U.S. patent application number 13/632809 was filed with the patent office on 2013-01-31 for thin film type solar cell and method for manufacturing the same.
This patent application is currently assigned to JUSUNG ENGINEERING CO., LTD.. The applicant listed for this patent is JUSUNG ENGINEERING CO., LTD.. Invention is credited to Hyun Jun CHO, Dong Woo KANG, Doo Young KIM, Won Hyun KIM, Dae Yup NA, Hyun Kyo SHIN, Yong Woo SHIN, Cheol Hoon YANG.
Application Number | 20130025661 13/632809 |
Document ID | / |
Family ID | 42234758 |
Filed Date | 2013-01-31 |
United States Patent
Application |
20130025661 |
Kind Code |
A1 |
SHIN; Yong Woo ; et
al. |
January 31, 2013 |
Thin Film Type Solar Cell and Method for Manufacturing the Same
Abstract
A thin film type solar cell and a method for manufacturing the
same is disclosed, which is capable of providing a wide
light-transmission area without lowering cell efficiency and
increasing processing time, so that the solar cell can be used as a
substitute for a glass window in a building. The thin film type
solar cell generally comprises a substrate; a plurality of front
electrodes at fixed intervals on the substrate; a plurality of
semiconductor layers at fixed intervals with a contact portion or
separating channel interposed in-between, the plurality of
semiconductor layers on the plurality of front electrodes; and a
plurality of rear electrodes at fixed intervals by the each
separating channel interposed in-between, the each rear electrode
being electrically connected with the each front electrode; wherein
the each rear electrode is patterned in such a way that a
light-transmitting portion is included in a predetermined portion
of the rear electrode.
Inventors: |
SHIN; Yong Woo; (Yongin,
KR) ; KIM; Won Hyun; (Cheonan, KR) ; NA; Dae
Yup; (Busan, KR) ; CHO; Hyun Jun; (Namyangju,
KR) ; KANG; Dong Woo; (Gwangju, KR) ; KIM; Doo
Young; (Taebaek, KR) ; SHIN; Hyun Kyo; (Seoul,
KR) ; YANG; Cheol Hoon; (Seongnam, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JUSUNG ENGINEERING CO., LTD.; |
Gwangju-si |
|
KR |
|
|
Assignee: |
JUSUNG ENGINEERING CO.,
LTD.
Gwangju-si
KR
|
Family ID: |
42234758 |
Appl. No.: |
13/632809 |
Filed: |
October 1, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12460005 |
Jul 10, 2009 |
8298852 |
|
|
13632809 |
|
|
|
|
Current U.S.
Class: |
136/255 ;
136/256 |
Current CPC
Class: |
Y02B 10/10 20130101;
Y02E 10/50 20130101; H01L 31/022425 20130101; Y02E 10/548 20130101;
H01L 31/0468 20141201; H01L 31/046 20141201 |
Class at
Publication: |
136/255 ;
136/256 |
International
Class: |
H01L 31/06 20120101
H01L031/06; H01L 31/075 20120101 H01L031/075; H01L 31/0224 20060101
H01L031/0224 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2008 |
KR |
10-2008-0135936 |
Apr 24, 2009 |
KR |
10-2009-0036121 |
Claims
1. A thin film type solar cell comprising: a substrate; a plurality
of front electrodes at fixed intervals on the substrate; a
semiconductor layer having a plurality of contact portions and
separating channels interposed therein on the front electrodes; a
transparent conductive layer on the semiconductor, wherein the
transparent conductive layer has a same pattern as the
semiconductor layer; and a plurality of rear electrodes separated
at fixed intervals by a corresponding separating channel, wherein
each rear electrode is electrically connected with one of the front
electrodes through one of the contact portions, and each rear
electrode includes a light-transmitting portion therein so as to
enhance a light-transmission area.
2. The thin film type solar cell of claim 1, wherein the
light-transmitting portion has a straight-line pattern, a
curved-line pattern, a letter-shaped pattern, or a symbol-shaped
pattern.
3. The thin film type solar cell of claim 1, wherein the front
electrode is exposed through the light-transmitting portion.
4. The thin film type solar cell of claim 1, wherein the front
electrode has an uneven structure.
5. The thin film type solar cell of claim 1, wherein the
semiconductor layer has a PIN structure.
6. The thin film type solar cell of claim 1, wherein the
semiconductor layer includes a first semiconductor layer, a buffer
layer, and a second semiconductor layer in sequence.
7. The thin film type solar cell of claim 6, wherein each of the
first semiconductor layer and the second semiconductor layer has a
PIN structure.
8. The thin film type solar cell of claim 6, wherein the first
semiconductor layer comprises amorphous semiconductor material, and
the second semiconductor layer comprises microcrystalline
semiconductor material.
9. The thin film type solar cell of claim 6, wherein the first
semiconductor layer consists essentially of amorphous semiconductor
material, and the second semiconductor layer consists essentially
of microcrystalline semiconductor material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/460,005 (Attorney Docket No.
OP09-JS-007-US-00), filed Jul. 10, 2009, pending, incorporated
herein by reference in its entirety, which in turn claims the
benefit of Korean Patent Application Nos. P2008-0135936 filed on
Dec. 29, 2008, and P2009-0036121 filed on Apr. 24, 2009, which are
hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a thin film type solar
cell, and more particularly, to a thin film type solar cell with a
large light-transmission area, which can be used as a substitute
for a glass window in a building.
[0004] 2. Discussion of the Related Art
[0005] A solar cell with a property of semiconductor converts a
light energy into an electric energy.
[0006] A structure and principle of the solar cell according to the
related art will be briefly explained as follows. The solar cell is
formed in a PN-junction structure where a positive (P)-type
semiconductor makes a junction with a negative (N)-type
semiconductor. When a solar ray is incident on the solar cell with
the PN-junction structure, holes (+) and electrons (-) are
generated in the semiconductor owing to the energy of the solar
ray. By an electric field generated in a PN-junction area, the
holes (+) are drifted toward the P-type semiconductor and the
electrons (-) are drifted toward the N-type semiconductor, whereby
an electric power is produced with an occurrence of electric
potential.
[0007] Solar cells can be largely classified into a wafer type
solar cell and a thin film type solar cell.
[0008] The wafer type solar cell uses a wafer made of a
semiconductor material such as silicon. In the meantime, the thin
film type solar cell is manufactured by forming a semiconductor in
type of a thin film on a glass substrate.
[0009] With respect to efficiency, the wafer type solar cell is
better than the thin film type solar cell. However, in the case of
the wafer type solar cell, it is difficult to realize a small
thickness due to difficulty in performance of the manufacturing
process. In addition, the wafer type solar cell uses a high-priced
semiconductor substrate, whereby its manufacturing cost is
increased. For the wafer type solar cell, it is difficult to obtain
a light-transmission area therein, so that the wafer type solar
cell cannot be used as a substitute for a glass window in a
building.
[0010] In the meantime, even though the thin film type solar cell
is inferior in efficiency to the wafer type solar cell, the thin
film type solar cell has advantages such as realization of thin
profile and use of low-priced material. Accordingly, the thin film
type solar cell is suitable for a mass production. In addition,
since the thin film type solar cell can obtain a light-transmission
area with easiness, the thin film type solar cell can be used as a
substitute for a glass window in a building.
[0011] Hereinafter, a related art thin film type solar cell will be
described with reference to the accompanying drawings.
[0012] FIG. 1 is a perspective view illustrating a related art thin
film type solar cell.
[0013] As shown in FIG. 1, the related art thin film type solar
cell includes a substrate 10; a plurality of front electrodes 20; a
semiconductor layer 30; and a transparent conductive layer 40. At
this time, the plurality of front electrodes 20 are formed at fixed
intervals on the substrate 10, and then the semiconductor layer 30
and the transparent conductive layer 40 are sequentially formed on
the plurality of front electrodes 20. Also, each contact portion 35
and each separating channel 55 are formed in the semiconductor
layer 30 and the transparent conductive layer 40. Then, a plurality
of rear electrodes 50 are formed on the transparent conductive
layer 40. Each rear electrode 50 is electrically connected with the
front electrode 20 by the contact portion 35, and the plurality of
rear electrodes 50 are formed at fixed intervals by each separating
channel 55 interposed in-between.
[0014] However, the related art thin film type solar cell when
being used as the substitute for the glass window in the building
has the following disadvantages.
[0015] In order to use the thin film type solar cell as the
substitute for the glass window in the building, it is necessary
for the thin film type solar cell to obtain the light-transmission
area therein at any size. Since the related art thin film type
solar cell includes the front electrode 20 using transparent metal
and the rear electrode 50 using opaque metal, the
light-transmission area is limited to the separating channel 55
positioned between each of the rear electrodes 50. Accordingly, the
limited light-transmission area in the related art type film type
solar cell cannot secure a wide visible range.
[0016] To widen the light-transmission area, the separating channel
55 positioned between each of the rear electrodes 50 may be
increased in its width. This method may cause problems of lowering
cell efficiency and increasing process time. That is, if increasing
the width of the separating channel 55, an effective area for
production of cell power, is decreased by the increased width of
the separating channel 5, this can lower the cell efficiency. Also,
the separating channel 55 is formed by a laser scribing process,
whereby the laser scribing process has to be performed repetitively
to increase the width of the separating channel 55, thereby causing
a problem of long process time.
SUMMARY OF THE INVENTION
[0017] Accordingly, the present invention is directed to a thin
film type solar cell and a method for manufacturing the same that
substantially obviates one or more problems due to limitations and
disadvantages of the related art.
[0018] An aspect of the present invention is to provide a thin film
type solar cell and a method for manufacturing the same, which is
capable of securing a wide light-transmission area without lowering
cell efficiency and increasing processing time, so that it can be
used as a substitute for a glass window in a building.
[0019] Additional features and aspects of the invention will be set
forth in part in the description which follows and in part will
become apparent to those having ordinary skill in the art upon
examination of the following or may be learned from practice of the
invention. The objectives and other advantages of the invention may
be realized and attained by the structure particularly pointed out
in the written description and claims hereof as well as the
appended drawings.
[0020] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, a thin film type solar cell comprises a substrate; a
plurality of front electrodes at fixed intervals on the substrate;
a plurality of semiconductor layers at fixed intervals by each
contact portion or separating channel interposed in-between, the
plurality of semiconductor layers on the plurality of front
electrodes; and a plurality of rear electrodes at fixed intervals
by the each separating channel interposed in-between, the each rear
electrode being electrically connected with the each front
electrode; wherein the each rear electrode is patterned in such a
way that a light-transmitting portion is included in a
predetermined portion of the rear electrode.
[0021] In another aspect of the present invention, a method for
manufacturing a thin film type solar cell comprises forming a
plurality of front electrodes at fixed intervals on a substrate;
forming a semiconductor layer on an entire surface of the substrate
including the plurality of front electrodes; forming a plurality of
contact portions and separating channels by removing predetermined
portions of the semiconductor layer; and patterning a plurality of
rear electrodes at fixed intervals by each separating channel
interposed in-between, wherein the each rear electrode is
electrically connected with the front electrode through the contact
portion, and the each rear electrode includes a light-transmitting
portion therein so as to enhance a light-transmission area.
[0022] In another aspect of the present invention, a method for
manufacturing a thin film type solar cell comprises forming a
plurality of front electrodes at fixed intervals on a substrate;
forming a semiconductor layer on an entire surface of the substrate
including the plurality of front electrodes; forming a plurality of
contact portions by removing predetermined portions of the
semiconductor layer; patterning a plurality of rear electrodes at
fixed intervals by each separating channel interposed in-between,
wherein the each rear electrode is electrically connected with the
front electrode through the contact portion, and the each rear
electrode includes a light-transmitting portion therein so as to
enhance a light-transmission area; and removing the semiconductor
layer from the light-transmitting portion and separating channel
under such circumstance that the rear electrode is used as a
mask.
[0023] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiment(s) of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
[0025] FIG. 1 is a perspective view illustrating a related art thin
film type solar cell;
[0026] FIG. 2 is a perspective view illustrating a thin film type
solar cell according to one embodiment of the present
invention;
[0027] FIG. 3(A) is a cross section view along A-A of FIG. 2, FIG.
3(B) is a cross section view along B-B of FIG. 2, and FIG. 3(C) is
a cross section view along C-C of FIG. 2;
[0028] FIGS. 4(A and B) is a series of plan views illustrating
various patterns of a light-transmitting portion according to the
present invention;
[0029] FIG. 5 is a perspective view illustrating a thin film type
solar cell according to another embodiment of the present
invention;
[0030] FIG. 6(A) is a cross section view along A-A of FIG. 5, FIG.
6(B) is a cross section view along B-B of FIG. 5, and FIG. 5(C) is
a cross section view along C-C of FIG. 5;
[0031] FIG. 7(A to D) is a series of perspective views illustrating
a method for manufacturing a thin film type solar cell according to
one embodiment of the present invention;
[0032] FIG. 8 is a schematic diagram illustrating a laser scribing
apparatus according to one embodiment of the present invention;
[0033] FIG. 9(A to E) is a series of perspective views illustrating
a method for manufacturing a thin film type solar cell according to
another embodiment of the present invention;
[0034] FIGS. 10(A and B) is a schematic diagram illustrating a wet
etching method according to various embodiments of the present
invention; and
[0035] FIG. 11 is a cross section view illustrating an over etching
occurred for a wet etching process; and
[0036] FIGS. 12(A to E) is a series of perspective views
illustrating a method for manufacturing a thin film type solar cell
according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers will be used throughout the drawings to
refer to the same or like parts.
[0038] Hereinafter, a thin film type solar cell according to the
present invention and a method for manufacturing the same will be
described with reference to the accompanying drawings.
[0039] Thin Film Type Solar Cell
[0040] FIG. 2 is a perspective view illustrating a thin film type
solar cell according to one embodiment of the present invention.
FIG. 3(A) is a cross section view along A-A of FIG. 2, FIG. 3(B) is
a cross section view along B-B of FIG. 2, and FIG. 3(C) is a cross
section view along C-C of FIG. 2.
[0041] As shown in FIG. 2 and FIG. 3(A to C), a thin film type
solar cell according to one embodiment of the present invention
includes a substrate 100, a plurality of front electrodes 200, a
plurality of semiconductor layers 300, a plurality of transparent
conductive layers 400, and a plurality of rear electrodes 500.
[0042] The substrate 100 may be formed of glass or transparent
plastic.
[0043] The plurality of front electrodes 200 may be formed at fixed
intervals on the substrate 100, wherein the front electrode 200 may
be made of a transparent conductive material, for example, ZnO,
ZnO:B, ZnO:Al, SnO.sub.2, SnO.sub.2:F, or ITO (Indium Tin Oxide).
The front electrode 200 corresponds to a solar-ray incidence face.
In this respect, it is important for the front electrode 200 to
transmit the solar ray into the inside of the solar cell with the
maximized absorption of solar ray. For this, the front electrode
200 may have an uneven structure. If forming the front electrode
200 of the uneven structure, a solar-ray reflection ratio on the
solar cell is decreased, and a solar-ray absorption ratio into the
solar cell is increased owing to a dispersion of the solar ray,
thereby improving cell efficiency.
[0044] The plurality of semiconductor layers 300 are formed on the
front electrodes 200, and are positioned at fixed intervals by each
contact portion 350 or each separating channel 550 interposed
in-between. The semiconductor layers 300 may be made of a
silicon-based semiconductor material, and the semiconductor layer
300 may be formed in a PIN structure where a P-type semiconductor
layer, an I-type semiconductor layer, and an N-type semiconductor
layer are deposited in sequence. In the semiconductor layer 300
with the PIN structure, depletion is generated in the I-type
semiconductor layer by the P-type semiconductor layer and the
N-type semiconductor layer, whereby an electric field occurs
therein. Thus, electrons and holes generated by the solar ray are
drifted by the electric field, and the drifted electrons and holes
are collected in the N-type semiconductor layer and the P-type
semiconductor layer, respectively. If forming the semiconductor
layer 300 with the PIN structure, the P-type semiconductor layer is
firstly formed on the front electrode 200, and then the I-type and
N-type semiconductor layers are formed thereon, preferably. This is
because a drift mobility of the hole is less than a drift mobility
of the electron. In order to maximize the efficiency in collection
of the incident light, the P-type semiconductor layer is provided
adjacent to the light-incidence face.
[0045] As shown in the expanded inset of FIG. 2, the semiconductor
layer 300 may be formed in a tandem structure in which a first
semiconductor layer 310, a buffer layer 320 and a second
semiconductor layer 330 are deposited in sequence.
[0046] Each of the first and second semiconductor layers 310 and
330 may be formed in the PIN structure (described above) where the
P-type semiconductor layer, the I-type semiconductor layer, and the
N-type semiconductor layer are deposited in sequence.
[0047] The first semiconductor layer 310 may be formed in a PIN
structure of amorphous semiconductor material, and the second
semiconductor layer 330 may be formed in a PIN structure of
microcrystalline semiconductor material.
[0048] The amorphous semiconductor material is characterized by
absorption of short-wavelength light, and the microcrystalline
semiconductor material is characterized by absorption of
long-wavelength light. A mixture of the amorphous semiconductor
material and the microcrystalline semiconductor material can
enhance light-absorbing efficiency, but it is not limited to this
type of mixture. That is, the first semiconductor layer 310 may be
formed of amorphous semiconductor/germanium material, or
microcrystalline semiconductor material; and the second
semiconductor layer 330 may be formed of amorphous semiconductor
material, or amorphous semiconductor/germanium material.
[0049] The buffer layer 320 is interposed between the first and
second semiconductor layers 310 and 330, wherein the buffer layer
320 enables smooth drift of electron and hole by a tunnel junction.
The buffer layer 320 may be made of a transparent material, for
example, ZnO.
[0050] Instead of the tandem structure, the semiconductor layer 300
may be formed in a triple structure. In case of the triple
structure, each buffer layer is interposed between each of first,
second and third semiconductor layers included in the semiconductor
layer 300.
[0051] The plurality of transparent conductive layers 400 are
formed on the semiconductor layers 300, in the same pattern type as
the semiconductor layers 300. That is, the plurality of transparent
conductive layers 400 are formed at fixed intervals separated by
each contact portion 350 or each separating channel 550 interposed
in-between. The transparent conductive layers 400 may be made of a
transparent conductive material, for example, ZnO, ZnO:B, ZnO:Al,
ZnO:H, or Ag. The transparent conductive layers 400 may be omitted
without departing from the scope and spirit of the invention.
However, in order to improve the cell efficiency, forming the
transparent conductive layer 400 is preferable to omitting the
transparent conductive layer 400. This is because the transparent
conductive layer 400 enables the solar ray transmitted through the
semiconductor layer 300 to be dispersed in all angles, whereby the
solar ray is reflected on the rear electrode layer 500 and is then
re-incident on the semiconductor layer 300, thereby resulting in
the improved cell efficiency.
[0052] The semiconductor layers 300 and transparent conductive
layers 400 may each initially be formed as a single continuous
layer, and the plurality of contact portions 350 and separating
channels 550 are then formed by removing predetermined portions of
the semiconductor layers 300 and transparent conductive layers 400
to yield the configuration shown. Thus, the plurality of contact
portions 350 and separating channels 550 are formed at fixed
intervals.
[0053] Each rear electrode 500 is electrically connected with the
front electrode 200 by the contact portion 350, wherein the
plurality of rear electrodes 500 are formed at fixed intervals by
each separating channel 550 interposed in-between. The rear
electrode 500 may be made of a metal material, for example, Ag, Al,
Ag+Mo, Ag+Ni, or Ag+Cu.
[0054] Next, a plurality of light-transmitting portions 570 are
formed in predetermined patterns in the respective rear electrodes
500. The light-transmitting portions 570 interrupt the metal
material of the rear electrode 500. Through the light-transmitting
portions 570, the transparent conductive layer 400 is exposed so
that the semiconductor layer 300, the front electrode 200, and the
substrate 100 (sequentially positioned beneath the exposed
transparent conductive layer 400) can transmit solar rays.
Eventually, the solar rays incident on the substrate 100 from its
lower side can be transmitted out through the light-transmitting
portion 570, and this effectively allows the light-transmission
area of the solar cell to be increased in size. If the transparent
conductive layer 400 is not formed on the semiconductor layer 300,
the semiconductor layer 300 may be exposed through the
light-transmitting portion 570.
[0055] As shown in FIG. 2, the light-transmitting portions 570 may
each be formed in a straight-line pattern, but are not limited to
this pattern. The light-transmitting portions 570 may be formed in
various patterns in the rear electrode 500.
[0056] FIGS. 4(A and B) are plan views (relative to FIG. 2)
illustrating various alternative patterns of the light-transmitting
portion 570 according to the present invention. As shown in FIG.
4(A), the light-transmitting portion 570 may be formed in a
curved-line pattern. As shown in FIG. 4(B), the light-transmitting
portion 570 may be formed in a letter-shaped pattern. Although not
shown, the light-transmitting portion 570 may be formed in a
symbol-shaped pattern, or other shapes as a matter of design
choice.
[0057] In case of the thin film type solar cell according to one
embodiment of the present invention, the solar ray can be
transmitted through the light-transmitting portion 570 as well as
the separating channel 550. In this case the light-transmission
area is increased because the light-transmitting portions 570
enable the transmittance of the solar rays, in contrast to the
related art. Consequently, the thin film type solar cell according
to the present invention can obtain the enough visible range to be
used as a substitute for a glass window. Moreover, the
light-transmission area of the solar cell can be determined by
adjusting the entire size of the light-transmitting portions 570.
The visible range can be changed appropriately if needed.
Furthermore, the light-transmitting portion 570 formed in the
letter-shaped pattern or symbol-shaped pattern can realize the
effect of advertisement.
[0058] FIG. 5 is a perspective view illustrating a thin film type
solar cell according to another embodiment of the present
invention. FIG. 6(A) is a cross section view along A-A of FIG. 5,
FIG. 6(B) is a cross section view along B-B of FIG. 5, and FIG.
5(C) is a cross section view along C-C of FIG. 5. A thin film type
solar cell according to the embodiment shown in FIGS. 5-6 can be
made by removing the transparent conductive layer 400 exposed
through the light-transmitting portion 570 from the thin film type
solar cell of FIG. 2, as well as the semiconductor layer 300
positioned beneath the removed transparent conductive layer 400.
This further enhances the light-transmitting efficiency.
Notwithstanding the increased depth of the light-transmitting
portion 570, the thin film type solar cell of FIG. 5 is otherwise
similar to the thin film type solar cell of FIG. 2. Thus, wherever
possible, the same reference numbers will be used throughout the
drawings to refer to the same or like parts as those of the
aforementioned embodiment, and the detailed explanation for the
same or like parts will be omitted.
[0059] As shown in FIG. 5 and FIG. 6(A to C), the thin film type
solar cell according to this alternative embodiment of the present
invention includes a light-transmitting portion 570 in a rear
electrode 500. Then, a front electrode 200 is exposed through the
light-transmitting portion 570. Accordingly, when solar rays being
incident on a substrate 100 from a lower side of the substrate 100
are transmitted through the light-transmitting portion 570, the
solar rays pass through only the substrate 100 and front electrode
200. Thus, the light-transmitting efficiency in the thin film type
solar cell of FIG. 5 is further enhanced when compared with that of
the thin film type solar cell of FIG. 2.
[0060] FIG. 5 illustrates that the front electrode 200 is exposed
through the light-transmitting portion 570 by removing the
transparent conductive layer 400 positioned in the
light-transmitting portion 570 and the semiconductor layer 300
positioned there under, but it is equally possible to remove only
the transparent conductive layer 400 positioned in the
light-transmitting portion 570.
[0061] Method for Manufacturing Thin Film Type Solar Cell
[0062] FIG. 7(A to D) is a series of perspective views illustrating
a method for manufacturing the thin film type solar cell according
to the embodiment of FIG. 2.
[0063] First, as shown in FIG. 7(A), the plurality of front
electrodes 200 are formed at fixed intervals on the substrate
100.
[0064] A process for forming the plurality of front electrodes 200
is comprised of steps for forming a transparent conductive layer of
ZnO, ZnO:B, ZnO:Al, SnO.sub.2, SnO.sub.2:F, or ITO (Indium Tin
Oxide) on an entire surface of the substrate 100 by sputtering or
MOCVD (Metal Organic Chemical Vapor Deposition); and removing
predetermined portions of the transparent conductive layer by a
laser-scribing method.
[0065] The front electrode 200 corresponds to the solar-ray
incidence face. In this respect, it is important for the front
electrode 200 to transmit the solar ray into the inside of the
solar cell with the maximized absorption of solar ray. For this,
the front electrode 200 may have an uneven surface which is made by
a texturing process. The texturing process may be, for example, an
etching process using photolithography, an anisotropic etching
process using a chemical solution, or a groove-forming process
using a mechanical scribing.
[0066] Then, as shown in FIG. 7(B), the semiconductor layer 300 and
the transparent conductive layer 400 are sequentially formed as
continuous layers over the entire surface of the substrate 100.
[0067] The semiconductor layer 300 may be made of the silicon-based
semiconductor material, and the semiconductor layer 300 may be
formed in the PIN structure or NIP structure by a plasma CVD
method.
[0068] As explained above with regard to the expanded inset of FIG.
2, the semiconductor layer 300 may be formed in a tandem structure
by depositing the first semiconductor layer 310, the buffer layer
320, and the second semiconductor layer 300 in sequence.
[0069] The transparent conductive layer 400 may be formed of a
transparent conductive material, for example, ZnO, ZnO:B, ZnO:Al,
or Ag, by sputtering or MOCVD (Metal Organic Chemical Vapor
Deposition). Again, the transparent conductive layer(s) 400 may be
omitted.
[0070] As shown in FIG. 7(C), the plurality of contact portions 350
and separating channels 550 are formed by removing the
predetermined portions of the semiconductor layer 300 and
transparent conductive layer 400, leaving the plurality of discrete
semiconductor layers 300 and transparent conductive layers 400
illustrated in FIG. 2.
[0071] A process for forming the contact portions 350 and
separating channels 550 may be performed by a laser-scribing
method. The separating channels 550 may be formed after first
forming the contact portions 350; the contact portions 350 may be
formed after first forming the separating channels 550; or the
contact portions 350 and separating channels 550 may be formed at
the same time.
[0072] For example, the contact portions 350 and separating
channels 550 may be simultaneously formed by one laser-beam
irradiation process, which will be explained with reference to FIG.
8.
[0073] FIG. 8 is a schematic diagram illustrating a laser scribing
apparatus according to the present invention. As shown in FIG. 8,
the laser scribing apparatus is provided with a laser oscillator
600, a first mirror 610, a second mirror 630, a first lens 650, and
a second lens 670. When a laser beam is emitted from the laser
oscillator 600, the emitted laser beam is incident on the first
mirror 610. In this case, the half of the incident laser beam
passes through the first mirror 610, and the other half of the
incident laser beam is reflected on the first mirror 610. Thus, the
laser beam passing through the first mirror 610 is applied to a
targeted object via the first lens 650, and the laser beam
reflected on the first mirror 610 is applied to the targeted object
via the second lens 670 after passing through the second mirror
630. At this time, the second mirror 630 totally reflects the
incident laser beam.
[0074] Eventually, the laser beam emitted from one laser oscillator
600 is divided into laser beams by the two different directions,
that is, the laser beams of the two different directions enable to
form the contact portion 350 and separating channel 550 at the same
time.
[0075] As shown in FIG. 7(D), the rear electrodes 500 are
patterned, thereby completing the thin film type solar cell of FIG.
2.
[0076] Each rear electrode 500 is electrically connected with the
front electrode 200 by the contact portion 350, wherein the
plurality of rear electrodes 500 are formed at fixed intervals by
each separating channel 550 interposed in-between. In the rear
electrode 500, there is the light-transmitting portion 570 to
increase the light-transmission area.
[0077] The plurality of rear electrodes 500 may be simultaneously
formed by a printing process. For example, the plurality of rear
electrodes 500 may be patterned through the use of metal paste such
as Ag, Al, Ag+Mo, Ag+Ni, or Ag+Cu, by a screen printing process, an
inkjet printing process, a gravure printing process, a gravure
offset printing process, a reverse offset printing process, a flexo
printing process, or a microcontact printing process.
[0078] Patterning the rear electrodes 500 by printing enables a
more simplified process, and it can decrease the risk of
contamination of the substrate as compared to patterning methods
using a laser-scribing process. In case of the method using the
printing method, it is possible to decrease the number of steps
involved in performing a cleaning process, so as to prevent the
substrate from being contaminated.
[0079] FIG. 9(A to E) is a series of perspective views illustrating
a method for manufacturing a thin film type solar cell according to
the embodiment of the thin film type solar cell of FIG. 5.
[0080] In case of the thin film type solar cell manufactured by the
aforementioned method explained with reference to FIG. 7(A to D),
the transparent conductive layer 400 is exposed through the
light-transmitting portion 570 (if not forming the transparent
conductive layer 400, the semiconductor layer 300 is exposed
through the light-transmitting portion 570). However, the thin film
type solar cell manufactured by the following method to be
explained with reference to FIG. 9(A to E) can realize the improved
light-transmitting efficiency by additionally removing the
semiconductor layer 300 and transparent conductive layer 400
exposed through the light-transmitting portion 570. Hereinafter,
the explanation for the same or like parts as those of the
aforementioned embodiment will be omitted.
[0081] First, as shown in FIG. 9(A), the plurality of front
electrodes 200 are formed at fixed intervals on the substrate
100.
[0082] Then, as shown in FIG. 9(B), the semiconductor layer 300 and
the transparent conductive layer 400 are sequentially formed on an
entire surface of the substrate 100. The transparent conductive
layer 400 may be omitted.
[0083] As shown in FIG. 9(C), the plurality of contact portions 350
and separating channels 550 are formed by removing the
predetermined portions of the semiconductor layer 300 and
transparent conductive layer 400.
[0084] As shown in FIG. 9(D), the plurality of rear electrodes 500
are patterned at fixed intervals by each separating channel 550
interposed in-between, wherein each rear electrode 500 is
electrically connected with the front electrode 200 through the
contact portion 350. For enhancement of the light-transmission
area, the rear electrode 500 is provided with the
light-transmitting portion 570.
[0085] Next, as shown in FIG. 9(E), the thin film type solar cell
of FIG. 5 is completed by removing the transparent conductive layer
400 exposed through the light-transmitting portion 570 and the
semiconductor layer 300 positioned thereunder.
[0086] FIG. 9(E) illustrates that the front electrode 200 is
exposed through the light-transmitting portion 570 by removing
together the transparent conductive layer 400 positioned in the
light-transmitting portion 570 and the semiconductor layer 300
positioned thereunder, but it is not limited to this. Instead, the
semiconductor layer 300 may be exposed through the
light-transmitting portion 570 by removing only the transparent
conductive layer 400 positioned in the light-transmitting portion
570.
[0087] A process of removing the transparent conductive layer 400
and semiconductor layer 300 exposed through the light-transmitting
portion 570 can be performed by a dry etching process. In this
case, the transparent conductive layer 400 and the semiconductor
layer 300 may be simultaneously removed by controlling an etching
gas. In another aspect, the etching gas may be supplied in twice,
whereby the transparent conductive layer 400 is firstly removed and
then the semiconductor layer 300 is secondly removed.
[0088] The etching gas for removing the transparent conductive
layer 400 may use at least one of CH.sub.4, C.sub.2H.sub.6,
BCl.sub.3, Cl.sub.2, Ar, and H.sub.2.
[0089] The etching gas for removing the semiconductor layer 300 may
a fluorine-based gas, a chlorine-based gas, or their mixture. At
this time, the fluorine-based gas may use at least one of
C.sub.2F.sub.6, SF.sub.6, CF.sub.4, and C.sub.4F.sub.8; and the
chlorine-based gas may use at least one of Cl.sub.2, BCl.sub.3, and
SiCl.sub.4.
[0090] After removing the transparent conductive layer 400 and
semiconductor layer 300 by the dry etching process, the substrate
100 from which the transparent conductive layer 400 and
semiconductor layer 300 are removed may be treated by a drying
process in an oven maintained at a temperature of about 80 to
150.degree. C. The drying process may be omitted.
[0091] A process of removing the transparent conductive layer 400
and semiconductor layer 300 exposed through the light-transmitting
portion 570 can be performed by a wet etching process using the
rear electrode 500 as a mask.
[0092] As shown in FIG. 10(A), the wet etching process may be
performed by submerging the substrate 100 into a predetermined
etchant 700 stored in an etching tub 710. As shown in FIG. 10(B),
the wet etching process may be performed by spraying a
predetermined etchant 700 onto the substrate 100 through the use of
nozzle 720. Especially, the method explained with reference to FIG.
10(B), spraying the etchant 700 onto the substrate 100, enables the
consecutive etching process by transferring the substrate 100
through the use of roller 730.
[0093] In comparison to the general dry etching method, the wet
etching method is advantageous in that the wet etching method
enables the decrease of manufacturing cost and the improved yield
by the rapid processing.
[0094] For realizing these advantages of the wet etching method, it
is important to satisfy the optimum conditions of the wet etching
process. Through repetitive tests, the optimum conditions of the
wet etching process can be summarized as follows. In detail, the
optimum conditions of the wet etching process are related with an
optimum composition of the etchant, an optimum temperature of the
etchant, and an optimum etching processing time period.
[0095] First, the optimum composition of the etchant will be
explained as follows. Preferably, the etchant includes at least one
etching material selected from a group of NaOH, KOH, HCl,
HNO.sub.3, H.sub.2SO.sub.4, H.sub.3PO.sub.3, H.sub.2O.sub.2, and
C.sub.2H.sub.2O.sub.4. Also, the etching material may be diluted
with water, whereby the water solution of the etching material may
be used as the etchant (if the etching material is in a solid
state, the solid-state etching material is inevitably diluted with
water). In this case, a weight ratio of etching material to water
is within a range of 0.1:9.9.about.9.9:0.1. More preferably, a
weight ratio of etching material to water is within a range of
1:9.about.9:1.
[0096] If the weight ratio of etching material to water is less
than 0.1:9.9 (for example, 0.01:9.99), the etching process is not
smooth and the etching processing time period is increased.
Meanwhile, if the weight ratio of etching material to water is more
than 9.9:0.1 (for example, 9.99:0.01), it is difficult to dissolve
the powdered etching material in water.
[0097] Both the optimum temperature of the etchant and the optimum
etching processing time period will be explained as follows. First,
the etchant is optimally maintained at a temperature of 20 to
200.degree. C., preferably. It is more preferable that the etchant
be optimally maintained at a temperature of 50 to 100.degree. C. If
the etchant temperature is maintained below 20.degree. C., it may
cause the unsmooth etching processing and long etching processing
time period. In the meantime, if the etchant temperature is
maintained above 200.degree. C., it is difficult to control the
extent of etching due to the rapid etching progress, thereby
causing an over-etching problem.
[0098] Referring to FIG. 11, when the front electrode 200 is
exposed through the light-transmitting portion 570 by removing the
transparent conductive layer 400 and the semiconductor layer 300
from the light-transmitting portion 570 under such circumstance
that the rear electrode 500 is used as the mask, the extent of
etching may be excessive due to the high-speed etching processing,
whereby the transparent conductive layer 400 and the semiconductor
layer 300 may be over-etched. In addition, the rear electrode 500
may peel off.
[0099] The optimal etching processing time period is about 30
seconds to 10 minutes, preferably. Furthermore, it is more
preferable that the optimal etching processing time period is about
2 minutes to 5 minutes. If the etching processing time period is
less than 30 seconds, it is an insufficient time to accomplish a
desired extent of etching, whereby the light-transmission area is
not increased. In the meantime, if the etching processing time
period is above 10 minutes, as explained with reference to FIG. 11,
the transparent conductive layer 400 and the semiconductor layer
300 may be over-etched, and the rear electrode 500 may peel
off.
[0100] FIG. 12(A to E) is a series of perspective views
illustrating a method for manufacturing a thin film type solar cell
according to another embodiment of the present invention, which is
related with the method for manufacturing the thin film type solar
cell of FIG. 5. Hereinafter, the explanation for the same or like
parts as those of the aforementioned embodiment will be
omitted.
[0101] First, as shown in FIG. 12(A), the plurality of front
electrodes 200 are formed at fixed intervals on the substrate
100.
[0102] Then, as shown in FIG. 12(B), the semiconductor layer 300
and the transparent conductive layer 400 are sequentially formed on
an entire surface of the substrate 100. The transparent conductive
layer 400 may be omitted.
[0103] As shown in FIG. 12(C), the plurality of contact portions
350 are formed by removing the predetermined portions of the
semiconductor layers 300 and transparent conductive layers 400. A
process of forming the contact portions 350 may be performed by a
laser scribing method.
[0104] In another embodiment of the present invention, the
separating channels (See `550` of FIG. 9(C)) are not formed when
forming the contact portions 350 in the semiconductor layer 300 and
the transparent conductive layer 400. Accordingly, a process for
forming the separating channels 550 may be omitted so that the
number of a laser scribing apparatus to be used may be decreased
and the process is simplified.
[0105] As shown in FIG. 12(D), the rear electrodes 500 are
patterned at fixed intervals by each separating channel 550
interposed in-between, wherein each rear electrode 500 is
electrically connected with the front electrode 200 through the
contact portion 350. For enhancement of the light-transmission
area, the rear electrode 500 is provided with the
light-transmitting portion 570.
[0106] As shown in FIG. 12(E), the transparent conductive layer 400
positioned in the light-transmitting portion 570 and the
semiconductor layer 300 positioned there under are removed together
under such circumstance that the rear electrode 500 is used as the
mask, whereby the front electrode 200 is exposed through the
light-transmitting portion 570. Since the rear electrode 500 is
used as the mask, the transparent conductive layer 400 positioned
in the separating channel 550 and the semiconductor layer 300
positioned thereunder are removed, thereby the front electrode 200
is exposed through the separating channel 550. Thus, the thin film
type solar cell of FIG. 5 is completed.
[0107] A process of removing the transparent conductive layer 400
and the semiconductor layer 300 positioned thereunder is performed
by the aforementioned dry etching process or wet etching
process.
[0108] Accordingly, the thin film type solar cell according to the
present invention and the method for manufacturing the same has the
following advantages.
[0109] In the thin film type solar cell according to the present
invention, the light-transmitting portion is patterned in the rear
electrode, whereby the solar ray can be transmitted through the
light-transmitting portion. In comparison to the related art thin
film type solar cell, the thin film type solar cell according to
the present invention obtains the light-transmission area which can
obtain the enough visible range to be used as the substitute for
the glass window.
[0110] In the thin film type solar cell according to the present
invention, the rear electrode is patterned by the various methods
using the printing process. In comparison to the related art method
using the laser-scribing process, the method according to the
present invention, that is, the method using the printing process,
can realize the simplified process and also prevent the
contamination of the substrate. Since the rear electrode is
patterned by the printing method, it is possible to control the
entire size of the light-transmitting portion with easiness. Thus,
if needed, the visible range can be controlled appropriately by
changing the light-transmitting portion of solar cell to a desired
range.
[0111] Accordingly, as the front electrode is exposed through the
light-transmitting portion by removing the transparent conductive
layer and the semiconductor layer, the solar ray being incident on
the substrate from the lower side of the substrate passes through
only the substrate and the front electrode when being transmitted
through the light-transmitting portion, thereby resulting in the
high transmittance of solar ray.
[0112] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the inventions. Thus,
it is intended that the present invention covers the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *