JP2003124483A - Photovoltaic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear surface electrode type photovoltaic element in which a performance is improved by preventing a leakage current from passing through between a p<+> -type layer and an n<+> -type layer provided as diffused layers on a rear surface by a tunnel effect by electrically separating the p<+> -type layer and the n<+> -type layer. SOLUTION: The rear surface electrode type photovoltaic element comprises a semiconductor substrate 10, a p<+> -type semiconductor layer 22 and an n<+> -type semiconductor layer 20 formed on the rear surface of the substrate 120 by diffusion and having higher carrier concentrations than the carrier concentration of the substrate 10, and a positive electrode 32 and a negative electrode 30 respectively connected to the layer 22 and the layer 20. In this photovoltaic element, a groove is formed between the layer 22 and the layer 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device for converting light energy into electric power, such as a solar cell.

[0002]

2. Description of the Related Art In a photovoltaic element, when an electrode is provided on the front surface side, the amount of incident light is reduced, and thus there is a back surface electrode type photovoltaic element having an electrode only on the back surface side. . As such a back electrode type photovoltaic element, one having a structure in which a diffusion layer is provided on the entire back surface in order to prevent surface recombination on the back surface and to improve performance is known (for example, Japanese Patent Laid-Open No. 8-213646). (See the official gazette).

[0003]

FIG. 1 is a sectional view showing the structure of a conventional back electrode type photovoltaic element in which a diffusion layer composed of ap ⁺ type layer and an n ⁺ type layer is formed on the entire back surface. . In this structure, the p ⁺ -type layer and the n ⁺ -type layer are in contact with each other, and the energy band structure when the p ⁺ -type layer and the n ⁺ -type layer are adjacent to each other as shown in FIG.

Due to the wave nature of the electrons, a tunnel phenomenon that penetrates the potential barrier as shown by the arrow in the figure occurs. This is part of the collected electrons to the n ⁺ -type layer is the p ⁺ -type layer (or, a portion of holes collected to the p ⁺ -type layer is the n ⁺ -type layer) means to flow. As a result, the amount of current generated by the photovoltaic device is reduced,
It will be a loss.

The present invention has been made in view of the above-described problems, and an object thereof is to electrically separate a p ⁺ type layer and an n ⁺ type layer provided as a diffusion layer on the back surface into a tunnel effect. Therefore, it is an object of the present invention to provide a back electrode type photovoltaic element having improved performance by preventing leakage current from passing through them.

[0006]

In order to achieve the above object, according to a first aspect of the present invention, a semiconductor substrate and a back surface of the semiconductor substrate are formed by diffusion, and the carrier concentration of the semiconductor substrate is higher than that of the semiconductor substrate. A back electrode type having a p ⁺ type semiconductor layer and an n ⁺ type semiconductor layer having a high carrier concentration, and a positive electrode and a negative electrode connected to the p ⁺ type semiconductor layer and the n ⁺ type semiconductor layer, respectively. In the photovoltaic element, there is provided a photovoltaic element, wherein a groove is formed between the p ⁺ type semiconductor layer and the n ⁺ type semiconductor layer.

The first aspect of the present invention configured as described above
In the photovoltaic element according to ⁺Type semiconductor layer and n⁺Type
A tunnel separates the semiconductor layer from the trench.
The phenomenon does not occur. Therefore, the collected electrons and positive
The holes can be efficiently taken out from the electrode,
The child's performance is improved.

Further, according to the second aspect of the present invention, in the photovoltaic element according to the first aspect of the present invention, the groove is filled with an insulating material.

In the photovoltaic element according to the second aspect of the present invention, the groove is filled with the insulating material,
The strength of the element is increased and contamination of the groove portion is prevented.

According to a third aspect of the present invention, in the photovoltaic element according to the second aspect of the present invention, the p ⁺
The area of the part where the p ⁺ type semiconductor layer or the n ⁺ type semiconductor layer is in contact with the positive electrode or the negative electrode is smaller than the area of the part where the type semiconductor layer or the n ⁺ type semiconductor layer is in contact with the semiconductor substrate. Thus, the groove is formed.

If the contact area between the semiconductor layer and the electrode is too large, the recombination of carriers is promoted, so that it is preferable that the contact resistance is small enough not to cause a problem. In the photovoltaic device according to the third aspect of the present invention, since the electrode can be formed on the insulating material, it is possible to increase the area of the electrode without increasing the contact area between the semiconductor layer and the electrode. You can As a result, the loss due to the resistance of the electrodes can be reduced.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 is a sectional view of the photovoltaic element according to the first embodiment of the present invention. p-type or n-type semiconductor substrate 1
On the back surface of 0, n ⁺ type semiconductor layers 20 and p ⁺ type semiconductor layers 22 are alternately formed by a diffusion method. In order to collect carriers, the carrier concentration of these n ⁺ type semiconductor layer 20 and p ⁺ type semiconductor layer 22 is higher than that of the p or n type semiconductor substrate 10.

On the back side of the semiconductor substrate 10, n ⁺
The negative (−) electrode 30 connected to the positive type semiconductor layer 20 and the positive (+) electrode 32 connected to the p ⁺ type semiconductor layer 22 are provided to realize a back electrode type structure.

In the photovoltaic element of FIG. 3, light incident from the front side is absorbed by the semiconductor substrate 10 and electrons and holes are generated. The generated electrons are the n ⁺ type semiconductor layer 2
The holes are diffused to the region of 0 and collected in the negative (−) electrode 30, while the generated holes are diffused to the p ⁺ type semiconductor layer 22 and collected in the positive (+) electrode 32. Thus,
Electrons and holes generated by absorption of light are separated,
Photovoltaic will be generated.

In the photovoltaic element shown in FIG. 3, the n ⁺ type semiconductor layer 20 and the p ⁺ type semiconductor layer 22 are separated from each other by forming a groove at the boundary between them by etching, machining or the like. Has been done. Therefore, the tunnel phenomenon described above with reference to FIGS. 1 and 2 does not occur, and the collected electrons and holes are efficiently taken out from the negative (−) electrode 30 and the positive (+) electrode 32. The performance of the power device is improved.

The characteristics of the photovoltaic element can be effectively improved by terminating (passivating) the surface exposed by the formation of the groove with hydrogen, a halogen element or the like.

The specific structure of the photovoltaic element shown in FIG. 3 will now be described. For example, the semiconductor substrate 10
Is a p-type Ge substrate having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ and a thickness of 100 μm.

Further, the n ⁺ type semiconductor layer 20 is an n ⁺ type G having a carrier concentration of 1 × 10 ¹⁹ cm ^-3 and a diffusion depth of 1 μm.
It is the e layer. Similarly, the p ⁺ type semiconductor layer 22 is a p ⁺ type Ge layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ and a diffusion depth of 1 μm.

The negative (-) electrode 30 is an Al electrode having a film thickness of 2 μm. Similarly, the positive (+) electrode 32 is
It is an Al electrode having a film thickness of 2 μm.

As the semiconductor substrate 10, a substrate of Si, SiGe, SiC, CSiGe or the like can be used instead of the Ge substrate.

Further, in FIG. 3, the p ⁺ type semiconductor layer 22 is shown to be larger than the n ⁺ type semiconductor layer 20, but it may have the opposite size or the same size.

FIG. 4 is a sectional view of a photovoltaic element according to the second embodiment of the present invention. 4, the same elements as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

The structure of FIG. 4 is different from the structure of FIG. 3 in that the groove formed between the n ⁺ type semiconductor layer 20 and the p ⁺ type semiconductor layer 22 is filled with the insulating material 40. In point.

Therefore, in the structure of FIG. 4, in addition to the function and effect of the structure of FIG. 3, since the groove is filled with the insulating material, the strength of the element is increased and contamination of the groove portion is prevented. There is a function and effect.

The specific structure of the photovoltaic element shown in FIG. 4 will now be described. For example, the semiconductor substrate 10
Is a p-type Ge substrate having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ and a thickness of 100 μm.

The n ⁺ type semiconductor layer 20 has an n ⁺ type G having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ and a diffusion depth of 1 μm.
It is the e layer. Similarly, the p ⁺ type semiconductor layer 22 is a p ⁺ type Ge layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ and a diffusion depth of 1 μm.

The negative (-) electrode 30 is an Al electrode having a film thickness of 2 μm. Similarly, the positive (+) electrode 32 is
It is an Al electrode having a film thickness of 2 μm. The insulating material 40 is SiNx.

As the semiconductor substrate 10, a substrate of Si, SiGe, SiC, CSiGe or the like can be used instead of the Ge substrate.

Although the p ⁺ type semiconductor layer 22 is shown to be larger than the n ⁺ type semiconductor layer 20 in FIG. 4, the size may be reversed or the same.

FIG. 5 is a sectional view of a photovoltaic element according to the third embodiment of the present invention. In FIG. 5, the same elements as those in FIGS. 3 and 4 are designated by the same reference numerals, and the description thereof will be omitted. The structure of FIG. 5 corresponds to that of FIG.
Alternatively, the following operational effects are obtained in addition to the operational effects provided by the structure shown in FIG.

The structure of FIG. 5 is different from the structure of FIG. 4 in the shape of the groove formed between the n ⁺ type semiconductor layer 20 and the p ⁺ type semiconductor layer 22. That is, the shape of the groove is V-shaped, and the p ⁺ type semiconductor layer 22 or the n ⁺ type semiconductor layer 2 is formed.
0 is smaller than the area where the semiconductor substrate 10 is in contact with p ⁺
The area of the portion where the type semiconductor layer 22 or the n ⁺ type semiconductor layer 20 is in contact with the positive electrode 32 or the negative electrode 30 is small.

If the contact area between the semiconductor layers 20 and 22 and the electrodes 30 and 32 is too large, the recombination of carriers is promoted. Therefore, it is preferable that the contact resistance is small enough not to cause a problem.

In the photovoltaic device having the structure shown in FIG. 5, since the electrodes 30 and 32 can be formed on the insulating material 40, the contact area between the semiconductor layers 20 and 22 and the electrodes 30 and 32 is increased. The area of the electrodes 30 and 32 can be increased without the need. As a result, the loss due to the resistance of the electrodes can be reduced.

Further, in the photovoltaic device having the structure shown in FIG. 5, since the groove has a surface that is not perpendicular to the incident light that is perpendicular to the front surface, the light that reaches the back surface side is reflected obliquely. As a result, there is a light confinement effect.

The specific structure of the photovoltaic element shown in FIG. 5 will now be described. For example, the semiconductor substrate 10
Is a p-type Si substrate having a carrier concentration of 1 × 10 ¹⁵ cm ⁻³ and a thickness of 150 μm.

The n ⁺ type semiconductor layer 20 is an n ⁺ type S having a carrier concentration of 1 × 10 ¹⁹ cm ^-3 and a diffusion depth of 2 μm.
It is the i layer. Similarly, the p ⁺ type semiconductor layer 22 is a p ⁺ type Si layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ and a diffusion depth of 2 μm.

The negative (-) electrode 30 is an Al electrode having a film thickness of 2 μm. Similarly, the positive (+) electrode 32 is
It is an Al electrode having a film thickness of 2 μm. The insulating material 40 is SiO ₂ .

As the semiconductor substrate 10, a substrate of Ge, SiGe, SiC, CSiGe or the like can be used instead of the Si substrate.

Although the V-shaped groove is formed in the structure shown in FIG. 5, an arc-shaped groove may be formed as shown in FIG. As shown, a stepped groove may be formed. However, in the case of forming a stepped groove as shown in FIG. 7, there is no light confinement effect.

[0041]

As described above, according to the present invention,
In the back electrode type photovoltaic element, the p ⁺ type layer and the n ⁺ type layer provided as a diffusion layer on the back surface are electrically separated from each other, so that the leakage current is prevented from passing through them due to the tunnel effect. The performance is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a conventional back electrode type photovoltaic element in which a diffusion layer including ap ⁺ type layer and an n ⁺ type layer is formed on the entire back surface.

FIG. 2 is a diagram showing an energy band structure when ap ⁺ type layer and an n ⁺ type layer are adjacent to each other.

FIG. 3 is a cross-sectional view of the photovoltaic element according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a photovoltaic element according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a photovoltaic element according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a modified example of the third embodiment.

FIG. 7 is a sectional view showing another modification of the third embodiment.

[Explanation of symbols]

10 ... P-type or n-type semiconductor substrate 20 ... N ⁺ type semiconductor layer 22 ... P ⁺ type semiconductor layer 30 ... Negative (-) electrode 32 ... Positive (+) electrode 40 ... Insulating material

Claims (3)

[Claims] 1. A semiconductor substrate, is formed by diffusion on the rear surface of the semiconductor substrate, a p ⁺ -type semiconductor layer and the n ⁺ -type semiconductor layer having a higher carrier concentration than the carrier concentration of the semiconductor substrate, the p ⁺ -type A back electrode type photovoltaic device comprising a positive electrode and a negative electrode connected to a semiconductor layer and an n ⁺ -type semiconductor layer, respectively, wherein the p ⁺ -type semiconductor layer and the n ⁺ -type semiconductor layer are between A photovoltaic device having a groove formed therein. 2. The photovoltaic device according to claim 1, wherein the groove is filled with an insulating material. 3. The area of the p ⁺ -type semiconductor layer or the n ⁺ -type semiconductor layer and the p ⁺
The photovoltaic device according to claim 2, wherein the groove is formed so that an area of a portion where the positive type semiconductor layer or the n ⁺ type semiconductor layer is in contact with the positive electrode or the negative electrode is small. element.