DOI: 10.1002/chem.201404428
Full Paper
&
Supramolecular Nanomaterials
Supramolecular Engineering of Oligothiophene Nanorods without
Insulators: Hierarchical Association of Rosettes and Photovoltaic
Properties
[
a, e]
[a]
[a]
[a]
[a]
Shiki Yagai,*
Mika Suzuki, Xu Lin, Marina Gushiken, Takuya Noguchi,
[a]
[a]
[b, e]
[c]
[c]
[d]
Takashi Karatsu, Akihide Kitamura, Akinori Saeki, Shu Seki, Yoshihiro Kikkawa,
Yuki Tani, and Ken-ichi Nakayama
[b]
Abstract: Supramolecular rosettes of oligothiophenes that
do not bear long aliphatic tails have been designed as semi-
conducting nanomaterials for solution-processable bulk het-
erojunction solar cells. The rosettes consist of six barbiturat-
took place through p–p stacking interactions upon casting
their toluene solutions, resulting in the growth of highly or-
dered nanorods whose widths are consistent with the diam-
eters of the rosettes. The nanorods could be generated in
the presence of soluble fullerene derivatives via solution
casting or the annealing of the resulting thin films. The solar
cells fabricated based on these bulk heterojunction films
showed power conversion efficiencies of 1–3%, which are
far higher than those of the non-hydrogen-bonded refer-
ence oligothiophene and the derivative that possesses long
aliphatic tails.
ed thienyl[oligo(hexylthiophene)] units (Bar-T-hT ; n=3,4,5)
n
aggregated by multiple hydrogen bonds, which have been
directly visualized by scanning tunneling microscopy (STM)
1
at
a
solid–liquid interface. H NMR spectroscopy in
[
D ]toluene showed that Bar-T-hT exists as a mixture of
8
n
monomers and small hydrogen-bonded aggregates. Hier-
archical organization of the hydrogen-bonded aggregates
Introduction
plored the construction of such columnar nanostructures by
supramolecular macrocyclization of heterocyclic small mole-
[2]
Hierarchical formation of well-defined nanostructures from syn-
thetically accessible small molecules through programmed
self-assembly would be a cost-effective approach toward the
fabrication of printable, large-area molecular devices. Columnar
nanostructures spontaneously formed by discoid or star-
shaped p-conjugated small molecules are particularly attractive
nanostructures as media for the quasi-one-dimensional trans-
cules directed by multiple hydrogen bonds. However, despite
vast examples of successful construction of such hierarchically
organized columnar nanostructures, little progress has been
made toward their application in organic devices, especially in
[3–5]
solution-processable bulk heterojunction (BHJ) solar cells.
This lack of progress is partly due to the fact that the forma-
tion of thermodynamically stable supramolecular macrocyclic
[
1]
[6]
port of charge carriers. Supramolecular chemists have ex-
assemblies (rosettes) requires “electronically inactive” long ali-
phatic chains to avoid irreversible (phase-separated) aggrega-
[7]
[8]
[
a] Prof. Dr. S. Yagai, M. Suzuki, Dr. X. Lin, M. Gushiken, T. Noguchi,
Prof. Dr. T. Karatsu, Prof. Dr. A. Kitamura
tion, which can generate kinetically trapped assemblies.
Such long aliphatic chains covering the semiconducting inter-
nal structure may hamper efficient charge separation with the
n-type semiconductor and charge transportation between the
nanostructures in BHJ films. Thus, the proper design of rosette-
forming p-conjugated small molecules with sufficient solubility
in organic media is necessary to afford highly organized nano-
structures applicable to BHJ solar cells, while minimizing the
unfavorable effects of the solubilizing chains on the electronic
properties of the devices.
Department of Applied Chemistry and Biotechnology
Graduate School of Engineering, Chiba University
1
-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)
Fax: (+81)43-290-3039
E-mail: yagai@faculty.chiba-u.jp
[
b] Y. Tani, Prof. Dr. K.-i. Nakayama
Graduate School of Science and Engineering, Yamagata University
1
-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan)
[
c] Prof. Dr. A. Saeki, Prof. Dr. S. Seki
Department of Applied Chemistry, Graduate School of Engineering
Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan)
We have previously demonstrated that the barbiturate unit
is a powerful functional group for the organization of various
p-conjugated units into unique nanostructures. A variety of
[
d] Dr. Y. Kikkawa
National Institute of Advanced Industrial Science and Technology (AIST)
1
-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan)
[
9]
[9b,10]
[10]
nanostructures such as rods, rings,
coils,
and inter-
[
e] Prof. Dr. S. Yagai, Prof. Dr. K.-i. Nakayama
CREST, JST, Chiyoda-ku, Tokyo 102-0075 (Japan)
[11]
locked rings (catenanes) have been obtained upon the cou-
pling of a barbiturate group with p-conjugated units whose
one end is equipped with a tridodecyloxyphenyl aliphatic tail
Supporting information for this article is available on the WWW under
Chem. Eur. J. 2014, 20, 16128 – 16137
16128
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim