JP2001135834A - Photoelectric conversion element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element having a high conversion efficiency and a method capable of manufacturing the element in a simple process. SOLUTION: In a photoelectric conversion element which has PN junctions in a semiconductor substrate 1 and a P side current collecting electrode 9 and an N side current collecting electrode 10 on the rear of the substrate 1, the peripheral part of the substrate 1 has the PN junction deeper than that in the center part of the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion element and a method for manufacturing the same, and more particularly, to a photoelectric conversion element having an improved method for extracting an electrode and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIGS. 18 to 26 are sectional views showing an example of a conventional method for manufacturing a solar cell.

Referring to FIG. 18, as a substrate 101, a P-type semiconductor made of a silicon substrate having an impurity concentration of 3 × 10 ¹⁵ to 4 × 10 ¹⁶ cm ^-3 and a main surface having a crystal axis of (100) is used. A substrate is used. First, a texture surface for reducing light reflection is formed on the light receiving surface of the substrate 101. That is, isopropyl alcohol is added to an aqueous solution containing several percent of sodium hydroxide,
The silicon substrate 101 is processed at a temperature of 20 to 30 minutes. Thus, many fine irregularities are formed on the light receiving surface of the substrate 101.

Next, referring to FIG. 19, a diffusion source 102 such as a phosphorus compound is applied to the main surface of P-type semiconductor substrate 101 by a spin method.

Next, referring to FIG. 20, a mask material 103 containing alkyl titanate in a solvent is provided on the back surface of substrate 101.
Is applied.

Referring to FIG. 21, heat treatment is performed at a temperature of about 900 ° C. for several tens of minutes to form an n ⁺ layer having a thickness of about 0.4 μm. Thereby, the n ⁺ layers 104 and 105 are formed on the main surface of the substrate 101 and on the side surfaces of the substrate 101.
Are respectively formed.

The n ⁺ layer 105 is formed on the P-type semiconductor substrate 10.
1 and a PN junction is formed. Then, referring to FIG. 22, phosphor glass 10 on the main surface of semiconductor substrate 101 is next referred to.
2 and the titanium dioxide film formed on the back surface of the substrate 101 are removed by etching with hydrofluoric acid.

[0008] Next, referring to FIG.
An anti-reflection film 106 is formed on the main surface of No. 01.

Next, referring to FIG. 24, after paste 107a containing aluminum and paste 109a containing silver are printed in a predetermined pattern and dried,
Heat treatment at 00 to 800 ° C. At this time, aluminum and silicon are alloyed to form an aluminum electrode (P-type current collecting electrode, positive electrode) 107 and a back surface silver electrode 109, and on the back side of the aluminum electrode 107,
A p ⁺ layer 108 is formed. This p ⁺ layer 108 has a thickness of about 5 μm.
m, forming a BSF structure.

[0010] Next, referring to FIG.
6, a paste 110a containing silver is printed in a predetermined pattern and dried.

Next, referring to FIG.
Heat treatment is performed at 800 ° C. to form a surface silver electrode (N-side current collecting electrode, negative electrode) 110. At this time, the surface silver electrode 110 penetrates the antireflection film 106 to form an ohmic connection with the n ⁺ layer.

Through the above steps, a solar cell is completed.

[0013]

However, in the above-mentioned conventional solar cell, the negative electrode is on the front side and the positive electrode is on the back side. There was a problem that the front and back had to be connected, making the work difficult.

For this reason, Japanese Patent Application Laid-Open Nos. 4-7879 and 9-18043 disclose a solar cell in which a positive electrode and a negative electrode are formed on the same surface. However, such a solar cell has a problem that the manufacturing process is complicated and the conversion efficiency is low.

An object of the present invention is to solve the above-mentioned problems and to provide a photoelectric conversion element having high conversion efficiency and a method for manufacturing the photoelectric conversion element with a simple process.

[0016]

A photoelectric conversion element according to the present invention is a photoelectric conversion element in which a PN junction is formed on a semiconductor substrate, and a P-side current collecting electrode and an N-side current collecting electrode are formed on the back surface of the substrate. The semiconductor device is characterized in that a peripheral portion has a deeper PN junction than a central portion of the semiconductor substrate.

Preferably, a PN junction is formed on the light receiving surface of the semiconductor substrate, and a PN junction is formed on at least a side surface along at least two sides and a peripheral portion of the back surface of the semiconductor substrate.

The photoelectric conversion element according to the present invention is a photoelectric conversion element in which a PN junction is formed on a light receiving surface of a semiconductor substrate and a P-side current collecting electrode and an N-side current collecting electrode are formed on the back surface of the substrate. A PN junction is formed on at least the side surface and the back surface peripheral portion along two sides.

Preferably, the pattern of the current collecting electrodes on the light-receiving surface is radially spread from the center of the substrate to the periphery.

The method for manufacturing a photoelectric conversion element according to the present invention comprises:
In the above-described method for manufacturing a photoelectric conversion element of the present invention, a diffusion source is dropped at a position shifted outward from the center of the substrate, the diffusion source is applied to the periphery of the substrate, and a PN junction is formed on the substrate by thermal diffusion. Is formed.

Preferably, a PN junction is formed on the substrate by coating and diffusion, and a diffusion mask is formed on another portion of the rear surface so that the junction is formed along at least two sides of the rear surface.

Preferably, when applying the diffusion source to the substrate, the diffusion source is dropped while rotating the substrate.

[0023]

1 and 2 are a sectional view and a plan view, respectively, showing the structure of a solar cell as an example of a photoelectric conversion element according to the present invention.

Referring to FIGS. 1 and 2, this solar cell comprises a P-type semiconductor substrate 1, n ⁺ layers 4 and 5b formed on one main surface of substrate 1, an antireflection film 6, and a substrate 1 P side and the n ⁺ layer 5a formed and on the rear surface, the rear surface silver electrode (positive electrode) 9 formed on the back surface of the substrate 1, the back surface of the substrate 1
A back surface silver electrode (negative electrode) 10 formed on the N junction (n ⁺ layer portion), an aluminum electrode 7, and a p ⁺ formed by diffusing aluminum of aluminum electrode 7 into substrate 1.
And a layer 8.

The P-type semiconductor substrate 1 is a silicon substrate, and the surface of the substrate 1 has fine irregularities to reduce light reflection. The back electrodes 9, 10, and 7 are formed using a substrate or aluminum as a material by a screen printing method.

Hereinafter, an example of a method of manufacturing the solar cell configured as described above will be described with reference to FIGS.

First, referring to FIG. 3, a P-type semiconductor substrate 1
Is treated with an acid solution or an aluminum solution to remove a damaged layer on the surface. If the substrate 1 is a single crystal having a crystal axis (100), the P-type semiconductor substrate 1 is immersed in a sodium hydroxide aqueous solution (concentration of several%) at 80 to 90 ° C.
The treatment is performed for 0 to 30 minutes to form a fine texture on the surface of the P-type semiconductor substrate 1.

Next, referring to FIG. 4, a dopant solution 2 containing phosphorus pentoxide is applied to the surface of the substrate 1 through a nozzle by a spin coater. At this time, the liquid 2 is dropped at a position off the center, and the dopant liquid 2 is applied only around the substrate 1. This is because a shallow junction is formed at the center and a deep junction is formed at the periphery, as described later.

Next, referring to FIG. 5, a P-type semiconductor substrate 1 will be described.
A mask material 3 obtained by diluting an alkyl titanate with a solvent is formed by a printing method or the like.

At this time, as shown in FIG. 2, the mask material 3 is not formed on the side surface and the back surface peripheral portion along at least two sides of the substrate 1 so as to form a PN junction. As described above, the portion where the PN junction is formed has at least two sides. In order to reduce the series resistance when a current flows from the front surface to the rear surface, it is advantageous that the side PN junction is longer. This is because the longer the back silver electrode (negative electrode) 10 is, the easier it is to connect the interconnector.
As shown in FIG. 2, in the present embodiment, the PN junction is formed along three sides of the substrate 1, so that the series resistance can be further reduced as compared with the case of two sides.

Next, referring to FIG. 6, by performing a heat treatment at a temperature of about 900 ° C. for several tens of minutes, an n ⁺ layer 4 having a thickness of about 0.4 μm is formed in a region where dopant solution 2 is applied. Is formed. In the region where the dopant liquid 2 is not applied, n ⁺ layers 5a and 5b having a thickness of about 0.2 μm are formed by out diffusion. On the other hand, no n ⁺ layer is formed below the mask material 3.

Next, referring to FIG. 7, the phosphor glass layer 2 on the main surface of the substrate 1 and the mask material 3 on the back surface are subjected to hydrofluoric acid treatment.
And remove.

Next, referring to FIG. 8, on the main surface of the substrate 1,
An anti-reflection film 6 is formed. As the antireflection film 6, AP
There is a titanium dioxide film formed by a CVD method or a silicon nitride film formed by a PCVD method.

Next, referring to FIG.
The paste 7 containing aluminum is printed and dried in a predetermined pattern.

Next, referring to FIG. 10, after printing and drying silver-containing pastes 9a and 10a in a predetermined pattern,
Heat treatment at 00 to 800 ° C. At this time, aluminum and silicon are alloyed to form aluminum electrode 7, and p ⁺ layer 8 is formed on the back side of aluminum electrode 7. It has a thickness of about 5 μm and forms a BSF structure. Further, the silver electrode 10 formed on the back surface n ⁺ layer 5a becomes the back surface negative electrode 10.

FIGS. 11 and 12 are diagrams for explaining an example of a method of applying a dopant liquid to a substrate.

As shown in FIG. 11, when the dopant liquid 2 is applied while rotating the substrate 1, the dopant liquid 2 is applied to the four corners on the back surface of the substrate 1 and the corresponding side surfaces of the substrate 1 as shown in FIG. Wrap around and the higher concentration n ⁺ layer 5
a can be formed on the back and side surfaces of the substrate 1. as a result,
When the n ⁺ layer 5a is brought into contact with the electrode on the back surface of the substrate 1, a contact with lower resistance can be achieved. Further, when a current flows from the front surface to the rear surface of the substrate 1, the current flows through the low resistance n ⁺ layer 5a, so that the series resistance is reduced.

In this embodiment, the dopant liquid 2 is applied around the main surface of the substrate 1 to form a shallow junction (sheet resistance 50-60 Ω / □) at the center of the substrate 1 and a deep junction around the substrate. The junction (sheet resistance: 20 to 40Ω / □) is formed because the generated current flows from the center to the periphery, so that the series resistance is reduced and the current flows.

To further reduce the series resistance,
Forming a front electrode is an effective means. At this time, it is better to make the electrode denser at a portion with a lower concentration and rougher the electrode at a portion with a higher concentration along the current flow and according to the concentration of the n ⁺ layer.

FIGS. 13 to 16 are plan views showing an example of a method of forming a front electrode. As shown in FIGS. 13 to 16, it is desirable to form a radial electrode 50 extending from the center to the periphery.

FIG. 17 is a plan view showing a state in which the solar cells shown in FIG. 1 are connected in series.

Referring to FIG. 17, in this solar cell, since negative electrodes 10 are formed along three sides on the back surface of substrate 1, serial connection can be easily performed.

[0043]

As described above, according to the present invention,
A solar cell in which a positive electrode and a negative electrode are formed on the same surface can be manufactured by an easy process.

Also, since the series resistance is small, the conversion efficiency can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a solar cell as an example of a photoelectric conversion element according to the present invention.

FIG. 2 is a plan view showing a configuration of a solar cell as an example of a photoelectric conversion element according to the present invention.

FIG. 3 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

FIG. 4 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

FIG. 5 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

FIG. 6 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

FIG. 7 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

FIG. 8 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

9 is a cross-sectional view illustrating an example of a method for manufacturing the solar cell illustrated in FIG.

FIG. 10 is a sectional view showing an example of a method for manufacturing the solar cell shown in FIG.

FIG. 11 is a diagram illustrating an example of a method of applying a dopant liquid to a substrate.

FIG. 12 is a diagram illustrating an example of a method of applying a dopant liquid to a substrate.

FIG. 13 is a plan view illustrating an example of a method for forming a front electrode.

FIG. 14 is a plan view illustrating an example of a method for forming a front electrode.

FIG. 15 is a plan view illustrating an example of a method for forming a front electrode.

FIG. 16 is a plan view illustrating an example of a method for forming a front electrode.

FIG. 17 is a plan view showing a state in which the solar cells shown in FIG. 1 are connected in series.

FIG. 18 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 19 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 20 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 21 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 22 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 23 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 24 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 25 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

FIG. 26 is a cross-sectional view illustrating an example of a conventional method for manufacturing a solar cell.

[Explanation of symbols]

1 substrate, 2 dopant solution, 3 mask material, 4 n ⁺
Layer (deep diffusion), 5an ⁺ layer (shallow diffusion), 5b n ⁺ layer (shallow diffusion), 6 antireflection film 7 of aluminum electrodes, 8 p ⁺ layer, 9a silver paste, 9 back surface silver electrode (positive electrode), 10a silver paste, 10 back silver electrode (negative electrode), 50 front electrode. In each drawing, the same reference numerals or the same or corresponding parts are shown.

Claims (7)

[Claims] 1. A photoelectric conversion element in which a PN junction is formed in a semiconductor substrate and a P-side current collecting electrode and an N-side current collecting electrode are formed on a back surface of the substrate, wherein a peripheral part is located closer to a peripheral part than to a central part of the semiconductor substrate. Having a deep PN junction. 2. A photoelectric conversion element in which a PN junction is formed on a light receiving surface of a semiconductor substrate and a P-side current collecting electrode and an N-side current collecting electrode are formed on a back surface of the substrate, wherein at least two sides of the semiconductor substrate are provided. A photoelectric conversion element, wherein a PN junction is formed at a side surface along the rear surface and a peripheral portion of the rear surface. 3. A PN junction is formed on a light receiving surface of the semiconductor substrate, and the PN junction is formed on a side surface along at least two sides of the semiconductor substrate and on a peripheral portion of a back surface. Item 7. The photoelectric conversion element according to Item 1. 4. The pattern of the current collecting electrode on the light receiving surface radially spreads from a central portion to a peripheral portion of the substrate.
3. The photoelectric conversion element according to item 1. 5. The method for manufacturing a photoelectric conversion element according to claim 1, wherein a diffusion source is dropped at a position shifted outward from a center of the substrate to form a peripheral portion of the substrate. A method of manufacturing a photoelectric conversion element, comprising: applying a diffusion source to the substrate; and forming the PN junction on the substrate by thermal diffusion. 6. The method according to claim 6, wherein the PN junction is formed on the substrate by coating and diffusion, and a diffusion mask is formed on another portion of the rear surface so that the junction is formed along at least two sides of the rear surface. The method for producing a photoelectric conversion element according to claim 5. 7. The method according to claim 5, wherein, when applying the diffusion source to the substrate, the diffusion source is dropped while rotating the substrate.