Simply planarizing nonfused perylene diimide based acceptors toward promising non-fullerene solar cells

Article abstract of DOI:10.1039/c9tc02013f

This work focuses on developing high-efficiency perylene diimide (PDI)-based small molecular nonfullerene acceptors with a simple synthetic strategy. We reported a new electron acceptor, Py-e-PDI, obtained via cross-coupling four PDI units with a planar pyrene core through ethynyl groups. Although the ring-fusion synthetic procedure was omitted, the large planar core and significantly reduced intramolecular steric hindrance endowed this nonfused PDI-tetramer derivative with moderate planarity. Differing from most of the PDI-tetramers with highly twisted geometries, Py-e-PDI could self-assemble into a highly ordered structure. The inverted solar cells with PTB7-Th/Py-e-PDI blends exhibited the best power conversion efficiency of up to 7.59%, which mainly resulted from the combined contribution of complementary absorption with a donor polymer, desirable aggregation and high electron mobility. Most importantly, this result demonstrates that simply planarizing 3D nonfused perylene diimide based acceptors is effective to improve the performance of the corresponding non-fullerene (NF) acceptors.

Full text of DOI:10.1039/c9tc02013f

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M at erials Chemistry C
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T. Lau, C. Sheng, X. Lu, H. Du, C. Zhang, Z. Qu, H. Chen and J. Wan, J. Mater. Chem. C, 2019, DOI:
1
0.1039/C9TC02013F.
Volume
4
Number
1
7
January 2016 Pages 1–224
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ISSN 2050-7526
PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
rsc.li/materials-c

Page 1 of 22
Journal of Materials Chemistry C
Simply Planarizing Nonfused Perylene Diimide Based Acceptor
View Article Online
DOI: 10.1039/C9TC02013F
Toward Promising Non-fullerene Solar Cells
#
a
# b
c
a
c
a
d
Gao-Feng Bian , Feng Zhao , Tsz-Ki Lau , Chun-Qi Sheng , Xinhui Lu , Hui Du , Cheng Zhang ,
a
b
a
Zhi-Rong Qu* , Hongzheng Chen* and Jun-Hua Wan*
#
Contributed equally
a. Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education,
Hangzhou Normal University, Hangzhou, 310012, P. R. China.
*
E-mail: wan_junhua@hznu.edu.cn, quzr@hznu.edu.cn
b.State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and
Functionalization, & Department of Polymer Science and Engineering, Zhejiang University,
Hangzhou 310027, P. R. China
*
E-mail: hzchen@zju.edu.cn
c. Department of Physics, Chinese University of Hong Kong, New Territories, Hong Kong, P. R.
China
d. State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, College of
Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, P. R. China
KEYWORDS: organic solar cell, nonfullerene acceptor, perylene diimide, nonfused
Abstract
This work focuses on developing high-efficiency perylene diimide (PDI)-based small molecular
nonfullerene acceptors with simply synthetic strategy. We reported a new electron acceptor,
Py-e-PDI, obtained via cross-coupling four PDI units with planar pyrene core through ethynyl
groups. Although the ring-fusion synthetic procedure was omitted, the large planar core as well as
significantly reduced intramolecular steric hindrance endowed this nonfused PDI-tetramer derivative

Journal of Materials Chemistry C
Page 2 of 22
with moderate planarity. Differing from most of PDI-tetramers with highly twisted geometries,
View Article Online
Py-e-PDI could self-assemble into highly ordered structure. The inverted so
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PTB7-Th/Py-e-PDI blends exhibited the best power conversion efficiency up to 7.59%, which
mainly resulted from the combined contribution of complementary absorption with a donor polymer,
desirable aggregation and high electron mobility. Most importantly, this result demonstrates that
simply planarizing 3D nonfused perylene diimide based acceptor is effective to improve the
performance of the corresponding non-fullerene(NF) acceptors.
Introduction.
Conventional fullerene derivatives-based organic solar cells (OSCs) have achieved great successes
in the past decade and their power conversion efficiencies (PCEs) had reached beyond 10% since
1
-4
2
014 . However, in recent several years, the further efforts of scientists to improve efficiency of
this type OSCs had made no substantial progress due to the serious drawbacks of fullerene acceptors.
Fullerene acceptors do not significantly contribute to light harvesting at wavelengths greater than
6
00 nm, and their energy levels cannot be fine-tuned to match the donor materials to maximize the
5
-6
open-circuit voltage (Voc) and minimize the energy loss . Recently, an emerging class of
7
-9
nonfullerene small molecule acceptors has rivaled the dominance of fullerene-based acceptors .
The single-junction non-fullerene OSCs can now achieve much higher PCEs (>14%) than
fullerene-based ones10-12. And more, very recently, 17.3% PCE has been realized for a tandem
1
3
device . The great adjustability of molecular structures for small molecule acceptors offers a wide
range of optoelectronic tunability.
Among the numerous non-fullerene electron acceptors, perylene diimide (PDI) based acceptors
have been one of the most intensively studied and promising alternatives to fullerene derivatives
because of their appropriate low-lying energy levels, high electron mobility and strong absorption in
the visible region14-17. And it is worth mentioning that PDI, the most extensively used dyes in

Page 3 of 22
Journal of Materials Chemistry C
industries, is readily scalable at low-cost, making it one of the few feasible candidates for
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commercial OSCs. Moreover, PDIs have complementary absorptions (300-600nm) wDOitI:
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narrow-band gap polymer donors, such as PTB7 and PTB7-Th. However, PDIs indicate the strong
tendency of forming large aggregates due to their rigid polycyclic aromatic core. Therefore, a
twisting strategy had been proposed to produce a twisted molecular geometry in PDI derivatives,
which can suppress the strong aggregation and assure effective dissociation of photogenerated
1
8
excitons into free charges . However, a challenge involved in this effort is the difficulty to maintain
the effective charge transport due to reduced π-π stacking between nonplanar PDIs. How much
twisting would be needed? The development of PDI-based acceptors have experienced three stages,
PDI monomers19-20, twisted PDIs (dimmer21-25, trimer26-29 and tetramer30-37) and fused PDI 38-45
.
Most of twisted PDIs showed PCE below 6%, while the fused PDIs obtained from oxidative
cyclization exhibited significantly improved efficiency. It is obvious that in some PDI derivatives the
twisted geometries greatly suppressed their crystallinities29- 33. After final oxidative cyclization, the
highly twisted molecules could be changed to more planar molecules and crystallinity was thus
significantly improved. According to the reported PDI based acceptors, a principle can be
summarized as a guidance: when nanoscale phase separation is within a reasonable range, i.e., not
too large for efficient exciton dissociation, the intermolecular π−π stacking is essential to enable the
device with good charge transporting, which usually plays a dominant role in overall device
performance. To develop high-efficiency PDI non-fullerene acceptor, the trade-off between the phase
separation and strong π-π stacking should be considered.
3
9
Encouragingly, the efficiency of the champion PDI based device has been boosted to over 10% ,
which is very close to the high-efficiency NF acceptors with A-D-A structure, such as ITIC.
However, to the best of our knowledge, most of PDI-based acceptors with PCE over 7% involved
ring-fusion of PDI unit and only a few contained no fused structure27-28, 46-49
.

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We focus on developing efficient PDI-based small molecular acceptors by simply synthetic
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procedure. A large molecular skeleton and slightly twisted configuration are consider
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geometry to achieve high electron mobility and good film-forming property.
Tetraphenylcarbon(TPC) , tetraphenylethylene (TPE) and spirofluorene(SF)32-33 cores possess
three-dimension (3D) molecular structure, which usually results in highly twisted molecules.
Moreover, one molecule with three or four PDI units in limited periphery would be overcrowded due
to a big fused ring aromatic structure of PDI. Therefore, the periphery of core should be expanded.
In 2017，Li and Wang et al reported a high-efficiency NF acceptor(PBI-Por), which has four PDI
5
0
30
4
6
units connected at the meso-positions of a porphyrin ring through acetenyl groups . In order to
reduce intramolecular steric hindrance of PDI-based acceptors, C–C triple bonds were also inserted
between 3D51 or small52 cores and PDI units as linkage to give PCEs of 5.84% and 6.0%,
respectively (Fig. 1). And also, in the past two years, other types of small molecular acceptors
with ethynyl group as linkers were developed53-54. Here, through a simply synthetic strategy, we
constructed a planar four-PDI based electron acceptor(Py-e-PDI) by introducing planar pyrene unit
as core, which is a four fused ring of polycyclic aromatic hydrocarbons (PAH). Similarly, C–C triple
bond was used to link pyrene core and PDI units for the sake of enlarging the distance between
pyrene core and PDI units (Fig. 2). A detailed investigation of the photophysical, electrochemical,
and self-assembly properties was performed. This PDI derivative was also investigated as NF
acceptors pairing PTB7-Th to fabricate OSCs.

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Journal of Materials Chemistry C
O
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R
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O
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DOI: 10.1039/C9TC02013F
O
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Zn
O
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O
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PDI-III
PCE = 6.0%
019
TPA-PDI3
PCE = 5.84%
PBI-Por
PCE = 7.4%
2
2018
2017
O
R
N
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R
O
N
O
O
N
R
O
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N
N
R
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O
N
R
O
O
N
R
O
Py-e-PDI
This work
Fig. 1. The chemical structures of PDI-based acceptors with an acetylene spacer as linkage.
Result and Discussion
Synthesis and Characterization.
The synthesis of the Py-e-PDI involves only two steps reaction. Fig. 2a shows the synthetic route
to convert 1,3,6,8-tetrabromopyrene into corresponding tetra acetylene derivative (3) with high yield.
Further Sonagashira coupling reaction between compound 3 and mono-brominated PDI (Br-PDI) at
a molar ratio of 1:6 afforded the desired four-arm molecule Py-e-PDI in moderate yields (around
5
0%). Although the PDI units bear two branching alkyl chains, Py-e-PDI is less soluble in CH
and CHCl than in aromatics solvents, such as toluene, chlorobenzene, and dichlorobenzene.
However, this limited solubility in CH Cl does not affect purification procedure through sel-gel
column chromatography using CH Cl mixed with a small amount of hexane as eluent. The chemical
structure of Py-e-PDI was confirmed by high-temperature 1H NMR spectroscopy in
ortho-dichlorobenzene-d (Fig. S2)，both low and high-resolution MALDI-TOF mass spectrometry,
Raman spectra and elemental analysis.
2
Cl
2
3
2
2
2
2
4

Journal of Materials Chemistry C
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(a)
O
R
N
O
R
O
N
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DOI: 10.1039/C9TC02013F
O
O
O
O
O
C6H13
C6H13
O
C6H13
C6H13
Si
Si
Si
Si
N
O
N
R
Br
Br
Br
Br
O
Br
Br-PDI
R
O
i
ii
O
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N
iii
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R
N
O
O
1
2
3
O
N
R
C6H13
C6H13
O
O
R =
N
R
O
Py-e-PDI
(b)
Fig. 2. (a) The chemical structure of Py-e-PDI and its synthetic route. (i) Pd(PPh
3
)
2
Cl
2
, CuI, PPh , 6 equiv
3
o
trimethysilylethyne, NEt
3
/toluene, 80 C, 81%; (ii) K
2
CO
3
, MeOH; (iii) Pd(PPh
3 4
)
, CuI, 6 equiv Br-PDI,
o
NEt
3
/toluene, 80 C, 47%. (b) Optimized geometries of Py-e-PDI, left: side view; right: top view, as calculated
from density functional theory (DFT).
In order to reveal the intramolecular steric hindrance, optimized ground state geometry of
Py-e-PDI was calculated using Gaussian 09 software package at the B3LYP/6-31G (d, p) level of
theory in the gas phase using density functional theory (DFT). In the calculations, the alkyl side
chains of the molecule were replaced by methyl groups. The corresponding ground-state geometries
(side view and top view) were shown in Fig. 2b. Normally, the introduction of C-C triple bond can
remarkably enlarge the space between two connected groups and thus largely reduce the steric
hindrance between them. As expected, in the Py-e-PDI model, four PDI units lie nearly in the plane
of pyrene core with interplanar angle of only 8°, which leads to less intramolecular twist. Such
geometry is beneficial for improving intermolecular packing and thus enhances the
charge-transporting ability of the NF acceptor.

Page 7 of 22
Journal of Materials Chemistry C
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DOI: 10.1039/C9TC02013F
Fig. 3. UV/vis absorption spectra of (a) Py-e-PDI in toluene solutions and as-casted films, (b) Py-e-PDI film,
PTB7 film and PTB7-Th films, (c) PTB7-Th/Py-e-PDI blend film, respectively. (d) Cyclic voltammogram of the
Py-e-PDI thin film.
Optical Properties.
The optical properties of Py-e-PDI were characterized using UV−vis absorption spectroscopy.
Fig.3a shows the absorption spectra of this PDI derivative in dilute toluene solution and in thin film.
In toluene solution, Py-e-PDI showed several distinct absorption bands including a weak band in the
shorter wavelength region and a strong band in the longer wavelength region (450–650 nm).
Noticeably, an obvious vibronic structure was observed for both absorption bands. The shorter
5
5
wavelength absorption band(300–450 nm) is associated with 1,3,5,7-tetraethynylpyrene core , while
the longer wavelength absorption originates from the intramolecular charge transfer (ICT) is
associated with the PDI. Interestingly, in dilute solution, apart from the intense absorption in the
region of 450-650 nm, a new small band at 606 nm occurs to Py-e-PDI. However, this shoulder peak
o
still exists even if the dilute solution was heated to 70 C (Fig. S6). It is obvious that the longest
wavelength feature is not assigned to an aggregate-based feature and probably originates from

Journal of Materials Chemistry C
Page 8 of 22
pyrene-to-PDI charge-transfer. In thin film, the absorption band of Py-e-PDI is significantly
View Article Online
broadened at the long-wavelength direction close to the absorption edge and extendsDOthI:
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onset to 675 nm, yielding an optical band gap of 1.83 eV. Additionally, the small absorption band at
around 600 nm was clearly red-shifted (13 nm) and became more evident. But mostly importantly, to
evaluate the new acceptor and maximize the cell efficiency, the donor polymers with complementary
absorption must be found. Fig. 3b shows that the absorptions of both PTB7 and PTB7-Th donor
polymers are complementary to that of Py-e-PDI. Nevertheless, since the absorption of PTB7-Th
mainly lies in the range of 550–800 nm, the PTB7-Th/Py-e-PDI blends (Fig. 3c) could produce
extended absorption spectra to favors solar energy harvesting.
Electrochemical Properties.
Cyclic voltammetry measurement was performed to determine the HOMO and LUMO of the novel
PDI derivative. As shown in Fig. 3d, Py-e-PDI undergoes a reversible multiple-electron reduction
originating from successive reduction of the peripheral PDI units. The onset reduction potential and
onset oxidation potential are found to be -0.54 and 1.50 V (versus a saturated calomel electrode
(SCE)). Therefore, the LUMO and HOMO energy levels are calculated to be -3.86 eV and -5.90 eV,
respectively. It is worth noting that, based a comparison, the HOMO and LUMO offsets between
PTB7-Th and Py-e-PDI is 0.68 eV and 0.20 eV, respectively. Although the LUMO offset is less
than 0.3 eV, more and more studies revealed that an energy offset below 0.3 eV was also sufficient
5
6
for charge separation in fullerene-free solar cells .

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DOI: 10.1039/C9TC02013F
Fig. 4. SEM images of pure Py-e-PDI film drop-casted from toluene solution (a, b) and chlorobenzene solution (d,
o
e). (a, d) as-casted and (b, e) thermal annealing at 100 C for 1 h, respectively. (c)TEM image and (f)electron
diffraction of thermal annealing sample from chlorobenzene solution.
Morphology of the Self-Assembled Nanostructures.
Now that solution-processed manufacturing technology is employed to fabricate the organic
semiconductor materials into thin-film active layer in organic optoelectronic devices, in all
probability, the intrinsic molecular self-assemblies of the organic materials are involved. The
morphology of self-assembled nanostructure of Py-e-PDI was investigated using scanning electron
microscopy(SEM) and transmission electron microscope(TEM). As shown in Fig. 4, interestingly,
planar Py-e-PDI assembled into highly ordered structure. A close examination of the structures
deposited from dilute toluene and chlorobenzene solution revealed that some rectangular flakes with
different size (from hundreds of nanometer to several micron) parallel to substrate were formed (Fig.
4
a and 4b). Moreover, for the sample prepared from chlorobenzene solution, thermal annealing
results in a slight increasement of order in the morphologies(Fig. 4e). Additional experiments with
TEM confirmed the existence of micron flakes (Fig. 4c). Furthermore, electron diffraction has been
used to determine the molecular packing structure of self-assembled small molecule. As shown in
Fig. 4f, data quickly collected for Py-e-PDI showed patterns consistent with highly crystalline
structures but are not sufficient for further analysis. In particular, it can be expected that a Py-e-PDI
film with highly ordered morphologies will exhibit better charge transporting properties.57

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Table 1. Photovoltaic parameters of the OSCs based on PTB7-Th/Py-e-PDI blends.
D/A
ratio
Solvent
additive
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DOI: 10.1039/C9TC02013F
V
oc/V
J
sc/mAcm-2 FF/%
PCE/%a
1
1
1
1
:1.5
:1.5
:1.5
:1.5
none
0.80
15.8
17.2
13.3
7.78
49.8 5.89±0.21(6.10)
56.2 7.41±0.18(7.59)
50.6 5.12±0.20(5.32)
45.1 2.64±0.08(2.72)
0.5%DIO 0.80
1.0%DIO 0.78
1.5%DIO 0.77
aAverage value from seven devices.
Photovoltaic performance
Py-e-PDI was used in bulk heterojunction solar cells, pairing PTB7-Th as the donor material due to
their complementary absorptions and appropriately matched energy levels. OSCs were fabricated
with the inverted configuration of ITO/ZnO/PTB7-Th:Py-e-PDI /MoO3/Ag and tested under
−2
simulated 100 mW cm AM 1.5G illumination. First, we performed the optimization of photovoltaic
performance of the OSCs of PTB7-Th: Py-e-PDI blends by changing the D/A weight ratios from
1
.5:1 to 1:1.5. The details on the effects of the blend ratios, the thermal annealing and the thickness
of active layers are provided in Table S1. The solar cells with 1:1.5 blend ratio show optimized
−2
power conversion efficiency (PCE) of 6.10% with Jsc of 15.8 mA cm , Voc of 0.90 V, and FF of
9.8%. Similar to most of reported PTB7-Th involved OSCs, thermal annealing has no positive
effect in improving device performance based on the Py-e-PDI acceptor. Nevertheless,
,8-diiodooctane (DIO) as solvent additive was proved effective to further enhance the performance
4
1
of devices. As shown in Table 1, addition of a small amount of DIO (0.5% v/v) substantially
improved the PCE from 6.10% to 7.59%, which is the highest PCE. It is worth noting that the PCE
enhancement comes from the obvious increase of both FF and Jsc despite reduced Voc. However, a
deterioration of the performance is observed when continuing to increase the concentration of DIO.
The current density−voltage (J−V) characteristics of the optimized device are presented in Fig. 5a.

Page 11 of 22
Journal of Materials Chemistry C
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(b)
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DOI: 10.1039/C9TC02013F
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50
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20
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-
12
16
20
0.0
0.2
0.4
0.6
0.8
1.0
300
400
500
600
700
800
900
Voltage (V)
Wavelength (nm)
Fig. 5. (a) J−V characteristics of PTB7-Th/Py-e-PDI based OSCs without/with 0.5% DIO as solvent additive. (b)
EQE of PTB7-Th/Py-e-PDI based OSCs with 0.5% DIO.
The external quantum efficiency (EQE) plot of optimized solar cell device based on Py-e-PDI is
shown in Fig. 5b. The EQE curve covers a broad spectral response from 300 to 800 nm. Apparently,
the range of 330–580 nm is dominantly from the photocurrent contributed by NF acceptor. One can
found that obvious difference exists in the range of 300-400nm when comparing the EQE curve with
the absorption of PTB7-Th/Py-e-PDI blend film (Fig. 3c), indicating a less efficient incident
photon-to-current conversion efficiency in this range.
Space-charge-limited current (SCLC) mobilities of the pristine acceptor and blend films were
measured. The structure of the hole-only devices is ITO/PEDOT:PSS/active layer/MoO3/Al, and the
structure of the electron-only devices is ITO/PFN/active layer/PFN/Al. The pure Py-e-PDI film
−
4
2
−1 −1
exhibited relatively high electron mobility (μ ) of (3.77 ± 0.8) × 10 cm V s , suggesting ordered
e
molecular packing in pristine films. However, normally, when blending with donor polymers, the
electron mobility decreased largely due to reduced ordered structure. The PTB7-Th:Py-e-PDI blend
with 0.5%DIO showed a hole mobility(μ
) of (1.70 ± 0.4) ×10 cm V s−1 and an electron
−
4
2
−1
h
−
5
2
−1 −1
mobility of (5.97 ± 0.7) ×10 cm V s . Clearly, quite balanced hole and electron mobilities
(μ
h
e
/μ = 2.8± 0.3) is observed for this optimized blend. SCLC J-V plots is provided in Fig. S7.

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DOI: 10.1039/C9TC02013F
Fig. 6. (a) 2D GIWAXS scattering patterns of as-cast pure Py-e-PDI and PTB7-Th films and the corresponding
scattering profiles in the in-plane (dashes lines) and out-of-plane (solid lines) directions. (b) 2D GISAXS scattering
patterns of PTB7-Th/Py-e-PDI blends films as cast (left) and with 0.5% DIO (right) and the corresponding
scattering profiles in the in-plane direction.
Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements were carried out to reveal
58
the morphology structure of as-cast pure Py-e-PDI and PTB7-Th films . As shown in Fig. 6(a), the
-1
lamellar distance of Py-e-PDI is 22.0 Å (q ~ 0.285 Å ), while the face to face stacking distance is
-1
4
.91 Å (q ~ 1.28 Å ) with a random orientation. PTB7-Th has a face-on orientation with lamellar
-1
-1
distance of 24.2 Å (q ~ 0.260 Å ) and a π-π stacking distance of 3.88 Å (q ~ 1.62 Å ).
Grazing-incidence small-angle X-ray scattering (GISAXS) measurements were employed to
59
investigate the nanoscale phase separation information of these blend thin films . The
two-dimensional GISAXS patterns and the corresponding in-plane intensity profiles were presented
in Fig. 6(b). We adopted a fractal-like network model to account for the scattering contribution from
-1
-4
the acceptor domains. The uplift in the small q (<0.006 Å ) regions were fitted with q dependence
to account for scattering resulted either from the surface roughness of the film or from the tail of a
6
0
large amorphous regime . The acceptor domain sizes (2Rg) of as-cast PTB7-Th/Py-e-PDI film are
estimated to be 42.2 nm. When 0.5% DIO was added, the domain size decreased substantially to
2
0.5 nm. The smaller pure phase domain size would benefit to the charge separation thus increase
the Jsc and FF. The results are consistent with the device performance.

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Conclusion.
In this study, we introduced pyrene unit as core to generate moderately planar PDI-
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NF acceptors. DFT calculations revealed that the nonfused Py-e-PDI displayed reduced
intramolecular twisting owing to acetylene linker and thus showed obvious crystallinity. GISAXS
characterization showed that the acceptor domain sizes (2Rg) of as-cast PTB7-Th/Py-e-PDI film
were estimated to be 42.2 nm. When 0.5% DIO was added, the domain size decreased substantially
to 20.5 nm. The smaller pure phase domain size contributed to the effective charge separation thus
increased the Jsc and FF. The optimized solar cells based on PTB7-Th/Py-e-PDI (1:1.5, 0.5%DIO)
have resulted in PCE up to 7.59%, which is among highest reported efficiencies for nonfused PDI
based acceptors. Most importantly, this result demonstrates that using PAH as core combined with
acetylene spacer to construct multiple PDI derivatives is an effective strategy for designing high
performance non-fullerene OSC acceptors.
Experimental
Materials.
All reagents were obtained from commercial suppliers and used as received. Toluene was dried over
sodium/ benzophenone and freshly distilled prior to use. Triethylamine was dried over solid KOH.
Measurements and Instruments.
1
NMR spectra were recorded on a Bruker DPX 400 ( H NMR 400, 500 MHz) spectrometer. The mass
spectra were obtained using an Ion-Spec 4.7 T HiRes MALDI instrument. UV absorption spectra
were obtained using a Scinco S-3150 UV/vis spectrophotometer. TGA measurements were
performed on a Netzsch TG209 apparatus. The electrochemical cyclic voltammogram was obtained
using a CHI 660C electrochemical workstation with Pt disk, Pt plate, and standard calomel electrode
(SCE) as working electrode, counter electrode, and reference electrode, respectively, in a 0.1 mol/L
tetrabutylammonium hexafluorophosphate (Bu NPF ) CH Cl solution or CH CN solution. The
4
6
2
2
3

Journal of Materials Chemistry C
Page 14 of 22
surface morphologies of pure Py-e-PDI films were examined by scanning electron microscopy
View Article Online
(
Zeiss ultra plus and HITACHI S-4800) with an energy dispersive X-ray spectroscopyDO
d
I
e
: 1
t
0
e
.
c
10
t
3
o
9
r
/
.
C
T
9T
E
C02013F
M
was performed with a JEOL JEM-2100 microscope operating at 200 kV. The selected-area electron
diffraction (SAED) pattern was collected using the same instrument. Samples for TEM were
prepared by dropping on the amorphous carbon film supported on a copper grid.
DFT calculation. Geometry optimizations were carried out by the density functional theory (DFT)
method at the B3LYP/6-31G level. All the calculations were performed using Gaussian 09 program.
Device Fabrication and Characterization.
Organic solar cells were fabricated on glass substrates commercially pre-coated with a layer of
indium tin oxide (ITO) with the inverted structure of ITO/ZnO/PTB7-Th:Py-e-PDI/MoO3/Ag. Prior
to fabrication, the substrates were cleaned using detergent, deionized water, acetone and isopropanol
consecutively every 15 min and then treated in an ultraviolet ozone generator for 15 min. A thin
layer of sol–gel ZnO (≈ 40 nm) was spin coated onto precleaned ITO-coated glass substrates and
o
then annealed at 180 C for 15 min. The PTB7-Th/Py-e-PDI active layers were deposited from 20
-1
mg mL solutions without or with DIO as the additive in chlorobenzene by spin-coating at 3000 rpm,
resulting in an active layer thickness of about 100 nm. MoO
3
(10 nm) and Ag (100 nm) were
2
evaporated through a shadow mask, giving an active area of 5.2 mm per device.
The current–voltage (J–V) curves were measured with Keithley 2400 measurement source units at
room temperature in air. The photocurrent was measured under a calibrated solar simulator (Abet
-2
3
00 W) at 100 mW cm , and the light intensity was calibrated with a standard silicon photovoltaic
reference cell. External quantum efficiency (EQE) spectrum was measured with Stanford lock-in
amplifier 8300 unit.
The hole and electron mobilities of Py-e-PDI and blends were measured using the
space-charge-limited current (SCLC) method. Hole-only devices were fabricated in a structure of

Page 15 of 22
Journal of Materials Chemistry C
ITO/PEDOT:PSS/pure Py-e-PDI or PTB7-Th/Py-e-PDI/MoO
3
(10 nm)/Al (100 nm). Electron-only
View Article Online
devices were fabricated in a structure of ITO/PFN/ PTB7-Th:Py-e-PDI /PFN/ADOl.I: 1
T
0.
h
10
e
39/
d
C9
e
T
v
C
i
02013F
c
e
characteristics were extracted by modeling the dark current under forward bias using the SCLC
expression described by the Mott-Gurney law.
Morphology Characterization.
GIWAXS and GISAXS measurements were carried out with a Xeuss 2.0 SAXS/WAXS laboratory
beamline using a Cu X-ray source (8.05 keV, 1.54 Å) and a Pilatus3R 300K detector. The incidence
angle is 0.2o.
Synthetic procedures.
Compound 2. 1,3,6,8-Tetrabromopyrene (0.25 g, 0.48 mmol), bis(triphenylphosphine)palladium(II)
dichloride (68 mg, 0.10 mmol), copper(I) iodide (36 mg, 0.19 mmol) and triphenylphosphine (50 mg,
0
.19 mmol) were placed in a two-neck round-bottom flask under argon, and then anhydrous
triethylamine (10 mL) and toluene (3 mL) were added via a syringe. While stirring, the reaction
mixture was heated to 60 ◦C and trimethylsilylethyne (0.28 g, 2.88 mmol) injected. The resulted
mixture was brought to reflux overnight and then cooled down to room temperature. The reaction
was quenched with water, and the layers were separated. The aqueous phase was extracted with
CH
2
Cl
2
three times, the combined organic phase was washed with brine, and then dried over
SO . After removal of the solvent under reduced pressure, the crude product was
anhydrous Na
2
4
purified by column chromatography (silica gel, hexane) to afford compound 2 an orange solid
1
2
28mg (yield: 81%). H NMR(400 MHz, CDCl
3
) δ 8.61 (m, 4 H), 8.32 (s, 2H), 0.38 (s, 36 H).
CO
3.6 mmol) was added and the reaction mixture stirred overnight and then poured into water (500
mL) and filtered. The filter was washed with water until the filtrate was neutral to afford compound
as a slightly brown solid 51mg. compound 3 is insoluble in common solvents and was used next
Compound 3. Compound 2 (1 g, 1.7 mmol) was suspended in methanol (100 mL). K
2
3
(1.9 g,
1
3

Journal of Materials Chemistry C
Page 16 of 22
reaction without NMR characterization.
Py-e-PDI. To a 50 mL two necked round-bottom flask were added compound 3DO(2I:
mmol), PDI-Br(416mg, 0.5 mmol), anhydrous toluene (12 mL) and triethylamine (6 mL), and then
the mixture was deoxygenated with argon for 30 min before Pd(PPh (11.55 mg, 0.01mmol) and
View Article Online
9
10
.
.
8
103
m
9/C
g
9
,
TC
0
02013F
.
1
)
3 4
CuI (1.9 mg, 0.01mmol) were added. The resulted mixture was stirred at 80 °C for 72 h under argon.
After cooled to room temperature, the reaction was quenched with water, and the layers were
separated. The aqueous phase was extracted with CH
2
Cl
2
three times, the combined organic phase
SO . After removal of the solvent under
was washed with brine, and then dried over anhydrous Na
2
4
reduced pressure, the crude product was purified by column chromatography (silica gel,
1
CH
2
Cl
-dichlorobenzene-d
2H), 5.43-5.73 (s, 4H),4.87-5.33 (m, 4H),0.55-2.77(m, 208H). MALDI-TOF-MS: m/z calculated
16: 3307.89 m/z found 3307.59. HRMS(MALD): Calcd for C224
307.8995; Found: 3307.8960; Anal. Calcd for C224 16: C, 81.27; H, 7.61; N, 3.38. Found: C,
2
/hexane) to afford Py-e-PDI as a purple solid 155mg (yield: 48%). H NMR (400 MHz, 1,
2
1
4
) δ 10.41-11.26 (m, 4 H), 9.14-9.82 (m, 10H), 8.61-9.09 (m, 8H), 8.09-8.50 (m,
for C224
H
250
N
8
O
H
250
N
8
16
O :
3
8
H
250
8
N O
-1
0.76; H, 8.01;N, 3.36. Raman spectra: 2192 cm (C≡C).
1
Supporting Information. HNMR spectra, Raman spectra, TGA curves, contact angle, SCLC J-V
plots, 2D GIWAXS scattering patterns and additional photovoltaic parameters.
*
Corresponding Author
wan_junhua@hznu.edu.cn, quzr@hznu.edu.cn, hzchen@zju.edu.cn
Author Contributions
#
These authors contributed equally
Conflicts of interest.

Page 17 of 22
Journal of Materials Chemistry C
There are no conflicts to declare
Acknowledgment
View Article Online
DOI: 10.1039/C9TC02013F
This work was supported by the National Natural Science Foundation of China (No. 21372057) and
by Zhejiang Provincial Natural Science Foundation of China (LY18B020014). X. Lu acknowledges
the financial support from CUHK direct grant.
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View Article Online
O
R
O
O
DOI: 10.1039/C9TC02013F
N
R
N
O
O
R
N
O
O
N
Enlarge distance
Reduce crowding
R
O
Endow molecule planarity
O
R
O
N
R
N
O
O
O
O
N
R
N
O
R
O
PCE = 7.59%
PTB7-Th
The pyrene core and significantly reduced intramolecular steric hindrance endows
nonfused PDI-tetramer with moderate planarity and good self-assembly property.