Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2000-07-21
2001-12-25
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S258000, C136S261000, C136S256000, C257S053000, C257S458000, C257S459000, C257S466000, C438S085000, C438S098000, C438S096000, C438S057000
Reexamination Certificate
active
06333456
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a silicon solar cell device achieving high conversion efficiency by improving open circuit voltage of the silicon solar cell device and a fabricating method of the same.
BACKGROUND TECHNOLOGY
FIG. 10
is a sectional view showing the structure of a conventional solar cell device
102
.
The solar cell device
102
has a structure in which a transparent oxide electrode
12
is formed on the surface of an insulating substrate
10
which is a transparent glass substrate, and a p-type semiconductor layer
18
, a buffer layer
20
, an intrinsic semiconductor layer
22
, an n-type semiconductor layer
24
, and a metal electrode
26
are laminated in that order on to the surface of the transparent oxide electrode
12
into a laminated structure.
The insulating substrate
10
transmits light incident from the surface on the side thereof (the lower side in the drawing), on which the transparent oxide electrode
12
is not formed, to the transparent oxide electrode
12
.
The transparent oxide electrode
12
is formed to lead light (mainly sunlight) incident through the insulating substrate
10
to the intrinsic semiconductor layer
22
through the p-type semiconductor layer
18
and the buffer layer
20
and to keep ohmic contact with the p-type semiconductor layer
18
.
The p-type semiconductor layer
18
is a layer composed of a p-type semiconductor, which is provided to lead carriers, produced in the intrinsic semiconductor layer
22
by the incident light, to the transparent oxide electrode
12
. The buffer layer
20
functions as a buffer layer for preventing a forbidden band width of the intrinsic semiconductor layer
22
from narrowing due to the mixing of p-type impurities (boron) contained in the p-type semiconductor layer
18
, into the intrinsic semiconductor layer
22
. The intrinsic semiconductor layer
22
is a layer made of an intrinsic semiconductor for producing carriers by absorbing incident light. The n-type semiconductor layer
24
is a layer made of an n-type semiconductor provided to lead the carriers produced in the intrinsic semiconductor layer
22
to the metal electrode
26
. The metal electrode
26
is connected with an interconnection for taking out electromotive force.
Next, the fabricating method of the aforesaid conventional solar cell device will be described using FIG.
11
through FIG.
15
.
First, tin oxide film is formed on the insulating substrate
10
to form a transparent oxide electrode
12
, and thereafter a photoresist
13
is applied on the entire surface of the tin oxide film. The photoresist
13
is exposed and developed with a predetermined mask to remain in a region which is to be the solar cell device
102
.
Next, as shown in
FIG. 11
, the transparent oxide electrode
12
is etched by means of a reactive ion etching system with the above photoresist
13
as an etching mask and with hydrogen iodide (HI) and argon (Ar) used as the raw material gas. Removing the photoresist
13
makes a state where the transparent oxide electrode
12
is provided on the surface of the insulating substrate
10
as shown in FIG.
12
.
Subsequently, the p-type semiconductor layer
18
is formed on the entire surface of the insulating substrate
10
so as to cover the transparent oxide electrode
12
, as shown in
FIG. 13
, by the plasma CVD (chemical-vapor deposition) method. At this time, mono-silane (SiH
4
) and diborane (B
2
H
6
) are used as the raw material gas. Methane gas (CH
4
) is simultaneously introduced to form silicon carbide in the p-type semiconductor layer
18
, thereby preventing the forbidden band width of the p-type semiconductor layer
18
from narrowing and the light conversion efficiency from lowering. Sequentially, the buffer layer
20
is formed over the entire surface of the p-type semiconductor layer
18
. This is carried out by the plasma CVD method with mono-silane (SiH
4
) and methane gas (CH
4
). The intrinsic semiconductor layer
22
is next formed on the entire surface of the buffer layer
20
. This is also carried out by the plasma CVD method with monosilane (SiH
4
) as the raw material gas.
Moreover, as shown in
FIG. 14
, the n-type semiconductor layer
24
is formed on the entire surface of the intrinsic semiconductor layer
22
. This is performed by the plasma CVD method with mono-silane (SiH
4
) and phosphine (PH
3
) as the raw material gas. Thereafter, a metal film
25
which becomes the metal electrode
26
is formed on the entire surface of the n-type semiconductor layer
24
by the sputtering method and a photoresist
15
is applied on the entire surface of the metal film
25
.
The photoresist
15
is exposed and developed with a predetermined mask, as shown in
FIG. 15
, to remain only in a region which is to be the solar cell device
102
. Then, the metal film
25
and the respective layers laminated thereunder are etched and removed by the reactive ion etching method using the photoresist
15
as an etching mask, and the photoresist
15
used for the etching mask is also removed.
Consequently, the solar cell device
102
can be fabricated as shown in
FIG. 10
, in which all layers from the p-type semiconductor layer
18
, the buffer layer
20
, the intrinsic semiconductor layer
22
, the n-type semiconductor layer
24
to the metal electrode
26
are laminated in that order on the transparent oxide electrode
12
.
Incidentally, although the solar cell device
102
in the prior art can be fabricated by the above fabricating method, the solar cell device
102
has a structure using tin oxide as the transparent oxide electrode
12
, and thus it has the following disadvantages regarding the structure. More specifically, tin oxide is a chemically very active substance and has a characteristic of being easy to react with a semiconductor layer laminated on the transparent oxide electrode
12
. Accordingly, interdiffusion of atoms tends to occur between the transparent oxide electrode
12
and the p-type semiconductor layer
18
, and thus there arise disadvantages that transparency of the transparent oxide electrode
12
deteriorates, resulting in a decrease in transmittance and that deterioration in film quality of an amorphous semiconductor layer (especially, the intrinsic semiconductor layer
22
) causes a decrease in open circuit voltage.
Generally, it is required to improve efficiency of converting light to electrical energy as much as possible in a solar cell. Since the conversion efficiency of energy is obtained by the ratio of energy which incident light possesses to the maximum output which is obtained by the product of open circuit voltage and short circuit current, a decrease in open circuit voltage causes a decrease in the maximum output of the solar cell, resulting in a decrease in conversion efficiency of energy. Accordingly, it is an extremely important subject to stabilize the surface of the transparent oxide electrode for the prevention of a decrease in open circuit voltage due to the deterioration of the film quality thereof to thereby improve the output characteristics of the solar cell.
An object of the present invention is to improve output characteristics of a solar cell device including enhancement of open circuit voltage by solving the disadvantages as described above in the solar cell device and the fabricating method of the same.
DISCLOSURE OF THE INVENTION
To achieve the above object, the present invention is characterized by a solar cell device in which a transparent oxide electrode is provided on an insulating substrate, a p-type semiconductor layer, an intrinsic semiconductor layer, and an n-type semiconductor layer are provided over the transparent oxide electrode in that order, and a metal electrode is provided on the n-type semiconductor layer, in which the transparent oxide electrode is provided by being patterned by dry etching and side faces thereof which are not provided with the p-type semiconductor layer are formed in a tapered shape gradually inclined outward from the top end thereof toward the insulating substrate; the transparent oxide
Armstrong Westerman Hattori McLeland & Naughton LLP
Citizen Watch Co. Ltd.
Diamond Alan
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