U.S. patent application number 13/034009 was filed with the patent office on 2011-06-16 for transparent conductive layer and method of manufacturing the same.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Seung-Jae JUNG, Byoung-Kyu LEE, Czang-Ho LEE, Mi-Hwa LIM, Yuk-Hyun NAM, Min-Seok OH, Joon-Young SEO, Myung-Hun SHIN.
Application Number | 20110143483 13/034009 |
Document ID | / |
Family ID | 41463716 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110143483 |
Kind Code |
A1 |
JUNG; Seung-Jae ; et
al. |
June 16, 2011 |
TRANSPARENT CONDUCTIVE LAYER AND METHOD OF MANUFACTURING THE
SAME
Abstract
A transparent conductive layer includes a substrate, a first
conductive layer disposed on the substrate, and a second conductive
layer disposed on the first conductive layer, wherein the second
conductive layer comprises a textured surface and an opening which
exposes the first conductive layer, wherein the opening comprises a
diameter of about 1 micrometer to about 3 micrometers. Also
disclosed is a method of manufacturing the transparent conductive
layer and a photoelectric device.
Inventors: |
JUNG; Seung-Jae; (Seoul,
KR) ; NAM; Yuk-Hyun; (Goyang-si, KR) ; LEE;
Czang-Ho; (Suwon-si, KR) ; SHIN; Myung-Hun;
(Suwon-si, KR) ; OH; Min-Seok; (Yongin-si, KR)
; LEE; Byoung-Kyu; (Suwon-si, KR) ; LIM;
Mi-Hwa; (Seocheon-gun, KR) ; SEO; Joon-Young;
(Seoul, KR) |
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
41463716 |
Appl. No.: |
13/034009 |
Filed: |
February 24, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12413979 |
Mar 30, 2009 |
7932576 |
|
|
13034009 |
|
|
|
|
Current U.S.
Class: |
438/71 ;
257/E31.124 |
Current CPC
Class: |
H01L 31/02366 20130101;
H01L 31/022466 20130101; H01L 31/1884 20130101; Y02E 10/50
20130101; H01L 31/022483 20130101; Y02E 10/548 20130101 |
Class at
Publication: |
438/71 ;
257/E31.124 |
International
Class: |
H01L 31/0224 20060101
H01L031/0224 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2008 |
KR |
10-2008-0065078 |
Claims
1. A method of manufacturing a transparent conductive layer, the
method comprising: disposing a first conductive layer and a second
conductive layer on a substrate, wherein the first conductive layer
and the second conductive layer are disposed sequentially; etching
the second conductive layer to form a textured surface on the
second conductive layer; and etching the second conductive layer to
form an opening which exposes a top surface of the first conductive
layer.
2. The method of claim 1, wherein the first conductive layer is
formed with In.sub.2O.sub.3, and the second conductive layer is
formed with a ZnO-based material.
3. The method of claim 2, wherein the etching of the second
conductive layer further comprises using an etching solution, which
has an etching selection ratio of equal to or greater than about
10:1 of the second conductive layer to the first conductive
layer.
4. The method of claim 3, wherein the etching solution comprises at
least one acid selected from the group consisting of nitric acid,
hydrochloric acid, sulfuric acid, acetic acid, and a combination
comprising at least one of the foregoing acids.
5. The method of claim 1, wherein the opening which exposes the top
surface of the first conductive layer comprises a diameter between
about 1 micrometer to about 3 micrometers.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 12/413,979, filed on Mar. 30, 2009, which claims priority to
Korean Patent Application No. 10-2008-0065078, filed on Jul. 4,
2008, and all the benefits accruing therefrom under 35 U.S.C.
.sctn.119, the contents of which in its entirety are herein
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] This disclosure relates to a transparent conductive layer
and a method of manufacturing the same.
[0004] (b) Description of the Related Art
[0005] A photoelectric device, such as a solar cell, converts light
energy into electric energy. Types of photoelectric devices can be
differentiated by the metals used therein for the active layers.
Thus a solar cell converts solar energy into electric energy, and
generates electricity using at least two kinds of semiconductors, a
P-type semiconductor, and an N-type semiconductor.
[0006] Classes of solar cells include crystalline silicon solar
cells, which are commercially available, thin film solar cells,
which are based on low cost substrates, and composite solar cells,
which can be a crystalline silicon-type solar cell or a thin
film-type solar cell.
[0007] Crystalline silicon solar cells, in which slices of silicon
ingots are used as substrates, are classified as monocrystalline
solar cells or polycrystalline solar cells, depending upon the
silicon processing method. A monocrystalline silicon solar cell has
a PN junction structure including an N-type semiconductor, which
includes a pentavalent element such as phosphorous, arsenic, or
antimony doped into the silicon, and a P-type semiconductor, which
includes a trivalent element, such as boron or gallium doped into
the silicon. The resulting structure is roughly the same as that of
a diode.
[0008] A thin film solar cell can be formed by disposing a film on
a substrate, which includes glass or plastic. In commercially
available thin film solar cells, the diffusion distance of carriers
is very short due to the characteristics of the thin film, as
compared to crystalline silicon solar cells. Also, if the thin film
solar cell is fabricated only with a PN junction structure, the
collection efficiency of light generated electron-hole pairs is
low. Therefore, a thin film solar cell can include a PIN structure
wherein an intrinsic semiconductor-based light-absorbing layer with
a high light absorption is interposed between a P-type
semiconductor and an N-type semiconductor. Commercially available
thin film solar cells include a structure where a front transparent
conductive layer, a PIN layer, and a rear reflective electrode
layer are sequentially disposed on a substrate. In this structure,
the light-absorbing layer is depleted due to the overlying P and
the underlying N layers, which include a high doping concentration,
so that an electric field is generated therein. As a result, when
light, such as sunlight, generates a carrier in the light-absorbing
layer, an electron is collected at the N layer and a hole is
collected at the P layer by way of drift of an internal electric
field, thereby generating an electric current.
[0009] In a solar cell, the light-absorbing layer includes a
multi-component compound such a Si, GaAs, CdTe, or CuInSe.sub.2.
Because silicon is an indirect transition material, the light
absorption coefficient of silicon is very low compared to that of
other compounds, such as CdTe or CuInSe.sub.2. For this reason,
where the light-absorbing layer is disposed as a thin film
including a thickness of several microns or less, it does not
absorb all of the incident light, and therefore current density
loss occurs due to transmitted light.
[0010] A textured transparent conductive layer may be used to
enhance the efficiency of the solar cell. A textured transparent
conductive layer can increase a distance light must travel because
of light scattering, thus improving light absorption and
significantly enhancing an efficiency of the solar cell. However, a
current textured transparent conductive layer preferentially
scatters short wavelength light, thus scatters long wavelength
light less.
[0011] Accordingly, an improved light scattering or trapping
technique including a front transparent conductive layer and a rear
reflective electrode, which can scatter loner wavelength light,
would be desirable to improve the efficiency of a solar cell.
BRIEF SUMMARY OF THE INVENTION
[0012] The disclosed transparent conductive layer, and method of
manufacturing the same, increases light scattering in a long
wavelength region, enhances a light efficiency, and includes a
first conductive layer and a second conductive layer, which can be
sequentially disposed on a substrate, wherein the second conductive
layer includes an opening, which exposes the first conductive
layer, and a top surface of the second conductive layer is a
textured surface.
[0013] Thus the above described and other drawbacks are alleviated
by a transparent conductive layer including a substrate; a first
conductive layer disposed on the substrate; and a second conductive
layer disposed on the first conductive layer, wherein the second
conductive layer includes a textured surface and an opening which
exposes the first conductive layer, wherein the opening includes a
diameter between about 1 micrometer (".mu.m") to about 3 .mu.m.
[0014] The first conductive layer may be formed with
In.sub.2O.sub.3, and the second conductive layer may be formed with
a ZnO-based material.
[0015] The first conductive layer may be formed with
In.sub.2O.sub.3 and equal to or less than 15 weight percent ("wt.
%") of at least one of SnO.sub.x, ZnO.sub.x, WO.sub.x, TiO.sub.x,
and a combination including at least one of the foregoing oxides,
based on the total weight of the first conductive layer.
[0016] The second conductive layer may be formed with ZnO and equal
to or less than 10 wt. % of at least one of AlO.sub.x, GaO.sub.x,
and a combination including at least one of the foregoing oxides,
based on the total weight of the second conductive layer.
[0017] The first conductive layer includes a thickness of between
about 500 angstroms (".ANG.") to about 3000 .ANG..
[0018] The second conductive layer includes a thickness of about
500 .ANG. to about 10,000 .ANG..
[0019] Also disclosed is a method of manufacturing a transparent
conductive layer, the method includes disposing a first conductive
layer and a second conductive layer on a substrate, wherein the
first conductive layer and the second conductive layer are disposed
sequentially, etching the second conductive layer to form a
textured surface on the second conductive layer, and etching the
second conductive layer to form an opening which exposes a top
surface of the first conductive layer.
[0020] The first conductive layer may be formed with
In.sub.2O.sub.3, and the second conductive layer may be formed with
a ZnO-based material.
[0021] Etching of the second conductive layer further comprises
using an etching solution, which has an etching selection ratio of
equal to or greater than 10:1 of the second conductive layer to the
first conductive layer.
[0022] The etching solution includes at least one acid selected
from the group consisting of nitric acid, hydrochloric acid,
sulfuric acid, acetic acid, and a combination including at least
one of the foregoing acids.
[0023] The opening which exposes the top surface of the first
conductive layer includes a diameter between about 1 .mu.m to about
3 .mu.m.
[0024] Also disclosed is a photoelectric device including a
substrate, a first conductive layer disposed on the substrate, a
second conductive layer disposed on the first conductive layer, the
second conductive layer including an opening which exposes the
first conductive layer; a semiconductor layer disposed on the
second conductive layer; and a rear electrode disposed on the
semiconductor layer, wherein a top surface of the second conductive
layer includes a textured surface, and the opening includes a
diameter between about 1 .mu.m to about 3 .mu.m.
[0025] The first conductive layer may be formed with
In.sub.2O.sub.3, and the second conductive layer may be formed with
a ZnO-based material.
[0026] The semiconductor layer includes a lower layer and an upper
layer, wherein the lower layer includes a P layer, an I layer, and
an N layer, which are sequentially disposed on the second
conductive layer, and wherein the upper layer includes a P layer,
an I layer, and an N layer which are sequentially disposed on the
lower layer, wherein the I layer of the lower layer may be formed
with amorphous silicon ("a-Si"), and the I layer of the upper layer
may be formed with micro-crystalline silicon (".mu.c-Si").
[0027] The semiconductor layer includes a multi-layered structure
including a plurality of sub-structures, wherein each sub-structure
includes a P layer, an I layer, and an N layer which are
sequentially disposed.
[0028] The semiconductor layer includes a P layer, an I layer, and
an N layer, which are sequentially disposed on the second
conductive layer.
[0029] In an exemplary embodiment, etching of an
In.sub.2O.sub.3-based first conductive layer can be substantially
reduced or prevented, a selected sheet resistance provided, and a
ZnO-based second conductive layer can include a dual texture
structure to thereby increase light scattering in a long wavelength
region. Consequently, the light efficiency of a photoelectric
device can be improved.
[0030] These and other features, aspects, and advantages of the
disclosed embodiments will become better understood with reference
to the following description and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The disclosed subject matter is particularly pointed out and
distinctly claimed in the claims at the conclusion of the
specification. The foregoing and other objects, features, and
advantages of the disclosed embodiments are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0032] FIG. 1 is a graph illustrating a transmittance of an
exemplary embodiment of a transparent conductive layer, which
comprises a textured surface;
[0033] FIG. 2 and FIG. 3 are cross-sectional views of an exemplary
embodiment of a transparent conductive layer, illustrating a method
of manufacturing the same;
[0034] FIG. 4 is a photograph of an exemplary embodiment of a
transparent conductive layer;
[0035] FIG. 5A is a graph illustrating variation in a transmittance
of a commercially available transparent conductive layer as an
etching time thereof is increased;
[0036] FIG. 5B is a graph illustrating a transmittance of an
exemplary embodiment of a transparent conductive layer as a
function of the wavelength; and
[0037] FIG. 6 is a cross-sectional view of an exemplary embodiment
of a photoelectric device.
[0038] The detailed description explains the exemplary embodiments,
together with aspects, advantages and features, by way of example
with reference to the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The exemplary embodiments are described more fully
hereinafter with reference to the accompanying drawings, in which
exemplary embodiments are shown. As those skilled in the art would
realize, the described embodiments may be modified in various ways,
all without departing from the spirit or scope of the
invention.
[0040] In the drawings, the thickness of layers, films, panels,
regions, etc., are exaggerated for clarity. It will be understood
that when an element such as a layer, film, region, or substrate is
referred to as being "on" another element, it can be directly on
the other element or intervening elements may also be present. Like
reference numerals designate like elements throughout the
specification.
[0041] The terms "the", "a" and "an" do not denote a limitation of
quantity, but rather denote the presence of at least one of the
referenced item.
[0042] A diffuse transmittance can be defined as the degree by
which a direction of light progression is varied when light passes
through a textured surface, and a parallel transmittance can be
defined as the degree by which a direction of light progression is
not varied when light passes through a textured surface. A total
transmittance is a sum of the diffuse transmittance and the
parallel transmittance. A textured surface is a surface which is
uneven or rugged, for example as a result of etching, thereby
increasing the absorption of light.
[0043] FIG. 1 is a graph illustrating a transmittance of an
exemplary embodiment of a transparent conductive layer comprising a
textured surface.
[0044] Methods of forming a transparent conductive layer comprising
a textured surface include a method which comprises disposing
SnO.sub.2:F, or the like, onto a target, the method comprising, for
example atmospheric pressure chemical vapor deposition, and a
method which comprises disposing ZnO:B, or the like, onto a target
by a method comprising, for example, low pressure chemical vapor
deposition. In an embodiment, where a ZnO-based thin film is
disposed by a method which comprises sputtering, or the like, and a
surface of the thin film is etched using an aqueous HCl solution
having a concentration between about 0.1 weight percent("wt %") to
about 5 wt %, specifically about 0.5 wt % to about 1 wt %, more
specifically about 0.75 wt %, a textured surface can be disposed
depending upon a fine structure of the thin film, an etching time,
or the like. FIG. 1 illustrates that a transparent conductive layer
comprising a textured surface can exhibit high diffuse
transmittance in a short wavelength region, but the diffuse
transmittance of the transparent conductive layer can be lower at
longer wavelengths. As is also shown in FIG. 1, amorphous silicon
("a-Si") has an absorption region of about 350 nanometers ("nm") to
about 700 nm, therefore it would be desirable to provide a light
scattering or diffusion effect with a textured transparent
conductive layer to extend the diffuse transmittance to longer
wavelengths. By contrast, the absorption region of
micro-crystalline silicon (".mu.c-Si") is about 700 nm to about
1200 nm, thus providing the desired diffusion effect is more
difficult for .mu.c-Si than a-Si because .mu.c-Si absorbs occurs at
longer wavelengths than a-Si. In an embodiment, a feature size of
the textured surface is between about 0.1 micrometers (.mu.m) to
about 10 .mu.m, specifically between about 0.3 .mu.m to about 7
.mu.m, more specifically equal to or greater than about 1 .mu.m,
and such features can diffuse long wavelength light. However it is
difficult with commercially available processes to dispose a
textured surface comprising this feature size. The feature size can
be defined as a diameter of a cone-shaped crater disposed by a
method of disposing a textured surface.
[0045] FIG. 2 and FIG. 3 are cross-sectional views of a transparent
conductive layer comprising a textured surface according to an
exemplary embodiment, and illustrate a manufacturing method
thereof.
[0046] A method of manufacturing a transparent conductive layer
according to an exemplary embodiment is shown in FIG. 2. In an
embodiment, a substrate 100 is first disposed. A first and a second
conductive layers 110 and 120 are then sequentially disposed onto
the substrate 100 by a method comprising sputtering, or the
like.
[0047] Disposing the first conductive layer 110 may comprise
disposing In.sub.2O.sub.3, or the like. Specifically, an indium
oxide may comprise indium tin oxide ("ITO"), indium zinc oxide
("IZO"), or the like, or a combination comprising at least one of
the foregoing indium oxides. The thickness of the first conductive
layer 110 may be between about 100 angstroms (".ANG.") to about
5000 .ANG., specifically about 500 .ANG. to about 3000 .ANG., more
specifically 1000 .ANG. to about 2000 .ANG.. Furthermore, the
resistivity of the first conductive layer 110 may be between about
1*10.sup.-5 ohm-centimeters (".OMEGA.cm") to about 1*10.sup.-3
.OMEGA.cm, specifically about 1*10.sup.-4 .OMEGA.cm to about
3*10.sup.-4 .OMEGA.cm, more specifically about 2*10.sup.-4
.OMEGA.cm. The first conductive layer 110 may comprise
In.sub.2O.sub.3 and equal to or less than 15 weight percent ("wt.
%") of at least one of SnO.sub.x, ZnO.sub.x, WO.sub.x, TiO.sub.x,
and the like, and a combination comprising at least one of the
foregoing oxides, based on the total weight of the first conductive
layer. In an embodiment, the first conductive layer 110 may be
disposed by disposing less than or equal to 15 wt. % of at least
one of SnO.sub.x, ZnO.sub.x, WO.sub.x, TiO.sub.x, and the like, and
a combination comprising at least one of the foregoing oxides, on
In.sub.2O.sub.3, based on the total weight of the first conductive
layer. When the first conductive layer comprises a combination of
at least one of the foregoing oxides and In.sub.2O.sub.3, the
conductivity of a first conductive layer can be increased, and a
moisture or air sensitivity of the first conductive layer can be
reduced. Disposing the second conductive layer 120 may comprise
disposing a ZnO-based material. The thickness of the second
conductive layer 120 may be between about 100 .ANG. to about 20,000
.ANG., specifically about 500 .ANG. to about 10,000 .ANG., more
specifically about 1000 .ANG. to about 5000 .ANG.. Furthermore, the
resistivity of the second conductive layer 120 may be between about
1*10.sup.-5 .OMEGA.cm to about 1*10.sup.-3 .OMEGA.cm, specifically
between about 2*10.sup.-4 .OMEGA.cm to about 10*10.sup.-4
.OMEGA.cm, more specifically about 4*10.sup.-4 .OMEGA.cm to about
8*10.sup.-4 .OMEGA.cm. The second conductive layer 120 may comprise
ZnO and less than or equal to 10 wt. % of at least one of
AlO.sub.x, GaO.sub.x, and the like, and a combination comprising at
least one of the foregoing oxides, based on the total weight of the
second conductive layer. The second conductive layer 120 may be
disposed by disposing less than or equal to 10 wt. % of at least
one of AlO.sub.x, GaO.sub.x, and the like, and a combination
comprising at least one of the foregoing oxides, based on the total
weight of the second conductive layer, on ZnO. When the second
conductive layer comprises a combination of at least one of the
foregoing oxides and a ZnO-based material, the conductivity of a
second conductive layer can be increased, while a moisture or air
sensitivity of the second conductive layer can be reduced.
[0048] A textured surface T is disposed at a top surface of the
second conductive layer 120 by etching the second conductive layer
120. In an embodiment, the second conductive layer 120 is etched
continuously, and a top surface of the first conductive layer 110
is partially exposed. Thus the second conductive layer 120 can be
disposed such that it comprises an opening A, which exposes the
first conductive layer 110.
[0049] In an embodiment, the first conductive layer 110 can also be
etched due to over-etching after the top surface of the first
conductive layer 110 is exposed. Etching of the first conductive
layer can decrease the electrical conductivity of the first
conductive layer 110 such that the first conductive layer 110,
which can be a transparent electrode, can have a wire resistance
which is less than a selected wire resistance. Therefore, it is
desirable to select the etching solution used for etching the
second conductive layer 120, and the materials for the first and
the second conductive layers 110 and 120, such that etching of the
first conductive layer is minimized or substantially
eliminated.
[0050] As described above, in an embodiment ITO is disposed as the
first conductive layer 110, a ZnO-based material is disposed as the
second conductive layer 120, and an etching solution, which has an
etching selection ratio, is used to conduct the etching. The
etching solution can have an etching selection ratio of the second
conductive layer 120 to the first conductive layer 110 of between
about 5:1 to about 150:1, specifically about 10:1 to about 100:1,
more specifically about 15:1 to about 50:1. The etching solution
can comprise at least one acid selected from the group consisting
of nitric acid, hydrochloric acid, sulfuric acid, acetic acid, and
the like, and a combination comprising at least one of the
foregoing acids.
[0051] The diameter of the top surface of the first conductive
layer 110 exposed through the opening A can be between about 0.1
.mu.m to about 10 .mu.m, specifically about 1 .mu.m to about 3
.mu.m, more specifically about 2 .mu.m. Accordingly, a feature size
of the textured surface can be greater than or equal to 0.5 .mu.m,
specifically greater than or equal to 1 .mu.m, more specifically
greater than or equal to 3.mu.m. A feature comprising a dimension
greater than or equal to 0.5 .mu.m, specifically greater than or
equal to 1 .mu.m, more specifically greater than or equal to 3
.mu.m is difficult to form with existing processes, and a feature
comprising such a dimension can diffuse long wavelength light.
[0052] In an embodiment, disposing the second conductive layer 120
comprises disposing a ZnO-based material, wherein one portion
thereof is etched entirely, and a remaining portion thereof is
partially etched.
[0053] In an embodiment a ZnO-based thin film is disposed by
sputtering, or the like. The ZnO-based thin film can be
poly-crystalline, and can comprise columns. When the etching is
performed using an acidic or a basic solution, the second
conductive layer can be etched anisotropically. Anisotropic etching
can occur if a portion of a layer, such as a grain boundary, is
etched preferentially. Therefore, when the second conductive layer
120 is etched, a cone-shaped crater can be disposed at a top
surface of the second conductive layer 120, and with additional
etching time the crater can be enlarged so that the top surface of
the first conductive layer 110 is partially exposed through the
second conductive layer 120.
[0054] FIG. 4 is a photograph of a top surface of a transparent
conductive layer according to an exemplary embodiment.
[0055] A transparent conductive layer comprising a textured surface
can be disposed by a manufacturing method according to an exemplary
embodiment, which is further described with reference to FIG. 3 and
FIG. 4.
[0056] A first conductive layer 110 is disposed on a substrate 100,
and a second conductive layer 120, which comprises an opening A, is
disposed on the first conductive layer 110. The first conductive
layer 110 is exposed through the opening A. As shown in FIG. 4, a
top surface of the first conductive layer 110 may be flat. This
configuration results because the etching solution, which can have
an etching selection ratio of about 10:1, is used in etching the
second conductive layer 120.
[0057] Accordingly, the transparent conductive layer can have a
selected wire resistance. A top surface of the second conductive
layer 120 is textured, thus the second conductive layer 120
comprises a textured surface. The diameter of the exposed top
surface of the first conductive layer 110 can be between about 0.1
.mu.m to about 10 .mu.m, specifically greater than or equal to
about 1 .mu.m, more specifically greater than or equal to about 3
.mu.m. Accordingly, the textured surface can include both large and
small features, thus can provide the desired light scattering
effect with respect to light of both long and short wavelengths.
Disposing the first conductive layer 110 can comprise disposing
In.sub.2O.sub.3, and disposing the second conductive layer 120 can
comprise disposing a ZnO-based material. Specifically, the first
conductive layer 110 can comprise ITO, IZO, or the like, or a
combination comprising at least one of the foregoing transparent
oxides. The thickness of the first conductive layer 110 can be
between about 100 .ANG. to about 5000 .ANG., specifically between
about 500 .ANG. to about 3000 .ANG., more specifically between
about 1000 .ANG. to about 2000 .ANG., and the thickness of the
second conductive layer 120 can be between about 100 .ANG. to about
20,000 .ANG., specifically between about 500 .ANG. to about 10,000
.ANG., more specifically between about 1000 .ANG. to about 5000
.ANG..
[0058] FIG. 5A is a graph illustrating variation in a transmittance
of a commercially available transparent conductive layer as the
etching time thereof is increased, and FIG. 5B is a graph
illustrating a transmittance of an exemplary embodiment of a
transparent conductive layer as a function of the wavelength.
[0059] Referring to FIG. 5A, TT indicates a total transmittance,
and DT indicates a diffuse transmittance. Increasing the etching
time of a commercially available ZnO-based single layer structure
can increase the diffuse transmittance in the long wavelength
region. However, as shown in FIG. 5A, when the etching time is
increased, the transmittance in the long wavelength region cannot
be improved. Furthermore, etching a ZnO-based single layer
structure can expose a bottom of the single layer structure so that
a sheet resistance may be increased.
[0060] By contrast, a diffuse transmittance DT of a transparent
conductive layer comprising a textured surface can be increased in
a long wavelength region B, as shown in FIG. 5B. Accordingly, in a
thin film solar cell comprising a light-absorbing layer in which it
is desirable to absorb light of long wavelengths, such as light
having a wavelength of equal to or greater than 600 nm, the
scattering of long wavelength light can be increased so that a
light conversion efficiency of the solar cell is improved.
Furthermore, because the transparent conductive layer can comprise
a non-etched first conductive layer based on In.sub.2O.sub.3, the
transparent conductive layer can have a selected sheet
resistance.
[0061] FIG. 6 is a cross-sectional view of a photoelectric device
according to another exemplary embodiment.
[0062] A solar cell comprising a transparent conductive layer
according to an exemplary embodiment is explained with reference to
FIG. 6.
[0063] A solar cell according to an exemplary embodiment includes a
transparent conductive layer disposed on a substrate 100. As
described above, the transparent conductive layer comprises a first
conductive layer 110, which comprises an indium oxide, and a second
conductive layer 120, which comprises a ZnO-based material,
sequentially disposed on the substrate 100. Specifically, the
indium oxide may comprise ITO, IZO, or the like, or a combination
comprising at least one of the foregoing indium oxides. The second
conductive layer 120 is disposed on the first conductive layer 110
such that a top surface of the first conductive layer 110 is
partially exposed. The disposing of the second conductive layer 120
may comprise etching with an etching solution having an etching
selection ratio of the second conductive layer 120 to the first
conductive layer 110 of equal to or greater than about 5:1,
specifically equal to or greater than about 10:1, more specifically
equal to or greater than about 50:1.
[0064] A semiconductor layer 200 is disposed on the transparent
conductive layer, which comprises the first and the second
conductive layers 110 and 120. The semiconductor layer 200 includes
a P layer 130, an I layer 140, and an N layer 150 sequentially
disposed on the transparent conductive layer. The disposing of the
P layer 130, the I layer 140, and the N layer 150 may comprise a
method including plasma chemical vapor deposition ("PECVD"). A rear
conductive layer 160 can be disposed on the N layer 150. A
reflective electrode layer 170 can be disposed on the rear
conductive layer 160.
[0065] The semiconductor layer 200 may comprise a multi-layered
structure comprising a plurality of sub-structures, each of which
comprises a P layer 130, an I layer 140, an the N layer 150, which
are sequentially disposed. In an embodiment, the multi-layered
structure may comprise a tandem structure where the layers are
sequentially disposed in the order PIN/PIN, or the multi-layered
structure may comprise a triple-junction structure where the layers
are sequentially disposed in the order PIN/PIN/PIN, or the
multi-layered structure may comprise a multi-junction structure. In
an embodiment, the semiconductor layer 200 has a multi-layered
structure, which has a broadened light-absorbing region.
[0066] In a tandem structure, a lower-region I layer may comprise
amorphous silicon ("a-Si"), and an upper-region I layer may
comprise micro-crystalline silicon (".mu.c-Si"). Because a light
absorption coefficient of .mu.c-Si is significantly lower than that
of a-Si, scattering of long wavelength light improves a light
efficiency. Accordingly, in a solar cell according to an exemplary
embodiment, the light efficiency can be enhanced, relative to a
light efficiency of a thin film solar cell with a light-absorbing
layer. Thus light absorption of long wavelengths is desirable, as
is the case with the above described tandem structure.
[0067] While this disclosure describes exemplary embodiments, it is
to be understood that the invention is not limited to the disclosed
embodiments. It will be also be understood by those skilled in the
art that various changes can be made and equivalents can be
substituted for elements thereof without departing from the scope
of the disclosed embodiments. In addition, many modifications can
be made to adapt a particular situation or material to the
teachings of this disclosure without departing from the essential
scope thereof. Thus various modifications and equivalent
arrangements are included within the spirit and scope of this
disclosure.
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