JPH10163513A - Solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make light once made incident to a solar battery difficult to come out of the battery by constituting the texture structure of the battery so that its main surface can be formed of a specific orientation plane and at least part of the main surface can be formed of another specific orientation plane. SOLUTION: This so-called texture structure composed of (100)-plane is formed by using (111)-plane as a main surface. Therefore, the textural structure is formed in a three-fold rotational symmetry. Since the textural structure is constituted in three-fold rotation symmetry, no plane corresponding to the incidence (100)-plane exists or, even if it exists, the plane only has a very small area. Namely, etching is performed from the position '9' by using a (111)-Si substrate. An etchant containing, for example, 63.3wt.% H2 O, 23.4wt.% KOH, and 13.3wt.% isopropanol is used as the etchant for the etching. Therefore, no surface which faced the incident surface of incident light 4 does not exist, and the light which is once made incident to a solar battery does not emerge from the battery. According to this etchant, the (100)-plane can be selectively exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell made of silicon.

[0002]

2. Description of the Related Art With the recent increase in energy demand and the decrease in reserves of fossil energy such as oil and coal, the importance of solar cells that effectively utilize solar energy, which has not been fully utilized in the past, has been increasing. . Among them, solar cells using silicon, which is rich in raw materials and does not contain toxic substances, are important. In a solar cell using silicon as a raw material, there is a method of texturing a substrate surface as one of means for increasing the efficiency. For example, the 13th European Photovoltaic Solar Energy Conference (13th
Europian Photovoltaic Solar Energy Conference: 199
(5 years) As shown on page 13, the (100) plane is the main surface, a concave part of an inverted pyramid structure composed of the (111) plane, a so-called texture structure is formed, and light incident from the (111) plane is generated in the solar cell. It was designed to extend the passing distance. This will be described with reference to FIG. 1 is a silicon solar cell, 2 is a (111) surface forming an inverted pyramid, 3 is a back surface of the substrate which is a substantially (100) surface, 4 is incident light, and 5 is outgoing light. The incident light 4 is refracted when entering from the (111) plane, and the distance passing through the solar cell is extended. In addition, although a part of the incident light is reflected by the (111) plane, there is a portion where the reflected light is incident again on the opposing (111) plane, and the amount of light reflected in the incident direction decreases, that is, the solar cell 1 The part which is incident on the surface increases.

[0003]

However, in the structure shown in FIG. 5, the light is not sufficiently confined in the solar cell. This will be described with reference to FIG. 6a and 6b are reflected light from the substrate, 7 is a valley of the inverted pyramid structure, and 8 is a peak of the inverted pyramid structure. For example, the incident light 4 is reflected from the back surface to the inverted pyramid portion in the solar cell as shown in FIG. FIG.
In this case, if the luminous flux is 6a, the light is reflected again by the pyramid portion and can remain in the solar cell 1. However, if it is 6b, the arrangement is equivalent to the outgoing light 5 in FIG. In order to make the reflected light 6a, it is necessary to calculate the pitch of the inverted pyramid based on the thickness and the refractive index of the substrate and to arrange the inverted pyramid in a predetermined arrangement, it is necessary to precisely control the thickness, and to maintain reproducibility It was difficult.

[0004]

To achieve the above object, the present invention relates to a solar cell containing silicon as a main component.
A feature of the present invention is a solar cell characterized in that a substantially (111) plane is a main surface and at least a part of the main surface is formed by a (100) plane. In other words, in the present invention, the following method is employed in order to prevent light incident on the silicon solar cell from exiting the solar cell. That is, the solar cell mainly composed of silicon has a texture structure in which a substantially (111) plane is a main surface and at least a part of the main surface is formed by a (100) plane. Further, the recess formed by the (100) plane is arranged so as to form a triangle. Alternatively, the recess formed by the (100) plane is arranged so as to form a square. Alternatively, the recess formed by the (100) plane is arranged so as to form a hexagon.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a so-called texture structure is formed by a (100) plane with a substantially (111) plane as a main plane. Therefore, the texture structure is three-fold rotationally symmetric. As in the conventional example, approximately (100)
In the case where the texture structure composed of the (111) plane is formed on the plane, the plane is rotationally symmetric four times, and the light always enters (11).
1) There is an optically equivalent surface corresponding to the surface, from which light can be emitted out of the solar cell. However, in the structure of the present invention, the incident light (10
0) There is no surface corresponding to the surface, or even if there is, there is only a fraction of the area of the conventional example. Therefore, the light once entering the solar cell does not go out of the solar cell, and the efficiency of the solar cell can be increased.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure shown in FIGS. 1 to 4 described below is manufactured by the following procedure. SiO ₂ is deposited on a silicon substrate. Here, it was deposited by sputtering with a thickness of about 200 nm. Next, a mask in which patterns having a diameter of 3 μm were arranged at intervals of 10 μm was prepared, and a hole of 3 μm was formed in the resist by ordinary photolithography. Using this as a mask, holes were made in SiO ₂ using buffered hydrofluoric acid. Etching is started from this hole and will be referred to as an etching start point below. The diameter of the holes and the interval between the holes are examples, and are not limited thereto. Similar results have been obtained with a hole spacing of 20 microns.

FIG. 7 is a photograph of an embodiment of a solar cell manufactured according to the present invention as viewed from the light incident surface. This is obtained by etching a silicon (111) plane substrate having a rough surface. A three-fold rotationally symmetric triangular projection formed by the (100) plane was obtained. On the other hand, smooth (111)
The back side of the surface remained smooth.

FIG. 1 is a view of one embodiment of a solar cell manufactured according to the present invention as viewed from a light incident surface. No. 9 was etched when producing this example. It is the starting point of the etching and is arranged in a triangle. FIG. 1 also shows the positional relationship between the crystal orientation and the starting point of the etching. Si
Using a (111) substrate, etching was performed from the position 9 in FIG. 63.3% by weight of H ₂ O as an etching solution;
Using 23.4 wt% KOH and 13.3 wt% isopropanol, the structure shown in the figure was obtained. There is no surface facing the incident surface of the incident light 4, and light once entering the solar cell does not go out of the solar cell. According to the above-mentioned etching solution, it is possible to make the (100) plane appear selectively. This is VLSI Process Data Handbook 4
Page 51: Science Forum (Issue 57)
This is a well-known matter.

FIG. 2 is a diagram showing one embodiment of a solar cell manufactured according to the present invention as viewed from a light incident surface. Reference numeral 9 denotes a starting point of the etching, which is performed in producing the present embodiment, and is arranged in a triangle. FIG. 2 also shows the positional relationship between the crystal orientation and the etching start point. Si
Using the (111) substrate, etching was performed from the position 9 in FIG. 63.3% by weight H as an etchant
_{Using 2} O, 23.4% by weight KOH and 13.3% by weight isopropanol, the structure shown in the figure was obtained. Incident light 4
There is a surface opposite to the incident surface of, and the outgoing light 5 exists, but the ratio of the area to the entire surface is smaller than that of the conventional example, and the ratio of the light once entering the solar cell to exit the solar cell is small.

FIG. 3 is a diagram showing one embodiment of a solar cell manufactured according to the present invention as viewed from a light incident surface. In the figure, 7 is a valley, 8 is a peak, and 9 is an etching for producing this embodiment. It is the starting point of the etching and is arranged in a square. FIG. 3 also shows the positional relationship between the crystal orientation and the starting point of the etching. Figure 3 using Si (111) substrate
Etching was performed from the position of No. 9. As an etching solution, 63.3% by weight of H ₂ O, 23.4% by weight of KOH,
Using 3.3% by weight isopropanol, a structure as shown in the figure was obtained. There is no surface facing the incident surface of the incident light 4, and light once entering the solar cell does not go out of the solar cell.

FIG. 4 is a view of one embodiment of a solar cell manufactured according to the present invention as viewed from a light incident surface. In the figure, 4 indicates incident light, 7 indicates a valley, and 8 indicates a peak. No. 9 was etched when producing this example. It is the starting point of the etching and is arranged in a hexagon. FIG. 4 also shows the positional relationship between the crystal orientation and the starting point of the etching. Si (11
1) Using a substrate, etching was performed from the position 9 in FIG. As an etching solution, 63.3% by weight of H ₂ O, 2
The structure as shown in the figure was obtained by using 3.4 wt% KOH and 13.3 wt% isopropanol and stopping at a certain stage of the etching. Although a part (111) surface remains, there is no surface facing the incident surface of the incident light 4.

[0012]

As described above, if the solar cell having the structure of the present invention is used, more light can be made to enter the inside of the solar cell, and the light once incident is hard to be emitted to the outside. Solar cell efficiency can be increased.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a solar cell according to the present invention.

FIG. 2 shows an embodiment of a solar cell according to the present invention.

FIG. 3 shows an embodiment of a solar cell according to the present invention.

FIG. 4 shows an embodiment of a solar cell according to the present invention.

FIG. 5 shows a conventional example of a solar cell according to the present invention.

FIG. 6 shows a state of reflection of a light beam.

FIG. 7 shows an embodiment of a solar cell manufactured according to the present invention as viewed from a light incident surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon solar cell 2 (111) surface 3 Substrate back surface 4 Incident light 5 Outgoing light 6a, 6b Reflected light 7 Valley 8 Peak 9 Etching start point

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takumi Yamada 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A solar cell comprising silicon as a main component, wherein the (111) plane is a principal plane, and at least a part of the principal plane is formed by a (100) plane. 2. The method according to claim 1, wherein (10)
0) A solar cell, wherein the concave portions formed by the plane are arranged so as to form a triangle. 3. The method according to claim 1, wherein (10)
0) A solar cell, wherein the concave portion formed by the plane is arranged so as to form a square. 4. The method according to claim 1, wherein (10)
0) A solar cell, wherein the recess formed by the plane is arranged so as to form a hexagon.