Metal complex photosensitizer and photovoltaic cell

Details Metal complex photosensitizer and photovoltaic cell Metal complex photosensitizer and photovoltaic cell

1999-11-02

2001-06-12

Diamond, Alan (Department: 1753)

Batteries: thermoelectric and photoelectric

Photoelectric

Cells

C136S252000, C257S040000, C257S428000, C257S431000, C546S002000, C546S010000, C546S011000, C546S012000, C546S008000, C546S009000, C548S101000, C548S107000, C548S108000, C548S109000, C556S137000, C556S138000, C556S140000, C556S145000, C556S146000, C534S014000, C429S111000

Reexamination Certificate

active

06245988

ABSTRACT:

The invention relates to a transition metal complex photosensitizer and its use in a photovoltaic cell comprising a nanocrystalline titanium dioxide layer.
Transition metal complexes, commonly designated as “dyestuffs”, useful as charge transfer photosensitizer for semiconductive titanium dioxide photoanode layers, in a photovoltaic cell, are already known. Such complexes consist of a light absorber and an anchoring group. The anchoring group allows the immobilization of the transition metal complex at the titanium dioxide layers and provides an electronic coupling between the light absorber and the titanium dioxide layers. The light absorber absorbs an incoming photon via a metal ligand charge transfer, and injects an electron into the conduction band of titanium dioxide through the anchoring group. The oxidized complex is then regenerated by a redox mediator.
In such a process, it is crucial to guide the charge transfer toward the semiconductor titanium dioxide surface and to guarantee tight electronic overlap between the LUMO anchoring group and the vacant orbitals of titanium.
In particular, such complexes, as well as dye sensitized nanocrystalline titanium dioxide photovoltaic cells, are disclosed in the International Patent Applications published as PCT Publication No. WO 94/04497 and PCT Publication No WO 95/29924.
PCT Publication No. WO 94/04497 describes ruthenium complexes in which ruthenium is surrounded by at least one dicarboxy bipyridine ligand, the carboxy groups playing the role of anchoring groups. The best performing charge transfer photosensitizer employed for this application is cis-dithiocyanatobis(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) complex. Using this complex in a nanocrystalline titanium dioxide photovoltaic cell has permitted to obtain a solar to electrical power conversion efficiency of 10% under standard spectral distribution of solar light emission AM 1.5, where the photosensitizer absorbs in the wavelength region from 400 to 650 nm. However, it has been found that in longer wavelength the incident photon to current conversion efficiency (IPCE) drops because of lack of spectral response of the photosensitizer.
PCT Publication No. WO 94/04497 describes other potent ruthenium complexes, being able to be immobilized at the titanium dioxide layers via at least one phosphonated group carried by polypyridine ligands. This particular anchoring group appeared to have a higher stability than the carboxy group on a wider pH range of 0 to 9, avoiding partial desorbtion of the complex. Unfortunately, the absorption spectrum upper limits of such complexes showed to be less than 600 nm.
The present invention aims at further improving the efficiency of solar to electric power conversion by providing a photosensitizer having an enhanced spectral response in the red and near infrared regions.
To that effect, according to the invention, there is provided a photosensitizer complex of formulae (Ia) or (Ib):
MX
3
L
t
  (Ia);
MXYL
t
  (Ib);
M is a transition metal selected from ruthenium, osmium, iron, rhenium and technetium;
each X is a co-ligand independently selected from NCS
−
, Cl
−
, Br
−
, I
−
, CN
−
, NCO
−
, H
2
O, NCH
2−
and pyridine unsubstituted or substituted by at least one group selected from vinyl, primary, secondary or tertiary amine, OH and C
1-30
alkyl;
Y is a co-ligand selected from o-phenanthroline, 2,2′-bipyridine, unsubstituted or substituted by at least one C
1-30
alkyl; and
L
t
is a tridentate ligand having a formula selected from the general formulae (IIa) and (IIb):
wherein
R
1
is selected from H, COOH, PO(OH)
2
, PO(OR
3
)
2
, CO(NHOH), pyrocatechol group and phenyl substituted by at least one of the groups selected from COOH, PO(OH)
2
, PO(OR
3
)(OH), PO(OR
3
)
2
and CO(NHOH); R
3
being selected from C
1-30
alkyl and phenyl;
R
2
is selected from H, C
1-30
alkyl and phenyl; and
A and B are same or different groups independently selected from the groups of formulae (IIIa), (IIIb), (IIIc), (IIId), (IIIe) and (IIIf):
wherein
R
4
has the same meaning as R
1
;
each R
5
, R
6
, R
7
, R
8
, R
9
, R
10
and R
11
has the same meaning as R
2
and R
2
, R
5
, R
6
, R
7
, R
8
, R
9
, R
10
and R
11
being same as or different from each other;
with the proviso that at least one of the substituents R
1
and R
4
is different of H.
More preferably, when the photosensitizer complex corresponds to formula (Ia):
MX
3
L
t
  (Ia),
M is ruthenium or osmium;
each X is independently selected from NCS
−
, CN
−
, and
L
t
has the formula (IIa):
wherein
R
1
is selected from H, COOH, PO(OH)
2
, PO(OR
3
)(OH), PO(OR
3
)
2
, CO(NHOH), pyrocatechol group and phenyl substituted by at least one of the groups selected from COOH, PO(OH)
2
, PO(OR
3
)
2
and CO(NHOH); R
3
being selected from C
1-30
alkyl and phenyl;
A and B are same or different and have the formula (IIIa):
wherein
R
4
has the same meaning as R
1
;
with the proviso that at least one of the substituents R
1
and R
4
is different of H.
More preferably, when the photosensitizer complex corresponds to formula (Ia):
MX
3
L
t
  (Ia),
M is ruthenium or osmium;
each X is independently selected from NCS
−
, CN
−
, and
L
t
has the formula (IIa):
wherein
R
1
is a phenyl substituted by at least one of the groups selected from COOH, PO(OH)
2
, PO(OR
3
)(OH), PO(OR
3
)
2
; R
3
being selected from C
1-30
alkyl and phenyl; and
A and B are both 2-pyridyl.
More preferably, when the photosensitizer complex corresponds to formula (Ia):
MX
3
L
t
  (Ia),
M is ruthenium or osmium;
each X is independently selected from NCS
−
, CN
−
, and
L
t
has the formula (IIa):
wherein
R
1
is COOH; and
A and B are both 4-carboxy-2-pyridyl.
Preferably, when the photosensitizer complex corresponds to formula (IIb):
MXYL
t
  (Ib),
M is ruthenium or osmium;
X is NCS
−
, CN
−
;
Y is selected from o-phenanthroline, 2,2′-bipyridine, unsubstituted or substituted by at least one C
1-30
alkyl; and
L
t
has the formula (IIa):
wherein
R
1
is selected from H, pyrocatechol group, phenyl substituted by at least one of the groups selected from COOH, PO(OH)
2
, PO(OR
3
)(OH), PO(OR
3
)
2
and CO(NHOH);
R
3
being selected from C
1-30
alkyl and phenyl;
A and B are same or different and have the formula (IIIa):
wherein
R
4
is selected from H, COOH, PO(OH)
2
, PO(OR
3
)(OH), PO(OR
3
)
2
, CO(NHOH), pyrocatechol group, phenyl substituted by at least one of the groups selected from COOH, PO(OH)
2
, PO(OR
3
)(OH), PO(OR
3
)
2
and CO(NHOH); R
3
being selected from C
1-30
alkyl and phenyl;
with the proviso that at least one of the substituents R
1
and R
4
is different of H.
More preferably, when the photosensitizer complex corresponds to formula (Ib):
MXYL
t
  (Ib),
M is ruthenium or osmium;
Y is 4,4′-dimethyl-2,2′-bipyridine; and
L
t
has the formula (IIa):
wherein
R
1
is a phenyl substituted by at least one of the groups selected from COOH, PO(OH)
2
, PO(OR
3
)(OH) and PO(OR
3
)
2
; R
3
being selected from C
1-30
alkyl and phenyl; and
A and B are both 2-pyridyl.
The invention results from extensive research which have shown that the transition metal complex of formulae (Ia) and (Ib) has the unexpected property of exhibiting a substantially enhanced spectral response in the red and near infrared regions, in comparison with the prior art transition metal complexes.
This property allows the use of the complex of formulae (Ia) or (Ib) as charge transfer photosensitizer for semiconductive titanium dioxide photoanode layers, in a photovoltaic cell with a very efficient panchromatic sensitization over the whole visible radiation spectrum, extending into the near infrared region up to 920 nm.
It appeared that the type of coordination around the transition metal, in particular ruthenium or osmium, and the nature of the ligand L
t
and the co-ligands Y and/or X surrounding the metal are crucial for obtaining such spectral properties

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