JPS6117155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar cell that converts light energy into electrical energy, and particularly to a structure of a solar cell suitable for use in outer space as a power source for an artificial satellite.

Currently, silicon solar cells are mainly used as such solar cells. However, when used in artificial hygiene and the like, solar cells with high conversion efficiency are required in order to obtain more power within a limited area. Furthermore, since radiation is pouring down in outer space,
It is required that the characteristics do not deteriorate due to radiation damage. In response to these demands, gallium arsenide (GaAs) solar cells, which currently have the highest conversion efficiency and excellent radiation resistance, are attracting attention.

Conventional examples of GaAs solar cells are shown in FIGS. 1 and 2. FIG. 1 is a plan view, and FIG. 2 is a sectional view taken along the - line in FIG. 1. In a conventional solar cell, a p-type GaAs layer 2 is formed on an n-type GaAs substrate 1, thereby forming a p-n junction surface 3 between the two, and a p-type layer 2 is formed on the p-type GaAs layer 2.
A GaAlAs layer 4 is formed. Further, the n-type electrode 5 is formed on the back surface of the n-type GaAs substrate 1, and the p-type electrode 6 is partially formed on the surface of the p-type GaAlAs layer 4. And on the surface of the p-type GaAlAs layer 4,
An antireflection film 7 is formed.

In the GaAs solar cell 11 having such a structure, most of the optical carriers effective for photocurrent generation are generated within the p-type GaAs layer 2. In addition, the p-type GaAs
Since the p-type GaAlAs layer 4 is provided on the layer 2, loss due to recombination of generated optical carriers on the surface of the p-type GaAs layer 2 can be significantly prevented, and a highly efficient solar cell can be realized. There is. Furthermore, optical carriers generated within the depletion layer region and the region within the n-type GaAs layer 1 from the p-n junction surface 3 to a distance approximately equal to the hole diffusion length can also contribute to photocurrent generation. Very few optical carriers are generated in the n-type GaAs layer 1 deeper than this, and such optical carriers do not reach the pn junction surface 3 and do not contribute to photocurrent generation. Also, p-type
Since the optical carriers generated within the GaAlAs layer 4 cannot contribute to photocurrent generation due to surface recombination, the absorption of light within this layer 4 should be minimized, and therefore the thickness of this layer 4 should be 1 μm or less. It is thinned out. Usually, the p-type GaAs layer 2 has a thickness of several μm or less, the depletion layer has a thickness of 1 μm or less, and the n-type
The diffusion length of holes in the GaAs layer 1 is several μm or less, and the effective light receiving area is the p-type GaAlAs layer 4 and the p-type
About 10μm from the interface of GaAs layer 2, at least 20μm deep
Extremely thin, less than m. For this reason, 10 to 20
Damage caused by radiation irradiation that occurs below µm does not affect the conversion efficiency, and compared to silicon solar cells, which have an effective light-receiving area of 200 to 300 µm from the surface,
It can be said that GaAs solar cells have excellent radiation resistance.

As described above, the GaAs solar cell 11 has excellent characteristics as a space solar cell, but since GaAs has a higher specific gravity than silicon, it is heavier than a silicon solar cell of the same size. This is a serious drawback when launching artificial satellites.

In addition, the effective light receiving area of GaAs solar cells is 10 to 20
Since the thickness is .mu.m, if a solar cell with this thickness can be obtained, the weight will be greatly reduced, which is preferable. However, the standard size of space solar cells is 2.
With current technology, it is quite difficult to obtain a crystal with the above thickness for a light-receiving surface measuring cm x 2 cm. Even if such a crystal were obtained, it would be extremely easy to break, making it difficult to form electrodes. It is extremely difficult to handle in the solar cell manufacturing process such as
In fact, it may be said that it is impossible to obtain a solar cell formed only from crystals having the above-mentioned thickness.

This invention has been made in view of the above points, and includes providing a plurality of recesses so as to leave the outer peripheral wall and the partition wall connected thereto on the surface opposite to the light incident surface, and all the recesses mentioned above are connected to the outer peripheral wall. It is also an object of the present invention to provide a solar cell that is lightweight, has sufficient mechanical strength, and is highly reliable, by communicating with the outside through communication passages in the partition walls.

An embodiment of the present invention is shown in FIGS. 3 and 4.
FIG. 3 is a diagram showing the back side of a solar cell according to an embodiment of the present invention, and FIG. 4 is a sectional view taken along the - line in FIG. 3. p-type on n-type GaAs substrate 1
The GaAs layer 2, the p-n junction surface 3, the p-type GaAlAs layer 4, the p-type electrode 6, and the anti-reflection film 7 are formed in the same way as a solar cell with a conventional structure, but the n-type GaAlAs
The structure of the substrate 1 is completely different.

That is, in the conventional structure, the n-type GaAs substrate 1
is plate-like, whereas in the structure of this example, a number of recesses 8 are formed in the n-type GaAs substrate 1;
It is not completely surrounded by the side walls (outer peripheral wall 90 and partition wall 9) that reach the bottom surface of the substrate 1. That is, adjacent recesses 8 are connected by a communication path 10 of at least one partition wall 10, and at least one of the outermost recesses 8 is connected by a communication path 10 of the outer peripheral wall.
It is connected to the space outside the element by. Therefore, the n provided on the lower surface of the outer peripheral wall 90 and the partition wall 9
By bonding the shaped electrode 5 to a flat substrate (not shown), even if the solar cell 21 of this embodiment is fixed to said substrate, any recesses 8 inside will not be in communication with the space outside the device. There will be.

The recessed portion 8 and communication path 10 as described above can be easily formed using appropriate photolithography, etching, or the like. Such a recessed portion is once formed in the n-type GaAs substrate 1, as in the conventional GaAs solar cell.
It may be formed after the n-type electrode 5 is formed on the entire back surface of the
An n-type electrode 5 may also be formed.

In addition, in this embodiment, the n-type
Outer peripheral wall 90 or partition wall 9 made of GaAs substrate 1
This maintains the mechanical strength of the element. Therefore, the ratio of the recessed portion 8 to the total bottom area and the depth of the recessed portion 8 are selected to be appropriate values. As an example, when the thickness of the device is 300 μm, a GaAs solar cell with sufficient mechanical strength could be obtained even if the area of the recess 8 was 50% of the total bottom surface and the depth of the recess 8 was about 200 μm. . In this case, compared to the GaAs solar cell 11 of the conventional structure shown in FIGS. 1 and 2, the weight per same light-receiving area can be reduced to 2/3 without significantly deteriorating the mechanical strength.

Here, the depth of the recessed portion 8 is set to an extent that does not impair the conversion efficiency of the solar cell, and this restriction is included in the conditions for guaranteeing the mechanical strength, and hereinafter this will be explained. Let's talk about.

Although the thickness of the n-type GaAs layer 1 in the portion where the recessed portion 8 is formed is thinner, it has a thickness necessary to maintain mechanical strength, and this thickness is usually
It is thicker than the hole diffusion length in n-type GaAs. That is, while the diffusion length of holes in n-type GaAs is approximately several μm, in this embodiment, the diffusion length of holes in n-type GaAs in the area where the recess 8 is formed
The layer thickness is over 100 μm. Therefore, the formation of the concave portion 8 does not impair mechanical strength or affect the effective light receiving area and reduce conversion efficiency.

Now, such GaAs solar cells are assembled on Earth under atmospheric pressure. If even one of the recesses 8 provided for the purpose of weight reduction is completely surrounded by the side wall (outer peripheral wall 90 and partition wall 9) of the recess 8 that reaches the bottom surface of the substrate 1. If the solar cell is mounted on a flat surface, the atmosphere will be trapped in the recess 8. When a GaAs solar cell mounted in this way is mounted on an artificial satellite and launched outside the atmosphere, it is constantly placed in a fairly high vacuum, so the concave portion 8 is formed and the thinned portion is under pressure. Due to the difference, there is a risk of deformation or damage, and the function of the solar cell may deteriorate or stop. Since space solar cells used for artificial sanitation and the like are required to have extremely high reliability, the above phenomenon poses a problem.

In the GaAs solar cell 21 of this example,
Any of the recessed portions 8 provided for the purpose of weight reduction is not completely surrounded by the side walls (outer wall 90 and partition wall 9) that reach the bottom surface of the n-type GaAs substrate 1. With the mount, there is no confined space. Therefore,
The atmosphere existing in the recess 8 due to assembly in the atmosphere is completely swept out through the communication path 10 when placed outside the atmosphere, so no pressure difference occurs between the inside and outside of the recess 8. . Therefore, according to the structure of this example, the above problems are solved and a highly reliable GaAs solar cell can be obtained.

It goes without saying that the shape of the recessed portion in the above embodiment may be other than that shown in FIGS. 3 and 4 as long as it does not impair the conversion efficiency and mechanical strength of the solar cell.

Furthermore, the present invention can be applied not only to GaAs solar cells having the specific structures shown in FIGS. 1 and 2, but also to GaAs solar cells having any other structure.

As described in detail above, according to the solar cell according to the present invention, a plurality of recesses are provided on the surface opposite to the light incident surface so as to leave the outer peripheral wall and the partition walls connected thereto, and any of the recesses are removed. Since the device is communicated with the outside via the communication path, it is possible to reduce the weight without sacrificing mechanical strength, and it is possible to obtain a highly reliable product.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a conventional GaAs solar cell, FIG. 2 is a sectional view taken along the - line in FIG. 1, and FIG. 3 is a plan view showing the back side of an example of the GaAs solar cell according to the present invention. , FIG. 4 is a sectional view taken along the - line in FIG. 3. In the figure, 1 is an n-type GaAs substrate, 2 is a p-type GaAs layer,
3 is a p-n junction surface, 8 is a recessed portion, 9 is a partition wall, 90
1 is an outer peripheral wall, and 10 is a communication path. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a solar cell that generates electrical energy by the incidence of light, an outer peripheral wall and its outer peripheral wall are arranged to form a plurality of recesses of a predetermined depth on a surface opposite to the surface on which light enters. A partition wall connected to the wall is provided, and all of the recessed portions communicate with the outside through a communication path provided in the partition wall and a communication path provided in the outer peripheral wall that communicate between adjacent recessed portions. Features of solar cells.