Polymer Solar Cells Based on the Copolymers of Naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) and Alkoxylphenyl Substituted Benzodithiophene with High Open-Circuit Voltages

Article abstract of DOI:10.1002/cjoc.201500265

Two novel naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) and alkoxylphenyl substituted benzodithiophene based copolymers were developed as the donor materials for polymer solar cells. The resulting copolymers exhibit broad absorption bands in the range of 500

Full text of DOI:10.1002/cjoc.201500265

FULL PAPER
DOI: 10.1002/cjoc.201500265
Polymer Solar Cells Based on the Copolymers of
Naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) and Alkoxylphenyl
Substituted Benzodithiophene with High Open-Circuit Voltages
Liqian Liu, Guichuan Zhang, Baitian He, and Fei Huang*
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials
and Devices, South China University of Technology, Guangzhou, Guangdong 510640, China
Two novel naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) and alkoxylphenyl substituted benzodithiophene based
copolymers were developed as the donor materials for polymer solar cells. The resulting copolymers exhibit broad
absorption bands in the range of 500－800 nm in thin films and deep highest occupied molecular orbital energy
levels of −5.39 eV and −5.36 eV, respectively. The best device performance was achieved by P1, with an
open-circuit voltage of 0.85 V, a short-circuit current density of 8.65 mA•cm−2, a fill factor of 37.8%, and a power
conversion efficiency of 2.78%.
Keywords polymer solar cells, donor materials, alkoxylphenyl substituted, naphtho[1,2-c:5,6-c]bis(1,2,5-
thiadiazole)
Introduction
donor polymers are not desired to attain high Voc.
Therefore, to obtain a good device performance, an
ideal low band gap polymer should make a trade-off
between its open circuit voltage and band gap.
The growing interests in polymer solar cells (PSCs)
are due to their unique advantages such as low-cost
manufacturing and easy processability over large-area
size via printing and roll-to-roll coating technologies,
and compatibility with flexible substrates and materials,
which enable them for potential applications in low-cost
photovoltaic systems.[1-6] The most common architec-
ture to build PSCs is the bulk heterojunction (BHJ)
structure prepared by mixing electron-rich donor poly-
mers and electron-deficient fullerenes, because high
power conversion efficiencies (PCEs) can be achieved
by this method.[7-24] Generally, there are three important
parameters that governed the PCEs of PSCs-short cur-
rent density (Jsc), open circuit voltage (Voc), and fill fac-
tor (FF). To improve the Jsc value of the resulting PSCs,
the narrow band gap donor polymers have been exten-
sively developed due to their good coverage of absorp-
tion in the solar spectrum. However, the excessively
narrowing band gaps of donor polymers may have a
negative effect on the overall device performance of the
resulting polymers, since the decreased band gap often
means the increased highest occupied molecular orbital
(HOMO) energy level and decreased lowest unoccupied
molecular orbital (LUMO) energy level. When consid-
ering that Voc is related to the difference between the
HOMO energy level of the donor and the LUMO en-
ergy level of the acceptor, the high HOMO levels for
Recently, many kinds of copolymers have been suc-
cessfully developed and showed excellent photovoltaic
properties. Among them, benzodithiophene (BDT) and
naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) (NT) based
polymer (i.e. PBDT-DTNT) exhibited promising photo-
voltaic properties.[25-27] For example, in a conventional
device structure, PBDT-DTNT exhibited a much im-
proved PCE of 6.0% compared to the analogous poly-
mer with BT as an acceptor.[25] By using a conjugated
polyelectrolyte interfacial layer within an inverted solar
cell device, the PCE of PBDT-DTNT was further en-
hanced to 8.4%.[28] The exciting PCE of this polymer
was mainly due to its broad solid absorption spectrum
and highly planar conjugated backbone, which are fa-
vorable for high Jsc. However, the relatively low Voc
value limits the further improvement of its photovoltaic
properties. If the Voc could be enhanced without sacri-
ficing much of the other properties, one could expect a
better device performance of BDT-NT based polymers.
In this work, we designed and synthesized two novel
polymer donor materials based on BDT and NT units
(Scheme 1, P1 and P2). Compared to their analogous
polymer PBDT-DTNT, the alkylthienyl substituted
BDT was replaced by alkoxylphenyl substituted BDT
(BDTP) to lower the HOMO energy levels of the
*
E-mail: msfhuang@scut.edu.cn
Received March 31, 2015; accepted May 13, 2015; published online June 10, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201500265 or from the author.
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Chin. J. Chem. 2015, 33, 902—908

Polymer Solar Cells with High Open-Circuit Voltages
Scheme 1 Synthetic routes of monomers and polymers
O
OR
S
OR
S
S
S
O
n-BuLi, THF
Br
3
Sn
Sn
Br
OH
S
S
O
Sn(CH3)3Cl
Mg, THF
DMF, K2CO3
1
RO
RO
Br
4
M1
OR
2
O
OR
S
S
O
S
n-BuLi, THF
Br
S
3
Sn
Sn
Br
S
O
Sn(CH3)3Cl
S
DMF, K2CO3
Mg,THF
OH
5
OR
M2
Br
OR
6
7
OR
S
OR
S
S
N
N
S
N
N
N
Br
S
S
S
Br
Sn
Sn
S
S
S
n
N
N
S
N
S
RO
RO
M3
P1
M1
OR
Microwave, Toluene, Pd(PPh3)4
R = Ethylhexyl
OR
S
N
N
S
S
S
Sn
Sn
S
S
n
S
N
N
S
OR
M2
OR
P2
resulting polymer.[29-31] As a result, P1 and P2 exhibited
deep HOMO energy levels of −5.39 and −5.36 eV, re-
spectively. Photovoltaic properties of P1 were investi-
gated. In a conventional device structure, a Voc of as
high as 0.92 V was realized. The best device perform-
ance was obtained in an inverted device structure and a
PCE value of 2.78% with a Voc of 0.85 V were achieved.
microwave-assisted Stille polycondensation reaction
with good yield. Detailed synthetic procedure can be
found in the Experimental Section. P1 shows good solu-
bility in chlorinated solvents such as chlorobenzene and
o-dichlorobenzene (o-DCB). However, P2 shows very
poor solubility in common solvents and can only be par-
tially dissolved in hot o-DCB and trichlorobenzene. The
poor solubility can be ascribed to both the axial symme-
try and centro symmetry structure of M2, which leads to
a very strong molecular packing interaction of the re-
sulting polymers. The number average molecular weight
(Mn) and polydispersity index (PDI) of polymer P1 are
Experimental
The synthetic routes of monomers and polymers are
shown in Scheme 1. The polymers are synthesized by
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Liu et al.
FULL PAPER
14.2 K and 2.3, respectively, which are estimated by
high temperature gel permeation chromatography (GPC)
using trichlorobenzene as the solvent and polystyrene
with narrow molecular weight distribution as a standard.
The thermogravimetric analysis (TGA) results show that
P1 and P2 have good thermal stability with an onset of
decomposition temperature of ca. 350 ℃ (See Figure
S1 in Supporting Information, SI).
Results and Discussion
UV-vis absorption spectra of the polymer in o-DCB
and as a solid film were shown in Figure 1a. P1 and P2
show three absorption bands in the range 300－800 nm
both in solution and in the solid film. The absorption
maxima of P1 and P2 are both located at ca. 580 nm in
solution, and P2 shows an obvious shoulder peak at ca.
635 nm, which illustrates that parts of polymer mole-
cules of P2 start to aggregate in solution. The strong
packing ability of P2 corresponds to its poor solubility.
In thin solid films, both P1 and P2 exhibited considera-
bly more significant red-shifted absorbance compared
with solution data, which is a common feature of linear
donor-acceptor conjugated polymers. This phenomenon
is caused by the increased polymer chain aggregation in
the solid state. The absorption maxima of P1 and P2 are
located at ca. 612 and 660 nm, respectively. The ab-
sorption edges (λedge) of polymer film of P1 and P2 are
located at ca. 755 and 793 nm, corresponding to optical
band gaps (Egopt) of 1.64 and 1.56 eV, respectively.
Cyclic voltammetry (CV) measurements are per-
formed in order to evaluate the electrochemical proper-
ties and molecular energy levels of the resulting poly-
mers. Graphite, platinum wire, and Ag/AgCl were used
as the working electrode, counter electrode, and refer-
ence electrode, respectively. All measurements are car-
ried out in tetrabutyl ammonium hexafluorophosphate
(Bu4NPF6) solution (0.1 mol/L in acetonitrile) at a scan
rate of 50 mV•s−1 under inert atmosphere. As shown by
the cyclic voltammograms in Figure 1b, the electro-
chemical oxidation onset potentials (Eox) of P1 and P2
referred to ferrocene/ferrocenium (Fc/Fc＋) were 0.59
and 0.56 V, respectively, which correspond to the
HOMO energy levels of −5.39 and −5.36 eV according
to the equation of HOMO＝−e(Eox＋4.80) (eV). Com-
pared to PBDT-DTNT with alkylthienyl substituted
BDT as donor unit with an HOMO energy of −5.19 eV,
both of the resulting polymers show a deeper HOMO
energy level. The deeper HOMO energy level demon-
strates that by changing chemical structure of side
chains of conjugated polymers, electrochemical property
of conjugated polymers could be effectively tuned. The
LUMO energy levels are calculated from the difference
between the HOMO energy levels and the optical band
gap energies according to the equation: LUMO ＝
(HOMO＋Egopt) eV, and the corresponding LUMO en-
ergy levels were −3.75 and −3.80 eV for P1 and P2, re-
spectively.
Figure 1 (a) The absorption spectra of the polymer in o-DCB
and in solid film. (b) Cyclic voltammogram of polymer film on a
glassy carbon electrode measured in 0.1 mol•L−1 Bu4NPF6 ace-
tonitrile solution at a scan rate of 50 mV•s−1.
Table 1 Photovoltaic performance of devices measured under
simulated light (AM 1.5G, 100 mW•cm−2)
Device
structure
Jsc/
(mA•cm−2)
D/A ration
PCE/%
Voc/V FF/%
1∶1
1∶2
1∶3
1∶1
1∶2
0.69
1.30
1.11
0.66
1.19
2.78
4.81
4.42
2.97
4.44
0.94 26.36
0.92 29.48
0.86 29.24
0.89 24.97
0.90 29.80
0.85 37.80
0.85 28.38
Conventional
structure
Inverted
structure
1∶2 (2% DIO) 2.78 8.65
1∶3 1.09 4.51
PSC devices were fabricated and characterized to
investigate the photovoltaic properties of the resulting
polymers. Firstly, the conventional device structure of
ITO/PEDOT:PSS/polymers:PC71BM/PFN/Al was used.
The conjugated polyelectrolytes were used to improve
charge injection from electrodes into organic active lay-
ers.[32,33] The BHJ photoactive materials were dissolved
in hot o-DCB with stirring overnight before spin-coating
on substrate. P1 exhibited a very good film forming ca-
pability. However, P2 can not form uniform thin films
through spin-coating due to its poor solubility. As a re-
sult, P2 based devices exhibited a very poor device per-
formance. Therefore, only device with P1/PC71BM
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Polymer Solar Cells with High Open-Circuit Voltages
blend as active layer was further carefully investigated.
PSC devices with different D/A ratios (P1/PC71BM, w/w)
were fabricated to optimize the D/A ratio of the blend.
Table 1 showed the photovoltaic parameters of the re-
sulting devices under the illumination of AM 1.5G (100
mW/cm2) with different D/A ratios (1∶1, 1∶2 and 1∶
3). It is clear that the optimal D/A ratio of the blend is
1∶2, and a PCE of 1.30% was obtained with a Voc of
0.92 V, a Jsc of 4.81 mA/cm2, and an FF of 29.48%.
Compared with PBDT-DTNT with the same device
structure (Voc＝0.80 V), a much improved Voc was ob-
tained in P1 based devices.
improved by adding a small amount of DIO (2%) as the
additive. Figure 2 showed the J-V curve and EQE of
solar cells based on the P1/PC71BM blend films without
and with 2% DIO as the additive. Table 1 summarized
the photovoltaic parameters of the resulting devices.
Compared to the devices processed without additive, the
devices processed with DIO showed a slightly lower Voc,
a slightly higher FF, and a remarkably improved Jsc.
Under optimal processing condition, the PCE of device
based on P1 was 2.78% with a Voc of 0.85 V, a Jsc of
8.65 mA/cm2 and an FF of 37.8 %. The nanoscale mor-
phology of blend film was tested by using atomic force
microscopy (AFM) and phase graphs are shown in Fig-
ure 3. The surface roughness measured from the topog-
raph image was 0.93 and 2.63 for P1 without and with
DIO, respectively. The film without DIO exhibits
smoother surface morphology. However, the film with
DIO shows much obvious nanoscale phase separation,
which is favorable for charge separation and transport.
Figure 3 AFM images: (a) P1 film without DIO; (b) P1 film
with DIO. All images are 5 μm×5 μm.
Figure 2 (a) J-V curves and (b) EQE spectra of devices with the
configuration: ITO/PFN/active-layer/MoO3/Al.
To investigate the influence of the DIO on the device
performance, hole mobility of the resultant polymers
was examined by using the space charge limited current
(SCLC) model with the device configuration of
ITO/poly(3,4-ethylenedioxythiophene):poly-(styrenesul-
fonate) (PEDOT:PSS)/active-layer/MoO3/Al. The mo-
bilities were determined by fitting the dark currents to
the model of a single carrier SCLC, which is described
by the equation J＝(9/8)ε0εrμh(V2/d3), where J is the
current, μh is the zerofield mobility, ε0 is the permittivity
of free space, εr is the relative permittivity of the mate-
rial, d is the thickness of the polymer layer, and V is the
The inverted PSCs with the structure of ITO/
PFN/P1:PC71BM/MoO3/Al was also fabricated to inves-
tigate the photovoltaic properties of P1 because inverted
devices typically demonstrate better ambient stability
compared to conventional devices.[34,35] It was found
that P1 showed similar PCEs compared to that in con-
ventional structure when using different D/A ratios. To
further improve the photovoltaic performance of the
device, 1,8-diiodooctane (DIO) was added to the solu-
tions prior to the spin-coating process. The photovoltaic
performance of the resulting device can be significantly
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effective voltage. The effective voltage was obtained by
subtracting the built-in voltage (Vbi) and the voltage
drop (Vs) from the series resistance of the substrate from
the applied voltage (Vappl), V＝Vappl−Vbi−Vs. The mobili-
ties were extracted by modeling the dark currents in the
SCLC region and calculated from the slope of the J1/2-V
curves as shown in Figure 4. It was found that the hole
mobility of active layer was hugely improved when
adding DIO. The hole mobilities of active layer before
and after adding DIO were 2.40×10−5 and 1.81×10−4
cm2•V−1•s−1, respectively. The remarkably improved Jsc
could be ascribed to the higher hole mobility.
were prepared according to the reported procedures.[31,36]
All chemicals and reagents were purchased from com-
mercial sources (Aldrich, Acros, and Alfa Aesar) and
used without further purification unless stated other-
wise.
2,6-Bis(trimethyltin)-4,8-bis(3-ethylhexyloxy-1-
phenyl)-benzo[1,2-b:4,5-b']-dithiophene (M1)
A
solution of compound 4 (1.2 g 2 mmol) in dry THF (30
mL) was deoxygenated with argon for 30 min, and then
2.4 mol/L n-butyllithium solution in n-hexane (3.33 mL,
8 mmol) was added dropwise at 0 ℃. Then the solution
was allowed to warm up to 40 ℃ for 2 h, and 1.0
mol/L trimethyltin chloride solution in THF (10 mL, 10
mmol) was added. Then the mixture was poured into
water and extracted with dichloromethane. The organic
phase was evaporated, and the residue was recrystallized
from 20 mL methanol to afford the pale yellow solid
1
(1.2 g, 65%). H NMR (600 MHz, CDCl3) δ: 7.48 (t,
J＝7.79 Hz, 2H), 7.41 (s, 2H), 7.31 (d, J＝7.21 Hz, 2H),
7.25 (s, 2H), 7.03 (dd, J＝8.32, 1.8 Hz, 2H), 3.90 (d,
J＝6.06 Hz, 4H), 1.80－1.77 (m, 2H), 1.56－1.38 (m,
16H), 0.99－0.93 (m, 12H), 0.35 (s, 18H); 13C NMR
(125 MHz, CDCl3) δ: 159.29, 141.97, 141.65, 140.79,
136.51, 130.41, 129.33, 128.51, 121.19, 114.88, 114.43,
70.35, 39.02, 30.20, 28.70, 23.57, 22.70, 13.72, 10.76,
−8.75.
4,8-Bis(4-ethylhexyloxy-1-phenyl)-benzo[1,2-
b:4,5-b']-dithiophene (7) 1-Bromo-4-(2-ethylhexyl-
oxy)benzene (17.1 g, 60 mmol) was added dropwise to
magnesium turnings (1.5 g, 62.5 mmol) in anhydrous
THF (35 mL) under the protection of argon. During the
process, I2 (10 mg) was added as catalyst in the reaction.
The solution was refluxed for 3 h then was cooled down.
The solution was added slowly to benzo[1,2-b:4,5-
b']dithiophene-4,8-dione (4.4 g, 20 mmol) dispersed in
40 mL THF. SnCl2 (25 g) was dissolved in 10% aque-
ous HCl (40 mL) and then added dropwise. The solution
was stirred for another 1 h at 50 ℃. After cooling to
room temperature, the mixture was poured into water
and extracted with dichloromethane, the organic extrac-
tion was washed successively with water and sodium
bicarbonate solution twice and the combined organic
phase was dried over magnesium sulfate and evaporated
to afford the crude product. The crude product was puri-
fied on a silica gel column, eluting with pure hexane.
Light yellow crystals were obtained (3.6 g, 30% yield).
1H NMR (600 Hz, CDCl3) δ: 7.63 (d, J＝8.69 Hz, 4H),
7.36－7.33 (m, 4H), 7.09 (d, J＝8.63 Hz, 4H), 3.96－
3.94 (m, 4H), 1.81－1.77 (m, 2H), 1.56－1.38 (m, 16H),
0.99－0.93 (m, 12H); 13C NMR (125 MHz, CDCl3) δ:
159.26, 138.30, 136.25, 131.41, 130.51, 130.02, 127.01,
123.11, 114.75, 70.56, 39.50, 30.62, 29.17, 23.96, 23.12,
14.16, 11.22.
Figure 4 J1/2–V characteristics of devices with the configura-
tion: ITO/PEDOT:PSS/active-layer/MoO3/Al. The solid lines
represent the fit curves.
Conclusions
In conclusion, we designed and synthesized two
novel polymer donor materials based on BDTP and NT
units. Compared to PBDT-DTNT with alkylthienyl sub-
stituted BDT as donor unit, both of the novel synthe-
sized polymers show a much deeper HOMO energy
level. As a result, solar cell devices based on polymer
P1 obtained a Voc as high as 0.92 V, much higher than
that of PBDT-DTNT with a Voc of 0.80 V in identical
device structure. Under optimal condition, PSCs based
on P1:PC71BM (1∶1, w/w) with 2% DIO showed a
PCE of 2.78% with a Voc of 0.85 V, a Jsc of 8.65
mA/cm2, and an FF of 37.8%, under the illumination of
AM 1.5G, 100 mW/cm2. Our results demonstrated that
by changing the chemical structure of side chains of
conjugated polymers, the Voc of polymers could be ef-
fectively tuned.
Experimental Section
Materials
2,6-Bis(trimethyltin)-4,8-bis(4-ethylhexyloxy-1-
Benzo[1,2-b:4,5-b']dithiophene-4,8-dione (3), 4,8-
bis(3-ethylhexyloxy-1-phenyl)-benzo[1,2-b:4,5-b']di-
thiphene (4), 3,7-(di(2-bromo-3-(2-ethylhexyl)-5-thi-
enyl)-naphtho[1,2-c:5,6-c]-bis[1,2,5]thiadiazole) (M3)
phenyl)-benzo[1,2-b:4,5-b']-dithiophene (M2)
A
solution of compound 7 (1.2 g, 2 mmol) in dry THF (30
mL) was deoxygenated with argon for 30 min, and then
2.4 mol/L n-butyllithium solution in n-hexane (3.33 mL,
906
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Polymer Solar Cells with High Open-Circuit Voltages
8 mmol) was added dropwise at 0 ℃. Then the solution
was allowed to warm up to 40 ℃ for 2 h, and 1.0
mol/L trimethyltin chloride solution in THF (10 mL, 10
mmol) was added. Then the mixture was poured into
water and extracted with dichloromethane. The organic
phase was evaporated, and the residue was recrystallized
from 20 mL methanol to afford the white solid (1.3 g,
in a nitrogen stream, followed by an oxygen plasma
treatment. To fabricate photovoltaic devices, a hole
transport thin layer (ca. 40 nm) of PEDOT:PSS (Bay-
tron PVP AI 4083, filtered at 0.45 μm) was spin coated
on the precleaned ITO-coated glass substrates at 5000
r/min and baked at 140 ℃ for 10 min under ambient
conditions. The substrates were then transferred into an
argon-filled glove box. Subsequently, the polymer:
PC71BM active layer (ca. 100 nm) was spin-coated on
the top of PEDOT:PSS layer from a homogeneous blend
solution. A thin layer of PFN (5 nm) was spin-coated
from methanol solution on the top of active layer. To
complete device fabrication, the substrates were pumped
down to a high vacuum (1×10−6 Torr), and aluminum
(100 nm) was thermally evaporated through shadow
masks. The effective devices area was measured to be
0.16 cm2.
Inverted device structure: ITO glass substrates were
used as the cathode in the polymer solar cells. The ITO
coated glass substrates were cleaned by sonication in
detergent, deionized water, acetone, and isopropyl al-
cohol and dried in a nitrogen stream. Then PFN (0.5
mg•mL−1) was spin-cast from V(methanol)∶V(acetic
acid)＝100∶1 onto the ITO substrate to form a 5 nm
thin film. The bulk heterojunction composite with
thickness of 100 nm was then spin coated on PFN layer
from o-DCB solution of polymer (5 mg•mL−1) and
PC71BM. After that, about 10 nm molybdenum oxide
(MoO3) was thermally deposited on top of the active
layer through a shadow mask in a vacuum chamber with
an evaporation rate of 0.1 Å•s−1 under a vacuum of ca. 3
×10−4 Pa. The effective area of a device was 0.16 cm2
as determined by the shadow mask used during deposi-
tion of Al electrode.
1
70%). H NMR (600 MHz, CDCl3) δ: 7.65 (d, J＝8.59
Hz, 4H), 7.38 (s, 2H), 7.11 (d, J＝8.62 Hz, 4H), 3.96 (d,
J＝5.50 Hz, 4H), 1.82－1.78 (m, 2H), 1.60－1.36 (m,
16H), 1.00－0.93 (m, 12H), 0.35 (s, 18H); 13C NMR
(125 MHz, CDCl3) δ: 159.07, 142.60, 141.63, 137.08,
132.07, 130.87, 130.59, 128.46, 114.66, 70.50, 39.55,
30.64, 29.18, 23.97, 23.12, 14.16, 11.23, −8.34.
Synthesis of P1
Compound M1 (92.4 mg, 0.10 mmol), compound
M3 (79.1 mg, 0.10 mmol), Pd(PPh3)4 (5 mg), and tolu-
ene (5 mL) were added to a 35 mL reaction vial. The
vial was purged with argon and subsequently sealed.
The vial was heated in a microwave reactor at 180 ℃
for 45 min. Then the reaction mixture was cooled to
ambient temperature and precipitated into methanol. The
solid was collected by filtration. After drying in the
vacuum drying oven, the crude product was purified by
Soxhlet extraction with methanol, acetone and hexane
and to remove oligomers and residual catalyst. Finally,
the polymer P1 was obtained as a dark-green solid (80.3
mg, 79% yield).
Synthesis of P2
The polymerization procedure for compound M2
(92.4 mg, 0.10 mmol) and compound M3 (79.1 mg, 0.10
mmol) was the same as that of P1. P2 was obtained as a
dark-green solid (91.5 mg, 90%).
Power conversion efficiencies (PCEs) were meas-
ured under an AM 1.5 G XES-40S1 150W AAA Class
Solar Simulator. The power of the sun simulation was
calibrated before the testing using a standard silicon
solar cell, giving a value of 100 mW•cm−2 during the
test. The current density-voltage (J-V) characteristics
were recorded with a Keithley 2400 Source Measure
Unit. The spectral response was measured with a com-
mercial photo modulation spectroscopic setup (Oriel). A
calibrated Si photodiode was used to determine the
photosensitivity. The external quantum efficiencies of
the inverted PSCs were measured with a commercial
photomodulation spectroscopic setup (DSR100UV-B)
including a xenon lamp, an optical chopper, a mono-
chromator, and a lock-in amplifier operated by a PC
computer (Zolix Instruments), and a calibrated Si pho-
todiode was used as a standard.
Instruments and characterization
The NMR data was collected on a Bruker AVANCE
Digital 600 MHz NMR workstation. Gel permeation
chromatography (150 ℃ in 1,2,4-trichlorobenzene)
was performed on a Polymer Laboratories PL220 Chro-
matograph with linear polystyrene as references. UV-vis
absorption spectra were measured using an HP 8453
spectrophotometer. The solutions that were used for the
UV-visible spectroscopy measurements were dissolved
in o-DCB, and the films were dropcoated from the
o-DCB solution onto a quartz substrate. Thermogravim-
etric analyses were carried out with a Netzsch TG 209
under N2 flow at a heating rate of 10 ℃•min−1. The
electrochemical cyclic voltammetry was conducted on
CHI 600D electrochemical workstation at a scan rate of
50 mV•s−1.
Acknowledgement
Fabrication and characterization of polymer solar
cells
The work was financially supported by the Ministry
of Science and Technology (No. 2014CB643501), the
Natural Science Foundation of China (Nos. 21125419,
51361165301) and Guangdong Natural Science Founda-
Conventional device structure: ITO coated glass
substrates were cleaned by sonication in detergent, de-
ionized water, acetone and isopropyl alcohol and dried
Chin. J. Chem. 2015, 33, 902—908
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
907

Liu et al.
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908
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© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2015, 33, 902—908