Efficient modulation of end groups for the asymmetric small molecule acceptors enabling organic solar cells with over 15% efficiency

Article abstract of DOI:10.1039/d0ta01032d

Non-fullerene organic solar cells (OSCs) have attracted tremendous interest and made an impressive breakthrough, largely due to advances in high-performance small molecule acceptors (SMAs). The relationship between short-circuit current density (J_SC) and open-circuit voltage (V_OC) is usually shown as one falls, the other rises. Controlling the trade-off between J_SC and V_OC to harvest high power conversion efficiencies (PCEs) still remains as a challenge. Herein, dithieno[3,2-b:2′,3′-d]pyrrole (DTP) based asymmetric SMAs with different chlorinated dicyanoindanone-based end groups, named TPIC, TPIC-2Cl and TPIC-4Cl, are designed and synthesized. These asymmetric acceptors exhibit a remarkable red-shifted absorption profile, while energy levels are simultaneously down-shifted when the numbers of chlorine atoms alter from 0, 1 to 2, due to the gradually improved electronegativity. As a result, PM7:TPIC-4Cl based OSCs achieved a champion PCE of 15.31%, which is the highest PCE for non-fullerene binary OSCs based on asymmetric SMAs. The superiority of the PM7:TPIC-4Cl system consists of the balanced charge transport, favorable phase separation, efficient exciton dissociation and extraction, coupled with the remarkable π-π stacking and crystallinity of the SMAs. Our results highlight the important strategy of asymmetric molecular design to optimize the trade-off between V_OC and J_SC, reaching a high PCE.

Full text of DOI:10.1039/d0ta01032d

View Article Online
View Journal
Journal of
Materials Chemistry A
Materials for energy and sustainability
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: G. Li, D. Li, R. Ma,
T. Liu, Z. Luo, G. Cui, L. Tong, M. Zhang, Z. Wang, F. Liu, L. Xu, H. Yan and B. Tang, J. Mater. Chem. A,
2020, DOI: 10.1039/D0TA01032D.
Volume
Number 12
28 March 2018
Pages 4883-5230
6
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry A
Materials for energy and sustainability
rsc.li/materials-a
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.
ISSN 2050-7488
COMMUNICATION
Zhenhai Wen et al.
An electrochemically neutralized energy-assisted low-cost
acid-alkaline electrolyzer for energy-saving electrolysis
hydrogen generation
rsc.li/materials-a

Please do not adjust margins
Journal of Materials Chemistry A
Page 1 of 10
View Article Online
DOI: 10.1039/D0TA01032D
ARTICLE
Efficient Modulation of End Groups for the Asymmetric Small
Molecule Acceptors Enabling Organic Solar Cells with over 15%
Efficiency
Received 00th January 20xx,
Accepted 00th January 20xx
Gang Li,*a‡ Dandan Li,a‡ Ruijie Ma,b‡ Tao Liu,*ab Zhenghui Luo,b Guanwei Cui,a Lili Tong,a Ming
DOI: 10.1039/x0xx00000x
Zhang,c Zaiyu Wang, c Feng Liu,*c Liang Xu,d He Yan*b and Bo Tang*a
Non-fullerene organic solar cells (OSCs) have attracted tremendous interest and made an impressive breakthrough, largely
due to advances in high-performance small molecule acceptors (SMAs). The relationship between short-circuit current
density (JSC) and open-circuit voltage (VOC) is usually shown as one falls and another rises. Controlling the trade-off
between JSC and VOC to harvest high power conversion efficiencies (PCEs) still remains as a challenge. Herein, dithieno[3,2-
b:2ʹ,3ʹ-d]pyrrole (DTP) based asymmetric SMAs with different chlorinated dicyanoindanone-based end groups, named TPIC,
TPIC-2Cl and TPIC-4Cl, are designed and synthesized. These asymmetric acceptors exhibit remarkable red-shifted
absorption profile, while energy levels are simultaneously down-shifted when the numbers of chlorine atoms alter from 0,
1 to 2, due to the gradually improved electronegativity. As a result, PM7: TPIC-4Cl based OSCs achieved a champion PCE of
15.31%, which is the highest PCEs for non-fullerene binary OSCs based on asymmetric SMAs. The superiority of PM7: TPIC-
4Cl system consists of the balanced charge transport, favorable phase separation, efficient exciton dissociation and
extraction, coupled with remarkable π–π stacking and crystallinity of the SMAs. Our results highlight the important
strategy of asymmetric molecular design to optimize the trade-off between VOC and JSC, reaching a high PCE.
indene-C60/C70 bisadducts (ICBAs) have played a dominant role
[6-11]
1. Introduction
as high-efficient electron acceptors
in the past two
decades due to their excellent charge transport performance.
However, the intrinsic defects of fullerene acceptors, such as
high cost, narrow and weak absorption in visible region,
limited tunability of energy levels, and poor flexibility seriously
hindered further development.[12-21] Therefore, much effort
has been devoted to non-fullerene acceptors (NFAs) to
Organic solar cells (OSCs) deliver the promising alternatives to
conventional Si-based inorganic analogue owing to their
advantages, such as low-cost, light-weight, and transparency.[1-
5]
Generally, active layers of OSCs consist electron-donors and
deficient electron-acceptors. Compared to versatile and highly
efficient donors, cost-effective acceptors are still scarce thanks
to synthetic challenge and photovoltaic characteristics
optimization. Fullerene derivatives such as [6,6]-phenyl-
C61/C71-butyric acid methyl ester (PC61BM/PC71BM) and
overcome abovementioned defects of fullerene molecules. [22-
24]
The pioneering research of fused-ring acceptor–donor–
acceptor
(A-D-A)
NFA,
3,9-bis(2-methylene-(3-(1,1-
(4-
dicyanomethylene)-indanone))-5,5,11,11-tetrakis
hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-sindaceno[1,2-b:5,6-
b ′ ]-dithiophene (ITIC) of Zhan’s group challenged the
fullerene-based devices, yielded a PCE of up to 6.8% in 2015.[25]
Power conversion efficiencies (PCEs) of NFA based OSCs have
been significantly improved and surpassed 16% within four
years.[24, 26-32] ITIC-like acceptors are comprised of ladder-type
fused-ring cores (D) peripherally connected with aryl or alkyl
side chains, and strong electron-accepting groups (A) end-
capped on both sides. The ladder-type fused-ring core plays a
crucial role for the delocalization of π-electrons,[33-37] and
central cores mainly include IDT,[38] IDTT[39] and DTP.[40] At
present, most fused-ring cores are synthesized by symmetric
regulation from both sides,[41-43] which restricts precise tuning
of spectral absorption range, molecular packing and
orientation. Nevertheless, the asymmetric molecular core can
a. Dr. G. Li, D. Li, Dr. T. Liu, Dr. G. Cui, Dr. L. Tong and Prof. B. Tang. College of
Chemistry, Chemical Engineering and Materials Science, Key Laboratory of
Molecular and Nano Probes, Ministry of Education, Collaborative Innovation
Center of Functionalized Probes for Chemical Imaging in Universities of Shandong,
Institute of Materials and Clean Energy, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal University, Jinan 250014,
China. E-mail: ligang@sdnu.edu.cn; tangb@sdnu.edu.cn
b.
Dr. R. Ma, Dr. T. Liu, Dr. Z. Luo and Prof. H. Yan. Department of Chemistry and
Hong Kong Branch of Chinese National Engineering Research Center for Tissue
Restoration & Reconstruction, Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong. E-mail: liutaozhx@ust.hk; hyan@ust.hk
c.
M. Zhang, Z. Zhang and Prof. F. Liu. Department of Physics and Astronomy, and
Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiaotong University,
Shanghai 200240, P. R. China. E-mail: fengliu82@sjtu.edu.cn
d. L. Xu. Key Laboratory for Preparation and Application of Ordered Structural
Materials of Guangdong Province, Shantou University, Shantou 515063, P. R.
China.
‡These authors contributed equally to this work.
Electronic Supplementary Information (ESI) available: [Details of syntheses and
characterizations]. See DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 2 of 10
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/D0TA01032D
Fig. 1 Donor and acceptor materials and their optical properties. (a) Donor PM7 molecular structures; Acceptors TPIC, TPIC-2Cl and TPIC-4Cl molecular structures. (b)
Absorption spectra of TPIC, TPIC-2Cl and TPIC-4Cl in dichloromethane solutions. (c) Solid-state absorptions for TPIC, TPIC-2Cl and TPIC-4Cl.
increase the molecular dipole moment and dielectric constant, 0, 1 to 2. When paired with polymeric donor PM7, PM7: TPIC-
reducing the exciton binding energy, which is greatly beneficial 4Cl based OSCs achieved a champion PCE of 15.31% with JSC of
to exciton dissociation and charge transportation.[44-52]
23.03 mA cm-2, a VOC of 0.881 V and FF of 75.5%,
Meanwhile, end group also matters a lot in burgeoning outperforming PM7: TPIC (13.33%) and PM7: TPIC-2Cl
efficient SMAs. Firstly, end groups can interact with donor counterparts (14.53%). The 15.31% PCE is the highest value
cores to reduce the bandgap, leading absorption spectra to among binary OSCs with asymmetrical fused core
near-infrared region.[53-55] Secondly, close π−π stacking of the functionalized SMAs. The superiority of PM7: TPIC-4Cl system
end groups can achieve high electron mobility and fill factor consists of the more balanced and higher hole and electron
(FF).[56-58] Finally, end groups have great influence on the mobilities, favorable phase separation, more efficient exciton
LUMO levels of A-D-A acceptors and the resultant open-circuit dissociation, charge transport, and extraction, coupled with
voltage (VOC) of the devices.[59-61] With the increase of remarkable π–π stacking and crystallinity of the SMAs.
electron-withdrawing properties of end groups, a distinct near-
infrared absorption and π−π interaction of the neighboring
molecular can be enhanced and thereby the JSC and FF, but the
2. Results and Discussion
VOC will drop due to the downshifted LUMO energy levels of
SMAs.[62] So how to better harmonize the VOC and JSC to yield a
high PCE still remains a big challenge.
2.1 Material synthesis and characterization
The structures of TPIC, TPIC-2Cl and TPIC-4Cl are shown in Fig.
1a, and the synthetic routes are displayed in Scheme 1.
Compound 1 was obtained through the Negishi coupling
reaction between 2,5-dibromo-terephthalic acid diethyl ester
and thiophen-2-ylzinc chloride (II). Then another Negishi
coupling reaction was conducted and compound 2 was
synthesized through 1 and N-(2-ethylhexyl)dithieno[3,2-b:2’,3’-
d]pyrrole-2-ylzinc chloride (II). Afterwards, double nucleophilic
addition reaction was implemented to convert the ester
groups into hydroxyls which were subjected to an acid-
mediated Friedel-Crafts reaction to yield fused compound 3.
Based on the abovementioned considerations, herein we
developed three electron acceptors, with an asymmetric
dithieno[3,2-b:2ʹ,3ʹ-d]pyrrole-like core and end-capped with
three different chlorinated dicyanoindanone terminal groups,
named TPIC, TPIC-2Cl and TPIC-4Cl with 0, 1, and 2 chlorine
atom(s). The photoelectrical properties and OSCs performance
of these three SMAs were measured. They exhibited broad
absorption ranging from 600 to 900 nm with ultralow bandgap
of 1.50, 1.45, and 1.40 eV, respectively. Their HOMOs and
LUMOs descended when chlorine atom(s) were changed from
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
Journal of Materials Chemistry A
Page 3 of 10
View Article Online
DOI: 10.1039/D0TA01032D
ARTICLE
Scheme 1. Synthetic routes of three acceptors.
Without further purification, the crude 3 was converted to the
important intermediate 4 by Vilsmeier–Haack reaction using 2.2 Optical properties
dry DMF and POCl3, which followed the end-capping by the
UV–Vis absorption spectra of the three SMAs are shown in Fig.
1b and 1c. In dichloromethane solutions, all three acceptors
exhibit strong and broad absorption (molar extinction
coefficient >105 M-1cm-1) ranging from 600 to 800 nm. The
dichlorinated and tetrachlorinated TPIC-2Cl and TPIC-4Cl
displayed remarkable and red-shifted intramolecular charge-
transfer absorption (ICT) relative to TPIC owing to highly
electronegative chlorine atoms. The maximal peaks of TPIC,
TPIC-2Cl and TPIC-4Cl are located at 711, 725 and 738 nm,
respectively (Table 1). In solid-state films (Fig. 1c), these three
asymmetrical SMAs displayed broad and structured vibration
shoulder peaks ranging from 600 to 900 nm. Considerable red-
shifts of 41 (TPIC), 57 (TPIC-2Cl) and 66 nm (TPIC-4Cl) are
observed upon moving from solution to the film state, which
demonstrated close π-π stacking interactions could be formed
in the films. Furthermore, the optical bandgaps of TPIC, TPIC-
2Cl and TPIC-4Cl calculated from solid-state absorption edges
are 1.50, 1.45, and 1.40 eV, which
Knoevenagel condensation with 2-(5,6-dichloro-3-oxo-2,3-
dihydro-1H-inden-1-ylidene)malononitrile (IC-2Cl) afforded the
target product TPIC-4Cl in high yields. The other two
asymmetrical analogues (TPIC and TPIC-2Cl) were also
synthesized according to the similar method. The detailed
synthesis procedure is provided in the Supporting Information.
The molecular structures of three molecules were
1
characterized by H NMR, 13C NMR, and matrix-assisted laser
desorption ionization time-of-flight mass spectrometry
(MALDI-TOF). Due to the sp3 carbon linked hexylphenyl side
chains and the branched 2-ethylhexyl groups, TPIC, TPIC-2Cl
and TPIC-4Cl were readily soluble in common organic solvents,
such as dichloromethane (DCM), chloroform (CF) and o-
dichlorobenzene (o-DCB) at room temperature. Furthermore,
thermogravimetric analysis indicated that TPIC, TPIC-2Cl and
TPIC-4Cl also exhibited excellent thermal stability with
decomposition temperature (Td, 5% weight loss) exceeding
300 °C in the nitrogen atmosphere (Fig. S8).
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 4 of 10
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/D0TA01032D
Fig. 2 (a) J-V curves of PM7: TPIC, PM7: TPIC-2Cl and PM7: TPIC-4Cl-based devices. (b) EQE curves of the devices. (c) Dark current density-voltage characteristics for
electron-only devices with optimized PM7: TPIC, PM7: TPIC-2Cl and PM7: TPIC-4Cl BHJ films. (d) Jph versus Veff of the optimized devices.
Table 1 Basic Properties of three SMAs
λmax
εmax
λonset
λfilm
(nm)
λfilm
Eg
HOMO
(eV)
LUMOd)
(eV)
μe
a)
a)
a)
b)
b)
onset
opt c)
e)
max
Acceptors
TPIC
(nm)
(M-1 cm-1)
(nm)
(nm)
(eV)
(cm2 V-1 s-1)
711
2.05 × 105
768
752
826
1.50
-5.30
-3.85
3.66×10-4
TPIC-2Cl
725
738
2.07 × 105
780
794
782
804
855
885
1.45
1.40
-5.36
-3.92
4.45×10-4
5.15×10-4
TPIC-4Cl
2.19 × 105
-5.35
-3.97
a)
b)
opt
In a dichloromethane solution. In a neat film. c) Calculated from empirical the formula: Eg = 1240 / λfilm
.
d) Cyclic voltammetry (CV) method by
onset
measuring in dichloromethane. e) Measured by the space charge limited current (SCLC) method.
Table 2 Performance of the optimized OSCs devices based on PM7: TPIC, PM7: TPIC-2Cl and PM7: TPIC-4Cl.
b)
Annealing
(oC)
VOC
(V)
JSC
calc. JSC
FF
(%)
PCE a)
(%)
Active layer
(mA cm-2)
(mA cm-2)
1.002
(0.994±0.005)
18.77
(18.59±0.265)
70.9
(70.8±0.3)
13.33
(13.07±0.159)
PM7:TPIC
100oC
100 oC
100 oC
18.50
0.941
(0.942±0.005)
21.37
(20.85±0.225)
72.2
(0.725±0.008)
14.53
(14.24±0.216)
PM7:TPIC-2Cl
PM7:TPIC-4Cl
21.10
22.81
0.881
(0.880±0.003)
23.03
(23.02±0.179)
75.5
(74.0±0.9)
15.31
(14.99±0.162)
a) Mean and mean error values are obtained from 20 devices for each. b) Values of integration based on IPCE spectra.
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 10
View Article Online
DOI: 10.1039/D0TA01032D
ARTICLE
show the gradually decreased trend with the increase of JSC of the TPIC-Cl-based solar cell than the TPIC-based
chlorine atoms.
counterpart is mainly due to its broader absorption. When
changed to TPIC-4Cl, the PCE of PM7:TPIC-4Cl is further
improved to a champion value of 15.31%, with a JSC of 23.03
mA cm−2, a VOC of 0.881 V and a FF of 75.5%, which is the
highest PCE among binary OSCs with asymmetric non-fullerene
SMAs. Although VOC is reduced gradually due to the deeper
LUMO energy level triggered by electron-withdrawing effect of
chlorine atoms, smaller bandgap and broader absorption
notably enhanced the corresponding JSC. Finally, TPIC-4Cl
balanced the level between VOC and JSC best among all three
NFAs.
The external quantum efficiency (EQE) measurement of the
photovoltaic devices based on TPIC, TPIC-2Cl and TPIC-4Cl
were carried out to exploring the JSC distinction. As shown in
Fig. 2b, with the increase of chlorine atoms from TPIC, TPIC-2Cl
to TPIC-4Cl, PM7: acceptor based devices gradually ascend the
photoresponse region, which is consistent with the absorption
range for the three SMAs. PM7: TPIC-4Cl obtained the highest
EQE, which is credited to the higher electron mobility.[66]
Furthermore, the integrated JSC of PM7: TPIC, PM7: TPIC-2Cl,
and PM7: TPIC-4Cl from EQE are 18.501, 21.907, 22.809, mA
cm−2, respectively, which exhibited good match with the
measured JSC from the J-V curves within 5% error (Table 2).
2.3 Electrochemical properties
The electrochemical properties of these three asymmetric
SMAs were evaluated by cyclic voltammetry (CV)
measurement in anhydrous dichloromethane solution with
Ag/AgCl as reference electrodes, the corresponding data are
summarized in Table 1. As shown in Fig. S3, the lowest
unoccupied molecular orbital (LUMO) and highest occupied
molecular orbital (HOMO) energy levels were estimated
through the onset reduction and oxidation potentials
according to the equation: E LUMO/HOMO = - (Ered/ox -E
+
+ 4.8)
Fc/Fc
(eV),[63] assuming the Fc/Fc+ to be −4.8 eV. [64] Thus the LUMO /
HOMO of TPIC, TPIC-2Cl and TPIC-4Cl was determined to be -
3.85 /- 5.30 eV, - 3.92 / - 5.36 eV and - 3.97 / - 5.35 eV,
respectively. These results demonstrated that both the LUMO
and HOMO energy levels of chlorinated NFAs (TPIC-2Cl and
TPIC-4Cl) are downshifted compared with the non-
halogenated counterpart (TPIC), which could be explained by
the electron-withdrawing effect of chlorine atoms. In addition,
the molecular energy levels are consistent with the trend of
the DFT calculations [65] (Table S1).
2.4 Photovoltaic Properties
2.5 Active Layer Charge Transport
The as-synthesized molecules were applied as electron-
acceptors partnering with the medium bandgap polymer PM7
as electron-donor for complementary absorption and matched
energy levels. The traditional device architecture of ITO
Charge transport properties were probed using the SCLC
(space charge limited current) method. Single-charge carrier
diodes of ITO/MoOx/organics/MoOX/Ag structure for hole-only
and of ITO/ZnO/organics/PNDIT-F3N/Ag for electron-only
devices were evaluated and shown in Fig. 2c, S4 and S5. The
extracted mobilities data demonstrated in Table S2. With
regard to neat TPIC, TPIC-2Cl and TPIC-4Cl films, the electron
mobilities (μes) upward from 6.66 × 10 −4, 7.53 × 10 −4 to 8.78 ×
10 −4 cm 2 V −1 s −1, illustrating the μe values of the pristine TPIC
films ascend with increasing number of chlorine atoms. This
trend was maintained in blend films. The μes of the
corresponding PM7 based blend films were 3.66 × 10−4, 4.45 ×
10−4, and 5.15 × 10−4 cm2V−1s−1. The corresponding μhs were
6.97 × 10−4, 7.96 × 10−4, and 8.49 ×10−4 cm2V−1s−1. The μh/μe of
TPIC, TPIC-2Cl and TPIC-4Cl blend films were 1.90, 1.78 and
1.64, respectively. It is obviously illustrated that PM7: TPIC-4Cl
blend film displayed simultaneously balanced and higher hole
and electron mobilities, which is beneficial to the charge
transport and thereby higher JSC and FF. [67]
(indium
tin
oxide)/
PEDOT:PSS
(styrene
(poly(3,4-
sulfonate))/
′ -(N,N-
ethylenedioxythiophene):poly
PM7:acceptor/ PNDIT-F3N (poly[(9,9-bis(3
dimethylamino)propyl)-2,7- fluorene)-alt-5,5 ′ -bis(2,2 ′ -
thiophene)-2,6-naphthalene-1,4,5,8- tetracaboxylic-N,N ′ -
di(2-ethylhexyl)imide)/ Ag were fabricated to check the device
performance of three acceptors, where PNDIT-F3N was used
as the cathode interfacial layer. The corresponding device-
fabrication conditions including the donor/acceptor weight
ratios, blend-film thickness, and thermal annealing in the
active layer were carefully optimized (the detailed
optimization process is shown in supporting information). The
photovoltaic parameters of the optimized OSCs are
summarized in Table 2 with corresponding current density-
voltage (J-V) curves are depicted in Fig. 2a. The optimized PM7:
TPIC based OSCs achieved a PCE of 13.33% with a short circuit
JSC of 18.77 mAcm−2, a VOC of 1.002V, and a FF of 70.9%.
Interestingly, when using dichlorinated analogue TPIC-2Cl as
electron acceptors, the PCE was improved to 14.53%, with a JSC
of 21.37 mAcm−2, a VOC of 0.941 V and FF of 72.2%. The higher
2.6 Exciton dissociation and charge extraction
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 6 of 10
View Article Online
DOI: 10.1039/D0TA01032D
ARTICLE
Fig. 3. Film morphology images, AFM height (a, c, e) and phase (b, d, f) images of blend films. a, b) PM7: TPIC, RMS = 0.818 nm; c, d) PM7: TPIC-2Cl, RMS = 1.05 nm; e,
f) PM7: TPIC-4Cl, RMS = 1.17 nm.
Fig. 4 2D GIWAXS patterns of (a) TPIC; (b) TPIC-2Cl; (c) TPIC-4Cl and (d) PM7: TPIC; (e) PM7: TPIC-2Cl; (f) PM7: TPIC-4Cl blend films.
To evaluate the exciton dissociation and charge extraction density under light and dark conditions. Veff = V0 − Vapp, where
processes, the dependence of photocurrent density (Jph) on V0 is the voltage when Jph = 0 and Vapp is the applied external
the effective voltage (Veff ) was measured (Fig. 2d and Table voltage. The saturated photocurrent (Jsat) is defined by Jsat
=
S3). Where Jph =JL − JD, JL and JD represent the photocurrent qGmaxL, where q means the electric charge, L reflects the
Please do not adjust margins

Page 7 of 10
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
thickness of the active layer and Gmax represents the maximum cm−2) and PM7: TPIC-2Cl (21.371 mA cm−2). So we can infer
View Article Online
DOI: 10.1039/D0TA01032D
generation rate of excitons dominated in principle by optical that Gmax for PM7: TPIC-4Cl system is significantly higher than
absorption. The optimized PM7: TPIC-4Cl achieved a Jsat of PM7: TPIC-2Cl and PM7: TPIC systems. The probabilities of
23.032 mA cm−2, obviously higher than PM7: TPIC (18.776 mA exciton dissociation (ηdiss) and the charge collection (ηcoll) of
Fig. 5 In-plane (black dotted lines) and out-of-plane (red lines) line-cut profiles of the GIWAXD results.
PM7: TPIC, PM7: TPIC-2Cl, and PM7: TPIC-4Cl based OSCs can they showed more discernible (010) out-of-plane diffraction
be derived by Jph /J sat under short current and maximal power peak considering preferential face-on orientation, so as
output conditions with the following equations: ηdiss = Jsc /Jsat polymer donor PM7 (Fig. S7). With regards to the three
and ηcoll = Jmax /Jsat. [65] Consequently, PM7: TPIC-4Cl based OSC blended PM7: SMAs films along the in-plane (IP) direction,
devices delivered the maximal values of ηdiss = 94.9% and ηcoll
=
PM7: TPIC, PM7: TPIC-2Cl and PM7: TPIC-4Cl showed strong
85.1%, obviously exceeded the other two OSCs. Therefore, the and similar (100) lamellar peaks at q ≈ 0.30 Å−1 (d ≈ 20.9 Å)
efficient exciton dissociation and charge extraction process in with crystalline coherent length (CCL) of 77.02, 82.42 and
PM7: TPIC-4Cl based device contributes to its high Jsc and FF. [68] 83.34 nm. Along the out-of-plane (OOP) direction, all three
blend films displayed strong π-π stacking with strong (010)
2.7 Morphology characterization
diffraction peak in its qz direction. The CCL calculated from out-
of-plane cut-line profiles is 20.56 nm for PM7: TPIC, 21.22 nm
for PM7: TPIC-2Cl and 23.89 nm for PM7: TPIC-4Cl systems.
The obviously larger coherence length in PM7: TPIC-4Cl blend
film indicated the stronger crystallinity than that of the TPIC
and TPIC-2Cl-based films, contributing to the charge transport
and photovoltaic performance in devices. [68]
The surface morphology of blend film is closely related with
photovoltaic performance, so atomic force microscope (AFM)
measurements were carried out and presented in Fig. 3 and S6.
AFM height images showed that all of blend films displayed
clear phase separation, and exhibited root-mean-square
roughness (RMS) value of 0.818 nm (PM7: TPIC), 1.05 nm (PM7:
TPIC-Cl), 1.17 nm (PM7: TPIC-2Cl), indicative of their smooth
and uniform surface morphology favorable for interface
contact. Whereas AFM phase images of the blend films, PM7:
TPIC-4Cl exhibited relatively bicontinuous interpenetrating
network morphology in relative to PM7: TPIC and PM7: TPIC-
2Cl, which is favorable to exciton dissociation and charge
transfer and thus results in high FF. [69, 70]
3. Conclusions
In conclusion, dithieno[3,2-b:2ʹ,3ʹ-d]pyrrole based asymmetric
small molecule acceptors with different chlorinated
dicyanoindanone-based end groups, named TPIC, TPIC-2Cl and
TPIC-4Cl, are synthesized and characterized. These materials
exhibit strong and broad absorption from 600 to 900 nm and
optical bandgaps of below 1.50 eV in films. With the increase
of chlorine atoms, the absorption edge of the SMAs show
significantly red-shifted and gradually decreased optical
bandgap, although they also simultaneously cause down-
shifted LUMO energy levels and notably enhanced electron
mobility. When combined with polymer donor PM7, PM7:TPIC-
4Cl based OSCs delivered a champion PCE of 15.31% with a
relatively low VOC of 0.881 V, significantly enhanced JSC of
23.03 mA cm−2 and FF of 75.5%, surpassing the TPIC (PCE =
13.33%) and TPIC-2Cl (PCE = 14.53%) based OSCs. The
photovoltaic efficiency of 15.31% is the highest value among
binary OSCs based on asymmetric acceptors eve reported.
2.8 Grazing Incidence Wide-Angle X-ray Scattering (GI-WAXS)
To reveal the intermolecular packing morphology and
orientation characteristics of neat and blend films, grazing
incidence
wide-angle
X-ray
scattering
(GI-WAXS)
measurements are performed. Fig. 4 presented the two-
dimensional (2D) GI-WAXS patterns of three SMAs based neat
and blend films and the corresponding cut-line profiles along
the in-plane and out-of-plane directions were shown in Fig. 5,
the calculated parameters listed in Table S4. The individual
components of TPIC, TPIC-2Cl and TPIC-4Cl displayed similar
crystallinity in the horizontal (100) lamellar scattering, and
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 10
ARTICLE
Journal Name
18 X. Che, C.-L. Chung, C.-C. Hsu, F. Liu, K.-T. Wong and S. R.
These results demonstrate that dithieno[3,2-b:2ʹ,3ʹ-d]pyrrole-
containing fused-ring as asymmetric donor core, together with
electron-withdrawing chlorinated dicyanoindanone as terminal
unit is a successful and expanded strategy to construct high-
performance NF-SMAs.
View Article Online
Forrest, Adv. Energy Mater., 2018, 8, 1D7O03I:6100.310. 39/D0TA01032D
19 A. Wadsworth, M. Moser, A. Marks, M. S. Little, N. Gasparini,
C. J. Brabec, D. Baran and I. McCulloch, Chem. Soc. Rev.,
2019, 48, 1596.
20 C. Dou, X. Long, Z. Ding, Z. Xie, J. Liu and L. Wang, Angew.
Chem. Int. Ed., 2016, 55, 1436.
21 B Kan, M Li, Q Zhang, F Liu, X Wan, Y Wang, W Ni, G Long, X
Yang, H Feng, Y Zuo, M Zhang, F Huang, Y Cao,T. P. Russell
and Y Chen, J.Am. Chem. Soc., 2015, 137, 3886.
22 C. Huang, X. Liao, K. Gao, L. Zuo, F. Lin, X. Shi, C. Li, H. Liu, X.
Li, F. Liu, Y. Chen, H. Chen and A. K.-Y. Jen. Chem. Mater.,
2018, 30, 5429.
Conflicts of interest
There are no conflicts to declare.
23 J. Yuan, Y. Zhang, L. Zhou, G. Zhang, H.-L. Yip, T.-K. Lau, X. Lu,
C. Zhu, H. Peng, P. A. Johnson, M. Leclerc, Y. Cao, J. Ulanski, Y.
Li and Y. Zou, Joule 2019, 3, 1140.
24 L. Meng, Y. Zhang, X. Wan, C. Li, X. Zhang, Y. Wang, X. Ke, Z.
Xiao, L. Ding, R. Xia, H.-L. Yip, Y. Cao and Y. Chen, Science.
2018, 361, 1094.
25 Y. Lin, J. Wang, Z. Zhang, H. Bai, Y. Li, D. Zhu and X. Zhan. Adv.
Mater., 2015, 27, 1170.
26 L. Hong, H. Yao, Z. Wu, Y. Cui, T. Zhang, Y. Xu, R. Yu, Q. Liao, B.
Gao, K. Xian, H. Y. Woo, Z Ge and J. Hou, Adv. Mater., 2019,
31, 1903441.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (No. 21535004, 21927811,
91753111), the Key Research, Development Program of
Shandong Province (2018YFJH0502) and Shandong Province
Natural Science Foundation (ZR2016BM24). L. Xu
acknowledges financial support the National Natural Science
Foundation of China (21702132). The authors gratefully
acknowledge Prof. Lian-Ming Yang and Fengting Li from
Institute of Chemistry, Chinese Academy of Sciences for the
MALDI-TOF characterization.
27 Y. Cui, H. Yao, J. Zhang, T. Zhang, Y. Wang, L. Hong, K. Xian, B.
Xu, S. Zhang, J. Peng, Z. Wei, F. Gao and J Hou, Nat. Commun.,
2019, 10, 2515.
28 X. Xu, K Feng, Z. Bi, W. Ma, G. Zhang and Q. Peng, Adv. Mater.
2019, 31, 1901872.
29 H. Sun, T. Liu, J. Yu, T. Lau, G. Zhang, Y. Zhang, M. Su, Y. Tang,
R. Ma, B. Liu, J. Liang, K. Feng, X. Lu, X. Guo, F. Gao and H.
Yan, Energy Environ. Sci., 2019, 12, 3328.
30 B. Fan, D. Zhang, M. Li, W. Zhong, Z. Zeng, L. Ying, F. Huang
and Y. Cao, Sci. China Chem., 2019, 62, 746.
31 Z. Luo, R. Sun, C. Zhong, Ta. Liu, G. Zhang, Y. Zou, X. Jiao, J.
Min and C. Yang, Sci. China Chem., 2020, DOI:
https://doi.org/10.1007/s11426-019-9670-2.
32 R. Ma, T. Liu, Z. Luo, Q. Guo, Y. Xiao, Y. Chen, X. Li, S. Luo, X.
Lu, M. Zhang, Y. Li and H, Yan, Sci. China Chem., 2020, DOI:
https://doi.org/10.1007/s11426-019-9669-3.
33 X. Liao, Z. Yao, K. Gao, X. Shi, L. Zuo, Z. Zhu, L. Chen, F. Liu, Y.
Chen, A. K.-Y. Jen. Adv. Energy Mater. 2018, 8, 1801214
34 X. Liao, X. Shi, M. Zhang, K. Gao, L. Zuo, F. Liu, Y. Chen and A.
K.-Y. Jen. Chem. Commun., 2019, 55, 8258.
35 Z. Yao, X. Liao, K. Gao, F. Lin, X. Xu, X. Shi, L. Zuo, F. Liu, Y.
Chen and A. K.-Y. Jen. J. Am. Chem. Soc., 2018, 140, 2054.
36 T. Liu, W. Gao, Y. Wang, T. Yang, R. Ma, G. Zhang, C. Zhong,
W. Ma, H. Yan and C. Yang, Adv. Funct. Mater., 2019, 29,
1902155.
37 T. Liu, Z. Luo, Q. Fan, G. Zhang, L. Zhang, W. Gao, X. Guo, W.
Ma, M. Zhang, C. Yang, Y. Li and H. Yan, Energy Environ. Sci.
2018, 11, 3275.
38 Y. Lin, Q. He, F. Zhao, L. Huo, J. Mai, X. Lu, C.-J. Su, T. Li, J.
Wang, J. Zhu, Y. Sun, C. Wang and X. Zhan, J. Am. Chem. Soc.,
2016, 138, 2973.
39 Z. Luo, T. Liu, Y. Xiao, T. Yang, Z. Chen, G. Zhang, C. Zhong, R.
Ma, Y. Chen, Y. Zou, X. Lu, H. Yan and C. Yang, Nano Energy,
2019, 66, 104146.
40 J. Sun, X. Ma, Z. Zhang, J. Yu, J. Zhou, X. Yin, L. Yang, R. Geng,
R. Zhu, F. Zhang and W. Tang, Adv. Mater., 2018, 30,
1707150.
41 R. Geng, X. Song, H.Feng, J. Yu, M. Zhang, N. Gasparini, Z.
Zhang, F. Liu, D. Baran, W. Tang. ACS Energy Lett., 2019, 4,
763.
42 H. Wang, Z. Zhang, J. Yu, X. Liu, S. Qu, S. Guang, W. Tang. J.
Mater. Chem. A., 2019, 7, 21903.
Notes and references
1
2
3
4
L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao and L. Yu,
Chem. Rev., 2015, 115, 12666.
J. Hou, O. Inganäs, R. H. Friend and F. Gao, Nat. Mater., 2018,
17, 119.
C. Yan, S. Barlow, Z. Wang, H. Yan, A. K. Y. Jen, S. R. Marder
and X. Zhan, Nat. Rev. Mater., 2018, 3, 18003.
Y. Huang, E. J. Kramer, A. J. Heeger and G. C. Bazan, Chem.
Rev., 2014, 114, 7006.
5
6
G. Li, R. Zhu and Y. Yang, Nat. Photon., 2012, 6, 153.
E. Wang, L. Hou, Z. Wang, S. Hellström, F. Zhang, O. Inganäs
and M. R. Andersson, Adv. Mater., 2010, 22, 5240.
D. Deng, Y. Zhang, J. Zhang, Z. Wang, L. Zhu, J. Fang, B. Xia, Z.
Wang, K. Lu, W. Ma and Z. Wei, Nat. Commun., 2016, 7,
13740.
7
8
9
H. Zhou, Y. Zhang, C.-K. Mai, S. D. Collins, G. C. Bazan, T.-Q.
Nguyen and A. J. Heeger, Adv. Mater., 2015, 27, 1767.
Z. He, B. Xiao, F. Liu, H. Wu, Y. Yang, S. Xiao, C. Wang, T. P.
Russell and Y. Cao, Nat. Photonics., 2015, 9, 174.
10 M. Li, K. Gao, X. Wan, Q. Zhang, B. Kan, R. Xia, F. Liu, X. Yang,
H. Feng, W. Ni, Y. Wang, J. Peng, H. Zhang, Z. Liang, H.-L. Yip,
X. Peng, Y. Cao and Y. Chen, Nat. Photon., 2016, 11, 85.
11 J. Zhao, Y. Li, G. Yang, K. Jiang, H. Lin, H. Ade, W. Ma and H.
Yan, Nat. Energy., 2016, 1, 15027.
12 L. Li, H. Lin, X. Kong, X. Du, X. Chen, L. Zhou, S. Tao, C. Zheng
and X. Zhang, Nanoscale, 2018, 10, 9971.
13 G. Feng, J. Li, F. J. M. Colberts, M. Li, J. Zhang, F. Yang, Y. Jin,
F. Zhang, R. A. J. Janssen, C. Li and W. Li, J. Am. Chem. Soc.
2017, 139, 18647.
14 J.-L. Wang, K.-K. Liu, L. Hong, G.-Y. Ge, C. Zhang and J. Hou,
ACS Energy Lett., 2018, 3, 2967.
15 Q. Tu, Y. Ma, X. Zhou, W. Ma and Q. Zheng, Chem. Mater.,
2019, 31, 5953.
16 Y. Liu, Z. Zhang, S. Feng, M. Li, L. Wu, R. Hou, X. Xu, X. Chen
and Z. Bo, J. Am. Chem. Soc., 2017, 139, 3356.
17 M. Zhang, J. Wang, F. Zhang, Y. Mi, Q. An, W. Wang, X. Ma, J.
Zhang and X. Liu, Nano Energy 2017, 39, 571.
43 S Dai, F Zhao, Q Zhang, T. Lau, T Li, K Liu, Q Ling,C Wang, X Lu,
W You and X. Zhan. J. Am. Chem. Soc., 2017, 39, 1336.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 10
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
44 W. Gao, M. Zhang, T. Liu, R. Ming, Q. An, K. Wu, D. Xie, Z. Luo,
C. Zhong, F. Liu, F. Zhang, H. Yan and C. Yang, Adv. Mater.,
2018, 30, 1800052.
View Article Online
DOI: 10.1039/D0TA01032D
45 W. Gao, T. Liu, C. Zhong, G. Zhang, Y. Zhang, R. Ming, L.
Zhang,J. Xin, K. Wu, Y. Guo, W. Ma, H. Yan, Y. Liu and C. Yang,
ACS Energy Lett., 2018, 3, 1760.
46 W. Gao, Q. An, C. Zhong, Z. Luo, R. Ming, M. Zhang, Y. Zou, F.
Liu, F. Zhang and C. Yang, Chem. Sci., 2018, 9, 8142.
47 X. Li, C. Li, L. Ye, K. Weng, H. Fu, H. S. Ryu, D. Wei, X. Sun, H. Y.
Woo and Y. Sun, J. Mater. Chem. A, 2019, 7, 19348.
48 J. Zhang, W. Liu, S. Chen, S. Xu, C. Yang and X. Zhu, J. Mater.
Chem.A, 2018, 6, 22519.
49 M. Li, Y. Zhou, J. Zhang, J. Song and Z. Bo, J. Mater. Chem. A
2019, 7, 8889.
50 T. J. Aldrich, M. Matta, W. Zhu, S. M. Swick, C. L. Stern, G. C.
Schatz,A. Facchetti, F. S. Melkonyan and T. J. Marks, J. Am.
Chem. Soc., 2019, 41, 3274.
51 C. Li, J. Song, L. Ye, C. Koh, K. Weng, H. Fu, Y. Cai, Y. Xie, D.
Wei, . Y. Woo and Y. Sun, Sol. RRL 2019, 3, 1800246.
52 J. Song, C. Li, L. Ye, C. Koh, Y. Cai, D. Wei, H. Y. Woo and Y.
Sun, J. Mater. Chem. A 2018, 6, 18847.
53 T. Liu, Z. Luo, Y. Chen, T. Yang, Y. Xiao, G. Zhang, R. Ma, X. Lu,
C. Zhan, M. Zhang, C. Yang, Y. Li, J. Yao and H. Yan, Energy
Environ. Sci., 2019, 12, 2529.
54 W. Zhao, S. Li, H. Yao, S. Zhang, Y. Zhang, B. Yang and J. Hou,
J. Am. Chem. Soc., 2017, 139, 7148.
55 S. Zhang, Y. Qin, J. Zhu and J. Hou, Adv. Mater., 2018, 30,
1800868.
56 F. Liu, Z. Zhou, C. Zhang, T. Vergote, H. Fan, F. Liu and X. Zhu,
J. Am. Chem. Soc., 2016, 138, 15523.
57 F. Shen, J. Xu, X. Li and C. Zhan, J. Mater. Chem. A., 2018, 6,
15433.
58 Y. Li, J.-D. Lin, X. Che, Y. Qu, F. Liu, L.-S. Liao and S. R. Forrest,
J. Am. Chem. Soc., 2017, 139, 17114.
59 W. He, M. Y. Livshits, D. A. Dickie, Z. Zhang, L. E. Mejiaortega,
J. J. Rack, Q. Wu and Y. Qin, J. Am. Chem. Soc., 2017, 139,
14109.
60 T. Liu, W. Gao, G. Zhang, L. Zhang, J. Xin, W. Ma, C. Yang, H.
Yan, C. Zhan and J. Yao, Sol. RRL 2019, 3, 1800376.
61 Z. Zhou, S. Xu, J. Song, Y. Jin, Q. Yue, Y. Qian, F. Liu, F. Zhang
and X. Zhu, Nat. Energy. 2018, 3, 952.
62 Y. Chen, T. Liu, H. Hu, T. Ma, J. Y. L. Lai, J. Zhang, H. Ade and
H. Yan, Adv. Energy Mater., 2018, 8, 1801203.
63 G. Li, S. Wang, T. Liu, P. Hao, Z. Liu, F. Li, L.-M. Yang, Y. Zhang,
D. Li, S. Yang, J. Zhao, J. Li, H. Yan and B. Tang, J. Mater.
Chem. C., 2018, 6, 12601.
64 G. Li, W. Yang, S. Wang, T. Liu, C. Yan, G. Li, Y. Zhang, D. Li, X.
Wang, P. Hao, J. Li, L. Huo, H. Yan and B. Tang, J. Mater.
Chem. C., 2019, 7, 10901.
65 Frisch, M. J. et al. Gaussian 09, Inc., Wallingford, CT, 2009,
see supporting information for full citation.
66 Z. Luo, T. Liu, Y. Wang, G. Zhang, R. Sun, Z. Chen, C. Zhong, J.
Wu, Y. Chen, M. Zhang, Y. Zou, W. Ma, H. Yan, J. Min, Y. Li
and C. Yang, Adv. Energy Mater., 2019, 9, 1900041
67 T. Liu, X. Xue, L. Huo, X. Sun, Q. An, F. Zhang, T. P. Russell, F.
Liu and Y. Sun, Chem. Mater., 2017, 29, 2914.
68 C. Yan, T. Liu, Y. Chen, R. Ma, H. Tang, G. Li, T. Li, Y. Xiao, T.
Yang, X. Lu, X. Zhan, H. Yan, G. Li and B. Tang, Sol RRL 2019, 3,
1900377.
69 G. Li, Y. Zhang, T. Liu, S. Wang, D. Li, J. Li, F. Li, L.-M. Yang, Z.
Luo, C. Yang, H. Yan, P. Hao, Q. Shang and B. Tang, J. Mater.
Chem. C., 2018, 6, 11111.
70 L. Zhu, W. Zhong, C. Qiu, B. Lyu, Z. Zhou, M. Zhang, J. Song, J.
Xu, J. Wang, J. Ali, W. Feng, Z. Shi, X. Gu, L. Ying, Y. Zhang and
F. Liu, Adv. Mater., 2019, 31, 1902899.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Journal of Materials Chemistry A
Page 10 of 10
View Article Online
DOI: 10.1039/D0TA01032D
The Table of Contents
Three asymmetric SMAs based on dithieno[3,2-b:2ʹ,3ʹ-d]pyrrole that exhibit a high
efficiency of 15.31%, which is the highest value in asymmetric acceptor-based binary
organic solar cells.