U.S. patent application number 10/570640 was filed with the patent office on 2007-02-15 for electronic device comprising an organic semiconductor, an organic semiconductor, and an intermediate buffer layer made of a polymer that is cationically polymerizable and contains no photoacid.
This patent application is currently assigned to COVION ORGANIC SEMICONDUCTORS GMBH. Invention is credited to Aurelie Falcou, Susanne Heun, Amir Parham, Jurgen Steiger.
Application Number | 20070034862 10/570640 |
Document ID | / |
Family ID | 34258390 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070034862 |
Kind Code |
A1 |
Parham; Amir ; et
al. |
February 15, 2007 |
Electronic device comprising an organic semiconductor, an organic
semiconductor, and an intermediate buffer layer made of a polymer
that is cationically polymerizable and contains no photoacid
Abstract
The present invention describes a novel design principle for
organic electronic elements by inserting at least one additional
crosslinkable layer. The properties of the electronic devices are
thereby improved. Structured construction of these devices is
furthermore facilitated.
Inventors: |
Parham; Amir; (Frankfurt,
DE) ; Falcou; Aurelie; (Frankfurt, DE) ; Heun;
Susanne; (Bad Soden, DE) ; Steiger; Jurgen;
(Frankfurt, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
COVION ORGANIC SEMICONDUCTORS
GMBH
FRANKFURT AM MAIN
DE
|
Family ID: |
34258390 |
Appl. No.: |
10/570640 |
Filed: |
September 4, 2004 |
PCT Filed: |
September 4, 2004 |
PCT NO: |
PCT/EP04/09902 |
371 Date: |
March 3, 2006 |
Current U.S.
Class: |
257/40 |
Current CPC
Class: |
H01L 51/0037 20130101;
Y10T 428/269 20150115; Y10T 428/31511 20150401; H01L 51/5088
20130101; Y10T 428/265 20150115; Y10T 428/31504 20150401; H01L
51/0015 20130101; H01L 51/0059 20130101; H01L 51/0039 20130101;
Y02E 10/549 20130101; H01L 51/0043 20130101; H01L 51/0035 20130101;
H01L 2251/308 20130101 |
Class at
Publication: |
257/040 |
International
Class: |
H01L 29/08 20060101
H01L029/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2003 |
DE |
103 40 711.1 |
Claims
1. An electronic device containing at least one layer of a
conductive doped polymer and at least one layer of an organic
semiconductor, characterized in that at least one conducting or
semiconducting organic buffer layer which is cationically
polymerizable, and to which less than 0.5% of a photoacid is added,
is introduced between these layers.
2. The electronic device as claimed in claim 1, characterized in
that no photoacid is added to the buffer layer.
3. The electronic device as claimed in claim 1, characterized in
that the crosslinking of the organic buffer layer is thermally
initiated.
4. The electronic device as claimed in claim 1, wherein the
electronic device comprises organic or polymeric light-emitting
diodes (OLEDs, PLEDs), organic solar cells (O-SCs), organic field
effect transistors (O-FETs), organic circuit elements (O-ICs),
organic field quench devices (O-FQDs), organic optical amplifiers
or organic laser diodes (O-lasers).
5. The electronic device as claimed in claim 1, wherein the
electronic device contains the following elements: substrate,
electrode, interlayer of a conductive doped polymer, conducting or
semiconducting organic cationically crosslinkable buffer layer,
organic semiconductor layer and back electrode.
6. The electronic device as claimed in claim 5, characterized in
that an interlayer of a material with a high dielectric constant is
introduced between a metal cathode and the organic
semiconductor.
7. The electronic device as claimed in claim 1, characterized in
that anode materials with a potential of more than 4.5 eV vs.
vacuum are used.
8. The electronic device as claimed in claim 1, characterized in
that the conductive doped polymer has a conductivity of
>10.sup.-8 S/cm and a potential of 4-6 eV vs. vacuum.
9. The electronic device as claimed in claim 8, characterized in
that derivatives of polythiophene or polyaniline are used as the
conductive polymer, and the doping is carried out via polymer-bound
Bronsted acids.
10. The electronic device as claimed in claim 5, wherein said
organic semiconductor is a low molecular weight oligomeric,
dendritic or polymeric semiconducting material.
11. The electronic device as claimed in claim 10, characterized in
that the organic semiconductor is a conjugated polymer.
12. The electronic device as claimed in claim 10, characterized in
that the organic semiconductor is a cationically crosslinkable
compound.
13. The electronic device as claimed in claim 12, characterized in
that the cationic crosslinking takes place via ring-opening
cationic polymerization of a heterocycle.
14. The electronic device as claimed in claim 13, characterized in
that the cationic crosslinking takes place via oxetane groups which
can be crosslinked via radiation by adding a photoacid.
15. The electronic device as claimed in claim 1, characterized in
that the crosslinkable buffer layer is low molecular weight
oligomeric, dendritic or polymeric before the crosslinking.
16. The electronic device as claimed in claim 1, characterized in
that the layer thickness of the buffer layer lies in the range of
5-300 nm.
17. The electronic device as claimed in claim 1, characterized in
that the potential of the buffer layer lies between the potential
of the conductive doped polymer and that of the organic
semiconductor.
18. The electronic device as claimed in claim 1, characterized in
that cationically crosslinkable hole-conductive materials are used
for the buffer layer.
19. The electronic device as claimed in claim 18, characterized in
that cationically crosslinkable triarylamine-based, thiophene-based
or triarylphosphine-based materials are used for the buffer
layer.
20. The electronic device as claimed in claim 1, characterized in
that materials in which at least one H atom is replaced by a
heterocyclic group, reacting by cationic ring-opening
polymerization, are used as materials for the buffer layer.
21. The electronic device as claimed in claim 20, characterized in
that the cationically polymerizable heterocycle is a group of the
formula (I), (II) or (III), ##STR12## in which R.sup.1 in each
occurrence is identically or differently hydrogen, a
straight-chained, branched or cyclic alkyl, alkoxy or thioalkoxy
group having from 1 to 20 C atoms, an aromatic or heteroaromatic
ring system having from 4 to 24 aromatic ring atoms or an alkenyl
group having from 2 to 10 C atoms, wherein one or more hydrogen
atoms may be replaced by halogen or by CN and one or more
non-neighboring C atoms may be replaced by --O--, --S--, --CO--,
--COO-- or --O--CO--; a plurality of R.sup.1 radicals may also form
a mono- or polycyclic, aliphatic or aromatic ring system with one
another or with R.sup.2, R.sup.3 and/or R.sup.4; R.sup.2 in each
occurrence is identically or differently hydrogen, a
straight-chained, branched or cyclic alkyl group having from 1 to
20 C atoms, an aromatic or heteroaromatic ring system having from 4
to 24 aromatic ring atoms or an alkenyl group having from 2 to 10 C
atoms, wherein one or more hydrogen atoms may be replaced by
halogen or by CN and one or more non-neighboring C atoms may be
replaced by --O--, --S--, --CO--, --COO-- or --O--CO--; a plurality
of R.sup.2 radicals may also form a mono- or polycyclic, aliphatic
or aromatic ring system with one another or with R.sup.1, R.sup.3
and/or R.sup.4; X in each occurrence is identically or differently
--O--, --S--, --CO--, --COO--, --O--CO-- or a bivalent
--(CR.sup.3R.sup.4).sub.n-- group; Z in each occurrence is
identically or differently a bivalent --(CR.sup.3R.sup.4).sub.n--
group; R.sup.3, R.sup.4 in each occurrence is identically or
differently hydrogen, a straight-chained, branched or cyclic alkyl,
alkoxy or thioalkoxy group having from 1 to 20 C atoms, an aromatic
or heteroaromatic ring system having from 4 to 24 aromatic ring
atoms or an alkenyl group having from 2 to 10 C atoms, wherein one
or more hydrogen atoms may be replaced by halogen or by CN; two or
more R.sup.3 or R.sup.4 radicals may also form a ring system with
one another or with R.sup.1, R.sup.2; n in each occurrence is
identically or differently an integer between 0 and 20; with the
proviso that the number of these groups according to formula (I)
and/or formula (II) and/or formula (III) is limited by the
maximally available, i.e. substitutable H atoms.
22. The electronic device as claimed in claim 21, characterized in
that the crosslinking of these units is carried out by thermal
treatment of the device.
23. The electronic device as claimed in claim 22, characterized in
that the crosslinking takes place at a temperature of from 80 to
200.degree. C. and for a duration of from 0.1 to 120 minutes in an
inert atmosphere.
Description
[0001] Electronic devices which contain organic, metallorganic or
polymeric semiconductors, or compounds of more than one of these
three groups, are more and more frequently being used in commercial
products or are shortly to be introduced onto the market. Examples
of existing commercial products include organic-based charge
transport materials (generally triarylamine-based hole
transporters) in copiers and organic or polymeric light emitting
diodes (OLEDs or PLEDs) in display devices. Organic solar cells
(O-SCs), organic field effect transistors (O-FETs), organic circuit
elements (O-ICs) or organic laser diodes (O-lasers) are at a highly
advanced research stage and could become very important in the
future.
[0002] Irrespective of the intended purpose, many of these devices
have the following general layer structure which is adapted
accordingly for the individual applications: [0003] (1) substrate
[0004] (2) contacting: conductive substance, electrode; often
metallic or inorganic, but also of organic or polymeric conductive
materials [0005] (3) optionally charge injection layer or
interlayer to compensate for unevennesses of the electrode
("Planarization Layer"), often of a conductive doped polymer [0006]
(4) organic semiconductor [0007] (5) optionally insulating layer
[0008] (6) second contacting: as (2); second electrode, materials
as mentioned in (2) [0009] (7) interconnection [0010] (8)
encapsulation.
[0011] One advantage which many of these organic devices have,
above all those which are based on polymeric or dendritic, or
oligomeric semiconductors, is that they can be produced from
solution which entails less technical and cost outlay than vacuum
processes, as are generally carried out for low molecular weight
compounds. For example, colored electroluminescent devices can be
produced comparatively simply by processing the materials by
surface coating from solution (for example by spin coating, doctor
blade technique, etc.). The structuring, i.e. driving of individual
image points, is usually carried out here in the "leads", i.e. for
example in the electrodes. This may, for example, be done using
shadow masks in the manner of a template. The structuring of
organic circuits and partially organic solar cell panels or laser
arrays can be carried out similarly. For industrial mass
production, however, this leads to significant disadvantages: after
they have been used one or more times, the masks become unusable
because of deposit formation, and must be elaborately regenerated.
For production, it would therefore be desirable to have a process
available for which shadow masks are not required.
[0012] Surface coating and structuring by shadow masks furthermore
cannot be readily employed when, for example, full-color displays
or organic circuits with different circuit elements are to be
produced. For full-color displays, the three primary colors (red,
green and, blue) in individual pixels (image points) must be
applied next to one another with a high resolution. Similar
considerations apply to electronic circuits with different circuit
elements. While the individual image points can be produced by
evaporating the individual colors using shadow masks in the case of
low molecular weight evaporatable molecules (with the associated
difficulties already mentioned above), this is not possible for
polymeric materials and materials processed from solution, and the
structuring can no longer be carried out merely by structuring the
electrodes. An alternative in this case is to directly apply the
active layer in a structured form (for example: the light emitting
layer in OLEDs/PLEDs; similar considerations apply to lasers or
charge transport layers in all applications). The fact that this
presents considerable problems can be understood merely from the
dimensions: it is necessary to provide structures in the range of a
few tens of .mu.m with layer thicknesses in the range of from less
than 100 nm to a few .mu.m. In particular, various printing
techniques have recently been considered for this, for example
inkjet printing, offset printing, etc. These printing techniques
have their own problems, however, and none of them has yet been
developed so that it might be usable for a mass production process.
The aforementioned mask technology is furthermore used here (in the
field of OLEDs) for the electrodes. Here again, this entails the
aforementioned problems of deposit formation. Structurability by
printing techniques must therefore still currently be regarded as
an unresolved problem.
[0013] Another approach to structurability has been proposed in WO
02/10129 and Nature 2003, 421, 829. There, structurable materials
are described which are suitable for use in structured devices such
as OLEDs, PLEDs, organic lasers, organic circuit elements or
organic solar cells. These are organic, in particular
electroluminescent materials, which contain at least one oxetane
group capable of crosslinking, the crosslinking reaction of which
can be deliberately initiated and controlled. Macromol. Rapid
Commun. 1999, 20, 225 describes N,N,N',N'-tetraphenylbenzidines
functionalized with oxetane groups, which can be crosslinked in a
photoinduced way. These compound classes are used as structurable
hole conductors directly on the anode of the organic electronic
device. At least one photoinitiator is added to the materials for
crosslinking. By exposure to actinic radiation, an acid is
generated which initiates a crosslinking reaction by cationic
ring-opening polymerization. A pattern of regions with crosslinked
material and regions with uncrosslinked material can thus be
obtained by structured exposure. The regions of uncrosslinked
material can then be removed by suitable operations (for example
washing with suitable solvents). This leads to the desired
structuring. The subsequent application of the various layers (or
other materials which are to be applied in proximity to the first
material) can thus be carried out after the crosslinking is
completed. Exposure, as employed for the structuring, is a standard
process in modern electronics and can, for example, be carried out
with lasers or by surface exposure using a suitable photomask. The
mask does not involve the risk of deposition here, since in this
case only radiation and no material flux has to be delimited by the
mask. In Chem Phys Chem 2000, 207, such a crosslinked triarylamine
layer is introduced as an interlayer between a conductive doped
polymer and an organic luminescent semiconductor. A higher
efficiency is obtained in this case. Here again, a photoacid is
used for the crosslinking. This appears to be necessary for
complete crosslinking of the triarylamine layer. However, the
photoacid or its reaction products remain as contamination in the
electronic device after the crosslinking. It is generally
acknowledged that both organic and inorganic impurities can perturb
the operation of organic electronic devices. For this reason, it
would be desirable to be able to reduce the use of photoacids as
much as possible.
[0014] EP 0637899 proposes electroluminescent arrangements having
one or more layers in which at least one layer is obtained by
thermal or radiation-induced crosslinking, which furthermore
contain at least one emitter layer and at least one charge
transport unit per layer. The crosslinking may take place
radically, ionically, cationically or via a photoinduced ring
closure reaction. An advantage mentioned is that a plurality of
layers can thereby be formed on one another, or that the layers can
also be structured in a radiation-induced way. However, no teaching
is given as to which of the various crosslinking reactions can be
used to produce a suitable device, and how the crosslinking
reaction can best be carried out. It is merely mentioned that
radically crosslinkable units or groups capable of
photocycloaddition are preferred, that various types of
auxiliaries, for example initiators, may be contained and that the
film is preferably crosslinked by means of actinic radiation and
not thermally. Suitable device configurations are also not
described. It is therefore unclear how many layers the device
preferably comprises, and how thick they should be, which material
classes are preferably used and which of them should be
crosslinked. It is therefore also not apparent to the person
skilled in the art how the described invention can be successfully
implemented in practice.
[0015] In devices for organic electronics, an interlayer of a
conductive doped polymer is often introduced as a charge injection
layer between the electrode (in particular the anode) and the
function material (Appl. Phys. Lett. 1997, 70, 2067-2069).
[0016] Alternatively, a conductive doped polymer may also be used
directly as the anode (or even as the cathode, depending on the
application). The most common of these polymers are polythiophene
derivatives (for example poly(ethylenedioxythiophene), PEDOT) and
polyaniline (PANI), which are generally doped with polystyrene
sulfonic acid or other polymer-bound Bronstedt acids and thus
brought into a conductive state. Without wishing to be bound by the
correctness of this special theory in the subsequent invention, we
suspect that during operation of the device protons or other
impurities diffuse from the acid groups into the functional layer
where they are likely to perturb the functionality of the device
significantly. It is thus suspected that these impurities reduce
the efficiency as well as the lifetime of the devices. Protons or
other cationic impurities have a negative effect in particular when
the functional semiconductor layer applied onto this layer is
cationically crosslinkable and, as described above, is intended to
be structured. We suspect that the functional layer is already
partially or fully crosslinked by the presence of protons or other
cationic impurities, without providing the opportunity to control
the crosslinking, for example by actinic radiation. The advantage
of the controlled structurability is therefore lost. Cationically
crosslinkable materials thus in principle do provide the
possibility of structuring and therefore an alternative to printing
techniques. However, technical implementation of these materials is
not to date possible since the problem of uncontrolled crosslinking
on a doped charge injection layer is not yet resolved.
[0017] Surprisingly, it has now been found that the electronic
properties of the devices can be significantly improved when at
least one buffer layer, which is cationically crosslinkable, is
introduced between the doped interlayer and the functional organic
semiconductor layer. Particularly good properties are obtained with
a buffer layer whose cationic crosslinking is induced thermally,
i.e. by a temperature rise to from 50 to 250.degree. C., preferably
from 80 to 200.degree. C., and to which no photoacid is added.
Another advantage of this buffer layer is that the uncontrollable
crosslinking of a cationically crosslinkable semiconductor can be
avoided by using the buffer layer, which for the first time permits
controlled structuring of the semiconductor. Yet another advantage
of crosslinking the buffer layer is that the glass transition
temperature of the material and therefore the stability of the
layer are increased by the crosslinking.
[0018] The invention therefore relates to electronic devices
containing at least one layer of a conductive doped polymer and at
least one layer of an organic semiconductor, characterized in that
at least one conducting or semiconducting organic buffer layer
which is cationically polymerizable, and to which less than 0.5% of
a photoacid is added, is introduced between these layers.
[0019] It is preferable that no photoacid is added to the
semiconducting organic buffer layer.
[0020] An organic buffer layer whose crosslinking in the
corresponding device arrangement can be induced thermally, i.e. by
a temperature rise to 50-250.degree. C., preferably 80-200.degree.
C., without adding further auxiliaries, for example photoacids, is
furthermore preferred.
[0021] A photoacid is a compound which releases a protic acid by a
photochemical reaction when exposed to actinic radiation. Examples
of photoacids are 4-(thio-phenoxyphenyl)-diphenylsulfonium
hexafluoroantimonate or
{4-[(2-hydroxytetradecyl)-oxyl]-phenyl}-phenyliodonium
hexafluoroantimonate and the like, as described for example in EP
1308781. The photoacid may be added for the crosslinking reaction,
in which case a proportion of from approximately 0.5 to
approximately 3% by weight is preferably selected according to the
prior art.
[0022] Electronic devices in the context of this invention are
organic or polymeric light emitting diodes (OLEDs, PLEDs, for
example EP 0676461, WO 98/27136), organic solar cells (O-SCs, for
example WO 98/48433, WO 94/05045), organic field effect transistors
(O-FETs, for example U.S. Pat. No. 5,705,826, U.S. Pat. No.
5,596,208, WO 00/42668), field quench elements (FQDs, for example
US 2004/017148), organic circuit elements (O-ICs, for example WO
95/31833, WO 99/10939), organic optical amplifiers or organic laser
diodes (O-lasers, WO 98/03566). Organic in the context of this
invention means that at least one layer of an organic conductive
doped polymer, at least one conducting or semiconducting organic
buffer layer and at least one layer containing at least one organic
semiconductor are present; further organic layers (for example
electrodes) may also be present in addition to these. Moreover,
layers which are not based on organic materials may also be
present, for example inorganic interlayers or electrodes.
[0023] In the simplest case, the electronic device is constructed
from a substrate (conventionally glass or a plastic sheet), an
electrode, an intermediate layer of a conductive doped polymer, a
crosslinkable buffer layer according to the invention, an organic
semiconductor and a back electrode. This device is accordingly
(depending on the application) structured, contacted and
hermetically sealed, since the lifetime of such devices is
drastically shortened in the presence of water and/or air. It may
also be preferred to use a conductive doped polymer as the
electrode material for one or both electrodes and not to introduce
an interlayer of conductive doped polymer. For applications in
O-FETs, in addition to the electrode and the back electrode (source
and drain), it is furthermore necessary that the structure also
contains a further electrode (gate) which is separated from the
organic semiconductor by an insulator layer generally having a high
dielectric constant. It may furthermore be expedient to introduce
yet other layers into the device.
[0024] The electrodes are selected so that their potential
coincides as well as possible with the potential of the adjacent
organic layer, in order to ensure maximally efficient electron or
hole injection. If the cathode is to inject electrons, as is the
case for example in OLEDs/PLEDs or n-type conducting O-FETs, or
receive holes, as is the case for example in O-SCs, then metals
with a low work function, metal alloys or multilayered structures
comprising different metals, for example alkaline-earth metals,
alkali metals, main group metals or lanthanides (for example Ca,
Ba, Mg, Al, In, Mg, Yb, Sm, etc.) are preferred for the cathode.
For multilayered structures, in addition to the aforementioned
metals it is also possible to use other metals which have a
relatively high work function, for example Ag, in which case
combinations of the metals are generally used, for example Ca/Ag or
Ba/Ag. The cathodes are conventionally between 10 and 10,000 nm,
preferably between 20 and 1000 nm, thick. It may also be preferred
to introduce a thin interlayer of a material having a high
dielectric constant between a metal cathode and the organic
semiconductor (or other functional organic layers which may
optionally be present). Alkali metal or alkaline-earth metal
fluorides, or alternatively the corresponding oxides, may for
example be suitable for this (for example LiF, Li.sub.2O,
BaF.sub.2, MgO, NaF, etc.). The layer thickness of this dielectric
layer is preferably between 1 and 10 nm.
[0025] Materials with a high work function are preferred for the
anode when holes are injected (as for example in OLEDs/PLEDs,
p-type conducting O-FETs) or electrons are received (as for example
O-SCs) at the anode. The anode preferably has a potential of more
than 4.5 eV vs. vacuum. On the one hand, metals with a high redox
potential are suitable for this, for example Ag, Pt or Au.
Metal/metal oxide electrodes (for example Al/Ni/NiO.sub.x,
Al/Pt/PtO.sub.x) may also be preferred. The anode may also consist
of a conductive organic material (for example a conductive doped
polymer).
[0026] For some applications, at least one of the electrodes must
be transparent in order to allow either irradiation of the organic
material (O-SCs) or output of light (OLEDs/PLEDs, O-lasers, organic
optical amplifiers). A preferred construction uses a transparent
anode. Preferred anode materials here are conductive mixed metal
oxides. Indium-tin oxide (ITO) or indium-zinc oxide (IZO) are
particularly preferred. Conductive doped organic materials, in
particular conductive doped polymers, are furthermore preferred. A
similar construction also applies to inverted structures, in which
the light is output from the cathode or incident on the cathode.
The cathode then preferably consists of the materials described
above, with the difference that the metal is very thin and
therefore transparent. The layer thickness of the cathode is
preferably less than 50 nm, particularly preferably less than 30
nm, and in particular less than 10 nm. A further transparent
conductive material is applied thereon, for example indium-tin
oxide (ITO), indium-zinc oxide (IZO) etc.
[0027] Various organic doped conductive polymers may be suitable
for the conductive doped polymer (either as an electrode or as an
additional charge injection layer or "Planarization Layer", in
order to compensate for unevennesses of the electrode and thus
minimize short circuits). Polymers which have a conductivity of
>10.sup.-8 S/cm, depending on the application, are preferred
here. In a preferred embodiment of this invention, the conductive
doped polymer is applied onto the anode or functions directly as
the anode. Here, the potential of the layer is preferably from 4 to
6 eV vs. vacuum. The thickness of the layer is preferably between
10 and 500 nm, particularly preferably between 20 and 250 nm. If
the conductive doped polymer itself is the electrode, then the
layers are generally thicker in order to ensure a good outward
electrical connection and a low capacitive impedance. Derivatives
of polythiophene are particularly preferably used (particularly
preferably poly(ethylenedioxythiophene), PEDOT) and polyaniline
(PANI). The doping is generally carried out using acids or
oxidizing agents. The doping is preferably carried out using
polymer-bound Bronsted acids. Generally polymer-bound sulfonic
acids, in particular poly(styrene sulfonic acid), poly(vinyl
sulfonic acid) and PAMPSA (poly(2-acrylamido-2-methyl-propane
sulfonic acid)) are particularly preferred for this. The conductive
polymer is generally applied from an aqueous solution or dispersion
and is insoluble in organic solvents. The subsequent layer can
thereby be readily applied from organic solvents.
[0028] Low molecular weight oligomeric, dendritic or polymeric
semiconducting materials are in principle suitable for the organic
semiconductor. An organic material in the context of this invention
is intended to mean not only purely organic materials, but also
metallorganic materials and metal coordination compounds with
organic ligands. The oligomeric, dendritic or polymeric materials
may be conjugated, non-conjugated or partially conjugated.
Conjugated polymers in the context of this invention are polymers
which contain primarily sp.sup.2-hybridized carbon atoms in the
main chain, which may also be replaced by corresponding
heteroatoms. In the simplest case, this means the alternate
presence of double and single bonds in the main chain. Primarily
means that naturally occurring defects, which lead to conjugation
interruptions, do not invalidate the term "conjugated polymer".
Furthermore, the term conjugated likewise applies in this
application text when the main chain contains for example arylamine
units and/or particular heterocycles (i.e. conjugation via N, O or
S atoms) and/or metallorganic complexes (i.e. conjugation via the
metal atom). Units such as, for example, simple alkene chains,
(thio)ether bridges, ester, amide or imide linkages would however
be unequivocally defined as non-conjugated segments. Furthermore,
the term conjugated organic material is also intended to include
.sigma.-conjugated polysilanes, -germylenes and analogues which
carry organic side groups, and can therefore be applied from
organic solvents, for example poly(phenylmethylsilane).
Non-conjugated materials are materials in which no lengthy
conjugated units occur in the main chain or in the dendrimer
backbone. The term partially conjugated materials is intended to
mean those materials which have lengthy conjugated sections in the
main chain or in the dendrimer backbone, which are bridged by
non-conjugated units, or which contain lengthy conjugated units in
the side chain. Typical examples of conjugated polymers, as may for
example be used in PLEDs or O-SCs, are poly-para-phenylenevinylene
(PPV), polyfluorenes, polyspirobifluorenes or systems which are
based in the broadest sense on poly-p-phenylene (PPP), and
derivatives of the structures. Materials with a high charge carrier
mobility are primarily of interest for use in O-FETs. These are for
example oligo- or poly(triarylamines), oligo- or poly(thiophenes)
and copolymers which contain a large proportion of these units.
[0029] The layer thickness of the organic semiconductor is
preferably 10-500 nm, particularly preferably 20-250 nm, depending
on the application.
[0030] Here, the term dendrimer is intended to mean a highly
branched compound which is constructed from a multifunctional core
to which branched monomers are bound in a regular structure, so
that a tree-like structure is obtained. Both the core and the
monomers may assume any branched structures which consist both of
purely organic units and of organometallic compounds or
coordination compounds. Here, dendrimers are to be understood as
described for example in M. Fischer, F. Vogtle, Angew. Chem., Int.
Ed. 1999, 38, 885-905.
[0031] In order to be able to apply a plurality of organic
semiconductors above one another from solution, which is
advantageous for many optoelectronic applications (for example
PLEDs), crosslinkable organic layers have been developed (WO
02/10129). After the crosslinking reaction, these are insoluble and
therefore can no longer be attacked by solvents during the
application of further layers. Crosslinkable organic semiconductors
also have advantages for the structuring of multicolored PLEDs. The
use of crosslinkable organic semiconductors is thus furthermore
preferred. Preferred crosslinking reactions are cationic
polymerizations, based on electron-rich olefin derivatives,
heteronuclear multiple bonds with heteroatoms or heterogroups or
rings with heteroatoms (for example O, S, N, P, Si, etc.).
Particularly preferred crosslinking reactions are cationic
polymerizations based on rings with heteroatoms. Such crosslinking
reactions are described in detail below for the buffer layer
according to the invention.
[0032] Semiconducting luminescent polymers which can be chemically
crosslinked are generally disclosed in WO 96/20253.
Oxetane-containing semiconducting polymers, as described in WO
02/10129, have proved particularly suitable. They can be
crosslinked deliberately and in a controlled way by adding a
photoacid and irradiation. Crosslinkable low molecular weight
compounds may furthermore be suitable, for example cationically
crosslinkable triarylamines (M. S. Bayer et al., Macromol. Rapid
Commun. 1999, 20, 224-228; D. C. Muller et al., Chem Phys Chem
2000, 207-211). These descriptions are incorporated into the
present invention by reference.
[0033] Without wishing to be bound by a particular theory, we
suspect that hydrogen atoms or other cationic impurities contained
in the conductive doped polymer can already initiate a cationic
polymerization when a cationically crosslinkable semiconductor is
applied thereon, and therefore make the latter impossible to
structure. But even layers of organic semiconductors, which are not
cationically crosslinkable, on conductive doped polymers are
problematic since impurities and their diffusion out of the doped
polymer are likely to limit the lifetime of the electronic device.
Furthermore, the hole injection out of the doped polymer into the
organic semiconductor is often unsatisfactory.
[0034] According to the invention, therefore, the introduction of a
buffer layer which is introduced between the conductive doped
polymer and the organic semiconductor, and which carries the
cationically crosslinkable units, is such that it can absorb low
molecular weight cationic species and intrinsic cationic charge
carriers which may diffuse out of the conductive doped polymer.
Before the crosslinking, the buffer layer may be both low molecular
weight and oligomeric, dendritic or polymeric. The layer thickness
is preferably in the range of 5-300 nm, particularly preferably in
the range of 10-200 nm. The potential of the layer preferably lies
between the potential of the conductive doped polymer and that of
the organic semiconductor. This can be achieved by a suitable
choice of the materials for the buffer layer and suitable
substitution of the materials.
[0035] Preferred materials for the buffer layer are derived from
hole-conductive materials, such as those used as hole conductors in
other applications. Cationically crosslinkable triarylamine-based,
thiophene-based or triarylphosphine-based materials or combinations
of these systems are particularly preferably preferred for this.
Copolymers with other monomer units, for example fluorene,
spirobifluorene, etc., with a high proportion of these
hole-conductive units are also suitable. The potentials of these
compounds can be adjusted by suitable substitution. By the
introduction of electron-withdrawing substituents (for example F,
Cl, CN, etc.) for instance, it is possible to achieve compounds
with a low HOMO (=highest occupied molecular orbital), while a high
HOMO can be achieved by introduction of electron-repelling
substituents (for example alkoxy groups, amino groups, etc.).
[0036] The buffer layer according to the invention may comprise low
molecular weight compounds which are crosslinked in the layer and
thus rendered insoluble. Oligomeric, dendritic or polymeric soluble
solutions, which are rendered insoluble by subsequent cationic
crosslinking, may also be suitable. Mixtures of low molecular
weight compounds and oligomeric, dendritic and/or polymeric
compounds may furthermore be used. Without wishing to be bound by a
special theory in this invention, cationic species that can diffuse
out of the conductive doped polymer are firstly protons which may
originally come from the dopant being used (often polymer-bound
sulfonic acids) but also ubiquitous water. Cationic species, for
example metal ions, may also be present as (undesired) impurities
in the conductive polymer. Another possible source of cationic
species is the electrode on which the conductive polymer is
applied. For example, indium ions may emerge from an ITO electrode
and diffuse into the active layers of the devices. Other low
molecular weight cationic species that may possibly be present are
monomeric and oligomeric constituents of the conductive polymer,
which are converted into a cationic state by protonation or by
other doping. It is furthermore possible for charge carriers
introduced by oxidative doping to diffuse into the semiconductor
layer. The cationically crosslinkable buffer layer can trap
diffusing cationic species so that the crosslinking reaction is
subsequently initiated; on the other hand, the buffer layer is
simultaneously rendered insoluble by the crosslinking, so that the
subsequent application of an organic semiconductor from
conventional organic solvents presents no problems. The crosslinked
buffer layer represents a further barrier against diffusion.
[0037] Preferred cationically polymerizable groups of the buffer
layer are the following functional groups: [0038] 1) electron-rich
olefin derivatives, [0039] 2) heteronuclear multiple bonds with
heteroatoms or heterogroups, or [0040] 3) rings with heteroatoms
(for example O, S, N, P, Si, etc.), which react by cationic
ring-opening polymerization.
[0041] Organic materials which carry at least one substituent that
reacts by cationic ring-opening polymerization are preferred. A
general review of cationic ring-opening polymerization is given,
for example, by E. J. Goethals et al., "Cationic Ring Opening
Polymerization" (New Methods Polym. Synth. 1992, 67-109).
Non-aromatic cyclic systems, in which one or more ring atoms are
identically or differently O, S, N, P, Si, etc., are generally
suitable for this.
[0042] Cyclic systems having from 3 to 7 ring atoms, in which from
1 to 3 ring atoms are identically or differently O, S or N, are
preferred. Examples of such systems are unsubstituted or
substituted cyclic amines (for example aziridine, azeticine,
tetrahydropyrrole, piperidine), cyclic ethers (for example oxiran,
oxetane, tetrahydrofuran, pyran, dioxane), as well as the
corresponding sulfur derivatives, cyclic acetals (for example
1,3-dioxolane, 1,3-dioxepane, trioxane), lactones, cyclic
carbonates, but also cyclic structures which contain different
heteroatoms in the cycle, for example oxazolines, dihydrooxazines
or oxazolones. Cyclic siloxanes having from 4 to 8 ring atoms are
furthermore preferred.
[0043] More particularly preferred are low molecular weight,
oligomeric or polymeric organic materials in which at least one H
atom is replaced by a group of the formula (I), (II) or (III),
##STR1## [0044] in which [0045] R.sup.1 in each occurrence is
identically or differently hydrogen, a straight-chained, branched
or cyclic alkyl, alkoxy or thioalkoxy group having from 1 to 20 C
atoms, an aromatic or heteroaromatic ring system having from 4 to
24 aromatic ring atoms or an alkenyl group having from 2 to 10 C
atoms, wherein one or more hydrogen atoms may be replaced by
halogen such as Cl and F or by CN and one or more non-neighboring C
atoms may be replaced by --O--, --S--, --CO--, --COO-- or
--O--CO--; a plurality of R.sup.1 radicals may also form a mono- or
polycyclic, aliphatic or aromatic ring system with one another or
with R.sup.2, R.sup.3 and/or R.sup.4; [0046] R.sup.2 in each
occurrence is identically or differently hydrogen, a
straight-chained, branched or cyclic alkyl group having from 1 to
20 C atoms, an aromatic or heteroaromatic ring system having from 4
to 24 aromatic ring atoms or an alkenyl group having from 2 to 10 C
atoms, wherein one or more hydrogen atoms may be replaced by
halogen such as Cl and F or by CN and one or more non-neighboring C
atoms may be replaced by --O--, --S--, --CO--, --COO--or --O--CO--;
a plurality of R.sup.2 radicals may also form a mono- or
polycyclic, aliphatic or aromatic ring system with one another or
with R.sup.1, R.sup.3 and/or R.sup.4; [0047] X in each occurrence
is identically or differently --O--, --S--, --CO--, --COO--,
--O--CO-- or a bivalent --(CR.sup.3R.sup.4).sub.n-- group; [0048] Z
in each occurrence is identically or differently a bivalent
--(CR.sup.3R.sup.4).sub.n-- group; [0049] R.sup.3, R.sup.4 in each
occurrence is identically or differently hydrogen, a
straight-chained, branched or cyclic alkyl, alkoxy or thioalkoxy
group having from 1 to 20 C atoms, an aromatic or heteroaromatic
ring system having from 4 to 24 aromatic ring atoms or an alkenyl
group having from 2 to 10 C atoms, wherein one or more hydrogen
atoms may be replaced by halogen such as Cl and F or by CN; two or
more R.sup.3 or R.sup.4 radicals may also form a ring system with
one another or with R.sup.1 or R.sup.2; [0050] n in each occurrence
is identically or differently an integer between 0 and 20,
preferably between 1 and 10, in particular between 1 and 6; with
the proviso that the number of these groups according to formula
(I) and/or formula (II) and/or formula (III) is limited by the
maximally available, i.e. substitutable H atoms.
[0051] The crosslinking of these units is preferably carried out by
thermal treatment of the device at this stage. It is not necessary,
and not even desirable, to add a photoacid for the crosslinking
since this would introduce impurities into the device. Without
wishing to be bound by a special theory, we suspect that the
crosslinking of the buffer layer is initiated by the protons
emerging from the conductive doped polymer. This crosslinking
preferably takes place at a temperature of from 80 to 200.degree.
C. and for a duration of from 0.1 to 120 minutes, preferably from 1
to 60 minutes, particularly preferably from 1 to 10 minutes, in an
inert atmosphere. This crosslinking particularly preferably takes
place at a temperature of from 100 to 180.degree. C. and for a
duration of from 20 to 40 minutes in an inert atmosphere. For the
crosslinking, it may also be advantageous for further auxiliaries
which are not photoacids, but which can promote the crosslinking,
to be added to the buffer layer. Salts, in particular inorganic
salts, for example tetrabutylammonium hexafluoroantimonate, which
are added as a supporting electrolyte in order to improve the
crosslinking, acids, in particular organic acids, for example
acetic acid, or further addition of polystyrene sulfonic acid to
the conductive polymer, or oxidizing substances, for example
nitrylium or nitrosylium salts (NO.sup.+, NO.sub.2.sup.+), may for
example be suitable for this. After the crosslinking has been
carried out, these auxiliaries can easily be washed out and
therefore do not remain as contamination in the film. The
auxiliaries have the advantage that the crosslinking can thereby be
fully carried out more easily and that thicker buffer layers can
thereby also be produced.
[0052] The following general method, which can be adapted
appropriately to the particular case without any further inventive
step, is in general employed for production of the devices: [0053]
A substrate (for example glass or a plastic) is coated with the
anode (for example indium-tin oxide ITO, etc.). The anode is
subsequently (for example photolithographically) structured and
interconnected according to the intended application. In this case,
the entire substrate and the corresponding interconnection may
first be produced using a quite elaborate process so as to
facilitate so-called active matrix control. The pre-cleaned
substrate coated with the anode is treated either with ozone or
with oxygen plasma or briefly exposed to an excimer lamp. [0054] A
conductive polymer, for example a doped polythiophene derivative
(PEDOT) or polyaniline derivative (PANI) is subsequently applied in
a thin layer, usually with a layer thickness of between 10 and 500
nm, preferably between 20 and 300 nm, onto the ITO substrate by
spin coating or other coating methods. [0055] The cationically
crosslinkable buffer layer according to the invention is applied
onto this layer. To this end, the corresponding compound is first
dissolved in a solvent or solvent mixture and filtered. Since
organic semiconductors and above all the surfaces of the layers are
sometimes extremely influenced by oxygen or other air constituents,
it is recommended to carry out this operation under a protective
gas. Aromatic liquids, for example toluene, xylene, anisole,
chlorobenzene and the like, for example cyclic ethers (for example,
dioxane, methyldioxane, THF), as well as amides, for example NMP or
DMF, but also solvent mixtures as described in application text WO
02/072714, are suitable as solvents for aromatic compounds. Other
organic solvents, which are selected as a function of the compound
class used, are also suitable for low molecular weight compounds.
Using these solutions, the previously coated support can be coated
or covered surface-wide, for example by spin-coating methods, flow
or wave coating or doctor blade techniques. The crosslinking of the
buffer layer can take place by heating the device at this stage in
an inert atmosphere. Here, it is not necessary and not even
desirable to add a photoacid; thermal treatment of the buffer layer
on the doped polymer is sufficient in order to carry out the
crosslinking reaction. Optionally, it may subsequently be flushed
with a solvent, for example THF. It is then optionally dried.
[0056] A solution of an organic semiconductor is then applied. The
choice of the semiconductor depends on the intended application. If
a crosslinkable organic semiconductor is used, this may be
structured according to the intended application by controlled
crosslinking. In the case of cationically crosslinkable
semiconductors, for example, this may be done by adding a
photoacid, exposure through a shadow mask and subsequent thermal
treatment. Since the underlying buffer layer is not acidic, the use
of a photoacid should not be ruled out here. The uncrosslinked part
of the semiconductor may subsequently be washed with an organic
solvent in which the semiconductor is soluble. This process can be
repeated for different materials, so as to successively apply a
plurality of materials in a structured way. For example,
electroluminescent polymers with different emission colors may be
successively applied in a structured way for a full-color display,
or organic field effect transistors with different functions may be
successively applied for organic circuits. It is also possible to
apply a plurality of crosslinkable layers above one another. [0057]
Further functional layers, for example charge injection or
transport layers, further emission layers and/or hole blocking
layers may optionally be applied on these polymer layers, for
example from solution by methods such as those described for the
buffer layer, but also by evaporation. [0058] A cathode is
subsequently applied. This is carried out according to the prior
art by a vacuum process and may, for example, be done by thermal
evaporation or plasma spraying (sputtering). The cathode may be
applied surface-wide or using a mask so that it is structured. The
contacting of the electrodes is then carried out. [0059] Since many
applications react sensitively to water, hydrogen or other
constituents of the atmosphere, effective encapsulation of the
device is indispensable. [0060] The structure described above is
adapted accordingly for the individual applications and can
generally be used for different applications, such as organic and
polymeric light emitting diodes, organic solar cells, organic field
effect transistors, organic circuit elements, organic optical
amplifiers or organic laser diodes.
[0061] Surprisingly, this crosslinkable buffer layer, which is
introduced between the conductive doped polymer and the organic
semiconductor, offers the following advantages: [0062] 1)
Introducing the crosslinkable buffer layer according to the
invention improves the optoelectronic properties of the electronic
device compared with a device which does not contain such a buffer
layer. For instance, a high efficiency and a longer lifetime with a
reduced operating voltage are observed. It turns out that this
effect is particularly pronounced when the crosslinking of the
buffer layer is thermally initiated. If a photoacid is added to the
buffer layer for crosslinking, as described in the literature, the
lifetime remains virtually unchanged. [0063] 2) Since the buffer
layer probably traps cationic species which emerge from the
conductive doped polymer, they are prevented from diffusing into
the organic semiconductor. If the organic semiconductor is a
cationically crosslinkable compound, then undesired crosslinking of
the semiconductor is thereby avoided. This for the first time
allows controlled structuring of the semiconductor, which has not
previously been possible in this way.
[0064] The present invention will be explained in more detail by
the following examples, which are not meant to restrict it. Only
organic and polymeric light emitting diodes will be discussed in
these examples. Without any inventive step, however, the person
skilled in the art will be able to produce other electronic devices
on the basis of the examples given, for example O-SCs, O-FETs,
O-ICs, optical amplifiers and O-lasers, to mention only a few
further applications.
EXAMPLES
Example 1
Synthesis of a Cationically Crosslinkable Compound P1 for Use as a
Buffer Layer
a) Synthesis of Precursors Known from the Literature
[0065] 3-Ethyl-3-(iodomethyl)oxetane (WO 96/21657),
11-(4-bromophenoxy)-1-undecanol (M. Trollsaas et al., Macromol.
Chem. Phys. 1996, 197, 767-779) and N,N'-diphenylbenzidine (K.
Wiechert et al., Zeitschrift Chem. 1975, 15, 49-50) were
synthesized according to the literature.
b) Synthesis of
N,N'-Bis-(4-bromophenyl)-N,N'-bis-(4-tert-butylphenyl)-biphenyl-4,4'-diam-
ine (monomer M1)
[0066] ##STR2##
[0067] The synthesis of monomer M1 is described in WO
02/077060.
c) Synthesis of N,N'-Bis-(4-pinacol
boronate)phenyl-N,N'-bis-(4-tert-butylphenyl)-biphenyl-4,4'-diamine
(monomer M2)
[0068] ##STR3##
[0069] The synthesis of monomer M2 is described in application DE
10337077.3 which has not yet been laid open.
d) Synthesis of
3-(11-(4-bromophenoxy)-undecan-1-oxy)methylene-3-ethyl-oxetane
[0070] ##STR4##
[0071] 1.6 g (30 mmol) of NaH were suspended in 70 ml of dry DMF
and stirred under a protective gas. A solution of 6.8 g (20 mmol)
11-(4-Bromophenoxy)-1-undecanol in 25 ml of DMF was added thereto
at 40.degree. C. After 1 h, 2.96 g (22 mmol) of
3-ethyl-3-(iodomethyl)oxetane and 0.166 g (1.0 mmol) of KI were
added and stirred for 24 h at 40.degree. C. After cooling to room
temperature, 200 ml of water and 200 ml of CH.sub.2Cl.sub.2 were
added to the reaction mixture, the organic phase was separated,
dried over Mg.sub.2SO.sub.4 and the solvent was removed in a
vacuum. The product was purified chromatographically (silica,
eluent hexane). The yield was 3.2 g (89% Th.) and the purity was
98% (according to HPLC).
[0072] .sup.1H-NMR (CDCl.sub.3, 500 MHz): 1.45 (t, J=7.3 Hz, 3H),
1.45 (m, 14H), 1.55 (m, 2H), 1.75 (m, 4H), 3.42 (t, J=6.3 Hz, 2H),
3.46 (s, 2H), 3.85 (t, J=6.3 Hz, 2H), 4.39 (d, J=5.9 Hz, 2H), 4.44
(d, J=5.9 Hz, 2H), 6.75 (d, J=9 Hz, 2H), 7.35 (d, J=9 Hz, 2H).
e) Synthesis of oxetane-substituted
N,N,N',N'-tetraphenylbenzidine
[0073] ##STR5##
[0074] A degassed solution of 5.1 g (9.7 mmol)
N,N'-diphenylbenzidine and 14 g (21.4 mmol)
3-(11-(4-bromophenoxy)-undecan-1-oxy)methylene-3-ethyl-oxetane in
250 ml of toluene was saturated for 1 h with N.sub.2. First 0.12 g
(0.39 mmol) of P(.sup.tBu).sub.3 then 69 mg (0.19 mmol) of
Pd(OAc).sub.2 were added to the solution. 3.8 g (50.4 mmol) of
solid NaO.sup.tBu were subsequently added. The reaction mixture was
heated for 5 h under reflux. After cooling to room temperature,
0.85 g NaCN and 10 ml of water were added. The organic phase was
washed with 4.times.50 ml of H.sub.2O, dried over MgSO.sub.4 and
the solvent was removed in a vacuum. The pure product was obtained
by recrystallization from dioxane with a purity of 99.2% (according
to HPLC). The yield was 12 g (75% Th.).
[0075] .sup.1H-NMR (CDCl.sub.3, 500 MHz): 0.81 (t, J=7.3 Hz, 6H),
1.17 (t, J=7.0 Hz, 12H), 1.23-1.35 (m, 28H), 3.94 (t, J=6.3 Hz,
4H), 4.03 (t, J=6.3 Hz, 8H), 4.21 (d, J=5.9 Hz, 4H), 4.29 (d, J=5.9
Hz, 4H), 6.91-7.01 (m, 14H), 7.04 (d, J=9 Hz, 4H), 7.27 (d, J=8 Hz,
4H), 7.49 (d, J=8.7 Hz, 4H).
f) Synthesis of oxetane-substituted, brominated
N,N,N',N'-tetraphenylbenzidine (monomer M3)
[0076] ##STR6##
[0077] 45.72 g (43.7 mmol) of oxetane-substituted
N,N,N',N'-tetraphenylbenzidine were prepared in 500 ml of THF. A
solution of 15.15 g (84.4 mmol) NBS in 300 ml of THF was added
drop-wise thereto at 0.degree. C. while excluding light. It was
allowed to reach RT and stirred for a further 4 h. 500 ml of water
were added, and the mixture was extracted with CH.sub.2Cl.sub.2.
The organic phase was dried over MgSO.sub.4 and the solvent was
removed in a vacuum. The product was hot extracted by stirring with
hexane and suctioned. After repeated chromatographic purification
(silica, hexane/ethyl acetate 4:1), the product was obtained with a
yield of 44 g (85% Th.) as a pale brown oil which had a purity of
99.2% (according to HPLC).
[0078] .sup.1H-NMR (DMSO-d.sub.6, 500 MHz): 0.81 (t, J=7.3 Hz, 6H),
1.17 (t, J=7.0 Hz, 12H), 1.23-1.35 (m, 28H), 3.94 (t, J=6.3 Hz,
4H), 4.03 (t, J=6.3 Hz, 8H), 4.21 (d, J=5.9 Hz, 4H), 4.29 (d, J=5.9
Hz, 4H), 6.91-7.02 (m, 12H), 7.04 (d, J=9 Hz, 4H), 7.29 (d, J=8 Hz,
4H), 7.51 (d, J=8.7 Hz, 4H).
g) Polymer synthesis: Synthesis of Polymer P1
[0079] 1.7056 g (2 mmol) of monomer M2, 0.9104 g (1.2 mmol) of
monomer M1, 0.9723 g (0.8 mmol) of monomer M3 and 2.03 g (4.4 mmol)
of hydrated potassium phosphate were dissolved in 12.5 ml of
toluene, 12.5 ml of dioxane and 12 ml of water (all the solvents
free of oxygen) and degassed at 40.degree. C. for 30 minutes with
an argon stream. 0.90 mg of Pd(OAc).sub.2 and 6.30 mg of
P(o-tol).sub.3 were added as a catalyst, and the reaction mixture
was heated for 3 h under reflux. 20 ml of toluene and as an end
capper 12 mg (0.04 mmol) of 3,4-bispentoxybenzeneboronic acid were
added, heated for 1 h under reflux, then 20 mg (0.06 mmol) of
3,4-bispentoxybenzene bromide were added and heated for 1 h under
reflux. The reaction solution was cooled to 65.degree. C. and
extracted by stirring for 4 h with 10 ml of 5% strength aqueous
sodium N,N-diethyidithiocarbamate solution. The organic phase was
washed with 3.times.80 ml of water and precipitated by adding it in
two times the volume of methanol. The raw polymer was dissolved in
chlorobenzene, filtered using celite and precipitated by adding two
times the volume of methanol. 2.24 g (78% Th.) of the polymer P1
were obtained.
Example 2
Synthesis of a Cationically Crosslinkable Polymer P2 for use as a
Buffer Layer
a) Synthesis of bis-(4-bromophenyl)-(4-.sup.secbutylphenyl)-amine
(monomer M4)
[0080] ##STR7##
[0081] The synthesis of M4 was carried out in analogy with the
synthesis in DE 19981010.
b) Synthesis of Bis-((4-pinacole
boronate)phenyl)-(4-.sup.secbutylphenyl)-amine (monomer M5)
[0082] ##STR8##
[0083] The synthesis of monomer M5 is described in application DE
10337077.3 which has not yet been laid open.
c) Synthesis of
2,7-dibromo-(2,5-dimethylphenyl)-9-(3,4-di(3-ethyl(oxetane-3-ethyloxy)-he-
xyloxyphenyl))-fluorene (monomer M6)
[0084] ##STR9##
[0085] The synthesis of monomer M6 is described in C. D. Muller et
al., Nature 2003, 421, 829.
d) Polymer synthesis: Synthesis of Polymer P2
[0086] 1.4695 g (3.2 mmol) of monomer M4, 2.2134 g (4 mmol) of
monomer M5, 0.7463 g (0.8 mmol) of monomer M6 and 4.05 g (8.8 mmol)
of hydrated potassium phosphate were dissolved in 25 ml of toluene,
25 ml of dioxane and 25 ml of water (all solvents free of oxygen)
and degassed at 40.degree. C. for 30 minutes in an argon stream.
1.80 mg of Pd(OAc).sub.2 and 14.61 mg of P(o-tol).sub.3 were then
added, and the reaction mixture was heated for 10 h under reflux.
The initial amounts of Pd(OAc).sub.2 and P(o-tol).sub.3 were
respectively added after 4 h, after 5.5 h and after 8.5 h. 2 ml of
toluene were added after a reaction time of 8 h. 24 mg (0.08 mmol)
of 3,4-bispentoxybenzolboronic acid were added as an end capper,
heated for 2 h under reflux, then 40 mg (0.12 mmol) of
3,4-bispentoxybenzenebromide were added and heated for 1 h under
reflux. The reaction solution was cooled to 65.degree. C. and then
extracted by stirring for 4 h with 20 ml of a 5% strength aqueous
solution of sodium N,N-diethyldithiocarbamate. The phases were
separated and the process was repeated once more with 40 ml of the
dithiocarbamate solution. The phases were separated, the organic
phase was washed with 3.times.150 ml of water and precipitated by
adding it in two times the volume of methanol. The raw polymer was
dissolved in chlorobenzene, filtered using celite and precipitated
by adding two times the volume of methanol. 1.84 g (64% Th.) of the
polymer P2 were obtained, which is soluble in chlorobenzene but
insoluble in toluene, THF or chloroform.
Example 3
Synthesis of a Cationically Crosslinkable Molecule V1 for use as a
Buffer Layer
[0087] ##STR10##
[0088] The synthesis of the cationically crosslinkable molecule V1
is described in M. S. Bayer et al., Macromol. Rapid Commun. 1999,
20, 224-228.
[0089] The device results, which were obtained when using the
polymers P1 and P2 or molecule V1 as the buffer layer, are
summarized in Examples 6-8.
Example 4
Production of LEDs with an Additional Buffer Layer
[0090] The LEDs were produced according to a general method which
was adapted to the respective conditions (for example solution
viscosity and optimal layer thickness of the functional layers in
the device) in the particular case. The LEDs described below were
respectively three-layer systems (three organic layers), i.e.
substrate//ITO//PEDOT//buffer layer//polymer//cathode. PEDOT is a
polythiophene derivative (Baytron P4083 from H. C. Stark, Goslar).
Ba from Aldrich and Ag from Aldrich were used for the cathode in
all cases. The way in which PLEDs can generally be produced is
described in detail in WO 04/037887 and the literature cited
therein.
[0091] In contrast to this, a cationically crosslinkable
semiconductor was applied as a buffer layer on the PEDOT layer.
Here, the crosslinkable polymers P1 and P2 or the crosslinkable low
molecular weight compound V1 were used as materials for the buffer
layer. A solution (with a concentration of 4-25 mg/ml in for
example toluene, chlorobenzene, xylene etc.) of the crosslinkable
material was taken and dissolved by stirring at room temperature.
Depending on the material, it may also be advantageous to stir for
some time at 50-70.degree. C. After the complete dissolving of the
compound, it was filtered through a 5 .mu.m filter. The buffer
layer was then spin coated at variable speeds (400-6000 rpm) with a
spin coater in an inert atmosphere. The layer thicknesses could
thus be varied in a range of from approximately 20 to 300 nm. The
crosslinking was subsequently carried out by heating the device to
180.degree. C. for 30 minutes on a hotplate in an inert atmosphere.
The organic semiconductor and the cathode were then applied onto
the buffer layer, as described in WO 04/037887 and the literature
cited therein.
Example 5
Production of Structured LEDs with an Additional Buffer Layer
[0092] The structured LEDs were produced similarly as Example 4 up
to and including the step of crosslinking the buffer layer. In
contrast to this, cationically crosslinkable semiconductors were
used for the organic semiconductors. These were red, green and blue
emitting conjugated polymers based on poly-spirobifluorene, which
were functionalized with oxetane groups. These materials and their
synthesis are already described in the literature (Nature 2003,
421, 829). A solution (generally with a concentration of 4-25 mg/ml
in for example toluene, chlorobenzene, xylene:cyclohexanone (4:1))
was taken and dissolved by stirring at room temperature. Depending
on the compound, it may also be advantageous to stir for some time
at 50-70.degree. C. Approximately 0.5% by weight (expressed in
terms of polymer) of the photoacid
{4-[(2-hydroxytetradecyl)-oxyl]-phenyl}-phenyliodonium
hexafluoroantimonate was added to the solutions of the cationically
crosslinkable semiconductor. The solution of the first cationically
crosslinkable semiconductor and the photoacid were then applied
onto the crosslinked buffer layer by spin coating under comparable
conditions as for the buffer layer. After drying the film,
structured crosslinking was carried out by exposure to a UV lamp
(10 W, 302 nm, 5 min.) using a mask. The film was then heat-treated
in an inert atmosphere for 3 minutes at 130.degree. C.,
subsequently treated with a 10.sup.-4 molar LiAlH.sub.4 solution in
THF and washed with THF. The non-crosslinked positions in the film
were thereby washed off. This process was repeated with the other
solutions of the crosslinkable organic semiconductors, and the
three primary colors were thereby successively applied in a
structured way. The evaporation coating of the electrodes and the
contacting were then carried out as described above.
Example 6
Lifetime Measurement of an LED with an Additional Buffer Layer
P1
[0093] The LED was produced as described in Example 4. 20 nm of
PEDOT were used. A 20 nm thick layer of polymer P1 was applied as
the buffer layer, which was thermally crosslinked as described in
Example 4. A blue emitting polymer was used as the semiconducting
polymer (composition: 50 mol % monomer M7, 30 mol % monomer M8, 10
mol % monomer M1, 10 mol % monomer M9). The monomers are depicted
below, and their synthesis is described in WO 03/020790. In
electroluminescence, the polymer exhibits a lifetime (=brightness
reduction to half the initial brightness) of approximately 1600 h
at room temperature and an initial brightness of 300 cd/m.sup.2. In
a comparative LED without the buffer layer, under otherwise equal
conditions, the polymer exhibits a lifetime of approximately 500 h.
An LED was also produced whose buffer layer was photochemically
crosslinked by adding 0.5% by weight of
{4-[(2-hydroxytetradecyl)-oxyl]-phenyl}-phenyliodonium
hexafluoroantimonate with exposure to UV radiation (3 s, 302 nm)
and subsequent heating to 90.degree. C. for 30 seconds. The buffer
layer was then washed with THF and heated to 180.degree. C. for 5
minutes. Under otherwise equal conditions, this LED had a lifetime
of approximately 630 h. ##STR11##
Example 7
Lifetime Measurement of an LED with an Additional Buffer Layer
P2
[0094] The measurement was repeated with polymer P2 as the buffer
layer, as described in Example 6 under otherwise identical
conditions. The polymer exhibits a lifetime of approximately 1500 h
without addition of photoacid to the buffer layer, and
approximately 600 h with addition of photoacid.
Example 8
Lifetime Measurement of an LED with an Additional Buffer Layer
V1
[0095] The measurement was repeated with compound V1 as the buffer
layer, as described in Example 6 under otherwise identical
conditions. The polymer exhibits a lifetime of approximately 1350 h
without addition of photoacid to the buffer layer, and
approximately 550 h with addition of photoacid.
* * * * *