Synergy effect of electronic characteristics and spatial configurations of electron donors on photovoltaic performance of organic dyes

Article abstract of DOI:10.1039/d0tc02556a

Considering the key role of electron donors to the intramolecular charge transfer of organic dyes, molecular arrangement and electron processes in dye-sensitized solar cells, four organic dyes (LI-133-136) were designed and synthesized with indolo[3,2-b]indole (IDID) as the main electron donor and various aromatics as the assistant ones. The broad light response was achieved by the strong electron-donating ability of IDID with a planar structure, and with the aid of the electron-rich property of carbazole and triphenylamine. Moreover, the twisted configuration and large size of triphenylamine on the head of dye LI-136 can be beneficial to suppressing dye aggregation and electron recombination, contributing to the improved photovoltaic performance. With the systematic investigation of their photophysical and electrochemical impedance properties, together with theoretical calculations, the electronic characteristics of IDID and the spatial configuration of triphenylamine were highlighted as a synergy effect on the photovoltaic performance, affording an efficient strategy to simultaneously enhance the light-harvesting property and suppress the charge recombination.

Full text of DOI:10.1039/d0tc02556a

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Nosang V. Myung, Yong-Ho Choa et al.
A
noble gas sensor platform: linear dense assemblies of
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DOI: 10.1039/D0TC02556A
ARTICLE
Synergy Effect of Electronic Characteristics and Spatial
Configurations of Electron Donors on Photovoltaic Performance of
Organic Dyes
Received 00th January 20xx,
Accepted 00th January 20xx
Jinfeng Wang,a,b Siwei Liu,a Kai Chang,a Qiuyan Liao,a Sheng Li,c Hongwei Han,c Qianqian Li,*a and
Zhen Li,*ab
DOI: 10.1039/x0xx00000x
Considering the key role of electron donors to the intramolecular charge transfer of organic dyes, molecular arrangement
and electron processes in dye sensitized solar cells, four organic dyes (LI-133-136) were designed and synthesized with indolo
[3,2-b]indole (IDID) as the main electron donor and various aromatics as the assistant ones. The broad light response was
achieved by the strong electron-donating ability of IDID with planar structure, with the aid of the electron-rich property of
carbazole and triphenylamine. Moreover, the twisted configuration and large size of triphenylamine on the head of dye LI-
136 can be beneficial to suppressing dye aggregation and electron recombination, contributing to the improved photovoltaic
performance. With the systematical investigation of their photophysical and electrochemical impedance properties,
together with theoretical calculations, electronic characteristic of IDID and spatial configuration of triphenylamine were
highlighted as synergy effect on photovoltaic performance, affording an efficient strategy to enhance the light-harvesting
and suppress the charge recombination simultaneously.
For the common organic dyes with D-π-A structures, electron
donors (D) not only act as the “electronic warehouse” and transfer
electrons from π bridge to the acceptor (A) continuously, but also
Introduction
Conversion of sunlight into electrical energy is considered as the
effective way to solve the energy crisis and environmental problems.
In the photoelectric conversion process, dyes play an essential role
to light harvesting and electron transitions in dye-sensitized solar
cells (DSCs).1-3 For example, porphyrins and their analogues draw
intense attention due to their excellent absorption in the visible
wavelength range and high conversion efficiencies. 4-8. As for metal
free organic sensitizer, the planar molecular configurations of
organic dyes with strong electronic pull-push structures can increase
intramolecular charge transfer, resulting in the broad absorption
spectra and strong light-harvesting abilities, positive to the
photovoltaic performance.9-12 However, the strong dipole-dipole and
π-π interactions among these dyes usually cause the severe
aggregate on the TiO2 surface, leading to the charge recombination,
negative to the photoelectric conversion process with energy loss.13
Thus, the adjustment of electronic characteristics and spatial
configurations of organic dyes is essential to optimize photovoltaic
performance of solar cells.
play the important role to regulate the arrangement of organic dyes
on the TiO2 surface, with the aim to suppress electron recombination
and facilitate dye regeneration from the redox shuttle.14-18 As to the
dye arrangements, the electron donors with large sizes and twisted
configurations can act as the isolated groups to enlarge the distances
between the conjugation skeletons of organic dyes by steric
hindrance, and suppress the dye aggregation in most cases. Also, the
dye arrangement can affect the electron processes at the interface,
for instance, the severe dye aggregation could lead to the
inhomogenous distribution of organic dyes on the TiO2 surface,
resulting in the electron recombination at the bare TiO2 surface.
Alternatively, the regular molecular packing is beneficial to form
compact barrier layer to suppress the possible electron
recombination. Until now, various electron donors have been
exploited, such as carbazole,19,20 indoline21,22 and triphenylamine,23-
25 which emerged nitrogen atom as the electron-rich unit in different
conjugated systems. Recently, Wang et. al. designed an organic dye
C279 containing N-annulated perylene as the electron donor with a
power-conversion efficiency (PCE) of 8%, which can further increase
to 13% by the expansion of fused-heterocycle donor system (Fig.
S1).26 Also, compared to the common carbazole-based dyes, the
indolocarbazole-based ones exhibited the increased conversion
efficiency, further confirming the advantage of expanded conjugated
systems with rigid structures as electron donors (Fig. S2).27 These
moieties can decrease vibrational relaxation of organic molecules
with less energy loss, and increase the intramolecular charge
transfer, favouring to the fast electron injection and broad light-
harvesting region.
a. Sauvage Center for Molecular Science, Department of Chemistry, Wuhan
University, Wuhan 430072, China
b. Institute of Molecular Aggregation Science, Tianjin University, Tianjin, 300072,
China.
c. Michael Grätzel Center for Mesoscopic Solar Cells, Wuhan National Laboratory for
Optoelectronics, Huazhong University of Science and Technology, Wuhan,
430072, China.
† Electronic Supplementary Information (ESI) available: [the 1H NMR, 13C NMR, EIS
spectra and Materials and Instrumentation, DSC device fabrication and
measurement]. See DOI: 10.1039/x0xx00000x
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DOI: 10.1039/D0TC02556A
Figure 1. The strategy of molecular design and structures of IDID-based organic dyes
Considered with these, based on the strong electron-donating conducted (Fig. 2)30. It was found that HOMOs of these dyes mainly
ability of TAPP moiety as proven by our previous study (Fig. 1),28 the focus on the IDID moiety, which revealed that IDID core acted as the
indolo[3,2-b]indole (IDID) unit with planar and rigid structure was efficient electron donor, and they varied subtly with different
designed and synthesized, which can be illustrated by the decreased auxiliary electron donors. For benzene and fluorene with weak
dihedral angles between pyrrolopyrrole and phenyl units from 30o electron donating capabilities, little electron distribution of HOMOs
(TAPP) to nearly zero (IDID). The fused ring can increase effective extended to these moieties, however, if these are replaced by
conjugation length and decrease the reorganization energy, triphenylamine and carbazole moieties, electron distribution of
favouring to the efficient charge transfer along the D-π-A direction. HOMOs can cover these auxiliary electron donors, meaning that they
Furthermore, auxiliary donor (D’) with different electronic properties can participate the intramolecular charge transfer efficiently. The
and spatial stereo structures are modified on the head of IDID moiety electron acceptor parts of these dyes are the same and LUMOs were
to form a new D’-D-π-A system. As shown in Figure 1, dyes LI-133-LI- mainly located on the cyanoacetic acid and thiophene moieties. The
136 bearing benzene, fluorine, carbazole and triphenylamine as the partial overlap of the HOMOs and LUMOs is conducive to
D’ moieties were synthesized by increasing electron-donating intramolecular electron transfer from electron donor to acceptor
abilities and steric hindrance gradually, which can promote the moieties. Additionally, their calculated HOMO and LUMO energy
intramolecular charge transfer and adjust molecular configurations. levels are shown in Table 1, which were consistent with the UV-vis
All of sensitizers exhibited the broad absorption region, and PCEs of absorption spectra and electrochemical properties (Fig. 3).
the corresponding solar cells increased gradually with auxiliary
electron donors changed from benzene to triphenylamine, which is
Photophysical properties
mainly related to the synergy effect of triphenyl amine and IDID The UV/Vis absorption spectra of these organic dyes in dilute
moieties as dual electron donors with suitable spatial configurations dichloromethane and anchored on TiO2 films (6.6 m) are shown in
and electronic characteristics. Herein, the photophysical properties, Fig. 3, and their maxima wavelengths (λmaxs) of absorption and
electrochemical properties, and photovoltaic properties of these absorption onsets (λonsets) are summarized in Table 1. These IDID-
four dyes will be discussed in detail, some relationship between based organic dyes displayed red-shifted absorption compared with
molecular structures and photovoltaic performance has been that of LI-128 (λmax = 506 nm) with TAPP as electron donor (Figure
proposed.
S3), which indicate that the formation of IDID core can promote the
charge transfer more efficiently for the rigid structure with planar
configuration. Upon adsorption on TiO2 film, their absorption spectra
exhibited broad light harvesting regions ranging from 300 nm to 700
nm, mainly attributing to the interactions between TiO2 and organic
dyes, together with molecule-molecule interactions in the
aggregated state.31-33 Either in solution or on TiO2 film, the
absorption spectra of LI-135 and LI-136 are slightly red-shifted with
respect to those of LI-133 and LI-134. It is mainly due to the stronger
Results and discussion
Synthesis and design of organic dyes
The synthetic routes of organic dyes were depicted in Scheme 1.
Through the Sonogashira coupling reaction, IDID moiety is obtained
with a moderate yield according to literatures.29 After the alkylation
of IDID unit with branched alky chains, different auxiliary electron
donors were introduced by Suzuki coupling reaction easily. The
target organic dyes were obtained by Knoevenagel condensation
with cyanoacetic acid as electron acceptor and anchoring group, and
have been fully characterized by H NMR, 13C NMR, ESI and EA (Fig.
1
S4-S20).
Theoretical calculations
With the aim to predict and investigate the influence of molecular
configuration and electronic properties of organic dyes on
photovoltaic performance, time-depending density functional
theory (TD-DFT) calculation at the B3LYP/6-31G* level was
Figure 2. Frontier orbitals of organic dyes based on TD-DFT
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to TiO2 (Fig. 3d).35 Thus, compound LI-133-LI-136 can act as efficient
organic dyes for the well-matched energy levels with TiO2
electrolyte.
40000
35000
30000
25000
20000
15000
10000
5000
View Article Online
DOI: 10.1039/D0TC025a5n6Ad
LI-133
LI-134
LI-135
LI-136
LI-133
LI-134
LI-135
LI-136
(a)
(b)
Photovoltaic performance
The photocurrent density-voltage (J-V) curves and IPCE plots of DSCs
based on LI-133-136 were conducted with an iodine electrolyte (0.05
M I2, 0.2 M LiI, 0.6 M DMPII, 0.1 M GuNCS and 0.5 M 4-TBP in
acetonitrile) under simulated AM 1.5G illumination (Fig. 4). The
photovoltaic parameters of DSCs based on dye LI-133-LI-136 were
displayed in Table 2 and Fig. S4. DSC based on dye LI-133 with
benzene as the D’ unit showed a PCE of 6.71% (Jsc = 14.56 mA cm-2,
Voc = 672 mV, FF = 0. 69). When D’ moiety was changed to fluorene
unit, the improved photovoltaic performance of dye LI-134 was
achieved with the conversion efficiency of 7.03%, which might be
related to the larger size of fluorene with the bigger steric effect on
the suppression of the possible electron recombination.36-39
Furthermore, dye LI-135 with carbazole as the assistant electron-
donating unit exhibited the further increased conversion efficiency
of 8.09%, since the electron-rich unit of carbazole can promote the
light harvesting by increasing intramolecular charge transfer. But the
planar structure of carbazole and IDID could induce the dye
aggregates to some extent, as proven by the increased dye loading
amount (1.78×10-8 mol cm-2 μm-1). Thus, triphenylamine as strong
electron donor with twisted configuration was incorporated into dye
LI-136. The resultant decreased dye loading amount (1.18×10-8 mol
cm-2 μm-1) was obtained with the suppression of dye aggregates on
the TiO2 film by the large steric hindrance of triphenylamine, and the
highest conversion efficiency of 8.34% was achieved with a Jsc of
16.75 mA cm-2, Voc of 705 mV, and FF of 0.71. The high Jsc value was
related to the dual electron donating effect of IDID and
triphenylamine on the intramolecular charge transfer and absorption
spectra. Also, the electronic effect by carbazole and triphenylamine
as efficient assistant electron donors can be further proven by the
boarder IPCE curves range from 300 to 750 nm (Fig. 4b), which are
consistent with the trend of Jsc and UV-vis absorption spectra on TiO2
film. Thus, the optimized photovoltaic performance of dye LI-136
was due to the synergy effect of suitable electronic characteristics
and spatial configuration of dual electron donors, and the spatial
configuration was not only related to the dye arrangement, but also
the electron process at the interface. Triphenylamine with large size
and twisted configuration can act as the isolated group to enlarge the
distance between the conjugation
0
300
400
500
600
700
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
(d)
(c)
LI-133
LI-134
LI-135
LI-136
0.0
0.5
1.0
1.5
Potential(V)
Figure 3. (a) Absorption spectra of IDID-based organic dyes
in the CH2Cl2 solution; (b)on the TiO2 films (6 m); (c) Cyclic
voltammograms of IDID-based organic dyes in CH2Cl2;
(d)Energy level diagram of the IDID-based organic dyes,
electrolyte and TiO2. ∆G1: energy gap for electron injection;
∆G2: energy gap for dye regeneration.

electron donating ability of triphenylamine and carbazole moieties,
favouring to intramolecular charge transfer with stronger electronic
pull-push effect. The enhanced light harvesting across wide spectra
could possibly facilitate DSCs to produce large photocurrents.
Electrochemical properties
Cyclic voltammetry was performed for these organic dyes to
determine their redox potentials and the corresponding HOMO and
LUMO levels (Fig. 3c). The first oxidation potentials (Eoxs) are related
to the IDID unit as electron donor (0.71~0.80 V vs. NHE),
corresponding to the HOMO levels. They were significantly more
positive than that of the liquid electrolyte I-/I3- redox potential (0.4 V
vs. NHE), indicating the suitable energy staircase for dye
regeneration.34 The second oxidation potentials may relate to the
assistant electron donors and  bridges, and the strong electron-
donating ability of triphenylamine unit can be further confirmed by
the smallest Eox. The excited state oxidation potentials Eox* (-1.20~-
1.16V vs. NHE), corresponding to the LUMO level, estimated from Eox
and zero-zero transition energy (E0–0), were more negative than the
conduction band of TiO2 (ECB, -0.5
V vs. NHE), implying
thermodynamically favoured electron injection from the excited dye
Table 1 Optical and Electrochemical Properties of organic dyes
b
e
maxa[nm]
E0-0
Eox[V]c
vs NHE
Eox*[V]d
vs NHE
HOMOe
[eV]
LUMOe
[eV]
E0-0
a
onset
Dye
(/104[M-1cm-1])
[eV]
1.94
1.98
1.93
1.92
[eV]
2.30
2.36
2.28
2.00
[nm]
639
626
642
646
LI-133 442(1.56), 529(2.25)
LI-134 447(2.00), 525(2.51)
LI-135 454(2.43), 530(3.08)
LI-136 446(2.00), 535(2.82)
0.74
0.80
0.73
0.71
-1.20
-1.18
-1.20
-1.21
-4.88
-4.96
-4.84
-4.56
-2.58
-2.60
-2.56
-2.56
a Absorption spectra of dyes measured in CH2Cl2. b The bandgap E0-0 was derived from the observed optical edge. c
Eox were measured in CH2Cl2 with 0.1 M TBAPF6 as electrolyte. The oxidation potential (Eox) referenced to calibrated
Ag/AgCl was converted to the NHE reference scale: Eox = Eoxon + 0.2, d Eoxwas calculated from Eox - E0-0/e, e HOMO
and LUMO levels were calculated by time-depending density functional theory (TD-DFT).
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Table 2 Photovoltaic parameters of DSCs based on these organic dyes
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DLA /[10-8mol
DOI:c1m0.1-20μ39m/D-10] cTC02556A
dye
Jsc/[mA•cm-2]
Voc/[mV]
FF
η/[%]
14.55  0.11 a (14.56) b
14.83  0.22 a (14.88) b
16.65  0.24 a (16.66) b
16.74  0.15 a (16.75) b
16.76  0.21 a (16.76) b
671  7 a (672) b
672  4 a (673) b
691  6 a (697) b
705  4 a (705) b
683  5 a (683) b
0.689  0.001 a (0.69)b
0.705  0.005 a (0.70) b
0.694  0.005 a (0.70) b
0.704  0.005 a (0.71) b
0.716  0.006 a (0.72) b
6.73  0.11 a (6.73) b
7.03  0.12 a (7.03) b
8.00  0.21 a (8.09) b
8.32  0.14 a (8.34) b
8.19  0.17 a (8.26) b
LI-133
LI-134
LI-135
LI-136
N719
1.25
1.23
1.78
1.18
—
aAverage values based on four pieces of DSCs; bthe photovoltaic parameters in the main text; c DLA: dye loading amount
skeleton of organic dye by steric hindrance, and suppress the dye further confirming the key role of spatial configurations of electron
aggregation. It can be partially proved by the lowest dye loading donors.
amounts of LI-136. The related electron process at the interface can
be investigated by the electrochemical analysis.
Accordingly, in order to investigate the interfacial charge
transfer in devices, electrochemical impedance spectroscopy (EIS)
The method of charge extraction (CE) and intensity-modulated was performed in dark under a forward bias of -0.69 V. Nyquist and
photovoltage spectroscopy (IMVS) were applying for good Bode phase plots for DSCs based on the four sensitizers are
investigating and understanding the energetic and dynamic origins presented in Fig. 5c and 5d. The interfacial charge transfer
of the different Voc in detail. Actually, the theoretical maximum resistances (RCT) at the TiO2/dye/electrolyte interface is closely
attainable Voc of a DSCs is limited by the difference between the related to the larger semicircle at lower frequencies in Nyquist plots.
quasi Fermi level (EF,n) of electrons in the oxide semiconductor and The smaller the RCT, the faster the charge recombination is. At a given
the potential of the redox shuttle in the electrolyte,40-42 since the voltage bias, the corresponding radius of semicircle is in the order of
-
related DSCs were fabricated with the same electrolyte (I3 /I-), Voc is LI-136  LI-135  LI-134  LI-133, indicating that the charge
mainly determined by the quasi-Fermi-level (EF,n), which is affected recombination between the electrons in TiO2 and redox electrolyte
by two main factors: (i) the position of the TiO2 conduction band, was well restrained by auxiliary electron donors with tunable
which could be inferred from the charge extraction (CE) method; (ii) configurations. The large size of triphenylamine with twisted
the electron density in the semiconductor, which is mainly controlled structures is beneficial to the well-organized molecular arrangement
by the interfacial recombination rate of electrons in TiO2 with an and formation of the contact inhibitor, resulting in the largest RCT
oxidized substance in the electrolyte and/or dye cations and can be value. The electron lifetime of devices in dark condition was
analysed by IMVS measurement that reflected in the electron correlated with frequency in Bode phase plots (Fig. 5d), which is also
lifetime (τ).43 As shown in Fig. 5, the four dyes of LI-133-LI-136 in agreement with the result from IMVS measurements. Additionally,
displayed an unconspicuous shifts in ECB, which probably due to their the co-sensitization with CDCA has been conducted. Although the Voc
similar dipole moments with the similar skeleton of sensitizers. values slightly increased with the addition of CDCA, all the dyes
However, LI-133 and LI-134 exhibited the shorter electron lifetime, exhibited decreased conversion efficiencies for the competitive
which means the higher electron recombination rate of I3- or cations adsorption of CDCA, resulting in the decrease of dye loading amounts
with the electrons injected into the TiO2 film, resulting in the lower and Jsc values.
Voc about 672 mV. As displayed in Fig. 5b, lifetime values lie in the
Thus, with the incorporation of assistant electron donors and
order of LI-136  LI-135  LI-134  LI-133, which is in good agreement the relation design of electron donor moieties, the optimized
with the trend of Voc. Thus, the auxiliary electron donors with spatial photovoltaic performance of dye LI-136 is achieved by the synergy
configurations can optimize the dye arrangement on the TiO2 surface effect of electronic characteristics and spatial configuration of dual
and act as the efficient barrier layer to inhibit the contact of
electrolyte with the electrons in TiO2 film. Despite low dye-loading of
LI-136 in this case, the higher conversion efficiency of DSC was
achieved for the preferred molecular arrangement on the TiO2
Surface. It is beneficial to the suppression of charge recombination,
80
(b)
(a)
LI-133
LI-134
LI-135
LI-136
70
60
50
40
30
20
10
0
16
12
8
LI-133
LI-134
LI-135
LI-136
4
0
-4
0.0
Figure 5 (a) Charge density and (b) electron lifetime at open
circuit as a function of Voc for DSCs based on LI-133-136-
sensitized solar cells; EIS spectra of DSCs tested in the dark:
(c) Nyquist plots, (d) Bode phase
300
400
500
600
700
80
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Potential (V)
Wavelength (nm)
Figure 4. (a) J-V characteristic curves and (b) IPCEsfor DSCs
based on LI-133 136
-
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A mixture solution of H2SO4 (70 mL) and deionizVeidewwAratictleerOn(l7in6e
DOI: 10.1039/D0TC02556A
mL) was added to a mixture solution of 4-bromo-2-nitroaniline
(21.70 g, 100 mmol) and glacial acetic acid (70 mL) at 0 oC
dropwisely. Then, a solution of NaNO2 (7.59 g, 110 mmol,
dissolved in 30 mL of deionized water) was dropwise added and
stirred for an hour. Afterwards, a solution of KI (19.92 g, 120
mmol, dissolved in 30 mL of deionized water) was added
dropwise and stirred at 65oC for 3 hours. Then the mixture was
cooled under ice-bath and dichloromethane (500 mL) was
added to dissolve the solid in the mixed solution completely,
and the organic phase was washed with a saturated sodium
thiosulfate solution (500 mL). After removal of the solvent by
rotary evaporator, the crude product was recrystallized from
ethanol and filtered to give intermediate 1 as a yellow solid
(24.7 g, 75.3 %). 1H NMR (400 MHz, CDCl3) δ (ppm): 7.99 (s, 1H,
ArH), 7.89 (d, 1H, J = 6.0 Hz, ArH), 7.39 (d, 1H, J = 3.0 Hz, ArH).
Figure 6 The proposed mechanism for the function of dual
electron donors with synergy effect
electron donors. The electronic effect is mainly from the strong
electron donating ability of IDID moiety with planar structures, which
can strengthen the intramolecular charge transfer to improve the
light harvesting ability. Also, the electron-rich property of assistant
electron donors can further broaden the absorption spectra and IPCE
curves. The spatial configuration was mainly constructed by the
twisted geometry of triphenylamine, which can suppress the dye
aggregates as the isolate group, resulting in the preferred molecular
arrangement on the TiO2 surface. Since the assistant electron donors
are on the head of organic dyes, the large size of triphenylamine can
favour to form the efficient barrier layer to inhibit the possible charge
recombination between the electrolyte and electrons in the TiO2
film. These combined effects result in the high conversion efficiency
of DSCs with less energy loss, and it gives an efficient strategy for
molecular design of organic dyes with excellent photovoltaic
performance by the incorporation of dual electron donors with
matched structures.
Synthesis of compound 2
A mixture of 1(12.35 g, 37.67 mmol), PdCl2(PPh3)2 (0.13 g, 0.19
mmol), CuI (71.8 mg, 0.38 mmol) and trimethylsilylacetylene (3
mL) in the mixture solvent (THF: 55 mL, Et3N: 15 mL) was placed
in Schlenk tube and stirred at room temperature for 3 hours
under an inert atmosphere. Then, the reaction mixture was
poured into water (100 mL) and extracted with CH2Cl2 for three
times. Afterwards, the organic layer was combined and dried
with anhydrous NaSO4. After the solvent was evaporated, a
yellow oil was obtained by column chromatography (10.53 g,
1
94.1%). H NMR (400 MHz, CDCl3) δ (ppm): 8.17 (d, 1H, J = 1.5
Hz, ArH), 7.69 (dd, 1H, J = 6.3 Hz, ArH), 7.52 (d, 1H, J = 6.0 Hz,
ArH), 0.28(s, 9H, CH3). The yellow oil (10.53 g, 35.46 mmol) and
K2CO3 (4.90 g, 35.46 mmol) were added to the mixture solvent
of CH2Cl2 (10 mL) and CH3OH (50 mL), stirring for 30 min at room
temperature. Then the reaction mixture was poured into water
Conclusion
Organic dyes with dual electron donors have been designed and
synthesized by the incorporation of IDID as the main electron
donor with the aid of various aromatic systems. The strong
electron-donating ability of IDID with planar structure can
strengthen the intramolecular charge transfer to enhance the
light-harvesting ability. Moreover, the improved photovoltaic
performance can be achieved by the increased steric effect of
assistant electron donors gradually, since their twisted
configuration with large sizes can suppress the possible dye
aggregates and charge recombination efficiently, once again
and filtered to give intermediate 2 as a bright yellow solid (7.28
g, 91.2%). 1H NMR (400 MHz, CDCl3) δ (ppm): 8.21 (d, 1H, J = 1.5
Hz, ArH), 7.73 (dd, 1H, J = 6.2 Hz, ArH), 7.56 (d, 1H, J = 6.2 Hz,
ArH), 3.58(s, 1H, CH).
Synthesis of compound 3
A mixture of compound 1 (10.56 g, 32.21 mmol), compound
2
(7.25 g, 32.21 mmol), CuI (61 mg, 0.32 mmol) and PdCl2(PPh3)2
(112 mg, 0.16mmol) in the mixture solvent (THF:50 mL, Et3N: 30
mL) was placed in Schlenk tube and stirred at room temperature
for 4 hours under an inert atmosphere. Then, the reaction
mixture was poured into water (100 mL) and extracted with
CHCl3 for three times. Afterwards, the organic layer was
combined and dried with anhydrous NaSO4. After removal of
the solvent by rotary evaporator, the crude product was
demonstrating the importance of rational molecular design44-50
.
Thus, Dye LI-136 with IDID and triphenylamine as dual electron
donors exhibited the highest conversion efficiency, and the
synergy effect of electronic characteristics by IDID and spatial
configuration of triphenylamine was highlighted as the key
factor, which provide an efficient way to promote the
development of solar cells by the rational design of electron
donors.
recrystallized from CH3OH and filtered to give intermediate
3 as
a brown solid (12.0 g, 87.9 %). 1H NMR (400 MHz, CDCl3) δ (ppm)
:
8.31 (d, 2H, J = 1.5 Hz, ArH), 7.80 (dd, 2H, J = 6.2 Hz, ArH), 7.69
(d, 2H, J = 6.2 Hz, ArH).
Experimental
Materials and Instrumentation, DSC device fabrication and
Synthesis of compound 4
measurement were displayed in supporting information.
A mixture of compound 3 (3.13 g, 7.38 mmol) and acetone (240
mL) was placed in two-necked flask and glacial acetic acid (1 mL)
was added slowly. After the mixture solution stirring at 65 oC for
Synthesis of compound 1
This journal is © The Royal Society of Chemistry 20xx
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Journal of Materials Chemistry C
Page 6 of 10
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/D0TC02556A
Scheme 1 The synthetic routs of organic dyes
(i) NaNO2,KI, H2SO4, H2O, AcOH; (ii) CuI, TEA, TMSA, PdCl2(PPh3)2; K2CO3, MeOH; (iii) CuI, TEA, 1, PdCl2(PPh3)2; (iv) KMnO4, AcOH,actone;
(v) Zn, HCl, AcOH; (vi) C20H41Br, NaH, THF; (vii) (5-formylthiophen-2-yl)boronic acid, K2CO3, Pd(PPh3)4, THF/H2O; (viii) Ar-Bpin
(corresponding to Ph-Bpin, Fl-Bpin, Cz-Bpin or TPA-Bpin respectively), K2CO3, Pd(PPh3)4, THF/H2O; (ix) cyanoacetic acid, piperidine,
CH3CN/THF.
10 min, potassium permanganate (2.33 g, 14.77 mmol) was NaSO4 and concentrated under reduced pressure. The crude
added and the reaction was gently refluxed for 5 hours. product was purified with column chromatography to afford
Afterwards, the mixture was poured into acetone (1 L) and compound 6
(7.75 g, 85.6 %). 1H NMR (400 MHz, CDCl3) δ (ppm)
sonicated for 30 minutes, then filtered, and the filtrate was 7.61 (d, 2H, J = 8.5 Hz, ArH), 7.53 (d, 2H, J = 1.5 Hz, ArH), 7.23 (d,
combined and evaporate under reduced pressure to give a 2H, J = 1.6 Hz, ArH), 4.21 (d, 4H, J = 7.5 Hz, NCH2), 2.14 (s, br, 2H,
1
yellow solid powder (2.36 g, 70.2%). H NMR (400 MHz, CDCl3) CH), 1.34-1.09 (m, 64H), 0.92-0.83 (m, 12H).
δ (ppm): 8.42 (d, 2H, J = 1.3 Hz, ArH), 8.02 (dd, 2H, J = 6.1 Hz,
ArH), 7.53 (d, 2H, J = 6.1 Hz, ArH).
Synthesis of compound 7
A mixture of compound
6 (6.98 g, 7.57 mmol), K2CO3 (5.23 g,
Synthesis of compound 5
37.83 mmol), and Pd(PPh3)4 (0.05 equiv.) in the mixture solvent
(THF/H2O = 5/1) was placed in Schlenk tube under an inert
atmosphere, then (5-formylthiophen-2-yl)boronic acid (1.77 g,
11.36 mmol) dissolved in THF(5 mL) was added dropwisely and
A mixture solution of acetic acid (40 mL), activated zinc powder
(12.75 g, 196.1 mmol) and hydrochloric acid (1 M, 4 mL) stirred
o
for 5 min under 0 C, then, compound 4 (8.94 g, 19.61 mmol)
o
stirred at 80 C for 12 hours. After reaction, the mixture was
was added in portions over 30 min. After the mixed solution
refluxing at 90 °C for 1 hour, an additional amount of Zn (1.27 g,
19.61 mmol) was added, and stirring was continued for another
4 h. After the reaction was completed, the mixture was cooled
to room temperature, and then poured into water, the solids
containing unreacted Zn and the product were isolated
byfiltration, then it was dissolved in hot DMF, and filtered and
removed Zn, and ice-water mixture (200 mL) was added to the
filtrate, and a milky white solid was precipitated and filtered to
poured into water and extracted with CH2Cl2 for three times.
The combined organic phase was dried with NaSO4 and
concentrated under reduced pressure. The crude product was
purified with column chromatography to afford compound
7
(2.19 g, 30.3%). 1H NMR (400 MHz, THF-d8) δ (ppm) 9.75 (s, 1H,
CHO), 7.80 (dd, 2H, J = 6.3, 4.9 Hz, ArH), 7.73 (d, 1H, J = 3.9 Hz,
ArH), 7.67 (d, 1H, J = 8.5 Hz, ArH), 7.62 (d, 1H, J = 1.5 Hz, ArH),
7.49 (d, 1H, J = 3.9 Hz, ArH), 7.44 (dd, 1H, J = 8.3, 1.4 Hz, ArH),
7.13 (dd, 1H, J = 8.5, 1.60 Hz, ArH), 4.39 (d, 2H, J = 7.5 Hz, NCH2),
4.32 (d, 2H, J = 7.6 Hz, NCH2), 2.13 (s, 2H, CH), 1.37-1.00 (m, 64H,
CH2), 0.76 (qd, 12H, J = 7.0, 1.9 Hz, CH3).
obtained compound 5 (3.55 mg, 50.1%)
CDCl3) δ (ppm): 10.39 (s, 2H, NH), 7.52-7.50 (m, 4H, ArH), 7.53
(m, 2H, ArH).
。
1H NMR (400 MHz,
General synthesis of compound 8
Synthesis of compound 6
A mixture of compound
7 (1.0 equiv.), arylboronic acid (1.0
NaH (942 mg, 39.24 mmol) was added slowly to the mixture of
compound 5 (3.55 g, 9.81 mmol) in THF (60 mL) at 0oC under an
inert atmosphere. Then 9-(bromomethyl)nonadecane (10.63 g,
29.4 mmol) was added to the mixture and refluxed for
overnight. After reaction finished, ice water was added
dropwisely to the mixture and and extracted with
dichloromethane. The combined organic phase was dried with
equiv.), Pd(PPh3)4 (0.05 equiv.) and K2CO3 (5.0 equiv.) in the
mixture solvent (THF/H2O = 5/1) was placed in Schlenk tube and
o
stirred at 80 C for 12 hours under an inert atmosphere. After
reaction, the mixture was poured into water and extracted with
CH2Cl2 for three times. The combined organic phase was dried
with NaSO4 and concentrated under reduced pressure. The
10 | J. Name., 2012, 00, 1-3
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Page 7 of 10
Journal of Materials Chemistry C
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Journal Name
ARTICLE
crude product was purified with column chromatography to 4H, CH2), 1.39-1.07 (m, 76H, CH2), 0.85-0.72 (m, 18H, CH3). 13C
View Article Online
afford compound
8a: Compound
8
.
NMR (100 MHz, THF-d8) δ (ppm):164.52, 1D5O6I.:8100,.1104399/.D002T,C104265.5766A,
(140 mg, 0.15 mmol), Ph-Bpin (91 mg, 0.22 143.74, 142.32, 141.99, 140.56, 136.63, 135.34, 129.37, 128.49,
7
mmol), yellow solid 8a (110 mg, 63.4%). 1H NMR (400 MHz, THF- 127.70, 127.42, 127.06, 124.29, 121.96, 119.38, 119.25, 118.48,
d8) δ (ppm): 9.75 (s, 1H, CHO), 7.78 (d, 2H, J = 8.8 Hz, ArH), 7.72 117.91, 117.07, 116.11, 114.16, 108.91, 108.70, 68.90, 50.32,
(dd, 2H, J = 6.1, 3.9 Hz, ArH), 7.56 (s, 1H, ArH), 7.47 (d, 1H, J = 39.94, 33.05, 32.81, 32.66, 31.15, 30.81, 30.70, 30.66, 30.53,
3.9 Hz, ArH), 7.41 (dd, 1H, J = 8.3, 1.4 Hz, ArH), 7.20 (d, 2H, J = 27.64, 27.58, 26.97, 23.76, 14.70,14.63. MS (ESI, m/z): [M] calcd
8.3 Hz, ArH), 6.52 (d, 1H, J = 2.3 Hz, ArH), 6.47 (dd, 1H, J = 8.4, for C80H121N3O4S: 1219.9, found 1219.9; Anal. Calcd for
2.3 Hz, ArH), 4.39 (d, 2H, J = 7.5 Hz, NCH2), 4.32 (d, 2H, J = 7.5 C80H121N3O4S: C, 78.70, H, 9.99; N; 3.44, S, 2.63; Found C, 78.32;
Hz, NCH2), 3.89 (dd, J = 14.8, 6.6 Hz, 4H, OCH2), 2.29-2.10 (m, H, 9.94; N; 3.59; S, 2.83.
2H, CH), 1.35-1.05 (m, 80H, CH2), 0.76 (m, 18H, CH3).
8b: Compound
(140 mg, 0.15 mmol), Fl-Bpin (101 mg, 0.22 0.24 mmol), red solid (77 mg, 75.5%). m.p. 89-91oC. IR (KBr, thin
mmol), orange solid 8b (118 mg, 65.2%). H NMR (400 MHz, film),
LI-134: 8b (100 mg, 0.08 mmol), cyanoacetic acid (20 mg,
7
1
1

(cm-1): 2215 (C≡N). H NMR (400 MHz, THF-d8) δ (ppm):
THF-d8) δ (ppm):9.76 (s, 1H, CHO),7.83 (t, 1H, J = 8.1 Hz, ArH), 8.25 (s, 1H, =CH), 7.85-7.77 (m, 4H, ArH), 7.74-7.61 (m, 5H, ArH),
7.73 (d, 1H, J = 3.9 Hz, ArH), 7.71-7.69 (m, 2H, ArH), 7.65-7.61 7.53-7.39 (m, 3H, ArH), 7.30-7.28 (m, 1H, ArH), 7.12-7.15 (m, 2H,
(m, 3H, ArH), 7.49 (d, 1H, J = 3.9 Hz, ArH), 7.42 (dd, 2H, J = 16.7, ArH), 4.45-4.40 (m, 4H, NCH2), 2.21 (s, br, 2H, CH), 2.02-1.93 (m,
8.90 Hz, ArH), 7.29 (d, 1H. J = 6.5 Hz, ArH), 7.19 (dd, 2H, J = 7.4, 4H, CH2), 1.34-0.95(m, 80H, CH2), 0.77-0.72 (m, 12H, CH2), 0.68-
5.6 Hz, ArH), 4.45-4.42 (m, 4H, NCH2), 2.22 (s, br, 2H, CH), 1.99- 0.63 (m, 6H, CH3). 13C NMR (100 MHz, THF-d8) δ (ppm): 167.90,
1.96 (m, 4H, CH2), 1.35-0.98 (m, 80H, CH2), 0.76-0.66 (m, 20H, 154.67, 152.23, 151.85, 145.16, 143.14, 142.54, 142.44, 142.20,
CH3).
141.07, 139.04, 136.75, 136.39, 133.84, 132.85, 131.83, 129.78,
8c: Compound
7
(160, 0.17 mmol), Cz-Bpin (95 mg,0.25 mmol), 129,17, 128.44, 128.16, 127.86, 127.82, 127.25, 125.34, 123.81,
1
orange solid 8c (143 mg, 74.9%). H NMR (400 MHz, THF-d8)
δ
122.46, 121.21, 120.78, 119.17, 119.02, 118.85, 117.76, 115.48,
(ppm): 9.75 (s, 1H, CHO), 8.35 (s, 1H, ArH), 8.06 (d, 1H, J = 7.7 Hz, 114.59, 109.48, 108.21, 104.93, 56.13, 50.33, 49.93, 41.59,
ArH), 7.85-7.79 (m, 3H, ArH), 7.77-7.73 (m, 3H, ArH), 7.49-7.39 40.08, 39.81, 33.08, 33.03, 32.83, 32.66, 31.56, 31.22, 30.92,
(m, 5H, ArH), 7.32 (d, 1H, J = 7.3 Hz, ArH), 7.08 (t, 1H, J = 7.4 Hz, 30.85, 30.79, 30.70, 30.65, 30.55, 30.11, 27.72, 27.62, 23.78,
ArH), 4.43 (d, 4H, J = 3.0 Hz, NCH2), 4.31 (t, 2H, J = 7.1 Hz, NCH2), 23.67, 14.72, 14.59, 11.49. MS (ESI, m/z): [M-1]- calcd for
2.23 (s, br, 2H, CH), 1.85-1.73 (m, 2H, CH2), 1.37-1.02 (m, 72H, C87H125N3O2S: 1274.9, found 1274.4; Anal. Calcd for
CH2), 0.80-0.67 (m, 15H, CH3).
8d Compound (150 mg, 0.16 mmol), TPA-Bpin (135 mg,0.24 H, 10.09; N; 3.01; S, 2.69.
mmol) LI-135: 8c (120 mg, 0.11 mmol), cyanoacetic acid (28 mg,
C87H125N3O2S: C, 81.83, H, 9.87; N; 3.29, S, 2.51; Found C, 81.56;
：
7
1
，
orange solid 8d (140 mg, 66.3%). H NMR (400 MHz,
THF-d8) δ (ppm): 9.75 (s, 1H, CHO), 7.80-7.76 (m, 3H), 7.73 (d, 0.33 mmol), red solid (100 mg, 75.8%). m.p. 137-139oC. IR (KBr,
1
1H, J = 3.9 Hz, ArH), 7.58 (s, 1H, ArH), 7.48 (d, 1H, J = 3.9 Hz, thin film),

(cm-1): 3418 (OH), 2216 (C≡N). H NMR (400 MHz,
ArH), 7.45-7.39 (m, 3H, ArH), 7.28 (dd, 1H, J = 8.3, 1.2 Hz, ArH), THF-d8) δ (ppm): 8.36-8.22 (m, 2H, =CH, ArH), 8.07-7.98 (m, 1H,
6.96-6.92 (m, 4H, ArH), 6.88 (d, 2H, J = 8.7 Hz, ArH), 6.76-6.72 ArH), 7.85-7.72 (m, 5H, ArH), 7.53-7.45 (m, 4H, ArH), 7.42-
(m, 4H, ArH), 4.39 (dd, 4H, J = 14.3, 7.5 Hz, NCH2), 3.84 (t, J = 6.4 7.30(m, 3H, ArH), 7.09-7.06 (m, 1H, ArH), 4.43 (t, 4H, J = 8.0 Hz,
Hz, 4H, OCH2), 2.19 (s, 2H, br, CH), 1.40-1.03 (m, 80H, CH2), 0.84- NCH2), 4.33-4.26 (m, 2H, OCH2), 2.22 (s, br, 2H, CH), 1.34-1.10
0.70 (m, 18H, CH3).
(m, 70H, CH2), 0.80-0.69 (m, 15H, CH3). 13C NMR (100 MHz, THF-
d8) δ (ppm): 163.79, 155.78, 145.13, 142.58, 141.13, 141.00,
139.75, 138.88, 136.72, 134.50, 133.39, 126.34, 126.06, 125.39,
General synthesis of organic dyes
The aromatic aldehyde (1.0 equiv) and cyanoacetic acid 125.23, 123.47, 123.14, 120.06, 118.51, 118.45, 118.16, 117.88,
(3.0 equiv) were dissolved in the mixture solution (MeCN/THF = 116.63, 114.93, 112.95, 108.79, 108.72, 108.33, 107.53, 49.19,
4/1, 10 mL) and refluxed. Then catalytic amount of piperidine in 42.68, 38.86, 38.79, 31.92, 31.89, 31.86, 31.67, 30.02, 29.67,
solvent was added dropwise. After being refluxed for 16 h, it 29.65, 29.62, 29.38, 29.34, 26.86, 26.55, 26.52, 22.60, 22.55,
was poured into hydrochloric acid aqueous solution (2 M, 100 22.52, 13.50, 13.42. MS (ESI, m/z): [M-1]- calcd for C80H112N4O2S:
mL). The crude product was extracted by chloroform for three 1191.8, found 1191.5; Anal. Calcd for C80H112N4O2S: C, 80.49, H,
times. The combined organic phase was dried with NaSO4 and 9.46; N; 4.69, S, 2.69; Found C, 80.50; H, 9.57; N; 4.88; S, 2.81.
concentrated under reduced pressure. The crude product was
purified with column chromatography to afford organic dyes.
LI-136
: 8d (131 mg, 0.10 mmol), cyanoacetic acid (26 mg,
0.30 mmol), red solid (97 mg, 69.8%). m.p. 155-157oC. IR (KBr,
LI-133: 8a (100 mg, 0.09 mmol), cyanoacetic acid (22 mg, thin film), 
(cm-1): 3421 (OH), 2216 (C≡N). 1H NMR (800 MHz,
0.27 mmol), red solid (70 mg, 63.6%). m.p. 105-107oC. IR (KBr, THF-d8) δ (ppm): 8.23 (s, 1H, =CH), 7.78 (m, 3H, ArH), 7.49-7.43
1
thin film),

(cm-1): 3405 (OH), 2216 (C≡N). H NMR (400 MHz, (m, 5H, ArH), 7.28 (s, br, 1H, ArH), 6.93-6.88 (m, 6H, ArH), 6.74
THF-d8) δ (ppm): 8.25 (s, 1H, =CH), 7.79 (dd, J = 14.6, 6.9 Hz, 3H, (d, 5H, J = 8.0, Hz, ArH), 4.36 (s, br, 4H, NCH2), 3.83 (t, 4H, J = 8.0
ArH), 7.72 (d, 1H, J = 8.3 Hz, ArH), 7.56 (s, 1H, ArH), 7.51 (d, 1H, Hz, OCH2), 2.17(s, br, 2H, CH), 1.68-1.64 (m, 4H, CH2), 1.39 (s, br,
J = 3.9 Hz, ArH), 7.45 (d, 1H, J = 8.9 Hz, ArH), 7.20 (d, 2H, J = 8.3 4H, CH2), 1.30-1.26 (m, 22H, CH2), 1.11-1.07 (m, 50H, CH2), 0.82
Hz, ArH), 6.52 (d, 1H, J = 2.2 Hz, ArH), 6.47 (dd, 1H, J = 8.3, 2.3 (s, br, 6H, CH2), 0.76-0.72 (m, 12H, CH3). 13C NMR (100 MHz,
Hz, ArH), 4.41 (d, 2H, J = 7.3 Hz, NCH2), 4.32 (d, 2H, J = 7.4 Hz, THF-d8) δ (ppm): 164.69, 160.80, 158.24, 157.39, 146.73, 143.03,
NCH2), 3.94-3.83 (m, 4H, OCH2), 2.20 (s, br, 2H), 1.71-1.65 (m, 142.22, 140.53, 135.27, 134.48, 132.33, 129.41, 127.42, 126.91,
This journal is © The Royal Society of Chemistry 20xx
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Journal of Materials Chemistry C
Page 8 of 10
ARTICLE
Journal Name
20 Y. Wang, B. Chen, W. Wu, X. Li, W. Zhu, H. Tian and Y. Xie,
125.47, 124.21, 121.59, 119.15, 118.26, 117.77, 117.12, 116.23,
113.79, 112.07, 108.83, 106.42, 101.45, 98.91, 69.35, 68.74,
50.54, 50.29, 39.98, 33.09, 33.05, 32.83, 31.18, 30.81, 30.73,
30.68, 30.53, 30.50, 23.78, 23.75, 14.69. MS (ESI, m/z): [M-1]-
calcd for C92H130N4O4S: 1385.9, found 1385.6; Anal. Calcd for
C92H130N4O4S: C, 79.60, H, 9.44; N; 4.04, S, 2.31; Found C, 79.26;
H, 9.64; N; 4.06, S, 2.35.
View Article Online
Angew. Chem. Int. Ed., 2014, 53, 10779.
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Conflicts of interest
26 Z. Yao, H. Wu, Y. Li, J. Wang, J. Zhang, M. Zhang, Y. Guo and P.
There are no conflicts to declare.
Wang, Energy Environ. Sci., 2015,
27 S. Cai, G. Tian X. Li, J. Su and H. Tian, J. Mater. Chem. A, 2013
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29 I. Cho, S. K. Park, B. Kang, J. W. Chung, J. H. Kim, K. Cho and S.
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We are grateful to the National Nature Science Foundation of
China (21875174, 21734007, and 51703183), and the
Fundamental Research Funds for the Central Universities
(2042018kf0014) for financial support.
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46 J. Yang, Z. Chi, W. Zhu, B. Z. Tang, Z. Li, Sci. China Chem.
2019, 62, 1090.
,
View Article Online
DOI: 10.1039/D0TC02556A
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DOI: 10.1039/D0TC02556A
Synergy Effect of Electronic Characteristics and Spatial Configurations of Electron
Donors on Photovoltaic Performance of Organic Dyes
Jinfeng Wang,a,b Kai Chang,a Siwei Liu,a Qiuyan Liao,a Sheng Li,c Hongwei Han,c Qianqian Li,*a Zhen Li,*ab
The dual electron donors with the combination of electron property and spatial configuration were incorporated to improve
the photovoltaic performance of organic dyes.
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