U.S. patent application number 12/858324 was filed with the patent office on 2011-06-09 for dye-sensitized solar cell and method for fabricating the same.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Po-Tsung Hsiao, Ming-De Lu, Hsisheng Teng, Yung-Liang Tung, Kai-Ping Wang.
Application Number | 20110132446 12/858324 |
Document ID | / |
Family ID | 44080822 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110132446 |
Kind Code |
A1 |
Lu; Ming-De ; et
al. |
June 9, 2011 |
DYE-SENSITIZED SOLAR CELL AND METHOD FOR FABRICATING THE SAME
Abstract
A dye-sensitized solar cell and method for fabricating the same
are provided. The dye-sensitized solar cell includes a photo
electrode including a first electrode and a Zn-doped TiO.sub.2
porous layer disposed on the first electrode, wherein the Zn-doped
TiO.sub.2 porous layer absorbs a dye. A second electrode is
disposed opposite to the photo electrode, wherein the Zn-doped
TiO.sub.2 porous layer is disposed between the first and second
electrodes. An electrolyte is disposed between the photo electrode
and the second electrode.
Inventors: |
Lu; Ming-De; (Miaoli County,
TW) ; Tung; Yung-Liang; (Hualien County, TW) ;
Wang; Kai-Ping; (Tainan City, TW) ; Teng;
Hsisheng; (Tainan City, TW) ; Hsiao; Po-Tsung;
(Taoyuan County, TW) |
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
Hsinchu
TW
|
Family ID: |
44080822 |
Appl. No.: |
12/858324 |
Filed: |
August 17, 2010 |
Current U.S.
Class: |
136/255 ;
257/E31.032; 438/98 |
Current CPC
Class: |
Y02E 10/542 20130101;
H01G 9/2036 20130101 |
Class at
Publication: |
136/255 ; 438/98;
257/E31.032 |
International
Class: |
H01L 31/0288 20060101
H01L031/0288; H01L 31/18 20060101 H01L031/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 2009 |
TW |
TW098141672 |
Claims
1. A dye-sensitized solar cell, comprising: a photo electrode
comprising a first electrode and a Zn-doped TiO.sub.2 porous layer
disposed on the first electrode, wherein the Zn-doped TiO.sub.2
porous layer absorbs a dye; a second electrode disposed opposite to
the photo electrode, wherein the Zn-doped TiO.sub.2 porous layer is
disposed between the first and second electrodes; and an
electrolyte disposed between the photo electrode and the second
electrode.
2. The dye-sensitized solar cell as claimed in claim 1, wherein the
Zn-doped TiO.sub.2 porous layer is represented by
Ti.sub.(1-x)Zn.sub.xO.sub.2, wherein 0<x.ltoreq.0.007.
3. The dye-sensitized solar cell as claimed in claim 1, wherein the
first electrode is a transparent electrode.
4. The dye-sensitized solar cell as claimed in claim 1, wherein the
second electrode comprises Pt, conductive polymer, carbon or
composite materials.
5. A method for fabricating a dye-sensitized solar cell,
comprising: (a) mixing a TiO.sub.2 powder, a Zn-containing compound
and an alkaline aqueous solution to form a mixture and performing a
thermal process on the mixture to form a Zn-doped TiO.sub.2 powder;
(b) mixing a binder solution with the Zn-doped TiO.sub.2 powder to
form a paste; (c) coating the paste on a first electrode, and the
paste is performed a sintering process to form a Zn-doped TiO.sub.2
porous layer, wherein the Zn-doped TiO.sub.2 porous layer and the
first electrode construct a photo electrode; (d) disposing a second
electrode opposite to the photo electrode after a dye is absorbed
by the Zn-doped TiO.sub.2 porous layer; and (e) disposing an
electrolyte between the photo electrode and the second
electrode.
6. The method for fabricating a dye-sensitized solar cell as
claimed in claim 5, wherein the thermal process further comprising:
(a) performing a first thermal process on the mixture; (b)
performing a washing process on the mixture using an acidic aqueous
solution; and (c) performing a second thermal process on the
mixture.
7. The method for fabricating a dye-sensitized solar cell as
claimed in claim 5, wherein the Zn-containing compound comprises
Zn-containing inorganic metal salts or organic Zn-containing
compounds.
8. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the first thermal process and the
second thermal process comprise a hydrothermal synthesis
process.
9. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the first thermal process has a process
time of between about 20 to 40 hours.
10. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the first thermal process has a process
temperature of between about 110.degree. C. and 140.degree. C.
11. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the second thermal process has a
process time of between about 10 and 20 hours.
12. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the second thermal process has a
process temperature of between about 180.degree. C. and 250.degree.
C.
13. The method for fabricating a dye-sensitized solar cell as
claimed in claim 5, wherein the alkaline aqueous solution is a
sodium hydroxide aqueous solution.
14. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the acidic aqueous solution is a nitric
acid or hydrogen chloride aqueous solution.
15. The method for fabricating a dye-sensitized solar cell as
claimed in claim 6, wherein the mixture after performing the
washing process reaches a pH value of between about 1.5 and 4.
16. The method for fabricating a dye-sensitized solar cell as
claimed in claim 5, wherein the Zn-doped TiO.sub.2 porous layer is
represented by Ti.sub.(1-x)Zn.sub.xO.sub.2, wherein
0<x.ltoreq.0.007.
17. The method for fabricating a dye-sensitized solar cell as
claimed in claim 5, wherein a solvent of the binder solution
comprises H.sub.2O, an alcohol of C.sub.1-4, terpineol or carbitol,
and a binder of the binder solution comprises sodium carboxymethyl
cellulose, carboxymethyl cellulose (CMC), polyethylene glycol
(PEG), ethyl cellulose (EC) or arcylic resin.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of Taiwan Patent
Application No. 098141672, filed on Dec. 7, 2009, the entirety of
which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a dye-sensitized solar cell
and a method for fabricating the same, and in particular, to a
photo electrode of a dye-sensitized solar cell and a method for
fabricating the same.
[0004] 2. Description of the Related Art
[0005] Solar energy is a promising alternative energy source.
Developments in solar energy technology are driven by the fact that
solar energy is continuous and sustainable. Also, solar energy is
environmentally friendly.
[0006] Generation of solar energy requires solar cells.
Simplistically, electricity is generated by circuitry, generated by
illumination of a material to generate electrons and holes. For
example, a dye-sensitized solar cell (DSSC) is formed by sintering
a semiconductor type metal oxide such as TiO.sub.2 on a conductive
substrate. A dye is then absorbed by a surface of the semiconductor
type metal oxide to form a photo-anode. An electrolyte between the
photo-anode and a cathode aids in electrical conduction. Currently,
technological development of DSSCs is popular due to its high
photo-induced electron transfer efficiency and low costs. However,
for a DSSC applied in a portable power supply, electron loss
resulting in decreased photo-induced electron transfer efficiency
is a problem when the DSSC is under a low light intensity
environment.
[0007] Meanwhile, conventionally used semiconductor photocatalytic
materials, may comprise TiO.sub.2, ZnO, SnO.sub.2 or CdS. Of the
materials, TiO.sub.2 is a popular material due to its high
oxidation-reduction ability, high chemical stability and the fact
that it is non-poisonous. The conventional metal ion-doped
photocatalytic materials are mainly applied to improve
photocatalytic activity by trapping oxides to increase the
absorption of light.
[0008] Thus, a novel dye-sensitized solar cell and a method for
fabricating the same are desired with minimum electron loss under a
low light intensity environment, resulting in increased
photo-induced electron transfer efficiency.
BRIEF SUMMARY OF INVENTION
[0009] A dye-sensitized solar cell and a method for fabricating the
same are provided. An exemplary embodiment of a dye-sensitized
solar cell comprises a photo electrode comprising a first electrode
and a Zn-doped TiO.sub.2 porous layer disposed on the first
electrode, wherein the Zn-doped TiO.sub.2 porous layer absorbs a
dye. A second electrode is disposed opposite to the photo
electrode, wherein the Zn-doped TiO.sub.2 porous layer is disposed
between the first and second electrodes. An electrolyte is disposed
between the photo electrode and the second electrode.
[0010] An exemplary embodiment of a method for fabricating a
dye-sensitized solar cell comprises: (a) mixing a TiO.sub.2 powder,
a Zn-containing compound and an alkaline aqueous solution to form a
mixture and performing a thermal process on the mixture to form a
Zn-doped TiO.sub.2 powder; (b) mixing a binder solution with the
Zn-doped TiO.sub.2 powder to form a paste; (c) coating the paste on
a first electrode, and the paste is sintered to form a Zn-doped
TiO.sub.2 porous layer, wherein the Zn-doped TiO.sub.2 porous layer
and the first electrode construct a photo electrode; (d) disposing
a second electrode opposite to the photo electrode after a dye is
absorbed by the Zn-doped TiO.sub.2 porous layer; and (e) disposing
an electrolyte between the photo electrode and the second
electrode.
[0011] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0012] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0013] FIG. 1 is a schematic diagram showing one exemplary
embodiment of a dye-sensitized solar cell;
[0014] FIG. 2 is an x-ray diffraction diagram showing various
exemplary embodiments of a photo electrode formed by a Zn-doped
TiO.sub.2 porous layer of the invention;
[0015] FIG. 3 is a Mott-Schottky plot showing one exemplary
embodiment of a photo electrode formed by a Zn-doped TiO.sub.2
porous layer of the invention;
[0016] FIGS. 4a to 4b are energy band diagrams showing the
conventional photo electrode formed by undoped TiO.sub.2 and the
one exemplary embodiment of photo electrode formed by a Zn-doped
TiO.sub.2 porous layer of the invention;
[0017] FIG. 5 is a current density-voltage (J-V) curve comparison
between the conventional photo electrode formed by undoped
TiO.sub.2 and various exemplary embodiments of photo electrode
formed by a Zn-doped TiO.sub.2 porous layer of the invention;
[0018] FIG. 6a is a short-circuit current density/light
intensity-light intensity curve comparison between the conventional
photo electrode formed by undoped TiO.sub.2 and various exemplary
embodiments of photo electrode formed by a Zn-doped TiO.sub.2
porous layer of the invention; and
[0019] FIG. 6b is a photoelectric conversion efficiency-light
intensity curve comparison between the conventional photo electrode
formed by undoped TiO.sub.2 and various exemplary embodiments of
photo electrode formed by a Zn-doped TiO.sub.2 porous layer of the
invention.
[0020] Table. 1 shows flat band voltage and donor density
comparisons between the conventional photo electrode formed by
undoped TiO.sub.2 and various exemplary embodiments of photo
electrode formed by a Zn-doped TiO.sub.2 porous layer of the
invention.
DETAILED DESCRIPTION OF INVENTION
[0021] The following description is of a mode for carrying out the
invention. This description is made for the purpose of illustrating
the general principles of the invention and should not be taken in
a limiting sense. The scope of the invention is best determined by
reference to the appended claims. Wherever possible, the same
reference numbers are used in the drawings and the descriptions to
refer the same or like parts.
[0022] The present invention will be described with respect to
particular embodiments and with reference to certain drawings, but
the invention is not limited thereto and is only limited by the
claims. The drawings described are only schematic and are
non-limiting. In the drawings, the size of some of the elements may
be exaggerated and not drawn to scale for illustrative purposes.
The dimensions and the relative dimensions do not correspond to
actual dimensions to practice of the invention.
[0023] One exemplary embodiment of the invention provides a
dye-sensitized solar cell, wherein a photo electrode of the
dye-sensitized solar cell comprises a Zn-doped TiO.sub.2 porous
layer having a continuous electron transport path, thereby
minimizing electron loss and increasing photoelectric conversion
efficiency; especially in low light intensity environments.
[0024] FIG. 1 is a schematic diagram showing one exemplary
embodiment of a dye-sensitized solar cell (DSSC) 500. The DSSC 500
may comprise a photo electrode 201 and an opposing second electrode
202, wherein the photo electrode 201 comprises a first electrode
200 and a Zn-doped TiO.sub.2 porous layer 204 disposed on the first
electrode 200. In one embodiment, the first electrode 200 may
comprise a transparent electrode, for example, a fluorine tin oxide
(FTO) glass or an indium tin oxide (ITO) conductive glass, to
enable outside light to transmit through the first electrode 200
into the DSSC 500. The second electrode 202 may serve as a counter
electrode used to transmit the electrons from the peripheral
circuit into the DSSC, thereby forming a current circuit. The
second electrode 202 may comprise Pt, conductive polymer, carbon or
composite materials. A Zn-doped TiO.sub.2 porous layer 204
absorbing a dye 208 is disposed between the first and second
electrodes 200 and 202. In one embodiment, the dye 208 may comprise
organic dyes or inorganic dyes. An electrolyte 206 is disposed
between the photo electrode 201 and the second electrode 202. In
one embodiment, the electrolyte 206 may comprise liquid or solid
electrolytes.
[0025] When operating one exemplary embodiment of the DSSC 500 of
the invention, the outside light is transmitted through the first
electrode 200 into the Zn-doped TiO.sub.2 porous layer 204 of the
DSSC 500, and the Zn-doped TiO.sub.2 porous layer 204 converts
light energy from the light into electrical energy.
[0026] In one embodiment, a method for fabricating the DSSC 500 may
comprise disposing the Zn-doped TiO.sub.2 porous layer 204 between
the first electrode 200 and the opposing second electrode 202.
Next, an electrolyte 206 is disposed between the photo electrode
201 and the second electrode 202 using an injection or coating
process. A method for fabricating the Zn-doped TiO.sub.2 porous
layer 204 may comprise steps as below.
[0027] Step (a): A TiO.sub.2 powder, a Zn-containing compound and
an alkaline aqueous solution are disposed in an autoclave and mixed
to form a mixture. In one embodiment, the TiO.sub.2 powder may
comprise a commercial TiO.sub.2 photocatalytic (Degussa P25). The
Zn-containing compound may comprise Zn-containing inorganic metal
salts or organic Zn-containing compounds, for example,
Zn(NO.sub.3).sub.26H.sub.2O or Zn(CH.sub.3COO).sub.2xH.sub.2O. The
alkaline aqueous solution may comprise a sodium hydroxidean aqueous
solution (NaOH), wherein the alkaline aqueous solution has a
normality of between about 5 to 15 N, preferably about 10 N.
[0028] Step (b): Performing a first thermal process on the mixture.
In one embodiment, the first thermal process may comprise a
hydrothermal synthesis process, wherein the first thermal process
may have a process time of between about 20 and 40 hours,
preferably about 20 hours. The first thermal process may have a
process temperature of between about 110.degree. C. and 140.degree.
C., preferably about 130.degree. C. After performing the first
thermal process, a flaky mixture is formed.
[0029] Step (c): A washing process is performed on the mixture
using an acidic aqueous solution to neutralize the alkaline aqueous
solution until the pH value of the mixture reaches about 1.5 to 4.
During this time, a Zn-doped TiO.sub.2 multiple layer nano tube is
formed. In one embodiment, the acidic aqueous solution may comprise
an aqueous solution of nitric acid (HNO.sub.3) or hydrogen chloride
(HCl), wherein the acidic aqueous solution has a normality of
between about 0.02 and 0.2N, preferably about 0.1N.
[0030] Step (d): A second thermal process is performed on the
mixture to recrystallize the mixture, thereby more Zn atoms are
doped in the TiO.sub.2. After performing the second thermal
process, Zn-doped TiO.sub.2 powder is formed. In one embodiment,
the second thermal process may comprise a hydrothermal synthesis
process, wherein the first thermal process may have a process time
of between about 10 and 20 hours, preferably about 12 hours. The
second thermal process may have a process temperature, which is
higher than the first thermal process, of between about 180.degree.
C. and 250.degree. C., preferably about 240.degree. C.
[0031] Step (e): A binder solution is mixed with the Zn-doped
TiO.sub.2 powder to form a paste. In one embodiment, a solvent of
the binder solution may comprise H.sub.2O, an alcohol of C.sub.1-4,
terpineol or carbitol. The binder of the binder solution may
comprise sodium carboxymethyl cellulose, carboxymethyl cellulose
(CMC), polyethylene glycol (PEG), ethyl cellulose (EC) or arcylic
resin. In an embodiment of the binder solution formed by the
H.sub.2O solvent and the PEG binder, the Zn-doped TiO.sub.2 powder
may have a weight percentage of between about 30 wt % and 50 wt %,
preferably about 40 wt %.
[0032] Step (f): The paste is coated on a first electrode 200 using
a blade coating or screen printing process and then the paste is
performed a sintering process to form a Zn-doped TiO.sub.2 porous
layer 204, wherein the Zn-doped TiO.sub.2 porous layer 204 and the
first electrode 200 construct a photo electrode 201.
[0033] Step (g): A second electrode 202 is disposed opposite to the
photo electrode 201, so that the Zn-doped TiO.sub.2 porous layer
204 is disposed between the first and second electrodes 200 and 202
with absorbing a dye.
[0034] FIG. 2 is an x-ray diffraction diagram showing the
conventional photo electrode formed by undoped TiO.sub.2 and
various exemplary embodiments of a photo electrode formed by a
Zn-doped TiO.sub.2 porous layer of the invention. Compared with a
peak position of the conventional photo electrode formed by undoped
TiO.sub.2 photo-anode x-ray diffraction curve 20, peak positions of
the exemplary embodiments including: a x-ray diffraction curve 22
of a photo electrode formed by a 0.2 at % (atom percent) Zn-doped
TiO.sub.2 porous layer (described as TZ02 hereinafter); a x-ray
diffraction curve 24 of a photo electrode formed by a 0.4 at %
Zn-doped TiO.sub.2 porous layer (described as TZ04 hereinafter); a
x-ray diffraction curve 26 of a photo electrode formed by a 0.7 at
% Zn-doped TiO.sub.2 porous layer (described as TZ07 hereinafter);
and x-ray diffraction curve 28 of a photo electrode formed by a 1.2
at % Zn-doped TiO.sub.2 porous layer (described as TZ12
hereinafter), all move toward a low diffraction angle. It is to be
understood that in one exemplary embodiment of a photo electrode
formed by a Zn-doped TiO.sub.2 porous layer, a Zn atom having a
large diameter (Zn.sup.2+:0.74 .ANG., Ti.sup.4+:0.6 .ANG.) may be
introduced into the TiO.sub.2 crystal lattice, thereby expanding
the TiO.sub.2 crystal lattice. From FIG. 2, one exemplary
embodiment of a photo electrode formed by a Zn-doped TiO.sub.2
porous layer is represented by Ti.sub.(1-x)Zn.sub.xO.sub.2.
[0035] Additionally, Zn-doped TiO.sub.2 may be used in
photocatalytic materials. In the fabrication process, Zn ion can be
oxidized to form ZnO or be introduced into the TiO.sub.2 crystal
lattice, thereby changing the material composition of TiO.sub.2.
Therefore, Zn-doped TiO.sub.2 photocatalytic performance under
visible light may be changed. Zn-doped TiO.sub.2 used in
photocatalytic materials, however, has a purpose that is different
from one exemplary embodiment of a photo electrode formed by a
Zn-doped TiO.sub.2 porous layer of the invention. The Zn-doped
TiO.sub.2 photocatalytic materials may be used to provide oxide
traps, thereby increasing absorption of light to improve
photocatalytic activity. One exemplary embodiment of a Zn-doped
TiO.sub.2 photo-anode is used to provide an electron transport path
with rapid transport velocity. Meanwhile, the fabricating method of
one exemplary embodiment of a Zn-doped TiO.sub.2 photo-anode is
different from the Zn-doped TiO.sub.2 photocatalytic.
[0036] FIG. 3 is a Mott-Schottky plot showing one exemplary
embodiment of a photo electrode formed by a Zn-doped TiO.sub.2
porous layer, wherein Ag/AgCl is used as a reference electrode.
FIGS. 4a to 4b are energy band diagrams showing the conventional
photo electrode formed by undoped TiO.sub.2 and one exemplary
embodiment of a photo electrode formed by a Zn-doped TiO.sub.2
porous layer. Table. 1 shows flat band voltage calculated from the
intercept of FIG. 3 and donor density results calculated from FIG.
3.
TABLE-US-00001 TiO.sub.2 TZ02 TZ04 TZ07 TZ12 flat band voltage
(E.sub.F -0.556 -0.568 -0.583 -0.640 -0.677 (V vs Ag/AgCl)) donor
density (donor 3.4 .times. 3.9 .times. 4.8 .times. 4.6 .times. 4.5
.times. density (cm.sup.-3)) 10.sup.19 10.sup.19 10.sup.19
10.sup.19 10.sup.19
[0037] From FIG. 3 and Table 1, compared with the conventional
photo electrode formed by undoped TiO.sub.2 photo-anode (labeled as
curve 30), one exemplary embodiment of the a photo electrode formed
by TZ02 (labeled as curve 32), a photo electrode formed by the TZ04
(labeled as curve 34), a photo electrode formed by the TZ07 and a
photo electrode formed by the TZ12 have higher flat band voltage
and donor density. As shown in FIG. 4a, the conventional photo
electrode formed by undoped TiO.sub.2 has a large number of
unoccupied state traps. When the electrons are transported in the
conventional photo electrode formed by undoped TiO.sub.2, the
electrons are easily captured by the unoccupied state traps,
thereby generating electron loss. The electron transport path
P.sub.1 of the conventional photo electrode formed by undoped
TiO.sub.2 is not continuous. FIG. 4b shows that one exemplary
embodiment of a photo electrode formed by the Zn-doped TiO.sub.2
porous layer has high Fermi energy E.sub.Fn, thereby causing a more
curved energy band CB curve. The number of unoccupied state traps
is thus reduced when compared to the conventional photo electrode
formed by undoped TiO.sub.2. Therefore, one exemplary embodiment of
a photo electrode formed by the Zn-doped TiO.sub.2 porous layer can
provide a more continuous electron transport path P.sub.2.
Therefore, electron transportation efficiency is increased, so that
the dye-sensitized solar cell still has high photoelectric
conversion efficiency; especially in low light intensity
environments.
[0038] FIG. 5 is a current density-voltage (J-V) curve comparison
between the conventional photo electrode formed by undoped
TiO.sub.2 (thickness: 15 .mu.m) and various exemplary embodiments
of a photo electrode formed by a Zn-doped TiO.sub.2 porous layer
(thickness: 15 .mu.m) of the invention. The current density versus
voltage result is measured under a simulated sun light source (100
mW*cm.sup.-2) with a bias voltage. From FIG. 5, it is shown that
the current density results of the photo electrode formed by the
TZ04 (labeled as curve 54), the photo electrode formed by the TZ07
(labeled as curve 56) and the photo electrode formed by the TZ12
(labeled as curve 58) are of between about 14 mA*cm.sup.-2 and 16
mA*cm.sup.-2. The photo electrode formed by the TZ04 especially has
the best current density result (16.2 mA*cm.sup.-2), while the
photo electrode formed by the TZ07 has the next best current
density result, which is almost the same with the conventional
photo electrode formed by undoped TiO.sub.2 (15.5
mA*cm.sup.-2).
[0039] FIG. 6a is a short-circuit current density/light
intensity-light intensity curve comparison between the conventional
photo electrode formed by undoped TiO.sub.2 and various exemplary
embodiments of a photo electrode formed by a Zn-doped TiO.sub.2
porous layer. FIG. 6b is a photoelectric conversion
efficiency-light intensity curve comparison between the
conventional photo electrode formed by undoped TiO.sub.2 and
various exemplary embodiments of a photo electrode formed by a
Zn-doped TiO.sub.2 porous layer. From FIG. 6a, it is shown that the
dye-sensitized solar cell with the conventional photo electrode
formed by undoped TiO.sub.2 (labeled as curve 60) has a much
reduced ratio to the short-circuit current density and light
intensity (Jsc/I(A*W.sup.-1)) when light intensity is reduced. The
short-circuit current density/light intensity result of the
dye-sensitized solar cell with the photo electrode formed by the
TZ04 (labeled as curve 64) is not effected when light intensity is
changed. The dye-sensitized solar cell with the photo electrode
formed by the TZ04 has a high output current especially in low
light intensity environments. The dye-sensitized solar cell with
the photo electrode formed by the TZ07 (labeled as curve 66) has
similar short-circuit current density/light intensity result to the
dye-sensitized solar cell with the conventional photo electrode
formed by undoped TiO.sub.2 (labeled as curve 60). Further, the
dye-sensitized solar cell with the photo electrode formed by the
TZ07 (labeled as curve 66) has a better short-circuit current
density/light intensity result than the conventional photo
electrode formed by undoped TiO.sub.2 (labeled as curve 60) in 60
to 80 mW*cm.sup.-2 light intensity environments. If the doping
content of the Zn-doped TiO.sub.2 is too much, for example, such as
the photo electrode formed by the TZ12 photo-anode (labeled as
curve 68), the dye-sensitized solar cell with the Zn-doped
TiO.sub.2 photo-anode has a poorer short-circuit current
density/light intensity result than that of the conventional photo
electrode formed by undoped TiO.sub.2 (labeled as curve 60).
Additionally, as shown in FIG. 6b, the dye-sensitized solar cell
with the photo electrode formed by the TZ04 photo-anode (labeled as
curve 74) has a photoelectric conversion efficiency that is 23%
higher than the conventional photo electrode formed by undoped
TiO.sub.2 (labeled as curve 70). The dye-sensitized solar cell with
the photo electrode formed by the TZ07 (labeled as curve 76) has
similar photoelectric conversion efficiency results as the
dye-sensitized solar cell with the conventional photo electrode
formed by undoped TiO.sub.2 (labeled as curve 70). Further, the
dye-sensitized solar cell with the photo electrode formed by the
TZ07 (labeled as curve 76) has a better photoelectric conversion
efficiency result than the conventional photo electrode formed by
undoped TiO.sub.2 (labeled as curve 70) in 60 to 80 mW*cm.sup.-2
light intensity environments. If the doping content of the Zn-doped
TiO.sub.2 porous layer is too much, for example, such as the photo
electrode formed by the TZ12 (labeled as curve 78), crystal lattice
defects occurs, thereby hindering electron transport in the
photo-anode and reducing photoelectric conversion efficiency. Note
that the photo electrode formed by the TZ12 is an example used for
comparison.
[0040] One exemplary embodiment provides a dye-sensitized solar
cell and a method for fabricating the same, wherein a photo
electrode of the dye-sensitized solar cell is formed by a Zn-doped
TiO.sub.2 porous layer represented by Ti.sub.(1-x)Zn.sub.xO.sub.2,
wherein 0<x.ltoreq.0.007. One exemplary embodiment of a photo
electrode formed by a Zn-doped TiO.sub.2 porous layer has high
Fermi energy E.sub.Fn, thereby causing a more curved energy band CB
curve. The number of unoccupied state traps of the photo electrode
formed by the Zn-doped TiO.sub.2 porous layer is reduced when
compared to conventional photo electrode formed by undoped
TiO.sub.2. Therefore, one exemplary embodiment of the photo
electrode formed by the Zn-doped TiO.sub.2 porous layer can provide
a more continuous electron transport path. Therefore, electron
transportation may be increased, so that the dye-sensitized solar
cell still has high photoelectric conversion efficiency and a high
output current; especially in low light intensity environments.
[0041] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded the
broadest interpretation so as to encompass all such modifications
and similar arrangements.
* * * * *