Single-strand and ladder-type polymeric acceptors based on regioisomerically-pure perylene diimides towards all-polymer solar cells

Article abstract of DOI:10.1016/j.polymer.2018.12.041

Since dibromo perylene diimides (DBPDIs) contain two isomers that are difficult to separate, isomeric effect on properties and applications of PDI polymers has been rarely studied. Few ladder-type polymers have been used in organic solar cells. Herein, si

Full text of DOI:10.1016/j.polymer.2018.12.041

Polymer162(2019)108–115
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Single-strand and ladder-type polymeric acceptors based on
regioisomerically-pure perylene diimides towards all-polymer solar cells
Lei Wanga,1, Ming Hua,1, Youdi Zhanga,b, Zhongyi Yuana,b,∗, Yu Hua, Xiaohong Zhaoa,
Yiwang Chena,b
a College of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031, China
b Institute of Polymers and Energy Chemistry (IPEC), Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China
H I G H L I G H T S
Regioisomerically-pure 1,7-DBPDIs lead to single-strand polymers (PrPDIT) with molecular weight distribution as low as 1.08.
Ladder-type polymers (FPrPDIT) were synthesized by the quantitative yield cyclization of PrPDIT.
Both PrPDIT and FPrPDIT are excellent acceptors with highest power conversion efficiency of 5.95% in all-polymer solar cells.
•
•
•
A R T I C L E I N F O
A B S T R A C T
Keywords:
Since dibromo perylene diimides (DBPDIs) contain two isomers that are difficult to separate, isomeric effect on
properties and applications of PDI polymers has been rarely studied. Few ladder-type polymers have been used
in organic solar cells. Herein, single-strand polymers (PrPDIT) were synthesized by the polymerization of re-
gioisomerically-pure 1,7-dibromo-PDIs (1,7-DBPDIs) and 2,5-bis(trimethylstannyl)thiophene. Furthermore,
ladder-type polymers (FPrPDIT) were obtained by the highly efficient photo-induced cyclization of polymers
PrPDIT. The effects of isomers and molecular weight on the absorption, electrochemistry, thermal stability, and
photovoltaic application of polymers were studied. Pure 1,7-DBPDIs lead to polymers with molecular weight
distribution as low as 1.08. These polymers with strong absorption in 300–700 nm, low-lying lowest unoccupied
molecular orbital (LUMO) energy levels around −4.0 eV and high thermal stability could be excellent electron
acceptors. Regioisomerically-pure polymers demonstrate better photovoltaic performance than that of mixed
ones. The highest power conversion efficiency (PCE) of all-polymer solar cells based on PrPDIT and FPrPDIT is
up to 5.95% and 4.52% respectively.
Regioisomerically-pure perylene diimides
Ladder-type polymers
All-polymer solar cells
1. Introduction
All-polymer solar cells (all-PSCs) are focused recently, because
polymeric semiconductors exhibit excellent flexibility, film forming
Aiming for efficient solar-to-electricity conversion, bulk hetero-
junction organic solar cells (BHJOSCs) have attracted more and more
attention because of light-weight, flexible, and low-cost devices [1–11].
Electronic donors and acceptors are both essential in BHJOSCs. Com-
pared to the prosperity and excellence of donor materials, electron
acceptors lag obviously [12–20]. Widely used fullerene acceptors (such
as PC61BM, PC71BM) have disadvantages of difficult modification, high
cost, and weak absorption [21–24]. Thus, much effort has been focused
on non-fullerene organic acceptors in the past several years, and they
show diverse and precise molecular structures, strong absorption, and
tunable energy levels [25–31].
ability, mechanical strength, and charge transport [32–34]. Perylene
diimides (PDIs) and naphthalene diimides (NDIs) are two promising
building blocks to construct polymeric acceptors [35–42]. Polymeric
PDIs have been widely reported for their advantages of suitable lowest
unoccupied molecular orbital (LUMO) energy levels, high stability, and
strong absorption [43–46]. Since dibromo perylene diimides (DBPDIs,
Fig. 1) contain two isomers of 1,6-dibromo PDIs (1,6-DBPDIs) and 1,7-
dibromo PDIs (1,7-DBPDIs) which are difficult to separate, pure major
isomer 1,7-DBPDIs are rarely used to construct conjugated polymers.
Different configurations of isomers result in polymers with different
arrangement and charge transport, which has significant effect on their
∗ Corresponding author. College of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031, China.
E-mail address: yuan@ncu.edu.cn (Z. Yuan).
1 Author contributions: L. Wang and M. Hu contributed equally to this work.
https://doi.org/10.1016/j.polymer.2018.12.041
Received 19 November 2018; Received in revised form 21 December 2018; Accepted 26 December 2018
Availableonline27December2018
0032-3861/©2018ElsevierLtd.Allrightsreserved.

L. Wang et al.
Polymer162(2019)108–115
Fig. 1. Structures of 1,7-DBPDI&1,6-DBPDI, PrPDIT, FPrPDIT, and optimized geometry of FPrPDIT.
Scheme 1. Synthetic route of PrPDIT,
FPrPDIT, and FPDI-Th. a) 1) KOH, H2O,
70 °C, 60 min; 2) TBAB, 1-butyl bro-
mide, 100 °C, 5 h, 92%; b) Br2, K2CO3,
CH2Cl2, rt, 12 h; c) CH2Cl2eCH3CN, rt,
recrystallization, 46%; d) ClSO3H, rt,
4 h, quantitative yield; e) alkyl amine,
NMP, AcOH, 80 °C, 40 min, 57%; f) 2,5-
bis(trimethylstannyl)thiophene,
Pd2(dba)3, P(o-tolyl)3, toluene, 110 °C,
48 h, 78%; g) 2,5-bis(trimethylstannyl)
thiophene, Pd(PPh3)4, toluene, 110 °C,
12 h, 91%; h) I2, CH2Cl2, hν, rt, 2 h,
quantitative yield; i) I2, CH2Cl2, hν, rt,
10 h, quantitative yield.
109

L. Wang et al.
Polymer162(2019)108–115
photovoltaic application [47]. Dahui Zhao and Jian Pei et al. reported a
regioisomerically-pure polymeric acceptor based on 1,7-DBPDIs and
bithiophene, and it reached the highest power conversion efficiency
(PCE) of 2.17%, and the regioisomerically-pure polymer shows im-
proved device performance compared to the irregular ones [44]. So it is
necessary to study this isomeric effect.
(Mn: 6.3 KDa) is as low as 1.08, while that of PPDIT (Mn: 6.9 KDa) is
1.78, as determined by gel permeation chromatography (GPC) using
THF as the eluent.
As shown in Scheme 1, to get well-defined ladder-type FPrPDIT, a
highly efficient cyclization of single-strand PrPDIT is necessary. A
model compound FPDI-Th was synthesized under different conditions.
With optimized reaction condition of photo-induced cyclization, the
precursor compound PDI-Th could be converted into FPDI-Th quanti-
tatively in the presence of catalytic amount I2. PDI-Th tends to de-
compose in the solvent under ambient condition, and it leads to a
complicated mixture in the absence of catalyst I2.
Single-strand PrPDIT could be converted into ladder-type FPrPDIT
gradually under irradiation of a xenon lamp HSX-F300 (350–780 nm) in
CH2Cl2, and the process can be tracked by UV–Visible absorption. The
absorption of reaction mixture was recorded after removing catalyst I2
by aqueous Na2SO3. As shown in Fig. 2, the absorption of starting
polymer hypsochromic shifted gradually in the reaction process in
2.5 h. The solution color changed from purple dark into red, which was
consistent with the reaction process of model compound. FPrPDIT was
characterized by high temperature NMR. Single-strand PrPDIT showed
clear NMR response at room temperature, while ladder-type FPrPDIT
gave low-field signal only at high temperature, because the rigid core
limits the free rotation of the molecule. 1H NMR signal of protons at
thienyl group (δ = 7.4 ppm) disappeared after cyclization, and a broad
peak (δ = 9.0–7.6 ppm) was observed in 1H NMR of FPrPDIT (see
Supporting Information). Due to bulky alkyl chains and twisted con-
jugated cores, target polymers FPrPDIT as the red solid showed good
solubility in common solvents like CH2Cl2, CHCl3, THF, and toluene.
Ladder-type semiconductor polymers in which conjugated cores are
connected by double bonds or aromatic rings have large rigid skeletons,
which lead to free intramolecular electron communication, unique
packing and special applications [48]. Ladder-type polymers with
perfect structures are rare due to synthetic difficulty. In single-strand
PDI polymers, PDIs and neighboring aromatic ring such as benzene,
thiophene, and thieno[3,2-b]thiophene could be cyclized by the dehy-
drogenation reaction, which lead to ladder-type polymers [49–54].
However, quantitative cyclization is essential to ensure flawless struc-
tures. Xiao et al. synthesized planar ladder-type polymers based on PDIs
and thieno[3,2-b]thiophene through a highly efficient photo-induced
cyclization [48]. However, they show limited solubility due to strong
intermolecular interaction. Furthermore, their isomeric effect was not
considered, and they did not exhibit any performance in photovoltaic
application. Herein, we are interested in single-strand and ladder-type
polymers based on regioisomerically-pure PDIs and thiophene, and they
show twisted well-defined structures (Fig. 1), good solubility, and ex-
cellent photovoltaic application.
Interestingly, when pure 1,7-DBPDIs were used for polymerization,
two fractions of PrPDIT (Fig. 1) with different molecular weight and
narrow molecular weight distribution (as low as 1.08) could be ob-
tained through the simple column separation. Molecular weight and
isomeric effect have little influence on the absorption and energy levels
of these polymers, while they show different performance in photo-
voltaic application. Ladder-type polymer of FPrPDIT (Fig. 1) was syn-
thesized by the quantitative yield cyclization of polymer PrPDIT. All-
PSCs based on these polymers achieved highest PCE of 5.95% without
adding any additives or post-treatment.
2.2. Optical and electrochemical properties
The absorption of these compounds in solution and thin film were
characterized. All the polymers in this study show strong absorption in
the range of 300–700 nm (Fig. 3a and b). Their solid absorption has
slight hypsochromic shift by 5–10 nm compared to their solution ab-
sorption because of stronger aggregation in solid state. Polymers with
different molecular weights show different solid absorption due to their
different aggregation and packing in solid state.
2. Results and discussion
2.1. Synthesis
As shown in Fig. 3a, solution absorption of ladder-type FPrPDIT
hypsochromic shifted by about 25 nm compared to that of single-strand
PrPDIT, which agrees with the model compound [24]. The optical band
gap of FPrPDIT is about 0.2 eV higher than that of PrPDIT (Table 1),
because LUMO energy levels keep consistent, while the highest occu-
pied molecular orbital (HOMO) energy levels decline after cyclization,
which is confirmed by the theoretical calculation (see Supporting
Information). The extinction coefficients (ε) of FPrPDIT in 300–550 nm
are obviously higher than those of single-strand polymers, and the
ladder-type polymers show clear absorption fine structure, which is the
reflection of their special rigid core. The optical data of these polymers
were summarized in Table 1.
As shown in Scheme 1, key intermediate 1,7-DBPDIs were synthe-
sized in five steps from commercial available perylene-3,4,9,10-tetra-
carboxylic dianhydride (1) according to literature method [43,55].
Some improvement was made as following. 1) Regioisomerically-pure
3a could be obtained directly after the evaporation of 10 mL mixed
solvent(CH2Cl2/CH3CN = 1:2, v/v)gradually, and the purity was char-
acterized by 1H NMR, while recrystallization for 2–3 times were re-
quired in literature method. 2) Compound 4 was obtained quantita-
tively by the hydrolysis of 3a in chlorosulfonic acid, while p-
toluenesulfonic acid was used in the literature method, which had a
complicated post-treatment.
Single-strand polymer PrPDIT was prepared via a Stille poly-
merization reaction using Pd2(dba)3/P(o-tolyl)3 as the catalyst. 1,7-
Dibromo-N, N′-bis(2-octyldodecyl)-3,4,9,10-perylene diimides (1,7-
DBPDIs) with bulky side chains were adopted to make target polymers
soluble. Molecular weight of polymers could be adjusted by the reaction
time. Notably, when the 1,7-DBPDIs were used, two fractions with
different molecular weight are easily separated through simple gel
column chromatography, and the molecular weight distribution is as
low as 1.08. As shown in Table 1, polymerization of 1,7-DBPDI for 48 h
lead to mixed polymers, and two polymers of PrPDIT with different
molecular weight (Mn = 6.3 KDa and 8.4 KDa) and low molecular dis-
tribution (Mw/Mn = 1.08 and 1.28) were isolated conveniently through
a silica gel column.
To study electrochemistry property of these compounds, their redox
properties in the solid state were measured by the cyclic voltammetry
(CV). All of them showed a semi-reversible reduction peak indicating
their ability to accept at least one electron, and no oxidation peak was
observed. The LUMO energy levels were estimated based on the as-
sumption that the energy level of Fc/Fc+ is −4.8 eV relative to vacuum
[56,57]. As shown in Table 1, these polymers have similar LUMO en-
ergy levels in the range of −3.96 ∼ −4.03 eV, the reason is that the
first electron-accepting position is at the oxygen atom in the carbonyl
group due to its strong electron-withdrawing property, and there is
little energy difference on the carbonyl groups among these polymers
[58].
The target polymers PrPDIT, FPrPDIT, and PPDIT exhibit excellent
thermal stability, and the 5% weight loss temperatures (Td) are 435,
440, and 431 °C respectively, which is confirmed by thermogravimetric
analysis (TGA, Fig. S2) in the air.
The molecular weight distribution of regioisomerically-pure poly-
mers (PrPDIT) was much lower than that of mixed polymers (PPDIT).
For example, the distribution of regioisomerically-pure polymer PrPDIT
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L. Wang et al.
Polymer162(2019)108–115
Table 1
Optical, electrochemical, and molecular weight data of polymers.
a
b
c
Polymers (Mn)
λ (nm)
Solution Film
ɛmax (M−1cm−1
)
Eg (eV)
LUMO (eV)
Mnc/KDa
Mw/Mn
PrPDIT (4.3 KDa)d
PrPDIT (5.1 KDa)e
PrPDIT (6.3 KDa)f
PrPDIT (8.4 KDa)g
PPDIT (6.9 KDa)h
PPDIT (8.0 KDa)i
FPrPDIT (6.3 KDa)
542
556
538
553
553
554
513
537
551
527
548
547
546
510
15900
15400
15500
15000
15600
15800
23400
1.71
1.71
1.78
1.71
1.72
1.74
1.96
−4.00
−4.01
−3.96
−4.01
−4.01
−4.02
−4.03
4.3
5.1
6.3
8.4
6.9
8.0
6.3
1.14
1.24
1.08
1.28
1.78
1.51
1.08
a
The molar extinction coefficient at λmax in solution.
b
c
d
e
f
Optical band gap.
Mn, Mw, and Mw/Mn were determined by GPC on the basis of polystyrene calibration.
The first and
second fraction of gel column, reaction lasted for 30 h.
The first and
second fraction of gel column, reaction last for 48 h.
Reaction last for 30 h.
g
h
i
Reaction lasted for 48 h.
Table 2
Photovoltaic properties of the all-PSCs based on different acceptors with D/A
ratio of 1:1.
d
Acceptor (Mn)
Voc (V) Jsc (mA
cm−2
FF (%) PCEmax (%) PCEavg (%)
)
PrPDIT (4.3 KDa)
PrPDIT (5.1 KDa)
PrPDIT (6.3 KDa)
PrPDIT (8.4 KDa)
PPDIT (6.9 KDa)
PPDIT (8.0 KDa)
FPrPDIT (6.3 KDa) 0.76
FPrPDIT 0.77
(6.3 KDa)c
0.73
0.73
0.74
0.74
0.75
0.74
12.00
12.34
14.01
11.53
10.88
10.22
12.22
11.81
58.49
54.47
57.23
53.37
53.50
51.73
45.34
49.83
5.16
4.92
5.95
4.58
4.36
3.93
4.21
4.52
4.95
4.76
5.78
4.44
4.28
3.82
4.11
4.36
0.21
0.16
0.17
0.14
0.08
0.10
0.11
0.16
a
b
Under the illumination of AM 1.5G, 100 mW cm−2
;
The film thickness of
c
around 100 nm ( 10 nm) was determined by AFM; 1% DIO was used as the
additive; The average PCE are calculated from 10 devices.
d
Fig. 2. The absorption of polymer PrPDIT in CHCl3 with different irradiation
time.
performances at different amounts of DIO were shown in Table S3, and
the optimized amount of DIO is 1%. Therefore, above optimized con-
ditions were adopted in the following device fabrication.
2.3. Photovoltaic properties
Table 2 shows parameters of solar cells fabricated at above optimal
conditions. Compared to mixed PPDIT, regioisomerically-pure PrPDIT
shows higher short-circuit current density (Jsc), fill factor (FF), and PCE,
which may be assigned to regular packing of the former polymers.
Molecular weight of single-strand polymers has little influence on the
device performance, and PrPDIT with Mn of 6.3 KDa gave the best PCE
of 5.95%, so it was selected to prepare ladder-type polymers. Single-
strand polymers with higher FF, Jsc, and PCE have better photovoltaic
performance than ladder-type ones, which is caused by different
To evaluate the photovoltaic properties of these electron acceptors,
all-PSCs with the structure of ITO/ZnO/donor:acceptor/MoO3/Ag were
fabricated. The PTB7-Th (structure is in Fig. S3) was selected as the
donor, because it has matched energy levels (Fig. S4) and com-
plementary absorption (Fig. S5) with those of target polymers. Table S1
shows the device properties of PTB7-Th:FPrPDIT (Mn: 6.3 KDa) with
different donor:acceptor ratios, and the optimal weight ratio is 1:1. The
detailed device parameters at different concentration were shown in
Table S2, and the best concentration is 16 mg mL−1. The detailed
Fig. 3. Absorption of polymers (a) in CHCl3 (1 × 10−5 M) and (b) in solid state.
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Polymer162(2019)108–115
Fig. 4. (a) J−V curves and (b) EQE spectra of solar cells based on PTB7-Th:PrPDIT and PTB7-Th:FPrPDIT.
morphology of active layers. Upon adding 1% DIO, PCE of ladder-type
FPrPDIT increased to 4.52% due to the improved morphology. While
single-strand polymers were insensitive to any solvent additives, they
are excellent polymeric acceptors for additive-free solar cells.
The external quantum efficiency (EQE) was measured to examine
the spectral response in the solar cells. As shown in Fig. 4b, these de-
vices show strong photoresponse in the broad range of 300–800 nm,
which indicates that both the absorption of PTB7-Th and PrPDIT/
FPrPDIT have significant contribution to the photocurrent. The highest
EQE for PTB7-Th:PrPDIT and PTB7-Th:FPrPDIT devices are 57% and
50% respectively, located at 695 nm. Specifically, the photon responses
between 300 and 600 nm are mainly contributed by PrPDIT or FPrPDIT,
while PTB7-Th provides the dominant role from 600 to 800 nm. Com-
pared to FPrPDIT, PrPDIT shows higher PCE, which is consistent with
its higher EQE.
To understand charge transport properties of all-PSCs based on
PrPDIT and FPrPDIT, their charge carrier mobilities were measured by
the space-charge-limited-current (SCLC) method. The typical J-V curves
of the hole-only and electron-only devices are shown in Fig. S7. The
calculated hole and electron mobilities are 5.72 × 10−4 cm2 V−1 s−1
and 6.69 × 10−7 cm2 V−1 s−1 for PTB7-Th:PrPDIT blend film, and they
are 7.58 × 10−4 cm2 V−1 s−1 and 1.61 × 10−6 cm2 V−1 s−1 for PTB7-
Th:FPrPDIT (Table S4). The electron mobility of ladder-type polymer
FPrPDIT is higher than single-strand polymer PrPDIT.
interpenetrating networks. The ideal morphology with a donor:acceptor
interpenetrating network could promote exciton dissociation and
charge transport, which is beneficial for achieving good performance in
all-PSCs. Combining AFM and TEM images (Fig. S8), blend film of
PTB7-Th:FPrPDIT shows larger domain size in phase separation. Too
large domain size hampered efficient charge separation and exciton
generation, which lead to its lower Jsc and PCE in solar cells.
Further studies on the basic operational mechanism were performed
to obtain the photo-generated current density (Jph = JL -JD, JL: current
density under illumination; JD: current density in the dark) versus ef-
fective voltage (Veff = V0-Va, V0: the voltage when Jph is zero; Va: ap-
plied voltage) curves of devices based on PTB7-Th:PrPDIT and PTB7-
Th:FPrPDIT, as shown in Fig. 6a [59–61].
The exciton dissociation probability (Pdiss) of devices based on
PTB7-Th:PrPDIT and PTB7-Th:FPrPDIT under the short circuit condi-
tion are 64% and 50%, respectively. The Pdiss of PTB7-Th:PrPDIT is
higher than that of PTB7-Th:FPrPDIT, which is consistent with the su-
perior photovoltaic performance of the former device. The Jsc of op-
timal all-PSCs under different light intensities (P) were also measured:
the relationship between Jsc and P can be described as Jsc ∝ PS [62]. The
light intensity dependence curve based on Jsc was shown in Fig. 6b, and
the scaling factor (S) value of devices based on PTB7-Th:PrPDIT and
PTB7-Th:FPrPDIT are 0.95 and 0.90, respectively. Therefore, all these
devices exhibited reduced bimolecular recombination, which are ben-
eficial to achieve high Jsc and high FF.
Atomic force microscopy (AFM) and transmission electron micro-
scopy (TEM) were used to study the morphology of active layers. As
shown in Fig. 5, the surface roughness of the PTB7-Th:PrPDIT and
PTB7-Th:FPrPDIT films show similar root-mean-square (RMS) as 3.03
and 2.57 nm. Blend film of PTB7-Th:PrPDIT shows better
3. Conclusion
Regioisomerically-pure 1,7-DBPDIs lead to high performance con-
jugated polymers with molecular weight distribution as low as 1.08.
Ladder-type polymers of FPrPDIT were synthesized by quantitative
yield cyclization of regioisomerically-pure polymer PrPDIT. These
polymers with strong absorption, low-lying LUMO energy levels, and
high thermal stability are excellent polymeric acceptors. Compared to
mixed polymers, regioisomerically-pure ones show higher Jsc, FF, and
PCE. Molecular weight of single-strand polymers has a little influence
on the device performance, and PrPDIT with Mn of 6.3 KDa gave the
best PCE of 5.95%. Single-strand polymers have better photovoltaic
performance than ladder-type ones, because the former lead to better
morphology. Thus, pure 1,7-DBPDIs are important in the construction
of high performance polymeric semiconductors, and twisted conjugated
ladder-type polymers with perfect structures are promising acceptors.
4. Experimental section
4.1. Materials
Known compound PDI-Th, FPDI-Th, 3a, 4, and polymer PPDIT were
synthesized according to literature method [43,63,64], and the detailed
Fig. 5. AFM images of PTB7-Th:PrPDIT and PTB7-Th:FPrPDIT film.
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Polymer162(2019)108–115
Fig. 6. (a) Photocurrent versus effective voltage plots and (b) light intensity dependence of short circuit intensity curves of polymer PrPDIT and FPrPDIT.
procedure is in Supporting Information. All the chemicals were ob-
tained commercially and used without further purification.
a xenon lamp HSX-F300 (350–780 nm) for 10 h. The reaction mixture
was washed with saturated Na2SO3 solution to remove I2. Next, the
polymer was precipitated from methanol to obtain FPrPDIT (49 mg,
quantitative yield) as dark red solid. 1H NMR (400 MHz, C2Cl4D2) δ
9.00–7.61 (m, 4H), 4.20–3.70 (m, 4H), 2.10 (m, 2H), 1.30 (m, 64H),
0.86 ppm (m, 12H).
4.2. Characterization
1H NMR and 13C NMR spectra were measured on a NMR spectro-
meter. Absorption spectra were recorded on a PerkinElmer lambda 750
spectrophotometer. TGA measurements were performed using a TGA
Mettler-Toledo Gmbh under flowing air at a heating rate of 10 K⋅min−1
.
4.6. All-polymer solar cell fabrication
Atomic force microscopy (AFM) images were obtained using
a
Organic photovoltaic (OPV) devices were fabricated with an in-
verted structure of ITO/ZnO/active layer/MoO3/Ag. The conductive
ITO substrates were sequentially cleaned with ultrasonication in de-
tergent, water, acetone, and isopropanol. After drying the ITO sub-
strates and treating the surface with UV ozone for 20 min, the ZnO
precursor solution was prepared by dissolving 0.5 g of zinc acetate di-
hydrate (Zn (CH3COO)2·2H2O, 99.9%) in 5 mL 2-methoxyethanol
(CH3OCH2CH2OH, 99.8%), and 138 μL ethanolamine (NH2CH2CH2OH,
99.8%). The ZnO precursor was spun-coated at 4000 r.p.m. for 1 min
onto the ITO surface. After being baked at 200 °C for 60 min in air, the
substrates were transferred into a nitrogen-filled glove box. Then the
active layers were spun-coated from solutions of donor:acceptor (1:1 w/
w) in chlorobenzene with a total concentration of 16 mg mL−1. To
ensure the donor polymer soluble, active solutions were heated at 70 °C
for 12 h prior to spin coating in a glovebox. MoO3 (7 nm) and Ag
(90 nm) were deposited by thermal evaporation under a vacuum
chamber to complete the device fabrication. The effective area of one
cell was 0.04 cm2. The current-voltage (J-V) characteristics were mea-
sured by a Keithley 2400 Source Meter under simulated solar light
(100 mW cm−2, AM 1.5 G, Abet Solar Simulator Sun 2000). The in-
cident photon-to-electron conversion efficiency (IPCE) spectra were
detected on an IPCE measuring system (Oriel Cornerstone mono-
chromator equipped with Oriel 70613NS QTH lamp). All the mea-
surement was performed at room temperature under nitrogen atmo-
sphere.
NanoMan VS microscope in the tapping mode. The thickness of the
active layer of the device was measured via a VeecoDektak 150 surface
profiler. TEM images of blend films were acquired by a JEOL 2200FS
transmission electron microscopy with 200 kV accelerating voltage.
4.3. Synthesis of polymer PrPDIT
1,7-Dibromo-N, N′-bis-(2-octyl dodecyl)-3,4,9,10-perylene diimides
(1,7-DBPDIs, 700 mg, 0.63 mmol), 2,5-bis (trimethylstannyl) thiophene
(258 mg, 0.63 mmol), catalyst of Pd2(dba)3 (23 mg, 0.025 mmol), P(o-
tolyl)3 (77 mg, 0.25 mmol), and 20 mL toluene were mixed and stirred
at 110 °C for 48 h under argon. The crude polymer was precipitated
from the solution by adding it to excess methanol, and the dried
polymer was purified through silica gel column with eluent of CHCl3.
The first fraction was precipitated from methanol to obtain PrPDIT (Mn:
6.3 KDa, 148 mg, 22.1%), and the second fraction PrPDIT (Mn: 8.4 KDa,
389 mg, 58.0%) was dark purple solid. PrPDIT (Mn: 6.3 KDa)
Mn = 6.3 KDa, Mw/Mn = 1.08; PrPDIT (Mn: 8.4 KDa) Mn = 8.4 KDa,
Mw/Mn = 1.28.1H NMR (400 MHz, C2Cl4D2) δ 8.97–8.16 (m, 6H), 7.43
(m, 2H), 4.08 (m, 4H), 1.97 (m, 2H), 1.16 (m, 64H), 0.78 ppm (m,
12H).
4.4. Synthesis of polymer PPDIT
(1,7&1,6)-DBPDI (260 mg, 0.23 mmol), 2,5-bis (trimethylstannyl)
thiophene (96 mg, 0.23 mmol), catalyst Pd2(dba)3 (9 mg, 0.01 mmol), P
(o-tolyl)3 (31 mg, 0.10 mmol), and 10 mL toluene were mixed and
stirred at 110 °C for 48 h under argon. The crude polymer was pre-
cipitated from the solution by adding it to excess methanol, and the
dried polymer was purified through silica gel column with eluent of
CHCl3. PPDIT (Mn: 8.0 KDa) was obtained (193 mg, 78%) as dark purple
solid. PPDIT (Mn: 8.0 KDa) Mn = 8.0 KDa, Mw/Mn = 1.51.1H NMR
(400 MHz, CDCl3) δ 8.92–8.23 (m, 6H), 7.36 (m, 2H), 4.11 (m, 4H),
1.99 (m, 2H), 1.44–1.00 (m, 64H), 0.78 ppm (m, 12H).
Conflicts of interest
The authors declare no competing financial interest.
Acknowledgements
The work was supported by grants National Natural Science
Foundation of China (No. 51863012, 21562031, and 51833004),
Natural Science Foundation of Jiangxi Province in China
(20171ACB21012, and 2018ACB21022), and the Innovation Fund
Designated for Graduate Students of Nanchang University (No.
CX2017050).
4.5. Synthesis of polymer FPrPDIT
The polymer PrPDIT (50 mg), I2 (5 mg, 0.02 mmol), and 300 mL
CH2Cl2 were mixed and stirred at room temperature and irradiated with
113

L. Wang et al.
Polymer162(2019)108–115
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