High-performance conjugated terpolymer-based organic bulk heterojunction solar cells

Article abstract of DOI:10.1039/c6ta05886h

Recently, conjugated terpolymers comprising three components have attracted tremendous attention. However, quite a few examples of high-performance terpolymers have been reported. We present here two novel terpolymers named PtDDA and PtDAA, in which bithiophene (BT) and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (T1) were chosen as the donor and acceptor units, respectively. Thieno[3,2-b]thiophene (TT) and thiazolo[5,4-d]thiazole (TTz) were used as the third component. It is interesting to find that the PtDDA terpolymer shows a typical D1-D2-D1-A1 structure while PtDAA shows a D1-A1-D1-A2 structure. Without using additives or post-annealing processes, PtDAA-based solar cells show a high PCE of 8.1%, with an unprecedented fill factor (FF) of 0.74, which is much higher than those of PtDDA-based devices (PCE = 3.4%, FF = 0.55). The high efficiency of 8.1% is one of the highest values reported so far for organic solar cells based on conjugated terpolymers. The high performance is mainly ascribed to the efficient carrier transport in the PtDAA:PC₇₁BM active layer, high crystallinity of PtDAA, and high domain purity. The results suggest that constructing conjugated terpolymers with one donor and two acceptor units is an effective strategy for designing high-performance solar cell materials.

Full text of DOI:10.1039/c6ta05886h

View Article Online
View Journal
Journal of
Materials Chemistry A
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Sun, B. Fan, X.
Xue, X. Meng, X. Sun, L. Huo and W. Ma, J. Mater. Chem. A, 2016, DOI: 10.1039/C6TA05886H.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/materialsA

Please do not adjust margins
Journal of Materials Chemistry A
Page 1 of 9
View Article Online
DOI: 10.1039/C6TA05886H
High‐Performance Conjugated Terpolymer‐Based Organic Bulk
Heterojunction Solar Cells
Bingbing Fan,a,b Xiaonan Xue,a,b Xiangyi Meng,c Xiaobo Sun,*a,b Lijun Huo,* a,b Wei Ma,*c and
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Yanming Sun*a,b
Recently, conjugated terpolymers comprising three components have attracted tremendous attention. However, quite
few examples of high‐performance terpolymers have been reported. We presented here two novel terpolymers named
PtDDA and PtDAA, in which bithiophene (BT) and benzo[1,2‐c:4,5‐c’]dithiophene‐4,8‐dione (T1) were chosen as the donor
and acceptor units, respectively. Thieno[3,2‐b]thiophene (TT) and thiazolo[5,4‐d]thiazole (TTz) were used as the third
component. It is interesting to find that PtDDA terpolymer shows a typical D1‐D2‐D1‐A1 structure while PtDAA shows a
D1‐A1‐D1‐A2 structure. Without using additives or post‐annealing processes, PtDAA‐based solar cells show a high PCE of
8.1%, with an unprecedented fill factor (FF) of 0.74, which is much higher than PtDDA‐based devices (PCE = 3.4%, FF =
0.55). The high efficiency of 8.1% is one of the highest values so far for organic solar cells based on conjugated terpolymers.
The high performance is mainly ascribed to the efficient carrier transport in PtDAA:PC71BM active layer, high crystallinity of
PtDAA, and high domain purity. The results suggest that constructing conjugated terpolymers with one donor and two
acceptors units is an effective strategy for designing high‐performance solar cell materials.
terpolymers featuring D‐A‐A type molecular structure with
quinoxaline and isoindigo as electron‐withdrawing units.38‐40 These
terpolymers showed broader absorption range compared to their
corresponding D‐A1 and D‐A2 parent copolymers. The extended
light absorption resulted in more generated excitons which mainly
contribute to high photocurrent, leading to a PCE of 7.0%.40 In
another case, Janssen and coworkers have reported a PDPP3TaltTPT
terpolymer (D‐D‐A type) composed of terthiophene (D1 = 3T),
1 Introduction
Solution‐processed polymer solar cells (PSCs) have been developed
rapidly over the last two decades due to their advantages of light
weight, low cost, flexibility and processability for mass
productions.1‐6 Nowadays, power conversion efficiencies (PCEs)
exceeding 11% have been reported for bulk heterojunction (BHJ)
PSCs, revealing a bright future for commercialization.7,8 The
dramatic increase in PCE is mainly ascribed to the development of
high‐performance conjugated polymers.9‐12 The copolymerization of
electron‐donating (D) and electron‐accepting (A) units has been
widely used to construct new donor polymers.13‐21 The properties of
copolymers, such as light absorption ability, energy levels and
charge carrier mobility etc. can be effectively tuned by using
different D and A monomers.22‐27
Recently, terpolymers comprising three different units in the
polymeric backbones have intrigued much attention since they can
show synergetic effects through incorporating a third component (D
or A) into D‐A copolymers to form D‐A‐A or D‐D‐A type
terpolymers,28‐31 rendering broad absorption, deep energy levels,
high mobility, good solubility and miscibility, etc.32‐37 Wang and
thiophene‐phenylene‐thiophene (D2
= TPT) donor units and
diketopyrrolopyrrole (DPP) acceptor unit, which appears refined
energy levels and optical bandgap comparing with its parent
copolymers and subsequently a higher PCE of 8.0% was achieved.41
Moreover, the crystallinity of copolymers can be fine‐tuned through
optimizing the monomers’ ratios in random terpolymers with
enhanced performance in PSCs.42 Therefore, the terpolymer
structure provides promising opportunities for finely tailoring
polymers with popular optical‐electronic properties through
selection of appropriate third component. However, very limited
examples of high‐performance terpolymers have been reported.
In this paper, we presented two novel terpolymers named
PtDDA and PtDAA, in which bithiophene (BT) and 5,7‐bis(2‐
ethylhexyl)‐4H,8H‐benzo[1,2‐c:4,5‐c’]dithiophene‐4,8‐dione
(T1)
coworkers have recently reported
a series of alternating
were chosen as the donor and acceptor units, respectively. To
ensure the coplanarity of terpolymers, thieno[3,2‐b]thiophene (TT)
and thiazolo[5,4‐d]thiazole (TTz) as a third component were
introduced into the polymer backbone. The molecular structures of
PtDDA and PtDAA are shown in Scheme 1. When incorporating the
a.
School of Chemistry and Environment, Beihang University, Beijing 100191, P. R.
China. E‐mail: sunxb@buaa.edu.cn; huolijun@buaa.edu.cn; sunym@buaa.edu.cn.
b. Heeger Beijing Research and Development Center, Beihang University, Beijing
100191, P. R. China.
c. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong electron‐rich TT unit, PtDDA terpolymer shows a typical D1‐D2‐D1‐
University, Xi’an 710049, P. R. China. E‐mail: msewma@mail.xjtu.edu.cn.
†Electronic Supplementary Information (ESI) available: [The experimental and
characterization details of terpolymers, optimization of devices, AFM top
morphology of active layers]. See DOI: 10.1039/x0xx00000x
A1 structure with two electron‐rich building blocks and one
electron‐deficient building block. However, PtDAA shows a D1‐A1‐
D1‐A2 structure where TTz fused unit acts as an electron‐deficient
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 1
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 2 of 9
ARTICLE
Journal Name
building block because of the electron‐withdrawing property of configuration in which the heavily n+‐doped Si layer acted as the
View Article Online
unsaturated nitrogen atom. The optical‐electronic properties of two gate electrode and the silicon oxide (SiO2) wDaOs Iu: s1e0d.10a3s9t/hCe6TdAie0l5e8c8t6riHc
terpolymers were systematically investigated. Compared to PtDDA, layer. Gold source/drain electrodes with titanium as the adhesion
PTDAA exhibits predominant advantages, such as broader layer were evaporated onto the SiO2 layer. PtDDA and PtDAA were
absorption range, deeper HOMO level, higher hole transport spin‐coated onto OTS‐treated SiO2/Si substrates from chloroform
mobility and favorable face‐on orientation in BHJ films, which are solutions (2.5 mg mL−1) at a spin‐coating rate of 2500 rpm. The films
beneficial to obtain excellent photovoltaic performance. As a result, were annealed at 160 °C for 5 min to get high mobility. The OFET
a promising PCE of 8.1% has been achieved for PtDAA‐based PSCs performance was measured by using
a
Keithley 4200
without using any additives or post‐solvent/thermal annealing semiconductor characterization system. The channel length (L) and
processes, which is much high than its analog PtDDA‐based devices width (W) are 20 μm and 1400 μm, respectively.
(PCE = 3.4%). Our results indicate that PtDAA terpolymer is a
UV‐vis absorpꢀon measurements were carried out on UV−vis
promising material for high‐performance organic solar cells. spectrophotometer (Shimadzu, UV‐3600). Atomic force microscopy
Moreover, it is found that the subtle changes in the polymeric (AFM) images were obtained using a NanoMan VS microscope in a
backbone (e.g. the replacement of the carbon atom with a nitrogen tapping mode.
atom) can dramatically influence the photovoltaic performance of
the terpolymers.
Hole‐only devices were fabricated with a diode configuration
of ITO/MoOx/(PtDDA or PtDAA)/MoOx/Al. The applied voltage is in
the range of 0‐6 V and the mobility was calculated by fitting the
curves according to the equation: J = 9ε0εrμhV2/8L3, where J is the
current density, ε0 is the permittivity of free space, εr is the relative
dielectric constant of the transport medium, μh is the hole mobility,
V is the applied voltage, L is the film thickness.
The GIWAXS measurements were acquired at beamline 7.3.3
at Advanced Light Source43. Samples were prepared on Si substrate,
and the 10 keV X‐ray beam was incident at a grazing angle of 0.11°‐
0.15°，which maximized the scattering intensity from the samples.
The data were analyzed by the Nika software package. The RSoXS
transmission measurements were acquired at beamline 11.0.1.2 at
Advanced Light Source44. Samples for RSoXS measurements were
prepared on a PSS modified Si substrate under the same conditions
as those used for device fabrication, and then transferred by
floating in water to a 1.5 mm × 1.5 mm, 100 nm thick Si3N4
membrane supported by a 5 mm × 5 mm, 200 μm thick Si frame.
The beam size at the sample is approximately 100 μm by 200 μm.
Integrated scattering intensity profiles represent total scattered
intensity at a given q. This was accomplished by averaging the data
along the azimuth captured by the CCD and subsequently scaling
the profiles by q2. Scattering from the sample was captured by the
CCD as far from the sample as possible (~150 mm) and with the CCD
as close as possible (~50 mm). The profiles acquired from the two
datasets were stitched together for an extended q‐range.
Scheme 1. Molecular structures of PtDDA (top) and PtDAA (down).
2 Experimental
The patterned ITO/glass substrates were ultrasonic cleaned
successively in soapy water, deionized water, acetone and
isopropanol. The cleaned ITO glasses were dried overnight in a
vacuum oven at 110 ℃ and treated by UV‐ozone for 20 min before
using. PEDOT:PSS was spin casting onto the ITO glass at 4000 rpm
for 40 s and annealed at 145 ℃ for 10 min in air. After that,
PEDOT:PSS coated ITO/glass substrates were transferred into a glove
box with nitrogen atmosphere. The mixture of PtDDA
(orPtDAA):fullerene with different DIO contents (v/v) and D:A
weight ratios was dissolved in 1,2‐dichlorobenzene (DCB) with a
total concentration of 30 mg/mL and stirred at 90 ℃ overnight. The
blends were spin‐cast onto PEDOT:PSS at 1600 rpm for 40 s to form
the BHJ layers. Finally, Al (100 nm)/Ca (10 nm) layers were
sequentially evaporated through a shadow mask. Current density‐
voltage (J–V) curves were measured using a Keithley 2400 Source
Measure Unit. Solar cell performance used an Air Mass 1.5 Global
(AM 1.5 G) solar simulator (Class AAA solar simulator, Model
94063A, Oriel) with an irradiation intensity of 100 mW•cm−2, which
was measured by a calibrated silicon solar cell and a readout meter
(Model 91150V, Newport). IPCE spectra were measured by using a
QEX10 Solar Cell IPCE measurement system (PV measurements,
Inc.).
3 Results and discussion
The synthetic routes of PtDDA and PtDAA are illustrated in Scheme
2. PtDDA and PtDAA were synthesized through the typical Stille‐
coupling polymerization in toluene, with Pd(PPh3)4 as the catalyst.
To better understand the electronic distribution and backbone
conformation of these two terpolymers, density functional theory
(DFT) calculations at the B3LYP/6–31G (d,p) level of theory were
performed. As shown in Figure S1 and S2, the highest occupied
molecular orbital (HOMO) is delocalized along the entire polymer
chain for both PtDDA and PtDAA. The lowest unoccupied molecular
orbital (LUMO) surface is more localized on the T1 and TTz. The
computational results confirm the electron‐withdrawing properties
of T1 and TTz. Meanwhile, the optimized molecular geometry of
OFETs were fabricated in
a bottom‐gate/bottom‐contact
2 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 3 of 9
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C6TA05886H
Scheme 2. Synthetic routes of PtDDA and PtDAA.
PtDAA trimers at the lowest energy exhibits a better planar
The UV–vis absorption spectra of PtDDA and PtDAA were
structure than that of PtDDA (Figure S3). In addition, the shown in Figure 1. The main absorption peak of PtDDA is located at
electrostatic potential (ESP) maps of PtDDA and PtDAA are partly 510 nm in a diluted chloroform solution and appears a pronounced
different (Figure S4), which is caused by the different red‐shifted absorption by 77 nm to 587 nm in the solid state (Figure
electronegativity of carbon and nitrogen atoms between fused‐ring 1a). Meanwhile, the shoulder peak in PtDDA thin film located at ca.
TT and TTz, respectively.
650 nm implies a weak aggregation in PtDDA thin film. By contrast,
the absorption spectra of PtDAA in solution and thin film appear
similar profiles and the maximum absorption peaks are almost
overlapped (~590 nm). Enhanced shoulder peak intensity was seen
for the PtDAA thin film compared to its solution, which originates
from the further strengthened intermolecular π‐π aggregations. The
results indicate PtDAA has stronger aggregated configurations than
PtDDA even in a diluted solution. Thus it is primarily concluded that,
as the third component inserted into D‐A copolymer to form
terpolymer, electronic‐deficient TTz unit can induce stronger
aggregation than TT unit. The maximum absorption coefficients of
PtDAA (ε = 5.8 × 104 cm‐1) is larger than that of PtDDA (4.9 × 104 cm‐
1), indicating its better light‐harvesting capability. The optical band
gaps are calculated to be the similar values of 1.79 and 1.78 eV for
PtDDA and PtDAA, respectively, from the onset of absorption
spectra in the solid state.
(a)
(b)
5
6
5
4
3
2
1
0
PtDDA
PtDDA
PtDAA
PtDAA
4
3
2
1
0
400
500
600
700
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
(c)
(d)
-2
-3
-4
-5
-6
PtDDA
PtDAA
-3.06
-3.19
LUMO
HOMO
-3.91
PtDDA
PtDAA
PC71BM
-5.87
-5.19
-5.31
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Potential (V vs Fc/Fc+)
Electrochemical cyclic voltammetry (CV) measurements were
performed to characterize the energy levels of the two terpolymers
(Figure 1c). The HOMO and LUMO levels were calculated from the
onset of oxidation and reduction potentials using equations HOMO
= −(Eox + 4.8) eV and LUMO = −(Ered + 4.8) eV. As shown in Figure 1d,
PtDDA exhibits a HOMO level of ‐5.19 eV, which is slightly higher
than that of PtDAA (‐5.31 eV). Considering that the open circuit
Figure 1. UV‐vis absorption spectra of PtDDA and PtDAA in
chloroform solution (a) and thin films (b); (c) Cyclic voltammogram
curves of PtDDA and PtDAA; (d) Energy level diagrams of active
layer components studied in the fabrication of devices.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 4 of 9
ARTICLE
Journal Name
voltage (Voc) of PSCs is closely related to the offset between the the highest values so far for the PSCs based on terpolymers (see
View Article Online
DOI: 10.1039/C6TA05886H
HOMO level of donor and the LUMO level of acceptor, a deeper Table 2). Additionally, an average PCE of 8.0% within a small
HOMO level of PtDAA will lead to a higher Voc. The LUMO level of standard deviation of 0.1% was obtained, revealing the good
PtDDA is higher than PtDAA as well, with an offset value of 0.13 eV. reproducibility of high performance for PtDAA‐based solar cells.
The downshifted HOMO/LUMO levels of PtDAA may be caused by Meanwhile, the a ddition of DIO could not further increase the cell
high electronegativity of unsaturated nitrogen atoms in TTz unit.
efficiency. When processed with 1% DIO, PtDAA:PC71BM device
exhibits a decreased PCE of 7.7%, with a Voc of 0.86 V, a Jsc of 12.25
mA/cm2 and a FF of 0.74. The relatively higher Voc achieved in
PtDAA‐based solar cells is consistent with the deeper HOMO level
of PtDAA than that of PtDDA.
(a)
PtDDA
0
PtDDA with 1%DIO
PtDAA
PtDAA with 1%DIO
-4
-8
To verify the Jsc difference between PtDAA‐ and PtDDA‐based
devices, the incident photon conversion efficiency (IPCE) spectra
were measured to make the direct comparison (Figure 2b). For
PtDDA‐based solar cells, the addition of DIO slightly increased the
IPCE values. However, the maximum IPCE value is about 40%.
Incontrast, higher IPCE values over 60% were observed in the
wavelength range of 370‐650 nm for PtDAA‐based devices.
Especially, the maximum value of 72.5% was found around 490 nm
for as‐cast PtDAA solar cells, indicating the efficient photon
generation and charge collection within the device. The integrated
Jsc of PTDAA solar cells obtained from IPCE curve is 12.72 mA/cm2,
which agrees well with the value of 12.87 mA/cm2 measured under
the simulated light with a mismatch less than 2%.
Charge carrier transport properties of PtDDA and PtDAA films
were studied using organic field‐effect transistors (OFETs). Typical
output and transfer curves are presented in Figure 3. As can be
seen from the transfer curves, the devices show typical p‐type
transport properties. PtDAA shows a high mobility of 0.28 cm2 V−1
s−1, which is approximately one order of magnitude of higher than
that of PtDDA (0.035 cm2 V‐1 s‐1). The significant difference in carrier
-12
0.0
0.2
0.4
0.6
0.8
Voltage (V)
(b)80
60
40
20
0
PtDDA
PtDDA with 1%DIO
PtDAA
PtDAA with 1%DIO
300
400
500
600
700
Wavelength (nm)
Figure 2. (a) J‐V and (b) IPCE curves of PSCs based on PtDDA and mobility strongly related to the molecular crystallinity and
PtDAA with PC71BM (1:1, w/w).
orientation, which will be discussed in the following analysis. The
mobility was also measured using space charge limited current
(SCLC) method (Figure S7) and the values are 0.77×10‐3 and
3.44×10‐3 cm2 V‐1 s‐1 for PtDDA and PtDAA, respectively, agreeing
well with OFETs results.
It is well‐known that photovoltaic properties are affected by
the active layer morphology. In order to gain insight into the
morphology of these terpolymer:PC71BM blends, atomic force
microscopy (AFM) measurements were carried out. As shown in
Figure S8, PtDDA:PC71BM blend films show smoother surface with a
root‐mean‐square (RMS) roughness of 0.45 nm. However, the
surface of PtDAA:PC71BM blend film exhibits lager domain size and
apparent rough surface morphology, with RMS value of 1.21 nm.
The addition of DIO increased the surface roughness of both
terpolymer: PC71BM blend films.
The molecular orientation and packing in neat and blended
films were investigated by grazing incidence wide angle X‐ray
scattering (GIWAXS) measurements. The two‐dimensional (2D)
GIWAXS patterns for neat and blend films of PtDDA and PtDAA,
with the corresponding out‐of‐plane and in‐plane scattering profiles
are shown in Figure 4. The reflection peaks located at q ≈ 0.30 Å‐1
for PtDAA and PtDDA neat films in the in‐plane direction are coming
from the (100) lamellar packing of the terpolymers. The lamellar
(100) peak and π‐π stacking (010) peak in the out‐of‐plane direction
To further investigate the photovoltaic properties of PtDDA
and PtDAA, organic solar cells were fabricated with a conventional
configuration of ITO/PEDOT:PSS /terpolymers:PC71BM/Ca/Al. The
current density–voltage (J–V) characteristics of solar cells were
measured under AM 1.5 G illumination with an intensity of 100
mW/cm2. The blend films with different additive (1,8‐diiodooctane,
DIO) concentrations and donor/acceptor weight ratios were
processed to optimize the device performance. It was found that
the use of DIO could improve the efficiency of PtDDA‐based solar
cells. In contrast, there is no effect for PtDAA‐based devices.
Without using DIO, the solar cells showed better PCEs (Figure S5,
S6). The optimized weight ratio was found to be at 1:1 for PtDDA
and PtDAA‐based devices (Figure S5, S6). Figure 2a showed the J‐V
curves of the champion cells and the device parameters are
summarized in Table 1. For PtDDA PSCs processed without DIO, the
Voc, Jsc and FF is 0.72 V, 7.18 mA/cm2 and 0.40, respectively,
resulting in a low PCE of 2.0%. When processed with 1% DIO, the
PCE was increased up to 3.4%, mainly due to the increased Jsc (8.69
mA/cm2) and FF (0.55%). For as cast BHJ films without using any
additive, PtDAA:PC71BM solar cells achieve a high Voc of 0.86 V, a Jsc
of 12.87 mA/cm2 and a high FF of 0.74, with an overall PCE of 8.1%.
To the best of our knowledge, the PCE of 8.1% represents one of
4 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 5 of 9
Journal Name
ARTICLE
Table 1. Device performance of solar cells based on PtDDA and PtDAA with PC71BM (1:1, w/w) in a conventional device architecture.
View Article Online
max
DIO
Voc
Jsc
FF
PCEa
DOI: 10P.1C0E39/C6TA05886H
Material
PtDDA
[%]
[V]
[mA/cm2]
7.02±0.12
8.29±0.22
12.87±0.18
11.83±0.30
[%]
[%]
2.1
0
1
0
1
0.715±0.005
0.706±0.001
0.859±0.003
0.859±0.003
0.40±0.02
0.54±0.01
0.73±0.01
0.74±0.01
2.0±0.1
3.2±0.1
8.0±0.1
7.5±0.2
3.4
8.1
PtDAA
7.7
a The average values are obtained from 6 devices.
(a)
(b)
(c)
10-3
VG=
PtDDA
PtDAA
VG=
-100 V
-100 V
-90 V
10-4
10-5
10-6
10-7
10-8
10-9
200
-20
-15
-200
-150
-100
-90 V
-80 V
150
-80 V
-70 V
DS
I
I
S
I
-10
-5
0
100
D
I
-70 V
-60 V
-60 V
-50 V
-50
0
50
-50 V
-40 V
0~-30 V
0~-40V
0
0
-20 -40 -60 -80 -100 -120
Vsd(V)
0
-20 -40 -60 -80 -100 -120
Vsd(V)
-20
-40
-60
VGS (V)
-80
-100
Figure 3. Output curves of OFETs based on a) PtDDA and b) PtDAA after thermal annealing at 160°C. c) Corresponding transfer
characteristics of PtDDA (red) and PtDAA (black).
for neat PtDDA film are located at q ≈ 0.35 and 1.72 Å‐1, with d‐ absence of π−π stacking reflecꢀon in PtDDA:PC71BM blend film
spacing of approximately 1.79 nm and 0.37 nm, respectively. In the indicates that the face‐on molecular orientation of PtDDA neat film
in‐plane direction, the (010) diffraction peak of PtDDA is is disrupted by the PC71BM. For PtDAA:PC71BM film, compared to its
nonexistent, indicating a preference for the face‐on molecular neat film, the (010) reflection peak located at 1.77 Å‐1 is enhanced
orientation in neat PtDDA film. For PtDAA neat film, a stronger in the out‐of‐plane direction and decreased in the in‐plane direction,
edge‐on and weak face‐on orientation of (010) π‐π stacking peaks indicating a more face‐on orientation of PtDAA polymer in the
are observed, and located at q ≈ 1.78 Å‐1, with corresponding blend. The face‐on crystallites were considered to be beneficial for
packing space of 0.35 nm. Thus, the edge‐on and face‐on polymer charge carrier transport. When processed with additive DIO, the
backbone orientation are coexisting in PtDAA film. However, (100) peak of PtDDA in the out‐of‐plane direction is stronger,
compared to PtDDA, PtDAA showed shorter π–π stacking distance, indicating the lamellar packing of PtDDA is significantly increased,
indicating better crystallinity, which agrees well with the SCLC which explains why the device performance is greatly enhanced
results.
after processed with additive. In contrast, the PtDAA blends show
When blended with PC71BM, two blend films show obvious and similar diffraction profiles with slightly enhanced π−π stacking in
broad diffraction halo at q ≈ 1.32 Å‐1, which are attributed to the the in‐plane and out‐of‐plane directions, which is in agreement with
aggregation of PC71BM. As for PtDDA blend film, either the in‐plane the trend of the device performance.
or out‐of‐plane profile shows no obvious reflection peak. The
Table 2. Comparison of optical bandgap, energy levels and photovoltaic characteristics of reported terpolymers with different alternating
structures.
opt
Alternating
structure
D1‐D2‐D1‐A
D‐A1‐D‐A2
D‐A1‐D‐A2
D1‐A‐D2‐A
Random
Eg
HOMO/LUMOa
(eV)/(eV)
Voc
(V)
Jsc
FF
(%)
PCE
(%)
3.4
8.1
3.9
5.5
5.2
6.2
Donor
Acceptor
Ref.
(eV)
1.79
1.78
1.23
1.42
1.41
1.50
(mA cm‐2)
PtDDA
PtDAA
PC71BM
PC71BM
PC71BM
PC71BM
PC71BM
PC71BM
‐5.19/‐3.06
‐5.31/‐3.19
‐5.26/‐3.68
−5.25/−3.83
−5.29/−3.88
‐5.44/‐3.84
0.70
0.86
0.43
0.62
0.61
0.84
8.69
12.87
16.6
12.29
13.18
11.74
0.55
0.74
0.54
0.71
0.65
0.63
This work
This work
PDPP2T‐DTP
Reg‐PBDPPT
Ran‐PBDPPT
BDTA‐PTQD
28
29
29
30
D‐A1‐D‐A2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 6 of 9
ARTICLE
Journal Name
PDTSTTBDTb
D1‐A‐D2‐A
D1‐A‐D2‐A
D1‐A‐D2‐A
D‐A1‐D‐A2
D1‐A‐D2‐A
Random
PC71BM
PC61BM
PC71BM
PC71BM
PC71BM
PC71BM
1.45
1.56
1.61
1.56
1.43
1.33
−5.19/−3.62
‐ / ‐
‐5.29/‐3.63
‐5.47/‐3.93
‐ /‐3.73
0.62
0.90
0.74
0.67
0.75
0.67
14.77
14.20
12.20
15.5
15.9
16.22
0.61
0.61
0.46
0.67
0.67
0.66
6.1
31
View Article Online
BFS4b
PBDT‐O‐ADAb
P3TQTI‐F
PDPP3TaltTPT
P2b
DO7I.:810.1039/C63T2A05886H
4.1
7.0
8.0
7.2
37
40
41
42
−5.22/−3.53
a Measured by the cyclic voltammetry. b Achieved with an inverted architecture.
(a)
(b)
(g)
(c)
(d)
(e)
(f)
Figure 4. GIWAXS patterns of neat films and blends with PC71BM. 2D GIWAXS patterns of a) PtDDA neat film, b) PtDAA neat film, c)
PtDDA:PC71BM blend film and d) PtDAA: PC71BM blend film (1% DIO), e) PtDAA:PC71BM blend film and f) PtDAA:PC71BM blend film (1% DIO).
g) Line curves in out‐of‐plane and in‐plane direction from 2D GIWAXS patterns.
Furthermore, resonant soft X‐ray scattering (R‐SoXS) was used However, PtDAA:PC71BM is less influenced by DIO. Higher average
to study the feature of phase separation in their respective blend domain purity results in enhanced FF but not the overall device
films (Figure 5). The resonant energy of 284.2 eV was selected to performance.
provide optimized scattering contrast.44 As cast PtDAA:PC71BM
blend shows an interference at q ~ 0.16 nm−1, corresponding to a
PtDDA:PC71BM
PtDAA:PC71BM
PtDDA:PC71BM(with DIO)
PtDAA:PC71BM(with DIO)
mode domain spacing (centre‐to‐centre) of ~39 nm, which is larger
than that of ~17 nm for PtDDA:PC71BM blend film. When DIO
additive was used, domain spacing of PtDAA:PC71BM and
106
PtDDA:PC71BM films are increased up to 45 nm and 70 nm,
respectively. This is consistent with the results observed from the
AFM morphology. In addition, it is noted that average composition
105
variations of BHJ blends can be estimated through integrating R‐
SoXS scattering profiles.45,46 As shown in Figure 5, the total
scattering intensity (TSI) for as cast PtDAA:PC71BM film is slightly
lower than that of blend processed with 1% DIO, latter. This is
0.01
0.1
consistent with the slight fluctuation of FF. Furthermore, the
scattering profiles of PtDDA based blend changes dramatically after
the addition of 1% DIO. The total scattering intensity of
q (nm-1)
PtDDA:PC71BM with 1% DIO is much higher than that without Figure 5. Resonant soft x‐ray scattering in log scale for
additive, revealing that the addition of DIO leads to higher average PtDDA:PC71BM and PtDAA:PC71BM blended films with and without
domain purity and result in the significant increases in the FF. 1% DIO.
Generally, high average domain purity is beneficial to restrain
charge carrier recombination and finally enhance the device
performance. Thus, DIO improved performance of PtDDA based
solar cells mainly attributes to the increase of the relative purity.
4. Conclusions
In conclusion, two novel terpolymers named PtDDA and PtDAA
6 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 7 of 9
Journal Name
ARTICLE
13 M. Svensson, F. Zhang, S. C. Veenstra, W. J. H. VVieewrhAretieclse,OJn.liCne.
Hummelen, J. M. Kroon, O. Inganäs DaOnId: 1M0.1.03R9./CA6nTdAe0r5s8s8o6nH,
Adv.Mater., 2003, 15, 988‐991.
14 J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J.
Heeger and G. C. Bazan, Nat. Mater., 2007, 6, 497‐500.
15 J. Hou, H.‐Y. Chen, S. Zhang, G. Li and Y. Yang, J. Am. Chem.
Soc., 2008, 130, 16144‐16145.
16 H. Zhou, L. Yang, A. C. Stuart, S. C. Price, S. Liu and W. You,
Angew. Chem. Int. Ed., 2011, 50, 2995‐2998.
17 L. Huo, T. Liu, B. Fan, Z. Zhao, X. Sun, D. Wei, M. Yu, Y. Liu
and Y. Sun, Adv.Mater., 2015, 27, 6969‐6975.
18 L. Huo, T. Liu, X. Sun, Y. Cai, A. J. Heeger and Y. Sun,
Adv.Mater., 2015, 27, 2938‐2944.
19 A. Najari, S. Beaupré, N. Allard, M. Ouattara, J.‐R. Pouliot, P.
Charest, S. Besner, M. Simoneau and M. Leclerc, Adv. Energy
Mater., 2015, 5, 1501213.
20 S. Nishinaga, H. Mori and Y. Nishihara, Macromolecules,
2015, 48, 2875‐2885.
were synthesized and characterized. The incorporation of TT and
TTz units afforded two different backbone alternating structures of
D1‐D2‐D1‐A1 (D‐D‐A type) for PtDDA and D1‐A1‐D1‐A2 (D‐A‐A type)
for PtDAA. Due to the higher electronegativity of nitrogen atoms in
TTz fused rings, PtDAA exhibits better ordered molecular structure,
stronger aggregation tendency and deeper HOMO level compared
to PtDDA. Solar cells based on PtDAA showed a high PCE of 8.1%,
with a Voc of 0.86 V, a Jsc of 12.87 mA/cm2 and FF of 0.74. The high
efficiency of 8.1% is one of the highest values so far for the PSCs
based on conjugated terpolymers, which mainly originates from the
efficient carrier transport in the active layer, high crystallinity of the
terpolymer, and high domain purity. This work shows that D‐A‐A
type terpolymer is a promissing candidate for the fabrication of
high performance solar cells.
21 S. Liu, X. Bao, W. Li, K. Wu, G. Xie, R. Yang and C. Yang,
Macromolecules, 2015, 48, 2948−2957.
22 S. Subramaniyan, F. S. Kim, G. Ren, H. Li and S. A. Jenekhe,
Macromolecules, 2012, 45, 9029‐9037.
23 J. D. Yuen, J. Fan, J. Seifter, B. Lim, R. Hufschmid, A. J. Heeger
and F. Wudl, J. Am. Chem. Soc., 2011, 133, 20799‐20807.
24 H. Hu, K. Jiang, G. Yang, J. Liu, Z. Li, H. Lin, Y. Liu, J. Zhao, J.
Zhang, F. Huang, Y. Qu, W. Ma and H. Yan, J. Am. Chem. Soc.,
2015, 137, 14149‐14157.
25 B. Xia, K. Lu, L. Yuan, J. Zhang, L. Zhu, X. Zhu, D. Deng, H. Li
and Z. Wei, Polym. Chem., 2016, 7, 1323‐1329.
Acknowledgements
B.F. and X.X. contributed equally to this work. This work was
financially supported by the National Natural Science Foundation of
China (NSFC) (nos. 51473009, 51273203, 51261160496, 21504006,
21534003), the International Science & Technology Cooperation
Program of China (no. 2014DFA52820) and the 111 project
(B14009). The authors thank Prof. Donghui Wei and Prof. Mingming
Yu (Zhengzhou University) for assistance in performing Gaussian
DFT calculations. Y.S. gratefully acknowledges Prof. Zhaohui Wang
(ICCAS) for the assistance with OFETs measurements. The X‐
ray data was acquired at beamline 7.3.3 and 11.0.1.2 at the
Advanced Light Source, which is supported by the Director, Office of
Science, Office of Basic Energy Sciences, of the U.S. Department of
Energy under Contract No. DE‐AC02‐05CH11231.
26 M. Zhang, X. Guo, W. Ma, H. Ade and J. Hou, Adv.Mater.,
2015, 27, 4655‐4660.
27 J. Zhao, Y. Li, A. Hunt, J. Zhang, H. Yao, Z. Li, J. Zhang, F.
Huang, H. Ade and H. Yan, Adv.Mater., 2015, 28, 1868‐1873.
28 W. Li, K. H. Hendriks, A. Furlan, A. Zhang, M. M. Wienk and R.
A. Janssen, Chem. Commun., 2015, 51, 4290‐4293.
29 E. Y. Ko, G. E. Park, D. H. Lee, H. A. Um, J. Shin, M. J. Cho and
D. H. Choi, ACS Appl. Mater. Interfaces, 2015, 7, 28303‐
28310.
30 H. Heo, H. Kim, D. Lee, S. Jang, L. Ban, B. Lim, J. Lee and Y.
Lee, Macromolecules, 2016, 49, 3328‐3335.
Notes and references
31 M. L. Keshtov, S. A. Kuklin, D. Y. Godovsky, A. R. Khokhlov, R.
Kurchania, F. C. Chen, E. N. Koukaras and G. D. Sharma, J.
Polym. Sci., Part A: Polym. Chem., 2016, 54, 155‐168.
32 T. Qin, W. Zajaczkowski, W. Pisula, M. Baumgarten, M. Chen,
M. Gao, G. Wilson, C. D. Easton, K. Mullen and S. E. Watkins,
J. Am. Chem. Soc., 2014, 136, 6049‐6055.
33 T. E. Kang, K.‐H. Kim and B. J. Kim, J. Mater. Chem. A, 2014, 2,
15252‐15267.
34 Q. Fan, Y. Liu, M. Xiao, W. Su, H. Gao, J. Chen, H. Tan, Y.
Wang, R. Yang and W. Zhu, J. Mater. Chem. C, 2015, 3, 6240‐
6248.
1
J. J. M. Halls, C. A. Walsh, N. C. Greenham, E. A. Marseglia, R.
H. Friend, S. C. Moratti and A. B. Holmes, Nature, 1995, 376
,
498–500.
2
S. H. Park, A. Roy, S. Beaupre, S. Cho, N. Coates, J. S. Moon, D.
Moses, M. Leclerc, K. Lee and A. J. Heeger, Nat. Photon.,
2009, 3, 297‐303.
3
4
5
6
7
8
9
R. Søndergaard, M. Hösel, D. Angmo, T. T. Larsen‐Olsen and F.
C. Krebs, Mater. Today, 2012, 15, 36‐49.
Y. Liu, J. Zhao, Z. Li, C. Mu, W. Ma, H. Hu, K. Jiang, H. Lin, H.
Ade and H. Yan, Nat. Commun., 2014, 5, 5293.
L. Lu, T. Xu, W. Chen, E. S. Landry and L. Yu, Nat. Photon.,
2014, 8, 716‐722.
S. Nam, J. Seo, S. Woo, W. H. Kim, H. Kim, D. D. Bradley and Y.
Kim, Nat. Commun., 2015, 6, 8929.
G. Yu, J. Gao, J. C. Hummelen, F. Wudl and A. J. Heeger,
Science, 1995, 270, 1789‐1791.
J. Zhao, Y. Li, G. Yang, K. Jiang, H. Lin, H. Ade, W. Ma and H.
Yan, Nat. Energy, 2016, 1, 15027.
Y.‐J. Cheng, S.‐H. Yang and C.‐S. Hsu, Chem. Rev., 2009, 109,
5868‐5923.
35 S. Hedstrom, Q. Tao, E. Wang and P. Persson, Phys. Chem.
Chem. Phys., 2015, 17, 26677‐26689.
36 K. H. Hendriks, G. H. L. Heintges, M. M. Wienk and R. A. J.
Janssen, J. Mater. Chem. A, 2014, 2, 17899‐17905.
37 X. Huang, G. Zhang, C. Zhou, L. Liu, Y. Jin, S. Liu, L. Ying, F.
Huang and Y. Cao, Polym. Chem., 2015, 6, 4154‐4161.
38 D. Dang, W. Chen, R. Yang, W. Zhu, W. Mammo and E. Wang,
Chem. Commun., 2013, 49, 9335‐9337.
39 W. Sun, Z. Ma, D. Dang, W. Zhu, M. R. Andersson, F. Zhang
and E. Wang, J. Mater. Chem. A, 2013, 1, 11141.
40 Q. Tao, Y. Xia, X. Xu, S. Hedström, O. Bäcke, D. I. James, P.
Persson, E. Olsson, O. Inganäs, L. Hou, W. Zhu and E. Wang,
Macromolecules, 2015, 48, 1009‐1016.
10 Y. Li, Acc. Chem. Res., 2012, 45, 723‐733.
11 L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao and L. Yu,
Chem. Rev., 2015, 115, 12666‐12731.
12 W. Yue, R. S. Ashraf, C. B. Nielsen, E. Collado‐Fregoso, M. R.
Niazi, S. A. Yousaf, M. Kirkus, H. Y. Chen, A. Amassian, J. R.
Durrant and I. McCulloch, Adv.Mater., 2015, 27, 4702‐4707.
41 K. H. Hendriks, G. H. Heintges, V. S. Gevaerts, M. M. Wienk
and R. A. Janssen, Angew. Chem. Int. Ed., 2013, 52, 8341‐
8344.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 8 of 9
ARTICLE
Journal Name
42 K.‐H. Kim, S. Park, H. Yu, H. Kang, I. Song, J. H. Oh and B. J.
Kim, Chem. Mater., 2014, 26, 6963‐6970.
View Article Online
DOI: 10.1039/C6TA05886H
43 E. Gann, A. T. Young, B. A. Collins, H. Yan, J. Nasiatka, H. A.
Padmore, H. Ade, A. Hexemer and C. Wang, Rev. Sci. Instrum.,
2012, 83, 045110.
44 A. Hexemer, W. Bras, J. Glossinger, E. Schaible, E. Gann, R. Kir
ian, A. MacDowell, M. Church, B. Rude, H. Padmore, J. Phys.
Conf. Ser., 2010, 247, 012007.
45 J. R. Tumbleston, B. A. Collins, L. Yang, A. C. Stuart, E. Gann,
W. Ma, W. You and H. Ade, Nat. Photon., 2014, 8, 385‐391.
46 Y. Lin, F. Zhao, Q. He, L. Huo, Y. Wu, T. C. Parker, W. Ma, Y.
Sun, C. Wang, D. Zhu, A. J. Heeger, S. R. Marder and X. Zhan,
J. Am. Chem. Soc., 2016, 138, 4955‐4961.
8 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C6TA05886H
ToC figure
0
PtDDA PCE = 3.4%
PtDAA PCE = 8.1%
-4
-8
-12
0.0
0.2
0.4
0.6
0.8
Voltage (V)