U.S. patent application number 09/791565 was filed with the patent office on 2001-10-11 for photovoltaic device and method of fabricating the same.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Ishimaru, Hiroshi, Ninomiya, Kunimoto, Sasaki, Manabu, Sayama, Katsunobu, Yata, Shigeo.
Application Number | 20010027803 09/791565 |
Document ID | / |
Family ID | 26586096 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027803 |
Kind Code |
A1 |
Sasaki, Manabu ; et
al. |
October 11, 2001 |
Photovoltaic device and method of fabricating the same
Abstract
Disclosed is a photovoltaic device comprising on a substrate (1)
a plurality of photovoltaic elements (10) each composed of a
lamination body of a first electrode (2), a photovoltaic conversion
layer (3), and a second electrode (4), the thickness of a side end
(B) in the first electrode (2) in the vicinity of a separating
trench (S) existing between the first electrode (2) and the
adjacent first electrode (2) being larger than the thickness of an
element region (A) in the first electrode (2).
Inventors: |
Sasaki, Manabu; (Osaka-shi,
JP) ; Sayama, Katsunobu; (Katano-shi, JP) ;
Ninomiya, Kunimoto; (Hirakata-shi, JP) ; Yata,
Shigeo; (Hirakata-shi, JP) ; Ishimaru, Hiroshi;
(Tondabayashi-shi, JP) |
Correspondence
Address: |
MARK WIECZOREK
Innercool Therapies, Inc.
3931 Sorrento Valley Boulevard
San Diego
CA
92121
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
|
Family ID: |
26586096 |
Appl. No.: |
09/791565 |
Filed: |
February 26, 2001 |
Current U.S.
Class: |
136/249 ;
136/244; 257/443; 438/80 |
Current CPC
Class: |
H01L 31/03762 20130101;
H01L 31/202 20130101; H01L 31/022466 20130101; Y02P 70/521
20151101; H01L 31/022425 20130101; Y02E 10/548 20130101; H01L
31/075 20130101; H01L 31/022483 20130101; H01L 31/02366 20130101;
H01L 31/1884 20130101; Y02P 70/50 20151101 |
Class at
Publication: |
136/249 ;
136/244; 438/80; 257/443 |
International
Class: |
H01L 021/00; H01L
031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2000 |
JP |
49192/2000 |
Feb 14, 2001 |
JP |
36824/2001 |
Claims
What is claimed is:
1. A photovoltaic device comprising: a substrate; a plurality of
first electrodes separated from one another by separating trenches
on the substrate; a photovoltaic conversion layer provided on the
substrate, including the first electrodes; and a plurality of
second electrodes provided on the photovoltaic conversion layer and
separated from one another by second separating trenches, the
thickness of a side end in the first electrode in the vicinity of
the separating trench existing between the first electrode and the
adjacent first electrode being larger than the thickness of an
element region in the first electrode.
2. The photovoltaic device according to claim 1, wherein the first
electrode is composed of zinc oxide.
3. The photovoltaic device according to claim 1, wherein the first
electrode is divided into a plurality of parts by laser beam
irradiation.
4. The photovoltaic device according to claim 2, wherein the
thickness of the side end in the first electrode is not less than
5000 .ANG..
5. The photovoltaic device according to claim 2, wherein the
thickness of the element region in the first electrode is in the
range of approximately 2100 .ANG. to approximately 5000 .ANG..
6. The photovoltaic device according to claim 2, wherein a textured
surface is formed in the element region in the first electrode.
7. The photovoltaic device according to claim 5, wherein the
element region in the first electrode is made thinner than the side
end in the step of forming the textured surface.
8. The photovoltaic device according to claim 1, wherein the
thickness of the side end in the first electrode is larger than the
thickness of the element region by forming a laser beam absorbing
member.
9. A photovoltaic device comprising: a substrate; an insulation
thin film provided in a portion corresponding to an element region
on the substrate; a plurality of first electrodes formed on the
substrate, including the insulation thin film, and separated from
one another by separating trenches; a photovoltaic conversion layer
provided on the substrate, including the first electrodes; and a
plurality of second electrodes provided on the photovoltaic
conversion layer and separated from one another by second
separating trenches, the thickness of a side end in the first
electrode in the vicinity of the separating trench existing between
the first electrode and the adjacent first electrode being larger
than the thickness of the element region in the first
electrode.
10. The photovoltaic device according to claim 9, wherein the first
electrode is composed of zinc oxide.
11. The photovoltaic device according to claim 9, wherein the
insulation thin film is selected from silicon dioxide (SiO.sub.2),
aluminum oxide (Al.sub.2O.sub.3), and titanium oxide
(TiO.sub.2).
12. The photovoltaic device according to claim 10, wherein a
textured surface is formed on a surface of the first electrode.
13. The photovoltaic device according to claim 12, wherein the
element region in the first electrode is made thinner than the side
end in the step of forming the textured surface.
14. A method of fabricating a photovoltaic device comprising on a
substrate a plurality of photovoltaic elements each composed of a
lamination body of a first electrode, a photovoltaic conversion
layer, and a second electrode, comprising the steps of: forming an
electrode film on the substrate; thinning a region serving as an
element region in the electrode film; irradiating laser beams into
a separating region in the electrode film, and removing the
electrode film in a portion irradiated with the laser beams, to
form a plurality of first electrodes in a separated manner.
15. The method according to claim 14, wherein the electrode film is
composed of zinc oxide.
16. The method according to claim 14, wherein the electrode film is
formed to a thickness of not less than 5000 .ANG..
17. The method according to claim 14, wherein in the step of
thinning the region serving as the element region in the electrode
film, the thickness of the region serving as the element region is
in the range of approximately 2100 .ANG. to approximately 5000
.ANG..
18. The method according to claim 14, wherein in the step of
thinning the region serving as the element region in the electrode
film, a textured surface is formed on a surface of the region
serving as the element region.
19. The method according to claim 14, wherein the step of thinning
the region serving as the element region in the electrode film is
carried out after the step of forming the plurality of first
electrodes in a separated manner.
20. A method of fabricating a photovoltaic device comprising on a
substrate a plurality of photovoltaic elements each composed of a
lamination body of a first electrode, a photovoltaic conversion
layer, and a second electrode, comprising the steps of: forming an
electrode film on the substrate; providing a laser beam absorbing
member on a separating region in the electrode film; and
irradiating laser beams into the laser beam absorbing member,
removing the laser beam absorbing member in a portion irradiated
with the laser beams, together with the electrode film just below
the laser beam absorbing member, to form a plurality of first
electrodes in a separated manner.
21. The method according to claim 20, wherein the electrode film is
formed of zinc oxide, and is formed to a thickness of approximately
2100 .ANG. to approximately 5000 .ANG..
22. A method of fabricating a photovoltaic device comprising on a
substrate a plurality of photovoltaic elements each composed of a
lamination body of a first electrode, a photovoltaic conversion
layer, and a second electrode, comprising the steps of: forming an
insulation thin film in a region corresponding to an element region
on the substrate; forming an electrode film on the substrate,
including the insulation thin film; etching the electrode film, to
make the electrode film serving as an element region positioned on
the insulation thin film thinner than the electrode film positioned
in the other region; and irradiating laser beams into a separating
region in the electrode film, and removing the electrode film in a
portion irradiated with the laser beams, to form a plurality of
first electrodes in a separated manner.
23. The method according to claim 22, wherein the electrode film is
formed of zinc oxide.
24. The method according to claim 23, wherein the insulation thin
film is selected from silicon dioxide (SiO.sub.2), aluminum oxide
(Al.sub.2O.sub.3), and titanium oxide (TiO.sub.2).
25. The method according to claim 22, wherein the electrode film is
formed to a thickness of not less than 5000 .ANG..
26. The method according to claim 22, wherein in the step of
thinning the region serving as the element region in the electrode
film, the thickness of the region serving as the element region is
in the range of approximately 3500 .ANG. to approximately 5500
.ANG..
27. The method according to claim 22, wherein in the step of
thinning the region serving as the element region in the electrode
film, a textured surface is formed on a surface of the electrode
film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention particularly provides, in a
photovoltaic device comprising a first electrode composed of zinc
oxide, a photovoltaic device whose characteristics are improved,
and a method of fabricating the same.
[0003] 2. Description of Prior Art
[0004] Photovoltaic devices composed of an amorphous semiconductor
such as amorphous silicon, amorphous silicon carbide, or amorphous
silicon germanium are low in fabrication cost and can be easily
increased in area. Accordingly, the photovoltaic devices have been
developed as low-cost solar cells.
[0005] Referring to a cross-sectional view of FIG. 18, description
is made of a photovoltaic element composed of an amorphous
semiconductor. A photovoltaic element 10 composed of an amorphous
semiconductor comprises a first electrode 2, a photovoltaic
conversion layer 3 composed of a lamination body of p-type, i-type,
and n-type amorphous semiconductor layers 3p, 3i, and 3n, and a
second electrode 4 laminated in this order on a substrate 1. When a
translucent member such as glass or plastic is used as the
substrate 1, the first electrode 2 is composed of a translucent
conductive material, and the second electrode 4 is composed of a
highly reflective conductive material.
[0006] As the translucent conductive material composing the first
electrode 2, tin oxide (SnO.sub.2) has been conventionally used.
However, it has been examined whether or not zinc oxide (ZnO) is
used in order to achieve low cost in recent years, so that a
photovoltaic element having high photovoltaic conversion
characteristics has been obtained.
[0007] For example, a first electrode 2 composed of ZnO is formed
by sputtering on a substrate 1 composed of glass, a photovoltaic
conversion layer 3 composed of a lamination body of a p-type layer
3p having a thickness of approximately 150 .ANG. composed of p-type
amorphous silicon carbide, an i-type layer 3i having a thickness of
approximately 4000 .ANG. composed of i-type amorphous silicon, and
an n-type layer 3n having a thickness of approximately 200 .ANG.
composed of n-type amorphous silicon is then formed by plasma CVD
(Chemical Vapor Deposition), and a second electrode 4 composed of
Ag is laminated using sputtering, thereby fabricating a
photovoltaic element 10.
[0008] As a result of changing the thickness of the first electrode
2 to various thicknesses to measure photovoltaic conversion
efficiency, high photovoltaic conversion efficiency in excess of
10.5% is obtained in a case where the thickness of the first
electrode 2 composed of ZnO is in the range of approximately 2100
.ANG. to approximately 5000 .ANG., as shown in a characteristic
view of FIG. 19.
SUMMARY OF THE INVENTION
[0009] In a photovoltaic element using ZnO for a first electrode,
however, high photovoltaic conversion efficiency is obtained, as
described above. In the case of an integrated photovoltaic device,
sufficient characteristics are not obtained.
[0010] The present invention has been made in order to solve such a
conventional problem, and its object is to provide a photovoltaic
device capable of obtaining superior photovoltaic conversion
characteristics when ZnO is used for a first electrode and a method
of fabricating the same.
[0011] A photovoltaic device according to the present invention is
characterized by comprising a substrate; a plurality of first
electrodes separated from one another by separating trenches on the
substrate; a photovoltaic conversion layer provided on the
substrate, including the first electrodes; and a plurality of
second electrodes provided on the photovoltaic conversion layer and
separated from one another by second separating trenches, and in
that the thickness of a side end in the first electrode in the
vicinity of the separating trench existing between the first
electrode and the adjacent first electrode is larger than the
thickness of an element region in the first electrode.
[0012] According to such construction, a portion irradiated with
laser beams for forming the separating trench is formed to a
thickness larger than the thickness of the element region. As a
result, the first electrodes can be formed in a separated manner
with a high yield, thereby making it possible to provide a
photovoltaic device having high photovoltaic conversion
characteristics.
[0013] The photovoltaic device is characterized in that the first
electrode is composed of zinc oxide, is characterized in that the
thickness of the side end in the first electrode is not less than
5000 .ANG., and is characterized in that the thickness of the
element region in the first electrode is in the range of
approximately 2100 .ANG. to approximately 5000 .ANG..
[0014] Furthermore, the photovoltaic device is characterized in
that a textured surface is formed in the element region in the
first electrode, and is characterized in that the element region in
the first electrode is made thinner than the side end in the step
of forming the textured surface.
[0015] Alternatively, the photovoltaic device is characterized in
that the thickness of the side end in the first electrode is larger
than the thickness of the element region by forming a laser beam
absorbing member.
[0016] As described in the foregoing, the thickness of the side end
in the vicinity of the separating trench in the first electrode is
made larger than the thickness of the element region by providing
the laser beam absorbing member on the first electrode. As a
result, the first electrodes can be formed in a separated manner
with a high yield, thereby making it possible to provide a
photovoltaic device having high photovoltaic conversion
characteristics.
[0017] In addition thereto, the photovoltaic device is
characterized in that the first electrode is divided into a
plurality of parts by laser beam irradiation.
[0018] The present invention is directed to a photovoltaic device,
characterized by comprising a substrate; an insulation thin film
provided in a portion corresponding to an element region on the
substrate; a plurality of first electrodes formed on the substrate,
including the insulation thin film, and separated from one another
by separating trenches; a photovoltaic conversion layer provided on
the substrate, including the first electrodes; and a plurality of
second electrodes provided on the photovoltaic conversion layer and
separated from one another by second separating trenches, and in
that the thickness of a side end in the first electrode in the
vicinity of the separating trench existing between the first
electrode and the adjacent first electrode is larger than the
thickness of the element region in the first electrode.
[0019] According to such construction, the portion irradiated with
the laser beams for forming the separating trench is formed to a
thickness larger than the thickness of the element region. Further,
it has a good film orientation. As a result, the first electrodes
can be formed in a separated manner with a high yield, thereby
making it possible to provide a photovoltaic device having high
photovoltaic conversion characteristics.
[0020] The photovoltaic device is characterized in that the first
electrode is composed of zinc oxide, and is characterized in that
the insulation thin film is selected from silicon dioxide
(SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), and titanium oxide
(TiO.sub.2).
[0021] The photovoltaic device is characterized in that the element
region in the first electrode is made thinner than the side end in
the step of forming the textured surface.
[0022] A method of fabricating a photovoltaic device according to
the present invention is a method of fabricating a photovoltaic
device comprising on a substrate a plurality of photovoltaic
elements each composed of a lamination body of a first electrode, a
photovoltaic conversion layer, and a second electrode,
characterized by comprising the steps of forming an electrode film
on the substrate; thinning a region serving as an element region in
the electrode film; irradiating laser beams into a separating
region in the electrode film, and removing the electrode film in a
portion irradiated with the laser beams, to form a plurality of
first electrodes in a separated manner.
[0023] According to the above-mentioned construction, the portion
irradiated with the laser beams for forming the separating trench
is formed to a thickness larger than that of the element region. As
a result, the first electrodes can be formed in a separated manner
with a high yield, thereby making it possible to provide a
photovoltaic device having high photovoltaic conversion
characteristics.
[0024] The method is characterized in that the electrode film is
composed of zinc oxide, is characterized in that the electrode film
is formed to a thickness of not less than 5000 .ANG., and is
characterized in that in the step of thinning the region serving as
the element region in the electrode film, the thickness of the
region serving as the element region is in the range of
approximately 2100 .ANG. to approximately 5000 .ANG..
[0025] Furthermore, the method is characterized in that in the step
of thinning the region serving as the element region in the
electrode film, a textured surface is formed on a surface of the
region serving as the element region, and is characterized in that
the step of thinning the region serving as the element region in
the electrode film is carried out after the step of forming the
plurality of first electrodes in a separated manner.
[0026] Alternatively, the present invention is directed to a method
of fabricating a photovoltaic device comprising on a substrate a
plurality of photovoltaic elements each composed of a lamination
body of a first electrode, a photovoltaic conversion layer, and a
second electrode, characterized by comprising the steps of forming
an electrode film on the substrate; providing a laser beam
absorbing member on a separating region in the electrode film; and
irradiating laser beams into the laser beam absorbing member,
removing the laser beam absorbing member in a portion irradiated
with the laser beams, together with the electrode film just below
the laser beam absorbing member, to form a plurality of first
electrodes in a separated manner. According to the above-mentioned
construction, the thickness of the side end in the vicinity of the
separating trench in the first electrode can be made larger than
the thickness of the element region by providing the laser beam
absorbing member on the first electrode. As a result, the first
electrodes can be formed in a separated manner with a high yield,
thereby making it possible to provide a photovoltaic device having
high photovoltaic conversion characteristics.
[0027] Furthermore, the method is characterized in that the
electrode film is formed of zinc oxide, and is formed to a
thickness of approximately 2100 .ANG. to approximately 5000
.ANG..
[0028] A method of fabricating a photovoltaic device according to
the present invention is a method of fabricating a photovoltaic
device comprising on a substrate a plurality of photovoltaic
elements each composed of a lamination body of a first electrode, a
photovoltaic conversion layer, and a second electrode,
characterized by comprising the steps of forming an insulation thin
film in a region corresponding to an element region on the
substrate; forming an electrode film on the substrate, including
the insulation thin film; etching the electrode film, to make the
electrode film serving as an element region positioned on the
insulation thin film thinner than the electrode film positioned in
the other region; and irradiating laser beams into a separating
region in the electrode film, and removing the electrode film in a
portion irradiated with the laser beams, to form a plurality of
first electrodes in a separated manner.
[0029] As described in the foregoing, when the insulation thin film
is selectively provided on the substrate, the crystallizability of
the first electrode which is directly formed on the substrate is
higher than that of the first electrode which is formed on the
insulation thin film. When etching using a solution of hydrochloric
acid (HC1) or a solution of acetic acid (CH.sub.3COOH) is
performed, therefore, the first electrode in the element region is
etched faster than the first electrode at the side end. As a
result, the thickness of the side end is made larger than the
thickness of the element region. The portion irradiated with the
laser beams for forming the separating trench is formed to a
thickness larger than that of the element region. Further, it has a
good film orientation. As a result, the first electrodes can be
formed in a separated manner with a high yield, thereby making it
possible to provide a photovoltaic device having high photovoltaic
conversion characteristics.
[0030] The method is characterized in that the electrode film is
formed of zinc oxide, and is characterized in that the insulation
thin film is selected from silicon dioxide (SiO.sub.2), aluminum
oxide (Al.sub.2O.sub.3), and titanium oxide (TiO.sub.2).
[0031] The method is characterized in that in the step of thinning
the region serving as the element region in the electrode film, the
thickness of the region serving as the element region is in the
range of approximately 3500 .ANG. to approximately 5500 .ANG., and
a textured surface is formed on a surface of the electrode
film.
[0032] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a cross-sectional view of a photovoltaic device
according to a first embodiment of the present invention;
[0034] FIG. 2 is a cross-sectional view by steps for explaining a
method of fabricating the photovoltaic device according to the
first embodiment of the present invention;
[0035] FIG. 3 is a cross-sectional view of a photovoltaic device
according to a second embodiment of the present invention;
[0036] FIG. 4 is a cross-sectional view by steps for explaining a
method of fabricating the photovoltaic device according to the
second embodiment of the present invention;
[0037] FIG. 5 is a characteristic view showing, in an integrated
photovoltaic device using ZnO for a first electrode, the
relationship between the thickness of the first electrode and a
low-illuminance voltage;
[0038] FIG. 6 is a cross-sectional view of a photovoltaic device
according to a third embodiment of the present invention;
[0039] FIG. 7 is a characteristic view showing the X-ray
diffraction peak intensity of a ZnO film;
[0040] FIG. 8 is a characteristic view showing the relationship
between the X-ray diffraction peak intensity ratio of a ZnO film
and the average of low-illuminance voltages;
[0041] FIG. 9A is a cross-sectional view showing a laser processing
region in the photovoltaic device according to the third embodiment
of the present invention;
[0042] FIG. 9B is a characteristic view showing the X-ray
diffraction peak intensity in an element region in the photovoltaic
device according to the third embodiment of the present
invention;
[0043] FIG. 9C is a characteristic view showing the X-ray
diffraction peak intensity in a laser processing region in the
photovoltaic device according to the third embodiment of the
present invention;
[0044] FIG. 10 is a characteristic view showing the relationship
between the X-ray diffraction peak intensity ratio of a ZnO film
and standardized current;
[0045] FIG. 11 is a characteristic view showing the relationship
between the X-ray diffraction peak intensity ratio of a ZnO film
and a standardized file factor;
[0046] FIG. 12 is a characteristic view showing the relationship
between the X-ray diffraction peak intensity ratio of a ZnO film
and the product of standardized current and a standardized file
factor;
[0047] FIG. 13 is a cross-sectional view showing the laser
processing region in the photovoltaic device according to the third
embodiment of the present invention;
[0048] FIG. 14 is a characteristic view showing the relationship
between the etching time and the thickness of a ZnO film in the
photovoltaic device according to the third embodiment of the
present invention;
[0049] FIG. 15 is a characteristic view showing the relationship
between the etching time and the product of standardized current
and a standardized file factor in the photovoltaic device according
to the third embodiment of the present invention;
[0050] FIG. 16 is a cross-sectional view by steps for explaining a
method of fabricating the photovoltaic device according to the
third embodiment of the present invention;
[0051] FIG. 17 is a cross-sectional view by steps for explaining a
method of forming an insulation thin film in a predetermined region
on a substrate;
[0052] FIG. 18 is a cross-sectional view of the element structure
of a photovoltaic element;
[0053] FIG. 19 is a characteristic view showing, in a photovoltaic
element using ZnO for a first electrode, the relationship between
the thickness of the first electrode and photovoltaic conversion
efficiency;
[0054] FIG. 20 is a cross-sectional view of a conventional
photovoltaic device; and
[0055] FIG. 2 1 is a characteristic view showing, in a photovoltaic
element using ZnO for a first electrode, the relationship between
the thickness of the first electrode and the yield.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0056] The premise of the present invention will be first
described.
[0057] The inventors and others of the present invention have first
examined the reason why characteristics are degraded in the case of
an integrated photovoltaic device irrespective of the fact that
high photovoltaic conversion efficiency is obtained in a
photovoltaic element of one cell using a first electrode composed
of ZnO, as described above.
[0058] Description is made of the construction of the integrated
photovoltaic device with reference to a cross-sectional view of
FIG. 20. In FIG. 20, portions having the same functions as those
shown in FIG. 18 are assigned the same reference numerals.
[0059] Referring to FIG. 20, a photovoltaic device 100 has a
structure in which a plurality of photovoltaic elements 10 are
arranged side by side on a substrate 1, and a first electrode 2 in
one of the adjacent photovoltaic elements 10 and a second electrode
4 in the other photovoltaic element 10 are electrically connected
to each other. According to such an integrated structure, the
plurality of photovoltaic elements 10 are electrically connected in
series or in parallel, thereby making it possible to take out an
arbitrary output voltage by one substrate.
[0060] The photovoltaic device 100 having such a structure is
generally fabricated using laser patterning. For example, a
translucent conductive film is formed on an approximately entire
surface of the substrate 1, and is divided into a plurality of
first electrodes 2 by laser patterning.
[0061] p-type, i-type, and n-type amorphous semiconductor layers
are laminated in this order on the approximately entire surface of
the substrate 1, including the plurality of first electrodes 2, and
the amorphous semiconductor layer is then divided using laser
patterning, to form a plurality of photovoltaic conversion layers
3. Finally, a highly reflective conductive film is formed on an
approximately entire surface of the substrate 1, including the
plurality of photovoltaic conversion layers 3, and is divided into
a plurality of second electrodes 4 by laser patterning. By the
foregoing steps, a photovoltaic device having the structure shown
in FIG. 20 is fabricated. Generally used as laser beams used for
such laser patterning are YAG lasers having a wavelength of 1.06
.mu.m.
[0062] As described in the foregoing, in the photovoltaic element
using the first electrode composed of ZnO, high photovoltaic
conversion efficiency in excess of 10.5% can be obtained by setting
the thickness of the first electrode in the range of approximately
2100 .ANG. to approximately 5000 .ANG.. However, the first
electrode does not sufficiently absorb the laser beams when it has
such a thickness. It is considered that a ZnO film which is a
translucent conductive film is not electrically separated
completely in forming the plurality of first electrodes in a
separated manner by laser patterning.
[0063] Therefore, the inventors and others have formed ZnO films
having various thicknesses on a glass substrate, have divided each
of the ZnO films into two electrodes by laser patterning, and have
measured resistance between both the electrodes, to examine the
relationship between the yield in a case where the ZnO film in
which the resistance between the electrodes is not less than 10 MQ
is taken as an acceptable product and the thickness of the ZnO
film. The results of the examination are shown in a characteristic
view of FIG. 21. The separating width between the two electrodes is
set to approximately 100 .mu.m which is approximately the same as
that in a case where the ZnO film is used for the integrated
photovoltaic device. As apparent from the result, a good yield of
not less than 90% is obtained when the thickness of the ZnO film is
not less than 5000 .ANG.. However, the yield is lowered when the
thickness of the ZnO film is decreased, and only a low yield of not
more than 40% is obtained when it is not more than 4500 .ANG..
[0064] Furthermore, the inventors and others of the present
invention have changed, in the integrated photovoltaic device, the
thickness of the ZnO film on the glass substrate in the range of
3000 .ANG. to 12000 .ANG., have divided the ZnO film into a
plurality of electrodes by laser patterning, and have formed the
photovoltaic conversion layers 3 and the second electrodes 4 on the
plurality of electrodes by the above-mentioned method, to fabricate
the integrated photovoltaic device having the structure shown in
FIG. 20.
[0065] At this time, the laser power density at the time of laser
patterning of the ZnO film has been also changed. Results of
measurement of the average of low-illuminance voltages in the
integrated photovoltaic device fabricated under a plurality of
conditions are shown in FIG. 5 and in the following Table 1.
1 TABLE 1 average low-illuminance voltage (V) laser power laser
power laser power thickness of density density density ZnO (.ANG.)
4 .times. 10.sup.7 W/cm.sup.2 3.2 .times. 10.sup.7 W/cm.sup.2 2.4
.times. 10.sup.7 W/cm.sup.2 12000 1.2 1.2 1.2 11000 1.2 1.2 1.2
10000 1.2 1.2 1.2 9000 1.2 1.2 1.2 8000 1.2 1.2 1.2 7000 0.9 1.2
1.2 6000 0.8 1.2 1.2 5000 0.1 0.3 1.2 4000 0.05 0.05 1.2 3000 0.05
0.05 0.8
[0066] From Table 1 and FIG. 5, it is considered that it is
effective in improving the yield to increase the thickness of the
ZnO film in a laser processing portion and decrease the laser power
density.
[0067] From the results of the foregoing preliminary experiments,
in the photovoltaic element using the first electrode composed of
ZnO, high photovoltaic conversion efficiency in excess of 10.5% is
obtained by setting the thickness of the first electrode in the
range of approximately 2100 .ANG. to approximately 5000 .ANG.,
while electrical separation is not sufficiently made in the case of
laser patterning when the first electrode has such a thickness.
Therefore, it is presumed that when the integrated photovoltaic
device is fabricated, the characteristics thereof are degraded.
[0068] The present invention provides a photovoltaic device capable
of obtaining superior photovoltaic conversion characteristics in a
case where ZnO is used for a first electrode and a method of
fabricating the same on the basis of such consideration.
[0069] Embodiments of the present invention will be described with
reference to the drawings.
[0070] FIG. 1 is a cross-sectional view for explaining a
photovoltaic device according to an embodiment of the present
invention. FIG. 2 is a cross-sectional view by steps for explaining
a method of fabricating the photovoltaic device shown in FIG. 1. In
FIGS. 1 and 2, portions having the same functions as those shown in
FIG. 20 are assigned the same reference numerals.
[0071] As shown in FIG. 1, adjacent first electrodes 2 are
separated from each other by a separating trench S. In a
photovoltaic device 100 according to the present embodiment, the
thickness of a side end B positioned in the vicinity of the
separating trench S in the first electrode 2 is made larger than
the thickness of an element region A. That is, according to such
construction, a portion irradiated with laser beams for forming the
separating trench S is formed to a thickness larger than that of
the element region A. As a result, the first electrodes 2 can be
formed in a separated manner with a high yield, thereby making it
possible to provide a photovoltaic device having high photovoltaic
conversion characteristics.
[0072] In a case where the first electrode 2 is composed of ZnO,
for example, if the thickness of the side end B is not less than
5000 .ANG., the first electrodes 2 can be formed in a separated
manner with a high yield by irradiating laser beams. In addition,
the thickness of the element region A is set in the range of
approximately 2100 .ANG. to approximately 5000 .ANG., thereby
making it possible to obtain high photovoltaic conversion
characteristics. According to the present invention, it is possible
to provide a photovoltaic device having high photovoltaic
conversion characteristics with a high yield.
[0073] Referring to FIG. 2, a method of fabricating the
photovoltaic device according to the present embodiment will be
described. In the first step shown in FIG. 2A, a translucent
conductive film 21 composed of zinc oxide (ZnO) is first formed on
an approximately entire surface of a substrate 1 composed of a
material having a translucent and insulating surface, for example,
glass or plastic.
[0074] In the second step shown in FIG. 2B, a portion serving as an
element region A of the conductive film 21 is then thinned. The
thinning can be performed by subjecting the conductive film 21 to
etching such as wet etching or dry etching in a state where a
removal region C including a portion to be removed in the
conductive film 21 by laser beam irradiation is masked by a resist
film, for example, in the third step, described below.
[0075] In the third step shown in FIG. 2C, laser beams L are then
irradiated into the removal region C having a large thickness. The
conductive film 21 in a portion irradiated with the laser beams L
is removed to form a separating trench S and form a plurality of
first electrodes 2 in a separated manner. In the laser patterning,
Nd: YAG lasers having a wavelength of 1.06 .mu.m and having a pulse
frequency of 3 kHz are used as the laser beams L, and are
irradiated into the removal region C in the conductive film 21 at a
laser power density of 4.times.10.sup.7 W/cm.sup.2 and at a
processing rate of 10 mm/sec. from the side of the substrate 1. The
laser power density is such intensity that the glass substrate is
not affected by heat.
[0076] Furthermore, in the fourth step shown in FIG. 2D, p-type,
i-type, and n-type amorphous semiconductor lasers are formed in
this order on the substrate 1, including the plurality of first
electrodes 2, by plasma CVD. Then a plurality of photovoltaic
conversion layers 3 are formed in a separated manner by laser
patterning. Each of the photovoltaic conversion layers 3 is formed
using a known parallel plate-type plasma CVD device. The discharge
electrode area is 1500 cm.sup.2, and the spacing between the
electrodes is 40 mm. Further, the laser patterning is performed at
a laser power density of 2.times.10.sup.7 W/cm.sup.2 and at a
processing rate of 10 mm/sec. using YAG laser secondary harmonics
having a wavelength of 0.53 .mu.m and having a pulse frequency of 3
kHz.
[0077] Finally, a metal film such as an Ag film or an Al film is
formed on the substrate 1, including the photovoltaic conversion
layers 3, by sputtering, and a plurality of second electrodes 4 are
then formed in a separated manner by laser patterning, to fabricate
the photovoltaic device shown in FIG. 1.
[0078] In the present invention, the A1 film is formed to a
thickness of 4000 .ANG. as a metal film by DC magnetron sputtering.
As forming conditions, the substrate temperature is 200.degree. C.,
Ar gas is caused to flow at a flow rate of 400 sccm, and a power of
0.1 kW is applied to an Al target having an area of 300 cm.sup.2
under a 1Pa atmosphere. Further, the laser patterning is performed
at a laser power density of 2.times.10.sup.7 W/cm.sup.2 and at a
processing rate of 10 mm/sec. using YAG laser secondary harmonics
having a wavelength of 0.53 .mu.m and having a pulse frequency of 3
kHz.
[0079] In such a fabricating method, when the first electrode 2,
for example, is composed of ZnO, the conductive film 21 composed of
ZnO is formed to a thickness of not less than 5000 .ANG. in the
first step. In the second step, the element region A is then
thinned to a thickness in the range of approximately 2100 .ANG. to
approximately 5000 .ANG..
[0080] According to such a method, the removal region C composed of
ZnO having a thickness of not less than 5000 .ANG. is irradiated
with the laser beams in the third step. Accordingly, the first
electrodes 2 can be formed in a separated manner with a high yield.
Further, the thickness of the element region A is in the range of
approximately 2100 .ANG. to approximately 5000 .ANG., thereby
making it possible to obtain high photovoltaic conversion
characteristics.
[0081] Furthermore, when the thinning in the second step is
performed by etching using a solution of hydrochloric acid (HCl) or
a solution of acetic acid (CH.sub.3COOH), an irregular surface
serving as a texture plane can be formed on a surface of the
element region A. According to this method, therefore, the
irregular surface serving as the texture plane can be formed on the
surface of the element region A simultaneously with the thinning of
the element region A, thereby making it possible to fabricate a
photovoltaic device having superior photovoltaic conversion
characteristics in a simple process.
[0082] Although in the above-mentioned fabricating method, after
the element region A is thinned, the laser beams L1 are irradiated
into the removal region C, to form the plurality of first
electrodes 2 in a separated manner, the element region A may be
thinned after the laser beams L1 are previously irradiated into the
removal region C to form the plurality of first electrodes 2 in a
separated manner.
[0083] For example, after the ZnO film 21 is formed to a thickness
of not less than 5000 .ANG. on the substrate 1, and the plurality
of first electrodes 2 are separated by laser beam irradiation, the
element region A may be thinned to a thickness in the range of
approximately 2100 .ANG. to approximately 5000 .ANG.. According to
such construction, even if the conductive film is not sufficiently
removed by laser beam irradiation so that the conductive film
remains in the separating trench S, the residual is removed by
etching in the subsequent step. Accordingly, electrical separation
is made more complete, thereby obtaining a more preferable
effect.
[0084] (Second Embodiment)
[0085] A photovoltaic device according to a second embodiment of
the present invention will be described with reference to a
structural sectional view of FIG. 3. Portions having the same
functions as those in the first embodiment are assigned the same
reference numerals and hence, the description thereof is not
repeated in order to avoid the overlapping of the description.
[0086] In the present embodiment, the thickness of a side end B in
the vicinity of a separating trench S in a first electrode 2 is
made larger than the thickness of an element region A by providing
a laser beam absorbing member 51 on the first electrode 2. Also in
such construction, the same effect as that in the above-mentioned
first embodiment is produced.
[0087] FIG. 4 is a cross-sectional view by steps for explaining a
method of fabricating a photovoltaic device according to the
present embodiment.
[0088] In the first step shown in FIG. 4A, a translucent conductive
film 21 is first formed on a substrate 1. When the conductive film
21 is formed using ZnO, it is formed to a thickness in the range of
approximately 2100 .ANG. to approximately 5000 .ANG..
[0089] In the second step shown in FIG. 4B, a laser beam absorbing
member 51 is then formed on a removal region C of the conductive
film 21. The laser beam absorbing member 51 may be composed of a
material having conductive properties or a material having
insulating properties, provided that the material absorbs laser
beams. When YAG lasers having a wavelength of 1.06 .mu.m are used
as laser beams, for example, the laser beam absorbing member 51 can
be composed of a material with low surface reflection, for example,
titanium or carbon. Alternatively, a conductive oxide such as tin
oxide (SnO.sub.2) or ]TO (Indium Tin Oxide) may be used as the
laser beam absorbing member 51.
[0090] In the third step shown in FIG. 4C, the laser beam absorbing
member 51 is then irradiated with laser beams L, and the laser beam
absorbing member 51 in a portion irradiated with the laser beams L
and the conductive film 21 positioned just below the
laser-irradiated portion of the laser beam absorbing member 51 are
simultaneously removed, thereby forming a separating trench S as
well as forming a plurality of first electrodes 2 in a separated
manner.
[0091] A plurality of photovoltaic conversion layers 3 and second
electrodes 4 are formed, as in the first embodiment, thereby making
it possible to fabricate a photovoltaic device having the structure
shown in FIG. 3.
[0092] Also in the present embodiment, it is possible to provide a
photovoltaic device having superior photovoltaic characteristics
with a high yield, as in the above-mentioned first embodiment.
[0093] (Third Embodiment)
[0094] A photovoltaic device according to a third embodiment of the
present invention will be described with reference to FIGS. 6 to
16. FIG. 6 is a structural sectional view showing a photovoltaic
device according to a third embodiment of the present invention.
Portions having the same functions as those in the first embodiment
are assigned the same reference numerals and hence, the description
thereof is not repeated in order to avoid the overlapping of the
description.
[0095] Furthermore, the inventors and others have examined what
effect is exerted by the orientation of a ZnO film serving as a
first electrode at the time of laser patterning. As the ZnO film to
be formed on a glass substrate 1, ZnO films respectively having
thicknesses fixed to 5000 .ANG. and having different orientations
are formed. The laser processing power is fixed to 80 mW, to
measure the average of low-illuminance voltages in an integrated
photovoltaic device in a case where a first electrode is
divided.
[0096] The orientation is measured by examining an X-ray
diffraction pattern of the formed ZnO film and changing the X-ray
diffraction peak intensity ratio I thereof. That is, the ZnO film
has X-ray diffraction peaks, respectively, in a (002) plane and a
(004) plane, as shown in FIG. 7. The (002) plane is a plane having
good crystallizability. The intensity means the number of electrons
(the unit is count) in a case where when the angle of incidence
.theta. of X-rays is continuously changed while rotating a sample
in X-ray diffractometry, the position of a detector is rotated
while being optically related such that the angle of the diffracted
X-rays is 2 .theta., to detect the X-rays diffracted and emitted
from a surface of the sample.
[0097] This indicates that the higher the ratio of the intensity in
the (002) plane to the intensity in the (004) plane, that is, the
X-ray diffraction peak intensity ratio I {(002)/(004)} is, the
better the orientation is. The X-ray diffraction peak intensity
ratio is changed depending on conditions such as sputter forming
temperature.
[0098] FIG. 8 shows the results of measurement of the average of
low-illuminance voltages in the integrated photovoltaic device in a
case where the X-ray diffraction peak intensity ratio I is changed
to form a ZnO film serving as a first electrode 2, and the ZnO film
is divided at a laser processing power of 80 mW. The thickness of
the ZnO film is fixed to 6000 .ANG..
[0099] As can be seen from FIG. 8, when the X-ray diffraction peak
intensity ratio I is not less than 40, good values are obtained in
all stages of the integrated photovoltaic device, and the laser
processing yield is improved.
[0100] Furthermore, it is known that the ZnO film having a high
orientation has a low etching rate. In the third embodiment,
therefore, the ZnO film having a high orientation is formed only in
a processing region to be subjected to laser patterning, and the
thickness of the ZnO film is changed by etching. That is, the
thickness of the region to be subjected to laser patterning is made
larger than the thickness of an element region A, thereby improving
the laser processing yield.
[0101] According to such construction, a portion irradiated with
laser beams for forming a separating trench S is formed to a
thickness larger than that of the element region A. Further, it has
a good film orientation. As a result, first electrodes can be
formed in a separated manner with a high yield, thereby making it
possible to provide a photovoltaic device having high photovoltaic
conversion characteristics.
[0102] As shown in FIG. 6, the adjacent first electrodes 2 are
separated by the separating trench S. In the photovoltaic device
100 according to the third embodiment, an insulation thin film 22
is formed in the element region A. Used as the insulation thin film
21 is silicon dioxide (SiO.sub.2), aluminum oxide
(Al.sub.2O.sub.3), or titanium oxide (TiO.sub.2). Further, no
insulation thin film is provided at a side end B positioned in the
vicinity of the separating trench S, that is, in a portion
corresponding to a laser processing portion.
[0103] After the insulation thin film 22 is selectively provided on
the substrate 1, the ZnO film serving as the first electrode 2 is
thus formed by sputtering. The crystallizability of the ZnO film
formed by sputtering, which is directly formed on the glass
substrate 1, is higher than that of the ZnO film which is formed on
the insulation thin film 22.
[0104] When etching using a solution of hydrochloric acid (HCl) or
a solution of acetic acid (CH.sub.3COOH) is made, therefore, a ZnO
film 23 in the element region A is etched faster than a ZnO film 24
at the side end B. As a result, the thickness of the side end B is
made larger than the thickness of the element region A. Further,
irregular surfaces serving as texture planes are formed on
respective surfaces of the ZnO films.
[0105] As described in the foregoing, the thickness of the ZnO film
24 at the side end B is made larger than the thickness of the ZnO
film 23 in the element region A by the etching, so that the
thickness of the ZnO film in only the laser processing portion can
be increased. That is, according to such construction, the portion
irradiated with laser beams for forming the separating trench S is
formed to a thickness larger than the thickness of the element
region A. Accordingly, the first electrodes 2 can be formed in a
separated manner with a high yield, thereby making it possible to
provide a photovoltaic device having high photovoltaic conversion
characteristics.
[0106] FIG. 9A is a schematic sectional view showing the vicinity
of the laser processing portion (the side end). As shown in FIG.
9A, etching progresses in a part of the ZnO film 23 in the element
region A faster, so that the thickness thereof is small. FIG. 9B
illustrates the X-ray diffraction pattern intensity of the ZnO film
23 examined in a part of the element region A (a portion denoted by
reference numeral 23A in FIG. 9A), and FIG. 9C illustrates the
X-ray diffraction pattern intensity of the ZnO film 24 examined in
a part of the laser processing portion (the side end) B (a portion
denoted by reference numeral 24B in FIG. 9A).
[0107] The ZnO film has X-ray diffraction peaks, respectively, in
the (002) plane and the (004) plane, as shown in FIGS. 9B and 9C.
As described above, the higher the ratio (002)/(004), that is, the
X-ray diffraction peak intensity ratio I is, the better the
orientation is. It is found that etching in the element region A is
faster than that in the laser processing portion (the side end)
B.
[0108] As described in the foregoing, the crystallizability of each
of the laser processing portion (the side end) B and the element
region A is then changed and at the same time, the laser processing
portion B and the element region A are made irregular and thinned
by etching. The X-ray diffraction peak intensity ratio I
(002)/(004) in each of the laser processing portion B and the
element region A is examined. Further, letting IB be the X-ray
diffraction peak intensity ratio in the laser processing portion
(the side end) B, and IA be the X-ray diffraction peak intensity
ratio in the element region A, the relationship between the ratio
of IA to IB (IA/IB) and the integrated photovoltaic device is
examined. The results are shown in FIGS. 10 to 12.
[0109] FIG. 10 shows that current is improved when the intensity
ratio ]A is lower than the intensity ratio IB, and the current is
improved when the intensity ratio IB is not less than twice the
intensity ratio IA. FIG. 11 shows that when the intensity ratio IB
is low, F.F. (a file factor) is not lowered. Further, FIG. 12 shows
that the product of the current and the F.F. is improved when the
ratio of the intensity ratio IA to the intensity ratio IB (IA/IB)
is not more than 0.5, that is, the intensity ratio in the laser
processing portion B is not less than twice the intensity ratio in
the element region A.
[0110] As shown in FIG. 13, the relationship between the respective
thicknesses L1 and L2 of the films and the respective depths d1 and
d2 of irregularities in the laser processing portion (the side end)
B and the element region A in a case where the intensity ratio IB
is not less than twice the intensity ratio IA and the integrated
photovoltaic device. The results are shown in FIGS. 14 and 15. From
FIGS. 13 and 14, it is preferable that the depth of the
irregularities on the surface of the element region A is not less
than 1500 .ANG. nor more than 3200 .ANG., and the depth of the
irregularities on the surface of the laser processing portion (the
side end) B is not more than 800 .ANG.. The thickness of the laser
processing portion (the side end) B is set to 7000 .ANG. when the
thickness of the element region A is in the range of approximately
3500 .ANG. to approximately 5500 .ANG., thereby making it possible
to form the first electrodes in a separated manner with a high
yield by laser beam irradiation. In addition, it is possible to
provide a photovoltaic device having high photovoltaic conversion
characteristics with a high yield.
[0111] FIG. 16 is a cross-sectional view by steps for explaining
the steps of fabricating the photovoltaic device according to the
present embodiment.
[0112] In the first step shown in FIG. 16, an insulation thin film
22 (an SiO.sub.2 film in the present embodiment) is first provided
in only a portion corresponding to an element region A on a
substrate 1.
[0113] In the second step shown in FIG. 16B, a translucent
conductive film 21 is then formed. When the conductive film 21 is
formed using ZnO, the conductive film 21 is formed to a thickness
of approximately 8000 .ANG..
[0114] In the third step shown in FIG. 16C, etching using a
solution of hydrochloric acid (HC1) is then performed. In the
etching, a ZnO film in the element region A is etched faster than a
ZnO film in a processing portion (a side end) B. Accordingly, an
irregular surface serving as a texture plane is formed on a surface
of the element region A, and the element region A is thinned.
[0115] In the fourth step shown in FIG. 16D, the processing portion
B is then irradiated with laser beams L, to remove the conductive
film 21 having a good orientation in a portion irradiated with the
laser beams L, thereby forming a separating trench S as well as
forming a plurality of first electrodes 2 in a separated
manner.
[0116] In the fifth step shown in FIG. 16E, a plurality of
photovoltaic conversion layers 3 and second electrodes 4 are formed
in the same manner as that in the first embodiment, thereby making
it possible to fabricate a photovoltaic device having the structure
shown in FIG. 6.
[0117] Also in the present embodiment, it is possible to provide a
photovoltaic device having superior photovoltaic characteristics
with a high yield, as in the above-mentioned first embodiment.
EXAMPLE 1
[0118] A specific example of the above-mentioned photovoltaic
device according to the first embodiment of the present invention
will be described below.
[0119] A glass substrate having dimensions of 10 cm.times.10 cm was
first prepared, and a conductive film composed of ZnO having a
thickness of 1 .mu.m was formed on an approximately entire surface
of the glass substrate using sputtering. The forming conditions of
ZnO are as shown in Table 2.
2 TABLE 2 target ZnO: Al.sub.2O.sub.3 (2 wt. %) sputtering gas Ar:
5.about.50 sccm RF power 300.about.450 W pressure 0.5.about.1.0 Pa
substrate temperature 100.about.250.degree. C.
[0120] A resist film was then formed on a removal region in a
conductive film, and was immersed in a 1% solution of HC1 for
approximately 30 seconds, to thin a region serving as an element
region in the conductive film. In the step, only the region serving
as the element region in the conductive film which was formed to a
thickness of 1 .mu.m was etched to a thickness of approximately
4000 .ANG., and an irregular surface in a pyramid shape was formed
on its surface.
[0121] Nd : YAC lasers having a wavelength of 1.06 .mu.m and having
a pulse frequency of 3 kHz were used as laser beams, and were then
irradiated into the removal region in the conductive film at a
laser power density of 4.times.10.sup.7 W/ cm.sup.2 and at a
processing rate of 10 mm/sec. from the side of the substrate. The
conductive film in a portion irradiated with the laser beams was
removed, thereby forming a separating trench as well as forming a
plurality of first electrodes in a separated manner.
[0122] Furthermore, a p-type layer having a thickness of
approximately 150 .ANG. composed of p-type amorphous silicon
carbide, an i-type layer having a thickness of approximately 4000
.ANG. composed of i-type amorphous silicon, and an n-type layer
having a thickness of approximately 200 .ANG. composed of n-type
amorphous silicon were formed in this order on an approximately
entire surface of the substrate, including the plurality of first
electrodes, using plasma CVD, to form a plurality of photovoltaic
conversion layers in a separated manner by laser patterning. The
forming conditions of each of the amorphous semiconductor layers
are as shown in Table 3.
3 TABLE 3 p layer i layer n layer material gas SiH.sub.4: 200 sccm
SiH.sub.4: 400 sccm SiH.sub.4: 200 sccm B.sub.2H.sub.6: 10 sccm
PH.sub.3: 200 sccm CH.sub.4: 100 sccm H.sub.2: 200 sccm substrate
200 200 200 temperature (.degree. C.) RF power (W) 100 100 100
pressure (Pa) 100 100 100
[0123] Finally, an Ag film was formed on the approximately entire
surface of the substrate, including the plurality of photovoltaic
conversion layers, using sputtering, and a plurality of second
electrodes were then formed in a separated manner by laser
patterning, to fabricate an integrated photovoltaic device
comprising photovoltaic elements in 10 stages electrically
connected in series. The photovoltaic conversion characteristics of
the photovoltaic device are shown in Table 4. For comparison, the
characteristics of a photovoltaic device in a comparative example
fabricated in the same steps as those in the example 1 except that
the step of forming the conductive film composed of ZnO to a
thickness of approximately 4000 .ANG. as well as thinning the
element region in the conductive film is not carried out.
4 TABLE 4 parallel Isc conversion resistance Voc/ (mA/ efficiency
component stage cm.sup.2) F.F. (%) (.OMEGA. cm.sup.2) example 1
1.53 9.7 0.71 10.5 7500 comparative 1.53 9.4 0.63 9.1 600
example
[0124] As can be seen from Table 4, higher photovoltaic conversion
efficiency is obtained in the device in the example 1. When a
parallel resistance component between the photovoltaic elements is
measured, the parallel resistance component is increased in the
device in the example 1, as shown in Table 4, so that it is found
that leak current is decreased. The following is the reason for
this. The thickness of the removal region irradiated with the laser
beams is approximately 1 .mu.m in the device in the example 1,
while being approximately 4000 .ANG. in the device in the
comparative example. Therefore, in the device in the comparative
example, the conductive film is not sufficiently removed, and the
undesired residual, for example, remains, so that it is considered
that leak current is increased.
[0125] On the other hand, in the device in the example 1, the
conductive film is sufficiently removed because the thickness of
the removal region is large, i.e., approximately 1 .mu.m.
Accordingly, the leak current is decreased. Further, the thickness
of the element region is in a range most suitable for improvement
of efficiency. Therefore, it is considered that high photovoltaic
conversion characteristics are obtained.
EXAMPLE 2
[0126] Description is made of a specific example of the
above-mentioned photovoltaic device according to the second
embodiment of the present invention.
[0127] In the example, a conductive film having a thickness of
approximately 4000 .ANG. composed of ZnO was formed on a substrate
composed of glass by sputtering. The forming conditions of the
conductive film are the same as those in the example 1. A laser
beam absorbing member composed of SnO.sub.2 was formed to a
thickness of 2000 .ANG. on a removal region in the conductive
film.
[0128] YAG laser beams having a wavelength of 1.06 .mu.m were then
irradiated into the removal region in the conductive film from the
side of the substrate, and the conductive film and the laser beam
absorbing member in a portion irradiated with the laser beams were
removed, forming a plurality of first electrodes in a separated
manner.
[0129] Furthermore, a p-type layer having a thickness of
approximately 150 .ANG. composed of p-type amorphous silicon
carbide, an i-type layer having a thickness of approximately 4000
.ANG. composed of i-type amorphous silicon, and an n-type layer
having a thickness of approximately 200 .ANG. composed of n-type
amorphous silicon were formed in this order on an approximately
entire surface of the substrate 1, including the plurality of first
electrodes, using plasma CVD, to form a plurality of photovoltaic
conversion layers in a separated manner by laser patterning. The
forming conditions of each of the amorphous semiconductor layers
are the same as those used in the example 1.
[0130] Finally, an Ag film was formed on the approximately entire
surface of the substrate, including the plurality of photovoltaic
conversion layers, by sputtering, and a plurality of second
electrodes were then formed in a separated manner by laser
patterning, to fabricate an integrated photovoltaic device
comprising photovoltaic elements in 10 stages electrically
connected in series. The photovoltaic conversion characteristics of
the photovoltaic device are shown in Table 5. The characteristics
of the above-mentioned photovoltaic device in the comparative
example are also shown.
5 TABLE 5 parallel Isc conversion resistance Voc/ (mA/ efficiency
component stage cm.sup.2) F.F. (%) (.OMEGA. cm.sup.2) example 2
1.53 9.5 0.71 10.3 7300 comparative 1.53 9.4 0.63 9.1 600
example
[0131] As can be seen from Table 5, higher photovoltaic conversion
efficiency is obtained in the device in the example 2. When a
parallel resistance component between the photovoltaic elements is
measured, the parallel resistance component can be decreased in the
device in the example 2, as shown in Table 5. The following is the
reason for this. The thickness of the removal region in the
conductive film irradiated with the laser beams is approximately
6000 .ANG. by forming the laser beam absorbing member in the device
in the example 2, while being approximately 4000 .ANG. in the
device in the comparative example. Therefore, in the device in the
comparative example, the conductive film is not sufficiently
removed, and the undesired residual, for example, remains, so that
the parallel resistance component is decreased, as described above.
As a result, it is considered that the photovoltaic conversion
characteristics are degraded.
[0132] On the other hand, in the device in the example 2, the
conductive film is sufficiently removed because the thickness of
the removal region is large, i.e., approximately 6000 .ANG..
Accordingly, the leak current is decreased. Further, the thickness
of the element region is in a range most suitable for improvement
of efficiency. Therefore, it is considered that high photovoltaic
conversion characteristics are obtained.
[0133] A material composing the laser beam absorbing member is not
limited to SnO.sub.2, described above. Another material can be also
used, provided that the material absorbs laser beams. Further, the
laser beam absorbing member may be removed after the first
electrodes are formed in a separated manner. Alternatively, the
laser beam absorbing member may be left as it is without being
removed, as in this example. In either case, the same effect is
produced.
EXAMPLE 3
[0134] Description is made of a specific example of the
above-mentioned photovoltaic device according to the third
embodiment of the present invention.
[0135] A method of forming an insulation thin film 22 composed of
SiO.sub.2 in a predetermined region on glass will be described in
accordance with FIG. 17.
[0136] In the step shown in FIG. 17A, an amorphous silicon layer 25
having a thickness of 300 .ANG. is formed on glass 1a by CVD. An Ag
film 26 having a thickness of 2000 .ANG. is then formed on the
amorphous silicon layer 25 by sputtering. The Ag film 26 and a film
surface of a glass substrate 1 serving as a substrate are opposed
to and made to adhere to each other.
[0137] In the step shown in FIG. 17B, lasers are irradiated from
the side of the glass 1a, to make an Ag film 26a to adhere on the
substrate 1 in a line shape.
[0138] In the step shown in FIG. 17C, an SiO.sub.2 film 22 having a
thickness of 1000 .ANG. is formed on the substrate 1, including the
Ag film 26a in a line shape, by sputtering. The forming conditions
of the SiO.sub.2 film 22 are a temperature of 250.degree. C., an RF
power of 300 W, a ultimate pressure of 13.3.times.10.sup.-6Pa, and
50 sccm Ar as sputtering gas.
[0139] In the step shown in FIG. 17D, the substrate 1 to which the
SiO.sub.2 film 22 adheres is immersed in a 20% solution of
hydrochloric acid (HCl) for 30 seconds. By immersing the substrate
1 in the hydrochloric acid, Ag melts, the Sio.sub.2 film formed on
Ag is removed, the SiO.sub.2 film 22 remains on only a surface of a
portion which is not positioned just below a portion irradiated
with the lasers, and the SiO.sub.2 film 22 is selectively formed on
the substrate 1.
[0140] A glass substrate having an Sio.sub.2 film selectively
formed thereon, as described above, was prepared, and a conductive
film composed of ZnO having a thickness of 8000 .ANG. was formed on
an approximately entire surface of the glass substrate using
sputtering. The forming conditions of ZnO are as shown in Table 2,
described above.
[0141] The glass substrate was then immersed in a 0.5% solution of
HC1 for approximately 110 seconds, to thin a region serving as an
element region in the conductive film. In the step, a large part of
the region serving as the element region in the conductive film
formed on the SiO.sub.2 film was etched. Accordingly, the element
region has a thickness of approximately 3000 .ANG.. Further, a
laser processing region having no SiO.sub.2 film has a thickness of
7000 .ANG.. An irregular surface in a pyramid shape was formed on a
surface of the laser processing region.
[0142] Nd: YAC lasers having a wavelength of 1.06 .mu.m and having
a pulse frequency of 3 kHz were used as laser beams, and were then
irradiated into the removal region in the conductive film at a
laser power density of 4.times.10.sup.7 W/cm.sup.2 and at a
processing rate of 10 mm/sec. from the side of the substrate. The
conductive film in a portion irradiated with the laser beams was
removed, thereby forming a separating trench as well as forming a
plurality of first electrodes in a separated manner.
[0143] Furthermore, a p-type layer having a thickness of
approximately 100 .ANG. composed of p-type amorphous silicon
carbide, an i-type layer having a thickness of approximately 3000
.ANG. composed of i-type amorphous silicon, and an n-type layer
having a thickness of approximately 200 .ANG. composed of
microcrystalline silicon (.mu.c-Si) were formed in this order on an
approximately entire surface of the substrate, including the
plurality of first electrodes, using plasma CVD, to form a
plurality of photovoltaic conversion layers in a separated manner
by laser patterning. The forming conditions of each of the
amorphous semiconductor layers are as shown in Table 6.
6 TABLE 6 p-type i-type n-type a-SiC layer a-Si layer .mu.c-Si
layer material SiH.sub.4: 80 sccm SiH.sub.4: SiH.sub.4: 40 sccm gas
1% B.sub.2H.sub.6/H.sub.2: 40 sccm 80 sccm 1% PH.sub.3/H.sub.2: 20
sccm CH.sub.4: 20 sccm H.sub.2: 100 substrate 250 250 250
temperature (.degree. C.) RF power 30 30 90 (W) pressure 50 50 50
(Pa)
[0144] Finally, an Ag film was formed on the approximately entire
surface of the substrate, including the plurality of photovoltaic
conversion layers, using sputtering, and a plurality of second
electrodes were then formed in a separated manner by laser
patterning, to fabricate an integrated photovoltaic device
comprising photovoltaic elements in 10 stages electrically
connected in series.
[0145] In the above-mentioned device in the example 3, the
conductive film is sufficiently removed because the thickness of
the removal region is large, i.e., approximately 7000 .ANG..
Accordingly, leak current is decreased, and the thickness of the
element region is in a range most suitable for improvement of
efficiency. Therefore, high photovoltaic conversion characteristics
are obtained, as in the device in the example 1.
[0146] Although in the above-mentioned embodiments, description was
made of a case where a pin junction having as a constituent element
amorphous silicon, amorphous silicon carbide, or microcrystalline
silicon is applied to a single photovoltaic deice, it goes without
saying that the same effect is obtained even in a photovoltaic
device using a thin semiconductor film containing another
constituent element, a laminated photovoltaic device including a
plurality of pin junctions, and a semiconductor device having
another structure.
[0147] As described in the foregoing, according to the present
invention, it is possible to provide a photovoltaic device having
high photovoltaic conversion characteristics with a superior
yield.
[0148] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *