be ensured without coating the surfaces of electrodes with solder. <P>SOLUTION: The solar battery element comprises a semiconductor board 1 having a semiconductor junction and the electrodes 5, 6 on the board surfaces. An electrode material is applied to the front and back faces of the board and is burned, while an organic material 9 is applied to respective surfaces of the front face and back face electrodes 5, 6 and is dried. As a result, the surfaces of the electrodes 5, 6 are protected from the fresh air even without coating the electrode surfaces with solder to prevent the moisture absorption of the electrodes, thus preventing the oxidization of the electrodes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solar cell element, and more particularly to a solar cell element having an electrode on a surface of a semiconductor substrate.
[0002]
2. Description of the Related Art
FIG. 2 shows a cross-sectional view of a conventional solar cell. 2, 1 denotes a semiconductor substrate, 2 denotes a diffusion layer, 4 denotes a BSF layer, 5 denotes a front electrode, 6 denotes a back electrode, and 7 denotes a solder layer.
[0003]
For example, on the surface side of the P-type silicon substrate 1, an N-type diffusion layer 2 containing P and an antireflection film (not shown) made of a silicon nitride film or the like are formed. On the back side of the silicon substrate 1, there is provided a high-concentration P-type BSF layer 4 formed by diffusing aluminum, for example. Further, electrodes 5 and 6 are formed on the front and back surfaces of the silicon substrate 1, respectively.
[0004]
FIG. 3 shows a general shape of a surface electrode of a conventional solar cell element. In FIG. 3, 5 indicates a surface electrode, and 8 indicates a solar cell element. As shown in FIG. 3, the surface electrode 5 is generally formed in a lattice shape, and is designed in consideration of increasing the light receiving area and reducing the resistance. Further, the surfaces of the electrodes 5 and 6 facilitate connection with inner leads (not shown) in order to connect the solar cell elements 8 in a later step, and also ensure long-term reliability of the solar cell element 8. Is generally covered with a solder layer 7 (for example, see Patent Document 1). That is, unless the surfaces of the electrodes 5 and 6 are coated with the solder 7, it is difficult to ensure long-term reliability due to problems such as the electrodes 5 and 6 absorbing moisture or being oxidized. Conventionally, as such solder 7, Sn-Pb eutectic solder has been used.
[0005]
However, in recent years, environmental issues have been taken up, and lead contained in Sn-Pb eutectic solder has become a problem, and lead-free solder has been developed. However, from the viewpoints of operating temperature and long-term reliability, a lead-free solder suitable for a solar cell element that is superior to the conventional Sn-Pb eutectic solder has not yet been developed.
[0006]
As a means for solving this problem, a method of not covering the surface of the electrode with solder can be considered. However, according to this method, there is a problem that long-term reliability cannot be ensured due to moisture absorption due to contact of the electrode with the atmosphere.
[0007]
The present invention has been made under such a background, and an object of the present invention is to provide a solar cell element which can ensure long-term reliability without coating the surface of the electrode with solder.
[0008]
[Patent Document 1]
JP 2002-11116 A
[Means for Solving the Problems]
In order to achieve the above object, in the solar cell element according to claim 1, in a solar cell element having an electrode on a surface of a semiconductor substrate having a semiconductor junction, the surface of the electrode is coated with an organic material. Features.
[0010]
In the solar cell element, the organic material desirably has a water absorbing property.
[0011]
Further, in the solar cell element, the organic material is any one of methanol, tetrahydrofuran, γ-butyrolactone, N, N-dimethylacetamide, N-methylpyrrolidone, N, O-bis (trimethylsilyl) trifluoroacetamide, and hexamethyldisilazane. Is desirable.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a sectional view showing one embodiment of a solar cell element according to the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor substrate, 2 denotes a diffusion layer, 4 denotes a BSF layer, 5 denotes a front electrode, and 6 denotes a back electrode.
[0013]
First, the semiconductor substrate 1 is prepared. This semiconductor substrate 1 is made of single crystal or polycrystalline silicon. This silicon substrate 1 is a substrate containing one conductivity type semiconductor impurity such as boron (B) at about 1 × 10 ¹⁶ to 1 × 10 ¹⁸ atoms / cm ³ and having a specific resistance of about 1.0 to 2.0 Ω · cm. is there. In the case of a single crystal silicon substrate, it is formed by a pulling method or the like, and in the case of a polycrystalline silicon substrate, it is formed by a casting method or the like. A polycrystalline silicon substrate can be mass-produced and is more advantageous than a single crystal silicon substrate in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced into a thickness of about 300 to 500 μm, and cut into a size of about 10 cm × 10 cm or 15 cm × 15 cm to obtain a semiconductor substrate 1.
[0014]
Next, the silicon substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ) or the like, so that the surface of the silicon substrate 1 has phosphorus atoms of 1 × 10 ¹⁶ to 1 × 10 ^18. The diffusion layer 2 is formed by diffusing about atoms / cm ³ . The diffusion layer 2 is formed at a depth of about 0.2 to 0.5 μm, and is formed so that the sheet resistance becomes 40Ω / □ or more. Next, an antireflection film 3 is formed on the front surface side of the silicon substrate 1. The antireflection film 3 is made of, for example, a silicon nitride film, and is formed by a plasma CVD method using a mixed gas of silane and ammonia. The antireflection film 3 is provided to prevent light from being reflected on the surface of the silicon substrate 1 and to effectively take in light into the silicon substrate 1.
[0015]
Then, an electrode material is applied to the back surface side, and a portion corresponding to the surface electrode 5 of the antireflection film (not shown) is etched, and then the electrode material is applied and fired. Alternatively, an electrode material is applied on the back surface side, and the electrode material is applied directly on the antireflection film and fired. Thereby, the front surface electrode 5 and the back surface electrode 6 are formed. As the electrode material, an electrode paste or the like obtained by adding 0.1 to 5 parts by weight of glass frit to 100 parts by weight of silver to silver powder and an organic vehicle is used, and the electrode paste is printed by a screen printing method. By baking at 650 to 900 ° C. for about 1 to 30 minutes. The electrode pattern shape itself is the same as the conventional electrode pattern shape shown in FIG.
[0016]
Thereafter, in the present invention, an organic material 9 is applied to the surfaces of the front electrode 5 and the back electrode 6 and dried. Organic materials include organic glass, organic pigments, and organometallic compounds, such as methanol, tetrahydrofuran, γ-butyrolactone, N, N-dimethylacetamide, N-methylpyrrolidone, N, O-bis (trimethylsilyl) trifluoroacetamide, and polystyrene. , Methyl methacrylate, celluloid, acetylcellulose, ethylcellulose, polyester, polypropylene, alkyl group, hexamethyldisilazane and the like. By doing so, the surfaces of the electrodes 5 and 6 do not come into contact with the outside air even if the surfaces of the electrodes are not coated with solder, preventing the electrodes from absorbing moisture and preventing oxidation, thereby ensuring long-term reliability. it can. Furthermore, since the solder layer 7 which has conventionally been about 200 μm can be reduced to about 50 μm by changing the solder layer 7 to an organic substance 9, irregularities on the surface of the solar cell element 8 can be reduced, and the solar cell element 8 can be formed in a later step. Even if an external force is applied to the entire surface, it is possible to prevent the solar cell element 8 from breaking.
[0017]
Further, when the electrodes of the solar cell element are connected by the inner leads (not shown) when the solar cell module is formed in a later process, the use of the organic material 9 will reach the boiling point below the melting point of the solder. There is no need to limit the places where the electrodes are connected. In addition, by applying the organic material 9 in this manner, the same long-term reliability effect as obtained by the conventional Sn-Pb eutectic solder can be obtained without using lead, and the environment is adversely affected. Will not be exerted.
[0018]
In the solar cell element according to the present invention, it is desirable that the organic material 9 has water absorption. Examples of the organic substance 9 having water absorption include methanol, tetrahydrofuran, γ-butyrolactone, N, N-dimethylacetamide, N-methylpyrrolidone, N, O-bis (trimethylsilyl) trifluoroacetamide, hexamethyldisilazane, and the like.
[0019]
The Sn-Pb eutectic solder is usually operated at a processing temperature of about 200 ° C. For this reason, in the conventional solar cell element, the moisture applied to the electrode surface before the solder coating was evaporated during the solder coating process. However, according to the method of the present invention, since high-temperature treatment is not performed after the formation of the electrode, the moisture deposited on the electrode surface before applying the organic material remains on the electrode surface or inside. Then, by applying a water-absorbing organic material to the electrode surface, the organic material sucks up moisture trapped in the electrode surface or in the electrode, so that long-term reliability can be further improved. Thereafter, the solar cell element is formed into a module and sealed in a resin, so that moisture does not adhere to the organic material from the outside.
[0020]
The presence or absence of water absorption can be determined by the discoloration, deterioration, or deformation of the surface when the resin comes into contact with water.
[0021]
Further, in the solar cell element of the present invention, hexamethyldisilazane ((CH ₃ ) ₃ SiNHSi (CH ₃ ) ₃ ) can be suitably used as the organic material 9. By doing so, the surfaces of the electrodes 5 and 6 do not come into contact with the outside air, so that oxidation and moisture absorption can be prevented, long-term reliability can be ensured, and hexamethyldisilazane is a colorless liquid. In addition, since it has a light-transmitting property, even if it is formed so as to protrude to the light-receiving surface portion other than the surface electrode 5 on the front surface side, it is possible to suppress a decrease in characteristics due to a decrease in the light-receiving area. Hexamethyldisilazane can be obtained by reacting ammonia with chlorotrimethylsilane. It is easily hydrolyzed and becomes hexamethyldisiloxane via trimethylsilanol. Since the boiling point is 126 ° C to 127 ° C, it can be easily dried at about 100 ° C.
[0022]
The present invention is not limited to the above embodiment, and many modifications and changes can be made within the scope of the present invention. For example, the structure of the solar cell element is not limited to this, and the solar cell element can be used for a solar cell element having electrodes on only one side, and is not limited to a crystalline silicon solar cell element.
[0023]
【The invention's effect】
As described in detail above, according to the solar cell element of the present invention, since the surface of the electrode is coated with the organic material, the surface of the electrode is exposed to the outside air without coating the surface of the electrode with solder. No longer touching, preventing the electrode from absorbing moisture and preventing oxidation, so that long-term reliability can be ensured. Further, by changing the solder layer, which was conventionally about 200 μm, to an organic material, it can be reduced to about 50 μm, so that the unevenness on the surface of the solar cell element can be reduced, and the entire surface of the solar cell element can be formed in a later step. Even if an external force is applied, it is possible to prevent the solar cell element from breaking. Furthermore, when connecting an electrode of a solar cell element by an inner lead when forming a solar cell module in a later process, if an organic material is used, the inner lead is connected to the electrode because the boiling point is reached below the melting point of solder. There is no need to limit the location. Furthermore, by applying an organic material to the surface of the electrode, the same long-term reliability effect as obtained by conventional Sn-Pb eutectic solder can be obtained without using lead. Will not be adversely affected.
[0024]
Further, when the organic material used has water absorbency, the organic material absorbs moisture even when it comes into contact with the outside air, so that the influence on the electrode can be suppressed.
[0025]
In addition, when the organic material used is any of hexamethyldisilazane ((CH ₃ ) ₃ SiNHSi (CH ₃ ) ₃ ), the surface of the electrode does not come into contact with the outside air, and oxidation and moisture absorption can be prevented. In addition to ensuring long-term reliability, hexamethyldisilazane is a colorless liquid and has a light-transmitting property. In addition, it is possible to suppress a decrease in characteristics due to a decrease in the light receiving area.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of a solar cell element according to the present invention.
FIG. 2 is a cross-sectional view illustrating a conventional solar cell.
FIG. 3 is a diagram showing a surface electrode of a conventional solar cell element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Diffusion layer, 4 ... BSF layer, 5 ... Surface electrode, 6 ... Back electrode, 7 ... Solder, 8 ... Solar cell element, 3 ... Organic materials

Claims (3)

A solar cell element having an electrode on a surface of a semiconductor substrate having a semiconductor junction, wherein the surface of the electrode is coated with an organic material. The solar cell element according to claim 1, wherein the organic material has water absorption. The organic material is any one of methanol, tetrahydrofuran, γ-butyrolactone, N, N-dimethylacetamide, N-methylpyrrolidone, N, O-bis (trimethylsilyl) trifluoroacetamide, and hexamethyldisilazane. The solar cell element according to claim 2.

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