Two methoxyaniline-substituted dibenzofuran derivatives as hole-transport materials for perovskite solar cells

Article abstract of DOI:10.1039/c6ta00976j

2,2′,7,7′-Tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), one of the classical organic photoelectric materials, has been widely used as a hole transport material (HTM) in perovskite solar cells (PSCs) due to its relatively higher conductivity, easier film formation, weak absorption in the visible region, etc. However, the complex synthesis process and the high synthesis cost of Spiro-OMeTAD severely limit the commercialization of this material. In this work, two economical methoxyaniline-substituted dibenzofuran derivatives, BF-002 and BF-003, are synthesized and successfully used as hole-transport materials in perovskite solar cells (PSCs). The important properties including light absorption, thermal stability, energy level, conductivity, as well as photovoltaic performance are systematically demonstrated. The highest power conversion efficiencies of the PSCs based on BF-002 and BF-003 are 14.20% and 14.07%, respectively, comparable to that of the PSCs based on Spiro-OMeTAD.

Full text of DOI:10.1039/c6ta00976j

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ARTICLE
Two Methoxyaniline-Substituted Dibenzofuran Derivatives as
Hole-Transport Materials for Perovskite Solar Cells†
Yantao Shi,*,a Kaili Hou,a Yanxiang Wang,b Kai Wang,a HuiCai Ren,c MaoYin Pang,c Fan Chena and
Sen Zhanga
Received 00th January 20××,
Accepted 00th January 20××
DOI: 10.1039/×0×00000×
2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylam-ine)-9,9′-spirobifluorene (Spiro-OMeTAD), one classical organic photoelectric
materials, has been widely used as hole transport material (HTM) in perovskite solar cells (PSCs) due to its relatively higher
conductivity, easier film formation and weak absorption in the visible region, etc. However, the complex synthesis process
and the high synthetic cost of Spiro-OMeTAD severely limit the commercialization of this material. In this work, two
economical methoxyaniline-substituted dibenzofuran derivatives, BF-002 and BF-003, are synthesized and successfully
used as hole-transport materials in perovskite solar cells (PSCs). The important properties including light absorption,
thermal stability, energy level, conductivity, as well as photovoltaic performance are systematically demonstrated. The
highest power conversion efficiencies of the PSCs based on BF-002 and BF-003 are 14.20% and 14.07%, respectively,
comparable to that of the PSCs based on Spiro-OMeTAD.
www.rsc.org/
Over the last three years, perovskite solar cells (PSCs), which utilize Moreover, the structures of small molecules are convenient to tailor
the organic–inorganic hybrid metal halide CH3NH3PbX3 as light for achieving satisfactory properties. Various smallꢀmolecule HTMs,
absorbing materials, have achieved remarkable progress in terms of such as pyrene arylamine derivative,18 3,4ꢀethylenedioxythiophene,19
high power conversion efficiencies (PCEs) of up to 20.1%.1 Notable starꢀshaped triazine,20 carbazole derivative,21 butadiene derivative,22
photovoltaic performances of PSCs mainly originate from the triphenylamine,23 triptycene,24 tetrathiafulvalene derivative,25 and
excellent characteristics, such as large absorption coefficients,2 high spiroꢀbased derivative,26 have been used in PSCs. To further reduce
carrier mobility,3 long carrier lifeꢀtime,4 and moderate bandgap,5 of the cost of HTMs and enrich our understanding of the relationship
this new perovskite material. Holeꢀtransport materials (HTMs) in between HTM structures and PSC performance, we should extend
PSCs are responsible for the extraction and transport of the scope of searching HTMs.
photogenerated holes, which are of considerable significance in
determining the final PCE. In general, a good HTM should exhibit
MeO
OMe
high hole mobility,6 suitable highest occupied molecular orbital
(HOMO) energy levels, and stable thermodynamic and optical
properties. At present, 2,2′,7,7′ꢀtetrakis(N,Nꢀdiꢀpꢀmethoxyphenylamꢀ
ine)ꢀ9,9′ꢀspirobifluorene (SpiroꢀOMeTAD), one classical HTM in
organic photoelectric devices, has been widely used in PSCs because
of its relatively higher conductivity, better solubility, easier film
formation and weak absorption in the visible region.7-10 However,
the high synthetic cost of SpiroꢀOMeTAD severely limits the
commercialization of this material and hinders the wide applications
of relevant photoelectric devices subsequently.
N
N
OMe
MeO
O
N
N
N
N
OMe
MeO
MeO
OMe
BF-002
To date, other kinds of alternatives to HTMs in PSCs have been
developed and studied. Although conductive polymers, such as
PTAA,11,12 P3HT,13,14 TFB,15 PCBTDPP,16 PDPPDBTE,17 and
PCPDTBT11 have been proven effective as HTMs in PSCs, smallꢀ
molecule HTMs are considerably easier to synthesize and purify.
MeO
OMe
N
N
OMe
O
MeO
N
N
N
N
a.State Key Laboratory of Fine Chemicals, School of Chemitry, Dalian University of
Techbology, Dalian, 116024, China.* E-mail: shiyantao@dlut.edu.cn
b.School of Material Science and Engineering, JingDeZhen Ceramic Institute,
JingDeZhen, China
OMe
MeO
MeO
OMe
c.Valiant Corporation Limited, Yantai, 264000, China.
BF-003
Fig. 1 Molecular structures of BF-002 and BF-003.
† Electronic supplementary information (ESI) available: distributions of power
conversion efficiencies and the stability test. See DOI: XXXX
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For the first time in this study, we designed and synthesized two BFꢀ003 are measured by thermogravimetic analysis (TGA). As
smallꢀmolecule HTMs of methoxyanilineꢀsubstituted dibenzofuran demonstrated in Fig. 2b, TGA results show that the decomposition
derivatives, BFꢀ002 and BFꢀ003, as shown in Fig. 1. The important temperature of BFꢀ002 and BFꢀ003 is about 400 °C, thereby
properties including light absorption, thermal stability, energy level, suggesting good thermal stability. This feature is thought to be
conductivity, as well as photovoltaic performance are systematically positive for the longꢀterm durability of PSCs.
demonstrated. Compared with SpiroꢀOMeTAD, the two new HTMs
in this work are more facile and economical to synthesize. In considerably influence the performance of PSCs. The conductivity
addition to high solubility, the new HTMs demonstrate good filmꢀ of films are determined by using twoꢀcontact electrical
The conductive property is important for HTMs because it will
a
forming property and high hole mobility. Based on BFꢀ002 and BFꢀ conductivity setꢀup.21 Fig. 3a shows the currentꢀvoltage
003, PSCs achieved PCEs of 14.20% and 14.07%, respectively, characteristics of BFꢀ002 and BFꢀ003 doped with lithium
which are comparable to that obtained using conventional Spiroꢀ bis(trifluoromethylsulphonyl)imide (LiꢀTFSI), 4ꢀtertꢀbutylpyridine
OMeTAD. More importantly, the dibenzofuran derivatives are (tBP), and tris(2ꢀ(1Hꢀpyrazolꢀ1ꢀyl)ꢀ4ꢀtertꢀbutylpyridinꢀe)cobalt(III)
believed to possess a more flexible molecular structure design, as a bis(trifluoromethylsulphonyl) imide (FK209). The conductivity of
variety of functional groups could be introduced into the structure.
BFꢀ003 is observed to be slightly higher than that of Spiroꢀ
The HTMs are synthesized through a simple reaction of 2, 8ꢀ OMeTAD and BFꢀ002, which is more favorable to hole transport in
dibromodibenzofuran with N,Nꢀbis[4ꢀ(diꢀ4ꢀanisylamino)phenyl]amiꢀ HTMs. So as to study the electrical properties of BFꢀ002 and BFꢀ
e and N3, N6ꢀbis(diꢀ4ꢀanisylamino)ꢀ9Hꢀcarbazole. The UVꢀvis 003, HOMO energy levels were determined by using cyclic
absorption spectra of the two HTMs in chlorobenzene are shown in voltammetry (CV) conducted in dilute solutions. As shown in Fig.
Fig. 2a. BFꢀ002 and BFꢀ003 exhibit maximum absorption peaks at 3b, the pair of redox peaks of the two HTMs are highly reversible,
323 and 306 nm, respectively. These peaks probably result from the indicating good electrochemical stability. The HOMO energy level
πꢀπ* electron transition of the large molecular conjugate system.27 can be calculated on the basis of the following equation: EHOMO
=
Notably, the HTMs almost show no absorption in the visible region. −5.1−(Eox,HTM vs. Fc/Fc+) (eV), where Eox,HTM versus Fc/Fc+ is the
On the other hand, the maximum absorption peak of BFꢀ002 exhibits onset of oxidation potential with reference to ferrocene.28 The
a red shift of 17 nm versus that of BFꢀ003. This bathochromic shift HOMO energy level of BFꢀ002 and BFꢀ003 were calculated to be
could be attributed to one more planar configuration of BFꢀ002. The −5.01 and −5.14 eV, respectively. In PSCs, the open circuit voltage
absorption onset wavelengths of BFꢀ002 and BFꢀ003 were found at (Voc) is determined by the difference between the Fermi level of
475 and 461 nm, which correspond to optical bandgaps (Eg) of 2.61 TiO2 and the HOMO of HTMs.29 The HOMO energy level of BFꢀ
eV and 2.69 eV, respectively. The thermal properties of BFꢀ002 and
003 is lower than that of BFꢀ002 by about 130 mV. Therefore, we
(a)-1.5
(a)
1.2
-2.0
-2.5
-3.0
BF-002
BF-003
0.9
0.6
0.3
0.0
-3.5
Spiro-OMeTAD
BF-002
BF-003
-4.0
-4.5
250 300 350 400 450 500 550 600
Wavelength (nm)
-1.0
-0.5
0.0
0.5
1.0
Applied Bias (V)
(b)-40
(b)100
-30
BF 002
BF 003
90
80
70
60
50
-20
-10
0
BF-002
BF-003
10
20
30
0
100 200 300 400 500 600 700 800
-0.3
0.0
0.3
0.6
0.9
1.2
Temperature ( )
oC
Potential (V vs. Ag/AgCl)
Fig. 2 (a) UV-vis absorption spectra of HTMs dissolved in chlorobenzene; Fig. 3 (a) Current–voltage characteristics of doped HTM films; (b) Cyclic
(b) Thermogravimetric analysis of BF-002 and BF-003.
voltammograms of HTMs with ferrocene as reference.
2 | J. Mater.Chem.A,2016
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25
(a)
(a)
20
15
-3.93
TiO2
-4.0
E (eV)
Ag
10
5
BF-002
-5.01
Spiro-OMeTAD
BF-002
BF-003
BF-003
-5.14
0
-5.44
0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
100
80
60
40
20
0
(b)
(b)
Ag
HTM
CH3NH3PbI3+Porous TiO2
Spiro-OMeTAD
BF-002
BF-003
Compact TiO2
FTO
300
400
500
600
700
800
Wavelength (nm)
25
20
15
10
5
(c)
Spiro-OMeTAD
BF-002
BF-003
Fig. 4 (a) Energy level diagram of perovskite solar cells with two HTMs; (b)
Cross-sectional SEM image of the perovskite solar cells.
anticipate a higher Voc value for devices with BFꢀ003 in comparison
with those with BFꢀ002.
Fig. 4a shows the energy level diagram of the corresponding
components in perovskite solar cells. The HOMO energy levels of
BFꢀ002 and BFꢀ003 were measured to be −5.01 eV and −5.14 eV by
CV. The reported HOMO energy level for CH3NH3PbI3 is −5.44
eV,4 obviously, the HOMO energy levels of our new HTMs are
located above the groundꢀstate level of the perovskite, implying that
the two HTMs possess favorable energetics for hole transfer from
perovskite into the HTM layer. In this work, PSCs were constructed
with a conventional configuration of FTO/compact TiO2/mesoporous
TiO2+perovskite/HTM/Ag. To be mentioned, the CH3NH3PbI3 was
subsequently deposited by using a twoꢀstep sequential method as
reported.30 The resulting perovskite films were coated with HTMs in
the presence of LiꢀTFSI, tBP, and FK209. Fig. 4b shows the crossꢀ
sectional scanning electron microscopy (SEM) image of the prepared
mesoporous PSCs, which exhibit a wellꢀdefined multiꢀlayer structure
with clear interfaces. The perovskite layer penetrates well into the
mesoporous TiO2 and forms an overlayer. Then, HTMs infiltrate into
the pores in the TiO2/perovskite layer and form a thin capping layer
on the top.
0
300
400
500
600
700
800
Wavelength (nm)
Fig. 5 (a) J–V curves for PSCs fabricated with BF-002, BF-003, and Spiro-
OMeTAD; (b) Corresponding IPCE spectra; (c) Corresponding integrated
photocurrent density curves.
Table 1 Summary of photovoltaic parameters of PSCs employing different
HTMs
HTM
JSC (mA cm-2
)
VOC (V)
FF
PCE(%)
Champion
Average
23.22
0.99
0.93 ± 0.04
1.01
0.66
0.68 ± 0.03
0.65
15.04
13.23 ± 0.72
14.20
Spiro-
OMeTAD
20.94 ± 1.46
21.56
Champion
Average
BF-002
BF-003
20.73 ± 0.93
21.22
0.98 ± 0.03
1.03
0.63 ± 0.02
0.64
12.77 ± 0.72
14.07
Champion
Average
19.70 ± 1.48
1.01 ± 0.02
0.67 ± 0.02
13.08 ± 0.81
The photovoltaic performances of PSCs employing BFꢀ002 and
BFꢀ003 as HTMs are measured under AM 1.5, 100 mW cm−2
simulated light illumination. Fig. 5a shows the current–voltage (J–V)
characteristics obtained from champion solar cells using each HTM.
The corresponding and average photovoltaic parameters are summaꢀ
rized in Table 1. For comparison, a reference cell with Spiroꢀ
OMeTAD as HTM was also fabricated under similar conditions. The
PCE of the champion cell with BFꢀ002 is 14.20%, with a shortꢀ
circuit current density (Jsc) of 21.56 mA cm−2, an open circuit
voltage (Voc) of 1.01 V, and a fill factor of (FF) 0.65. The champion
cell prepared with BFꢀ003 yielded a Jsc of 21.22 mA cm−2, a Voc of
1.03 V, and a FF of 0.64, leading to a PCE of 14.07%. The results
are comparable with that of PSCs based on SpiroꢀOMeTAD
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fabricated under the same conditions, with a Jsc of 23.22 mA cm−2, a
Voc of 0.99 V, and an FF of 0.66 and yielding a PCE of 15.04%. As
excepted, the BFꢀ003ꢀbased device shows a slightly higher average
Voc in comparison with that of the BFꢀ002 based device. This higher
Voc can be attributed to the lower HOMO energy level of BFꢀ003
than that of BFꢀ002, which is consistent with the electrochemical
measurement result. The higher Voc of the BFꢀ003ꢀbased device is
responsible for the slightly higher average PCE than that of the BFꢀ
002 based device. The average FF of the BFꢀ003ꢀbased cell is also
slightly higher than that of BFꢀ002, which may be caused by higher
conductivity of the former. On the other hand, the reproducibility in
PCE of the devices based on each HTM molecule is satisfactory, as
can be seen in Fig. S1.
Table 2 Summary of photovoltaic parameters of the solar cells with Spiro-
OMeTAD, BF-002, and BF-003 as the HTMs, respectively, evaluated under
one sun condition with different scan directions.
PCE(%
)
HTM
Scan direction
JSC (mA cm-2
)
VOC (V)
FF
Reverse
Forward
Reverse
Forward
Reverse
Forward
22.73
24.44
21.56
22.44
19.83
20.73
0.96
0.92
1.01
0.97
1.03
1.01
0.68
0.53
0.65
0.52
0.64
0.54
14.89
11.88
14.20
11.21
12.98
11.15
Spiro-
OMeTAD
BF-002
BF-003
conversion range from 350 nm to 700 nm. The maximum intensities
The incident photon to current conversion efficiency (IPCE) of the IPCE spectra obtained at about 500 nm for the three devices
spectra of the PSCs based on the three HTMs are presented in Fig. all exceed 80%. As shown in Fig. 5c, the integrated photocurrent
5b. The devices based on BFꢀ002 and BFꢀ003 exhibit a broad
densities of BFꢀ002 and BFꢀ003 are 21.08 mA cmꢀ2 and 20.58 mA
cm−2, respectively, which are in good agreement with the Jsc values
acquired from the J–V curves. Stability is another important issue for
evaluating new HTM materials. Bu it should be mentioned firstly
that the stability of PSCs using SpiroꢀOMeTAD reported up to now
demonstrates mixed results probably due to the different fabrication
methods and test conditions.17,25 In this work, PSCs based on the
three HTM molecules were fabricated and tested under the same
conditions for parallel comparison. After fabrication, the devices
were stored in air without light illumination and the stability test was
conducted by measuring the JꢀV curves per 12 h. It can be seen from
Fig. S1, PSCs using BFꢀ002 and BFꢀ003 showed slightly better
stability within 100 h.
(a) 30
25
20
15
Spiro-OMeTAD-Based
10
Reverse Scan
5
0
Forward Scan
0.0
0.2
0.4
0.6
0.8
1.0
As often reported, hysteresis in the currentꢀvoltage measurement
is a phenomenon frequently observed in PSCs. Uncovering the
intrinsic reasons for the anomalous hysteresis is still onꢀgoing. To
date, some conclusions have been put forward. For example, some
groups ascribed hysteresis to the ions migration of within perovskite
film, or the transient ferroelectric polarization. In the meantime, it is
widely accepted that the slow kinetic processes, like charge transport
or interfacial separation, will lead to pronounced hysteresis certainly.
In this work, the J–V curves obtained through forward and reverse
scans for PSCs employing the three HTMs are shown in Fig. 6.
Notably, the J–V curves of the two PSCs show hysteretic
behaviours. Detailed photovoltaic parameters are summarized in
Table 2. In good accordance with the results demonstrated in Fig. 3a,
the device based on BFꢀ003 is less pronounced in terms of hysteresis,
which could be ascribed to its higher conductivity that facilities hole
transport, one important dynamic process of charge transfer in PSCs.
To further suppress hysteresis in PSCs, some strategies can be used
Voltage (V)
30
25
20
15
10
5
(b)
BF-002-based
Reverse Scan
Forward Scan
0
0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
(c) 30
25
20
15
10
5
through improving perovskite crystallinity and surface coverage,23ꢀ24
,
passivating trap states at perovskite grain boundaries,25 accelerating
charge extraction,26 or optimizing cell structures.24
BF-003-based
Conclusions
Reverse Scan
Forward Scan
In summary, we designed and synthesized two new smallꢀ
molecule HTMs based on methoxyanilineꢀsubstituted dibenzofuran
derivatives. Then, we have successfully fabricated perovskite solar
cells with the derivatives as HTMs. The devices fabricated from BFꢀ
002 and BFꢀ003 show PCEs of 14.20% and 14.07%, which are
comparable to that (15.04%) of the SpiroꢀOMeTAD based cell.
0
0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
Fig. 6 J-V characteristics of the solar cells with Spiro-OMeTAD, BF-002, and
BF-003 as the HTMs, respectively, evaluated under one sun condition with
different scan directions.
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Moreover, BFꢀ002 and BFꢀ003 exhibit stable thermodynamic and Synthesis of N-tert-Butoxycarbonyl-N,N-bis[4-(di-4-anisylamino)
optical properties, high conductivity, and moderate HOMO energy phenyl]amine (2).[32] To a 1 L threeꢀnecked roundꢀbottomed flask,
levels, indicating the two materials can be promising HTMs in PSCs. diꢀ4ꢀanisylamine (23.7 g, 100 mmol), compound 1 (20.0 g, 47.0
We believe that these new materials will offer a new design strategy mmol), potassium tertꢀbutoxide (15.8 g, 141 mmol) and dry toluene
toward developing potential alternatives to expensive traditional (450 mL) were added. The mixture was purged with N2 for 10 min.
HTMs for the fabrication of costꢀeffective and highꢀperformance and then (tꢀBu)3PH·BF4 (0.54 g, 1.88 mmol) and Pd2(dba)3 (0.86 g,
photovoltaic devices.
0.94 mmol) were added. The reaction mixture was heated to reflux
for 4 h under N2. After cooling, the reaction was poured into water,
extracted with dichloromethane, washed with brine and concentrated
in vacuo. The crude product was suspended in hexane, then heated to
reflux and filtered to give compound 2 as a white powder (27.2 g,
Experimental section
HTMs Synthesis and Characterization
1
The synthetic routes for BFꢀ002 and BFꢀ003 are shown in Fig. 7.
80%). H NMR (500 MHz, CDCl3): δ 7.02 (dd, J = 8.3 Hz, 12H),
Synthesis of N-tert-Butoxycarbonyl-N,N-bis(4-bromophenyl)ami- 6.85 (d, J = 9 Hz, 4H), 6.80 (d, J = 9 Hz, 8H), 3.78 (s, 12H), 1.44 (s,
ne (1).[31] To a solution of N,Nꢀbis(4ꢀbromophenyl)amine (20.0 g, 9H). MS: m/z 723.33 [M+].
62.0 mmol) and diꢀtertꢀbutyl dicarbonate (20.1 g, 92.0 mmol) in Synthesis of N,N-Bis[4-(di-4-anisylamino)phenyl]amine (3).[32] To
THF (90 mL), 4ꢀ(dimethylamino)pyridine (1.5 g, 12.0 mmol) was a 250 mL threeꢀnecked roundꢀbottomed flask, compound 2 (4.1 g,
added slowly. Then the mixture was heated to reflux for 3 h with 5.67 mmol) was dissolved in dichloromethane (20 mL). Then
stirring. After cooling, the solvent was removed under reduced trifluoroacetic acid (63 mL, 97 g) was added. The reaction mixture
pressure. The crude product was filtered through a pad of silica gel was stirred at room temperature for 10 min. Evaporation of the
using dichloromethane as the eluent and concentrated in vacuo. The solvent and recrystallization from toluene and hexane afforded
1
residue was stirred in methanol at 60 oC to give compound 1 (23.7 g, compound 3 as a white solid (3.1 g, 88.6%). H NMR (400 MHz,
1
90%) as a white powder. H NMR (500 MHz, CDCl3): δ 7.35 (d, J D6ꢀDMSO): δ 7.24 ~ 6.83 (m, 24H), 3.78 (s, 12H). MS: m/z 623.28
=8.5 Hz, 4H), 6.99 (d, J = 8.5 Hz, 4H), 1.37 (s, 9H). MS: m/z 449.95 [M+].
[M+Na]+ , 876.91 [2M+Na]+.
Synthesis of BF-002. To a 250 mL threeꢀnecked roundꢀbottomed
flask, 2,8ꢀdibromoꢀ dibenzofuran (2.1 g, 6.4 mmol),[33] compound 3
(8.8 g, 14 mmol) and potassium tertꢀbutoxide (1.8 g, 16 mmol) and
dry toluene (115 mL) were added. The mixture was flushed with N2
for 10 min, and then (tꢀBu)3PH·BF4 (0.074 g, 0.26 mmol) and
Pd2(dba)3 (0.12 g, 0.13 mmol) were added. The reaction mixture was
heated to reflux for 9 h under N2. After cooling, the solution was
filtered to remove insoluble solids. The solvent of the filtrate was
removed and the resulting solid was purified by column
OMe
N
OMe
N
Br
Br
Br
Br
(b)
(a)
N
N
MeO
OMe
H
BOC
1
MeO
N
OMe
N
H
BOC
2
(c)
OMe
MeO
OMe
OMe
N
O
MeO
N
OMe
chromatography (silica gel, toluene) to give
a yellow solid.
(d)
O
N
N
N
N
Recrystallization from hexane and ethyl acetate afforded BFꢀ002 as
a light yellow solid (4.8 g, 53.2%). The overall yield of BFꢀ002 was
MeO
N
H
OMe
Br
Br
3
N
MeO
N
1
OMe
33.9%. HPLC: 99.3%. H NMR (400 MHz, (CD3)2CO): δ 7.00 (d,
OMe
MeO
18H), 6.89 ~ 6.80 (m, 36H), 3.75 (s, 24H). MS: m/z 1410.58 [M+].
Synthesis of N-tert-Butoxycarbonyl-3,6-dibromo-9H-carbazole
(4). To a solution of 3,6ꢀdibromoꢀ9Hꢀcarbazole (11.5 g, 35.4 mmol)
and diꢀtertꢀbutyl dicarbonate (11.6 g, 53.1 mmol) in THF (50 mL),
4ꢀ(dimethylamino)pyridine (0.86 g, 7.1 mmol) was added. Then the
mixture was heated to reflux for 3 h with stirring. After cooling, the
solvent was removed under reduced pressure. The crude product was
filtered through a pad of silica gel using dichloromethane as the
eluent and concentrated in vacuo. The residue was stirred in
methanol and water at 60oC to give compound 4 (14.0 g, 93%) as a
light yellow solid. 1H NMR (500 MHz, CDCl3): δ 8.06 (d, J = 9 Hz,
2H), 7.92 (d, J = 2 Hz, 2H), 7.48 (dd, J = 9, 2 Hz, 2H), 1.67 (s, 9H).
MS: m/z 447.93 [M+Na]+, 872.88 [2M+Na]+.
BF-002
OMe
N
OMe
N
Br
Br
Br
Br
(e)
(f)
N
N
BOC4
MeO
OMe
H
MeO
N
OMe
N
H
BOC
5
(g)
OMe
MeO
OMe
N
OMe
N
N
O
MeO
N
OMe
N
(h)
N
MeO
N
H
OMe
6
N
MeO
N
OMe
MeO
OMe
Synthesis of N-tert-Butoxycarbonyl-N3,N6-bis(di-4-anisylamino)-
9H-carbazole (5).[32] To a 500 mL threeꢀnecked roundꢀbottomed
flask, diꢀ4ꢀanisylamine (28.3 g, 124 mmol), compound 4 (25.0 g,
58.8 mmol), sodium tertꢀbutoxide (17.0 g, 176 mmol) and dry
toluene (250 mL) were added. The mixture was purged with N2 for
10 min. and then (tꢀBu)3PH·BF4 (1.36 g, 4.7 mmol) and Pd2(dba)3
(2.15 g, 2.35 mmol) were added. The reaction mixture was heated to
reflux for 5 h under N2. After cooling, the reaction was poured into
BF-003
Fig. 7 The synthetic routes of BF-002 and BF-003. Reaction conditions: (a) 4-
(dimethylamino)pyridine, THF, reflux; (b) potassium tert-butoxide,
Pd2(dba)3/(t-Bu)3PH·BF4, toluene, reflux; (c) TFA, rt, 10 min.; (d) potassium
tert-butoxide, Pd2(dba)3 (t-Bu)3PH·BF4, toluene, reflux,
9 h; (e) 4-
(dimethylamino)pyridine, THF, reflux; (f) sodium tert-butoxide, Pd2(dba)3/(t-
Bu)3PH·BF4, toluene, reflux; (g) potassium tert-butoxide, toluene, reflux; (h)
sodium tert-butoxide, Pd2(dba)3/(t-Bu)3PH·BF4, toluene, reflux, 20 h.
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Paper
Journal of Materials Chemistry A
Device Fabrication
water, extracted with toluene, washed with brine and concentrated in
vacuo. The crude product was filtered through a pad of silica gel.
Then washed with hot hexane and ethyl acetate throughly to afford
To fabricate the devices, Fluorinedoped Tin Oxide (FTO) glass
was patterned by etching with Zn powder and hydrochloric acid (4
M). Then the substrate was cleaned in a detergent solution using an
ultrasonic bath for 30 min, rinsed with deionized water, acetone, and
isopropanol. The compact TiO2 layer was deposited by spin coating
TiO2 organic sol on the substrate at 3000 rpm for 30 s, followed by
sintering in a furnace at 450°C for 2 h. Organic sol for TiO2 compact
layer was prepared according to previous literature.[34] Mesoporous
TiO2 film was prepared by spin coating a commercial TiO2 paste
(Dyesolꢀ18NRT, 1:3.5 w/w diluted in ethanol) at 5000 rpm for 30 s.
The film was successively sintered at 500°C for 30 min.
CH3NH3PbI3 layer was fabricated by two step method reported in the
literature.[30] The TiO2/FTO substrate was infiltrated with PbI2 by
spin coating at 5000 rpm for 5 s and dried on a hot plate at 70°C for
30 min. After cooling down, the film was dipped in a solution of
CH3NH3I in 2ꢀpropanol (10 mg mlꢀ1) for 60 s, rinsed with 2ꢀ
propanol, and dried at 70°C for 30 min to form the crystallized
CH3NH3PbI3. The HTM layers were deposited by spin coating at
3000 rpm for 30 s. The spinꢀcoating formulation was prepared by
dissolving 72.3 mg BFꢀ002, BFꢀ003 or spiroꢀMeOTAD, 28.8 ꢂL 4ꢀ
tertꢀbutylpyridine (tBP), 17.5 ꢂL of a stock solution of 520 mg mLꢀ1
lithium bis (trifluoromethylsulphonyl)imide(LiꢀTFSI) in acetonitrile,
and 20 ꢂL of a stock solution of 300 mg mLꢀ1 tris(2ꢀ(1Hꢀpyrazolꢀ1ꢀ
1
compound 5 as a light yellow solid (31.1 g, 73.8%). H NMR (500
MHz, CDCl3): δ 8.03 (d, J = 8.5 Hz, 2H), 7.368 (s, 2H), 7.03 (d, J =
8.5 Hz, 2H), 6.91 (d, J = 7Hz, 8H), 6.71 (d, J = 9Hz, 8H), 3.70 (s,
12H), 1.63 (s, 9H). MS: m/z 721.31 [M+].
Synthesis of N3,N6-bis(di-4-anisylamino)-9H-carbazole (6).[32] To
a 1 L threeꢀnecked roundꢀbottom flask, compound 5 (31.1 g, 43
mmol), potassium tertꢀbutoxide (14.5 g, 129 mmol) and dry toluene
(600 mL) were added. The reaction mixture was heated to reflux for
1 h. After cooling, the solution was poured into water, extracted with
ethyl acetate. The combined organic phase was dried over anhydrous
Na2SO4 and concentrated in vacuo. The residue was washed with hot
toluene to give compound 6 as a light yellow solid (25.1 g, 93.7%).
1H NMR (400 MHz, D6ꢀDMSO): δ 11.17 (s, 1H), 7.64 (s, 2H), 7.41
(d, J = 8.4 Hz, 2H), 7.07 (dd, J = 8.8Hz, 2H), 6.87 ~ 6.79 (m, 16H),
3.70 (s, 12H). MS: m/z 621.26 [M+].
Synthesis of BF-003. To a 250 mL threeꢀnecked roundꢀbottom
flask,
2,8ꢀdibromoꢀ dibenzofuran (0.5 g, 1.53 mmol ),[33] compound 6 (2.1
g, 3.38 mmol) and sodium tertꢀbutoxide (0.37 g, 3.84 mmol) and dry
toluene (100 mL) were added. The mixture was flushed with N2 for
10 min. and then (tꢀBu)3PH·BF4 (0.018 g, 0.06 mmol) and Pd2(dba)3
(0.028 g, 0.03 mmol) were added. The reaction mixture was heated
to reflux for 20 h. After cooling, the solution was filtered to remove
insoluble solids. The solvent of the filtrate was removed and the
resulting solid was purified by column chromatography (silica gel,
hexane : ethyl acetate = 4:1(v:v) as eluent) to give BFꢀ003 as a light
yellow solid (1.5 g, 55.5%). The overall yield of BFꢀ002 was 35.7%.
yl)ꢀ4ꢀtertꢀbutylpyridine)cobalt(III)
bis(trifluoromethylsulphonyl)
imide(FK209) in acetonitrile in 1 mL chlorobenzene. Finally, 50 nm
Ag was thermally evaporated on top of the device to form the back
contact. The active area of these solar cells was 0.12 cm2. All
devices were fabricated in a glove box.
HPLC: 99.69%. 1H NMR (500 MHz, D6ꢀDMSO): δ 8.55 (s, 2H), Device Performance Measurement
8.03 (d, J = 8.5 Hz, 2H), 7.78 (d, J = 9.15 Hz, 6H), 7.29 (d, J = 8.1
Microscopic morphologies of the typical device cross sections
Hz, 4H), 7.08 ~ 6.81 (m, 36H), 3.68 (s, 24H). 13C NMR (126 MHz,
CDCl3): δ 155.77, 125.31, 124.48, 114.51, 113.25, 110.37, 77.32,
77.06, 76.81,55.54. MS: m/z 1406.55 [M+].
were characterized by scanning electron microscopy (SEM, FEI
Quanta 450). The current density–voltage (J–V) curves of PSCs were
measured under simulated AM 1.5 illumination (100 mWꢁcmꢀ2,
PECꢀL15, Peccell, Japan) using a Keithley digital source meter
(Keithley 2601, USA). IPCE values were measured as a function of
wavelength from 300 nm to 800 nm using the monochromatic light
from a system made of a xenon lamp, a monochromator, and
appropriate filters.
Characterization
1H and 13C NMR spectra were recorded on a Varian INOVA
400MHz or Varian INOVA 500MHz Spectrometer. Matrix assisted
laser desorption/ionization timeꢀofꢀflight mass spectra (MALDIꢀ
TOF) were performed on a Waters MALDI micro MX instrument.
The UVꢀVis absorbance spectra of the two HTMs in chlorobenzene
were measured with a UVꢀVis spectrophotometer (HP 8543, Hewlett
Packard, USA). The thermal analysis was performed through TGA
Acknowledgements
This work was financially supported by the National Natural
(TGA/SDT851, Switzerland) at a heating rate of 10 oC minꢀ1 in a Science Foundation of China (Grant No. 51402036), the
temperature range of 0 oC to 800 oC under nitrogen atmosphere. International Science & Technology Cooperation Program of China
Tafel measurements were employed using an electrochemical (Grant No. 2013DFA51000), and the Fundamental Research Funds
workstation (CHI 630D, Chenhua, Shanghai) with the structure of for the Central Universities (Grant No. DUT15YQ109).
FTO/HTM//FTO, with an effective working area of 1.9 cm2 and at a
scan rate of 10 mVꢁsꢀ1. Cyclic voltammetry was carried out with a Notes and references
electrochemical workstation (CHI 630D) using a conventional threeꢀ
electrode configuration. A threeꢀelectrode system consisting of a
1 W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo and S. I.
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Journal of Materials Chemistry A
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Journal of Materials Chemistry A
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DOI: 10.1039/C6TA00976J
Graphical Abstract
Two low-cost methoxyaniline-substituted dibenzofuran derivatives were synthesized
and used as hole-transport materials for efficient perovskite solar cells