Dendritic-Like Molecules Built on a Pillar[5]arene Core as Hole Transporting Materials for Perovskite Solar Cells

Article abstract of DOI:10.1002/chem.202101110

Multi-branched molecules have recently demonstrated interesting behaviour as charge-transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer-like compounds, which have been used as hole-transporting materials (HTMs) for PSCs. The performances of the solar cells containing these novel compounds have been extensively investigated. Interestingly, a positive dendritic effect has been evidenced as the hole transporting properties are improved when going from the first to the second-generation compound. The stability of the devices based on the best performing pillar[5]arene material has been also evaluated in a high-throughput ageing setup for 500 h at high temperature. When compared to reference devices prepared from spiro-OMeTAD, the behaviour is similar. An analysis of the economic advantages arising from the use of the pillar[5]arene-based material revealed however that our pillar[5]arene-based material is cheaper than the reference.

Full text of DOI:10.1002/chem.202101110

Accepted Article
Accepted Article
Title: Dendritic-like Molecules Built on a Pillar[5]arene Core as Hole
Transporting Materials for Perovskite Solar Cells
Authors: Ottavia Bettucci, Jorge Pascual, Silver-Hamill Turren-Cruz,
Andrea Cabrera-Espinoza, Wakana Matsuda, Sebastian F.
Völker, Hans Köbler, Iwona Nierengarten, Gianna Reginato,
Silvia Collavini, Shu Seki, Jean-Francois Nierengarten,
Antonio Abate, and Juan Luis Delgado
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202101110
Link to VoR: https://doi.org/10.1002/chem.202101110
01/2020

10.1002/chem.202101110
Chemistry - A European Journal
FULL PAPER
Dendritic-like Molecules Built on a Pillar[5]arene Core as Hole
Transporting Materials for Perovskite Solar Cells
Ottavia Bettucci,[a,b,c]Jorge Pascual,[d] Silver-Hamill Turren-Cruz,[d] Andrea Cabrera-Espinoza,[e]
Wakana Matsuda,[f] Sebastian F. Völker,[e] Hans Köbler,[d] Iwona Nierengarten,[g] Gianna Reginato,[a]
Silvia Collavini,*[e] Shu Seki,*[f] Jean-François Nierengarten,*[g] Antonio Abate,*[d,h] and Juan Luis
Delgado*[e,i]
In memory of Prof. François Diederich
[a]
Dr. O. Bettucci, Dr. G. Reginato
Institute for the Chemistry of Organometallic Compounds (ICCOM),
Consiglio Nazionale delle Ricerche (CNR),
Via Madonna del Piano 10, 50019, Sesto Fiorentino, Italy
Dr. O. Bettucci
Department of Biotechnology, Chemistry and Pharmacy, University of Siena
Via A. Moro 2, 53100, Siena, Italy
[b]
[c]
[d]
Dr. O. Bettucci
Center for Advanced Biomaterials for Healthcare, Istituto Italiano di Tecnologia
Largo Barsanti e Matteucci 53, Naples 80125, Italy
Dr. J. Pascual, Dr. S.-H. Turren-Cruz, H. Köbler, Prof. A. Abate
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH,
Hahn-Meitner-Platz 1, 14109 Berlin, Germany
E-mail: antonio.abate@helmholtz-berlin.de
A. Cabrera-Espinoza, Dr. S. F. Völker, Dr. S. Collavini, Prof. J. L. Delgado
POLYMAT, University of the Basque Country UPV/EHU
Avenida de Tolosa 72, 20018 Donostia–San Sebastián, Spain
E-mail: juanluis.delgado@polymat.eu
[e]
E-mail: silvia.collavini@polymat.eu
[f]
Dr. W. Matsuda, Prof. S. Seki
Department of Molecular Engineering, Kyoto University
Nishikyo-ku, Kyoto 615-8510, Japan
E-mail: seki@moleng.kyoto-u.ac.jp
[g]
Dr. I. Nierengarten, Prof. Jean-François Nierengarten
Laboratoire de Chimie des Matériaux Moléculaires
Université de Strasbourg et CNRS (UMR 7402 LIMA)
Ecole Européenne de Chimie, Polymères et Matériaux
25 rue Becquerel, 67087 Strasbourg Cedex 2 France
E-mail: nierengarten@unistra.fr
[h]
[i]
Prof. A. Abate
Department of Chemical Materials and Production Engineering,
University of Naples Federico II
Piazzale Tecchio 80, 80125 Fuorigrotta, Naples, Italy
Prof. J. L. Delgado
Ikerbasque, Basque Foundation for Science
48013 Bilbao, Spain
Supporting information for this article is given via a link at the end of the document.
Abstract: Multi-branched molecules have recently demonstrated
interesting behaviour as charge-transporting materials within the
fields of perovskite solar cells (PSCs). For this reason, extended
triarylamine dendrons have been grafted onto a pillar[5]arene core to
generate dendrimer-like compounds which have been used as hole-
transporting materials (HTMs) for PSCs. The performances of the
solar cells containing these novel compounds have been extensively
from spiro-OMeTAD, the behaviour is similar. An analysis of the
economic advantages arising from the use of the pillar[5]arene-based
material revealed however that our pillar[5]arene-based material is
cheaper than the reference.
Introduction
investigated. Interestingly,
a positive dendritic effect has been
evidenced as the hole transporting properties are improved when
going from the first to the second-generation compound. The stability
of the devices based on the best performing pillar[5]arene material
has been also evaluated in a high-throughput ageing setup for 500 h
at high temperature. When compared to reference devices prepared
Owing to their high number of peripheral subunits, dendrimers
have been intensively used to generate multifunctional
nanomaterials with specific properties.[1] Typical examples are
light harvesting molecular devices mimicking the natural
1
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10.1002/chem.202101110
Chemistry - A European Journal
FULL PAPER
photosynthetic system,[2] liquid crystalline dendrimers with
unusual self-assembly properties,[3] globular polycationic systems
for gene delivery,[4] and multivalent glycoclusters for biological
applications.[5] The preparation of dendritic structures is however
often associated with a large number of synthetic steps thus
limiting their applicability. More recently, another concept
emerged for the fast preparation of dendritic-like molecules. It
relies on the peripheral functionalization of compact molecular
scaffolds such as fullerene hexa-adducts,[6] silsesquioxanes,[7] or
pillar[5]arenes.[8] In this particular case, the grafting of small
dendrons onto the multifunctional core unit already generates
globular structures even for low generation numbers.[9] Owing to
the versatile chemistry developed for the functionalization of such
molecular scaffolds,[10] a plethora of nanomaterials became easily
available for various applications at the interface of chemistry with
physics and biology.[11-15] For example, fullerene hexa-adducts
decorated with boron-dipyrromethene (bodipy) dyes have been
used as solar energy concentrators to improve the light-to-
electricity conversion of amorphous silicon photocells.[15] Multi-
branched three-dimensional hole-transporting materials (HTMs)
have been also prepared by grafting extended triarylamine (TAA)
produce which is a clear advantage for future applications.
Moreover, the pillar[5]arene core is totally transparent in the
visible region and thus parasitic light absorption by the HTM layer
should be totally prevented in the PSCs.
Results and Discussion
Synthesis. The synthesis of pillar[5]arene derivatives PA02 and
PA03 is shown in Scheme 1. Their preparation is based on the
post-functionalization of pillar[5]arene PA01[8,24] with TAA building
blocks under copper-catalyzed alkyne-azide cycloaddition
(CuAAC) conditions. The TAA derivatives bearing a terminal
alkyne group were prepared from TAA1 by adapting reported
procedures.[25] Sonogashira coupling between TAA1 and
triethylsilylacetylene followed by treatment of the resulting TAA2
with tetra-n-butylammonium fluoride (TBAF) in CH2Cl2 provided
clickable building block TAA3. The corresponding extended
derivative (TAA5) was also prepared from TAA1. A Buchwald-
Hartwig reaction between 4-[(trimethylsilyl)ethynyl]aniline and
TAA1 gave TAA4 in a moderate yield (44%). Finally, treatment
with TBAF provided terminal alkyne TAA5 in 90% yield.
Compounds PA02 and PA03 were then obtained through a 10-
fold CuAAC reaction between decaazide PA01 and the
appropriate TAA precursor (TAA5 and TAA3, respectively).
Specifically, the classical CuAAC reaction conditions developed
by Sharpless (CuSO4·5H2O, sodium ascorbate, CH2Cl2/H2O)[26]
were used to prepare PA02 and PA03. Purification by flash
column chromatography followed by recrystallization gave PA02
and PA03 in 55 and 50% yield, respectively.
residues onto
a
fullerene hexa-adduct core.[16-17] These
compounds showed interesting features as HTMs in perovskite
solar cells (PSCs).[16] In addition to high photochemical stability,
an increased number of peripheral TAA units appeared beneficial
to the performances of the photocells.[16,19-21] As part of this
research, we became interested in using a pillar[5]arene[22-23] core
to generate dendrimer-like structures with peripheral extended
TAA subunits and further investigate the potential of multimeric
systems as HTMs in PSCs. Compounds PA02 and PA03 are
depicted in Figure 1. When compared to their fullerene-based
analogues, pillar[5]arene scaffolds are by far less expensive to
OMe
N
MeO
OMe
OMe
MeO
N
MeO
OMe
OMe
N
MeO
MeO
N
MeO
OMe
OMe
OMe
OMe
MeO
MeO
MeO
OMe
N
N
N
MeO
N
N
N
N
OMe
OMe
N
N
N
MeO
N
N
N
N
OMe
MeO
N
N
N
N
N
N
N
N
N
N
OMe
OMe
N
N
N
N
N
N
N
N
N
N
N
N
OMe
OMe
N
N
N
N
N
N
O
O
N
N
N
N
O
O
O
O
MeO
O
O
O
O
O
O
MeO
O
O
N
N
MeO
MeO
O
OMe
O
N
N
N
N
O
O
O
O
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
MeO
N
N
N
N
N
N
N
N
N
N
N
N
OMe
MeO
OMe
N
N
N
MeO
MeO
N
N
N
N
OMe
OMe
OMe
N
N
N
MeO
MeO
MeO
OMe
N
MeO
MeO
N
OMe
N
OMe
OMe
MeO
MeO
N
OMe
PA03
MeO
OMe
OMe
MeO
MeO
PA02
Figure 1. Structure of the dendrimer-like pillar[5]arene derivatives PA02 and PA03.
2
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10.1002/chem.202101110
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band gap. The optical band gaps of the two compounds were
estimated through the determination of the onset wavelength of
the spectra (Table 1).
Their structure was confirmed by IR, 1H and 13C NMR
spectroscopies and MALDI-TOF mass spectrometry (Figures S1-
3). The NMR spectra of PA02 and PA03 were in full agreement
with their D5-symmetrical structure. In both cases, all the
peripheral substituents are equivalent and gave rise to a single
set of signals. The characteristic features of the pillar[5]arene core
1
were also clearly observed. In the H NMR spectra, a singlet is
seen in the aromatic region for the ten equivalent aromatic
protons of the pillar[5]arene moiety (d = 6.45 ppm for PA02 and
6.52 ppm for PA03). The structure of both compounds was further
confirmed by MALDI-TOF mass spectrometry showing the
expected molecular ion peak at m/z = 8539.6 for PA02 and 4595.6
for PA03. Importantly, mass spectrometry also provided good
evidence for the monodispersity of both compounds. Indeed, no
signals corresponding to defected by-products resulting from the
incomplete functionalization of PA01 could be observed. The
absence of unreacted azide residues was further confirmed by the
IR spectra recorded for PA02 and PA03. Effectively, the
diagnostic signature of azide units observed at 2085 cm-1 for
starting material PA01 could not be detected anymore in the case
of PA02 and PA03 (Figure S2).
MeO
R
N
(a)
(c)
MeO
MeO
TAA2 R = SiEt3
TAA3 R = H
MeO
MeO
(b)
(d)
N
Br
TAA1
N
MeO
MeO
N
R
N
TAA4 R = SiMe3
TAA5 R = H
Figure 2. (a) UV-vis spectra of PA02 and PA03 recorded in CH2Cl2 at 25°C. (b)
Cyclic voltammograms of PA02 and PA03 on a Pt electrode in CH2Cl2 + 0.1 M
[nBu4N][PF6] at a scan rate of 250 mVs-1.
MeO
N3
O
N3
O
N3
N3
O
N3
(e)
(f)
PA02
PA03
Upon excitation at their optical bandgap, PA02 and PA03 show
no clear signature of exciplexes reflecting the intramolecular
donor-acceptor (CT) interactions, and give a single fluorescence
peak with small Stokes shift at 475 and 428 nm, respectively
(Figure S4). The transient profiles of fluorescence show single
exponential decays with negligible peak shifts (Figure S5-8) both
in CH2Cl2 solutions and in thin films, showing lifetimes of 2.8 (2.2)
and 1.8 (1.2) ns, respectively (lower values were observed in thin
films). The partial suppression of the degradation reactions in
solid state is a good signal for the stability of the compounds.
The electrochemical characterization of PA02 and PA03 was
carried out by cyclic voltammetry (CV) measurements on a Pt
electrode in CH2Cl2 solution + 0.1 M [nBu4N][PF6]. The ground-
state oxidation potentials are reported in Table 1 and typical
voltammograms are shown in Figure 2b.
O
O
O
O
O
O
O
N3
N3
N3
N3
N3
PA01
Scheme 1. Preparation of compounds PA02 and PA03. Reagents and
conditions: (a) Triethylsilylacetylene, Pd(PPh3)2Cl2, CuI, PPh3, piperidine, PhMe,
90°C (76%); (b) TBAF, CH2Cl2 (90%); (c) 4-[(trimethylsilyl)ethynyl]aniline,
Pd2(dba)3, P(tBu)3, tBuONa, PhMe, D (44%); (d) TBAF, CH2Cl2 (90%); (e) TAA5,
CuSO4∙5H2O, sodium ascorbate, CH2Cl2:H2O (2:1), rt (55%); (f) TAA3,
CuSO4∙5H2O, sodium ascorbate, CH2Cl2:H2O (2:1), rt (50%).
Electronic properties. The UV-Vis spectra of both compounds
recorded in CH2Cl2 (Figure 2a) confirmed that they do not
significantly absorb light in the visible region, indicating that the
molecules would not compete with light harvesting of the
perovskite layer in a solar cell. The red-shift observed for
compound PA02 is probably induced by the superior electron-
donor ability of the extended triarylamine group bearing two
di(anisyl)amino substituents, with the consequence of enhancing
the highest occupied molecular orbital (HOMO) and reducing the
The HOMO energy levels were estimated from the oxidation
potentials in solution vs. vacuum for both molecules (Table 1).
PA02 showed higher HOMO values than the reference spiro-
OMeTAD[27] (-4.82 eV vs. vacuum, voltammograms are shown in
Figure S9 and the chemical structure in Figure 3). The lowest
unoccupied molecular orbital (LUMO) energy levels were
estimated from the difference between the HOMO and the
bandgap. These values agree with the spectroscopic analysis,
which confirm the higher HOMO energy for compound PA02, as
3
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10.1002/chem.202101110
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could be expected due to the presence of stronger electron-
donating TAA groups. This view was further supported by DFT
calculations (see the Supporting Information for details). For their
incorporation in PSCs , the HOMO level of HTM materials has to
be higher than the valence band energy of the perovskite.[21]
Importantly, this requirement is fully satisfied for both synthesized
pillar[5]arene derivatives.
Table 1: Spectroscopic and electrochemical properties of compounds PA02 and PA03
Optical Properties
Electrochemical Properties
a
d
λmax
CH2Cl2 (nm)
Egap
HOMOb
(eV)
LUMOc
(eV)
Eox
HTM
(eV)
(V)
PA02
PA03
344, 309
324, 307
3.06
3.31
–4.70
–5.01
–1.64
–1.71
–0.10
0.21
a Estimated from the onset wavelength of the UV-Vis spectra; b Estimated from the Eox against ferrocene/
ferrocenium couple of the respective redox waves by means of the following equation: HOMO = −4.8−Eox eV; c
LUMO = HOMO – Bandgap; d obtained from CV measurements and referenced internally to ferrocene.
transparent nature in the visible spectrum as well as the
appropriate HOMO levels. To evaluate their potential as HTM, the
hole mobility was examined by flash-photolysis time resolved
microwave conductivity (FP-TRMC) measurements with spiro-
OMeTAD as a reference.[30, 31] Clear and competitive signature of
electrical conductivity transients were observed for both PA02
and PA03, relative to spiro-OMeTAD, as depicted in Figure 4. The
results obtained for spiro-OMeTAD are shown in Figure S11.
MeO
OMe
N
N
N
N
MeO
MeO
OMe
OMe
MeO
OMe
spiro-OMeTAD
Figure 3. Structure of spiro-OMeTAD used as a reference compound in the
present study.
Thermal characterization. Both thermogravimetric (TGA, Figure
S10a) and differential scanning calorimetry (DSC, Figure S10b)
analyses were performed. The decomposition temperature
registered for both PA02 and PA03 (respectively, 308 and 306°C)
is lower than that registered for spiro-OMeTAD, the reference
HTM. Nonetheless, they are both far above the operational
temperature of PSCs. On the other side, the transition
temperature registered through DSC is lower for spiro-OMeTAD,
indicating that a change in the physical state may occur earlier for
the reference material. The information extrapolated from DSC
analysis might be promising for the stability of the solar cells
incorporating these materials with respect to the spiro-OMeTAD
reference.
Analysis of the Costs. One of the drawbacks of spiro-OMeTAD
is its cost. This is mainly due to the cost of the spiro moiety
precursor, 2,2′,7,7′-Tetrabromo-9,9′-spirobifluorene (155 €/g)[28]
and the low yields of the synthesis.[29] This implies that the final
cost of the reagents required to obtain 1 g of spiro-OMeTAD is
228.99 €. On the contrary, the high overall yields and the cheap
starting materials make the synthesis of the pillar[5]arene
molecules much more affordable. In fact, the cost of the
precursors required for 1 g of PA02 is calculated to be only 57.40
€. A detailed analysis of the costs can be found in the Supporting
Information (Tables S1-S4).
Figure 4. Conductivity transients observed in thin solid films of a) PA02 and b)
PA03 upon exposure at 355 nm, 9 × 1015 photons cm–2. Red and blue transients
are recorded for pristine films and those after iodine doping, respectively.
Hole transporting properties. The potential application of PA02
and PA03 as optoelectronic materials is supported by their
4
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The transients indicated 1.5-fold higher photoconductivity in PA02
than in PA03 and spiro-OMeTAD. Upon iodine doping,
remarkable enhancement of the transient conductivity was seen
in both PA02 and PA03, and recorded 2-fold higher than the
reference spiro-OMeTAD. The enhancement suggests clearly the
major contribution from photo-injected positive holes as charge
carriers. The kinetic traces after I2-doping shows initial pseudo-
first order decays for < 1 µs regime with the recombination rate
constants of 4.1 and 2.0 × 106 s-1. This gives the minimum
estimates of hole mobility as 4.0 and 2.6 × 10-4 cm2V-1s-1 for PA02
and PA03, respectively. These potential hole transporting
properties of the novel compounds further motivated us to apply
them as hole transporting layer in PSCs.
LiTFSI) yields
a
working cell, although still presenting
performance problems. It also shows that the optimum amount of
TBP is half of the equivalents of LiTFSI with respect to the relative
amount in spiro-OMeTAD, to which the recipe was adjusted.
Figure S18 includes the external quantum efficiency (EQE)
measurements for the best-performing devices, showing
integrated Jsc values comparable to the ones obtained from the J-
V curves.
The results obtained in this optimization suggest that the doping
strategy might have to be adapted to each new case depending
on the structure of the molecule to be incorporated. The best
doping conditions are summarized in Tables S5 and S6. Once
selected the best processing conditions, both HTMs were
compared to spiro-OMeTAD. As it can be seen in Figure 5a,
devices based on PA03 barely surpassed efficiencies of 10%, in
comparison to the reference devices with spiro-OMeTAD with
PCE values over 18%. However, when PA02 was used as HTM,
efficiency values around 16% were reproducibly achieved. Figure
S19 summarizes the statistic of the performances of PA02 and
PA03-containing cells. The PCE statistics are reported in Figure
5.
Incorporation into PSCs. PA02 and PA03 were both introduced
in n-i-p mesoporous PSCs to evaluate their potential as HTMs.
The novel molecules were deposited by spin-coating on top of
Cs0.05(MA0.17FA0.83 0.95
)
PbI3
perovskite
in
the
following
architecture: fluorine-doped tin oxide (FTO)-glass/c-TiO2/mp-
TiO2/perovskite/HTM/Au. Unless otherwise stated, considering
the structural similarity to spiro-OMeTAD, PA02 and PA03 were
doped with lithium trifluoromethanesulfonate (LiTFSI), 4-tert-
butylpyridine (TBP), and Co(III)TFSI (FK 209) in accordance to
their number of N-triaryl moieties (i.e. spiro has 4, PA03 10, and
PA02 30). Additional information on the processing of these
materials can be found in the Supporting Information.
Optimization of the devices required several steps. The first one
involved finding the right thickness for these HTM layers, which
were modified by spin-coating different concentrations of the
HTMs in chlorobenzene. A wide range of concentrations was
covered, finding the best device performance for PA02 and PA03
around 0.003 M, with better initial results for PA02 (Figure S12-
S13). Scanning-electron microscopy (SEM) measurements of
cells cross-sections revealed the corresponding thickness to each
of the solution concentrations used for the deposition (Figure S14).
Figure S15a shows the change in performance of the cells with
the thickness of PA02 layer, suggesting 100 nm as the optimum
thickness for this configuration.
The level of doping of the HTMs was also investigated for the
better-working HTM PA02. By varying the number of equivalents
of the dopants in the HTM solution, it was found that our current
conditions of 7.5 equivalents (with respect to spiro-OMeTAD)
were the best-performing ones (Figure S15b and S16). A
summary of the doping used for each case is included in Tables
S5 and S6. These results confirmed that the optimal equivalents
of dopants are in direct relationship with the number of N-aryl
moieties. In this sense, the equivalents used for the less-branched
PA03 were only 2.5 times in respect to spiro-OMeTAD. The
influence of the use of FK 209 was also studied, finding that
avoiding its use gave improved performance of the cells (Figure
S15c). Considering that the use of FK 209 was detrimental, it was
not used and just the influence of the other additives was
investigated. While it is a very widely employed additive, which
has shown many advantages for spiro-OMeTAD, we did not find
it beneficial for PA02. There could be reasons related to the
properties of the HTMs affecting this behaviour, although it would
also be possible to implement this additive for PA02 with further
optimization in other experimental conditions. In the same line,
Figures S15b-c, S16, and S17 show that none of the dopants is
essential for the cell to work. While using no dopant at all leads to
a non-working device, using each of them separately (i.e. TBP or
Figure 5. a) Distribution of PCE values in reverse and forward- (for) and
reverse-bias (rev) and b) Current density-voltage (J-V) curves of PSCs with
spiro-OMeTAD, PA03 and PA02 as HTMs. Reverse-bias curves are
represented as continuous lines and forward-bias curves as dashed lines.
There seems to be also no improvement in hysteresis with the use
of PA02 or PA03 in comparison to spiro-OMeTAD. Figure 5b
shows the current density-voltage (J-V) curves for both reverse
and forward scan measurements for the best performing PSCs for
each HTM. The photovoltaic (PV) parameters for these devices
5
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are listed in Table 2. The most efficient device containing PA02
showed a similar short-current density (JSC) to spiro-OMeTAD
(20.67 mA cm-2), however efficiency loss is due to both open-
circuit voltage (VOC,1.07 V) and fill factor (FF, 74.8%).
same temperature gets bigger the more elevated the temperature
is. In addition, the hysteresis increased particularly when the
devices were being aged at 45 °C, which can be observed
comparing J-V curves of spiro-OMeTAD when starting and
finishing the measurement at 45 °C. Overall, no difference can be
seen in the decrease of PCE for both HTMs at high temperatures,
therefore the higher thermal stability of PA02 in the TG and DSC
analysis (Figure S10) does not translate into higher stability of
devices at high temperature. This suggests that the thermal
properties of the HTM might not be that crucial, or at least not the
only factor, to further improve the stability of n-i-p devices. We can
see, however, clear behaviour differences for the different HTMs
at high temperature, where PA02-based devices decrease in FF,
while spiro-OMeTAD ones suffer from VOC and JSC losses. This
could then mean that the HTM nature can lead to different
degradation process types.
Table 2. Photovoltaic (PV) parameters for most efficient PSCs with spiro-
OMeTAD, PA03 and PA02 in both scan directions.
Scan
direction
JSC (mA
cm-2)
HTM
VOC (V)
FF (%)
PCE (%)
reverse
forward
reverse
forward
reverse
forward
20.77
20.73
20.51
20.11
20.67
20.63
1.13
1.09
1.06
0.99
1.07
1.05
77.9
70.4
47.2
31.6
74.8
64.5
18.21
15.86
10.24
6.31
spiro-
OMeTAD
PA03
PA02
16.56
14.01
The lower VOC value for PA02 might be related to the slight
mismatch in the HOMO energy (-4.70 eV) in comparison to PA03
(-5.01 eV) and spiro-OMeTAD values (-4.82 eV). Meanwhile, the
poor performance of cells with PA03 (up to 10.24%) is due to the
low FF values, which might be indicating a poor charge extraction
in this interface. These findings might give a hint on the relevance
of the arrangement of the hole-transporting moieties in space,
where a higher branching degree of the molecules would lead to
improved extraction and hole-transport ability. Therefore, the
results give relevant information on the guidelines to follow when
designing triarylamine-containing HTMs.
Conclusion
Two novel multi-branched molecules, PA02 and PA03, have
been synthesized and characterized. These compounds have
been used in perovskite solar cells as hole-transporting materials.
The performances of the solar devices containing these novel
compounds have been optimized carefully and compared to a
reference model compound (spiro-OMeTAD). The optimized
pillar[5]arene-containing cells afforded power conversion
efficiencies of 16.56% for PA02 and 10.24% for PA03. Since the
performances of PA02 are satisfactory enough when compared
to the 18.21% obtained with the reference spiro-OMeTAD, this
novel HTM has been also investigated in terms of stability under
heating conditions, demonstrating to be highly comparable to the
reference after 500 h. Furthermore, an analysis of the costs
required for the preparation of PA02 with respect to spiro-
OMeTAD revealed a relevant economic advantage for the
pillar[5]arene-based compound. Our design principle based on
the use of easy to functionalize molecular scaffolds is therefore
highly attractive for the preparation of new advanced materials.
Importantly, the apparent structural complexity of PA02 is not
associated to a difficult synthesis. This is a clear advantage for
future developments and this strategy will without any doubt
provide new generations of materials associating improved hole
transporting capabilities and high stability. Our groups are now
working in this direction.
Stability measurements. The stability of devices fabricated with
the more efficient PA02 as HTM were compared to the ones with
spiro-OMeTAD. A custom-built high-throughput ageing setup was
used to measure the stability for 500 h at different temperatures
of 4 devices of each type, each of them containing 6 pixels.
Stability tests were carried out at 25, 45 and 65 °C for around 160
h at each temperature in N2 atmosphere and under MPP load
conditions. Additionally, J-V scans were taken every 2 h in order
to study changes in photovoltaic parameters. Pixels showing
significantly different performances were removed from the
statistical analysis. Also, a UV-filter was applied to avoid damage
due to the sensitization of the TiO2 layer. Therefore, it should be
noted that the JSC and PCE values shown on the stability are
underestimated.
Figure 6a shows the evolution of PCE, VOC, JSC and FF at the
different temperatures for devices built with both HTMs PA02 and
spiro-OMeTAD. After a quick burn in FF for spiro-OMeTAD at the
beginning of the measurement, that is not occurring with PA02,
both device types were stable at 25 °C. However, at 45 °C the two
HTMs behaved quite differently. Devices based on PA02
presented a strong decrease in FF, while spiro-OMeTAD-
containing ones experienced a significant reduction in VOC and
JSC, parameters in which PA02 was more robust. The devices
were not very stable at 45 °C, having decreased in PCE to half of
their initial values. This degradation happened to be even more
pronounced at 65 °C, after which cells were showing inferior
performance. The enhanced decrease in performance at higher
temperatures can be observed in Figure 6b, where the difference
between J-V curves measured at the beginning and the end of the
Experimental Section
The preparation and the characterization of all the new compounds as well
as the experimental details for the mobility measurements and the device
fabrication are described in the Supporting Information.
6
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Figure 6. a) Solar cell parameters PCE, VOC, JSC and FF over ageing time for solar cells with the HTMs PA02 and Spiro-OMeTAD. Shown is the average of 11
(PA02) and 10 (spiro-OMeTAD) solar cells, error bars show the standard deviation. Ageing was performed in nitrogen with a UV-filter under continuous MPP-
tracking (MPP tracks not shown). Additionally, J-V curves were taken every 2 h with 100 mV s-1. Temperature was actively controlled and raised from 25°C to 45 °C
after 160 h of ageing and to 65 °C after 330 h. Stars mark the J-V scans shown in Figure b): Current-voltage behaviour of aged solar cells. The figure shows the
scans that were taken at the beginning (solid lines) and at the end (lines with dots) of the ageing periods with 25, 45 and 65 °C.
RED2018-102815-T and RTI 2018-101782-B-I00), the
Forschungszentrum Jülich GmbH (SolarWAVE project), the
International Center for Frontier Reserch in Chemistry and
the LabEx “Chimie des Systèmes Complexes“ is gratefully
Acknowledgements
acknowledged. S. C. and A. C.-E. acknowledge the Polymat
Foundation for a Postdoctoral and a PhD research position,
respectively.
Financial support by Ikerbasque, the Basque Foundation for
Science and the Polymat Foundation, (“Ikerbasque Research
Associate contract“ to J.-L. D.), the MICINN of Spain (grants
7
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[17] Other examples of fullerene hexa-adducts with peripheral TAA subunits
have been reported. These compounds have been used to generate 3D-
nanostructures owing to their light-induced self-assembly capabilities,
see: O. Gavat, T. M. Nguyet Trinh, E. Moulin, T. Ellis, M. Maaloum, E.
Buhler, G. Fleith, J.-F. Nierengarten, N. Giuseppone, Chem. Commun.
2018, 54, 7657-7660.
Keywords: Pillar[5]arene • Triarylamine • Hole Transporting
Material • Perovskite Solar Cells • Photovoltaics
[1]
a) G. R. Newkome, C. N. Moorefield, F. Vögtle, Dendrimers and
Dendrons: Concepts, Syntheses, Applications; Wiley-VCH: Weinheim,
Germany, 2001; b) J.M.J. Fréchet, D. A. Tomalia (Eds.), Dendrimers and
Other Dendritic Polymers; John Wiley & Sons: Chichester, UK, 2001; c)
F. Vögtle, G. Richardt, N. Werner, Dendrimer Chemistry: Concepts,
Syntheses, Properties, Applications, Wiley-VCH: Weinheim, Germany,
2009; d) A.-M. Caminade, C.-O. Turrin, R. Laurent, A. Ouali, B.
Delavaux-Nicot (Eds.), Dendrimers: Towards Catalytic, Material and
Biomedical Uses; John Wiley & Sons: Chichester, UK, 2011; e) S.
Campagna, P. Ceroni, F. Puntoriero, (Eds.), Designing dendrimers; John
Wiley & Sons: Hoboken, New Jersey, USA, 2012; f) A.-M. Caminade, C.-
O. Turrin, J.-P. Majoral,(Eds.), Phosphorous Dendrimers in Biology and
Nanomedicine: Syntheses, Characterization, and Properties, Pan
Stanford Publishing: Singapore, 2018.
[18] J. Chen, J. Xia, W.-J. Gao, H.-J. Yu, J.-X. Zhong, C. Jia, Y.-S. Qin, Z.
She, D.-B. Kuang, G. Shao, ACS Appl. Mater. Interfaces 2020, 12,
21088–21099.
[19] For a recent review on TAA materials for solar cells, see: J. Wang, K. Liu,
L. Ma, X. Zhan, Chem. Rev. 2016, 116, 14675-14725.
[20] S. Park, J. H. Heo, J. H. Yun, T. S. Jung, K. Kwak, M. J. Ko, C. H. Cheon,
J. Y. Kim, S. H. Im, H. J. Son, Chem. Sci. 2016, 7, 5517-5522.
[21] To achieve high-performance PSCs, HTMs should possess several
properties. First, their HOMO should lay higher than the valence band of
the perovskite, to effectively transport holes. Thus, the hole mobility
should also be satisfyingly high. Second, the molecules should be stable
to guarantee long-term performances. Moreover, to ensure easy
processability, they should be soluble in organic solvents and have good
film-forming properties. Finally, to avoid parasitic light absorption, they
should not absorb in the visible and near-infrared regions of the spectrum.
See: a) S. Ameen, M. A. Rub, S. A. Kosa, K. A. Alamry, M. S. Akhtar, H.-
S. Shin, H.-K. Seo, A. M. Asiri, M. K. Nazeeruddin, ChemSusChem 2016,
9, 10- 27; b) S. Collavini, J. L. Delgado, Sustainable Energy Fuels 2018,
2, 2480-2493; c) J. Urieta-Mora, I. García-Benito, A. Molina-Ontoria, N.
Martín, Chem. Soc. Rev. 2018, 47, 8541-8571; d) C. Lu, I. T. Choi, J.
Kim, H. K. Kim, J. Mater. Chem. A, 2017, 5, 20263-20276; e) M. S. Kang,
S. D. Sung, I. T. Choi, H. Kim, M. Hong, J. Kim, W. I. Lee , H. K. Kim,
ACS Appl. Mater. Interfaces, 2015, 7, 22213-22217; f) S. D. Sung, M. S.
Kang, I. T. Choi, H. M. Kim, H. Kim, M. Hong, H. K. Kim, W. I. Lee, Chem.
Commun., 2014, 50, 14161-14163; g) M. Shasti, S. F. Völker, S. Collavini,
S. Valero, F. Ruipérez, A. Mortezaali, S. M. Zakeeruddin, M. Grätzel, A.
Hagfeldt, J. L. Delgado, Org. Lett. 2019, 21, 3261-3264; h) S. Valero, S.
Collavini, S. F. Völker, M. Saliba, W. R. Tress, S. M. Zakeeruddin, M.
Grätzel, J. L. Delgado, Macromolecules 2019, 52, 2243-2254; i) N.
Marinova, S. Valero, J. L. Delgado, J. Colloid Interface Sci., 2017, 488,
373-389.
[2]
a) A. Adronov, J. M. J. Fréchet, Chem. Commun. 2000, 1701-1710; b) V.
Balzani, P. Ceroni, A. Juris, M. Venturi, S. Campagna, F. puntoriero, S.
Serroni, Coord. Chem. Rev. 2001, 219-221, 545-572.
[3]
[4]
[5]
B. M. Rosen, C. J. Wilson, D. A. Wilson, M. Peterca, M. R. Imam, V.
Percec, Chem. Rev. 2009, 109, 6275–6540.
M. Guillot-Nieckowski, S. Eisler, F. Diederich, New J. Chem. 2007, 31,
1111-1127.
a) Y. M. Chabre, R. Roy, Adv. Carbohydrate Chem. & Biochem. 2010,
63, 165-393; b) Y. M. Chabre, R. Roy, Chem. Soc. Rev. 2013, 42, 4657-
4708; c) P. Hoyos, A. Perona, O. Juanes, A. Rumbero, M. J. Hernaiz,
Chem. Eur. J. 2021, doi.org/10.1002/chem.202005065.
[6]
[7]
For reviews on fullerene hexa-adducts, see: a) A. Hirsch, O. Vostrowsky,
Eur. J. Org. Chem. 2001, 829-848; b) I. Nierengarten, J.-F. Nierengarten,
Chem. Rec. 2015, 15, 31-51.
a) Y. Gao, A. Eguchi, K. Kakehi, Y. C. Lee, Org. Lett. 2004, 6, 3457-
3460; b) Z. Ge, D. Wang, Y. Zhou, H. Liu, S. Liu, Macromolecules 2009,
42, 2903-2910; c) B. Trastoy, M. E. Pérez-Ojeda, R. Sastre, J. L. Chiara,
Chem. Eur. J. 2010, 16, 3833-3841.
[8]
[9]
For a review on clickable pillar[5]arene building blocks, see: T. Kakuta,
T. Yamagashi, T. Ogoshi, Chem. Commun. 2017, 53, 5250-5266.
a) X. Camps, H. Schönberger, A. Hirsch, Chem. Eur. J. 1997, 3, 561-
567; b) D. Sigwalt, M. Holler, J. Iehl, J.-F. Nierengarten, M. Nothisen, E.
Morin, J.-S. Remy, Chem. Commun. 2011, 47, 4640-4642; c) I.
Nierengarten, M. Nothisen, D. Sigwalt, T. Biellmann, M. Holler, J.-S.
Remy, J.-F. Nierengarten, Chem. Eur. J. 2013, 19, 17552-17558.
[22] For reviews on pillar[n]arenes, see: a) P. J. Cragg, K. Sharma, Chem.
Soc. Rev. 2012, 41, 597-607; b) M. Xue, Y. Yang, X. Chi, Z. Zhang, F.
Huang, Acc. Chem. Res. 2012, 45, 1294-1308; c) T. Ogoshi, J. Incl.
Phenom. Macrocycl. Chem. 2012, 72, 247-262; d) T. Ogoshi, T.-a.
Yamagishi, Eur. J. Org. Chem. 2013, 2961-2975; e) D. Cao, H. Meier,
Asian J. Org. Chem. 2014, 3, 244-262; f) T. Ogoshi, T. Yamagishi, Chem.
Commun. 2014, 50, 4776-4787; g) N. L. Strutt, H. Zhang, S. T.
Schneebeli, J. F. Stoddart, Acc. Chem. Res. 2014, 47, 2631-2642; h) K.
Yang, Y. Pei, Z. Pei, Chem. Commun. 2016, 52, 9316-9326; i) T. Ogoshi,
T.-a. Yamagishi, Y. Nakamoto, Chem. Rev. 2016, 116, 7937-8002.
[23] A polycationic pillar[5]arene derivative has been used in the cathode
buffer layer of PSCs, see: H. Lei, X. Chen, L. Xue, L. Sun, J. Chen, Z.
Tan, Z.-G. Zhang, Y. Li, G. Fang, Nanoscale 2018, 10, 8088-8098.
[24] a) I. Nierengarten, S. Guerra, M. Holler, J.-F. Nierengarten, R.
Deschenaux, Chem. Commun. 2012, 48, 8072-8074; b) I. Nierengarten,
S. Guerra, M. Holler, L. Karmazin-Brelot, J. Barbera, R. Deschenaux, J.-
F. Nierengarten, Eur. J. Org. Chem. 2013, 3675-3684.
[10] a) J. Iehl, R. Pereira de Freitas, B. Delavaux-Nicot, J.-F. Nierengarten,
Chem. Commun. 2008, 2450-2452; b) P. Pierrat, S. Vanderheiden, T.
Muller, S. Bräse, Chem. Commun. 2009, 1748-1750; c) J. Iehl, J. F.
Nierengarten, Chem. Eur. J. 2009, 15, 7306-7309; d) P. Pierrat, C.
Réthoré, T. Muller, S. Bräse, Chem. Eur. J. 2009, 15, 11458-11460 ; e)
J. Iehl, J.-F. Nierengarten, Chem. Commun. 2010, 46, 4160-4162.
[11] I. Nierengarten, J.-F. Nierengarten, Chem. Asian J. 2014, 9, 1436-1444.
[12] J.-F. Nierengarten, Chem. Commun. 2017, 53, 11855-11868.
[13] a) I. Nierengarten, K. Buffet, M. Holler, S. P. Vincent and J.-F.
Nierengarten, Tetrahedron Lett., 2013, 54, 2398-2402; b) G. Yu, Y. Ma,
Y. Yao, G. Tang, Z. Mao, C. Gao, F. Huang, J. Am. Chem. Soc. 2013,
135, 10310-10313; c) N. Galanos, E. Gillon, A. Imberty, S. E. Matthews,
S. Vidal, Org. Biomol. Chem. 2016, 14, 3476-3481; d) S. P. Vincent, K.
Buffet, I. Nierengarten, A. Imberty, J.-F. Nierengarten, Chem. Eur. J.
2016, 22, 88-92.
[25] a) M. Planells, A. Abate, D. J. Hollman, S. D. Stranks, V. Bharti, J. Gaur,
D. Mohanty, S. Chand, H. J. Snaith, N. Robertson, J. Mater. Chem. A
2013, 1, 6949-6960; b) C. Lambert, G. Nöll, J. Am. Chem. Soc. 1999,
121, 8434-8442.
[14] a) B. Delavaux-Nicot, H. Ben Aziza, I. Nierengarten, T. M. N. Trinh, E.
Meichsner, M. Chessé, M. Holler, R. Abidi, E. Maisonhaute, J.-F.
Nierengarten, Chem. Eur. J. 2018, 24, 133-140; b) M. Steffenhagen, A.
Latus, T. M. N. Trinh, I. Nierengarten, I. T. Lucas, S. Joiret, J. Landoulsi,
B. Delavaux-Nicot, J.-F. Nierengarten, E. Maisonhaute, Chem. Eur. J.
2018, 24, 1701-1708.
[26] a) V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless, Angew.
Chem. Int. Ed. 2002, 41, 2596-2599; Angew. Chem. 2002, 114, 2708-
2711, b) H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. Int. Ed.
2001, 40, 2004–2021; Angew. Chem. 2001, 113, 2056-2075.
[27] 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene
(spiro-OMeTAD) is the reference HTM for regular structure PSCs.
However, it is not immune to drawbacks such as its high cost, which limits
the scaling up of these solar cells, and the low long-term stability due to
the degradation processes induced by temperature, additives, film
quality and environmental conditions, see: T. A. Berhe, W.-N. Su, C.-H.
[15] J. Iehl, J.-F. Nierengarten, A. Harriman, T. Bura, R. Ziessel, J. Am.
Chem. Soc. 2012, 134, 988-998.
[16] S. F. Völker, M. Vallés-Pelarda, J. Pascual, S. Collavini, F. Ruipérez, E.
Zuccatti, L. E. Hueso, R. Tena-Zaera, I. Mora-Seró, J. L. Delgado, Chem.
Eur. J. 2018, 24, 8524-8529.
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Chen, C.-J. Pan, J.-H. Cheng, H.-M. Chen, M.-C. Tsai, L.-Y. Chen, A. A.
Dubale, B.-J. Hwang, Energy Environ. Sci. 2016, 9, 323-356.
[28] Sigma-Aldrich, 2,2′,7,7′-Tetrabromo-9,9′-spirobifluorene,
https://www.sigmaaldrich.com/catalog/product/aldrich/763888?lang=e&r
egion=ES.
[29] N. J. Jeon, H. G. Lee, Y. C. Kim, J. Seo, J. H. Noh, J. Lee, S. I. Seok, J.
Am. Chem. Soc., 2014, 136, 7837-7840.
[30] Y. Tsutsui, W. Zhang, S. Ghosh, T. Sakurai, H. Yoshida, M. Ozaki, T.
Akutagawa, S. Seki, Adv. Opt. Mater., 2020, 8, 1902158
[31] W. Zhang, T. Sakurai, M. Aotani, G. Watanabe, H. Yoshida, V. S.
Padalkar, Y. Tsutsui, D. Sakamaki, M. Ozaki, S. Seki, Adv. Opt. Mater.,
2019, 7, 1970008.
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Entry for the Table of Contents
Multi-branched three-dimensional organic molecules are an appealing class of compounds that can be employed as hole-transporting
materials in high-performance perovskite solar cells. In this work, we present two innovative pillar[5]arene-based HTMs decorated
with different triphenylamine fragments. Solar cell performances, stability, and production costs have been deeply investigated with
respect to the reference compound spiro-OMeTAD.
Institute and/or researcher Twitter usernames: @JuanLDelgadoC - @nierengarten6 - @IwonaNieren (Researchers) / @INC_CNRS -
@Unistra - @LIMA_UMR7042 - @POLYMAT_BERC (Institutions)
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