Phosphonate-functionalized donor polymer as an underlying interlayer to improve active layer morphology in polymer solar cells

Article abstract of DOI:10.1021/ma5008754

A novel polymer is developed and used as underlying interlayer to improve donor polymer/acceptor material blend morphology of active layer in polymer solar cells (PSCs). The polymer poly{N-9-[1, 17-bis-(diethylphosphonate)heptadecanyl]-2, 7-carbazole-alt-5, 5-(4, 7-di-2-thienyl-2, 1, 3-benzothiadiazole)} (PCDTBT-Pho) is designed by attaching polar phosphonate moieties to the side chain of the donor polymer, poly[N-9-heptadecanyl-2, 7-carbazole-alt-5, 5-(4, 7-di-2-thienyl-2, 1, 3-benzothiadiazole)] (PCDTBT). The pendant phosphonate moieties lead to different solubility and proper surface energy of PCDTBT-Pho. As a result, in PSC devices, the underlying PCDTBT-Pho layer facilitates the formation of biscontinuous network morphology in the active layer, makes the donor polymer enriched at the anode side, and induces the donor polymer to crystallize. These improvements contribute to improved charge separation and transport, leading to short-circuit current density enhancement by 12% and power conversion efficiency enhancement by 8% of the PSC devices. Thus, the design and application of PCDTBT-Pho indicate a novel approach to optimize active layer morphology and improve photovoltaic efficiency of PSCs.

Full text of DOI:10.1021/ma5008754

Article
pubs.acs.org/Macromolecules
Phosphonate-Functionalized Donor Polymer as an Underlying
Interlayer To Improve Active Layer Morphology in Polymer Solar
Cells
†
,‡
†
†
,†
,†
Bin Meng, Yingying Fu, Zhiyuan Xie, Jun Liu,* and Lixiang Wang*
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, P. R. China
‡
University of Chinese Academy of Sciences, Beijing 100039, P. R. China
*
S Supporting Information
ABSTRACT: A novel polymer is developed and used as
underlying interlayer to improve donor polymer/acceptor
material blend morphology of active layer in polymer solar
cells (PSCs). The polymer poly{N-9-[1,17-bis-
(
diethylphosphonate)heptadecanyl]-2,7-carbazole-alt-5,5-(4,7-
di-2-thienyl-2,1,3-benzothiadiazole)} (PCDTBT-Pho) is de-
signed by attaching polar phosphonate moieties to the side
chain of the donor polymer, poly[N-9-heptadecanyl-2,7-
carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)]
(
PCDTBT). The pendant phosphonate moieties lead to different solubility and proper surface energy of PCDTBT-Pho. As a
result, in PSC devices, the underlying PCDTBT-Pho layer facilitates the formation of biscontinuous network morphology in the
active layer, makes the donor polymer enriched at the anode side, and induces the donor polymer to crystallize. These
improvements contribute to improved charge separation and transport, leading to short-circuit current density enhancement by
1
2% and power conversion efficiency enhancement by 8% of the PSC devices. Thus, the design and application of PCDTBT-Pho
indicate a novel approach to optimize active layer morphology and improve photovoltaic efficiency of PSCs.
7
8
9
1. INTRODUCTION
annealing, solvent annealing, and using solvent additive.
Good active layer morphology and high efficiency of PSCs have
been achieved by modifying chemical structures and optimizing
active layer processing conditions.
Polymer solar cells (PSCs) are receiving great attention due to
their advantages of low cost, flexibility, and light weight. A PSC
device involves an active layer of a blend of a donor material
1
Generally, properties of the underlying layer also play an
(
e.g., poly[N-9-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-
important role on the morphology of polymer blend by
thienyl-2,1,3-benzothiadiazole)], PCDTBT, Scheme 1) and an
acceptor material (e.g., [6,6]-phenyl-C71 butyric acid methyl
ester, PC BM, Scheme 1) sandwiched between an anode and a
10,11
regulating the phase separation during the film formation.
For PSCs, the effect of the surface energy of the underlying
71
layer on the active layer morphology has been proved by Cho
cathode. The PSC device efficiency is determined not only by
the donor material and the acceptor material but also by the
morphology of their blend and by the interfaces between the
12
et al. However, little attention has been paid to using a
specific underlying layer to further improve the active layer
morphology and increase the PSC device efficiency. In this
article, we report the development of a morphology-inducing
layer (MIL) (see Scheme 1), which is used beneath the active
layer to further improve the morphology of the active layer and
consequently enhance the PSC device performance.
2
,3
active layer and the electrodes. It has been widely accepted
that the optimal morphology of the donor/acceptor blend
should be a bicontinuous interpenetrating network with the
phase domain size of 10−20 nm, which facilitates both exciton
2
dissociation and charge transport. Moreover, the optimal
The material in MIL is designed by introducing polar
moieties to side chain of donor polymers, leading to different
solubility and proper surface energy. The different solubility of
the MIL material and the donor polymer enable solution
processing of the active layer on top of the MIL during PSC
device fabrication. Owing to the polymer backbone and the
morphology should have the vertical ingredient distribution
with the donor accumulating at the anode side and the acceptor
enriched at the cathode side. A lot of efforts have been devoted
2
to improve morphology of donor/acceptor blend to increase
PSC device efficiency. Material chemists have controlled the
morphology by modifying chemical structures of donor
polymers, e.g., substitution of bridge atoms in the main
4
5
chain, optimization of side chains, and using specific end-
Received: April 28, 2014
Revised: August 16, 2014
6
capping moieties. Device physicists have developed several
approaches to improve the morphology, such as thermal
©
XXXX American Chemical Society
A
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Scheme 1. Schematic of PCDTBT-Pho as MIL in PSC Devices
a
proper surface energy, the MIL can facilitate the formation of
bicontinuous donor/acceptor network, make the donor
polymer preferentially accumulate at the MIL surface, and
induce the donor polymer to crystallize in the active layer. All
these improvements in the active layer morphology are
expected to increase PSC device efficiency.
Scheme 2. Synthetic Route of PCDTBT-Pho
PCDTBT is a typical efficient donor polymer, which can give
13
device power conversion efficiency (PCE) of about 6%.
Herein, we select PCDTBT as the donor polymer in the active
layer. On the basis of our expertise on phosphonate-
14
functionalized conjugated polymers, we introduce phospho-
nate moieties to the side chain of PCDTBT to develop the MIL
material, poly{N-9-[1,17-bis(diethylphosphonate)-
heptadecanyl]-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-ben-
zothiadiazole)} (PCDTBT-Pho). The chemical structures of
PCDTBT-Pho and PCDTBT are shown in Scheme 1. As a
result, incorporation of PCDTBT-Pho as MIL in
a
Reagents and conditions: (i) phenol, K CO , acetone, reflux, 95%;
2
3
PCDTBT:PC BM device leads to much improved morphol-
71
(ii) Mg, THF, 50 °C, ethyl formate, 0 °C to rt, 70%; (iii) 4-
toluenesulfonyl chloride, (CH ) NHCl, (C H ) N, dichloromethane,
0 °C, 100%; (iv) 2,7-dibromo-9H-carbazole, KOH, DMSO, 30 °C,
ogy of the active layer (see Scheme 1) and consequently short-
3
3
2
5 3
circuit current density (J ) enhancement by 12% and PCE
SC
enhancement by 8%. We believe that the strategy of MIL can
be used to further improve active layer morphology and
photovoltaic performance of many high performance PSC
devices.
60%; (v) BBr , dichloromethane, −78 °C to rt, 61%; vi)
3
bis(pinacolato)diboron, Pd(dppf)Cl , KOAc, 1,4-dioxane, 80 °C,
2
8
5%; (vii) triethyl phosphonate, reflux, 61%; (viii) Pd(PPh ) ,
3 4
K CO (aq 2 M), toluene, Aliquat 336, 100 °C, 80%.
2
3
The introduction of phosphonate moieties to the side chain
2
. RESULTS AND DISCUSSION
of PCDTBT-Pho does not obviously affect the electronic
structure of the polymer backbone but greatly changes the
solubility of the polymer. As shown in Figure 1a and listed in
Table 1, the absorption spectra in hot o-DCB solution and in
thin film of PCDTBT-Pho and PCDTBT are similar. The
LUMO/HOMO energy levels of PCDTBT-Pho and PCDTBT
Scheme 2 outlines the synthetic route of PCDTBT-Pho. After 2
was synthesized by Williamson reaction of 1,8-dibromooctane
and phenol, its Grignard reagent reacted with ethyl formate to
afford 3. The tosylation of 3 and subsequent alkylation with
2,7-dibromocarbazole readily gave 5, which was deprotected to
afford 6. The key monomer 8 was prepared by Pd-catalyzed
Miyaura borylation reaction of 6 and bis(pinacolato)diboron,
followed by treatment with triethyl phosphonate. Finally, the
monomer 8 was copolymerized with 4,7-di(2′-bromothien-5′-
yl)-2,1,3-benzothiadiazole using Suzuki polycondensation con-
(
Table 1), as estimated from cyclic voltammetry (Figure 1b),
are also very close. These results imply the minimal effect of the
pendant phosphonate moieties on the electronic structure of
14
the polymer backbone in PCDTBT-Pho. On the other hand,
PCDTBT is soluble in chloroform, chlorobenzene (CB), and o-
DCB. In contrast, PCDTBT-Pho is insoluble in chloroform and
CB, and only soluble in hot o-DCB or hot m-methylphenol,
indicating that the polar phosphonate moieties on the side
chain change the solubility of PCDTBT-Pho. We test the
solubility of PCDTBT-Pho in the solvent of CB/o-DCB =1/1,
which is always used in solution processing of
PCDTBT:PC BM-based PSC devices. As shown in Figure
dition with Pd(PPh ) as the catalyst to afford the target
3
4
polymer PCDTBT-Pho. During the polymerization, end-
capping was carried out by sequential adding phenyl boric
acid and bromobenzene to the reaction mixture. The polymer
was purified by sequential Soxhlet extraction with acetone,
toluene, and chloroform, followed by washing with hot
chlorobenzene (CB). The chemical structure of PCDTBT-
71
1
Pho is confirmed by H NMR in deuterated o-dichlorobenzene
1c, the absorbance of PCDTBT-Pho thin film keeps unchanged
after washing with the CB/o-DCB = 1/1 solvent. Therefore, the
changed solubility by phosphonate moieties in PCDTBT-Pho
enable us to fabricate multilayer PSC devices with PCDTBT-
Pho as the underlying layer.
(o-DCB) at 125 °C (Figure S3) and elemental analysis. Gel
permeation chromatography (GPC) at 150 °C with 1,2,4-
trichlorobenzene as the eluent indicates its number-average
molecular weight (M ) of 43 200 with polydispersity index of
n
3
.36. According to thermogravimetric analysis (TGA),
PSC devices were fabricated with the configuration of indium
tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with
PCDTBT-Pho is stable up to 330 °C.
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Figure 2. J−V curves (a) and EQE curves (b) of PSC devices with and
without PCDTBT-Pho as MIL.
significantly out of the error of device fabrication. Indeed, other
PSC devices with PCDTBT-Pho layer of different thickness
also show increased JSC compared to the control device (see
Figure S5 and Table S1). Increase of the PCDTBT-Pho layer
thickness results in decreased VOC and FF, which are possibly
attributed to the poor hole-transporting property of PCDTBT-
Pho.
Figure 1. UV−vis absorption spectra (a) and cyclic voltagram (b) of
PCDTBT-Pho and PCDTBT. (c) Absorption spectra of a PCDTBT-
Pho film without and with washing with CB/o-DCB = 1/1.
It is interesting and important to investigate the origin of the
JSC increase with the underlying PCDTBT-Pho layer.
Considering that PCDTBT-Pho has similar LUMO/HOMO
energy levels with PCDTBT and that the incorporation of thin
PDCTBT-Pho layer does not increase the absorption of the
active layer (see Figure S6), we pay attention to the
morphology of the active layer. Transmission electron
microscopy (TEM) image of the active layer in the control
device (Figure 3a) reveals a rather homogeneous morphology.
In contrast, the active layer in the device with the underlying
PCDTBT-Pho layer (Figure 3b) shows clear fibrillar structure
arising from the aggregated PCDTBT chains. The fine fibrillar
structure morphology is beneficial for charge separation and
charge transport in the active layer. In grazing incidence X-ray
diffraction (GI-XRD) pattern of the active layer (Figure 3c), an
extra peak at 2θ = 9.5° is observed for the active layer with
underlying PCDTBT-Pho layer, implying that the PCDTBT
Table 1. Absorption Maxima, Bandgap, and LUMO/HOMO
Energy Levels of PCDTBT-Pho and PCDTBT
a
opt
λmax (sol)
nm]
λmax (film)
Eg
HOMO
[eV]
LUMO
[eV]
[
[nm]
[eV]
1.87
PCDTBT-
Pho
548
584
−5.18
−3.28
PCDTBT
559
582
1.90
−5.23
−3.19
aDetermined in 10−5 M solution of o-DCB at 90 °C.
poly(styrenesulfonate) (PEDOT:PSS) (40 nm)/PCDTBT-Pho
1 nm)/PCDTBT:PC BM (80 nm)/LiF (1 nm)/Al (100
(
7
1
nm). PCDTBT-Pho was spin-coated with its solution in o-DCB
at 120 °C, and the PCDTBT:PC BM active layer was spin-
7
1
15
coated subsequently with the solution in CB/o-DCB = 1/1. A
control device without the PCDTBT-Pho layer was also made
for comparison. Figure 2a shows the current density−voltage
chains are more ordered and crystalline possibly due to the
inducing effect of the underlying PCDTBT-Pho layer. The
improved crystallinity is expected to facilitate hole transport in
PSCs. The inducing effect of PCDTBT-Pho is also investigated
by X-ray photoelectron spectroscopy (XPS) of the bottom
surface of the PCDTBT:PC BM active layer (Figure S7). The
(
J−V) characteristics of the devices. The control device reveals
2
the open-circuit voltage (V ) of 0.90 V, J of 9.13 mA/cm ,
OC
SC
and fill factor (FF) of 0.68, corresponding to PCE of 5.61%. In
71
comparison, the device with PCDTBT-Pho layer shows the
VOC of 0.89 V, JSC of 10.18 mA/cm , FF of 0.67, and PCE of
S 2p peak in XPS spectra comes from PCDTBT and can be
referred as the signature of PCDTBT. The C 1s peak
represents the sum of PCDTBT and PC BM. Therefore, the
2
6.03%. The two devices have virtually identical parameters,
71
except for a 12% increase in JSC for the device with PCDTBT-
Pho layer. The increase in JSC is confirmed by the higher
external quantum efficiency (EQE) of the PCDTBT-Pho-
containing device compared to the control device (Figure 2b).
As shown in Table S1, the JSC increase and PCE increase are
S 2p/C 1s peak ratio can be correlated to the content of
16
PCDTBT in the blend. As listed in Table 2, the S 2p/C 1s
peak ratio (AS 2p/AC 1s) is much higher for the device with
PCDTBT-Pho underlying layer (AS 2p/AC 1s = 0.073) compared
to the control device (AS 2p/AC 1s = 0.049), suggesting that
C
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surface energy more favorable to enrich on the top of the active
layer. Moreover, the small surface energy difference between
the underlying layer and the active layer components leads to
less favored dewetting process and gives rise to more
pronounced phase separation. Our argument is somewhat
consistent with Bulliard et al.’s report that a surface energy of
about 50 mN m− of the underlying layer gives the optimized
active layer morphology and the best PSC device perform-
1
12
ance. On the other hand, PCDTBT-Pho has similar polymer
backbone with that of PCDTBT. When using as the underlying
layer for spin-coating of the active layer, PCDTBT-Pho may
induce PCDTBT to crystallize and to accumulate in the vicinity
region.
3
. CONCLUSIONS
In summary, we have developed a novel polymer PCDTBT-
Pho with polar phosphonate moieties attached to the side chain
of PCDTBT, which can be used as the underlying layer to
improve the morphology of PCDTBT:PC BM active layer for
Figure 3. TEM images of the PCDTBT:PC BM active layers without
71
71
better PSC device performance. Owing to its chemical structure
and proper surface energy, PDCTBT-Pho facilitates the
formation of biscontinuous network morphology in the active
layer, makes the donor polymer enriched at the anode side, and
induces the donor polymer to crystallize. These improvements
contribute to improved charge separation and transport, leading
to increased JSC and PCE of the PSC devices. The development
of MIL represents a novel strategy to further optimize active
layer morphology and improve efficiency of high performance
PSCs.
(
a) and with (b) PCDTBT-Pho as MIL. (c) GI-XRD patterns of the
PCDTBT:PC BM active layer in the PSC devices without and with
PCDTBT-Pho as MIL.
71
Table 2. Hole Mobility and XPS S 2p/C 1s Peak Area Ratio
of the Bottom Surface of the Active Layer with and without
PCDTBT-Pho Underlying Layer
hole mobility
S 2p/C 1s peak area
ratio
2
−1 −1
(
cm V
s
)
2.6 × 10−
2.1 × 10−
5
0.073
0.049
with PCDTBT-Pho
6
without PCDTBT-
Pho
4
. EXPERIMENTAL SECTION
Synthesis of 1-(8-Bromooctyloxy)benzene (2). In a three-
necked round-bottom flask, a mixture of K CO (311 g, 2.25 mol),
2
3
PCDTBT is more accumulated on the PCDTBT-Pho surface
than on the PEDOT:PSS surface in the control device. That
means the PCDTBT-Pho underlying layer results in enrich-
ment of the donor polymer on the anode side. This gradient
distribution in the active layer (so-called vertical phase
separation) is ideal for charge collection. All the TEM, XRD,
and XPS results suggest improved active layer morphology with
PCDTBT-Pho, which is expected to facilitate charge gen-
eration/transport. To confirm these results, we estimate the
hole mobility of the PCDTBT:PC BM active layer using space
phenol (53 g, 0.56 mol), 1,8-dibromooctane (460 g, 1.69 mol), and
acetone (1.2 L) was heated to reflux for 15 h with vigorous stirring.
After removing most of the acetone, the residual was dissolved in
deionized water and dichloromethane. The organic phase was
collected and washed with brine, followed by drying over anhydrous
Na SO . After filtration, the solvent was removed by rotatory
2
4
evaporation, and the excessive 1,8-dibromooctane was removed by
distillation under reduced pressure. The residue was purified by silica
gel column chromatography with petroleum ether/dichloromethane =
2
0/1 as eluent to afford the title compound as a white solid (151 g,
1
7
1
95%). H NMR (300 MHz, CDCl ), δ (ppm): 7.33−7.26 (m, 2H),
3
charge limited current (SCLC) method according to the J−V
curves of the hole-only devices (device structure: ITO/
PEDOT:PSS/PCDTBT-Pho/PCDTBT:PC BM/Au). As
6
.98−6.85 (m, 3H), 3.95 (t, J = 6.5 Hz, 2H), 3.41 (t, J = 6.8 Hz, 2H),
1.92−1.72 (m, 4H), 1.52−1.31 (m, 8H).
Synthesis of 1,17-Diphenoxyheptadecan-9-ol (3). In a three-
necked round-bottom flask, a solution of 2 (76.3 g, 268 mmol) in THF
7
1
shown in Table 2, the hole mobility with underlying
−
5
2
−1 −1
(
500 mL) was added dropwise to magnesium chips (6.8 g, 280 mmol),
PCDTBT-Pho layer (μ = 2.6 × 10 cm V s ) is much
h
−6
2
−1 −1
followed by stirring at 50 °C for 3 h to give the Grignard reagent. After
being cooled down to room temperature, the reaction mixture was
added ethyl formate (9.8 mL, 122 mmol) dropwise. The resulting
reaction mixture was stirring overnight at room temperature, followed
by quenching with 1 M hydrochloric acid. This mixture was extracted
with diethyl ether, and the organic phase was washed with brine and
dried over anhydrous Na SO . After filtration and removing the
higher than that (μ = 2.1 × 10 cm V s ) of the control
h
device without PCDTBT-Pho layer. Therefore, we believe
PCDTBT-Pho is an effective MIL for PCDTBT:PC BM active
71
layer.
We attribute the morphology regulating capability of
PCDTBT-Pho to its proper surface energy and its chemical
structure. It is well-known that surface energy of underlying
layer can effectively alter phase separation process and
2
4
solvent under reduced pressure, the crude product was purified by
silica gel column chromatography with petroleum ether/dichloro-
17
methane = 2/1 as eluent to afford the title compound as a white solid
consequently affect morphology. PCDTBT-Pho has smaller
1
−
1
−1
(37.2 g, 70%). H NMR (300 MHz, d -DMSO), δ (ppm): 7.26 (t, J =
6
surface energy (40.5 mN m ) than that (91.6 mN m ) of
PEDOT:PSS (Table S2). When PCDTBT-Pho MIL is used in
PSC devices, the decreased surface energy of the underlying
7
.9 Hz, 4H), 6.92−6.88 (m, 6H), 4.22−4.00 (m, 1H), 3.93 (t, J = 6.5
Hz, 1H), 3.33 (br, 1H), 1.74−1.64 (m, 4H), 1.39−1.27 (m, 24H).
Synthesis of 1,17-Diphenoxyheptadecan-9-yl-4-methylben-
zenesulfonate (4). To a stirred solution of 3 (36.5 g, 82.9 mmol),
triethylamine (23.2 mL, 165.8 mmol), and trimethylamine hydro-
chloride (7.9 g, 82. 9 mmol) in dichloromethane (300 mL) in an ice−
−1
layer makes PCDTBT (26.8 mN m ) with smaller surface
energy more favorable to accumulate on the bottom of the
−1
active layer and makes PC BM (32.8 mN m ) with higher
7
1
D
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water bath, a solution of p-toluenesulfonyl chloride (19.8 g, 103.6
mmol) in dichloromethane (200 mL) was added dropwise. Then
reaction mixture was allowed to warm to room temperature and stirred
for 2 h. After work-up, the reaction mixture was washed with brine for
three times, dried over anhydrous Na SO , filtered, concentrated, and
33.72, 32.67, 29.20, 29.00, 28.47, 27.94, 26.58, 24.91. Anal. Calcd for
C H B Br NO : C, 60.39; H, 7.79; N, 1.72. Found: C, 60.68; H,
8.02; N, 1.74.
41
63
2
2
4
Synthesis of 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)-N-9-[1,17-bis(diethylphosphonate)heptadecanyl]-
carbazole (8). A mixture of 7 (3.0 g, 3.7 mmol) and triethyl
phosphonate (50 mL) was refluxed with vigorous stirring for 12 h.
After work-up, excessive triethyl phosphonate was removed under
reduced pressure. The residual was purified by silica gel column
chromatography (dichloromethane/methanol = 50/1 as eluent) to
2
4
dried under vacuum to afford the crude product as a yellow oil (49.3 g,
00%). The crude product was used in the next reaction without
1
further purification.
Synthesis of N-9-(1,17-Diphenoxy)heptadecanyl-2,7-dibro-
mocarbazole (5). In a three-necked round-bottom flask equipped
with an pressure-equalizing dropping funnel was charged with 2,7-
dibromo-9H-carbazole (22.5 g, 69.1 mmol), potassium hydroxide
1
afford the title compound as a light yellow oil (2.1 g, 61%). H NMR
(
400 MHz, CDCl ), δ (ppm): 8.12 (t, J = 9.4 Hz, 2H), 8.01 (s, 1H),
3
(22.8 g, 345.4 mmol), and dimethyl sulfoxide (DMSO) (100 mL). A
7
.87 (s, 1H), 7.66 (d, J = 5.6 Hz, 2H), 4.71−4.66 (m, 1H), 4.12−4.02
solution of 4 (49.3 g, 82.9 mmol) in DMSO (100 mL) was added
dropwise to the flask at room temperature. After being stirred for 1
day, the reaction mixture was poured into deionized water and
extracted with dichloromethane for three times. The combined organic
phase was washed with brine, dried over anhydrous Na SO , filtered,
(
m, 8H), 2.35−2.30 (m, 2H), 1.96−1.92 (m, 2H), 1.69−1.45 (m, 8H),
1
0
1
6
2
.39 (s, 24H), 1.29 (t, J = 7.1 Hz, 12H), 1.26−1.10 (m, 18H), 1.00−
.94 (m, 2H). 13C NMR (100 MHz, CDCl ), δ (ppm): 141.81,
3
38.53, 125.92, 124.55, 119.93, 119.62, 117.93, 115.27, 83.61, 61.29,
1.22, 56.22, 33.70, 30.42, 30.25, 29.26, 28.98, 28.81, 26.60, 26.15,
2
4
and concentrated. Finally, the residual was purified by silica gel column
4.82, 22.20, 22.16, 16.36, 16.31. MALDI-TOF (m/z): Calcd for
chromatography with petroleum ether/ethyl acetate = 200/1 as eluent
+
1
C H B NO P (M ): 929.57. Found: 929.60. Anal. Calcd for
to afford the title compound as a white solid (31.0 g, 60%). H NMR
49 83
2
10 2
C H B NO P : C, 63.30; H, 9.00; N, 1.51; Found: C, 62.08; H,
(
(
2
4
1
400 MHz, CDCl ), δ (ppm): 7.92−7.86 (m, 2H), 7.69 (s, 1H), 7.53
49 83
2
10 2
3
s, 1H), 7.36−7.29 (m, 2H), 7.27−7.24 (m, 4H), 6.92 (t, J = 7.3 Hz,
8.85; N, 1.44.
H), 6.87 (d, J = 8.0 Hz, 4H), 4.44−4.39 (m, 1H), 3.89 (t, J = 6.6 Hz,
Synthesis of PCDTBT-Pho. In a two-necked round-bottom flask, a
mixture of 8 (0.303 g, 0.326 mmol), 4,7-di(2-bromothien-5-yl)-2,1,3-
benzothiadiazole (0.149 g, 0.326 mmol), Pd(PPh ) (0.005 g), Aliquat
H), 2.25−2.17 (m, 2H), 2.02−1.87 (m, 2H), 1.73−1.66 (m, 4H),
13
.37−1.12 (m, 18H), 1.04−0.92 (m, 2H). C NMR (100 MHz,
3
4
CDCl ), δ (ppm): 159.07, 142.88, 139.39, 129.36, 122.32, 121.50,
336 (0.015 g), degassed toluene (12.0 mL), and aqueous K CO (2.0
3
2 3
1
3
21.25, 120.82, 120.40, 119.76, 119.18, 114.45, 112.12, 67.74, 56.88,
3.42, 29.17, 29.16, 29.13, 29.12, 26.62, 25.87. Anal. Calcd for
M, 1.0 mL) was vigorously stirred at 100 °C for 5 h under an argon
atmosphere. End-capping was carried out by sequentially adding
phenylboric acid (0.5 M solution in anhydrous toluene, 0.6 mL) and
bromobenzene (0.4 mL) to the reaction mixture. After being cooled to
room temperature, the mixture was filtered. The solid was collected,
dispersed in deionized water, and ultrasonicated for 1 h. Filtration of
the dispersion afford the crude product, which was further purified by
Soxhlet extraction with acetone, toluene, and chloroform, followed by
washing with hot chlorobenzene (CB). The dark solid was collected
C H Br NO : C, 65.87; H, 6.61; N, 1.87. Found: C, 66.13; H, 6.57;
N, 1.84.
41
49
2
2
Synthesis of N-9-(1,17-Dibromo)heptadecanyl-2,7-dibromo-
carbazole (6). To a stirred solution of 5 (18.5 g, 24.7 mmol) in
anhydrous dichloromethane (200 mL) at −78 °C was added dropwise
a solution of boron tribromide (5.5 mL, 59.3 mmol) in dichloro-
methane (50 mL). After the addition, the reaction was allowed to
warm to room temperature and stirred for 2 h. Then the reaction
mixture was poured into deionized water and extracted with
dichloromethane for three times. The combined organic phase was
washed with brine, dried over anhydrous Na SO , filtered, and
1
and dried in vacuum overnight. Yield: 0.25 g (80%). H NMR (400
MHz, d -o-DCB, 125 °C), δ (ppm): 8.23−7.90 (br, 8H), 7.67−7.57
4
(br, 4H), 4.84 (br, 1H), 4.02 (br, 8H), 2.52 (br, 2H), 2.16 (br, 2H),
2
4
1
.94 (br, 2H), 1.63−1.22 (m, 38H). GPC (1,2,4-trichlorobenzene,
concentrated. The crude product was purified by silica gel column
chromatography (hexane as eluent) and recrystallization in acetonitrile
to afford the title compound as white crystals (10.9 g, 61%). H NMR
polystyrene standard, 150 °C): M = 43 200, PDI = 3.36. Anal. Calcd
n
1
for C H N O P S : C, 62.88; H, 6.72; N, 4.31; S, 9.87. Found: C,
51 65
3
6 2 3
(
400 MHz, CDCl ), δ (ppm): 7.91 (m, 2H), 7.69 (s, 1H), 7.53 (s,
62.32; H, 6.63; N, 4.23; S, 9.88.
3
1
4
1
H), 7.34 (t, J = 6.9 Hz, 2H), 4.44−4.39 (m, 1H), 3.35 (t, J = 6.9 Hz,
PSC Device Fabrication and Measurement. Indium tin oxide
(ITO) glass substrates were cleaned by sequential ultrasonication in
detergent, deionized water, acetone, and isopropyl alcohol, followed by
dried at 120 °C for 30 min and treated with UV-ozone for 25 min.
Then PEDOT:PSS (Baytron P Al 4083) was spin-coated on the ITO
glass substrates at 5000 rpm for 40 s to give a thickness of 40 nm,
followed by baking at 125 °C for 30 min. The ultrathin layer of
PCDTBT-Pho was deposited on the PEDOT:PSS layer by spin-
coating with its solution in o-DCB (0.02 or 0.05 mg/mL) at 120 °C at
H), 2.25−2.18 (m, 2H), 1.95−1.86 (m, 2H), 1.80−1.70 (m, 4H),
13
.40−1.09 (m, 18H), 1.00−0.92 (m, 2H). C NMR (100 MHz,
CDCl ), δ (ppm): 142.91, 139.43, 122.41, 121.54, 121.30, 120.87,
1
2
3
19.81, 119.23, 114.50, 112.14, 56.90, 33.95, 33.44, 32.73, 29.08,
9.03, 28.48, 28.00, 26.60. MALDI-TOF (m/z), calcd for C H Br N
29
39
4
+
(
M ): 716.98. Found: 717.00. Anal. Calcd for C H Br N: C, 48.29;
29 39 4
H, 5.45; N, 1.94. Found: C, 48.46; H, 5.45; N, 1.91.
Synthesis of 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
-yl)-N-9-(1,17-dibromo)heptadecanylcarbazole (7). A mixture
2
2
000 rpm for 40 s. Subsequently, the PCDTBT:PC BM active layer
71
of N-9-(1,17-dibromo)heptadecanyl-2,7-dibromocarbazole (6) (3.84 g,
.32 mmol), bis(pinacolato)diboron (4.05 g, 15.96 mmol), Pd(dppf)-
Cl (0.13 g, 0.16 mmol), KOAc (4.70 g, 47.88 mmol), and anhydrous
was spin-coated on the PCDTBT-Pho layer with the solution of
5
PCDTBT (3.5 mg/mL) and PC BM (14 mg/mL) in o-DCB:CB = 1/
71
2
1
at room temperature to give a thickness of 80 nm. Then the film was
1
,4-dioxane (50 mL) was stirred at 80 °C for 20 h under an argon
thermal annealed at 80 °C for 30 min. Finally, the device was
transferred to a vacuum chamber, and LiF (1 nm)/Al (100 nm) was
sequentially deposited by thermal evaporation at the pressure of about
atmosphere. After being cooled down, the mixture was poured into
deionized water and extracted with ethyl acetate for three times. The
combined organic phase was washed with brine, dried over anhydrous
Na SO , and concentrated. The residual was fruther purified by silica
−4
2
4
× 10 Pa. The active area was 8 mm .
2
4
The J−V characteristics of PSC devices were measured using a
computer-controlled Keithley 236 source meter and an oriel 150 W
gel column chromatography with petroleum ether/ethyl acetate = 50/
as eluent to afford the title compound as a white solid (3.70 g, 85%).
1
1
solar simulator with an AM 1.5G filter. The light intensity was 100
H NMR (400 MHz, CDCl ), δ (ppm): 8.13 (t, J = 9.1 Hz, 2H), 8.02
3
2
mW/cm , as determined by a calibrated silicon diode with KG-5 filter.
(
3
s, 1H), 7.88 (s, 1H), 7.67 (d, J = 7.3 Hz, 2H), 4.72−4.67 (m, 1H),
.33 (t, J = 6.9 Hz, 4H), 2.37−2.30 (m, 2H), 1.97−1.89 (m, 2H),
The EQE measurement was performed under short-circuit conditions
with a lock-in amplifier (SR830, Stanford Research System) at a
chopping frequency of 280 Hz during illumination with a
monochromatic light from a xenon lamp.
1
(
.78−1.70 (m, 4H), 1.40 (s, 24H), 1.30−1.13 (m, 18H), 0.98−0.95
m, 2H). 13C NMR (100 MHz, CDCl ), δ (ppm): 141.88, 138.60,
3
1
26.00, 124.63, 120.01, 119.71, 117.98, 115.31, 83.66, 56.25, 33.89,
E
dx.doi.org/10.1021/ma5008754 | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Z.; Xia, J.; Tsai, S.-T.; Wu, Y.; Li, G.; Ray, C.; Yu, L. Adv. Mater. 2010,
ASSOCIATED CONTENT
Supporting Information
Characterization, fabrication of hole-only devices, H NMR and
C NMR spectra of the monomer 8 and PCDTBT-Pho, TGA
■
2
(
(
2, E135.
10) (a) Heriot, S. Y.; Jones, R. A. L. Nat. Mater. 2005, 4, 782.
b) Chen, F.-C.; Lin, Y.-K.; Ko, C.-J. Appl. Phys. Lett. 2008, 92,
*
S
1
1
3
0
23307.
curves, absorption of the active layer in the PSC devices, J−V
curves of the PSC devices with different PCDTBT-Pho layer
thickness, J −V curves of the hole-only devices, contact angles,
and surface energies. This material is available free of charge via
the Internet at http://pubs.acs.org.
(11) (a) Li, C.-Y.; Wen, T.-C.; Guo, T.-F. J. Mater. Chem. 2008, 18,
4478. (b) Murray, I. P.; Lou, S. J.; Cote, L. J.; Loser, S.; Kadleck, C. J.;
Xu, T.; Szarko, J. M.; Rolczynski, B. S.; Johns, J. E.; Huang, J. X.; Yu, L.
P.; Chen, L. X.; Marks, T. J.; Hersam, M. C. J. Phys. Chem. Lett. 2011,
2
, 3006.
12) Bulliard, X.; Ihn, S.-G.; Yun, S.; Kim, Y.; Choi, D.; Choi, J.-Y.;
Kim, M.; Sim, M.; Park, J.-H.; Choi, W.; Cho, K. Adv. Funct. Mater.
010, 20, 4381.
13) (a) Blouin, A.; Michaud, A.; Leclerc, M. Adv. Mater. 2007, 19,
295. (b) Park, S. H.; Roy, A.; Beaupre, S.; Cho, S.; Coates, N.; Moon,
J. S.; Moses, D.; Leclerc, M.; Lee, K.; Heeger, A. J. Nat. Photonics 2009,
, 297.
14) (a) Zhou, G.; Qian, G.; Ma, L.; Cheng, Y.; Xie, Z. Y.; Wang, L.
(
AUTHOR INFORMATION
Corresponding Authors
E-mail: liujun@ciac.ac.cn (J.L.).
E-mail: lixiang@ciac.ac.cn (L.W.).
■
2
(
*
2
́
*
3
(
Notes
The authors declare no competing financial interest.
X.; Jing, X. B.; Wang, F. S. Macromolecules 2005, 38, 5416. (b) Qin, C.
J.; Cheng, Y.; Wang, L. X.; Jing, X. B.; Wang, F. S. Macromolecules
ACKNOWLEDGMENTS
This work was financially supported by the 973 project (No.
014CB643504), the Nature Science Foundation of China
No. 51373165), the Strategic Priority Research Program of
■
2
008, 41, 7798. (c) Guo, X.; Qin, C. J.; Cheng, Y.; Xie, Z. Y.; Geng, Y.
H.; Jing, X. B.; Wang, F. S.; Wang, L. X. Adv. Mater. 2009, 21, 3682.
(d) Zhang, B. H.; Qin, C. J.; Ding, J. Q.; Chen, L.; Xie, Z. Y.; Cheng,
Y. X.; Wang, L. X. Adv. Funct. Mater. 2010, 20, 2951.
2
(
Chinese Academy of Sciences (No. XDB12010200), and
(15) (a) Fang, G.; Liu, J.; Fu, Y. Y.; Meng, B.; Zhang, B. H.; Xie, Z.
Y.; Wang, L. X. Org. Electron. 2012, 13, 2733. (b) Liu, J. G.; Chen, L.;
Gao, B. R.; Cao, X. X.; Han, Y. C.; Xie, Z. Y.; Wang, L. X. J. Mater.
Chem. A 2013, 1, 6216. (c) Jiang, G. X.; Bian, C. L.; Ding, J. Q.; Wang,
L. X.; Jing, X. B.; Wang, F. S. Chin. J. Polym. Sci. 2013, 31, 787.
“Thousand Talents Program” of China.
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dx.doi.org/10.1021/ma5008754 | Macromolecules XXXX, XXX, XXX−XXX