Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2000-10-25
2002-04-30
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S072000, C438S071000, C438S677000
Reexamination Certificate
active
06379995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a solar battery and, more particularly, to a solar battery capable of improving conversion efficiency by reducing received light loss and power transmission loss, and a method of producing the same.
2. Description of the Related Art
FIGS. 12A-12E
are schematic sectional views of producing processes showing an example of a method of producing a solar battery widely used in solar power generation systems for residential buildings. First, a p-type silicon substrate
101
is wet-etched on the surface thereof by using a solution of potassium hydroxide or sodium hydroxide with a concentration in a range from 10% to 50%, thereby forming a texture. Then phosphorus is diffused in the surface of the p-type silicon substrate
101
thereby to form an n-type impurity diffused layer
102
over the entire surface of the p-type silicon substrate
101
, and further an anti-reflective layer
103
made of silicon nitride is formed on the surface of the n-type impurity diffused layer
102
(FIG.
12
A). Then the front surface of the anti-reflective layer
103
is coated with a silver paste by, for example, screen-printing, thereby to form a comb-shaped silver paste electrode
104
′ (FIG.
12
B). Next, the back surface of the p-type semiconductor substrate
101
is coated with an aluminum paste by, for example, screen-printing thereby to form an aluminum paste electrode
105
′ (FIG.
12
C). The silver paste electrode
104
′ and the aluminum paste electrode
105
′ are sintered by firing at a temperature not lower than 600° C., thereby to form a front electrode
104
and a back electrode
105
and complete a solar battery (FIG.
12
D).
During the sintering process, silicon nitride contained in the anti-reflective layer
103
is molten and the silver paste electrode
104
′ penetrates through the anti-reflective layer
103
to reach the n-type impurity diffused layer
102
, thereby establishing electrical continuity between the front electrode
104
and the n-type impurity diffusion layer
102
. This technique is called fire-through process and is disclosed in, for example, Japanese Laid-open Patent Publication No. 10-233581.
FIG. 13
is a schematic perspective view showing the structure of a solar battery produced by the method described above. A plurality of front electrodes
104
having a ridge shape are disposed at predetermined spaces from each other on the surface of the n-type impurity diffused layer
102
, and the anti-reflective layers
103
are disposed on both sides of the ridge-shaped front electrodes
104
. The front electrode formed by the screen-printing process has a cross section of, for example, mountain-like shape 55 &mgr;m in width and about 15 &mgr;m in height (J. Nijs et al.,
First World Conference on Photovoltaic Energy Conversion,
1994, p.1242). The operation of the solar battery will be described below with reference to FIG.
14
. Incident light
106
that has passed through the anti-reflective layer
103
and reached the p-type semiconductor substrate
101
generates a current
107
. The current
107
is collected through the n-type impurity diffused layer
102
to the front electrode
104
, and is taken out of the solar battery through the front electrode
104
. In the drawing, detail of the texture is omitted in order to make the structure of the front electrode easier to comprehend.
As shown in
FIG. 14
, the front electrode
104
is opaque and therefore reflects the incident light
106
on the surface thereof, resulting in reduced light reception area and a loss in received light. Also because the front electrode
104
has an electrical resistance that is inversely proportional to the sectional area thereof, the electrode causes a transmission loss when taking out the current
107
to the outside. Consequently, it is necessary to decrease the width of the front electrode and increase the cross sectional area of the front electrode in order to reduce the received light loss and the transmission loss. For this purpose, the cross-section of the front electrode is preferably small in width and large in height.
However, there has been such a problem that, even when a silver paste electrode having a small width is formed by the screen-printing process or the like on the surface of the anti-reflective layer, the resultant front electrode that is formed has a flat cross section that is large in width. When the ratio of height to width is used as an index of sectional profile of the electrode, the electrode in the case of J. Nijs et al. quoted above has the ratio of height to width as small as 0.27, and it has been difficult to achieve a ratio greater than this value.
The present inventors have found that the cause of the front electrode being formed only in a flat cross section that is large in width is that the silver paste electrode spreads in the crosswise direction after printing.
FIG. 15
is a schematic diagram showing the shape of the silver paste electrode, that was formed by the screen-printing process or the like on the surface of the anti-reflective layer, changing with time. The silver paste electrode
108
′ immediately after being printed spreads with time along the surface of the anti-reflective layer
103
in the crosswise direction by gravity, thereby turning to the flat silver paste electrode
104
′. Although viscosity of the silver paste may be increased in order to restrict the lateral spreading, the increased viscosity increases the time taken to print the silver paste electrode, thus making it difficult to decrease the production cost.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problems described above and provide a solar battery reducing receiver light loss and power transmission loss, and a method of producing the same by controlling the sectional shape of the front electrode.
In order to achieve the object described above, the method of producing a solar battery of the present invention comprises the steps of stacking a semiconductor layer of second conductivity type and an anti-reflective layer on the surface of a semiconductor substrate of first conductivity type, forming a coated-film electrode by applying a coating solution containing an electrode material on the anti-reflective layer, and forming a front electrode that penetrates the anti-reflective layer and electrically connects with the semiconductor layer by firing the coated-film electrode, wherein a water-repellent layer is formed on the anti-reflective layer prior to the formation of the coated-film electrode, the coated-film electrode having a desired fine line is formed by printing the coating solution on the water-repellent layer, so that the coating solution is suppressed from spreading over the surface of the water-repellent layer, and the coated-film electrode of narrow ridge shape is thereby formed.
According to the method of the present invention, since the water-repellent layer is formed on the light receiving surface prior to the formation of the coated-film electrode, and the coated-film electrode is formed on the surface of the water-repellent layer by printing, the coating solution can be prevented from spreading along the surface of the water-repellent layer, thereby making it possible to form the coated-film electrode having small width. Specifically, although the coating solution is forced to spread along the surface of the water-repellent layer by the gravity during printing, the water-repellent layer is difficult to wet with the coating solution and the coating solution contracts to minimize the surface area thereof. Thus the narrow coated-film electrode is formed. The water-repellent layer in the present invention refers to a layer having not only water repellency that is difficult to wet with water solution but also oil repellency that is difficult to wet with an organic solvent. Consequently, a coating solution containing an electrode material and an organic solvent added as a dispersion m
Imada Katsuhiro
Kawama Yoshitatsu
Kojima Kazuyoshi
Morikawa Hiroaki
Leydig , Voit & Mayer, Ltd.
Niebling John F.
Simkovic Viktor
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