Effect of side chains on phenanthrene based D-A type copolymers for polymer solar cells

Article abstract of DOI:10.1016/j.orgel.2017.01.014

A series of low band gap conjugated copolymers containing 9,10-modified phenanthrene and diketopyrrolopyrrole (DPP) units were synthesized as electron donor materials for bulk heterojunction organic solar cells. These donor-acceptor type PDPP copolymers have varying solubilizing groups on their identical conjugated backbones. The optical bandgap of PDPP copolymers is about 1.6?eV which corresponds to the long wavelength region of the solar spectrum. Through the incorporation of phenanthrene units into the conjugated backbone instead of commonly used thiophene derivatives, a higher open-circuit voltage of about 0.8?V could be achieved, as a result of their deeper HOMO level. Of all the devices, the P4:PC₆₁BM BHJ system showed the best performance with a V_oc of 0.79?V, a J_sc of 5.97?mA?cm^?2, a fill factor of 0.62 and a power conversion efficiency of 2.73% due to superior nanoscale phase separation between the electron donor and electron acceptor materials than in the other polymers arising from short-branched solubilizing groups on the phenanthrene side of its conjugated backbone.

Full text of DOI:10.1016/j.orgel.2017.01.014

Accepted Manuscript
Effect of side chains on phenanthrene based D-A type copolymers for polymer solar
cells
Yeong-A. Kim, Kyeong-Il Hwang, Minji Kang, Nam-Koo Kim, Soo-young Jang, In-Bok
Kim, Juhwan Kim, Dong-Yu Kim
PII:
S1566-1199(17)30014-9
10.1016/j.orgel.2017.01.014
ORGELE 3926
DOI:
Reference:
To appear in: Organic Electronics
Received Date: 17 August 2016
Revised Date: 6 January 2017
Accepted Date: 9 January 2017
Please cite this article as: Y.-A. Kim, K.-I. Hwang, M. Kang, N.-K. Kim, S.-y. Jang, I.-B. Kim, J. Kim,
D.-Y. Kim, Effect of side chains on phenanthrene based D-A type copolymers for polymer solar cells,
Organic Electronics (2017), doi: 10.1016/j.orgel.2017.01.014.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Effect of Side Chains on Phenanthrene based D-A Type
Copolymers for Polymer Solar Cells
a
a
a
a
a,c
b
d
Yeong-A Kim , Kyeong-Il Hwang , Minji Kang , Nam-Koo Kim , Soo-young Jang , In-Bok Kim , Juhwan Kim and
a,b,*
Dong-Yu Kim
a
School of Materials Science & Engineering, Gwangju Institute of Science and Technology (GIST), 123
Cheomdangwagi-ro, Buk-gu, Gwangju 61002, Republic of Korea
b
Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST), 123
Cheomdangwagi-ro, Buk-gu, Gwangju 61002, Republic of Korea
c
Department of Chemistry and Centre for Plastic Electronics, Imperial College London, Exhibition Rd, London,
SW7 2AZ, UK.
d
Department of Chemical Engineering and Materials Science, University of California-Irvine, Irvine, California,
92697, United States
KEYWORDS conjugated polymer, organic semiconductor, polymer solar cells, phenanthrene, diketopyrrolopyrrole
ABSTRACT: A series of low band gap conjugated copolymers containing 9,10-modified phenanthrene
and diketopyrrolopyrrole (DPP) units were synthesized as electron donor materials for bulk
heterojunction organic solar cells. These donor-acceptor type PDPP copolymers have varying
solubilizing groups on their identical conjugated backbones. The optical bandgap of PDPP copolymers
is about 1.6 eV which corresponds to the long wavelength region of the solar spectrum. Through the
incorporation of phenanthrene units into the conjugated backbone instead of commonly used
thiophene derivatives, a higher open-circuit voltage of about 0.8 V could be achieved, as a result of their
deeper HOMO level. Of all the devices, the P4:PC BM BHJ system showed the best performance with a
61
−
2
V of 0.79 V, a J of 5.97 mA cm , a fill factor of 0.62 and a power conversion efficiency of 2.73% due to
oc
sc
superior nanoscale phase separation between the electron donor and electron acceptor materials than
in the other polymers arising from short-branched solubilizing groups on the phenanthrene side of its
conjugated backbone.
1. Introduction
Bulk heterojunction (BHJ) organic solar cells (OSCs) composed of an electron donor and phenyl-C -
61
butyric acid methyl ester (PCBM) as the electron acceptor material have been actively researched over the
past decades because of their great advantages of being light-weight, being low-cost to manufacture, and
being suitable for flexible substrates as a consequence of solution processing[1–5]. To attain the highest
possible performance, research has focused on new photoactive materials as well as device optimization
and architecture. In particular, electron-donating conjugated polymers, one of the most important
elements in such solar cells, need to have several properties to achieve high power conversion efficiency.
First, low band gap properties (<1.6 eV) and a high absorption coefficient are required to extensively
absorb light in the near IR region and to achieve a high short circuit current (J ).[5,6] The most efficient
sc
strategy to enhance light absorption at longer wavelengths is to incorporate a push-pull concept into the
conjugated backbone through alternating electron-rich units (D) and electron-deficient units (A) by
copolymerization of these two units.[7–9] Second, reasonable hole mobilities and well-ordered nanoscale
phase separation from the acceptor materials are needed to obtain a r reasonable fill factor (FF).[10,11]
The hole mobility of conjugated molecules can be facilitated by enhanced intramolecular charge carrier
transport and intermolecular interaction through not only D-A interaction between neighboring

ACCEPTED MANUSCRIPT
molecules but also fused planar structure which improves the intermolecular charge-carrier
transport.[10,11] Last but not least, a deep highest occupied molecular orbital (HOMO) energy level is
essential because this is directly related to high open circuit voltage (V ).[12–14] One way to lower the
oc
HOMO energy level is substitute an electronegative atom or molecules, such as halogen atom, ester or
cyano groups, on the π-conjugated structure of polymers. Another effective way is to incorporate
polyaromatic structures into conjugated backbone as “weak” donor units. Through the combination of
“
weak” donor and “strong” acceptor building blocks in D-A type conjugated structure, copolymers can
meet the requirements for not only low band gap properties but also deep HOMO energy levels.[7,15,16]
Phenanthrene, comprising three fused benzene rings, is one kind of polycyclic aromatic compound along
with others such as fluorene, carbazole, germafluorene.[17–20] Phenanthrene possesses curved structure
and is more stable than its linear isomer, anthracene.[21] If phenanthrene is used as a donating building
block, the resulting conjugated polymers, they have chance to achieve high Voc due to their high
oxidation potential in comparison with thiophene derivatives resulting from their polyaromatic
structures.[21,22] In addition, phenanthrene units can easily form strong π-π stacking by virtue of their
rigid and planar structure, which may give rise to reasonable charge carrier mobilities. Furthermore, the
9,10-positions of phenanthrene can be easily substituted with alkoxy groups, which not only affect the
solubility of polymers without interfering with the main conjugated system but also enhance the electron
density throughout the polymer chains.[22–24] However, some research about into phenanthrene has
reported that the optical energy band gaps of its homopolymers are as large as about 3 eV which cause a
scarcity of light absorption, resulting in reduced J value in BHJ OSCs. [22,23] Thus, strong acceptor unit
sc
was required in order to reduce the optical band gap of phenanthrene based D-A type copolymers.
In this study, we synthesized a series of low band gap copolymers using phenanthrene as an electron-
donating building block and a diketopyrrolopyrrole (DPP) unit as an electron-deficient moiety. The latter
is well known for its strong extinction coefficient and the ability to form strong π-π stacking by virtue of
its lactam structure.[25–27] In order to investigate the properties of phenanthrene-alt-
diketopyrrolopyrrole (PDPP) copolymers, six different PDPP copolymers bearing different side chains
were synthesized. As varying solubilizing groups of PDPP copolymers, P1 and P2 have a short branched
side chain on DPP, while P3 and P4 have a bulkier alkyl chain, together with the alkoxy side chain, on
phenanthrene units. Finally, P5 and P6 are distinguished from the others by their extended 2-
dimensional π-conjugated system due to an additional phenyl ring that was added at the 9- and 10-
positions of phenanthrene. We investigated the properties of these PDDP copolymers and investigated
their performance in OSC device.

ACCEPTED MANUSCRIPT
Scheme 1. Synthetic routes to monomers and PDPP copolymers
2. Experimental section
2.1 Synthesis of monomer
All reagents were commercially available and used without further purification. The synthetic routes to
the compounds and polymers are shown in Scheme 1. Compounds 2, 3, 5 and 8 were prepared by
procedures similar to those in the literature[23,24,26,28]. The details of the procedures are as follows.
Synthesis of 2,7-dibromophenanthrene-9,10-dione (2)
N-bromosuccinimide (19.6 g, 110mmol) was added with small portion to a solution of phenanthrene-
9,10-dione (1) (10.4 g, 50 mmol) in 500 ml of concentrated sulfuric acid and the mixture was stirred
overnight at room temperature. The reaction was stopped by pouring into sufficient quantity of ice and
then the solid compound was filtered. The orange powder was washed with water several times.
Recrystallization from dimethyl sulfoxide (DMSO) gave the product as needle-like red crystals. (yield: 11.3
1
g, 63%). H NMR (DMSO-d , 400 MHz) : δ = 7.93 (d, 2H), 8.05 (d, 2H), 8.23 (d, 2H).
6
Synthesis of 2,7-dibromo-9,10-bis(alkoxy)phenanthrene (3)
Synthesis of 2,7-dibromophenanthrene-9,10-dione (2) (5 g, 13.7 mmol) was dissolved in 100 ml of
anhydrous N,N-dimethylformamide. Sodium hydrosulfite (5.7 g, 32.8 mmol) was added in one portion to
the solution and stirred for 30 min, after which potassium carbonate (K CO , 5.7 g, 41.1 mmol), tetrabutyl
2
3
ammoniumbromide, and alkyl bromide (RBr, 4 equiv, 54.8 mmol) were added. The mixture was heated
for 12 hours at 140 °C then cool down to room temperature. The yellow-white solution was extracted with
chloroform three times. Column chromatography on silica with hexane as an eluent afforded white
1
crystal (3a) and colorless sticky oil (3b), respectively. (3a, yield : 7.82 g, 81%). H NMR (CDCl , 400 MHz) :
3
8
.40 (d, 2H), 7.36 (s, 2H), 7.67 (d, 2H), 4.18 (t, 4H), 1.88 (m, 4H), 1.56 (m, 4H), 1.32 (m, 36H), 0.85 (t, 6H),

ACCEPTED MANUSCRIPT
1
(
3b, yield : 3.73 g, 46%). H NMR (CDCl , 400 MHz) : 8.39 (d, 2H), 7.37 (s, 2H), 7.67 (d, 2H), 4.14 (t, 4H),
3
1
.88 (m, 2H), 1.57 (m, 12H), 1.38 (m, 4H), 0.85 (m, 12H).
Synthesis
of
2,2'-(9,10-bis(alkoxy)phenanthrene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (4)
To a 100 ml two-neck round flask, compound 3 (5 mmol), bis(pinacolato)diboron (3 g, 12 mmol), [1,1′ -
bis(diphenylphosphino)ferrocene]dichloropalladium(II) (0.6 g, 0.1 mmol), potassium acetate (2.5 g, 25
mmol,), and anhydrous 50 ml of 1,4-dioxane were added. The mixture was heated at reflux under
nitrogen for 72 hours. The cooled mixture was extracted with chloroform. The organic layer was stirred
with Celite/activated carbon and filtered. Column chromatography on silica with hexane and ethyl
acetate (9:1) afforded a white solid and further purified by recrystallization from methanol. The product
1
was needle-like white crystal. (4a, yield: 3.4 g, 85%). H NMR (CDCl , 400 MHz, δ): 8.78 (s, 2H), 8.63 (d,
3
1
3
2
H), 7.96 (d, 2H), 4.09 (m, 4H), 1.89 (m, 2H), 1.74-1.34 (m, 60H), 1.03-0.91 (m, 6H). C NMR (CDCl , 400
3
MHz, δ): 14.24, 22.81, 25.04, 26.52, 29.49, 29.83, 30.56, 32.04, 73.74, 83.95, 122.15, 129.51, 129.96, 130.48,
1
1
(
30.91, 143.45. Anal.Calcd for C H B O : C, 75.18; H, 10.10; B, 2.71; O, 12.02. Found: C, 75.17; H, 10.10; O,
50 80 2 6
1
1.88. (4b, yield: 2.2 g, 65%). H NMR (CDCl , 400 MHz, δ): 8.77 (s, 2H), 8.55 (d, 2H), 7.96 (d, 2H), 4.08
3
13
m, 4H), 1.90 (m, 2H), 1.72-1.37(m, 36H), 1.03-0.91 (m, 12H). C NMR (CDCl , 400 MHz, δ): 11.33, 14.31,
3
23.25, 23.90, 25.04, 29.38, 30.79, 40.80, 76.51, 83.90, 122.14, 129.44, 130.14, 130.52, 130.76, 143.66. Anal.Calcd
for C H B O : C, 73.47; H, 9.40; B, 3.15; O, 13.98. Found: C, 73.21; H, 9.54; O, 13.31.
4
2
64
2
6
Synthesis of 3,6-bis(5-bromothiophen-2-yl)-2,5-dimethyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-
dione (5)
1
Compound 5 was prepared by same procedure as described in the literature. (5a) H NMR (CDCl , 400
3
MHz, δ): 8.64 (d, 2H), 7.20 (d, 2H), 3.90 (m, 4H), 1.89 (m, 2H), 1.38-1.19 (m, 16H), 0.91-0.84 (m, 12H).
Anal.Calcd for C H Br N O S : C, 52.79; H, 5.61; N, 4.10; O, 4.69; S, 9.39. Found: C, 52.68; H, 5.61; N, 4.12;
3
0
38
1
2
2
2 2
O, 4.79; S, 9.39. (5b) H NMR (CDCl , 400 MHz, δ): 8.60 (d, 2H), 7.20 (d, 2H), 3.90 (d, 4H), 1.89 (m, 2H),
3
1
.38-1.19 (m, 48H), 0.90-0.80 (m, 12H).Anal.Calcd for C H Br N O S : C, 60.92; H, 7.78; N, 3.09; O, 3.53;
46 70 2 2 2 2
S, 7.07. Found: C, 60.99; H, 7.72; N, 3.07; O, 3.76; S, 7.06.
Synthesis
of
2,2'-(9,10-bis(alkoxy)phenanthrene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (9)
Compound 8 was prepared by same procedure as described in the literature. Compound 9 was
1
synthesized in same procedure of compound 4. (9a, yield: 3.6 g, 76%). H NMR (CDCl , 400 MHz, δ): 8.81
3
(
d, 2H), 8.09 (s, 2H), 7.02 (d, 4H), 6.79 (d, 4H), 4.12 (5, 4H), 1.80 (m, 4H), 1.47-1.25 (m, 60H), 1.01-0.91 (m,
13
6
8
H). C NMR (CDCl , 400 MHz, δ): 14.23, 22.80, 24.93, 26.20, 29.47, 29.62, 29.74, 29.80, 32.03, 68.07,
3
3.87, 113.79, 122.04, 131.68, 131.89, 132.01, 132.36, 135.05, 137.69, 157.42. Anal.Calcd for C H B O : C, 78.31;
62
88
2
6
1
H, 9.33; B, 2.27; O, 10.09. Found: C, 78.17; H, 9.31; O, 10.11. (9b, yield: 2.7 g, 68%). H NMR (CDCl , 400
3
MHz, δ): 8.80 (d, 2H), 8.10 (s, 2H), 7.01 (d, 4H), 6.80 (d, 4H), 4.08 (t, 4H), 1.88 (m, 2H), 1.71-1.34(m, 36H),
1
3
1
.03-0.91 (m, 12H). C NMR (CDCl , 400 MHz, δ): 11.22, 14.22, 23.16, 23.94, 24.92, 29.22, 30.65, 39.50, 70.78,
3
8
3.86, 113.93, 122.04, 131.65, 131.83, 131.91, 132.03, 132.34, 135.08, 137.70, 157.72. Anal.Calcd for C H B O : C,
54 72 2 6
7
7.33; H, 8.65; B, 2.58; O, 11.44. Found: C, 77.28; H, 8.61; O, 11.5.
.2 General Procedure of Polymerization
PDPP (phenanthrene-alt-diketopyrrolopyrrole) copolymers with varying solubilizing group were
2
synthesized via Suzuki polymerization according to literature.[27] To a 50 ml two-necked flask, 0.5 mmol
of comonomers, 0.5 ml of Aliquat 336, 20 mg of tri(o-tolyl)phosphine, 0.45 g of potassium phosphate,

ACCEPTED MANUSCRIPT
1
ml of deionized water and 15 ml of toluene was added. Before addition of catalysts, this reaction
container was degassed via nitrogen bubbling at least 30 min to remove the oxygen. After putting 10 mg
o
of tris(dibenzylideneacetone)dipalladium, the flask was heated up to 115 C and vigorously stirred for
three days. Subsequently, in order to remove the activated chain end, 1mg of phenyl boronic acid in
tetrahydrofuran and 1 ml of bromobenzene was added as end-cappers and stirred for additionally 5 hours
each. Reaction mixture was cool down to room temperature and poured into 200 ml of methanol
containing 100ml of HCl. Precipitated solid was filtered and washed with hot solvent of methanol,
acetone and hexane using the method of Soxhlet extraction to remove metal catalyst and low molecular
weight oligomer. Purified chloroform fraction of polymer solution was re-precipitated in methanol and
dried in vacuum oven for at least 12 hours.
P1 (82 mg, yield: 15.3%) Anal.Calcd for C H N O S : C, 76.36; H, 9.05; N, 2.62; O, 5.98; S, 5.99. Found :
68
96
2
4 2
-1
-1
C, 76.28; H, 9.03; N, 2.54; O, 6.07; S, 6.02. M = 12.0 kg mol , M = 21.6 kg mol , PDI = 1.80.
n
w
P2 (97 mg, yield: 20.23%) Anal.Calcd for C H N O S : C, 75.27; H, 8.42; N, 2.93; O, 6.68; S, 6.70. Found:
60
80
2
4 2
-1
-1
C, 74.85; H, 8.59; N, 2.46; O, 7.04; S, 5.94. M = 7.5 kg mol , M = 13.5 kg mol , PDI = 1.81.
n
w
1
P3 (383 mg, yield: 59.2%) H NMR (CDCl , 400 MHz, δ): 9.21-9.02 (br, 2H), 8.85-8.40 (m, 4H), 8.36-7.96
3
(
br, 2H), 7.75-7.29 (m, 2H), 4.42-4.03 (br, 8H) 2.28-1.86 (br, 6H), 1.85-0.98 (m, 84H), 1.02-0.58 (m, 18H).
Anal.Calcd for C H N O S : C, 77.96; H, 9.97; N, 2.16; O, 4.95; S, 4.95. Found: C, 77.47; H, 9.93; N, 2.13;
8
4
128
2
4 2
-1
-1
O, 5.27; S, 5.16. M = 21.5 kg mol , M = 39.4 kg mol , PDI = 1.83.
n
w
1
P4 (392 mg, yield: 66.3%) H NMR (CDCl , 400 MHz, δ): 9.18-9.06 (br, 2H), 8.89-8.38 (m, 4H), 8.32-7.91
3
(
br, 2H), 7.81-7.29 (m, 2H), 4.37-3.93 (br, 8H) 2.10-1.91 (br, 4H), 1.88-0.96 (m, 64H), 0.95-0.57 (m, 24H).
Anal.Calcd for C H N O S : C, 77.24; H, 9.55; N, 2.37; O, 5.41; S, 5.43. Found: C, 77.02; H, 9.64; N, 2.36;
76
112
2
4 2
-1
-1
O, 5.34; S, 5.33. M = 34.1 kg mol , M = 66.5 kg mol , PDI = 1.90.
n
w
1
P5 (378 mg, yield: 52.3%) H NMR (CDCl , 400 MHz, δ): 9.20-9.06 (br, 2H), 8.82-8.41 (m, 4H), 8.33-7.98
3
(
br, 2H), 7.94-7.29 (m, 2H), 7.15-6.68 (m, 4H), 4.25-3.78 (br, 8H) 2.09-1.87 (br, 6H), 1.87-0.99 (m, 84H),
1
.00-0.51 (m, 18H). Anal.Calcd for C H N O S : C, 79.73; H, 9.48; N, 1.94; O, 4.42; S, 4.43. Found: C,
9
6
136
2
4 2
-1
-1
7
9.68; H, 9.43; N, 1.87; O, 4.54; S, 4.39. M = 23.2 kg mol , M = 39.9 kg mol , PDI = 1.72.H17
n w
1
P6 (452 mg, yield: 67.8%) H NMR (CDCl , 400 MHz, δ): 9.21-9.09 (br, 2H), 8.89-8.36 (m, 4H), 8.28-7.99
3
(
br, 2H), 7.92-7.27 (m, 2H), 7.13-6.60 (br, 4H), 4.21-3.79 (br, 8H) 2.28-1.94 (br, 4H), 1.90-0.97 (m, 64H),
.98-0.53 (m, 24H). Anal.Calcd for C H N O S : C, 79.29; H, 9.00; N, 2.10; O, 4.80; S, 4.81. Found: C,
0
8
8
120
2
4 2
-
1
-1
7
7.30; H, 8.92; N, 2.04; O, 5.44; S, 4.25. M = 33.2 kg mol , M = 66.7 kg mol , PDI = 2.01.
n
w
2.3 Measurements and Characterization
1
H NMR spectra of the synthesized compounds were recorded on a JEOL JNM-ECX400 with 400MHz
o
at 25 C in CDCl . The molecular weight of the polymers was measured by gel permeation
3
chromatography (GPC), calibrated with a polystyrene standard. Polymer was dissolved in high purity
liquid chromatography (HPLC) grade 1,2,4-trichlorobenzene, the eluent, at a concentration of 5 mg/ml,
and GPC was performed using an Acme 9000 (YOUNGLIN instrument) at a flow rate of 1 ml/min at 150
o
C. Polymer solution was filtered through PTFE filters (0.45 μm) before injection. The thermal
properties of copolymers were investigated by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC) analysis. The thermal stability of the copolymers was measured by TGA
with a TA-2050 instrument at a heating rate of 10 °C/min in a nitrogen atmosphere, and the thermal
o
behavior of copolymer was investigated by DSC on a TA2010 instrument at a heating rate of 10 C/min
o
o
from 50 C to 290 C in a nitrogen atmosphere. The optical properties of polymers by investigated by

ACCEPTED MANUSCRIPT
ultraviolet-visible (UV/Vis) absorption spectral measurement using a Perkin-Elmer Lambda 750
spectrophotometer. The UV-Vis absorption spectra of polymer solutions and spin-coated thin films
were obtained in chloroform in a quartz cell and on a glass substrate, respectively. Electrochemical
properties of the polymers were investigated in a 0.1 M solution of tetrabutylammonium perchlorate
(
Bu NClO ) in degassed anhydrous acetonitrile by means of a potentiostat (Eco Chemi. AUTOLAB) at a
4 4
scan rate of 50 mV/s. Polymer-coated ITO glass, Pt wire and Ag/AgCl were as the materials for the
working, counter and reference electrode, respectively. The reference electrode was calibrated with a
ferrocene solution prior to measurement. The working electrodes were prepared by spin coating with
polymer solution in chlorobenzene on the ITO glass. Electrochemical shifts were standardized to the
half potential of the ferrocene redox couple of 0.50 V. The J-V curves of photovoltaic cells were measured
2
using a Keithley 4200 under 100 mW/cm illumination from a 1 kW Oriel solar simulator with AM 1.5 G
2
filter in a nitrogen atmosphere. The photoactive area was 4.64 mm . The measurement conditions were
confirmed by means of a calibrated silicon reference solar cell, certified by the National Renewable
Energy Laboratory (NREL). The film morphology of photoactive layers was investigated by transmission
electron microscopy (TEM) using a Dimension 3100 system (Digital Instruments/Veeco).
2.4 Fabrication and Characterization of Organic Field-Effect Transistors
A top gate/bottom contact organic field-effect transistors (OFETs) device configuration was used to
characterize the charge transport properties of PDPP copolymers. Each of the polymers was dissolved to
o
obtain a concentration of 7 mg/ml in chlorobenzene, and the solutions were vigorously stirred at 130 C
for 24 hours. The source and drain electrodes (70 nm Au) were pre-patterned on corning glass. These
substrates were cleaned with acetone, deionized water, and isopropyl alcohol for 10 min each, and then
dried for 1 hour. After UV/ozone treatment for 20 min, the substrates were coated with a semiconducting
layer by means of the polymer solutions at 2000 rpm for 60 s under N atmosphere. The semiconducting
2
layers were ~35 nm thick. The dielectric layer was deposited by means of a PMMA solution (80 mg/ml in
o
n-butyl acetate) and then baked at 80 C for 2 hours under N . Subsequently, gate aluminum electrodes
2
about 50 nm in thickness were deposited on top of the polymer thin film layer by thermal evaporation
through a shadow mask. The OFET devices had a channel length of 20 μm and a width of 1 mm.
2.5 Fabrication and Characterization of Bulk Heterojunction Organic Solar Cells
BHJ OSCs with normal structure were fabricated to investigate the photovoltaic properties of each
copolymer. PDPP copolymer:PC BM, made with 7 mg of each copolymer and 14 mg of PC BM, were
61
61
o
dissolved in 0.5 ml of chlorobenzene under vigorous stirring over night at 100 C. Indium tin oxide-
coated glass substrates were washed with detergent and ultrasonicated in acetone, deionized water and
isopropyl alcohol for 10 min each, and then oven dried for 1 hour. The substrates were treated with
UV/ozone for 20 min, then a PEDOT:PSS (AI4083) layer was deposited on the substrate at a 5000 rpm for
o
4
0 s. After baking at 150 C for 10 min, the substrates were transferred to N -filled glove box. Several
2
devices were fabricated with the blend solutions. Also, before film deposition, 5 vol% of 1-
chloronaphthalene (CN) was added to the chlorobenzene blend solution, which was then stirred for an
additional 30 min. The photoactive layers were deposited by spin-coating at a rate of 2000 rpm for 60 s
and dried at room temperature for 10 min, then the cathode metal was deposited, by thermal evaporation
as a 20 nm layer of calcium and a 100 nm layer of aluminum.
3
. Result and Discussion
3
.1 Synthesis and Thermal Properties
A series of PDPP copolymers of poly{2,7-[9,10-bis(dodecyloxy)phenanthrene]-alt-3,6-bis(thiophen-2-

ACCEPTED MANUSCRIPT
yl)-2,5-bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione}(P1),
poly{2,7-[9,10-bis(2-
ethylhexyloxy)phenanthrene-alt-2,5-bis(2-ethylhexyl)-3,6-bis(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione}(P2), poly{2,7-[9,10-bis(dodecyloxy)phenanthrene-alt-2,5-bis(2-hexyldecyl)-3,6-
bis(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione}(P3), poly{2,7-[9,10-bis(2-
ethylhexyl)phenanthrene-alt-2,5-bis(2-hexyldecyl)-3,6-bis(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione}(P4), poly{2,7-[9,10-(4-(dodecyloxyphenyl)phenanthrene-alt-2,5-bis(2-hexyldecyl)-
3
,6-bis(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione}(P5),
poly{2,7-[9,10-bis(4-((2-
ethylhexyl)oxy)phenyl)phenanthrene-alt-2,5-bis(2-hexyldecyl)-3,6-bis(thiophen-2-yl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione}(P6) were prepared via Suzuki polymerization as represented in
scheme 1, respectively. All of monomers were highly soluble in toluene, the solvent for Suzuki
polymerization, before the addition of the catalyst. As the polymer chains grew, they readily precipitated
in case of P1 and P2, which bore a short side chain on the DPP unit, as a consequence of extremely low
solubility, and this lead to low molecular weight polymers. In contrast, P3, P4, P5 and P6, which bore
longer and bulkier side chains on the DPP unit, attained higher molecular weights accompanied with
reasonable solubility in common processing solvents such as chloroform, chlorobenzene and o-
dichlorobenzene. The molecular weights of the polymers were determined by gel permeation
o
chromatography (GPC) analysis with a polystyrene standard in 1,2,4-trichlorobenzene at 150 C in order
to avoid overestimation of molecular weight due to molecular aggregation of polymeric chains.[29] The
number-average molecular weights (M ) and weight-average molecular weights (M ) are presented in
n
w
Table 1. PDPP copolymers exhibited a favorable stability with decomposition temperatures (T ) above
d
3
00 °C. The decomposition temperature with 5% weight loss of PDPP copolymers are also presented in
Table 1. P5 and P6 exhibit better thermal stability than the other polymers due to the additional phenyl
ring substituent in their conjugated backbone. Investigation of the thermal behavior of these polymers
by differential scanning calorimetry (DSC), did not reveal show any noticeable thermal transitions such
as a glass transition temperature (T ), melting temperature (T ) or crystallization temperature (T ) in the
g
m
c
temperature range from 55 °C to 290 °C.
Table 1. Molecular weight, thermal, optical and electrochemical properties of PDPP copolymers
b
d
Solution
Film
Film
opt
c
M / Mw
T
λ max
λ max
λonset
Eg
HOMO
(eV)
LUMO
n
Polymer
a
o
(
g/mol)
( C)
(nm)
(nm)
(nm)
(eV)
(eV)
P1
P2
P3
P4
P5
P6
12,000/21,600
7,500/13,500
331
316
340
350
422
410
638
636
697
697
733
731
715
703
708
703
734
731
756
775
760
760
780
780
1.64
1.60
1.63
1.63
1.59
1.59
5.25
5.23
5.24
5.24
5.14
5.14
3.61
3.63
3.64
3.65
3.55
3.55
21,500/39,400
34,100/66,500
23,200/39,900
33,200/66,700
3
.2 Optical Properties
The optical characteristics of PDPP copolymers both in dilute chloroform solutions and as spin-coated
films on glass substrates were studied by ultraviolet-visible (UV-Vis) absorption spectroscopy. Figure 1
depicts the absorption spectra of copolymers, and the maximum absorption wavelengths (λmax), the
opt
absorption onset wavelengths (λonset) and the optical band gaps (Eg ) are summarized in Table 1. The

ACCEPTED MANUSCRIPT
absorption spectra of the copolymers in both dissolved and film states show two absorption band located
between 300~500 nm and 500~780 nm, respectively. The short-wavelength absorption peak is known to
*
originate from localized π-π transition in the conjugated polymer main chains, and the long-wavelength
absorption peak is due to a transition between the electron-rich phenanthrene moieties and the electron-
deficient DPP moiety, which is called “intramolecular charge transfer (ICT)”. All copolymers show high
*
absorption intensity for the ICT transition relative to the π-π transition due to the pronounced electron
accepting ability of DPP units. They exhibit intensive shoulder peaks even in solution as a consequence of
strong intermolecular interactions. The optical band gaps derived from the absorption edge of the PDPP
copolymers are around 1.6 eV regardless of the shape of side chains. Accompanying low band gap
properties, the film absorption coefficient of the alkoxy-substituted phenanthrene based copolymers P3
5
-1
and P4 is about 1.3×10 cm , a value which is comparable to that of P3HT at the maximum absorption
wavelength.[31,32] Incorporation of an additional phenyl ring at the 9- and 10-positions of phenanthrene,
led to a slight reduction in the absorption coefficient, while the maximum absorption wavelength of P5
and P6 is red-shifted by about 26 nm, and the optical band gap slightly decreases relative to those of P3
and P4, respectively. It is generally known that a 2D-extended π-conjugation through an aromatic side
chain, such as a 2-thiophenyl side chain, allows the polymers to absorb substantially more photons,
accompanied by low band gap properties. [33–36] In case of PDPP copolymers, p-alkoxyphenyl
substituents on the coattails of π-conjugated structure lead to low band gap properties compared to
alkoxy substituents. However, absorption coefficient of p-alkoxyphenyl substituted PDPP copolymers
showed lower than their counterpart. It would come from the solid stated packing structure. Taking into
account the steric hinderance of phenyl ring, aggregation of conjugated polymers could be suppressed,
then intermolecular interaction of P5 and P6 might be weaker than that of P3 an P4. In both cases, with
the absorption coefficient and the wavelength of maximum absorption were less influenced by the shape
of side chain.

ACCEPTED MANUSCRIPT
Figure 1. Normalized UV-Vis absorption spectra of P3 (black), P4 (red), P5 (blue) and P6 (green)
in chloroform (a) and absorption coefficient in a thin film state (b).
3
.3 Electrochemical Properties
The HOMO levels of PDPP copolymers were determined from cyclic voltammetry (CV) measurements
and calculated from the onset oxidation potential (E ) on the basis of the half potential of ferrocene:
ox
+
HOMO = - [Eox - E (ferrocene) + 4.8] eV. The half-wave potential of ferrocene/ferrocenium (Fc/Fc )
1/2
(
E (ferrocene)) was estimated at 0.50 V. The LUMO energy level of the polymers was calculated from
1/2
HOMO energy levels and optical energy band gap. The electrochemical results are summarized in Table
and cyclic voltammograms are represented in Figure S2 (for P1 and P2) and Figure 2 (for P3, P4, P5
1

ACCEPTED MANUSCRIPT
and P6). The HOMO levels of copolymers containing alkoxy substituent on phenanthrene units, P1, P2,
P3 and P4 were similar at around -5.24 eV owing to their same conjugated backbone. Based on these
results, the length and size of alkoxy groups at the 9- and 10-positions of phenanthrene and alkyl side
chains on DPP units do not significantly affect the HOMO levels of these polymers. In contrast, the
HOMO energy level of P5, P6 is about 0.1 eV higher than that of the other polymers, due to the
additionally incorporated phenyl rings at the 9- and 10-positions of phenanthrene which probably
enhanced the electron density of the conjugated backbone as a consequence of a called mesomeric effect
exerted through the p-alkoxyphenyl side chain.[30] This means that p-alkoxyphenyl side chains have
stronger electron-donating properties than plain alkoxy side chains with respect to an identical
conjugated backbone. For both types of polymers, the HOMO energy levels are deeper than that of
P3HT (5.0 eV) derived under the same conditions, which would be beneficial in obtaining higher Voc in
bulk heterojunction organic solar cells (OSCs) with these donor materials since the Voc of OSCs is
proportional to the difference between the HOMO energy level of electron donor and the LUMO
energy level of electron acceptor. As the LUMO level of PDPP copolymers is located around -3.7 eV,
PDPP copolymers possess sufficient energy offset for efficient exciton disassociation with respect to the
LUMO level of PCBM. [18,26,37]
Figure 2. Cyclic voltammograms of P3 (black), P4 (red), P5 (blue) and P6 (green) films on a platinum
electrode measured with 0.1 mol/L tetrabutyl ammonium perchlorate acetonitrile solutions at a scan rate
of 50 mV/s.

ACCEPTED MANUSCRIPT
3
.4 Charge Transport Properties
Grazing Incidence X-ray diffraction (GIXRD) analysis was conducted to evaluate the crystallinity of the
PDPP copolymers, as shown in Figure S3. No obvious lamella diffraction peak was found for pristine films
of PDPP copolymers in out-of-plane direction. As the annealing temperature was increased, P3 and P4
-1
films exhibited upto (300) diffraction peaks with q = 0.30 and 0.36 Å , which corresponds to a lamella d-
z
spacing of 20.9 Å and 17.4 Å respectively, which is related to the edge-on orientation of polymer. P3 and
-1
P4 additionally showed a (010) diffraction peak at q = 1.69 and 1.68 Å corresponding to a distance of
z
3
.71Å and 3.73 Å, which may be the π-π stacking distance in a face-on orientation. Although, P4 which
have short side chain on phenanthrene showed higher degree of molecular orderting, both P3 and P4
showed mixed orientation of edge-on and face-on orientation. In contrast, no remarkable diffraction
peaks that reflected molecular orientation even under thermal annealing conditions were observed in
the case of P5 which possess a phenyl ring that can suppress intermolecular aggregation via a steric effect
due to its orthogonal orientation to the conjugated backbone. Similarly, pristine P6 film didn’t show any
obvious diffraction peak. However, thermal annealed film of P6 with short p-alkoxy phenyl side chin on
-1
phenanthrene showed only weak (100) lamella d-spacing diffraction with qxy = 0.29 Å in in-plane
direction. We suggest that the additional phenyl ring of P5 and P6 can suppress the intermolecular
aggregation of polymers.
The charge transport properties of these copolymers were characterized by organic field effect
transistors (OFETs) devices with top gate/bottom contact configuration. As mentioned earlier, the field
effect mobility of P1 and P2 could not be demonstrated due to poor solubility in common organic
solvents. The semiconducting layer was deposited by spin-coating a chlorobenzene solution (7 mg/ml)
onto the pre-patterned glass substrates. Figure S4 shows the transfer curve at +/-60V of source-drain
voltage (V ). The carrier mobilities of pristine and thermally annealed polymer films were determined
ds
from a saturation regime and are summarized in Table S1. PDPP copolymers showed ambipolar charge
transport characteristics with predominant hole-transport character, regardless of side chain. The hole
-
3
-3
-3
-3
2
-1 -1
mobility of pristine P3, P4, P5 and P6 were 1.14ⅹ10 , 1.1.14ⅹ10 , 1.28ⅹ10 and 9.67ⅹ10 cm V s ,
respectively. Both hole and electron transport of these polymers slightly improved after thermal
o
annealing at 250 C. Mobility only varied slightly with varying solubilizing groups. All else being equal,
replacing short branched side chains on the phenanthrene units of P4 and P6 with linear alkyl groups
was be beneficial to the hole mobilities of the thermally treated devices.
3
.5 BHJ Solar Cells Performance and Morphology Characterization
To investigate the photovoltaic properties of the PDPP copolymers, BHJ organic solar cell devices with
a ITO/PEDOT:PSS/polymer:PC BM(1:2 w/w)/Ca/Al configuration were fabricated using PDPP
61
copolymers as the donor materials and [6,6]-phenyl-C -butyric acid methyl ester (PC BM) as the
61
61
acceptor material. Figure 3 shows the current-voltage (J-V) characteristics of these devices under AM 1.5G
2
(
100 mW/cm ) and the photovoltaic parameters of each device are summarized in Table 2. P3, P4, P5 and
P6, which bear longer branched alkyl side chains on DPP units, were highly soluble in processing
solvents such as chloroform, chlorobenzene (CB), and o-dichlorobenzene (DCB). As mentioned above,
photovoltaic devices incorporating P1 and P2 could not be trialed due to the unfavorable solubility of
these polymers in common solvents. CB was chosen as the solvent for polymer:PC BM, and 1-
61
chloronaphthalene (CN) was employed as a processing additive in order to optimize active layer
morphology for enhanced device performance. As shown in Table 2, all devices containing the PDPP
copolymers exhibited high Voc values of 0.75 V-0.78 V. Given that the Voc of OSC devices is proportional

ACCEPTED MANUSCRIPT
to the difference between the HOMO level of the conjugated polymer and the LUMO level of PCBM, this
high Voc resulted from deep HOMO level of PDPP copolymers. The P3:PC BM device made with mixed
61
2
solvent (CB with 4 v/v% CN) attained a Voc of 0.77 V, J of 2.66 mA/cm , FF of 58%, and PCE of 1.2%.
sc
Replacing the dodecyloxy side chains on phenanthrene with 2-ethylhexyloxy groups in the P4:PC BM
61
2
device resulted in a slightly higher Jsc of 5.97 mA/cm than in the P3:PC BM device under identical
61
conditions. Since p-alkoxyphenyl substituted PDPP copolymers P5 and P6 showed a slightly lower Voc of
0
.75 V, reflecting the relatively higher HOMO levels than in P3 and P4, the value of J exhibited a similar
sc
tendency to P3 and P4. The optimized devices incorporating P3 and P4 with mixed solvent achieved PCE
of 1.2% and 2.7% respectively. In all PDPP copolymer-incorporating OSC devices, the PCEs were
improved by the addition of a small amount of CN. In particular, incorporating 4 vol% CN into the
respective chlorobenzene solution improved the J value of the devices while maintaining V . This was
sc
oc
mainly due to a morphological improvement upon adding the solvent additive. Interestingly, despite
their higher OFET hole mobilities, the OSC devices incorporating P3 and P5, with their dodecyloxy
groups, exhibited a poor J compared with that of their counterparts, P4 and P6.
sc
Table 2. Photovoltaic properties of BHJ solar cells incorporating PDPP copolymers:PC BM
6
1
-
b
c
Voc
V]
J [mAcm
FF
PCE
[%]
Hole mobility
Electron mobility
sc
Polymer
P3
Solvent
CB
2
2
-1 -1
2 -1 -1
[
]
[%]
[cm V s ]
[cm V s ]
-
5
-5
0.78
0.77
0.79
0.78
0.74
0.75
0.75
2.29
2.66
4.02
5.97
2.45
2.74
4.78
5.18
57
58
61
1.02
1.20
1.90
2.71
0.96
1.08
1.79
2.06
2.3 × 10
2.5 × 10
a
-5
-5
CB:CN
4.4 × 10
2.4 × 10
-
5
-5
P4
P5
P6
CB
4.5 × 10
4.9 × 10
2.2 × 10
1.8 × 10
a
-5
-5
CB:CN
58
53
53
50
53
3.0 × 10
-
6
-5
CB
1.8 × 10
a
-6
-5
CB:CN
7.9 × 10
1.9 × 10
4.2 × 10
1.9 × 10
-
6
-5
CB
1.6 × 10
a
-6
-5
CB:CN
0.75
2.3 × 10
a
b
c
4
v/v % CN was added. SCLC mobilities of ITO/PEDOT/Active layer/Au. SCLC mobilities of
ITO/ZnO /Active layer/Ca/Al.

ACCEPTED MANUSCRIPT
Figure 3. Current density-voltage of P3:PC BM (black), P4:PC BM (red), P5:PC BM (blue) and
6
1
61
61
P6:PC BM (green) spin-coated with the help of chlorobenzene solution (a) and chlorobenzene
6
1
containing 4 v/v% CN (b).
Transmission electron microscopy (TEM), which is useful for investigating the nanostructure of
donor/acceptor phase separation in the photoactive layer, was used to investigate the reasons for the
lower J value of the P3- and P5-based devices compared to the counterpart P4- and P6-based devices in
sc
spite of similar optical and electrochemical properties. TEM images of each blend film are shown in
Figure 4, and the dark and bright regions represent the electron-deficient PCBM and the electron-rich
PDPP copolymers respectively.[27,38] Considering that the exciton diffusion length of a conjugated
polymer is about ~10 nm, donor/acceptor materials should have large interfaces within a 20 nm scale in
order to enhance exciton dissociation for efficient charge generation.[39,40] In the case of P3 and P5,
there was coarse phase separation at a 100 nm scale, while P4 and P6 domains showed fine nanoscale
phase separation with continuous interpenetration. Taking into account similar absorption coefficients
accompanying as well as optical band gaps and energy levels, the much poorer J values of both P3- and
sc

ACCEPTED MANUSCRIPT
P5-based devices might be due to inefficient charge separation owing to unfavorable phase separation
compared to P4- and P6-based devices, respectively. In view of their identical backbone, it seems that
miscibility with PCBM was largely affected by the shape of the alkoxy side chain rather than the presence
or absence of an additional phenyl ring on phenanthrene. In all cases, the addition of a small amount of
processing additive to the solution, led to finer phase separation of the donor/acceptor blend and higher
Jsc through better exciton dissociation, resulting in enhanced efficiency. The best PDPP copolymer cell
exhibited a PCE of 2.73%, Jsc of 5.97mA/cm2, FF of 58%, and Voc of 0.78 V, which was for P4:PC BM
61
based OSCs with additive treatment.
Figure 4. TEM images of P3:PC BM (a), P4:PC BM (b), P5:PC BM (C) and P6:PC BM (d) spin-
6
1
61
61
61
coated with the help of chlorobenzene solution containing 4 v/v% CN.
4. Conclusion
In conclusion, we have successfully designed and synthesized a series of six phenanthrene-based donor-
acceptor alternating copolymers, P1, P2, P3, P4, P5 and P6, with varying side chains by Suzuki
polymerization for application in organic photovoltaic cells. These polymers showed favorable absorption
in the visible region from 500nm to 780 nm with a low optical bandgap of 1.6 eV and a deep HOMO level
of -5.2 eV. The incorporation of phenyl rings into 9,10-alkoxy phenanthrene, in P5 and P6 produced a
slightly lower absorption coefficient and higher HOMO level but these polymers showed good thermal
stability compared with others. BHJ devices based on copolymers:PC BM, except P1 and P2 which have
61
poor solubility in common organic solvents, showed reasonable V values of around 0.78 V, which is
oc
related to deep HOMO level of polymer. Our result show that the shape of side chain on the conjugated
polymer can affect the nanoscale morphology of the photoactive layer, and this induces variation in the
photocurrent value in PDPP copolymer based photovoltaic devices regardless of whether the polymer
bears a phenyl ring or not. Of all the devices, P4-based cells exhibited the best PCE of 2.73% reflecting its
−
2
higher J of 5.4 mAcm due to better phase separation as a consequence of the addition of 4 vol% CN, as
sc

ACCEPTED MANUSCRIPT
a processing additive.
AUTHOR INFORMATION
Corresponding Author
E-mail: kimdy@gist.ac.kr
ACKNOWLEDGMENT
This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea
government (NRF-2015R1A2A1A10054466) the Korea Institute of Energy Technology Evaluation and
Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No.
20153010012110). The GIXD was measured using the synchrotron radiation sources 9A beamline at the Pohang
Accelerator Laboratory (PAL).
REFERENCES
[
1]
G. Yu, A.J. Heeger, Charge separation and photovoltaic conversion in polymer composites with internal
donor/acceptor heterojunctions, J. Appl. Phys. 78 (1995) 4510–4515. doi:10.1063/1.359792.
[
2]
G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Polymer Photovoltaic Cellsꢀ: Enhanced Efficiencies via a
Network of Internal Donor-Acceptor Heterojunctions, Science (80-. ). 270 (1995) 1789–1791.
doi:10.1126/science.270.5243.1789.
[
3]
J.J.M. Halls, C.A. Walsh, N.C. Greenham, E.A.. Marseglla, R.H. Frlend, S.C. Morattl, A.B. Holmes, Efficient
Photodiode from Interpenetrating Polymer Networks.pdf, Nature. 376 (1995) 498–500.
doi:doi:10.1038/376498a0.
[
[
[
[
[
[
[
[
4]
5]
F.C. Krebs, Fabrication and processing of polymer solar cells: A review of printing and coating techniques,
Sol. Energy Mater. Sol. Cells. 93 (2009) 394–412. doi:10.1016/j.solmat.2008.10.004.
A.C. Arias, J.D. MacKenzie, I. McCulloch, J. Rivnay, A. Salleo, Materials and applications for large area
electronics: Solution-based approaches, Chem. Rev. 110 (2010) 3–24. doi:10.1021/cr900150b.
6]
7]
F. Yang, S.R. Forrest, Photocurrent generation in nanostructured organic solar cells, ACS Nano. 2 (2008)
1022–1032. http://pubs.acs.org/doi/abs/10.1021/nn700447t.
C. Winder, N.S. Sariciftci, Low bandgap polymers for photon harvesting in bulk heterojunction solar cells, J.
Mater. Chem. 14 (2004) 1077. doi:10.1039/b306630d.
8]
9]
10]
11]
R. Kroon, M. Lenes, J.C. Hummelen, P.W.M. Blom, B. de Boer, Small Bandgap Polymers for Organic Solar
Cells (Polymer Material Development in the Last 5 Years), 2008. doi:10.1080/15583720802231833.
C.A. Junwu, C. Yong, Development of novel conjugated donor polymers for high-efficiency bulk-
heterojunction photovoltaic devices, Acc. Chem. Res. 42 (2009) 1709–1718. doi:10.1021/ar900061z.
D. Gupta, S. Mukhopadhyay, K.S. Narayan, Fill factor in organic solar cells, Sol. Energy Mater. Sol. Cells. 94
(
2010) 1309–1313. doi:10.1016/j.solmat.2008.06.001.
P. Peumans, S. Uchida, S.R. Forrest, Efficient bulk heterojunction photovoltaic cells using small-molecular-

ACCEPTED MANUSCRIPT
weight organic thin films., Nature. 425 (2003) 158–162. doi:10.1038/nature01949.
[
[
[
[
[
[
[
12]
13]
14]
15]
16]
17]
18]
B.C.J. Brabec, A. Cravino, D. Meissner, N.S. Sariciftci, T. Fromherz, M.T. Rispens, L. Sanchez, J.C.
Hummelen, Origin of the Open Circuit Voltage of Plastic Solar Cells, Adv. Funct. Mater. 11 (2001) 374–380.
http://onlinelibrary.wiley.com/doi/10.1002/1616-3028(200110)11:5<374::AID-ADFM374>3.0.CO;2-W/epdf.
A. Gadisa, M. Svensson, M.R. Andersson, O. Inganas, Correlation between oxidation potential and open-
circuit voltage of composite solar cells based on blends of polythiophenes/fullerene derivative, Appl. Phys.
Lett. 84 (2004) 1609–1611. doi:10.1063/1.1650878.
M. Reyes-Reyes, K. Kim, D.L. Carroll, High-efficiency photovoltaic devices based on annealed poly(3-
hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1- phenyl- (6,6) C61 blends, Appl. Phys. Lett. 87 (2005)
13–16. doi:10.1063/1.2006986.
M.-C. Yuan, M.-Y. Chiu, C.-M. Chiang, K.-H. Wei, Synthesis and Characterization of Pyrido[3,4-
b ]pyrazine-Based Low-Bandgap Copolymers for Bulk Heterojunction Solar Cells, Macromolecules. 43 (2010)
6
270–6277. doi:10.1021/ma100522a.
S. Xiao, A.C. Stuart, S. Liu, H. Zhou, W. You, Conjugated polymer based on polycyclic aromatics for bulk
heterojunction organic solar cells: A case study of quadrathienonaphthalene polymers with 2% efficiency,
Adv. Funct. Mater. 20 (2010) 635–643. doi:10.1002/adfm.200901407.
M. Svensson, F. Zhang, S.C. Veenstra, W.J.H. Verhees, J.C. Hummelen, J.M. Kroon, O. Inganäs, M.R.
Andersson, High-performance polymer solar cells of an alternating polyfluorene copolymer and a fullerene
derivative, Adv. Mater. 15 (2003) 988–991. doi:10.1002/adma.200304150.
H. Cha, H. Kong, D.S. Chung, W.M. Yun, T.K. An, J. Hwang, Y.H. Kim, H.K. Shim, C.E. Park, Thermally
stable amorphous polymeric semiconductors containing fluorene and thiophene for use in organic
photovoltaic cells, Org. Electron. Physics, Mater. Appl. 11 (2010) 1534–1542. doi:10.1016/j.orgel.2010.06.009.
[
[
19]
N. Blouin, A. Michaud, M. Leclerc, A low-bandgap poly(2,7-carbazole) derivative for use in high-
performance solar cells, Adv. Mater. 19 (2007) 2295–2300. doi:10.1002/adma.200602496.
20]
N. Allard, R.B. Aïch, D. Gendron, P.L.T. Boudreault, C. Tessier, S. Alem, S.C. Tse, Y. Tao, M. Leclerc,
Germafluorenes: New heterocycles for plastic electronics, Macromolecules. 43 (2010) 2328–2333.
doi:10.1021/ma9025866.
[
[
[
[
[
[
21]
H. Tian, J. Shi, S. Dong, D. Yan, L. Wang, Y. Geng, F. Wang, Novel highly stable semiconductors based on
phenanthrene for organic field-effect transistors., Chem. Commun. (2006) 3498–3500. doi:10.1039/b606759j.
22]
23]
24]
25]
26]
C. Yang, H. Scheiber, E.J.W. List, J. Jacob, K. Mu, Polyphenylene and Poly ( phenylenevinylene ) Analogues,
Macromolecules. 39 (2006) 5213–5221.
B.N. Boden, K.J. Jardine, A.C.W. Leung, M.J. MacLachlan, Tetraalkoxyphenanthrene: A new precursor for
luminescent conjugated polymers, Org. Lett. 8 (2006) 1855–1858. doi:10.1021/ol060433s.
R. Grisorio, G.P. Suranna, P. Mastrorilli, A Versatile Synthesis for New 9 , 10- Useful Precursors for
Conjugated Polymers, Org. Lett. 9 (2007) 3149–3152.
S. Qu, H. Tian, Diketopyrrolopyrrole (DPP)-based materials for organic photovoltaics, Chem. Commun. 48
(
2012) 3039. doi:10.1039/c2cc17886a.
L. Huo, J. Hou, H.Y. Chen, S. Zhang, Y. Jiang, T.L. Chen, Y. Yang, Bandgap and molecular level control of
the low-bandgap polymers based on 3,6-dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione toward
highly efficient polymer solar cells, Macromolecules. 42 (2009) 6564–6571. doi:10.1021/ma9012972.
[
27]
J.C. Bijleveld, V.S. Gevaerts, D. Di Nuzzo, M. Turbiez, S.C.J. Mathijssen, D.M. De Leeuw, M.M. Wienk, R.A.J.
Janssen, Efficient solar cells based on an easily accessible diketopyrrolopyrrole polymer, Adv. Mater. 22

ACCEPTED MANUSCRIPT
(
2010) 3–7. doi:10.1002/adma.201001449.
[
[
[
28]
29]
30]
Y. Qin, Alginate fibers: an overwiew of the production processes and applications in wound management,
Polym. Int. 57 (2008) 171–180. doi:10.1002/pi.
A.P. Zoombelt, S.G.J. Mathijssen, M.G.R. Turbiez, M.M. Wienk, R. a. J. Janssen, Small band gap polymers
based on diketopyrrolopyrrole, J. Mater. Chem. 20 (2010) 2240. doi:10.1039/b919066j.
J. Lee, M. Kim, B. Kang, S.B. Jo, H.G. Kim, J. Shin, K. Cho, Side-chain engineering for fine-tuning of energy
levels and nanoscale morphology in polymer solar cells, Adv. Energy Mater. 4 (2014) 1–12.
doi:10.1002/aenm.201400087.
[
31]
V.D. Mihailetchi, H. Xie, B. De Boer, L.J.A. Koster, P.W.M. Blom, Charge transport and photocurrent
generation in poly(3-hexylthiophene): Methanofullerene bulk-heterojunction solar cells, Adv. Funct. Mater.
16 (2006) 699–708. doi:10.1002/adfm.200500420.
[
[
32]
33]
M. Zhang, X. Guo, W. Ma, H. Ade, J. Hou, A polythiophene derivative with superior properties for practical
application in polymer solar cells, Adv. Mater. 26 (2014) 5880–5885. doi:10.1002/adma.201401494.
K. Cao, Z. Wu, S. Li, B. Sun, G. Zhang, Q. Zhang, A low bandgap polymer based on isoindigo and
bis(dialkylthienyl) benzodithiophene for organic photovoltaic applications, J. Polym. Sci. Part A Polym.
Chem. 51 (2013) 94–100. doi:10.1002/pola.26275.
[
[
34]
35]
L. Wang, D. Cai, Q. Zheng, C. Tang, S. Chen, Z. Yin, Low Band Gap Polymers Incorporating a Dicarboxylic
Imide-Derived Acceptor Moiety for E ffi cient Polymer Solar Cells, ACS Macro Lett. (2013) 8–11.
N. Wang, Z. Chen, W. Wei, Z. Jiang, Fluorinated benzothiadiazole-based conjugated polymers for high-
performance polymer solar cells without any processing additives or post-treatments, J. Am. Chem. Soc. 135
(
2013) 17060–17068. doi:10.1021/ja409881g.
[
[
36]
37]
J. Yuan, X. Huang, F. Zhang, J. Lu, Z. Zhai, C. Di, Z. Jiang, W. Ma, Design of benzodithiophene-
diketopyrrolopyrrole based donor–acceptor copolymers for efficient organic field effect transistors and
polymer solar cells, J. Mater. Chem. 22 (2012) 22734. doi:10.1039/c2jm34004f.
L.J. Lindgren, F. Zhang, M. Andersson, S. Barrau, S. Hellström, W. Mammon, E. Perzpn, O. Inganäs, M.R.
Andersson, Synthesis, characterization, and devices of a series of alternating copolymers for solar cells,
Chem. Mater. 21 (2009) 3491–3502. doi:10.1021/cm802949g.
[
[
[
38]
39]
40]
H. Hoppe, N.S. Sariciftci, Morphology of polymer/fullerene bulk heterojunction solar cells, J. Mater. Chem.
16 (2006) 45–61. doi:10.1039/b510618b.
T. Stübinger, W. Brütting, Exciton diffusion and optical interference in organic donor-acceptor
photovoltaic cells, J. Appl. Phys. 90 (2001) 3632–3641. doi:10.1063/1.1394920.
M. Theander, A. Yartsev, D. Zigmantas, V. Sundström, W. Mammo, M. Andersson, O. Inganäs,
Photoluminescence quenching at a polythiophene/C60 heterojunction, Phys. Rev. B. 61 (2000) 12957–12963.
doi:10.1103/PhysRevB.61.12957.

ACCEPTED MANUSCRIPT
Supporting information
Development of New D-A Type Polymer based on
Phenanthrene Derivatives for Polymer Solar Cells
a
a
a
a
b
b
Yeong-A Kim , Kyeong-Il Hwang , Minji Kang , Nam-Koo Kim , Soo-young Jang , In-Bok Kim , Juhwan
c
a,b,*
Kim and Dong-Yu Kim
a
School of Materials Science & Engineering, Gwangju Institute of Science and Technology (GIST), 123
Cheomdangwagi-ro, Buk-gu, Gwangju 61002, Republic of Korea
b
Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology
(
GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61002, Republic of Korea
c
Department of Chemical Engineering and Materials Science, University of California-Irvine, Irvine,
California, 92697, United States
kimdy@gist.ac.kr
*

ACCEPTED MANUSCRIPT
Table S1. Performance of the top-gate bottom-contact OFET devices before and after thermal annealing
o
at 250 C for 30 min.
o
Pristine
annealed at 250 C
h
e
h
e
μ
V
th
μ
V
th
μ
V
th
μ
V
th
polymer
2
-1 -1
2
-1 -1
2
-1 -1
2
-1 -1
[
cm V s ]
[V]
-6.42
-8.51
-11.4
-12.4
[cm V s ]
[V]
[cm V s ]
[V]
[cm V s ]
[V]
-
3
3
-5
-3
-4
P3
P4
P5
P6
1.14 × 10
1.14 × 10
2.58 × 10
55.36
52.31
57.39
57.44
3.25 × 10
-36.31
-24.61
-40.25
-34.56
4.47 × 10
55.36
52.06
52.38
52.42
-
-4
-3
-3
4.47 × 10
1.38 × 10
2.52 × 10
-3
-4
-3
-3
1.28 × 10
1.93 × 10
9.90 × 10
2.12 × 10
-
4
-5
-3
-4
9.67 × 10
6.33 × 10
3.92 × 10
5.1 ×10

ACCEPTED MANUSCRIPT
o
Figure S1. TGA plots of P3 (black), P4 (red), P5 (blue) and P6 (green) at a heating rate of 10 C/min under
a nitrogen atmosphere (a). DSC trace of P3 (black), P4 (red), P5 (blue) and P6 (green) in the
temperature range from 55 °C to 290 °C (b).

ACCEPTED MANUSCRIPT
Figure S2. Normalized UV-Vis absorption spectra of P1 (black) and P2 (red) in chloroform (a) and
absorption coefficient in a thin film state (b). Cyclic voltammograms of P1 (black) and P2 (red) films on a
platinum electrode measured with 0.1 mol/L tetrabutyl ammonium perchlorate acetonitrile solutions at a
scan rate of 50 mV/s (c).

ACCEPTED MANUSCRIPT
Figure S3. Out-of-plane and in-plane (insets) XRD patterns of thin films of P3 (a), P4 (b), P5 (c) and P6
(
d) on Si/SiO2 substrates.

ACCEPTED MANUSCRIPT
o
Figure S4. Transfer curves of P3 (a), P4 (b), P5 (c) and P6 (d) based OFETs devices annealed at 250 C for
3
0 min in a glove box under nitrogen atmosphere.

ACCEPTED MANUSCRIPT
o
Figure S5. Output curves of P3 (a), P4 (b), P5 (c) and P6 (d) based OFETs devices annealed at 250 C for
3
0 min in a glove box under nitrogen atmosphere.

ACCEPTED MANUSCRIPT
Figure S6. TEM images of P3:PC BM (a), P4:PC BM (b), P5:PC BM (C) and P6:PC BM (d) in
61
61
61
61
chlorobenzene.

ACCEPTED MANUSCRIPT
Highlights (for review)
★
★
★
D-A type copolymers based on phenanthrene were synthesized for organic electronics.
Film morphology was highly affected by solubilizing groups on polymers.
Phenyl rings produced a lower absorption coefficient and higher HOMO level.