Functionalizing tetraphenylpyrazine with perylene diimides (PDIs) as high-performance nonfullerene acceptors

Article abstract of DOI:10.1039/c9tc05643b

Perylene diimide (PDI)-based small molecular acceptors with a three-dimensional structure are thought to be essential for efficient photocurrent generation and high power conversion efficiencies (PCEs). Herein, a couple of new perylene diimide acceptors (

Full text of DOI:10.1039/c9tc05643b

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Functionalizing tetraphenylpyrazine with perylene
diimides (PDIs) as high-performance nonfullerene
acceptors†
Cite this: J. Mater. Chem. C, 2019,
7, 14563
Gang Li,‡*a Shufan Yang,‡a Tao Liu,*ab Jiewei Li,c Wenbin Yang,a Zhenghui Luo,b
Cenqi Yan,a Dandan Li,a Xinyu Wang,a Guanwei Cui,a Tao Yang,d Liang Xu,e
e
a
Shun-Ze Zhan,
Lijun Huo, *f He Yan *b and Bo Tang
*
Perylene diimide (PDI)-based small molecular acceptors with a three-dimensional structure are thought to be
essential for efficient photocurrent generation and high power conversion efficiencies (PCEs). Herein, a couple
of new perylene diimide acceptors (PPDI-O and PPDI-Se) have been designed and successfully synthesized
using pyrazine as the core-flanking pyran and selenophene-fused PDIs, respectively. Compared to PPDI-O,
PPDI-Se exhibits a blue-shifted absorption in the 400–600 nm range, a comparable LUMO level, and a more
distorted molecular geometry. The PPDI-Se-based organic solar cell device with PDBT-T1 as the donor
achieved the highest PCE of 7.47% and a high open-circuit voltage (Voc) of up to 1.05 V. The high photovoltaic
performance of PPDI-Se-based devices can be attributed to its high LUMO energy level, complementary
absorption spectra with donor materials, favorable morphology and balanced carrier transport. The results
demonstrate the potential of this type of fullerene-free acceptor for high efficiency organic solar cells.
Received 15th October 2019,
Accepted 25th October 2019
DOI: 10.1039/c9tc05643b
rsc.li/materials-c
community.1–5 With regard to conventional acceptor molecules,
fullerene derivatives, such as [6,6]-phenyl-C61-butyric acid methyl
Introduction
In the past three decades, organic solar cells (OSCs), composed ester (PC61BM) and [6,6]-phenyl-C71-butyric acid methyl ester
of bulk heterojunction (BHJ) structure with p-type polymer (PC71BM) have benefited from their high electron affinity, isotropic
donor and n-type small molecular acceptor, have been proven electron transport, and large electron mobility.6–11 Therefore,
to be promising candidates for next-generation photovoltaic fullerene-based OSCs have moved into the fast lane, and the power
technology and have aroused great interest among the scientific conversion efficiency (PCE) of single-junction OSCs have exceeded
10%.12–14 However, the inherent defects of the fullerene derivatives
restrict the further improvement of device performances assigned to
a College of Chemistry, Chemical Engineering and Materials Science, Key Laboratory
limited optical cross-section as well as poor environmental and
of Molecular and Nano Probes, Ministry of Education, Collaborative Innovation
phase stability issues.15–18 Therefore, non-fullerene small molecule
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,
P. R. China. E-mail: ligang@sdnu.edu.cn, tangb@sdnu.edu.cn
b Department of Chemistry and Energy Institute, The Hong Kong University of
Science and Technology, Clear Water Bay, Hong Kong.
acceptors (SMAs) emerged as great strides to OSC development.19,20
Except for the merits of low-cost, light weight, and mechanism
flexibility, SMAs also show substantially strong absorption in the
visible region, relatively simple synthesis and purification, easy
modulation of their energy levels through developing versatile
molecular structures, and morphological compatibility with different
types of donor materials.21,22 So far, a number of SMAs have been
developed and applied in OSCs that have achieved PCEs exceeding
13%,23–36 which outperformed those of PC61BM/PC71BM-based
counterparts. To date, highly efficient OSCs almost exclusively are
focused on indacenodithiophene (IDT) or indacenodithienothio-
phene (IDTT) donor building blocks and 1,1-dicyanomethylene-3-
indanone (IC) acceptor moiety.37–40 However, the superiority of the
non-fullerene acceptors consisting of other structures is quite rare.
Thus, continued progress will require the design, synthesis, and
testing of new motifs for electron acceptors.41
E-mail: Liutaozhx@ust.hk;hyan@ust.hk
c Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials
(IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials
(SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing,
211816, P. R. China
d Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess
Technology, Chinese Academy of Sciences, P. R. China
e Key Laboratory for Preparation and Application of Ordered Structural Materials of
Guangdong Province, Shantou University, Shantou 515063, P. R. China
f School of Chemistry, Beihang University, Beijing 100191, P. R. China.
E-mail: huolijun@buaa.edu.cn
† Electronic supplementary information (ESI) available: Details of synthesis and
characterization. See DOI: 10.1039/c9tc05643b
‡ These authors contributed equally to the work.
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Perylene diimide (PDI) derivatives, which are classic industrial properties and structure–property relationships remains the key
dyes, have been widely used to construct high-performance SMAs issue that the scientists from the fields of chemistry and material
owing to high electron affinity and mobility, intense absorption, science need to focus on.
and excellent thermal and photochemical stability.42–45 Further-
In this study, to take advantage of the chalcogen-decorated PDIs
more, PDIs can be functionalized in various positions, for example and investigate the impact of different chalcogen-fused PDIs
imide, bay and ortho positions, to construct versatile PDI acceptors on the photovoltaic properties, a couple of low-cost SMAs
derivatives.46–49 Hence, incremental endeavors have been devoted (PPDI-O and PPDI-Se), which employed tetraphenylpyrazine as the
to developing high-performance PDI-based SMAs. However, their central 3D conformation core and were armed by four pyran and
flat configurations and p-conjugated polyaromatic core are inclined selenophene fused PDI motifs, were designed and successfully
to form microscale or submicroscale aggregates, which hamper synthesized (Scheme 1). The influence of the molecular geometry
the exciton diffusion, charge transport, and collection to the on the OSC performance was investigated by studying the optical,
electrodes.50 Hence, the twisted three-dimensional (3D) struc- photophysical, and morphological properties in the BHJ blended
tures were adopted to suppress aggregation trends. However, the films. As a result, the OSCs based on PPDI-Se delivered a maximum
twisted structures induced by steric congestion among the PDI PCE of 7.47% with an open-circuit voltage (Voc) of 1.05 V, a short-
units will reduce their charge transport abilities and impede the circuit current (Jsc) of 10.7 mA cmÀ2, and a fill factor (FF) of 66.3%,
further improvement in the OSC performance.51,52 Hence, which were superior to those of the PPDI-O based device (PCE =
chalcogen-fused PDIs have been actively investigated recently 4.51%). These remarkable results demonstrated that PPDI-Se is an
for overcoming the problems mentioned above. For example, excellent acceptor for achieving favorable efficiency.
Wang et al. developed S/Se annulated PDI dimers (s-diPBI-S and
s-diPBI-Se) as splendid acceptors. Both acceptors exhibited quite
twisted configurations due to the large steric repulsion, and high
Results and discussion
Material synthesis and characterization
PCEs of 7.16% and 8.4% were achieved by using PDBT-T as a
donor.53,54 Yan et al. used the ring-fusion strategy to obtain a PDI
tetramer named FTTB-PDI4 with a ‘‘double-decker’’ molecular The syntheses of PPDI-O and PPDI-Se are displayed in Scheme 1.
shape, which demonstrated an outstanding PCE of 10.58% when First, compound PDI-NO2 was converted to PDI-Se in N-methyl-
combined with the polymer P3TEA.55 Accordingly, these promising pyrrolidone with selenium powder at 190 1C. Subsequently, PDI-Se-
properties with 3D architecture and chalcogen-decorated PDIs have Br was synthesized by brominating the compound PDI-Se under
proved to be effective in designing highly efficient SMAs. Despite dichloromethane at room temperature.54 Then, PPDI-Se was
the great progress that has been achieved in the conjugated obtained by the Suzuki-coupling of borylated tetraphenylpyrazine
multidimensional PDIs, it has not yet reached the stage of and PDI-Se-Br. The synthetic method of PPDI-O was similar to that
commercialization. Thus, the development of PDIs based high- of PPDI-Se, according to our reported method.56 The as-synthesized
efficiency OSCs and further understanding of their optoelectronic new molecules were fully characterized by 1H NMR, 13C NMR, and
Scheme 1 The synthesis routes of PPDI-O and PPDI-Se.
14564 | J. Mater. Chem. C, 2019, 7, 14563--14570
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Fig. 1 (a) Absorption spectra of PPDI-O and PPDI-Se in chloroform solutions. (b) Absorption spectra of PBDB-T1, PPDI-O and PPDI-Se in thin films state.
(c) Energy level diagrams of the involved materials in organic solar cells. (d) The molecular structure of donor PDBT-T1.
MALDI-TOF mass spectrometry. Furthermore, the two molecules, can form more obvious complementary absorption with donor of
i.e., PPDI-O and PPDI-Se were found to be highly soluble in most PDBT-T1 (Fig. 1d), which are beneficial in enhancing light harvest-
of the commonly used organic solvents, for example, dichloro- ing, so as to increase Jsc. The optical edges of the thin film are 1.96
methane, chloroform, chlorobenzene, and o-dichlorobenzene. and 2.16 eV for PPDI-O and PPDI-Se, respectively, which were
Thermogravimetric analysis measurements (Fig. S15, ESI†) demon- consistent with the theoretically calculated results (Table S1, ESI†).
strated that both compounds exhibited good thermal stability, with
Cyclic voltammetry (CV) was performed to investigate the
a decomposition temperature (Td, 5% weight loss) exceeding 300 1C electrochemical properties of PPDI-O and PPDI-Se (Fig. S1,
under nitrogen atmosphere.
ESI†), and the data are summarized in Table 1. The lowest
unoccupied molecular orbital (LUMO) energy levels of PPDI-O
and PPDI-Se were estimated to be À3.80 and À3.74 eV, respec-
tively, according to the equation ELUMO = Àe(Ered + 4.80) (eV),55
assuming that Fc/Fc+ was À4.80 eV. The energy level of HOMO
can be calculated from the following equation: EHOMO = À
(ELUMO + Eg) eV, and found to be À5.76 and À5.90 eV for PPDI-O and
PPDI-Se, respectively. As expected, both acceptors exhibited relatively
upshifted LUMO energy levels, which were beneficial for obtaining
higher Voc in the corresponding OSC devices.
Optical and electrochemical properties
The normalized UV-vis absorption spectra of PPDI-O and PPDI-Se in
chloroform solutions and in the form of thin films were measured
and presented in Fig. 1a and b, with the spectral data being
summarized in Table 1. The solution spectrum of PPDI-O exhibited
strong absorption from 450–650 nm, with an absorption maximum
(lmax) at 583 nm, while the lmax of PPDI-Se blue-shifted by 73 nm
compared with that of its PPDI-O counterpart. In the thin-film state,
both PPDI-O and PPDI-Se spectra exhibited red shift and broader
absorption than their corresponding solution spectra, with the
Theoretical analysis
maximum absorption peak at 586 nm for PPDI-O and 515 nm for The geometries of PPDI-O and PPDI-Se were obtained by
PPDI-Se. The blue-shifted absorption of PPDI-Se relative to PPDI-O, employing the density functional theory (DFT) method at the
Table 1 Basic Properties of PPDI-O and PPDI-Se
emax (MÀ1 cmÀ1
)
lonset (nm)
lmax (nm)
lonset (nm)
Eogpt c (eV)
HOMO (eV)
LUMOd (eV)
a
a
a
b
b
Acceptors
lmax (nm)
PPDI-O
PPDI-Se
583
510
1.36 Â 105
620
545
586
516
630
572
1.96
2.16
À5.76
À5.90
À3.80
À3.74
1.72 Â 105
In a dichloromethane solution. In a neat film. Calculated from empirical the formula: Eogpt = 1240/lonset
.
Cyclic voltammetry(CV) method by
a
b
c
d
measuring in dichloromethane.
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Table 2 Performance of the optimized OSCs devices based on PDBT-T1:PPDI-O and PDBT-T1:PPDI-Se (1 : 1, w/w)
Jsc (mA cmÀ2
a
)
Jsc (mA cmÀ2
b
)
FF (%)
PCEa (%)
a
Active layer
Additive
Voc (V)
PDBT-T1:PPDI-O
PDBT-T1:PPDI-Se
0.25% DIO
0.25% DIO
1.03 (1.03 Æ 0.004)
1.05 (1.05 Æ 0.006)
8.51 (8.45 Æ 0.197)
10.7 (10.5 Æ 0.202)
8.14
10.5
51.1 (49 Æ 0.015)
66.3 (65 Æ 0.016)
4.51 (4.29 Æ 0.180)
7.47 (7.21 Æ 0.217)
a
b
Values are for the highest-PCE device, with the average values obtained from 20 devices listed in parentheses. Jsc value from the integration of
the EQE spectra.
B3LYP/6-31G(d,p) level in the Gaussian 09 software,57 where the We selected DCB as a processing solvent and 100 1C as the annealing
long alkyl chain (–C11H23) was simplified to isopropyl groups. temperature. The total concentration of donor and acceptor was
The original configurations (input-configurations in Gaussian) selected to be 20 mg mLÀ1, with the donor : acceptor weight ratio of
of PPDI-O and PPDI-Se were similar. Based on the optimized 1 : 1. The optimized device parameters are summarized in Table 2,
geometries, the frontier molecular orbitals and the corresponding with the corresponding J–V curves shown in Fig. 2a. The optimized
energy levels were calculated (Fig. S2, ESI†). The HOMO and LUMO OSC device based on PDBT-T1:PPDI-Se exhibited a high PCE of
of PPDI-O are delocalized on two pyran-fused PDI subgroups, 7.48% with a high Voc of 1.05 V, Jsc of 10.7 mA cmÀ2, and FF of
respectively. On the other hand, the HOMO and LUMO of 66.3%, while PDBT-T1:PPDI-O based devices achieved an inferior
PPDI-Se are localized on one selenophene fused PDI sub-group. PCE of 4.51%, with similar Voc of 1.04 V, lower Jsc of 8.51 mA cmÀ2
,
The different wave function distribution between PPDI-O and PPDI- and relatively poor FF of 51.1%. Compared with PPDI-O, the
Se are mainly due to the degenerate orbitals of the same four substantial superiority of PPDI-Se-based OSC performances can be
groups. In addition, the dihedral angle between the PDI unit and attributed to the preferable Jsc and FF.
the adjacent benzene ring for PPDI-O (Fig. S3, ESI†) was calculated
The external quantum efficiency (EQE) spectra of the blend
to be 61.391, 61.411, 62.611, and 62.651. On the other hand, in the films were acquired from two different NFA-based devices and
case of PPDI-Se, the corresponding dihedral angle (Fig. S4, ESI†) displayed in Fig. 2b. The variation in the calculated Jsc by the
was found to be 63.511, 72.721, 73.991, and 74.501. The more twisted integration of the EQE spectra was found to be consistent with the
geometry of PPDI-Se was expected to effectively prevent the four PDI variation in the measured Jsc (Table 2). Significant enhancement of
units from forming the large aggregate domains in the solid-state, EQE responses between 350 and 700 nm for the PDBT-T1:PPDI-Se-
which is beneficial for the PDI blend film applied in the OSCs.5 The based device can be attributed to the much more complementary
calculated HOMOs and LUMOs of PPDI-O and PPDI-Se were found absorption from PPDI-Se and PDBT-T1. Overall, the greater optical
to be À5.87 and À3.55 eV and À6.13 and À3.59 eV (Table S1, ESI†), absorption range of the PPDI-Se blend relative to PPDI-O blends
respectively, which are in accordance with the changing trend of was unequivocally confirmed from the greater Jsc value (10.7 versus
the energy levels measured by the CV method.
8.51 mA cmÀ2).
Photovoltaic properties
Morphology characterization
The OPV devices of these two new electron acceptors were fabricated The morphology of the BHJ films is known to be closely correlated to
and evaluated with a conventional device structure of ITO (indium Jsc, mobility, and PCE. Thus, the atomic force microscopy (AFM)
tin oxide)/PEDOT:PSS(poly(3,4-ethylenedioxythiophene):poly (styrene amplitude and phase images in the tapping mode were obtained to
sulfonate))/PDBT-T1:acceptor/ZrAcAc (zirconium acetylacetonate)/Al. characterize the morphology of PDBT-T1:PPDI-O and PDBT-T1:PPDI-
The detailed device fabrication processes are described in the sup- Se active layers (Fig. S5, ESI†). The optimized PDBT-T1:PPDI-O
porting information. A medium-bandgap polymer PDBT-T1 was blend film showed a smooth surface, with a relatively small root-
chosen as the polymer donor due to its complementary absorption mean-square (RMS) roughness of 1.01 nm, but clear phase
and matched energy levels with PPDI-O and PPDI-Se (Fig. 1c). separation was not observed (Fig. S4a and c, ESI†). In contrast,
Fig. 2 (a) Characteristic J–V curves of the PDBT-T1:PPDI-O and PDBT-T1:PPDI-Se based solar cells under AM 1.5G irradiation (100 mW cmÀ2). (b) EQE
curves of the corresponding devices.
14566 | J. Mater. Chem. C, 2019, 7, 14563--14570
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Fig. 3 Dark current density–voltage characteristics for (a) hole-only and (b) electron-only devices with optimized PDBT-T1:PPDI-O and PDBT-T1:PPDI-
Se BHJ films. (c) Jph versus Veff curves. (d) Light intensity dependence of Jsc
.
the PDBT-T1:PPDI-Se-based blend film showed a slightly higher devices, the photocurrent density (Jph) versus the effective
RMS of 1.07 nm and better defined fibril texture (Fig. S4b and d, applied voltage (Veff) curves were determined (Fig. 3c), where
ESI†) with suitable phase separation, which are beneficial for Jph = JL À JD ( JL and JD are the current density under illumina-
exciton dissociation and charge transport, and thus lead to tion and dark, respectively) and Veff = V0 À Va, (V0 is the voltage
better photovoltaic performance. The morphologies of the at Jph = 0 and Va is the measured voltage under different
PDBT-T1:PPDI-O and PDBT-T1:PPDI-Se blend films were also current density). PDBT-T1:PPDI-Se demonstrated a higher Jph
characterized by transmission electron microscopy (TEM) to of 10.734 mA cmÀ2 than the PDBT-T1:PPDI-O-based device,
better understand the BHJ morphologies in the devices. As which exhibited Jph of 8.51 mA cmÀ2 at Veff Z 2.0 V. This was
shown in Fig. S6 (ESI†), the TEM images showed similar mainly caused by the much higher light absorbing combination
nanofibrillar structures of both the blend systems.
of PDBT-T1:PPDI-Se. The charge dissociation and collection
probability (P) could be assessed by the formula P = Jph/Jsat
Under the short-circuit condition, the probabilities of exciton
.
Active layer charge transport
To investigate the charge-transporting behavior and explore the dissociation for the PDBT-T1:PPDI-O-bases and PDBT-T1:PPDI-
reasons for the different FF of the studied devices, the hole (mh) Se-based devices were estimated to be 81.7% and 89.5%, respec-
and electron mobilities (me) of the blend films were evaluated tively. Moreover, the probabilities of charge collection at the
through the space charge limited current (SCLC) method (Fig. 3a maximal power output condition were determined to be 50.7%
and b). The electron mobilities of both the acceptor neat films and 74.2% for PDBT-T1:PPDI-O-based and PDBT-T1:PPDI-Se-based
were found to be 5.32 Â 10À4 and 6.57 Â 10À4 cm2 VÀ1 sÀ1
,
OSCs, respectively. Hence, we can infer that PDBT-T1:PPDI-Se
respectively. When blended with the donor of PDBT-T1, the showed superior charge dissociation and collection probability,
PDBT-T1:PPDI-Se-based blend film exhibited relatively higher which is beneficial to the resulting Jsc and FF.
and more balanced hole and electron mobilities (mh = 6.51 Â
10À4 cm2 VÀ1 sÀ1, me = 3.40 Â 10À4 cm2 VÀ1 sÀ1, and mh/me = 1.91)
Charge-recombination mechanism
compared with the PDBT-T1:PPDI-O counterpart (mh = 6.24 Â The carrier recombination kinetics of PPDI-O-based and PPDI-
10À4 cm2 VÀ1 sÀ1, me = 2.78 Â 10À4 cm2 VÀ1 sÀ1, and mh/me = 2.24), Se-based devices were also investigated through J–V curves
which results in efficient charge transport and corresponds to under different light intensities (Plight), with the curves being
higher FF for the PDBT-T1:PPDI-Se-based device.58
shown in Fig. 3d. The power-law exponents (a) for the two
acceptor-based devices were extracted according to the formula
Jsc p PSlight, where S approaching 1 implies that the bimolecular
Exciton dissociation and charge extraction
In order to further study the exciton dissociation, charge recombi- recombination is negligible. The S values of the two devices were
nation and charge extraction properties of the above-mentioned found to be 0.96 (PDBT-T1:PPDI-O) and 0.98 (PDBT-T1:PPDI-Se),
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thus suggesting the less bimolecular recombination in the PPDI- (9.68 g, 70 mmol), Aliquat 336 (4 drops), and dry toluene/H2O
Se based devices. (70 mL/35 mL) and then, the mixture was degassed with nitrogen for
Fig. S7 (ESI†) reveals the dependence of Voc on various light 15 min. Subsequently, the reaction mixture was heated at 120 1C for
intensities (Plight), giving the relationship Voc p (nkT/q)ln(Plight), 48 h. After cooling to room temperature, the reaction mixture was
where n = 1 suggests only bimolecular charge recombination, but extracted by CH2Cl2. The crude product was purified by silicon
n 4 1 suggests defect-mediated recombination. The n values for chromatography (petroleum ether/CH2Cl2) to get the pure product as
PDBT-T1:PPDI-O and PDBT-T1:PPDI-Se were fitted to be 1.26 and a red solid (380 mg, yield 45%). 1H NMR (400 MHz, CDCl3): d 9.39
1.74, respectively. This indicates that the bimolecular recombina- (d, 2H), 8.85 (s, 1H), 8.50 (s, 1H), 8.34 (d, 3H), 7.81 (d, 2H), 5.36–5.06
tion dominates in the device based on the PDBT-T1:PPDI-O-based (m, 2H) 2.26–2.02 (m, 4H), 1.86–1.71 (m, 4H), 1.26–1.16 (m, 24H),
device, whereas the defect-mediated charge recombination dom- 0.80–0.72 (m, 12H). 13C NMR (100 MHz, CDCl3): d 165.24, 164.89,
inates in the PDBT-T1:PPDI-Se-based device.
164.07, 163.83, 147.66, 143.20, 141.37, 140.72, 140.05, 138.83, 134.78,
134.62, 134.05, 132.01, 131.20, 129.39, 128.87, 128.56, 126.52, 126.19,
126.06, 125.83,122.51, 54.99, 54.73, 33.71, 32.38, 32.22, 31.94, 31.74,
31.65, 30.17, 29.71, 29.37, 26.63, 26.52, 23.19, 22.70, 22.53, 22.48,
14.12, 14.01, 13.96. HRMS: C212H119N10O16Se4 (M+ À H): calcd –
3480.3445; found – 3480.3443.
Conclusions
In summary, two new small molecule acceptors, PPDI-O and
PPDI-S, consisting of a tetraphenylpyrazine core and peripheral
chalcogen-decorated perylene diimides, were successfully
synthesized and characterized. Compared with the pyran-fused
PDI (PPDI-O), the incorporation of the Se atom (PPDI-Se) exhibited
an obviously blue-shifted optical absorption, improved and more
balanced charge transport properties, and more favorable blend film
morphology. BHJ OSCs based on PPDI-Se and PDBT-T1 achieved
a high PCE of 7.47% with improved Voc of 1.05 V, a well-
maintained Jsc of 10.7 mA cmÀ2 despite its blue-shifted absorp-
tion, and FF of 66.3%. This result successfully demonstrates that
building 3D structures with an extended effective p-conjugation
could be a promising methodology to aspire highly efficient PDI-
based acceptors.
Fabrication and characterization of photovoltaic cells
Solar cells were fabricated in a conventional device configuration of
ITO/PEDOT: PSS/active layer/ZrAcAc/Al. The ITO substrates were first
scrubbed by detergent and then sonicated with deionized water,
acetone, and isopropanol, in sequence, and dried overnight in an
oven. The glass substrates were then treated by UV–Ozone for 30 min
before use. A PEDOT:PSS (Heraeus Clevios P VP A 4083) layer was
spin-cast onto the ITO substrates at 4000 rpm for 40 s, and then
dried at 150 1C for 15 min in air. The donor : acceptor blends with
1 : 1 ratio were dissolved in dichlorobenzene (the concentration of
blend solutions was 20 mg mLÀ1 for all blend films) and stirred
overnight in a nitrogen-filled glove box. The blend solution was then
spin-cast at 1600 rpm for 40 s on the top of PEDOT:PSS layer,
followed by annealing at 100 1C for 5 min to remove the residual
solvent. A thin ZrAcAc layer (10 nm) and Al layer (100 nm) were
sequentially evaporated through a shadow mask under the vacuum
of 5 Â 10À5 Pa. The area of each device was 5.90 mm2, as defined by
a shadow mask. The optimal blend thickness was about 95 nm,
measured on a Bruker Dektak XT stylus profilometer. Current
density–voltage (J–V) curves were measured in a Keithley 2400 Source
Measure Unit. Photocurrent was measured in an Air Mass 1.5 Global
(AM 1.5 G) solar simulator (Class AAA solar simulator, Model
94063A, Oriel) with an irradiation intensity of 100 mW cmÀ2, which
was measured by a standard Si diode (with KG5 filter, purchased
from PV Measurement to bring the spectral mismatch to unity).
EQEs were measured using an Enlitech QE-S EQE system equipped
with a standard Si diode. Monochromatic light was generated from a
Newport 300 W lamp source.
Experimental section
Synthesis of PPDI-O
A Schlenk tube was initially charged with TPP-Bpin4 (216 mg,
0.243 mmol, 1 eq.), compound PDI-O-Br (1.12 g, 1.338 mmol,
5.5 eq.), Pd(PPh3)4 (100 mg, 0.017 mmol), anhydrous K2CO3
(9.68 g, 70 mmol), Aliquat 336 (4 drops), and dry toluene/H2O (70
mL/35 mL), and then, the mixture was degassed with nitrogen for
15 min. Subsequently, the reaction mixture was heated at 120 1C for
48 h. After cooling to room temperature, the reaction mixture was
extracted by CH2Cl2. The crude product was purified by silicon
chromatography (petroleum ether/CH2Cl2) to get the pure product
as a red solid (536 mg, yield 65%). 1H NMR (400 MHz, CDCl3): d 8.55
(d, 1H), 8.42 (d, 1H), 8.15–7.96 (m, 5H), 7.64 (d, 2H), 5.17–5.05
(m, 2H), 2.22–1.94 (m, 10H), 1.94–1.73 (m, 4H), 1.43–1.18 (m, 24H),
0.88–0.76 (m, 12H). 13C NMR (100 MHz, CDCl3): d 164.95, 164.45,
163.84, 163.52, 152.18, 147.43, 143.58, 140.73, 138.50, 136.51, 134.54,
133.29, 133.07, 132.00, 130.19, 128.64, 127.88, 126.99, 126.81, 126.30,
124.43, 122.43, 121.87, 116.33, 80.75, 54.79, 54.60, 32.35, 32.20, 31.74,
31.66, 29.71, 29.03, 26.60, 26.50, 22.70, 22.53, 22.48, 14.12, 14.03,
13.98. HRMS: C224H244N10O20 (M+): calcd – 3395.8; found – 3395.8.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
Synthesis of PPDI-Se
A Schlenk tube was initially charged with TPP-Bpin4 (216 mg, This study was financially supported by the National Natural Science
0.243 mmol, 1 eq.), compound PDI-Se-Br (1.14 g, 1.338 mmol, Foundation of China (No. 21535004, 21927811, 91753111), the
5.5 eq.), Pd(PPh3)4 (100 mg, 0.017 mmol), anhydrous K2CO3 Key Research Development Program of Shandong Province
14568 | J. Mater. Chem. C, 2019, 7, 14563--14570
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These authors gratefully acknowledge Prof. Lian-Ming Yang
and Fengting Li from Institute of Chemistry, Chinese Academy
of Sciences for the MALDI-TOF characterization.
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