Synthesis and optical properties of n-type polymers containing perylene moieties

Article abstract of DOI:10.1080/15421406.2010.497101

Three n-type polymers, Ppe01, Ppe02, and Ppe03, containing both perylene moieties and fluorine atoms were synthesized. The synthesiszed polymeric perylene derivatives with good compatibility for solution processes were chosen as new acceptor candidates fo

Full text of DOI:10.1080/15421406.2010.497101

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Synthesis and Optical Properties of n-
Type Polymers Containing Perylene
Moieties
Ki-Soo Kim b , Seonju Jeong a , Cham Kim a , Hoyoung Kim a , Yu Suk
Yang c , Jae Hong Kim c , Younghwan Kwon d , Weon-Pil Tai b & Yoon
Soo Han a
a Division of Nano-Bio Technology, DGIST , Daegu, Korea
b Ulsan Fine Chemical Industry Center, Ulsan Technopark , Ulsan,
Korea
c Department of Chemical Engineering , Yeungnam University ,
Gyeongsangbuk-do, Korea
d Department of Chemical Engineering , Daegu University ,
Gyeongsan, Gyeongbuk, Korea
Published online: 14 Nov 2010.
To cite this article: Ki-Soo Kim , Seonju Jeong , Cham Kim , Hoyoung Kim , Yu Suk Yang , Jae Hong
Kim , Younghwan Kwon , Weon-Pil Tai & Yoon Soo Han (2010) Synthesis and Optical Properties of
n-Type Polymers Containing Perylene Moieties, Molecular Crystals and Liquid Crystals, 532:1, 29/
[445]-38/[454], DOI: 10.1080/15421406.2010.497101
To link to this article: http://dx.doi.org/10.1080/15421406.2010.497101
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Mol. Cryst. Liq. Cryst., Vol. 532: pp. 29=[445]–38=[454], 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2010.497101
Synthesis and Optical Properties of n-Type
Polymers Containing Perylene Moieties
KI-SOO KIM,2 SEONJU JEONG,1 CHAM KIM,1
HOYOUNG KIM,1 YU SUK YANG,3 JAE HONG KIM,3
YOUNGHWAN KWON,4 WEON-PIL TAI,2 AND
YOON SOO HAN1
1Division of Nano-Bio Technology, DGIST, Daegu, Korea
2Ulsan Fine Chemical Industry Center, Ulsan Technopark, Ulsan, Korea
3Department of Chemical Engineering, Yeungnam University,
Gyeongsangbuk-do, Korea
4Department of Chemical Engineering, Daegu University,
Gyeongsan, Gyeongbuk, Korea
Three n-type polymers, Ppe01, Ppe02, and Ppe03, containing both perylene
moieties and fluorine atoms were synthesized. The synthesiszed polymeric perylene
derivatives with good compatibility for solution processes were chosen as new
acceptor candidates for substitution of C60 derivatives in poly(3-hexylthiophene)-
based organic photovoltaic application, by considering the results based on good
thermal stability, high electron affinity ranging from 3.81 to 3.96 eV, absorption
property in visible region, and effective photoluminescence quenching in the blend
films with P3HT. The potential of the synthesized perylene polymers was investi-
gated by measuring the current-voltage property of the polymeric P3HT: Ppe01
OPV device.
Keywords Electron acceptor; organic photovoltaic; P3HT; perylene; PL
quenching
Introduction
The development of organic photovoltaic devices (OPVs) has attracted considerable
attention in recent years due to the demand for making flexible large area devices
with low cost, easy process, and lightweight [1,2]. A well studied system is bulk
heterojunction (BHJ)-type OPVs, where the conjugated polymer is often used as
the electron donor and the fullerene (C60) derivative is used as the electron acceptor.
One of the BHJ OPVs consisting of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric
acid methyl ester (P3HT:PC61BM) as a donor:acceptor pair showed the power
conversion efficiency (PCE) of 4 ꢀ 5% [3,4]. However, it is especially attractive for
Address correspondence to Yoon Soo Han, Division of Nano-Bio Technology, Daegu
Gyeongbuk Institute of Science and Technology (DGIST), Hosan-dong, Dalseo-gu, Daegu
704-230, Korea (ROK). Tel.: þ82-53-430-8411; Fax: þ82-53-430-8422; E-mail: yshan@
dgist.ac.kr
29=[445]

30=[446]
K.-S. Kim et al.
further improving the PCE to replace the C60 derivatives with materials that allow
light absorption in visible. Conjugated polymers, such as PCNEPV and MEH-CN-
PPV, which include -CN and -F group to provide high electron affinity, have been
used as electron acceptors [5,6]. Various inorganic electron acceptors, such as CdSe,
ZnO, etc. have been also studied to improve the PCE of OPVs [7–9]. Unfortunately,
the electron acceptors mentioned above have found to be inadequate for commercial
use in OPVs. Therefore, it is still of great importance in developing new electron
acceptors which can tune the electron affinity and electron mobility to improve both
open circuit voltage (Voc) and short circuit current (Jsc), thus resulting in higher
PCE [10–12].
Perylene derivatives with low molecular weight have been studied as electron
acceptors in bilayered OPVs fabricated by vapor deposition [13–15], since it has been
known that they have high carrier mobility and easy control of the electron affinity
through chemical modification with functional groups. In addition, various perylene
derivatives are relatively easy to synthesize, and can be applied as electronic materi-
als in various fields.
In this paper, polymeric perylene derivatives were chosen as new acceptor
candidates for substitution of C60 derivatives, with good compatibility for solution
processes. We synthesized three new perylene-based polymers as electron acceptors,
and their optical properties and electronic band structures for application to all poly-
meric OPVs were investigated. We also demonstrate their potential usefulness with
the current-voltage property of BHJ OPV fabricated with the blend film of P3HT
and the synthesized perylene polymer.
Experimental
Materials
Thin layer chromatography (TLC) analyses were carried out on a pre-coated 0.2 mm
HPTLC silica gel 60 plate (Merck, Darmstadt). Flash column chromatography was
performed with silica gel (Merck silica gel 60, 70–230 mesh). Commerical grade
solvents were used as received, and isoquinoline was distilled with calcium hydride
under reduced pressure. 4,40-Biphenyldiboronic acid, 4-n-butoxyphenol, 4,40-
diaminooctafluorobiphenyl and 2,20-bis(trifluoromethyl)benzidine were purchased
from TCI Chemical Co. All other reagents were purchased from Aldrich Chemical
Co. and used without purification. The substrate glass with patterned indium-tin
oxide (ITO, 20X=&) for OPV device was purchased from SUNIC Co. (Korea).
98% Regioregular P3HT[poly(3-hexyl thiophene)] was purchased from Rieke
Metals. The weight-averaged molecular weight of P3HT was 6.4 ꢁ 104 g=mol.
Poly-3,4-ethyleneoxythiophene:poly-4-sytrensulfonate (PEDOT:PSS, Baytron P VP
Al 4083) used as buffer layer was received from P. H. Stark GmbH.
Synthesis of Perylene Monomers
The synthetic scheme of the perylene monomers, compound 5 and 6, is illustrated in
Figure 1.
N,N0-Bis-n-propyl-3,4,9,10-perylenetetra-carboxdiimide (1). Propylamine (11.53 mL,
15 eq) was added to a suspension of 3,4,9,10-perylenetetracarboxdiimide (5.0 g,

Synthesis and Optical Properties
31=[447]
Figure 1. Synthetic route to perylene monomers, 5 and 6.
12.74 mmol) in 300 mL of water=propanol (1:1). The mixture was stirred under
argon at 65ꢂC for 12 hr. After cooling to room temperature, the mixture was
poured into 150 mL of a 2 M HCl aqueous solution under stirring. The red solid
was washed with water and dried at 90ꢂC, yielding 6.05 g of compound 1 as a red
powder with a yield of 92%. This product was used without further purification
for the synthesis of 2.
N,N0-Bis-n-propyl-1,6,7,12-tetrachloroperylene-3,4,9,10- Tetracarboxdiimide (2).
Compound 1 (5.0 g, 10.54 mmol), nitrobenzene (30 mL), iodine (800 mg, 3 eq), and
iodobenzene (0.36 mL, 3 eq) were added to the round flask under nitrogen flow.
And then, sulfuryl chloride (SO2Cl2, 5.28 mL, 6 eq) was added dropwise for 2 hr at
80ꢂC while stirring. The reaction mixture was stirred under nitrogen at 80ꢂC for
12 hr. Methanol (200 mL) was added, and then stirred for an additional 6 hr. The
precipitate was filtered to obtain 5.16 g of 2 as an orange powder, with a yield of
80% [13]. Purification was performed via flash recrystallization from
dichlorobenzene. Rf 0.32 (CH2Cl2); FAB-MS calcd for C30H18Cl4N2O4: 610.00,
found: m=z 611.11 (M þ H)þ.
N,N0-Bis-n-propyl-1,6,7,12-tetrakis(4-n-Butyloxyphenoxy)perylene-3,4,9,10-tetra-
Carboxdiimide (3). Compound 2 (5.0 g, 8.17 mmol), 4-n-butyloxyphenol (8.15 g,
6 eq), potassium carbonate (6.78 g, 6 eq), and N-methylpyrrolidinone (200 mL)
were added to a round bottom flask charged with N2, and the reaction mixture
was stirred at 160ꢂC for 6 hr. After cooling to room temperature, 2 M HCl solution
(200 mL) was added dropwise with stirring to obtain a dark-red precipitate. The
precipitate was filtered, washed with water and methanol, and then vacuum-dried.

32=[448]
K.-S. Kim et al.
The crude product was purified by flash column chromatography (SiO2, CH2Cl2) to
obtain 7.30 g of 3 as an orange powder with a yield of 79%. Rf 0.40 (EtOAc-hexane
1:9); FAB-MS calcd for C70H70N2O12: 1130.49, found: m=z 1129.08 (M-H)þ.
N,N0-Bis-n-propyl-1,6,7,12-tetrakis(4-tert-Butylphenoxy)perylene-3,4,9,10-tetra-
Carboxdiimide (4). The synthetic route and work-up were similar to those of 3
except that p-tert-butylphenol (7.42 g, 49.02 mmol) instead of 4-n-butyloxyphenol
was used. Compound 4 was obtained as a red powder with a yield of 86%. Rf
0.35 (EtOAc-hexane 1:9); FAB-MS calcd for C70H70N2O8: 1066.51, found: m=z
1066.18 (M ꢃ H)þ.
1,6,7,12-Tetrakis(4-n-butyloxyphenoxy)perylene-3,4,9,10-tetracarboxylic
dianhyd-
ride (5). To a suspension of diimide 3 (5.0 g, 4.52 mmol) in 1 L of 2-propanol
were added to 100 mL of water and 150 g of KOH. The vigorously stirred reaction
mixture was refluxed under N2 for 24 hr. During the reaction, the color changed
from red to green. After cooling to room temperature, the reaction mixture was
poured under stirring into 2.0 L of a 2 M HCl aqueous solution. A precipitate was
washed with water, and then dried under vacuum. Recrystallization from CH2Cl2=
MeOH afforded 3.71 g of 5 as a dark-red powder with a yield of 80%. Rf 0.25
1
(EtOAc-hexane 1:9); H NMR (CDCl3, 400 MHz) d (ppm) 8.22 (s, 4H), 7.15 (d,
J ¼ 8.5 Hz, 8H), 7.05 (d, J ¼ 8.5 Hz, 8H), 4.39 (t, J ¼ 7.5 Hz, 8H), 1.78 (m, 8H),
1.55 (m, 8H), 0.99 (t, J ¼ 7.1 Hz, 12H); FAB-MS calcd for C64H56O14: 1048.37,
found: m=z 1048.58 (M)þ.
1,6,7,12-Tetrakis(4-tert-butylphenoxy)perylene-3,4,9,10-tetracarboxylic dianhydride
(6). The synthetic route and work-up were similar to those of 5. The compound
6 was obtained as a red powder with a yield of 86%. Rf 0.20 (EtOAc-hexane 1:9);
1H NMR (CDCl3, 400 MHz) d (ppm) 8.33 (s, 4H), 7.29 (d, J ¼ 8.2 Hz, 8H), 6.99
(d, J ¼ 8.2 Hz, 8H), 1.34 (s, 36H); FAB-MS calcd for C64H56O10: 984.39, found:
m=z 985.11 (M þ H)þ.
Synthesis of Perylene Polymers. The synthetic scheme of the perylene polymers
studied in this study is illustrated in Figure 2.
Synthesis of Ppe01. 1.0 g (0.95 mmol) of 5 and 464 mg (4 eq) of benzoic acid were
added to 5 mL of m-cresol under N2 atmosphere. The mixture was stirred at room
temperature for 10 min. 2,20-Bis(trifluoromethyl)benzidine (310 mg, 1 eq) was
dissolved in 2 mL of m-cresol, and added to the above reaction mixture. The
temperature was raised to 190ꢂC. After stirring for 12 hr, 253 mg (2 eq) of
isoquinoline dissolved in 2 mL of m-cresol were added, and the reaction time was
extended to 48 hr. After cooling to room temperature, 5 mL of CH2Cl2 was added,
and the resulting solution was poured dropwise into 500 mL of MeOH. The
resulting precipitate was centrifuged, and redissolved in 5 mL of CH2Cl2, and then
reprecipitated from MeOH. This procedure was repeated three times, and the final
product was dried in vacuum at 90ꢂC. The polymerized compound Ppe01 was
1
obtained in a yield of 88% as a red powder. H NMR (CDCl3, 400 MHz) d (ppm)
8.38 (bs, 4H), 7.55–7.47 (m, 22H), 4.49 (bs, 8H), 1.82 (bs, 8H), 1.58 (bs, 8H), 1.02
(bs, 12H); GPC (THF) Mw 12,340 Mn 8,200; Anal. calcd for (C78H62F6N2O12)n:
C, 70.26; H, 4.69; N, 2.10. found C, 71.22; H, 4.11; N, 2.61; UV-vis (CH2Cl2):
kmax ¼ 460, 558, 602 nm.

Synthesis and Optical Properties
33=[449]
Figure 2. Synthetic routes to perylene polymers.
Synthesis of Ppe02. Ppe02 was obtained from compound 6 (1 g, 1.02 mmol), as a red
powder, with a yield of 68%. The synthetic route and work-up were similar to those
of Ppe01. 1H NMR (CDCl3, 400 MHz) d (ppm) 8.47 (s, 4H), 7.78 (d, J ¼ 8.0 Hz, 8H),
7.43 (m, 14H), 1.37 (s, 36H); GPC (THF) Mw 7,500 Mn 5,772; Anal. calcd for
(C78H62F6N2O8)n: C, 73.81; H, 4.92; N, 2.21. found C, 73.02; H, 5.51; N, 2.21;
UV-vis (CH2Cl2): kmax ¼ 460, 547, 590 nm.
Synthesis of Ppe03. The synthetic route and work-up were similar to those of Ppe01,
except that 4,40-diaminooctafluorobiphenyl (312 mg, 0.95 mmol) instead of
2,20-bis(trifluoromethyl)benzidine was used. Ppe03 was obtained as a red powder
1
with a yield of 71%. H NMR (CDCl3, 400 MHz) d (ppm) 8.52 (bs, 4H), 7.39 (m,
16H), 4.59 (bs, 8H), 1.80 (bs, 8H), 1.65 (bs, 8H), 1.00 (bs, 12H); GPC (THF) Mw
9,940 Mn 7,993; Anal. calcd for (C76H56F8N2O12)n: C, 68.06; H, 4.21; N, 2.09.
found C, 68.82; H, 4.71; N, 2.01; UV-vis (CH2Cl2): kmax ¼ 464, 550, 593 nm.
Device Fabrication. ITO glasses were cleaned by ultrasonic treatment in acetone,
detergent, de-ionized water and iso-propyl alcohol sequentially, and dried in a
vacuum oven. Afterward, the O2 plasma treatment was conducted for 3 min. to
remove organic residue on ITO. PEDOT:PSS was spin-coated onto ITO at
3000 rpm, and dried at 140ꢂC for 15 min. to give a thickness of 30 nm. The
chlorobenzene solution containing P3HT and Ppe01 (1:2 by weight) were
spin-coated onto the PEDOT:PSS layer at 700 rpm and dried at 50ꢂC for 40 min.
to give a thickness of 120 nm. Finally, 1 nm of LiF layer and 120 nm of Al film

34=[450]
K.-S. Kim et al.
were vapor-deposited under a pressure of 1.33 ꢁ 10ꢃ4 Pa to yield an OPV device with
the configuration of ITO=PEDOT:PSS=P3HT:Ppe01=LiF=Al. The device was sealed
with glass cap to protect from the air. The active area of the device, defined by
shadow mask, is 3 ꢁ 3 mm2. The devices were annealed directly on the top of a
hotplate.
Measurements
1
The H NMR spectra of the synthesized materials in CDCl3 were recorded using a
400 MHz Bruker AM-400 spectrometer. Elemental analyses were performed on a
Carlo Erba 1106 analyzer. Thermal properties were obtained from a TG=DTA
SDT Q600 analyzer (TA Instrument). Mass spectral data were obtained from the
Korea Basic Science Institute (Daegu) on a Jeol JMS 700 high resolution mass spec-
trometer. UV-visible absorption spectra were obtained using a Varian Easy 50 Conc
spectrophotometer. The photoluminescence spectra excited by a 150-W Xe lamp
were monitored with a Jasco FP-6500 spectrofluorometer. The ionization potential
(Ip) was measured using a photoelectron spectroscope (Riken Keiki, AC-2). The
weight (Mw) and number (Mn) average molecular weight of the polymers were
evaluated using gel permeation chromatography (Waters, alliance 2000, THF, poly-
styrene universal calibration) at room temperature. Photocurrent-voltage measure-
ment was performed with a Keithley model 2400 Source Meter and a Newport
91192 solar simulator system (equipped with 1 KW xenon arc lamp, Oriel). Light
intensity was adjusted to simulated AM 1.5 radiation at 100 mW=cm2 with a Radiant
Power Energy Meter (model 70260, Oriel). All measurements were carried out under
ambient conditions at room temperature.
Results and Discussion
Synthesis and Characterization
We have designed and synthesized three perylene polymers, Ppe01, Ppe02, and
Ppe03, with n-type characteristics to apply to OPVs. These perylene polymers were
modified with the introduction of strong electron withdrawing F atoms in order to
improve the solubility and air-stability by raising their polarities and electron
affinities [16]. Compound 5 and 6 as perylene monomers were obtained from
3,4,9,10-perylenetetracarboxdiimide using condensation, chlorination, alkylation,
and dehydro-condensation reactions according to previously reported procedures
[13]. The polymeric compounds were synthesized by a condensation reaction as
shown in Figure 2.
1H NMR and elemental analysis confirmed the structure of the intermediates
and target materials. For the final polymeric compounds, the proton signals of the
parent perylene structure were all shifted down-field relative to those of monomeric
compounds (5 and 6) in the 1H NMR spectra. This effect was probably induced by a
de-shielding effect from electron withdrawing moieties, such as octafluorobiphenyl
and bis(trifluoromethyl)benzidine. The proton signals were also broader due to
the polymeric state of the compounds (Ppe01, Ppe02, and Ppe03).
The synthesized compounds were also confirmed by elemental analysis, showing
the analyzed data in good agreement with the calculated values and implying high
purity of the synthesized compounds [17]. Thermo gravimetric analysis (TGA)
showed that the decomposition temperature of Ppe01 ꢀ 03, where over 95% of their

Synthesis and Optical Properties
35=[451]
mass remained, under nitrogen atmosphere was in the range of 430 and 456ꢂC,
demonstrating good thermal stability of the compounds. The molecular weight of
the compounds was measured by gel permeation chromatography (GPC) using poly-
styrene standards and THF as an eluent. The molecular weights (Mw) of Ppe01, 02,
and 03 were 12,340, 7,500, and 9,940 g=mol with polydispersity indices (PDI) of 1.29,
1.62, and 1.48, respectively.
Optical and Electronic Band Structures of Perylene Polymers
Figure 3 presents UV-Visible absorption and PL spectra of the polymers measured in
0.1 mM CH2Cl2 solution. All absorption spectra show three absorption maxima
attributed to perylene moieties [18]. The absorption maxima (kmax,UV) of Ppe01 ꢀ 03
were measured to be 602, 590, and 593 nm, and PL maxima (kmax,PL) were observed
at 649, 624, and 624 nm, respectively. Absorption maxima of monomers, 5 and 6,
were detected at 590 and 585 nm, and their PL maxima were showed at 626 and
622 nm, respectively. Absorption and PL maxima of the polymers were red-shifted
relative to the corresponding monomers. This result showed that expanded
p-conjugation along the polymer backbone yielded low electron transition energy.
The absorption maximum of Ppe01 was showed in rather longer wavelength
compared to those of other polymers. This may be due to the stronger electron
donating effect of 4-n-butyloxyphenoxy group in Ppe01 than that of p-tert-butylphe-
noxy moiety in Ppe02. In addition, the octafluoro groups have stronger electron
withdrawing character than that of bis(trifluoromethyl) groups [19].
The ionization potentials (HOMO, Ip) of Ppe01 ꢀ 03 measured by photoelectron
spectroscopic analysis were 5.84, 5.79, and 5.77 eV, respectively. The band gap ener-
gies (Eg) of Ppe01 ꢀ 03 calculated from the absorption onset of a 0.1 mM solution in
dichloromethane were 1.88, 1.91, and 1.96 eV, respectively. The electron affinities
(LUMO, Ea) were calculated to be 3.96, 3.72, and 3.81 eV, respectively. These high
electron affinities suggest that the synthesized compounds have a potential as elec-
tron acceptors to apply to OPV device. Table 1 summarizes the optical and molecu-
lar orbital energies of Ppe01 ꢀ 03.
Figure 3. Absorption and PL spectra of Ppe01, Ppe02, and Ppe03.

36=[452]
K.-S. Kim et al.
Table 1. Optical and electrochemical properties of Ppe01, Ppe02, and Ppe03
a
a
e
f
kmax,UV
(nm)
kmax,PL Td
(nm)
Eg
Mw PDI (eV) (eV) (eV)
Ip
Ea
Polymers
(ꢂC) Mn
Ppe01
Ppe02
Ppe03
460b, 558c, 602d
460b, 547c, 590d
464b, 550c, 593d
649
624
628
456 8,200 12,340 1.29 1.88 5.84 3.96
430 5,772 7,500 1.62 1.91 5.79 3.88
456 7,993 9,940 1.48 1.96 5.77 3.81
aMeasured in 0.1 mM CH2Cl2 solution.
bS0 ! S1 absorption peak.
cS1 ! S0 absorption peak.
dT1 ! Tn absorption peak [13].
eThermal decomposition temperature.
fCalculated by Ea ¼ Ip–Eg.
Photovoltaic Properties of Ppe01
From the measured Ea and Ip, it was thought that Ppe01 would be able to act as an
electron acceptor in OPV devices. Figure 4 shows PL spectra of P3HT and
P3HT:Ppe01 thin films excited at 510 nm. As compared to P3HT, blend film of
P3HT:Ppe01 (1:1 by weight) displayed sharp drop of PL intensity, and P3HT:Ppe01
(1:2) film also showed more effective PL quenching. It demonstrates that the PL
intensity of P3HT dramatically quenched by the presence of perylene polymer.
The phenomenon of PL quenching which is essential to obtain photovoltaic effects
must be originated from efficient intramolecular electron transfer from the electron
donor (P3HT) to the electron acceptor (Ppe01).
An OPV with the configuration, ITO (150 nm)=PEDOT:PSS (30 nm)=
P3HT:Ppe01 (1:2 by weight, 120 nm)=LiF (1 nm)=Al (150 nm), was fabricated in
order to investigate photovoltaic properties of Ppe01. Figure 5 shows the energy
diagram of the materials used in the OPV device. It appears that the molecular
energy levels of Ppe01 and P3HT are relatively positioned to each other such that
they are allowed to separate excitons and generate free charges at the interface of
Figure 4. PL spectra of films; P3HT, P3HT=Ppe01 (1:1) and P3HT=Ppe02 (1:2).

Synthesis and Optical Properties
37=[453]
Figure 5. Energy diagram of OPV containing Ppe01.
P3HT and Ppe01. The device exhibited Jsc of 0.214 mA=cm2, Voc of 0.563 V, and fill
factor (FF) of 26.45% under the illumination of 100 mW=cm2. The PCE for this solar
cell was 0.03%.
The reason for the poor photovoltaic properties, such as low Jsc and PCE, is
possibly attributable to the incomplete formation of bicontinuous phase between
the electron donor (P3HT) and electron acceptor (Ppe01). The bicontinuous phase
which is one of the main factors to improve PCE in bulk hetero-junction type OPVs
can be obtained by formation of phase separation (or nanodomain) between the elec-
tron donor and acceptor. Various methods such as post thermal annealing [20,21],
solvent annealing [22], and incorporation of an additive [23] in active layer have been
investigated to enhance phase separation by increasing structural order of the
electron donor and acceptor.
In the viewpoint of chemical structure, the electron donor and acceptor should
have crystallinity enough to easily form phase separation. Therefore, improvements
in PCE in this study could be likely realized by controlling phase separation of
P3HT:Ppe01 active layer or modifying the chemical structure to get increased crys-
tallinity of Ppe01, for example, insertion of aliphatic spacer into mainchain of Ppe01.
Further studies aimed at optimizing the OPV devices are in progress using thermal
annealing, incorporation of an additive and chemical modification of Ppe01.
Conclusions
In summary, highly soluble n-type perylene polymers were synthesized, and their
optical and electronic properties were investigated. The synthesized polymers
showed high thermal stabilities and high electron affinities. When considering their
electron affinities, the synthesized perylene polymers were suitable candidates for
the electron acceptor with P3HT as the electron donor in OPV devices. Although
the synthesized perylene derivatives provided excellent thermal stability, high

38=[454]
K.-S. Kim et al.
electron affinity and absorption property in visible region, the performance of all
polymeric OPV device fabricated with P3HT: Ppe01 blend films as the active layer
was found to be limited from unfavorable phase separation, indicating that
additional improvement on the performance of OPV devices could be possible with
further controlling morphology of the blend films with the device processing
conditions.
Acknowledgments
This work was supported by the DGIST Basic Research Program of the Ministry of
Education, Science and Technology (MEST) of Korea.
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