U.S. patent application number 12/998630 was filed with the patent office on 2011-11-03 for novel anchoring ligands for sensitizers of dye-sensitized photovoltaic devices.
This patent application is currently assigned to UNIVERSITAT ULM. Invention is credited to Peter Bauerle, Markus Fischer, Michael Graetzel, Cedric Klein, Amaresh Mishra, Mohammad Khaja Nazeeruddin, Shaik Mohammad Zakeeruddin.
Application Number | 20110265876 12/998630 |
Document ID | / |
Family ID | 41632439 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110265876 |
Kind Code |
A1 |
Zakeeruddin; Shaik Mohammad ;
et al. |
November 3, 2011 |
NOVEL ANCHORING LIGANDS FOR SENSITIZERS OF DYE-SENSITIZED
PHOTOVOLTAIC DEVICES
Abstract
The present invention relates to novel pyridine compounds that
can be used as anchoring ligands in metal-based sensitizing dyes of
dye sensitized solar cells (DSC.sub.S). The dyes comprising the
polypyridine compounds exhibit improved light harvesting ability
and lead to increased conversion efficiencies, in particular in
thin TiO.sub.2 film devices.
Inventors: |
Zakeeruddin; Shaik Mohammad;
(Bussigny-Lausanne, CH) ; Klein; Cedric; (Brumath,
FR) ; Nazeeruddin; Mohammad Khaja; (Ecublens, CH)
; Graetzel; Michael; (St-Sulpice, CH) ; Mishra;
Amaresh; (Neu-Ulm, DE) ; Fischer; Markus;
(Hanau, DE) ; Bauerle; Peter; (Elchingen,
DE) |
Assignee: |
UNIVERSITAT ULM
Ulm
DE
ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE (EPFL)
Lausanne
CH
|
Family ID: |
41632439 |
Appl. No.: |
12/998630 |
Filed: |
November 11, 2009 |
PCT Filed: |
November 11, 2009 |
PCT NO: |
PCT/IB2009/055011 |
371 Date: |
July 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61274019 |
Aug 12, 2009 |
|
|
|
Current U.S.
Class: |
136/263 ;
257/E51.024; 546/10; 546/256 |
Current CPC
Class: |
Y02E 10/542 20130101;
H01L 51/0086 20130101; C09B 57/00 20130101; Y02E 10/549 20130101;
C09B 23/145 20130101; C09B 57/10 20130101; H01L 51/4226
20130101 |
Class at
Publication: |
136/263 ;
546/256; 546/10; 257/E51.024 |
International
Class: |
H01L 51/46 20060101
H01L051/46; C07D 495/04 20060101 C07D495/04; C07F 15/00 20060101
C07F015/00; C07D 409/14 20060101 C07D409/14 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2008 |
EP |
08105761.4 |
Claims
1-19. (canceled)
20. A compound of formula (III) and/or (IV) below, respectively:
##STR00018## wherein, A.sub.1 and A.sub.2 are defined as a
substituent of formula (1) below: ##STR00019## wherein n is an
integer of 1-2, and Z is an integer of the group of integers 1, . .
. , n, wherein any A.sub.Z represents the Z.sup.th moiety of the n
successive moieties A, wherein any A.sub.Z may be different from
any other A.sub.Z; wherein any A.sub.Z is independently selected
from a C4-C20 aryl, said aryl being, besides the substituent Anc,
further substituted or not further substituted, and said aryl
comprising from 1-10 heteroatoms; wherein, if n=2, A.sub.Z may also
be selected from vinylene () and ethynylene (), wherein said
vinylene may be substituted; with the proviso that at least one
A.sub.Z is an aryl as defined above; wherein, if n.gtoreq.1, the
first moiety A.sub.1 (A.sub.Z=1) is selected from the moieties of
formula (2)-(24) as defined below: ##STR00020## ##STR00021##
##STR00022## wherein A and B, if applicable, are each selected
independently from S (sulfur), O (oxygen), and Se (selenium); X is
selected from any one of C, Si, Ge, Sn or Pb; preferably from C and
Si, most preferably it is C; substituents R.sub.51-R.sub.131, if
applicable, are independently one from the others selected from H,
halogen and a C1-C20 hydrocarbon comprising from 0 to 20
heteroatoms; wherein A.sub.2 may be present (n=2) or may be absent
(n=1), wherein, if A.sub.2 is absent, the anchoring group Anc is
directly connected to A.sub.1; wherein Anc is an independently
selected anchoring group; wherein any one of R.sub.20-R.sub.34 is,
independently from the others, selected from H, halogen or a C1-C20
hydrocarbon comprising from 0 to 20 heteroatoms or a substituent of
formula (1); wherein, if more than one of R.sub.20-R.sub.34 are a
substituent of formula (1), any n of such substituent may be the
same or different from the n of another such substituent of formula
(1), and any A.sub.Z may be different from the respective A.sub.Z
of another such substituent of formula (1).
21. The compound of claim 20, wherein said compound of formula
(III) and/or (IV) is selected from a compound of formula (V) or
(VI) below: ##STR00023## wherein A.sub.1 and A.sub.2 are defined as
A.sub.Z above; wherein, if n=2, Az may also be selected from
vinylene () and ethynylene (), wherein said vinylene may be
substituted; with the proviso that at least one A.sub.Z is an aryl
as defined above; wherein, if n.gtoreq.1, the first moiety A.sub.1
(A.sub.Z=1) is selected from the moieties of formula (2)-(24) as
defined above; wherein A.sub.2 may be present (n=2) or may be
absent (n=1), wherein, if A.sub.2 is absent, the anchoring group
Anc is directly connected to A.sub.1; wherein Anc is defined as
above; wherein R.sub.1, R.sub.2, R.sub.4, R.sub.5, R.sub.7,
R.sub.10, R.sub.12, R.sub.13, R.sub.15, R.sub.16, R.sub.18 and
R.sub.19 are defined as R.sub.20-R.sub.34 above.
22. The compound of claim 20, wherein any moiety A.sub.Z, A.sub.1
and A.sub.2, as applicable, may be independently selected from the
moieties (2)-(24) above and from the moieties (25)-29) below, with
the proviso that at least one moiety is selected from any one of
moieties (2)-(24) above: ##STR00024## wherein A and B, if
applicable, are each selected independently from S (sulfur), 0
(oxygen), and Se (selenium); X is selected from any one of C, Si,
Ge, Sn or Pb; preferably from C and Si, most preferably it is C;
substituents R.sub.132-R.sub.143, if applicable, are independently
one from the others selected from H, halogen and a C1-C20
hydrocarbon comprising from 0 to 20 heteroatoms.
23. The compound of claim 20, wherein, if in a substituent of
formula (1) n>1, the first moiety A.sub.1 (A.sub.Z=1) is
selected from the moieties of formula (2)-(5).
24. The compound of claim 20, wherein the anchoring group (Anc) is
selected from --COOH, --PO.sub.3H.sub.2, --PO.sub.4H.sub.2,
--P(R.sub.100)O.sub.2H, --SO.sub.3H.sub.2, --CONHOH.sup.-,
acetylacetonate, deprotonated forms of the aforementioned, salts of
said deprotonated forms, and chelating groups with .pi.-conducting
character; wherein R.sub.100 is a hydrocarbon comprising from 1 to
20 carbons and 0-20 heteroatoms, said hydrocarbon being covalently
bound to the P atom of said phosphinic acid group by a carbon atom;
and wherein R.sub.100 may be further covalently connected to the
bi- or polypyridine ligand carrying the anchoring group Anc.
25. The compound of claim 20, wherein A.sub.1 is the moiety of
formula (2) or (4).
26. The compound of claim 20, R.sub.20-R.sub.34 of formula (III)
and (IV) are independently selected from H, halogen or C1-C10
alkyl, C2-C10 alkenyl, C2-C10 alkynyl, and from C4-C15 aryl, said
alkyl, alkenyl, and alkynyl being linear or branched and said
alkyl, alkenyl, and alkynyl optionally being further substituted,
and wherein said aryl, if is a C4 aryl, comprises at least one
heteroatom selected from O, S and N in the ring so as to provide an
aromatic ring.
27. The compound of claim 21, wherein R.sub.1, R.sub.2, R.sub.4,
R.sub.5, RrRio, R.sub.12, R.sub.13, R.sub.15, R.sub.16, R.sub.18
and R.sub.19 formula (V) and/or (VI) are independently selected
from H, halogen or C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl,
and from C4-C15 aryl, said alkyl, alkenyl, and alkynyl being linear
or branched and said alkyl, alkenyl, and alkynyl optionally being
further substituted, and wherein said aryl, if is a C4 aryl,
comprises at least one heteroatom selected from O, S and N in the
ring so as to provide an aromatic ring.
28. The compound of claim 20, wherein n is 1 and wherein in every
substituent of formula (1), A.sub.1 (A.sub.Z=1) is selected from
any one of any of moieties of (25)-(32) below: ##STR00025##
29. The compound of claim 28, wherein the substituents
R.sub.51-R.sub.143, in as far as present, are independently
selected from H, halogen, anchoring groups as defined herein,
cyano, C1-C10 alkyl and C2-C10 alkenyl, said alkyl and alkenyl
being linear or branched and optionally further substituted.
30. The use of the compounds of formula (III) and/or (IV) as
defined in claim 20 as an anchoring ligand in an organometallic
sensitizer of a dye sensitized solar cell.
31. A dye of formula (XI), (XII) or (XIII): M L.sub.1 L.sub.2
L.sub.3 L.sub.4 (XI) M L.sub.5 L.sub.3 L.sub.4 L.sub.6 (XII) M
L.sub.5 L.sub.2 L.sub.4 (XIII) wherein M is a metal atom selected
from Ru, Os, Ir, Re, Rh, and Fe; wherein L.sub.1 is a bipyridine
ligand of formula (III) according to claim 20; wherein L.sub.2 is,
independently from L.sub.I, a ligand of formula (III) of claim 20
or a bidentate ligand being a C3-C30 hydrocarbon comprising from 2
to 20 heteroatoms; wherein L.sub.3, L.sub.4 and L.sub.6 are
monovalent ligands independently selected from H.sub.2O, --Cl,
--Br, --I, --CN, --NCO, --NCS and --NCSe; L.sub.5 is a ligand of
formula (IV) according to claim 20.
32. A dye of formula (XI), (XII) or (XIII): M L.sub.1 L.sub.2
L.sub.3 L.sub.4 (XI) M L.sub.5 L.sub.3 L.sub.4 L.sub.6 (XII) M
L.sub.5 L.sub.2 L.sub.4 (XIII) wherein M is a metal atom selected
from Ru, Os, Ir, Re, Rh, and Fe; wherein L.sub.1 is a bipyridine
ligand of formula (V) according to claim 21; wherein L.sub.2 is,
independently from L.sub.1, a ligand of formula (V) of claim 21 or
a bidentate ligand being a C3-C30 hydrocarbon comprising from 2 to
20 heteroatoms; wherein L.sub.3, L.sub.4 and L.sub.6 are monovalent
ligands independently selected from H.sub.2O, --Cl, --Br, --I,
--CN, --NCO, --NCS and --NCSe; L.sub.5 is a ligand of formula (VI)
according to claim 21.
33. The dye of claim 31, wherein L.sub.2 is a bipyridine ligand of
formula (XV) ##STR00026## wherein the substituents R.sup.1-R.sup.8
are selected, independently one from the other, from H, halogen,
and C1-C20 hydrocarbons comprising from 0 to 20 heteroatoms.
34. The dye of claim 33, wherein one or more of R.sup.1-R.sup.8 are
selected, independently one from the other, from substituents of
formula (51) below: ##STR00027## wherein m is an integer of 1-10,
and X is an integer of the group of integers 1, . . . , m, wherein
any B.sub.X represents the X.sup.th moiety of the m successive
moieties B, wherein any B.sub.X may be different from any other
B.sub.X; wherein, if more than one of R.sup.1-R.sup.8 of the
compound of formula (XV) are a substituent of formula (51), any m
of such substituent may be the same or different from another such
substituent of formula (51), and any B.sub.X may be different from
the respective B.sub.X of another such substituent of formula (51);
wherein any B.sub.X is independently selected from a C4-C20 aryl,
said aryl being, besides the substituent R.sup.10, further
substituted or not further substituted, and said aryl comprising
from 0-5 heteroatoms; wherein any B.sub.X may also be independently
selected from substituted or unsubstituted-vinylene () and from
ethynylene (); wherein R.sup.10 is independently selected from H,
halogen, and a C1-C20 hydrocarbon comprising from 0-20
heteroatoms.
35. The dye of claim 34, wherein any B.sub.X is independently
selected from the moieties of formula (2)-(29) above.
36. A photoelectric conversion device comprising a compound of
formula (III) and/or (IV) as defined in claim 20 and/or a dye
according to claim 31.
37. The device of claim 36, comprising a light absorption layer
(3), which comprises a semiconductor material (4) and, absorbed
thereto, a dye layer (5) comprising a dye according to claim 31
and/or a dye (5) comprising a compound according to claim 20.
Description
TECHNICAL FIELD
[0001] The present invention relates to new compounds, to the use
of these compounds as ligand in organometallic compounds, in
particular dyes, to organometallic compounds and dyes comprising
the compounds, to the use of the compounds and of the dyes in
photoelectric conversion devices, in particular dye-sensitized
photovoltaic cells and to photoelectric conversion devices
comprising the novel compounds or the novel dyes.
PRIOR ART AND THE PROBLEM UNDERLYING THE INVENTION
[0002] During the past two decades, mesoscopic dye-sensitized solar
cells (DSCs) have emerged as promising candidates for practical
photovoltaic applications by virtue of their low manufacturing
costs and good conversion efficiencies DSCs with power conversion
efficiencies over 10% were initially demonstrated using
cis-di(thiocyanato)-bis[2,2'-bipyridyl-4,4'-dicarboxylic acid]
ruthenium(II) (N3) or its bis-tetrabutylammonium (TBA) salt
counterpart N719 as sensitizers in combination with a thicker
titania film (>12-15 .mu.m) and a volatile electrolyte. In DSCs,
the sensitizer is one of the critical components as it absorbs
sunlight and induces the charge separation process. In order to
enhance power conversion efficiencies of DSCs, it is imperative to
design novel sensitizers resulting in devices with higher
conversion efficiencies.
[0003] It is an objective of the present invention to provide
sensitizing dyes that can be used in DSCs, which exhibit an
improved light-harvesting ability.
[0004] It is another objective of the present invention to provide
ways of preparing dyes for such cells, which exhibit an enhanced
molar absorptivity.
[0005] Furthermore, it is an objective of the present invention to
provide dyes, which exhibit a red-shifted absorption band compared
to dyes of the state of the art, such as N719 and Z907.
[0006] In addition, it is an objective of the invention to prepare
more economic devices requiring less raw materials.
[0007] The objectives above are addressed by the present invention
and therefore form part of it.
SUMMARY OF INVENTION
[0008] The present invention provides new organometallic compounds
for optoelectronic devices, electrochemical devices, photoelectric
conversion devices, photovoltaic cells and solar cells. In
particular, the present invention provides new sensitizing
organometallic compounds that can be used for sensitizing such
devices.
[0009] The novel dyes comprise a new anchoring ligand comprising an
extended .pi.-conjugated system. Substituted or unsubstituted
arenes comprising heteroatoms, such as thiophene and derivatives
thereof, and possibly vinylene and ethynylene moieties are inserted
between bi-, ter-, or polypyridine and anchoring groups, such as
carboxylic acid groups, for example.
[0010] The new compounds can be used as anchoring ligands in
organometallic sensitizing dyes. Surprisingly, the anchoring
ligands of the invention can improve the spectral response of
corresponding sensitizing dyes. In particular, the anchoring
ligands increase the molar extinction coefficient of the dyes and
also improve their light-harvesting ability.
[0011] Surprisingly, the dyes comprising the new anchoring ligands
of the present invention result in devices having high photovoltaic
performances, in particular high conversion efficiencies. In
particular, devices based on thin semiconducting photoelectrode
films show increased conversion efficiencies if compared to devices
comprising state of the art dyes with a comparable structure.
[0012] Accordingly, in an aspect, the present invention provides a
compound formula (I) or (II) below:
##STR00001##
wherein at least one of the substituents R.sub.1-R.sub.8 of the
compound of formula (I) and at least one of the substituents
R.sub.9-R.sub.19 of the formula (II) is a substituent of formula
(1) below
##STR00002##
wherein n is an integer of 1-5, and Z is an integer of the group of
successive integers 1, . . . , n, wherein any A.sub.Z represents
the Z.sup.th moiety of the n successive moieties A, wherein any
A.sub.Z may be different from any other A.sub.Z; wherein, if more
than one of R.sub.1-R.sub.8 of the compound of formula (I) or more
than one of substituents R.sub.9-R.sub.19 of the compound of
formula (II), respectively, are a substituent of formula (1), any n
of such substituent may be the same or different from the n of
another such substituent of formula (1), and any A.sub.Z may be
different from the respective A.sub.Z of another such substituent
of formula (1); wherein any A.sub.Z is independently selected from
a C4-C30 aryl, said aryl being, besides the substituent Anc,
further substituted or not further substituted, and said aryl
comprising from 1-10 heteroatoms; wherein said aryl, when it
comprises only 4 ring carbons (C4 aryl) comprises at least one ring
heteroatom selected from O, S and Se; wherein, if n.gtoreq.2,
A.sub.Z may also be selected from vinylene and ethynylene , wherein
said vinylene may be substituted; with the proviso that at least
one A.sub.Z is an aryl as defined above; wherein Anc is an
anchoring group; wherein any one of R.sub.1-R.sub.8 of formula (1)
or any one of R.sub.9-R.sub.19 of formula (II), which is not a
substituent of formula (1), is, independently from the others,
selected from H, halogen or a C1-C20 hydrocarbon comprising from 0
to 20 heteroatoms.
[0013] In a second aspect, the present invention provides the use
of a pyridine compound of the invention as a component, for example
as an anchoring ligand, of an organometallic compound. For example,
the organometallic compound is a dye and/or a sensitizing dye.
[0014] In a third aspect, the present invention provides a dye of
formula (XI), (XII) or (XIII):
M L.sub.1 L.sub.2 L.sub.3 L.sub.4 (XI)
M L.sub.5 L.sub.3 L.sub.4 L.sub.6 (XII)
M L.sub.5 L.sub.2 L.sub.4 (XIII)
wherein M is a metal atom selected from Ru, Os, Ir, Re, Rh, and Fe;
preferably from Ru, Os, and Rh; wherein L.sub.1 is a bipyridine
ligand of formula (I), (III) or (V) as defined herein; wherein
L.sub.2 is, independently from L.sub.1, a ligand of formula (I),
(III) or (V) as defined herein or a bidentate ligand being a C3-C30
hydrocarbon comprising from 2 to 20 heteroatoms; wherein L.sub.3,
L.sub.4 and L.sub.6 are monovalent ligands independently selected
from H.sub.2O, --Cl, --Br, --I, --CN, --NCO, --NCS and --NCSe;
L.sub.5 is a terpyridine ligand of formula (II), (IV) or (VI) as
defined herein.
[0015] In a fourth aspect, the present invention provides an
optoelectronic device, an electrochemical device, a photoelectric
conversion device, a solar cell, and/or photovoltaic cell
comprising one or more selected from the compound, the
organometallic compound, the dye, and the sensitizing dye of the
present invention. Preferably, the device is a dye-sensitized solar
cell (DSCs).
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows Scheme 1 illustrating the synthesis of compound
2, which can be used as an anchoring ligand in accordance with the
invention.
[0017] FIG. 2 shows Scheme 2 illustrating the synthesis of
compounds 3a and 3b, which represent heteroleptic dyes according to
the invention, the dyes comprising compound 2 as an anchoring
ligand.
[0018] FIG. 3 shows Scheme 3 illustrating the synthesis of compound
4, which is a homoleptic dye according to the invention, the dye
comprising two times compound 2 as anchoring ligands.
[0019] FIG. 4 shows examples of terpyridine compounds of the
present invention.
[0020] FIG. 5 shows examples of dyes of the present invention.
[0021] FIG. 6 shows examples of bipyridine compounds of the present
invention.
[0022] FIG. 7 shows the electronic absorption spectrum of compound
3b.
[0023] FIG. 8 shows the photocurrent-voltage characteristics of
dye-sensitized solar cells with compound 3a (blue rhombi line,
Example 6), compound 3b (green triangle line, Example 7) and
compound 3a with one equivalent tetrabutylammonium hydroxide (red
square line). Respective dark currents are shown with broken lines.
The cells comprise a double layer (7+5 .mu.m) TiO.sub.2 film. Z946
(a low-volatile) electrolyte was used in these devises and the
composition of the electrolyte is described in the examples.
Conversion efficiencies with these dyes according to the invention
were all in the range of 6.6-7.6.
[0024] FIG. 9 shows IPCE spectra obtained with the same cells as
described with respect to FIG. 8.
[0025] FIG. 10 shows the photocurrent-voltage characteristics of
dye-sensitized solar cells with sensitizer compound 3b of the
present invention, without coadsorbant (blue rhombi line) or
coadsorbed with different coadsorbants (3b+DINHOP in 4:1 ratio, red
square line); (3b+GBA in 1:1 ratio, green triangle line, see
examples) on the TiO.sub.2 surface. Cells comprise a double layer
(8.5+5 mm) TiO.sub.2 film. Conversion efficiencies with these dyes
according to the invention were all in the range of 7.5-8 (Examples
8-10).
[0026] FIG. 11 shows IPCE spectra obtained with the same cells as
described with respect to FIG. 10.
[0027] FIG. 12 shows the stability of the cells as shown in FIGS.
10 and 11 over 1000 hours under the visible light-soaking (1 sun;
100 mW/cm.sup.2) at 60.degree. C. It can be seen that short-circuit
photocurrent density (J.sub.sc), open current voltage (V.sub.OC),
fill factor (FF) and conversion efficiency (%) do change only
marginally in this time, resulting in a stability of 90-106%
(Examples 15-17).
[0028] FIG. 13 shows the photocurrent-voltage characteristics of
dye-sensitized solar cells with sensitizer compound 3b of the
present invention adsorbed with coadsorbant guanidine buryric acid
(3b+GBA) on a 5 .mu.m single film TiO.sub.2 photoelectrode (red
squares line). These cells of the invention are compared to
corresponding cells prepared with sensitizer Z907
[cis-RuLL'(SCN).sub.2] (L=4,4'-dicarboxylic acid-2,2'-bipyridine,
L'=4,4'-dinonyl-2,2'-bipyridine) co-adsorbed with GBA of the state
of the art (blue rhombi line) (Examples 11 and 12).
[0029] FIG. 14 shows IPCE spectra obtained with the same cells as
described with respect to FIG. 13. Cells with a 5 .mu.m single thin
film TiO.sub.2 comprising a dye according to the invention exhibit
about 24% increased conversion efficiencies if compared to the same
cells with a dye of the state of the art. Conversion efficiencies
of 7% are obtained with dyes of the invention, which is close to
the efficiencies obtained with the much thicker cells with a
doubled layer TiO.sub.2 film.
[0030] FIG. 15 shows the same as FIG. 13, with the difference that
cells comprising a 3 .mu.m single film TiO.sub.2 photoelectrode are
used (Examples 13 and 14).
[0031] FIG. 16 shows IPCE spectra obtained with the same cells as
described with respect to FIG. 15. Cells comprising the dye of the
invention have more than 5% higher conversion efficiencies than
cells comprising structurally comparable dyes of the state of the
art.
[0032] FIG. 17 shows electronic absorption and emission spectra of
the compound 4 (bis (tetrabutylammonium)-cis-dithio cyanato-di
[5-(4'-(5-carboxythiophen-2-yl)-2,2'-bipyridin-4-yl)thiophene-2-carboxyla-
te]ruthenium(II)) according to the invention and of the dye N719
[bis(tetrabutylammonium)-cis-dithiocyanato-bis(4'-carboxy-2,2'-bipyridine-
-4-carboxylate)ruthenium(II)] of the state of the art (Example
22).
[0033] FIG. 18 shows the absorption spectra of compound 4 (upper,
blue line) and N719 (lower, red line) adsorbed on 3.3 .mu.m thin
transparent mesoporous TiO.sub.2 films.
[0034] FIG. 19 shows IPCE (Incident-Photon-to-electron Conversion
Efficiency) spectra of compound 4 of the invention (blue rhombi
line) and N719 (red squares line) sensitizers on 3.3 .mu.m thin
nanocrystalline TiO.sub.2 films.
[0035] FIG. 20 shows photocurrent-voltage characteristics of
dye-sensitized solar cells with compound 4 (blue rhombi line) and
N719 (red square line) dyes (AM 1.5G; 100 mW cm.sup.-2). Cell area:
0.158 cm.sup.2.
[0036] FIG. 21 Schematically illustrates the structure of an
embodiment of the dye-sensitized solar cell of the present
invention.
[0037] FIG. 22 Schematically shows the structure of the light
absorption layer (3) of the dye-sensitized solar cell shown in FIG.
21.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The pyridine compounds of the present invention are useful
as ligands in organometallic compounds, in particular of metal
based sensitizing dyes. The ligands are suitable as anchoring
ligands, allowing the anchoring of the entire dye to a surface of
choice, for example to a semiconductor surface. The new anchoring
ligands comprise an extended .pi.-conjugated system. Substituted
and/or unsubstituted arenes comprising one or more heteroatoms,
such as thiophene and derivatives thereof, and possibly substituted
and/or unsubstituted vinylene and ethynylene moieties, are inserted
between mono- or polypyridine and anchoring groups, such as
carboxylic acid groups.
[0039] The compounds of the invention are pyridine compounds and
preferably polypyridine compounds. Term "polypyridine", for the
purpose of the present invention, refers to compounds comprising
two or more pyridine moieties, such as bipyridine, terpyridine, for
example. The term pyridine compounds, for the purpose of the
present invention, encompasses mono-, bi-, and ter-pyridine
compounds, including polypyridines comprising more pyridine
units.
[0040] The pyridine compounds of the invention, as exemplified by
formula (I) and (II), may by further substituted in addition to the
presence of at least one substituent of formula (1):
##STR00003##
[0041] In particular, substituents R.sub.1-R.sub.19, if they are
not substituents of formula (1), may be selected from H, halogen or
a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.
[0042] According to a preferred embodiment, R.sub.1-R.sub.19 are
selected, independently one from the others, selected from H,
halogen and a C1-C15 hydrocarbon comprising from 0-15, preferably
O-10 heteroatoms, preferably C1-C10 hydrocarbon comprising 0-10,
preferably 0-5 heteroatoms, and more preferably C1-05 hydrocarbon
comprising from 0 to 5 heteroatoms. Further embodiments and
preferred embodiments of substituents R.sub.1-R.sub.19 (which are
different from the substituent of formula (1)), are exactly as
defined for substituents R.sub.51-R.sub.143 further below, but are,
of course, independently selected from said substituents
R.sub.51-R.sub.143.
[0043] According to an embodiment, one or both selected from
R.sub.3 and R.sub.6 in the compound of formula (I) are selected
from substituents of formula (1); and/or one, two or all three
selected from R.sub.11 and R.sub.14 and R.sub.17 in the compound of
formula (II) are selected from substituents of formula (1).
[0044] In the compounds of formula (I) and (II) above, as well in
further embodiments of these compounds described further below,
said substituted or unsubstituted arene comprising one or more
heteroatoms, and possibly in addition vinylene and ethynylene
moieties, is generally referred to herein as A.sub.Z. Since n is an
integer from 1-5, the invention provides the following successions
of A.sub.Z: n=1: -A.sub.1-; n=2: -A.sub.1-A.sub.2-; n=3:
-A.sub.1-A.sub.2-A.sub.3-; n=4: -A.sub.1-A.sub.2-A.sub.3-A.sub.4-;
n=5: -A.sub.1-A.sub.2-A.sub.3-A.sub.4-A.sub.5-. According to a
preferred embodiment, n is an integer selected from 1-3, preferably
1-2. Most preferably, n is 1 or 2.
[0045] Each pyridine compound of the invention comprises at least
one substituent of formula (1): If the compound comprises two or
more substituents of formula (1), each such substituent may be the
same or different from the other such substituents.
[0046] According to an embodiment, the compound comprises one or
more, preferably exactly one, substituent of formula (1) on each
pyridine ring comprised in the compound.
[0047] According to an embodiment, at two or more and/or possibly
all of the substituents of formula (1) on the polypyridine compound
are identical.
[0048] According to an embodiment, the polypyridine compound is
symmetrical. The term "symmetrical" also applies in cases where
there are two or more identical anchoring groups, which are
differentially protonated or deptotonated and optionally provided
in the form of salts. In other words, if the only asymmetry in an
otherwise symmetrical compound is the nature of a cation or its
absence on two separate anchoring group, this is not considered to
affect the question whether or not a compound of the invention is
symmetrical.
[0049] According to an embodiment of the pyridine compound of the
invention, one or more (in case there more than one pyridine
rings), two or more and/or possibly all substituents of formula (1)
are attached to the carbon at position 4 of the pyridine ring
comprising a substituent of formula (1).
[0050] Examples of the aryl moiety A.sub.Z in the pyridine compound
of the invention are the moieties of formula (2)-(29) given below.
According to an embodiment, any moiety A.sub.Z, for example A.sub.1
and/or A.sub.2, as applicable, may be independently selected from
these moieties (2)-(29), with the proviso that at least one moiety
A.sub.Z is selected from any one of moieties (2)-(24) below:
##STR00004## ##STR00005## ##STR00006## ##STR00007##
wherein A and B, if applicable, are each selected independently
from S (sulfur), O (oxygen), and Se (selenium); X is selected from
any one of C, Si, Ge, Sn or Pb; preferably from C and Si, most
preferably it is C; substituents R.sub.51-R.sub.143, if applicable,
are independently one from the others selected from H, halogen and
a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.
[0051] According to an embodiment, if A is S, B is O or Se within
the same moiety. According to an embodiment A is S and B is O.
[0052] As indicated above, if n is greater than 1, A.sub.Z may also
be selected from phenylene, vinylene () and ethynylene (), wherein
said phenylene and vinylene may be further substituted, with the
proviso that at least one A.sub.Z is neither phenylen, vinylene nor
ethynylene but is an aryl comprising at least one heteroatom in the
aromatic ring (heteroaryl).
[0053] According to a preferred embodiment of the moieties (2)-(21)
above, A is S and B is O.
[0054] According to a preferred embodiment of the pyridine compound
of the invention any A.sub.Z, A.sub.1 and A.sub.2, as applicable,
is independently selected from the moieties of formula (25)-(37)
below, with the proviso that if n is 2 or greater, at least one
moiety is selected from any one of moieties (25)-(37) below, and if
n=1, said moiety A.sub.1 (A.sub.Z=1) is selected from any one of
formula (30)-(37) below,
##STR00008## ##STR00009##
wherein R.sub.51-R.sub.75, R.sub.132-R.sub.143, if applicable, are,
independently one from the others, defined as elsewhere in this
specification.
[0055] Accordingly, in the compounds of the invention, if n is 1,
A.sub.1 is selected from moieties (2)-(24) as defined above,
preferably from moieties (30)-(37), and, if n is .gtoreq.1, any
A.sub.Z may be selected from moieties (2)-(29), preferably from
(25)-(37) with the proviso that at least one moiety A.sub.Z in at
least one substituent of formula (1) is selected from the moieties
of formula (2)-(24), preferably from the moieties (30)-(37).
[0056] According to an embodiment, if in a substituent of formula
(1) n is greater than 1, the first moiety A.sub.1 (A.sub.Z=1) is
selected from the moieties of formula (2)-(24), preferably from
(30)-(37), and most preferably from moieties (2)-(5), preferably
(30), (31), (32) and (33).
[0057] According to an embodiment, n is 1 and in every substituent
of formula (1), A.sub.1 (A.sub.Z=1) is selected from any one of
(2)-(24), preferably (30)-(37), preferably it is the moiety of
formula (30) or (32). Preferably, substituents R.sub.51, R.sub.52,
R.sub.55, and R.sub.56 are H.
[0058] According to an embodiment, if n is 2 or greater, the
moieties -A.sub.1-A.sub.2- are selected from the moieties of
formula (38)-(49) below:
##STR00010## ##STR00011##
wherein substituents R.sub.51-R.sub.101, in as far as present, are
defined as substituents R.sub.51-R.sub.143; A and B are as defined
as above; and, Ar is selected from substituted or unsubstituted
vinylene (moiety 25 and 26 above), ethynylene (moiety 27 above) and
from a substituted or unsubstituted Ar-diyl devoid of any
heteroatom; Preferably, Ar comprises from 6 to 25 carbon atoms;
Preferably, Ar represents a substituted or unsubstituted phenylene,
preferably, an 1,4-para-phenylene (moiety 28) or 1,3-meta-phenylene
(moiety 29).
[0059] According to an embodiment, the compounds of formula (I) and
(II), respectively, are selected from compounds of formula (III)
and (IV) below:
##STR00012##
wherein A.sub.1 and A.sub.2 are defined as A.sub.Z above; wherein
A.sub.2 may be present (n=2) or may be absent (n=1), wherein, if
A.sub.2 is absent, the anchoring group Anc is directly connected to
A.sub.1; wherein at least one of A.sub.1 and A.sub.2 is a
heteroaryl comprising an aromatic ring with at least one heteroatom
selected from S, O and Se; wherein Anc is defined as above;
R.sub.20-R.sub.34 are independently defined as R.sub.1-R.sub.19
above. Accordingly, substituents R.sub.20-R.sub.34 may or may not
be substituents of formula (1) above and are most preferably H.
[0060] According to a still more preferred embodiment, the
compounds of formula (I) and (II), respectively, are selected from
compounds of formula (V) or (VI) below
##STR00013##
wherein A.sub.1 and A.sub.2 are defined as A.sub.Z above; A.sub.2
may be present (n=2) or may be absent (n=1), wherein, if A.sub.2 is
absent, the anchoring group Anc is directly connected to A.sub.1;
wherein at least one of A.sub.1 and A.sub.2 is a heteroaryl
comprising an aromatic ring with at least one heteroatom selected
from S, O and Se; Anc is defined as above; wherein R.sub.1,
R.sub.2, R.sub.4, R.sub.5, R.sub.7-R.sub.10, R.sub.12, R.sub.13,
R.sub.15, R.sub.16, R.sub.18 and R.sub.19 are defined as
R.sub.1-R.sub.19 above. Accordingly, these substituents may or may
not be substituents of formula (1) above.
[0061] According to an embodiment of the compounds of formula
(III)-(VI) above, A.sub.2 is absent. According to another
embodiment, A.sub.1 and A.sub.2 are identical in each respective
compound of formula (III)-(VI). This does not mean that A.sub.1 is
identical to A.sub.2, but it also may be the case.
[0062] As indicated above, substituents R.sub.51-R.sub.143 are
selected, if applicable, independently one from the others, from H,
halogen, and a C1-C20 hydrocarbon comprising from 0 to 20
heteroatoms.
[0063] According to a preferred embodiment, the hydrocarbon is a
C1-C15 hydrocarbon comprising 0-15, preferably 0-10 heteroatoms;
preferably a C1-C10 hydrocarbon comprising 0-10, preferably 0-5
heteroatoms; more preferably a C1-C5 hydrocarbon with 0-5
heteroatoms.
[0064] According to a preferred embodiment, R.sub.51-R.sub.143,
including thus R.sub.51-R.sub.75, the hydrocarbon is independently
selected from alkyl, alkenyl, alkynyl, and aryl, wherein said
alkyl, alkenyl, alkynyl and aryl may be linear, branched or cyclic
and optionally further substituted. The alkyl, alkenyl, alkynyl and
aryl may comprise heteroatoms. For example, a heteroatom selected
from O, S, N, may be provided within a hydrocarbon structure.
Heteroatoms may also be provided in the form of a functional group.
The number of carbons in said alkyl, alkenyl, alkynyl and aryl is
as defined for the overall hydrocarbon above. Of course, if the
hydrocarbon is alkenyl or alkynyl, it comprises at least 2 carbons,
and if it is aryl at least 4 carbons (heteroaryl) or at least 6
carbons (phenyl).
[0065] According to an embodiment, a heteroatom as referred to in
this specification is selected from halogen, in particular F, Cl,
Br, and I; O, S, Se, N, P, As, Si, B, and from metals. More
preferably, heteroatoms are selected from halogen, O, S, Se, and N
and from halogen, even more preferably from O, S and N.
[0066] According to an embodiment, R.sub.51-R.sub.143 are
independently selected from H, halogen, --CN and alkyl, wherein
said alkyl may be linear, branched or cyclic and may be further
substituted, and may comprise one or more heteroatoms, for example
O, S and/or N, wherein said alkyl may be partially or totally
halogenated. The number in carbons in said alkyl is preferably as
defined for the overall hydrocarbon.
[0067] For example, R.sub.51-R.sub.143 may be selected from
substituents of formula (47) below:
##STR00014##
in which q is an integer from 1-7 and R.sub.144 is selected from H
and from C1-C5 alkyl.
[0068] According to another embodiment, R.sub.51-R.sub.143 are
independently selected from H, halogen, anchoring groups as defined
herein, --CN (cyano), and C1-C10 alkyl, C2-C10 alkenyl, C2-C10
alkynyl and C4-C10 aryl, wherein said alkyl, alkenyl and alkynyl
may be linear, branched or cyclic and wherein one or more carbons
of said alkyl, alkenyl, alkynyl and aryl may be replaced by one or
more selected from oxygen, sulphur and nitrogen, and wherein
hydrogen atoms of said alkyl, alkenyl, alkynyl and aryl may partly
or totally be substituted by halogen; wherein said aryl may be
substituted by C1-C5 alkyl and C2-C5 alkenyl, and wherein said
aryl, if is a C4 aryl, comprises at least one heteroatom selected
from O, S and N in the ring so as to provide an aromatic ring.
[0069] According to another embodiment, R.sub.51-R.sub.143 are
independently selected from H; halogen; --CN (cyano); C1-C5 alkyl;
--NR.sub.145R.sub.146; --R.sub.147--N--R.sub.145R.sub.146, wherein
R.sub.145 and R.sub.146 are selected from H and C1-C5 alkyl and
R.sub.147 is a C1-C5 alk-diyl; C1-C5 alkoxyl;
--R.sub.147--O--R.sub.148, wherein R.sub.147 is as defined before
and R.sub.148 is a C1-C5 alkyl; and from thioalkyl. According to a
more preferred embodiment, R.sub.51-R.sub.143 are independently
selected H or halogen.
[0070] According to another embodiment, R.sub.51-R.sub.143 are
independently selected from H, halogen, --CN (cyano), C1-C5 alkyl,
C1-C5 alkoxyl. According to a more preferred embodiment,
R.sub.51-R.sub.143 are independently selected H or halogen.
[0071] Preferably one, several or all of R.sub.51-R.sub.143, if
applicable, are H.
[0072] According to an embodiment, the anchoring group (Anc) is
selected from --COOH, --PO.sub.3H.sub.2, --PO.sub.4H.sub.2,
--P(R.sub.100)O.sub.2H (phosphinic acid), --SO.sub.3H.sub.2,
--CONHOH.sup.-, acetylacetonate, deprotonated forms of the
aforementioned, salts of said deprotonated forms, and chelating
groups with .PI.-conducting character wherein R.sub.100 is a
hydrocarbon comprising from 1 to 20 carbons and 0-20 heteroatoms,
said hydrocarbon being covalently bound to the P atom of said
phosphinic acid group by a carbon atom; and wherein R.sub.100 may
be further covalently connected to the bi- or polypyridine ligand
carrying the anchoring group Anc. For example, the substituent
R.sub.100 may be covalently bound to a moiety A.sub.Z. Preferably
R.sub.100 is a C1-C10 with 0-10 heteroatoms, for example a C1-C6
hydrocarbon comprising 0-6 heteroatoms. R.sub.100, may, for
example, be selected from substituted or unsubstituted alkyls,
alkenyls, alkynyls and aryls, wherein carbons of said alkyls,
alkenyls, alkynyls and aryls may be replaced by a heteroatom
selected from O, N, and S, and wherein said alkyls, alkenyls, and
alkynyls may be linear, or branched and/or cyclic compounds.
[0073] An example of an anchoring group is acetylacetonate of
formula (Anc1) below, wherein Anc1 is connected to the terminal
moiety A.sub.n carrying it by a covalent bond to one selected from
carbon 1, 3 or 5, preferably carbon 3, of the compound of formula
(Anc1):
##STR00015##
[0074] As the skilled person appreciates, the keto and enol
tautomeric forms of the anchoring group Anc1 coexist in solution,
which are thus both encompassed by the present invention.
[0075] Salts of the deprotonated forms of the above anchoring
groups may be selected from salts of organic or inorganic cations.
Preferably the salt is selected from H+, Na+, K+, Li+ or an
ammonium salt of the above compound. An example of a frequently
used ammonium compound is tetrabutyl-ammonium.
[0076] Importantly, anchoring groups present in a single pyridine
compound, for example the two anchoring groups in the bipyridine
compounds of formula (III) and (VII), may be different.
Furthermore, anchoring groups present in a single pyridine compound
may be differently protonated, deprotonated and/or be provided in
the form of organic or inorganic salts of deprotonated anchoring
groups.
[0077] According to an embodiment, at least one anchoring group of
a bi- or terpyridine compound is protonated, the other is
deprotonated, for example provided as a negatively charged group or
as a salt of a positively charged organic compound or of a
metal.
[0078] According to a preferred embodiment, the anchoring groups
are independently selected from carboxylic acid (--COOH),
deprotonated forms thereof and salts thereof.
[0079] Examples of chelating anchoring groups with .PI.-conducting
character are oxyme, dioxyme, hydroxyquinoline, salicylate, and
.alpha.-keto-enolate groups.
[0080] According to an embodiment, a substituent of formula (1)
comprises one or more, for example two anchoring groups Anc. For
example, if n is 1, A.sub.1 of an individual substituent of formula
(1) may carry two anchoring groups Anc. According to another
example, if n is 2, A.sub.1 and A.sub.2 of an individual
substituent of formula (1) may each comprise an anchoring group Anc
or A.sub.2 of an individual substituent of formula (1) may comprise
two anchoring groups.
[0081] The present invention thus provides dyes comprising one or
more pyridine compounds of the invention, in particular for use as
one or more anchoring ligands. The anchoring ligand is suitable to
bind the dye to a surface of choice, for example to a semiconductor
surface.
[0082] The dyes of the invention preferably have the formula (XI),
(XII) or (XIII) as defined above.
[0083] According to an embodiment of the dye of the invention,
ligand L.sub.2 may be selected of a pyridine compound of formula
(XV) below:
##STR00016##
wherein the substituents R.sup.1-R.sup.8 are selected,
independently one from the other, from H, halogen, and C1-C20
hydrocarbons comprising from 0 to 20 heteroatoms.
[0084] According to an embodiment, one or more of R.sup.1-R.sup.8
are selected, independently one from the other, from substituents
of formula (51) below:
##STR00017##
wherein m is an integer of 1-10, and X is an integer of the group
of integers 1, . . . , m, wherein any B.sub.X represents the
X.sup.th moiety of the m successive moieties B, wherein any B.sub.X
may be different from any other B.sub.X; wherein, if more than one
of R.sup.1-R.sup.8 of the compound of formula (XV) are a
substituent of formula (51), any m of such substituent may be the
same or different from another such substituent of formula (51),
and any B.sub.X may be different from the respective B.sub.X of
another such substituent of formula (51); wherein any B.sub.X is
independently selected from a C4-C20 aryl, said aryl being, besides
the substituent R.sup.10, further substituted or not further
substituted, and said aryl comprising from 0-5 heteroatoms; with
the proviso that if B.sub.X is a C4 aryl, it comprises at least one
heteroatom in the aromatic ring so as to provide said aryl, wherein
any B.sub.X may also be independently selected from substituted or
unsubstituted vinylene () and ethynylene (); wherein R.sup.10 is
independently selected from H, halogen, and a C1-C20 hydrocarbon
comprising from 1-20 heteroatoms.
[0085] According to a preferred embodiment, R.sup.10 is
independently as defined substituents R.sub.51-R.sub.143.
[0086] According to an embodiment, any B.sub.X is independently
selected from the moieties of formula (2)-(29) and (25-37) above,
as further defined above. According to an embodiment, B.sub.X is
independently as A.sub.Z defined above.
[0087] According to an embodiment, R.sup.1-R.sup.8 and R.sup.10 are
defined as R.sub.51-R.sub.143 above.
[0088] According to an embodiment, the substituents R.sup.1-R.sup.8
are selected, independently one from the other, from H, halogen,
and from substituents comprising .pi.-system conjugated to the
.pi.-system of the bipyridine ligand of formula (XV). Preferably,
the substituents R.sup.1-R.sup.8 are selected, independently one
from the other, from H, and from a substituted or unsubstituted
C2-C20 alkenyl and from a substituted or unsubstituted aryl, and
may comprise 0-10 heteroatoms. For example, the alkenyl may be
substituted by an aryl and vice versa. The aryl and or alkenyl may
both be substituted by alkoxyl and/or by a polyether, for
example.
[0089] According to an embodiment, ligand L.sub.2 corresponds to
the pyridine ligands (a), (b), (c), (d), (g), (h), (i), or (j) as
defined and disclosed in WO 2006/010290A1 (page 6-8). Preferably,
the bipyridine ligand of formula (XV) is a ligand of formula (a) or
(a') of WO 2006/010290 (for (a'), see page 8).
[0090] The compounds of the invention are useful as ligands in
organometallic compounds, in particular in dyes. The invention thus
also encompasses organometallic compounds, in particular dyes
comprising the compounds of the invention. The dyes of the
invention have advantageous properties when used as sensitizing
dyes in optoelectronic and/or electrochemical devices. In
particular, the dyes of the invention have advantageous properties
when used as sensitizing dyes in photoelectric conversion devices,
such as photovoltaic cells and/or solar cells, these terms
considered to be equivalents. Preferably, the dyes of the invention
are used as sensitizing dyes of dye-sensitized solar cells
(DSCs).
[0091] The present invention further concerns a photoelectric
conversion device comprising a compound of formula (I) or (II)
and/or of the embodiments of this compound described above, and/or
of a organometallic compound comprising the compound as a ligand.
Preferably, the photoelectric conversion device comprises a
sensitising dye as defined herein above, in particular a dye
selected from the dyes of formula (XI) to (XIII).
[0092] Preferably, the photoelectric conversion device is a
regenerative cell, preferably a regenerative DSC.
[0093] FIGS. 21 and 22 show an embodiment of the dye-sensitized
solar cell of the present invention.
[0094] According to an embodiment of the present invention, the
photoelectric conversion device comprises a light absorption layer
3, which comprises a semiconductor material 4 and, absorbed
thereto, a dye layer 5 comprising a dye according to the invention
and/or a dye 5 comprising a compound according to the present
invention.
[0095] According to an embodiment, the DSC of the present invention
comprises one or two transparent substrate layers 1, a conductive
layer 2, a light absorption layer 3, a charge transport layer 6 and
counter electrode 7. Said conductive layer 2, said light absorption
layer 3, said electrolyte layer 6 and said counter electrode 7 are
preferably connected in this order, for example between two
transparent substrate layers 1. The said semiconductor nanoparticle
layer 4 is preferably electrically connected with the said
conductive layer 2 and the said dyes layer 5 is in electrical
contact with the said charge transport layer 6.
[0096] According to an embodiment, the photoelectrode comprises one
or two semiconductor material films or layers, for example one or
two mesoscopic, porous films layers. An example for a preferred
semiconductor material is TiO.sub.2. For example, the device
comprises a photoelectrode comprising and/or consisting of a single
mesoscopic, porous semiconductor material layer. The single layer
may have a thickness of .ltoreq.10 .mu.m, preferably .ltoreq.8
.mu.m, more preferably .ltoreq.6 .mu.m and most preferably
.ltoreq.5 .mu.m.
[0097] Preferably, the semiconductor material 4 provides at least
part of a photoelectrode. The photoelectrode preferably comprises a
nanocrystalline, porous layer of a semiconductor material, said
porous layer being characterized by a roughness factor of larger
than 20, preferably larger than 200 and even larger than 1000.
Preferably, the photoelectrode is a photoanode. The photoelectrode
and the counter electrode are preferably provided on support
substrates 1, such as transparent glass or plastic, at least one of
which is transparent.
[0098] Electrode (photo- and counter electrode) materials, and
electrolytes that are suitable for the present invention are
disclosed in EP1507307, WO2006/010290, WO2007/093961, and in many
more. Devices containing electrically conductive charge
transporting materials are disclosed in WO2007/107961. In the above
references, the manufacturing of such devices is also disclosed. In
FIG. 1 of EP1507307, an embodiment of a possible structure of
devices of the present invention is disclosed. On page 8, line 10
to page 9, line 51, general information and suitable materials of
the preparation of devices encompassed by the present invention is
disclosed. Of course, the present invention is not limited to
devices as disclosed in these references.
[0099] The invention is illustrated by the Examples below, which
are not intended to limit the scope of the invention.
EXAMPLES
Experimental
[0100] NMR spectra were recorded on a Bruker AMX 500 (.sup.1H NMR:
500 MHz, .sup.13C NMR: 125 MHz) or an Avance 400 spectrometer
(.sup.1H NMR: 400 MHz, .sup.13C NMR: 100 MHz), at 25.degree. C.
Chemical shift values (8) are expressed in parts per million using
residual solvent protons (DMSO-d.sub.6: .sup.1H .delta.=2.5 ppm and
.sup.13C .delta.=39.4 ppm) as internal standard. Melting points
were determined using a BuchiB-545 apparatus. Elemental analyses
were performed on an Elementar Vario EL (University of Ulm). ESI
and EI mass spectra were recorded on a micromass ZMD or a
VarianSaturn 2000 GC-MS, MALDI-TOF on a Bruker Daltonics Reflex
III. Optical measurements were carried out in 1 cm cuvettes with
Merck Uvasol grade solvents, absorption spectra recorded on a
Perkin Elmer Lambda 19 spectrometer and fluorescence spectra on a
Perkin Elmer LS 55 spectrometer. Cyclic voltammetry experiments
were performed with a computer-controlled EG&G PAR 273
potentiostat in a three-electrode single-compartment cell with a
platinum working electrode, a platinum wire counter electrode, and
an Ag/AgCl reference electrode. All potentials were internally
referenced to the ferrocene/ferrocenium couple.
Example 1
4,4'-Di(thiophen-2-yl)-2,2'-bipyridine (1)
[0101] To a mixture of 4,4'-Dibromo-2,2'-bipyridine (2 g, 6.36
mmol), tributylstannyl thiophene (5.7 g, 15.28 mmol) in 10 mL dry
degased toluene:THF (2:1) in a schlenk tube was added
Pd(PPh).sub.3Cl.sub.2 (134 mg, 191 .mu.mol) and CsF (4.84 g, 31.8
mmol). The reaction mixture was heated at 110.degree. C. for 8 h.
The completion of the reaction was checked by TLC. The solvent was
removed under reduced pressure and the crude product was purified
by column chromatography (basic Al.sub.2O.sub.3) eluting with a
mixture of 1:1 (v/v) ratio hexane:DCM. After evaporation of the
solvent 1 (1.93 mg, 6.03 mmol, 95%) was obtained as a colorless
solid. M.p.>250.degree. C.; .sup.1H NMR: (d.sub.6-DMSO, 400 MHz)
.delta. ppm: .delta. ppm 7.25 (t, 1H), 7.78 (d, J=4.97 Hz, 2H),
7.89 (d, J=3.32 Hz, 1H), 8.59 (s, 1H), 8.72 (d, J=5.13 Hz, 1H).
.sup.13C NMR: (d.sub.6-DMSO, 100 MHz) .delta. ppm: 115.89, 119.85,
126.64, 128.43, 128.95, 140.25, 141.66, 150.10, 155.59. Elemental
analysis: calc. for C.sub.18H.sub.12N.sub.2S.sub.2 C, 67.47; H,
3.77; N, 8.74%; found: C, 67.52; H, 3.81%; N, 8.71%.
Example 2
5,5'-(2,2'-bipyridine-4,4'-diyl)dithiophene-2-carboxylic acid
(2)
[0102] To a solution of n-BuLi (4.29 mL, 6.87 mmol, 1.6 M in
n-hexane) in 60 mL dry THF at -78.degree. C. was added
diisopropylamine (759 .mu.L, 7.5 mmol) dropwise. The reaction
mixture was stirred for 30 min and then allowed to warm to room
temperatre for 10 min and recooled to -78.degree. C. 1 (1 g, 3.12
mmol.) in 100 mL THF was added slowly and the reaction mixture was
stirred for 30 min. Dry ice was taken in another flask and then
CO.sub.2 was bubbbled to the reaction flask via a cannula. White
solid was precipitated. To this 1M HCl was added slowly to make the
pH to .about.5. The solid was filtered and washed with water and
methanol. Recrystallized from hot DMSO to obtain the desired
product 2 (FIG. 1) as white solid (892 mg, 2.2 mmol, 78%).
M.p.>300.degree. C.; .sup.1H NMR: (d.sub.6-DMSO, 400 MHz)
.delta. ppm: 7.81 (d, J=3.89 Hz, 1H), 7.88 (dd, J=5.02, 1.69 Hz,
1H), 7.96 (d, J=3.93 Hz, 1H), 8.66 (d, J=1.43 Hz, 1H), 8.81 (d,
J=5.20 Hz, 1H); .sup.13C NMR: (d.sub.6-DMSO, 100 MHz) .delta. ppm:
116.22, 119.88, 126.44, 133.45, 140.56, 145.68, 149.79, 155.47,
161.63, 169.08. Elemental analysis for
C.sub.20H.sub.12N.sub.2O.sub.4S.sub.2: calcd. C, 58.81; H, 2.96; N,
6.86%, found: C, 58.91; H, 2.93; N, 6.81%.
Example 3
Ru(5,5'-(2,2'-bipyridine-4,4'-diyl)dithiophene-2-carboxylic acid)
(4,4'-dinonyl-2,2'-bipyridine)(NCS).sub.2 (3)
[0103] RuCl.sub.2(p-cymene).sub.2 (112.4 mg, 0.184 mmol) and dnbpy
(150 mg, 0.367 mmol) were taken in a Schlenk tube and dissolved in
dry DMF (30 mL). The reaction mixture was heated to 60.degree. C.
under argon for 4 h with constant stirring. Subsequently, dtcbpy
(150 mg, 0.367 mmol) was added to this reaction flask and the
reaction mixture was refluxed under dark at 140.degree. C. for 4 h.
Finally, an excess of NH.sub.4NCS (837 mg, 11.0 mmol) was added to
the reaction mixture and the reflux continued for another 4 h. The
reaction mixture was cooled to room temperature, and the solvent
was removed by using a rotary evaporator under vacuum. Water was
added to the flask, and the insoluble solid was collected on a
sintered glass crucible by suction filtration. The solid was washed
with distilled water and diethyl ether and then dried under vacuum.
The crude complex was dissolved in methanolic sodium hydroxide
solution and purified on a Sephadex LH-20 column with methanol as
eluent. The collected main band was concentrated and divided into
two halves and one part titrated quickly to pH 3.2 to isolate
compound 3a. The second half then slowly titrated with an acidic
methanol solution (HNO.sub.3) to pH 4.8 to isolate compound 3b. The
precipitated 3a was collected on a sintered glass crucible by
suction filtration and dried. .sup.1H NMR (d.sub.4-MeOH, 400 MHz)
.delta. ppm: 0.8 (t, 3H), 0.85 (t, 3H), 1.1-1.5 (m, 24H), 1.57 (m,
2H), 1.82 (m, 2H), 2.65 (t, 2H), 2.91 (t, 2H), 7.12 (dd, J=5.76,
0.93 Hz, 1H), 7.48 (d, J=5.73 Hz, 1H), 7.54 (d, J=2.20 Hz, 1H),
7.76 (d, J=3.55 Hz, 1H), 7.83 (dd, J=5.61, 0.96 Hz, 1H), 7.88 (d,
J=3.53 Hz, 1H), 8.03 (d, J=3.84 Hz, 1H), 8.24 (d, J=3.90 Hz, 1H),
8.27 (dd, J=5.91, 1.71 Hz, 1H), 8.54 (s, 1H), 8.69 (s, 1H), 9.03
(s, 1H), 9.09 (d, J=5.76 Hz, 1H), 9.16 (s, 1H), 9.26 (d, J=5.91 Hz,
1H).
Example 4
Ru(bis[5,5'-(2,2'-bipyridine-4,4'-diyl)dithiophene-2-carboxylic
acid)] (NCS).sub.2 (4)
[0104] RuCl.sub.2(p-cymene).sub.2 (74 mg, 0.122 mmol) and dtbpy
(200 mg, 0.489 mmol) were taken in a Schlenk tube purged with argon
and dissolved in dry DMF (30 mL). The reaction mixture was heated
in dark to 145.degree. C. for 5 h with constant stirring.
Subsequently, an excess of NH.sub.4NCS (1.1 g, 14.6 mmol) was added
to the reaction mixture and the reflux continued for another 4 h.
The reaction mixture was cooled to room temperature, and the
solvent was removed by using a rotary evaporator under vacuum.
Small amount of water was added to the dried solid and filtered on
a sintered glass crucible by suction filtration. The solid was
further washed with distilled water and diethyl ether and then
dried under vacuum. The crude complex was dissolved in methanolic
tetrabutylammonium hydroxide solution and purified on a Sephadex
LH-20 column with methanol as eluent. The collected main band was
concentrated and then slowly titrated with an acidic methanol
solution (HNO.sub.3) to pH 4.4. The precipitate (compound 4 in FIG.
3) was collected as 2TBA salt on a sintered glass crucible by
suction filtration and dried under vacuum. .sup.1H NMR
(d.sub.4-MeOH/d.sub.6-DMSO, 400 MHz) .delta. ppm: 0.9 (t, 12H),
1.29 (m, 8H), 1.52 (m, 8H), 3.2 (t, 8H), 7.38 (dd, J=6.11, 1.88 Hz,
1H), 7.57 (d, J=3.76 Hz, 1H), 7.61 (d, J=6.13 Hz, 1H), 7.70 (d,
J=3.63 Hz, 1H), 7.84 (d, J=3.94 Hz, 1H), 8.05 (d, J=3.87 Hz, 1H),
8.08 (dd, J=5.97, 1.77 Hz, 1H), 8.99 (s, 1H), 9.14 (s, 1H), 9.31
(d, J=5.96 Hz, 1H). Elemental Analysis for
C.sub.74H.sub.94N.sub.8O.sub.8RuS.sub.6.1[(C.sub.4H.sub.9).sub.4N].5H.sub-
.2O calcd. C, 50.97; H, 5.16; N, 7.17%, found. C, 51.12; H, 4.44;
N, 7.15%.
Example 5
General Device Fabrication
[0105] The cells consisted of a mesoscopic TiO.sub.2 film composed
of a 7 .mu.m thick transparent layer of 20 nm sized TiO.sub.2
anatasenanoparticles onto which a second 5 .mu.m thick scattering
layer of 400 nm sized TiO.sub.2 was superimposed. The double layer
films were heated to 520.degree. C. and sintered for 30 min, then
cooled to 80.degree. C. The electrode was immersed for 16 hours
into the dye solution (150 .mu.M) containing 10% DMSO in a
acetonitrile/tert-butyl alcohol-mixture (volume ratio:1:1). The
devices were fabricated with the low-volatile electrolyte coded
Z946. The Z946 electrolyte contains 3-methoxypropionitrile as a
solvent and 1.0 M 1,3-dimethylimidazolium iodide (DMII), 0.15 M
1.sub.2, 0.5 M n-butylbenzimidazole as well as 0.1
guanidiniumthiocyanate (GuNCS) as solutes. The cell was sealed with
a 25 .mu.m-thick transparent Surlyn ring (from DuPont) at
130.degree. C. for 15 seconds to the counter electrode (FTO glass,
15 .OMEGA.cm.sup.-2, coated with a platinum solution chemically
deposited at 450.degree. C. for 15 min). The cells were filled with
the electrolyte through a pre-drilled hole in the counter
electrode. The hole was then sealed with a Bynel disc and a thin
glass to avoid leakage of the electrolyte.
Examples 6-14
Results obtained with dye 3 of Example 3
Device Fabrication:
[0106] Dye sensitized solar cells (DSCs) with double or single thin
layers of TiO.sub.2 particles were prepared and coated with
different dyes with or without co-adsorbed compounds.
[0107] 5.5 and 3.3 .mu.m thick transparent layers of 20 nm
TiO.sub.2 particles were screen printed on a fluorine-doped
SnO.sub.2 (FTO) conducting glass electrode.
[0108] Double layered films of TiO.sub.2 particles (7+5 .mu.m) were
prepared by first screen printing a 7 .mu.m of 20 nm TiO.sub.2
particles on the fluorine-doped SnO.sub.2 (FTO) conducting glass
electrode, followed by coating with a 5 .mu.m thick second layer of
400 nm light scattering anatase particles.
[0109] The details for the preparation of the TiO.sub.2 films have
been described by Wang, P.; Zakeeruddin, S. M.; Comte, P.; Charvet,
R.; Humphry-Baker, R.; Gratzel, M. J. Phys. Chem. B 2003, 107,
14336.
[0110] The TiO.sub.2 films are first sintered at 500.degree. C. for
30 min and then cooled to about 80.degree. C. in air. Then, the
TiO.sub.2 film electrodes are dipped into dye solutions (150 .mu.M)
with and without the coadsorbent in a mixture of 10% DMSO and
acetonitrile and tert-butyl alcohol (volume ratio, 1:1) at room
temperature for 16 h to adsorb the dye. Thereafter, the films were
washed with acetonitrile and dried by air flow.
[0111] The cells were sealed to the counter electrode and supplied
with the low-volatile Z946 electrolyte solution as described in
Example 5 above.
[0112] The photoelectric characterization of the various
dye-sensitized solar cells is detailed in Table 3 below and is
further illustrated in FIGS. 7-16.
TABLE-US-00001 TABLE 1 Structure and photoelectric characteristics
of DSCs of the invention and of the prior art. IPCE V.sub.OC Eff.
max .lamda.max Ex. TiO.sub.2 film Dye Co-adsorbant (V)
J.sub.SC.sup.1 FF (%) (%) (nm) 6 double 3a -- 0.678 13.7 0.71 6.6
58.8 530 7 (7 + 5 .mu.m) 3b -- 0.709 14.8 0.72 7.6 60.1 550 8
double 3b -- 0.709 14.8 0.72 7.6 60.1 550 9 (8.5 + 5 3b
DINHOP.sup.2 (4:1) 0.732 14.9 0.72 8.0 63.8 550 10 .mu.m) 3b
GBA.sup.3 (1:1) 0.778 12.9 0.74 7.5 65.1 550 11 single thin
Z907.sup.4 GBA.sup.3 (1:1) 0.800 11.1 0.74 6.6 73.8 520 12 (5
.mu.m) 3b GBA.sup.3 (1:1) 0.744 12.7 0.73 7.0 62.5 520 13 single
thin Z907.sup.4 GBA.sup.3 (1:1) 0.810 8.9 0.74 5.4 70.7 520 14 (3
.mu.m) 3b GBA.sup.3 (1:1) 0.753 10.5 0.71 5.7 66.6 540
.sup.1(mA/cm.sup.2); .sup.2DINHOP =
bis-(3,3-dimethyl-butyl)-phosphinic acid; .sup.3GBA = 4-guanidino
butyric acid was obtained from Fluka; .sup.4state of the art dye
[cis-RuLL'(SCN).sub.2] (L = 4,4'-dicarboxylic acid-2,2'-bipyridine,
L' = 4,4'-dinony1-2,2'-bipyridine).
Synthesis of DINHOP (bis-(3,3-dimethyl-butyl)-phosphinic acid)
[0113] To 3,3-dimethylbutene (4.00 g, 47.5 mmol) hypophosphrous
acid (aq. 50%) (0.80 g, 11.9 mmol) and di-tert.-butylperoxide
(neat, 0.30 g, 2.4 mmol) was added in a Buchi reactor (10 ml),
heated to 135.degree. C. and stirred for 22 hours. The reaction
mixture was filtered, and the solid was washed thoroughly with
water twice, and with a little acetone. Recrystallization from
n-hexane yielded 1.01 g (73%) bis-(3,3-dimethyl-butyl)-phosphinic
acid. .sup.1H NMR (CDCl.sub.3) d ppm: 0.92 (18H, s), 1.49 (4H, m),
1.64 (4H, m), 9.15 (1H, br)
[0114] 31P NMR (CDCl.sub.3) d ppm: 62.8 (s),
[0115] HR-MS m/z 235.1821 (C12H.sub.27O.sub.2P).
Conclusion for Examples 8-14
[0116] As can be seen in particular from comparing Examples 11-14
in Table 1 (FIGS. 13-16), the dye 3b of the present invention
surprisingly results in devices with higher conversion efficiencies
(Eff. (%)) than the state of the art dye Z907
([cis-RuLL'(SCN).sub.2 (L=4,4'-dicarboxylic acid-2,2'-bipyridine,
L'=4,4'-dinonyl-2,2'-bipyridine)], if the dye is provided on a thin
TiO.sub.2 film of 3 or 5 .mu.m.
[0117] Such high conversion efficiencies (7%, Example 12; 5.7%
Example 14 in Table 1) are very surprising for a Ru-dye on such
thin TiO.sub.2 films (5 and 3 .mu.m, respectively). In particular,
in the cells of Examples 12 and 14, the J.sub.SC values are 14.4%
and 18%, respectively, higher than in the cells of the comparative
Examples 11 and 13 using dyes of the prior art.
[0118] These results show that dyes of the present invention has
superior performance over the prior art dyes with thin TiO.sub.2
films due to red shift in the absorption spectra and increase in
the molar extinction coefficient. This approach allows designing
efficient panchromatic sensitizers with increased photovoltaic
conversion efficiencies with ultra thin titania films.
Examples 15-17
Device Stability Tests
[0119] The devices obtained in Examples 8-10 were subjected to the
visible light-soaking (1 sun; 100 mW/cm.sup.2) at 60.degree. C. for
1000 h.
[0120] The results can be seen in FIG. 12 and Table 2 below. It can
be seen that the devices with the compound 3b dye exhibit excellent
stability.
TABLE-US-00002 TABLE 2 DSCs of Examples 8-10 (Table 1), following
exposure to full sunlight for 1000 hours V.sub.OC J.sub.SC Eff.
Stability Example Dye Co-adsorbent EL State (V) (mA/cm.sup.2) FF
(%) (%) 15 3b -- Z946 Final 0.648 14.2 0.74 6.8 90 16 3b DINHOP
(4:1) Z946 Final 0.660 16.0 0.73 7.7 98 17 3b GBA (1:1) Z946 Final
0.710 15.0 0.74 7.9 106
Examples 18-21
Dye Sensitized Solid State Solar Cells with Dyes of the Invention
on 2 .mu.m Mesoporous TiO.sub.2 Film
Device Fabrication:
[0121] For solid-state device fabrication, a spray pyrolysis
technique was used to coat the FTO conducting glass substrates (LOF
Industries, TEC 15.OMEGA./square, 2.2 mm thickness) with a thin
compact layer of TiO.sub.2 in order to prevent electron-hole
recombination arising from direct contact between the
hole-conductor (spiro-OMeTAD) and the highly doped FTO layer. A 1.8
.mu.m mesoporous layer of the TiO.sub.2 nanoparticles with a
typical diameter of 20 nm was deposited by doctor-blading on top of
this compact layer. The TiO.sub.2 electrodes were stained by
dipping in a dye solution for 5 h of 0.3 mM dye and 10 mM cheno in
dichloromethane. The spiro-OMeTAD solution (137 mM in
chlorobenzene) contained final concentrations of 112 mM
tert-butylpyridine and 21 mM Li--[CF.sub.3SO.sub.2].sub.2N (added
from highly concentrated acetonitrile solutions). Finally, a gold
contact (100 nm) was deposited on the organic semiconductor film by
evaporation (EDWARDS AUTO 500 Magnetron Sputtering System).
Results and Conclusion:
[0122] As shown in Table 3 the dye 3b with spiro-MeOTAD as hole
transport material gave superior photovoltaic performance compared
to prior art dye Z907 under similar conditions using ultra thin
mesoporous TiO.sub.2 films.
TABLE-US-00003 TABLE 3 Solid-state device results with
Acedic-TiO.sub.2, 2 .mu.m film, overnight dipping Exam- Efficien-
ple Condition Substrate J.sub.SC V.sub.OC FF cy(%) 18 3b
Acidic-TiO.sub.2 6.98 708.72 48.5 2.4 19 3b + GBA 9.15 776.32 45.6
3.2 20 3b + GBA 50 nm 7.52 796 60 3.6 21 Z907 + GBA 50 nm 6 824.3
63.5 3.1
Example 22
Results of Compound 4 of Example 4
[0123] The electronic absorption spectrum of compound 4 in DMF is
displayed in FIG. 17 and the data are summarized in Table 4 below.
Compound 4 showed broad absorption bands in the 300 to 750 nm
region. The two high-energy bands at 287 and 331 nm are due to
intra-ligand .pi.-.pi.* transitions. The absorption spectrum of
compound 4 is dominated by metal to ligand charge transfer
transitions (MLCT). The lowest energy MLCT band at 563 nm is 28 nm
red-shifted compared to the standard N719 sensitizer (see below)
because of the extention of 7C-conjugation in the anchoring ligand
and increased HOMO energy level.
[0124] The N719 dye described previously is the
bis-tetrabutylammonium (TBA) salt of
cis-di(thiocyanato)-bis[2,2'-bipyridyl-4,4'-dicarboxylic acid]
ruthenium(II), see (a) M. K. Nazeeruddin, A. Kay, L. Rodicio, R.
Humpbry-Baker, E. Miiller, P. Liska, N. Vlachopoulos, M. Gratzel,
J. Am. Chem. Soc. 1993, 115, 6382. (b) Md. K. Nazeeruddin, F. De
Angelis, S. Fantacci, A. Selloni, G. Viscardi, P. Liska and M.
Gratzel, J. Am. Chem. Soc. 2005, 127, 16835.
TABLE-US-00004 TABLE 4 Spectroscopic and electrochemical data of
compound 4 and N719 measured in DMF. (HOMO/LUMO vs.
Fc/Fc.sup.+.sub.vac = -5.1 eV) .lamda..sub.abs (nm) .lamda..sub.em
E.sup.0.sub.ox E.sup.0.sub.red1 E.sup.0.sub.red2 HOMO LUMO .DELTA.E
Dye (.epsilon. [L mol.sup.-1 cm.sup.-1]) (nm) (V) (V) (V) (eV) (eV)
(eV) 4 287 (59000) 800 0.28 -1.86 -2.08 -5.33 -3.37 1.96 331
(62300) 426 (24800) 563 (23200) N719 312 (47200) 800 0.39 -2.17 --
-5.38 -3.06 2.32 388 (13800) 535 (13500)
TABLE-US-00005 TABLE 5 Comparison of photovoltaic parameters under
full sunlight intensity of compound 4 and N719 adsorbed on
nanocrystalline TiO.sub.2 films of various thicknesses. TiO.sub.2
Film J.sub.sc Thickness (mA Dye (.mu.m) V.sub.oc (V) cm.sup.-2) FF
.eta. (%) 4 3.3 0.68 12.2 0.74 6.1 5.5 0.67 14.1 0.73 6.9 7 + 5
0.66 15.8 0.73 7.6 N719 3.3 0.74 9.1 0.71 4.8 5.5 0.72 12.5 0.70
6.3 7 + 5 0.71 15.3 0.71 7.7
[0125] Importantly, an increase of 72% of the molar extinction
coefficient was observed for the longest wavelength MLCT band as a
consequence of the insertion of thiophene units to the ligand
compared to N719 sensitizer. The emission data of compound 4 were
obtained in an air-equilibrated DMF solution at 298K by exciting at
the low energy MLCT absorption band, showing a week emission
maximum at 800 nm.
[0126] HOMO and LUMO energy levels of compound 4 were determined by
cyclic voltammetry (Table 4). The complex showed an oxidation wave
at 0.28 V (vs. Fc VFc), which is assigned to the oxidation of the
Ru.sup.II center. Compared to standard N719 dye, the metal centre
oxidation is cathodically shifted by 110 mV indicating the
electron-rich character of the new ligand as a result of the
thiophene insertion. Two reversible reduction waves at -1.86 and
-2.08 V (vs. Fc.sup.+/Fc) can be assigned to successive one
electron reductions of the bipyridine ligands. The first cathodic
potential of compound 4 is by 310 mV more positive than that of
N719.
[0127] The excited state oxidation potential of a sensitizer plays
an important role in electron transfer processes. The quasi-Fermi
level of the TiO.sub.2 photoanode and the redox level of the
I.sub.3.sup.-I.sup.--based electrolyte are situated at around -4.0
eV and -4.83 eV vs. vacuum, respectively. The HOMO level of
compound 4 is located at -5.33 eV, the LUMO level at -3.37 eV.
Overall, the HOMO-LUMO band gap of compound 4 (E.sub.g=1.96 eV) is
approximately 360 meV smaller compared to N719 (E.sub.g=2.32 eV),
which is also reflected in the red-shift of the absorption
spectrum. The position of the LUMO level of compound 4 is
sufficiently more negative than the TiO.sub.2 conduction band to
facilitate efficient electron transfer from the excited dye to
TiO.sub.2. On the other hand, the HOMO level of compound 4 is
sufficiently below the energy level of the redox mediator allowing
dye regeneration.
[0128] Absorption spectra of compound 4 and N719 adsorbed on a 3.3
.mu.m transparent TiO.sub.2 thin film showed features similar to
those of corresponding spectra in solution, but exhibited a slight
red-shift due to interaction of the anchoring groups and the
TiO.sub.2 surface (FIG. 18). These transparent thin films were used
to investigate differences in photovoltaic performance of N719 and
compound 4 dyes.
[0129] The monochromatic incident photon-to-current conversion
efficiency (IPCE) is defined as the number of electrons generated
by light in the external circuit divided by the number of incident
photons as a function of excitation wavelength. FIG. 19 shows the
IPCE spectra obtained with DSSC devices of compound 4 and N719 dye
with 3.3 .mu.m transparent photoanodes and a 3-methoxypropionitrile
(MPN) containing low volatile electrolyte. N719 and compound 4
exhibited at 550 nm IPCE values of 67 and 74%, respectively, with
an extended red response for compound 4. Under standard global AM
1.5 solar conditions, compound 4 sensitized cells gave a
short-circuit photocurrent density (J.sub.sc) of 12.2 mA cm.sup.-2,
an open-circuit voltage (V.sub.oc) of 0.68 V, and a fill factor
(FF) of 0.74, corresponding to an overall conversion efficiency of
6.1% (FIG. 20). Such a high performance is very intriguing for a
Ru.sup.II-dye on a 3.3 .mu.m thin TiO.sub.2 film in combination
with a low volatile electrolyte. Under similar conditions N719
dye-sensitized cells gave an overall conversion efficiency of only
4.8%. The photovoltaic parameters are given in Table 5. The
J.sub.sc value of the compound 4 sensitizer is 34% higher compared
to N719. This observation is in accordance with the red-shifted
absorption in the visible region and the increased molar extinction
coefficient.
[0130] The influence of nanocrystalline TiO.sub.2 film thickness on
the photovoltaic performance with compound 4 sensitizer was studied
using film thicknesses of 3.3 and 5.5 .mu.m. Additionally, a thick
TiO.sub.2 film composed of 7 .mu.m transparent layer and 5 .mu.m
scattering layer was tested. The detailed photovoltaic parameters
of corresponding devices with compound 4 and N719 are given in
Table 5. Increasing the film thickness from 3.3 over 5.5 to 7+5
.mu.m for compound 4 resulted in an increase of the current
densities from 12.2 over 14.1 to 15.8 mA cm.sup.-2. As a
consequence, the overall cell performance was increased from 6.1 to
7.6% under full sunlight. It is interesting to note that with
thinner films the photovoltaic performance of compound 4 devices
outperformed N719 devices, whereas, with double layer films the
performance was nearly identical.
[0131] In conclusion, we have designed and synthesized a new
anchoring ligand,
5,5'-(2,2'-bipyridine-4,4'-diyl)-bis(thiophene-2-carboxylic acid)
and its ruthenium complex compound 4 Extending the .pi.-conjugation
of the anchoring ligand increased the device performance in thin
films as a result of the increased molar extinction coefficient and
enhanced spectral response in the red wavelength region. This class
of sensitizers containing thiophene in the anchoring site has not
been previously reported. This approach allows designing efficient
panchromatic sensitizers with increased photovoltaic conversion
efficiencies.
* * * * *