Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
1996-08-22
2003-02-11
Ver Steeg, S. H. (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S255000, C136S256000, C136S258000, C148S033200, C257S465000
Reexamination Certificate
active
06518494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silicon structure which can be applied to a light-emitting device or a solar battery, the method and apparatus for producing the same, and a solar battery using the silicon structure.
2. Disclosure of the Prior Art
In order to reduce the reflection of sunlight at its surface, a solar battery using silicon has been provided with an antireflection coating or an uneven surface.
The structure of a conventional solar battery will be explained with reference to
FIG. 7
, which is a cross-sectional diagram of a conventional silicon solar battery having a textured surface structure. As
FIG. 7
illustrates, an uneven surface is formed at the light incident side of a p type silicon substrate
31
so as to reduce the reflection of the sunlight. Commonly used methods of forming the unevenness include a chemical formation method using photolithography and chemical etching, and a mechanical formation method using a dicing machine. Examples of silicon substrates include single crystal substrates produced by the Czochralski method and polycrystalline substrates produced by casting. An n type silicon layer
32
is formed on the uneven surface of the p type silicon substrate
31
. The n type silicon layer
32
is formed by diffusing P (phosphorus) using a gas such as POCl
3
on the uneven surface of the p type silicon substrate
31
so as to convert part of the p type silicon substrate
31
to n type. An antireflection coating
33
comprising materials such as SiN and MgF
2
is formed on the n type silicon layer
32
. Further, a front surface electrode
34
is formed on the light receiving side of the p type silicon substrate
31
via an n++ silicon layer
35
, and the front surface electrode
34
is exposed on the surface of the antireflection coating
33
. A back side electrode
36
is formed on the back side of the p type silicon substrate
31
via a p+ silicon layer
37
. By forming a p+ silicon layer
37
between the back side electrode
36
and the p type silicon substrate
31
, the energy conversion efficiency can be improved (see the Third “High Efficiency Solar Battery” workshop preliminary reports, hosted by the Institute of Electrical Engineers, Semiconductor Electric Power Conversion Technology Committee, in Toyama, Japan, Oct. 5, 1992, Vol. A5-A6, pages 28-35).
Although the above mentioned conventional silicon solar battery configuration enables efficient collection of sunlight, the method of manufacture includes complicated processes to form the unevenness. This increases the production cost and thus the method is not suitable for practical use.
SUMMARY OF THE INVENTION
In order to solve the above mentioned problems in the conventional technology, an object of the present invention is to provide a silicon structure exhibiting little sunlight reflection, the method and apparatus for producing the same, and a solar battery using the silicon structure.
In order to achieve the above mentioned object, a configuration of the silicon structure of the present invention comprises an aggregate of a plurality of columnar silicon members mainly comprising silicon and having random orientations. According to the configuration of the silicon structure, since the light beam incident on one columnar silicon member is reflected thereby and re-enters another columnar silicon member, the sunlight can be absorbed efficiently. That is, according to the configuration of the silicon structure of the present invention, a silicon structure having little sunlight reflection can be obtained. It is preferable that the silicon content of the columnar silicon members is 95 weight % or more, and in addition to the silicon, about 1 weight % of chlorine and a few weight % of oxygen can be included.
In the above mentioned configuration of the silicon structure of the present invention, it is preferable that a substrate is provided and the silicon structure is formed on the substrate via a film mainly comprising silicon. According to the preferable embodiment, a transparent electrode does not come in contact with a lower electrode in the process of producing a solar battery using the silicon structure.
In the above mentioned configuration of the silicon structure of the present invention, it is more preferable that the diameter of the columnar silicon member is 0.1 to 10 &mgr;m. According to this embodiment, an adequate strength of the columnar silicon can be maintained and the depth of the junction formed when converting to an n type or a p type does not need to be limited. Further, the light absorption does not deteriorate.
According to the configuration of the silicon structure of the present invention, it is further preferable that the periphery of the columnar silicon member is amorphous and the center thereof is polycrystalline.
Further, the silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon having random orientations can be produced by a method wherein an atomized or vaporized silicon material containing chlorine is introduced to a heated substrate with oxygen gas. According to this production method, since a silicon containing raw material less dangerous than silane gas (SiH
4
) can be used, the silicon containing raw material can be supplied in a great amount. As a consequence, since the silicon formation rate can be improved, a silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon can be obtained. In this case, an inert gas can be introduced to the substrate at the same time in order to convey a silicon containing raw material also containing chlorine. Besides, by conveying a silicon containing raw material with an inert gas including hydrogen, or with only hydrogen, the amount of chlorine in the silicon structure can be reduced. Further, since a complicated process to form an uneven shape is not necessary unlike with the conventional textured structure, the production cost can be reduced.
According to the production method of the silicon structure of the present invention, it is preferable that the silicon containing raw material also containing chlorine is Si
2
Cl
6
. According to the preferable embodiment, since the decomposition temperature is approximately 350° C., which is low, and the decomposition can be conducted by radiating an ultraviolet beam (188 nm), a silicon structure comprising an aggregate of a plurality of columnar silicon members mainly comprising silicon and having random orientations can be obtained easily. In this case, it is more preferable that an n type or p type silicon structure is formed using a liquid material containing PCl
3
or BCl
3
as the silicon containing raw material comprising Si
2
Cl
6
.
In the above mentioned production method, it is more preferable that the oxygen gas is introduced so that the oxygen content in the vicinity of the centers of the columnar silicon members becomes 3% or less. According to this embodiment, the resistance of the silicon structure can be kept at a low level and thus the silicon structure can be used in an electronic device.
Further, an apparatus for producing the silicon structure of the present invention comprises a chamber, means to supply an atomized or vaporized liquid material comprising silicon and oxygen gas to the chamber, a support for the substrate to be treated by the apparatus, a heater for the substrate, and a filter having an area that is at least as large as the area of the substrate, through which the atomized or vaporized liquid material and oxygen gas are introduced to the substrate. According to the configuration of this apparatus, since the atomized or vaporized liquid material is uniformly diffused in the area of approximately the size of the filter at the time of passing through the filter and introduced to the surface of the substrate, a silicon layer can be formed uniformly on the substrate.
In the above mentioned production apparatus of the silicon structure of the present invention, it
Kitagawa Masatoshi
Mukai Yuuji
Shibuya Munehiro
Yoshida Akihisa
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Ver Steeg S. H.
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