1. Field
[0001] The present disclosure relates to a solar cell.
BACKGROUND
[00023
10 2. Description of the Related Art
[0003] As demands on energy increase, demands on solar cells for converting
sunlight energy into electrical energy increase. Solar cells are clean energy sources
that produce electricity from the sun. Solar cells have come into the spotlight as new
growth engines with a high industrial growth rate every year.
15 [0004] A copper-indium-gallium-(di)selenide (CIGS) solar cell is a solar ceH that can
be implemented as a thin film and does not use Si. Thus, it is expected that the CIGS
solar cell will play an important role in spreading use of sunlight energy by Jowering
production cost of solar cells. Further, it is known that since the CIGS solar cell is
thermally stable, a decrease in efficiency with time is small. Therefore, various studies
20 have been conducted to increase power-generating capacity of the CIGS solar cell.
Particularly, a plan should be proposed for improving power-generating capacity while
fabricating a thin CIGS.solar cell.
SUMMARY
25 [0005] Aspects of embodiments of the present invention are directed toward a solar
cell capable of improving power generation efficiency while being-implemented to be
thin.
-m
[0006] In an embodiment, a solar cell is provided. The solar cell includes a
substrate, a first electrode layer on the substrate, a second electrode layer on the first
5 electrode layer, anda light absorbing layer on the second electrode Ja^er. In this
embodiment^ the fir§t electrode layer has a first through-region, the second electrode
layer is a transparent electrode layer and has a second through-region, and the second
through-region is narrower than the first through-region and is at a position
corresponding to the first through region.
10 [0007] In one embodiment, the second electrode layer covers an upper surface and
a side surface of the first electrode layer, and the side surface is inside the first
through-region.
[0008] In one embodiment, the second electrode layer covers a portion of the upper
surface of the substrate by a distance equal to a thickness of the second electrode
15 layer.
[0009] In one embodiment, the second electrode layer covers a portion of the upper
surface of the substrate by a distance greater than a thickness of the second electrode
layer.
[0010] In one embodiment, the light absorbing layer contacts at least a portion of
20 the substrate.
[0011] in one embodiment, the difference in a width of the first through-region and a
width of the second through-region is less than the width of the first through-region.
[0012] In one embodiment, the difference in a width of the first through-region and a
width of the second through-region is 10ym or more.
25 [0013] In one embodiment, the difference in a width of the first through-region and a
width of the second through-region is 30ym or more.
[0014] In one embodiment, the first electrode layer is a back surface electrode
layer, and includes at least one selected from Ag, Al, Cu, Au, Pt and Cr.
^i^k
[0015] In one embodiment, the light absorbing layer includes a Group l-lll-VI based
compound semiconductor or a Group l-ll-IV-VI based compound semiconductor.
5 [0016] In one embodiment, the light absorbing layer includes at least one selected
from Cu, In, Ga, S, Se, Zn, and Sjri.
[0017] In one embodiment, the second electrode layer includes at least one
selected from zinc oxide, indium oxide, tin oxide, titanium oxide, and zinc oxide doped
with one or more of Al, Ga and B.
10 [0018] In one embodiment, the second electrode layer has a thickness of at least 10
nm or a thickness of from 50 to 150nm.
[0019] In one embodiment, the solar cell further includes at least one selected from
an adhesion improving layer between the first electrode layer and the substrate, a
diffusion barrier layer between the first electrode layer and the substrate, a contact
15 resistance improving layer between the second electrode layer and the light absorbing
layer, a buffer layer on the light absorbing layer, and a rear surface electrode layer on
a buffer layer on the light absorbing layer.
[0020] in one embodiment, the adhesion improving layer includes at least one
selected from Ti, Cr, Mo and Ni.
20 [0021] In one embodiment, the diffusion barrier layer includes an oxide or nitride
material selected from silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide,
aluminum oxynitride, titanium nitride, tantalum nitride, and tungsten nitride.
[0022] In one embodiment, the contact resistance improving layer includes at least
one of MSex or MSx, wherein M is selected from Mo, W, Ta, Nb, Ti, Cr, V and Mn.
25 [0023] In one embodiment, the solar cell has a thickness of less than ^^m.
[0024] In another embodiment, a method of making a solar cell is provided. The
method includes: forming a first electrode layer on a substrate; forming a first throughregion
through the first electrode layer, to expose a first portion of the substrate;
forming a second electrode layer covering the first electrode layer and the exposed first
portion of the substrate; and forming a second through-region through the second
5 electrode layer in a region of the second electrode layer which is inside the first
through region, to expose a second portion of substrate; forming a light absorbing layer
covering the second electrode layer and the exposed second portion of the substrate.
[0025] In one embodiment, at least one of the forming of the through-region of the
first electrode layer or the forming of the through-region of the second electrode layer
10 includes patterning the first electrode layer or the second electrode layer, respectively.
[0026] In one embodiment, the first electrode layer is formed through a sputtering
process, a deposition process, a plating process, or a screen printing process.
[0027] In one embodiment, the second electrode layer is formed through a
sputtering process, a deposition process, or a chemical vapor deposition (CVD)
15 process.
[0028] Other features and advantages of the present invention will become more
apparent from the following detailed description, taken in conjunction with the
accompanying drawings.
[0029] Terms or words used in this specification and claims should not be
20 restrictively interpreted as ordinary meanings or dictionary-based meanings, but should
be interpreted as meanings and concepts conforming to the scope of the present
disclosure.
[0030] Aspects of embodiments of the present disclosure are directed toward a
solar cell, which allows, in some embodiments, to implement a thin solar cell and to
25 improve power generating efficiency by forming a transparent electrode layer between
a back surface electrode layer and a light absorbing layer.
[0031] In one embodiment, the back surface electrode layer is configured as a high
reflection electrode, thereby improving a re-absorption rate of the solar cell.
^J^
[0032] In one embodiment, the exposed back surface electrode layer is covered
with the transparent electrode layer, so that it is possible to prevent (or reduce)
5 selenization of the back surface electrode layer. Accordingly, in some embodiments, it
is possible to prevent a decrease in resistance of the back surface electrode layer, a
peeling phenomenon and/or a defect caused by diffusion of the high reflection
electrode into the light absorbing layer.
10 BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The accompanying drawings, together with the specification, illustrate
embodiments of the present invention, and, together with the description, serve to
explain the principles of the present invention by way of example.
[0034] FIG. 1 is a cross-sectional view of a solar cell according to an embodiment of
15 the present invention.
[0035] FIGS. 2 and 3 are cross-sectional views comparing solar ceils with the solar
cell shown in FIG. 1.
[0036] FIGS. 4 to 6 are cross-sectional views illustrating a method of fabricating the
solar cell shown in FIG. 1.
20 [0037] FIG. 7 is a cross-sectional view of a solar cell according to another
embodiment of the present invention.
[0038] FIGS. 8 to 11 are cross-sectional views of solar cells according to further
embodiments of the present invention.
25 DETAILE£>©ESCRIPTION
[0039] In the following detailed description, only certain embodiments of the present
invention have been shown and described, by way of example. As those skilled in the
art would realize, the described embodiments may be modified in various different
6
• • ^ ^
ways, all without departing from the spirit or scope of the present invention.
Accordingly, the drawings and description are to be regarded as illustrative in nature
5 and not restrictive. In addition, when an element is referred to as being "on" another
element, it can be directly on the other element or can be indirectly on the other
element with one or more intervening elements interposed therebetween. Also, when
an element is referred to as being "connected to" another element, it can be directly
connected to the other element or can be indirectly connected to the other element
10 with one or more intervening elements interposed therebetween. Hereinafter, like
reference numerals refer to like elements.
[0040] Hereinafter, embodiments of the present invention will be described in more
detail with reference to the accompanying drawings.
[0041] According to an embodiment of the present disclosure, a solar cell is
15 provided, which includes a substrate, a first electrode layer on the substrate, a second
electrode layer on the first electrode layer; and a light absorbing layer on the second
electrode layer. In this embodiment, the first electrode layer has a first through-region,
the second electrode layer has a second through-region, and the second throughregion
is narrower than the first through-region and is at a position corresponding to
20 the first through region. In one embodiment, the second electrode layer is a
transparent electrode layer. In one embodiment, the first electrode layer is a back
surface electrode layer.
[0042] FIG. 1 is a cross-sectional view of a solar cell 100 according to an
embodiment of the present invention. Hereinafter, the solar cell 100 according to this
25 embodiment will be described with reference to FIG. 1.
[0043] As shown in FIG. 1, the solar cell 100 according to this embodiment
sequentially includes a substrate 110, a first electrode layer 120in which a la-th
through-hole 121 is formed, a second electrode layer 130, in which a Ib-th through4
1
hole 131 is formed, and a light absorbing layer 140. In one embodiment, the second
electrode layer 130 is a transparent electrode layer 130. In one embodiment, the first
5 electrode layer 120 is a back surface-electrode layer 120.
[0044] According to some embodiments, the substrate 110 is a member that
provides a base on which the back surface electrode layer 120 and the transparent
electrode layer 130 are formed. That is, in one embodiment, the substrate 110 is the
base of the solar cell 100.
10 [0045] In one embodiment, the substrate 110 is a glass substrate, ceramic
substrate, metal substrate, or polymer substrate. For example, in one embodiment,
the substrate 110 is a glass substrate including alkali elements such as Na, K or Cs. In
some embodiments, the substrate 110 is a sodalime glass substrate or high strained
point soda glass substrate.
15 [0046] in some embodiments, the back surface electrode layer 120 is a member
which is formed on the substrate 110, and includes the la-th through-region 121.
[0047] In one embodiment, the la-th through-hole 121 is formed in the back surface
electrode layer 120 through a patterning process. The term "through-region" as used
herein (e.g. in referring to the la-th through-region 121) refers to a through-hole or a
20 space in which inner walls of the patterned back surface electrode layers 120 defining
the through-hole or the space, are spaced apart from each other. In one embodiment
the back surface electrode layer 120 is made of metal having good stability at a high
temperature and high electrical conductivity. In this embodiment, the back surface
electrode layer 120 is made of high {©flection metal such as Ag, Al, Cu, Pt or Cr. In
25 some embodiments, an particularly in embodiments where the high reflection metal is
used as the back surface electrode layer 120, the reflectivity of light transmitted into
the solar cell 100 is high even though the solar cell 100 is implemented to be thin.
4
1
Thus, in some embodiments, the amount of light reabsorbed in the solar cell 100
increases, thereby reducing current loss.
5 [0048] In some embodiments, the transparent electrode layer 130 is a member
formed on the back surface electrode layer 120 having the 1a-th through-region 121
formed therein.
[0049] In one embodiment, the Ib-th through-region 131 is formed in the
transparent electrode layer 130 through a patterning process. In one embodiment, the
10 1b-th through-region 131 is formed at a position corresponding to the la-th throughregion
121. In one embodiment, a portion of the substrate 110 is exposed by the 1b-th
through-region 131, so as to contact the light absorbing layer 140. In some
embodiments, the width of the Ib-th through-region 131 is narrower than that of the lath
through-region 121. That is, in these embodiments, a width along a direction that
15 spaces apart inner walls of the patterned back surface electrode layers 120 (e.g. the
la-th through-region 121) defining the through-hole or the space, is larger than a width
of the Ib-th through-region 131 along the same direction. To put it another way, the
width is along a direction that spaces apart the inner walls of the transparent electrode.
In one embodiment, the difference in a width of the la-th 4hrough-region 121 and a
20 width of the Ib-th through-region 131 is less than the width of the la-th through-region
121. In one embodiment, the difference in width between the la-th through-region 121
and the Ib-th through-region 131 is lOf/m or more. In another embodiment, the
difference in width between the la-th through-region 121 and the Ib-th through-region
131 is 30f/in or more. In some embodiments, and particularly in embodiments where
25 the width of the Ib-th through-region 131 is narrower than that of the la-th throughregion
121 as described above, the transparent electrode layer 130 is positioned to
extend to the upper surface of the back surface electrode layer 120, the side surface of
the back surface electrode layer 120, exposed by the la-th through-region 121, and a
1
portion of the upper surface of the substrate 110, exposed by the la-th through-region
121. In some of these embodiments, the transparent electrode layer 130 is positioned
5 at a portion adjacent to the back surface electrode layer 120 on the upper surface of
the substrate 110, such that the Ib-th through-region 131 is positioned to correspond
to the la-th through-region 121. In one embodiment, the transparent electrode layer
130 is formed to have, for example, a thickness of 50 to 150nm. In one embodiment,
the thickness of the transparent electrode layer 130 positioned at the exposed side
10 surface of the back surface electrode layer 120 is, for example, lOnm or more in order
to prevent or reduce a selenization reaction between the back surface electrode layer
120 and the light absorbing layer 140.
[0050] Although it has been described in this embodiment that the width of the 1 b-th
through-region 131 is narrower by ^0m or more than that of the la-th through-region
15 121, and therefore, the transparent electrode layer 130 is extended up to the exposed
upper surface of the substrate 110, the present invention is not limited thereto. For
example, embodiments where the width of the 1b-th through-region 131 is
implemented to be slightly narrower than that of the la-th through-region 121, so that
the transparent electrode layer 130 is formed on only the upper and side surfaces of
20 the back surface electrode layer 120 are included within the scope of the present
invention. For example, in some embodiments, the second electrode layer covers a
portion of the upper surface of the substrate by a distance equal to a thickness of the
second electrode layer (e.g. as shown in FIG. 2) and, in other embodiments, the
second electrode layer covers a portion of the upper surface of the substrate by a
25 distance greater than a thickness of the second electrode layer (e.g. as shown in FIG.
1)-
[0051] In one embodiment, a transparent and conductive material is used for the
transparent electrode layer 130, which in some embodiments, allows for improvement
10
of reflectivity and refractive index. In some embodiments, the transparent electrode
layer 130 is made of a transparent conductive oxide (TOC), for example, zinc oxide,
5 indium oxide, tin oxide, titanium oxide, and/or zinc oxide doped with one or more of Al,
Ga, and/or B (e.g. ZnO; ZnO doped with Al, Ga, and/or B; In203; Sn02; and/or Ti02).
[0052] In one embodiment, the light absorbing layer 140 is a member which is
formed on the transparent electrode layer 130 having the 1b-th through-region 131
formed therein.
10 [0053] In one embodiment, the light absorbing layer 140 is a portion of the solar cell
absorbing light. In one embodiment, the light absorbing layer includes at least one
selected from Cu, In, Ga, S, Se, Zn, and Sn. In one embodiment, the light absorbing
layer is formed of a Group l-lll-VI based compound semiconductor or Group l-ll-IV-VI
based compound semiconductor. Examples of the Group I element according to some
15 embodiments include Cu, Ag, and Au. Examples of the Group II element according to
some embodiments include Zn and Cd. Examples of the Group III element according
to some embodiments include In, Ga, and Al. Examples of the Group IV element
according to some embodiments include Si, Ge, Sn, and Pb. Examples of the Group
VI element according to some embodiments include S, Se, and Te.
20 [0054] Specifically, examples of the Group l-lll-VI based compound semiconductor
include a compound semiconductor such as CIS, CGS or CIGS (here, C denotes
copper (Cu), I denotes indium (In), G denotes gallium (Ga), and S denotes one or more
of sulfur (S) and selenium (Se)). An example of the Group l-ll-IV-VI based compound
semiconductor is a compound semiconductor such as CZTS (here, C denotes copper
25 (Cu), Z denotes zinc (Zn), T denotes tin (Sn), and S denotes one or more of sulfur (S)
and selenium (Se)).
11
%
1
[0055] FIGS. 2 and 3 are cross-sectional views comparing solar cells (10 and 20)
with the solar cell 100 shown in FIG. 1. Hereinafter, the solar cell 100 according to this
5 embodiment will be described in more detailed with reference to FIGS. 2 and 3.
[0056] As shown in FIG. 2, in one embodiment, a general back surface electrode
layer 12 formed on a substrate 11 of a solar cell 10 is made of molybdenum (Mo).
Here, the Mo is stable under the selenization atmosphere of a light absorbing layer 14,
but the reflectivity of the Mo is relatively low. Therefore, in a case where the thickness
10 of the solar cell 10 is implemented to be thin, the re-absorption of light is reduced.
Particularly, in a case where the solar cell 10 is implemented to have a thickness of
lym or less, current loss of a few mA/cm^ is expected. Here, reference numeral 13
denotes an alloy layer, and in an embodiment, corresponds to a layer formed by a
selenization reaction between the Mo and the light absorbing layer 14.
15 [0057] in an embodiment, in order to improve re-absorption , a solar cell 20 includes
a high reflection metal such as Ag as a back surface electrode layer 22, which is
formed on a substrate 21 as shown in FIG. 3. However, the high reflection metal such
as Ag is unstable under a selenization atmosphere of 400°C or more, and therefore, the
entire back surface electrode layer 22 may be transferred into AgSex. In a case where
20 the entire back surface electrode layer 22 is transferred into AgSex, the resistance of
the back surface electrode layer 22 is lost, and the AgSex has a low adhesive property
with the substrate 21. As shown in FIG. 3, the peeling phenomenon may occur in a
subsequent process. The Ag of the back surface electrode layer 22 is diffused in a
light absorbing layer 24 configured with GIGS, and therefore, a defect may occur in the
25 light absorbing layer 24.
[0058] The solar cell 100 according to an embodiment is derived at least in part,
from the above considerations, and aspects of embodiments of the present invention,
12
f
for example, the solar cell 100 as shown in FIG. 1, are directed toward overcoming the
aforementioned problems.
5 [0059] Specifically, although the solar cell 100 according to embodiments of the
present disclosure is implemented to have a thickness of O.S/ym or less using high
reflection metal such as Ag or Al as the back surface electrode layer 120, current loss
is low, thereby increasing a re-absorption rate of light. In one embodiment, the
transparent electrode layer 130 is formed after the la-th through-region 121 is formed
10 in the back surface eJectrode layer 120, and thus it is possible, in embodiments of the
present disclosure, to prevent or substantially prevent the back surface electrode layer
120 and the light absorbing layer 140 from coming in direct contact with each other. In
these embodiments, the transparent electrode layer 130 is formed not only on the
upper surface of the back surface electrode layer 120 but also on the exposed side
15 surface of the back surface electrode layer 120, so that it is possible to prevent or
substantially prevent, in advance, the high reflection metal such as Ag and the Se of
the light absorbing layer 140 from reacting with each other through the exposed side
surface of the back surface electrode layer 120. Thus, it is possible, in some
embodiments, to prevent or substantially prevent, in advance, the entire back surface
20 electrode layer 120 from being transferred into AgSex due to the reaction between Se
and Ag through the exposed side surface of the back surface electrode layer 120.
Accordingly, it is possible to prevent or reduce resistance loss due to the transfer of the
back surface electrode layer into AgSex, occurrence of a peeling phenomenon, and/or
occurrence of a defect.
25 [0060] In one embodiment, the transparent electrode layer 130 is also formed on
the upper surface of the substrate 110, exposed by the la-th through-region 121,
because, for example, the width of the la-th through-region 121 is wider than that of
the Ib-th through-region 131. In embodiments where the transparent electrode layer
13
1
130 is formed to extend up to the upper surface of the substrate 110, it is possible to
more certainly prevent or reduce the high reflection metal from reacting with the Se of
5 the light absorbing layer 140.
[0061] FIGS. 4 to 6 are cross-sectional views illustrating a fabricating method of the
solar cell 100 shown in FIG. 1. Hereinafter, the fabricating method of the solar cell 100
according to this embodiment will be described with reference to FIGS. 4 to 6.
[0062] First, as shown in FIG. 4, a patterned back surface electrode layer 120 is
10 formed on the upper surface of a substrate 110.
[0063] In some embodiments, a la-th through region 121 Is formed in the back
surface electrode layer through a patterning process, and a portion of the upper
surface of the substrate 110 is exposed to the outside by the la-th through-region 121.
In some embodiments, the back surface electrode layer 120 is formed through a
15 sputtering process, a deposition process, a plating process, and/or a screen printing
process. In some embodiments, the la-th through-region 121 is formed through, for
example, a laser process.
[0064] Next, as shown in FIG. 5, a transparent electrode layer 130 is formed on the
back surface electrode layer 120 having the la-th through-region 121 formed therein.
20 [0065] In some embodiments, a 1b-th through-region 131 Is formed In the
transparent electrode layer 130 through a patterning process. In some embodiments,
the 1b-th through-region 131 is formed to correspond to the position at which the la-th
through-region 121 is formed. In some embodiments, the transparent electrode layer
130 is formed through a sputtering process, a deposition process, or a chemical vapor
25 deposition (CVD) process. In some embodiments, the Ib-th through-region 131 Is
formed through a laser process. In some embodiments, the width of the 1 b-th throughregion
131 is narrower by lOym or more or narrower by SOym or iwMer-compared to that
14
•
1
of the 1a-th through-region 121, for example, depending on mechanical tolerance
according to the laser process.
5 [0066] Next, as shown in FIG. 6, according to one embodiment, a light absorbing
layer 140 is formed on the transparent electrode layer 130 having the Ib-th throughregion
131 formed therein, thereby fabricating the solar cell 100.
[0067] FIG. 7 is a cross-sectional view of a solar cell 200 according to another
embodiment of the present invention. Hereinafter, the solar cell 200 according to this
10 embodiment will be described with reference to FIG. 7.
[0068] As shown in FIG. 7, the solar cell 200 according to this embodiment includes
a substrate 210, a back surface electrode layer 220 in which a la-th through-region is
formed, a transparent electrode layer 230 in which a Ib-th through-region 231 is
formed, and a light absorbing layer 240, as shown in FIG. 1. In some embodiments,
15 the solar cell 200 further includes a buffer layer 250 and a rear surface electrode layer
260.
[0069] In some embodiments, the buffer layer 250 is formed with at least one layer
on the light absorbing layer 240. Here, the light absorbing layer 240 formed beneath
the buffer layer 250 acts as a p-type semiconductor, and the rear surface electrode
20 layer 260 formed on the buffer layer 250 acts as an n-type semiconductor, so that a pn
junction can be formed between the light absorbing layer 240 and the rear surface
electrode layer 260. In these embodiment, the buffer layer 250 is formed to have a
bandgap at a middle level between those of the light absorbing layer 240 and the-rear
surface electrode layer 260, so that an good junction between the light absorbing layer
25 240 and the rear surface electrode layer 260 can be implemented. In one
embodiment, the buffer layer 250 is made, for example, of CdS or ZnS. In some
embodiments, the buffer layer 250 is patterned together with the light absorbing layer
15
240. Accordingly, in some embodiments, the buffer layer 250 includes a second
through-region 251.
5 [0070] In some embodiments, the rear surface electrode layer 260 is formed on the
buffer layer 260. In one embodiment, the rear surface electrode layer 260 is a
conductive layer and acts as an n-type semiconductor. For example, in one
embodiment, the rear surface electrode layer 260 is made of a transparent conductive
oxide (TOC). In one embodiment, the rear surface electrode layer 260 is made of
10 ZnO. In one embodiment, the rear surface electrode layer 260 is patterned together
with the buffer layer 250 and the light absorbing layer 240. Accordingly, in one
embodiment, the rear surface electrode layer 260 has a third through-region 261.
[0071] FIGS. 8 to 11 are cross-sectional views of solar cells 300, 400, 500 and 600
according to still other embodiments of the present invention. Hereinafter, the solar
15 cells 300, 400, 500 and 600 according to these embodiments will be described with
reference to FIGS. 8 to 11.
[0072] First, as shown in FIG. 8, the solar cell 300 according to this embodiment
includes a substrate 310, a back surface electrode layer 320 in which a 1a-th throughregion
321 is formed, a transparent electrode layer 330 in which a Ib-th through-region
20 331 is formed, and a light absorbing layer 340, as described in FIG. 1. In one
embodiment, the solar cell 300 further includes an adhesion improving layer 350,
[0073] Here, the adhesion improving layer 350 is interposed between the back
surface electrode layer 320 and the substrate 310. According to one embodiment, the
adhesion improving layer 350 is a member for improving adhesion between the
25 substrate 310 and the back surface electrode layer 320 made of high reflection metal.
In one embodiment, the adhesion improving layer 350 is formed between the substrate
310 and a portion of the back surface electrode layer 320 at which the la-th throughregion
321 is not formed therein. In some embodiments, the adhesion improving layer
16
350 includes at least one of Ti, Cr, Mo and Ni. In one embodiment, the adhesion
improving layer 350 is formed before the formation of the back surface electrode layer
5 320. In one embodiment, the adhesion improving layer 350 is patterned together with
the back surface electrode layer 320 when the 1a-th through-region 321 is formed,
after the formation of the back surface electrode layer 320.
[0074] As shown in FIG. 9, the solar cell 400 according to this embodiment includes
a substrate 410, a back surface electrode layer 420 in which a 1a-th through-region
10 421 is formed, a transparent electrode layer 430 in which a Ib-th through-region 431 is
formed, and a light absorbing layer 440, as described in FIG. 1. In one embodiment,
the solar cell 400 further includes a diffusion barrier layer 450.
[0075] In one embodiment, the diffusion barrier layer 450 is formed between the
back surface electrode layer 420 and the substrate 410. More specifically, in one
15 embodiment, the diffusion barrier layer 450 is formed between the substrate 410 and a
portion of the back surface electrode layer at which the la-th through-region 421 is not
formed therein. In one embodiment, the diffusion barrier layer 450 is a member for
preventing (or reducing) alkali ions such as Na or K ions, or Fe ions from being
diffused from the substrate 410. In one embodiment, the diffusion barrier layer 450
20 includes at least one an oxide and/or a nitride material such as silicon oxide, silicon
nitride, silicon oxynitride, aluminum oxide, aluminum oxynitride, titanium nitride,
tantalum nitride, or tungsten nitride (e.g. SiOx, SiNx, SiOxNy, AI2O3, AlOxNy, TiN, TaN
and/or WN). In one embodiment, the diffusion barrier layer 450 is formed before the
formation of the back surface electrode layer 420. In one embodiment, the diffusion
25 barrier layer 450 is patterned together with the back surface electrode layer 420 when
the la-th through-region 421 is formed after the formation of the back surface
electrode layer 420.
17
1
[0076] As shown in FIG. 10, the solar cell 500 according to this embodiment
includes a substrate 510, a back surface electrode layer 520 in which a 1a-th through-
5 region 521 is formed, a transparent electrode layer 530 in which a Ib-th through-region
531 is formed, and a light absorbing layer 540, as described in FIG. 1. In one
embodiment, the solar cell 500 further includes a diffusion barrier layer 550.
[0077] That is, the diffusion barrier layer 550 according to this embodiment is
formed between the substrate 510 and the back surface electrode layer 520. Unlike
10 FIG. 9, the diffusion barrier layer 550, in one embodimentVfS'also formed on the upper
surface of the substrate 510 having the 1a-th through-region 521 formed thereon. In
this embodiment, the diffusion barrier layer 550 is also formed on the upper surface of
the substrate 510 having the la-th through-region 521 formed thereon, and thus it is
possible to prevent impurities from being diffused through the la-th through-region
15 521. In one embodiment, the diffusion barrier layer 550 is formed before the formation
of the back surface electrode layer 520. In some embodiments, the diffusion barrier
layer 550 remains on the upper surface of the substrate 510 when the la-th throughregion
521 is formed after the formation of the back surface electrode layer 520, e.g.,
by controlling energy of laser.
20 [0078] As shown in FIG. 11, the solar cell 600 according to this embodiment
includes a substrate 610, a back surface electrode layer 620 in which a la-th throughregion
621 is formed, a transparent electrode layer 630 in which a Ib-th through-region
631 is formed, and a light absorbing layer 640, as described in FIG. 1. In one
embodiment, the solar cell 600 further includes a contact resistance improving layer
25 650.
[0079] In one embodiment, the contact resistance improving layer 650 is a member
for improving contact resistance between the transparent electrode layer 630 and the
light absorbing layer 640. In one embodiment, the contact resistance improving layer
18
650 is made of a p-type semiconductor material having a higher concentration of holes
than that of the light absorbing layer 640. in one embodiment, the contact resistance
5 improving layer 650 includes at least one of IVISex and MS^ (here, M is, for example,
any one of IVIo, W, Ta, Nb, Ti, Cr, V or Mn). In one embodiment, the contact resistance
improving layer 650 is formed between the transparent electrode layer 630 and the
light absorbing layer 640. In this case, the contact resistance improving layer 650 is
formed before the formation of the transparent electrode layer 630. In one
10 embodiment, the contact resistance improving layer 650 is patterned together with the
transparent electrode layer 630 when the 1b-th through-region 631 is formed.
[0080] While the present invention has been described in connection with certain
exemplary embodiments, it is to be understood that the invention is not limited to the
disclosed embodiments, but, on the contrary, is intended to cover various modifications
15 and equivalent arrangements included within the spirit and scope of the appended
claims, and equivalents thereof.
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[0081] 12 NOV 2 08
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[0082] WE CLAIM:
5 1. A solar cell comprising:
a substrate;
a first electrode layer on the substrate;
a second electrode layer on the first electrode layer; and
.^ a light absorbing layer on the second electrode layer,
wherein:
the first electrode layer has a first through-region;
the second electrode layer is a transparent electrode layer and has a second
through-region; and
the second through-region is narrower than the first through-region and is at a
position corresponding to the first through region.
2. The solar cell as claimed in claim 1, wherein the second electrode layer covers
an upper surface and a side surface of the first electrode layer, and wherein the
side surface is inside the first through-region.
3. The solar cell as claimed in claim 2, wherein the second electrode layer covers
25 a portion of the upper surface of the substrate by a distance equal to a thickness
of the second electrode layer.
4. The solar cell as claimed in claim 2, wherein the second electrode layer covers
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a portion of the upper surface of the substrate by a distance greater than a
thickness of the second electrode layer.
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5. The solar cell as claimed in claim 1, wherein the light absorbing layer contacts
at least a portion of the substrate.
10 6. The solar cell as claimed in claim 1, wherein the difference in a width of the first
through-region and a width of the second through-region is ^0^m or more.
7. The solar cell as claimed in claim 1, wherein the difference in a width of the first
.(- through-region and a width of the second through-region is 30um or more.
8. The solar cell as claimed in claim 1, wherein the first electrode layer is a back
surface electrode layer, and comprises at least one selected from Ag, Al, Cu,
Au, Pt and Cr.
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9. The solar cell as claimed in claim 1, wherein the light absorbing layer comprises
a Group l-lll-VI based compound semiconductor or a Group l-ll-IV-VI based
compound semiconductor.
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10. The solar cell as claimed in claim 1, wherein the light absorbing layer comprises
at least one selected from Cu, In, Ga, S, Se, Zn, and Sn.
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11. The solar cell as claimed in claim 1, wherein the second electrode layer
5
comprises at least one selected from zinc oxide, indium oxide, tin oxide, titanium
oxide, and zinc oxide doped with one or more of Al, Ga and B.
12.The solar cell as claimed in claim 1, wherein the second electrode layer has a
10 thickness of at least 10 nm or a thickness of from 50 to 150nm.
13. The solar cell as claimed in claim 1, further comprising at least one selected
from:
.c an adhesion improving layer between the first electrode layer and the
substrate;
a diffusion barrier layer between the first electrode layer and the
substrate;
a contact resistance improving layer between the second electrode layer
and the light absorbing layer;
a buffer layer on the light absorbing layer; and
and a rear surface electrode layer on a buffer layer on the light absorbing
layer.
14. The solar cell as claimed in claim 13, wherein the adhesion improving layer
comprises at least one selected from Ti, Cr, Mo and Ni.
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15. The solar cell as claimed in claim 13, wherein the diffusion barrier layer
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comprises an oxide or nitride material, and wherein the oxide or nitride material
is selected from silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide,
aluminum oxynitride, titanium nitride, tantalum nitride, and tungsten nitride.
10 16. The solar cell as claimed in claim 13, wherein the contact resistance improving
layer comprises at least one of MSex or MSx, wherein M is selected from Mo,
W, Ta, Nb, Ti, Cr, V and Mn.
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17. The solar cell as claimed in claim 1, wherein the solar cell has a thickness of
less than 1ym.
18. A method of making a solar cell, the method comprising:
forming a first electrode layer on a substrate;
forming a first through-region through the first electrode layer, to expose a first
portion of the substrate;
forming a second electrode layer covering the first electrode layer and the
exposed first portion of the substrate; and
forming a second through-region through the second electrode layer in a region
of the second electrode layer which is inside the first through region, to expose a
second portion of substrate;
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forming a light absorbing layer covering the second electrode layer and the
exposed second portion of the substrate.
19. The method as claimed in claim 18, wherein at least one of the forming of the
through-region of the first electrode layer or the forming of the through-region of
the second electrode layer comprises patterning the first electrode layer or the
10 second electrode layer, respectively.
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20. The method as claimed in claim 18, wherein the second electrode layer is
formed through a sputtering, deposition, or chemical vapor deposition (CVD)
process.