Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2000-11-22
2003-02-04
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S244000, C438S098000, C438S056000, C438S064000, C438S066000, C219S121630, C219S121640, C219S121680, C219S121690
Reexamination Certificate
active
06515218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photovoltaic element including a solar cell, a process for producing said photovoltaic element, a method for removing a cover portion of a covered wire, and a method for joining a covered wire and a conductor. More particularly, the present invention relates to a photovoltaic element having an improved electrode structure, and a process for producing said photovoltaic element.
2. Related Background Art
In recent years, public attention has been focusing on a sunlight power generation system. Along with this, there is an increased demand for providing a large area photovoltaic element at a reasonable cost which enables one to establish a desirable sunlight power generation system at a reasonable cost. In general, a photovoltaic element has a photovoltaic layer (comprising a photoelectric conversion semiconductor layer), and in the photovoltaic element, the resistivity of a charge in the photovoltaic layer against its migration in an elemental face direction is large. Because of this, in the case of a large area photovoltaic element, in order to diminish a joule loss due to the migration of the charge in the elemental face direction, an electrode comprising a metal (this electrode will be hereinafter referred to as metal electrode) which has high conductivity is provided on the surface of the photovoltaic element.
In the case where the metal electrode is provided on the side where light is impinged, because the metal electrode is generally opaque, it is formed such that it does not shut out incident light as much as possible. On the other hand, in the case where the metal electrode is provided on the side where no light is impinged, it may be formed on the entire surface involved but in view of reducing the cost, it is often formed at a minimum necessary portion thereof.
Now, for instance as shown in FIGS.
7
(
a
) and
7
(
b
) it is known that an electrode
700
is formed in a comb-shaped form on a light incident side face or a back side face of a photovoltaic element (not shown). FIG.
7
(
a
) is a schematic plan view of said electrode, and FIG.
7
(
b
) is a schematic cross-sectional view taken along the line H-H′ in FIG.
7
(
a
).
In the case where the electrode
700
is formed on the light incident side face, when the electrode
700
comprises a comb-shaped electrode comprising a plurality of wire electrodes being arranged at a prescribed equal interval as shown in FIG.
7
(
a
), it is possible to effectively collect charges while restraining the joule loss. In the case where the electrode is formed on the back side face, it can be formed at a low cost because it can be formed using an electrode-forming material in a small amount. However, the formation of such electrode is generally conducted by a method wherein an electrically conductive resin material
702
is screen-printed on the surface of the photovoltaic element, followed by subjecting to sintering treatment, and a solder paste
701
is screen-printed thereon, followed by subjecting to reflow soldering. However, in this method, it is difficult to thicken the thickness of the electrode, and therefore, in the case where the photovoltaic element involved is of a larger area, it is difficult to attain an effect of sufficiently diminishing the joule loss.
In order to improve this situation, Japanese Unexamined Patent Publication No. 36395/1997 discloses a configuration for a comb-shaped electrode as shown in FIGS.
8
(
a
) and
8
(
b
) in that a core wire
801
whose thickness being capable of being thinned and an electrode
802
are used. FIG.
8
(
a
) is a schematic plan view of said comb-shaped electrode, and FIG.
8
(
b
) is a schematic cross-sectional view taken along the line I-I′ in FIG.
8
(
a
). Particularly, the comb-shaped electrode shown in FIGS.
8
(
a
) and
8
(
b
) comprises a covered wire comprising a metal core wire
801
covered by an electrically conductive resin material
803
which is bonded onto the surface of a photovoltaic element (not shown) by way of thermocompression bonding. And in said publication, there is described that the covered wire is joined with an electrode
802
through a metal layer comprising a solder or the like or an electrically conductive resin material.
Incidentally, for the conventional comb-shaped electrode in which the core wire and the electrode having such configuration as above described, it is difficult to make the comb-shaped electrode to have a sufficient resistance to stress. For instance, in the case where the core wire is joined with the electrode only through a metal layer by way soldering, although the joining may be conducted in a low resistance state, the joined portion is poor in flexibility and therefore, there is a problem in that the stress added to the core wire is converged to the joint of the joining portion of the core wire, where the core wire is liable to readily fracture at the joint thereof. In the case of a solar cell module in which such photovoltaic element is used, there is a tendency in that the above situation lead to entailing such problems as will be described in the following. That is, due to the stress remained at the core wire and a load applied onto the solar cell module by virtue of wind or snow, the solar cell module is flexed, where stress is eventually applied to the core wire and further stress is applied to the core wire when the temperature of the photovoltaic element is changed and as a result, the core wire is ruptured at the joint of thereof, resulting in a decrease in the energy conversion efficiency (the photoelectric conversion efficiency) of the solar cell module.
Separately, in the case where the core wire is joined with the electrode only through the electrically conductive resin material which comprises a composition comprising electrically conductive fine particles dispersed in a given resin, a current flow passage comprising said electrically conductive fine particles is formed between the core wire and the electrode, where gaps among the electrically conductive fine particles are filled with the resin to retain the current flow passage. In this case, it is also difficult to make the comb-shaped electrode to have a sufficient resistance to stress. That is, when it is intended to increase the current flow passage so as to lower the resistance, it is necessary to increase the content ratio of the electrically conductive fine particles in the electrically conductive resin material. In this case, the content ratio of the resin which serves to retain the current flow passage is decreased and as a result, the flexibility of the joining portion is diminished, where a sufficient resistance to stress cannot be attained. Therefore, there is also a tendency in that such problems as above described are entailed.
In the following, description will be made of a covered wire.
The covered wire means a composite comprising a core wire covered by a coating material. There are known various covered wires such configured, which are used in various fields. For instance there are known covered wires whose core wire comprising a wire for transmitting light such as an optical fiber which are used in the field of optical instrument; covered wires whose core wire comprising a wire for transmitting heat which are used in the field of refrigeration and also in the field of temperature measurement; and covered wires whose core wire comprising a wire for transmitting electromagnetic field which are used in the field of electronics. Particularly, in the field of solar cells, it is a common technique that a covered wire comprising an electrically conductive core wire covered by an electrically conductive resin material is disposed on the surface of photovoltaic element in order to collect power generated by the photovoltaic element.
The cover of the covered wire is generally used for the purpose of preventing a thing to be transmitted by the core wire from leaking to the outside or for the purpose of releasing said thing while adjusting the quantity
Murakami Tsutomu
Shimizu Koichi
Takeyama Yoshifumi
Tsuzuki Koji
Yoshino Takehito
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