U.S. patent application number 11/561037 was filed with the patent office on 2007-12-27 for dispersant compound and method for preparing the same.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Jin Young BAE, Won Cheol JUNG, Eun Sung LEE, Sang Cheol PARK.
Application Number | 20070295957 11/561037 |
Document ID | / |
Family ID | 38872731 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070295957 |
Kind Code |
A1 |
LEE; Eun Sung ; et
al. |
December 27, 2007 |
DISPERSANT COMPOUND AND METHOD FOR PREPARING THE SAME
Abstract
Disclosed herein are a novel oligomeric compound with improved
dispersion performance and a method for preparing the same. The
oligomeric compound comprises a tail structure consisting of
hydrophilic and hydrophobic blocks and an amine or imidazole head
structure. The dye containing the compound can be used to prepare a
paste composition for a semiconductor electrode of a solar cell. A
semiconductor electrode produced using the paste composition and a
solar cell fabricated using the semiconductor electrode exhibit
greatly improved power conversion efficiency and superior
processability.
Inventors: |
LEE; Eun Sung; (Seoul,
KR) ; PARK; Sang Cheol; (Seoul, KR) ; JUNG;
Won Cheol; (Seoul, KR) ; BAE; Jin Young;
(Seoul, KR) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Seoul
KR
|
Family ID: |
38872731 |
Appl. No.: |
11/561037 |
Filed: |
November 17, 2006 |
Current U.S.
Class: |
257/40 ;
257/E51.02; 548/341.1; 977/700 |
Current CPC
Class: |
C07D 233/14 20130101;
H01G 9/2031 20130101; Y02E 10/542 20130101; B82Y 30/00
20130101 |
Class at
Publication: |
257/40 ;
548/341.1; 977/700; 257/E51.02 |
International
Class: |
H01L 51/00 20060101
H01L051/00; C07D 233/14 20060101 C07D233/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2006 |
KR |
10-2006-0056909 |
Claims
1. A compound represented by Formula 1 below: ##STR00009## wherein
R.sub.1 is an amine or imidazole group, X.sub.1, X.sub.2, X.sub.3
and X.sub.4 are each independently H or methyl, A is a substituted
or unsubstituted C.sub.6-C.sub.30 arylene group, a substituted or
unsubstituted C.sub.6-C.sub.30 arylalkylene group, or a substituted
or unsubstituted C.sub.6-C.sub.30 cycloalkylene group, B is a
substituted or unsubstituted C.sub.1-C.sub.20 alkyl group, a
substituted or unsubstituted C.sub.1-C.sub.20 alkenyl group, or a
substituted or unsubstituted C.sub.1-C.sub.20 alkynyl group,
wherein B has a linear or branched structure, m is an integer from
1 to 20, and n is 0 or 1.
2. The compound according to claim 1, wherein the compound is a
compound represented by Formula 2 below: ##STR00010## R.sub.2,
R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each independently H or
methyl, k is an integer from 5 to 10, l is 0 or 1, and m is an
integer from 4 to 10.
3. The compound according to claim 1, wherein the compound is a
compound represented by Formula 3 below: ##STR00011## R.sub.2,
R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each independently H or
methyl, k is an integer from 5 to 10, l is 0 or 1, and m is an
integer from 4 to 10.
4. The compound according to claim 2, wherein the compound is the
compound represented by Formula 4 below: ##STR00012##
5. The compound according to claim 3, wherein the compound is the
compound represented by Formula 5 below: ##STR00013##
6. A paste composition comprising a metal oxide powder, a dye
containing a compound represented by Formula 1 below: ##STR00014##
wherein R.sub.1 is an amine or imidazole group, X.sub.1, X.sub.2,
X.sub.3 and X.sub.4 are each independently H or methyl, A is a
substituted or unsubstituted C.sub.6-C.sub.30 arylene group, a
substituted or unsubstituted C.sub.6-C.sub.30 arylalkylene group,
or a substituted or unsubstituted C.sub.6-C.sub.30 cycloalkylene
group, B is a substituted or unsubstituted C.sub.1-C.sub.20 alkyl
group, a substituted or unsubstituted C.sub.1-C.sub.20 alkenyl
group, or a substituted or unsubstituted C.sub.1-C.sub.20 alkynyl
group, wherein B has a linear or branched structure, m is an
integer from 1 to 20, and n is 0 or 1; and a binder solution.
7. The paste composition of claim 6, comprising 20 to 50% by weight
of the metal oxide powder, 0.1 to 10% by weight of the dye
containing the compound of Formula 1 with respect to the weight of
the metal oxide powder, and wherein the balance of the paste
composition comprises the binder solution.
8. The paste composition of claim 6, wherein the dyes include
ruthenium complexes; xanthene colorants; cyanine colorants; basic
dyes; phenosafranine; Capri blue; thiosine; Methylene Blue;
porphyrinoid compounds; azo colorants; phthalocyanine compounds;
anthraquinone colorants; polycyclic quinone colorants; or a
combination comprising two or more of the foregoing dyes.
9. The paste composition of claim 8, wherein the dyes include
ruthenium trisbipyridyl, Rhodamine B, Rose Bengal, eosin,
erythrosine, quinocyanine cryptocyanine, chlorophyll, zinc
porphyrin, magnesium porphyrin, or mixtures thereof.
10. The paste composition of claim 6, wherein the binder
composition comprises a solvent and t-butanol in a weight ratio
(w/w) of 1:1 to 1:10.
11. The paste composition of claim 10, wherein the solvent
comprises water, glycols, glycerols, or an acetate-based
solvent.
12. The paste composition of claim 6, wherein the metal oxide
comprises at least one metal oxide selected from the group
consisting of titanium oxides, niobium oxides, hafnium oxides,
indium oxides, tin oxides, zinc oxides, or a combination comprising
at least one of the foregoing metal oxides.
13. The paste composition of claim 6, wherein the metal oxide has a
nanostructure selected from nanotubes, nanowires, nanobelts, and
nanoparticles.
14. A metal oxide layer prepared by coating the paste composition
of claim 6 on a substrate, and annealing the coated paste
composition.
15. A semiconductor electrode comprising a transparent electrode
comprising a substrate and an electrically conductive material
coated on a surface of the substrate, a metal oxide layer formed on
a surface of the transparent electrode having the electrically
conducting material, and a dye present in the metal oxide layer
wherein the dye contains the compound of claim 1.
16. A solar cell comprising the semiconductor electrode of claim
15.
17. A method for preparing a compound represented by Formula 1
below: ##STR00015## wherein R.sub.1 is an amine or imidazole group,
X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are each independently H or
methyl, A is a substituted or unsubstituted C.sub.6-C.sub.30
arylene group, a substituted or unsubstituted C.sub.6-C.sub.30
arylalkylene group, or a substituted or unsubstituted
C.sub.6-C.sub.30 cycloalkylene group, B is a substituted or
unsubstituted C.sub.1-C.sub.20 alkyl group, a substituted or
unsubstituted C.sub.1-C.sub.20 alkenyl group, or a substituted or
unsubstituted C.sub.1-C.sub.20 alkynyl group, wherein B has a
linear or branched structure, m is an integer from 1 to 20, and n
is 0 or 1, the method comprising the steps of: (1) adding organic
solvents to a compound of Formula 6 below: ##STR00016## (wherein
X.sub.1, X.sub.2, X.sub.3, X.sub.4, A, B, m and n are as defined in
Formula 1), and reacting the compound of Formula 6 with
methanesulfonyl chloride for a specified time to prepare a compound
represented by Formula 7 below: ##STR00017## (wherein X.sub.1,
X.sub.2, X.sub.3, X.sub.4, A, B, m and n are as defined in Formula
1); and (2) adding an amine or imidazole compound to the compound
of Formula 7 and allowing the mixture to react for a specified time
to prepare the compound of Formula 1.
18. The method according to claim 17, wherein the organic solvent
is selected from the group consisting of: aliphatic hydrocarbon
solvents, including hexane and heptane; aromatic hydrocarbon
solvents, including toluene, pyridine, quinoline, anisole,
mesitylene, and xylene; ketone-based solvents, including methyl
isobutyl ketone, N-methyl-2-pyrrolidone (NMP),
1-methyl-2-pyrrolidinone, cyclohexanone, and acetone; ether-based
solvents, including dimethoxy ether, tetrahydrofuran and isopropyl
ether; alcohol-based solvents, including ethanol, isopropyl
alcohol, butyl alcohol and t-butyl alcohol; amide-based solvents,
including dimethylacetamide and dimethylformamide; silicon-based
solvents; nitrile-based solvents, including acetonitrile;
methanesulfonyl chloride; dichloromethane (CH.sub.2Cl.sub.2);
triethylamine; and mixtures thereof.
19. The method according to claim 17, wherein the reaction of step
(1) is carried out at room temperature for 2-4 hours.
20. The method according to claim 17, wherein the reaction of step
(2) is carried out at 150-200.degree. C. for 2-24 hours.
Description
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn. 119(a) to Korean Patent Application No. 2006-56909,
filed on Jun. 23, 2006, the content of which is herein incorporated
by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a dispersant compound and a
method for preparing the same. More specifically, the present
invention relates to a novel oligomeric compound with improved
dispersion performance, which comprises a tail structure consisting
of hydrophilic and hydrophobic blocks and an amine or imidazole
head structure, and a method for preparing the oligomeric
compound.
[0004] 2. Description of the Related Art
[0005] Dye-sensitized solar cells are photoelectrochemical solar
cells that are essentially composed of photosensitive dye molecules
capable of absorbing visible light rays to form electron-hole pairs
and a transition metal oxide for transferring the generated
electrons.
[0006] Such dye-sensitized solar cells comprise a semiconductor
electrode, an electrolyte, and a counter-electrode wherein the
semiconductor electrode consists of a transparent conductive
substrate, and a light-absorbing layer including a metal oxide and
a dye.
[0007] Generally, the semiconductor electrode is produced by
forming a metal oxide film on a substrate, and adsorbing a dye on
the surface of the metal oxide film. Specifically, the
semiconductor electrode is produced by the following procedure.
First, a paste composition comprising particles of a metal oxide is
applied to a transparent substrate. The paste composition is formed
into a metal oxide film by high-temperature annealing at
400-550.degree. C. The metal oxide film is treated with a solution
containing a dye for a specified time to adsorb the dye on the
available surface of the metal oxide film, thus completing
production of the final semiconductor electrode.
[0008] According to the general method for producing the
semiconductor electrode, since the dye is adsorbed after the metal
oxide film is formed on the substrate, the overall surface area of
the metal oxide particles is not sufficiently utilized. That is,
the area occupied by the dye adsorbed on the metal oxide particles
is very small when compared to the optical cross-section of light
such that low power conversion efficiency of the solar cells is
caused.
[0009] When nanoparticles are used to form the metal oxide film,
they tend to aggregate within the paste composition. The
aggregation of the nanoparticles can lead to a deterioration in
uniformity and a low density for the metal oxide film, which in
turn can cause low power conversion efficiency in the solar
cells.
[0010] To address this, many attempts have been made to solve the
problems of conventional dye-sensitized solar cells. For example,
Korean Patent Laid-open No. 2005-82624 discloses a dye-sensitized
solar cell with improved power conversion efficiency, which
comprises a semiconductor electrode produced by forming a porous
metal oxide film by an electrochemical process using a surfactant,
and with a dye adsorbed on the metal oxide film. Further, Japanese
Unexamined Patent Publication No. 2002-50413 discloses a
dye-sensitized solar cell which comprises an optical semiconductor
layer containing porous optical semiconductor particles, wherein
the porous optical semiconductor particles are prepared by firing
an optical semiconductor powder together with a surfactant or a
hydrophilic polymeric compound and dispersion medium at 400.degree.
C. or higher, followed by crushing this admixture to form the
porous optical semiconductor particles.
[0011] According to the conventional dye-sensitized solar cells,
however, a surfactant or a dispersant is simply added to a metal
oxide powder or optical semiconductor particles and the mixture is
formed into a metal oxide film. The introduction of the surfactant
advantageously increases the porosity of the metal oxide or the
optical semiconductor particles, which in turn allows for the
amount of dye that can be adsorbed to be increased and thereby
improves the uniformity of the metal oxide film to some extent.
However, problems still remain in that since the dye is adsorbed
after the metal oxide film or semiconductor layer is formed, the
overall surface area of the metal oxide particles is not fully or
sufficiently utilized, and as a result, the amount of the dye
adsorbed does not substantially or satisfactorily increase and the
power conversion efficiency of the solar cells does not therefore
improve any further.
[0012] There is thus a need to develop a new dispersant that can
overcome the above-mentioned problems.
BRIEF SUMMARY OF THE INVENTION
[0013] Therefore, the present invention provides, in an embodiment,
a novel oligomeric dispersant compound with improved dispersion
performance which comprises a tail structure consisting of
hydrophilic and hydrophobic blocks and an amine or imidazole head
structure.
[0014] In another embodiment, a method for preparing the oligomeric
dispersant compound is provided.
[0015] In another embodiment, a novel dispersant compound is
provided, which comprises a tail structure consisting of
hydrophilic and hydrophobic blocks, and an amine or imidazole head
structure in which the compound is contained as a ligand in a dye
having a reactive group such as for example COO.sup.- or POO.sup.-,
and which is capable of being bound to the surface of metal oxide
particles so that the tail structure functions as a stabilizer to
prevent the metal oxide particles from aggregating within a paste
composition.
[0016] In another embodiment, a paste composition comprises a metal
oxide, the oligomeric dispersant compound, a dye, and a binder
solution. Sequentially, a metal oxide layer, semiconductor
electrode, and solar cell can be formed from the paste
composition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other features and advantages of the present
invention will be more clearly understood from the following
detailed description taken in conjunction with the accompanying
drawings, in which:
[0018] FIG. 1 is a process chart schematically showing exemplary
production of a Tergitol-mesylate as an intermediate of a
dispersant compound, which is prepared in step (1) of Synthesis
Example 1;
[0019] FIG. 2 shows .sup.1H-NMR spectra identifying the structure
of a Tergitol-mesylate as an exemplary intermediate of a dispersant
compound of the present invention, which is prepared in step (1) of
Synthesis Example 1;
[0020] FIG. 3 shows .sup.1H-NMR spectra identifying the structure
of a Tergitol-amine prepared in step (2) of Synthesis Example 1;
and
[0021] FIG. 4 shows .sup.1H-NMR spectra identifying the structure
of an exemplary Tergitol-imidazole prepared in step (3) of
Synthesis Example 1.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention will now be described in greater
detail.
[0023] It will be understood in the following disclosure of the
present invention, that as used herein, the term "and/or" includes
any and all combinations of one or more of the associated listed
items. In addition, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. It will be further understood that the
terms "comprise", "comprises", and "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, components, and/or combination of the
foregoing, but do not preclude the presence and/or addition of one
or more other features, integers, steps, operations, elements,
components, groups, and/or combination of the foregoing. The use of
the terms "first", "second", and the like, where included, are for
purposes of distinguishing elements only, and therefore should not
be considered as implying any particular order or sequence unless
otherwise specified.
[0024] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0025] The present invention provides a compound represented by
Formula 1 below:
##STR00001##
[0026] wherein R.sub.1 is an amine or imidazole group,
[0027] X.sub.1, X.sub.2, X.sub.3 and X.sub.4 are each independently
H or methyl,
[0028] A is a substituted or unsubstituted C.sub.6-C.sub.30 arylene
group, a substituted or unsubstituted C.sub.6-C.sub.30 arylalkylene
group, or a substituted or unsubstituted C.sub.6-C.sub.30
cycloalkylene group,
[0029] B is a substituted or unsubstituted C.sub.1-C.sub.20 alkyl
group, a substituted or unsubstituted C.sub.1-C.sub.20 alkenyl
group, or a substituted or unsubstituted C.sub.1-C.sub.20 alkynyl
group, wherein B may have a linear or branched structure,
[0030] m is an integer from 1 to 20, and
[0031] n is 0 or 1.
[0032] That is, the compound of Formula 1 according to the present
invention comprises four moieties, i.e. an amine moiety, a
polyethylene glycol ("PEG") moiety, a cyclic moiety, and an
aliphatic hydrocarbon moiety, along the molecular chain of the
compound.
[0033] Of these moieties, the cyclic moiety (corresponding to `A`
in Formula 1) may be a substituted or unsubstituted
C.sub.6-C.sub.30 arylene group, a substituted or unsubstituted
C.sub.6-C.sub.30 arylalkylene group, or a substituted or
unsubstituted C.sub.6-C.sub.30 cycloalkylene group. The aliphatic
hydrocarbon moiety (corresponding to `B` in Formula 1) may be a
substituted or unsubstituted C.sub.1-C.sub.20 alkyl group, a
substituted or unsubstituted C.sub.1-C.sub.20 alkenyl group, or a
substituted or unsubstituted C.sub.1-C.sub.20 alkynyl group, which
may exist in a linear or branched form.
[0034] Specific examples of the alkyl group include linear or
branched alkyl groups, such as methyl, ethyl, propyl, isobutyl,
sec-butyl, tert-butyl, pentyl, iso-amyl and hexyl, but is not
limited to these. At least one hydrogen atom contained in the alkyl
group may be substituted with a halogen atom, a hydroxyl group, a
nitro group, a cyano group, an amino group, an amidino group, a
hydrazine group, a hydrozone group, or the like.
[0035] The term "alkenyl" or "alkynyl" as used herein refers to a
group that contains at least one carbon-carbon double or triple
bond at an intermediate or terminal position of the alkyl group
defined above. At least one hydrogen atom contained in the alkenyl
or alkynyl group may be substituted with the same substituent as
defined with respect to the alkyl group.
[0036] The term "arylene" as used herein refers to a carbocyclic
aromatic system including one or more aromatic rings in which the
rings may be attached together in a pendant manner or may be fused.
Specific examples of the arylene group include aromatic groups,
such as phenyl, naphthyl, and tetrahydronaphthyl. At least one
hydrogen atom contained in the arylene group may be substituted
with the same substituent as defined with respect to the alkyl
group.
[0037] The term "arylalkylene" as used herein refers to a group in
which a part of hydrogen atoms contained in the arylene group
defined above are substituted with lower alkyl radicals, such as
methylene, ethylene and propylene. Examples of the arylalkylene
group include benzylene and phenylethylene. At least one hydrogen
atom contained in the arylalkylene group may be substituted with
the same substituent as defined with respect to the alkyl
group.
[0038] The term "cycloalkylene" as used herein refers to a
C.sub.6-C.sub.30 monovalent monocyclic system. At least one
hydrogen atom contained in the cycloalkylene group may be
substituted with the same substituent as defined with respect to
the alkyl group.
[0039] in an embodiment, the average number (m) of the repeating
units in the polyethylene glycol moiety is 5 to 10. In another
embodiment, the aliphatic hydrocarbon moiety is a branched form
having greater than or equal to 5 carbon atoms. As the length of
the polyethylene glycol moiety decreases, the adsorption of the
compound of Formula 1 to particles increases. As the aliphatic
hydrocarbon moiety has a long chain and is bulky, it can maintain
constant spacing interval between particles, which in turn can
mitigate or reduce the agglomeration of particles and thus improve
the stability of the particles toward agglomeration.
[0040] Specific examples of compounds that can be represented by
Formula 1 include compounds represented by Formulae 2 and 3
below:
##STR00002##
[0041] R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each
independently H or methyl,
[0042] k is an integer from 5 to 10,
[0043] l is 0 or 1, and
[0044] m is an integer from 4 to 10; and
##STR00003##
[0045] wherein X, R.sub.2; R.sub.3, R.sub.4, R.sub.5, R.sub.6, k, l
and m are as defined in Formula 2.
[0046] More specifically, the compound of Formula 1 according to
the present invention may be a compound represented by Formula 4 or
5 below:
##STR00004##
[0047] The compound of Formula 1 according to the present invention
may be synthesized by the following reaction scheme 1 below:
##STR00005##
[0048] wherein
[0049] R.sub.1, X.sub.1, X.sub.2, X.sub.3, X.sub.4, A, B, m and n
are as defined in Formula 1.
[0050] Specifically, the dispersant compound of Formula 1 may be
synthesized by a method comprising the following steps:
[0051] (1) adding organic solvents to a compound of Formula 6
below:
##STR00006##
[0052] wherein X.sub.1, X.sub.2, X.sub.3, X.sub.4, A, B, m and n
are as defined in Formula 1, and reacting the compound of Formula 6
with methanesulfonyl chloride for a specified time to prepare a
compound represented by Formula 7 below:
##STR00007##
[0053] wherein X.sub.1, X.sub.2, X.sub.3, X.sub.4, A, B, m and n
are as defined in Formula 1; and
[0054] (2) adding an amine or imidazole compound to the compound of
Formula 7, and allowing the mixture to react for a specified time
to prepare the compound of Formula 1.
[0055] More specifically, the compound of Formula 1 according to
the present invention may be synthesized in accordance with the
following procedure. An organic solvent is added to the compound of
Formula 6. The compound of Formula 6 is allowed to react with
methanesulfonyl chloride for a specified time. The organic solvent
is removed, and the resulting residue is dried to prepare an
intermediate (Formula 7) having a methanesulfonyl group. After an
amine or imidazole compound is added to the intermediate of Formula
7 in an organic solvent, the mixture is allowed to react for a
specified time. The organic solvent is removed, and the resulting
residue is filtered, purified and dried to prepare the final
compound of Formula 1.
[0056] Non-limiting examples of suitable organic solvents that can
be used in the reactions include: aliphatic hydrocarbon solvents,
such as hexane and heptane; aromatic hydrocarbon solvents, such as
toluene, pyridine, quinoline, anisole, mesitylene, and xylene;
ketone-based solvents, such as methyl isobutyl ketone,
N-methyl-2-pyrrolidone ("NMP"), 1-methyl-2-pyrrolidinone,
cyclohexanone, and acetone; ether-based solvents, such as dimethoxy
ether, tetrahydrofuran and isopropyl ether; alcohol-based solvents,
such as ethanol ("EtOH"), isopropyl alcohol, butyl alcohol and
t-butyl alcohol; amide-based solvents, such as dimethylacetamide
and dimethylformamide ("DMF"); silicon-based solvents;
nitrile-based solvents, such as acetonitrile; methanesulfonyl
chloride; dichloromethane (CH.sub.2Cl.sub.2); triethylamine
(NEt.sub.3); and mixtures thereof.
[0057] The reaction of step (1) is carried out under a nitrogen
atmosphere at room temperature for 2-4 hours, and the reaction of
step (2) is carried out at 150-200.degree. C. for 2-24 hours, more
specifically for 10-14 hours.
[0058] The washing, distillation and drying steps may be
subsequently carried out after step (2). The subsequent steps may
be carried out without limitation by conventional methods.
[0059] The dispersant compound comprises a tail structure
consisting of hydrophilic and hydrophobic blocks and an amine or
imidazole head structure. Based on this structure, the dispersant
compound functions to prevent aggregation of metal oxide particles
within a paste to improve the uniformity of the metal oxide
particles and to increase the density of a film formed of the
paste.
[0060] The dispersant compound is included as a ligand with a dye,
to thereby constitute a tail part of the dye. That is, the dye
containing the dispersant compound includes the dispersant compound
as a functional group which acts as a dispersant. Accordingly, the
dye containing the dispersant compound performs the following two
functions: (1) the dye containing the dispersant compound is
adsorbed on the surface of metal oxide particles to transfer
electrons exited by absorbed light to a conduction band of the
metal oxide; and (2) the dye containing the dispersant compound
itself functions as a dispersant to prevent aggregation of the
metal oxide particles, thereby improving the uniformity of the
particles within a paste and increasing the density of a film
formed of the paste. The dye containing the dispersant compound can
be used to prepare a paste composition for a semiconductor
electrode of a solar cell. A semiconductor electrode produced using
the paste composition and a solar cell fabricated using the
semiconductor electrode exhibit improved power conversion
efficiency and superior processability.
[0061] Exemplary dyes that may be combined with the dispersant
compound include ruthenium complexes such as ruthenium
trisbipyridyl; xanthene colorants, including Rhodamine B, Rose
Bengal, eosin, and erythrosine; cyanine colorants, including
quinocyanine and cryptocyanine; basic dyes; phenosafranine, Capri
blue, thiosine, and Methylene Blue; porphyrinoid compounds,
including chlorophyll, zinc porphyrin, and magnesium porphyrin; azo
colorants; phthalocyanine compounds; anthraquinone colorants;
polycyclic quinone colorants; and mixtures thereof. These dyes may
be used alone or in combinations comprising two or more of the
dyes. Any dye material that can be generally used in the field of
solar cells may be used without any limitation. In an embodiment,
Grazel-type dyes, such as ruthenium compounds (e.g., N3, N719,
Black Dye, and the like), are specifically useful.
[0062] The present invention also provides a paste composition for
the formation of a semiconductor electrode which comprises a dye
containing the compound of Formula 1.
[0063] Specifically, the paste composition comprises a dye, a
binder solution for low-temperature annealing and a metal oxide
powder wherein the dye contains the compound of Formula 1.
[0064] In a conventional method for producing a semiconductor
electrode of a dye-sensitized solar cell, the dye is adsorbed after
a metal oxide film is formed on a substrate, and therefore the
overall surface area of metal oxide particles is not sufficiently
utilized. The area actually occupied by the dye adsorbed on the
metal oxide particles is generally only a tenth of the optical
cross-section of light.
[0065] According to the paste composition of present invention, the
dye containing the dispersant compound, acting as a dispersant, is
added to a slurry dispersion to increase the amount of the dye
adsorbed over the entire surface of the metal oxide particles, as
well as to improve the dispersibility and uniformity of the metal
oxide particles. As a result, a semiconductor electrode and a solar
cell using the paste composition exhibit superior processability
and improved power conversion efficiency.
[0066] On the other hand, the paste composition uses a binder that
can be easily removed by low-temperature annealing. One example of
the binder for low-temperature annealing is t-butanol. Since
t-butanol has a melting point of 25-26.degree. C. and a boiling
point of 80.degree. C., it is completely removed even by
low-temperature annealing at 350.degree. C. and exists in a solid
state at 25.degree. C. or lower. Based on these characteristics,
t-butanol serves to provide strong binding effects due to its
hydrogen bonding to the paste composition after drying.
[0067] Therefore, conventional paste compositions which use binders
that can be removed only by high-temperature annealing at
350.degree. C. or higher can have poor applicability to flexible
plastic substrates. In contrast, since the paste composition
disclosed herein uses a binder for low-temperature annealing, e.g.,
t-butanol, in view of the aforementioned characteristics, the paste
composition disclosed herein can be advantageously applied to
flexible substrates, including plastic substrates.
[0068] The paste composition, as disclosed herein, comprises 20 to
50% by weight of the metal oxide powder, 0.1 to 10% by weight of
the dye containing the compound of Formula 1 with respect to the
weight of the metal oxide powder, and the balance of the paste
composition comprises the binder solution.
[0069] When the dye containing the compound of Formula 1 is used in
an amount of less than 0.1% by weight, relative to the weight of
the metal oxide powder, the desirable properties (for example, an
increase in the amount of the dye adsorbed on the metal oxide
powder, sufficient injection of electrons excited by absorbed light
into a conduction band of the metal oxide, and desired dispersion
effects of the dye) cannot be attained. Meanwhile, when the dye
containing the compound of Formula 1 is used in an amount exceeding
10% by weight, relative to the weight of the metal oxide powder,
the excess dye that remains unadsorbed to the metal oxide (e.g.,
TiO.sub.2) may cause electrochemical side reactions, which can
result in decreased power conversion efficiency.
[0070] In an embodiment, the binder solution for low-temperature
annealing is prepared by mixing a solvent and t-butanol in a weight
ratio (w/w) of 1:1 to 1:10. If t-butanol and the solvent are mixed
in a weight ratio of less than 1:1 (i.e. the amount of the solvent
is relatively large, compared to that of the t-butanol), the
viscosity of the paste composition is reduced. Low viscosity of the
paste composition can cause poor adhesiveness, for example, leading
to degradation in the quality of a semiconductor electrode produced
using the paste composition. If the solvent and t-butanol are mixed
in a weight ratio of greater than 1:10 (i.e. where the amount of
the solvent is relatively small when compared to that of the
t-butanol), the initial viscosity of the paste composition is high.
High initial viscosity reduces the amount of TiO.sub.2 loaded,
making it impossible to produce a semiconductor electrode having
the intended quality and desired physical properties.
[0071] A general organic solvent or water can be used as the
solvent of the binder solution. PA solvent that is more polar and
has a higher hydrogen bond index than t-butanol is desirable.
Examples of such solvents include water, glycols, and glycerols. In
an embodiment, an aqueous solvent is used.
[0072] The presence of increasing amounts of hydroxyl ("OH") groups
in the paste composition, such as those provided by the solvent,
increases the viscosity of the paste composition, making coating of
the composition difficult. For better coatability of the
composition, an acetate-based solvent selected from ethyl acetate,
butyl acetate, propylene glycol methyl ether acetate, propylene
glycol mono ether acetate ("PGMEA") and dihydroterpineol acetate
("DHTA") may be added to the paste composition.
[0073] The paste composition comprises at least one metal oxide
selected from the group consisting of titanium, niobium, hafnium,
indium, tin, and zinc oxides. The metal oxide may be used alone or
in a combination comprising at least one of the foregoing metal
oxides. In an exemplary embodiment, titanium oxide (TiO.sub.2) is a
useful metal oxide.
[0074] The metal oxide desirably has a large surface area so that
the dye adsorbed on the surface of the metal oxide can absorb as
much light as possible, and the degree of adsorption to an
electrolyte layer can be increased. In an embodiment, the metal
oxide can have a nanostructure selected from nanotubes, nanowires,
nanobelts, and nanoparticles. In a specific embodiment, the
particle diameter of the metal oxide is preferably within 5 nm and
400 nm.
[0075] Further, as disclosed herein, a semiconductor electrode is
produced using the paste composition.
[0076] Specifically, the semiconductor electrode comprises a
transparent electrode composed of a substrate and an electrically
conductive material coated on the substrate, a metal oxide layer
formed on the transparent electrode on the side of the transparent
electrode having the electrically conducting material, and a dye
present in the metal oxide layer, wherein the dye contains the
dispersant compound of Formula 1.
[0077] The substrate may be of any type as long as it is
transparent. Examples of substrates include glass substrates,
silica substrates, and plastic substrates.
[0078] Electrically conductive material for coating on the
substrate include, for example, indium tin oxide ("ITO"),
fluorine-doped tin oxide ("FTO"), ZnO--Ga.sub.2O.sub.3,
ZnO--Al.sub.2O.sub.3, or SnO.sub.2--Sb.sub.2O.sub.3.
[0079] The semiconductor electrode is produced by a method
comprising applying the paste composition to a transparent
substrate coated with an electrically conductive material, and
low-temperature annealing the coated composition at a temperature
of 80 to 200.degree. C. for 0.5-5 hours, to form a light-absorbing
layer.
[0080] The use of the paste composition, which comprises the dye
containing the compound of Formula 1 and the metal oxide, in the
production of the semiconductor electrode avoids the need to
separately perform the steps of forming a metal oxide layer and
adsorbing a dye on the surface of the metal oxide layer in
accordance with conventional methods for the production of a
transparent electrode. In addition, the use of t-butanol having a
boiling point of 80.degree. C. as a binder in the method of the
present invention enables the formation of a light-absorbing layer
through low-temperature annealing at 80-200.degree. C. Accordingly,
the method of the present invention is economically advantageous in
terms of production cost and processing.
[0081] Furthermore, since the low-temperature annealing permits the
method to be applied to flexible substrates (e.g., plastic
substrates) without any particular difficulty, the method disclosed
herein is advantageous for a wide range of applications.
[0082] The application of the paste composition may be carried out
by a general coating technique, for example, spraying, spin
coating, dipping, printing, doctor blading, sputtering, chemical
deposition, physical deposition, or electrophoresis. The coating of
the electrically conductive material may be carried out by a
general coating technique.
[0083] The coated composition is subjected to low-temperature
annealing at 80-200.degree. C. for 0.5-5 hours and preferably
90-150.degree. C. for 1-3 hours to form a light-absorbing
layer.
[0084] The surface shape of the light-absorbing layer may be planar
or irregular. The light-absorbing layer preferably has an irregular
surface shape so that it can be sufficiently adsorbed to an
electrolyte layer. Suitable irregular surface shapes of the
light-absorbing layer include steps, needles, meshes, scars, and
other shapes, but are not limited thereto.
[0085] The light-absorbing layer may be formed into a monolayer or
a bilayer structure. The bilayer structure of the light-absorbing
layer can be formed using two paste compositions which comprise
different metal oxides having different particle sizes in order to
improve the transmittance of light incident on the light-absorbing
layer. In an embodiment, a bilayer structure of the light-absorbing
layer consists of a 10-20 .mu.m thick layer formed of a metal oxide
with a particle size of 9-20 nm and a 3-5 .mu.m thick layer formed
of a metal oxide with a particle size of 200-400 nm.
[0086] The semiconductor electrode thus has excellent
processability, the amount of the dye adsorbed to the metal oxide
is greater than can be obtained using conventional methods, and the
physical properties of the metal oxide film are uniform. Therefore,
the semiconductor electrode of the present invention can be used to
fabricate dye-sensitized solar cells with improved power conversion
efficiency.
[0087] The present invention also provides a dye-sensitized solar
cell comprising the semiconductor electrode, an electrolyte layer,
and a counter electrode.
[0088] The electrolyte layer is composed of an electrolyte
solution, for example, a solution of iodine in acetonitrile, an NMP
solution, or a 3-methoxypropionitrile solution. Any electrolyte
solution may be used, without limitation, so long as it exhibits
hole conductivity.
[0089] The counter electrode can be made of, without any
limitation, an electrically conductive material. As long as a
conductive layer is disposed on the surface of the counter
electrode facing the semiconductor electrode, any suitable
insulating material may be used to form the counter electrode. In
an embodiment, an electrochemically stable material is used to form
the counter electrode. Specific examples of electrochemically
stable materials include platinum, gold, and carbon. For the
purpose of improving the catalytic effects of oxidation and
reduction, the surface of the counter electrode facing the
semiconductor electrode can have a microstructure with increased
surface area. In an exemplary embodiment, the counter electrode is
made of platinum black or porous carbon. A platinum black counter
electrode can be produced by anodic oxidation of platinum, by
treatment of platinum with hexachloroplatinate, and the like. The
porous carbon counter electrode can be produced by sintering of
fine carbon particles or by baking of an organic polymer.
[0090] The dye-sensitized solar cell of the present invention can
be fabricated by any suitable method including known methods.
[0091] Hereinafter, the present invention will be explained in more
detail with reference to the following examples. These examples are
provided for the purpose of illustration and are not to be
construed as limiting the scope of the invention.
EXAMPLES
Synthesis Example 1
Synthesis of Oligomeric Compound
##STR00008##
[0093] The Tergitol-mesylate was synthesized as depicted in
Reaction Scheme 3 and FIG. 1. In step S1, 4.86 g (48 mmol) of
triethylamine (Aldrich) was added to a solution of
Tergitol.RTM.NP-9 (16 mmol, Aldrich) in anhydrous methylene
chloride (20 ml) in a reactor. The mixture was stirred under a
nitrogen atmosphere for 10 minutes.
[0094] Also in step S1, after the reactor was placed in an ice
bath, the mixture was allowed to react while adding 5.5 g (48 mmol)
of methanesulfonyl chloride (Aldrich) portionwise to the mixture
over one hour. Thereafter, the reactor was slowly allowed to warm
to room temperature with stirring over 12 hours.
[0095] After completion of the reaction, the reaction mixture was
poured into cold water, followed by phase separation. The obtained
organic layer was sequentially washed with a hydrochloric acid
solution (.times.1, step S2) and water (.times.3, step S3). The
solvents were removed from the methylene chloride solution using a
rotary evaporator to obtain a viscous liquid (step S4). The liquid
was dried in a vacuum oven to give the Tergitol-mesylate (step
S4).
[0096] The structure of the product was identified by .sup.1H-NMR
spectroscopy (step S5 in FIG. 1; .sup.1H-NMR spectrum of
Tergitol-mesylate shown in FIG. 2).
[0097] (2) Synthesis of Tergitol-amine
[0098] 0.44 g (0.64 mmol) of the Tergitol-mesylate prepared in (1)
was dissolved in 20 ml of ethanol. The solution was stirred at room
temperature for 15 minutes. 0.065 g (0.64 mmol) of ammonia
(Aldrich) was added to the solution and refluxed with stirring at
160.degree. C. for 12 hours.
[0099] After completion of the reaction, the reaction mixture was
poured into an excess of cold water, and extracted with methylene
chloride. The obtained organic layer was washed with a hydrochloric
acid solution.
[0100] The solvents were removed from the methylene chloride
solution using a rotary evaporator to obtain a viscous liquid. The
liquid was dried in a vacuum oven to give the Tergitol-amine.
[0101] The structure of the product was identified by .sup.1H-NMR
spectroscopy (FIG. 3). The .sup.1H-NMR analysis shows that peaks
corresponding to the ethylene oxide (--CH.sub.2CH.sub.2O--) were
shifted and a peak at around 3 ppm corresponding to the mesylate
disappeared, indicating the introduction of the amine group in a
yield of 80%.
[0102] (3) Synthesis of Tergitol-imidazole
[0103] 0.44 g (0.65 mmol) of the Tergitol-mesylate prepared in (1)
was dissolved in 20 ml of ethanol. The solution was stirred at room
temperature for 15 minutes. 0.394 g (0.64 mmol) of imidazole (2.0 M
in dimethylformamide, Aldrich) was added to the solution and
refluxed with stirring at 160.degree. C. for 12 hours.
[0104] After completion of the reaction, the reaction mixture was
poured into an excess of cold water, and extracted with methylene
chloride. The obtained organic layer was washed with a hydrochloric
acid solution.
[0105] The solvents were removed from the methylene chloride
solution using a rotary evaporator to obtain a viscous liquid. The
liquid was dried in a vacuum oven to give the
Tergitol-imidazole.
[0106] The structure of the product was identified by .sup.1H-NMR
spectroscopy (FIG. 4). The .sup.1H-NMR analysis shows that new
peaks of the aromatic compound appeared at 7-8 ppm and a peak at
around 3 ppm corresponding to the mesylate disappeared, indicating
the introduction of the imidazole group in a yield of 100%.
Synthesis Example 2
Synthesis of Ruthenium Dye Containing Tergitol-amine
[0107] 70 mg (0.094 mmol) of ruthenium 535 (N3 dye, Solaronix) and
394 mg (0.64 mmol) of the Tergitol-amine were dissolved in 10 ml of
ethanol and stirred at room temperature for one hour.
[0108] The solvent was removed from the reaction solution using a
rotary evaporator to obtain a viscous liquid. The liquid was
dissolved in a small amount of methylene chloride, and poured into
n-hexane to obtain a precipitate. The precipitate was dried in a
vacuum oven to give a ruthenium dye containing the
Tergitol-amine.
Synthesis Example 3
Synthesis of Ruthenium Dye Containing Tergitol-imidazole
[0109] A ruthenium dye containing the Tergitol-imidazole was
prepared in the same manner as in Synthesis Example 2, except that
425 mg (0.64 mmol) of the Tergitol-imidazole was used instead of
the Tergitol-amine.
Preparative Example 1
Preparation of Paste Composition
[0110] Water and t-butanol were mixed in a weight ratio of 1:2
(w/w) to prepare a binder solution. 7 g of the binder solution was
mixed with 120 mg of the dye prepared in Synthesis Example 2 and
stirred for 30 minutes. To the mixture was added 3 g of a TiO.sub.2
powder (particle diameter: 13 nm), followed by stirring for one
hour to prepare a paste composition.
Example 1
Production of Semiconductor Electrode and Fabrication of Solar Cell
(1)
[0111] (1) Production of Semiconductor Electrode
[0112] Fluorine-doped tin oxide (FTO) was applied to a glass
substrate using a sputter coater. The paste composition prepared in
Preparative Example 1 was applied to the resulting substrate by
screen printing and annealed at 120.degree. C. for one hour to form
a light-absorbing layer having a thickness of about 20 .mu.m,
completing the production of a semiconductor electrode.
[0113] (2) Fabrication of Solar Cell
[0114] Platinum was coated on the surface of an ITO-coated
transparent conductive glass substrate to form a counter electrode.
The counter electrode (i.e. positive electrode) and the
semiconductor electrode (i.e. negative electrode) produced in
Example 1 were assembled. At this time, both electrodes were
arranged in such a manner that the conducting surfaces of the
electrodes faced to each other. After a polymer film (SURLYN.RTM.,
DuPont) having a thickness of about 40 .mu.m was interposed between
the two electrodes, the two electrodes were adhered to each other
under a pressure of 1 to 2 atm (0.1 to 0.2 MPa) on a hot plate at
100-140.degree. C. An electrolyte solution was filled in a space
formed between the two electrodes through a fine hole penetrating
the positive electrode to complete fabrication of a dye-sensitized
solar cell. As the electrolyte solution, an I.sub.3.sup.-/I.sup.-
electrolyte solution of 0.6 moles of
1,2-dimethyl-3-octyl-imidazolium iodide, 0.2 moles of LiI, 0.04
moles of I.sub.2 and 0.2 moles of 4-tert-butylpyridine ("TBP") in
acetonitrile was used.
Example 2
Production of Semiconductor Electrode and Fabrication of Solar Cell
(2)
[0115] A semiconductor electrode was produced in the same manner as
in Example 1, except that a TiO.sub.2 layer having a thickness of
17.720 .mu.m was used as the metal oxide layer. A dye-sensitized
solar cell was fabricated using the semiconductor electrode by the
procedure of Example 1.
Comparative Example 1
Production of Semiconductor Electrode and Fabrication of Solar
Cell
[0116] A semiconductor electrode was produced in the same manner as
in Example 1, except that ruthenium 535 (N3 dye) was used as the
dye and a TiO.sub.2 layer having a thickness of 16.600 .mu.m was
used as the metal oxide layer. A dye-sensitized solar cell was
fabricated using the semiconductor electrode by the procedure of
Example 1.
Comparative Example 2
Production of Semiconductor Electrode and Fabrication of Solar
Cell
[0117] A semiconductor electrode was produced in the same manner as
in Comparative Example 1, except that a TiO.sub.2 layer having a
thickness of 17.288 .mu.m was used as the metal oxide layer. A
dye-sensitized solar cell was fabricated using the semiconductor
electrode by the procedure of Example 1.
Comparative Example 3
Production of Semiconductor Electrode and Fabrication of Solar
Cell
[0118] A semiconductor electrode was produced in the same manner as
in Example 1, except that N719 was used as the dye and a TiO.sub.2
layer having a thickness of 16.559 .mu.m was used as the metal
oxide layer. A dye-sensitized solar cell was fabricated using the
semiconductor electrode by the procedure of Example 1.
Comparative Example 4
Production of Semiconductor Electrode and Fabrication of Solar
Cell
[0119] A semiconductor electrode was produced in the same manner as
in Comparative Example 3, except that a TiO.sub.2 layer having a
thickness of 17.258 .mu.m was used as the metal oxide layer. A
dye-sensitized solar cell was fabricated using the semiconductor
electrode by the procedure of Example 1.
Test Example 1
Evaluation of Power Conversion Efficiency of Solar Cells
[0120] The photovoltages and photocurrents of the solar cells
fabricated in Examples 1 and 2 and Comparative Examples 1 to 4 were
measured to calculate the power conversion efficiency of the solar
cells. For the measurements, a xenon lamp (01193, Oriel) was used
as a light source, and a standard solar cell (Frunhofer Institute
Solar Engeriessysteme, Certificate No. C-ISE369, Type of material:
Mono-Si.sup.+ KG filter) was used to compensate for the solar
conditions (AM 1.5) of the xenon lamp.
[0121] The photocurrent density ("I.sub.sc"), open-circuit voltage
("V.sub.oc") and fill factor ("FF") of the solar cells were
determined from the obtained respective photocurrent-photovoltage
curves, and the power conversion efficiency (.eta..sub.e) of the
solar cells was calculated according to the following equation:
.eta..sub.e(%)=(V.sub.ocI.sub.scFF)/(P.sub.inc).times.100
[0122] where P.sub.inc is 100 mw/cm.sup.2 (1 sun).
[0123] The obtained results are shown in Table 1. The thicknesses
of the TiO.sub.2 layers used in the dye-sensitized solar cells are
shown in Table 1.
TABLE-US-00001 TABLE 1 J.sub.sc V.sub.oc .eta..sub.e Thickness of
TiO.sub.2 Example No. (mA/cm.sup.2) (mV) FF (%) layer (.mu.m)
Example 1 10.572 640.922 0.738 5.023 16.739 Example 2 10.546
620.904 0.713 4.688 17.720 Comparative 8.773 589.706 0.699 3.631
16.600 Example 1 Comparative 9.787 603.938 0.745 4.421 17.288
Example 2 Comparative 9.333 637.220 0.762 4.548 16.559 Example 3
Comparative 9.212 596.140 0.700 3.861 17.258 Example 4
[0124] As can be seen from the results of Table 1, the solar cells
in which the Tergitol dispersant having a high affinity for
TiO.sub.2 was introduced into the metal oxide layer with the metal
oxide particles and ruthenium dye, showed high power conversion
efficiency.
[0125] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications and variations are
possible, without departing from the scope and spirit of the
invention as disclosed in the appended claims. Accordingly, such
modifications and variations are intended to come within the scope
of the appended claims.
[0126] As apparent from the above description, the dispersant
compound is contained as a ligand in a dye to constitute a tail
part of the dye. That is, the dye containing the dispersant
compound has a functional group acting as a dispersant.
Accordingly, the dye containing the dispersant compound performs
the following two functions: (1) the dye is adsorbed on the surface
of metal oxide particles to transfer electrons excited by absorbed
light to a conduction band of the metal oxide; and (2) the dye
functions as a dispersant to prevent aggregation of the metal oxide
particles, thereby improving the uniformity of the particles within
a paste and increasing the density of a film formed of the paste.
The dye containing the dispersant compound can be used to prepare a
paste composition for a semiconductor electrode of a solar cell. A
semiconductor electrode produced using the paste composition and a
solar cell fabricated using the semiconductor electrode exhibit
greatly improved power conversion efficiency and superior
processability.
* * * * *