Highly selective and scalable fullerene-cation-mediated synthesis accessing cyclo[60]fullerenes with five-membered carbon ring and their application to perovskite solar cells

Article abstract of DOI:10.1021/acs.chemmater.9b02468

Cyclo[60]fullerenes are widely used in many applications including photovoltaic devices owing to their high electron affinity and mobility for an organic molecule. However, their synthesis has been limited to certain derivatives with low yields. In this work, a fullerene-cation-mediated synthesis, accessing a new class of five-membered carbon ring cyclo[60]fullerenes with high yields of up to 93% is showcased. This method utilizes aryl[60]fullerene cations, ArC₆₀ ⁺, as intermediates, which are generated in situ by heating the aryl[60]fullerenyl dimers in the presence of CuBr₂. In addition, five-membered carbon ring cyclo[60]fullerenes display excellent device applicability when they are used in perovskite solar cells as over-coating layers of electron-transporting layers. A power conversion efficiency of 20.7% is achieved owing to the favorable energy alignment, optimized substrate design, and electrochemical stability of the five-membered carbon ring fullerenes.

Full text of DOI:10.1021/acs.chemmater.9b02468

Subscriber access provided by ECU Libraries
Article
Highly Selective and Scalable Fullerene-Cation-Mediated
Synthesis accessing Cyclo[60]fullerenes with 5-Membered-
Carbon-Ring and their Application to Perovskite Solar Cells
Hao-Sheng Lin, Il Jeon, Yingqian Chen, Xiao-Yu Yang, Takafumi
Nakagawa, Shigeo Maruyama, Sergei Manzhos, and Yutaka Matsuo
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b02468 • Publication Date (Web): 11 Sep 2019
Downloaded from pubs.acs.org on September 12, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 11
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Highly Selective and Scalable Fullerene-Cation-Mediated Synthesis
accessing Cyclo[60]fullerenes with 5-Membered-Carbon-Ring and
their Application to Perovskite Solar Cells
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Hao-Sheng Lin,1 Il Jeon,*,1 Yingqian Chen,2 Xiao-Yu Yang,3 Takafumi Nakagawa,1 Shigeo
Maruyama,1,4 Sergei Manzhos,2,5 and Yutaka Matsuo*,1,3,6
1 Department of Mechanical Engineering, School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
2 Department of Mechanical Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1,
Singapore 117576, Singapore
3 Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China,
96 Jinzhai Road, Hefei, Anhui 230026, P. R. China
4 Energy NanoEngineering Laboratory, National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba, 305-8564 Japan
5
Centre Énergie Matériaux Télécommunications, Institut National de la Recherche Scientifique, 1650 boulevard
Lionel-Boulet, Varennes QC J3X1S2, Canada
6 Institute of Materials Innovation, Institutes of Innovation for Future Society, Nagoya University, Furo-cho, Chikusa-
ku, Nagoya 464-8603, Japan
ABSTRACT: Cyclo[60]fullerenes are widely used in many applications including photovoltaic devices owing to their high
electron affinity and mobility for an organic molecule. However, their synthesis has been limited to certain derivatives with
low yields. In this work, a fullerene-cation-mediated synthesis, accessing a new class of 5-membered-carbon-ring
+
cyclo[60]fullerenes with high yields of up to 93% is showcased. This method utilizes aryl[60]fullerene cations, ArC60 as
intermediates, which are generated in situ by heating the aryl[60]fullerenyl dimers in the presence of CuBr2. In addition, 5-
membered-carbon-ring cyclo[60]fullerenes display excellent device applicability when they are used in perovskite solar
cells as over-coating layers of electron-transporting layers. A power conversion efficiency of 20.7% is achieved thanks to the
favorable energy alignment, optimized substrate design, and electrochemical stability of the 5-membered-carbon-ring
fullerenes.
instability.21-23 Accordingly, cyclo[60]fullerenes with a full-

INTRODUCTION
carbon-ring, such as 3-membered-carbon-rings (e.g.
PC61BM)18-20,24,25 and 6-membered-carbon-rings (e.g. ICBA,
MIF),7,26-28 have been the preferred choices for the over-
coating layers of metal oxide ETLs. Yet, cyclo[60]fullerenes
Fullerene and its derivatives have attracted much
attention owing to their versatile applicability in the fields
of photovoltaics, bioscience, and space science.1-5 In thin-
film photovoltaics, cyclo[60]fullerenes have been used as
electron acceptors in organic solar cells6-10 and as electron-
transporting layers (ETLs) in perovskite solar cells11-13. In
particular, cyclo[60]fullerenes as an over-coating layer of
metal oxide ETLs have been one of the most exploited
applications in perovskite solar cells, demonstrating a
dramatic reduction hysteresis and enhancement of the
device charge-dynamics.14-20 With respect to such
applications, heterocyclo[60]fullerene,14-19 which is one of
the most abundant types of cyclo[60]fullerene, have shown
relatively poor performance compared with full-carbon-
ring cyclo[60]fullerenes because of their electrochemical
with
a
5-membered-carbon-ring,
namely
indano[60]fullerenes, have never been demonstrated to
date.29-34 This is because the existing synthetic methods
exhibit low yields and a limited substrate scope of fullerene
derivatives.
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 11
Unless otherwise noted, all materials including dry
1
2
3
4
5
6
7
8
solvents were obtained from commercial suppliers
(Adamas-beta, TCI) and used without further purification.
C60 and PC61BM were purchased from American dye Inc.
PbI2 (99.9985%) and methylammonium iodide (MAI) was
purchased from Sigma-Aldrich Inc. Anhydrous N,N-
dimethylformamide (DMF), dimethyl sulfoxide (DMSO),
ortho-dichlorobenzene (o-DCB), and chlorobenzene (CB)
were purchased from Alfa Aesar. Spiro-MeOTAD was
purchased from Luminescence Technology Corp. (Lumtec).
SnO2 precursor solution preparation. 27.1 mg
SnCl2∙2H2O (Aldrich, >99.995%) white powder was
dissolved in 4.0 mL of anhydrous ethanol (TCI), which
was filtered by 0.22 μm syringe filter before using.
Fullerene solution preparation. 5.0 mg of
fullerene, or FIFs was dissolved in 1.0 mL anhydrous o-
DCB and then filtered by 0.22 μm syringe filter before
using.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Concept of this work. The newly generated
LUMO has unique reactivity, enabling the production of
cylclo[60]fullerenes with 5-membered-carbon-ring.
MAPbI3 precursor solution preparation. 355 mg
of PbI2, 122 mg of CH3NH3I, and 54.7 μL of DMSO
(molar ratio 1:1:1) were mixed in 490.5 μL of DMF
solution at room temperature with stirring for 1 h. The
In this work, we report a cyclo[60]fullerene synthesis
mediated by fullerene-cation intermediates, which
accesses cyclo[60]fullerenes with a 5-membered-carbon-
ring in scalable yields. The fullerene-cation-mediated
reactions can render more facile and controlled
derivatization of fullerenes than conventional fullerene-
anion-mediated or fullerene-radical-mediated reactions
(Figure 1).35-37 This is because the fullerene-cation-
mediated reaction harnesses in situ-generated fullerene
cations, which are highly reactive due to exceptionally low
energy level of the newly formed lowest unoccupied
molecular orbitals (LUMOs).38 Such high reactivity of the
intermediates leads to high selectivity, thus a scalable yield
with an excellent functional group tolerance. Accordingly,
this fullerene-cation-mediated methodology enabled the
production of rare fullerenes, indano[60]fullerene
solution was filtered through
a
0.45 μm
polytetrafluoroethylene filter prior to use.
Spiro-MeOTAD solution preparation. A solution
was prepared by mixing 85.8 mg Spiro-MeOTAD, 19.3 μL
of
a
stock solution of 520 mg mL-1 lithium
bis(trifluoromethylsulphonyl)-imide
in
anhydrous
acetonitrile, and 33.8 μL of 4-tert-butylpyridine in 1.0 mL
anhydrous chlorobenzene.
Synthesis of 5-membered-carbon ring fullerenes.
Unless otherwise noted, all reactions were performed with
dry solvents under an atmosphere of argon in flame-dried
glassware with standard vacuum-line techniques.
Synthesis of aryl bromides (1a–g).54-57 MeOH (20.0
mL) was slowly added to sodium (517.5 mg, 22.5 mmol) at
0oC. After Na completely reacted with MeOH, different
functionalized benzyl bromide (15 mmol) was added into
the resulting solution at room temperature for 5 hours.
Then, the resulting suspension was quenched by 10 mL
H2O and extracted with CH2Cl2 (10×3 mL). Combined
organic layers were dried by MgSO4, and the solvent was
removed under the reduced pressure to give a crude
product. The further separation was carried on a silica gel
column with n-hexane/ethyl acetate (10/1, v/v) as eluent,
producing 1a–g as a colorless oil.
Synthesis of Grignard reagents (2a–g). An
anhydrous tetrahydrofuran (THF) (10.0 mL) solution
of aryl bromides 1a–g (10 mmol) was slowly dropped
into polished Mg powder (360.0 mg, 15 mmol) in a
trace amount of I2 as initiator under an argon
atmosphere at 0 oC. After vigorously stirred 1 hour, the
prepared Grignard solution (2a–g) was transferred by
Schlenk operation and stocked in a Schlenk bottle. The
concentration was confirmed before using through
anhydrous titration by using menthol as titrant with a
trace amount of 1,10-phenanthroline as indicator
under an argon atmosphere.
derivatives
in
this
work.
The
synthesis
of
indano[60]fullerenes showed high yields as expected (the
highest ca. 93%). The mechanism of this new synthetic
route was investigated and discussed as well. Moreover, we
explored the device application of indano[60]fullerenes in
perovskite solar cells as 3- or 6-membered-carbon-rings18-
20,26-28,39-41
and 5-membered-heteroatom-rings14-19,42-44 have
been widely used in devices. We found that the
hydrophobicity,45-47 solubility, reorganization energy of
fullerene,48-51 and the ability to passivate the perovskite
interface52-53 were crucial in obtaining high power
conversion efficiency (PCE). Among different fullerene
derivatives synthesized in this work, indano[60]fullerene
(5a) gave a PCE of 20.7% when used as the over-coating
layer in perovskite solar cells. The obtained PCE was higher
than 19.0% and 16.5% of the reference devices in which C60
and PC61BM were used, respectively. Not only was it, the
efficiency of 20.7% stands the highest among the reported
fullerene over-coating ETL-based NH3CH3PbI3(MAPbI3)-
used perovskite solar cells.

EXPERIMENTAL SECTION
Materials.
ACS Paragon Plus Environment

Page 3 of 11
Chemistry of Materials
Synthesis of arylhydro[60]fullerenes (ArC60H,
and reference electrodes, respectively. The valence band
and Fermi levels measurements were performed using
Riken Keiki PYS-A AC-2 and Kelvin probe spectroscopy in
the air (ESA), respectively
1
3a–g). C60 (300.0 mg, 0.417 mmol) was dissolved in
anhydrous o-dichlorobenzene (o-DCB) (50.0 mL)
containing 1,3-dimethyl-2-imidazolidinone (DMI) (1.4
mL, 12.5 mmol) as co-solvent. Then, previous
synthesized Grignard reagent (2a–g) was added into
the solution at 25 oC under an argon atmosphere. After
stirring for 15 min, CH3COOH (0.1 mL, 1.75 mmol) was
added to quench the reaction and then the solvent was
evaporated in vacuo. The residue was dissolved in CS2
and purified through a silica gel column via
CS2/CH2Cl2 as the eluent to afford product 3a–g.
Synthesis of aryl[60]fullerenyl dimers (ArC60–
C60Ar, 4a–g). Above synthesized monoadducts (3a–g)
(0.048 mmol) was dissolved in 5.0 mL anhydrous o-
DCB solution. Then, a solution of t-BuOK (58 μL, 0.058
mmol, 1M) in THF was added and vigorously stirred at
room temperature under an argon atmosphere for 15
min. Subsequently, N-bromosuccinimide (NBS) (34.2
mg, 0.192 mmol) was added. The reaction mixture was
vigorously stirred for 12 hours at room temperature
under the argon atmosphere. Then the resulting
brownish suspension was quenched by 1.0 mL H2O and
an excess amount of MeOH was added to precipitate
the crude product. Finally, titled dimers (4a–g) were
collected as a residue by filtration without necessities
of further purifications.
2
3
4
5
6
7
8
9
Device fabrication. Indium-doped tin oxide (ITO)
patterned glass substrates were cleaned and sonicated with
detergent, distilled water, acetone and isopropanol in an
ultrasonic bath for 15 min, respectively. Next, the cleaned
ITO substrates were treated with UV/O3 for 15 min.
Subsequently, 25 μL of SnO2 precursor solution was spin-
coated on the cleaned ITO substrate at 3000 rpm for 30 s,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
which was annealed at 150 C for 45 min. After cooling
down to room temperature, the spin-coating process was
repeated one more time followed by annealing at 180 oC for
1 h. Then, the SnO2 coated ITO glass was further treated
with UV/O3 for 15 min before spin-coating of fullerene
solution. 25 μL of fullerene solution was spin-coated on the
top of the SnO2 layer at 4000 rpm for 30 s. Next, 25 μL of
perovskite precursor solution was spin-coated on the
fullerene layer at 4000 rpm for 30 s, with slowly dropping
0.5 mL of anhydrous diethyl ether onto the substrate 10 s
after the start of the spin-coating process, followed up with
annealing at 100oC for 10 min. The hole transporting layer
was spin-coated from the 20 μL of Spiro-MeOTAD solution
at 4000 rpm for 20 s. Finally, a 70-nm-thick of Au anode
was fabricated by thermal deposition at a constant
evaporation rate of 0.05 nm s-1 under pressure of 10-6 Torr.
Photovoltaic characterization and measurement.
The current density vs voltage (J–V) characteristics were
Synthesis of titled FIFs (5a–g). 0.030 mmol of
dimers (4a–g) was dissolved in 10.0 mL of anhydrous
o-DCB solution in the presence of CuBr2 (26.8 mg,
0.120 mmol) as oxidant. After being vigorously stirred
measured using
a software-controlled source meter
(Keithley 2400 SourceMeter) under dark conditions and
the simulated sunlight irradiation of 1 sun (AM 1.5G; 100
mW cm-2) using a solar simulator (EMS-35AAA, Ushio Spax
Inc.) with an Ushio Xe short arc lamp 500. The source
meter was calibrated using a silicon diode (BS-520BK,
Bunkokeiki). When evaluating, devices were masked with
a black aperture to set the active area of the device to 0.1
cm2. Shimadzu IRAffinity-1s was used for the Fourier
transform infrared spectroscopy (FT-IR) measurement.
External quantum efficiency (EQE) spectra were measured
using machine spectrometer with a wavelength ranging
from 300 nm to 850 nm. Steady-state PL spectra were
measured using a photoluminescence (PL) spectrometer
(JASCO Spectrofluorometer FP-8300) with Xenon as the
excitation source (excitation at 560 nm). The detected
emission wavelength of the steady-state PL was from 675
nm to 875 nm. The water contact angle measurements
were performed using a contact angle meter (DMo-501,
Kyowa Interface Science Co., Ltd.). Scanning electron
microscopy (SEM) measurements were carried out on an
S-4800 scanning electron microscopy (Hitachi).
o
at 100 C for 3 h, the resulting mixture was directly
filtered through a silica gel plug to remove insoluble
salt and then evaporated in vacuo to remove the
solvent. Next, the residue was further separated on a
silica gel column with CS2 as eluent to afford products
5a–g.
Molecular characterization. All NMR spectra were
taken at 400 MHz (Bruker AVANCE III 400 spectrometer),
500 MHz (Bruker AVANCE III 500 spectrometer) or 600
MHz (Bruker AVANCE III 600 spectrometer). Unless
otherwise specified, all the NMR spectra were recorded in
parts per million (ppm, scale) with the proton of CDCl3
(7.260 ppm) or the proton of 1,1,2,2-tetrachloroethane-d2
1
(TCE-d2) (6.000 ppm) for H NMR and carbon of CDCl3
13
(77.16 ppm) or carbon of TCE-d2 (73.78 ppm) for C NMR
as internal reference, respectively. The data were presented
as following order: chemical shift, multiplicity (s = singlet,
d = doublet, t = triplet, hept = heptet, m = multiplet and/or
multiplet resonances), coupling constant in hertz (Hz),
and signal area integration in natural numbers, assignment
(italic). High-resolution mass spectra (HRMS) were
obtained by MALDI using a time-of-flight mass analyzer on
a Bruker Ultra exTOF/TOF spectrometer. Potentials in V
vs a ferrocene/ferrocenium (Fc/Fc+) couple were recorded
by cyclic voltammetry in an o-DCB solution containing
Space-charge-limited
current
(SCLC)
measurement. The structure of the ETL-only device was
ITO/Fullerenes(30 nm)/Al(80 nm). The mobility was
determined by fitting the dark current to a model of a
single-carrier SCLC, which is described by the equation,
휀 휀 휇푉2/8퐿3
o
Bu4N+CF3SO2N– (0.1 M) as supporting electrolyte at 25 C
JSCLC = 9
, where JSCLC is the current density, μ is
0
푟
with a scan rate of 0.05 V/s. Platinum disk, platinum wire,
the mobility, ε0 is the permittivity of free space, εr is the
relative permittivity of the material, L is the thickness of
and Ag/Ag+ electrodes were used as the working, counter,
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 11
the fullerenes layer, and V is the effective voltage. The substrate, 5a. This can be attributed to the poor solubility
of methoxy-substituted fullerene derivatives.63-64 In
addition, fullerene derivatives with long carbon chains as
the R2 functional group were synthesized, because long
carbon chains on fullerenes are known to enhance the
solubility.65-67 Hexyl substituted derivative (5e) and 2-
ethylhexyl substituted derivative (5f) were produced in
yields of 56% and 41%, respectively (Table 1, Entry 5 and
6). Expectedly, 5e and 5f possessed high solubility that they
could be dissolved in o-DCB with saturated concentrations
1
2
3
4
5
6
7
8
thicknesses of the fullerene layer were measured using
cross-sectional SEM images. Over-coating fullerene on
SnO2 ETL layers failed to give mobility data that can
differentiate between the samples, due to the low thickness
of the over-coating fullerene layers. Therefore, we
measured a single layer of fullerene by using CS2 (25 mg
mL-1) as the solvent. The experimental dark current density
was measured under an applied voltage swept from 0 to –5
V.
Trap density and trap-filling limit voltage
measurement.58-61 Trap density (nt) and trap-filling limit
voltage (VTFL) were measured based on SCLC using charge
carrier only devices with a structure of ITO/SnO2(30
9
o
of 22.8 mg mL-1 and 28.6 mg mL-1 at 25 C, respectively.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Notably, the fullerene-cation-mediated cyclo[60]fullerene
synthetic protocol can be extended to produce 6-
membered ring derivatives. The 6-membered ring
fullerene derivative (5g) was synthesized for comparison
and its yield was 89% (Table 1, Entry 7). It should be
nm)/Fullerenes(5
nm)/MAPbI3(400
nm)/PC61BM(30
nm)/Au(60 nm). The nt and VTFL values are calculated from
푛 푒푑2/2휀 휀
highlighted
that
this
fullerene-cation-mediated
the equation, VTFL
=
푟, where e is electric charge
0
푡
(1.602×10-19 V/m), d is thickness of the active layer,
is
cyclo[60]fullerene showed a total yield of up to 87%, which
is a scalable yield.
휀
0
the vacuum permittivity (8.85×10-14 F/cm) and
is the
휀
푟
relative dielectric constant taken as 46.9.59 The
experimental dark current density was measured under an
applied voltage swept from 0 to –5 V.
Table 1. Fullerene-cation-mediated intramolecular
cyclization with versatile substratesa

RESULTS AND DISCCUSION
Arylhydro[60]fullerenes (ArC60H, 3a–g), the precursor
of aryl[60]fullerenyl dimers, were prepared by nucleophilic
addition of functionalized Grignard reagents (2a–g) in
isolated yields up to 95% (Table S1).62 It is worth noting
that 1,3-dimethyl-2-imidazolidinone (DMI) was introduced
as co-solvent instead of dimethyl sulfoxide (DMSO) or
N,N-dimethylformamide
(DMF)
to
obtain
arylhydro[60]fullerenes in high selectivity. DMI has a
planar configuration unlike DMSO or DMF, which means
that DMI can form more stable coordination to the Mg2+,
prohibiting a multi-addition. Next, the key precursors,
aryl[60]fullerenyl dimers (ArC60–C60Ar, 4a–g) were
synthesized using N-bromosuccinimide (NBS) in a high
stoichiometric yield. Such high yield comes from the fact
that NBS functions as an oxidant in the single-electron
oxidation of arylfullerenyl anions (ArC60–), which is
produced by the deprotonation of C60ArH in the presence
t
of BuOK (Table S2). Therefore, ArC60–C60Ar did not
require a laborious further purification, for example,
chromatography. Then, the reaction conditions were
optimized to heating aryl[60]fullerenyl dimer (4a) at 100 oC
in the presence of 4.0 equiv. CuBr2 under an ambient
atmosphere for 3.0 hours (Table S3). The optimized
condition produced indano[60]fullerene (5a) with a yield
of 93% (Table 1, Entry 1). Another fullerene derivative,
methyl substituted indano[60]fullerene (5b) was
synthesized and isolated in a yield of 90% (Table 1, Entry
2). To investigate the electronegativity influence of the
substituents on fullerenes, electron-donating methoxyl-
and electron-withdrawing fluoro moiety-attached
fullerene derivatives were synthesized. The corresponding
derivatives 5c and 5d gave yields of 86% and 73%,
respectively (Table 1, Entry 3 and 4). Although fullerenes
with electron-donating groups, in general, give good yields,
the yield of 5c was lower than that of the non-substituted
a Unless otherwise specified, all reactions were performed
with 0.03 mmol of 4a–g and 0.12 mmol of CuBr2 in 5.0 mL
of ortho-dichlorobenzene (o-DCB) solution at 100 oC for 3.0
h under an ambient atmosphere. b Isolated yield.
Additional experiments provide an insight into the
reaction mechanism. Two control experiments were
ACS Paragon Plus Environment

Page 5 of 11
Chemistry of Materials
conducted to explore the possibility of intramolecular
cyclization through radical pathway or cationic
Subsequently, we investigated the applicability of the
1
2
3
4
5
6
7
8
a
indano[60]fullerenes to perovskite solar cells. Energy
levels are important for the ETL application in
photovoltaics.68-70 Therefore, we conducted the cyclic
voltammograms (CVs) and photoelectron yield
spectroscopy (PYS) along with the Kelvin probe
measurement on the cyclo[60]fullerene derivatives, 5a–g,
to evaluate the LUMO levels, the highest occupied
molecular orbital (HOMO) levels, and the Fermi levels,
respectively. The CV data show that all the derivatives
possess slightly higher LUMO levels to C60, which is a
commonly used ETL for perovskite solar cells (Figure S2).
It should be mentioned that 5g, which has a 6-membered
ring, manifested an irreversible peak at its third reductive
wave, which clearly demonstrates poor electrochemical
stability compared with the other fullerene derivatives
containing a 5-membered ring. Density functional theory
(DFT) also predicts that the LUMOs of the selected
fullerene derivatives have similar energies (Figure S3 and
S4; Table S4). The PYS and the Kelvin probe data in Table
S4 show that all the fullerene derivatives have comparable
HOMO levels and Fermi levels that they are energetically
compatible as the ETL.
mechanism. When aryl[60]fullerenyl dimer 4a was heated
to 100 °C in the absence of CuBr2, the reaction produced
insoluble fullerene aggregations instead of the target
molecule 5a (Figure S1b). Similarly, when the reaction was
conducted in the presence of CuBr2 and 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO), the latter of which
is a radical scavenger, there was no trace of 5a (Figure S1c).
These additional experiments conclusively demonstrate
that the fullerene-cation-intermediate is generated by the
oxidation of fullerenyl radical in the presence of Cu[II].
Therefore, a plausible mechanism is proposed like the
following (Scheme 1): First, the radical intermediate I is
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
generated
aryl[60]fullerenyl dimers 4. Then, the radical intermediate
is further oxidized by Cu[II] to form the key
through
thermolysis
upon
heating
I
aryl[60]fullerenyl cation II. Finally, II undergoes an
intramolecular cyclization triggered by the bromide with
loss of one proton, producing the target molecule
cyclo[60]fullerenes 5.
Scheme 1. Plausible reaction mechanism of the fullerene-
cation-mediated intramolecular cyclization reaction.
Table 2. Photovoltaic parameters of the normal-type perovskite solar cells using fullerenes as the over-coating layer of ETL
under 1 sun (AM 1.5 G, 100 mW cm-2). Average values with standard deviation are obtained from 20 devices in the same
batch and the statistical analyses provided in Figure S12.
Hysteresis
Entry
Fullerenes
JSC (mA cm-2)
VOC (V)
FF
RS (Ω cm2)
RSH (Ω cm2)
PCEbest
PCEaverage
Index71
0.073
0.056
0.132
0.038
0.115
0.114
0.065
0.067
0.107
1
2
3
4
5
6
7
8
9
–
C60
PC61BM
5a
22.8 ±0.2
23.2 ±0.3
23.5 ±0.3
23.7 ±0.2
22.3 ±0.3
22.8 ±0.2
23.2 ±0.3
23.6 ±0.2
23.0 ±0.2
1.070 ±0.004
1.070 ±0.005
1.040 ±0.005
1.089 ±0.003
1.064 ±0.003
1.070 ±0.004
1.074 ±0.005
1.070 ±0.004
1.058 ±0.004
0.73 ±0.01
0.75 ±0.02
0.65 ±0.01
0.78 ±0.01
0.75 ±0.01
0.71 ±0.01
0.74 ±0.01
0.73 ±0.02
0.71 ±0.02
48.2
34.2
44.1
29.7
46.9
52.8
32.8
30.9
53.2
1.46x105
7.58x105
5.21x105
8.03x105
1.09x105
8.62x104
1.38x105
3.35x105
2.65x105
18.6%
19.0%
16.5%
20.7%
18.5%
18.6%
18.7%
18.8%
17.6%
18.1 ±0.5%
18.6 ±0.4%
16.1 ±0.3%
20.5 ±0.2%
18.0 ±0.5%
18.1 ±0.5%
18.5 ±0.2%
18.4 ±0.4%
17.2 ±0.4%
5b
5d
5e
5f
5g
We fabricated normal-type perovskite solar cells, in
which the fullerenes over-coat SnO2 (Figure 2a, S5, S6, and
S7; Table S5). Perovskite solar cells with 5a as the over-
coating layer showed the highest PCE of 20.7% with a
short-circuit current density (JSC) of 23.8 mA cm-2, an open-
circuit voltage (VOC) of 1.09 V, and a fill factor (FF) of 0.79
(Figure 2b; Table 2: Entry 4). The PCE was significantly
higher than those of the reference devices without
fullerene (18.6%), with C60 (19.0%), and PC61BM (16.5%)
(Figure 2b; Table 2: Entry 1, 2, and 3). Such higher
performance can be attributed to the higher LUMO level
of 5a (58-π system) compared with C60 (60-π system)
(Figure S2) and a passivation effect of the ether addend
(Figure 2c and S8). In addition, the photoluminescence
(PL) measurement showed a greater PL quenching of
MAPbI3 on a 5a film than that on a C60 film (Figure S9).
Moreover, the PL peak of MAPbI3 on the 5a film was more
blue-shifted than that on the C60 film, indicating more
reduced trap states at the interface between the 5a film and
MAPbI3.50 Furthermore, the space-charge limited current
(SCLC) measurement was carried out to compare 5a and
C60 films, respectively (Figure S10 and Table S6). The 5a
film possessed a similar electron mobility (4.06×10-6 cm2 Vs-
1) compared with C60 (7.25×10-6 cm2 Vs-1). Additional SCLC
experiments using charge only devices were carried out to
compare the trap density (nt) and trap-filling limit voltage
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 11
(VTFL) of the 5a- and C60- applied devices, respectively 9). We ascribe this to the hydrophobicity and subsequent
1
2
3
4
5
6
7
8
(Figure S11 and Table S7). The 5a- applied device showed
lower VTFL (0.31 V) and nt (1.00×1016 cm-3) compared with
VTFL (0.47 V) and nt (1.52×1016 cm-3) of the C60- applied
device. Accordingly, the higher FF of the 5a-based devices
is not from the electron mobility, rather from the
mentioned reduced surface trap-sites and the higher
LUMO level of 5a. The effective passivation meant that the
perovskite crystal grain size was affected by this. The
average grain size of perovskite film on the SnO2/5a is
larger than that of the bare SnO2 according to the SEM
images shown in Figure S12. It can be deduced that the
passivation effect of 5a retarded the crystal growth, which
is also reflected by the higher JSC value of the 5a-based
devices compared with the reference.70 To ascertain this,
X-ray diffraction (XRD) spectroscopy was conducted
(Figure S13 and Table S8). The tetragonal phase of
perovskite films was depicted with a dominant peak (110)
at 14.0o. The full-width at half-maximum (FWHM) of the
(110) peaks was calculated through the Debye-Scherrer
equation to estimate the crystal grain size.72 The bare
SnO2/MAPbI3 film, the SnO2/C60/MAPbI3 film, and the
SnO2/5a/MAPbI3 film showed (110) peaks with FWHM
values of 0.467, 0.463, and 0.419, respectively, indicating
that the crystal grain size of the SnO2/5a/MAPbI3 films is
the largest. Moreover, the intensity ratio of the (110) peak
to the (220) peak demonstrates the growth of the (110)-
oriented grains, which indicates the favorable hole
injection from the perovskite to hole-transporting layer.73-
poor coverage of MAPbI3 (Figure S14 and S15), less
favorable effective driving force and reorganization energy
of 5g (Table S9). Further, the CV of 5g showed an
irreversible peak at its third redox potential, which
suggests a possible cleavage of the 6-membered ring on 5g
under an operating condition. This points to the fact that
cyclo[60]fullerenes with a 6-membered-ring are not
feasible for the solar cell application, which is probably
why there has not been a report on device application of
9
cyclo[60]fullerenes with
a
6-membered-ring. It is
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
important to emphasize that the best PCE of 20.7%
obtained from the 5a-based perovskite solar cells is highly
reproducible (Figure S17) and stands by far the highest
among the reported fullerene over-coating ETL-based
MAPbI3-used perovskite solar cells (Figure S18 and Table
S10).14-20,24,25,77-87
75
The perovskite film on a SnO2/5a film presented the
greatest ratio of 1.78 compared with 1.63 and 1.67 of the
perovskite films on SnO2 and SnO2/C60, respectively.
However, not all the cyclo[60]fullerene derivatives gave
good performance. Spin-coating 5b on SnO2 resulted in
poor film coverage (Figure S14 and S15; Table 2: Entry 5).
Poor coverage led to the formation of pinholes in the ETL
as evidenced by low VOC and larger hysteresis of the JV
curves (Figure S6).76 Besides, despite 5b having a similar
structure to 5a, it possessed a lower reorganization energy,
, which accounts for the low performance due to a
decreased charge separation rate (Table S9). In the case of
5c, the fullerene could not be coated at all, due to the
intrinsic low solubility as mentioned above. The 5d film
had a problem of being too hydrophobic, because of the
attached F atom. As a result, perovskite films could not be
coated uniformly on the fullerene layer (Figure S6 and S15;
Table 2, Entry 6). Although 5e- and 5f-used devices
exhibited high JSC and VOC, their FF values were also not as
high as that of the 5a-used devices. This is because the
ether group on 5e and 5f could not passivate the perovskite
interface due probably to the steric effect of the long alkyl
chains (Figure 2e and 2f; Table 2: Entry 7 and 10).
Additionally, the reorganization energy of 5f was lower
than that of 5a (Figure S16 and Table S9). 5g has a 6-
membered-carbon-ring as opposed to the 5-membered-
carbon-rings of other fullerene derivatives tested in this
work. The device performance of the 5g-based perovskite
solar cells was not as high as the other fullerene-based
perovskite solar cells (Figure S7 and S16; Table 2: Entry
Figure 2. (a) Illustration of normal-type perovskite solar
cells structure used in this work with fullerenes as over-
coating layers. Cross-sectional SEM observations provided
in Figure S7. (b) J–V curves of selected examples: reference
(black line), PC61BM (blue line), 5a (red line). Reflective
Fourier transform infrared (FTIR) spectra of
cyclo[60]fullerenes 5a (red line) for (c) ν(C–H) and (d) ν(C–O)
,
5f (blue line) for (e) ν(C–H) and (f) ν(C–O) with and without the
presence of PbI2.

CONCLUSIONS
In summary, we report a new synthetic strategy of
cyclo[60]fullerenes using fullerene cation intermediates,
ACS Paragon Plus Environment

Page 7 of 11
Chemistry of Materials
(5) Maier, J. P.; Campbell, E. K. Fullerenes in space. Angew.
which give by far greater yields than the conventional
Chem. Int. Ed. 2017, 56, 4920-4929.
1
2
3
4
5
6
7
8
approach. We revealed the mechanism of how the in situ
aryl[60]fullerene cations function as intermediates that
enhance the selectivity of the reaction and enables a broad
substrate scope. Using the new synthetic method, various
designs of cyclo[60]fullerenes with a 5-membered-ring
were synthesized. Their device application as the ETL over-
coating layer in perovskite solar cells was demonstrated as
well, which resulted in the extremely high PCE compared
with the values reported in the literatures. We conclude
that the design of fullerene derivatives with the balance of
the solubility, high reorganization energy, and ability to
passivate the active layer interface is equally as important
as the conventional approaches of tuning the LUMO levels
for the ETL application in perovskite solar cells. We believe
(6) Zhao, G.; He, Y.; Li, Y. 6.5% Efficiency of polymer solar cells
based on poly(3-hexylthiophene) and indene-C60 bisadduct
by device optimization. Adv. Mater. 2010, 22, 4355-4358.
(7) Matsuo, Y.; Kawai, J.; Inada, H.; Nakagawa, T.; Ota, H.;
Otsubo, S.; Nakamura, E. Addition of dihydromethano group
to fullerenes to improve the performance of bulk
heterojunction organic solar cells. Adv. Mater. 2013, 25, 6266-
6269.
(8) Chen, J.-D.; Cui, C.; Li, Y.-Q.; Zhou, L.; Ou, Q.-D.; Li, C.; Li,
Y.; Tang, J.-X. Single-junction polymer solar cells exceeding
10% power conversion efficiency. Adv. Mater. 2015, 27, 1035-
1041.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(9) Jeon, I.; Delacou, C.; Nakagawa, T.; Matsuo, Y. Enhancement
of open-circuit voltage by using the 58-π silylmethyl
fullerenes in small-molecule organic solar cells. Chem. Asian
J. 2016, 11, 1268-1272.
that this communication will provide
a
better
understanding of the fullerene cation chemistry as well as
the fullerene design for device applications.
(10) Jeon, I.; Sakai, R.; Seo, S.; Morse, G. E.; Ueno, H.; Nakagawa,
T.; Qian, Y.; Maruyama, S.; Matsuo, Y. Engineering high-
performance
and
air-stable
PBTZT-stat-BDTT-8:
PC61BM/PC71BM organic solar cells. J. Mater. Chem. A 2018,
6, 5746-5751.

ASSOCIATED CONTENT
Supporting Information
(11) Castro, E.; Murillo, J.; Fernandez-Delgado, O.; Echegoyen, L.
Progress in fullerene-based hybrid perovskite solar cells. J.
Mater. Chem. C 2018, 6, 2635-2651.
The Supporting Information includes experimental details,
reaction
mechanism,
morphology
investigation,
computational study, 1H NMR, 13C NMR, UV-Vis spectroscopy,
PL spectroscopy, SCLC measurement and device performance
tests. The Supporting Information is available free of charge
on the ACS Publications website at DOI:
(12) Jeon, I.; Ueno, H.; Seo, S.; Aitola, K.; Nishikubo, R.; Saeki, A.;
Okada, H.; Boschloo, G.; Maruyama, S.; Matsuo, Y. Lithium-
ion endohedral fullerene (Li+@C60) dopants in stable
perovskite solar cells induce instant doping and anti-
oxidation. Angew. Chem. Int. Ed. 2018, 57, 4607-4611.
(13) Chiang, C.-H.; Wu, C.-G. Bulk heterojunction perovskite-
PCBM solar cells with high fill factor. Nature Photonics, 2016,
10, 196-200.
(14) Abrusci, A.; Stranks, S. D.; Docampo, P.; Yip, H.-L.; Jen, A. K.-
Y.; Snaith, H. J. High-performance perovskite-polymer
hybrid solar cells via electronic coupling with fullerene
monolayers. Nano Lett. 2013, 13, 3124-3128.
(15) Wojciechowski, K.; Stranks, S. D.; Abate, A.; Sadoughi, G.;
Sadhanala, A.; Kopidakis, N.; Rumbles, G.; Li, C.-Z. R.; Friend,
H.; Jen, A. K.-Y.; Snaith, H. J. Heterojunction modification for
highly efficient organic–inorganic perovskite solar cells. ACS
Nano 2014, 8, 12701-12709.
(16) Wang, C., Zhao, D. C.; Grice, R.; Liao, W.; Yu, Y.; Cimaroli,
A.; Shrestha, N.; Roland, P. J.; Chen, J.; Yu, Z.; Liu, P.; Cheng,
N.; Ellingson, R. J.; Zhao, X.; Yan, Y. Low-temperature
plasma-enhanced atomic layer deposition of tin oxide
electron selective layers for highly efficient planar perovskite
solar cells. J. Mater. Chem. A 2016, 4, 12080-12087.

AUTHOR INFORMATION
Corresponding Author
*E-mail: il.jeon@spc.oxon.org (I.J.).
*E-mail: matsuo@photon.t.u-tokyo.ac.jp (Y.M.)
Notes
The authors declare no competing financial interests.

ACKNOWLEDGMENT
We gratefully acknowledge Japan Society for the Promotion of
Science (JSPS) KAKENHI Grant Numbers JP15H05760,
JP16H02285, JP17H06609, and JP19K15669, the Research and
Education Consortium for Innovation of Advanced Integrated
Science by Japan Science and Technology (JST), and Yashima
Environment Technology Foundation for financial support.
(17) Liu, X.; Tsai, K.-W.; Zhu, Z.; Sun, Y.; Chueh, C.-C.; Jen, A. K.-

REFERENCES
Y.
A Low-temperature, solution processable tin oxide
electron-transporting layer prepared by the dual-fuel
combustion method for efficient perovskite solar cells. Adv.
Mater. Interfaces 2016, 3, 1600122.
(1) Mishra, A.; Bäuerle, P. Small molecule organic
semiconductors on the move: promises for future solar
energy technology. Angew. Chem. Int. Ed. 2012, 51, 2020-2067.
(2) Lai, Y.-Y.; Cheng, Y.-J.; Hsu, C.-S. Applications of functional
fullerene materials in polymer solar cells. Energy Environ. Sci.
2014, 7, 1866-1883.
(3) Campbell, E. K.; Holz, M.; Gerlich, D.; Maier, J. P. Laboratory
confirmation of C60+ as the carrier of two diffuse interstellar
bands. Nature 2015, 523, 322-323.
(4) Martinez, Z. S.; Castro, E.; Seong, C.-S.; Cerόn, M.R.;
Echegoyen, L.; Llano, M. Fullerene derivatives strongly
inhibit HIV-1 replication by affecting virus maturation
without impairing protease activity. Antimcrob. Agents and
Chemother. 2016, 60, 5731-5741.
(18) Kim, J.; Kim, G.; Kim, T. K.; Kwon, S.; Back, H.; Lee, J.; Lee, S.
H.; Kang, H.; Lee, K. Efficient planar-heterojunction
perovskite solar cells achieved via interfacial modification of
a sol-gel ZnO electron collection layer. J. Mater. Chem. A
2014, 2, 17291-17296.
(19) Tao, C.; Neutzner, S.; Colella, L.; Marras, S.; Kandada, A. R.
S.; Gandini, M.; Bastiani, M. D.; Pace, G.; Manna, L.; Caironi,
M.; Bertarelli, C.; Petrozza, A. 17.6% stabilized efficiency in
low-temperature processed planar perovskite solar cells.
Energy Environ. Sci. 2015, 8, 2365-2370.
(20) Li, Y.; Zhao, Y.; Chen, Q.; Yang, Y. (M.); Liu, Y.; Hong, Z.; Liu,
Z.; Hsieh, Y.-T.; Meng, L.; Li, Y.; Yang, Y. Multifunctional
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 11
fullerene derivative for interface engineering in perovskite
solar cells. J. Am. Chem. Soc. 2015, 137, 15540-15547.
functionalized aryl groups onto [60]fullerene. Org. Lett.
2018, 20, 3372-3376.
1
2
3
4
5
6
7
8
(21) Yang, W.-W.; Li, Z.-J.; Li, F.-F.; Gao, X. Electrochemical and
(38) Lin, H.-S.; Matsuo, Y. Functionalization of [60]fullerene
through fullerene cation intermediates. Chem. Comm. 2018,
54, 11244-11259.
(39) Xing, Y.; Sun, C.; Yip, H. L.; Bazan, G. C.; Huang, F.; Cao, Y.
New fullerene design enables efficient passivation of surface
traps in high performance p-i-n heterojunction perovskite
solar cell. Nano Energy 2016, 26, 7-15.
(40) Meng, X.; Bai, Y.; Xiao, S.; Zhang, T.; Hu, C.; Yang, Y.; Zheng,
X.; Yang, S. Designing new fullerene derivatives as electron
transporting materials for efficient perovskite solar cells with
improved moisture resistance. Nano Energy 2016, 30, 341-
346.
(41) Heo, J. H.; Han, H. J.; Kim, D.; Ahn, T. K.; Im, S. H.
Hysteresis-less inverted CH3NH3PbI3 planar perovskite
hybrid solar cells with 18.1% power conversion efficiency.
Energy Environ. Sci. 2015, 8, 1602-1608.
(42) Zhu, Z.; Chueh, C.-C.; Lin, F.; Jen, A. K. Y. Enhanced ambient
stability of efficient perovskite solar cells by employing a
modified fullerene cathode interlayer. Adv. Sci. 2016, 3,
1600027.
(43) Watson, B. L.; Rolston, N.; Bush, K. A.; Leijtens, T.; McGehee,
M. D.; Dausardt, R. H. Cross-linkable, solvent-resistant
fullerene contacts for robust and efficient perovskite solar
cells with increased JSC and VOC. ACS Appl. Mater. Interfaces,
2016, 8, 25896-25904.
H/D-labeling
study
of
oxazolino[60]fullerene
rearrangement. J. Org. Chem. 2011, 76, 1384-1389.
(22) Xiao, Y.; Zhu, S.-E.; Liu, D.-J.; Suzuki, M.; Lu, X.; Wang, G.-
W. Regioselective electrosynthesis of rare 1,2,3,16-
functionalized [60]fullerene derivatives. Angew. Chem. Int.
Ed. 2014, 53, 3006-3010.
(23) Lin, H.-S.; Matsuo, Y.; Wang, J.-J.; Wang, G.-W.
Regioselective
acylation
and
carboxylation
of
9
[60]fulleroindoline via electrochemical synthesis. Org.
Chem. Front. 2017, 4, 603-607.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(24) Xiao,W. Ke, C.; Wang, C.; Saparov, B.; Duan, H.-S.; Zhao, D.;
Xiao, Z.; Schulz, P.; Harvey, S. P.; Liao, W.; Meng, W.; Yu, Y.;
Cimaroli, A. J.; Jiang, C.-S.; Zhu, K.; Al-Jassim, M.; Fang, G.;
Mitzi, D. B.; Yan, Y. Employing lead thiocyanate additive to
reduce the hysteresis and boost the fill factor of planar
perovskite solar cells. Adv. Mater. 2016, 28, 5214-5221.
(25) Liu, K.; Chen, S.; Wu, J.; Zhang, H.; Qin, M.; Lu, X.; Tu, Y.;
Meng, Q.; Zhan, X. Fullerene derivative anchored SnO2 for
high-performance perovskite solar cells. Energy Environ. Sci.
2018, 11, 3463-3471.
(26) He, Y.; Chen, H.-Y.; Hou, J.; Li, Y. Indene−C60 bisadduct: a
new acceptor for high-performance polymer solar cells. J.
Am. Chem. Soc. 2010, 132, 1377-1382.
(27) Gil-Escrig, L.; Momblona, C.; Sessolo, M.; Bolink, H. J.
Fullerene imposed high open-circuit voltage in efficient
perovskite based solar cells. J. Mater. Chem. A 2016, 4, 3667-
3672.
(28) Xue, Q.; Bai, Y.; Liu, M.; Xia, R.; Chen, Z.; Hu, Z.; Jiang, X.-F.;
Huang, F.; Yang, S.; Matsuo, Y.; Yip, H.-L.; Cao, Y. Dual
interfacial modifications enable high performance
semitransparent perovskite solar cells with large open circuit
voltage and fill factor. Adv. Energy Mater. 2017, 7, 1602333.
(29) Bingel, C. Cyclopropanierung von fullerenen. Chem. Ber.
1993, 126, 1957-1959.
(44) Sandoval-Torrientes, R.; Pascual, J.; Garíca-Benito, I.;
Collavini, S.; Kosta, I.; Tena-Zaera, R.; Martín, N.; Delgado, J.
L. Modified fullerenes for efficient electron transport layer-
free
perovskite/fullerene
blend-based
solar
cells.
ChemSusChem 2017, 10, 2023-2029.
(45) Ruoff, R. S.; Tse, D. S.; Malhotra, R.; Lorents, D. C. Solubility
of fullerene (C60) in a variety of solvents. J. Phys. Chem. 1993,
97, 3379-3383.
(46) Makowski, M.; Czaplewski, C.; Liwo, A.; Scheraga, H. A.
Potential of mean force of association of large hydrophobic
particles: toward the nanoscale limit. J. Phys. Chem. B 2010,
114, 993-1003.
(30) Maggini, M.; Scorrano, G.; Prato, M. Addition of azomethine
ylides
to
C60:
synthesis,
characterization,
and
functionalization of fullerene pyrrolidines. J. Am. Chem. Soc.
1993, 115, 9798-9799.
(47) Zangi, R. Are buckyballs hydrophobic?. J. Phys, Chem. B 2014,
118, 12263-12270.
(31) Matsuo, Y.; Nakamura, E. Selective multiaddition of
organocopper reagents to fullerenes. Chem. Rev. 2008, 108,
3016-3028.
(32) Guldi, D. M.; lllescas, B. M.; Atienza, C. M.; Wielopolski, M.;
Martín, N. Fullerene for organic electronics. Chem. Soc. Rev.
2009, 38, 1587-1597.
(33) Liu, T.-X.; Li, F.-B.; Wang, G.-W. Synthesis of [60]fullerene-
fused tetrahydronaphthalene and indane derivatives via a
pathway switched by aluminum chloride. Org. Lett. 2011, 13,
6130-6133.
(34) Su, Y.-T.; Wang, G.-W. FeCl3-mediated cyclization of
[60]fullerene with N-benzhydryl sulfonamides under high-
speed vibration milling conditions. Org. Lett. 2013, 15, 3408-
3411.
(35) Iwashita, A.; Matsuo, Y.; Nakamura, E. AlCl3-mediated
mono-, di-, and trihydroarylation of [60]fullerene. Angew,
Chem. Int. Ed. 2007, 46, 3513-3516.
(36) Matsuo,Y.; Ogumi, K.; Zhang, Y.; Okada, H.; Nakagawa, T.;
Ueno, H.; Gocho, A.; Nakamura, E. Fullerene cation-
mediated demethylation/cyclization to give 5-and 7-
membered cyclo[60] fullerene derivatives. J. Mater. Chem. A
2017, 5, 2774-2783.
(48) Nakamura, J.; Nakayama, T.; Watanabe, S.; Aono, M.
Structural and cohesive properties of a C60 monolayer. Phys.
Rev. Lett. 2001, 87, 048301.
(49) Nápoles-durate, J. M.; Reyes-Reyes, M.; Ricardo-Chavez, J. L.;
Garibay-Alonso, R.; López-Sandoval, R. Effect of packing on
the cohesive and electronic properties of methanofullerene
crystals. Phy. Rev. B 2008, 78, 035425.
(50) Lin, H.-S.; Jeon, I.; Xiang, R.; Seo, S.; Lee, J.-W.; Li, C.; Pal, A.;
Manzhos, S.; Goorsky, M. S.; Yang, Y.; Maruyama, S.; Matsuo,
Y. Achieving high efficiency in solution-processed perovskite
solar cells using C60/C70 mixed fullerenes. ACS Appl. Mater.
Interfaces 2018, 10, 39590-39598.
(51) Santo, Y.; Jeon, I.; Yeo, K. S.; Nakagawa, T.; Matsuo, Y.
Mixture of [60] and [70]PCBM giving morphological stability
in organic solar cells. Appl. Phys. Lett. 2013, 103, 073306.
(52) Shin, Y.-C.; Wang, L.; Hsieh, H.-C.; Lin, K.-F. Effect of
fullerene passivation on the charging and discharging
behavior of perovskite solar cells: reduction of bound charges
and ion accumulation. ACS Appl. Mater. Interfaces 2018, 10,
11722-11731.
(53) Fang, Y.; Bi, C.; Wang, D.; Huang, J. The functions of
fullerenes in hybrid perovskite solar cells. ACS Energy Lett.
2017, 2, 782-794.
(54) Kobin, B.; Bianchi, F.; Halm, S.; Leistner, J.; Blumstengel, S.;
Henneberger, F.; Hecht, S. Green emission in ladder-type
(37) Yang, X.-Y.; Lin, H.-S.; Jeon, I.; Matsuo, Y. Fullerene-cation-
mediated noble-metal-free direct introduction of
ACS Paragon Plus Environment

Page 9 of 11
1
Chemistry of Materials
quarterphenyl: beyond the fluorenone-defect. Adv. Funct.
Mater. 2014, 24, 7717-7727.
derivatives for interface engineering of perovskite solar cells.
J. Mater. Chem. A 2018, 6, 21368-21378.
(55) Dai, Y.; Feng, X.; Liu, H.; Jiang, H.; Bao, M. Synthesis of 2-
naphthols via carbonylative stille coupling reaction of 2-
bromobenzyl bromides with tributylallylstannane followed
by the heck reaction. J. Org. Chem. 2011, 76, 10068-10077.
(56) Carpino, L. A.; Lin, Y. Z. Benz[f]indene. J. Org. Chem. 1990,
55, 247-250. (d) Reich, H. J.; Goldenberg, W. S.; Sanders, A.
W.; Jantzi, K. L.; Tzschucke, C. C. Amine- and ether-chelated
aryllithium reagents structure and dynamics. J. Am. Chem.
Soc. 2003, 125, 3509-3521.
(57) Kohn, W.; Sham, L. Self-consistent equations including
exchange and correlation effects. J. Phy. Rev. 1965, 140, A1133.
(58) Rose, A. Space-charge-limited currents in solids. Phys. Rev.
1955, 97, 1538.
(70) Seo, S.; Jeon, I.; Xiang, R.; Lee, C.; Zhang, H.; Tanaka, T.; Lee,
J.-W.; Suh, D.; Ogamoto, T.; Nishikubo, R.; Saeki, A.; Chiashi,
S.; Shiomi, J.; Kataura, H.; Lee, H. M.; Yang, Y.; Matsuo, Y.;
Maruyama, S. Semiconducting carbon nanotubes as crystal
growth templates and grain bridges in perovskite solar cells.
J. Mater. Chem. A 2019, 7, 12987-12992.
2
3
4
5
6
7
8
9
(71) Lee, J.-W.; Kim, S.-G.; Bae, S.-H.; Lee, D.-K.; Lin, O.; Yang, Y.;
Park, N.-G. The interplay between trap density and hysteresis
in planar heterojunction perovskite solar cells. Nano Lett.
2017, 17, 4270-4276.
(72) Hall, B. D.; Zanchet, D.; Ugarte, D. Estimating nanoparticle
size from diffraction measurements. J. Appl. Crystallogr.
2000, 33, 1335-1341.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(59) Han, Q.; Bae, S.-H.; Sun, P.; Hsieh, Y.-T.; Yang, Y. (Michael),
Rim, Y. S.; Zhao, H.; Chen, Q.; Shi, W.; Li, G.; Yang, Y. Single
crystal formamidinium lead iodide (FAPbI3): insight into the
structural, optical, and electrical properties. Adv. Mater.
2016, 28, 2253-2258.
(60) Min, H.; Kim, G.; Paik, M. J.; Lee, S.; Yang, W. S.; Jung, M.;
Seok, S. I. Stabilization of precursor solution and perovskite
layer by addition of sulfur. Adv. Energy Mater. 2019, 9,
1803476.
(73) Yin, J.; Cortecchia, D.; Krishna, A.; Chen, S.; Mathews, N.;
Grimsdale, A. C.; Soci, C. Interfacial charge transfer
anisotropy in polycrystalline lead iodide perovskite films. J.
Phys. Chem. Lett. 2015, 6, 1396-1402.
(74) Wang, Q.; Lyu, M.; Zhang, M.; Yun, J.-H.; Chen, H.; Wang, L.
Transition from the tetragonal to cubic phase of
organohalide perovskite: the role of chlorine in crystal
formation of CH3NH3PbI3 on TiO2 substrates. J. Phys. Chem.
Lett. 2015, 6, 4379-4384.
(61) Son, D.-Y.; Kim, S.-G.; Seo, J.-Y.; Lee, S.-H.; Shin, H.; Lee, D.;
Park, N.-G. Universal approach toward hysteresis-free
perovskite solar cell via defect engineering. J. Am. Chem. Soc.
2018, 140, 1358-1364.
(62) Matsuo, Y.; Iwashita, A.; Abe, Y.; Li, C.-Z.; Matsuo, K.;
Hashiguchi, M.; Nakamura, E. Regioselective synthesis of 1,4-
(75) Li, Z.; Kolodziej, C.; McCleese, C.; Wang, L.; Kovalsky, A.;
Samia, A. C.; Zhao, Y.; Burda, C. Effect of chloride
substitution on interfacial charge transfer processes in
MAPbI3 perovskite thin film solar cells: planar versus
mesoporous. Nanoscale Adv. 2019, 1, 827-833.
(76) Liu, C.; Wang, K. Du, P.; Meng, T.; Yu, X.; Cheng, S. Z. D.;
Gong, X. High performance planar heterojunction perovskite
solar cells with fullerene derivatives as the electron transport
layer. ACS Appl. Mater. Interfaces 2015, 7, 1153-1159.
(77) Tao, C.; Velden, J. V. D.; Cabau, L.; Montcada, N. F.;
Neutzner, S.; Kandada, A. R. S.; Marras, S.; Brambilla, L.;
Tommasini, M.; Xu, W.; Sorrentino, R.; Perinot, A.; Caironi,
M.; Bertarelli, C.; Palomares, E.; Petrozza, A. Fully solution-
processed n-i-p-like perovskite solar cells with planar
junction: how the charge extracting layer determines the
open-circuit voltage. Adv. Mater. 2017, 29, 1604493.
(78) Zhou, W.; Zhen, J.; Liu, Q.; Fang, Z.; Li, D.; Zhou, P.; Chen,
T.; Yang, S. Successive surface engineering of TiO2 compact
layers via dual modification of fullerene derivatives affording
hysteresis-suppressed high-performance perovskite solar
cells. J. Mater. Chem. A 2017, 5, 1724-1733.
(79) Y.-C. Wang, X. Li, L. Zhu, X. Liu, W. Zhang and J. Fang,
Efficient and hysteresis-free perovskite solar cells based on a
solution processable polar fullerene electron transport layer.
Adv. Energy Mater. 2017, 7, 1701144.
(80) Wojciechowski, K.; Ramirez, I.; Gorisse, T.; Dautel, O.;
Dasari, R.; Sakai, N.; Hardigree, J. M.; Song, S.; Marder, S.;
Riede, M.; Wantz, G.; Snaith, H. J. Cross-linkable fullerene
derivatives for solution-processed n-i-p perovskite solar
cells. ACS Energy Lett. 2016, 1, 648-653.
di(organo)[60]fullerenes
through
DMF-assisted
monoaddition of silylmethyl grignard reagents and
subsequent alkylation reaction. J. Am. Chem. Soc. 2008, 130,
15429-15436.
(63) Su, Y.-T.; Wang, Y.-L.; Wang, G.-W. Palladium-catalyzed
heteroannulation of [60]fullerene with N-(2-arylethyl)
sulfonamides via C–H bond activation. Org. Chem. Front.
2014, 1, 689-693.
(64) Zhou, D.-B.; Wang, G.-W. Synthesis of [60]fullerene-fused
tetralones via palladium-catalyzed ketone-directed sp2 C–H
activation and sp3 C–H functionalization. Adv. Synth. Catal.
2016, 358, 1548-1554.
(65) Gao, K.; Li, L.; Lai, T.; Xiao, L.; Huang, Y.; Huang, F.; Peng, J.;
Cao, Y.; Liu, F.; Russell, T. P.; Janssen, R. A. J.; Peng, X. Deep
absorbing porphyrin small molecule for high-performance
organic solar cells with very low energy losses. J. Am. Chem.
Soc. 2015, 137, 7282-7285.
(66) Cuesta, V.; Vartanian, M.; Cruz, P. d. l.; Singhal, R.; Sharma,
G. D.; Langa, F. Comparative study on the photovoltaic
characteristics of A–D–A and D–A–D molecules based on Zn-
porphyrin; a D–A–D molecule with over 8.0% efficiency. J.
Mater. Chem. A 2017, 5, 1057-1065.
(67) Tian, C.-B.; Castro, E.; Betancourt-Solis, G.; Nan, Z.-A.;
Fernandez-Delgado, O.; Jankuru, S.; Echegoyen, L. Fullerene
derivative with a branched alkyl chain exhibits enhanced
charge extraction and stability in inverted planar perovskite
solar cells. New, J. Chem. 2018, 42, 2896-2902.
(68) Azimi, H.; Ameri, T.; Zhang, H.; Hou, Y.; Quiroz, C. O. R.;
Min, J.; Hu, M.; Zhang, Z.-G.; Przybilla, T.; Matt, G. J.;
Spiecker, E.; Li, Y.; Brabec, C. J. A Universal interface layer
based on an amine-functionalized fullerene derivative with
dual functionality for efficient solution processed organic
and perovskite solar cells. Adv. Energy Mater. 2015, 5,
1401692.
(81) Dong, Y.; Li, W.; Zhang, X.; Xu, Q.; Liu, Q.; Li, C.; Bo, Z.
Highly efficient planar perovskite solar cells via interfacial
modification with fullerene derivatives. Small 2016, 12, 1098-
1104.
(82) Xu, Q.; Lu, Z.; Zhu, L.; Kou, C.; Liu, Y.; Li, C.; Meng, Q.; Li,
W.; Bo, Z. Elimination of the J–V hysteresis of planar
perovskite solar cells by interfacial modification with a
thermo-cleavable fullerene derivative. J. Mater. Chem. A
2016, 4, 17649-17654.
(83) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.;
Saliba, M.; Hörantner, M. T.; Haghighirad, A.; Sakai1, N.;
Korte, L.; Rech, B.; Johnston, M. B.; Herz1, L. M.; Snaith, H. J.
(69) Wang, H.; Cai, F.; Zhang, M.; Wang, P.; Yao, J.; Gurney, R. S.;
Li, F.; Liu, D.; Wang, T. Halogen-substituted fullerene
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 11
A mixed-cation lead mixed-halide perovskite absorber for
tandem solar cells. Science 2016, 351, 151-155.
(86) Ryu, S.; Seo, J.; Shin, S. S.; Kim, Y. C.; Jeon, N. J.; Noh, J. H.;
Seok, S. I. Fabrication of metal-oxide-free CH3NH3PbI3
perovskite solar cells processed at low temperature. J. Mater.
Chem. A 2015, 3, 3271-3275.
1
2
3
4
5
6
7
8
(84) Zhang, Y.; Wang, P.; Yu, X.; Xie, J.; Sun, X.; Wang, H.; Huang,
J.; Xu, L.; Cui, C.; Lei, M.; Yang, D. Enhanced performance
and light soaking stability of planar perovskite solar cells
using an amine-based fullerene interfacial modifier. J. Mater.
Chem. A 2016, 4, 18509-18515.
(85) Cao, T.; Wang, Z.; Xia, Y.; Song, B.; Zhou, Y.; Chen, N.; Li, Y.
Facilitating electron transportation in perovskite solar cells
via water-soluble fullerenol interlayers. ACS Appl. Mater.
Interfaces 2016, 8, 18284-18291.
(87) Ke, W.; Zhao, D.; Grice, C. R.; Cimaroli, A. J.; Ge, J.; Tao, H.;
Lei, H.; Fang, G.; Yan, Y. Efficient planar perovskite solar cells
using room-temperature vacuum-processed C60 electron
selective layers. J. Mater. Chem. A 2015, 3, 17971-17976.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

Page 11 of 11
1
2
3
Chemistry of Materials
Highly selective and scalable fullerene-cation-mediated synthesis accessing cyclo[60]fullerenes with 5-membered-
carbon-ring and their application to perovskite solar cells
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment