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A triazatruxene-based molecular dyad for single-component organic solar cells

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A triazatruxene-based molecular dyad for single-component organic solar cells

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The synthesis, characterization and use of a new donor-acceptor molecular dyad in single component organic solar cells are reported. The dyad, composed of a triazatruxene-based push-pull 'donor' unit linked to a C60 'acceptor' unit through a non-conjugated σ connector, led to promising power conversion efficiencies of 0.6% when embedded in simple devices exhibiting the architecture: indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS)/dyad/Al.
Article
doi: 10.28954/2018.csq.10.001 1
A triazatruxene-based molecular dyad for
single-component organic solar cells
Antoine Labrunie a, Giacomo Londi b, Sergey V. Dayneko c, Martin Blais a,
Sylvie Dabos-Seignon a, Gregory C. Welch c, David Beljonne b, Philippe Blanchard a,*,
Clément Cabanetos a,*
Email(s): philippe.blanchard@univ-angers.fr; clement.cabanetos@univ-angers.fr
a CNRS UMR 6200, MOLTECH-Anjou, University of Angers, 2 Bd Lavoisier, 49045 Angers, France
b Chimie des Matériaux Nouveaux & Centre d'Innovation et de Recherche en Matériaux Polymères,
Université de Mons - UMONS / Materia Nova, Place du Parc, 20, B-7000 MONS
c Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta T2N
1N4, Canada
Abstract: The synthesis, characterization and use of a new donor-acceptor molecular dyad in single
component organic solar cells are reported. The dyad, composed of a triazatruxene-based push-pull
‘donor’ unit linked to a C60 ‘acceptor’ unit through a non-conjugated σ connector, led to promising
power conversion efficiencies of 0.6% when embedded in simple devices exhibiting the architecture:
indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid
(PEDOT:PSS)/dyad/Al.
Keywords: Single component organic solar cells, triazatruxene, dyad, fullerene, organic synthesis, click
chemistry.
I. Introduction
With power conversion efficiency (PCE) now exceeding 15% for tandem architectures [1, 2] and 13% for
single layers [3], organic photovoltaics (OPV) continues to demonstrate their potential as a viable
renewable energy conversion technology [4]. To reach such high efficiencies, efforts have been devoted to
controlling the nano-morphology of the bulk heterojunction active layer, usually composed of an electron
donor (D) blended with an electron acceptor (A), via chemical and device-processing engineering [5-7].
Hence, to improve free charge-carrier generation and transport, several empirical parameters such as the
donor/acceptor (D/A) ratio, the nature of the processing solvent, different annealing conditions, and/or
the use of additives are routinely assessed and adjusted [8, 9]. However, even if the optimized morphology
is luckily achieved, the latter usually evolves leading, in general, to a drastic decrease in the device
performance.
In this context, the concept of single-component organic solar cells (SCOSCs) was introduced in the late
90’s in which the active layer is solely based on an “all-in-one” molecule built by connecting the donor
and the acceptor through a covalent linkage [10,11]. Designed to ensure efficient charge separation,
simplified device fabrication and a stable phase segregation, such molecular architectures are generally and
unfortunately impeded by high carrier recombination and low photocurrent in solar cells [12].
Consequently, with PCEs lagging behind those of blend devices, such approach has clearly been
dismissed by the organic photovoltaic community. However, trends observed from scarce examples
dealing with molecular system based on SCOSCs indicate a significant and gradual improvement in
efficiencies, from less than 0.5% to more than 2.4%, as a result of a better understanding of the structure-
properties-function relationships [13-17].
Chem2, 2018, 2-3
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Motivated by this challenging topic, we have recently reported the synthesis and characterization of a
donor-σ-acceptor molecular dyad, consisting of a triphenylamine-based push-pull π-conjugated system
linked to a fullerene (C60) through a non-conjugated σ linker (TPA-σ-C60, Figure 1) [18]. Beyond a
modest efficiency (0.4%), we have demonstrated that such a simple architecture can lead to charge
percolations within the active layer and, above all, that the simple synthetic strategy/methodology
implemented in this study can be easily extended to other building blocks with different electrochemical
and optical properties.
Figure 1. Illustration of the molecular dyads TPA-σ-C60 and TAT-σ-C60
To improve the photovoltaic efficiencies, the effect of substituting the triphenylamine electron-rich block
by a triazatruxene moiety is evaluated herein (TAT-σ-C60, Figure 1). Indeed, though barely used in OPV
[19-21], mainly as end-capping moiety, triazatruxene has already shown unique properties owing to a
perfectly flat and symmetrical -conjugated core and tunable solubility through easy modulation of the
side chains on the indole units.
II. Results and Discussion
The synthetic protocol for the preparation of the molecular dyad TAT-σ-C60 is depicted in Scheme 1.
The N-hexyl substituted triazatruxene TAT, synthesized according to reported procedures [19], was first
brominated in the presence of N-bromosuccinimide, and the thiophene unit was incorporated via reaction
with tributyl(thiophen-2-yl)stannane under Stille pallado-catalyzed conditions. The resulting compound
(TAT-T) was functionalized with a formyl moiety, which was subjected to a Knoevenagel condensation
with the CH2-activated 6-azidohexyl-2-cyanoacetate, affording the azido-functionalized push-pull
molecule TAT-σ-N3. Reaction of TAT-σ-N3 with the [6,6]-phenyl-C61 butyric acid propargyl ester C60-A
via a copper-catalyzed 1,3-dipolar Huisgen cyclo-addition finally, led to the target TAT-σ-C60 dyad.
The optical signature of the dyad, recorded in diluted dichloromethane solutions, corresponds to the
superimposition of both constituents, namely the TAT-σ-N3 and the fullerene derivative C60-A,
confirming the weak electronic coupling between these two entities in the ground state (Figure 2).
According to time-dependent density-functional theory (TD-DFT) calculations (see Supporting
Information), the broad band centered around 500 nm can be attributed to an internal charge transfer
(ICT) from the electron-rich triazatruxene moiety to the electron-withdrawing cyanoacrylate group, thus
highlighting the strong push-pull behavior of the donor part of the dyad (Figure 3).
Chem2, 2018, 2-3
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N
N
N
C
6
H
13
C
6
H
13
C
6
H
13
N
N
N
C
6
H
13
C
6
H
13
C
6
H
13
S
SnBu
3
Pd(PPh
3
)
4
Toluene
n-BuLi
DMF
THF
64 %
35 %
S
S
O
N
N
N
C
6
H
13
C
6
H
13
C
6
H
13
N
N
N
C
6
H
13
C
6
H
13
C
6
H
13
NBS
CHCl
3
DMF
73 %
Br
TAT TAT-B r TAT-T
TAT-T-C H O
Et
3
N
CHCl
3
CuBr
PMDETA
Toluene
NN
N
O
O
N
N
N
C
6
H
13
C
6
H
13
C
6
H
13
N
N
N
C
6
H
13
C
6
H
13
C
6
H
13
S
NC O
O
6
76 % 96 %
O
O
C
6
H
12
N
3
NC
S
NC
O
O
N
3
6
TAT- -N
3
TAT- -C
60
C
60
-A
O
O
Scheme 1. Synthesis of the molecular dyad TAT-σ-C60
Figure 2. UV-Vis absorption spectra of TAT-σ-C60 (purple), TAT-σ-N3 (red), and C60-A (blue)
recorded in diluted CH2Cl2 solutions (ca 1 x 10-5 M).
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Figure 3. Theoretical simulated spectrrum of TAT-σ-N3 in dichloromethane (left) and corresponding
electronic transitions (right).
The cyclic voltammogram of the dyad TAT-σ-C60, performed in dichloromethane with Bu4NPF6 as the
supporting electrolyte and exhibiting reversible oxidation and reduction waves, corresponds to the
superimposition of both the donor and the acceptor moieties contributions (Figure 4).
Figure 4. Cyclic voltammograms of TAT-σ-N3 (red), TAT-σ-C60 (purple), and the PC61BM as a
reference fullerene (blue) in 0.1 M Bu4NPF6/CH2Cl2, scan rate 100 mV s1, Pt working and counter
electrode.
In accordance with the electrochemical signature of TAT-σ-N3, a first reversible one-electron oxidation
wave, assigned to the formation of the stable radical cation of the triazatruxene push-pull block, was
recorded for TAT-σ-C60. In the negative region, the two first successive reversible reduction waves can
be attributed to the step-by-step, one-electron reduction of the fullerene moiety, as deduced from the
cyclic voltammogram of PC61BM. Finally, the third irreversible reduction process corresponds to the
formation of a radical-anion on the push-pull system, once again in agreement with the pattern recorded
for TAT-σ-N3 (Table 1 and S10).
Table 1. Electrochemical data. V vs Fc+/Fc. *irreversible process. a) EHOMO (eV) = (Onsetox + 5.1),
ELUMO (eV) = (Onsetred + 5.1) [22].
Compound Epc1
(V)
Epc2
(V)
Epc3
(V)
Epa1
(V)
Epa2
(V)
HOMO
(eV)a)
LUMO
(eV)a)
PC61BM -1.17 -1.56 -2.06 1.21* - -6.15 -4.02
T
AT-
σ
-N -1.71* - - 0.41 0.92 -5.33 -3.49
T
AT-
σ
-C60 -1.15 -1.51 -1.68* 0.38 0.92 -5.37 -4.05
Chem2, 2018, 2-3
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Frontier molecular orbitals, either simulated by quantum chemistry (see Supporting Information) or
estimated from the onset potentials of the oxidation and reduction processes, show favorable matching
between the donor (TAT-σ-N3) and the fullerene-based acceptor, a prerequisite for an efficient photo
induced electron transfer (Figure 4 and Table 1).
To evaluate the utility of the dyad as single photoactive material for organic solar cells, devices with an
architecture indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid
(PEDOT:PSS)/TAT-σ-C60/Al were fabricated and tested. Owing to its good solubility, different
processing solvents, namely 2-methyltetrahydrofuran (MeTHF), chlorobenzene (CB) and chloroform
(CF) were used to solubilize TAT-σ-C60. It turns out that in the same conditions of concentration and
deposition spin-speed, i.e., 10 mg mL-1 and 4000 rpm respectively, the best quality films, and therefore
best efficiencies, were obtained from chloroform solutions (Table S1). Power conversion efficiencies of
ca 0.41 %, 0.22% and 0.01% were indeed obtained when the dyad is processed with CF, the CB and the
MeTHF respectively.
To gain further insights, the corresponding nano-scale morphologies were investigated by atomic-force
microscopy (AFM). As shown in Figure 5, both chloroform (CF) and chlorobenzene (CB) processed
active layers showing small and homogenous nanodomains. However, with CB, a broad number of large
size defects (white spots) are noticed, which are detrimental to the device performance. On the other
hand, the surface topography of the active layer spun cast from the MeTHF solution reveals a quite
different organization with villi-like microscopic patterns characterized by a roughness of ca 21 nm vs. 0.7
nm for the other two films (not taking into account the large defects, see Supporting Information).
CF CB MeTHF
Figure 5. Surface topography images of the different active layers probed by atomic-force microscopy.
To optimize the efficiencies, the thickness dependence of the chloroform-processed active layer was then
investigated, revealing an optimum around 80 nm associated to a maximum PCE of ca 0.56 % (Table 2).
Table 2. Photovoltaic data obtained with active layers of different thicknesses
Thickness
(nm)
Voc
(V)
Jsc
(mA·cm-1)
FF
(%)
PCE
(%)
50 0.87 1.70 31.3 0.47
80 0.89 2.05 30.7 0.56
95 0.88 1.96 28.6 0.49
110 0.88 1.57 26.7 0.37
120 0.87 1.57 27.0 0.37
The corresponding current density-voltage (J-V) characteristic and the external quantum-efficiency (EQE)
spectrum, performed under monochromatic irradiation, are plotted in Figure 6.
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Figure 6. Top: J-V characteristics measured under AM 1.5 simulated solar light illumination (100
mW·cm-2) and bottom: external-quantum efficiency spectrum of the best SCOSC based on TAT-σ-C60.
In agreement with the UV-Vis experiments, the two bands at 520 nm and 420 nm can be attributed to the
contribution of the TAT-based push-pull donor, while the third one, found at 360 nm, corresponds to the
photon-to-current conversion of the fullerene derivative.
III. Conclusions
The synthesis of an original donor-acceptor molecular dyad and its use as electroactive material for
single-component organic solar cells are demonstrated herein. Power conversion efficiencies of ca 0.6%
were indeed measured in basic and simple devices. In addition, it is noteworthy that active layers thicker
than a hundred nanometers still generate a photo-current. Although modest and still far from those of
well performing bulk heterojunction blend devices, these promising results highlight the potential of
such triazatruxene-based dyad to convert light into electricity, and hopefully, will contribute to a
continuing surge of interest in this understudied area, namely the single-component organic
photovoltaics.
Chem2, 2018, 2-3
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IV. Additional Information
Supporting information is available online. Correspondence and requests for materials should be
addressed to the corresponding author.
V. Materials and Methods
General
Ground-state DFT geometry optimizations and TD-DFT single-point calculations were carried out using
GAUSSIAN 16 [23] suite package. 6-31G** basis sets were chosen for all the atomic species. The
optimally-tuned ωB97X-D [24] exchange-correlation energy functional was used throughout the
simulations. In order to take into account solvation effects in the reproduction of the absorption spectra,
solvent dichloromethane molecules were treated as a polarizable continuum (PCM).
All reagents and chemicals from commercial sources were used without further purification. Solvents
were dried and purified using standard techniques. Column chromatography was performed with
analytical-grade solvents using Aldrich silica gel (technical grade, pore size 60 Å, 230-400 mesh particle
size). Flexible plates ALUGRAM® Xtra SIL G UV254 from MACHEREY-NAGEL were used for
TLC. Compounds were detected by UV irradiation (Bioblock Scientific) or staining with iodine, unless
otherwise stated. NMR spectra were recorded with a Bruker AVANCE III 300 (1H, 300 MHz and 13C,
75 MHz) and a Bruker AVANCE DRX 500 (1H, 500 MHz and 13C, 125 MHz). Chemical shifts are given
in ppm relative to tetramethylsilane (TMS) and the coupling constants J in Hz. Residual non-deuterated
solvent was used as an internal standard. UV-Vis absorption spectra were recorded at room temperature
on a Perkin Elmer Lambda 950 spectrometer or with a Shimadzu UV-1800. Matrix Assisted Laser
Desorption/Ionization was performed on MALDI-TOF MS BIFLEX III Bruker Daltonics
spectrometer using dithranol, DCTB or α-terthiophene as matrix. Cyclic voltammetry was performed
using a Biologic SP-150 potentiostat with positive feedback compensation in dichloromethane solutions
purchased from Carlo Erba (HPLC grade). Tetrabutylammonium hexafluorophosphate (0.1 M as
supporting electrolyte) was purchased from Sigma-Aldrich and recrystallized prior to use. Experiments
were carried out under an inert atmosphere (Ar) using a glovebox, by scanning the negative potential
first, in a one-compartment cell equipped with a platinum working microelectrode (Ø = 2 mm) and a
platinum wire as counter electrode. A silver wire immersed in 0.10 M Bu4NPF6/CH2Cl2 was used as
pseudo-reference electrode and checked against the ferrocene/ferrocenium couple (Fc/Fc+) before and
after each experiment. Atomic-force microscopy (AFM) experiments were performed using the Nano-
Observer device from CS Instrument. The topographic images were obtained at room temperature in
tapping mode. Images were processed with the Gwyddion free SPM data analysis software.
6-Azidohexyl-2-cyanoacetate and [6,6]-phenyl-C61 butyric acid propargyl ester C60-A were prepared
according to the literature [18].
Synthesis of Compounds
TAT-Br (3-Bromo-5,10,15-trihexyl-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole): A solution of
NBS (134 mg, 0.753 mmol) in DMF (7 mL) was added dropwise to a stirred mixture of TAT (500 mg,
0.836 mmol) in CHCl3 (15 mL) at 0 °C. The resulting mixture was slowly warmed up to room
temperature and stirred for an additional hour before being poured into water. The organic phase was
extracted, dried over Na2SO4 and concentrated under vacuum. The crude product was purified by
column chromatography on silica gel (eluent: Petroleum ether/Toluene 95/5 v/v) to afford TAT-Br
(415 mg, 0.613 mmol, 73.3 %) as a white solid. 1H NMR (300 MHz, CDCl3): δ 8.26 (m, 2H), 8.09 (d, J =
8.6 Hz, 1H), 7.73 (d, J = 1.7 Hz, 1H), 7.63 (dd, J = 7.7, 2.6 Hz, 2H), 7.52 – 7.29 (m, 5H), 4.95 – 4.77 (m,
6H), 2.06 – 1.85 (m, 6H), 1.27 (s, 18H), 0.85 – 0.75 (m, 9H).
TAT-T (5,10,15-Trihexyl-3-(thiophen-2-yl)-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole ): TAT-Br
(400 mg, 0.591 mmol) and Pd(PPh3)4 (41 mg, 0.035 mmol) were combined in a dry Schlenk flask and
purged several time by argon-vacuum cycles. Then, a freshly prepared tributyl(thiophen-2-yl)stannane
(276 mg, 0.236 mL, 0.740 mmol) solution in degassed toluene (40 mL) was added and the reaction
Chem2, 2018, 2-3
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mixture was stirred at 80 °C overnight. Upon cooling to room temperature, water was added (40 mL)
and the organic phase was separated. The aqueous phase was extracted with DCM. The combined
organic phases were washed over brine, dried with MgSO4 and concentrated under vacuum. The crude
was finally purified by column chromatography on silica gel (eluent: DCM/ PE 2/8 v/v) yielding TAT-
T as a pale yellow solid (140 mg, 0.206 mmol, 34.8 %). 1H NMR (300 MHz, CDCl3): δ 8.29 (d, J = 8.0
Hz, 2H), 8.25 (d, J = 8.5 Hz, 1H), 7.83 (bs, 1H), 7.62 (m, J = 9.2 Hz, 2H + 1H), 7.46 (m, J = 7.5 Hz, 2H
+ 1H), 7.39 – 7.30 (m, 1H + 2H), 7.17 (dd, J = 4.8, 3.7 Hz, 1H), 4.99 – 4.86 (m, 6H), 2.08 – 1.91 (m,
6H), 1.26 (s, 18H), 0.87 – 0.77 (m, 9H).
13C NMR (76 MHz, CDCl3): δ 145.86, 141.64, 141.24, 141.13, 139.66, 139.16, 138.75, 129.29, 128.24,
124.36, 123.58, 123.24, 122.94, 122.77, 121.87, 121.69, 119.87, 118.45, 110.70, 110.62, 107.99, 103.52,
103.41, 103.35, 47.22, 47.12, 31.60, 31.57, 31.51, 29.95, 29.91, 29.82, 26.52, 26.50, 26.45, 22.62, 14.04.
TAT-CHO (5-(5,10,15-Trihexyl-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazol-3-yl)thiophene-2-
carbaldehyde): A solution of n-BuLi 1.6 M in hexanes (165 µL, 0.265 mmol) was added dropwise at -78
°C to a stirred solution of TAT-T (120 mg, 0.176 mmol) solubilized in 15 mL of dried THF. The
mixture was stirred for 30 min at this temperature before adding DMF (26 mg, 27 µL, 0.353 mmol). The
resulting mixture was stirred and allowed to warm up to room temperature overnight. The reaction was
quenched with water, extracted with DCM, washed with brine, dried over MgSO4 and concentrated
under vacuum. The crude product was purified by column chromatography on silica gel (eluent: DCM)
affording TAT-CHO (80 mg, 0.113 mmol, 64 %) as an orange solid. 1H NMR (300 MHz, CDCl3): δ
9.89 (s, 1H), 8.23 (d, J = 8.1 Hz, 1H), 8.19 (d, J = 8.2 Hz, 1H), 8.06 (d, J = 8.5 Hz, 1H), 7.72 (d, J = 4.0
Hz, 1H), 7.70 (d, J = 1.4 Hz, 1H), 7.58 (t, J = 8.2 Hz, 2H), 7.52 – 7.43 (m, 1H + 2H), 7.42 (d, J = 4.0 Hz,
1H), 7.34 (t, J = 7.5 Hz, 2H), 4.87 – 4.63 (m, 6H), 1.96 (d, J = 19.4 Hz, 6H), 1.38 – 1.13 (m, 18H), 0.89 –
0.78 (m, 9H).
TAT-σ-N3: To a stirred solution of TAT-CHO (80 mg, 0.113 mmol) and 6-Azidohexyl-2-cyanoacetate
(36 mg, 0.170 mmol) in CHCl3 (15 mL) were added 2-3 drops of Et3N. The reaction mixture was
refluxed under argon for 3 days. Then, the solvent was removed under vacuum and the residue was
purified by column chromatography on silica gel (eluent: DCM) affording TAT-σ-N3 as a red solid (98
mg, 0.109 mmol, 96.3 %). 1H NMR (300 MHz, CDCl3): δ 8.33 – 8.30 (m, 1H), 8.30 – 8.21 (m, 3H), 7.86
(d, J = 1.2 Hz, 1H), 7.80 (d, J = 4.1 Hz, 1H), 7.67 – 7.60 (m, 3H), 7.54 (d, J = 4.0 Hz, 1H), 7.51 – 7.43
(m, 2H), 7.40 – 7.31 (m, 2H), 5.00 – 4.81 (m, 6H), 4.32 (t, J = 6.6 Hz, 2H), 3.31 (t, J = 6.8 Hz, 2H), 1.99
(s, 6H), 1.87 – 1.74 (m, 2H), 1.72 – 1.60 (m, 2H), 1.52 – 1.40 (m, 4H), 1.34 – 1.16 (m, 18H), 0.84 – 0.75
(m, 9H). 13C NMR (76 MHz, CDCl3): δ 163.50, 156.77, 146.80, 141.33, 141.12, 141.01, 140.28, 139.74,
139.60, 138.58, 134.33, 127.07, 125.01, 123.91, 123.37, 123.13, 121.97, 121.71, 121.69, 120.09, 120.00,
118.73, 116.47, 110.76, 110.70, 108.27, 103.67, 103.29, 103.28, 96.79, 66.32, 51.49, 47.21, 31.59, 31.55,
31.45, 29.95, 29.83, 28.90, 28.60, 26.52, 26.36, 25.64, 22.62, 22.53, 14.10, 14.06, 14.03. HRMS (FAB):
calculated for C56H65N7O2S: 899.49, found: 899.4908
TAT-σ-C60: Five drops of N,N,N,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) dispersed in
HPLC grade toluene (50 mL) were degassed three times via the “freeze, pump and thaw” technic. This
solution was transferred using a cannula into a schlenk flask containing C60-A (68 mg, 0.073 mmol),
CuBr (5 mg) and TAT-σ-N3 (60 mg, 0.067 mmol) under an argon atmosphere. The reaction mixture was
protected from light and stirred for one night. The solvent was then removed under vacuum and the
residue was purified by chromatography on silica gel using a mixture of dichloromethane and ethyl
acetate as eluent (from 100:0 v/v to 90:10 v/v). The resulting solid was further purified by dissolution in
dichloromethane and subsequent precipitation with pentane to afford the pure expected TAT-σ-C60 (93
mg, 0.051 mmol, 76 %) as a brown red powder. 1H NMR (499 MHz, CDCl3): δ 8.33 (s, 1H), 8.29 – 8.22
(m, 3H), 7.87 (d, J = 6.9 Hz, 3H), 7.81 (d, J = 3.8 Hz, 1H), 7.68 – 7.60 (m, 4H), 7.57 – 7.42 (m, 6H),
7.39 – 7.33 (m, 2H), 5.24 (s, 2H), 5.01 – 4.84 (m, 6H), 4.38 (t, J = 7.2 Hz, 2H), 4.31 (t, J = 6.3 Hz, 2H),
2.91 – 2.80 (m, 2H), 2.56 (s, 2H), 2.24 – 2.12 (m, 2H), 2.06 – 1.89 (m, 8H), 1.82 – 1.72 (m, 2H),
1.54 – 1.47 (m, 2H), 1.47 – 1.38 (m, 2H), 1.37 – 1.31 (m, 4H), 1.30 – 1.15 (m, 14H), 0.82 (t, J = 6.6 Hz,
6H), 0.77 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3): δ 173.08, 163.45, 156.95, 148.85, 147.83,
146.89, 145.88, 145.24, 145.20, 145.18, 145.11, 145.08, 144.83, 144.78, 144.73, 144.69, 144.54, 144.46,
144.07, 143.81, 143.77, 143.16, 143.06, 143.02, 142.95, 142.25, 142.22, 142.16, 142.12, 141.41, 141.15,
141.04, 140.80, 140.37, 139.90, 139.65, 138.64, 138.09, 137.63, 136.85, 134.37, 132.22, 128.57, 128.37,
127.07, 125.15, 123.99, 123.82, 123.44, 123.17, 122.06, 121.75, 120.13, 120.05, 118.82, 116.53, 110.75,
Chem2, 2018, 2-3
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108.36, 103.81, 103.40, 96.72, 79.92, 66.22, 57.97, 51.88, 50.38, 47.25, 34.05, 33.75, 31.61, 31.58, 31.47,
30.28, 30.00, 29.86, 28.41, 26.55, 26.51, 26.40, 26.21, 25.60, 22.63, 22.55, 22.36, 14.11, 14.07, 14.04.
HRMS (FAB): calculated for C130H79N7O4S: 1833.59, found: 1833.5903
Device fabrication and testing: Pre-patterned indium-tin oxide coated glass slides of 24 x 25 x 1.1 mm3
with a sheet resistance of RS = 7 /sq were purchased from Visiontek Systems. The substrates were
washed by successive ultrasonic baths, namely diluted Deconex® 12 PA-x solution (2% in water),
acetone and isopropanol for 15 min each. Once dried under a stream of air, UV-ozone plasma treatment
(Ossila UV/Ozone cleaner E511) was performed for 15 min. A filtered aqueous solution of poly(3,4-
ethylenedioxy-thiophene)-poly(styrenesulfonate) (PEDOT:PSS; Ossila Al 4083) through a 0.45 m RC
membrane (Minisart® RC 15) was spun-cast onto the ITO surface at 5000 rpm for 40 s before being
baked at 120 °C for 30 min. The dyad TAT-σ-C60 was then spun-cast and devices were completed by the
thermal deposition of aluminum (100 nm) at a pressure of 1.5 x 105 Torr through a shadow mask
defining six cells of 27 mm2 each (13.5 mm x 2 mm). J-V curves were recorded in the dark and under
illumination using a Keithley 236 source-measure unit and a home-made acquisition program. The light
source is an AM1.5 Solar Constant 575 PV simulator (Steuernagel Lichttecknik, equipped with a metal
halogen lamp, 100 mW·cm2). The light intensity was measured by a broad-band power meter
(13PEM001, Melles Griot). EQE were performed under ambient atmosphere using a halogen lamp
(Osram) with an Action Spectra Pro 150 monochromator, a lock-in amplifier (Perkin-Elmer 7225) and a
S2281 photodiode (Hamamatsu).
VI. Conflict of Interests
The authors declare there are no conflicts of interests.
VII. Acknowledgements
The Région Pays de la Loire and the RFI LUMOMAT are thanked for the PhD grant of A. L. and the
funding of the SAMOA project (Etoile Montante 2017). Authors thank the MATRIX SFR of the
University of Angers and more precisely the ASTRAL and CARMA platforms for the characterization of
organic compounds and device preparation/characterization respectively. G. L. thanks the European
Union’s Horizon 2020 research and innovation program under Marie Sklodowska Curie Grant
agreement No.722651 (SEPOMO). The work in the Laboratory for Chemistry of Novel Materials was
supported by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la
Recherche Scientifiques de Belgique (F.R.S.- FNRS) under Grant No. 2.5020.11, as well as the Tier-1
supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under
Grant Agreement No. 1117545. D.B. is a FNRS Research Director .G. C. W. and S. V. D thank the
University of Calgary and the Canadian Foundation for Innovation for salary and solar cell equipment
support, respectively.
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Received: 30 August 2018
Accepted: 17 October 2018
Published online: 31 October 2018
ORCID ID for authors
Clément Cabanetos: 0000-0003-3781-887X
Phillippe Blanchard: 0000-0002-9408-8108
Gregory Welch: 0000-0002-3768-937X
Giacomo Londi: 0000-0001-7777-9161
Sergey Dayneko: 0000-0002-0604-6099
Sylvie Dabos-Seignon: 0000-0002-7900-6354
Chem2, 2018, 2-3
11
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... The synthesis of such a compound would lead to single-materials organic solar cells (SMOSCs) characterized by a potential simplified fabrication and improved stability since the morphology of the active layer should be less subjected to phase segregation. Despite the obvious interest of this concept, only few molecular materials have been evaluated in SMOSCs and even fewer reached PCEs above 0.5% [15][16][17][18][19][20] with a maximum reported at 2.2% and 2.4% for a C 60 based dyad and a triad respectively [21,22]. ...
... In this challenging context, our group has recently reported several synthetically accessible examples of molecular dyads consisting of arylamine based donor push−pulls linked to a fullerene (C 60 ) derivative via a triazole σ-linker ( Figure 1) [20,23]. Although modest efficiencies were achieved in both cases (0.4% and 0.6% for TPA-T-C 60 and TAT-T-C 60 respectively), these preliminary results demonstrated that (i) click chemistry is an efficient, versatile and easy strategy to build such D-A architectures and (ii) charge percolation within the respective active layers is somehow possible. ...
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The synthesis and characterization of a new molecular dyad consisting of a benzodithiophene-based push-pull linked to a fullerene derivative through the use of the well-known Copper Azide-Alkyne Huisgen Cycloaddition (CuAAC) reaction is reported herein. Once fully characterized at the molecular level, single component organic solar cells were fabricated to demonstrate photon-to-electron conversion, and therefore the design principle.
... An asymmetric BTI-based molecule with boron-dipyrromethene (BODIPY) moiety was used as a donor material in BHJ OSCs [37]. Another asymmetric dyad architecture, composed of a BTI core linked with C 60 acceptor unit through a non-conjugated σ-bridge was used as an active material for SMOSCs [38]. In addition, the application of BTI-based derivatives to elaborate effective dye-sensitized solar cells has been reported [39]. ...
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The search of the novel building blocks for π-conjugated donor-acceptor (D-π-A) molecules remains an urgent task to design promising materials for organic solar cells (OSCs) and other electronic devices. Here we report on the design and synthesis of two benzotriindole (BTI) based star-shaped D-π-A small molecules, BTI(2T-DCV-Hex)3 and BTI(2T-CNA-EHex)3, end-capped with either hexyldicyanovinyl or 2-ethylhexylcyanoacetate acceptor groups. Comprehensive investigation and comparison of the optical, thermal and physicochemical properties of these molecules and their analogue with the triphenylamine (TPA) core, N(Ph-2T-DCV-Hex)3, revealed the effect of the electron-withdrawing groups and type of the donor core on their properties. The BTI-based material BTI(2T-DCV-Hex)3 differs from the amorphous TPA-based analogue by high crystallinity and blue-shifted absorption and luminescence spectra. The change of electron-withdrawing group from hexyldicyanovinyl to 2-ethylhexylcyanoacetate leads to higher energy of the lowest unoccupied molecular orbital, the increased crystallinity, the lower solubility and several times higher photoluminescence quantum yield in solutions achieving 67%. Evaluation of the photovoltaic performance of these materials in single-material OSCs and as a donor material in bulk heterojunction OSCs with PC71BM as an acceptor revealed that the devices based on BTI(2T-DCV-Hex)3 are more efficient as compared to those based on BTI(2T-CNA-EHex)3. In comparison to N(Ph-2T-DCV-Hex)3, the photovoltaic devices based on BTI(2T-DCV-Hex)3 showed the comparable performance in bulk heterojunction OSCs and two times higher performance in single-material OSCs. As a result, we conclude that the BTI core is a promising block for the design of semiconducting materials for organic photovoltaics and other related applications.
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The synthesis, characterization and use of three donor-σ-acceptor molecular dyads as organic photoactive layer are reported herein. Based on push-pull π-conjugated systems, the donor moiety is connected through a non-conjugated σ-linker to a PC61BM derived block. Three different π-connectors, constituting the push-pull unit, namely a bithiophene (BT), a thienothiophene (TT) and a cyclopentadithiophene (CPDT) units were selected to assess the impact of the chemical bridging (CPDT) or fusing (TT) on the electronic, electrochemical and therefore photovoltaic properties. Hence through a better understanding of the structure-property relationships, power conversion efficiencies exceeding the symbolic percent have been reached in single-molecule organic solar cells.
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A series of triazatruxene (TAT)-functionalized Bodipy dyes were prepared by a sequence of reactions involving either cross-coupling reactions promoted by Pd complexes or a Knoevenagel reaction leading to a vinyl linker. The new dyes show large absorption coefficients and fluorescence quantum yields as well as interesting electrochemical properties. The blue dyes of this series exhibit interesting photovoltaic effects (V(OC) = 0.83 V, J(SC) = 3.6 mA/cm(2), efficiency 0.9%) in bulk heterojunction solar cells, due to the good hole mobility imported by the TAT entity.
  • L Meng
  • Y Zhang
  • X Wan
  • C Li
  • X Zhang
  • Y Wang
  • X Ke
  • Z Xiao
  • L Ding
  • R Xia
  • H.-L Yip
  • Y Cao
  • Y Chen
Meng, L., Zhang, Y.; Wan, X., Li, C., Zhang, X., Wang, Y., Ke, X., Xiao, Z., Ding, L., Xia, R., Yip, H.-L., Cao, Y., Chen, Y., Science, 2018, 1094-1098.
  • Che X Li
  • Y Qu
  • Y Forrest
Che X., Li, Y., Qu Y., Forrest, S. R., Nature Energy, 2018, 3, 422-427.
  • W Zhao
  • S Li
  • H Yao
  • S Zhang
  • Y Zhang
  • B Yang
  • J Hou
Zhao, W., Li, S., Yao, H., Zhang, S., Zhang, Y., Yang B., Hou, J., J, Am. Chem. Soc., 2017, 139, 7148-7151.
  • S Antohe
  • S Iftimie
  • L Hrostea
  • V A Antohe
  • M Girtan
Antohe, S., Iftimie, S., Hrostea, L., Antohe V. A., Girtan, M., Thin Solid Films, 2017, 642, 219-231.
  • P M Beaujuge
  • J M J Fréchet
Beaujuge P. M., Fréchet, J. M. J., J. Am. Chem. Soc., 2011, 133, 20009-20029.
  • J Warnan
  • A El Labban
  • C Cabanetos
  • E T Hoke
  • P K Shukla
  • C Risko
  • J.-L Brédas
  • M D Mcgehee
  • P M Beaujuge
Warnan, J., El Labban, A., Cabanetos, C., Hoke, E. T., Shukla, P. K., Risko, C., Brédas, J.-L., McGehee M. D., Beaujuge, P. M., Chem. Mater., 2014, 26, 2299-2306.
  • K R Graham
  • C Cabanetos
  • J P Jahnke
  • M N Idso
  • A El Labban
  • G O Ngongang Ndjawa
  • T Heumueller
  • K Vandewal
  • A Salleo
  • B F Chmelka
  • A Amassian
  • P M Beaujuge
  • M D Mcgehee
Graham, K. R., Cabanetos, C., Jahnke, J. P., Idso, M. N., El Labban, A., Ngongang Ndjawa, G. O., Heumueller, T., Vandewal, K., Salleo, A., Chmelka, B. F., Amassian, A., Beaujuge P. M., McGehee, M. D.,, J. Am. Chem. Soc., 2014, 136, 9608-9618.
  • M T Dang
  • G Wantz
  • H Bejbouji
  • M Urien
  • O J Dautel
  • L Vignau
  • L Hirsch
Dang, M. T., Wantz, G., Bejbouji, H., Urien, M., Dautel, O. J., Vignau L., Hirsch, L., Solar Energy Materials and Solar Cells, 2011, 95, 3408-3418.
  • M T Dang
  • L Hirsch
  • G Wantz
  • J D Wuest
Dang, M. T., Hirsch, L., Wantz G., Wuest J. D., Chem. Rev., 2013, 113, 3734-3765.