Note: Descriptions are shown in the official language in which they were submitted.
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03SGL0149CAP
Schott AG
Hermetic encapsulation of organic, electro-optical elements
Description
The invention relates in general terms to organic; electro-
optical elements,~and to a process for producing them. In
particular, the invention relates to a process for producing
hermetically encapsulated organic, electro-optical elements,
and to a hermetically encapsulated electro-optical .element.
to
Organic light-emitting diodes (OLEDs) are the subject of
intensive development work, since they have a number of
advantages over other illumination and display means. For
example, OLEDs can be made very thin and even flexible.
Moreover, compared to liquid-crystal displays, OLEDs have the
benefit of being self-illuminating.
However, the main problem with OLEDs is their service life,
which has hitherto been very limited. It has proven almost
2o impossible to extend the operating time of OLEDs to more than
5000 operating hours. Metal cathodes with a low work function
are generally used for OLEDs. In this context, inter alia
metallic calcium is customary. However, these materials with
a low work function are generally highly reactive. Chemical
reactions undergone by the metal layer and associated changes
in the work function are considered to be one of the main
factors limiting the service life.
In particular the reaction with air or with the water which
3o is present as moisture in the air is responsible in this
context for the degradation of the metal electrode of an
OLED.
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2
To solve the problem, US 5,882,761 proposes an OLED in
which the OLED structures are covered with a curved metal
sheet. In addition, the OLED described in that document has a
reservoir of drying agent or Better. The drying-agent
s reservoir and the OLED structures are separated from one
another by a porous adhesive tape. The metal sheet is joined
to the glass substrate by means of a UV adhesive. A drawback
of this solution is that organic layers, such as the bonding
area between metal sheet and glass substrate, are relatively
to easy for small gas molecules to penetrate. Therefore, the
adhesive bonding represents a passage, in particular for
atmospheric oxygen and water. Therefore, it is only a
question of time until the drying agent is exhausted and
degradation of the metal electrode commences. Furthermore,
15 this type of encapsulation makes it impossible to implement
significant properties of the OLED technology, such as the
encapsulation of extremely thin or flexible components.
Examples of known Better materials are liquids such as those
2o described in JP 7211456, US 5,821,692, or
US 5,962,962. Furthermore, EP 0776147 describes the us.e of
solid-state materials as Betters. As disclosed in WO
99/03112, gases can also be used as Better medium for organic
components. However, a common feature of all these solutions
2s which are known from the prior art is that the efficiency of
the Better material falls as the incidence of gas continues,
and consequently there is no permanent protection against
degradation.
3o Therefore, the invention is based on the object of slowing
the degradation of organic, electro-optical elements, such as
for example OLEDs, and of increasing their service life.
This object is achieved, in a very surprisingly simple way,
35 by a process for producing an organic, electro-optical
element, and an organic electro-optical element as claimed in
the independent claims. Advar~tac~ous refinements are in each
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3
case given in the dependent claims.
Accordingly, the process according to the invention for
producing an organic, electro-optical element comprises the
s steps of:
- providing a substrate,
- applying a first conductive layer,
- applying at least one layer (15) which includes at least
one organic, electro-optical material,
to - applying a second conductive layer, andthe step of
- depositing at least one layer (7, 71, 72,... 7N) with a
vitreous structure.
Layers with a vitreous structure are known for their
i5 extremely good barrier action. In this context, a layer
without a long-range order of the elements and/or substances
which make up the material with a vitreous structure and, at
the same time, with a close-range order of the substances
and/or elements is to be understood as a layer with a
2o vitreous structure. Therefore, the term layer with a vitreous
structure denotes a vitreous, amorphous layer. Accordingly,
layers of this type do not only comprise glasses. Rather, in
addition to glasses, vitreous layers may also encompass, for
example, organic materials, alloys or amorphous element
25 layers. Compared to non-vitreous, i.e. substantially
microcrystalline, polycrystalline or crystalline layers, the
layers which are applied by means of the process according to
the invention are distinguished by the absence of grain
boundaries, inter alia on account of the amorphous structure.
3o However, grain boundaries of this type are in fact
essentially responsible for the higher permeability rate for
small molecules, such as for example oxygen or water, through
crystalline or polycrystalline media.
35 A particularly preferred embodiment of the invention provides
in particular for the deposition of at least one layer with a
vitreous structure to comprise the step of depositing a
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4
glass, in particular an inorganic glass.
With regard to the barrier properties of evaporation-coating
glass for the encapsulation of components and other
s substrates, reference is also made to the applications
DE 20205 830.1, filed on 04.15.2002,
DE 102 22 964.3, filed on 05.23.2002;
DE 102 22 609.1, filed on 05.23.2002;
DE 102 22 958.9, filed on 05.23.2002;
DE 102 52 787.3,'filed on 11.13.2002;
DE 103 O1 599.0, filed on 01.16.2003
in the name of the same applicant, the content of disclosure
of which is hereby expressly incorporated by reference.
With regard to th'e barrier properties of evaporation-coating
glass layers, measurements have shown that, at evaporation-
coating glass layer thicknesses in the range from 8 ~m to
18 Vim, helium Leak rates of less than 10' mbar 1 s-' or less
than 10-B mbar 1 s-' are reliably achieved. For layers with a
layer thickness of 8 Vim, and 18 Vim, the measurements have
even given helium leak rates of between 0 and 2 x 10-9 mbar
1 s-', and these upper limit values are already substantially
influenced by the measurement inaccuracy of the tests carried
out.
There are numerous known glasses whose permeability to all
gases with the exception of helium cannot be recorded using
the available measurement means even at layer thickn.esses of
50 Vim. A summary of diffusion rates through glasses is to be
3o found, for example, in "Handbook of Gas Diffusion in Solids
and Melts". Helium itself, however, on account of its inert
nature, does not affect the layers of the OLED and is
therefore of no importance to the service life of OLEDs.
In particular, a layer with a vitreous structure which
comprises an alkali-metal-containing glass is particularly
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suitable for hermetic encapsulation. The alkali
metal ions fill up interstices in the glass skeleton and
thereby provide dense layers with a very low permeability.
5 In particular, borosilicate glasses are also particularly
suitable materials for the layer with a vitreous structure.
These glasses may also include alkali metal ions in order to
reduce the permeability.
to The term an organic, electro-optical material encompasses
both an organic material which has electroluminescent
properties and is therefore suitable for the construction of
an OLED and an organic material which has photovoltaic
properties. In the following text, for the sake of simplicity
i5 the term OLED is used in general terms for light-converting
elements, i.e. both for light-emitting elements and for
photovoltaic elements, on account of their equivalent
structure.
2o A wide range of substances which are known to the person
skilled in the art can be used as organic, electro-optical
material. Inter alia, metal-organic materials, in particular
metal-organic complexes, such as triplet emitters or
lanthanide complexes, can be used for this purpose. By way of
25 example, tris-(8-hydroyquinolino)-aluminum (Alq3) or MEH-PPV
(poly(2-methoxy, 5-(2'-ethyl-hexyloxy) paraphenylene vinylene
(MEH-PPV) is used as electroluminescent material. The layer
may also comprise an organic or inorganic matrix layer which
is doped with emitters, such as for example fluorescent dyes,
3o as organic, electro-optical material. The inorganic matrix
used was, inter alia, porous titanium dioxide.
Further electroluminescent substances are described, for
example, in US 6,107,452, EP 0 573 549, EP 800563 A1, EP
35 800563 B1 and EP 1006169 A1, which are completely
incorporated by reference in the present application.
Although it is known to the person skilled in the art,
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reference is also made to the structure of the OLEDs
described in these documents, and this description is assumed
to form part of the present application.
s Moreover, the inventive deposition creates an intimate join
between the layer with a vitreous structure and the material
below it without the formation of cavities or joining points
which can be penetrated by gases, since the layer grows
directly on the surface below it. Layers with a vitreous
to structure, i.e. substantially without crystalline partial
regions or subregions are, moreover, distinguished by better
tolerance with respect to mechanical loads compared to
crystalline materials. This means that the very good barrier
actions of such materials are retained even in the event of
15 deformation within the mechanical load limits of the
material. Therefore, the process according to the invention
even makes it possible to produce flexible OLEDs with a high
service life.
2o The deposition of the layer with a vitreous structure, in
accordance with the invention, comprises the vacuum or low-
pressure deposition of the layer, for example the deposition
of the layer by vacuum or low-pressure coating. All vacuum-
coating processes may be suitable for this purpose.
25 Accordingly, to deposit the layer with a vitreous structure,
it is possible, inter alia, to use PVD or CVD processes. It
is also possible for a plurality of deposition processors to
be combined with one another. Vacuum-coating processes or
low-pressure coating processes, such as for example PVD or
3o CVD, are advantageous inter alia because these processes can
be carried out in vacuo and/or in a dry atmosphere, thereby
preventing contamination of moisture-sensitive OLED layers
during the coating.
35 According to a particularly preferred embodiment, the at
least one layer with a vitreous structure is deposited by
evaporation coating. Evaporation coating makes it possible to
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achieve high layer growth rates, which makes this
variant of the process according to the invention
particularly fast and therefore economical for large numbers.
s The deposition of the layer with a vitreous structure by
evaporation coating may advantageously also comprise the step
of plasma ion assisted deposition (PIAD?. In this case, an
ion beam is additionally directed onto the substrate which is
to be coated. The ion beam can be generated by means of a
to plasma source, for example by ionization of a suitable gas.
The gas ions additionally accelerate the particles emitted
from the evaporation-coating source. This leads to layers
which are particularly dense and deposited with few defects.
15 The step of depositing the layer with a vitreous structure
may particularly preferably also comprise the step of
depositing an evaporation-coating glass. Glasses of this type
are materials which can be deposited by evaporation coating.
It has been found that evaporation-coating glasses have
2o excellent encapsulation properties. In addition to the
preferred deposition by evaporation coating, however, these
glasses may, of course, also be deposited using other vacuum
or low-pressure coating processes.
2s By way of example, electron-beam coating is particularly
suitable for the evaporation coating. For this purpose, an
electron beam is directed onto a target and the impact causes
the electrons to release their kinetic energy to the target,
which is heated as a result. Ultimately, the target material
3o is evaporated by the heating. The evaporated material then
comes into contact with the surface which is to be coated,
where it is deposited as a layer with a vitreous structure.
The step of evaporation-coating to form a layer with a
35 vitreous structure may, moreover, comprise the step of ~o-
evaporation from at least two evaporation sources. In this
way, it is possible, for example, to adjust the stoichiometry
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of the layer which is deposited by means of the
,evaporation-coating rates of the sources. In particular, the
step of co-evaporation may also comprise the step of varying,
in particular periodically varying, the evaporation-coating
s rate of at least one of the evaporation sources. The material
properties of the layer with a vitreous structure can be
influenced and adapted in the direction perpendicular to the
evaporation-coated surface by varying the evaporation-coating
rates. For example, by varying the layer stoichiometry, it is
to possible, for example, to match the coefficient of thermal
expansion of the layer to that of the coated surface, so that
thermal stresses between the surface material and the
evaporation-coated layer are avoided or reduced. A periodic
variation in the evaporation-coating rates can be used, for
15 example, to produce periodic variations in the refractive
index in the evaporation-coating layer perpendicular to the
coated surface .
However, the deposition by evaporation coating generally
2o requires special evaporation-coating materials with
relatively high vapor pressures. Since for special OLED
applications materials with low vapor pressures and,
correspondingly, generally high melting points may also be
suitable, the step of depositing at least one layer with a
25 vitreous structure by means of physical and/or chemical vapor
deposition may also advantageously comprise the step of
sputtering on a layer with a vitreous structure. in this
context, the term sputtering on layers is understood as
meaning one of the PVD processes. The sputtering of layers,
3o unlike evaporation-coating, can be carried out even with
materials which are relatively difficult to evaporate.
However, layers with vitreous structures can also
advantageously be produced using other processes, f-or example
35 chemical vapor deposition, for example by means of plasma-
enhanced chemical vapor deposition (PCVD). In this respect,
in particular plasma impulse chemical vapor deposition
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(PICVD) is particularly suitable; in this process, the
plasma is not produced constantly over the course of time,
but rather in pulsed fashion, which inter alia leads to a
lower thermal load on the element which is to be coated.
Moreover, the deposition of the layer with a vitreous
structure may also, in an advantageous configuration of the
process, comprise the step of co-deposition of an organic
material. The co-deposition, or simultaneous deposition, of
to the organic material together with the layer material which
forms a layer with a vitreous structure may be effected, for
example, by co-evaporation or deposition from the residual
gas atmosphere. In this case, the molecules of the organic
material are incorporated in the layer with a vitreous
structure. The organic material may have a positive influence
on the layer properties in many ways. By way of example, in
this context mention may be made of a higher flexibility of
the layer under mechanical load, the matching of optical and
mechanical properties, the improvement to the layer bonding
2o for example as a result of the layer being deposited as a
gradient layer with a change in the organic content, the
change in the packing density and the layer microstructure,
and the influencing of the chemical properties of the layer,
in particular by adding hydrophobic materials or Better
materials.
The layers are advantageously applied in such a way that one
of the conductive layers has a lower work function than the
other conductive layer. On account of the difference in work
3o function between the first and second conductive layers,
which are used as electrodes and between which the layer
which includes an organic, electro-optical material is
located, and given correct polarity of the voltage applied to
the electrodes, electrons are injected at the layer acting as
a cathode into unoccupied electronic states of the organic,
electro-optical material. At the same time, defect electrons
or holes are injected from the layer with a lower work
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function, which is acting as an anode, with the result
that light quanta are emitted in the organic material as a
result of recombination of the electrons with the defect
electrons.
5
In many cases, additional functional layers, which are
applied in particular between the first and second conductive
layers, are used to produce OLEDs. Accordingly, the process
may advantageously also include the step of applying at least
to one hole injection layer and/or a potential-matching layer
and/or an electron blocker layer and/or a hole blocker layer
and/or an electron conductor layer and/or a hole conductor
layer and/or an electron injection layer. Particularly high
quantum or light efficiency yields are achieved by applying
~5 the layers in the following preferred sequence: potential-
matching layer/hole injection layer/electron blocker
layer/layer which includes at least one electro-optical
material/hole blocker layer/electron conductor layer/electron
injection layer/potential-matching layer.
For the sake of simplicity, the sequence of functional layers
of the organic, electro-optical element is referred to below
as the OLED layer structure. This comprises in particular the
first and second conductive layers and the layer which
includes an organic, electro-optical material. In addition,
the OLED layer structure may also comprise, for example, the
further functional layers mentioned above.
To allow light to be output or input, it is advantageous if
one of the conductive layers is at least partially
transparent. Inter alia, indium tin oxide or fluorine-doped
tin oxide (Sn02:F) has proven suitable for this layer.
A further advantage of the process is that the order in which
the layers are applied is not immutable. Generally, OLEDs are
produced by applying a transparent conductive layer to a
transparent substrate, and then depositing the layer which
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includes an organic, electro- optical material on the
transparent conductive layer. This structure is then covered
by a conductive layer, which for example may have a lower
work function than the transparent conductive layer, as
further electrode. In this case, the light which is emitted
can be output or introduced via the transparent substrate.
According to a preferred configuration of the process, the
step of depositing the at least one layer with a vitreous
so structure takes p ace after the application of the at least
one layer which includes at least one organic, electro-
optical material and of the first and second conductive
layers. If these layers are applied from the same side of the
substrate, for example by being deposited, the layer which
includes at least one organic, electro-optical material is
located between the substrate and the layer with a vitreous
structure. In this way, the OLED layer structure is
encapsulated between the substrate and the layer with a
vitreous structure.
Since the layers with a vitreous structure which are applied
in accordance with the invention may, for example, also
themselves be transparent, it is also possible, however, for
the layer sequence to be arranged in such a way that the
transparent conductive layer is applied to the substrate
after the layer with the organic, electro-optical material.
In this way, it is also possible to produce an OLED with, for
example, a non-transparent substrate, in which case the light
passes through the layer with a vitreous structure and the
3o transparent conductive layer.
It is advantageously also possible for one or both of the
conductive layers and also the layer which includes an
organic, electro-optical material to be applied or deposited
in structured form. In particular, these layers may also be
produced in structured form in the lateral direction, i.e.
along the surface. Structuring of this nature allows a large
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dumber of properties of such elements to be influenced. By
way of example, light-passage openings can be created in a
conductive layer. Furthermore, a layer arrangement in which,
the layers do not necessarily have to be applied on top of
one another is also possible. Rather, it is possible, by way
of example, for structured layers to intermesh with one
another. By way of example, the first and/or second
conductive layers may also be applied such that they are
structured in a comb shape. The layer which includes at least
to one organic, electro-optical material may then, for example,
be located completely or partially between the comb
structures. Moreover, structuring is appropriate for
pixelated structures which are operated by dedicated
switching elements, or for the production of an organic
is electro-optical element as an active matrix display.
Layers with a vitreous structure which comprise an at least
binary system of materials are particularly suitable for
hermetic encapsulation of OLEDs. Layers of this type are
2o generally distinguished by particularly low permeability
rates, since they have scarcely any tendency to form
crystalline areas, unlike quartz glasses, for example, and
they also have denser structures. Such at least binary
systems of materials may, for example, be composed of at
2s least two metal oxides or silicon dioxide and one or more
metal oxides.
Furthermore, the process may also be configured in such a way
that the step of depositing the at least one layer with a
3o vitreous structure takes place before the application of one
of the conductive layers. As a result, the layer with a
vitreous structure is located between the substrate and the
OLED layer structure. One such variant of the process
produces an OLED in which the diffusion through the substrate
35 into the OLED layer structure can also be suppressed. This
also makes it possible to achieve hermetic encapsulation on
the substrate side of the OLED. This is advantageous, for
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example, for flexible OLEDs if the substrate comprises a
flexible plastic material which typically has a high
permeability to small gas molecules. The vitreous layer can
in this case also fulfill the function of an outputting or
s introduction layer for the light emitted by the OLED, in
order to increase the yield of the OLED by matching the
refractive indices.
Moreover, the at least one layer with a vitreous structure
io may be applied to the opposite side of the substrate from the
side to which the layer which includes an organic, electro-
optical material is applied. Therefore, the layer is applied
to that side of the substrate on which the light is output
into the environment in a standard layer structure of the
z5 OLED. In this case too, matching of the refractive indices by
means of the layer with a vitreous structure can increase the
output efficiency, since otherwise there is a considerable
change in refractive index, with correspondingly strong back
reflections, in particular at the material/air interface. In
2o addition, a layer of this type can also create a diffusion
barrier in order to lengthen the service life of the OLED.
A refinement of the process according to the invention for
producing OLEDs in which the step of applying a layer with a
vitreous structure by means of physical and/or chemical vapor
25 deposition comprises the step of applying a multipla layer is
also highly advantageous for the properties of OLEDs. The
plurality of individual layers of a multiple layer of this
type may, for example, have different chemical compositions,
so that, for example, barrier actions of individual layers
3o can be tailored to specific gases which have an adverse
effect on the service life. The mechanical properties, such
as for example the flexibility, layer bonding or intrinsic
layer stress, can also be improved, for example by the
introduction of flexible interlayers. Not all the individual
35 layers of the multiple layer have to have a vitreous
structure. Rather, individual layers with a vitreous layer
material can be combined with other individual layers of
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different chemical composition, such as for
example metal layers or organic layers, such as in particular
polymer layers, in order to match the chemical and physical
layer properties to the specific requirements. Accordingly,
in this refinement of the process according to the invention,
the step of applying a multiple layer comprises the step of
applying a multiple layer with different chemical
compositions andJor different mechanical properties in at
least two of the individual layers. In this context, it is
1o also possible to'combine different production processes for
the individual layers, for example adhesive bonding, dip-
coating or spin-coating, with one another and with the
deposition of at least one layer with a vitreous structure.
In particular, th'e plurality of individual layers can also be
applied in such a way that at least two of the individual
layers have different refractive indices. This can be
achieved by applying different layer materials. However, it
is also possible to influence the refractive index by the
2o selection of the process parameters during application, for
example the selection of the evaporation-coating rate. A
multiple layer with a varying refractive index of this type
is particularly suitable for matching refractive indices.
In many deposition processes for layers with a vitreous
structure, a certain thermal load is applied to the OLED
layer structure and may have adverse effects on the layers.
In particular, the thermal load may affect the layer
composition in CVD or PVD coatings. To reduce adverse effects
3o from the thermal load, it is additionally possible for at
least one pre-encapsulation layer to be applied. A pre-
encapsulation coating of this type may, for example, reduce
the heat transfer and thus prevent the OLED layers from being
heated.
Moreover, by way of example, a suitable pre-encapsulation
coating can prevent the layer with a vitreous structure
CA 02505014 2005-05-04
,penetrating or chemically changing another layer during
application by means of PVD or CVD coating. This may be the
case, for example, with the second conductive layer if the
latter is made from very soft or reactive metals, such as for
s example calcium.
Moreover, the process may advantageously comprise the step of
applying a cover. To protect the generally very thin layer
with a vitreous structure or the other layers of the OLED
to from damage, the cover can be applied to the layer with a
vitreous structure.
Moreover, however, it is also possible to apply a layer with
a vitreous structure in such a way that the contact surface
15 between the cover and the substrate is sealed and
hermetically closed up by the layer with a vitreous
structure. For this purpose, the step of depositing at least
one layer with a vitreous structure comprises the step of
covering the boundary edge of the bearing surface of the
2o cover with at least one layer with a vitreous structure. This
can not only achieve the objective of providing a hermetic
seal, but also allows the layer, such as for example the
evaporation-coating glass to be used to secure the cover, in
a similar manner to a soldering glass. The term the bearing
surface is not to be understood strictly as the surface on
which the contact points between further components and the
cover are formed. For example, since the OLED layer structure
is generally slightly elevated, there may be a short distance
between the cover and the corresponding base, for example the
3o substrate, in adjoining regions next to the OLED layer
structure. However, these regions are also to be understood
as part of the bearing surface. Therefore, the bearing
surface can be understood as a projection surface of that
side of the cover which faces the base onto the base.
Furthermore, the process according to the invention can
advantageously be improved if it additionally comprises the
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step of applying at least one bonding layer, in particular
a bonding layer to which the at least one layer with a
vitreous structure is applied. A layer of this type can in
particular improve the bonding properties of the layer with a
vitreous structure on plastic surfaces, which has
advantageous effects on the mechanical stability of the layer
microstructure under thermal or mechanical loads, for example
a bending load. In this way, a continuous layer is produced
more quickly and it is possible to achieve smoother layers
to with a lower porosity.
The invention also envisages the provision of an organic
photoelectric element which is producible in particular by
the process described above.
Accordingly, an element according to the invention comprises:
- a substrate,
- a first conductive layer,
- at least one layer which includes at least one organic,
2o electro-optical material, and
- a second conductive layer, as well as
- a deposited layer with a vitreous structure.
As has already been described above in connection with the
process for producing OLEDs, a layer with a vitreous
structure is particularly suitable as a diffusion barrier for
small molecules, and therefore provides effective protection
against degradation of the element. The fact that the layer
is deposited on a surface of the element means that there is
3o a join between the layer and the surface without intermediate
or transition layers, which is particularly expedient with a
view to achieving a hermetic seal. The layer is preferably
deposited on the surface by means of CVD and/or PVD, for
example by sputtering, evaporation-coating, PCVD or PICVD.
It is preferable for one of the conductive layers to have a
lower work function than the other conductive layer, in order
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to create a difference in work function between the
layers. In the case of a light-emitting element, when a
voltage is applied to the conductive layers electrons are
injected from the layer with a lower work function into
unoccupied energy states. Recombination with defect electrons
which are injected from the layer with a higher work function
then leads to light quanta being emitted.
To increase the quantum efficiency of an OLED according to
the invention, the OLED may additionally have further
functional layers. In this context, by way of example, at
least one hole injection layer and/or at least one potential-
matching layer and/or at least one electron Mocker layer
and/or at least one hole blocker layer and/or at least one
i5 electron conductor layer and/or hole conductor layer and/or
at least one electron injection layer are advantageous.
To allow the emitted light quanta to be -output, it is
advantageous if one of the conductive layers is at least
2o partially transparent to the light emitted by the layer which
includes an organic, electro-optical material. These required
properties may be fulfilled, inter alia, if the first
conductive layer includes indium tin oxide or fluorine-doped
tin oxide.
Moreover, the at least one layer with a vitreous structure
does not have to be located on that side of the substrate on
which the layer which includes the organic electro-optical
material is located. Rather, the layer with a vitreous
3o structure may also be arranged on the opposite side of the
substrate from this side. In this way, it is on the one hand
possible to limit the diffusion of gas molecules through the
substrate and on the other hand also to have a positive
influence on, for example, the optical properties of the
OLED, for example as a result of the layer with a vitreous
structure creating matching of refractive indices.
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The at least one layer with a vitreous structure may,
furthermore, have a composition and/or refractive index which
varies along the direction perpendicular to the coated
surface. A variation in the composition perpendicular to the
s surface allows the layer to have correspondingly varying
materials properties in this direction, for example a varying
coefficient of thermal expansion or refractive index.
However, the refractive index can also be influenced in other
ways, for example by the morphology of the layer. In
to particular, the composition and/or refractive index can also
vary periodically. A layer with a vitreous structure and a
periodically varying refractive index is particularly
suitable for outputting or introducing light into the
element.
The at least one layer with a vitreous structure may also
particularly advantageously be arranged between the substrate
and the first or~second conductive layer. This arrangement
also suppresses the diffusion of gas molecules through the
2o substrate. Moreover, in this way it is possible to produce
refractive index matching between the OLED layer structure
and the substrate.
The organic, electro-optical element may also include a
2s multiple layer which comprises at least one layer with a
vitreous structure. This may be advantageous both for the
optical properties, or in particular for the outputting or
introduction of light, and for the mechanical properties,
such as the bending tolerance.
A particularly favorable capacity for outputting and
introducing light can be achieved in particular if the
individual layers of the multiple layer have different
refractive indices.
Moreover, the OLED may also include at least one pre-
encapsulation layer which can serve as a thermal barrier
CA 02505014 2005-05-04
19
coating and reduces the thermal load on the OLED
during the coating with the layer or layers with a vitreous
structure. Moreover, a pre-encapsulation coating can serve to
create a stable base for the layer with a vitreous structure.
To protect the layer with a vitreous structure or the other
layers in particular from mechanical damage, the OLED may
advantageously also have a cover.
to In addition, the OLED may advantageously include at least one
bonding layer, which preferably adjoins the at least one
layer with a vitreous structure. A bonding layer of this type
results in improved bonding of the layer with a vitreous
structure. As a result, relatively high growth rates and in
i5 relative terms smoother layers can be achieved during the
deposition. Moreover, a bonding layer of this type can be
used to reduce intrinsic layer stresses.
Moreover, an electro-optical element according to the
2o invention may advantageously include structured layers. By
way of example, the first and/or second conductive layers
and/or the at least one layer which includes at least one
organic, electro-optical material may be structured in order
to integrate additional functionality in one or more of these
25 layers. In particular, the first and/or second conductive
layers may be structured in a comb shape. The finger
electrodes of the layers which are structured in a comb shape
may, for example, engage in one another so that a voltage can
be applied or tapped between conductive layers located at one
30 level .
However, other structures of the layers are also suitable. 8y
way of example, the conductive layers may have lines, for
example interconnects, which cross one another on the
35 substrate in different levels and allow pixel activation of
individually switched pixel structures, in particular for
display applications. In this case, the layer which is
CA 02505014 2005-05-04
,located between the conductive layers and
includes at least one electro-optical material is locally
excited to electroluminescence in the vicinity of a cross
point of two driven interconnects of the conductive layers.
s Conversely, a corresponding photovoltaic arrangement can be
used for local signal scanning for sensor applications, for
example image recording.
Moreover, the invention provides a device for carrying out
to the production process described above and/or for producing a
photoelectric element according to the invention. In addition
to the means for producing the OLED layer structure, a device
of this type has a coating means for depositing at least one
layer with a vitreous structure.
The invention is described in more detail below on the basis
of preferred embodiments and with reference to the appended
drawings, in which identical reference numerals in the
drawings denote identical or similar parts. In the drawings:
Fig. 1 shows a first embodiment of an OLED according
to the invention,
Fig. 2 shows a further em3~odiment of
an OLED according to the invention with an
inverse layer structure,
Fig. 3 shows an embodiment of an OLED
with a pre-encapsulation layer,
Figs. 4A to 4D show embodiments with an additional cover to
protect the OLED layer structure,
Fig. 5 sr~ows an embodiment of the OLED
with the layer with a vitreous structure
arranged between the OLED layer structure and
the substrate,
CA 02505014 2005-05-04
21
Fig. 6 shows an embodiment with a
multilayer encapsulation of the OLED layer
structure,
Fig. 7 shows an embodiment with a
multilayer encapsulation of the OLED layer
structure and different refractive indices in
the individual layers,
to
Figs. 8A and 8B show the curve of the refractive index in a
layer with a vitreous structure in accordance
with two further embodiments of an OLED, and
Fig. 9 shows an embodiment of an OLED with
conductive layers structured in a comb shape,
Fig. 10 shows a comparison of two specimens
with calcium strips coated with Si02 and
2o evaporation-coating glass, respectively,
Fig. 11 shows a graph illustrating the
optical density of encapsulated calcium strips
as a function of time,
Fig. 12 shows a comparison of the efficiency
of various encapsulated OLEDs, and
Fig. 13 shows the luminosity of various
3p encapsulated OLED elements as a function of
the residence time in a climate chamber.
Fig. 1 shows a diagrammatic cross-sectional view through a
first embodiment of an OLED according to the invention, which
is denoted overall by 1. The OLED comprises a substrate 3, to
which an OLED layer structure 5 is applied on one side 9. The
layer structure 5 comprises a first conductive layer 13, a
CA 02505014 2005-05-04
22
,layer 15 which includes at least one organic, el.ectro-
optical material, and a second conductive layer 17. The layer
structure 5 of the OLED is covered with a layer 7 with a
vitreous structure and has been applied by means of ~~~TD
s andJor CVD coating. On account of its low permeability, the
layer 7 creates a hermetic encapsulation of the OLED layer
structure 5, in particular with respect to small gas
molecules from natural atmosphere, such as water or oxygen.
In this way, the degradation of the OLED according to the
to invention as a result of chemical reactions between reactive
gases and materials of the layer structure is greatly
reduced, and this manifests itself in an increased service
life of the OLED. Inorganic glass has proven to be a
particularly expedient material for the layer 7, on account
15 of its low permeability. In particular alkali-metal-
containing glasses have a particularly low permeability, and
borosilicate glasses are also particularly suitable.
It is preferable for the layer with a vitreous structure to
2o comprise an evaporation-coating glass which has been
deposited by evaporation-coating on the element 1.
The layer 15 which includes an organic, electro-optical
material is referred to below as an organic, light-emitting
25 layer, for the sake of simplicity. However, this layer may
also be designed as a light-absorbing, photovoltaic layer for
a photovoltaic element.
The evaporation-coating glass type 8329 produced by Schott,
3o which has the following composition in percent by weight:
Si0_ 84.1%
Bz03 11 . 0
3 s Na~O ~ 2 . 0
K_0 ~ 0.3% ~ (in the layer ~ 3.3%)
Li_O ~ 0 . 3
CA 02505014 2005-05-04
23
A1z03 ~ 2.6% (in th.e layer < 0.5%)
has proven particularly suitable.
The values given in parentheses are the proportions by weight
of the corresponding component in the layer deposited by ,
evaporation coating.
to The electrical resistance of this borosilicate glass is
approximately 101° S2/cm (at 100°C) .
Furthermore, in the pure form, this glass has a refractive
index of approximately 1.469.
The dielectric constant s is approximately 4.7 (at 25°C, 1
MHz), tan8 is approximately 45 x 104 (at 25°C, 1 MHz). The
evaporation-coating process and the differing volatility of
the components of this system result in slightly different
stoichiometries between the target material and the layer
2o which is applied by evaporation-coating. The deviations in
the layer which is applied by evaporation-coating are given
in parentheses.
Another suitable evaporation-coating glass, referred to below
as glass 2, has the following composition, in percent by
weight:
Components: Glass 2
SiOZ 71%
B20~ 2 6
Na_O 0 . 5
Li_O 0 . 5%
K_O 1.00
A1203 1 . 0
These two borosilicate glasses which are preferably used in
CA 02505014 2005-05-04
24
particular have the properties listed in the
table below:
Properties 8329 Glass 2
-6 1 2.75 3.2
a2o-Sao L 10 K ]
Density (g/cm) 2.201 2.12
Transformation point [C] 562C 742
Refractive index nD = 1,469 1.465
Hydrolytic resistance class HGB 1 HGB 2
in accordance with ISO 719
Acid resistance class in 0.6 2
accordance with DIN 12 116
Alkali resistance class in 3
accordance with DIN 52322
Dielectric constant s (25C) 4.7 3.9
(1 MHz) (40 GHz)
tan8 (25C) 45*10 ' 26*10 '
(1 MHz) (40 GHz)
s The application of the layer 7 by means of vacuum deposition,
such as for example CVD and/or PVD, results in the formation
of an intimate bonding of the layer 7 both to the surface of
the layer structure 5 and to the substrate itself in areas
next to the OLED structure. As a result, p-ermeability
to passages at the edge regions of the OLED layer structure are
also avoided; in OLEDs which have been known hitherto, such
passages are encapsulated, for example by adhesive bonding.
It is preferable for the layer 7 to be deposited by means of
evaporation coating, in particular by means of electron beam
is evaporation of a glass target having one of th.e compositions
given above.
To produce particularly dense, low-defect layers, it has also
proven advantageous to us-e an APS (APS = advanced plasma
2o source) and to carry out a plasma ion assisted deposition, in
particular evaporation coating assisted by plasma ions.
CA 02505014 2005-05-04
In this embodiment, the substrate is transparent.
Light emitted from the organic, light-emitting layer 15 first
of all passes through the first, conductive layer 13 and then
passes through the interface with the environment on the side
5 11 of the transparent substrate.
In this embodiment, the first conductive layer 13 comprises a
transparent, conductive material, such as for example indium
tin oxide, in order to allow the light to pass through.
10 '
The second conductive layer comprises a material with a lower
work function than that of the first conductive layer, the
work function in the case of an indium tin oxide layer being
approximately 4.9 eV. Calcium is a particularly suitable
i5 material for the second conductive layer. However, calcium is
highly reactive and reacts in particular with the atmospheric
oxygen and with the water which is present as moisture in the
air. In particular to protect this layer, hermetic
encapsulation of the OLED layer structure is important in
20 order to avoid degradation.
This embodiment of an OLED comprises the layer sequence
substrate/first conductive layer/organic, light-emitting
layer/second conductive layer. This corresponds to the
25 standard structure of OLEDs. However, a structure with an
inverse layer sequence can also be achieved by the
application of a layer with a vitreous structure which at the
same time effectively encapsulates the OLED layer structure
5. This variant is illustrated in Fig. 2. In the embodiment
3o shown in Fig. 2, the layer sequence is accordingly:
substrate/second conductive layer/organic, light-emitting
layer/first conductive layer. In this embodiment, the
substrate 3 may also comprise an opaque material. The light
which is emitted from the organic, light-emitting layer 15
then, after it has passed through the first conductive layer
13, emerges at the outer side 19 through the layer 7 with a
vitreous structure.
CA 02505014 2005-05-04
26
Fig. 3 diagrammatically depicts an embodiment with a pre-
encapsulation layer 21. This pre-encapsulation layer is used
inter alia to create a stable base for the layer 7 with a
vitreous structure. The second conductive layer 17 preferably
comprises the very soft metal calcium. The pre-encapsulation
layer 21 prevents molecules from the layer 7 penetrating into
this layer. Moreover, the layer 21 also forms a thermal
barrier coating which, on account of its low thermal
to conductivity, prevents high levels of heat output from being
transferred to the OLED layer structure during the
application of the layer 7 with a vitreous structure.
Figures 4A to 4D show embodiments of the organic, electro-
optical element l~with an additional cover 23. The cover 23
is used to protect in particular against mechanical damage.
Since the layers 13 to 17 of the element 1 may be relatively
soft, the layer ~7 is joined in the region of the OLED layer
structure 5 to a base which is not very stable, so that the
layer 7 may be sensitive to mechanical effects. The cover 23
may advantageously be adhesively bonded to the OLED. In the
embodiment shown in Fig. 4A, the cover 23 is joined to the
further components of the element via a synthetic resin or
plastic layer 25. The synthetic resin or plastic layer 25 is
suitable for compensating for unevenness on the surface, for
example caused by the protruding OLED layer structure.
In the embodiment shown in Fig. 4B, the layer 7 with a
vitreous structure was deposited in such a way that the
3o boundary edge of the bearing surface of the cover is also
covered. For this purpose, the cover 23 was applied to the
coated substrate before the layer 7 with a vitreous
structure. The layer 7 with a vitreous structure was then
deposited on the cover and over its edge which defines the
boundary curve of the bearing surface, so that the edge of
the cover 23 is sealed by the layer 7. This prevents gases
from penetrating between cover and substrate and being able
CA 02505014 2005-05-04
27
to reach the OLED layer structure 5.
In the embodiment shown in Fig. 4C, adhesive bonding of the
cover to the base was dispensed with. In this case, the layer
s 7 with a vitreous structure is itself used to secure the
cover 23. In addition to sealing of the edges of the cover,
the deposition of the layer with a vitreous structure
accordingly also results in bonding of the cover, in a
similar manner to that achieved with a soldering glass, but
to without the OLED layer structure having to be exposed to any
particular thermal load. By way of example, the layer 7 is
not designed as a continuous layer, but rather is only
deposited on the edges of the cover or the boundary curve of
the bearing surface of the cover. Naturally, the layer 7 may
15 also be deposited so as to cover the entire surface of the
coated side of the element, in a similar manner to that shown
in Fig. 4B.
Fig. 4D shows a further embodiment of an element 1 which has
2o been provided with a cover 23 and in which the boundary curve
of the bearing surface of the cover is covered with a layer 7
with a vitreous structure. In this case too, as in the
embodiment which has been shown with reference to Fig. 4C, in
addition to a seal, securing of the cover is also achieved by
25 means of the layer 7. By contrast, however, the layer 7 is
evaporation-coated laterally onto the element, so that the
edges of the element 1 axe sealed.
In the embodiment shown with reference to Fig. 4E, a seal, or
3o a hermetic closure, of the OLED layer structure and a
securing of a cover 23 was achieved by deposition from the
opposite side from the cover. In this case too, a common
feature to the embodiments shown in Figs. 4B, 4C and 4D, the
boundary curve of the bearing surface of the cover 23 is
35 covered by the layer 7 with a vitreous structure.
Fig. 5 illustrates an embodiment in which the layer with a
CA 02505014 2005-05-04
28
vitreous structure is applied to the substrate 3 before the
application of the first and second conductive layers and of
the organic, light-emitting layer. As a result, the layer
with a vitreous structure is located between the substrate
and the OLED layer structure. In this way, the diffusion
through the substrate into the OLED layer structure is
suppressed. Moreover, the encapsulation of the OLED from the
side of the substrate 3 which is achieved with this
arrangement of the layer 7 between OLED layer structure 5 and
to substrate 3 makes it possible far a material which -can be
penetrated by gas molecules to be used for the substrate 3.
By way of example, in this way it is even possible to use a
plastic substrate through which gas molecules would otherwise
migrate into the OLED layer structure on account of the poor
is barrier action of plastics. The use of plastic substrates is
particularly suitable for the production of flexible OLEDs.
Moreover, the OLED may include a banding layer 10 for joining
the layer 7 with a vitreous structure to a plastic substrate.
2o The bonding layer 10 adjoins the layer 7 with a vitreous
structure and is located between substrate 3 and layer 7. The
bonding layer 10 creates a fixed and permanent join between
the layer 7 with a vitreous structure and the -substrate 3, so
that separation of the layer 7 from the flexible substrate 3
2s in particular when the OLED is bent can be prevented. Of
course, it is also possible for the embodiments which have
been described above and those which are described below to
include bonding layers of this type.
so In addition, a further encapsulation (not shown in Fig. 5)
can hermetically seal the OLED layer structure 5, this
encapsulation preferably likewise being effected by
application of a layer with a vitreous structure by means of
CVD and/or PVD coating. The layer with a vitreous structure
3s which is applied between the OLED layer structure 5 and the
substrate 3 may, in addition to its function as a diffusion
barrier, also serve to match refractive indices between OLED
CA 02505014 2005-05-04
29
layer structure 5 and substrate 3, in order to
improve the outputting of the light emitted from the organic
layer 15.
In the case of OLEDs with flexible substrates 3 which are
constructed as shown in Fig. 5, the layer 7 should run as far
as possible along the neutral fiber of the structure, so that
it is impossible for any cracks which could increase the
degradation again to form in this layer when the OLED is
to bent. Fig. 6 shows an embodiment in which a multiple layer 27
has been applied, in order to increase the flexibility of the
structure. In this case, the multiple layer 27 is applied to
the side 9 of the substrate, between substrate 3 and OLED
layer structure 5. In this embodiment, the multiple layer 27
comprises N layers with a vitreous structure 71, 72,..., 7N.
N flexible layers 81, 82,..., 8N are applied alternately with
these layers 71, 72,..., 7N. The flexible layers 81, 82,...,
8N may, by way of example, comprise polymer layers. If the
2o OLED is bent, shear forces occur between the individual
layers. The shear forces are absorbed by deformation of these
layers on account of the flexibility of the layers 81 to 8N.
Of course, the same principle can also be applied to the
opposite side of the OLED layer structure in order to
completely and, at the same time, flexibly encapsulate the
OLED layer structure 5.
In each case for the sake of clarity, the encapsulation of
the OLED layer structure on the opposite side from the
3o substrate is not illustrated in Figures 5 and 6.
Fig. 7 shows, in a similar manner to the embodiment
illustrated in Fig. 6, an OLED according to the invention
with a multiple layer 27 which comprises layers 71, 72,...,
7N with a vitreous structure and further layers 81, 82,...,
8N. Unlike in the embodiment shown in Fig. 6, however, in
this case the layers are applied to the opposite side 11 of
CA 02505014 2005-05-04
the substrate 3 from the side 9 to which the OLED layer
structure 5 is applied. An encapsulation of the OLED layer
structure 5 similar to the embodiments illustrated with
reference to Figures 1 to 4 by a layer 7 with a vitreous
5 structure is additionally illustrated.
In this case, the multiple layer 27, in addition to the
barrier action which is achieved by the layers 71 to 7N, is
also used for refractive index matching in order to improve
to the output of the'light emitted by the organic layer 15 at
the interface between the OLED and the environment. The
individual layers 71 to 7N and 81 to 8N of the multiple layer
27 for this purpose have different refractive indices. In
particular, the layer 27 is constructed in such a way that
is the layers 71 to 7N with a vitreous structure have the same
refractive indices, and the layers 81 to 8N likewise have the
same refractive indices. In this way, the refractive index
alternates from layer to layer through the alternating
arrangement of the layers.
However, a variation in the refractive index can be produced
not only by combining different layers. Rather, it is also
possible for a layer with a vitreous structure to have a
composition which varies along the direction perpendicular to
the coated surface and/or a refractive index which varies
along this direction. A variation in the refractive index is
preferably also achieved by varying the layer composition.
However, variation by means of a layer morphology which
changes along this direction, for example a changing density,
3o is also conceivable. Layers with a variation in the
refractive index as a result of changing layer composition
can be produced by depositing the layer by means of co-
evaporation, the evaporation-coating rate of at least one of
the evaporation sources being changed during the evaporation-
coating process. Therefore, a periodic change in the
evaporation-coating rate, for example by periodically
changing the output from one of the sources, makes it
CA 02505014 2005-05-04
31
,possible to produce a corresponding layer with a
vitreous structure which has a refractive index which varies
periodically perpendicular to the coated surface.
s Such a curve of the refractive index is illustrated by way of
example in Figures 8A and 8B. The coordinate z in these
figures indicates the direction perpendicular to the coated
surface. Both curves reveal a periodic variation in the
refractive index in the z direction. The curve of the
to refractive index illustrated in Fig. 8B has, in addition to
the periodic variation, a decrease in the amplitude in the z
direction, which may additionally be of benefit to the
outputting and introduction efficiency of the element.
15 Finally, Fig. 9 shows a further embodiment of an OLED or of
an organic, electro-optical element, which has structured
functional layers. In this embodiment, the conductive layers
13 and 17 are structured in a comb shape and are both located
at the same level on the substrate 3.~The layers 13 and 17
2o each have finger electrodes 30 which are connected to at
least one web 32. The voltage supply or voltage tap in the
case of a photovoltaic element is effected via the webs 32.
The layer 15 which includes at least one organic, electro-
optical material is applied to the structured layers 13 and
2s 17, so that there is also material of the layer 15 between
the finger electrodes. In this exemplary embodiment, in order
to be encapsulated, the OLED layer structure produced in this
way is once again, in a similar manner to the embodiment
which has been explained with reference to Fig. 1, covered
3o with a layer 7 with a vitreous structure.
Of course, the exemplary embodiments which have been
presented above can also be combined in a wide range of ways,
for example by layers with a vitreous structure being applied
3s to a plurality of sides of the substrate. For example, inter
alia, the embodiment shown with reference to Fig. 7 can be
combined with a coating on trat side of the substrate which
CA 02505014 2005-05-04
32
,faces the OLED layer structure 5, for example as
in the embodiments shown in Figures 5 or 6. Also, virtually
any other desired combinations of the embodiments which have
been shown are possible. It is also possible for all the
embodiments to be used in pixel displays, for example by
using a matrix arrangement of the elements described or by
using correspondingly structured conductive layers with
interconnects which cross one another.
to Fig. 10 shows photographic images of the light transmission
through two specimens. The specimens are glass substrates to
which two calcium strips have been applied. The substrates
were then encapsulated on the side bearing the calcium
strips. In the case of the specimen shown on the left-hand
i5 side of Fig. 10, an evaporation-coating glass was applied for
encapsulation, while in the case of the specimen illustrated
on the right-hand side of Fig. 10 a silicon oxide layer was
selected for the encapsulation, for comparative purposes.
2o The images were taken after the specimens had been shred for
20 hours in air. Undegraded regions of the calcium layer
appear dark in the images. It can be seen from the two images
that the calcium strips coated with evaporation-coating glass
are much less corroded. The degradation of the specimen
25 coated with silicon oxide is further advanced over the entire
surface than in the case of the comparison specimen with an
evaporation-coating glass coating.
Fig. 11 shows the optical density of calcium strips for a
3o plurality of specimens, each coated with evaporation-coating
glass or silicon oxide, as a function of the duration of
action of air. The specimens on which the measurements were
carried out are similar to the specimens shown in Fig. 10. In
this case too, calcium strips were deposited on a substrate,
35 and the side bearing the strips was then encapsulated by
evaporation coating with an evaporation-coating glass or a
silicon oxide layer.
CA 02505014 2005-05-04
33
The graph shown in Fig. 11 reveals that the degradation of
the calcium strips occurs considerably more quickly when
silicon oxide is used as encapsulation material than with the
s specimens encapsulated using evaporation-coating glass.
Fig. 12 shows a bar chart representing a comparison of the
efficiency of differently encapsulated OLEDs. OLEDs which had
been encapsulated with evaporation-coating glass were
to compared with OLEDs without encapsulation and OLEDs with a
silicon oxide encapsulation. The efficiency measurements were
measured shortly after the encapsulation at two different
luminescences. The OLEDs were tested in a shielding gas
atmosphere in order to prevent degradation of the
i5 unencapsulated OLEDs.
It can be seen from the measurements shown in Fig. 12 that
the deposition of evaporation-coating glass, unlike the
deposition of silicon oxide, has substantially no effect on
2o the quality of the finished OLEDs, since the efficiency of
the OLEDs encapsulated with evaporation-coating glass reveals
scarcely any differences compared to the unencapsulated
OLEDs. By contrast, the efficiency of the OLEDs encapsulated
with silicon oxide is considerably reduced.
2s
The following text refers to Fig. 13, which shows a graph
illustrating the luminosity of two differently encapsulated
OLED elements as a function of the residence time in a
climate chamber. An OLED encapsulated with silicon oxide was
3o compared with an OLED encapsulated with evaporation-coating
glass. The luminosity was measured using a photographic
element, and the measured values are given in relative units.
The luminosity was determined at a constant operating current
of 2 mA for the OLEDs.
The specimens were stored in the climate chamber at an air
temperature of 85°C and a relative atmospheric humidity of
CA 02505014 2005-05-04
34
.85%. It can be seen that the OLED encapsulated with
silicon oxide has only approximately a quarter of the
original luminosity after ten days in the climate chamber. By
contrast, the OLED encapsulated with evaporation-coating
glass even has a slightly increased luminosity.
CA 02505014 2005-05-04
List of reference numerals
1 Organic, electro-optical element
3 Substrate
5 OLED layer structure
7, 71, 72, ... 7N Layer with a vitreous structure
9 First side of the substrate
10 Bonding layer
11 , Second side of the substrate
13 First conductive layer
15 Organic, light-emitting layer
17 Second conductive layer
19 Outer side of the OLED
21 Pre-encapsulation layer
23 Cover
25 Adhesive bonding
27 ' Multiple layer
30 Finger electrodes
32 Web
81, 82, ..., 8N Layers of the multiple layer
27
