U.S. patent application number 10/469443 was filed with the patent office on 2006-04-20 for formulation and method for depositing a material on a substrate.
Invention is credited to ChristopherJ Bright, Martin Cacheiro, Julian Carter, Peter Lyon.
Application Number | 20060082627 10/469443 |
Document ID | / |
Family ID | 34276789 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060082627 |
Kind Code |
A9 |
Bright; ChristopherJ ; et
al. |
April 20, 2006 |
Formulation and method for depositing a material on a substrate
Abstract
A formulation for depositing a material on a substrate, the
formulation comprising the material to be deposited on the
substrate dissolved in a solvent system comprising a first solvent
component having a relatively high boiling point and which exhibits
a relatively low solubility with respect to the material to be
deposited, and a second solvent component having a relatively low
boiling point and which exhibits a relatively high solubility with
respect to the material to be deposited.
Inventors: |
Bright; ChristopherJ;
(Huntingdon, GB) ; Carter; Julian;
(Cambridgeshire, GB) ; Cacheiro; Martin; (A
Coruna, ES) ; Lyon; Peter; (Cambridgeshire,
GB) |
Correspondence
Address: |
James P Zeller;Marshall Gerstein & Borun
6300 Sears Tower
233 South Wacker Drive
Chicago
IL
60606-6357
US
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20040109051 A1 |
June 10, 2004 |
|
|
Family ID: |
34276789 |
Appl. No.: |
10/469443 |
Filed: |
February 27, 2002 |
PCT Filed: |
February 27, 2002 |
PCT NO: |
PCT/GB02/00845 |
371 Date: |
January 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60291684 |
May 17, 2001 |
|
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Current U.S.
Class: |
347/95 ;
252/301.16 |
Current CPC
Class: |
H01L 51/0005 20130101;
H01L 51/0036 20130101; H01L 51/0043 20130101; C09D 11/36 20130101;
Y10S 428/917 20130101 |
Class at
Publication: |
347/095 ;
252/301.16 |
International
Class: |
B41J 2/17 20060101
B41J002/17; C09K 11/06 20060101 C09K011/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2001 |
CN |
90 1 04585 |
Feb 28, 2001 |
GB |
0104875.0 |
Mar 28, 2001 |
GB |
0107740.3 |
Claims
1. A formulation for depositing a material on a substrate according
to an ink-jet technique, the formulation comprising the material to
be deposited on the substrate dissolved in a solvent system
comprising a first solvent component having a relatively high
boiling point and which exhibits a relatively low solubility with
respect to the material to be deposited, and a second solvent
component having a relatively low boiling point and which exhibits
a relatively high solubility with respect to the material to be
deposited.
2. A formulation according to claim 1 wherein the second solvent
component has a boiling point in the range of 100 to 200.degree.
C.
3. A formulation according to claim 1 or claim 2 wherein the first
solvent component has a boiling point in the range of 130 to
300.degree. C.
4. A formulation according to claim 1 wherein the difference in
boiling point between the first and second solvent components is in
the range of 30 to 250.degree. C.
5. A formulation according to claim 4 wherein the difference in
boiling point between the first and second solvent components is in
the range of 70 to 150.degree. C.
6. A formulation according to any preceding claim wherein the
solubility of the material to be deposited in the first solvent
component is up to 0.5% weight per volume.
7. A formulation according to claim 6 wherein the solubility of the
material to be deposited in the first solvent component is in the
range of 0.03 to 0.3% weight per volume.
8. A formulation according to any preceding claim wherein the
solubility of the material to be deposited in the second solvent
component is greater than 0.5% weight per volume.
9. A formulation according to claim 8 wherein the wherein the
solubility of the material to be deposited in the second solvent
component is greater than 1.5% weight per volume.
10. A formulation according to any preceding claim wherein the
amount of material in the formulation and the proportion of the
first solvent component are selected such that upon removal of the
second solvent component the remaining solution of the material in
the first solvent component would be at or above saturation.
11. A formulation according to claim 1 wherein the first solvent
component comprises .alpha.-tetralone and the second solvent
component comprises 1,2-dimethylbenzene.
12. A formulation according to claim 1 wherein the first solvent
component comprises cyclohexylbenzene and the second solvent
component comprises 1,2-dimethylbenzene.
13. A formulation according to claim 1 wherein the first solvent
component comprises xylene and 1,2,4-trimethylbenzene and the
second solvent component comprises isopropylbiphenyl.
14. A method of depositing a material on a substrate comprising
depositing one or more drops of a solution of the material onto the
substrate through a nozzle according to an ink-jet technique and
drying the drops, wherein the solution of the material comprises a
formulation according to any preceding claim.
15. A method according to claim 14 wherein the variation in
thickness of the dried drop is less than 30% of the maximum
thickness.
16. A method of producing a light-emitting device comprising a
layer of an electroluminescent material sandwiched between two
electrodes such that charge carriers can move between the
electrodes and the layer of electroluminescent material, wherein
the layer of electroluminescent material is produced by a method
according to claim 14 or claim 15.
17. A use of a formulation according to any of claims 1 to 13 for
reducing or avoiding a ring deposition effect.
18. A formulation according to claim 1 excluding 1% w/v of a
triblend containing approximately 14 wt. % of a ternary polymer
containing fluorene (FB8) units, benzothiadiazole (BT) units and
triarylene units, 56 wt. % of F8BT and 30 wt. % TFB in a solvent
mixture containing 20 vol. % 1,2,4-trimethylbenzene and 80 vol. %
xylene or a solvent mixture containing 50 vol. %
1,2,4-trimethylbenzene and 50 vol. % xylene.
Description
[0001] The present invention relates to a formulation for
depositing a material on a substrate, to a method of depositing a
material on a substrate particularly by an ink-jet deposition
technique, and to a method of producing a light-emitting device by
such a deposition method.
[0002] As shown schematically in FIG. 1, a light-emitting device
typically comprises a layer of an electroluminescent polymer 3
sandwiched between a cathode 2 and an anode 1 such that charge
carriers can move between the electrodes and the layer of
electroluminescent polymer. It is typically produced by depositing
a layer of electroluminescent polymer 3 on a glass substrate 5
coated with an anode layer 1 such as a layer of indium-tin oxide
(ITO) and depositing a cathode layer 2 such as a calcium layer over
the layer of electroluminescent polymer 3. The device may comprise
further layers, such as a hole transport layer 4 (such as a layer
of doped polyethylene dioxythiophene as described in EP0686662)
provided between the anode 1 and the electroluminescent polymer
layer 3 and an electron transport layer provided between the
cathode and the electroluminescent layer (not provided in the
device shown in FIG. 1).
[0003] An ink-jet technique may be used for depositing the layer of
electroluminescent polymer. Such a technique is described in
EP0880303A1, whose content is incorporated herein by reference.
This technique basically involves the controlled deposition of
drops of a solution of the electroluminescent polymer through a
nozzle followed by evaporation of the solvent. This technique is
particularly suited to the deposition of patterned layers of the
electroluminescent polymer. For example, in some applications, it
may be required to have a layer of electroluminescent polymer
comprising an ordered array of pixels, wherein each pixel is
produced by the deposition of a single drop of solution of the
electroluminescent polymer. It is desirable in such cases that the
polymer is distributed uniformly in the spot remaining after
evaporation of the solvent.
[0004] Solutions of the electroluminescent polymer in solvents such
as isodurene have conventionally been used in this technique.
However, there has been noticed the problem with conventional
solvents that after a drop of the deposited solution has dried most
of the electroluminescent polymer is deposited as a ring around the
edge of the remaining spot leaving only a very thin film of the
polymer at the centre of the spot. This can result in relatively
poor device efficiency.
[0005] It is an aim of the present invention to provide a
formulation with which a film of the desired thickness profile can
be deposited on a substrate according to a technique involving
controlled drop deposition.
[0006] According to a first aspect of the present invention, there
is provided a formulation for depositing a material on a substrate,
the formulation comprising the material to be deposited on the
substrate dissolved in a solvent system comprising a first solvent
component having a relatively high boiling point and which exhibits
a relatively low solubility with respect to the material to be
deposited, and a second solvent component having a relatively low
boiling point and which exhibits a relatively high solubility with
respect to the material to be deposited.
[0007] References to the solubility of each solvent component with
respect to the material are references to the solubility of the
material in each solvent component.
[0008] Ink-jet techniques typically, require formulations having a
viscosity of up to about 20 cps. A typical viscosity for an ink-jet
formulation is about 10 cps.
[0009] The first solvent component may comprise one or more
solvents that have a relatively high boiling point and exhibit a
relatively low solubility with respect to the material to be
deposited (in relation to the second solvent component), and the
second solvent component may likewise comprise one or more solvents
that have a relatively low boiling point and exhibit a relatively
high solubility with respect to the material to be deposited (in
relation to the first solvent component).
[0010] In one embodiment, the second solvent component has a
boiling point in the range of 100 to 200.degree. C. and the first
solvent component has a boiling point in the range of 130 to
300.degree. C. The difference in boiling point between the first
and second solvent components is preferably in the range of 30 to
250.degree. C., further preferably in the range of 70 to
150.degree. C. The solubility of the material to be deposited in
the first solvent component is preferably up to 0.5% weight per
volume, further preferably in the range of 0.03 to 0.3% weight per
volume, and the solubility of the material to be deposited in the
second solvent is preferably greater than 0.5% weight per volume,
further preferably greater than 1.5% weight per volume.
[0011] The proportion of the first solvent component should
preferably be selected such that upon removal of the second solvent
component the remaining solution of the material in the first
solvent component would be substantially at or above saturation. In
one embodiment, the proportion of the first solvent component is in
the range of 10 to 60 volume percent, further preferably 20 to 50
volume percent.
[0012] In one embodiment, the proportion of the second solvent
component is in the range of 40 to 90 volume percent, preferably 50
to 80 volume percent.
[0013] According to another aspect of the invention, there is
provided a method of depositing a material on a substrate
comprising depositing one or more drops of a solution of the
material onto the substrate through a nozzle according to an
ink-jet technique and drying each deposited drop, wherein the
solution of the material comprises a formulation as described
above.
[0014] The solvent system is selected such that the material begins
to precipitate at a relatively early stage in the drying of the
drop, i.e. such that precipitation occurs whilst a substantial
amount of solvent remains unevaporated.
[0015] The solvent system is selected such that the variation in
thickness of the dried drop of material on the substrate is less
than 80% of the maximum thickness, preferably less than 50%, and
further preferably less than 30%. It is most preferred that the
thickness variation is less than 15%.
[0016] In one embodiment, the solvent system is selected such that
in a formulation having 0.5% w/v of the material to be deposited,
the dried drop has a thickness at its centre (i.e. the region
enclosed by the ring of increased thickness, if present) of 60 to
140 nm, preferably about 70 nm to 100 nm, which is desirable for EL
efficiency and lifetime of an organic light-emitting device.
[0017] In the above, the material for deposition on the substrate
may, for example, be an organic material such as a polymer or a
blend of polymers. In one application, it comprises one or more
semiconducting conjugated polymers such as a charge transport
polymer or a light-emissive polymer, or a blend of the two.
[0018] According to yet another aspect of the present invention,
there is provided a method of producing a light-emitting device
comprising a layer of an electroluminescent material sandwiched
between two electrodes such that charge carriers can move between
the electrodes and the layer of electroluminescent material,
wherein the layer of electroluminescent material is produced by a
method as described above.
[0019] According to another aspect of the present invention, there
is provided a use of a formulation as described above for reducing
or avoiding a ring deposition effect.
Embodiments of the present invention shall be described hereunder,
by way of example only, with reference to the accompanying drawings
in which:
[0020] FIG. 1 is a schematic view of a light-emissive device;
[0021] FIGS. 2 and 3 are graphs showing the thickness profile for a
spot obtained by an ink-jet technique using a formulation according
to embodiments of the present invention;
[0022] FIG. 4 is a graph showing the thickness profile for a spot
of an electroluminescent polymer deposited using a solvent
consisting entirely of 1,2-dimethylbenzene;
[0023] FIG. 5 is a graph showing the thickness profile, for a spot
obtained by an ink-jet technique using a formulation according to
another embodiment of the present invention; and
[0024] FIG. 6 illustrates some recurring units and polymers.
EXAMPLE 1
[0025] A solvent blend was prepared from 60 vol. %
1,2-dimethylbenzene (b.p.: 144.4.degree. C.) and 40 vol. %
.alpha.-tetralone (b.p.: 255.degree. C.). A 0.5% w/v solution of an
alternating polymer of 9,9-dioctylfluorene units and
benzothiadiazole units (F8BT) having a peak molecular weight of
about 266,000 was prepared using this solvent blend. Drops of this
solution were deposited by an ink-jet method on the surface of a
polyimide substrate that had been modified to lower its surface
energy. The drops were allowed to dry at room temperature and
humidity (20.degree. C..+-.1.0.degree. C. and 30-40% R.H.), and
Dektak measurements of the profile of the dried drops were taken.
The results of the measurements are shown in FIG. 2.
EXAMPLE 2
[0026] A solvent blend was prepared from 60 vol. %
1,2-dimethylbenzene and 40 vol. % cyclohexylbenzene. Drops of a
0.5% w/v solution of the same F8BT polymer as Example 1 were
deposited on a surface-modified polyimide substrate by an ink-jet
method. Dektak measurements of the profile of the dried drops were
taken. The results of the measurements are shown in FIG. 3.
COMPARATIVE EXAMPLE
[0027] Drops of a 0.5% w/v solution of the same F8BT polymer as
Examples 1 and 2 in 1,2-dimethylbenzene were deposited on a
surface-modified polyimide substrate by an ink-jet method. Dektak
measurements of the profile of the dried drops were taken. The
results of the measurements are shown in FIG. 4.
[0028] As can be seen from a comparison of FIGS. 2, 3 and 4, the
use of the formulations according to the present invention produced
dried drops that were significantly improved in terms of uniformity
of thickness compared to the comparative example. It is thought
that the improved thickness uniformity is a result of the following
mechanism. During drying of the drop, the volatile low boiling
point solvent evaporates quickly leaving behind a saturated
solution in the high boiling point solvent; this in turn causes the
polymer to be precipitated rapidly preventing radial flow within
the drop and thus creating a relatively uniform distribution of the
polymer in the drop.
[0029] Furthermore, the improved uniformity of thickness results in
an increased thickness at the centre of the drop for the same
concentration of material in the formulation. Being able to control
the thickness at the centre of the drop is considered to be an
important factor in improving the efficiency of a light-emitting
device produced by an ink-jet technique. The present invention thus
allows an increase in centre thickness without increasing the
concentration in the formulation of the material to be deposited.
This can have advantages in producing a device having pixels of the
desired size at the desired resolution.
[0030] Good results have also been achieved using a solvent blend
consisting of 40 vol. % mixed isomers of xylene (b.p.:138.degree.
C.); 40 vol. % 1,2,4-trimethylbenzene (b.p.:168.degree. C.) and 20
vol. % 3-isopropylbiphenyl (b.p.:295.degree. C.). FIG. 5 shows a
Dektak measurement profile of a dried drop deposited by an ink-jet
technique using a 0.5% w/v solution of a polymer blend in this
three component solvent system. The polymer blend is relatively
highly soluble in the first two, low boiling point solvents
relative to the third high boiling point solvent.
* * * * *