Side chain modification: An effective approach to modulate the energy level of benzodithiophene based polymers for high-performance solar cells

Article abstract of DOI:10.1039/c5ta05096k

Over the past few years, it has been proven that deepening the highest occupied molecular orbital (HOMO) levels of conjugated polymers is one of the most successful strategies to develop novel materials for high performance bulk heterojunction polymer solar cells. Here we report an effective approach of side chain modification in a donor moiety to modulate the highest occupied molecular orbital (HOMO) energy level of benzo[1,2-b:4,5-b′]dithiophene (BDT) based two-dimensional conjugated polymers and hence obtain improved power conversion efficiency. Through the introduction of 2,3-dioctylthienyl groups instead of conventional 2-ethylhexylthienyl groups as side chains in the 4,8-positions of the BDT moiety, four mono-fluorinated quinoxaline based alternating polymers: poly{4,8-di(2-ethylhexylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-b′]dithiophene-alt-5,5-[5′,8′-di-2-thienyl-(6′-fluoro-2′,3′-bis(3″-octyloxyphenyl)quinoxaline)]} (PBDTTFTQ-EH), poly{4,8-di(2-ethylhexythiophene-5-yl)-2,6-benzo[1,2-b:4,5-b′]dithiophene-alt-5,5-[5′,8′-di-2-thienyl-(6′-fluoro-2′,3′-bis(5″-octylthiophen-2″-yl)quinoxaline)]} (PBDTTFTTQ-EH), poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-b′]dithiophene-alt-5,5-[5′,8′-di-2-thienyl-(6′-fluoro-2′,3′-bis-(3″-octyloxyphenyl)-quinoxaline)]} (PBDTTFTQ-DO) and poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-b′]dithiophene-alt-5,5-[5′,8′-di-2-thienyl-(6′-fluoro-2′,3′-bis(5″-octylthiophen-2″-yl)quinoxaline)]} (PBDTTFTTQ-DO) were synthesized, in which the former two EH-based polymers contain the 2-ethylhexylthienyl side chain and the latter two DO-based polymers contain the 2,3-dioctylthienyl side chain. The results clearly indicated that the variation in the side chain of the BDT unit from the 2-ethylhexylthienyl group to the 2,3-dioctylthienyl group can cause a deep HOMO level and slightly enlarged bandgap of the polymer. Consequently, polymer solar cells from PBDTTFTQ-DO and PBDTTFTTQ-DO showed high V_ocs of 0.88 V and 0.85 V, while those of 0.78 V and 0.72 V were observed in PBDTTFTQ-EH and PBDTTFTTQ-EH based devices, respectively. Both polymers deliver high power conversion efficiency (PCE) exceeding 6.8%, with an outstanding efficiency of 7.61% and an excellent fill factor (FF) of 75.9% for PBDTTFTQ-DO after tetrahydrofuran solvent vapour annealing for 30 s (while a PCE of 7.29% for PBDTTFTQ-EH). Similar results were investigated in PBDTTFTTQ-EH (a PCE of 6.82%) and PBDTTFTTQ-DO (a PCE of 7.25% with high FF of 75.7%) based solar cells. This finding should provide valuable guidelines for the design and synthesis of novel polymer donor materials for highly efficient polymer solar cells via fine tuning of the molecular energy levels and absorption spectra through a modulation of the side chain onto the donor moiety.

Full text of DOI:10.1039/c5ta05096k

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DOI: 10.1039/C5TA05096K
Journal of Materials Chemistry A
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Side Chain Modification: An Effective Approach to Modulate the
Energy Level of Benzodithiophene Based Polymer for High-
Performance Solar Cells ‡
Received 00th January 20xx,
Accepted 00th January 20xx
Haimei Wu,a, † Baofeng Zhao,a, b, † Weiping Wang,a Zhaoqi Guo,a Wei Wei, c Zhongwei An,a Chao
Gao,a,* Hui Chen,b Biao Xiao,b Yuan Xie, b Hongbin Wu,b,* Yong Caob
DOI: 10.1039/x0xx00000x
www.rsc.org/
In the past few years, it had been proven that deepening the highest occupied molecular orbital (HOMO) levels of
conjugated polymer is one of the most successful strategies to develop novel materials for high performance bulk
heterojunction polymer solar cells. Here we report an effective approach of side chain modification in donor moiety to
modulate the highest occupied molecular orbital (HOMO) energy level of benzo[1,2-b:4,5-b']dithiophene (BDT) based two-
dimensional conjugated polymers and hence obtained improved power conversion efficiency. Through introduction 2,3-
dioctylthienyl groups instead of conventional 2-ethylhexylthienyl groups as side chain in 4,8-positions of BDT moiety, four
mono-fluorinated quinoxaline based alternating polymers: poly{4,8-di(2-ethylhexylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-
b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-fluoro-2’,3’-bis(3’’-octyloxyphenyl)quinoxaline)]} (PBDTTFTQ-EH), poly{4,8-
di(2-ethylhexythiophene-5-yl)-2,6-benzo[1,2-b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-fluoro-2’,3’-bis(5’’-
octylthiophen-2’’-yl)quinoxaline)]}
(PBDTTFTTQ-EH),
poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-
(PBDTTFTQ-DO) and
b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-fluoro-2’,3’-bis-(3’’-octyloxyphenyl)-quinoxaline)]}
poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-fluoro-2’,3’-bis(5’’-
octylthiophen-2’’-yl)quinoxaline)]} (PBDTTFTTQ-DO) were synthesized, in which the former two EH-based polymers using
2-ethylhexylthienyl side chain and the latter two DO-based polymers containing 2,3-dioctylthienyl side chain. The results
clearly indicated that the variation in the side chain of BDT unit from 2-ethylhexylthienyl group to 2,3-dioctylthienyl group
can cause deep HOMO level and slightly enlarged bandgap of the polymer. Consequently, polymer solar cells from
PBDTTFTQ-DO and PBDTTFTTQ-DO showed high Voc of 0.88 V and 0.85 V, while that of 0.78 V and 0.72 V were observed in
PBDTTFTQ-EH and PBDTTFTTQ-EH based devices, respectively. Both polymers deliver high power conversion efficiency
(PCE) exceeding 6.8%, with an outstanding efficiency of 7.61% and an excellent filled factor (FF) of 75.9% for PBDTTFTQ-
DO after tetrahydrofuran solvent vapour annealing 30 sec (while PCE of 7.29% for PBDTTFTQ-EH). Similar results were
investigated in the PBDTTFTTQ-EH (PCE of 6.82%) and PBDTTFTTQ-DO (PCE of 7.25% with high FF of 75.7%) based solar
cells. This finding should provide valuable guideline for the design and synthesis of novel polymer donor materials for
highly efficient polymer solar cells via fine tuning the molecular energy levels and absorption spectra through a
modulation of the side chain onto the donor moiety.
developments of the synthesis of novel photoactive materials
and their successful applications in high performance PSCs, [5-8]
however, the relatively lower power conversion efficiency
1. INTRODUCTION
Bulk heterojunction (BHJ) polymer solar cells (PSCs) have
attracted much attention due to their advantages of low-cost,
(PCE) of PSCs when compared with their inorganic counterpart
still represent some limitations toward commercialization and
lightweight energy sources over large area size on flexible
[1-4]
widespread utilization. There are many factors limiting the
[9,10]
substrates.
In recent years, it witnessed the rapid
performance of BHJ solar cells,
in which the polymer
electron donor materials play an important role in the whole
performances of the device. Ideally, polymers should possess a
broad absorption (small bandgap) to ensure effective
harvesting of the solar photons and high hole mobility for
charge transport. Furthermore, suitable energy levels of the
polymers are required to match those of the fullerene
derivatives so that excitons (bound electron-hole pairs) can
readily dissociate at the donor–acceptor (D/A) interface to
produce separated charge carriers. That is, a low-lying highest
a.Centre of Optoelectronic Materials, Xi’an Modern Chemistry Research Institute,
Xi’an, 710065, China. E-Mail:chaogao1974@hotmail.com (C. Gao).
b.Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory
of Luminescent Materials and Devices, South China University of Technology,
Guangzhou, 510640, China. E-Mail: hbwu@scut.edu.cn (H. Wu).
c. Nanjing University of Posts and Telecommunications, Nanjing, 210003, China.
† These authors contributed equally to this work.
‡
Electronic Supplementary Information (ESI) available: 1H NMR and 13C NMR
spectra of monomers, TGA plot, absorption spectra of the solutions, SCLC results, J-
V characteristics of the polymer:PC71BM devices. This material is available free of
charge via the Internet at http://pubs.acs.org.. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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occupied molecular orbital (HOMO) energy level to provide a electron-withdrawing moiety to build the D-A polymers, due to
large open-circuit voltage (Voc) and suitable lowest their excellent electron-deficient N-heterocycle structure and
unoccupied molecular orbital (LUMO) energy level to ensure facile synthesis process. [19-23] The structures of the mentioned
enough offset for the charge separation. [11,12]
alternating polymers: poly{4,8-di(2-ethylhexylthiophene-5-yl)-
a
Based on these considerations, much effort have been done 2,6-benzo[1,2-b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-
to tune the optical bandgaps, molecular energy levels and (6’-fluoro-2’,3’-bis(3’’-octyloxyphenyl)quinoxaline)]}
carrier mobilities by incorporating electron-rich (donor) units
with the electron-withdrawing (acceptor) units in one benzo[1,2-b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-
conjugated polymer. variety of donor-acceptor (D-A) fluoro-2’,3’-bis(5’’-octylthiophen-2’’-yl)quinoxaline)]}
polymers that can deliver promising performances have been PBDTTFTTQ-EH), poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-
developed and successfully been used as donor materials in benzo[1,2-b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-
(
PBDTTFTQ-EH)
,
poly{4,8-di(2-ethylhexythiophene-5-yl)-2,6-
A
(
[13]
PSCs.
To further deepen the HOMO levels of the polymer fluoro-2’,3’-bis-(3’’-octyloxyphenyl)-quinoxaline)]} (PBDTTFTQ-
and achieve enhanced device performances, strong electron DO) and poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-benzo[1,2-
deficient groups such as ketone groups, sulfonyl groups and b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-thienyl-(6’-fluoro-2’,3’-
fluorine atoms were introduced into the acceptor (A) units in bis(5’’-octylthiophen-2’’-yl)quinoxaline)]}
(PBDTTFTTQ-DO)
the polymers. [14] For instance, significant progress has been were shown in Scheme 1, in which the former two EH-based
achieved by deepening the HOMO levels of benzo[1,2-b:4,5- polymers using 2-ethylhexylthienyl side chain and the latter
b']dithiophene (BDT)-based conjugated polymers through the two DO-based polymers containing 2,3-dioctylthienyl side
substitution of fluorine atoms on various acceptor units, chain. It is worthy to note that the PBDTTFTQ-DO and
resulting in a high Voc and PCE in PSCs in comparison with the PBDTTFTTQ-DO possess both deeper HOMO energy levels and
corresponding non-fluorinated derivatives in the past few slightly larger bandgaps in comparison with those of
years. [15]
PBDTTFTQ-EH and PBDTTFTTQ-EH. With the conventional BHJ
To ensure good solubility and processability of the polymer solar cell device structure, the devices based on
conjugated polymers donor for film fabrication, in most cases, PBDTTFTQ-EH and PBDTTFTTQ-EH exhibited remarkable PCEs
2-ethylhexyloxy groups were usually introduced to the 4,8- of 7.29% and 6.82% with corresponding Voc of 0.78V and
position of BDT units to build the corresponding polymers. 0.72V, while PBDTTFTQ-DO and PBDTTFTTQ-DO-based devices
Furthermore, alkylthienyl substituted BDT, especially 2- showed excellent results of 7.61% and 7.25% with higher Voc of
ethylhexylthienyl substituted BDT were designed as electron- 0.88V and 0.85V.
rich unit and applied in constructing two-dimensional (2D)
conjugated polymers for high performance photovoltaic
2. EXPERIMENTAL SECTION
devices because the thienyl-substitution is helpful to broaden
the absorption band, lower the HOMO level and improve the
[16]
hole mobility of the related copolymers.
Although many
2.1 Materials
routes have been developed to tailor the energy levels and
bandgaps through modification the acceptor of the BDT-based
2D conjugated polymers, there are seldom attempts to
modulate the molecular energy level by fine adjusting the
flexible side chain (alkyl group or alkoxy groups) on the BDT
moiety.[17] It should be noted that the electron affinity of the
flexible side chains affect both HOMO and LUMO levels of the
2D conjugated polymers. In addition, the steric hindrance of
All chemicals and solvents were purchased from Aldrich or
Alfa
&
Aesar. Tetrahydrofuran (THF) is dried over
Na/benzophenone ketyl and freshly distilled prior to use. 5,8-
Bis(5-bromothiophen-2-yl)-6-fluoro-2,3-bis(3-
[24,25]
octyloxy)phenyl)quinoxaline (3)
and 1,2-bis(5-
were synthesized
[26]
octylthiophen-2-yl)ethane-1,2-dione (5)
according to the literatures. 2,6-Bis(trimethyltin)-4,8-di(2(2-
ethylhexyl)thiophen-5-yl)-benzo[1,2-b:4,5-b’]dithiophene (2a)
[16a]
long alkyl or alkoxy chains may decrease the
π-conjugation
and 2,6-bis(trimethyltin)-4,8-di(2,3-dioctylthiophen-5-yl)-
degree of the polymer backbone to some extent.
Consequently, the flexible side chains on the 2D conjugated
BDT moiety play an important role not only in the aspect of
solubility but also in their optical and electrical properties.
Recently, to tune the molecular energy levels of the polymers,
researchers have devoted to finely modify the flexible side
chains of the 2D conjugated BDT moiety by replacing the 2-
ethylhexylthienyl group with meta-alkoxy-phenyl unit, as
benzo[1,2-b:4,5-b’]dithiophene (2b) [27] were prepared through
an modification routine of the references. The synthetic routes
of monomers and polymers are shown in Scheme 1
4,8-Di(2-(2-ethylhexyl)thiophen-5-yl)-benzo[1,2-b:4,5-
b’]dithiophene 1a and 4,8-Di(2,3-dioctylthiophen-5-yl)-
benzo[1,2-b:4,5-b’]dithiophene 1b). 2-Ethylhexylthiophene
.
(
)
(
(3.92 g, 20 mmol) was dissolved in anhydrous THF (60 ml)
under an argon atmosphere, the solution was cooled to 0 oC in
an ice water bath, and n-BuLi (2.5 M, 20 mmol) was added
slowly dropwise to the mixture, then the reaction was heated
and kept at 50 oC for 1 h. Subsequently, 4,8-dehydrobenzo[1,2-
b:4,5-b’]dithiophene-4,8-dione (1.58 g, 7.22 mmol) was added
and the mixture was stirred at 50 oC for 2 h. After cooling
down to the room temperature, a solution of SnCl2·2H2O (13 g,
expected, the resulting polymer showed deeper HOMO level,
[18]
consequently leading to an enhanced Voc and PCE.
To
modulate the molecular energy levels of BDT based 2D
conjugated polymers through another effective side chain
modification approach, in this paper, two types of alkylthienyl
groups were introduced to the BDT units, meanwhile two
mono-fluorinated quinoxaline derivatives were chosen as the
2 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry A
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R1
S
R2
R1
R2
S
O
O
F
F
F
O
O
F
c
S
S
d
a
b
e
S
Br
S
Br
S
Br
Br
+
Br
H2N
Br
NH2
Sn
Sn
S
S
S
S
S
S
S
S
；
S
N
N
N
N
N
N
C8H17
C8H17
S
S
S
S
S
S
4
5
R2
R1
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
R2
R1
6
7
8
2a: R1=2-ethylhexyl, R2=H
2b: R1=R2=octyl
1a: R1=2-ethylhexyl, R2=H
1b: R1= R2=octyl
C4H9
C2H5
C4H9
C2H5
S
S
F
F
F
F
S
f
S
f
2a
*
*
n
Br
Br
+
Br
2a
Br
+
*
*
；
S
S
S
S
S
S
n
S
S
S
S
N
N
N
N
N
N
N
N
S
S
S
S
S
S
C8H17
O
OC8H17
C8H17
O
OC8H17
C8H17
C8H17
C8H17
C4H9
C8H17
C2H5
C2H5
8
C4H9
3
PBDTTFTQ-EH
PBDTTFTTQ-EH
C8H17
C8H17
C8H17
C8H17
S
F
S
F
F
F
f
Br
Br
2b
f
S
+
S
S
S
2b
Br
+
Br
*
*
n
*
*
S
S
；
S
S
n
S
S
N
N
S
S
N
N
N
N
N
N
S
S
S
S
S
S
C8H17
O
OC8H17
C8H17
C8H17
C8H17O
OC8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
8
3
PBDTTFTQ-DO
PBDTTFTTQ-DO
o
o
Scheme 1. The synthetic routes of the polymers. (a) n-BuLi, THF, 0 C, then 50 C; SnCl2·2H2O, 10% HCl aq. (b) n-BuLi, 0 oC,then
room temperature; Me3SnCl, 0 C, room temperature. (c) CH3COOH. (d) Pd(PPh3)2Cl2, toluene. (e) NBS, THF. (f) Pd2(dba)3, P(o-
Tol)3, toluene.
o
57.52 mmol) in 10% hydrochloric acid (17 ml) was added, b’]dithiophene (2b). Compound 1a (5.8 g, 10 mmol) was
and the reaction was stirred for additional 2 h. The mixture dissolved in anhydrous THF (80 mL) under the protection of
o
was extracted with ethyl acetate and organic phase was argon. The solution was cooled to 0 C and n-BuLi (2.5 M , 24
washed with brine and dried over MgSO4. The crude was mmol) was added dropwise to the mixture. Then the reaction
purified by silica gel chromatography using hexane as eluent to was warmed to ambient temperature and stirred for 2 h,
afford compound 1a (2.28 g) as a viscous liquid in yield 53.5 %. SnMe3Cl (5.5 g, 27.6 mmol) was quickly added in one portion
1H NMR (CDCl3, 500 MHz) δ(ppm): 7.68(d, 2H), 7.44 (d, 2H), at
0
oC, and then the mixture was warmed to room
7.34 (d,2H), 6.93 (d, 2H), 2.87 (d, 4H), 1.75 (m, 2H), 1.51–1.17 temperature and stirred for 6 h. The reactant was poured into
(br, 16H), 0.92–0.85 (m, 12H). 13C NMR (CDCl3, 125 MHz) water and extracted with hexane and the organic layer was
δ(ppm): 145.21, 139.07, 137.49, 136.46, 127.61, 127.30, washed with brine and dried over MgSO4. The residue was
125.30, 124.03, 123.29, 41.55, 34.33, 32.55, 29.43, 25.83, recrystallized with isopropanol for three times and afforded
1
yellow green crystal (5.54 g, 61.5% ). H NMR (CDCl3, 500MHz)
23.06, 15.67, 11.02.
For compound 1b. The synthetic route was the same as δ(ppm): 7.68 (s, 2H), 7.35 (d, 2H), 6.89 (d, 2H), 2.88 (d, 4H),
compound 1a. (2.97g ,51.2%). 1H NMR (CDCl3, 500MHz) 1.74 (m, 2H), 1.57–1.33 (br, 16 H), 0.94 (m, 12H), 0.42 (s, 18H).
δ(ppm): 7.70 (d, 2H), 7.45 (d, 2H), 7.22 (s, 2H), 2.82 (t, 4H), 13C NMR (CDCl3, 125MHz) δ(ppm): 145.37, 143.29, 142.22,
2.61 (t, 4H), 1.73 (dt, 4H), 1.65 (dt, 4H), 1.39 (m, 40H), 0.90 (td, 138.01, 137.31, 131.18, 127.55, 125.30, 122.42, 41.57, 34.24,
12H). 13C NMR (CDCl3, 125 MHz) δ(ppm): 140.19, 138.84, 32.52, 28.98, 25.82, 23.04, 15.41, 10.99, -8.35. Anal. calcd for
138.13, 136.35, 135.08, 129.86, 127.29, 124.13, 123.61, 77.29, C40H58S4Sn2(%): C 53.11, H 6.46; Found (%): C 52.82, H 6.45.
77.04, 76.79, 31.95, 31.93, 31.88, 30.87, 29.57, 29.55, 29.44,
29.38, 29.31, 28.34, 28.03, 22.74, 14.25.
For compound 2b. The synthetic route was the same as
1
compound 2a. (6.21g, 55%). H NMR (CDCl3, 500MHz) δ(ppm):
2,6-Bis(trimethyltin)-4,8-di(2(2-ethylhexyl)thiophen-5-yl)-
7.73 (s, 2H), 7.23 (s, 2H), 2.84 (t, 4H), 2.62 (m, 4H), 1.75 (dt,
benzo[1,2-b:4,5-b’]dithiophene (2a) and 2,6-Bis(trimethyltin)- 4H), 1.67 (m, 4H), 1.46 (dt, 8H), 1.34 (m, 32H), 0.89 (m, 12H),
0.40 (m, 18H). 13C NMR (CDCl3, 125 MHz) δ(ppm): 139.81,
4,8-di(2,3-dioctylthiophen-5-yl)-benzo[1,2-b:4,5-
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137.99, 137.18, 135.76, 131.42, 129.82,122.49, 31.97, 31.91, overnight and afforded PBDTTFTQ-EH (110 mg) as purple-black
31.84, 30.85, 29.62, 29.53, 29.46, 29.35, 29.32, 28.34, 28.05, fiber in yield 86%. GPC (tetrahydrofuran, polystyrene
22.70, 14.14, -6.87, -6.94, -8.35, -9.76, -9.82. Anal. calcd for standard): Mn=64.74 kDa, Mw=181.08 kDa, PDI=2.79.
C56H90S4Sn2 (%): C 59.58, H 8.03; Found (%): C 59.31, H 8.01.
PBDTTFTQ-EH: 1H NMR (CDCl3, 500MHz) δ(ppm): 7.93-7.49(br,
5,8-dibromo-6-fluoro-2,3-bis(5-octylthiophen-2-
7H), 7.02-6.67(br, 12H), 3.72(m, 4H), 2.96(m, 4H), 1.74-1.57
yl)quinoxaline (6) 3,6-dibromo-4-fluorobenzene-1,2-diamine (br, 26H), 1.28-1.23(br, 16H), 0.91(m, 18H). Anal. calcd for
(4) (2.84 g, 10 mmol) and 1,2-bis(5-octylthiophen-2-yl)ethane- C78H87FN2O2S6 (%): C 72.29, H 6.77, N 2.16; Found (%): C 72.03,
1,2-dione (5) (4.46 g,10 mmol) were dissolved in acetic acid H 8.02, N 2.00.
o
(300 ml), the mixture was briefly warmed to 60 C and stirred
For PBDTTFTQ-DO. This polymer was synthesized according
for 10 min, then stirred at room temperature for 2 h. The to the same route as that for PBDTTFTQ-EH. (128 mg, 84.7%).
precipitate was collected by filtration, washed with ethanol, GPC (tetrahydrofuran, polystyrene standard): Mn=75.96 kDa,
1
and dried to afford 5,8-dibromo-6-fluoro-2,3-bis (5- Mw=250.07 kDa, PDI=3.29. H NMR (CDCl3, 500MHz) δ(ppm):
octylthiophen-2-yl)quinoxaline (6) (6.28 g) as a yellow solid in 8.01 (s, 1H), 7.84 (s, 2H), 7.45-7.31 (br, 4H), 7.19-7.06(br, 6H),
yield 90.5%. 1H NMR(500 MHz, CDCl3) δ(ppm): 7.79 (d, 1H, 7.02-6.86 (br, 4H), 3.74(m, 4H), 2.78(m, 8H), 1.84-1.63 (br,
J=5Hz), 7.41 (dd, 2H, J=5Hz), 6.72 (m, 2H), 2.87 (t, 4H, J=7.5Hz), 12H), 1.41-1.14(br, 60H), 0.89(m, 18H). Anal. calcd for
1.75 (m, 4H), 1.42-1.25 (m, 20H), 0.89 (t, 6H, J=5Hz). 13C NMR C94H119FN2O2S6 (%): C 74.26, H 7.89, N 1.84; Found (%): C
(125 MHz, CDCl3) δ(ppm): 160.01, 158.06, 151.87, 147.73, 73.66, H 8.03, N 1.57.
For PBDTTFTTQ-EH. This polymer was synthesized basing on
compound and compound 2a according to the same route as
that for PBDTTFTQ-EH with high yield (82.3%). GPC
135.45, 130.13, 124.91, 122.58, 58.48, 31.90, 31.51, 30.43,
29.22, 22.66, 18.44, 14.11. Anal. calcd for C32H39Br2FN2S2 (%): C
55.33, H 5.66, N 4.03; Found (%):C 55.46, H 5.64, N 3.98.
5,8-bis(5-bromothiophen-2-yl)-6-fluoro-2,3-bis(5-
8
a
(tetrahydrofuran, polystyrene standard): Mn=18.45 kDa,
Mw=101.38 kDa, PDI=5.49. H NMR (CDCl3, 500MHz) δ(ppm):
1
octylthiophen-2-yl)quinoxaline (8). A mixture of compound 6
(3.48 g, 5 mmol), tributyl(thiophen-2-yl)stannane (4.10 g, 11
mmol), dichlorobis-(triphenylphosphine)palladium(II) (0.14 g)
and toluene (150 ml) were heated under reflux overnight. It
was then cooled and the toluene was removed under reduced
pressure and the residue was recrystallized by hexane and
obtained compound 7 (2.87 g) in 82% yield. To a suspension of
compound 7 (0.70 g, 1 mmol) in THF (30 ml) was added NBS
(0.37 g, 2.1 mmol), the mixture was heated at 40 oC for 3 h and
poured into methanol, the precipitate was collected by
filtration and purified by column chromatography on silica gel
using hexane/ethyl acetate (100:1) as eluent to afford
compound 5,8-bis(5-bromothiophen-2-yl)-6-fluoro-2,3-bis(5-
octylthiophen-2-yl)quinoxaline (8) (0.56 g) in yield 65%. 1H
NMR (500 MHz, CDCl3) δ(ppm): 7.70 (m, 2H), 7.48 (d, 1H,
J=5Hz), 7.39 (dd, 2H, J=5Hz), 7.11 (dd, 2H, J=5Hz), 6.73 (d, 2H,
J=3Hz), 2.91 (t, 4H, J=5Hz), 1.79 (m, 4H), 1.37-1.26 (m, 20H),
0.90 (t, 6H, J=5Hz). 13C NMR (CDCl3, 125MHz) δ(ppm):159.68,
157.67, 151.87, 145.67, 138.36, 132.94, 130.35, 129.24, 126.35,
124.80, 117.94, 115.39, 58.50, 31.92, 31.50, 30.45, 29.26,
22.71, 18.46, 14.15. Anal. calcd for C40H43Br2FN2S4 (%): C 55.94,
H 5.05, N 3.26; Found (%):C 56.21, H 5.05, N 3.12.
7.92-7.36 (br, 7H), 7.15-6.40 (br, 8H), 2.89 (m, 8H), 1.88-1.65
(br, 8H), 1.46-1.20(br, 34H), 0.92(m, 18H). Anal. calcd for
C74H83FN2S8 (%): C 69.66, H 6.56, N 2.20; Found (%): C 69.11, H
6.70, N 1.95.
For PBDTTFTTQ-DO
.
This polymer was synthesized
according to the similar route as that for PBDTTFTTQ-EH with a
high yield of 88.5%. GPC (tetrahydrofuran, polystyrene
standard): Mn=135.95 kDa, Mw=863.63 kDa, PDI=6.35. 1H NMR
(CDCl3, 500MHz) δ(ppm): 7.93 (s, 1H), 7.77-7.34 (br, 6H), 7.17-
6.96(br, 2H), 6.84-6.60 (br, 2H), 3.28-2.24(m, 12H), 1.99-1.63
(br, 12H), 1.44-1.16(br, 60H), 0.89(m, 18H). Anal. calcd for
C90H115FN2S8 (%): C 72.04, H 7.73, N 1.87; Found (%): C 72.31, H
7.77, N 1.93.
2.2 Measurements
All compounds were characterized by nuclear magnetic
resonance spectra (NMR) recorded on a Bruker AV 500
spectrometer in CDCl3 at room temperature. Molecular
weights and distributions of the copolymers were estimated by
gel permeation chromatography (GPC) method, THF as eluent
and polystyrene as standard. The absorption spectra were
determined by a Unico UV-2102 scanning spectrophotometer.
Thermogravimetric analysis (TGA) of the polymers was
Synthesis of the polymers
investigated on
a Universal V2.6D TA instruments. The
Compound 2a (91 mg, 0.1 mmol) and compound
3 (87.8 mg,
electrochemical cyclic voltammetry was conducted on a CHI
660D Electrochemical Workstation with glassy carbon, Pt wire,
and Ag/Ag+ electrode as working electrode, counter electrode,
0.1 mmol) were dissolved in degassed toluene (20 ml) and
purged with argon for 30 min, tris(dibenzylideneacetone)
dipalladium(0) (Pd2(dba)3) (1.8 mg) and tri(otolyl) phosphine
(P(o-Tol)3) (3.5 mg) were added and flushed with argon for
another 30 min, then the mixture was vigorously stirred at 100
oC for 24 h under argon. After cooling down to the room
temperature, the solution was poured into the methanol. The
polymer was collected by filtration and soxhlet-extracted in
order with methanol, hexane and chloroform, the chloroform
solution was concentrated to a small volume and precipitated
by pouring into methanol again. Finally, the polymer was
collected by filtration and dried under vacuum at 50 oC
and reference electrode respectively in
tetrabutylammonium hexafluorophosphate
a
0.1mol/L
(Bu4NPF6)
acetonitrile solution. Polymer thin films were formed by drop-
casting chloroform solution (analytical reagent, 1mg/mL) onto
the working electrode, and then dried in the air. Atomic force
microscopy (AFM) images were collected in air under ambient
conditions using the MultiMode scanning probe microscope
(AFM, Veeco MultiMode V).
4 | J. Name., 2012, 00, 1-3
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2.3 THF solvent vapour annealing (SVA)
amplitude of TPV is much less than Voc. Transient photocurrent
measurement was performed with the device being held at
short circuit condition by connecting the device to the ground
through a small resistor. The resulting current transient was
SVA was conducted in ambient conditions at room
temperature in glove box. THF (2 ml) was injected into a 30
mm glass Petri dish. The Petri dish was closed for 1 min to let
the THF vapour saturate the treatment chamber. Then the as- measured using an oscilloscope (Tektronix DPO4104, 1GHz) in
cast film was transferred to the Petri dish. The film was about
1 cm above the solvent level during the SVA. After 30 sec, the
film was removed from the treatment chamber.
parallel with a small resistor of 50 Ω. The excitation pulse was
generated using a pulsed laser (OPOTEK Vibrant 355, with a 5
ns optical pulse).
2.4 Fabrication and characterization of PSCs
3. RESULTS AND DISSCUSSION
The
ITO/PEDOT:PSS/polymer:PC71BM/PFN/Al,
device
structure
a
was
40-nm-thick
3.1 Materials design and synthesis
PEDOT:PSS anode buffer layer was spin-cast on the ITO
substrate, then dried in a vacuum oven at 100 oC overnight.
The polymer:PC71BM active layer was prepared by spin-coating
their 1,2-dichlorobenzene solution with various weight ratios.
A 5 nm PFN layer was then spin-coated from methanol
solution in presence of a trace amount of acetic acid onto the
active layer. Subsequently, the films were transferred into a
vacuum evaporator and 100 nm of Al were deposited as
cathode. The effective area of a device was 0.16 cm2 as
determined by the shadow mask used during deposition of Al
cathode. PCE values were determined from J–V curve
measurements (using a Keithley 2400 source meter) under 1
sun, AM 1.5G spectrum from a solar simulator (Oriel model
91192; 1,000 W m-2). External quantum efficiency (EQE)
measurements were taken using a monochromator (Newport,
Cornerstone 130) joined to the same xenon lamp and a lock-in
amplifier (Stanford Research Systems, SR 830) coupled to a
light chopper.
The synthetic routes of the four polymers are shown in
Scheme 1. In our synthetic design, the two octyl groups were
introduced to the 2,3-position of the side chain conjugated
thiophene rings to replace the 2-ethylhexyl groups. The 5-octyl
thienyl and 3-octyloxyphenyl groups were chosen to build the
quinoxaline units for their good performances in the donor-
acceptor polymers for PSCs.[19] The four polymers were
synthesized through typical Stille-coupling reaction with good
yield
(>82
%),
using
toluene
as
solvent,
tris(dibenzylideneacetone) dipalladium (Pd2(dba)3) and
tri(otolyl)phosphine (P(o-tol)3) as catalyst. Both four polymers
showed good solubility in chloroform, o-dichlorobenzene
(oDCB) and other common solvents, especially the two
polymers containing two octyl groups in the BDTT units
(
molecular weight of PBDTTFTQ-EH PBDTTFTQ-DO
PBDTTFTQ-DO and PBDTTFTTQ-DO). The number-average
,
,
PBDTTFTTQ-EH and PBDTTFTTQ-DO are 64.74, 75.96, 18.45
and 135.95 kDa, with corresponding polydispersity index (PDI)
as 2.79, 3.29, 5.49 and 6.35, respectively, which were
measured by gel permeation chromatography (GPC).
2.5 Hole mobility measurement
The device structure of space charge limited current (SCLC)
studies is ITO/PEDOT:PSS/polymer/MoO3(10nm)/Al. The
mobility was determined by fitting the dark current to the
model of a single carrier SCLC, which is described by the
equation: J= (9/8)ε0εrμ((V2)/(d3)), where J is the current, μ is
the zero-field mobility, ε0 is the permittivity of free space, εr is
the relative permittivity of the material, d is the thickness of
the active layer, and V is the effective voltage. The effective
voltage can be obtained by subtracting the built-in voltage (Vbi)
and the voltage drop (Vs) from the substrate’s series resistance
from the applied voltage (Vappl), V=Vappl–Vbi–Vs. The hole-
mobility can be calculated from the slope of the J1/2 ~ V curves.
The effective area was also 0.16 cm2.
3.2 Properties of the polymers
All of the polymers have decomposition temperature
(defined as the 5% weight-loss temperature, Td) over 300 oC
and the PBDTTFTQ-EH shows the highest Td (427 oC for
PBDTTFTQ-EH
,
329 oC for PBDTTFTQ-DO
,
399 oC for
o
PBDTTFTTQ-EH and 370 C for PBDTTFTTQ-DO respectively,
see Figure S8 in ESI) under nitrogen as determined by
thermogravimetric analysis (TGA), indicating their excellent
thermal stabilities.
The optical properties of the polymers were investigated by
ultraviolet-visible (UV-vis) absorption spectroscopy both in
CHCl3 solutions (see Figure S9 in ESI) and in thin films (see
Figure 1a and 1b). The detailed data obtained from these
absorption spectra are summarized in Table 1. As shown in
Figure S9 and Figure 1, in comparison with the two EH-based
2.6 Transient photovoltage and transient photocurrent
measurements
Transient photovoltage measurement was performed by polymers, the DO-substituted polymers (PBDTTFTQ-DO and
PBDTTFTTQ-DO) exhibited slightly blue-shifted spectra both in
solution and in solid film; i.e. the films of PBDTTFTQ-EH and
PBDTTFTTQ-EH showed absorption peaks at 625 nm and 644
nm, however, the corresponding absorption peaks of
PBDTTFTQ-DO and PBDTTFTTQ-DO were located at 608 nm
and 626 nm, respectively, implying that the replacement of
PBDTTFTQ-EH and PBDTTFTTQ-EH with PBDTTFTQ-DO and
PBDTTFTTQ-DO slightly increases the optical bandgaps. The
holding the devices at open-circuit condition under
illumination of a 100W tungsten halogen lamp. The devices
were connected to an oscilloscope (Tektronix DPO4104, 1GHz)
that has an input impedance of the oscilloscope of 1 MΩ to
hold the device at open circuit. The excitation pulse was
generated using a pulsed laser (OPOTEK Vibrant 355, with a 5
ns optical pulse). The perturbation light intensity was
attenuated by a set of neutral density filter so that the
absorption edges (
λ
edge) of the four polymer films are 740 nm
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1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
a
b
PBDTTFTQ-EH
PBDTTFTQ-DO
PBDTTFTTQ-EH
PBDTTFTTQ-DO
300
400
500
600
700
800
900
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
c
20
PBDTTFTQ-EH
PBDTTFTQ-DO
PBDTTFTTQ-EH
PBDTTFTTQ-DO
60
40
20
0
d
16
12
8
Eox=0.58V
Eox=0.41 V
Eox=0.60 V
Eox=0.66V
4
0
-20
-40
-4
-2.5 -2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
-2.0 -1.5 -1.0 -0.5
0.0
0.5
1.0
Potential/ V vs. Ag/Ag+
Potential / V vs. Ag/Ag+
Figure 1. Absorption spectra of PBDTTFTQ-EH and PBDTTFTQ-DO films (a) and absorption spectra of PBDTTFTTQ-EH and
PBDTTFTTQ-DO films (b); Cyclic voltammograms of PBDTTFTQ-EH and PBDTTFTQ-DO films (c) and cyclic voltammograms of
PBDTTFTTQ-EH and PBDTTFTTQ-DO films (d) on a glassy carbon electrode measured in 0.1 mol/L Bu4NPF6 solutions at a scan
rate of 50 mV/s.
-2.99 eV
-3.03 eV
-3.03 eV
-3.05eV
-3.91 eV
PFN/Al
ITO
-4.80 eV
-4.30 eV
-5.12 eV
-5.29 eV
-5.31 eV
-5.37 eV
-5.93 eV
Figure 2. Schematic illustration of relative positions of HOMO/LUMO energy levels of the materials in the PSCs
(
PBDTTFTQ-EH),
720
PBDTTFTTQ-EH) and 722nm (PBDTTFTTQ-DO) respectively, PBDTTFTTQ-EH), which are ascribed to the big steric hindrance
nm
(
PBDTTFTQ-DO)
,
745nm corresponding EH-based polymers (PBDTTFTQ-EH and
(
from which the corresponding optical bandgaps (Egopt) can be of the two octyl groups on the side chains. Furthermore, it
calculated as 1.68 eV, 1.72 eV, 1.66eV and 1.72 eV separately, should be noted that when replacing the pendent m-
according to the equation Egopt=1240/
λedge. It is found that the
absorption edges of DO-substituted polymers (PBDTTFTQ-DO
and PBDTTFTTQ-DO) are slightly smaller than that of the
octyloxyphenyl side groups (PBDTTFTQ-EH and PBDTTFTQ-DO
by 5-octylthiophene rings (PBDTTFTTQ-EH and PBDTTFTTQ-
)
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Figure 3. Calculated HOMO (a, c) and LUMO (b,d) distribution for PBDTTFTQ-EH (a,b) and PBDTTFTQ-DO (c, d)
Figure 4. Calculated HOMO (a,c) and LUMO (b,d) distribution for PBDTTFTTQ-EH(a,b) and PBDTTFTTQ-DO (c,d)
Table 1. Optical, electrochemical properties of the polymers
opt a)
b)
c)
c)
c)
Eg
HOMO b)
LUMO b)
Eg
Eox
[V]
Ered
[V]
HOMO c)
LUMO c) Eg
λedge
[nm]
740
720
745
722
Polymer
[eV]
1.68
1.72
1.66
1.72
[eV]
[eV]
[eV]
2.52
2.61
2.48
2.52
[eV]
[eV]
[eV]
2.24
2.34
2.09
2.32
PBDTTFTQ-EH
PBDTTFTQ-DO
PBDTTFTTQ-EH
PBDTTFTTQ-DO
-4.79
-4.83
-4.76
-4.77
-2.27
-2.22
-2.28
-2.25
0.58
0.66
0.41
0.60
-1.66
-1.68
-1.68
-1.72
-5.29
-5.37
-5.12
-5.31
-3.05
-3.03
-3.03
-2.99
a) estimated from the onset of electronic absorption of the polymer films (Egopt =1240/λ(nm)). b) calculated results from the DFT at
B3LYP/6-31G(d) level. c) cyclic voltammetry results.
DO), red-shifted absorption spectra and decreased bandgaps efficient polymer materials with enhanced photovoltage.
were achieved, which were in good agreement with the Because Voc of BHJ PSCs is closely related to the gap between
literatures.[23]
the HOMO of the donor polymer and the LUMO of the
acceptor material in their blended films, higher Voc can be
expected in the PSCs based on PBDTTFTQ-DO and
Cyclic voltammetry (CV) was employed to measure
oxidation and reduction potentials of the polymers (Figure 1c
and 1d). The HOMO and LUMO energy levels of the polymers
were determined from the onset oxidation potentials (Eox) and
the onset reduction potentials (Ered) according to the following
equations: HOMO=-e(Eox + 4.71) (eV); LUMO=-e(Ered+4.71) (eV),
where the unit of potential is V vs Ag/Ag+.[28] As shown in
Figure 1c and 1d, the onset oxidation potential (Eox) and the
PBDTTFTTQ-DO compared to the devices based on PBDTTFTQ-
To make a clear comparison, the
[30]
EH and PBDTTFTTQ-EH.
energy levels diagrams of the materials used in this study were
summarized in Figure 2. It is obvious that the LUMO energy
levels of the four polymers are both significantly higher than
that of PC71BM, which facilitate electron transferring from the
polymers to the PC71BM at the photoactive layer of PSCs.
onset reduction pontential (Ered) are 0.58 V/-1.66 V
(PBDTTFTQ-EH), 0.66 V/-1.68 V (PBDTTFTQ-DO), 0.41 V/-1.68
In order to explore the electronic properties of the polymers,
V (PBDTTFTTQ-EH) and 0.60 V/-1.72 V (PBDTTFTTQ-DO) vs. molecular simulations were performed on single repeated
Ag/Ag+, corresponding to a HOMO/LUMO level of -5.29 eV/- donor-acceptor unit with all alkyl chains reserved using the
3.05 eV, -5.37 eV/-3.03 eV, -5.12 eV/-3.03 eV and -5.31 eV/- Density Functional Theory (DFT) at B3LYP/6-31G(d) level.[30] As
2.99 eV, respectively. Obviously, when the 2-ethlyhexyllthienyl shown in Figure 3 and 4, the localization of HOMOs distributed
group was replaced by the 2,3-dioctylthienyl unit, HOMO level along the polymer backbone while the LUMOs of both
of the corresponding polymer can be significantly reduced, polymers were somewhat more localized on the acceptor units,
0.08eV for PBDTTFTQ-DO and 0.19 eV for PBDTTFTTQ-DO. To indicating the significant charge-transfer character between
the best of our knowledge, this finding had never been BDT and quinoxaline unit, which was consistent with the
[29]
reported in scientific literatures that with similar structure. observed strong low-energy absorption band in Figure 1. From
Thus, this strategy can be a guideline for the design of highly the simulation data it can be seen that deeper HOMO levels
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2
a
70
60
50
40
30
20
10
0
b
0
-2
PBDTTFTQ-EH
PBDTTFTQ-DO
-4
-6
-8
-10
-12
-14
PBDTTFTQ-EH
PBDTTFTQ-DO
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
400 450 500 550 600 650 700 750 800
Voltage (V)
Wavelength (nm)
2
70
d
c
0
60
50
40
30
20
10
0
PBDTTFTTQ-EH
PBDTTFTTQ-DO
-2
-4
-6
-8
-10
-12
-14
PBDTTFTTQ-EH
PBDTTFTTQ-DO
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
400 450 500 550 600 650 700 750 800
Voltage (V)
Wavelength (nm)
Figure 5. (a) The J-V curves of PSCs based on PBDTTFTQ-EH:PC71BM (1:1.5, w/w ; 2% CN, v/v) and PBDTTFTQ-DO:PC71BM (1:3)
with THF-SVA for 30 sec under the illumination of AM 1.5G, 100 mW cm-2 ; (b) the corresponding EQE curves of PBDTTFTQ-EH
and PBDTTFTQ-DO devices; (c) the J-V curves of PSCs based on PBDTTFTTQ-EH:PC71BM (1:2) and PBDTTFTTQ-DO:PC71BM (1:3)
with THF-SVA for 30 sec under the illumination of AM 1.5G, 100 mW cm-2; (d) the corresponding EQE curves of PBDTTFTTQ-EH
and PBDTTFTTQ-DO devices.
Table 2. Photovoltaic performances of copolymers measured under illumination of AM 1.5 G condition, 100 mW cm-2
a)
Polymer:PC71BM
THF SVA Time Voc
Jsc
FF
PCEmax(PCEave
[%]
)
Polymer
[w/w]
(sec)
30
[V]
[mA cm-2] [%]
PBDTTFTQ-EH
PBDTTFTQ-DO
PBDTTFTTQ-EH
PBDTTFTTQ-DO
1:1.5(2%CN, v/v)
0.78
0.88
0.72
0.85
13.2
11.4
13.4
11.3
70.8
75.9
70.8
75.7
7.29 (7.15)
7.61 (7.42)
6.82 (6.65)
7.25 (7.09)
1:3
1:2
1:3
30
30
30
a) Calculated from 5 individual PSCs.
for DO-based polymers and smaller calculated bandgap for EH
based polymers were investigated, which were consistent with polymers, PSCs with a device structure of ITO/poly(3,4-
the measured HOMO levels and optical bandgaps in Figure 1 ethylenedioxythiophene):poly(styrene sulfonic acid
The absorption parameters and energy levels of the four (PEDOT:PSS)/polymer:PC71BM/poly[(9,9-dioctyl-2,7-fluorene)-
-
To investigate the photovoltaic properties of the obtained
.
polymers were also listed in Table 1.
alt-(9,9-bis(3-N,N-dimethylamino)propyl)-2,7-fluorene]) (PFN,
5 nm)/Al that followed our previous work,[31] were fabricated.
The photoactive layer were spin-coated on top of pre-
fabricated PEDOT:PSS layer from their 1,2-dichlorobenzene
solution. After that, the blend film was pre-thermal annealed
3.3 Characteristics and Optimization of Photovoltaic Devices
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at 90 oC for 10 min and followed by a THF-SVA of 30 sec. Then individual PSCs from each polymer are 7.42 %, 7.15 %, 7.09%
a thin layer of 5 nm water/alcohol soluble PFN that can serve and 6.65%, separately. Obviously, the slightly better
as the electron-collecting layer was spin-coated atop photovoltaic performances in the PBDTTFTQ-DO and
photoactive layer from methanol solution in the presence of a PBDTTFTTQ-DO devices mainly attributed to the higher FF and
trace amount of acetic acid before deposition of cathode.
enhanced Voc resulting from their deepened HOMO levels
compared with that of PBDTTFTQ-EH and PBDTTFTTQ-EH
To illuminate the effects of SVA on the device performances,
.
Optimal weight ratios between polymers: PC71BM were
found to be 1:1.5 for PBDTTFTQ-EH, 1:3 for PBDTTFTQ-DO, 1:2
for PBDTTFTTQ-EH, and 1:3 for PBDTTFTTQ-DO respectively atomic force microscopy (AFM) study was carried out to
Figure S10 and Table S1). In order to optimize morphology of investigate the phase-separated morphologies of the
(
the blend films and thus to improve the photovoltaic polymers:PC71BM blends corresponding to the best
properties, 2% (v/v) of 1-chloronaphthalen (CN) was used as performance, which were shown in Figure 6-8. The light and
additive for PBDTTFTQ-EH based devices. The device dark domains correspond to the aggregations of polymer and
performances of both polymers are critically dependent on the PC71BM, respectively. For the pristine films of PBDTTFTQ-EH
processing conditions (donor/acceptor blend ratios, additive and PBDTTFTQ-DO, it can be observed clearly that both two
and solvent-vapour annealing (SVA) [32]), which were detailed blend films exhibit interpenetrating feature with bicontinuous
summarized in Figure S10-12 and Table S1-3. The current network between polymer and PC71BM. In addition, smooth
density versus voltage (J-V) characteristics and the external surface with a root-mean-square roughness (RMS) value of
quantum efficiency (EQE) curves of the corresponding 0.54 nm for PBDTTFTQ-DO and 1.75 nm for PBDTTFTQ-EH
optimized PSCs under AM 1.5 G at 100 mW cm-2 illumination were recorded, respectively. As described ahead, the devices
are presented in Figure 5. Photovoltaic parameters deduced from PBDTTFTQ-DO showed strong dependence on the THF-
from the corresponding
summarized in Table
PBDTTFTQ-EH exhibited optimized device performance when
J
2. It is interesting to note that change of film morphology upon treatment. As seen in Figure
-
V
curves in Figure 5a and 5c are SVA (see Figure S12 and Table S3), which should correlate the
6, the RMS roughness and the domain size of the films exhibit
combination of CN and THF-SVA were used, while PBDTTFTQ- a continuous enlargement as the SVA time increase. The
DO reached its highest PCE (~7.61 %) in case of a simple THF- optimal THF-SVA time is found to be around 30 sec for the
SVA process. For the PSCs devices prepared under the optimal PBDTTFTQ-DO blend film. Under this treatment process, the
conditions, the PBDTTFTQ-DO based devices showed a Voc of film showed a RMS roughness of 1.35 nm with an ideal domain
0.88 V, which is 0.10 V larger than that of the device of size of 10-20nm (Figure 6b), which is pretty favorable for
PBDTTFTQ-EH. Like PBDTTFTQ-DO, higher Voc of 0.85V (about efficient diffusion of excitons to donor-acceptor interface. [33,34]
0.13V larger than that of PBDTTFTTQ-EH) with relative high Annealing duration exceeding this optimized condition could
PCE (7.25%) was also achieved for the optimized PBDTTFTTQ- lead to significantly increased domain size in the PBDTTFTQ-
DO based devices after THF SVA 30 sec. The enhanced Voc of DO blend film, resulting in a reduction in overall performance
the DO-substituted polymer based devices were ascribed to (see Figure S12 and Table S3). When the THF-SVA duration
the deeper HOMO energy levels as discussed above.
reached 3 min, the resulting film showed unexpected phase
separation with corresponding domain size over 200 nm,
which is much larger than typical exciton diffusion length of ca.
10 nm, [35] thus is not desired for efficient excitons dissociation
at the D/A interface. We also found that in order to obtain
optimal performance in PBDTTFTQ-EH device, SVA in
conjunction with incorporation of additive, such as CN (2%, v/v)
into the blend solution is required (see Figure S11 and Table
S2). This combination was found to be able to promote the
As shown in Figure 5b and 5d, the devices of these four
polymers processed under each optimal conditions showed
similar EQE peak values of >60 %, while the response peaks
were 461 nm with the corresponding EQE peak value of 63.50%
for PBDTTFTQ-DO, 572 nm for PBDTTFTQ-EH (60.35%), 454
nm for PBDTTFTTQ-DO (63.99%), and 455nm for PBDTTFTTQ-
EH (62.42%), respectively. Nevertheless, the response range of
the PBDTTFTQ-EH and PBDTTFTTQ-EH-based devices at long
wavelength region are 22 nm and 24 nm red-shifted compared
to that of the corresponding PBDTTFTQ-DO and PBDTTFTTQ-
DO-based devices, which are in accord with the film
absorption spectra of the polymers as shown in Figure 1a and
1b. As a result, the PBDTTFTQ-EH and PBDTTFTTQ-EH devices
showed relatively higher short-circuit current densities (Jsc) of
13.2 mA cm-2 and 13.4 mA cm-2, while the PBDTTFTQ-DO and
PBDTTFTTQ-DO devices exhibited decreasing Jsc of 11.4 mA
cm-2 and 11.3mA cm-2. Except for the differences in Voc and Jsc,
FF values of the devices from these four polymers are
essentially high (same 70.8 % for the two EH-based polymers
vs. 75.9 % for PBDTTFTQ-DO and 75.7% for PBDTTFTTQ-DO),
both implying very good charge separation, transporting and
collecting efficiency in these optimal devices. The higher FF of
the two DO-based polymers might be resulted from their good
solubility and film processibility. More importantly, the overall
efficiency of the devices from both polymers exceeds 6.8%.
The best PCE is 7.61 % for PBDTTFTQ-DO, 7.29 % for
demixing of the polymer and PCBM in the blend film, so as to
[36]
optimize film morphology.
morphologies were also investigated in Figure
Optimal phase-separated
for
8
PBDTTFTTQ-EH and PBDTTFTTQ-DO blend films after THF SVA
30 sec, excepted for the RMS values of the treated films
decreasing slightly.
3.4 Effects of Solvent Vapour Annealing on Charge Transport
Properties
To get insight into the effects of the SVA on charge
transporting, the hole mobilities, ꢀhole of the blends of
polymers and PC71BM were measured using the space-charge-
limited current (SCLC) method (Figure S13-S15) for the four
polymers with different treatment and film thickness. For
PBDTTFTQ-DO blend films, a high hole mobility (up to 5.28×10-
4
cm2 V-1 s-1) was achieved after the THF-SVA 30 sec, while the
pristine film only showed a moderate
s-1
Table S5). These results were consistent with the
ꢀ
hole of 1.45×10-4 cm2 V-1
PBDTTFTQ-EH, 7.25% for PBDTTFTTQ-DO and 6.82% for
PBDTTFTTQ-EH respectively, while the average PCE over 5
(
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Figure 6. Surface topographic AFM images (size: 5
obtained at tapping mode, (a) as cast (RMS:0.54 nm), (b)THF-SVA 30 sec (RMS:1.35 nm), (c) THF-SVA 60 sec (RMS: 1.61 nm), (d)
ꢀ
m×5ꢀ
m) of PBDTTFTQ-DO:PC71BM blend films with a weight ratio of 1:3
THF-SVA 180 sec (RMS: 3.89 nm).
Figure 7. AFM topography images (5 ꢀm ×5 ꢀm) of ITO/PEDOT:PSS/PBDTTFTQ-EH:PC71BM (1:1.5) films.(a): Without CN , As cast
film (RMS:1.75 nm); (b): Without CN, THF-SVA 30 sec (RMS:4.63 nm); (c): With CN(2%, v/v%), As cast (RMS:1.39 nm); (d): With
CN(2%, v/v%), THF-SVA 30 sec (RMS:1.76 nm).
Figure 8. AFM topography images (5 ꢀm ×5 ꢀm) of ITO/PEDOT:PSS/PBDTTFTTQ-DO:PC71BM (1:3) films.(a): As cast film (RMS:0.79
nm); (b): THF-SVA 30 sec (RMS: 0.64 nm); and ITO/PEDOT:PSS/PBDTTFTTQ-EH:PC71BM (1:2) films; (c): As cast film(RMS:0.80 nm);
(d): THF-SVA 30 sec (RMS: 0.73 nm).
performance of each device and the film morphology induced technique has previously been used to study the charge decay
by the THF-SVA as shown in Figure 6b. Similar results were dynamics in organic solar cells under a given steady-state
[38]
observed for PBDTTFTQ-EH film except that the hole mobility illumination,
while TPC was used to determine the charge
showed a decrease after the CN addition (3.14×10-4 cm2 V-1 s-1 density in the devices.
For the TPV measurement, the
[39]
vs. 1.29×10-4 cm2 V-1 s-1, see Table S4). Furthermore, the perturbation from pulsed laser was attenuated by a set of
corresponding hole mobilities of the other two polymers after neutral density filter so that the amplitude of TPV is much
THF SVA 30 sec (Figure S15) are 1.14×10-4 cm2 V-1 s-1 smaller as compared to Voc. Since there is no charge collected
( under the Voc condition, the excess charge carriers that excited
respectively, which are consistent well with their photovoltaic by the pulsed laser are recombined and their lifetime can be
PBDTTFTTQ-EH) and 1.49×10-4 cm2 V-1 s-1
(
PBDTTFTTQ-DO
)
performances.
extracted from the exponential fitting on the decay of the
transient photovoltage. Figure 9a shows the typical results of
TPV measurement for the PBDTTFTQ-DO devices before and
after THF-SVA for 30 sec, as obtained under 1 sun illumination
and open-circuit voltage conditions, and the extracted carriers
To further shed light on the role of SVA, we performed
transient photovoltage (TPV)
[37]
and transient photocurrent
(TPC) [38] measurements to probe the charge recombination in
the PBDTTFTQ-DO devices with/without the SVA. The TPV
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Journal of Materials Chemistry A
ARTICLE
10-1
3
2
1
0
a
wo THF-SVA
wi THF-SVA
Fit 1
b
wo THF-SVA
wi THF-SVA
Fit 2
10-2
10-3
0
1
2
3
4
5
0
1
2
3
4
5
Times (us)
Time (us)
Figure 9. (a) Transient photovoltage and (b) transient photocurrent signals for the PBDTTFTQ-DO devices before and after 30 sec
SVA, measured under 1 sun illumination and open-circuit voltage conditions using the same intensity laser pulse. The dashed
lines in Figure 9a are mono-exponential decay fits.
PBDTTFTQ-EH (-5.29 eV) and PBDTTFTTQ-EH (-5.12 eV), the
devices from PBDTTFTQ-DO and PBDTTFTTQ-DO showed high
Voc values of 0.88 V and 0.85V, while that of 0.78 V and 0.72V
Lifetimes are 0.187 us and 0.320 us for the PBDTTFTQ-DO
devices with/without SVA, respectively. The observed shorter
were observed in PBDTTFTQ-EH and PBDTTFTTQ-EH devices.
carrier lifetime in the device with SVA is consistent with its
relatively lower Voc than that of the device without the
treatment (0.88 V vs 0.98 V, Table S3). On the other side, the factor of 75.9% in PBDTTFTQ-DO as obtained via solvent
Both polymers deliver high power conversion efficiency, with
an outstanding efficiency of 7.61% and an excellent filled
vapour annealing, which mainly resulted from the improved
carrier diffusion length of the devices after proper SVA process.
device underwent SVA showed higher charge carrier density
than that without SVA (Figure 9b), which are in good
agreement with the observed higher Jsc after 30 sec treatment
(
Table S3) and was ascribed to a more preferable morphology
Acknowledgements
for efficient excitons dissociation as shown in Figure 6b. By
taking the extracted lifetime and mobility together, the
calculated carrier diffusion length in the device after 30 sec
SVA is obviously higher than that of the control device, which
is expected to be responsible for the largely improved FF after
the SVA.
We would like to thank the financial support of the National
Natural Science Foundation of China (Nos. 61177031,
61274054, 51225301, and 91333206).
References
[1] Y. Li, Accounts Chem. Res. 2012,45, 723
[2] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science.
1995, 270, 1789.
[3] S. H. Liao, H. J. Jhuo, Y. S. Cheng, S. A. Chen, Adv. Mater.
2013, 25, 4766.
3. CONCLUSION
In summary, four D-A polymers based on side chain
modified 2D conjugated BDT and mono-fluorinated
quinoxaline derivatives, PBDTTFTQ-EH
PBDTTFTTQ-EH and PBDTTFTTQ-DO were synthesized and
characterized. The results clearly indicated that the variation in
the side chain of BDT unit from 2-ethylhexylthienyl group to
,
PBDTTFTQ-DO,
[4] Z. B. Henson, K. Mullen, G. C. Bazan, Nat. Chem. 2012,
[5] Z. C. He, C. M. Zhong, S. J. Su, M. Xu, H. B. Wu, Y. Cao, Nat.
Photo. 2012, , 591.
[6] Y. Liang, Z. Xu, J. Xia, S-T. Tsai, Y. Wu, G. Li, C. Ray, L. Yu, Adv
4, 699.
6
2,3-dioctylthienyl group can cause big impact on their optical Mater, 2010, 22, E135.
[7] S-H. Liao, H-J. Jhuo, P-N. Yeh, Y-S. Cheng, Y-L. Li, Y-H. Lee, S.
Sharma, S-A. Chen. Sci. Rep. 2014, , 6813
[8] Y. Liu, J. Zhao, Z. Li, C. Mu, W. Ma, H. Hu, K. Jiang, H. Lin, H.
Ade, H. Yan, Nat. Common. 2014, , 5293
[9] C. J. Brabec, A. Cravino, D. Meissner, N. S. Saricici, T.
Fromherz, M. T. Rispens, L. Sanchez, J. C. Hummelen, Adv. Funct.
Mater. 2001, 11, 374.
properties and electronic HOMO levels. This finding should
provide valuable guideline for the design and synthesis of
novel polymer donor materials for highly efficient polymer
solar cells with high open-circuit voltage via fine tuning the
molecular energy levels and absorption spectra through a
modulation of the side chain onto the donor moiety. In good
agreement with the deeper HOMO level of PBDTTFTQ-DO (-
5.37 eV) and PBDTTFTTQ-DO (-5.31 eV) than that of
4
5
This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C5TA05096K
ARTICLE
Journal Name
[10] J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J. [29] Y. Dong, X. Hu, C. Duan, P. Liu, S. Liu, L. Lan, D. Chen, L. Ying,
Heeger, G. C. Bazan, Nat. Mater. 2007, , 497. S. Su, X. Gong, F. Huang, Y. Cao. Adv. Mater. 2013, 25, 3686.
[11] G. Li, V. Shrotriya, J. S. Huang, Y. Yao, T. Moriarty, K. Emery, [26] G. Dennler, M. C. Scharber, T. Ameri, P. Denk, K. Forberich,
Y. Yang, Nat. Mater. 2005, , 864. C. Waldauf, C. J. Brabec. Adv. Mater. 2008, 20, 579.
[12] M. C. Scharber, D. Mühlbacher, M. Koppe, P. Denk, C. [30] a) R. Kroon, R. Gehlhaar, T. T. Steckler, P. Henriksson, C.
Waldauf, A. J. Heeger, C. J. Brabec, Adv. Mater. 2006, 18, 789. Muller, J. Bergqvist, A. Hadipour, P. Heremans, M. R Andersson.
[13] a) M. Svensson, F. Zhang, S. C. Veenstra, W. J. H. Verhees, J. Sol. Energ. Mat. Sol C. 2012, 105, 280; b) G. K. Dutta, T. Kim, H.
6
4
C. Hummelen, J. M. Kroon, O. Inganas, M. R. Andersson. Adv. Choi, J. Lee, D. S. Kim, J. Y. Kim, C. Yang. Polym. Chem, 2014,
Mater. 2003, 15, 988; b) J. You, L. Dou, K. Yoshimura, T. Kato, K. 2540.
5,
Ohya, T. Moriarty, K. Emery, C.-C. Chen, J. Gao, G. Li, Y. Yang. [31] Z. C. He, C. M. Zhong, X. Huang, W. Y. Wong, H. B. Wu, L. W.
Nat. Commun. 2013, ,1446; c) M. Zhang, X. Guo, W. Ma, S. Chen, S. J. Su, Y. Cao. Adv. Mater. 2011, 23, 4636.
4
Zhang, L. Huo, H. Ade, J. Hou. Adv. Mater. 2014, 26, 2089; d) S. [32] a) J. Liu, L. Chen, B. Gao, X. Gao, Y. Han, Z. Xie, L. Wang, J.
H. Park, A. Roy, S. Beaupre, S. Cho, N. Coates, J. S. Moon, D. Mater. Chem. A, 2013, 1, 6216, b) B. Kan, Q. Zhang, M. Li, X.
Moses, M. Leclerc, K. Lee, A. J. Heeger. Nat. Photo. 2009,
[14] a)D. Dang, W. Chen, R. Yang, W. Zhu, W. Mammo, E. Wang, Chem. Soc. 2014, 136, 15529
3, 297
Wang, W. Ni, G. Long, Y. Wang, X. Yang, H. Feng, Y. Chen, J. Am.
Chem. Commun. 2013, 49, 9335; b) N. Wang, Z. Chen, W. Wei, Z. [33] J. K. Lee, W. L. Ma, C. J. Brabec, J. Yuen, J. S. Moon, J. Y. Kim,
,
Jiang. J. Am. Chem. Soc. 2013, 135, 17060; c) Y. Deng, J. Liu, J. K. Lee, G. C. Bazan, A. J. Heeger. J. Am. Chem. Soc. 2008, 130
Wang, L. Liu, W. Li, H. Tian, X. Zhang, Z. Xie, Y. Geng, F. Wang. 3619.
Adv. Mater. 2014, 26, 471. d) Y. Huang , X. Guo , F. Liu , L. Huo , [34] J. Liu, L. Chen, B. Gao, X. Cao, Y. Han, Z. Xie, L. Wang. J.
Y. Chen , T. P. Russell, C. C. Han , Y. Li, J. Hou. Adv. Mater. 2012, Mater. Chem. A, 2013, , 6216.
24, 3383 [35] J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J.
[15] a) H.-Y. Chen, J. Hou, S. Zhang, Y. Liang, G. Yang, Y. Yang, L. Heeger, G. C. Bazan. Nat. Mater. 2007, , 497
Yu, Y. Wu, G. Li. Nat. Photo, 2009, , 649; b) J. Hou, H.-Yu Chen, [36] C. G. Shuttle, B. O’Regan, A. M. Ballantyne, J. Nelson, D. D.
1
6
3
S. Zhang, R. I. Chen, Y. Yang, Y. Wu, G. Li. J. Am. Chem. Soc. 2009, C. Bradley, J. de Mello, J. R. Durrant. Appl. Phys. Lett. 2008, 92
131,15586; c) Y. Liang, D. Feng, Y. Wu, S.-T. Tsai, G. Li, C. Ray, L. 093311.
,
Yu. J. Am. Chem. Soc. 2009, 131, 7792; d) Y. Huang, L. Huo, S. [37] Y. Kim, H. R. Yeom, J. Y. Kim, C. Yang. Enegry Environ. Sci,
Zhang, X. Guo, C. C. Han, Y. Li, J. Hou, Chem. Commun. 2011, 47 2013, 6, 1909.
8904; e) H. J. Son, B. Carsten, I. H. Junga, L. P. Yu, Energy Envir. [38] A. Maurano, C. G. Shuttle, R. Hamilton, A. M. Ballantyne, J.
Sci, 2012, , 8158. Nelson, W. M. Zhang, M. Heeney, J. R. Durrant. J. Phys. Chem. C,
,
5
[16] a) L. Huo, S. Zhang, X. Guo, F. Xu, Y. Li, J. Hou. Angew. Chem. 2011, 115, 5947.
Int. Ed. 2011, 50, 9697; b) C. Cui, W.-Y. Wong, Y. Li. Energy [39] C. G. Shuttle , N. D. Treat , J. D. Douglas , J. M. J. Fréchet , M.
Environ. Sci, 2014,
7, 2276.
L. Chabinyc. Adv. Energy Mater. 2011, 2, 111119.
[17] a) Z. G. Zhang, Y. F. Li. Side-chain engineering of high-
efficiency conjugated polymer photovoltaic materials. Sci China
Chem, 2015, 58,192;b) Li. Chen, P. Shen, Z. G. Zhang, Y. Li. J.
Mater. Chem. A, 2015,3,12005
[18] M. Zhang, X. Guo, W. Ma, S. Zhang, L. Huo, H. Ada, J. Hou,
Adv. Mater. 2014, 26, 2089
[19] a) H.-C. Chen,Y.-H Chen, C.-C. Liu, Y.-C. Chien, S.-W. Chou,
P.-T. Chou. Chem. Mater. 2012, 24, 4766; b) H.-C. Chen, Y.-H.
Chen, C.-H. Liu, Y.-H. Hsu, Y.-C. Chien, W.-T. Chuang, C.-Y. Cheng,
C.-L. Liu, S.-W. Chou, S.-H. Tung, P.-T. Chou. Polym. Chem. 2013,
4, 3411.
[20] A. Iyer, J. Bjorgaard, T. Anderson, M. E. Kose.
Macromolecules 2012, 45, 6380.
[21] a) E. Wang, L. Hou, Z. Wang, S. Hellström, F. Zhang, O.
Inganäs, M. R. Andersson. Adv. Mater. 2010, 22, 5240; b) A.
Gadisa, W. Mammo, L. M. Andersson, S. Admassie, F. Zhang, M.
R. Andersson, Olle Inganäs. Adv. Funct. Mater. 2007, 17, 3836; c)
L. Huo, Z. Tan, X. Wang, Y. Zhou, M. Han, Y, Li. J. Polym. Sci. Pol.
Chem. 2008, 46, 4038; d) M.-H. Lai, C.-C. Chueh, W.-C. Chen, J.-L.
Wu, F.-C. Chen. J. Polym. Sci. Pol. Chem. 2009, 47, 973.
[22] Y. Huang, M. Zhang, L. Ye, X. Guo, C. C. Han, Y. Li, J. Hou. J.
Mater. Chem. 2012, 22, 5700.
[23] R. Kroon, A. Lundin, C. Lindqvist, P. Henriksson, T. T. Steckler,
M. R. Andersson. Polymer. 2013, 54, 1285
[24] H. Wu, B. Qu, D. Tian, Z. Cong, B. Gao, J. Liu, Z. An, C. Gao, L.
Xiao, Z. Chen, Q. Gong, W. Wei, React. Funct. Polym. 2013, 73
1432
,
[25] Y. Lu, Z. Xiao, Y. Yuan, H. Wu, Z. An, Y. Hou, Chao Gao, J.
Huang, J. Mater. Chem. C. 2013, ,630
1
[26] F. Babudri, V. Fiandanese, G. Marchese, A. Punzi,
Tetrahedron Lett. 1995, 36, 7305.
[27] M. Wang, X. Hu, P. Liu, W. Li, X. Gong, F. Huang, Y. Cao, J.
Am. Chem. Soc. 2011, 133, 9638.
[28] J. Hou, Z. Tan, Y. Yan, Y. He, C. Yang, Y. Li, J. Am. Chem. Soc.
2006, 128, 4912
12 | J. Name., 2012, 00, 1-3
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