JPH11312814A - Solar cell element - Google Patents

Abstract

(57) [Problem] To provide a solar cell element capable of preventing carriers generated in a substrate from moving to an incident surface side, reducing recombination loss of carriers, and improving photoelectric conversion efficiency. An insulating film is formed on a light incident surface side of a substrate, and ap ⁺ layer and an n ⁺ layer having a higher impurity concentration than the substrate are formed independently on a back surface side.
The positive electrode 18 and the negative electrode 20 are connected via the insulating film 12, respectively. A diffusion layer 22 having a higher impurity concentration than the substrate 10 is provided between the substrate 10 and the insulating film 12 on the front side. As a result, a potential difference occurs between the substrate 10 and the diffusion layer 22, and minority carriers generated on the substrate 10 do not move toward the interface between the substrate 10 and the insulating film 12.
Recombination loss can be suppressed. Thereby, photoelectric conversion efficiency can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell device, and more particularly to an improvement in a solar cell device having an electrode provided on the back surface of a substrate.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a solar cell element in which both positive and negative electrodes are provided on the back surface of a substrate (the surface opposite to the light receiving surface). For example, JP-A-5-75149 also discloses
A solar cell element in which an electrode is provided on the back surface of a substrate is disclosed.

FIG. 6 is a cross-sectional view of a conventional solar cell element having electrodes formed on the back surface of a substrate. In FIG. 6, an insulating film 12 is formed on the front side of the substrate 10,
Light enters the substrate 10 via the insulating film 12. In addition, ap ⁺ layer 14 and an n ⁺ layer 16 having a higher impurity concentration than the substrate 10 are formed on the back surface side of the substrate 10, that is, on the surface opposite to the light receiving surface. The p ⁺ layer 14 and the n ⁺ layer 16 include
The positive electrode 18 and the negative electrode 20 are connected via the insulating film 12, respectively. When light enters the substrate 10, positive and negative carriers generated in the substrate 10 are converted into p ⁺ layer 14 and n ⁺ layer 16.
Through the positive electrode 18 and the negative electrode 20, respectively.

[0004]

However, in the above conventional example, a part of the carriers generated near the front surface of the substrate 10 due to the incident light does not move to the back surface where the positive electrode 18 and the negative electrode 20 are located. It moves to a certain surface side of the insulating film 12. As a result, the generated carriers disappear at the interface between the substrate 10 and the insulating film 12 by recombination, and there is a problem that the photoelectric conversion efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to prevent carriers generated in a substrate from moving to the incident surface side and to reduce the recombination loss of carriers. An object of the present invention is to provide a solar cell element capable of improving photoelectric conversion efficiency.

[0006]

In order to achieve the above object, the present invention relates to a solar cell element having a positive electrode and a negative electrode provided on the back surface of a substrate. Is characterized by having a high diffusion layer.

[0007]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a sectional view of one embodiment of a solar cell element according to the present invention. In FIG. 1 as well, a p ⁺ layer 14 and an n ⁺ layer 16 are formed on the back surface of the substrate 10 as in FIG. 6, and the positive electrode 18 and the negative electrode 20 are connected via the insulating film 12 respectively. As the substrate 10, a p-type or n-type semiconductor can be used, and its impurity concentration is preferably set to 1.0 × 10 ¹⁷ cm ⁻³ or less. If the impurity concentration is further increased, the substrate 10
This is not preferable because the recombination loss of carriers increases inside.

The feature of this embodiment is that the substrate 1
The point is that a diffusion layer 22 having an impurity concentration higher than that of the substrate 10 is formed between the substrate 10 and the insulating film 12 on the light incident surface side. By forming such a diffusion layer 22, a barrier is generated between the substrate 10 and the diffusion layer 22 due to a potential difference based on a difference in the impurity concentration. This is shown in FIG. FIG. 2 shows a case where a p-type semiconductor is used for the substrate 10. In this case, the diffusion layer 2
2 is also a p-type and has a high impurity concentration, and is described as ap ⁺ layer. As shown in FIG. 2, a substrate 10 which is a p-layer
As described above, a potential difference is caused between the diffusion layer 22 and the p ⁺ layer due to the difference in impurity concentration. For this reason, electrons, which are minority carriers generated in the substrate 10, are prevented from moving to the surface side by the barrier. Therefore, the substrate 10 which is likely to cause carrier recombination
Electrons, which are minority carriers, do not move to the interface between the substrate and the insulating film 12, and recombination loss there can be reduced.

[0010] As the impurity concentration of the diffusion layer 22, it is preferable that a 10 to 10 ⁶ times the concentration to the impurity concentration of the substrate 10. If the impurity concentration of the diffusion layer 22 is 10 ⁶ times or more that of the substrate 10, recombination loss of carriers in the diffusion layer 22 increases, which is not preferable. Also,
When the impurity concentration of the diffusion layer 22 becomes 10 times or less, the potential difference shown in FIG. 2 becomes insufficient, and it becomes impossible to suppress the minority carriers that cross the barrier. Therefore, it is preferable that the impurity concentration of the diffusion layer 22 be 10 times or more the impurity concentration of the substrate 10.

Since the impurity concentration of the diffusion layer 22 is higher than that of the substrate 10 as described above, the probability that carriers disappear by recombination also increases. Therefore, it is preferable that the thickness of the diffusion layer 22 be 5.0 μm or less.

With the above-described configuration, the number of minority carriers that decrease due to recombination at the interface between the substrate 10 and the insulating film 12 can be suppressed, and the photoelectric conversion efficiency can be improved.
Further, a voltage that can be taken out from the solar cell element can be increased by a potential difference between the substrate 10 and the diffusion layer 22.

Hereinafter, a specific example of the solar cell element according to the present invention will be described as an example.

Embodiment 1 FIG. 3 shows an embodiment of the solar cell element according to the present invention. In FIG. 3, a single crystal p-type silicon containing boron (B) at a concentration of about 1.0 × 10 ¹⁴ cm ⁻³ is used as the substrate 10. This substrate 1
0, an oxide film pattern is formed on the back surface, and 1.0 × 10
P ⁺ layer 14 which is a high concentration boron diffusion layer of about ¹⁹ cm ^-3
Is partially formed. Similarly, 1.0 × 10 ¹⁹
An n ⁺ layer 16 which is a phosphoric acid diffusion layer having a high concentration of about cm ⁻³ is also partially formed. Further, an oxide film is formed as the insulating film 12 by thermal oxidation.

After the light receiving surface side of the substrate 10 is thinned to about 100 μm by etching or polishing,
A texture 24 having an uneven structure is formed on the light receiving surface. Boron is diffused in the portion where the texture 24 is formed, and a p ⁺ layer is formed as the diffusion layer 22. This diffusion layer 2
2 has a surface concentration of about 1.0 × 10 ¹⁸ cm ⁻³ and a thickness of about 0.5 μm. After that, a high-quality thermal oxide film is formed on the diffusion layer 22 as the insulating film 12.
A positive electrode 18 and a negative electrode 20 are formed on the back surface of the substrate 10 by vapor deposition so as to be connected to the p ⁺ layer 14 and the n ⁺ layer 16.

Thus, the solar cell device according to the present embodiment is completed. FIG. 4 shows the relationship between the photoelectric conversion efficiency of this solar cell element and the surface recombination speed. As a comparative example, p as a diffusion layer 22 was formed on the light receiving surface side of the solar cell element.
The relationship between the photoelectric conversion efficiency and the surface recombination speed when there is no ⁺ layer is also shown. Here, the surface recombination speed is a factor indicating the ease of carrier recombination on the light receiving surface. In FIG. 4, the solid line indicates the case where the diffusion layer 22 is provided, and the broken line indicates the case where the diffusion layer 22 is not provided. FIG.
As can be seen, even if the surface recombination rate is the same,
When the diffusion layer 22 is provided, the photoelectric conversion efficiency is higher. This is because, as described above, the diffusion layer 22
This is because the minority carriers generated in the substrate 10 do not move to the light receiving surface side, so that the disappearance of minority carriers due to recombination at the interface between the substrate 10 and the insulating film 12 is suppressed.

FIG. 5 shows the relationship between the impurity concentration of the diffusion layer 22 and the photoelectric conversion efficiency. As can be seen from FIG. 5, the impurity concentration of the diffusion layer 22 is 1.0 × 10
^{17 ~10 18} cm ^-3 (10 ³ of the impurity concentration of the substrate 10-1
0 ^4x) around it it can be seen that the photoelectric conversion efficiency is high in. Therefore, as the impurity concentration in the diffusion layer 22, 10 to 10 ⁶ times the impurity concentration of the substrate 10, preferably is considered better to the 10 ² to 10 ⁴ times.

Although a p-type substrate is used in the present embodiment, the present invention can also be realized when an n-type substrate is used. In this case, the minority carrier changes from an electron to a hole, and the potential has the opposite behavior.

[0019]

As described above, according to the present invention,
Minority carriers generated in the substrate are suppressed from moving to the light incident side due to the energy barrier based on the presence of the diffusion layer, and as a result, recombination loss at the interface between the insulating film on the surface side and the substrate is reduced. Can be done. Thereby, the photoelectric conversion efficiency of the solar cell element can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of a solar cell element according to the present invention.

FIG. 2 is a diagram showing a band structure of the solar cell element shown in FIG.

FIG. 3 is a view showing an embodiment of a solar cell element according to the present invention.

FIG. 4 is a diagram showing the relationship between the photoelectric conversion efficiency and the surface recombination speed with and without a diffusion layer.

FIG. 5 is a diagram showing a relationship between photoelectric conversion efficiency and impurity concentration of a diffusion layer.

FIG. 6 is a cross-sectional view of a conventional solar cell element having an electrode on the back surface of a substrate.

[Explanation of symbols]

10 substrate, 12 insulating film, 14 p ⁺ layer, 16 n
⁺ Layer, 18 positive electrode, 20 negative electrode, 22 diffusion layer, 24 texture.

Claims (1)

[Claims] 1. A solar cell element having positive and negative electrodes provided on a back surface of a substrate, wherein the solar cell element has a diffusion layer having a higher impurity concentration than the substrate on a light incident surface side of the substrate. .