JPH11214723A - Manufacture of solar battery element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a surface electrode, without destroying an N-layer by applying an electrode material and baking it by means of leaving a phosphorous glass layer, generated at the time of forming the N-layer on one main face side of a silicon substrate. SOLUTION: A P-type polycrystalline silicon wafer 1 is arranged in a diffusion furnace and is heated in phosphorus oxychloride(POCl3 ). An N-layer 2 is formed, and a P-N junction 3 is formed. A phosphorus glass layer 4 is formed on the outer surface of the wafer 1 through thermal diffusion. A resist 7 is applied to a region where the surface electrode of the wafer 1 is formed and it is immersed in an aqueous HF solution. Then, the phosphorus layer 4 remaining on the surface of the N-layer 2 is removed. The region where the surface electrode is formed is not removed. An electrode material is printed/ applied to the remained phosphorus glass layer 4, is baked at a temperature of 700 deg.C, so that a surface electrode 8 is formed.

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 a PN junction in a silicon substrate.

[0002]

2. Description of the Related Art As shown in FIG. 2, a solar cell element formed by using a silicon substrate has a PN junction for forming an internal electric field in a silicon wafer 21. 22, a front electrode 23 and a back electrode 24 for collecting minority charge carriers generated by incident light.
It is composed of Further, an anti-reflection film 25 is formed on the light receiving surface of the silicon wafer 21 as needed.

In such a solar cell element, in order to improve the spectral sensitivity on the short wavelength side and obtain high photoelectric conversion characteristics, the PN junction 22 is formed shallowly as shown in FIG. Surface electrode 23 and N layer 21 of silicon wafer 21
It is known that an N ⁺ region 21 a ′ having a high concentration of an N-type dopant such as phosphorus is formed in a region where a is joined.

That is, the lightly doped region 2 is formed in the N layer 21a.
H / L where 1a is coupled to heavily doped region 21a '
(High-low) joining. This H / L junction is used to set the N-layer region 21a to be irradiated with light to an appropriate resistance value in order to improve the life of the minority charge carriers, and to improve the spectral sensitivity on the short wavelength side. A high photoelectric conversion efficiency is obtained by forming a shallow -N junction portion 22 and setting an N + region 21a 'to be joined to the electrode 23 to a low resistance value to achieve ohmic contact between the electrode 23 and the silicon wafer 21. Things.

As a method for manufacturing a solar cell element having the above-described H / L bonded N layer 21a with high productivity, there is a method disclosed in Japanese Patent Application Laid-Open No. 59-79580. This is to reuse the phosphorus glass layer 26 formed on the outer surface of the silicon wafer 21 when forming the PN junction 22.

That is, when an N layer 21a is formed on a P-type silicon wafer 21 by diffusing phosphorus atoms using phosphorus oxychloride (POCl ₃ ), a glass layer containing phosphorus atoms is formed on the outer surface of the silicon wafer 21. 26 are formed (FIG. 4A). The phosphor glass layer 26 is subjected to a heat treatment at about 900 ° C. using a resist film and a predetermined etching solution except for a portion where the surface electrode 23 is to be deposited (FIG. 4B). As a result, the remaining phosphorus atoms of the phosphorus glass layer 26 are re-diffused into the N layer 21a, and the N + region 21
a 'is formed (FIG. 4C). Thereafter, the unnecessary N layer 21a on the side and the back of the phosphor glass layer 26 and the silicon wafer 21 is removed (FIG. 4D), and the anti-reflection film 4,
The front electrode 2 and the back electrode 3 are formed (FIG. 2).

However, in this manufacturing method, the N ⁺ region 21a 'is formed by patterning the phosphor glass layer 26 in a high-temperature step, and after removing the phosphor glass layer 26, the N ⁺ region 21a' is further formed on the N ⁺ region 21a '. Since the surface electrode 23 (see FIG. 3) must be formed by applying and baking an electrode material, an extremely high-temperature process of about 900 ° C. is required, the manufacturing process is complicated, and the manufacturing is extremely difficult. There was a problem.

In order to solve such a problem, the N layer 2
It is conceivable that the surface electrode 23 is formed directly on the N layer 21a by lowering the sheet resistance of the N layer 21a to, for example, about 40 Ω / □. Induces a problem of reduced efficiency.

Further, if the surface resistance 23 is formed directly on the N layer 21a by increasing the sheet resistance of the N layer 21a to, for example, about 60 Ω / □, the glass in the electrode material paste is formed when the surface electrode 23 is formed. Frit etc. are N layer 21a
When the solar cell element is formed by piercing through to the P layer 21b and forming the solar cell element, there is a problem that the leak current increases and the output characteristics deteriorate. In particular, if the sheet resistance is to be increased in order to improve the current value, the N layer 21a must be formed shallow, and the glass frit in the electrode material may penetrate the N layer 21a when firing the electrode material. Becomes larger.

The present invention has been made in view of the problems of the conventional method, and an electrode is formed on the N layer without destroying the N layer even if the N layer has a relatively high resistance. It is an object of the present invention to provide a method for manufacturing a solar cell element that can be used.

[0011]

In order to achieve the above object, in a method for manufacturing a solar cell element according to the present invention, an N layer and a surface electrode are formed on one principal surface of a P-type silicon substrate, In a method for manufacturing a solar cell element in which a back electrode is formed on the main surface of the silicon substrate, an electrode material is applied and baked while leaving a phosphor glass layer generated when an N layer is formed on one main surface of the silicon substrate. Thus, the surface electrode is formed.

Further, in the method for manufacturing a solar cell element according to the present invention, only a region where the surface electrode is to be formed is left in a phosphor glass layer formed when an N layer is formed on one main surface side of the silicon substrate. It is preferable that the surface electrode is formed by applying and baking the electrode material on the phosphor glass layer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a process chart showing a method for manufacturing a solar cell element of the present invention. The P-type polycrystalline silicon wafer 1 is placed in a diffusion furnace, and the phosphorous oxychloride (P
By heating in OCl ₃ ), phosphorus atoms are diffused into the surface portion of the wafer 1 to form an N layer 2, and PN
The joint 3 is formed. Due to this thermal diffusion, a phosphorus glass layer 4 containing phosphorus atoms is formed on the outer surface of the wafer 1.
Reference numeral 5 denotes a P region in the silicon wafer (FIG. 1)
(A)).

Next, a resist film 6 is applied to one main surface side of the silicon wafer 1 and immersed in an etching solution containing hydrofluoric acid (HF) and nitric acid (N 2 O) as main components to form a side surface of the silicon wafer 1. And the other main surface side phosphor glass layer 4 and N layer 2
Is removed, the resist film 6 on one main surface side of the silicon wafer 1 is removed, and the silicon wafer 1 is washed with pure water (FIG. 1B).
(C)).

Next, a resist film 7 is applied to a region on one main surface of the silicon wafer 1 where a surface electrode is to be formed, and is dipped in an aqueous solution of hydrofluoric acid (HF) to form an N layer 2.
The phosphor glass layer 4 remaining on the surface of the substrate is removed (FIG. 1).
(D) (e)). The phosphor glass layer 4 in the region where the surface electrode is to be formed is not removed. In this case, the N layer 2 is 0.3 μm
It is formed so as to have a thickness up to the order, and the sheet resistance is 60 Ω / □ or more.

Next, an electrode material is printed and applied on the remaining phosphor glass layer 4 by a screen printing method or the like, and baked at a temperature of about 700 ° C. to form a surface electrode 8 (FIG. 1F). . The electrode material contains silver powder, glass frit, a binder, a solvent, and the like. When such an electrode material is baked at a temperature of about 700 ° C.,
The binder and the solvent in the electrode material volatilize, leaving only the silver powder and the glass frit as the electrode. Further, since the electrode material is applied on the phosphor glass layer 4, even if this electrode material is heated, the glass frit in the electrode material only adheres to the phosphor glass and does not enter the silicon substrate 1. Absent. Therefore, the N layer 2 is formed by the glass frit in the electrode material.
Is not destroyed.

Next, an antireflection film 10 is formed on one main surface side of the silicon wafer 1 (FIG. 1G). Anti-reflection film 1
0 is plasma CVD of mixed gas of silane and ammonia
It is formed using a method. The antireflection film 10 at the surface electrode pattern 8 is removed and washed with pure water (FIG. 1 (g)).

Finally, after printing and baking aluminum (Al) paste on the other main surface of the silicon wafer to form the back electrode 11, the surfaces of the front electrode 8 and the back electrode 11 are formed by a solder dipping method. Covering with solder layers 12 and 13 (FIG. 1 (h)).

In the above-described embodiment, the electrode 3 is formed by a thick film method using Al paste. However, the electrode 3 may be formed by a thin film method such as a vacuum evaporation method or a plating method. It may be applied after the electrodes are formed.

[0020]

EXAMPLE A solar cell element according to the method of the embodiment of the present invention in which the surface electrode was baked while the phosphor glass layer in the surface electrode portion was left, and a conventional structure in which the surface electrode was baked by removing all the phosphor glass layer. Was formed, and the characteristics of each were measured. The sheet resistance of the N layer portion is 6
It is set to 0Ω / □. Table 1 shows the results.

[0021]

[Table 1]

As is clear from Table 1, in the solar cell device according to the method of the present invention, the open-circuit voltage (V _oc ) is improved by 52 mV and the fill factor (FF) is increased as compared with the solar cell device according to the conventional method. Is improved by 0.226, and the conversion efficiency (Eff
i) is improved by 5.3%.

[0023]

As described above, according to the method for manufacturing a solar cell element of the present invention, N
Since the surface electrode is formed by coating and baking the electrode material while leaving the phosphor glass layer generated when forming the layer, the surface electrode can be formed without breaking the N layer, and the leakage current can be reduced. Can be provided, and the fill factor and the open circuit voltage can be improved.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of a method for manufacturing a solar cell element according to the present invention.

FIG. 2 is a cross-sectional view showing a conventional solar cell element.

FIG. 3 is a partially enlarged sectional view showing a conventional solar cell element.

FIG. 4 is a process chart showing a conventional method for manufacturing a solar cell element.

[Explanation of symbols]

1 ‥‥‥ silicon wafer, 2 ‥‥‥ N layer, 3 ‥‥‥ P
−N junction, 4 ° phosphor glass layer, 5 ° P region, 8
{Surface electrode, 9} N ⁺ region, 10} Anti-reflective coating, 11} Back electrode

Claims (3)

[Claims] 1. A method of manufacturing a solar cell element, comprising: forming an N layer and a surface electrode on one principal surface of a P-type silicon substrate; and forming a back electrode on another principal surface. A method for manufacturing a solar cell element, wherein the surface electrode is formed by applying and baking an electrode material while leaving a phosphor glass layer generated when an N layer is formed on a surface side. 2. The method according to claim 1, wherein, of the phosphor glass layer formed when the N layer is formed on one main surface side of the silicon substrate, only the region for forming the surface electrode is left, and the electrode material is formed on the phosphor glass layer. The method according to claim 1, wherein the surface electrode is formed by applying and baking. 3. The method for manufacturing a solar cell element according to claim 1, wherein the N layer formed on one main surface side of the silicon substrate has a sheet resistance of 60 Ω / □ or more. .