Method of fabricating film for solar cells

Details Method of fabricating film for solar cells Method of fabricating film for solar cells

1999-10-08

2001-08-28

Bowers, Charles (Department: 2813)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S057000, C136S262000, C136S264000, C136S265000

Reexamination Certificate

active

06281036

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film for solar cells.
2. Description of the Prior Art
Solar cells in recent years have achieved a high maximum conversion efficiency of 17.7% by using films consisting of Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
(hereinafter also referred to as “CIGS”). However, when such films are grown under conditions in which there is an excessive supply of group III elements In and Ga, it is possible to fabricate single phase CIGS, but it has a high defect density and high resistance that degrade the properties of the resultant solar cell. On the other hand, while using an excess supply of Cu, a group I element, does provide large, good-quality crystals, it also results in the surface and boundary formation of the low resistance Cu—Se metal phase that makes devices prone to short circuit.
In order to grow high-quality CIGS films for solar cells, a complicated method is currently used, comprising first using an excess supply of Cu to form large-grain, high-quality CIGS, and followed by a step of using excess Ga and In to thereby remove a Cu—Se phase on the surface. Moreover, since a high temperature of around 550° C. is used to ensure the adequate reaction of each element, the method can only be used with substrates able to withstand such temperatures.
An object of the present invention is to provide a method of fabricating CIGS film for solar cells in which the generation of point defects (divacancies) and twin-crystal stacking faults is suppressed to thereby fabricate high-quality film.
Another object of the invention is to simplify the formation process by providing a method of fabricating high-quality CIGS films for solar cells in which the film is formed at a low temperature.
SUMMARY OF THE INVENTION
In accordance with the present invention, the object is attained by a method of fabricating Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
films for solar cells, said method comprising forming an electrode on a substrate and supplying Cu, In, Ga, Se, and S from a first source to the electrode to form a Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film on the electrode and at the same time supplying thereto water vapor or a gas containing a hydroxyl group, wherein 0≦x≦1, 0≦y≦1, and &agr;, &bgr;, and &ggr; are arbitrary integers.
The objective is also attained by a method of fabricating Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film for solar cells, said method comprising forming a Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film onto a substrate in a vacuum chamber by depositing or sputtering Cu, In, Ga, Se, and S on the substrate and at the same time supplying to the substrate water vapor or a gas containing a hydroxyl group, wherein 0≦x≦1, 0≦y≦1, and &agr;, &bgr;, and &ggr; are arbitrary integers.
The objective is also attained by a method of fabricating Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film for solar cells, said method comprising forming a Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film on a substrate in a gas reaction chamber by effecting a flow of gas to the substrate, that includes Cu, In, Ga, Se, and S and at the same time supplying to the substrate water vapor or a gas containing a hydroxyl group, wherein 0≦x≦1, 0≦y≦1, and &agr;, &bgr;, and &ggr; are arbitrary integers.
The objective is also attained by a method of fabricating Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film for solar cells, said method comprising forming a Cu
&agr;
(In
x
Ga
1−x
)
&bgr;
(Se
y
S
1−y
)
&ggr;
film on a substrate in a vacuum chamber by depositing or sputtering Cu, In, Ga, Se, and S on the substrate, then placing the substrate in a gas reaction chamber and carrying out annealing in a gaseous atmosphere containing Se, and wherein during either or both of the deposition or sputtering and the annealing the substrate is supplied with water vapor or a gas containing a hydroxyl group, wherein 0≦x≦1, 0≦y≦1, and &agr;, &bgr;, and &ggr; are arbitrary integers.
As described in the foregoing, by supplying water vapor or a gas containing a hydroxyl group during the formation of the CIGS film, anion vacancies and cation-anion composite vacancies that develop during the formation of the film are suppressed by the anion vacancies being filled with oxygen. As this also reduces the density of twin crystals, which are correlated to anion vacancies, it makes it possible to produce high-quality films for solar cells.
Moreover, supplying at least one gas selected from the group consisting of water vapor or a gas containing a hydroxyl group during the formation of the CIGS film enables the amount of Cu, In, Ga, Se, and S supplied to be kept constant and the reaction temperature to be reduced to around 450° C., thus simplifying the process and expanding the range of substrates that can be used.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.


REFERENCES:
patent: 4612411 (1986-09-01), Wieting et al.
patent: 5871630 (1999-02-01), Bhattacharya et al.
C.W. Bates Jr., Materials Letters, vol. 30, No. 1, pp. 87-91, “Preparation of Metal-Semiconductor Composite Films by Chemical Spray Pyrolysis”, Jan. 1997.
S. Niki, et al., Solar Energy Materials and Solar Cells, vol. 49, No. 1-4, pp. 319-326, “Effects of Annealing on CulnSe2Films Grown by Molecular Beam Epitaxy”, 1997.
S. Weng, et al., Journal of Applied Physics, vol. 3, No. 74, pp. 2046-2052, “Preparation of Copper Indium Diselenide by Selenization of Copper Indium Oxide”, Aug. 1, 1993.

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