Design of fullerene-free electron-acceptor materials containing perylenediimide units for solution-processed organic electronic devices

Article abstract of DOI:10.1246/bcsj.20140167

Organic electron-accepting materials with light absorbance and wide absorption bands are sorely needed as alternatives to fullerene derivatives for organic electronics, in particular for organic photovoltaic (OPV) applications. In the present study, we ha

Full text of DOI:10.1246/bcsj.20140167

Selected Papers
Design of Fullerene-Free Electron-Acceptor Materials Containing
Perylenediimide Units for Solution-Processed Organic Electronic Devices
1
1
2
1
1,3
Koutarou Aoyagi, Yu Shoji, Saika Otsubo, Susumu Kawauchi, Mitsuru Ueda,
Hidetoshi Matsumoto,* and Tomoya Higashihara*3,4
1
1Department of Organic and Polymeric Materials, Graduate School of Science and Engineering,
Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550
2Mitsubishi Chemical Group Science and Technology Research Center, Inc,
1
000 Kamoshida-cho, Aoba-ku, Yokohama, Kanagawa 227-8502
3Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University,
-3-16 Jonan, Yonezawa, Yamagata 992-8510
4
4PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012
E-mail: matsumoto.h.ac@m.titech.ac.jp, thigashihara@yz.yamagata-u.ac.jp
Received: June 10, 2014; Accepted: July 7, 2014; Web Released: July 11, 2014
Organic electron-accepting materials with light absorbance and wide absorption bands are sorely needed as
alternatives to fullerene derivatives for organic electronics, in particular for organic photovoltaic (OPV) applications. In
the present study, we have designed and synthesized a series of novel donor­acceptor­donor (D­A­D) electron-accepting
molecules based on perylenediimide (PDI) and oligothiophene units, that is, PDI-alkoxy, PDI-Th, PDI-BiTh, and PDI-
TerTh. The optical and electrochemical properties of the obtained PDI derivatives and performances of organic field-effect
transistor (OFET) and OPV devices based on PDI derivatives were investigated. The PDI derivatives showed a higher
light absorption intensity and wider absorption region than those of [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM).
¹
4
2
¹1 ¹1
The highest electron mobility (2.33 © 10 cm V
s ) was shown using an OFET device based on PDI-BiTh, and the
¹2
highest power conversion efficiency (PCE) of 5.2 © 10 % was given by the OPV device based on the PDI-BiTh
acceptor. The device performances demonstrated that PDI derivatives with a D­A­D architecture are potentially useful for
solution-processed organic electronics.
Organic photovoltaics (OPVs) are a promising alternative
energy technology that can help address current and future
energy problems. By utilizing small molecule or polymer
organic semiconductors to directly convert sunlight into elec-
tric energy, OPVs have several potential advantages over con-
ventional inorganic solar cells, including low-cost fabrication,
solution processing, device flexibility, transparency/semitrans-
parency, and visual tunability, as their colors vary from blue to
near IR region and they are inferior in terms of obtaining high
5
,22­25
open-circuit voltages.
These problems have been reduced,
to some extent, with PC BM, which possesses a relatively
7
1
stronger absorption than that of PC BM in the visible
6
1
2
4­27
25
region,
and with high-LUMO-level fullerene derivatives.
However, the low absorption of fullerene acceptors in the solar
spectral region restricts light harvesting in BHJ OPVs. There-
fore, novel n-type organic semiconductors that could poten-
tially replace fullerene acceptors are strongly required.
1
­6
red. Among bulk heterojunction (BHJ) solar cells, solution-
processed OPVs have attracted significant attention during
the past decade. Until now, one of the most successful systems
utilized a blend of regioregular poly(3-hexylthiophene) (P3HT)
and [6,6]-phenyl-C -butyric acid methyl ester (PC BM) as the
2
8­36
Small-molecule organic semiconductors,
gated polymers,
various conju-
3
7­43
44
and graphene-based materials have been
explored as non-fullerene acceptor materials for BHJ OPVs.
Despite the major current challenges in developing more
efficient fullerene-free BHJ OPVs, the design of promising
n-type organic semiconductors with solution processability,
tunable HOMO­LUMO energies, excellent charge mobility,
and other properties are still pending issues. Among n-type
acceptor materials, perylenediimide (PDI) derivatives have
large molar absorption coefficients in the visible to near-
infrared spectral region, excellent electron-accepting properties,
6
1
61
active layer, normally giving power conversion efficiencies
­9
(
PCEs) in the range of 4­5%.7 Fullerenes and their deriva-
tives, such as PC BM and PC BM, have been the dominant
6
1
71
electron-acceptor materials in BHJ solar cells8 because of
their large electron affinity, good electron mobility,1 and the
development of new synthetic routes toward soluble full-
­15
6,17
1
8­21
erenes.
However, fullerene acceptors have a disadvantage
4
5,46
in OPVs: they have negligible light absorption in the visible­
and conduction along the π­π stacking axis.
In addition,
Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan | 1083

C12H25O
C12H25O
C12H25O
OR
OR
O
N
O
O
N
O
OR
RO
OR
RO
OC12H25
OC12H25
OC12H25
RO
R = (S)-2-methylbutyl
RO
tBu
tBu
O
N
O
O
N
O
N
N
N
N
N
Zn
N
N
Zn
N
N
C10H21
C10H21
C10H21
C10H21
N
O
N
O
O
N
O
tBu
N
N
N
N
tBu
S
S
N
N
N
N
tBu
tBu
S
C12H25
C12H25
C12H25
C12H25
S
O
N
O
O
N
O
C10H21
C10H21
C10H21
C10H21
O
N
O
O
N
O
N
N
n
n
n = 0–4
Figure 1. Chemical structures of representative PDI derivatives with D­A­D architectures.
PDI derivatives are advantageous in film processing, producing
thinner thicknesses than fullerene derivatives, for light absorp-
tion. This advantage enables the use of solution-processed
example of PDI derivatives with a D­A­D architecture, where
two donor units link the imide nitrogens of a central PDI unit,
that were investigated for their OPV properties.
4
7
nanocoating techniques such as layer-by-layer assembly
Results and Discussion
for device fabrication. Recently, n-type organic semiconduc-
tors consisting of PDI with functionalized donor units have
Synthesis and Characterization. The D­A­D molecules
based on perylenediimide with oligothiophene units, PDI-
alkoxy 16, PDI-Th 17, PDI-BiTh 18, and PDI-TerTh 19, were
synthesized according to Scheme 1. The molecular structures of
4
8­57
been reported.
In particular, PDI derivatives with donor­
acceptor­donor (D­A­D) architectures, where two donor units
5
4­57
link the imide nitrogens of a central PDI unit (Figure 1),
1
13
have attracted much attention due to their unique properties
such as photoinduced energy and/or electron-transfer pro-
cesses. However, research into the synthesis of novel PDI
derivatives with such architectures has been limited. Specifi-
cally, PDI derivatives functionalized by oligothiophenes
the four PDI derivatives were confirmed by H NMR, C NMR,
FT-IR spectroscopy, MALDI-TOF mass spectrometry, and
1
elemental analysis. As a typical example, the H NMR spec-
trum of PDI-TerTh is shown in Figure S1. Characteristic signals
were both attributed clearly, thus it was found that synthesis
of the target molecule was successful. PDI-alkoxy, PDI-BiTh,
and PDI-TerTh are readily soluble in chloroform, toluene, and
o-dichlorobenzene. However, PDI-Th is only soluble in chloro-
form and o-dichlorobenzene at high temperature.
The thermal stability of the PDI derivatives was determined
by thermogravimetric analysis (TGA) (Figure S2). All four
molecules were thermally stable up to 400 °C (Td5%) (Table 1),
which is sufficient thermal stability for fabricating an OPV
device.
(OTh), which are among the most versatile and effective π-
conjugated organic backbones, remain largely unexplored.
In this study, we focused on a series of novel electron-
acceptor materials with a D­A­D architecture containing a
central PDI electron-withdrawing group and two OTh electron-
donating end groups, because their HOMO­LUMO energies
and optical band gaps can be easily controlled by the D­A­D
architecture. We report the synthesis, optical properties, and
electrochemical properties of the novel OTh-functionalized
PDI derivatives along with the performances of organic
electronic devices, including a fullerene-free BHJ OPV, and
the morphology of the active layer. The purpose of this study is
to design novel non-fullerene acceptor materials for solution-
processed organic electronic devices such as organic field-
effect transistors (OFETs) and fullerene-free BHJ OPVs.
Indeed, the novel OTh-functionalized PDI derivatives were
successfully synthesized. It was found that PDI derivatives
have more than doubled molar absorption coefficients and
longer wavelength absorptions than those of PC61BM. The
OFET based on PDI-BiTh showed the highest electron mobility
The thermal transition temperatures of the PDI derivatives
were also investigated by differential scanning calorimetry
(DSC) as shown in Figure S3, and the melting temperature (Tm)
and crystallization temperature (T ) are summarized in Table 1.
c
In the heating process, PDI-alkoxy, PDI-Th, and PDI-BiTh
showed large endothermic peaks corresponding to melting
points, T , of 279, 205, and 239 °C, respectively. Also, the
m
crystallizing points, T , were determined to be 276, 177, and
c
228 °C in the cooling process, respectively. On the other hand,
PDI-TerTh showed no phase transition below the 1% weight
loss temperature, indicating its amorphous nature.
¹
4
2
¹1 ¹1
of 2.33 © 10 cm V s . The BHJ OPV based on the PDI-
Quantum Calculations.
To examine the electronic
¹
2
BiTh acceptor gave the highest PCE of 5.2 © 10 % under
properties and geometries of the PDI derivatives, quantum
chemical calculations were performed using DFT at the
¹2
1
00 mW cm AM1.5 solar illumination in air. This is the first
1084 | Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan

HO
NO2
Br2
C10H21
PPh3, imidazole
C10H21
K2CO3, CH3CN
C10H21
Pd/C, H2, EtOAc C10H21
r.t., overnight
OH
C8H17
Br
C8H17
, 82%
O
NO2
O
NH2
CH2Cl2
r.t., overnight
reflux, overnight
C8H17
C8H17
1
2, 70%
3, 99%
S
THF, hexane
reflux, overnight
O
B
O
Li
NO2
[
Pd(PPh3)4]
K2CO3
Aliquat 336
C10H21
S
NBS
C10H21
S
C10H21
S
Pd/C, H2, EtOAc C10H21
r.t., overnight C8H17
S
Br
NO2
NH2
C8H17
, 64%
CHCl3, CH3COOH
r.t., 3h
C8H17
toluene, THF, H2O
reflux, overnight
C8H17
4
5, 95%
6, 78%
7, 99%
C6H13
B
[
Pd(PPh3)4]
Cs2CO3
Aliquat 336
O
toluene, THF, H2O
reflux, overnight
O
B
O
S
NO2
O
[
Pd(PPh3)4]
K2CO3
Aliquat 336
C6H13
C6H13
S
C6H13
S
C6H13
S
C10H21
S
C10H21
S
NBS
Pd/C, H2, EtOAc
C10H21
S
C10H21
S
C8H17
S
C8H17
CHCl3, CH3COOH
r.t., 3h
toluene, THF, H2O
reflux, overnight
r.t., overnight
NO2
C8H17
, 89%
C8H17
Br
NH2
8
9, 96%
10, 84%
11, 99%
C6H13
[Pd(PPh3)4]
dimethoxyethane
reflux, 23h
O
K2CO3
Aliquat 336
B
S
O
B
O
NO2
O
C6H13
S
C6H13
S
[Pd(PPh3)4]
K2CO3
Aliquat 336
C6H13
C6H13
C10H21
S
C10H21
S
C10H21
S
C10H21
S
NBS
Pd/C, H2, EtOAc
r.t., overnight
S
S
S
S
C8H17
C8H17
C8H17
S
NO2
C8H17
S
NH2
CHCl3, CH3COOH
r.t., 3h
Br toluene, THF, H2O
reflux, overnight
C6H13
C6H13
13, 84%
C6H13
C6H13
1
2, 93%
14, 89%
15, 94%
O
N
O
O
N
O
C10H21
C8H17
C8H17
O
O
C10H21
1
6, 80%
O
N
O
O
O
O
O
O
O
O
C10H21
C8H17
S
C8H17
C10H21
N
O
S
imidazole
80 °C, 3h
17, 80%
3
, 7, 11, or 15
1
C8H17
C10H21
O
N
O
O
N
O
C6H13
S
S
S
S
C6H13
C10H21
1
8, 65%
C8H17
C6H13
C10H21
C8H17
S
O
N
O
O
N
O
C6H13
S
S
S
S
C8H17
C10H21
C6H13
S
19, 41%
C6H13
Scheme 1. Synthesis of PDI derivatives.
Table 1. Thermal Properties of PDI Derivatives
Td5%a)
Tmb)
/°C
Tcb)
/°C
/°C
PDI-alkoxy
PDI-Th
PDI-BiTh
PDI-TerTh
439
419
415
414
279
205
239
®
276
177
228
®
a) 5% weight loss temperatures were measured at a scan rate of
¹1
Figure 2. Pictorial representations of the frontier molecular
orbitals of PDI-TerTh (LUMO: top; HOMO: bottom).
1
0 °C min under a nitrogen atmosphere. b) Phase-transition
temperatures were measured by DSC at a scan rate of
¹1
1
0 °C min under a nitrogen atmosphere.
orbitals were delocalized over the conjugated backbone of
OTh, while the excited electrons in the LUMO orbitals were
localized over the quinoid-like perylene plane, creating a D­A­
D structure with OTh acting as a donor and PDI acting as an
acceptor (Figures 2 and S4). For PDI-alkoxy, on the other
hand, the π-electrons in the HOMO and LUMO orbitals were
B3LYP/6-31G(d,p) level of theory. In the optimized geo-
metries of the molecules, the π-conjugated OTh planes were
twisted nearly perpendicular to the perylene plane. For PDI-
Th, PDI-BiTh, and PDI-TerTh, the π-electrons in the HOMO
Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan | 1085

localized over the perylene plane, implying that PDI-alkoxy
cannot form a D­A­D structure.
The calculated HOMO­LUMO energy and energy band gaps
The absorption spectra of the PDI derivatives with poly-
(methyl methacrylate) (1:1, w/w) as thin films are shown
in Figure 3b, and the ­max and optical band gap (Eg ) are
opt
(
Eg cal) of the PDI derivatives are summarized in Table 2. With
summarized in Table 3. These spectra were normalized against
the maximum absorption bands derived from the PDI units.
The large red shift of the absorption spectra in the thin films
compared with the solution spectra can be attributed to the
planarization of the molecular backbone in the solid state,
resulting in intermolecular interactions. Similar to the absorp-
tion spectra in solution, the bands corresponding to the π­π*
transition of OTh in the absorption spectra of the thin films
were gradually red-shifted with an increase in the number of
thiophene rings. Additionally, absorption bands derived from
an increase in the number of thiophene rings, the HOMO
energy increased and the band gap narrowed. From this result,
it is estimated that the wavelength of the light absorption
shifted toward the long-wavelength region with an increase in
the number of the thiophene rings.
Optical Properties. To characterize the optical properties
of the PDI derivatives, UV­vis absorption spectroscopy of the
molecules was performed in both dilute solutions and thin
films.
opt
Figure 3a shows the absorption spectra of the PDI derivatives
the PDI unit were also red-shifted slightly. The Eg values of
¹
5
in dilute chloroform solutions ((1­4) © 10 M), and their
maximum wavelengths (­max) are summarized in Table 3. The
PDI derivatives show two absorption bands: broad absorption
bands in the range of 300­420 nm and bands with three sharp
peaks in the 420­550 nm range (Figure 3a). These spectra were
characterized as the summation of the spectra for each donor
and acceptor unit, indicating the absence of significant inter-
action in the ground state between the OTh and PDI units. The
bands in the range of 300­420 nm correspond to the π­π*
transition of OTh, which gradually red shifts with an increase in
the number of thiophene rings. This indicates that the extent of
the π-conjugation in the OTh backbone increases, as expected.
The other bands in the range of 420­550 nm (with maxima at
ca. 460, 490, and 530 nm) correspond to the π­π* transition of
the PDI unit, in which the peak at 460 nm originates from the
S ­S transition, while the peaks at 490 and 530 nm derive from
1
2
0
8
6
4
2
(
a)
PC61BM
1
PDI-alkoxy
PDI-Th
PDI-BiTh
PDI-TerTh
ε
0
3
00
400
500
600
700
800
Wavelength / nm
PDI-alkoxy
(
b)
0
2
PDI-alkoxy anneal
PDI-Th anneal
PDI-BiTh
PDI-BiTh anneal
PDI-TerTh
1
1
.5
.0
the transitions from S0 to the 1- and 0-vibronic states of S1,
5
7,58
respectively.
tives have more than doubled molar absorption coefficients and
longer wavelength absorptions than PC BM.
Moreover, it was found that the PDI deriva-
61
PDI-TerTh anneal
Table 2. Calculated HOMO and LUMO Energy Levels and
Eg of PDI Derivatives
0.5
HOMOcala)
LUMOcala)
/eV
Eg calb)
/eV
/eV
0
.0
3
00
400
500
600
700
800
PDI-alkoxy
PDI-Th
PDI-BiTh
PDI-TerTh
¹5.90
¹5.58
¹5.15
¹4.90
¹3.36
¹3.44
¹3.45
¹3.46
2.54
2.14
1.70
1.44
Wavelength / nm
Figure 3. UV­vis absorption spectra of PDI derivatives (a)
in CHCl3 and (b) in a PMMA film (1:1, w/w) (normalized
to the absorbance at the top of the band corresponding
to the π­π* transition of the PDI unit, dotted line: as-cast
films, solid line: films annealed at 150 °C for 5 min).
a) HOMO and LUMO energies as determined by DFT at the
B3LYP/6-31G(d,p) level of theory. b) Energy band gaps were
calculated from (LUMO ¹ HOMO).
Table 3. Optical Properties of PDI Derivatives
In solution
Annealed film
a)
¾a)
­maxb)
/nm
­onsetb)
/nm
Egopt c)
/eV
­
/
max
/10 L cm mol¹1
4
¹1
nm
PC61BM
PDI-alkoxy
PDI-Th
PDI-BiTh
PDI-TerTh
328
527
306, 528
351, 529
368, 529
4.29
9.66
10.7
11.4
9.23
®
498
300, 561
361, 486
391, 477
®
®
599
603
614
627
2.07
2.06
2.02
1.98
a) In CHCl3 solution. b) Drop-cast thin films of PDI derivatives with PMMA (1:1, w/w) annealed at
50 °C for 5 min. c) Calculated from Egopt = 1240/­onset.
1
1086 | Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan

Table 4. Electrochemical Properties of PDI Derivatives
(
a)
PDI-alkoxy
PDI-Th
0
0
.5
.0
Ega)
/eV
HOMO
eV
LUMO
/eV
PDI-BiTh
PDI-TerTh
/
¹5.72b)
®
b)
PC61BM
PDI-alkoxy
PDI-Th
PDI-BiTh
PDI-TerTh
¹3.71
¹3.88
¹3.85
¹3.92
2.01
®
c)
b)
b)
¹5.68
1.83
1.40
1.22
-
-
0.5
1.0
c)
c)
¹5.32
c)
c)
¹5.12
¹3.89
a) Energy band gaps were calculated from (LUMO ¹ HOMO).
b) Data were obtained from cyclic voltammetry in 0.1 M
o-dichlorobenzene/n-Bu4NPF6 solution at a scan rate of
-
1.6
-1.4
-1.2
-1.0
-0.8
-0.6
+
¹1
ox
+
Potential/V vs. Ag/Ag
10 mV s
,
HOMO = ¹[E onset ¹ E1/2
(Fc/Fc ) + 4.8];
red
+
LUMO = ¹[E onset ¹ E1/2 (Fc/Fc ) + 4.8]. c) In 0.1 M
CH2Cl2/n-Bu4NPF6 solution.
PDI-alkoxy
PDI-Th
(
b)
1
0
0
.0
PDI-BiTh
PDI-TerTh
Table 5. Field-Effect Electron-Transport Properties of PDI
Derivatives
®
e
Vt
/V
.5
.0
I /I
2
¹1
on off
/
cm V s¹1
¹
3
4 © 103
2 © 103
®
3 © 103
®
PC61BM
PDI-alkoxy
PDI-Th
PDI-BiTh
PDI-TerTh
6.38 © 10
3.70 © 10
®
¹3.7
6.8
®
¹11.7
®
¹5
¹4
2.33 © 10
®
0
.4
0.6
0.8
1.0
1.2
1.4
1.6
+
Potential/V vs. Ag/Ag
to an Ag/AgCl reference electrode.59 Since the LUMO ener-
gies of the PDI derivatives are comparable, the LUMO energy
is considered to be derived from the PDI moiety acting as an
acceptor unit. On the other hand, the HOMO energy of the
PDI derivatives rose and the energy band gap narrowed
to 1.22 eV from 1.83 eV with an increase in the number of
thiophene rings, as expected.
Figure 4. Cyclic voltammograms of PDI derivatives (1 mM
solution), showing the (a) reduction waves and (b) oxida-
tion waves.
5
7
the PDI derivatives, which were calculated from the onset
wavelengths, were 1.98­2.07 eV. It was found that the energy
band gap narrowed with an increase in the number of thiophene
rings.
Properties of Solution-Processed Organic Electronic
Devices. To evaluate the OFET properties of the PDI deriv-
atives, OFET devices were fabricated using spin-coating with
a bottom-gate and bottom-contact configuration on Si/SiO2
substrates. All devices were fabricated and measured under a
dry nitrogen atmosphere, except for the device using PDI-Th,
due to its poor solubility in chlorobenzene. The FET character-
istics of the PDI derivatives are summarized in Table 5. Typical
output and transfer characteristics of the OFET device based on
PDI-BiTh are shown in Figure 5, and those of the OFET based
on PDI-alkoxy are shown in Figure S5. Fabrication of the
OFET device of PDI-Th failed due to its lower solubility. The
electron mobility (®e) values of PDI-alkoxy and PDI-BiTh
Electrochemical Properties. The electrochemical prop-
erties of the PDI derivatives were investigated by cyclic
voltammetry (CV), which was carried out in degassed CH Cl
2
2
or o-dichlorobenzene containing 0.1 M n-Bu4NPF6 as a sup-
porting electrolyte under a nitrogen atmosphere. The results
revealed that PDI-Th, PDI-BiTh, and PDI-TerTh exhibited
amphoteric redox behaviors (Figure 4). As shown in Figure 4a,
two-electron chemically reversible reduction processes, ascrib-
ed to the successive formation of the anion radical and dianion
of the PDI unit, were observed on the negative side of the
cyclic voltammograms.57 On the positive side of the CVs for
PDI-Th, PDI-BiTh, and PDI-TerTh, oxidation waves were
observed (Figure 4b), attributed to the one-electron oxidation
in the formation of radical cations in the OTh units. However,
on the positive side of the CV for PDI-alkoxy, no oxidation
wave was observed due to the absence of a donor unit such as
the thiophene moiety.
¹5
¹4
2
¹1 ¹1
were 3.70 © 10 and 2.33 © 10 cm V s , respectively.
The ® value of PDI-BiTh is one-order higher than that of PDI-
e
alkoxy. This might be due to more efficient electron transport
in the bithiophene units in addition to the PDI unit. However,
the electron mobility of PDI-TerTh could not be measured
¹
7
2
¹1 ¹1
HOMO­LUMO energies obtained from cyclic voltammo-
(the ® value is less than 10 cm V s ) due to the low
e
grams and energy band gaps (E ) are summarized in Table 4.
crystallinity (Figure 8c).
g
The HOMO­LUMO energies were calculated from the onset
To estimate the potential of the PDI derivatives as novel
non-fullerene acceptor materials, BHJ OPV devices composed
of an ITO-coated glass substrate/PEDOT:PSS/PDI-derivative:
P3HT (2:1, w/w)/Ca (15 nm)/Al (130 nm) were fabricated.
The current density­voltage (J­V) curves of the BHJ OPV
ox
oxidation potentials (E onset) and onset reduction potentials
red
(
E
), respectively, based on the following equations:
onset
ox
+
HOMO = ¹[E
¹ E
(Fc/Fc ) + 4.8] V and LUMO =
onset
1/2
+
red
¹
[E
¹ E1/2 (Fc/Fc ) + 4.8] V, where the potentials refer
onset
Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan | 1087

devices are shown in Figure 6. The photovoltaic parameters
calculated from the J­V curves, including open-circuit voltage
in charge transport60­62 between the P3HT and PDI derivatives.
To improve J , selection of the appropriate donor material for
sc
(
V ), short-current (J ), and fill factor (FF), are summarized in
PDI derivatives is required.
oc
sc
Table 6. The OPV device based on the PDI-BiTh acceptor gave
We attempted to optimize the performance of the OPV
device based on the PDI-BiTh acceptor, which showed the
highest PCE, by exploring the use of a processing additive. We
fabricated the PDI-BiTh:P3HT (2:1, w/w) device processed
¹
2
the highest power conversion efficiency (PCE) of 2.7 © 10 %,
¹
2
with a V of 0.49 V, J of 0.16 mA cm , and FF of 0.33. The
oc
sc
large differences in the Voc, due to the gaps in the HOMO
energy level of P3HT and LUMO energy levels of the PDI
6
3
from chlorobenzene with 1 vol % 1,8-diiodooctane (DIO).
¹
2
derivatives, which are intrinsically constant (¦EHOMO­LUMO
=
A slightly improved Jsc of 0.25 mA cm and FF of 0.44
¹
2
ca. 1.1 eV), indicate that the two-phase morphology is not well-
optimized. For P3HT/fullerene BHJ OPV devices, it is known
that the Voc can be changed by tuning factors such as the scale
gave a PCE of 5.2 © 10 % (Table 6). It is considered that
this improvement is realized by the enhanced charge carrier
mobility resulting from fine-tuning of the nanoscale morphol-
ogy via different evaporation rates of the host solvent and
60
61,62
of the two-phase morphology or blend compositions
6
4
of the donors and acceptors. The highest Jsc may be derived
from the highest electron mobility of PDI-BiTh. However, all
additive. AFM images (Figure S6) show the additive DIO
promoted phase separation, which contains larger-sized inter-
connected regions of both the PDI-BiTh and P3HT compo-
nents. The external quantum efficiency (EQE) spectra of this
device are shown in Figure S7. A photoresponse is exhibited
between 300 and 650 nm, indicating that the absorption of the
PDI-BiTh:P3HT blend film (Figure S8) reflects the photo-
current in this wavelength region.
devices show low J . This may be due to the poor balance
sc
0
0
0
0
.15
.10
.05
.00
V =+60 V
(
a)
gs
V =+40 V
gs
V =+20 V
gs
V =0 V
gs
At present, we have not accomplished the optimization of
the bicontinuous two-phase morphology between P3HT and the
PDI derivatives. The use of a processing additive and tuning
the morphology enhanced the OPV performance. Further
improvement in the device performance using PDI derivatives
is underway.
V =-20 V
gs
Morphology and Microstructure of the Active Layer. To
investigate the morphology and microstructure of the active
0
10
20
30
40
50
60
Vds / V
0
0
0
.8
.6
.4
Vds=60 V
(
b)
0.0
-
-
-
-
-
1
2
3
4
5
1
0
0
0
0
0
1
1
1
1
-
-
0.1
0.2
PDI-alkoxy:P3HT ( annealed )
PDI-BiTh:P3HT
PDI-TerTh:P3HT
0.2
PDI-BiTh:P3HT ( with DIO )
Dark
0.0
-0.3
-20
0
20
Vgs / V
40
60
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Voltage / V
Figure 5. (a) Output and (b) transfer characteristics for
PDI-BiTh in a bottom-gate/bottom-contact OFET.
Figure 6. Current density­voltage curves of PDI-derivative:
P3HT OPV devices under AM 1.5G illumination.
Table 6. OPV Properties of PDI Derivatives
Voc
Jsc
/mA cm
PCEavg (PCEmax)
/%
Conditions
FF
¹2
/V
PC61BMa)
PDI-alkoxy
PDI-Th
Annealed
Annealed
®
b)
b)
0.63
0.42
®
8.86
0.06
®
0.62
0.26
®
3.45 (3.58)
0.65 © 10¹2 (0.67 © 10¹2
®
)
¹2
¹2
PDI-BiTh
PDI-TerTh
As-cast
As-cast
As-cast
0.49
0.50
0.46
0.16
0.12
0.25
0.33
0.32
0.44
2.5 © 10 (2.7 © 10
)
)
¹2
¹2
2.0 © 10 (2.0 © 10
c)
5.1 © 10 (5.2 © 10¹2)
¹2
PDI-BiTh
(
DIO 1 vol %)
a) Device structure: ITO/PEDOT:PSS/PC61BM:P3HT (0.8:1 w/w)/Ca (30 nm)/Al (100 nm). b) Annealed at
50 °C for 10 min. c) The active layer was deposited from chlorobenzene with 1 vol % 1,8-diiodooctane (DIO).
1
1088 | Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan

(
a)
(b)
(c)
R = 8.09 nm
R = 3.94 nm
R = 2.35 nm
q
q
q
2
Figure 7. AFM topographical height images (5 © 5 ¯m ) of (a) PDI-alkoxy:P3HT (2:1, w/w) annealed at 150 °C for 10 min,
b) PDI-BiTh:P3HT (2:1, w/w), and (c) PDI-TerTh:P3HT (2:1, w/w) as thin films.
(
2
1
1
0
5
0
5
0
20
15
10
5
20
15
10
5
(a)
(b)
(c)
θ
0
0
0
5
10
15
20
0
5
10
15
20
0
5
10
15
20
2
θ
/ degree
2
θ
/ degree
2θ / degree
Figure 8. GIWAXS spectra of (a) PDI-alkoxy, (b) PDI-BiTh, and (c) PDI-TerTh. All samples were drop-cast from
o-dichlorobenzene solution and annealed at 150 °C for 10 min.
layer in BHJ OPV devices based on PDI-derivative:P3HT
blends, atomic force microscopy (AFM) and two-dimensional
grazing incidence X-ray scattering (GIWAXS) analyses were
performed.
Table 7. Values of π­π Spacing in PDI Derivatives
π­π Spacing
/¡
a)
2
PDI-alkoxy
PDI-BiTh
PDI-TerTh
3.26
3.55
®
AFM topographical height images (5 © 5 ¯m ) including the
a)
root-mean-square surface roughness (R ) of the active layer
q
a)
composed of a PDI-derivative:P3HT (2:1, w/w) blend are
b),c)
PDI-alkoxy:P3HT
PDI-BiTh:P3HT
PDI-TerTh:P3HT
3.38
3.45
3.45
shown in Figure 7. The R values of PDI-BiTh and PDI-TerTh
q
b)
are lower than that of PDI-alkoxy. This is one reason for the
higher FF of the OPV devices: the smooth surfaces help main-
tain good contact with the Ca layer. In addition, the decrease in
Rq is due to the amorphous nature of PDI derivatives with OTh
units (Figures 8b and 8c).
b)
a) Drop-cast thin films of pure PDI derivatives annealed at
50 °C for 10 min. b) Drop-cast thin films of PDI-deriva-
1
tive:P3HT (2:1, w/w) blend. c) Annealed at 150 °C for 10 min.
GIWAXS analysis was performed for drop-cast films of
the PDI derivatives with and without P3HT. The GIWAXS pat-
terns and profiles of the pure PDI-derivative annealed films are
shown in Figures 8 and S9. The GIWAXS diffraction pattern of
the PDI-alkoxy films showed a diffraction peak at 2ª = 17.62°,
which corresponds to a d-spacing of 3.26 ¡ and can be assigned
to the π­π spacing. For the PDI-BiTh film, a diffraction peak
was observed at 2ª = 16.18°, which corresponds to a d-spacing
of 3.55 ¡. The π­π spacing values obtained from GIWAXS are
summarized in Table 7. The π­π spacing of the PDI units
calculated from the single-crystal structure analysis of N,N¤-
tion peaks at 2ª = 1.41 and 3.50° and an amorphous halo
around 2ª = 13.0°. A peak corresponding to π-stacking was
not observed. This result suggests that this material has low
crystallinity, attributed to the twisted form of the PDI deriv-
atives and side chains in the OTh units. This is considered to be
a reason why the electron mobility of PDI-TerTh could not be
measured.
The GIWAXS patterns and profiles of the PDI-derivative:
P3HT blend films are shown in Figures 9 and S10, respec-
tively. The GIWAXS diffraction patterns of the PDI-derivative:
P3HT blend films showed diffraction peaks at 2ª = 17.02
(PDI-alkoxy), 16.65 (PDI-BiTh), and 16.66° (PDI-TerTh),
corresponding to d-spacings of 3.38, 3.45, and 3.45 ¡, respec-
tively. These peaks correspond to the π­π spacing of the PDI
units, which suggests that most of the molecular backbones are
6
5
diphenyl-3,4,9,10-perylenetetracarboxylic diimide is 3.44 ¡.
Since the obtained values of the π­π spacing are comparable to
the calculated π­π spacing of the PDI units, these π­π spacing
values are considered to be π-stacking of the PDI units. The
PDI-TerTh thin films showed no peaks other than diffrac-
Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan | 1089

2
1
1
0
5
0
5
0
20
15
10
5
20
15
10
5
(a)
(b)
(c)
θ
0
0
0
5
10
15
20
0
5
10
15
20
0
5
10
15
20
2
θ
/ degree
2
θ
/ degree
2θ / degree
Figure 9. GIWAXS spectra of (a) PDI-alkoxy:P3HT (2:1, w/w) annealed at 150 °C for 10 min, (b) PDI-BiTh:P3HT (2:1, w/w), and
c) PDI-TerTh:P3HT (2:1, w/w). All samples were drop-cast from o-dichlorobenzene solution.
(
vertically oriented to the substrate. This edge-on orientation is
not a suitable orientation for charge transport in photovoltaic
devices. In order to improve fullerene-free OPV device perfor-
mances based on PDI-based D­A­D molecules, the induction
of a face-on orientation is desired. To achieve this, the precise
phase-separated morphology in BHJ structures must be con-
trolled, for example, by selection of the appropriate donor
material and/or processing additive.
precipitate the crude product. The product was purified by
Soxhlet extraction using methanol and CHCl . After evaporat-
3
ing CHCl , the product was further purified by silica gel
3
column chromatography using CH Cl as an eluent, followed
2
2
by freeze-drying from its absolute benzene solution to afford
1
16 as red solid (0.462 g, 80%). H NMR (300 MHz, CDCl ,
3
25 °C): ¤ 8.57 (d, J = 7.8 Hz, 4H, aromatic proton), 8.32
(d, J = 8.4 Hz, 4H, aromatic proton), 7.30 (d, J = 9.0 Hz, 4H,
aromatic proton), 7.06 (d, J = 9.0 Hz, 4H, aromatic proton),
Conclusion
3
.90 (d, J = 5.7 Hz, 4H, O­CH ­), 1.88­1.75 (m, 2H, O­CH ­
2 2
Novel organic semiconductors made of oligomers with D­
A­D architectures containing PDI as an acceptor unit and OTh
as a donor unit (PDI-Th, PDI-BiTh, and PDI-TerTh) have been
synthesized and characterized. As the number of thiophene
rings increased, the PDI derivatives exhibited wider absorp-
tion bands in the visible-light region. The PDI derivatives had
more than doubled molar absorption coefficients and absorbed
longer wavelength light compared with PC BM. The LUMO
CH), 1.55­1.23 (m, 64H, ­CH ­), 0.96­0.85 (m, 12H, ­CH ).
2 3
1
3
C NMR (75 MHz, CDCl , 25 °C): ¤ 163.56, 159.70, 134.38,
3
131.44, 129.64, 129.38, 127.12, 126.17, 123.55, 123.15,
115.41, 71.23, 38.14, 32.09­27.04 (14 carbons), 22.85
¹
1
(2 carbons), 14.29 (2 carbons). IR (KBr), v (cm ): 2924 (alkyl
C­H), 1707, 1666 (C=O stretching), 1360 (C­N stretching).
+
MS (MALDI-TOF) m/z [M + H ]: Calcd for C H N O ,
7
6
98
2
6
1134.74; found, 1135.09. Anal. Calcd for C H N O : C,
61
76 98
2
6
of the PDI derivatives were relatively constant at ca. ¹3.9 eV,
whereas the HOMO could be tuned from ¹5.12 in PDI-TerTh
80.38; H, 8.70; N, 2.47%. Found: C, 80.29; H, 8.69; N, 2.45%.
Synthesis of N,N¤-Bis{4-[5-(2-octyldodecyl)thiophen-2-
yl]phenyl}-3,4,9,10-perylenetetracarboxylic Diimide (17):
The title compound, 17, was synthesized by the same procedure
as 16 with 0.622 g (1.36 mmol) of 1-amino-4-[5-(2-octyl-
dodecyl)thiophene-2-yl]benzene (7), 0.188 g (0.479 mmol) of
3,4,9,10-perylenetetracarboxylic dianhydride, and 3.25 g of
imidazole. The compound, 17 (0.487 g, 80%) was then isolated
as a red solid and purified by silica gel column chromatography
to ¹5.68 eV in PDI-Th. The ® values of OFETs based on
e
¹5
¹4
PDI-alkoxy and PDI-BiTh were 3.70 © 10 and 2.33 © 10
cm V s , respectively. The BHJ OPV based on the PDI-
2
¹1 ¹1
¹2
BiTh acceptor gave the highest PCE of 5.2 © 10 %, with a
¹
2
Voc of 0.46 V, J of 0.25 mA cm , and FF of 0.44 under 100
sc
¹2
mW cm
AM1.5 solar illumination in air. These results
indicate that PDI-based organic semiconductors with D­A­D
architectures, by linking donor units with N-imides, are poten-
tial acceptor materials for solution-processed organic electronic
devices, including fullerene-free OPVs.
1
(solid) using CH Cl as an eluent. H NMR (300 MHz, CDCl ,
2
2
3
25 °C): ¤ 8.64 (d, J = 7.8 Hz, 4H, aromatic proton), 8.46
(d, J = 7.8 Hz, 4H, aromatic proton), 7.72 (d, J = 8.1 Hz, 4H,
aromatic proton), 7.36 (d, J = 8.4 Hz, 4H, aromatic proton),
Experimental
7
.17 (d, J = 3.6 Hz, 2H, aromatic proton), 6.74 (d, J = 3.6 Hz,
Materials. All reagents and solvents were used as received.
2H, aromatic proton), 2.77 (d, J = 6.3 Hz, 4H, thiophene­
CH ­), 1.74­1.60 (m, 2H, thiophene­CH ­CH), 1.42­1.15
(m, 64H, ­CH ­), 0.887 (t, J = 6.3 Hz, 12H, ­CH ). C NMR
2 3
Regioregular poly(3-hexylthiophene) (P3HT) (M = 25000
n
2
2
¹
1
13
g mol , Ð µ 2, regioregularity ca. 98.5%) was purchased from
Rieke Metals, Inc., and [6,6]-phenyl-C -butyric acid methyl
(75 MHz, CDCl , 40 °C): ¤ 163.47, 145.23, 141.13, 135.69,
61
3
ester (PC BM) was obtained from Nano-C.
Synthetic Procedures. Synthesis of N,N-Bis[4-(2-octyl-
dodecyloxy)phenyl]-3,4,9,10-perylenetetracarboxylic Di-
imide (16): A mixture of 1-amino-4-(2-octyldocecyloxy)-
benzene (3) (0.591 g, 1.52 mmol), 3,4,9,10-perylenetetra-
carboxylic dianhydride (0.199 g, 0.508 mmol), and imidazole
134.85, 133.70, 131.76, 129.81, 129.25, 126.65, 126.52,
126.34, 123.76, 123.63, 123.35, 40.25, 35.00, 33.59­26.88
(14 carbons), 22.85 (2 carbons), 14.23 (2 carbons). IR (KBr),
6
1
¹
1
v (cm ): 2922 (alkyl C­H), 1705, 1660 (C=O stretching),
+
1357 (C­N stretching). MS (MALDI-TOF) m/z [M + H ]:
Calcd for C H N O S , 1266.73; found, 1267.27. Anal.
8
4
102
2
4 2
(3.17 g) was heated at 180 °C for 3 h under an argon atmos-
Calcd for C H N O S : C, 79.58; H, 8.11; N, 2.21%. Found:
84 102 2 4 2
phere. Then, the reaction mixture was poured into methanol to
C, 79.90; H, 8.29; N, 2.21%.
1090 | Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan

Synthesis of N,N¤-Bis{4-[3-hexyl-5¤-(2-octyldodecyl)-2,2¤-
bithiophen-5-yl]phenyl}-3,4,9,10-perylenetetracarboxylic
Diimide (18): The title compound, 18, was synthesized by
the same procedure as 16 with 0.410 g (0.659 mmol) of 1-
amino-4-[3-hexyl-5¤-(2-octyldodecyl)-2,2¤-bithiophen-5-yl]-
benzene (11), 0.0910 g (0.232 mmol) of 3,4,9,10-perylene-
tetracarboxylic dianhydride, and 2.04 g of imidazole. The
compound, 18 (0.243 g, 65%) was then isolated as a red solid
and purified by silica gel column chromatography using
spectra were measured on a Horiba FT-720 spectrometer.
Matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectra were recorded on a Shimadzu
AXMACFR mass spectrometer. The spectrometer was equip-
ped with a nitrogen laser (337 nm) with pulsed ion extraction.
The operation was performed at an accelerating potential of
20 kV in the linear-positive ion mode. Dithranol was used as a
matrix. Mass values were calibrated by the three-point method
with insulin plus H+ at m/z 5734.62, insulin ¢ plus H+ at m/z
3497.96, and α-cyanohydroxycinnamic acid dimer plus H+ at
m/z 379.35. Elemental analysis was carried out on a Yanaco
CHN corder MT-6. Thermal analysis was performed on a Seiko
EXSTAR 6000 TG/DTA 6300 thermal analyzer at a heating
1
CH Cl as an eluent. H NMR (300 MHz, CDCl , 25 °C): ¤
2
2
3
8
.69 (d, J = 8.1 Hz, 4H, aromatic proton), 8.55 (d, J = 8.4
Hz, 4H, aromatic proton), 7.74 (d, J = 8.7 Hz, 4H, aromatic
proton), 7.37 (d, J = 8.4 Hz, 4H, aromatic proton), 7.18
¹
1
(
s, 2H, aromatic proton), 6.96 (d, J = 3.6 Hz, 2H, aromatic
proton), 6.71 (d, J = 3.6 Hz, 2H, aromatic proton), 2.80­2.69
m, 8H, thiophene­CH ­), 1.74­1.58 (m, 6H, thiophene­CH ­
rate of 10 °C min for thermogravimetry (TG) and a TA
Instruments Q-100 connected to a cooling system at a heating
¹
1
(
rate of 10 °C min for differential scanning calorimetry (DSC).
UV­vis absorption spectra were recorded using a JASCO
V-560 spectrophotometer. For the solution spectra, compounds
2
2
CH, ­CH ­), 1.47­1.16 (m, 76H, ­CH ­), 0.95­0.81 (m, 18H,
2
2
1
3
­
1
1
1
CH3). C NMR (75 MHz, CDCl , 40 °C): ¤ 163.41, 145.02,
3
¹5
40.43, 140.16, 135.12, 134.60, 134.12, 133.99, 131.91,
31.60, 129.58, 129.53, 126.93, 126.53, 126.37, 125.73,
25.68, 123.64, 123.37, 40.292, 34.917, 33.655­26.962 (18
were dissolved in CHCl at a concentration of ca. 10 M.
3
For the thin film spectra, compounds and poly(methyl meth-
acrylate) (1:1, w/w) were first dissolved in o-dichlorobenzene,
followed by filtering through a 0.45 ¯m pore size PTFE
membrane syringe filter, and then spin-coated at 450 rpm for
60 s onto quartz substrates. The absorption coefficients were
calculated by Beer’s law, and the film thickness was determined
carbons), 22.946­22.879 (3 carbons), 14.317­14.297 (3 car-
¹1
bons). IR (KBr), v (cm ): 2924 (alkyl C­H), 1707, 1666
C=O stretching), 1355 (C­N stretching). MS (MALDI-TOF)
(
+
m/z [M + H ]: Calcd for C104H130N O S , 1599.89; found,
2
4 4
3
1
597.95. Anal. Calcd for C104H130N O S : C, 78.05; H, 8.19;
with a Veeco Instrument Dektak surface profiler (Surfcorder
2
4 4
N, 1.75%. Found: C, 77.80; H, 8.25; N, 1.78%.
Synthesis of N,N¤-Bis{4-[3,4¤-dihexyl-5¤¤-(2-octyldodecyl)-
ET3000, Kosaka Laboratory, Ltd.). CV was performed with
the use of a three-electrode cell in which platinum was used
as a working electrode. A platinum wire was used as an
auxiliary electrode. All cell potentials were taken in CH Cl
2
,2¤:5¤,2¤¤-terthiophen-5-yl]phenyl}-3,4,9,10-perylenetetra-
carboxylic Diimide (19): The title compound, 19, was
synthesized by the same procedure as 16 with 0.130 g
0.165 mmol) of 1-amino-4-[3,4¤-dihexyl-5¤¤-(2-octyldodecyl)-
,2¤:5¤,2¤¤-terthiophen-5-yl]benzene (15), 0.0213 g (0.0543
mmol) of 3,4,9,10-perylenetetracarboxylic dianhydride, and
.699 g of imidazole. The compound, 19 (0.0434 g, 41%) was
2
2
¹
1
or o-dichlorobenzene with 1 mmol L compounds and 100
¹1
(
2
mmol L tetrabutylammonium perchlorate degassed by N
2
¹
1
bubbling for 10 min at a scan rate of 0.01 V s with the use
of a homemade Ag/AgCl, KCl (sat.) reference electrode. The
surface morphologies of the active layers were characterized
using an atomic force microscope (AFM, SPA400, SII Nano-
technology) in tapping mode. Two-dimensional grazing inci-
dence X-ray scattering (GIWAXS) experiments were conducted
at SPring-8 on beamline BL19B2. The samples were irradiated
at a fixed incident angle on the order of 0.12° through a
Huber diffractometer, and the GIWAXS patterns were recorded
with a 2-D image detector (Pilatus 300K). GIWAXS patterns
were recorded with an X-ray energy of 12.39 keV (­ = 1 ¡).
The samples for GIWAXS were prepared by drop-casting the
0
then isolated as a red solid and purified by recrystallization
from EtOAc after silica gel column chromatography using
1
EtOAc then CH Cl as eluents. H NMR (300 MHz, CDCl ,
2
2
3
2
(
5 °C): ¤ 8.69 (d, J = 8.1 Hz, 4H, aromatic proton), 8.55
d, J = 8.4 Hz, 4H, aromatic proton), 7.75 (d, J = 8.4 Hz, 4H,
aromatic proton), 7.37 (d, J = 8.7 Hz, 4H, aromatic proton),
7
6
2
1
.18 (s, 2H, aromatic proton), 6.97 (s, 2H, aromatic proton),
.95 (d, J = 3.6 Hz, 2H, aromatic proton), 6.71 (d, J = 3.6 Hz,
H, aromatic proton), 2.89­2.67 (m, 12H, thiophene­CH ­),
2
.81­1.52 (m, 10H, thiophene­CH ­CH, ­CH ­), 1.52­1.16
sample solution on a Si/SiO substrate.
2
2
2
13
(
(
m, 88H, ­CH ­), 1.02­0.80 (m, 24H, ­CH ). C NMR
75 MHz, CDCl3, 40 °C): ¤ 163.40, 144.98, 140.70, 140.56,
Fabrication and Characterization of Field-Effect Tran-
2
3
sistors.
The OFET device of the PDI derivatives were
6
6
1
1
1
3
39.40, 134.96, 134.70, 134.12, 133.72, 133.58, 131.67,
31.54, 131.29, 129.65, 129.41, 128.73, 127.02, 126.51,
26.49, 125.64, 125.59, 123.64, 123.34, 40.21, 34.84,
3.57­26.87 (22 carbons), 22.85­22.78 (4 carbons), 14.21
fabricated as follows. On top of the 300 nm thermally grown
SiO on an Sb-doped n-type Si substrate (capacitance (C ) =
2
i
¹
2
11.5 nF cm ), the source and drain electrodes were formed by
photolithography of Au (90 nm) and Cr (10 nm). The standard
channel length and width were 10 and 500 ¯m, respectively.
The substrate was immersed in a 233 mg L toluene solution
of trichloro(octadecyl)silane for 30 min at room temperature.
The 10 mg mL chlorobenzene solution of the PDI derivatives
was spin-coated at the channel region under a dry nitrogen
atmosphere. The OFET properties were measured with an
Agilent 4155C Semiconductor Device Analyzer under a dry
nitrogen atmosphere. Mobility (®) and threshold voltage (Vt)
¹1
(4 carbons). IR (KBr), v (cm ): 2924 (alkyl C­H), 1707, 1668
¹
1
(
C=O stretching), 1356 (C­N stretching). MS (MALDI-TOF)
+
m/z [M + H ]: Calcd for C124H158N O S , 1932.06; found,
2
4 6
¹1
1
931.98. Anal. Calcd for C124H158N2O4S6: C, 77.05; H, 8.24;
N, 1.45%. Found: C, 76.89; H, 8.55; N, 1.50%.
Characterization. H and 13C NMR spectra were recorded
1
on a Bruker DPX (300 MHz) in chloroform-d calibrated to
tetramethylsilane as an internal standard (¤ = 0.00). FT-IR
H
Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan | 1091

were obtained from the I
­V plot, using the relationship
Materials at the Tokyo Institute of Technology for the
supporting quantum calculations.
sat 0.5
2
g
Isat = [(C W)/(2L)]®(V ¹ V ) , where I , C , W, and L stand
i
g
t
sat
i
for the saturation current, capacitance of the insulator layer per
unit area, channel width, and channel length, respectively. The
current on/off ratio was defined as the ratio of drain current
between V = +60 V and V = ¹20 V at V = +60 V.
Supporting Information
1
Synthetic procedures of compounds 1­15, H NMR spectra
of PDI-TerTh, TGA curves of PDI derivatives, DSC thermo-
grams of PDI derivatives, pictorial representations of the
frontier molecular orbitals, output and transfer characteristics
of PDI-alkoxy in the OFET device, EQE spectra of the device
based on PDI-BiTh:P3HT (DIO 1 vol %), AFM images of
PDI-BiTh:P3HT thin films without and with DIO (1 vol %),
absorption spectra of PDI-derivative:P3HT blend films, and
GIWAXS face-on profiles of the pure PDI-derivative films and
PDI-derivative:P3HT (2:1, w/w) blend films. This material is
available electronically on J-STAGE.
g
g
d
Fabrication and Characterization of the OPV Devices.
All BHJ OPVs were prepared using the same device fabrication
procedure as follows: The indium tin oxide (ITO)-coated glass
¹1
substrates (obtained from Lumtec, Ltd. (7 ³ sq )) were first
patterned by lithography, then cleaned with detergent, ultra-
sonicated in acetone and isopropyl alcohol, subsequently dried
on a hot plate at 120 °C for 5 min, and finally treated with
oxygen plasma for 7 min. Poly(3,4-ethylenedioxythiophene):
poly(styrenesulfonate) (PEDOT:PSS, Baytron P VP AI4083)
was passed through a 0.45 ¯m filter before being deposited on
ITO at a thickness of around 30 nm by spin-coating at 3500
rpm for 70 s in air and dried at 140 °C for 20 min inside of a
glovebox. The PDI-derivative:P3HT (2:1 w/w) blend film was
prepared by dissolving the molecules in anhydrous chloro-
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Bull. Chem. Soc. Jpn. 2014, 87, 1083–1093 | doi:10.1246/bcsj.20140167
© 2014 The Chemical Society of Japan | 1093