Dodecacyclic-Fused Electron Acceptors with Multiple Electron-Deficient Units for Efficient Organic Solar Cells

Article abstract of DOI:10.1002/cssc.202100592

Fused aromatic cores in non-fullerene electron acceptors (NFEAs) play a significant role in determining their optoelectronic properties and photovoltaic performance. In this work, a dodecacyclic-fused core with three electron-deficient units is synthesized through a double intramolecular Cadogan reduction cyclization. Terminal groups with different halogen substitution (F or Cl) are grafted onto the dodecacyclic-fused core to afford MS-4F and MS-4Cl, both of which showed strong and broad absorption, narrow bandgaps around 1.40 eV, and variable molecular packing model in pristine and blend films. Photovoltaic performance of solar cells containing MS-4F and MS-4Cl as NFEAs were investigated with resultant power conversion efficiencies (PCEs) of 11.75 % and 11.79 %, respectively. The mechanism study indicates that both of PBDB-T : MS-4F- and PBDB-T : MS-4Cl-based devices displayed high hole and electron mobility values, efficient charge transfer, and low charge recombination etc. These results indicate that designing multiple-fused aromatic cores with multiple electron-deficient units is a promising strategy to obtain high-performance NFEAs.

Full text of DOI:10.1002/cssc.202100592

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ChemSusChem
Dodecacyclic-Fused Electron Acceptors with Multiple
Electron-Deficient Units for Efficient Organic Solar Cells
+
[a]
+ [a]
[a]
[a]
[a]
Shanshan Ma , Hexiang Feng , Xiang Liu, Zhicheng Hu,* Xiye Yang,
[
a]
[a]
[a]
[a]
Yuanying Liang, Jie Zhang, Fei Huang,* and Yong Cao
Fused aromatic cores in non-fullerene electron acceptors
NFEAs) play a significant role in determining their optoelec-
Photovoltaic performance of solar cells containing MS-4F and
MS-4Cl as NFEAs were investigated with resultant power
conversion efficiencies (PCEs) of 11.75% and 11.79%, respec-
tively. The mechanism study indicates that both of PBDB-T:MS-
4F- and PBDB-T:MS-4Cl-based devices displayed high hole and
electron mobility values, efficient charge transfer, and low
charge recombination etc. These results indicate that designing
multiple-fused aromatic cores with multiple electron-deficient
units is a promising strategy to obtain high-performance NFEAs.
(
tronic properties and photovoltaic performance. In this work, a
dodecacyclic-fused core with three electron-deficient units is
synthesized through a double intramolecular Cadogan reduc-
tion cyclization. Terminal groups with different halogen sub-
stitution (F or Cl) are grafted onto the dodecacyclic-fused core
to afford MS-4F and MS-4Cl, both of which showed strong and
broad absorption, narrow bandgaps around 1.40 eV, and
variable molecular packing model in pristine and blend films.
Introduction
Therefore, a wide range of fused aromatic cores with different
core size (from pentacyclic-fused cores to undecacyclic-fused
[22–32]
Organic solar cells (OSCs) have versatile features, such as semi-
transparency, light weight, and flexibility, endowing them with
great potential for applications in flexible solar panels and
building-integrated photovoltaics.
heterojunction (BHJ) microstructure of OSCs is usually formed
cores) have been designed.
Moreover, the extension of
conjugation length and introduction of heteroatoms in multi-
ple-fused aromatic cores could modify their electronic proper-
ties, resulting in narrowed bandgaps, enhanced absorption in
[
1–8]
The active layer with bulk
[33,34]
vis-NIR region, and improved PCEs of OSCs.
Furthermore,
[9]
by a polymer donor and a molecular acceptor. Compared with
conventionally used fullerene-derived electron acceptors, non-
fullerene electron acceptors (NFEAs) show significantly im-
proved photovoltaic performance and great potential for
insertion of electron-deficient units in multiple-fused aromatic
cores can create a charge-deficient region and form donor-
acceptor-donor (D-A-D) structure facilitating electron delocaliza-
[
35,36]
tion and enhance intramolecular charge transfer.
For
[10–12]
applications.
The rational molecular engineering of NFEAs
example, Y-series NFEAs, such as Y6 with an electron-deficient
unit of benzothiadiazole in multiple-fused aromatic cores,
showed broad and strong absorption region, narrow bandgaps
and unique 3D network structure with multiple co-facially
packing between the core and terminal groups, which gave rise
enables diversiform chemical structures, tunable energy levels,
and strong absorption in the visible and near-infrared region
(vis-NIR), contributing to enhanced power conversion efficien-
[13–16]
cies (PCEs) over 18% for NF-OSCs.
[37–41]
The design principle of high-performance NFEAs usually
employ electron-donating groups as center cores and two
symmetry/asymmetry electron-withdrawing groups as terminal
to remarkably enhanced PCEs of OSCs.
These results
indicate that inserting electron-deficient units in multiple-fused
aromatic cores is an effective strategy to design high-perform-
ance NFEAs. Therefore, developing novel fused cores is
important to investigate the relationship between chemical
structure, physical properties, and the resulting device perform-
ances. However, it is still challenging to design high-perform-
ance NFEAs with multiple electron-deficient units in the fused
core and realize applications in optoelectronic devices.
[17–19]
units.
Multiple-fused aromatic cores are widely used as the
center cores of NFEAs, owing to their strong backbone rigidity,
molecular planarity, and strong electron delocalization.
[20,21]
+
+
[
a] S. Ma, H. Feng, Dr. X. Liu, Dr. Z. Hu, Dr. X. Yang, Y. Liang, Dr. J. Zhang,
Prof. F. Huang, Prof. Y. Cao
Institute of Polymer Optoelectronic Materials and Devices
State Key Laboratory of Luminescent Materials and Devices
South China University of Technology
Guangzhou, 510640 (P. R. China)
E-mail: scut_hzc@126.com
In this study, we designed and synthesized a novel
dodecacyclic-fused core with three electron-deficient units,
which was further applied to design high-performance NFEAs
by grafting with different terminal groups. In designing of
multiple-fused aromatic cores, some features are significantly
important such as strong electron delocalization, backbone
rigidity, and molecule planarity etc. To form intramolecular
push-pull electron interactions and ensure effective electron
delocalization, electron-deficient units with different electron-
withdrawing ability are encouraged to design multiple-fused
msfhuang@scut.edu.cn
+
[
] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cssc.202100592
This publication is part of a collection of invited contributions focusing on
“
Advanced Organic Solar Cells”. Please visit chemsuschem.org/collections to
view all contributions.
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[
20]
aromatic cores. The benzothiadiazole unit is a widely used
unit with strong electron-deficient block, and dithienobenzo-
triazole is a moderate electron-deficient block, both of which
are beneficial for acquiring outstanding photovoltaic
charge found that PBDB-T:MS-4F and PBDB-T:MS-4Cl displayed
high electron mobility values, efficient charge transfer, and low
charge recombination. These results indicate that designing
multiple-fused aromatic cores with multiple electron-deficient
units is a promising strategy to obtain high-performance NFEAs.
[37,42]
properties.
Moreover, good planarity is conducive to
ordered molecular packing, and appropriate electron-withdraw-
ing ability helps lead to appropriate bandgaps and energy
levels. Therefore, the dodecacyclic-fused core was synthesized Results and Discussion
by double intramolecular Cadogan reduction cyclization using a
strong electron-deficient unit, benzothiadiazole, as central unit
and two moderate electron-deficient units, dithienobenzotria-
zole, as peripheral units. Two different electron-withdrawing
terminal groups of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-
Synthesis and characterization
The synthetic routes for the two dodecacyclic-fused NFEAs are
depicted in Scheme 1 and the detailed synthetic procedures
and structure characterization results are showed in Supporting
Information. Compounds 1–5 were synthesized according to
1
-ylidene)malononitrile (INCN-2F) and 2-(5,6-dichloro-2,3-dihy-
dro-3-oxo-1H-inden-1-ylidene) malononitrile (INCN-2Cl) were
respectively grafted onto the dodecacyclic-fused core to afford
two NFEAs: MS-4F and MS-4Cl. Both of MS-4F and MS-4Cl
showed strong and broad absorption in vis-NIR region, narrow
bandgaps around 1.40 eV, and variable molecular stacking
model in pristine and blend films. Photovoltaic performance of
PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based solar cells were
investigated, exhibiting PCEs of 11.75% and 11.79%, respec-
tively. Furthermore, by studying behaviors of excitons and
[42,43]
the previously reported procedure.
5 was then used to
synthesize 6 by an electrophilic reaction. 7 was obtained from 6
in high yield by using a Stille coupling. Compound 8 was
synthesized by double intramolecular Cadogan reduction
cyclization reaction. In formation of 8, triethyl phosphite
(P(OEt) ) must be completely removed to avoid formation of
3
byproducts with one ethyl chain (from reaction of P(OEt) with
bromoalkyl chain to generate dihydrocarbyl phosphate and
3
Scheme 1. Synthetic routes for MS-4F and MS-4Cl.
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ethyl bromide) in the nitrogen atom being generated in the
next reaction. The alkyl chains play an important role in the
solubility of the target molecule. By continuously adjusting the
length of alkyl chains, compound 9, with 9-ethylnonadecane
chains, was finally obtained with high solubility. Afterwards,
compound 10 was prepared by Vilsmeier-Haack reaction.
Finally, MS-4F and MS-4Cl were obtained by Knoevenagel
condensation from compound 10 and the terminal groups
INCN-2F and INCN-2Cl, respectively. NMR spectroscopy and
high-resolution mass spectrometry (MALDI-TOF; see the Sup-
porting Information, Figures S1–S6) confirmed the preparation
of MS-4F and MS-4Cl. Both compounds showed high solubility
in common solvents including chloroform (CF) and chloroben-
zene (CB) at room temperature, which is beneficial for
fabricating high-quality films by solution processing method for
photovoltaic devices. Furthermore, the thermal properties of
the two NFEAs were measured by thermogravimetric (TGA)
analysis. As shown in Figure S5, MS-4F and MS-4Cl showed high
thermal stability with decomposition temperatures (5% weight
loss) over 350°C.
the terminal INCN groups, whereas the highest occupied
molecular orbital (HOMO) energy levels were mainly distributed
in the dodecacyclic-fused core.
The HOMO and LUMO energy levels of MS-4F were then
calculated to be À 5.64 eV and À 3.73 eV, respectively. In
contrast, MS-4Cl exhibited deeper HOMO (À 5.73 eV) and LUMO
(À 3.83 eV) energy levels. This result is generally interpreted that
the empty 3d orbitals of the chlorine atom could facilitate π-
electron delocalization more effectively and further lower the
[44,45]
frontier energy levels.
Optical and electrochemical properties
The UV/Vis absorption spectra of MS-4F and MS-4Cl were
collected and the detailed parameters are summarized in
Table 1.
As shown in Figure 2a, MS-4F displayed a maximum peak
(λmax) at 727 nm with a maximum extinction coefficient (ɛmax) of
5
À 1
À 1
1.61×10 m cm in CF solution, whereas MS-4Cl exhibited a
The molecular configurations and energy levels of MS-4F
and MS-4Cl were evaluated using the density functional
theoretical (DFT) calculation (based on the B3LYP/6-31G(d) level
by Gaussian 16). The alkyl chains of MS-4F and MS-4Cl were
replaced with methyl groups to simplify the calculation process
slightly red-shifted λ at 742 nm and a slightly higher ɛmax of
max
5
À 1
À 1
1.66×10 m cm . Compared to the absorption spectra in
solution, the absorption spectra of MS-4F and MS-4Cl as thin-
film states showed remarkable bathochromic shift of 73 nm and
69 nm, respectively, indicating the existence of strong intermo-
lecular π-π packing. In addition, MS-4F and MS-4Cl displayed
strong and broad absorption from 600 nm to 900 nm with
peaks locating at 800 nm and 813 nm, respectively. The optical
(Figure 1). From the horizontal view, MS-4F and MS-4Cl showed
planar backbone configurations as a whole. However, two
terminal groups in both NFEAs exhibited slightly distortion
relative to the dodecacyclic-fused core in the opposite
direction, which can prevent NFEAs from over-aggregation at a
certain extent. According to the calculated wave function
distributions, the lowest unoccupied molecular orbital (LUMO)
energy levels of MS-4F and MS-4Cl were mainly distributed in
bandgaps (E ) of
g
MS-4F and MS-4Cl were estimated to be 1.41 eV and
1.37 eV, respectively, from their thin-film absorption onsets.
Therefore, modulation of terminal groups indeed has great
impacts on optoelectronic properties of NFEAs. The energy
levels of both NFEAs were measured by cyclic voltammetry (CV;
+
Figure 2b). The ferrocene/ferrocenium (Fc/Fc ) was used as a
reference and the potential was 0.39 V. The oxidation /reduc-
tion potential were estimated to be 1.22/À 0.50 V for MS-4F and
1
.27/À 0.42 V for MS-4Cl, respectively. The HOMO energy level
of MS-4F was calculated to be À 5.63 eV, whereas it shifted
down to À 5.68 eV for MS-4Cl. LUMO energy levels also showed
similar trend reducing from À 3.91 eV for MS-4F to À 3.99 eV for
MS-4Cl (Figure 2c), which was consistent with the results of DFT
calculations. The similar phenomenon also was reported in
[30,46]
some NFEAs systems.
In addition, both NFEAs showed
matched energy levels and complementary absorption spectra
with donor polymer PBDB-T (Figure S7b).
Figure 1. Optimized geometries of MS-4F and MS-4Cl calculated by using
density functional theory.
Table 1. Optical and electrochemical properties of MS-4F and MS-4Cl.
5
À 1
À 1
[b]
[b]
NFA
λ
max [nm]
ɛ (10 ) m cm (solution)
λ
max [nm]
λ
onset [nm]
E
g
[eV]
HOMO [eV]
LUMO [eV]
[
a]
(
solution)
(film)
(film)
(film)
MS-4F
MS-4Cl
727
742
1.61
1.66
800
813
878
900
1.41
1.37
À 5.63
À 5.68
À 3.91
À 3.99
[
a] Calculated from the absorption onset of films using the formula: E
g
=1240/λonset(film). [b] Estimated from CV measurements.
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+
Figure 2. a) Normalized UV/Vis absorption spectra for MS-4F and MS-4Cl in solution and as films. b) Cyclic voltammograms of Fc/Fc , MS-4F, and MS-4Cl. c)
Energy level diagram of PBDB-T, MS-4F, and MS-4Cl. d) Architecture of the OSC device.
Photovoltaic performances
Compared with PBDB-T:MS-4F-based device, which showed
an open-circuit voltage (V ) of 0.85 V, a short-circuit current
OC
À 2
To investigate the photovoltaic performance of OSCs using MS-
(J ) of 19.61 mAcm , fill factor (FF) of 70.59%, and resultant
SC
4
F and MS-4Cl as electron acceptors, devices with a conven-
PCE of 11.75%, photovoltaic device with MS-4Cl as electron
tional of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophe-
ne):poly-(styrenesulfonate)(PEDOT:PSS)/PBDB-T:NFEA/PFNDI-
Br/Ag structure (Figure 2d) were fabricated. Detailed fabrication
processes and optimization conditions, such as processing
solvents, additive volume ratio, thermal annealing temper-
atures, and electron transport materials are summarized in the
Supporting Information (Tables S1–S11). The optimal device
was obtained from chlorobenzene solution containing a donor-
acceptor showed a lower VOC of 0.81 V due to its deeper LUMO
energy level. However, PBDB-T:MS-4Cl-based device displayed
À 2
slightly higher JSC of 20.30 mAcm due to the narrower E and
g
broader photo response, which was evidenced by the external
quantum efficiency (EQE) spectra. Consequently, PBDB-T:MS-
4Cl-based devices exhibited a slightly higher PCE of 11.79%.
Compared to the state-of-the-art NFEAs, the MS-4F and MS-4Cl-
based devices deliver moderate PCEs. There are several reasons
to account for the result. Firstly, absorption onsets of MS-4F and
MS-4Cl films are relatively blue-shifted in comparison with Y-
series NFEAs, which leads to a low JSC for PBDB-T:MS-4F- and
PBDB-T:MS-4Cl-based devices. Secondly, imperfect molecular
stacking of MS-4F and MS-4Cl may impact the morphology of
acceptor (D/A ratio=1:1) with a total concentration of
À 1
1
8 mgmL and 1% (vol%) 1-chloronaphthalene as the solvent
additive by thermal annealing at 120°C for 10 min. The current
density-voltage (J-V) curves of optimized devices are given in
Figure 3a and the relevant results are listed in Table 2.
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Figure 3. Photovoltaic characteristics of PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based devices: a) J-V characteristics. b) EQE spectra with integrated JSC(EQE) curves.
Table 2. Photovoltaic parameters of optimal devices based on PBDB-T:MS-4F and PBDB-T:MS-4Cl.
[
a]
[b]
D:A
VOC [V]
J
SC
J
SC(EQE)
FF [%]
PCE (PCEave
)
[%]
μ
h
μ
e
h e
μ /μ
À 2
À 2
2
À 1 À 1
2
À 1 À 1
[
mA cm
]
[mA cm
]
[cm V
s
]
[cm V
s
]
À 3
À 4
PBDB-T:MS-4F
PBDB-T:MS-4Cl
0.85
0.85�0)
0.81
0.81�0)
19.61
(19.67�0.08)
20.30
(20.14�0.12)
18.49
70.59
11.75 (11.67�0.04)
11.79 (11.51�0.19)
1.94×10
2.95×10
3.14×10
6.07×10
6.18
4.86
(
(70.01�0.33)
À 3
À 4
19.30
71.20
(
(70.31�0.86)
[a] Calculated from the integration of EQE spectra. [b] Average values from at least 12 devices.
[18]
À 2
the blend films leading to low FF. Finally, large HOMO energy
showed a slightly higher value of 21.78 mAcm . The maximum
levels offsets (>0.30 eV) between donor and NFEAs leading to
photoinduced carrier generation rates (Gmax) of the photovoltaic
[47]
large energy loss. It should be noted that further adjustment
on the alkyl chains and terminal groups could optimize energy
levels, absorption and molecular stacking of NFEAs, resulting in
improved PCEs. The external quantum efficiency (EQE) spectra
and corresponding JSC curves integrated from the EQE data
devices were calculated by equation: Gmax ¼ J =ðqLÞ, where q
sat
[49]
is the elementary charge and L is film thickness. The G
max
values of PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based devices
2
7
27
À 3 À 1
were calculated to be 9.51×10 and 9.72×10
m s , respec-
tively. The higher Gmax of PBDB-T:MS-4Cl-based device may
originate from the broader absorption and higher extinction
coefficients of MS-4Cl. The charge collection probability P
(Figure 3b) indicated that both of PBDB-T:MS-4F- and PBDB-
T:MS-4Cl-based devices delivered broad photo response vis-NIR
spectral region. More specifically, PBDB-T:MS-4F-based device
showed photo response ranging from 300 nm to 880 nm. The
EQE curve of PBDB-T:MS-4Cl-based device was slightly broad-
ened with a difference of 25 nm in near-infrared spectral region.
Correspondingly, the EQE maxima were 69% and 68% for the
two devices. The integrated JSC values of PBDB-T:MS-4F- and
PBDB-T:MS-4Cl-based devices extracted from the EQE plots
(
E,T)
[50]
was estimated using equation: P
¼ J =J . Under short-
ðE;TÞ
ph sat
circuit condition, it can be observed that P(E,T) values of PBDB-
T:MS-4F- and PBDB-T:MS-4Cl-based device were 92.1% and
93.2%, respectively, suggesting that more efficient charge
collection occurs in PBDB-T:MS-4Cl-based device. These results
may be one of the reasons for higher JSC and FF values for
PBDB-T:MS-4Cl-based device.
À 2
were 18.49 and 19.30 mAcm , respectively, which were in line
The steady-state photoluminescence (PL) emission spectra
of neat donor and acceptor as well as their blend films were
measured to investigate hole and electron transfer efficiency
between donor and acceptor. The neat film of PBDB-T and
blend films of PBDB-T:MS-4F and PBDB-T:MS-4Cl were excited
using 500 nm laser, respectively. As shown in Figure 4b, PBDB-T
presented a PL emission peak locating at 675 nm. The PL
emission intensity peak of blend films (PBDB-T:MS-4F and
PBDB-T:MS-4Cl) was greatly reduced, indicating that MS-4F and
MS-4Cl could efficiently quench the excited state of PBDB-T.
The PL quenching efficiency of PBDB-T:MS-4F and PBDB-T:MS-
4Cl blend film reached to 91.2% and 92.5%, respectively,
indicating both devices exhibited effective electron transfer
from PBDB-T to NFEAs. Moreover, the transfer efficiency of hole
with the JSC values calculated from J-V curves.
Charge generation, dissociation, recombination, and
transport
To study the photoinduced carrier generation and charge
collection dynamic of devices, the photocurrent (J ) versus
ph
[48]
applied voltage (V ) was measured. At the saturation point,
eff
the saturation photocurrent densities (J ) are determined
sat
mainly by the number of generated carriers. As shown in
Figure 4a, the Jsat of PBDB-T:MS-4F-based device was
À 2
2
1.30 mAcm , whereas the PBDB-T:MS-4Cl-based device
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Figure 4. a) Jph vs. Veff for PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based devices. b) PL spectra of pure films and blend films at 500 nm. c) PL spectra of pure films
and blend films @750 nm. d) Light intensity dependence of JSC for PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based devices. e) Light intensity dependence of VOC of
PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based devices; (f)TPC curves of PBDB-T:MS-4F- and PBDB-T:MS-4Cl-based devices.
[
53]
from NFEAs to PBDB-T was measured using a 750 nm laser to
excite neat NFEAs and blend films. As shown in Figure 4c, the
PL quenching efficiencies of PBDB-T:MS-4F and PBDB-T:MS-4Cl
blend films were 92.5% and 93.3%, respectively, suggesting
both devices exist effective hole transfer from NFEAs to PBDB-T.
The slightly higher charge transfer efficiency in PBDB-T:MS-4Cl
blend film over that of PBDB-T:MS-4F blend film, which may be
due to slightly larger HOMO and LUMO energy offsets between
PBDB-T and NFEAs and giving a larger driving force.
nation or trap-assisted monomolecular recombination.
As
shown in Figure 4e, the slope of PBDB-T:MS-4F- and PBDB-
T:MS-4Cl-based devices were found to be 1.42 kT/q and
1.34 kT/q, respectively, which indicated lower trap-assisted
monomolecular recombination existed in PBDB-T:MS-4Cl-based
device. The transient photocurrent (TPC) characteristic was
employed to investigate charge extraction behaviors of photo-
voltaic devices. TPC was measured under short-circuit current
condition by recording the photocurrent decay time of devices
to reveal charge extraction behavior. As shown in Figure 4f,
PBDB-T:MS-4Cl-based device delivered a faster charge extrac-
tion with charge extraction time of 0.81 μs than that of PBDB-
T:MS-4F-based device (0.88 μs), suggesting more efficient
charge extraction occurred in PBDB-T:MS-4Cl-based device.
The electron mobility (μ ) and hole mobility (μ ) were
e
h
separately estimated by electron-only devices (ITO/ZnO/Active
layer/PFNÀ Br/Ag) and hole-only device (ITO/PEDOT:PSS/Active
layer/MoO /Ag) using the space-charge limited current (SCLC)
3
[51]
model (Figure S8). The μ and μ of PBDB-T:MS-4F blend film
h
e
À 3
were respectively estimated to be 1.94×10
with a ratio of 6.18. For PBDB-T:MS-4Cl blend
film, both of μh (2.95×10 cm V s ) and μe (6.07×
and 3.14×
À 4
2
À 1 À 1
1
0
cm V
s
À 3
2
À 1 À 1
Film microstructure and morphology
À 4
2
À 1 À 1
1
0
cm V s ) slightly increased with a smaller ratio 4.86,
which could be interpreted as higher JSC and FF values for
PBDB-T:MS-4Cl-based device. The VOC and JSC as a function of
light intensity (Plight) was conducted to explore the charge
recombination properties of photovoltaic devices. As shown in
The nanoscale phase separation of both blend films was
investigated by atomic force microscopy (AFM) and high-
resolution transmission electron microscopy (TEM; Figure S9).In
AFM images, both blend films showed smooth surfaces with
root-mean-square roughness values of 1.75 nm for PBDB-T:MS-
4F blend film and 1.61 nm for PBDB-T:MS-4Cl blend film,
respectively. In TEM images, more fibril network structures were
observed in PBDB-T:MS-4Cl blend film than that in PBDB-T:MS-
4F blend film, which is in line with the trend of charge mobility
values.
Figure 4d, the relationship between J and Plight can be
SC
S
[52]
expressed as JSC / P
.
The S values of PBDB-T:MS-4F- and
light
PBDB-T:MS-4Cl-based devices were calculated to be 0.97 and
.98, respectively. Under short-circuit condition, S values close
0
to 1 indicates negligible bimolecular recombination in both
devices. For VOC / P plots, the slope tendency to kT/q or 2kT/
light
q respectively represented predominant biomolecular recombi-
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To further investigate the microstructure and molecular
packing behaviors of these dodecacyclic-fused NFEAs, we
performed the grazing-incidence wide-angle X-ray scattering
packing orientation in pristine and blends, enable them
potential candidates not only applied as active layer in OSCs,
but also acting as channel materials in OFET.
(GIWAXS) to the neat and blend films. As shown in Figure 5,
both of MS-4F and MS-4Cl exhibited distinct lamellar peak (100)
À 1
at q ꢀ0.31 Å with a d-spacing of 20.26 Å in out-of-plane
Stability
(
OOP) direction, which indicated the tendency of edge-on
orientation relative to their respective substrate for both films.
Surprisingly, the blend films with PBDB-T showed a dominated
face-on orientation. As shown in Figure 5e, a (100) diffraction
The light, thermal, and air stabilities of PBDB-T:MS-4F- and
PBDB-T:MS-4Cl-based devices were further separately eval-
uated. The corresponding results were showed in Figure S10.
Under the stimulated AM 1.5G solar spectrum irradiation in the
glove box with dry nitrogen atmosphere, PBDB-T:MS-4F- and
PBDB-T:MS-4Cl-based devices retained 66% and 75% PCE (in
comparison with initial PCE) after 90 h, respectively, indicating
that chlorinated molecule might show better photo-chemical
À 1
peak in blend film was detected at q ꢀ0.31 Å in IP direction,
which also existed in all neat films. In addition, a strong π-π
À 1
stacking peak (010) at q ꢀ1.78 Å (d=3.67 Å) in OOP direction
were found in PBDB-T:MS-4F and PBDB-T:MS-4Cl blend films,
À 1
which was different from that of PBDB-T neat film (q ꢀ1.71 Å ,
[61]
d=3.67 Å). These results indicate that PBDB-T may induce
NFEAs to form face-on stacking in blend films.
stability than that of fluorinated molecular. After exposing
these devices at 80°C for 96 h in the glove box filling with dry
A similar phenomenon was observed in PTB7-Th:ITIC-Th:
nitrogen atmosphere, PCEs of both devices retained 80% for
PBDB-T:MS-4F-based devices and 82% for PBDB-T:MS-4Cl-
based devices, respectively, inferring that PBDB-T:MS-4Cl blend
film might possess slightly better thermal stability than PBDB-
[54]
TPE-4PDI three-component system.
The crystal coherence
length (CCL) was calculated according to the Scherrer equation
CCL ¼ 2pK=Dq, where K is a shape factor (typically 0.9) and Δq
is the full width at half-maximum (FWHM) of a diffraction
[62]
T:MS-4F blend film.
However, both devices were very
[55]
peak. The CCL of PBDB-T:MS-4F and PBDB-T:MS-4Cl blend
films were 19.80 Å and 19.91 Å, respectively, which indicates
PBDB-T:MS-4Cl blend film possess larger crystallite size than
PBDB-T:MS-4F blend film. This result was in line with higher
charge mobility values obtained in PBDB-T:MS-4Cl-based
unstable in air and only retained about 50% of the initial
efficiency in 3 h (Figure S10c), indicating that oxygen and water
[63]
may play additional role in the degradation of OSCs.
device. Generally, high-performance OSCs require face-on Conclusion
[56–58]
orientations in D:A blend films,
while high-performance
organic semiconductors for organic field effect transistor (OFET)
In this work, we prepared the dodecacyclic-fused molecules MS-
4F and MS-4Cl for application in organic solar cells. The optical
and electrochemical properties, molecular geometry, thin-film
[59,60]
prefer to an edge-on orientation in neat film.
The interest-
ing properties of MS-4F and MS-4Cl that can change molecular
Figure 5. a–d) 2D GIWAXS: a) MS-4F neat film; b) MS-4Cl neat film; c) PBDB-T:MS-4F blend film; d) PBDB-T:MS-4Cl blend film; (e) In-plane (dashed line) and
out-of-plane (solid lines) scattering profiles for the corresponding film.
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orientation, and performance in OSCs were systematically
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Put 12rings on it: Two non-fullerene
electron acceptors for organic solar
cells have been developed, which
consist of a fused dodecacyclic core
with three electron-deficient units
and two terminal groups. Both MS-4F
and MS-4Cl (see figure) show strong
and broad absorption in the visible-
near-infrared region, narrow
S. Ma, H. Feng, Dr. X. Liu, Dr. Z. Hu*,
Dr. X. Yang, Y. Liang, Dr. J. Zhang,
Prof. F. Huang*, Prof. Y. Cao
1
– 10
Dodecacyclic-Fused Electron
Acceptors with Multiple Electron-
Deficient Units for Efficient Organic
Solar Cells
bandgaps around 1.40 eV, and
excellent photovoltaic performance.
#
SCUT #cscOrganicSolarCells
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Shanshan Ma
Hexiang Feng
Dr. Xiang Liu
Dr. Zhicheng Hu
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Yuanying Liang
Dr. Jie Zhang
Prof. Fei Huang http://orcid.org/0000-0001-9665-6642
Prof. Yong Cao