Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2000-10-18
2003-04-22
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S249000, C136S252000, C136S262000, C257S461000, C257S443000, C257S448000, C438S073000, C438S074000, C438S093000, C438S514000, C438S518000, C438S519000, C438S526000, C438S527000, C438S531000
Reexamination Certificate
active
06552259
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to solar batteries for converting optical energy into electrical energy and, more particularly, to a bypass-function added solar cell to which is added a bypass-diode function for protecting the solar cell from reverse bias voltage.
Generally, solar cells are used as a solar cell module in which a plurality of solar cells are combined together in series and parallel.
In this solar cell module, when part of the cells are shadowed, voltages generated by other cells are applied to these cells in reverse directions.
For example, in space solar cell modules, there can occur a shadow of part of the satellite body or structures such as antenna onto the solar cell module during the posture control of the satellite. Also, in ground solar cell modules, for example, shadows of neighboring buildings can occur or shadows of attached droppings of birds that have come over flying.
As an example, here is discussed a case where there has occurred a shadow onto part of partial submodules of a solar cell module which is made up of an array of parallel-connected solar cells.
Referring to
FIG. 9A
, in a shunt mode in which both ends of a solar cell module M are nearly short-circuited, a voltage V
12
generated by unshadowed other groups of submodules
312
is applied as a reverse bias voltage to a shadowed submodule
311
. If the voltage of this submodule
311
is V
11
, then
V
11
=−V
12
.
As shown in
FIG. 9B
, when an external power supply V
B
is connected to a solar cell module M, it follows that V
11
=V
B
−V
12
. That is, a positive voltage is applied to an N electrode of the shadowed submodule
311
, where if the reverse bias voltage of the voltage is higher than the breakdown voltage of the solar cells constituting the submodule
311
, the cells would break down, causing a large amount of current to flow. In this case, if a crystal defect or the like is present in a cell, the current concentrates at the place, which may lead to a short-circuit breakdown of the cell occasionally. When this occurs, the shadowed submodule and further the entire solar cell module M are deteriorated in output characteristic.
In order to prevent accidents due to the application of this reverse bias voltage, bypass diodes are attached every solar cell or every particular module units, or so-called diode-integrated solar cells in which bypass diodes are integrated on solar cells are used.
Otherwise, there have been provided solar cells with the bypass diode function added. The structure of a bypass-diode-function added solar cell according to the prior art (Japanese Patent Laid-Open Publication HEI 8-88392) is described below with reference to
FIGS. 4A-4C
.
FIG. 4B
is a plan view showing the structure of this solar cell, and
FIG. 4C
is a sectional view taken along the line
4
C-
4
C′ of FIG.
4
B. In this solar cell, an electrically conductive region for adding a bypass diode function is provided just under the light-receiving side electrode, thus the solar cell being equipped with the bypass-diode function is obtained without reducing the effective area of the light-receiving surface of the solar cell.
As shown in
FIG. 4C
, a light-receiving surface on top of a silicon p-type substrate
101
is covered with a transparent antireflection film
108
, and under the antireflection film
108
, a comb-tooth like n electrode
107
branched from an n-electrode connecting portion
105
, which is a bar electrode, is placed on an n-type region
102
on top of the p-type substrate
101
. Also, as shown in FIGS.
4
B and
4
C, a plurality of island-like p
+
type regions
104
are provided just under the light-receiving electrode
107
with an insulating film
109
interposed therebetween, by which the function of such a bypass diode D as shown in
FIG. 4A
is added.
For this solar cell, as shown in
FIG. 5B
, oxide
110
is formed on the p-type substrate
101
shown in FIG.
5
A. Then a plurality of openings
114
are formed in this oxide
110
as shown in
FIG. 5C
, and a p
+
impurity is injected thereinto, by which the island-like p
+
type regions
104
are formed as shown in FIG.
5
D. Next, as shown in
FIG. 5E
, the n-type region
102
is formed on the top and side surfaces of the p-type substrate
101
by thermal diffusion or the like. Thereafter, as shown in
FIG. 5F
, the insulating film
109
, the n electrode
107
and the n-electrode connecting portion
105
are formed and, further thereon, the antireflection film
108
and a rear-surface p electrode
106
are formed by vacuum deposition or the like. By cutting along both-side broken lines, the solar cell shown in
FIG. 4C
can be obtained.
This solar cell is connected in multiplicity in series and in parallel as shown in
FIG. 9A
so that desired voltage and current can be obtained. This product is used as the solar cell module M, generally.
In order to form the insulating film
109
on a plurality of island-like p
+
-type regions
104
as in the cross-sectional structure shown in
FIG. 4C
, after forming the p
+
-type regions
104
, an insulating film
109
such as oxide is deposited by CVD process (Chemical Vapor Deposition Process) or the like all over the substrate surface. Thereafter, heat treatment such as RTA (Rapid Thermal Anneal) is required to compact this insulating film
109
, and further a step of patterning the insulating film
109
into an island shape on the p
+
-type regions
104
is required. As a result, there has been a problem that the manufacturing cost becomes higher.
Further, a high-precision technique is involved in the patterning of the insulating film
109
in order that the p
+
-type regions
104
do not make contact with the light-receiving electrode
107
. This poses another problem of complicated process.
Meanwhile, a manufacturing method including a steps of providing an electrically conductive type region for adding the bypass-diode function with the ion implantation process is described in Japanese Patent Laid-Open Publication HEI 5-110121. The structure of a solar cell with the bypass-diode function manufactured by this manufacturing method is shown FIG.
6
and
FIGS. 7A
,
7
B and
7
C.
In a bypass-diode function added solar cell as shown in
FIGS. 7A and 7B
, an n-type region
202
is formed on a p-type region
201
and a small island-like p
+
-type region
204
is formed in this n-type region
202
. Further, an n-type electrode connecting portion
205
is formed on this n-type region
202
. In a solar cell shown in
FIG. 7C
, an island-like p
+
-type region
204
is formed in a p-type region
201
, and an n-type electrode connecting portion
205
is formed on the n-type region
202
.
With regard to this solar cell, first, as shown in
FIG. 8B
, oxide film
209
is formed by thermal oxidation or the like all over a silicon p-type substrate
201
shown in FIG.
8
A and then, as shown in
FIG. 8C
, a plurality of openings
214
are formed in the oxide film
209
. Next, a p-type impurity is implanted into the p-type region
201
with the oxide film
209
used as a mask, and thereafter the oxide film
209
is removed, by which an island-like p
+
-type region
204
is formed on top of the p-type substrate
201
as shown in FIG.
8
D. Next, as shown in
FIG. 8E
, the n-type region
202
is formed by thermal diffusion or the like on the top, bottom and side surfaces of the p-type substrate
201
, and further an n electrode connecting portion
205
shown in FIG.
8
F and an n electrode
207
shown in
FIG. 6
are formed, and thereafter an antireflection film
208
and a rear-surface p electrode
206
are formed by vacuum deposition or the like. Finally, by cutting along both-side broken lines, a solar cell having a structure shown in
FIGS. 6 and 7
can be fabricated.
However, in the solar cell shown in
FIGS. 7A and 7B
, there is a problem that the presence of the small island-like p
+
-type region
204
, which is an electrically conductive region for adding the bypass-di
Hisamatsu Tadashi
Hosomi Shigeyuki
Diamond Alan
Nixon & Vanderhye P.C.
LandOfFree
Solar cell with bypass function and multi-junction stacked... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solar cell with bypass function and multi-junction stacked..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solar cell with bypass function and multi-junction stacked... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3016887