JP2004296799A - Solar battery element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery element on which solder is stuck to electrodes more firmly. <P>SOLUTION: A semiconductor board 1 having a diffusion layer 2 of inverse conductivity and a reflection preventive film 3 is provided with a front surface electrode 5 on the front surface of the board 1, and with a back surface electrode 6 on the back surface. The electrodes 5, 6 are coated with solder layers 8, 9. The front surface electrode 5 and the solder layer 8 coating it contain a plurality of identical elements, such as Ag, Ti, P, or one or more kinds of compounds composed of these elements. <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 electrodes coated with solder.
[0002]
2. Description of the Related Art
FIG. 2 shows a structure of a conventional general solar cell element. In FIG. 2, 11 is a semiconductor substrate, 12 is a diffusion layer, 13 is an antireflection film, 14 is a BSF layer, 15 is a front surface electrode, 16 is a back silver electrode, 17 is a back aluminum electrode, 18 is a front solder layer, and 19 is a front solder layer. 3 shows a backside solder layer.
[0003]
For example, an N-type impurity is diffused to a predetermined depth over the entire surface near the surface of the P-type semiconductor substrate 11 to provide an N-type diffusion layer 12, and an anti-reflection film 13 made of a silicon nitride film or the like is provided on the surface of the semiconductor substrate 11. In addition, the front surface electrode 15 is provided on the front surface, and the back surface electrodes 16 and 17 composed of the back surface aluminum electrode 17 and the back surface silver electrode 16 are provided on the back surface. On the back surface of the semiconductor substrate 11, a BSF layer 14, which is a high-concentration P-type diffusion layer, is formed. A front surface solder layer 18 and a back surface solder layer 19 are formed on the surfaces of the front surface electrode 15 and the back surface silver electrode 16, respectively.
[0004]
The surface electrode 14 of this solar cell element is a so-called fire-through in which the surface electrode material is applied on the antireflection film 13 and baked to melt the antireflection film 13 under the electrode material and directly contact the semiconductor substrate 11. Formed by the method.
[0005]
To form the back electrodes 16 and 17 of the solar cell element, a paste containing aluminum as a main component is applied to most of the semiconductor substrate 11 except for a part of the back surface and dried, and then the paste is applied. A paste containing silver as a main component is applied so as to cover the uncoated portion and the periphery thereof, and dried. Finally, a paste containing silver as a main component is applied to the surface side of the semiconductor substrate 11 and dried. A simultaneous firing method, that is, a simultaneous firing method is used (for example, see Patent Document 1).
[0006]
However, according to this method, a stable ohmic contact was not obtained, and an electrode strength that could sufficiently withstand modularization was not obtained.
[0007]
In order to avoid this problem, there is a method in which one or more of Ti, Bi, Co, Zn, Zr, Fe, Cr powder or oxide powder thereof is contained in an electrode material to be baked on the antireflection film 13. (For example, see Patent Document 1). By doing so, good ohmic contact can be obtained even if an electrode material is applied from above the antireflection film 13 and fired, and sufficient electrode strength that can withstand modularization can be obtained.
[0008]
Further, there is a method in which a phosphorus compound is contained in an electrode material to be baked on the antireflection film 13 (for example, see Patent Document 2). As typical phosphorus compounds, phosphorus oxides such as P ₂ O ₅ and P ₂ O ₄ , Ag ₃ PO ₄ and silver pyrophosphate are used. By doing so, the contact resistance can be reduced.
[0009]
However, when an additive is added to the electrode material by these methods, there have been problems in that the electrode itself becomes brittle, the adhesion between the electrode and the solder is reduced, and the solder does not wet.
[0010]
In a conventional solar cell element in which an additive is not contained in an electrode material, there is a method of adding Ag to solder to solve this problem (for example, see Patent Document 3). According to this method, it is possible to prevent so-called silver erosion in which Ag of the electrode melts into the solder, and to improve the adhesion between the solder and the electrode since the same element is included in the solder and the electrode.
[0011]
However, solar cells with additives in the electrode material have poorer adhesion between the electrode and solder than solar cells without additives in the electrode material, so this method completely solves the problem. I couldn't.
[0012]
The present invention has been made in view of such a problem, and has as its object to provide a solar cell element having high adhesion between an electrode and solder.
[0013]
[Patent Document 1]
JP 2001-313400 A [Patent Document 2]
JP-A-11-163377 [Patent Document 3]
JP 2001-274426 A
[Means for Solving the Problems]
In order to achieve the above object, according to the solar cell element of the first aspect, a front surface electrode is provided on the front surface side of the semiconductor substrate having the reverse conductivity type diffusion layer and the antireflection film, and a back surface electrode is provided on the rear surface side. A solar cell element in which these electrodes are covered with solder is characterized in that the surface electrode and the solder covering the same contain a plurality of the same elements.
[0015]
One of the plurality of identical elements is preferably Ag, and the other identical element is preferably Ti, P, or one or more of these compounds.
[0016]
It is preferable that the other same element is contained in the solder in an amount of 10 to 100 ppm.
[0017]
Further, it is preferable that the other same element is contained in the surface electrode in an amount of 0.05 to 5% by weight.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing the structure of the solar cell element of the present invention. In FIG. 1, 1 is a semiconductor substrate, 2 is a diffusion layer, 3 is an anti-reflection film, 4 is a BSF layer, 5 is a front electrode, 6 is a back silver electrode, 7 is a back aluminum electrode, 8 is a front solder layer, 9 is 3 shows a backside solder layer.
[0019]
First, the semiconductor substrate 1 is prepared. This semiconductor substrate 1 is made of single crystal or polycrystalline silicon. This semiconductor substrate 1 is a substrate containing about 1 × 10 ¹⁶ to 10 ¹⁸ atoms / cm ³ of one conductivity type semiconductor impurity such as boron (B) and having a specific resistance of about 1.5 Ωcm. In the case of single crystal silicon, it is formed by a pulling method or the like, and in the case of polycrystalline silicon, it is formed by a casting method or the like. Polycrystalline silicon can be mass-produced and is more advantageous than monocrystalline silicon in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced into a thickness of about 300 μm and cut into a size of about 15 cm × 15 cm to obtain a semiconductor substrate.
[0020]
Next, in order to clean the cut surface of the substrate, a very small amount of the surface is etched with hydrofluoric acid, hydrofluoric acid, or the like.
[0021]
Next, the semiconductor substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ) to diffuse phosphorus atoms into the surface portion of the semiconductor substrate 1 so that the sheet resistance is 30 to 300 Ω / □. The diffusion layer 2 having another conductivity type is formed.
[0022]
Next, after removing other portions except for the surface side of the semiconductor substrate 1, the semiconductor substrate 1 is washed with pure water. The removal of the portion other than the surface side of the semiconductor substrate 1 is performed by applying a resist film on the surface side of the semiconductor substrate 1, etching away using a mixed solution of hydrofluoric acid and nitric acid, and then removing the resist film.
[0023]
Next, an antireflection film 3 is formed on the front surface side of the semiconductor substrate 1. The antireflection film 3 is made of, for example, a silicon nitride film, and is formed by, for example, a plasma CVD method in which a mixed gas of silane (SiH ₄ ) and ammonia (NH ₄ ) is glow discharge-decomposed, turned into plasma, and deposited. . The antireflection film 3 is formed so as to have a refractive index of about 1.8 to 2.3 in consideration of a refractive index difference from the semiconductor substrate 1 and the like, and has a thickness of about 500 to 1000 °. The silicon nitride film 3 has a passivation effect when formed, and has an effect of improving the electrical characteristics of the solar cell together with the function of preventing reflection.
[0024]
Then, a back surface aluminum electrode 7 is formed by applying and baking a paste containing aluminum as a main component on the back surface, and aluminum is diffused into the semiconductor substrate 1 to form a BSF layer 4 which is a P-type high concentration layer. Is done. Further, the front surface electrode 5 and the back surface silver electrode 6 are formed by applying and baking an electrode material made of silver on the front and back surfaces. This electrode material is obtained by adding 10 to 30% by weight and 0.1 to 5% by weight of silver, an organic vehicle, and a glass frit to 100% by weight of silver, respectively, to form a paste. And baked at 600 to 800 ° C. for about 1 to 30 minutes.
[0025]
The organic vehicle used at this time is a resin used for converting a powdery material into a paste, and examples thereof include a cellulose-based resin and an acrylic-based resin. Since these are decomposed and volatilized at about 400 ° C., their components do not remain in the electrodes 5 and 6 after firing. The glass frit is used to impart strength to the baked electrodes 5 and 6. Glass frit contains oxides such as lead, boron and silicon, and has various softening points of about 300 to 600 ° C., but some remain in electrodes 5 and 6 after firing, and some Has a function of bonding the electrodes 5 and 6 to the semiconductor substrate 1 for welding.
[0026]
In the present invention, the surface electrode material contains Ti or P having a particle size of about 0.1 to 5 μm, or one or more of these compounds, for example, oxides. The particle size of Ti, P or these compounds is desirably 0.1 to 5 μm. If the thickness is less than 0.1 μm, the dispersibility in the electrode material becomes poor, and sufficient electrode strength cannot be obtained, which is not desirable. If the particle size is 5 μm or more, the screen printability (line breakage, line width uniformity) deteriorates, and sufficient electrode strength cannot be obtained, which is not desirable. The content is desirably 0.05 to 5% by weight. If it is less than 0.05% by weight, sufficient electrode strength cannot be obtained, which is not desirable. On the other hand, if the content is 5% by weight or more, the line resistance of the electrode material increases, which is not desirable.
[0027]
By including one or more of Ti, P, and these compounds in the electrode material, even if the electrode material is applied from above the antireflection film 3, the ohmic contact property is good and the electrode strength is high. A solar cell element is obtained. This is because these materials act on the glass frit component contained in the electrode material to promote the reaction between the antireflection film 3 and the glass frit. By doing so, sufficient ohmic contact and adhesive strength can be obtained even with the surface electrode 5 formed by the fire-through method.
[0028]
The surfaces of the front electrode 5 and the back electrode 6 are coated with solders 8 and 9 to secure long-term reliability and to connect inner leads (not shown) for connecting solar cell elements in a later step.
[0029]
The present invention is characterized in that the solder 8 covering the surface electrode 5 contains the same element as the plurality of elements contained in the surface electrode 5. By doing so, the wettability between the electrode and the solder is increased and the adhesion strength is improved as compared with the case where only Ag is conventionally included in the solder and the electrode.
[0030]
At this time, it is preferable that one of the plurality of identical elements is Ag and the other identical element is Ti, P, or one or more of these compounds, for example, oxides. By doing so, even if it is added to the solder, its properties are not adversely affected, and the long-term reliability required for the solder can be secured.
[0031]
It is preferable that 10 to 100 ppm of Ti, P, or one or more of these compounds be contained in the solder. If it is 10 ppm or less, it becomes difficult to achieve the original purpose of increasing the wettability between the electrode and the solder and improving the adhesion strength. On the other hand, if it is 100 ppm or more, the brittleness of the solder increases and the brittleness becomes brittle, so that it becomes difficult to secure long-term reliability, and it becomes difficult to connect to the inner lead in a later process.
[0032]
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 above-mentioned solder exerts its effect particularly effectively when used on the front electrode 5, but can also be used on the back electrode 6.
[0033]
【The invention's effect】
As described above, according to the solar cell element of the present invention, since the surface electrode and the solder covering the same contain a plurality of the same elements, the wettability between the electrode and the solder is increased, and the adhesion strength is improved. I do.
[0034]
At this time, if one of the plurality of the same elements is Ag and the other of the same elements is Ti, P, or one or more of these compounds, the electrode material is directly applied on the antireflection film. By applying and baking, the anti-reflection film is melted and a good ohmic contact can be obtained even in a so-called fire-through method in which the semiconductor substrate and the surface electrode are brought into direct contact. High adhesion strength can be obtained. Further, even if added to the solder, the properties are not adversely affected, and the long-term reliability required for the solder can be secured.
[0035]
At this time, when one or more of Ti, P, and one or more of these compounds are contained in the solder in an amount of 10 to 100 ppm, the wettability between the electrode and the solder is increased, and the adhesion strength can be improved. Is low in brittleness and long-term reliability can be ensured, so that it can be connected well to the inner lead in a later step.
[0036]
Furthermore, when 0.05 to 5% by weight of Ti, P, or any one of these compounds is contained in the surface electrode, sufficient strength is obtained and the line resistance of the electrode material is also reduced. A good ohmic contact can be obtained even by the so-called fire-through method of directly applying and baking from above the antireflection film, and a sufficient adhesion strength of the surface electrode that can withstand modularization can be obtained. be able to.
[0037]
Further, the present invention can be used not only for Sn-Pb-based solder, but also effectively exerts its effects on various types of solders regardless of the type of solder. In particular, when used for so-called lead-free solders such as Sn-Ag, Sn-Ag-Bi, and Sn-Ag-Cu, which tend to cause problems in wettability and adhesion between the electrodes and the solder, the wettability between the electrodes and the solder is improved. And the adhesion strength is improved. Also, when the surface electrode is formed by a method other than fire-through, the wettability of the solder is increased and the adhesion strength between the solder and the electrode can be improved.
[Brief description of the drawings]
FIG. 1 is a view showing one embodiment of a solar cell element according to the present invention.
FIG. 2 is a view showing a conventional solar cell element.
[Explanation of symbols]
1: semiconductor substrate, 2: diffusion layer, 3: antireflection film, 4: BSF layer, 5: front electrode, 6: back silver electrode, 7: back aluminum electrode, 8: front solder layer, 9: back solder layer

Claims (4)

A front surface electrode is provided on a front surface side of a semiconductor substrate having a diffusion layer and an anti-reflection film of a reverse conductivity type, and a back surface electrode is provided on a back surface side. A solar cell element, wherein a plurality of the same elements are contained in the solder to be formed. 2. The solar cell according to claim 1, wherein one of the plurality of identical elements is Ag, and the other identical element is Ti, P, or any one or more of these compounds. 3. Battery element. The solar cell element according to claim 2, wherein the other same element is contained in the solder in an amount of 10 to 100 ppm. The solar cell element according to claim 2, wherein the other same element is contained in the surface electrode in an amount of 0.05 to 5% by weight.

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