FULL PAPER
DOI: 10.1002/chem.201301658
Tailor-Made Hole-Conducting Coadsorbents for Highly Efficient Organic
Dye-Sensitized Solar Cells
[
a]
[a]
[a]
[a]
In Taek Choi, Myung Jong Ju, Sang Hyun Song, Sang Gyun Kim,
[
b]
[c]
[a]
Dae Won Cho, Chan Im, and Hwan Kyu Kim*
Abstract: The Y-shaped, low molecular
mass, hole-conductor (HC), acidic co-
adsorbents 4-{3,7-bis[4-(2-ethylhexylox-
y)phenyl]-10H-phenothiazin-10-yl}ben-
zoic acid (PTZ1) and 4-{3,7-bis[4-(2-
ethylhexyloxy)phenyl]-10H-phenothia-
venting p–p stacking of dye molecules,
harvesting light of shorter wavelengths,
and faster dye regeneration. By using
PTZ2 as the tailor-made HC coadsorb-
to an NKX2677-based DSSC without
an HC coadsorbent. This is due to the
HC coadsorbent having
a HOMO
energy level well matched to that of
the NKX-2677 dye to induce the de-
sired cascade-type hole-transfer pro-
cesses, which are associated with
a slower charge recombination, fast
dye regeneration, effective screening of
liquid electrolytes, and an induced neg-
ative shift of the quasi-Fermi level of
the electrode. Thus, this new class of Y-
shaped, low molecular weight, organic,
HC coadsorbents based on phenothia-
zine carboxylic acid derivatives hold
promise for highly efficient organic
DSSCs.
ent on the TiO surface with the organ-
2
ic dye NKX2677, an extremely high
conversion efficiency of 8.95% was
zin-10-yl}biphenyl-4-carboxylic
acid
ꢀ2
(
PTZ2) were developed. Owing to
achieved under 100 mWcm AM 1.5G
simulated light (short-circuit current
their tuned and negative-shifted
HOMO levels (vs. NHE), they were
used as HC coadsorbents in dye-sensi-
tized solar cells (DSSCs) to improve
cell performance through desired cas-
ꢀ
2
JSC =16.56 mAcm , open-circuit volt-
age VOC =740 mV, and fill factor of
73%). Moreover, JSC was increased by
13%, VOC by 27% and power-conver-
sion efficiency by 49% in comparison
cade-type
hole-transfer
processes.
Their detailed functions as HC coad-
sorbents in DSSCs were investigated to
obtain evidence for the desired cas-
cade-type hole-transfer processes. They
have multiple functions, such as pre-
Keywords: charge transfer · dyes/
pigments · electrochemistry · photo-
physics · solar cells
Introduction
high incident solar light-to-electricity conversion efficiency,
colorful and decorative nature, and low cost of production.
[2]
Since OꢀRegan and Grꢁtzel reported high solar-cell perfor-
mance for dye-sensitized solar cells (DSSCs) based on poly-
pyridyl ruthenium(II) complex dyes adsorbed on a nanocrys-
To date, power conversion efficiencies greater than 12%
have been reported for DSSCs based on nanoporous TiO2
electrodes, cosensitization of YD2-o-C8/Y123 organic sensi-
[1]
[3]
talline n-type semiconductor TiO2 electrode in 1991,
tizers, and a Co-complex redox system.
DSSCs have received considerable attention as a new gener-
ation of sustainable photovoltaic devices because of their
The typical components of such DSSCs are a dye sensitiz-
er, a TiO metal oxide coated onto conductive glass, a redox
2
electrolyte couple, and a counterelectrode (CE). As illus-
trated in Scheme 1, the power-conversion efficiency (PCE)
of DSSCs is strongly dependent on the minimization of
+
+
[
a] I. T. Choi, Dr. M. J. Ju, S. H. Song, S. G. Kim, Prof. Dr. H. K. Kim
Global GET-Future Laboratory and
charge-recombination losses at the TiO /dye/electrolyte in-
2
Department of Advanced Materials Chemistry
Korea University, 2511 Sejong-ro, Jochiwon, Sejong 339-700 (Korea)
Fax : (+82)44-860-1739
terface (k
and kCR2), as well as on the dye-regeneration
CR1
[4]
efficiency. Two recombination pathways are of importance
in DSSCs: electrons photoinjected into the TiO electrode
E-mail: hkk777@korea.ac.kr
2
can recombine with dye cations or with redox electrolytes.
Moreover, such charge recombination leads to losses in both
[
b] Dr. D. W. Cho
Department of Chemistry
Yeungnam University
Gyeongsan, Gyeongbuk 712-749 (Korea)
the short-circuit current (J ) and the open-circuit voltage
SC
(
VOC), which result in a decrease in overall energy conver-
[
c] Prof. Dr. C. Im
sion efficiency.
To reduce the number of possible charge-recombination
Konkuk University-Fraunhofer ISE
Next Generation Solar Cell Research Center
Konkuk University, Seoul 143-701 (Korea)
pathways occurring at the TiO /dye/electrolyte interface,
2
+
several kinds of coadsorbents, such as decylphosphonic acid,
dineohexyl bis(3,3-dimethylbutyl)phosphinic acid, and che-
nodeoxycholic acid, have been introduced to be adsorbed
[
] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301658.
Chem. Eur. J. 2013, 00, 0 – 0
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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