Solar cell

Details Solar cell Solar cell

1999-05-28

2001-02-13

Chapman, Mark (Department: 1753)

Batteries: thermoelectric and photoelectric

Photoelectric

Cells

C136S262000, C136S264000

Reexamination Certificate

active

06188013

ABSTRACT:

FIELD OF THE INVENTION
The present invention is related in general to a solar cell and more particularly to a solar cell having an improved electrode structure.
BACKGROUND OF THE INVENTION
The thin film semiconductor solar cell of copper-indium-gallium-selenide (Cu,In,Ga,Se) having the chalcopyrite structure has been studied in recent years as is shown in some patent applications such as WO94/24696, WO96/06454. The structure of the solar cell is shown in
FIG. 3
in which on a glass substrate
9
, a bottom side electrode layer
2
of molybdenum (Mo), a photoelectric semiconductor layer of Cu,In,Ga,Se 1, a buffer layer of CdS 4 and a top side electrode layer
3
are formed sequentially. The top side electrode layer
3
is made by forming transparent electrode layers of ZnO, ZnO/Al
3
a
,
3
b
on the buffer layer
4
sequentially, and by forming an Al electrode
3
c
comprising a plurality of separated strips
3
c
1
,
3
c
2
of non-transparent conductive layers.
The molybdenum is selected as a material to form the bottom side electrode layer
2
, because the Cu(In,Ga)Se2 photoelectric semiconductor layer
1
of the good quality can be formed on it. The soda-lime silica glass is one of suitable materials for the glass substrate
9
. One reason why it is suitable for the glass substrate is that it has almost an equal thermal expansion coefficient to that of the Cu(In,Ga)Se2 semiconductor layer
1
which results in the reduction of the thermal strain in the stacked composite structure to improve the reliability of the solar cell.
The strips
3
c
1
,
3
c
2
of the non-transparent conductive layers of the top side electrode
3
c
are extended in the direction diagonal to the cross section keeping an appropriate predetermined distance between each other. The width of each of the strips of the electrode layers
3
c
should be made as large as possible to decrease the resistance of the electrode. However, their width should be made as small as possible to minimize the amount of the solar light which will be reflected by them. Accordingly, their width, more precisely, the ratio of their width to their distance, should be determined to be the optimum value considering both factors.
The conventional solar cell shown in
FIG. 3
has a problem that the Joule loss becomes large in the electrode layer
2
, because the material molybdenum has high electrical resistance. As a result, the efficiency of photoelectric energy conversion of the solar cell will be decreased.
In the conventional solar cell shown in
FIG. 3
, so called scribing method has been applied to make the electrical connection to the bottom side electrode layer
2
at it's peripheral area. In the scribing method, the top side electrode layer
3
and the semiconductor photoelectric conversion layer
1
at the peripheral area of the bottom side electrode layer
2
will be removed by scratching and breaking the overlying layers
1
,
3
using a sharp metal claw to expose the underlying electrode layer
2
. However, this scribing method is difficult because only the very thin underlying electrode layer
2
must be left exposed without suffering substantial damage, which results in decrease of the yield of the fabrication.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a solar cell having a bottom electrode layer of low resistivity to reduce Joule loss, which thereby results in the high photoelectric conversion efficiency of the cell.
It is also an object of this invention to provide a solar cell of high fabrication yield, to thereby cause a low manufacturing cost.
These and other objects of the present invention are achieved by the solar cell of this invention comprising: a substrate formed of insulator material; a bottom side electrode layer formed on one side of said substrate; a semiconductor photoelectric conversion layer formed on said bottom side electric layer; a transparent top side electrode layer formed on said semiconductor photoelectric conversion layer; a non-transparent electrode comprising a plurality of strips of non-transparent conductive layers disposed separately form each other on said top side transparent electrode layer; an additional bottom side electrode layer formed on an opposite side of said substrate and a plurality of conductive paths connecting said bottom side electrode layer and said additional bottom side electrode layer through holes or slits formed to penetrate said substrate.


REFERENCES:
patent: 5356839 (1994-10-01), Tuttle et al.
patent: 6020556 (2000-02-01), Inaba et al.
patent: 59-115576 (1984-07-01), None
patent: 60-035554 (1985-02-01), None
patent: 2016776 (1990-01-01), None
patent: 4223378 (1992-08-01), None
patent: 5259487 (1993-10-01), None
patent: 6029560 (1994-02-01), None
patent: 6196743 (1994-07-01), None
patent: 6268241 (1994-09-01), None

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