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Thin Solid Films 519 (2011) 3695–3702
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Thin Solid Films
journal homepage: www.elsevier.com/locate/tsf
Film formation properties of inkjet printed
poly(phenylene-ethynylene)-poly(phenylene-vinylene)s
Anke Teichler a,b , Rebecca Eckardt a,b , Christian Friebe a , Jolke Perelaer a,b , Ulrich S. Schubert a,b, ⁎
a Laboratory of Organic and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstraβe 10, 07743 Jena, Germany
b Dutch Polymer Institute (DPI), P.O. Box 513, 5600 MB Eindhoven, The Netherlands
article
info
abstract
Article history:
Received 16 June 2010
Received in revised form 18 January 2011
Accepted 18 January 2011
Available online 27 January 2011
Keywords:
Inkjet printing
Poly(phenylene-ethynylene)
Poly(phenylene-vinylene
Thin films
Combinatorial screening
Inkjet printing was used here as a precise and fast dispensing technique to prepare thin-film libraries of a
poly-(phenylene-ethynylene)-poly(phenylene-vinylene)s copolymer. The films were prepared with a
systematic variation of the ink composition, the dot spacing and the substrate temperature. Homogeneous
films with a thickness of 100 nm were obtained when printed at room temperature and from a solvent
mixture of toluene and ortho-dichlorobenzene in a volume ratio of 90/10. This approach can be used for
optoelectronic applications, where the layer homogeneity is extremely important but where the ink
compositions may vary per device, as well as the exact layer thickness. Our approach can be applied for the
preparation of films by inkjet printing for any other (polymer) ink solution and represents a fast and efficient
screening of the parameters to obtain homogeneous films with a precise thickness.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Currently, there is a growing interest in conjugated polymers for
usage in optoelectronic devices because of their semiconducting
properties [1]. Organic semiconductors show advanced processing
properties due to solubility in organic solvents and their film
formation characteristics. In recent research, conjugated polymers,
like poly(phenylene)s or polythiophenes, have been used in optoelectronic
devices, for example in organic light emitting diodes
(OLED) [2,3], organic photovoltaics [4,5] and organic field-effect
transistors (OFET) [6,7]. The possibility of altering the material
properties and the usage of cheap processing methods such as inkjet
printing classify conjugated polymers as interesting materials for
optoelectronic applications [8,9]. The usage of semiconducting
polymers results in smaller, flexible and, most importantly, cheaper
devices.
Poly(phenylene-ethynylene)-poly(phenylene-vinylene)s (PPE-
PPV) combine good photophysical characteristics of PPVs and charge
transport properties of PPEs [10]. PPE-PPV derivatives are soluble in
organic solvents due to the alkoxy side chains that are grafted to the
polymer backbone, hence improving the processability of the
polymers in solution [11]. The use of PPE-PPV copolymers as
electron-donating compounds in organic solar cells with an active
⁎ Corresponding author at: Laboratory of Organic and Macromolecular Chemistry,
Friedrich-Schiller-University Jena, Humboldtstraβe 10, 07743 Jena, Germany.
E-mail address: ulrich.schubert@uni-jena.de (U.S. Schubert).
layer consisting of PPE-PPV/PCBM (1-[3-(methoxycarbonyl)propyl]-
1-phenyl)-[6,6]C 61 ) yielded device efficiencies up to 1.8% [12–14].
The most common procedure for the preparation of the photoactive
layer is by using spin-coating. However, this method is
unfavorable in terms of materials efficiency, since most of the
material is wasted during processing. Moreover, a combinatorial
workflow is not possible [15]. In contrast, inkjet printing is
characterized by reduced production costs due to its low material
waste and controlled deposition of materials [16,17]. Additionally,
inkjet printing is a non-contact processing technique and does not
require expensive masks, which further reduce processing costs.
The control over pattern formation of inkjet printed droplets, lines
and films is required to form homogeneous features upon drying. The
well-known coffee drop effect forms a major problem for the usage of
the inkjet printing technique. An increased evaporation of solvent at
the edges of the droplet as well as a pinned contact line lead to an
outward flow of material and subsequently to accumulation of
material at the rim of the droplet [18,19]. A solution to this problem
was found by using a solvent mixture that contains a minor part of a
high-boiling solvent [20]. In addition to investigations on the behavior
of single printed droplets on a surface, also the formation of lines was
studied [21]. The control and optimization of line morphology is
important for electronic applications, e.g. electrical contacts for
transistors. Soltman et al. classified five different line morphologies
depending on the dot spacing, which is the center-to-center distance
between two adjacent droplets, and their drying time [22].
Inkjet printing of thin-film libraries allows a combinatorial workflow
to investigate structure-property relations [23,24]. With this
0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.tsf.2011.01.274

3696 A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
approach, the influence of ink composition, substrate properties, and
different printing parameters to the film properties can be studied in a
fast and reproducible way. Tekin et al. investigated a selection of
parameters that influences the quality of inkjet printed polystyrene
films, including solvent combinations, printing speed and dot spacing
[25]. Furthermore, the optical properties of the inkjet printed films
consisting of various PPE-PPV copolymers were investigated as
function of film thickness [26].
In this contribution, we use inkjet printing as a tool to prepare
two-dimensional thin films of a PPE-PPV copolymer, in order to screen
various parameters of the film formation properties. The influence of
dot spacing, solvent system, concentration as well as substrate
temperature on the quality of inkjet printed films will be discussed.
Topographical and optical measurements are performed to investigate
the homogeneity, luminescence and reproducibility of the
resulting film. This procedure enables a fast and efficient screening
of thin-film PPE-PPV libraries.
2. Experimental details
2.1. Materials
The synthetic route of the PPE-PPV copolymer (Mn=8,600 g mol −1 ,
Mw=34,000 g mol −1 , PDI=3.95) was described elsewhere [27]. The
polymer was dissolved in the solvent mixtures of toluene and orthodichlorobenzene
(o-DCB), and the solutions were filtered before
printing (pore size 1 μm) to prevent nozzle clogging. The solvents
(toluene, o-DCB) were purchased from Biosolve (Valkenswaard, The
Netherlands) and used as delivered. The polymer has a viscosity of
0.72 and 0.79 mPa s for a concentration of 4 mg mL −1 and 8 mg mL −1
in the solvent system toluene/o-DCB 90/10, respectively.
2.2. Preparation of substrates
Microscope slides (3×2 in.) from Marienfeld (Lauda-Königshofen,
Germany) were used as substrates. For cleaning, the microscope slides
were ultrasonicated in a soap solution and washed afterwards with
demineralized water to remove the soap [28]. This was followed by
additional ultrasonication steps in acetone and iso-propanol. Finally,
the substrates were rinsed with iso-propanol and dried with an air
flow.
2.3. Instrumentation
The inkjet printing experiments were carried out with an
Autodrop system from microdrop Technologies (Norderstedt,
Germany). The printer was equipped with a piezo-based printhead
(dispenser system) with an inner diameter of 70 μm. The microscope
slides were placed onto a heatable table which can be moved in x- and
y-direction. A voltage of 70 V and a pulse length of 35 μs revealed a
stable droplet formation for the PPE-PPV in the solvent system
toluene/o-DCB. These settings resulted in an in-flight droplet diameter
of approximately 60 μm, which corresponds to a droplet volume of
113 pL. The printing speed was set to 10 mm s −1 for all experiments.
Surface topography as well as film thicknesses were measured
using an optical interferometric profiler Wyko NT9100 (Veeco,
Mannheim, Germany). In each film a scratch was made with a scalpel
in a controlled manner. At five different positions of the film the depth
of the scratch was measured with the optical profiler. Two separate
films per dot spacing were measured in order to obtain an average
film thickness.
The contact angles from alle solution were measured, using a
Dataphysics OCA 30 (Filderstadt, Germany), and found to be below
10°.
A UV-vis/fluorescence plate reader from Analytik Jena (FLASHScan
530, Jena, Germany) was used to measure the UV-vis absorption and
emission spectra of the printed films. The films (5×5 mm 2 ) were
printed into a microtiter plate pattern, i.e. the films were printed with
an interdistance of 4 mm to cover the positions of the wells. This
allowed the characterization of a microtiter plate format with 96 UVvis
spectra within 50 seconds. For measuring the microscope slides an
adapter was used. All measurements were referenced to air. UV-vis
absorption measurements of the solutions were carried out with a
Specord 250 (Analytik Jena, Jena, Germany) and UV-vis emission
measurements with a FP 6500 from JASCO Inc. (Easton, USA). Quartz
cuvettes with a diameter of 1 cm and filled with pristine solvent as
reference were used. All emission spectra were obtained by excitation
at the wavelength of the maximum absorption.
Viscosity measurements were performed using an AMVn viscosimeter
(Anton Paar, Graz, Austria). The dynamic viscosity was
measured at three different angles 30°, 50° and 70° and an average
value was calculated.
3. Results and discussion
A schematic representation of the chemical structure of the PPE-
PPV copolymer used in the experiments is shown in Fig. 1. The
octyloxy side chains are grafted to the PPE part and octadecyloxy
chains to the PPV part of the polymer and improve the solubility
significantly [11].
Many parameters influence the quality and homogeneity of inkjet
printed thin films. Jabbour et al. reported inkjet printing of poly(3,4-
ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) layers
using a standard desktop printer in gray-scale mode. An increased
intensity of the “black” ink, which in fact was replaced with a PEDOT:
PSS ink, resulted in an increased PEDOT:PSS layer thickness. The
printed conductive polymer layer is used as an anode in OLEDs [29].
This simple but straight-forward approach revealed the influence of
the film thickness on the device properties.
Investigation of each single parameter would cost too much time
and, moreover, synergies between parameters remained unnoticed.
Therefore, we use here a two-dimensional and combinatorial approach
to study multiple parameters at the same time: for example, on one axis
the dot spacings are systematically varied, while on the other axis the
concentration of the polymer is varied. In the next sections, the effect of
solute concentration, substrate temperature, and varied ratios of the
solvent mixture toluene/ortho-dichlorobenzene (toluene/o-DCB) are
described as function of the dot spacing.
3.1. Influence of the dot spacing
The polymer was dissolved in the solvent system toluene/o-DCB in
a ratio of 90/10 and a concentration of 4 mg mL −1 . Films were inkjet
printed with dot spacings between 80 μm and 160 μm. Fig. 2 shows
the influence of the dot spacing on the film formation. The optical
profiler images showed that with a dot spacing of 80 μm (Fig. 2a)
homogeneously dried film were obtained, but when using a dot
spacing of 120 μm a more homogeneous film formation was obtained
(Fig. 2b). When further increasing the dot spacing adjacent droplets
were not able to merge into a continuous film. This resulted first in
R 1 O
OR 1
R 2 O
OR 2
Fig. 1. Schematic representation of the chemical structure of the investigated PPE-PPV
copolymer (R 1 =octyl, R 2 =octadecyl).
n

A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
3697
Fig. 3 shows a comparison of the solvent mixtures with a dot
spacing of 120 μm. For a solvent ratio of 90/10 and 95/5 (Fig. 3a, b)
homogeneous films were obtained. In contrast, a solvent ratio of 99/1
(Fig. 3c) led to the formation of inhomogeneous films due to a fast and
irregular drying, which can be ascribed to the low amount of o-DCB in
the solvent mixture. Moreover, when using a solvent ratio of 99/1 no
homogeneous films could be formed at any dot spacing between 80
and 160 μm. For all three solvent ratios, a dot spacing of 80 μm
revealed irregular films since too much material was dispensed, while
a dot spacing of 160 μm did not result in continuous films, since the
droplets were not able to merge. Therefore, the content of o-DCB in
Fig. 2. Optical profiler images of PPE-PPV films inkjet printed with a dot spacing of
a) 80 μm, b) 120 μm, and c) 160 μm. Solvent system was toluene/o-DCB in a ratio of
90/10 and a concentration of 4 mg mL −1 .
line instead of film formation (Fig. 2c), while even larger dot spacings
led to single droplets, which have a diameter of approximately
140 μm.
3.2. Influence of the solvent system
The influence of the solvent system was investigated by inkjet
printing the PPE-PPV copolymer with a concentration of 4 mg mL −1 in
the solvent system toluene/o-DCB while the ratio between the two
solvents systematically varied. The ratios 90/10, 95/5 and 99/1 were
used with dot spacings between 80 μm and 160 μm. Ratios with a
larger amount of the lower boiling solvent toluene are known to show
irregular films after being printed [25].
Fig. 3. Optical profiler images of PPE-PPV films inkjet printed from the solvent system toluene/
o-DCB in the ratios a) 90/10, b) 95/5, and c) 99/1 (dot spacing 120 μm, c=4 mg mL −1 ).

3698 A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
the experiments performed here is recommended to be at least 5 vol%,
but preferably 10 vol%, in order to obtain homogeneous films.
3.3. Influence of the concentration
The effect of the solute concentration on their film forming
properties was investigated for three different concentrations,
including 4 mg mL −1 , 6 mg mL −1 and 8 mg mL −1 . The solvent
system toluene/o-DCB 90/10 was chosen following the good results
from the previous section. Fig. 4 shows optical profiler images of
typical inkjet printed films from the solutions with a systematically
varied concentration and dot spacing. It can be seen that a variation
of the concentration of the solutions strongly affects the film
formation.
A concentration of 4 mg mL −1 (Fig. 4a) and a dot spacing of 80 μm
led to inhomogeneous films because too much material was
deposited. Homogeneous films were obtained for a dot spacing of
120 μm, while a dot spacing of 160 μm resulted in inhomogeneous
films and line formation. When having a closer look at the dot spacing
of 120 μm still a faint line formation can be observed. This may be
ascribed to the velocity of the printhead: at low printing velocities a
printed line may dry just before the following line will be printed,
hampering a smooth merging of the two lines (in our experiments we
have not varied the printhead velocity.).
A concentration of 6 mg mL −1 (Fig. 4b) revealed inhomogenous
films when printed with a dot spacing of 80 μm, while 120 μm
resulted in homogeneous films. Again at a dot spacing of 160 μm line
formation appeared. A solute concentration of 8 mg mL −1 (Fig. 4c)
was not suitable to create homogeneous films since separate lines
were formed at any dot spacing above 120 μm.
As a conclusion, the best solute concentration was found to be
4mg mL −1 , since a broader range of dot spacings could be used to
obtain homogeneous films.
3.4. Influence of the substrate temperature
To study the effect of the substrate temperature, a polymer
concentration of 4 mg mL −1 in toluene/o-DCB 90/10 was chosen,
Fig. 4. Optical profiler images of PPE-PPV films inkjet printed with concentrations of a)4 mg mL −1 , b) 6 mg mL −1 , and c) 8 mg mL −1 (solvent system toluene/o-DCB 90/10).

A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
3699
Fig. 5. Optical profiler images of PPE-PPV films inkjet printed with a dot spacing of 80 μm (a), 120 μm (b) and 160 μm (c). The columns show, from left to right, a substrate
temperature of room temperature, 35 °C and 50 °C, respectively (solvent system toluene/o-DCB 90/10, c=4 mg mL −1 ).
based on the results from previous experiments. The temperature
varied between room temperature and 50 °C. Fig. 5a–c shows the
comparison between the different substrate temperatures at a dot
spacing of 80 μm, 120 μm, and 160 μm, respectively.
At a dot spacing of 80 μm (Fig. 5a) homogeneous films could only
be obtained at room temperature, while increasing the temperature
showed irregular films or films with line formation. For a dot spacing
of 120 μm (Fig. 5b) the formation of lines took place already at a
slightly increased temperature of 35 °C. At room temperature smooth
films were printed. With a dot spacing of 160 μm (Fig. 5c) no
homogeneous films could be printed; already at room temperature
line formation was observed. The increase of the temperature to 50 °C
did not improve the film formation.
Increased temperatures did not have a positive effect on the film
formation; only at room temperature well-defined films were formed.
Furthermore, when using a substrate temperature greater than 50 °C,
the films consisted only of individual lines due to a faster drying
process, which prevents the lines from merging into a homogeneous
film. It has been shown in literature that the nozzle-to-substrate
distance as well as the substrate temperature strongly influences the
in-flight droplet diameter [30]. An increased substrate temperature
stimulates solvent evaporation during the dispensing of the ink,
resulting in a reduced droplet diameter on the substrate. We believe
that the effect of inkjet printing a wet droplet (line) next to a semidried
droplet (line), i.e. an as-printed droplet (line) that is evaporating,
is the cause of the less homogeneous film formation, as seen here, at
elevated temperatures.
3.5. Influence on the film thickness
For all homogeneous films the thickness was measured using
optical profilometry; the results are summarized in Table 1. For a
concentration of 4 mg mL −1 and a solvent ratio 90/10 film thicknesses
between 104 nm and 79 nm were obtained for a dot spacing between
100 and 130 μm, respectively. Smaller film thicknesses between
94 nm and 68 nm were obtained for films printed from toluene/o-DCB
in a ratio of 95/5 at the same concentration and dot spacing.
Films inkjet printed either from the solvent ratio 90/10 or 95/5

3700 A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
Table 1
Film thickness, maximum absorption and standard deviation of the absorption of inkjet
printed PPE-PPV films for different dot spacings, concentrations, and solvent ratios.
Concentration
(mg mL −1 )
Solvent ratio
(toluene/o-DCB)
showed the same homogeneity as can be seen by the standard
deviation between 13 nm and 24 nm. This confirms the observation in
a previous section that the amount of high boiling solvent o-DCB
should be at least 5 vol%.
The films printed from a concentration of 6 mg mL −1 and a dot
spacing between 115 and 130 μm revealed a film thickness of approximately
95 nm. As expected, these films showed a greater thickness
than those printed at the same dot spacings from a 4 mg mL −1
solution. Standard deviations were for both concentrations in the same
range; hence their film homogeneity was comparable.
As mentioned before, it was found that the range of dot spacings,
wherein homogeneous films could be printed, decreased with a
higher solute concentration in the ink. For a 4 mg mL −1 solution
homogeneous films were obtained with dot spacings between 100
and 130 μm, whereas a 6 mg mL −1 solution led to homogeneous films
between 115 and 130 μm. An 8 mg mL −1 solution could not be printed
into homogeneous films at any dot spacing.
3.6. Optical characterization
Dot
spacing
(μm)
Film
thickness
(nm)
A max
(a.u.)
Standard
deviation,
A max (%)
4 90/10 100 104±14 0.400 9.1
105 102±20 0.372 3.5
110 91 ±20 0.367 11.3
115 88 ±14 0.306 11.0
120 83 ±13 0.306 8.7
125 80 ±16 0.403 14.0
130 79 ±14 0.369 4.2
4 95/5 100 93 ±24 0.032 4.2
105 94 ±18 0.063 9.3
110 83 ±15 0.025 4.0
115 75 ±16 0.155 22.2
120 83 ±19 0.084 16.2
125 68 ±18 0.057 10.5
6 90/10 115 95 ±20 0.856 15.1
120 95 ±18 0.775 14.3
125 94 ±17 0.698 10.8
130 93 ±15 0.751 17.2
UV-vis absorption spectra were recorded for the PPE-PPV
copolymer in solution with a concentration of 0.1 μg mL −1 in
toluene and in solid state from the printed films (toluene/o-DCB 90/
10, 4 mg mL −1 ) and shown in Fig. 6a. The maximum absorbance
peak in solution was found at a wavelength of 453 nm, while the
printed films showed a maximum at 470 nm and a shoulder around
515 nm. The observed shoulder can be ascribed to band splitting
that is attributed to different arrangements of the polymer, including
H- (475 nm) and J-aggregates (515 nm) [26]. These aggregates are
formed by interactions between the polymers or the polymer
segments [31].
The photoluminescence spectrum of the solution (Fig. 6b) shows a
maximum at 514 nm and a small shoulder at a higher wavelength
(550 nm). The inkjet printed films revealed emission at a wavelength
of 588 nm. A bathochromic shift was observed for absorption as well
as photoluminescence of the films when compared to the solutions.
This can be attributed to the formation of aggregates in the films, and,
thus, an enhanced planarization of the polymer backbone takes place
[27].
The reproducibility of the inkjet printed films was estimated by
comparing the optical properties of multiple films. Hereto, five films
were inkjet printed next to each other and with equal print settings.
Table 1 summarizes the solution properties, the printing parameters,
the average maximum absorbance values as well as the
Absorption (normalized)
Photoluminescence (normalized)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
a)
300 350 400 450 500 550
b)
Wavelength (nm)
solution
film
500 550 600 650 700 750 800
Wavelength (nm)
solution
film
Fig. 6. a) Normalized absorption and b) photoluminescence spectra of the PPE-PPV
copolymer in solution (solid line, c=0.1 μg mL −1 in toluene) and in thin film (dashed
line, printed from 4 mg mL −1 in toluene/o-DCB with a ratio of 90/10).
standard deviations of the respective maximum absorption. It was
found that for a concentration of 4 mg mL −1 the most reproducible
films were obtained for a solvent ratio of 90/10 and a dot spacing
between 100 μm and 130 μm. The standard deviations obtained for
the maximum absorption were between 4% and 14%, which
corroborates in the optical profiler results in the proceeding section.
In contrast, a solvent ratio of 95/5 was less reproducible, indicated by
the slightly larger standard deviations between 4% and 22%. Finally,
standard deviations between 11% and 17% were obtained for films
that were printed from a higher concentration (6 mg mL −1 ) in
toluene/o-DCB 90/10.
The absorption spectra of five samples inkjet printed with equal
conditions from the PPE-PPV copolymer with a concentration of
4mgmL −1 , a solvent ratio of 90/10 and a dot spacing of 130 μm are
shown in Fig. 7. At the maximum peak, the difference between the
spectra is approximately 4%.
Concluding the combinatorial screening, optimal settings for a
homogeneous film formation for the PPE-PPV copolymer with a good
reproducibility are: a solvent concentration of 4 mg mL −1 , a solvent
system of toluene/o-DCB in a ratio 90 to 10, a dot spacing of 120 μm,
and processing at room temperature. Fig. 8 shows a three-dimensional
optical profiler image of the optimal settings (Fig. 8a) and, as a
comparison, films of a 4 mg mL −1 solution, toluene/o-DCB ratio 95/5
with a dot spacing of 110 μm (Fig. 8b) and of a 6 mg mL −1 solution
with a solvent ratio of 90/10 and a dot spacing of 120 μm (Fig. 8c).

A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
3701
Fig. 7. Absorption spectra of five films inkjet printed with equal conditions from
PPE-PPV copolymer in toluene/o-DCB 90/10 with a concentration of 4 mg mL −1 and
a dot spacing of 130 μm (samples1–5).
4. Conclusions
In this study, inkjet printing was used as a precise and reproducible
patterning technique to create thin-film libraries of the in-house
synthesized copolymer poly(phenylene-ethynylene)-poly(phenylenevinylene)
(PPE-PPV). Inkjet printing of thin-film libraries allow a
combinatorial workflow to investigate structure-property relationships.
Here, we systematically varied a set of parameters that strongly
influence the film forming properties, including the ink composition
(solute concentration, solvent mixture ratios and solute concentration),
as well as the substrate temperature and dot spacing.
All parameters were studied as function of the dot spacing, which
directly relates to the film thickness. When using the solvent system
toluene and ortho-dichlorobenzene (o-DCB), a ratio between the two
solvents of 90 to 10 and a solute concentration of 4 mg mL −1 leads to
the formation of homogeneous films when printed at room temperature
with a dot spacing between 100 and 130 μm. The resulting film
thicknesses are between 80 and 100 nm, which is promising for
printed electronics applications, such as organic light emitting diodes
(OLEDs) and organic photovoltaics.
With a decreased amount of the high boiling solvent o-DCB or
increased substrate temperature, the formation of lines became
visible, which indicates a too fast drying of the solvent, resulting in
inhomogeneous films.
Optical characterization was performed in a fast and reproducible
manner using a UV-vis plate reader. The films were printed in a
microtiter plate format where each film is located at the position of a
well. It was found that the polymer had its maximum absorption in
solution at a wavelength of 453 nm and emitted at 514 nm. In the
solid state, the absorption and emission were red-shifted due to the
increased planarization of the polymer backbone.
By using inkjet printing, film forming properties could be
optimized in a combinatorial approach, which did not only save
time and (materials) costs, but also revealed synergies between
different parameters that would not have been discovered when
optimizing each parameter individually.
In optoelectronic devices the homogeneity is of utmost importance,
but the film thickness and used inks may vary. Our approach
can now be applied for film preparation by inkjet printing for any
other (polymer) ink solution and represents a fast and efficient
screening of the parameters to obtain homogeneous films with a
precise thickness.
Acknowledgements
The authors would like to thank the DPI for financial support
(projects #620 and #589).
References
Fig. 8. 3D optical profiler images of films prepared from a) 4 mg mL −1 , toluene/o-DCB
90/10, dot spacing 120 μm, b) 4 mg mL −1 , toluene/o-DCB 95/5, dot spacing 110 μm and
c) 6 mg mL −1 , toluene/o-DCB 90/10, dot spacing 120 μm.
[1] A.C. Grimsdale, K.L. Chan, R.E. Martin, P.G. Jokisz, A.B. Holmes, Chem. Rev. 109
(2009) 897.
[2] J.H. Burroughes, D.D.C. Bradley, A.R. Brown, R.N. Marks, K. Mackay, R.H. Friend, P.L.
Burns, A.B. Holmes, Nature 347 (1990) 539.
[3] A. Menon, H. Dong, Z.I. Niazimbetova, L.J. Rothberg, M.E. Galvin, Chem. Mater. 14
(2002) 3668.
[4] S. Günes, H. Neugebauer, N.S. Sariciftci, Chem. Rev. 107 (2007) 1324.
[5] G. Dennler, M.C. Scharber, C.J. Brabec, Adv. Funct. Mater. 21 (2009) 1323.
[6] T. Kawase, T. Shimoda, C. Newsome, H. Sirringhaus, R.H. Friend, Thin Solid Films
437 (2003) 279.
[7] H.N. Tsao, D. Cho, J.W. Andreasen, A. Rouhanipour, D.W. Breiby, W. Pisula, K.
Müllen, Adv. Mater. 21 (2009) 209.
[8] E. Tekin, D.A.M. Egbe, J.M. Kranenburg, C. Ulbricht, S. Rathgeber, E. Birckner, N.
Rehmann, K. Meerholz, U.S. Schubert, Chem. Mater. 20 (2008) 2727.
[9] B.-J. de Gans, P.C. Duineveld, U.S. Schubert, Adv. Mater. 16 (2004) 203.
[10] D.A.M. Egbe, C.P. Roll, E. Birckner, U.-W. Grummt, R. Stockmann, E. Klemm,
Macromolecules 35 (2002) 3825.
[11] D.A.M. Egbe, H. Tillmann, E. Birckner, E. Klemm, Macromol. Chem. Phys. 202
(2001) 2712.
[12] M. Al-Ibrahim, A. Konkin, H.K. Roth, D.A.M. Egbe, E. Klemm, U. Zhokhavets, G.
Gobsch, S. Sensfuss, Thin Solid Films 474 (2005) 201.
[13] D.A.M. Egbe, L.H. Nguyen, H. Hoppe, D. Mühlbacher, N.S. Sariciftci, Macromol.
Rapid Commun. 26 (2005) 1389.
[14] H. Hoppe, N.S. Sariciftci, D.A.M. Egbe, D. Mühlbacher, M. Koppe, Mol. Cryst. Liq.
Cryst. 426 (2005) 255.
[15] F.C. Krebs, Sol. Energy Mat. Sol. C 93 (2009) 394.
[16] E. Tekin, P.J. Smith, U.S. Schubert, Soft Matter 4 (2008) 703.
[17] M. Singh, H.M. Haverinen, P. Dhagat, G.E. Jabbour, Adv. Mater. 22 (2010) 673.
[18] R.D. Deegan, Phys. Rev. E 61 (2000) 475.
[19] R.D. Deegan, O. Bakajin, T.F. Dupont, G. Huber, S.R. Nagel, T.A. Witten, Phys. Rev. E
62 (2000) 756.
[20] B.-J. de Gans, U.S. Schubert, Langmuir 20 (2004) 7789.
[21] E. Tekin, E. Holder, D. Kozodaev, U.S. Schubert, Adv. Funct. Mater. 17 (2007) 277.
[22] D. Soltman, V. Subramanian, Langmuir 24 (2008) 2224.

3702 A. Teichler et al. / Thin Solid Films 519 (2011) 3695–3702
[23] B.-J. de Gans, E. Kazancioglu, W. Meyer, U.S. Schubert, Macromol. Rapid Commun.
25 (2004) 292.
[24] B.-J. de Gans, U.S. Schubert, Macromol. Rapid Commun. 24 (2003) 659.
[25] E. Tekin, B.-J. de Gans, U.S. Schubert, J. Mater. Chem. 14 (2004) 2627.
[26] E. Tekin, H. Wijlaars, E. Holder, D.A.M. Egbe, U.S. Schubert, J. Mater. Chem. 16
(2006) 4294.
[27] D.A.M. Egbe, C. Bader, E. Klemm, L. Ding, F.E. Karasz, U.-W. Grummt, E. Birckner,
Macromolecules 36 (2003) 9303.
[28] A.M.J. van den Berg, A.W.M. de Laat, P.J. Smith, J. Perelaer, U.S. Schubert, J. Mater.
Chem. 17 (2007) 677.
[29] Y. Yoshioka, G.E. Jabbour, Synth. Met. 156 (2006) 779.
[30] J. Perelaer, P.J. Smith, M.M.P. Wijnen, E. van den Bosch, R. Eckardt, P.H.J.M.
Ketelaars, U.S. Schubert, Macromol. Chem. Phys. 210 (2009) 387.
[31] S. Siddiqui, F.C. Spano, Chem. Phys. Lett. 308 (1999) 99.