U.S. patent application number 13/324420 was filed with the patent office on 2013-06-13 for split electrode for organic devices.
This patent application is currently assigned to Universal Display Corporation. The applicant listed for this patent is Ruiqing Ma, Prashant Mandlik. Invention is credited to Ruiqing Ma, Prashant Mandlik.
Application Number | 20130146875 13/324420 |
Document ID | / |
Family ID | 48571155 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130146875 |
Kind Code |
A1 |
Mandlik; Prashant ; et
al. |
June 13, 2013 |
SPLIT ELECTRODE FOR ORGANIC DEVICES
Abstract
A device is provided. The device includes a first electrode, an
organic layer disposed over the first electrode and a second
electrode disposed over the organic layer. The second electrode
further includes a first conductive layer having an extinction
coefficient and an index of refraction, a first separation layer
disposed over the first conductive layer, and a second conductive
layer disposed over the first separation layer. The first
separation layer has an extinction coefficient that is at least 10%
different from the extinction coefficient of the first conductive
layer at 500 nm, or an index of refraction that is at least 10%
different from the index of refraction of the first conductive
layer at 500 nm. The device also includes a barrier layer disposed
over the second conductive layer.
Inventors: |
Mandlik; Prashant;
(Lawrenceville, NJ) ; Ma; Ruiqing; (Morristown,
NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mandlik; Prashant
Ma; Ruiqing |
Lawrenceville
Morristown |
NJ
NJ |
US
US |
|
|
Assignee: |
Universal Display
Corporation
Ewing
NJ
|
Family ID: |
48571155 |
Appl. No.: |
13/324420 |
Filed: |
December 13, 2011 |
Current U.S.
Class: |
257/52 ;
257/E21.09; 257/E29.068; 438/482 |
Current CPC
Class: |
H01L 51/5234 20130101;
H01L 51/5275 20130101; H01L 51/5253 20130101; H01L 51/5259
20130101; H01L 51/56 20130101 |
Class at
Publication: |
257/52 ; 438/482;
257/E29.068; 257/E21.09 |
International
Class: |
H01L 29/12 20060101
H01L029/12; H01L 21/20 20060101 H01L021/20 |
Claims
1. A device, comprising: a first electrode; an organic layer
disposed over the first electrode, and; a second electrode disposed
over the organic layer, the second electrode further comprising, a
first conductive layer having an extinction coefficient and an
index of refraction; a first separation layer disposed over the
first conductive layer, the first separation layer having an
extinction coefficient that is at least 10% different from the
extinction coefficient of the first conductive layer at 500 nm; or
wherein the first separation layer has an index of refraction that
is at least 10% different from the index of refraction of the first
conductive layer at 500 nm; a second conductive layer disposed over
the first separation layer; and a barrier layer disposed over the
second conductive layer.
2. The device of claim 1, wherein the first separation layer has an
extinction coefficient that is at least 10% different from the
extinction coefficient of the first conductive layer at 500 nm.
3. The device of claim 2, wherein the first separation layer has an
extinction coefficient less than 5 at 500 nm.
4. The device of claim 2 wherein the first separation layer has an
extinction coefficient less than 3 at 500 nm.
5. The device of claim 2, wherein the first separation layer has an
extinction coefficient less than 1 at 500 nm.
6. The device of claim 1, wherein the first separation layer
consists essentially of an organic material.
7. The device of claim 6, wherein the first separation layer has a
thickness of at least 20 nm.
8. The device of claim 1, wherein the first separation layer
consists essentially of an inorganic material.
9. The device of claim 1, wherein the first conductive layer has a
thickness not more than 150 nm.
10. The device of claim 1, wherein the first conductive layer has a
water vapor transmission rate at least 5% different from that of
the first separation layer, and the second conductive layer has a
water vapor transmission rate at least 5% different from that of
the first separation layer.
11. The device of claim 1, wherein the first conductive layer has a
water vapor transmission rate at least 10% different from that of
the first separation layer, and the second conductive layer has a
water vapor transmission rate at least 10% different from that of
the first separation layer.
12. The device of claim 1, wherein the first conductive layer has a
water vapor transmission rate at least 25% different from that of
the first separation layer, and the second conductive layer has a
water vapor transmission rate at least 25% different from that of
the first separation layer.
13. The device of claim 1, wherein the first conductive layer is a
low work function metallic layer or an inorganic layer.
14. The device of claim 13, wherein the first conductive layer is a
low work function metallic layer comprising a material selected
from Al, Ca and MgAg.
15. The device of claim 1, wherein the second conductive layer is a
low work function metallic layer or an inorganic layer.
16. The device of claim 15, wherein the second conductive layer is
a low work function metallic layer comprising a material selected
from Al, Ca, and MgAg.
17. The device of claim 1, wherein the first conductive layer and
the second conductive layer have the same material composition.
18. The device of claim 1, wherein the first conductive layer and
the second conductive layers have different material
compositions.
19. The device of claim 1, wherein the first separation layer is a
metallic layer, an inorganic layer, or an organic layer.
20. The device of claim 1, wherein the device further comprises a
substrate, and the first electrode is disposed over the
substrate.
21. The device of claim 20, wherein the substrate is a rigid
substrate having a flexural rigidity greater than 2.times.10.sup.-2
Nm.
22. The device of claim 21, wherein the substrate is a flexible
substrate having a flexural rigidity less than 2.times.10.sup.-2
Nm.
23. The device of claim 22, wherein the first electrode is a anode,
and the device further comprises: a permeation barrier layer
disposed between the anode and the substrate; and a water reacting
layer disposed between the substrate and the anode.
24. The device of claim 20, further comprising a lamination layer
disposed over the barrier layer.
25. The device of claim 1, wherein the second electrode further
comprises: a second separation layer disposed over the second
conductive layer, and a third conductive layer disposed over the
second separation layer.
26. The device of claim 1, wherein the first separation layer
consists essentially of a single material.
27. The device of claim 1, wherein the first separation layer
comprises a mixture of at least two different materials.
28. The device of claim 1, wherein the first separation layer
comprises a plurality of sublayers, wherein at least two of the
sublayers have a different material composition.
29. The device of claim 1, wherein the barrier layer is
transparent.
30. A method, comprising: depositing over a substrate: a first
electrode; an organic layer; a second electrode; and a barrier
layer; wherein depositing the second electrode further comprises
depositing, in order, a first conductive layer having an extinction
coefficient and an index of refraction; a first separation layer
disposed over the first conductive layer, the first separation
layer having an extinction coefficient that is at least 10%
different from the extinction coefficient of the first conductive
layer at 500 nm; a second conductive layer disposed over the first
separation layer.
Description
[0001] The claimed invention was made by, on behalf of, and/or in
connection with one or more of the following parties to a joint
university corporation research agreement: Regents of the
University of Michigan, Princeton University, The University of
Southern California, and the Universal Display Corporation. The
agreement was in effect on and before the date the claimed
invention was made, and the claimed invention was made as a result
of activities undertaken within the scope of the agreement.
FIELD OF THE INVENTION
[0002] The present invention relates to a split electrode.
BACKGROUND
[0003] Opto-electronic devices that make use of organic materials
are becoming increasingly desirable for a number of reasons. Many
of the materials used to make such devices are relatively
inexpensive, so organic opto-electronic devices have the potential
for cost advantages over inorganic devices. In addition, the
inherent properties of organic materials, such as their
flexibility, may make them well suited for particular applications
such as fabrication on a flexible substrate. Examples of organic
opto-electronic devices include organic light emitting devices
(OLEDs), organic phototransistors, organic photovoltaic cells, and
organic photodetectors. For OLEDs, the organic materials may have
performance advantages over conventional materials. For example,
the wavelength at which an organic emissive layer emits light may
generally be readily tuned with appropriate dopants.
[0004] OLEDs make use of thin organic films that emit light when
voltage is applied across the device. OLEDs are becoming an
increasingly interesting technology for use in applications such as
flat panel displays, illumination, and backlighting. Several OLED
materials and configurations are described in U.S. Pat. Nos.
5,844,363, 6,303,238, and 5,707,745, which are incorporated herein
by reference in their entirety.
[0005] One application for phosphorescent emissive molecules is a
full color display. Industry standards for such a display call for
pixels adapted to emit particular colors, referred to as
"saturated" colors. In particular, these standards call for
saturated red, green, and blue pixels. Color may be measured using
CIE coordinates, which are well known to the art.
[0006] One example of a green emissive molecule is
tris(2-phenylpyridine) iridium, denoted Ir(ppy).sub.3, which has
the following structure:
##STR00001##
[0007] In this, and later figures herein, we depict the dative bond
from nitrogen to metal (here, Ir) as a straight line.
[0008] As used herein, the term "organic" includes polymeric
materials as well as small molecule organic materials that may be
used to fabricate organic opto-electronic devices. "Small molecule"
refers to any organic material that is not a polymer, and "small
molecules" may actually be quite large. Small molecules may include
repeat units in some circumstances. For example, using a long chain
alkyl group as a substituent does not remove a molecule from the
"small molecule" class. Small molecules may also be incorporated
into polymers, for example as a pendent group on a polymer backbone
or as a part of the backbone. Small molecules may also serve as the
core moiety of a dendrimer, which consists of a series of chemical
shells built on the core moiety. The core moiety of a dendrimer may
be a fluorescent or phosphorescent small molecule emitter. A
dendrimer may be a "small molecule," and it is believed that all
dendrimers currently used in the field of OLEDs are small
molecules.
[0009] As used herein, "top" means furthest away from the
substrate, while "bottom" means closest to the substrate. Where a
first layer is described as "disposed over" a second layer, the
first layer is disposed further away from substrate. There may be
other layers between the first and second layer, unless it is
specified that the first layer is "in contact with" the second
layer. For example, a cathode may be described as "disposed over"
an anode, even though there are various organic layers in
between.
[0010] As used herein, "solution processible" means capable of
being dissolved, dispersed, or transported in and/or deposited from
a liquid medium, either in solution or suspension form.
[0011] A ligand may be referred to as "photoactive" when it is
believed that the ligand directly contributes to the photoactive
properties of an emissive material. A ligand may be referred to as
"ancillary" when it is believed that the ligand does not contribute
to the photoactive properties of an emissive material, although an
ancillary ligand may alter the properties of a photoactive
ligand.
[0012] As used herein, and as would be generally understood by one
skilled in the art, a first "Highest Occupied Molecular Orbital"
(HOMO) or "Lowest Unoccupied Molecular Orbital" (LUMO) energy level
is "greater than" or "higher than" a second HOMO or LUMO energy
level if the first energy level is closer to the vacuum energy
level. Since ionization potentials (IP) are measured as a negative
energy relative to a vacuum level, a higher HOMO energy level
corresponds to an IP having a smaller absolute value (an IP that is
less negative). Similarly, a higher LUMO energy level corresponds
to an electron affinity (EA) having a smaller absolute value (an EA
that is less negative). On a conventional energy level diagram,
with the vacuum level at the top, the LUMO energy level of a
material is higher than the HOMO energy level of the same material.
A "higher" HOMO or LUMO energy level appears closer to the top of
such a diagram than a "lower" HOMO or LUMO energy level.
[0013] As used herein, and as would be generally understood by one
skilled in the art, a first work function is "greater than" or
"higher than" a second work function if the first work function has
a higher absolute value. Because work functions are generally
measured as negative numbers relative to vacuum level, this means
that a "higher" work function is more negative. On a conventional
energy level diagram, with the vacuum level at the top, a "higher"
work function is illustrated as further away from the vacuum level
in the downward direction. Thus, the definitions of HOMO and LUMO
energy levels follow a different convention than work
functions.
[0014] More details on OLEDs, and the definitions described above,
can be found in U.S. Pat. No. 7,279,704, which is incorporated
herein by reference in its entirety.
SUMMARY OF THE INVENTION
[0015] A device is provided. The device includes a first electrode,
an organic layer disposed over the first electrode and a second
electrode disposed over the organic layer. The second electrode
further includes a first conductive layer having an extinction
coefficient and an index of refraction, a first separation layer
disposed over the first conductive layer, and a second conductive
layer disposed over the first separation layer. The first
separation layer has an extinction coefficient that is at least 10%
different from the extinction coefficient of the first conductive
layer at 500 nm, or an index of refraction that is at least 10%
different from the index of refraction of the first conductive
layer at 500 nm. Preferably, the first separation layer has an
extinction coefficient that is at least 10% different from the
extinction coefficient of the first conductive layer at 500 nm.
More preferably, the first separation layer also has an index of
refraction that is at least 10% different from the index of
refraction of the first conductive layer at 500 nm. The device also
includes a barrier layer disposed over the second conductive
layer.
[0016] Preferably, the first separation layer has an extinction
coefficient at 500 nm less than 5, more preferably less than 3, and
most preferably less than 1.
[0017] In one embodiment, the first separation layer consists
essentially of an organic material. When the first separation layer
is an organic material, the first separation layer preferably has a
thickness of at least 20 nm.
[0018] In one embodiment, the first separation layer consists
essentially of an inorganic material.
[0019] Preferably, the first conductive layer has a thickness not
more than 150 nm.
[0020] Preferably, the first conductive layer has a water vapor
transmission rate at least 5% different from that of the first
separation layer, and the second conductive layer has a water vapor
transmission rate at least 5% different from that of the first
separation layer. More preferably, the first conductive layer has a
water vapor transmission rate at least 10% different from that of
the first separation layer, and the second conductive layer has a
water vapor transmission rate at least 10% different from that of
the first separation layer. Most preferably, the first conductive
layer has a water vapor transmission rate at least 25% different
from that of the first separation layer, and the second conductive
layer has a water vapor transmission rate at least 25% different
from that of the first separation layer.
[0021] In one embodiment, the first conductive layer is a low work
function metallic layer or an inorganic layer. Preferred low work
function metallic layer materials for the first conductive layer
include Ca and MgAg.
[0022] In one embodiment, the second conductive layer is a low work
function metallic layer or an inorganic layer. Preferred low work
function metallic layer materials for the second conductive layer
include Ca and MgAg.
[0023] In one embodiment, the first conductive layer and the second
conductive layer have the same material composition.
[0024] In one embodiment, the first conductive layer and the second
conductive layers have different material compositions.
[0025] In one embodiment, the first separation layer is a metallic
layer, an inorganic layer, or an organic layer.
[0026] The device may further comprise a substrate, and the first
electrode may be disposed over the substrate.
[0027] In one embodiment, the substrate is a rigid substrate having
a flexural rigidity greater than 2.times.10.sup.-2 Nm. Preferred
materials for a rigid substrate include glass, ceramic, and metal
having a thickness sufficient to result in the desired flexural
rigidity.
[0028] In one embodiment, the substrate is a flexible substrate
having a flexural rigidity less than 2.times.10.sup.-2 Nm.
Preferred materials for a flexible substrate include metal,
plastic, paper, fabric and a composite material. The materials have
a thickness sufficiently low to result in the desired flexural
rigidity. Composites can be ceramic matrix composites, metal matrix
composites, or polymer matrix composites.
[0029] In one embodiment, the first electrode is a anode, and the
device further includes a permeation barrier layer disposed between
the anode and the substrate. The device also further includes a
water reacting layer disposed between the substrate and the anode.
This embodiment is particularly preferred for use with flexible
substrates, which tend to be more susceptible to moisture
penetrating the substrate.
[0030] In one embodiment, the device further includes a lamination
layer disposed over the barrier layer. A lamination layer can be a
thin polymer membrane attached to the substrate using an adhesive,
a thin spun-on polymer layer, an evaporated polymer layer, a spray
coated, or an aerosol dispersed polymer layer.
[0031] In one embodiment, the second electrode further includes a
second separation layer disposed over the second conductive layer,
and a third conductive layer disposed over the second separation
layer. Parameters described above with respect to the second
conductive layer and the first separation layer are preferred for
use with the third conductive layer and the second separation layer
as well.
[0032] In one embodiment, the first separation layer consists
essentially of a single material.
[0033] In one embodiment, the first separation layer comprises a
mixture of at least two different materials.
[0034] In one embodiment, the first separation layer comprises a
plurality of sublayers, wherein at least two of the sublayers have
a different material composition.
[0035] Preferably, the barrier layer is transparent.
[0036] A method is also provided. The following layers are
deposited, in order, over a substrate: a first electrode; an
organic layer; a second electrode; and a barrier layer. Depositing
the second electrode further comprises depositing, in order: a
first conductive layer having an extinction coefficient and an
index of refraction; a first separation layer disposed over the
first conductive layer, and a second conductive layer disposed over
the first separation layer. The first separation layer has an
extinction coefficient that is at least 10% different from the
extinction coefficient of the first conductive layer at 500 nm.
Preferably, the first separation layer also has an index of
refraction that is at least 10% different from the index of
refraction of the first conductive layer at 500 nm.
[0037] Embodiments and preferences described above with respect to
devices also apply to the method.
[0038] Embodiments of the invention may be used with a variety of
organic devices. While many embodiments are described herein with
respect to organic light emitting devices, other types of devices,
such as organic photovoltaic devices and organic transistors, may
benefit from the electrode and moisture protective structures
described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 shows an organic light emitting device.
[0040] FIG. 2 shows an inverted organic light emitting device that
does not have a separate electron transport layer.
[0041] FIG. 3 shows an organic light emitting device that includes
a split electrode.
[0042] FIG. 4 shows schematic 3-D and cross-sectional views of a
device with single layer cathode. Formation of dark spots at
cathode-organic interface is also shown.
[0043] FIG. 5 shows a schematic 3-D and the cross-sectional views
of a device with multiple layer cathode. Formation of defects (not
forming dark spots) away from the cathode-organic interface is
shown.
[0044] FIG. 6 shows a cross-sectional view of a flexible device
with bottom desiccant layer and multiple layer cathode. Formation
of defects (not forming dark spots) away from the cathode-organic
interface above and below the device is shown.
[0045] FIG. 7 shows a cross-sectional view of a device with
multiple layer cathode with bridges between the two cathode layers
via breaks in the sandwich layer.
[0046] FIG. 8 shows a cross-sectional view of a flexible device
with multiple layer cathode with bridges between the two cathode
layers via breaks in the sandwich layer.
[0047] FIG. 9 shows a schematic cross-sectional view of organic
layer of the OLED device and CL-1 and -2 with a defect separation
layer (DSL) in between. The DSL has higher water vapor transmission
rate than the cathode. This allows the water molecules to disperse
across the layer quickly at the same time allowing the CL-2 to
react with water and form defects which are not visible as dark
spots in the device.
[0048] FIG. 10 shows a schematic cross-sectional view of organic
layer of the OLED device and CL-1 and -2 with DSL in between. The
DSL has lower water vapor transmission rate than the cathode. This
forces the water molecules to disperse across the interface of the
CL-2 with the DSL and react with the cathode to form defects which
are not visible as dark spots in the device.
[0049] FIG. 11 shows a schematic cross-sectional view of organic
layer of the OLED device and CL-1 and an extended cathode. The
pinholes and other defects in the cathode continue to grow. The end
result is not much different than if only the first CL were
present. The defects form at the CL-1--organic interface and are
visible as dark spots.
[0050] FIG. 12 shows photographs of active areas of bottom-emitting
OLED devices during the shelf-life tests at 85.degree. C. and 85%
RH encapsulated with similar thin film encapsulation. (a) The
cathode is single layer 200 nm Al. (b) The cathode is 100 nm Al,
followed by 60 nm NPD, followed by 100 nm Al. The lag time (time
for the onset of degradation) is about 480 hrs in the first case,
whereas it is about 650 hrs in the second.
[0051] FIG. 13 shows a photographs of active areas of
bottom-emitting OLED devices during the shelf-life tests at
85.degree. C. and 85% RH encapsulated without thin film
encapsulation. (a) and (b) The cathode is single layer 200 nm Al.
(c) and (d) The cathode is 100 nm Al, followed by 60 nm NPD,
followed by 100 nm Al. All the devices got disintegrated by water
vapor within 10 min at 85.degree. C. and 85% RH.
DETAILED DESCRIPTION
[0052] Generally, an OLED comprises at least one organic layer
disposed between and electrically connected to an anode and a
cathode. When a current is applied, the anode injects holes and the
cathode injects electrons into the organic layer(s). The injected
holes and electrons each migrate toward the oppositely charged
electrode. When an electron and hole localize on the same molecule,
an "exciton," which is a localized electron-hole pair having an
excited energy state, is formed. Light is emitted when the exciton
relaxes via a photoemissive mechanism. In some cases, the exciton
may be localized on an excimer or an exciplex. Non-radiative
mechanisms, such as thermal relaxation, may also occur, but are
generally considered undesirable.
[0053] The initial OLEDs used emissive molecules that emitted light
from their singlet states ("fluorescence") as disclosed, for
example, in U.S. Pat. No. 4,769,292, which is incorporated by
reference in its entirety. Fluorescent emission generally occurs in
a time frame of less than 10 nanoseconds.
[0054] More recently, OLEDs having emissive materials that emit
light from triplet states ("phosphorescence") have been
demonstrated. Baldo et al., "Highly Efficient Phosphorescent
Emission from Organic Electroluminescent Devices," Nature, vol.
395, 151-154, 1998; ("Baldo-I") and Baldo et al., "Very
high-efficiency green organic light-emitting devices based on
electrophosphorescence," Appl. Phys. Lett., vol. 75, No. 3, 4-6
(1999) ("Baldo-II"), which are incorporated by reference in their
entireties. Phosphorescence is described in more detail in U.S.
Pat. No. 7,279,704 at cols. 5-6, which are incorporated by
reference.
[0055] FIG. 1 shows an organic light emitting device 100. The
figures are not necessarily drawn to scale. Device 100 may include
a substrate 110, an anode 115, a hole injection layer 120, a hole
transport layer 125, an electron blocking layer 130, an emissive
layer 135, a hole blocking layer 140, an electron transport layer
145, an electron injection layer 150, a protective layer 155, and a
cathode 160. Cathode 160 is a compound cathode having a first
conductive layer 162 and a second conductive layer 164. Device 100
may be fabricated by depositing the layers described, in order. The
properties and functions of these various layers, as well as
example materials, are described in more detail in U.S. Pat. No.
7,279,704 at cols. 6-10, which are incorporated by reference.
[0056] More examples for each of these layers are available. For
example, a flexible and transparent substrate-anode combination is
disclosed in U.S. Pat. No. 5,844,363, which is incorporated by
reference in its entirety. An example of a p-doped hole transport
layer is m-MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50:1,
as disclosed in U.S. Patent Application Publication No.
2003/0230980, which is incorporated by reference in its entirety.
Examples of emissive and host materials are disclosed in U.S. Pat.
No. 6,303,238 to Thompson et al., which is incorporated by
reference in its entirety. An example of an n-doped electron
transport layer is BPhen doped with Li at a molar ratio of 1:1, as
disclosed in U.S. Patent Application Publication No. 2003/0230980,
which is incorporated by reference in its entirety. U.S. Pat. Nos.
5,703,436 and 5,707,745, which are incorporated by reference in
their entireties, disclose examples of cathodes including compound
cathodes having a thin layer of metal such as Mg:Ag with an
overlying transparent, electrically-conductive, sputter-deposited
ITO layer. The theory and use of blocking layers is described in
more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application
Publication No. 2003/0230980, which are incorporated by reference
in their entireties. Examples of injection layers are provided in
U.S. Patent Application Publication No. 2004/0174116, which is
incorporated by reference in its entirety. A description of
protective layers may be found in U.S. Patent Application
Publication No. 2004/0174116, which is incorporated by reference in
its entirety.
[0057] FIG. 2 shows an inverted OLED 200. The device includes a
substrate 210, a cathode 215, an emissive layer 220, a hole
transport layer 225, and an anode 230. Device 200 may be fabricated
by depositing the layers described, in order. Because the most
common OLED configuration has a cathode disposed over the anode,
and device 200 has cathode 215 disposed under anode 230, device 200
may be referred to as an "inverted" OLED. Materials similar to
those described with respect to device 100 may be used in the
corresponding layers of device 200. FIG. 2 provides one example of
how some layers may be omitted from the structure of device
100.
[0058] The simple layered structure illustrated in FIGS. 1 and 2 is
provided by way of non-limiting example, and it is understood that
embodiments of the invention may be used in connection with a wide
variety of other structures. The specific materials and structures
described are exemplary in nature, and other materials and
structures may be used. Functional OLEDs may be achieved by
combining the various layers described in different ways, or layers
may be omitted entirely, based on design, performance, and cost
factors. Other layers not specifically described may also be
included. Materials other than those specifically described may be
used. Although many of the examples provided herein describe
various layers as comprising a single material, it is understood
that combinations of materials, such as a mixture of host and
dopant, or more generally a mixture, may be used. Also, the layers
may have various sublayers. The names given to the various layers
herein are not intended to be strictly limiting. For example, in
device 200, hole transport layer 225 transports holes and injects
holes into emissive layer 220, and may be described as a hole
transport layer or a hole injection layer. In one embodiment, an
OLED may be described as having an "organic layer" disposed between
a cathode and an anode. This organic layer may comprise a single
layer, or may further comprise multiple layers of different organic
materials as described, for example, with respect to FIGS. 1 and
2.
[0059] Structures and materials not specifically described may also
be used, such as OLEDs comprised of polymeric materials (PLEDs)
such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al.,
which is incorporated by reference in its entirety. By way of
further example, OLEDs having a single organic layer may be used.
OLEDs may be stacked, for example as described in U.S. Pat. No.
5,707,745 to Forrest et al, which is incorporated by reference in
its entirety. The OLED structure may deviate from the simple
layered structure illustrated in FIGS. 1 and 2. For example, the
substrate may include an angled reflective surface to improve
out-coupling, such as a mesa structure as described in U.S. Pat.
No. 6,091,195 to Forrest et al., and/or a pit structure as
described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are
incorporated by reference in their entireties.
[0060] Unless otherwise specified, any of the layers of the various
embodiments may be deposited by any suitable method. For the
organic layers, preferred methods include thermal evaporation,
ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and
6,087,196, which are incorporated by reference in their entireties,
organic vapor phase deposition (OVPD), such as described in U.S.
Pat. No. 6,337,102 to Forrest et al., which is incorporated by
reference in its entirety, and deposition by organic vapor jet
printing (OVJP), such as described in U.S. patent application Ser.
No. 10/233,470, which is incorporated by reference in its entirety.
Other suitable deposition methods include spin coating and other
solution based processes. Solution based processes are preferably
carried out in nitrogen or an inert atmosphere. For the other
layers, preferred methods include thermal evaporation. Preferred
patterning methods include deposition through a mask, cold welding
such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which
are incorporated by reference in their entireties, and patterning
associated with some of the deposition methods such as ink jet and
OVJD. Other methods may also be used. The materials to be deposited
may be modified to make them compatible with a particular
deposition method. For example, substituents such as alkyl and aryl
groups, branched or unbranched, and preferably containing at least
3 carbons, may be used in small molecules to enhance their ability
to undergo solution processing. Substituents having 20 carbons or
more may be used, and 3-20 carbons is a preferred range. Materials
with asymmetric structures may have better solution processability
than those having symmetric structures, because asymmetric
materials may have a lower tendency to recrystallize. Dendrimer
substituents may be used to enhance the ability of small molecules
to undergo solution processing.
[0061] Devices fabricated in accordance with embodiments of the
invention may be incorporated into a wide variety of consumer
products, including flat panel displays, computer monitors, medical
monitors, televisions, billboards, lights for interior or exterior
illumination and/or signaling, heads up displays, fully transparent
displays, flexible displays, laser printers, telephones, cell
phones, personal digital assistants (PDAs), laptop computers,
digital cameras, camcorders, viewfinders, micro-displays, vehicles,
a large area wall, theater or stadium screen, or a sign. Various
control mechanisms may be used to control devices fabricated in
accordance with the present invention, including passive matrix and
active matrix. Many of the devices are intended for use in a
temperature range comfortable to humans, such as 18 degrees C. to
30 degrees C., and more preferably at room temperature (20-25
degrees C.).
[0062] The materials and structures described herein may have
applications in devices other than OLEDs. For example, other
optoelectronic devices such as organic solar cells and organic
photodetectors may employ the materials and structures. More
generally, organic devices, such as organic transistors, may employ
the materials and structures.
[0063] The terms halo, halogen, alkyl, cycloalkyl; alkenyl,
alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and
heteroaryl are known to the art, and are defined in U.S. Pat. No.
7,279,704 at cols. 31-32, which are incorporated herein by
reference.
[0064] A structure and method to prolong the shelflife of OLEDs
encapsulated with thin film encapsulation has been discovered. An
electrode having a separation layer disposed between two conductive
layers is used to direct the formation of defects caused by
insulating film formation or interface delamination to locations in
the device that are away from cathode-organic interface, such that
dark spots are not formed.
[0065] A cathode layer (CL) may be divided into two or more
conductive layers sandwiching a separation layer between them.
Because of this division the water vapor penetrating through the
encapsulation layer attacks the top most conductive or the
separation layer of the CL. This often results in a reaction that
forms an insulating (oxide-like) layer and/or causes delamination.
Because the water reacts before reaching the bottommost conductive
layer of the CL, that layer remains unaffected by the formation of
this defect. As a result, the bottommost conductive layer of the CL
continues functioning as a cathode. In addition, the bottommost
conductive layer of the CL undergoing much less degradation when
compared to a single layer cathode, thereby extending the shelf
life of the device.
[0066] Another function for the top layer of such a divided cathode
is acting as a desiccant to absorb moisture. The function of
desiccant can be utilized on the anode side of the device in
addition to the cathode side when the substrate is permeable, which
is seen most often in the context of a plastic substrate or a
flexible substrate. Plastic substrates are preferably used with a
barrier film between the substrate and the device to prevent the
device from degrading via the water vapor permeating through the
substrate. If there is a thin layer of moisture absorbing material
between the cathode and the encapsulation layer, it can react with
the water molecules, delaying them from reaching the
cathode-organic interface and forming dark spots.
[0067] There have been attempts to describe the utility of
multilayer cathode. E.g., the experiment in the article, "Improved
flexibility of flexible organic light-emitting devices by using a
metal/organic multilayer Cathode, by Lian Duan, Song Liu, Deqing
Zhang, Juan Qiao, Guifang Dong, Liduo Wang and Yong Qiu, J. Phys.
D: Appl. Phys. 42 (2009) 075103" describes improvements in device
flexibility and lifetime (operational lifetime, not shelf lifetime)
by using a multilayer (Al/Alq/Al) cathode topped with encapsulation
consisting of four stacks of Alq/LiF, followed by CaO desiccant,
followed by Al foil.
[0068] In contrast to the device disclosed in Duan, the multilayer
cathode described herein is suitable for use in a device that emits
light through the cathode, and that can be used, for example, in
conjunction with a barrier layer that is a transparent thin film
encapsulation layer disposed over the cathode.
[0069] There have been other attempts to use multilayer cathodes.
E.g. US2006/018199A1 demonstrates a metal/inorganic/metal
multilayer cathode in an OLED device.
[0070] FIG. 3 shows an organic device 300 having a split electrode.
The device is disposed over a substrate 310. The device includes,
in order, a permeation barrier 320, a water reacting layer 330, a
first electrode 340, an organic layer 350, a second electrode 360,
a barrier layer 370, and a lamination layer 380, Second electrode
360 is a split electrode that further includes a first conductive
layer 361, a first separation layer 362, a second conductive layer
363, a second separation layer 364, and a third conductive layer
365. Many features shown in FIG. 3 are optional.
[0071] A device is provided. The device includes a first electrode,
an organic layer disposed over the first electrode and a second
electrode disposed over the organic layer. The second electrode
further includes a first conductive layer having an extinction
coefficient and an index of refraction, a first separation layer
disposed over the first conductive layer, and a second conductive
layer disposed over the first separation layer. The first
separation layer has an extinction coefficient that is at least 10%
different from the extinction coefficient of the first conductive
layer at 500 nm, or an index of refraction that is at least 10%
different from the index of refraction of the first conductive
layer at 500 nm. Preferably, the first separation layer has an
extinction coefficient that is at least 10% different from the
extinction coefficient of the first conductive layer at 500 nm.
More preferably, the first separation layer also has an index of
refraction that is at least 10% different from the index of
refraction of the first conductive layer at 500 nm. The device also
includes a barrier layer disposed over the second conductive
layer.
[0072] The organic layer may include multiple sublayers. For
example, in an OLED, the organic layer may include all or some of
the organic layers described with respect to FIGS. 1 and 2. In
other types of organic devices, the organic layer may include
multiple layers as well.
[0073] By "at least 10% different," it is meant, for example, that
the first separation layer has an extinction coefficient that is
either 10% greater or 10% less than that of the first conductive
layer.
[0074] When light passes through a material, the measured intensity
I of light transmitted through is related to the incident intensity
I0 according to the inverse exponential power law called as
Beer-Lambert Law. The expression is given by:
I=I.sub.0e.sup.-.sup.x,
where x denotes the path length and is the absorption or
attenuation coefficient. The absorption coefficient is one way to
describe the absorption of electromagnetic waves in a medium. It
can be expressed in terms of the imaginary part of the refractive
index, .kappa., and the wavelength of the light in free space,
.lamda..sub.0, as =4.pi..kappa./.lamda..sub.0. The imaginary part
of the refractive index is also commonly called the extinction
coefficient. The extinction coefficient, just like the real part of
the refractive index, has not units. The real part of the
refractive index (commonly called as the refractive index) of a
medium denotes the ratio of the speed of the wave in a reference
medium (such as vacuum) to that in the given medium.
[0075] A difference in the extinction coefficient and refractive
index between the separation layer and other layers is desirable
because such a difference means that there is also a difference in
material growth, chemistry, composition, density, and atomic
arrangement and/or other physical properties such as the water
vapor transmission rate. It is desirable to have a separation layer
whose material properties are different from that of the conduction
layer to perform its function as a separation layer. A material
with different physical properties will allow the water vapor
permeating through the permeation barrier get distributed instead
of continuing down to the device in the absence of such layer as
shown in FIG. 11. Extinction coefficient and refractive index,
while correlating to water vapor transmission coefficient, are more
readily obtainable from published references and can be measured
more easily than water vapor transmission coefficient and hence can
be used to pick materials suitable as the separation layer.
Extinction coefficient or refractive index higher or lower than the
conduction layer would imply difference in the physical properties
and hence would ensure its proper functioning as the separation
layer. As an example, the extinction coefficient and the refractive
index of a commonly used conduction layer Al at 500 nm are 6.04 and
0.82. An inorganic film such as SiON would work well as the
separation layer because of the difference in physical properties
between the two materials. It has an extinction coefficient of 0
and a refractive index of 1.49 at 500 nm. From the previous example
we see that both extinction coefficient and refractive index can be
used to select a separation layer suitable for a conduction layer.
The measurement of these two parameters is very simple and requires
only a few minutes using an ellipsometer
[0076] Barrier layers can be inorganic, such as SiNx, SiOx, and
SiOxNy, or other oxides such as TiO.sub.2, HfO.sub.2 or nitrides
such as TiN or AlTiN, or organometallic, such as SiOxCy, SiOxCyHz,
SiCxOyNz or hybrid (mixtures of) inorganic-organic films, or
multiple layers of alternate inorganic-organic films grown using
evaporation techniques such as chemical vapor deposition (hot-wire
or plasma assisted), or e-beam or thermal evaporation, or
sputtering or atomic or molecular layer deposition. Organic films
are compounds containing carbon such as Alq, NPD, polyacrylates,
polycarbonates, etc. The barrier films can be deposited using
aforementioned vacuum techniques or non-vacuum techniques such as
printing or spin-on and sintering. Barrier layers are known, and
any suitable barrier layer may be used.
[0077] Preferably, the first separation layer has an extinction
coefficient less than 5 at 500 nm. More preferably, the first
separation layer has an extinction coefficient less than 3 and even
more preferably less than 1 at 500 nm
[0078] Extinction coefficient and index of refraction are generally
functions of wavelength. 500 nm is selected as a point at which to
definitively quantify the effects of extinction coefficient and
index of refraction because higher energy visible light, such as
that around 500 nm, may generally cause more issues of various
types in various devices than lower energy light.
[0079] In one embodiment, the first separation layer consists
essentially of an organic material. When the first separation layer
is an organic material, the first separation layer preferably has a
thickness of at least 20 nm.
[0080] In one embodiment, the first separation layer consists
essentially of an inorganic material.
[0081] Preferably, the first conductive layer has a thickness not
more than 150 nm.
[0082] Preferably, the first conductive layer has a water vapor
transmission rate at least 5% different from that of the first
separation layer, and the second conductive layer has a water vapor
transmission rate at least 5% different from that of the first
separation layer. More preferably, the first conductive layer has a
water vapor transmission rate at least 10% different from that of
the first separation layer, and the second conductive layer has a
water vapor transmission rate at least 10% different from that of
the first separation layer. Most preferably, the first conductive
layer has a water vapor transmission rate at least 25% different
from that of the first separation layer, and the second conductive
layer has a water vapor transmission rate at least 25% different
from that of the first separation layer.
[0083] By "at least 5% different," it is meant, for example, that
the first separation layer has a water vapor transmission rate
(WVTR) that is either 5% greater or 5% less than that of the first
conductive layer. A significant difference in the WVTR of these
layers means that water traveling through the electrode somewhere
hits a layer with a relatively high WVTR, where it can travel in a
direction parallel to the electrode relatively easily and react to
form an oxide over a wide area prior to reaching an interface where
such a reaction causes a dark spot.
[0084] In one embodiment, the first conductive layer is a low work
function metallic layer or an inorganic layer. Preferred low work
function metallic layer materials for the first conductive layer
include Ca and MgAg (Mg doped with Ag).
[0085] In one embodiment, the second conductive layer is a low work
function metallic layer or an inorganic layer. Preferred low work
function metallic layer materials for the second conductive layer
include Ca and MgAg.
[0086] In one embodiment, the first conductive layer and the second
conductive layer have the same material composition.
[0087] In one embodiment, the first conductive layer and the second
conductive layers have different material compositions.
[0088] In one embodiment, the first separation layer is a metallic
layer, an inorganic layer, or an organic layer.
[0089] The device may further comprise a substrate, and the first
electrode may be disposed over the substrate.
[0090] In one embodiment, the substrate is a rigid substrate having
a flexural rigidity greater than 2.times.10.sup.-2 Nm. Preferred
materials for a rigid substrate include glass, ceramic, and metal
having a thickness sufficient to result in the desired flexural
rigidity.
[0091] In one embodiment, the substrate is a flexible substrate
having a flexural rigidity less than 2.times.10.sup.-2 Nm.
Preferred materials for a flexible substrate include metal,
plastic, paper, fabric and a composite material. The materials have
a thickness sufficiently low to result in the desired flexural
rigidity. Composites can be ceramic matrix composites, metal matrix
composites, or polymer matrix composites.
[0092] In one embodiment, the first electrode is a anode, and the
device further includes a permeation barrier layer disposed between
the anode and the substrate. The device also further includes a
water reacting layer disposed between the substrate and the anode.
This embodiment is particularly preferred for use with flexible
substrates, which tend to be more susceptible to moisture
penetrating the substrate.
[0093] The permeation barrier can be anywhere from 100 nm thick
film in a low defect, low particulate scenario to a 50 .mu.m thick
film such as a combination of some thin inorganic film (like
SiOxCyNz) with spun-on or evaporated or printed polymer film (like
polyacrylate or polyepoxide). Preferably, the overall barrier layer
is less than 25 .mu.m thick and most preferably less than 10 .mu.m
thick. Reducing the thickness would improve the mechanical
flexibility of the barrier film. The water reacting layer can be as
thin as 5 nm when it is a thin metal film or as thick as 25 .mu.m
when it is a polymer film. The water reactive film, when it is
polymer, can also act as a planarization layer used to minimize the
surface roughness of the substrate.
[0094] In one embodiment, the device further includes a lamination
layer disposed over the barrier layer. Its purpose is to prevent
the barrier layer from mechanical degradation upon handling and
transport. A lamination layer can be a thin polymer membrane
attached to the substrate using an adhesive, a thin spun-on polymer
layer, an evaporated polymer layer, a spray coated, or an aerosol
dispersed polymer layer.
[0095] The lamination layer can be a layer of an organic or
organometallic compound such as polyacrylates, polyepoxides,
polysiloxanes, and other suitable materials. These can be UV or
heat curable compounds, which will polymerize, or cross-link or set
upon treating with UV light or heating or applying pressure, or
simply leaving at room temperature for some interval of time. The
lamination can also be such polymer adhesive layers followed by a
polymer membrane or sheet such as PEN (polyethylene nepthlate), or
polycarbonate, or polyimide or other suitable materials.
[0096] In one embodiment, the second electrode further includes a
second separation layer disposed over the second conductive layer,
and a third conductive layer disposed over the second separation
layer. Parameters described above with respect to the second
conductive layer and the first separation layer are preferred for
use with the third conductive layer and the second separation layer
as well.
[0097] An additional separation layer increases the number of
interfaces and layers in which water can travel laterally and react
prior to reaching an interface with the organic material, where the
presence of water would cause a dark spot.
[0098] In one embodiment, the first separation layer consists
essentially of a single material.
[0099] In one embodiment, the first separation layer comprises a
mixture of at least two different materials.
[0100] In one embodiment, the first separation layer comprises a
plurality of sublayers, wherein at least two of the sublayers have
a different material composition.
[0101] Preferably, the barrier layer is transparent. As used
herein, "transparent" means that the layer transmits more than 90%
of incident light having a wavelength of 500 nm.
[0102] A method is also provided. The following layers are
deposited, in order, over a substrate: a first electrode; an
organic layer; a second electrode; and a barrier layer. Depositing
the second electrode further comprises depositing, in order: a
first conductive layer having an extinction coefficient and an
index of refraction; a first separation layer disposed over the
first conductive layer, and a second conductive layer disposed over
the first separation layer. The first separation layer has an
extinction coefficient that is at least 10% different from the
extinction coefficient of the first conductive layer at 500 nm.
Preferably, the first separation layer also has an index of
refraction that is at least 10% different from the index of
refraction of the first conductive layer at 500 nm.
[0103] Embodiments and preferences described above with respect to
devices also apply to the method.
[0104] Embodiments of the invention may be used with a variety of
organic devices. While many embodiments are described herein with
respect to organic light emitting devices, other types of devices,
such as organic photovoltaic devices and organic transistors, may
benefit from the electrode and moisture protective structures
described herein.
[0105] FIG. 4 shows schematic 3-D and cross-sectional views of a
device with single layer cathode. Formation of dark spots at
cathode-organic interface is also shown. The device of FIG. 4
includes a substrate 410, an anode 420, organic layers 430, a
cathode 440 and a barrier film 450. A bus line 460 provides current
to the cathode. Dark spot 470 is also shown.
Embodiment 1
[0106] In one embodiment, a moisture sensitive electrode of an
electronic device is divided in to two or more layers with another
metallic, inorganic or organic layer sandwiched in between to
mitigate degradation. By way of comparative example, FIG. 4 shows
the 3-D and the cross-sectional views (both schematic) of a device
with single layer cathode. The dark spots form when water vapor
penetrates through the encapsulation film to reach the
cathode-organic interface, causing affected regions to stop
emitting.
[0107] FIG. 5 shows a schematic 3-D and the cross-sectional views
of a device with a multiple layer or "split" cathode. Formation of
defects (not forming dark spots) away from the cathode-organic
interface is shown. The device of FIG. 5 includes a substrate 510,
an anode 520, organic layers 530, a cathode, and a barrier film
550. The cathode includes first conductive layer 541, separation
layer 542 and second conductive layer 543. Dark spot 460 is also
shown.
[0108] In FIG. 5, which shows the 3-D and the cross-sectional views
of a device with split-cathode, the delamination defects form at
the interface between the second conductive layer and the
separation layer. As the defects are away from the active area, the
device continues to emit light. The defect separation layer (DSL)
has a different water vapor permeation rate than the cathode. In
one case, it has much higher water vapor permeation rate than the
cathode. The high permeation rate results in quick dispersion of
water molecules across the sandwich layer and allows sufficient
time for the second conductive layer (cathode layer 2 or CL-2)--DSL
interface to react with the moisture. Note that the first
conductive layer may also be referred to as cathode layer 1 or
CL-1. In another case, the permeation rate across the sandwich
layer is much less than the cathode. In that case, the water vapor
will be forced to travel across the interface of the CL-2--DSL
interface allowing it to react with the cathode.
Embodiment 2
[0109] FIG. 6 shows a cross-sectional view of a flexible device
with bottom desiccant layer and multiple layer cathode. Formation
of defects (not forming dark spots) away from the cathode-organic
interface is shown. The device of FIG. 6 includes a substrate 610,
a permeation barrier layer 611 (also called a bottom barrier
layer), a water reacting layer 612 (also called a bottom dessicant
layer), bottom an anode 620, organic layers 630, a cathode, and a
barrier film 650. The cathode includes first conductive layer 641,
separation layer 642 and second conductive layer 643. Dark spot 660
is also shown.
[0110] The embodiment of FIG. 6 involves a flexible substrate which
is permeable to water vapor. Such a substrate preferably involves
the use of a bottom barrier film. In such a device water vapor
travels from both top and bottom sides. As in previous embodiment,
water vapor coming from both top and bottom sides may reach the
water sensitive cathode and form defects at the cathode-organic
interface which would appear as dark spots in the device. In
addition to the split-cathode, this embodiment has thin moisture
reacting layer sandwiched between the bottom barrier and the anode.
This layer acts as a desiccant layer absorbing the water molecules
coming through the plastic substrate and the bottom barrier
layer.
Embodiment 3
[0111] FIG. 7 shows a cross-sectional view of a device with
multiple layer cathode with bridges between the two cathode layers
via breaks in the sandwich layer. Formation of defects (not forming
dark spots) away from the cathode-organic interface is shown. The
device of FIG. 7 includes a substrate 710, a first electrode 720,
organic layers 730, a second electrode, and a barrier film 750. The
cathode includes first conductive layer 741, separation layer 742
and second conductive layer 743. Dark spot 760 is also shown.
[0112] In the embodiment of FIG. 7, the first and second conductive
layers are bridged by bridges 744. That is, separation layer 742
has regions where it allows the first and second conductive layers
to touch. Separation layer 742 is not necessarily continuous. This
configuration utilizes the conductivity of the second conductive
layer. Over a period of storage, because of defect formation, the
second conductive layer may become completely electrically isolated
from the underlying device. For a thin cathode, this would mean
that only the first conductive layer would participate in carrier
transport. A very thin cathode would have high resistance which can
make the device non-uniform when operated. If the second (and
possibly any additional) conductive layers are bridged to the first
conductive layer, the combined stack would still have an input in
the overall conduction. Because the bridges occupy only a fraction
of the area of the second electrode, they do not have as
deleterious an effect on the formation of dark spots as a simple
single layer electrode. FIGS. 7 and 8 illustrate this embodiment
for rigid and flexible substrates, where FIG. 8 adds to FIG. 7 a
permeation barrier layer 711 (also called a bottom barrier layer),
a water reacting layer 712 (also called a bottom dessicant
layer).
[0113] FIG. 9 shows a schematic cross-sectional view of organic
layer of the OLED device and CL-1 and -2 with a defect separation
layer (DSL) in between. The DSL has higher water vapor transmission
rate than the cathode. This allows the water molecules to disperse
across the layer quickly at the same time allowing the CL-2 to
react with water and form defects which are not visible as dark
spots in the device.
[0114] FIG. 10 shows a schematic cross-sectional view of organic
layer of the OLED device and CL-1 and -2 with DSL in between. The
DSL has lower water vapor transmission rate than the cathode. This
forces the water molecules to disperse across the interface of the
CL-2 with the DSL and react with the cathode to form defects which
are not visible as dark spots in the device.
[0115] FIG. 11 shows a schematic cross-sectional view of organic
layer of the OLED device and CL-1 and an extended cathode. The
pinholes and other defects in the cathode continue to grow. The end
result is not much different than if only the first CL were
present. The defects form at the CL-1--organic interface and are
visible as dark spots.
Method of Device Fabrication
[0116] The device fabrication method can be divided into the
following steps:
1. Substrate, planarization*, and bottom permeation barrier* 2.
Bottom desiccant*(only for flexible permeable substrate)
3. OLED Deposition
4. Cathode Deposition
5. Thin Film Encapsulation
6. Lamination
[0117] The use of a planarization layer and a bottom permeation
barrier are preferred only for use with flexible substrates, which
tend to have significant water permeability. Rigid substrates can
generally be made thick enough that water permeation through the
substrate is not an issue, although there may be exceptions.
[0118] 1. Substrate, planarization, and bottom permeation barrier:
Rigid substrates could be any glass, or ceramic, or thick metallic
substrate. Flexible substrates could be thin metal foils, such as
Al or stainless steel, or plastics, such as PET or PEN, or paper or
fabric or composites such as ceramic matrix composites, metal
matrix composites, or polymer matrix composites. Substrates could
comprise a single material, compound materials and/or laminated
layers.
[0119] Flexible substrates are preferably planarized prior to OLED
growth. Flexible metal and plastic substrates often suffer from
high asperity count and high rms roughness. Various planarization
methods can be used, such as deposition of a resist (e.g.
polyimide), followed by a hard bake, or alternatively deposition of
an inorganic dielectric using methods such as PECVD. The
planarization layer may remove electrical contact between the OLED
and the substrate. This is particularly desirable in the case of
metal foils, where in some circumstances it may be advantageous not
to have electrical current flowing through the substrate. The
planarization layer may also act as a permeation barrier, which is
particularly desirable in the case of plastic substrates, where
oxygen and moisture can permeate through the substrate.
[0120] 2. Bottom desiccant: For permeable substrates, it is
preferred to deposit a thin film layer after the barrier layer that
is a moisture consuming or water reacting layer. It can be any
metal, or inorganic, or organic material or combinations thereof
which can form a chemical compound with water.
[0121] 3. OLED Deposition: The anode and/or bus lines could be
deposited by any suitable technique, including VTE or sputtering
through a shadow mask, or blanket deposited and then patterned
using photolithography. Examples of anode materials include IZO,
ITO, Al, Ag or combinations thereof. Individual anode areas are
preferably patterned around the cuts/scores in the substrate.
[0122] Examples of bus line materials include Al, Ag, Au, Cu. Bus
lines may pass over score marks made on the reverse of the
substrate. In some examples individual pixel areas are connected in
parallel using bus lines, whereas in other examples pixels are
connected in series. In some examples, a single large area pixel
could be used.
[0123] 4. Cathode Deposition: The layer on top of the OLED stack is
the CL (cathode layer). The split-CL for both rigid and flexible
substrates is, as described before, a stacked cathode in which the
first layer is acts as a conduction and electron injection layer,
whereas the remaining layers act to move dark spot forming defects
away from the cathode-organic interface. The first CL be any
suitable low work function layer such as Ca or MgAg, deposited by
evaporation or other thin film deposition processes. The DSL can be
any thin metallic, organic, or inorganic layer whose function is to
separate the coming second CL from the first CL. The DSL must be
different from the cathode in terms of water vapor transmission. It
should either have higher permeation rate than the cathode so that
water molecules upon reaching the DSL get dispersed quickly at the
interface allowing them to form defects at the interface itself.
FIG. 6 describes this situation. Or it should have lower permeation
rate that the cathode so that water molecules are forced to follow
the interface path, react with cathode and form defects. FIG. 7
describes this situation. In both the cases the defects form away
from the cathode-organic interface which is what intended. The DSL
cannot be an extended (thicker) cathode. In such a case, the water
vapor would travel unintruded to the cathode-organic interface.
FIG. 8 describes this situation. The sandwich layer itself can
absorb moisture. The second CL can be another low work function
metal or inorganic film like the first cathode. It can be different
from the first cathode. In some cases more than two cathode layers
can be used to enhance the defect separation and moisture
consumption effect. In some cases the top most CL can be topped by
another organic or inorganic layer to prevent the cathode from
getting damaged by the encapsulation process to follow.
[0124] 5. Thin Film Encapsulation (TFE): When fabricating an OLED
on a flexible substrate, especially, but many times on rigid
substrates also, thin film encapsulation (TFE) is used to prolong
the shelflife of device. Thin film encapsulation layers can be
inorganic or a combination of inorganic and organic materials. The
inorganic materials provide an effective barrier against the
permeation of moisture and oxygen, while the organic materials
provide mechanical flexibility and help to distribute any faults in
the inorganic layers, which increase the diffusion path length
through the barrier.
[0125] In the first embodiment descried above we used PECVD to
deposit a TFE layer of thickness <10 microns through the shadow
mask design.
[0126] 6. Lamination: For all devices with TFE, the top layer after
the encapsulation is the lamination layer. If can consist of a thin
polymer membrane attached to the substrate using an adhesive, or a
thin spun-on polymer layer, or an evaporated polymer layer, or a
spray coated, aerosol dispersed polymer layer. The lamination layer
prevents the thin film encapsulation from getting scratched or
damaged during handling. It can also perform optical function when
desired. In the fluttering lighting device embodiment, the
lamination layer is an aerosol dispersed polymer film on top of the
thin film encapsulation.
[0127] While the method above is described with respect to a device
having a cathode as the second electrode, it is understood that
embodiments may also involve an anode used as the second electrode,
i.e., the electrode further away from the substrate.
Example 1
[0128] Some of the inventive concepts were tested by preparing
bottom-emitting OLED (BOLED) devices and encapsulating them with
thin film encapsulation. The first device had 200 nm thick Al
cathode and the second had 100 nm Al, 60 nm NPD, and 100 nm Al
cathode. The devices were encapsulated with similar thin film (same
thickness) encapsulation barrier films and then were stored at
85.degree. C. and 85% RH for shelf-life tests. FIG. 12 shows the
photographs of active areas of the devices during the shelf-life
tests. Using the single layer cathode (left side), the maximum lag
time (i.e., the time until noticeable device degradation occurs)
obtained was around 500 hrs. Using the bifurcated cathode (right
side), the lag time increased to about 650 hrs. Under the
accelerated conditions of 85.degree. C. and 85% RH this is a 30%
increase in the lag time.
[0129] A comparison was also made of the devices discussed with
respect to FIG. 12 to similar devices without thin film
encapsulation. FIG. 13 shows photographs of active areas of
bottom-emitting OLED devices during the shelf-life tests at
85.degree. C. and 85% RH encapsulated with and without thin film
encapsulation, and with and without a split cathode. (a) shows
photographs for a single layer 200 nm Al cathode, without
encapsulation (b) shows photographs for a single layer 200 nm Al
cathode, with encapsulation. (c) shows photographs for a cathode
that is 100 nm Al, followed by 60 nm NPD, followed by 100 nm Al,
without encapsulation. (d) shows photographs for devices similar to
those of (c), but with encapsulation. The devices with and without
the defect separation layer lasted only 10 min in such harsh
atmospheric conditions, but the devices with a defect separation
layer performed lasted noticeably longer.
Combination with Other Materials
[0130] The materials described herein as useful for a particular
layer in an organic light emitting device may be used in
combination with a wide variety of other materials present in the
device. For example, emissive dopants disclosed herein may be used
in conjunction with a wide variety of hosts, transport layers,
blocking layers, injection layers, electrodes and other layers that
may be present. The materials described or referred to below are
non-limiting examples of materials that may be useful in
combination with the compounds disclosed herein, and one of skill
in the art can readily consult the literature to identify other
materials that may be useful in combination.
HIL/HTL:
[0131] A hole injecting/transporting material to be used in the
present invention is not particularly limited, and any compound may
be used as long as the compound is typically used as a hole
injecting/transporting material. Examples of the material include,
but not limit to: a phthalocyanine or porphryin derivative; an
aromatic amine derivative; an indolocarbazole derivative; a polymer
containing fluorohydrocarbon; a polymer with conductivity dopants;
a conducting polymer, such as PEDOT/PSS; a self-assembly monomer
derived from compounds such as phosphonic acid and silane
derivatives; a metal oxide derivative, such as MoO.sub.x; a p-type
semiconducting organic compound, such as
1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex,
and a cross-linkable compounds.
[0132] Examples of aromatic amine derivatives used in HIL or HTL
include, but not limit to the following general structures:
##STR00002##
[0133] Each of Ar.sup.1 to Ar.sup.9 is selected from the group
consisting aromatic hydrocarbon cyclic compounds such as benzene,
biphenyl, triphenyl, triphenylene, naphthalene, anthracene,
phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene,
azulene; group consisting aromatic heterocyclic compounds such as
dibenzothiophene, dibenzofuran, dibenzoselenophene, furan,
thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole,
indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole,
imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole,
dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine,
triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole,
indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole,
quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline,
naphthyridine, phthalazine, pteridine, xanthene, acridine,
phenazine, phenothiazine, phenoxazine, benzofuropyridine,
furodipyridine, benzothienopyridine, thienodipyridine,
benzoselenophenopyridine, and selenophenodipyridine; and group
consisting 2 to 10 cyclic structural units which are groups of the
same type or different types selected from the aromatic hydrocarbon
cyclic group and the aromatic heterocyclic group and are bonded to
each other directly or via at least one of oxygen atom, nitrogen
atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain
structural unit and the aliphatic cyclic group. Wherein each Ar is
further substituted by a substituent selected from the group
consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,
heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,
cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,
carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,
sulfinyl, sulfonyl, phosphino, and combinations thereof.
[0134] In one aspect, Ar.sup.1 to Ar.sup.9 is independently
selected from the group consisting of:
##STR00003##
[0135] k is an integer from 1 to 20; X.sup.1 to X.sup.8 is C
(including CH) or N; Ar.sup.1 has the same group defined above.
[0136] Examples of metal complexes used in HIL or HTL include, but
not limit to the following general formula:
##STR00004##
[0137] M is a metal, having an atomic weight greater than 40;
(Y.sup.1-Y.sup.2) is a bidentate ligand, Y.sup.1 and Y.sup.2 are
independently selected from C, N, O, P, and S; L is an ancillary
ligand; m is an integer value from 1 to the maximum number of
ligands that may be attached to the metal; and m+n is the maximum
number of ligands that may be attached to the metal.
[0138] In one aspect, (Y.sup.1-Y.sup.2) is a 2-phenylpyridine
derivative.
[0139] In another aspect, (Y.sup.1-Y.sup.2) is a carbene
ligand.
[0140] In another aspect, M is selected from Ir, Pt, Os, and
Zn.
[0141] In a further aspect, the metal complex has a smallest
oxidation potential in solution vs. Fc.sup.+/Fc couple less than
about 0.6 V.
Host:
[0142] The light emitting layer of the organic EL device of the
present invention preferably contains at least a metal complex as
light emitting material, and may contain a host material using the
metal complex as a dopant material. Examples of the host material
are not particularly limited, and any metal complexes or organic
compounds may be used as long as the triplet energy of the host is
larger than that of the dopant. While the Table below categorizes
host materials as preferred for devices that emit various colors,
any host material may be used with any dopant so long as the
triplet criteria is satisfied.
[0143] Examples of metal complexes used as host are preferred to
have the following general formula:
##STR00005##
[0144] M is a metal; (Y.sup.3-Y.sup.4) is a bidentate ligand,
Y.sup.3 and Y.sup.4 are independently selected from C, N, O, P, and
S; L is an ancillary ligand; m is an integer value from 1 to the
maximum number of ligands that may be attached to the metal; and
m+n is the maximum number of ligands that may be attached to the
metal.
[0145] In one aspect, the metal complexes are:
##STR00006##
[0146] (O--N) is a bidentate ligand, having metal coordinated to
atoms O and N.
[0147] In another aspect, M is selected from Ir and Pt.
[0148] In a further aspect, (Y.sup.3-Y.sup.4) is a carbene
ligand.
[0149] Examples of organic compounds used as host are selected from
the group consisting aromatic hydrocarbon cyclic compounds such as
benzene, biphenyl, triphenyl, triphenylene, naphthalene,
anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,
perylene, azulene; group consisting aromatic heterocyclic compounds
such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan,
thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole,
indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole,
imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole,
dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine,
triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole,
indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole,
quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline,
naphthyridine, phthalazine, pteridine, xanthene, acridine,
phenazine, phenothiazine, phenoxazine, benzofuropyridine,
furodipyridine, benzothienopyridine, thienodipyridine,
benzoselenophenopyridine, and selenophenodipyridine; and group
consisting 2 to 10 cyclic structural units which are groups of the
same type or different types selected from the aromatic hydrocarbon
cyclic group and the aromatic heterocyclic group and are bonded to
each other directly or via at least one of oxygen atom, nitrogen
atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain
structural unit and the aliphatic cyclic group. Wherein each group
is further substituted by a substituent selected from the group
consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,
heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,
cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,
carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,
sulfinyl, sulfonyl, phosphino, and combinations thereof.
[0150] In one aspect, host compound contains at least one of the
following groups in the molecule:
##STR00007## ##STR00008##
[0151] R.sup.1 to R.sup.7 is independently selected from the group
consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,
heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,
cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,
carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,
sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is
aryl or heteroaryl, it has the similar definition as Ar's mentioned
above.
[0152] k is an integer from 0 to 20.
[0153] X.sup.1 to X.sup.8 is selected from C (including CH) or
N.
[0154] Z.sup.1 and Z.sup.2 is selected from NR.sup.1, O, or S.
HBL:
[0155] A hole blocking layer (HBL) may be used to reduce the number
of holes and/or excitons that leave the emissive layer. The
presence of such a blocking layer in a device may result in
substantially higher efficiencies as compared to a similar device
lacking a blocking layer. Also, a blocking layer may be used to
confine emission to a desired region of an OLED.
[0156] In one aspect, compound used in HBL contains the same
molecule or the same functional groups used as host described
above.
[0157] In another aspect, compound used in HBL contains at least
one of the following groups in the molecule:
##STR00009##
[0158] k is an integer from 0 to 20; L is an ancillary ligand, m is
an integer from 1 to 3.
ETL:
[0159] Electron transport layer (ETL) may include a material
capable of transporting electrons. Electron transport layer may be
intrinsic (undoped), or doped. Doping may be used to enhance
conductivity. Examples of the ETL material are not particularly
limited, and any metal complexes or organic compounds may be used
as long as they are typically used to transport electrons.
[0160] In one aspect, compound used in ETL contains at least one of
the following groups in the molecule:
##STR00010##
[0161] R.sup.1 is selected from the group consisting of hydrogen,
deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,
alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,
heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,
carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,
sulfonyl, phosphino, and combinations thereof, when it is aryl or
heteroaryl, it has the similar definition as Ar's mentioned
above.
[0162] Ar.sup.1 to Ar.sup.3 has the similar definition as Ar's
mentioned above.
[0163] k is an integer from 0 to 20.
[0164] X.sup.1 to X.sup.8 is selected from C (including CH) or
N.
[0165] In another aspect, the metal complexes used in ETL contains,
but not limit to the following general formula:
##STR00011##
[0166] (O--N) or (N--N) is a bidentate ligand, having metal
coordinated to atoms O, N or N, N; L is an ancillary ligand; m is
an integer value from 1 to the maximum number of ligands that may
be attached to the metal.
[0167] In any above-mentioned compounds used in each layer of the
OLED device, the hydrogen atoms can be partially or fully
deuterated.
[0168] In addition to and/or in combination with the materials
disclosed herein, many hole injection materials, hole transporting
materials, host materials, dopant materials, exiton/hole blocking
layer materials, electron transporting and electron injecting
materials may be used in an OLED.
[0169] It is understood that the various embodiments described
herein are by way of example only, and are not intended to limit
the scope of the invention. For example, many of the materials and
structures described herein may be substituted with other materials
and structures without deviating from the spirit of the invention.
The present invention as claimed may therefore include variations
from the particular examples and preferred embodiments described
herein, as will be apparent to one of skill in the art. It is
understood that various theories as to why the invention works are
not intended to be limiting.
* * * * *