Batteries: thermoelectric and photoelectric – Photoelectric – Panel or array
Reexamination Certificate
2000-02-23
2001-09-25
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Panel or array
C136S251000, C136S258000, C136S261000, C257S466000
Reexamination Certificate
active
06294722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film photoelectric conversion devices and sputtering-deposition methods usable in manufacturing the same, and in particular to a back metal electrode layer of a thin-film photoelectric conversion device that is formed on a transparent insulator substrate and to a sputtering-deposition method usable in forming the layer.
2. Description of the Background Art
Thin-film solar batteries, TFT (Thin-Film Transistor) arrays, mirrors and the like require that a film including at least one conductive layer be formed on an insulator substrate.
FIG. 1
is a schematic cross section showing an exemplary conventional sputtering-deposition method used to form on an insulator substrate film including at least one conductive layer. In this sputtering-deposition method, a substrate holder
1
is initially prepared. Substrate holder
1
is generally in the form of a frame with an opening
1
a
at its central area. Substrate holder
1
preferably has along a peripheral edge of opening,
1
a
a step
1
b
for accepting substrate
2
. Furthermore, substrate holder
1
is formed of a conductive material such as stainless steel and electrically grounded.
On conductive substrate holder
1
, an insulator substrate
2
such as a glass plate is positioned to be fit on step
1
b
to cover opening
1
a
. Superposed on insulator substrate
2
is a back plate
3
formed of a conductive plate, such as an aluminum plate or a carbon plate. Back plate
3
is fixed to holder
1
with a screw or bolt
4
to press insulator substrate
2
against conductive holder
1
.
In such condition, metal, oxide, nitride or the like is sputtered to deposit a layer thereof on a region of insulator substrate
2
exposed in the holder's opening
1
a
. In such film deposition through sputtering, Ar ions used in general to sputter a target and sputtered particles to contribute to the film deposition are positively charged. As such, when a conductive layer of metal, transparent conductive oxide (TCO) or the like is formed on insulator substrate
2
, when an additional conductive layer of metal, TCO or the like is formed on a surface of a layered structure including at least one conductive layer already formed on insulator substrate
2
, as in a case of forming a back electrode to fabricate a thin-film solar battery with a transparent electrode, a semiconductor layer and the back electrode successively formed on a transparent insulator substrate of glass or the like, or when a layer of a metal such as Cr (a conductive layer) is initially formed on transparent insulator substrate
2
such as a glass plate and then an insulating layer is formed on the metal layer, as in a case of forming a gate insulating film of a TFT, the positive charge of Ar ions and sputtered particles flying toward and colliding against insulator substrate
2
is transferred to the conductive layer on the substrate. To release the electric charge transferred to the conductive layer on insulator substrate
2
, conductive substrate holder
1
is earthed.
If substrate
2
is electrically floating from conductive holder
1
, however, the electric charge from Ar ions and sputtered particles is accumulated in the conductive layer on insulator substrate
2
and voltage of the conductive layer is increased, and when the voltage of the conductive layer exceeds a certain value, the layer discharges as if a thunder were caused. The discharge occurs between the conductive layer on substrate
2
and the target or other portions of the sputtering apparatus, and such portions suffer damage traces due to the discharge. As a result, the film on substrate
2
is severely damaged and the whole substrate must be discarded.
In particular, for an integrated thin-film solar battery, a back electrode is formed through deposition at an almost final step of the whole process, i.e., after forming a transparent electrode layer on a glass substrate, patterning the transparent electrode layer, forming a semiconductor layer such as a thin film of amorphous silicon, crystalline silicon or the like, and patterning the semiconductor layer. As such, the discharge damage of the back electrode leads to economically severe damage and it is a matter of concern.
With the recent heightened public awareness of protection of global environment, solar power generation is increasingly used as a clean energy source. Solar battery modules are often installed on roofs and walls of buildings and in such case they play a role as parts of the buildings. As such, architects demand a solar battery module having an appearance harmonious with the building of interest, in particular that having a color tone harmonious with the building. As such, for example a thin-film solar battery module with a continuous browny color across the entire surface of a transparent insulator substrate such as a glass plate, is preferable to a monocrystilline-type solar battery module including a plurality of mutually discontinuous monocrystalline cells joined to a glass substrate.
In general, a thin-film solar battery module is fabricated by successively stacking a transparent electrode layer, a semiconductor layer and a metal electrode layer on a transparent insulator substrate through vapor-phase deposition. In stacking the layers, normally the region for forming the semiconductor layer and that for forming the metal electrode layer are set to be substantially identical. As such, if an actually deposited metal electrode layer has a peripheral edge region positionally offset and thus protruding from a peripheral edge of the semiconductor layer, then as seen from a light-incident side of the transparent substrate the peripheral edge region of the metal electrode layer can be disadvantageously observed in the form of a white line showing outside the dark browny peripheral edge of the semiconductor layer region to spoil a unified good appearance of the thin-film solar battery module.
Furthermore for a monocrystalline-type solar battery module a sealing resin material of white color or similar colors is normally used to protect back surfaces of a plurality of monocrystalline cells of the module and if such material is applied to protect a back surface of a thin-film solar battery module then the module has an appearance with its semiconductor layer region's peripheral edge surrounded by a white frame and thus has an aesthetically degraded appearance.
In a thin-film solar battery module, in general a transparent electrode layer, a semiconductor layer and a metal electrode layer stacked on a substrate are for example laser-described and thus divided into a plurality of photoelectric conversion cells which are in turn electrically interconnected and thus integrated. An industrial standard of thin-film solar battery modules requires that a cell region be insulated from any peripheral edge region outside the cell region, and accordingly a thin-film solar battery module typically has a cell region laser-scribed and thus electrically isolated from any peripheral edge region that may electrically contact a frame holding the module. As such, if the semiconductor region deposited on the transparent insulator substrate is inward of a peripheral edge of the metal electrode layer deposited on the semiconductor region and at a location for forming the aforementioned peripheral isolation groove the metal electrode layer directly contact the transparent electrode layer or the transparent insulator substrate, then a laser beam incident on and transmitted through the transparent substrate to laser-scribe the metal electrode layer can hardly form a satisfactory such groove in the metal layer due to its high reflectance and thus often fails to provide a sufficient withstand voltage.
A thin-film solar battery module typically has a back electrode covered with an organic protection film with a sealing resin layer therebetwen to prevent its back metal layer from deteriorating while the module is used outdoor and also to prevent its power generation performance fro
Kondo Masataka
Suzuki Takayuki
Diamond Alan
Hogan & Hartson LLP.
Kaneka Corporation
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