D
V. S. Manthou et al.
Letter
Synlett
fied by a positive shift of the cathodic dark current. Similar
results were observed in the cobalt-based cells (see Sup-
porting Information, Figure S1, Table S1).
and Lifelong Learning” in the framework of ARISTEIA I (Ad-MatD-
SC/1847). Financial support from European Union (Marie Curie Initial
Training Network DESTINY/316494) is also acknowledged.
In order to better understand the mechanism of the sen-
sitization enhancement employing the newly synthesized
molecules, solar cells with the analogous alkylcarboxylic
acids (butanoic, octanoic, and dodecanoic acid) as co-adsor-
bents were developed and evaluated using both io-
dide/triiodide and cobalt-based electrolytes (see Support-
ing Information, Figure S2, Table S2). In this case, both the
photocurrent densities and the open-circuit voltage values
are drastically lower than those of the reference device
(without co-adsorbent). Some positive effects are evident
on increasing the alkyl chain length, but their poor overall
performance as compared to the reference is not altered.
The above results can be rationalized if we consider the
chemical structure of the new co-adsorbents. It is the com-
bination of the strongly coordinating bidentate hydroxy-
quinoline group with the long alkyl chain that assures the
chemisorption of a high amount of the MK-2 dye, concomi-
tantly preventing electron recombination (back electron
transfer from the semiconductor’s conduction band to the
oxidized form of the redox couple) thus leading to reduced
dark current and higher Voc values. The positive effect of the
long alkyl chain could be furthermore attributed to the pre-
vention of dye aggregation.
In conclusion, a new family of 5-alkyl-8-quinolinols
with variable alkyl chain lengths has been synthesized and
their performance as co-adsorbents in DSCs has been evalu-
ated. Initial attempts to prepare the targeted compounds
from the 5-chloro-8-methoxyquinoline through lithium–
halogen exchange failed, instead yielding the corresponding
2-alkyl or aryl 5-chloroquinoline derivatives. A high-yield-
ing modular synthesis was accomplished via Suzuki cou-
pling, using alkyltrifluoroborates as alkylating agents.
When employed as co-adsorbents, these compounds afford
DSC devices with improved performance, in comparison to
the corresponding alkylcarboxylic acid derivatives. Addi-
tionally, it was found that the longer the alkyl chain of the
co-adsorbent, the better the efficiency of the cell. Thus, the
5-dodecyl derivative increases the DSCs power-conversion
efficiency by 11%, suggesting not only that 5-alkyl-8-quino-
linols are promising co-adsorbents in DSCs, but also that
the 8-quinolinol moiety can be of general use substituting
the currently employed carboxylic anchoring strategy. The
same family of quinolinol derivatives is currently being uti-
lized as passivating agents in perovskite solar cells, as well
as in polydiacetylene vesicles as metal-ion receptors.
Supporting Information
Supporting information for this article is available online at
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References and Notes
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(12) Spectroscopic Data for Compound 4
1H NMR (500 MHz, CDCl3): δ = 8.43 (d, J = 8.7 Hz, 1 Η), 7.45 (d,
J = 8.4 Hz, 1 Η), 7.44 (d, J = 8.7 Hz, 1 Η), 6.94 (d, J = 8.4 Hz, 1 Η),
4.06 (s, 3 H), 3.07–3.04 (m, 2 H), 1.83–1.77 (m, 2 H), 1.45 (sext,
J = 7.4 Hz, 2 Η), 0.96 (t, J = 7.4 Hz, 3 Η). 13C NMR (126 MHz,
CDCl3): δ = 161.94, 153.50, 139.52, 132.21, 124.63, 124.62,
Acknowledgment
The authors acknowledge funding from the European Social Fund and
Greek national funds through the Operational Program “Education
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E