Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
1997-01-09
2001-02-20
Chapman, Mark (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S257000, C136S259000
Reexamination Certificate
active
06191353
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solar cell module excelling especially in moisture resistance and transparency. More particularly, the present invention relates to a solar cell module improved so that the solar cell characteristics are effectively prevented from being deteriorated due to a reduction in the shunt resistance and the like of the photovoltaic element when used under environmental conditions with high temperature and high humidity over a long period of time.
2. Related Background Art
Recently, a number of solar cell modules have been proposed.
FIG. 1
is a schematic cross-sectional view illustrating the constitution of a typical example of these solar cell modules. In
FIG. 1
, reference numeral
1101
indicates a photovoltaic element (or a solar cell) having a collecting electrode
1108
, reference numeral
1102
a surface side filler, reference numeral
1103
a surface protective layer (or film), reference numeral
1105
a back side filler, reference numeral
1106
a insulating member, and reference numeral
1107
a support member (or a back face reinforcing member). Particularly, the surface protective layer
1103
comprises a fluororesin film such as an ethylene-tetrafluoroethylene copolymer (ETFE) film or polyvinyl fluoride (PVF) film; the surface side filler
1102
comprises ethylene vinyl acetate copolymer (EVA) or butyral resin; the back side filler
1105
comprises EVA (which is the same as the surface side filler
1102
) or ethylene-ethyl acrylate copolymer (EEA); and the insulating member
1106
comprises a film of an organic resin such as nylon or polyethylene terephthalate (PET) or a member comprising an aluminum foil sandwiched with Tedlar (trademark name). In this solar cell module, the surface side filler
1102
serves also as an adhesive between the photovoltaic element
1101
and the fluororesin film as the surface protective layer
1103
, and the back side filler
1105
serves also as an adhesive between the photovoltaic element
1101
and the insulating member
1106
. The fluororesin film as the surface protective layer
1103
together with the surface side filler
1102
serve to prevent the photovoltaic element
1101
from being eternally damaged and from being damaged from external shock. The insulating member
1106
is disposed in order to reinforce the solar cell module while adding an appropriate rigidity thereto.
The collecting electrode
1108
of the photovoltaic element is usually formed by using a metallic wire coated by an electrically conductive composition or by way of screen printing of an electrically conductive paste.
In such solar cell module, EVA is usually used as the surface side filler
1102
. And in order to sufficiently enclose the photovoltaic element
1101
, a crosslinking agent such as 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane (one-hour half life temperature: 138° C.) is incorporated into the EVA as the surface side filler. Besides this, it is known to use a peroxide compound capable of being decomposed at low temperature as the crosslinking agent for the EVA, where the EVA is crosslinked by way of decomposition of said peroxide compound at low temperature. In the case of using said peroxide compound as the crosslinking agent for the EVA as the surface side filler, in the lamination process for producing a solar cell module, the crosslinking of the EVA as the surface side filler proceeds at a high speed (this will be hereinafter referred to as high speed EVA crosslinking manner) and therefore, the heat treatment in the lamination process can be accomplished in a short period of time, resulting in reducing the period of time required for the lamination process. The use of the high speed EVA crosslinking manner provides other advantages since the heat treatment in the lamination process can be accomplished for a short period of time as above described, the quantity of heat energy applied to covering materials including the EVA as the surface side filler and a fluororesin film as the surface protective film in the heat treatment is relatively small so that the covering materials are prevented from being yellowed due to the heat energy applied. Therefore, the formation of a surface side cover excelling in optical initial characteristics can be attained for the photovoltaic element.
In the case of a solar cell module having the foregoing surface side cover excelling in optical initial characteristics formed by way of the high speed EVA crosslinking process, the fluororesin film which is present in the surface side cover as the surface protective film situated on the outermost surface side has a satisfactory water repelling effect for preventing moisture damage but it is difficult to attain a satisfactory moisture barrier function by the fluororesin film only. In addition, the photovoltaic element is sealed by the EVA having a high water absorbability which is situated under the fluororesin film. Because of this, the solar cell module is not sufficiently stable for the long-term case where the solar cell module is continuously used under environmental conditions with high temperature and high humidity. Further, in the case where the collecting electrode of the photovoltaic element comprises a metallic wire coated by an electrically conductive composition comprising particles of an electrically conductive material and a binder resin, the coat of the metallic wire is unavoidably accompanied by gaps present among the electrically conductive particles The gaps are left by insufficient filling with the binder resin. The metallic wire is therefore not sufficiently protected from contact with moisture.
Now, the high speed EVA crosslinking process is advantageous in that the EVA can be crosslinked in a short period of time, but it exhibits a problem in that the period of time during which the EVA is maintained in a fluidized state is short. Because of this, irregularities present at the photovoltaic element and the gaps present at the collecting electrode comprising the metallic wire coated by the electrically conductive composition are not sufficiently filled by the EVA and such irregularities and gaps provide unfilled defects in the solar cell module. This situation is liable to cause such problems as will be described as follows. When moisture invades the solar cell module, the moisture passes through said unfilled defects to reach the metallic wire of the collecting electrode. In this case, the metallic wire is oxidized to cause an increased series resistance (Rs) or/and the metal of the surface of the metallic wire is ionized or/and precipitated, when the photovoltaic element is in a voltage applied state. The ionized or precipitated metal migrates to deposits in the defects of the photovoltaic element, thus resulting in short circuits (or shunts) in the photovoltaic element. These deteriorate the photoelectric conversion performance of the solar cell module particularly when the solar cell module is continuously used under severe environmental conditions of high temperature and high humidity over a long period of time.
Further, for the collecting electrode comprising the metallic wire coated by the electrically conductive composition, when the moisture invaded the electrically conductive composition as above described, there is a tendency that the adhesion between the collecting electrode and the photovoltaic element gradually becomes inferior to provide an increased contact resistance between them, and the electric power generated by the photovoltaic element cannot be efficiently utilized over a long period of time.
Even in the case where the collecting electrode is formed by way of screen printing of an electrically conductive metal paste, the collecting electrode formed of the metal paste is liable to have gaps as well as in the case of the collecting electrode comprising the metallic wire coated by the electrically conductive composition. Therefore, there is a tendency that when moisture invades the solar cell module, there is a tendency that problems similar to the
Kataoka Ichiro
Mori Takahiro
Shiotsuka Ayako
Shiotsuka Hidenori
Yamada Satoru
Canon Kabushiki Kaisha
Chapman Mark
Fitzpatrick, Cellar, Harper & Scinto
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