U.S. patent application number 12/646659 was filed with the patent office on 2010-07-01 for laser firing apparatus for high efficiency solar cell and fabrication method thereof.
Invention is credited to Hwa Nyeon Kim, Jong Hwan KIM, Ju Hwan Yun.
Application Number | 20100167457 12/646659 |
Document ID | / |
Family ID | 42285436 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100167457 |
Kind Code |
A1 |
KIM; Jong Hwan ; et
al. |
July 1, 2010 |
LASER FIRING APPARATUS FOR HIGH EFFICIENCY SOLAR CELL AND
FABRICATION METHOD THEREOF
Abstract
Disclosed are a laser firing apparatus for a high efficiency
solar cell including laser generating unit and a fabrication method
thereof. The laser firing apparatus for a high efficiency solar
cell includes at least one laser generating unit that irradiates a
laser irradiation on to an electrode region formed on a
semiconductor substrate for the solar cell and heat-treats the
electrode region. In addition, the fabrication method of a solar
cell includes forming an electrode material on a semiconductor
substrate for the solar cell; and forming an electrode by heat
treating the electrode material by laser irradiation.
Inventors: |
KIM; Jong Hwan; (Seoul,
KR) ; Kim; Hwa Nyeon; (Seoul, KR) ; Yun; Ju
Hwan; (Seoul, KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
42285436 |
Appl. No.: |
12/646659 |
Filed: |
December 23, 2009 |
Current U.S.
Class: |
438/72 ;
219/121.6; 257/E21.158 |
Current CPC
Class: |
B23K 26/0619 20151001;
B23K 26/0738 20130101; B23K 26/40 20130101; B23K 2103/50 20180801;
B23K 26/0838 20130101; H01L 31/022425 20130101; B23K 26/066
20151001; Y02E 10/50 20130101 |
Class at
Publication: |
438/72 ;
219/121.6; 257/E21.158 |
International
Class: |
H01L 31/18 20060101
H01L031/18; B23K 26/00 20060101 B23K026/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 2008 |
KR |
10-2008-0137176 |
Claims
1. A laser firing apparatus for a solar cell, comprising: at least
one laser generating unit that irradiates a laser irradiation on to
an electrode region formed on a semiconductor substrate for the
solar cell and heat-treats the electrode region.
2. The laser firing apparatus for the solar cell according to claim
1, wherein the laser irradiation is in a line form.
3. The laser firing apparatus for the solar cell according to claim
1, wherein the laser irradiation is in a line form, and the line
form is formed by a slit.
4. The laser firing apparatus for the solar cell according to claim
1, wherein the at least one laser generating unit further comprises
a plurality of laser generating units disposed on a line.
5. The laser firing apparatus for the solar cell according to claim
1, wherein the at least one laser generating unit includes a first
laser generating unit that is positioned to irradiate a front
surface of the semiconductor substrate and a second laser
generating unit that is positioned to irradiate a back surface of
the semiconductor substrate and the first laser generating unit and
the second laser generating unit are disposed to oppose each
other.
6. The laser firing apparatus for the solar cell according to claim
1, wherein the at least one laser generating unit includes a first
laser generating unit a the second laser generating unit that are
positioned to irradiate one surface of the semiconductor substrate
and are disposed to be parallel with each other.
7. The laser firing apparatus for the solar cell according to claim
1, further comprising a stage used to seat the semiconductor
substrate.
8. The laser firing apparatus for the solar cell according to claim
7, wherein the stage is at least one belt type moving unit that
moves the semiconductor substrate.
9. The laser firing apparatus for the solar cell according to claim
8, wherein the at least one belt type moving unit includes a first
belt type moving unit and a second belt type moving unit.
10. A fabrication method of a solar cell, comprising: forming an
electrode material on a semiconductor substrate for the solar cell;
and forming an electrode by heat treating the electrode material by
laser irradiation; wherein the electrode material comprising
electrode paste, electrode ink and aerosol for electrode.
11. The fabrication method of the solar cell according to claim 10,
wherein the electrode material is formed according to a front
electrode pattern and is formed on the front surface of the
semiconductor substrate.
12. The fabrication method of the solar cell according to claim 11,
wherein the material for the front electrode is heat-treated at a
temperature of 600.degree. C. to 1000.degree. C. by the laser
irradiation.
13. The fabrication method of the solar cell according to claim 10,
wherein the electrode material is formed according a back electrode
pattern and is formed on the back surface of the semiconductor
substrate.
14. The fabrication method of the solar cell according to claim 13,
wherein the material for the back electrode formed according to the
back electrode pattern is heat-treated at a temperature of
450.degree. C. to 750.degree. C. by the laser irradiation.
15. The fabrication method of the solar cell according to claim 13,
wherein the material for the back electrode formed on the back
surface of the semiconductor substrate is formed into the back
electrode by heat treatment, and a back surface field (BSF) layer
is formed at an interface between the back surface and back
electrode of the semiconductor substrate.
16. The fabrication method of the solar cell according to claim 11,
wherein the material for the front electrode and the material for
the back electrode are simultaneously fired by simultaneous laser
irradiations.
17. The fabrication method of the solar cell according to claim 13,
wherein the material for the front electrode and the material for
the back electrode are simultaneously fired by simultaneous laser
irradiations.
18. The fabrication method of the solar cell according to claim 10,
wherein the semiconductor substrate is heat-treated by laser
irradiations.
19. The fabrication method of the solar cell according to claim 10,
wherein the semiconductor substrate is a p type impurity
semiconductor substrate or an n type impurity semiconductor
substrate.
20. The fabrication method of the solar cell according to claim 10,
further comprising forming an antireflective layer on a front
surface of the semiconductor substrate prior to forming the
electrode material.
21. The fabrication method of the solar cell according to claim 10,
further comprising forming a back passivation layer on the back
surface of the semiconductor substrate prior to forming the
electrode material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Korean Patent
Application No. 10-2008-0137176, filed on Dec. 30, 2008, in the
Korean Intellectual Property Office, the entire contents of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The embodiments of the present invention relate to a laser
firing apparatus for a high efficiency solar cell, and more
specifically, to a laser firing apparatus for a high efficiency
solar cell including at least one laser generating unit that forms
a front electrode unit by irradiating a laser to the front
electrode unit formed on a front surface of a semiconductor
substrate for the solar cell, and forms a back surface field (BSF)
layer by irradiating a laser to a back metal paste region formed on
a back surface of the semiconductor substrate, and a fabrication
method thereof.
[0004] 2. Description of the Related Art
[0005] Upon classifying a solar cell based on a substrate material
therefor, the solar cell may be further classified largely into
three types, such as a crystalline silicon based solar cell, an
amorphous silicon based solar cell, and a compound semiconductor
based solar cell. Further, types of the crystalline silicon based
solar cell includes a single crystalline solar cell and a
polycrystalline solar cell.
[0006] In a fabrication process of the silicon crystalline solar
cell, a firing process performed by heating the silicon crystalline
solar cell is essential. At this time, the firing process is
generally performed by a method that performs heat treatment for
several minutes at a high temperature by using a belt furnace.
During performing of the firing process, a phenomenon occurs
whereby lifetime of carriers is reduced, which has an effect on the
efficiency of the solar cell. Therefore, in order to maintain the
lifetime of the carriers, a study on the method that minimizes the
heat treatment time of the silicon substrate is urgently
needed.
SUMMARY OF THE INVENTION
[0007] The embodiments of the present invention proposes to address
the problems in the related art as described above. It is an object
of the present invention to provide a firing apparatus that can
perform heat treatment of a solar cell within a short time.
[0008] In addition, it is another object of the present invention
to provide a fabrication method of a solar cell with increased
efficiency by using the firing apparatus.
[0009] In order to achieve the above and other objects, there is
provided a laser firing apparatus for a solar cell according to one
aspect of the present invention including at least one laser
generating unit that irradiates a laser irradiation on to an
electrode region formed on a semiconductor substrate for the solar
cell and heat-treats the electrode region.
[0010] In another aspect, the laser irradiation is in a line
form.
[0011] In another aspect, the laser irradiation is in a line form
whose output light is formed by a slit.
[0012] In another aspect, the laser firing apparatus for the solar
cell further includes a plurality of laser generating units
disposed on a line.
[0013] In another aspect, the laser generating unit includes a
first laser generating unit that is positioned to irradiate a front
surface of the semiconductor substrate and a second laser
generating unit that is positioned to irradiate a back surface of
the semiconductor substrate, and the first laser generating unit
and the second laser generating unit are disposed to be oppose each
other.
[0014] In another aspect, the laser generating unit includes the
first laser generating unit and the second laser generating unit
that irradiate one surface of the semiconductor substrate and are
disposed to be parallel with each other.
[0015] In another aspect, the laser firing apparatus for the solar
cell further includes a stage that seats the semiconductor
substrate.
[0016] In another aspect, the stage is at least one belt type
moving unit that moves the semiconductor substrate.
[0017] In another aspect, the at least one belt type moving unit
includes a first belt type moving unit and a second belt type
moving unit.
[0018] In accordance with another aspect of the present invention,
there is provided a fabrication method of a solar cell, including
forming an electrode material on a semiconductor substrate for the
solar cell; and forming an electrode by heat treating the electrode
material by laser irradiation; wherein the electrode material
comprising electrode paste, electrode ink and aerosol for
electrode.
[0019] In another aspect, the electrode material is formed
according to a front electrode pattern and is formed on the front
surface of the semiconductor substrate.
[0020] In another aspect, the material for the front electrode
formed according to the front electrode pattern is heat-treated at
a temperature of 600.degree. C. to 1000.degree. C. by the laser
irradiation.
[0021] In another aspect, the electrode material is formed
according the back electrode pattern and is formed on the back
surface of the semiconductor substrate.
[0022] In another aspect, the material for the back electrode
formed according to the back electrode pattern is heat-treated at a
temperature of 450.degree. C. to 750.degree. C. by the laser
irradiation.
[0023] In another aspect, the material for the back electrode
formed on the back surface of the semiconductor substrate is formed
as the back electrode by heat treatment and a back surface field
(BSF) layer is formed at an interface between the back surface and
back electrode of the semiconductor substrate.
[0024] In another aspect, the material for the front electrode and
the material for the back electrode are simultaneously fired by
simultaneous laser irradiations.
[0025] In another aspect, the semiconductor substrate is
heat-treated by laser irradiations.
[0026] In another aspect, the semiconductor substrate is a p type
impurity semiconductor substrate or an n type impurity
semiconductor substrate.
[0027] In another aspect, the fabrication method of a solar cell
further comprises forming an antireflective layer on the front
surface of the semiconductor substrate prior to forming the
electrode material.
[0028] In another aspect, the fabrication method of a solar cell
further includes forming a back passivation layer on the back
surface of the semiconductor substrate prior to forming the
electrode material.
[0029] The heat treatment is performed in a short time by using the
laser firing apparatus of the present invention, such that the
lifetime of the carriers affecting the efficiency of the solar cell
can be increased as compared to the case of using the existing belt
furnace.
[0030] In addition, with the fabrication method of the high
efficiency solar cell according to the present invention, the solar
cell with the increased efficiency can be fabricated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The above and other objects, features and advantages of the
present invention will become apparent from the following
description of example embodiments given in conjunction with the
accompanying drawings, in which:
[0032] FIG. 1 is a cross-sectional view of a solar cell;
[0033] FIG. 2 is an exemplified diagram of a laser firing apparatus
of a solar cell that includes a first laser generating unit and a
second laser generating unit according to one embodiment of the
present invention;
[0034] FIG. 3 is an exemplified diagram of a laser firing apparatus
of a solar cell that includes one laser generating unit according
to one embodiment of the present invention;
[0035] FIG. 4 is an exemplified diagram showing a laser in a line
form according to one embodiment of the present invention;
[0036] FIG. 5 is an exemplified diagram showing a laser in a line
form whose output light is formed by a slit according to one
embodiment of the present invention;
[0037] FIG. 6 is an exemplified diagram showing the time and the
temperature applied according to high speed firing and existing
firing; and
[0038] FIG. 7 is an exemplified diagram showing the measurement of
the short current density (J.sub.sc) and the open circuit voltage
(V.sub.oc) according to high speed firing-Solar cell and existing
firing-Solar cell.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0039] The embodiments of the present invention will now be
described more fully hereinafter with reference to the accompanying
drawings forming a part of this specification wherein like
reference characters designate corresponding parts in the several
views. In the embodiments of the present invention, detailed
description of the functions and configurations that make the
purport of the present invention unnecessarily obscure are
omitted.
[0040] In order to more clearly describe a function of a laser
firing apparatus for a solar cell according to embodiments of the
present invention, a conventional fabrication method of a solar
cell will be first described for contrast.
[0041] FIG. 1 is a cross-sectional view of a solar cell. Referring
to FIG. 1, a conventional fabrication method of the solar cell will
be briefly described below. Thereafter, the solar cell of FIG. 1
will be referred to in describing a fabrication method of the solar
cell according to embodiments of the present invention.
[0042] First, an n+ layer 102 is formed by diffusing phosphorous on
a front surface of a p type impurity semiconductor substrate 101
and an antireflective layer 103 is then formed on the n+ layer 102.
A metal paste is subsequently screen-printed and dried on the front
surface and a back surface of the substrate 101, and the substrate
101 is then heat-treated in a belt furnace.
[0043] As a result, on the front surface of the substrate, silver
(Ag) contained in the metal paste passes through the antireflective
layer 103 to contact the n+ layer 102, thereby forming a front
electrode unit (fire-through contact) 104. In addition, on the back
surface of the substrate, an Al containing paste 106 is diffused
into the substrate to form a back surface field (BSF) layer 105 and
form a back surface electrode unit 107 together therewith.
[0044] When performing the heat treatment to form the BSF layer 105
and electrode units 107, 107 of the solar cell according to a
conventional fabrication method, the time spent on the belt furnace
is about 1 to 2 minutes and the maximum temperature reached is
about 800.degree. C. In the heat treatment process according to the
conventional fabrication method, a lifetime of charge carriers is
suddenly reduced. If the life time is reduced, a probability of
recombining holes and electrons generated by receiving light is
large and thus, the efficiency of the solar cell is reduced.
[0045] Generally, when the metal paste containing the Ag disposed
on the front surface and back surface of the substrate is subjected
to a screen printing and drying step in a predetermined pattern, a
lifetime of charge carriers corresponds to about 18 to 20 .mu.s.
However, when being subjected to the heat treatment step of the
belt furnace, the lifetime is suddenly reduced to about 4
.mu.s.
[0046] As described above, in order to prevent or reduce the
phenomenon of the decreased lifetime of the charge carriers, which
affects the efficiency of the solar cell due to the
high-temperature heat treatment using the belt furnace, in
embodiments of the present invention, the solar cell is fabricated
using a laser (laser beam or laser irradiation) that can locally
heat the semiconductor substrate and the heat treatment is
performed within a short time.
[0047] Generally, the conversion efficiency .eta. of the solar cell
refers to a value that divides open circuit voltage Voc.times.short
current density Jsc.times.fill factor (FF) by total light energy
(device area S.times.intensity I of light irradiated to a solar
cell). Therefore, in order to increase the conversion energy .eta.
of the solar cell, it is important to make the short current
density Jsc and/or the open circuit voltage Voc large. One of the
factors affecting the values of the short current density Jsc
and/or the open circuit voltage Voc are a firing time of the solar
cell.
[0048] As can be appreciated from FIG. 6, the firing process is
performed at a temperature of about 800.degree. C. during the
fabrication process of the solar cell. At this time, the solar cell
is fabricated by being divided into two cases, i.e., existing
firing and high-speed firing. The existing firing refers to the
case of firing during a relatively long time according to the
existing method and the high-speed firing refers to a case of
firing during a relatively shorter time as compared to the existing
method.
[0049] In order to review the effect on the conversion efficiency
.eta. of the solar cell fabricated by changes in the firing time as
described above, the short current density Jsc and the open circuit
voltage Voc are measured. The measured results are shown in FIG.
7.
[0050] As can be appreciated from FIG. 7, the high-speed firing of
the solar cell obtains the short current density Jsc and the open
circuit voltage Voc, all of which have a higher value than the
existing firing of the solar cell. In other words, in order to
obtain the solar cell having the high conversion efficiency .eta.,
a need exists for the fabrication method of the solar cell by the
high-speed firing.
[0051] Therefore, a fabrication method of the solar cell by the
high-speed firing using a laser (a laser beam or a laser
irradiation) by the laser firing apparatus for the high efficiency
solar cell according to one embodiment of the present invention
will be described with reference to FIG. 2.
[0052] The laser firing apparatus for the solar cell of FIG. 2
includes a first laser generating unit 201, a second laser
generating unit 202, a first belt type moving unit 203, and a
second belt type moving unit 204. As shown in FIG. 2, the first
belt type moving unit 203 and the second belt type moving unit 204
are disposed to be separated by a predetermined distance to allow a
laser (a laser beam or a laser irradiation) generated in the second
laser generating unit 202 to pass between the first and second belt
type moving units 203 and 204 where they are separated.
[0053] First, an n+ layer is formed on a front surface of a
semiconductor substrate 205, and the semiconductor substrate 205
for the solar cell, on which a back metal paste region is formed on
a back surface of the substrate, is seated on the first belt type
moving unit 203. The embodiment uses a p type impurity
semiconductor substrate, but is not limited thereto. Therefore, the
embodiment can also use an n type impurity semiconductor
substrate.
[0054] The semiconductor substrate 205 for the solar cell seated on
the first belt type moving unit 203 is irradiated by a first laser
(a first laser beam or a first laser irradiation) and a second
laser (a second laser beam or a second laser irradiation) while
moving to the second belt type moving unit 204. The first laser is
generated in a line form in the first laser generating unit 201 and
the temperature of the semiconductor substrate 205 for the solar
cell irradiated by the first laser reaches a temperature range of
600 to 1000.degree. C. The first laser is irradiated on the front
electrode unit of the semiconductor substrate 205 for the solar
cell to fire and allow the front electrode unit to contact the n+
layer.
[0055] In addition, the second laser is generated in a line form in
the second laser generating unit 202 and the temperature of the
semiconductor substrate for the solar cell irradiated by the second
laser reaches a temperature range of 450 to 750.degree. C. The
second laser is irradiated on the back metal paste region of the
semiconductor substrate for the solar cell, thereby forming a back
surface field (BSF) layer. The line form of output light of the
first and/or second laser may be formed by a slit, for example, the
slit containing panel.
[0056] As such, according to the embodiment of the present
invention, only the front electrode unit and/or the back metal
paste region of the semiconductor substrate for the solar cell are
locally heated by at least one laser in a line form and
heat-treated in a short time, thereby making it possible to
increase (maintain or not reduce) the lifetime of the carriers. As
described above, when the lifetime is increased (maintained or not
reduced), a probability of recombining holes and electrons is
reduced, thereby making it possible to fabricate the solar cell
with the increased efficiency.
[0057] When the lifetime is about 4 .mu.s upon fabricating the
solar cell through the heat treatment process of the belt furnace
by the existing method, the theoretical maximum Jsc value, that is
verified by computer simulation, is only 92%. However, when
fabricating the solar cell using the laser firing apparatus for the
high efficiency solar cell, the lifetime is 10 .mu.s or more and
the theoretical maximum Jsc value, which is verified by computer
simulation, can reach up to 97% Jsc or more, thereby making it
possible to fabricate the solar cell with the increased
efficiency.
[0058] The laser firing apparatus for the solar cell may further
include a blowing system 206 and/or an evacuation system 207. The
blowing system 206 plays a role of blowing air, in order to
discharge a fume generated when a laser is irradiated on the front
electrode unit away from the solar cell. In addition, the
evacuation system 207 plays a role of absorbing or sucking the
fume, in order to discharge the fume away from the solar cell
quickly.
[0059] As shown in FIG. 2, in the fabrication method of the solar
cell according to one embodiment of the present invention, the
first laser generating unit 201 is positioned to irradiate the
front surface of the semiconductor substrate and the second laser
generating unit 202 is positioned to irradiate the back surface of
the semiconductor substrate for the high efficiency solar cell,
such that they may be disposed to be opposed to each other.
[0060] However, the positions of the first laser generating unit
201 and the second laser generating unit 202 are not necessarily
limited to the above-mentioned positions. In other words, the first
laser generating unit 201 and the second laser generating unit 202
may be arranged on a line. Both the first laser generating unit 201
and the second laser generating unit 202 may be positioned to
irradiate the front surface of the semiconductor substrate 101 or
the back surface of the semiconductor substrate 101, such that they
may be disposed in parallel with each other.
[0061] In addition, in the above-mentioned embodiment, the laser
irradiated to the front electrode unit and the back metal paste
region is irradiated from separate laser generating units, that is,
the first laser generating unit and the second laser generating
unit, respectively, but is not limited thereto. In other words, as
can be appreciated from FIG. 3, the laser irradiated to the front
electrode unit and the back metal paste region may be generated
from the same laser generating unit 301.
[0062] When the laser irradiated to the front electrode unit and
the back metal paste region is generated from the same laser
generating unit 301, a P type semiconductor impurity substrate 305
may be moved by the belt type moving unit at least twice in the
firing process of the front electrode unit and the process of
forming the BSF layer respectively in order to fabricate the high
efficiency solar cell.
[0063] FIG. 4 is an exemplified diagram showing a laser in a line
form according to one embodiment of the present invention and FIG.
5 is an exemplified diagram showing a laser in a line form whose
output light is formed by a slit according to one embodiment of the
present invention.
[0064] FIG. 4 shows a plurality of laser generating units 401 that
are arranged along a line to irradiate a plurality of lasers in a
line form, and FIG. 5 shows a laser generated by one laser
generating unit 501 irradiates the laser in a line form, whose
output light is formed (or guided) by a slit 502, on a
semiconductor substrate 503.
[0065] According to another embodiment of the present invention, a
fabrication method of a solar cell in another form by the laser
firing apparatus for the high efficiency solar cell will be
described. In other words, referring to FIG. 2, a fabrication
method of a solar cell including the front electrode unit and the
rear electrode unit using the laser firing apparatus for the high
efficiency solar cell according to the present invention will be
described.
[0066] First, an antireflective layer is formed on an upper portion
of the front surface of the p type impurity semiconductor
substrate. Thereafter, the n+ layer and the front metal paste
region are sequentially formed, and the back passivation layer is
formed on the upper portion of the back surface of the substrate.
Then, the semiconductor substrate for the solar cell, on which the
back metal paste region is formed, is seated on the first belt type
moving unit. The present embodiment uses the p type impurity
semiconductor substrate, but is not limited thereto. Therefore, the
present embodiment can also use the n type impurity semiconductor
substrate.
[0067] The semiconductor substrate for the solar cell seated on the
first belt type moving unit is irradiated by the first laser and
the second laser while moving to the second belt type moving unit.
The first laser, which is generated in a line form by the first
laser generating unit, is irradiated on the front electrode unit of
the semiconductor substrate for the solar cell to fire and allow
the front electrode unit to contact the n+ layer. In addition, the
second laser, which is generated in a line form by the second laser
generating unit, is irradiated on the back metal paste region and
back electrode unit of the semiconductor substrate for the solar
cell to form the back surface field (BSF) layer to fire and allow
the back electrode unit to contact the semiconductor substrate. The
laser in a line form whose output light is formed by a slit may be
used.
[0068] The laser firing apparatus for the solar cell further
includes a blowing system or an evacuation system and when a laser
is irradiated, can rapidly discharge a fume occurring in the
semiconductor substrate away from the solar cell.
[0069] By being subject to the above processes, the fabrication of
the solar cell where the antireflective layer and the front
electrode unit are formed on the semiconductor substrate and the
back surface field (BSF) layer, the back passivation layer, and the
back electrode unit are sequentially formed is completed.
[0070] In one embodiment, the laser formed by the first laser
generating unit and the laser formed by the second laser generating
unit are simultaneously irradiated, thereby simultaneously forming
the front electrode unit and back electrode unit of the solar cell.
However, the laser generated from the first laser generating unit
and the laser generated from the second laser generating unit need
not be irradiated at the same time. Thus, they may be irradiated at
different times such that the front electrode unit and back
electrode unit of the solar cell are not simultaneously formed.
[0071] In addition, in one embodiment, the first laser generating
unit and the second laser generating unit are disposed at a
position opposite to each other, but are not limited to the
position. In other words, the first laser generating unit and the
second laser generating unit are arranged on a line such that the
laser generated from the first laser generating unit and the laser
generated from the second laser generating unit are irradiated at
different times, and the front electrode unit and back electrode
unit of the solar cell are not simultaneously fired.
[0072] Although the present invention has been described in detail
with reference to example embodiments, it will be understood by
those skilled in the art that various modifications and equivalents
can be made without departing from the spirit and scope of the
present invention, as set forth in the appended claims. Also, the
substances of each constituent features explained in the
specification can be easily selected and processed by those skilled
in the art from the well-known various substances. Also, those
skilled in the art can remove a part of the constituent features as
described in the specification without deterioration of performance
or can add constituent features for improving the performance.
Furthermore, those skilled in the art can change the order to
methodic steps explained in the specification according to
environments of processes or equipments. Thus, it is intended that
embodiments of the present invention cover the modifications and
variations of this invention provided they come within the scope of
the appended claims and their equivalents.
* * * * *