.
Angewandte
Communications
DOI: 10.1002/anie.201305975
Panchromatic Sensitizers
Highly Efficient Dye-Sensitized Solar Cells Based on Panchromatic
Ruthenium Sensitizers with Quinolinylbipyridine Anchors
Chun-Cheng Chou, Fa-Chun Hu, Hsiu-Hsuan Yeh, Hsin-Pei Wu, Yun Chi,* John N. Clifford,*
Emilio Palomares, Shih-Hung Liu, Pi-Tai Chou,* and Gene-Hsiang Lee
II
Abstract: Panchromatic Ru sensitizers TF-30–TF-33 bearing
a new class of 6-quinolin-8-yl-2,2’-bipyridine anchor were
synthesized and tested under AM1.5 G simulated solar irradi-
ation. Their increased p conjugation relative to that of the
traditional 2,2’:6’,2’’-terpyridine-based anchor led to a remark-
able improvement in absorptivity across the whole UV–Vis–
NIR spectral regime. Furthermore, the introduction of a bulky
tert-butyl substituent on the quinolinyl fragment not only led to
an increase in the JSC value owing to the suppression of dye
aggregation, but remarkably also resulted in no loss in VOC in
comparison with the reference sensitizer containing a tri-
carboxyterpyridine anchor. The champion sensitizer in DSC
sensitizers with optimal device stability. However, for prac-
tical use, the current records of device efficiency still must be
improved upon; better sensitizers are therefore urgently
needed to push forward the frontiers of this field of
[4]
research. Naturally, ingenious dye design is required for
maximizing the conversion efficiency (h), the short-circuit
[
5]
current (J ), and the open-circuit voltage (VOC). To over-
SC
come this challenge, panchromatic sensitizers are needed with
high absorptivity extending well into the near-infrared (NIR)
regime to harvest a wider coverage of solar irradiation for
a higher photocurrent. Simultaneously, sensitizer structures
can be modified and cell designs optimized to suppress the
dark current and maintain the high open-circuit voltage
necessary for outstanding cells.
devices was found to be TF-32 with a performance of J
9.2 mAcm , V = 740 mV, FF = 0.72, and h = 10.19%. This
=
SC
ꢀ
2
1
OC
6
-quinolin-8-yl-2,2’-bipyridine anchor thus serves as a proto-
The fulfillment of all of these goals, however, is far from
trivial. In the case of the black dye, the lowest-lying
absorption-band maximum is located at 606 nm with
a shoulder extending down to approximately 800 nm. These
absorptions are assigned to the spin-allowed and spin-
forbidden metal-to-ligand charge-transfer transitions, that is,
II
type for the next generation of Ru sensitizers with any
tridentate ancillary.
T
he establishment of a low-carbon society requires emerging
renewable energy sources, for which third-generation photo-
voltaic technology, such as dye-sensitized solar cells, is
1
3
[2a]
MLCT and MLCT, respectively.
This and similar dyes
[
1]
considered to be one of the best candidates. To date,
ruthenium(II)-based sensitizers, such as {(C H ) N} [Ru-
generally have inferior absorptivity. As a result, it is necessary
to fabricate cells with thicker TiO layers to maximize the
4
9
4
2
2
(
Hdcbpy) (NCS) ] (N719; dcbpy = 4,4’-dicarboxy-2,2’-bipyri-
short-circuit current. However, this strategy generally results
in a trade-off in the form of a lower device voltage VOC. The
situation was somewhat improved in a class of thiocyanate-
free sensitizers, including TF-1 (Scheme 1), the absorption
2
2
[
6]
dine), {(C H ) N} [Ru(Htctpy)(NCS) ] (black dye or N749;
tctpy = 4,4’,4’’-tricarboxy-2,2’:6’,2’’-terpyridine), and func-
tionalized derivatives, have received the greatest amount
of academic and industrial attention, and have exhibited
conversion efficiencies among the highest reported for
4
9
4
3
3
[
2]
[
3]
[
+]
[+]
[
*] C.-C. Chou, F.-C. Hu, H.-H. Yeh, H.-P. Wu, Y. Chi
Department of Chemistry and Low Carbon Energy Research Center
National Tsing Hua University
Hsinchu 30013 (Taiwan)
E-mail: ychi@mx.nthu.edu.tw
J. N. Clifford, E. Palomares
Institute of Chemical Research of Catalonia (ICIQ)
Avda. Paꢀsos Catalans 16, 43007 Tarragona (Spain)
E-mail: jnclifford@iciq.es
Scheme 1. Structures of black dye and TF-1.
E. Palomares
ICREA, Avda. Lluꢁs Companys 28
Barcelona E-08030 (Spain)
bands of which were slightly more intense in both the higher-
energy and NIR regions of the spectrum. However, the
absorptivity was unexpectedly low (as compared with that of
S.-H. Liu, P.-T. Chou, G.-H. Lee
Department of Chemistry and Center for Emerging Material and
Advanced Devices, National Taiwan University
Taipei 10617 (Taiwan)
[7]
black dye) in the spectral range of 550 to 700 nm (Figure 1).
E-mail: chop@ntu.edu.tw
In this study, with the goal of finding a better molecular
design, we turned to the 6-quinolin-8-yl-2,2’-bipyridine
anchor, Qbpy, which was expected to show greater chelate
p conjugation relative to that of the traditional 2,2’:6’,2’’-
+
[
] These authors contributed equally.
1
78
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 178 –183