JPS635576A - Solar cell - Google Patents

Abstract

PURPOSE:To obtain a large weight ratio output without damaging mechanical strength, by a method wherein a plurality of recessed parts are formed by an etching in the manner in which a grating type protrusion is left containing the peripheral part of a rear surface, and a metal electrode is formed only on the protrusion. CONSTITUTION:On the back main surface of a light receiving surface 3, a plurality of recessed parts 6 are formed in the manner in which a grating type protrusion 5 is left containing the peripheral part. A metal electrode on the rear side is formed only on the protrusion 5 and not formed in the recessed parts 6. Thereby, the strain or warpage of a GaAs substrate in a severe heat shock test and the like is reduced, and the cracks and the like of a solar cell are prevented. The protrusion is left along the peripheral part, so that the cracks and the cutouts at the peripheral part can be prevented, and the mechanical strength of the GaAs solar cell wherein the recessed parts are formed can be maintained. Further the weight of this GaAs solar cell is reduced by 20%, which improves the weight ratio output of 20% when the same conversion efficiency as the conventional cell is obtaind.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a solar battery used, for example, in space.

In particular, it relates to weight reduction of GaAs solar cells.

[Conventional technology]

FIG. 3 is a perspective cross-sectional view of an example of a conventional GaA3 solar cell used for space applications. In FIG. 0, 111 is a GaAs solar cell substrate, 1 is p-AlGaAs or p-
2 is a GaAs layer, 2 is an n-GaAs layer, 3 is a light receiving surface on which an antireflection film is formed, 4 is a metal electrode of the p layer, and 5 is a back electrode of the n layer. do is the substrate thickness of the GaAs solar cell,
This do is, for example, 270 to 300 μm. Usually Ti-Ag or Au-Zn-Ag is used for the metal electrode 4, and Au/Ge-N1-Au-Ag is used for the back electrode 5.
is formed. The thickness of Ag is usually 4 to 5 μm in order to assemble GaAs solar cells in series or parallel. Additionally, # each metal electrode 4 is formed into a fine pattern to obtain maximum efficiency;
The back electrode 5 is formed on the entire surface.

Incidentally, solar cells mounted on artificial satellites and the like are required to have a large electrical output per unit weight (weight-specific output) from the viewpoint of rocket launch capability or economics. Conventional 2cm x 2am”.

In the case of a GaAs solar cell with a thickness of 300 μm, the weight specific output is about 150 mW/g.

[Problem that the invention seeks to solve]

By the way, in order to increase the weight-specific output of a GaAs solar cell, it is possible to increase the conversion efficiency or reduce the weight by reducing the thickness of the substrate. However, there is a limit to increasing the conversion efficiency, and For example, set the substrate thickness to 100 to 15
When the thickness is reduced to 0 μm, the mechanical strength of the GaAs solar cell decreases, causing problems such as cell cracking and destruction during manufacturing or during severe thermal shock tests. In addition, for example, solar cells installed on artificial satellites etc.
℃ thermal cycle is applied, but since conventional solar cells have metal electrodes on the entire surface of the back side, distortion and stress occur due to the difference in thermal expansion coefficient between the electrode material and the solar cell substrate, sometimes leading to destruction. There was a problem.

The present invention was made to solve the above-mentioned problems, and its purpose is to reduce the weight of GaAs solar cells without impairing their mechanical strength, and to obtain a GaAs solar cell with a high weight-specific output. do.

[Means for solving problems]

In the GaAs solar cell according to the present invention, a plurality of concave portions are formed by etching so that convex portions remain in a lattice shape including the peripheral portion of the back surface, and a metal electrode is formed only on the convex portions. .

[Effect]

In this invention, the recess provided on the back surface is made of GaA
The convex portion reduces the weight of the solar cell and maintains the mechanical strength of the GaAs solar cell. Furthermore, since the metal electrode is formed only on the convex portion, distortion and cracking of the solar cell due to thermal stress can be prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows 2CIIX21Ja according to an embodiment of this invention.
In Figure 0, which is a perspective cross-sectional view of a GaAs solar cell,
100 is a GaAs solar cell substrate, 6 is a concave portion, 5 is a convex portion,
d is the depth of the recess, dt is the substrate thickness of the recess, a and b are the widths of the lattice-shaped recess and projection, respectively, and C is the width of the peripheral projection. do is the total substrate thickness of 280 μm, a
, is 150 μm, dz is 130 μm, c is 2 m, a is 4 m, and b is 1 n. Although various shapes can be considered, the width of the convex portion at the periphery is required to be about 2 fl in order to maintain mechanical strength. Also, a/b
The ratio may be about 4 or 5. The 21-plane electrode is formed only on the convex portion 5 and not on the concave portion 6.

FIG.
b) is the process of coating resist 7 on both sides of the GaAs substrate 111 shown in figure (a), and figure (11,) is the process of coating the resist 7 on both sides of the GaAs substrate 111 shown in figure (11,).
and a step of selectively etching the GaAs substrate 111. In the process shown in Figure (C), Ag is first etched with a nitric acid-based etching solution, and the underlying Au/Ge-N
Etch the i-Au using a gold stripper and a nitric acid-based etching solution. Further, the GaAs substrate 111 is etched with a mixed solution of tartaric acid and hydrogen peroxide. The etching rate at this time is approximately 1 .mu.m/+win, and therefore approximately 150 minutes are required to etch 150 .mu.m. FIG. 4(d) shows the step of removing the resist 7 after these etchings are completed.

In the GaAs solar cell produced in this way, the metal electrode on the back side is not formed in the recessed part but only on the convex part, which makes it difficult to perform GaAs solar cells in severe thermal shock tests.
It is possible to reduce distortion or warpage of the solar cell and prevent cracking of the solar cell. In addition, since a convex portion remains along the periphery, it prevents cracking and chipping at the periphery, and
The mechanical strength of the GaAs solar cell in which the recessed portion is formed can be maintained. 3. Moreover, the weight of the q GaAs solar cell is reduced by about 20%, and if the same conversion efficiency as the conventional one is obtained, the weight-specific power output will be improved by 20%.

In the above embodiment, the shape of the recess is square, but it may also be circular or rectangular.
It can also be applied to solar cells other than aAS solar cells, and the same effects as in the above embodiments can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, a plurality of concave portions are formed by etching so that convex portions remain in a grid pattern including the peripheral portion of the back surface, and the metal electrode is formed only on the convex portions. This has the effect of providing a GaAs solar cell that is less affected by thermal stress and has a high weight specific output without reducing mechanical strength.

[Brief explanation of the drawing]

FIG. 1 is a perspective cross-sectional view of a GaAs solar cell according to an embodiment of the present invention, and FIG. 2 is a diagram showing the manufacturing process of the present invention.
Figure 3 is a perspective cross-sectional view of a conventional GaAs solar cell6.
In the figure, 1 is a p-AjiGaAS layer or a p-GaAs layer, 2 is an n-G, aAs layer, 3 is a light receiving surface on which an antireflection film is formed, 4 is a p-metal electrode, 5 is an n-back electrode, 6 is the recess, a, b is the grid-like recess, the width of the protrusion, C is the width of the protrusion in the peripheral area, do is the substrate thickness, d is the depth of the recess, d! is the substrate thickness of the recess. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In a solar cell using GaAs as a semiconductor substrate, a plurality of concave portions are formed on the main surface behind the light-receiving surface so that convex portions remain in a lattice shape including the peripheral portion, and a metal electrode is placed on the convex portions. A solar cell characterized in that: (2) The solar cell according to claim 1, wherein the substrate thickness of the concave portion is 100 to 150 μm, and the substrate thickness of the convex portion is 250 to 300 μm.