JP2000150937A - Solar battery cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the output of a solar battery cell by forming a large texture area in such a way that the textures formed in the peripheral section of a texture forming area and the texture formed in the inside area of the peripheral edge section are set at different sizes. SOLUTION: In the texture forming area F of a solar battery cell excluding the outer peripheral section and surface electrode forming spots of the cell, textures 9a-9d having inverted pyramid-like shapes are formed. The sizes of the textures 9b-9d formed in the peripheral section of the area F are made smaller than that of the texture 9a formed in the inside area of the peripheral section. Consequently, the area of the flat section in the area F becomes smaller and the occupying areas of the textures 9a-9d become larger, Therefore, the electric output of the solar battery cell 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 having a non-reflective surface shape (hereinafter referred to as "texture") and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 9 shows an example of a cross section of a conventional solar cell.

[0003] In general, this solar cell 1 _O has an NRS /
BSF (Non-Reflective Surface / Back Surface Fiel
d) Type solar cell, which is a P-type silicon substrate 4
An N ⁺ diffusion layer 3 for efficiently taking in carriers generated by light energy is formed on the light receiving surface side of the substrate 4 by thermally diffusing N-type impurities, and reduces surface reflection. In order to make the texture, an irregular pyramid-shaped texture 8 is applied. An oxide film layer 7 is formed on the N ⁺ diffusion layer 3 in order to reduce the recombination of carriers on the surface, and electricity generated in an opening where the oxide film layer 7 is not formed is efficiently used. A surface electrode 2 for extraction is formed in a comb shape and is directly connected to the N ⁺ diffusion layer 3. Furthermore, an antireflection film 10 for reducing surface reflection of incident light is coated on almost the entire surface of the solar cell 1 _O except for an N-electrode connection portion (not shown).

On the back side of the P-type silicon substrate 4, a carrier is provided.
In order to increase the amount of ⁺Diffusion layer 5 is not P-type
It is formed by thermal diffusion of a pure substance, on which a carrier
Oxide layer 7 to reduce recombination of
Reflected long wavelength light that escaped
The back electrode 6 for extracting electricity covers almost the entire surface
Is formed. And P⁺Diffusion layer 5 and back electrode 6
Is formed through an opening (not shown) formed in the oxide film layer 7.
Connected.

In an NRS / BSF type solar cell 1 _O as shown in FIG. 9, the texture 8 formed on the light receiving surface side serves to multiply reflect incident light to increase the amount of light reaching the inside of the battery. It depends on the size, the formation area ratio, the formation condition, etc., because the generated electric energy changes and greatly affects the output,
How to set the size and shape of the texture 8 is a very important factor.

That is, as shown in FIG. 10, the incident light is multiple-reflected on the light receiving surface by the texture 8, and the surface reflectance is reduced. As a result, the amount of light absorbed by the substrate 4 increases, so that more current can be generated. In particular, in the case of a solar cell for space, it is exposed to radiation (cosmic rays). However, if the substrate 4 has a texture 8, the texture 8 reduces the average thickness of the substrate, and the incident light is reflected on the light receiving surface. Since the light is refracted and enters the substrate in an oblique direction, P formed near the surface of the solar cell
Carriers generated near the N-junction increase, making it less likely to be affected by carrier lifetime due to radiation degradation.

Therefore, forming a larger texture region on the light receiving surface is effective in improving the output of the solar cell 1 _O.

Therefore, in the conventional solar cell 1 _O ,
For example, the configuration is such that the textures 8 are arranged as shown in FIGS. Here, FIG. 11 is a plan view showing the entire solar battery cell, FIG. 12 is a plan view showing an enlarged portion indicated by reference numeral B in FIG. 11, and FIG. 13 is an enlarged view showing a portion indicated by reference numeral D in FIG. It is a top view. In the figure, 1 _O is a solar cell, 2 is a grid electrode, 3 is a bar electrode, and 4 is a connector (pad) electrode for extracting output power.

In the conventional solar cell 1 _O , the surface electrode 2
Are formed in a state where the textures 8 are arranged vertically and horizontally in all the regions except for the formation portions of the textures. It has square inverted pyramid-shaped irregularities, and its size and shape are all the same. The intervals d between the textures 8 are all the same. Furthermore, as shown in the partial enlarged view of FIG. 11, the texture 8 are formed in the solar cell 1 _O of the outer peripheral portion 18.

In order to form a texture 8 having a shape as shown in FIGS.
4 (a) to 4 (g).

First, as shown in FIG. 1A, a silicon substrate 4 is prepared. Next, as shown in FIG. 1B, an oxide film layer 7 is formed on the surface of the silicon substrate 4 by using thermal oxidation or CVD. Subsequently, a resist 15 is applied on the oxide film layer 7 as shown in FIG. Then, as shown in FIG. 4D, a predetermined texture pattern is exposed and developed on the light receiving surface side. Thus, a texture pattern is formed on the oxide film layer 7 by the resist 15. Next, as shown in FIG. 2E, unnecessary portions of the oxide film layer 7 are removed by etching or the like, and thereafter, the resist 15 is removed. Thus, a texture pattern is formed on the silicon substrate 4 by the oxide film layer 7. In this state, as shown in FIG. 1F, etching is performed for a predetermined time with an etching solution such as a high-temperature alkaline solution having a predetermined temperature and concentration. In the case of the silicon substrate 4, there is a difference in the rate of corrosion by a chemical agent for each crystal plane, and a fine inverted pyramid type texture 8 can be formed by anisotropic etching using this.
Finally, as shown in FIG. 2G, the oxide film layer 7 is removed, so that the texture 8 is formed on the light receiving surface side of the silicon substrate 4.
Is completed.

[0012]

However, the conventional solar cell has the following problems.

As described above, in the conventional solar cell, the textures 8 formed at locations other than the cell outer peripheral portion on the silicon substrate 4 have the same size and shape as shown in FIG. In addition, the intervals d between the textures 8 are all the same.

For this reason, the texture forming area on the solar cell 1 _O may be reduced. That is, a texture pattern having the same size cannot be formed in the periphery of the electrode 2 in the texture 8 formation region, and the texture 8 becomes a flat portion. As a result, many area occupied by the flat portion on the light receiving surface of the cell, As a result, the effect of reducing the reflectance becomes smaller leading to reduction in the output of the solar cell 1 _O.

Further, the conventional texture, as shown in the partial enlarged view of FIG. 11, is also formed on the solar cell 1 _O of the outer peripheral portion 18. For this reason, even during the manufacture of the solar cell 1 _O , when the cell is cut out in the dicing process, cracks or, in the worst case, cracks occur from the outer peripheral portion 18 of the cell 1 _O , which makes handling difficult. , Causing a decrease in productivity and contamination of the production line.

The present invention solves the above problems and forms a texture area larger than that of the conventional product,
A first object is to provide a solar cell with improved output, and a second object is to provide a solar cell which has a texture structure and is less likely to crack or crack.

[0017]

In order to solve the above-mentioned problems, the present invention has the following arrangement.

That is, according to the present invention, in a photovoltaic cell in which a texture is formed in a region other than a portion where a surface electrode is formed on a light receiving surface side, the texture is located in a peripheral portion of the texture forming region and inward of the peripheral portion. The size of the solar cell is different from that of the inner part.

In the present invention, the texture means a non-reflective surface shape. This non-reflective surface shape means that the reflectance when the reflectance of the mirror surface is 100% is 0.5 to 1.
In the absence of an anti-reflection coating for light having a wavelength of 0 μm, about 1
The surface shape may be 0% or less, and desirably, the surface substantially absorbs light and does not reflect light. Examples of such a shape include a rectangular opening depressed in an inverted pyramid shape, an opening having a cavity inside, and the like. The solar battery cell of the present invention has a structure in which many minute textures are formed on the light receiving surface.

In the above configuration, the size of the texture formed on the peripheral portion may be set smaller than the size of the texture formed on the inner portion. Further, the interval between the textures formed in the peripheral portion and the interval between the textures formed in the inner portion may be set to different sizes. At this time, the size of the texture formed in the peripheral portion may be different. When the size of the texture formed on the inner portion is set to be smaller than that of the texture formed on the inner portion, it is preferable that the interval between the textures formed on the peripheral portion is set wider than the interval of the texture formed on the inner portion. .

It is desirable that the solar cell has a non-formation area in which the texture is not formed on the outer peripheral portion. When the non-formation area is provided, the width of the non-formation area is 5
It may be 0 μm or more.

The present invention also relates to a solar cell in which a texture is formed in a region other than a portion where a surface electrode is formed on a light receiving surface side, wherein the texture is formed in a peripheral portion of the texture forming region and inward of the peripheral portion. The solar cell is characterized in that the shape is different from the shape of the inner part located at the center.

In the above structure, the texture formed on the inner portion has an inverted pyramid shape having a rectangular bottom, and the texture formed on the peripheral portion has an inverted pyramid having a polygonal bottom having a sharp end. The shape may be a mold. The texture formed on the inner part is V
The texture that is groove-shaped and formed on the peripheral portion may be an inverted pyramid type.

According to another aspect, the present invention is different in a region other than a portion where a surface electrode is formed on a light receiving surface side between a peripheral portion of a texture forming region and an inner portion located inside the peripheral portion. What is claimed is: 1. A method for manufacturing a photovoltaic cell forming a texture having a size, wherein an oxide film on a substrate has a line width of a masking pattern located in a region where a small texture is formed, and a line width of a masking pattern located in a region where a large texture is formed And forming a lattice-like texture on the substrate by forming a masking pattern larger than the line width of the substrate and etching the substrate using the masking pattern as a mask.

The present invention also provides a solar cell in which a texture is formed in a region other than a formation portion of a surface electrode on a light receiving surface side, in which a size of a peripheral portion is smaller than a size of an inner portion located inside the peripheral portion. In a method of manufacturing a cell, an oxide film on a substrate is used to form a masking pattern in which a line width of a masking pattern located in a region where a small texture is formed is larger than a line width of a masking pattern located in a region where a large texture is formed. This is a method for manufacturing a solar cell, comprising forming a lattice-like texture on a substrate by forming the substrate and etching the substrate using the masking pattern as a mask.

[0026]

FIG. 1 is a plan view showing an example of a solar cell according to an embodiment of the present invention, FIG. 2 is an enlarged plan view of a portion indicated by reference numeral A in FIG. 1, and FIG. It is a top view which expands and shows the part shown with the code | symbol C of 2.

In the figure, 1 is a solar cell, 2 is a grid electrode, 3 is a bar electrode, and 4 is a connector (pad) electrode for extracting output power. The bar electrode 3 extends from the connector electrode 4 in the horizontal direction in the figure, and the grid electrode 2 extends from the bar electrode 3 in the vertical direction in the figure.

On the light-receiving surface side of the solar cell 1, a surface electrode composed of the connector electrode 4, the bar electrode 3 and the grid electrode 2 is formed. Have been. The current generated in the texture area is extracted from the connector electrode 4 via the grid electrode 2 and the bar electrode 3.

In this embodiment, the size of the solar cell 1 is about 35 mm in length and about 69 mm in width, and the size of the connector electrode 4 is about 1.5 mm in length and about 3 mm in width. The bar electrode 3 becomes thicker as it approaches the connector electrode 4,
The grid electrode 2 becomes thicker as it approaches the bar electrode 3. The thickness of the leading end of the grid electrode 2 is about 5 μm, and the thickness of the base end (the connecting portion of the bar electrode 3) is about 22 μm. The pitch of the grid electrode 2 is about 0.54 mm.

In this solar cell 1, a non-formation area (flat portion) where a texture is not formed is secured in the outer peripheral portion 18 on the light receiving surface side. As described above, by securing the area where the texture is not formed in the outer peripheral portion 18 of the solar cell 1, although the output is slightly reduced, cracks and cracks may be generated from the portion as compared with the conventional product. Therefore, a device with high productivity and high reliability can be provided. The portion 18 of the non-formation area of this texture
If the width is about 50 μm from the end of the cell, the effect is remarkably exhibited. Further, since the width is narrow, it is possible to prevent a significant decrease in output due to no formation of a texture structure, which is convenient.

The outer peripheral portion 18 of the solar cell 1
As shown in FIG. 3, inverted pyramid-shaped textures 9a to 9d are formed in the texture forming region F excluding the surface electrode forming portions. In the embodiment of FIG. 3, the texture 9a has a side of 18 μm and the texture 9b
Is 15 μm on a side, 5 μm on a side of the texture 9c, and a square inverted pyramid having a side of 3 μm on the texture 9d. The distance d ₁ is 2 μm, and the distance d ₂ is 3 μm. In addition, it is not limited to this size and can be set to any size.

Each of the textures 9a to 9d has a different size from each other, but has a square similar shape.

In particular, in this embodiment, the size of the textures 9b to 9d formed in the peripheral portion of the texture forming region F is smaller than the size of the texture 9a formed in the inner portion.

Thus, FIG. 11, FIG. 12 and FIG.
The area of the flat portion in the texture forming region F is smaller than that of the conventional structure shown in FIG. 1, and the area occupied by the textures 9a to 9d is larger.

Further, in this embodiment, the texture type
Each small-sized tech formed in the peripheral portion in the
Spacing d between Schures 9b-9d_TwoIs formed on its inner part
Distance d between large textures 9a₁than
So that (d₁<D _Two) Is set.

The reason will be described below.

FIGS. 4 and 5 show a case where textures having different sizes (for example, the textures 9a and 9b in FIG. 3) are formed in the etching of the silicon substrate 4 in the step shown in FIG. FIGS. 4A and 4B show cross-sectional views of each process before and after etching. FIG. 4 shows a case where all of the textures 9a and 9b have the same interval d regardless of the size of the textures 9a and 9b. In this case, the intervals d ₁ and d ₂ between the textures are changed accordingly.

As shown in FIG. 4A, in the state where a texture pattern having the same interval d between the textures is formed on the silicon substrate 4 by the oxide film layer 7, etching proceeds to the portion shown by the solid line. Lateral etching begins. Then, the etching is performed until the apex of the pyramid indicated by the broken line can be formed. In this case, the lateral etching of the small-sized texture 9b becomes completely over-etched when the etching of the large-shaped texture 9a is completed. However, the vertices of the small texture 9b are missing. As a result, when the oxide film layer 7 is removed, as shown in FIGS. 7B and 7C, the texture 9b having a small shape has a slightly lower output because a texture structure as designed cannot be formed. In addition, it also causes poor appearance.

On the other hand, as shown in FIG.
The distance d between different textures depending on the oxide film layer 7₁, D_Two
Texture pattern is formed on the silicon substrate 4
When the etching progresses to the part shown by the solid line in the state where
Lateral etching begins. Then, the dashed line
Etching is performed until the top of the lamid can be formed,
In that case, the oxide film layer 7 of the small-sized texture 9b
Spacing d between textures _TwoIs a large texture 9
The distance d between the textures of the oxide film layer 7 of a₁Greater than
(D₁<D_Two) From the large texture 9a
When the ending is finished, the small texture
Since the etching of 9b is also completed at the same time, it is shown in FIG.
Texture 9b is over-etched
It will not be. As a result, when the oxide film layer 7 is removed
Is a small-sized texture as shown in FIG.
9b also can form the texture structure as designed
become.

FIG. 6 shows the difference between the crystal orientations of the substrates.
This figure shows a case where the formation direction of the silicon texture is different, and the basic configuration is the same as the embodiment shown in FIGS. 1, 2 and 3. In the embodiment of FIG.
The texture 9f is 18 μm on a side, the texture 9g is a 15 μm on a side, and the texture 9h is a square inverted pyramid having a size of 13 μm on a side. The interval d ₁ is 2μ
m and the distance d ₂ are 3 μm. In addition, it is not limited to this size and can be set to an arbitrary size.
In this manner, in the case of FIG. 6 as well, the inverted pyramid-shaped textures 9f to 9h are formed in the texture forming region F excluding the outer peripheral portion 18 of the solar cell 1 and the surface electrode forming portion. The size of the textures 9g to 9h formed on the portion is smaller than the size of the texture 9f formed on the inner portion.

FIG. 7 shows another modified example. In a texture forming area F, textures 9j and 9f are formed on the periphery and inside thereof, and the inside texture 9f is a square of an inverted pyramid. However, the texture 9j in the peripheral portion is not square but pointed. Thereby, the textures 9j and 9f are different from those of the related art shown in FIGS. 11, 12 and 13.
Occupied area can be secured larger.

FIG. 8 shows still another modified example. In a texture forming area F, textures 9k and 9m are formed on the periphery and inside thereof, respectively.
The inner texture 9k has a V-groove shape, and the peripheral texture 9m has an inverted pyramid shape. Also in this case, by forming the texture 9m in the peripheral portion, it is possible to secure a larger area occupied by the textures 9k and 9m than in the related art.

In the above embodiment, the textures 9a, 9f, and 9k of the inverted pyramid type and the V-groove are described, and the combination of textures of other shapes is not particularly described. Of course, the present invention can also be applied.

Further, in this embodiment, NRS / BS
The FRS type solar cell has been described as an example.
LBSF (Non-Reflective Surface / Locally diffused
It is needless to say that the present invention can be similarly applied to a back surface field type solar cell or a solar cell using a crystal other than silicon, since only the structure and the crystal are different.

[0045]

According to the present invention, the following effects can be obtained.

(1) Since the occupation area of the texture can be made larger than that of the related art, the electric output can be improved.

In particular, in the case of a solar cell for space, it is effective to improve the output of the solar cell by forming a larger texture area in order to reduce the influence of the carrier lifetime due to radiation deterioration.

(2) In the outer peripheral portion of the solar cell, a flat non-texture forming area is secured so that the output does not decrease so much that cracks and cracks can be prevented, and productivity and reliability are improved. Device with high reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a solar cell according to an embodiment of the present invention.

FIG. 2 is an enlarged plan view showing a portion indicated by reference numeral A in FIG. 1;

FIG. 3 is an enlarged plan view showing a portion indicated by reference numeral C in FIG. 2;

FIG. 4 is a cross-sectional view of each process before and after etching in the case of forming textures having different sizes, in which all intervals between textures are formed at the same interval regardless of the size of the texture.

FIG. 5 is a cross-sectional view of each process before and after etching in the case of forming textures having different sizes, in which the interval between the textures is changed according to the size of the texture.

FIG. 6 is a plan view showing an example of a solar cell according to another embodiment of the present invention.

FIG. 7 is a plan view showing an example of a solar cell according to another embodiment of the present invention.

FIG. 8 is a plan view showing an example of a solar cell according to another embodiment of the present invention.

FIG. 9 is a cross-sectional view of an NRS / BSF type solar cell.

FIG. 10 is an explanatory diagram of light reflection and refraction on a texture surface.

FIG. 11 is a plan view showing an example of a conventional solar cell.

FIG. 12 is an enlarged plan view showing a portion indicated by reference numeral B in FIG. 11;

13 is an enlarged plan view showing a portion indicated by reference numeral D in FIG.

FIG. 14 is a cross-sectional view of each process when a texture structure is formed.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 solar cell 2 front electrode 3 N ⁺ diffusion layer 4 silicon substrate 5 P ⁺ diffusion layer 6 back electrode 7 oxide film layer 8 texture 9 a to 9 k texture 10 antireflection film 15 photoresist 18 outer peripheral portion d, d ₁ , d ₂ Interval F Texture formation area

Claims (12)

[Claims] 1. A photovoltaic cell in which a texture is formed in a region other than a portion where a surface electrode is formed on a light receiving surface side, wherein the texture includes a peripheral portion of the texture forming region and an inner portion located inside the peripheral portion. Wherein the solar cells are set to different sizes. 2. The solar cell according to claim 1, wherein the size of the texture formed on the peripheral portion is smaller than the size of the texture formed on the inner portion. 3. The solar cell according to claim 1, wherein the interval between the textures formed on the peripheral portion and the interval between the textures formed on the inner portion are set to different sizes. 4. The solar cell according to claim 3, wherein the interval between the textures formed on the peripheral portion is wider than the interval between the textures formed on the inner portion. 5. The photovoltaic cell according to claim 1, wherein the photovoltaic cell has a non-formation area where no texture is formed on an outer peripheral portion thereof. 6. The solar cell according to claim 5, wherein the width of the non-formation region is 50 μm or more. 7. The solar cell according to claim 1, wherein the solar cell is an NRS / BSF type solar cell. 8. A photovoltaic cell in which a texture is formed in a region other than a portion where a surface electrode is formed on a light receiving surface side, wherein the texture is a peripheral portion of the texture forming region and an inner side located inside the peripheral portion. A photovoltaic cell, wherein the shape of the photovoltaic cell is different for each part. 9. The texture formed on the inner portion is an inverted pyramid shape having a rectangular bottom, and the texture formed on the peripheral portion is formed in an inverted pyramid shape having a polygonal bottom having a sharp end. The solar cell according to claim 8, which is in a shape. 10. The texture formed on the inner part is V
9. The solar cell according to claim 8, wherein the solar cell has a groove shape and the texture formed in a peripheral portion is an inverted pyramid type. 11. A solar cell in which a texture of a different size is formed in a region other than a formation portion of a surface electrode on a light receiving surface side in a peripheral portion of a texture forming region and an inner portion located inside the peripheral portion. A method of manufacturing a cell, comprising: forming an oxide film on a substrate so that a masking pattern located in a region where a small texture is formed has a larger line width than a line width of a masking pattern located in a region where a large texture is formed. A method for manufacturing a solar cell, comprising forming a lattice-like texture on a substrate by forming the substrate and etching the substrate using the masking pattern as a mask. 12. A method of manufacturing a solar cell in which a texture whose peripheral portion is smaller than a size of an inner portion located inside the peripheral portion is formed in a region other than a portion where the surface electrode is formed on the light receiving surface side. An oxide film on the substrate forms a masking pattern in which the line width of the masking pattern located in the formation region of the small texture is larger than the line width of the masking pattern located in the formation region of the large texture. A method for manufacturing a solar cell, comprising forming a lattice-like texture on a substrate by etching the substrate using the masking pattern as a mask.