Impact of the arrangement of functional moieties within small molecular systems for solution processable bulk heterojunction solar cells

Article abstract of DOI:10.1039/c3nj00218g

A series of molecules based on thienofluorene derivatives as electron donating (D) and benzothiadiazole as electron accepting (A) moieties have been assembled into DAD and ADA architectures in order to investigate the influence of the way of assembling the D and A units along the conjugated backbone, on the photovoltaic performances of bulk heterojunction solar cells. It was found that the major difference in going from ADA to DAD architecture is the change in molecular organization (nematic to crystalline), which increases the charge transport mobility and probably also affects the structural organization in blends with PCBM that ultimately leads to higher photovoltaic performances.

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In a series of solution-processable small molecules, the optoelectronic and
photovoltaic properties are strongly impacted by the way of assembling the chemical
building blocks.

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ARTICLE TYPE
Impact of the arrangement of functional moieties within small molecular
systems for solution processable bulk heterojunction solar cells
Pierre-Olivier Schwartz, a Elena Zaborova, b Rony Bechara, c Patrick Lévêque,c Thomas Heiser, c
Stéphane Méry*a and Nicolas Leclerc*b
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A series of molecules based on thienofluorene derivatives as electron donating (D) and benzothiadiazole
as electron accepting (A) moieties have been assembled into a DAD and an ADA architectures in order to
investigate the influence of the way of assembling the D and A units along the conjugated backbone, on
10 the photovoltaic performances of bulk heterojunction solar cells. It was found that the major difference
from going from ADA to DAD architecture is the change of molecular organization (nematic to
crystalline) which increases the charge transport mobility and probably also affects the structural
organization in blends with PCBM that ultimately leads to higher photovoltaic performances.
acceptorꢀdonorꢀacceptor (ADA) conjugated molecules, while
maintaining the same aromatic units and approximately the same
number of double bonds. The number and nature of the
50 solubilizing alkyl chains were also kept constant in order to
minimize related changes in material properties [10,11]. The
molecules are made of dioctylfluorene (F) and benzothiadiazole
(Bz) units as electronꢀrich and electronꢀpoor moieties,
respectively, and are associated to thiophene (T) units.
55 Thieno(dialkyl)fluorene derivatives are wellꢀknown for their high
electron donating ability, their good solubility and for promoting
the formation of wellꢀordered films [13,14]. Benzothiadiazole
(Bz) is a good electron acceptor, relatively easy to synthesize and
intensively used with success for OPV applications [15].
60 Using these moieties, two different assemblies were then
designed: FTꢀTBzTꢀTF for the DAD architecture, and the reverse
TBzTꢀTFTꢀTBzT assembly for the ADA architecture. It is fair to
notice that comparable DAD molecular structures have been
reported in the literature but were used as electroluminescent
65 materials [16], chemosensors [17] or for morphological studies
[18]. The structures of the investigated molecules are presented in
figure 1.
Introduction
15 Recently, organic small molecules have attracted a great interest
for their promising photovoltaic properties [1,2]. Reported power
conversion efficiencies (PCE) of solution processed small
molecules bulk heterojunction (BHJ) solar cells have increased
considerably over the last two years reaching values over 7%
20 [3,4]. In regards to their polymer counterparts, small molecules
present some advantages. Among them are the better batchꢀtoꢀ
batch reproducibility due to their monodisperse nature and the
easier purification achievable by using classical chemical
techniques such as column chromatography and recrystallization.
25 The chemistry of organic semiconducting small molecules for
organic photovoltaic (OPV) applications is extremely dense and
diversified. Indeed, this field benefits from the remarkable
progress in synthetic organic chemistry tools allowing a wide
variety of conjugated aromatic moieties and proꢀquinoid units.
30 Unfortunately, it is very difficult to anticipate the properties of a
new class of organic semiconductors due to the lack of systematic
studies. Indeed, numerous parameters influence the
optoelectronic properties of an organic semiconductor. Some are
obvious, such as the choice of the chemical subunits that
35 constitute the material [5ꢀ9]. On the other hand some parameters
are more elusive, such as the nature and the position of
solubilizing side chains [10,11], or the way the chosen subunits
are assembled [1,12].
The purpose of this paper is to investigate how properties are
40 influenced by the way the specific moieties are assembled into a
molecular structure designed for OPV applications. A classical
molecular architecture, composed of alternating electronꢀrich
(acceptor A) and electronꢀpoor (donor D) units, known for
leading to low bandgap organic materials has been chosen as
45 model system. In the present study, the molecular structure was
modified so as to obtain donorꢀacceptorꢀdonor (DAD) or
Figure 1: Chemical structures of DAD and ADA molecules.
70
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S
N
N
Sn
Sn
S
S
S
SnMe3
S
S
Br
NBS
Br
DAD
Pd2(dba)3
P(o-tolyl)3
toluene
Pd2(dba)3
P(o-tolyl)3
toluene
CHCl3
C8H17C8H17
C8H17 C8H17
C8H17C8H17
1
2
3
S
N
N
S
C8H17
SnMe3
S
S
S
Br
Br
N
N
N
N
N
N
I
NIS
CHCl3 / AcOH
S
SnMe3
C8H17
C8H17
S
S
S
S
S
S
S
S
S
Pd2(dba)3
P(o-tolyl)3
toluene
Br
Pd2(dba)3
P(o-tolyl)3
toluene
4
5
6
7
C8H17 C8H17
Pd2(dba)3
P(o-tolyl)3
K2CO3
(HO)2B
B(OH)2
THF / H2O
ADA
Figure 2: Synthetic routes for the preparation of the molecules.
microscopy (POM) have been performed to investigate the
thermal properties of the molecules. The results reveal a very
different thermal behavior and a different type of organization for
40 both molecules. Indeed, a crystalline state is observed for the
DAD molecule, with a melting point at 134°C. On the other hand,
a nematic liquid crystal phase is observed for the ADA molecule,
as evidenced by the characteristic Schlieren texture obtained by
POM observation (Fig. 3). The nematic phase in ADA is quite
45 stable and extends up to Tiso = 206°C. At low temperatures, a
Results and discussion
Synthesis and characterizations
The molecules have been prepared using synthetic routes
presented in figure 2.
All molecules are based on the same aromatic units using
thiophene and fluorene derivatives as electronꢀrich moieties and
benzothiadiazole as electronꢀdeficient moiety. Bromofluorene
5
crystalline state, only present during the first heating ramp (Tm
=
derivative
1 is condensed by Stille reaction onto a 2ꢀ
102°C), leaves out a glassy state at low temperature, ca Tg = 38°C
10 trimethyltinthiophene to obtain the corresponding compound 2. A
subsequent bromination at the 5ꢀposition of thiophene by using
NBS in chloroform solution led to the brominated derivative 3.
The final DAD molecule is synthesized by crossꢀcoupling of
previous brominated compounds with the TBzT trimer
15 functionalized with two trimethyltin groups: 4,7ꢀbisꢀ(5ꢀ
(trimethylstannyl)thiophenꢀ2ꢀyl) benzo[1,2,5]thiadiazole [19].
The ADA molecule has been synthesized following another
synthetic route, starting from the synthesis of the unsymmetrical
bithiopheneꢀbenzothiadiazole compound 4, by Stille crossꢀ
20 coupling between the 4,7ꢀdibromobenzothiadiazole unit and 5ꢀ
trimethylstannylꢀ2,2'ꢀbithiophene [21]. After purification by
column chromatography, compound 5 is condensed to 5ꢀoctylꢀ2ꢀ
trimethylstannylthiophene [22] to give compound 6. The latter is
then iodinated by adding with 1 equivalent of NIS in a mixture of
25 chloroform and acetic acid to give the iodide compound 7.
Finally, the ADA molecule is obtained by a Suzuki crossꢀ
coupling of compound 6 and the commercially available 2,7ꢀ
diboronic acidꢀ9,9ꢀdioctylfluorene. All molecules have been
(Fig. 3).
50 Figure 3: DSC thermograms of ADA (heating and cooling run at 10 and
5°C.minꢀ1, respectively) with the image of the nematic texture as observed
by polarized optical microscopy at 100°C (inset). Once melted, the
nematic phase is limited at room temperature by a glassy state.
1
characterized by H and 13C NMR, and the final molecules were
30 additionally analyzed by MALDIꢀTOF technique (see
Experimental section).
55 Optical and electrochemical properties
UVꢀvis absorption spectra of the molecules in chloroform
solution and in thin films are given in Fig. 4. Values are presented
in Table 1.
Thermal and structural properties
Differential scanning calorimetry (DSC) and polarized optical
35
2
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of the πꢀπ* and ICT bands.
Furthermore, extinction coefficients have been measured for both
40 molecules in solution. DAD presents a slightly higher extinction
coefficient of 77000 Mꢀ1cmꢀ1 compared to 70000 Mꢀ1cmꢀ1 in the
case of ADA. This could be due to a higher molecular orbital
HOMO and LUMO overlap in the DAD molecule. In order to
better understand this specific point, we performed Density
45 Functional Theory (DFT) calculations (in vacuum) using Spartan
10 on each molecule [24]. The structures obtained for the two
molecules are presented in Fig. 5. To keep the calculation time
reasonable, the alkyl sideꢀchains were substituted by methyl
groups.
DAD
Figure 4: UVꢀvisible spectra of the molecules recorded at 10ꢀ5 mol.Lꢀ1 in
chloroform solution (straight lines), and in thin film (dashed lines). DAD
spectra in bold lines and ADA spectra in thin lines. Measurements in
films are normalized.
ADA
5
Table 1. Optical absorption properties of the molecules.
50
Figure 5: Conformation and electronic structures of the conjugated core
of molecules DAD and ADA, with the frontier molecular orbital surfaces
HOMO (left) and LUMO (right).
Solution
Solid state
Molecule
λ
max (nm)
E
opt (eV)
1.78
λ
max (nm)
[ε (M.cmꢀ1)]
392 [77000]
535 [59000]
418 [59000]
510 [70000]
405
557
412
552
DAD
ADA
The results clearly show that both the HOMO and LUMO orbitals
55 are localized in the central part of the molecule in DAD,
explaining the higher extinction coefficient measured for this
latter molecule. The HOMO orbitals in ADA are similarly
localized in the central part. In this case however, the LUMO
orbitals is more localized onto the two benzothiadiazole moieties.
60 The lower molecular orbital overlap, resulting from this
unsymmetrical nature, might therefore be responsible for the
slightly lower absorption coefficient in the ADA molecule.
Cyclic voltammetry investigations were performed in solid state
in order to measure the redox potentials and subsequently
65 determine the HOMO and LUMO energy levels of the molecules.
The redox potentials as well as the corresponding HOMO and
LUMO levels for all molecules in the solid state are summarized
in Table 2.
1.85
Both molecules exhibit a two bands feature spectrum as usually
10 observed for an alternating DꢀA molecule [23]. The high energy
band is attributed to a πꢀπ* transition while the low energy one is
ascribed to an internal charge transfer (ICT) band. In solution, the
ADA UVꢀvisible spectrum presents an interesting feature with a
significant merging of both bands in comparison to the DAD
15 analogue. The redꢀshift of about 26 nm of the πꢀπ* band could be
explained by a conjugation extension of the electronꢀdonating
segment in the ADA molecule compared to the DAD one (i.e. 6
aromatic units in the unique donor segment of ADA vs only 4
aromatic units per donor segment in DAD). On the other hand,
20 the origin of the 25 nm blueꢀshift of the ICT band remains
unclear.
70 Table 2. Electrochemical properties and energy levels of the molecules.
In solid state, both DAD and ADA molecules show a redꢀshift of
their maximum absorption wavelengths. The redꢀshift of both
absorption peaks points out enhanced
onset
onset
Eox
(V)
Ered
(V)
HOMO
(eV)
LUMO
(eV)
π
ꢀstacking interactions in
Molecules
25 the solid state for every investigated molecule. The DAD
molecule presents a redꢀshift of 22 nm leading to an optical
bandgap of 1.78 eV which has been estimated from the
absorption peak onset in the solid state. In agreement with the
DSC analysis previously described, this redꢀshift indicates clearly
30 a rather good solidꢀstate organization for the DAD molecule
(crystalline). The ADA molecule shows a stronger redꢀshift of
around 42 nm in solid state, leading to an optical band gap of
1.85 eV. It remains unclear why the ADA molecule leads to such
a bathochromic effect in its nematic phase, far exceeding what is
35 observed in the DAD counterpart in its crystalline state (22 nm).
Finally, it is worth noting that the ADA thin solid film presents
very broad absorption spectrum with an almost complete merging
DAD
ADA
1.07
0.96
–
5.47
5.36
3.69
3.51
ꢀ0.86
In solid state, no reduction wave could be detected for the DAD
molecule. However, it presents a reversible oxidation wave. The
HOMO levels have been calculated by using the following
75 equation: HOMO (eV) = Eox
assumption that the energy level of ferrocene is 4.4 eV below
vacuum level), while the LUMO levels have been calculated by
adding the optical bandgap E
onset
(V) + 4.4 eV (with the
opt
previously measured to the
former HOMO value.
80 The ADA molecule presents both quasiꢀreversible oxidation and
reduction waves. The oxidation potential is observed for a lower
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voltage than for DAD, leading to a HOMO level value of 5.36
eV. Despite the presence of two electronꢀaccepting
a relatively low temperature thermal annealing (below 80°C). It is
worth mentioning that BHJ solar cells based on blends of
benzothiadiazole units in the ADA molecule, the electronic 55 PC61BM with (smectic) liquid crystal polymers have already been
affinity is only slightly decreased in comparison to the DAD
molecule. The LUMO level is located at 3.51 eV.
reported in the literature. In most cases, moderate to low PCEs
were measured due to poor nanoscale morphology and/or poor
exciton dissociation, thus strongly corroborating the fullerene
eviction phenomenon from the liquid crystal medium [27ꢀ31].
60 This peculiarity should be amplified in the case of ADA
molecules because of the quite higher fluidity of the nematic
phase (vs smectic phase) and the lower molecular weight of the
system. The experimental results obtained in the present study
constitute therefore a good example of how morphology can
65 dominate over frontier orbital energy position in such a complex
system as a bulk heterojunction solar cell. A similar conclusion
was furthermore drawn from another recent study on donorꢀ
acceptor based smallꢀmolecules [32].
5
Charge transport and photovoltaic properties
The charge transport was investigated by means of fieldꢀeffect
transistors (FET). The hole mobility value measured for the
10 nematic ADA molecule is 1.4×10ꢀ5 cm2.Vꢀ1.sꢀ, which is low value
but is typical of nematic compounds of low molecular weight
[25]. The hole mobility measured for the crystalline DAD
molecule gives only a slightly higher value of 4×10ꢀ5 cm2.Vꢀ1.sꢀ1.
This last value is surprisingly low, when considering the
15 crystalline nature of the corresponding compound. However,
since in FET devices charge transport takes place parallel to the
substrate plane along the interface with the dielectric layer, this
result may point out that the preferential charge transport axes
(along the ꢀꢀꢀ stacking) for the DAD molecule is oriented out of
20 plane.
70 Conclusions
We synthesized molecules made of thieno(dioctyl)fluorene
derivatives as electron donating (D) units and benzothiadiazole as
electronꢀaccepting (A) units, assembled in DAD and ADA
architectures in order to investigate the structureꢀproperty
75 relationships of small molecules for solution processable bulk
heterojunction solar cells. Surprisingly, both molecules present
similar optical properties as well as electronic properties.
However, a major difference is observed in their structural
behaviors. While DAD molecule presents a crystalline nature,
80 ADA is a nematic liquid crystal. This structural difference results
in deep morphological variations in both molecules in when
blended with PC61BM. Indeed, the DAD molecule showed the
highest PV performances with a PCE of 2.2% against only 0.5%
for the ADA molecule. This indicates that if the optoelectronic
85 properties are strongly dependent on the nature of the chemical
subꢀunit and less to the way they are assembled along the
conjugated backbone, the molecular architecture has also a
considerable impact on the solidꢀstate structure and ultimately on
the PV performances. Other series of molecules based on the
The photovoltaic performances of the two molecules were
investigated through their application in classical BHJ solar cells
using [6,6]ꢀphenylꢀC61ꢀbutyric acid methyl ester (PC61BM) as
electronꢀaccepting component. The devices were fabricated using
25 a glass/ITO/PEDOT:PSS/molecule:PC61BM blend/Al structure,
with various molecule:PC61BM weight ratios. The best
performances achieved for each molecule are reported in Table 3,
together with the corresponding blend ratio.
30 Table 3. Photovoltaic performance of devices based on blends of the
molecules and PC61BM, under AM 1.5G illumination of 100 mW.cmꢀ2.
Voc
(V)
FF
PCE
(%)
Molecule
Ratio a
Jsc (mA.cmꢀ2)
(%) b
DAD
ADA
1:1
1:1
0.73
0.68
7.3
2.5
46
33
2.19
0.55
a Molecule:PC61BM weight ratio ; b Fill factor
The highest power conversion efficiency (PCE) of 2.2% was 90 DAD architecture are currently being investigated as solution
35 obtained on a device using a DAD:PC61BM blend with a 1:1
weight ratio and a 180 nm thick active layer (measured by
profilometer). This active layer has been obtained by spinꢀcoating
a DAD solution in chlorobenzene (15 mg.mLꢀ1) using spinꢀ
coating parameters listed in the experimental part. Under
40 identical experimental conditions (but differing in optimal blend
processable smallꢀmolecules for photovoltaic applications.
Experimental section
Materials
All reagents and chemicals were purchased from commercial
weight ratio with PC61BM), a surprisingly low PCE of 0.55% was 95 sources (Aldrich, Across, Fluka) and used without further
achieved with the ADA molecule, despite its relevant
optoelectronic properties, and the good Voc value of 0.68 V in
accordance with the HOMO level measured by cyclic
45 voltammetry [26]. This result most likely arises from the liquid
purification. All reactions were carried out in an argon
atmosphere. All solvents were distilled over appropriate drying
agent(s) prior to use and were purged with nitrogen. The starting
2ꢀbromo(dioctyl)fluorene derivate 1 was prepared by classical
crystalline nature of the ADA molecule that prevents suitable 100 reaction alkylation of the commercial 2ꢀbromofluorene [33].
bulk morphology when blended with PC61BM. Despite the longꢀ
range molecular organization in the nematic phase that should be
Characterizations
beneficial for charge transport, its high fluidity is thought to be
1H and 13C NMR spectra were recorded on a Bruker Avance 300
50 detrimental by favoring the expulsion of PC61BM out of the
and a Bruker 400 UltrashieldTM NMR spectrometers, with an
105 internal lock on the Hꢀsignal of the solvent (CDCl3). UVꢀvisible
nematic ADA medium. This assumption is supported by the rapid
collapse of the short circuit current density Jsc of the devices with
2
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absorption spectroscopy measurements were performed using a
Hitachi Uꢀ3000 spectrophotometer. Differential scanning 60 for 120 seconds (speed: 2500 rpm, acceleration: 600 rpm.sꢀ1).
seconds (speed: 2200 rpm, acceleration: 600 rpm.sꢀ1), then step 2
calorimetry (DSC) experiments were performed on a DSC Q2000
from TA Instrument. Optical microscopy observations were made
with a polarizing Leitz Weitzlar microscope equipped with a
Mettler FP82 heating stage. Cyclic voltammetry analyses were
Finally, a 120 nm thick aluminum layer was thermally evaporated
and used as cathode. The device active area was 9 mm2, while
each sample included four independent diodes. The photovoltaic
devices were characterized in a controlled (N2) atmosphere. The
5
carried out with a BioLogic VSP potentiostat using platinum 65 light source was a class A LotꢀOriel solar simulator fitted with a
electrodes at scan rates of 20 mV.sꢀ1. The measurements were
performed on thin films dropꢀcasted from chloroform solutions
AM1.5G filter. The standard 100 mW.cmꢀ2 illumination power
was checked before the photovoltaic measurements using a
singleꢀcrystal calibrated silicon solar cell. The current vs voltage
measurements were performed using a Keithley 2400 Source
10 onto a platinum working electrode. A Pt wire was used as counter
electrode and Ag/Ag+ as reference electrode in acetonitrile
containing 0.1 mol.Lꢀ1 of tetrabutylammonium tetrafluoroborate. 70 Measurements Unit.
Ferrocene was used as internal standard to convert the values
obtained in reference to Ag/Ag+ to the saturated calomel
Synthesis
15 electrode scale (SCE).
Compound
2:
Compound
1
(1
eq.)
and
2ꢀ
Field Effect Transistors in bottomꢀcontact configuration were
elaborated on commercially available preꢀpatterned test structures
whose source and drain contacts were composed of a 30 nm thick
gold layer on top of a 10 nm thick Indium Tin Oxide (ITO) layer.
20 A 230 nm thick silicon oxide was used as gate dielectric and nꢀ
doped (3x1017 cmꢀ3) silicon as gate electrode. The channel length
and channel width were 20 ꢁm and 10 mm respectively. The test
structures were cleaned in acetone and isopropyl alcohol and
subsequently for 15 minutes into an ultraꢀviolet ozone system.
25 Then, hexamethyldisilazane (HMDS) was spin coated (500 rpm
for 5 s and then 4000 rpm for 50 s, acceleration 200 rpm.sꢀ1)
under nitrogen ambient and followed by an annealing step at
135°C for 10 minutes. Finally, 4 mg.mLꢀ1 anhydrous chloroform
small moleculesꢀbased solutions were spin coated (1250 rpm for
30 60s and 2000 rpm for 120s, acceleration: 200 rpm.sꢀ1) to complete
the FET devices. The samples were then left overnight under
vacuum (<10ꢀ6 mbar) to remove residual solvent traces. The
output and transfer transistor characteristics were measured using
a Keithley 4200 Semiconductor Characterization System. All
(trimethylstannyl)thiophene (1 eq.) were dissolved in toluene
75 (0.05 M). Then, tris(dibenzylideneacetone) dipalladium (0)
(Pd2dba3) (0.03 eq) and tris(2ꢀmethylphenyl)phosphine (Pꢀ(oꢀ
tolyl)3) (0.12 eq) were added. The reaction was degassed and
stirred at 110°C for 2 days under argon atmosphere. The mixture
was filtered through
a celite pad and the solution was
80 concentrated under high vacuum. The crude product was purified
by column chromatography on silica gel (petrolum ether:CH2Cl2)
providing the desired compound as a white solid. Yield: 92%. 1H
NMR (300 MHz, CDCl3,) δ: 7,75ꢀ7.69 (m, 2H), 7.66ꢀ7.58 (m,
2H), 7.41ꢀ7.27 (m, 5H), 7.11 (dd, 1H, J = 3.5 Hz, 1.5 Hz), 2.04ꢀ
85 1.93 (m, 4H), 1.29ꢀ0.94 (m, 20H), 0.81 (t, 6H, J = 6.9 Hz), 0.73ꢀ
0.55 (m, 4H). 13C NMR (75 MHz, CDCl3) δ: 151.5, 150.9, 145.3,
140.7, 140.6, 133.2, 128.0, 127.1, 126.9, 124.9, 124.5, 122.9,
120.2, 120.0, 119.7, 55.2, 40.4, 31.8, 30.0, 29.2, 23.7, 22.6.
Compounds 3: Compound 2 (1 eq) was solubilized in chloroform
90 (0.02 M) at ꢀ50°C under argon. Then, NBS (1 eq) was added in
one portion and the mixture was stirred over night at room
temperature. The organic phase was washed with H20 (×3), dried
over MgSO4 and concentrated under vacuum. The crude product
was purified by column chromatography on silica gel (petroleum
95 ether:CH2Cl2) to provide compound 4 as a green solid. Yield:
35 measurements were performed under
a
controlled (N2)
atmosphere and the charge carrier mobility was extracted from
the saturation regime of the transistors transfer characteristics.
Bulk heterojunction devices were elaborated using the different
synthesized molecules as electron donor and PC61BM as electron
40 acceptor. The standard device structure was the following:
ITO/PEDOT:PSS(~40 nm)/small molecules:PC61BM/Al(~120
nm). ITOꢀcoated glass with a surface resistance lower than 20
ꢂ.sqꢀ1 was used as transparent substrate. Substrates were cleaned
sequentially by ultrasonic treatments in acetone, isopropyl
45 alcohol, and deionized water. After an additional cleaning for 30
minutes under ultraꢀviolet generated ozone, a 40 nm thick
PEDOT:PSS layer was spin coated (1550 rpm for 180 s with an
acceleration of 500 rpm.sꢀ1) from an aqueous solution and dried
for 30 minutes at 120°C under vacuum before being transferred to
50 the nitrogen filled glove box. The chlorobenzene small
molecules:PC61BM solutions were stirred for at least 24 hours at
70°C before spinꢀcoating. An extra stirring for 30 minutes at
100°C was added just before the active layer deposition. The
1
94%. H NMR (300 MHz, CDCl3,) δ: 7.72ꢀ7.66 (m, 2H), 7.53ꢀ
7.44 (m, 2H), 7.38ꢀ7.29 (m, 3H), 7.18 (d, 1H, J = 3.8 Hz), 7.12
(d, 1H, J = 3.8 Hz), 2.02ꢀ1.91 (m, 4H), 1.32ꢀ0.96 (m, 20H), 0.81
(t, 6H, J = 7.1 Hz), 0.73ꢀ0.59 (m, 4H). 13C NMR (75 MHz,
100 CDCl3) δ: 152.1, 151.3, 147.1, 141.6, 140.8, 132.7, 131.3, 127.7,
127.2, 124.8, 123.4, 123.3, 120.4, 120.3, 120.2, 111.1, 55.6, 40.6,
32.1, 30.3, 29.5, 24.1, 22.9, 14.2.
Compounds DAD: 4,7ꢀbisꢀ(5ꢀ(trimethylstannyl)thiophenꢀ2ꢀ
yl)benzo[1,2,5]thiadiazole [19] (1 eq) and compound 3 (1.2 eq)
105 were dissolved in dry toluene (0.05 M). Then, Pd2dba3 (0.03 eq)
and Pꢀ(oꢀtolyl)3 (0.12 eq) were added and the reaction was stirred
at 120°C for 2 days under argon atmosphere. Then, the mixture
was filtered through
a celite pad and the solution was
concentrated under high vacuum. The crude product was purified
110 by column chromatography on silica gel (petrolum ether:CH2Cl2)
providing the desired final compound as a purple solid. Yield:
63%.1H NMR (300 MHz, CDCl3,) δ: 8.09 (s, 2H), 7,90 (s, 2H),
7.76ꢀ7.74 (m, 4H), 7.66ꢀ7.63 (m, 4H), 7.47ꢀ7.27 (m, 12H), 2.18ꢀ
1.98 (m, 8H), 1.38ꢀ1.03 (m, 40H), 0.84 (t, 12H, J = 6.7 Hz), 0.77ꢀ
115 0.58 (m, 8H). 13C NMR (75 MHz, CDCl3) δ: 152.5, 151.6, 150.9,
144.5, 141.0, 140.5, 139.0, 137.9, 136.1, 132.7, 128.3, 127.2,
molecule concentration of the solution was varied from 5 mg.mLꢀ
1
55
up to 20 mg.mLꢀ1 in order to obtain different active layer
thicknesses (see ESI). The small molecules:PC61BM weight ratio
was also varied from 1:0.5 to 1:3. The active layer spinꢀcoating
conditions were made in a twoꢀstep procedure: step 1 for 180
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126.8, 125.5, 125.1, 124.9, 124.5, 124.3, 123.6, 122.9, 120.1,
cooled to room temperature and water was added. The crude
119.8, 119.7, 55.2, 40.3, 31.8, 30.0, 29.2, 23.7, 22.6, 14.0. MS 60 product was extracted from CH2Cl2 (3×5 mL). The combined
(MaldiꢀTOF): m/z calcd 1240.586; found 1240.644 [M+].
Compound 4: To a solution of 4,7ꢀdibromobenzothiadiazole [20]
(7.32 g, 26.52 mmol) and 5ꢀtrimethylstannylꢀ2,2'ꢀbithiophene
[21] (8.73 g, 26.52 mmol) in toluene (200 mL), Pꢀ(oꢀtolyl)3 (0.65
dichloromethane extracts were washed with brine and dried over
Na2SO4. The desiccant was filtered off, the solvent was removed
in vacuo, and the crude product was purified by column
chromatography on silica gel (petroleum ether with gradual
5
g, 2.12 mmol) and Pd2dba3 (0.49 g, 0.53 mmol) were added. The 65 introduction of CH2Cl2) and recrystallization (CH2Cl2:methanol)
reaction mixture was degassed and heated at 110°C during 2
days. After cooling, the reaction mixture was filtered through a
10 silica pad and the solvent was removed in vacuo. The crude
to give ADA compound as a red solid (0.13 mg, 65 %). 1H NMR
(300 MHz, CDCl3,) δ: 7.99 (d, 2H, J = 3.9 Hz), 7.94 (d, 2H, J =
3.6 Hz), 7.82 (d, 2H, J = 7.6 Hz), 7.76 (d, 2H, J = 7.6 Hz), 7.64
(d, 2H, J = 8.4 Hz), 7.59 – 7.53 (m, 4H), 7.34 (d, 2H, J
product was purified by column chromatography on silica gel
(petroleum ether with gradual introduction of CH2Cl2) to give the 70 = 3.7 Hz), 7.29 (d, 2H, J = 3.7 Hz), 7.26 (d, 2H, J = 3.6 Hz),
3
product as a redꢀorange solid (2.92 g, 29 %). 1H NMR (300
MHz, CDCl3,) δ: 8.03 (d, 1H, J = 3.9 Hz), 7.86 (d, 1H, J = 7.8
15 Hz), 7.71 (d, 1H, J = 7.8 Hz), 7.33ꢀ7.24 (m, 3H), 7.06 (dd, 1H, J
= 3.6 Hz, J = 5.1 Hz).
6.87 (d, 2H, J = 3.6 Hz), 2.88 (t, 4H, J = 7.6 Hz), ), 2.12ꢀ1.96
(m, 4H), 1.83ꢀ1.67 (m, 4H), 1.49ꢀ0.99 (m, 40H), 0.94ꢀ0.65 (m,
16H). 13C NMR (75 MHz, CDCl3) δ:152.7, 152.6, 152.0, 148.2,
144.4, 140.6, 138.8, 138.2, 136.9, 136.5, 133.0, 128.2, 127.8,
Compound 5: To a solution of bromide 4 (2.92 g, 7.69 mmol) 75 126.4, 125.4, 125.2, 124.8, 124.5, 123.9, 120.5, 119.8, 55.5, 40.5,
and trimethyl(5ꢀoctylꢀ2ꢀthienyl)ꢀstannane [22] (4.15 g, 11.55
mmol) in toluene (70 mL), Pꢀ(oꢀtolyl)3 (0.18 mg, 0.62 mmol) and
20 Pd2dba3 (0.14 mg, 0.15 mmol) were added. The reaction mixture
was degassed and heated at 110°C during 2 days. After cooling,
the reaction mixture was filtered through a silica pad and the
solvent was removed in vacuo. The crude product was purified by
column chromatography on silica gel (petroleum ether with
25 gradual introduction of CH2Cl2) and by recrystallization
(CH2Cl2:methanol) to give the product as a red solid (2.73 g,
32.04, 31.96, 31.7, 30.5, 30.2, 29.8, 29.5, 29.5, 29.2, 24.0, 22.8,
22.7, 14.25, 14.21. MS (MaldiꢀTOF): m/z calcd 1374.493; found
1374.508 [M+].
Acknowlegments
80 The research was supported by the French government via the
ANR grant (PICASSO project ANRꢀ11ꢀBS08ꢀ0009) and the
European Community via the Interreg IVꢀA program (C25, Rhinꢀ
Solar, www.rhinsolar.eu). The authors are grateful to Dr. Benoît
Heinrich for carrying out the DSC analyses and Nicolas
85 Zimmermann for his contribution to device elaborations.
1
72 %). H NMR (300 MHz, CDCl3,) δ: 8.02 (d, 1H, J = 3.9 Hz),
7.95 (d, 1H, J = 3.7 Hz), 7.84 (d, 1H, J = 7.7 Hz), 7.79 (d, 1H, J
= 7.7 Hz), 7.32 – 7.24 (m, 3H), 7.06 (dd, 1H, J = 3.6 Hz, 5.1 Hz),
30 6.88 (d, 1H, J = 3.4 Hz), 2.89 (t, 2H, J = 7.6 Hz), 1.83ꢀ1.68 (m,
2H), 1.48ꢀ1.19 (m, 10H), 0.89 (t, 3H, J = 6.9 Hz). 13C NMR
(75 MHz, CDCl3) δ: 152.7, 152.6, 148.3, 138.7, 138.3, 137.5,
136.8, 128.1, 127.8, 126.4, 125.5, 125.4, 125.1, 124.9, 124.7,
124.1, 32.0, 31.8, 30.5, 29.5, 29.4, 29.3, 22.8, 14.3.
Notes and references
a Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS),
Université de Strasbourg, CNRS UMR 7504, 23 rue du Loess, BP 43,
67034 Strasbourg Cedex 2, France. Eꢀmail:
90 stephane.mery@ipcms.unistra.fr
35 Compound 6: NIS (231 mg, 1.027 mmol) was added in 2
portions at room temperature to a solution of compound 5 (0.48
g, 0.98 mmol) in a mixture of chloroform (22 mL) and acetic acid
(13 mL) under argon and in darkness. The reaction mixture was
stirred overnight, then water was added (30 mL). The organic
40 phase was washed with H2O (×3), dried over Na2SO4, filtered and
concentrated. The crude product was purified by column
chromatography on silica gel (petroleum ether:CH2Cl2 ; 8:1) to
b Institut de Chimie et Procédés pour l’Energie, l’Environnement et la
Santé (ICPEES), Université de Strasbourg, CNRS UMR 7515, 25 rue
Becquerel, 67087 Strasbourg Cedex 2, France. Eꢀmail:
leclercn@unistra.fr
95 c Laboratoire ICube, Université de Strasbourg, 23 rue du Loess, CNRS
UMR 7357, 67087 Strasbourg Cedex 2, France.
1
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100
105
110
115
provide the final compound as an orange solid (0.55 g, 91%). H
2
3
A. Mishra and P. Bäuerle, Angew. Chem. Int. Ed., 2012, 51, 2020.
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NMR (300 MHz, CDCl3,) δ: 7.98 (d, 1H, J = 3.9 Hz), 7.95 (d,
45 1H, J = 3.7 Hz), 7.83 (d, 1H, J = 7.6 Hz), 7.78 (d, 1H, J = 7.6
Hz), 7.19 (d, 2H, J = 3.8 Hz), 6.95 (d, 2H, J = 3.8 Hz), 6.88 (d,
2H, J = 3.7 Hz), 2.87 (dd, 2H, J = 7.5 Hz, 7.6 Hz), 1.83ꢀ1.67 (m,
2H), 1.49ꢀ1.18 (m, 10H), 0.89 (t, 3H, J = 6.9 Hz). 13C NMR (75
MHz, CDCl3) δ: 152.7, 152.6, 148.4, 143.4, 138.9, 138.0, 137.4,
50 136.8, 128.0, 127.9, 126.7, 125.7, 125.5, 125.4, 125.1, 125.0,
124.9, 32.0, 31.8, 30.5, 29.5, 29.4, 29.3, 22.8, 14.3.
Compound ADA: THF (4 mL) and water (1 mL) were added to a
stirred, degassed mixture of iodide 6 (0.20 g, 0.32 mmol), 9,9ꢀ
dioctylfluoreneꢀ2,7ꢀdiboronic acid (0.07 g, 0.14 mmol) and
55 potassium carbonate (0.08 mg, 0.56 mmol). The mixture was
degassed and Pꢀ(oꢀtolyl)3 (7 mg, 0.02 mmol) and Pd2dba3 (5 mg,
0.0056 mmol) were added. The reaction mixture was degassed
again and heated at 80°C for 3 days. Then the solution was
4
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7