U.S. patent application number 10/183717 was filed with the patent office on 2004-01-08 for buffer layers for organic electroluminescent devices and methods of manufacture and use.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Baetzold, John P., Jones, Todd D., Lamansky, Sergey A., McCormick, Fred B., Nirmal, Manoj, Roberts, Ralph R..
Application Number | 20040004433 10/183717 |
Document ID | / |
Family ID | 29999217 |
Filed Date | 2004-01-08 |
United States Patent
Application |
20040004433 |
Kind Code |
A1 |
Lamansky, Sergey A. ; et
al. |
January 8, 2004 |
Buffer layers for organic electroluminescent devices and methods of
manufacture and use
Abstract
Organic electroluminescent device can be formed with multiple
layers including an electrode, an emission layer, and a buffer
layer. The emission layer includes a light emitting material. The
buffer layer is disposed between and in electrical communication
with the electrode and the emission layer and includes a
triarylamine hole transport material and an electron acceptor
material. The buffer layer optionally includes one or more of a) a
polymeric binder, b) a color converting material, and c) light
scattering particles. The buffer layer can also be formed using a
polymeric hole transport material having a plurality of
triarylamine moieties.
Inventors: |
Lamansky, Sergey A.; (Apple
Valley, MN) ; Nirmal, Manoj; (St. Paul, MN) ;
McCormick, Fred B.; (Maplewood, MN) ; Roberts, Ralph
R.; (Cottage Grove, MN) ; Baetzold, John P.;
(North St. Paul, MN) ; Jones, Todd D.; (St. Paul,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
29999217 |
Appl. No.: |
10/183717 |
Filed: |
June 26, 2002 |
Current U.S.
Class: |
313/506 |
Current CPC
Class: |
H01L 51/0013 20130101;
H01L 51/0035 20130101; H01L 51/5268 20130101; H01L 51/506 20130101;
H01L 51/5036 20130101; H01L 51/0051 20130101; H01L 51/0062
20130101; H01L 2251/5361 20130101; H01L 51/0052 20130101; H01L
51/0043 20130101; H01L 51/004 20130101; H01L 51/0059 20130101; H01L
51/5088 20130101 |
Class at
Publication: |
313/506 |
International
Class: |
H05B 033/00 |
Claims
What is claimed is:
1. An electroluminescent device comprising: an electrode; an
emission layer comprising a light emitting material; and a buffer
layer disposed between and in electrical communication with the
electrode and the emission layer, wherein the buffer layer
comprises a polymeric binder, a triarylamine hole transport
material disposed in the polymeric binder, and an electron acceptor
material disposed in the polymeric binder.
2. The electroluminescent device of claim 1, wherein the buffer
layer further comprises a color converting material disposed in the
polymeric binder.
3. The electroluminescent device of claim 1, wherein the buffer
layer further comprises a plurality of light scattering particles
disposed in the polymeric binder.
4. The electroluminescent device of claim 1, wherein the
triarylamine hole transport material comprises a polymer.
5. The electroluminescent device of claim 1, wherein the polymeric
binder of the buffer layer is crosslinked.
6. The electroluminescent device of claim 1, wherein the buffer
layer further comprises crosslinking agents.
7. The electroluminescent device of claim 1, wherein the polymeric
binder comprises a charge transporting polymer.
8. The electroluminescent device of claim 1, wherein the polymeric
binder comprises ionic moieties.
9. The electroluminescent device of claim 1, wherein the electrode
is an anode and the electroluminescent device further comprises a
cathode in electrical communication with the emission layer.
10. The electroluminescent device of claim 1, further comprising a
hole transport layer disposed between the buffer layer and the
emission layer.
11. An electroluminescent device comprising: an electrode; an
emission layer comprising a light emitting material; and a buffer
layer disposed between and in electrical communication with the
electrode and the emission layer, wherein the buffer layer
comprises (a) a polymeric hole transport material comprising a
plurality of triarylamine moieties and (b) an electron acceptor
material disposed in the polymeric hole transport material.
12. The electroluminescent device of claim 11, wherein the buffer
layer further comprises a color converting material disposed in the
polymeric binder.
13. The electroluminescent device of claim 11, wherein the buffer
layer further comprises a plurality of light scattering particles
disposed in the polymeric binder.
14. The electroluminescent device of claim 11, wherein the
polymeric hole transport material comprises a backbone with at
least a portion of the plurality of triarylamine moieties disposed
in the backbone.
15. The electroluminescent device of claim 11, wherein the
polymeric hole transport material comprises a backbone wherein the
plurality of triarylamine moieties are pendent groups extending
from the backbone.
16. The electroluminescent device of claim 11, wherein the
polymeric hole transport material of the buffer layer is
crosslinked.
17. The electroluminescent device of claim 1, wherein the buffer
layer further comprises crosslinking agents.
18. An electroluminescent device comprising: an electrode; an
emission layer comprising a light emitting material; and a buffer
layer disposed between and in electrical communication with the
electrode and the emission layer, wherein the buffer layer
comprises a triarylamine hole transport material, a color
converting material disposed in the triarylamine hole transport
material, and an electron acceptor material disposed in the
triarylamine hole transport material.
19. The electroluminescent device of claim 18, wherein the buffer
layer further comprises a plurality of light scattering particles
disposed in the polymeric binder.
20. The electroluminescent device of claim 18, wherein the
triarylamine hole transport material is a polymer.
21. The electroluminescent device of claim 18, wherein the color
converting material comprises a dye material.
22. The electroluminescent device of claim 18, wherein the color
converting material is configured and arranged to absorb light
generated by the light emitting material of the emission layer.
23. The electroluminescent device of claim 18, wherein the color
converting material is configured and arranged to reemit light
after absorbing light generated by the light emitting material of
the emission layer.
24. The electroluminescent device of claim 18, wherein the color
converting material comprises an inorganic or organometallic
material.
25. An electroluminescent device comprising: an electrode; an
emission layer comprising a light emitting material; and a buffer
layer disposed between and in electrical communication with the
electrode and the emission layer, wherein the buffer layer
comprises a triarylamine hole transport material, a plurality of
light scattering particles disposed in the triarylamine hole
transport material, and an electron acceptor material disposed in
the triarylamine hole transport material.
26. The electroluminescent device of claim 25, wherein the
plurality of light scattering electroluminescent devices comprise
an inorganic material.
27. A method of making an electroluminescent device comprising:
forming an electrode; coating a buffer layer from solution over the
electrode, the buffer layer comprising a polymeric binder, a
triarylamine hole transport material, and an electron acceptor
material; and disposing a emission layer over the buffer layer,
wherein the electrode, buffer layer, and emission layer are in
electrical communication and the emission layer comprises a light
emitting material.
28. The method of claim 27, further comprising disposing a hole
transport layer over the buffer layer prior to disposing the
emission layer over the buffer layer.
29. A method of making an electroluminescent device comprising:
forming a hole injection transfer layer on a donor substrate, the
buffer layer comprising a triarylamine hole transport material and
an electron acceptor material; forming an electrode on a receptor
substrate; selectively thermally transferring a portion of the
buffer layer onto the receptor substrate and in electrical
communication with the electrode; and disposing an emission layer
over the portion of the buffer layer that was selectively thermally
transferred onto the receptor substrate.
Description
BACKGROUND OF THE INVENTION
[0001] Organic electroluminescent devices (OELs) include layers of
organic materials, at least one of which can conduct a charge.
Examples of organic electroluminescent devices include organic
light emitting diodes (OLEDs). Specific OEL devices, sometimes
referred to as lamps, are desirable for use in electronic media
because of their thin profile, low weight, and low driving voltage.
OEL devices have potential use in applications such as, for
example, lighting applications, backlighting of graphics, pixelated
displays, and large emissive graphics.
[0002] OEL devices typically include an organic light emitter layer
and optionally one or more charge transport layers, all of which
are sandwiched between two electrodes: a cathode and an anode.
Charge carriers, electrons and holes, are injected from the cathode
and anode, respectively. Electrons are negatively charged atomic
particles and holes are vacant electron energy states that behave
as though they are positively charged particles. The charge
carriers migrate to the emitter layer, where they combine to emit
light.
[0003] This basic OEL device structure can be modified to improve
or enhance one or more electrical, chemical, or physical properties
of the device. Such modification can include the addition or
modification of one or more of the basic layers.
SUMMARY OF THE INVENTION
[0004] Generally, the present invention relates to organic
electroluminescent devices, articles containing the organic
electroluminescent devices, and methods of making and using the
organic electroluminescent devices and articles.
[0005] One embodiment is an electroluminescent device having
multiple layers including, but not limited to, an electrode, an
emission layer, and a buffer layer. The emission layer includes a
light emitting material. The buffer layer is disposed between and
in electrical communication with the electrode and the emission
layer and includes a triarylamine hole transport material and an
electron acceptor material. The buffer layer optionally includes
one or more of a) a polymeric binder, b) a color converting
material, and c) light scattering particles.
[0006] Another embodiment is a method of making an
electroluminescent device. The method includes forming an
electrode, coating a buffer layer from solution over the electrode,
and disposing an emission layer over the buffer layer. The
electrode, buffer layer, and emission layer are in electrical
communication. The emission layer includes a light emitting
material. The buffer layer includes a triarylamine hole transport
material and an electron acceptor material. Optionally, the buffer
layer includes one or more of a) a polymeric binder, b) a color
converting material, and c) light scattering particles.
[0007] Yet another embodiment is an electroluminescent device
having multiple layers including, but not limited to, an electrode,
an emission layer, and a buffer layer. The emission layer includes
a light emitting material. The buffer layer is disposed between and
in electrical communication with the electrode and the emission
layer. The buffer layer includes (a) a polymeric hole transport
material having triarylamine moieties and (b) an electron acceptor
material. Optionally, the buffer layer includes one or more of a) a
color converting material, and b) light scattering particles.
[0008] Another embodiment is a method of making an
electroluminescent device. The method includes forming an
electrode, coating a buffer layer from solution over the electrode,
and disposing an emission layer over the buffer layer. The
electrode, buffer layer, and emission layer are in electrical
communication. The emission layer includes a light emitting
material. The buffer layer includes (a) a polymeric hole transport
material having triarylamine moieties and (b) an electron acceptor
material. Optionally, the buffer layer includes one or more of a) a
color converting material, and b) light scattering particles.
[0009] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The Figures and the detailed description
which follow more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0011] FIG. 1 is a schematic side view of an organic
electroluminescent display construction;
[0012] FIG. 2 is a schematic side view of a first embodiment of an
electroluminescent device, according to the present invention;
[0013] FIG. 3 is a schematic side view of a second embodiment of an
electroluminescent device, according to the present invention;
[0014] FIG. 4 is a schematic side view of a third embodiment of an
electroluminescent device, according to the present invention;
and
[0015] FIG. 5 is a schematic side view of an organic
electroluminescent display according to the present invention.
[0016] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] The present invention is believed to be applicable to
electroluminescent devices, articles containing the
electroluminescent devices, and methods of making and using the
electroluminescent devices and articles. In particular, the present
invention is directed to organic electroluminescent devices
containing a buffer layer with a triarylamine material and an
electron acceptor material, articles containing the organic
electroluminescent devices, and methods of making and using the
organic electroluminescent devices and articles. Pixelated and
non-pixelated electroluminescent displays, backlights, and other
lighting components are examples of some of the articles that can
include organic electroluminescent devices. While the present
invention is not so limited, an appreciation of various aspects of
the invention will be gained through a discussion of the examples
provided below.
[0018] Organic electroluminescent device refers to an
electroluminescent device that includes an organic emissive
material. The emissive material can include, for example, a small
molecule (SM) emitter, a SM doped polymer, a light emitting polymer
(LEP), a doped LEP, a blended LEP, or any combination of these
materials. This emissive material can be provided alone or in
combination with any other organic or inorganic materials,
including, for example, binders, color converting materials, and
scattering materials, that are functional or non-functional in the
organic electroluminescent device.
[0019] R. H. Friend, et al. ("Electroluminescence in Conjugated
Polymers" Nature, 397, 1999, 121, incorporated herein by reference)
describe one mechanism of electroluminescence as including the
"injection of electrons from one electrode and holes from the
other, the capture of oppositely charged carriers (so-called
recombination), and the radiative decay of the excited
electron-hole state (exciton) produced by this recombination
process."
[0020] As an example of electroluminescent device structure, FIG. 1
illustrates an organic electroluminescent device 100 that includes
a device layer 110 and a substrate 120. Any other suitable device
component can also be included with the device 100. Optionally,
additional optical elements or other devices suitable for use with
electronic displays, devices, or lamps can be provided between the
display 100 and a viewer position 140 as indicated by an optional
element 130.
[0021] Substrate 120 can be any substrate suitable for the
electroluminescent device application. For example, substrate 120
can include glass, clear plastic, or other suitable material(s)
that are substantially transparent to visible light. Examples of
suitable plastic substrates include those made of polymers such as
polyolefins, polyethersulfones, polycarbonates, polyesters, and
polyarylates. Substrate 120 can also be opaque to visible light
such as, for example, stainless steel, crystalline silicon,
poly-silicon, or the like. Because some materials in
electroluminescent devices can be particularly susceptible to
damage due to exposure to oxygen or water, substrate 120 preferably
provides an adequate environmental barrier or is supplied with one
or more layers, coatings, or laminates that provide an adequate
environmental barrier.
[0022] Substrate 120 can also include any number of devices or
components suitable in electroluminescent devices and displays such
as, for example, transistor arrays and other electronic devices;
color filters, polarizers, wave plates, diffusers, and other
optical devices; insulators, barrier ribs, black matrix, mask works
and other such components; and the like. Generally, one or more
electrodes is coated, deposited, patterned, or otherwise disposed
on substrate 120 before forming the remaining layer or layers of
the electroluminescent device or devices of the device layer 110.
When a light transmissive substrate 120 is used and the organic
electroluminescent device or devices are bottom emitting, the
electrode or electrodes that are disposed between the substrate 120
and the emissive material(s) are preferably substantially
transparent to light. For example, transparent conductive
electrodes such as indium tin oxide (ITO) or any of a number of
other semi-transparent or transparent conductive oxides or
nitrides, or semi-transparent or transparent metals can be
used.
[0023] Element 130 can be any element or combination of elements
suitable for use with electroluminescent device 100. For example,
element 130 can be an LCD module when device 100 is a backlight.
One or more polarizers or other elements can be provided between
the LCD module and the backlight device 100, for instance an
absorbing or reflective clean-up polarizer. Alternatively, when
device 100 is itself an information display, element 130 can
include one or more of polarizers, wave plates, touch panels,
antireflective coatings, anti-smudge coatings, projection screens,
brightness enhancement films, scattering films, light extraction
films, refractive index gradient films, or other optical
components, coatings, user interface devices, or the like.
[0024] In some embodiments like the one shown, device layer 110
includes one or more electroluminescent devices that emit light
through the substrate toward a viewer position 140. The viewer
position 140 is used generically to indicate an intended
destination for the emitted light whether it be an actual human
observer, a screen, an optical component, an electronic device, or
the like. In other embodiments (not shown), device layer 110 is
positioned between substrate 120 and the viewer position 140. The
device configuration shown in FIG. 1 (termed "bottom emitting") may
be used when, for example, substrate 120 is transmissive to light
emitted by device layer 110 and when a transparent conductive
electrode is disposed in the device between the emissive layer of
the device and the substrate. The inverted configuration (termed
"top emitting") may be used when, for example, substrate 120 does
or does not transmit the light emitted by the device layer and the
electrode disposed between the substrate and the light emitting
layer of the device does not transmit the light emitted by the
device. In yet other embodiments, the device may emit from both the
top and bottom, in which case both conductive electrodes are
preferably transparent or semi-transparent.
[0025] Device layer 110 can include one or more electroluminescent
devices arranged in any suitable manner. For example, in lamp
applications (e.g., backlights for liquid crystal display (LCD)
modules), device layer 110 can constitute a single
electroluminescent device that spans an entire intended backlight
area. Alternatively, in other lamp applications, device layer 110
can constitute a plurality of closely spaced electroluminescent
devices that can be contemporaneously activated. For example,
relatively small and closely spaced red, green, and blue light
emitters can be patterned between common electrodes so that device
layer 110 appears to emit white light when the emitters are
activated. Other arrangements for backlight applications are also
contemplated.
[0026] In direct view or other display applications, it may be
desirable for device layer 110 to include a plurality of
independently addressable electroluminescent devices that emit the
same or different colors. Each device can represent a separate
pixel or a separate sub-pixel of a pixilated display (e.g., high
resolution display), a separate segment or sub-segment of a
segmented display (e.g., low information content display), or a
separate icon, portion of an icon, or lamp for an icon (e.g.,
indicator applications).
[0027] In at least some instances, an electroluminescent device
includes a thin layer, or layers, of one or more suitable materials
sandwiched between a cathode and an anode. When activated,
electrons are injected into the layer(s) from the cathode and holes
are injected into the layer(s) from the anode. As the injected
charges migrate towards the oppositely charged electrodes, the
charges can recombine to form electron-hole pairs which are
typically referred to as excitons. The region of the device in
which the exitons are generally formed can be referred to as the
recombination zone. These excitons, or excited state species, can
emit energy in the form of light as they decay back to a ground
state.
[0028] Other layers can also be present in electroluminescent
devices such as hole transport layers, electron transport layers,
hole injection layers, electron injection layers, hole blocking
layers, electron blocking layers, buffer layers, and the like. In
addition, photoluminescent materials can be present in the
electroluminescent or other layers in electroluminescent devices,
for example, to convert the color of light emitted by the
electroluminescent material to another color. These and other such
layers and materials can be used to alter or tune the electronic
properties and behavior of the layered electroluminescent device,
for example, to achieve one or more features such as a desired
current/voltage response, a desired device efficiency, a desired
color, a desired brightness, a desired device lifetime, or a
desired combination of these features.
[0029] FIGS. 2, 3, and 4 illustrate examples of different
electroluminescent device configurations where like elements are
provided the same reference numeral. Each configuration includes a
substrate 250, an anode 252, a buffer layer 254, an emission layer
256, and a cathode 258. The configurations of FIGS. 3 and 4 also
include a hole transport layer 260 between the buffer layer 254 and
the emission layer 256. Alternatively or additionally, a hole
transport layer (not shown) may be positioned between the anode and
the buffer layer. The configuration of FIG. 4 includes an electron
transport or electron injection layer 262. The substrate 250 can be
made of any of the materials discussed with respect to substrate
120 of FIG. 1. Optionally, a hole injection layer, electron
injection layer, or both can also be added or the hole transport
layer 260 could be removed. In some embodiments, the buffer layer
254 acts, at least in part, as a hole injection layer or hole
transport layer. In addition, any of the layers illustrated in
FIGS. 2, 3, and 4 can be formed using a single layer of material or
multiple layers of the same or different materials. The material
for each layer can be a single compound or a combination of two or
more different compounds.
[0030] The anode 252 and cathode 258 are typically formed using
conducting materials such as metals, alloys, metallic compounds,
metal oxides, conductive ceramics, conductive dispersions, and
conductive polymers, including, for example, gold, silver, copper,
platinum, palladium, aluminum, calcium, barium, magnesium,
titanium, titanium nitride, indium oxide, indium tin oxide (ITO),
vanadium oxide, zinc tin oxide, fluorine tin oxide (FTO),
polyaniline, polypyrrole, polythiophene, and combinations or alloys
of these materials. The anode 252 and the cathode 258 can be single
layers of conducting materials or they can include multiple layers.
For example, an anode or a cathode can include a layer of aluminum
and a layer of gold, a layer of calcium and a layer of aluminum, a
layer of lithium fluoride and a layer of aluminum, a layer of
magnesium and silver, a layer of magnesium and silver followed by
another layer of silver, or a metal layer and a conductive organic
layer.
[0031] The emission layer 256 includes one or more light emitting
materials, such as a small molecule (SM) emitter, a SM doped
polymer, a light emitting polymer (LEP), a doped LEP, a blended
LEP, another organic emissive material, or any combination of these
materials. Examples of classes of suitable LEP materials include
poly(phenylenevinylene)s (PPVs), poly-para-phenylenes (PPPs),
polyfluorenes (PFs), other LEP materials now known or later
developed, and co-polymers or blends thereof. Suitable LEPs can
also be molecularly doped, dispersed with luminescent dyes or other
photoluminescent (PL) materials, blended with active or non-active
materials, dispersed with active or non-active materials, and the
like. Examples of suitable LEP materials are described in, for
example, Kraft, et al., Angew. Chem. Int. Ed., 37, 402-428 (1998);
U.S. Pat. Nos. 5,621,131; 5,708,130; 5,728,801; 5,840,217;
5,869,350; 5,900,327; 5,929,194; 6,132,641; and 6,169,163; and PCT
Patent Application Publication No. 99/40655, all of which are
incorporated herein by reference.
[0032] SM materials are generally non-polymer organic or
organometallic molecular materials that can be used in organic
electroluminescent displays and devices as emitter materials,
charge transport materials, as dopants in emitter layers (e.g., to
control the emitted color) or charge transport layers, and the
like. Commonly used SM materials include metal chelate compounds,
for example, tris(8-hydroxyquinoline) aluminum (AlQ) and
derivatives thereof, and organic compounds, for example,
N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)benzidine (TPD). Other SM
materials are disclosed in, for example, C. H. Chen, et al.,
Macromol. Symp. 125, 1 (1997), Japanese Laid Open Patent
Application 2000-195673, U.S. Pat. Nos. 6,030,715, 6,150,043, and
6,242,115 and, PCT Patent Applications Publication Nos. WO 00/18851
(divalent lanthanide metal complexes), WO 00/70655 (cyclometallated
iridium compounds and others), and WO 98/55561, all of which are
incorporated herein by reference.
[0033] The optional hole transport layer 260 facilitates the
injection of holes from the anode into the device and their
migration towards the recombination zone. The hole transport layer
260 can further act as a barrier for the passage of electrons to
the anode 252. The hole transport layer 260 can include, for
example, a diamine derivative, such as
N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)benzidine (also known as
TPD) or N,N'-bis(3-naphthalen-2-yl)-N,N'-bis(phenyl)benzidine
(NPD), or a triarylamine derivative, such as,
4,4',4"-Tris(N,N-diphenylamino)tripheny- lamine (TDATA),
4,4',4"-tris(N-3-methylphenyl-N-phenylamino)triphenylamine
(MTDATA), 4,4',4"-tri(N-phenothiazinyl) triphenylamine (TPTTA),
4,4',4"-tri(N-phenoxazinyl) triphenylamine (TPOTA). Other examples
include copper phthalocyanine (CuPC);
1,3,5-Tris(4-diphenylaminophenyl)be- nzenes (TDAPBs); poly(vinyl
carbazole); and other compounds such as those described in Shirota,
J. Mater. Chem., 10, 1 (2000), H. Fujikawa, et al., Synthetic
Metals, 91, 161 (1997), and J. V. Grazulevicius, P. Strohriegl,
"Charge-Transporting Polymers and Molecular Glasses", Handbook of
Advanced Electronic and Photonic Materials and Devices, H. S. Nalwa
(ed.), 10, 233-274 (2001), all of which are incorporated herein by
reference.
[0034] The optional electron transport layer 262 facilitates the
injection of electrons and their migration towards the
recombination zone. The electron transport layer 262 can further
act as a barrier for the passage of holes to the cathode 258, if
desired. As an example, the electron transport layer 262 can be
formed using the organometallic compound tris(8-hydroxyquinolato)
aluminum (AlQ). Other examples of electron transport materials
include 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphen-
yl)-1,2,4-triazole (TAZ),
1,3-bis[5-(4-(1,1-dimethylethyl)phenyl)-1,3,4-ox-
adiazol-2-yl]benzene,
2-(biphenyl-4-yl)-5-(4-(1,1-dimethylethyl)phenyl)-1,-
3,4-oxadiazole (tBuPBD) and other compounds described in Shirota,
J. Mater. Chem., 10, 1 (2000), C. H. Chen, et al., Macromol. Symp.
125, 1 (1997), and J. V. Grazulevicius, P. Strohriegl,
"Charge-Transporting Polymers and Molecular Glasses", Handbook of
Advanced Electronic and Photonic Materials and Devices, H. S. Nalwa
(ed.),10, 233 (2001), all of which are incorporated herein by
reference.
[0035] The buffer layer 254 facilitates the injection of holes from
the anode into the hole transport layer 260 or emission layer 256.
The buffer layer may also assist in planarization of previously
formed layers, such as the anode. This planarization may also
assist in reducing or eliminating short circuits due to
non-uniformity in the anode. In addition, the buffer layer may
facilitate formation of other layers on the buffer layer, including
the forming of other layers by thermal transfer onto the buffer
layer.
[0036] The buffer layer includes a triarylamine material and an
electron acceptor material. The triarylamine material includes at
least one compound, including polymers, that has one or more
triarylamine moieties with formula 1: 1
[0037] where Ar.sub.1, Ar.sub.2, and Ar.sub.3 are substituted or
unsubstituted aryl or arylene functional groups and where,
optionally, the triarylamine moiety(ies) is/are coupled to other
portions of the compound through one or more of the arylene
functional groups, if present. Examples of suitable materials
include triphenylamine and biphenyldiamines such as, for example,
N,N'-bis(naphthalene-2-yl)-N,N'-bi- s(phenyl)benzidine (NPD),
N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)benzidi- ne (TPD), and
4,4'-bis(carbazol-9-yl)biphenyl (CPB).
[0038] Other examples include triarylamine compounds with
tetrahedral cores such as compounds having formulas 2, 3, and 4:
2
[0039] where each R.sub.1 is independently selected (i.e., each
R.sub.1 can be the same or different from the other R.sub.1
substituents in the formula) from triarylamine moieties (including
moieties which form a triarylamine structure in combination with
the phenyl group to which R.sub.1 is attached). Examples of
suitable triarylamine moieties for R.sub.1 include formulas 5, 6,
7, and 8: 3
[0040] where R.sub.2 is alkyl or aryl and each R.sub.3, R.sub.4,
and R.sub.5 is independently H, alkyl, aryl, alkoxy, aryloxy, halo,
alkylthio, arylthio, or --NR.sub.aR.sub.b, where R.sub.a and
R.sub.b are aryl or alkyl. With respect to Formula 8, in some
embodiments, all R.sub.3 are the same, all R.sub.4 are the same,
all R.sub.5 are the same, or any combination thereof (e.g., all
R.sub.3 and R.sub.4 are the same). Each aryl or alkyl portion of
any of these substituents can be substituted or unsubstituted
including, for example, fluorinated and perfluorinated alkyls.
[0041] In some embodiments, the triarylamine material preferably
incorporates one or more arylenediamine linkages of the formula 9:
4
[0042] where Ar.sub.4, Ar.sub.5, Ar.sub.6, Ar.sub.7, and Ar.sub.8
are substituted or unsubstituted aryl or arylene groups and where,
optionally, the arylenediamine linkage(s) is/are coupled to other
portions of the compound through one or more of the arylene
functional groups, if present. One preferred arylenediamine linkage
is a phenylenediamine linkage where Ar.sub.8 is a phenylene group.
Examples of suitable compounds of this type include those compounds
illustrated in Formulas 10-12: 5
[0043] where each R.sub.2 is independently alkyl or aryl and each
R.sub.3 and R.sub.4 is independently H, alkyl, aryl, alkoxy,
aryloxy, arylthio, alkylthio, halo, or --NR.sub.aR.sub.b, where
R.sub.a and R.sub.b are aryl or alkyl. Each aryl or alkyl portion
of any of these substituents can be substituted or unsubstituted.
In some embodiments, one of the following conditions applies: all
of the R.sub.3 and R.sub.4 substituents are the same; all of the
R.sub.3 substituents are the same; all of the R.sub.4 substituents
are the same; or all of the R.sub.3 substituents and all of the
R.sub.4 substituents are the same, but R.sub.3 and R.sub.4 are
different.
[0044] Specific examples of suitable compounds of this type include
4,4',4"-tris(N,N-diphenylamino)triphenylamine (TDATA) (Formula 13),
4,4',4"-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (MTDATA)
(Formula 14), 4,4',4"-tris(carbozol-9-yl)triphenylamine (TCTA)
(Formula 15), 4,4',4"-tris(N-naphthyl-N-phenylamino)triphenylamine
(2-TNATA) (Formula 16): 67
[0045] Another example is Formula 17 where each X is independently
O or S (and preferably all of the X substituents are the same).
8
[0046] As an alternative to small molecule triarylamine materials,
polymeric materials with triarylamine moieties can be used. The
triarylamine moieties can be in the backbone of the polymeric
material, can be pendent groups extending from the backbone of the
polymeric material, or both. Polymers with triarylamine moieties in
the backbone include, for example, the polymers of Formulas 18, 19,
20, and 21: 9
[0047] where R.sub.3 and R.sub.4 are independently H, alkyl, aryl,
alkoxy, aryloxy, arylthio, alkylthio, halo, or --NR.sub.aR.sub.b,
where R.sub.a and R.sub.b are aryl or alkyl, Ar.sub.9 is aryl or
arylene, CM is one or more comonomers, n is an integer of three or
greater and preferably 10 or greater, and m is an integer of zero
or greater. Each aryl or alkyl portion of any of these substituents
can be substituted or unsubstituted. Suitable comonomers, CM,
include, for example, another triarylamine-containing monomer such
as those illustrated in Formulas 18-21 or 33-34 below, arylene
(including substituted or unsubstituted para- or meta-phenylene),
substituted or unsubstituted styrene comonomers, derivatized
carbazole comonomers (such as N-alkyl carbazole or N-aryl
carbazole, for example, the comomoners as illustrated in Formulas
29 and 32), ether- and polyether-linked comonomers, carbonate
comonomers, urethane-linked comonomers, thioether-linked
comonomers, ester-linked comonomers, and imide- and amide-linked
comonomers. Examples of such comonomers include, but are not
limited to, --O--(C.sub.nH.sub.2nO)-- and
--Ar.sub.10--O--(C.sub.nH.sub.2nO)--A.sub.1- 1-- where Ar.sub.10
and Ar.sub.11 are arylene.
[0048] In some instances, the comonomer contains one or more photo-
or thermocrosslinking functional groups, such a benzocyclobutene
(Formula 22) or acrylate or methacrylate groups, such as, for
example, the acrylate group of Formula 23. 10
[0049] Other examples of cross-linkable moieties are described in,
for example, PCT Patent Application Publication No. WO 97/33193,
incorporated herein by reference. In some embodiments, the polymers
containing such cross-linkable moieties are selected to crosslink
under relatively mild photochemical or thermal conditions. For
example, thermal crosslinking may occur at 100 to 150.degree. C.
Alternatively, UV-visible radiation in the range of 300 to 700 nm
might be used to crosslink the polymers.
[0050] Typically the comonomer is copolymerized with the
triarylamine-containing monomer unit. However, in some instances,
the comonomer can be coupled to the triarylamine-containing monomer
unit prior to polymerization. Such a polymer might not be
considered a copolymer, but rather a homopolymer with the coupled
triarylamine-containing unit/comonomer unit as the basic monomer
unit of the polymer. Examples of such polymers are illustrated by
Formulas 24-27. 11
[0051] Specific examples of the polymers of Formulas 24-27 include
the polymers of Formulas 28-32: 12
[0052] In Formulas 29-32, the comonomer unit is coupled to the
triarylamine moiety-containing monomer unit in such a way that the
two monomer units alternate in the polymer.
[0053] Formulas 33 and 34 illustrate polymers with triarylamine
pendent groups: 13
[0054] where R.sub.3, R.sub.4, and R.sub.5 are independently H,
alkyl, aryl, alkoxy, aryloxy, arylthio, alkylthio, halo, or
--NR.sub.aR.sub.b, where R.sub.a and R.sub.b are aryl or alkyl, CM
is one or more comonomers, n is an integer of three or greater and
preferably 10 or greater, and m is an integer of zero or greater.
Each aryl or alkyl portion of any of these substituents can be
substituted or unsubstituted. Suitable comonomers, CM, include, for
example, another triarylamine-containing monomer containing one or
more chain polymerizable moieties, arylenes (including substituted
or unsubstituted para- or meta-phenylene) with one or more chain
polymerizable moieties, derivatized carbazole comonomers (such as
N-vinyl carbazole), carbonate comonomers, urethane-linked
comonomers, thioether-linked comonomers, ester-linked comonomers,
imide- and amide-linked comonomers, substituted or unsubstituted
styrene comonomers, (meth)acrylate comonomers of, for example,
C1-C12 alcohols, diene comonomers such as, for example, butadiene,
isoprene and 1,3 cyclohexadiene, and other chain-polymerizable
comonomers.
[0055] Typically the comonomer is copolymerized with the
triarylamine-containing monomer unit. However, in some instances,
the comonomer can be coupled to the triarylamine-containing monomer
unit prior to polymerization. Such a polymer might not be
considered a copolymer, but rather a homopolymer with the coupled
triarylamine-containing unit/comonomer unit as the basic monomer
unit of the polymer. One example is illustrated as Formula 35.
14
[0056] It will be understood that the pendent groups can also
extend from backbone moieties other than the ethylene moieties
illustrated in Formulas 33 and 34. Examples of other backbone units
from which the triarylamine pendent groups can extend include, for
example, alkylene (such as propylene, butylenes, isoprene, or
1,3-cyclohexadiene), silane, arylenes (including substituted or
unsubstituted para- or meta-phenylene), derivatized carbazole
monomers (as illustrated in Formulas 29 and 32), carbonate
monomers, urethane-linked monomers, thioethers-linked monomers,
ester-linked monomers, imide- and amide-linked monomers,
substituted and unsubstituted styrene monomers, and (meth)acrylate
monomers. The triarylamine may not be directly attached to the
backbone, but may be separated from the backbone by a spacer group
such as, for example, an alkylene group (e.g., methylene or
ethylene), alkenylene (e.g., --(CH.dbd.CH).sub.n--, n=1-6),
alkynylene (e.g., --(C.ident.C).sub.n--, n=1-6), arylene, an alkyl
ether (e.g., --CH.sub.2--O--) group, or any combination of these
groups.
[0057] Specific examples of suitable polymers with pendent
triarylamine groups include, for example, the polymers of Formulas
36-38: 15
[0058] where each R.sub.3, R.sub.4, R.sub.5, R.sub.6, and R.sub.7
is independently H, alkyl, aryl, alkoxy, aryloxy, arylthio,
alkylthio, halo, or --NR.sub.aR.sub.b, where R.sub.a and R.sub.b
are aryl or alkyl. Each aryl or alkyl portion of any of these
substituents can be substituted or unsubstituted. In some
embodiments, one or more of the following conditions applies: all
of the R.sub.3, R.sub.4, and R.sub.5 substituents are the same; all
of the R.sub.3 substituents are the same; all of the R.sub.4
substituents are the same; all of the R.sub.5 substituents are the
same; all of the R.sub.7 substituents are the same; or all of the
R.sub.3 substituents and all of the R.sub.4 substituents are the
same, but R.sub.3 and R.sub.4 are different. For example, R.sub.3,
R.sub.5, R.sub.6, and R.sub.7 can be H and R.sub.4 can be methyl in
any of Formulas 36-38.
[0059] Unless otherwise indicated, the term "alkyl" includes both
straight-chained, branched, and cyclic alkyl groups and includes
both unsubstituted and substituted alkyl groups. Unless otherwise
indicated, the alkyl groups are typically C1-C20. Examples of
"alkyl" as used herein include, but are not limited to, methyl,
ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, and isopropyl, and
the like.
[0060] Unless otherwise indicated, the term "aryl" refers to
monovalent unsaturated aromatic carbocyclic radicals having one to
fifteen rings, such as phenyl or bipheynyl, or multiple fused
rings, such as naphthyl or anthryl, or combinations thereof.
Examples of aryl as used herein include, but are not limited to,
phenyl, 2-naphthyl, 1-naphthyl, biphenyl, 2-hydroxyphenyl,
2-aminophenyl, 2-methoxyphenyl and the like.
[0061] Unless otherwise indicated, the term "arylene" refers to
divalent unsaturated aromatic carbocyclic radicals having one to
fifteen rings, such as phenylene, or multiple fused rings, such as
fluorene, naphthylene or anthrylene, or combinations thereof.
Examples of "arylene" as used herein include, but are not limited
to, benzene-1,2-diyl, benzene-1,3-diyl, benzene-1,4-diyl,
naphthalene-1,8-diyl, anthracene-1,4-diyl, fluorene,
phenylenevinylene, phenylenedivinylene, and the like.
[0062] Unless otherwise indicated, the term "alkoxy" refers to the
functional group --OR where R is a substituted or unsubstituted
alkyl group. Unless otherwise indicated, the alkyl group is
typically C1-C20. Examples of "alkoxy" as used herein include, but
are not limited to, methoxy, ethoxy, n-propoxy, and 1-methylethoxy,
and the like.
[0063] Unless otherwise indicated, the term "aryloxy" refers to the
functional group --OAr where Ar is a substituted or unsubstituted
aryl group. Examples of "aryloxy" as used herein include, but are
not limited to, phenyloxy, naphthyloxy, and the like.
[0064] Suitable substituents for substituted alkyl, aryl, and
arylene groups include, but are not limited to, alkyl, alkylene,
aryl, arylene, heteroaryl, heteroarylene, alkenyl, alkenylene,
--NRR', F, Cl, Br, I, --OR, --SR, cyano, nitro, --COOH, and
--COO-alkyl where R and R' are independently hydrogen, alkyl, or
aryl.
[0065] Unless otherwise indicated, the term "halo" includes fluoro,
chloro, bromo, and iodo.
[0066] Unless otherwise indicated, the term "polymer" includes
homopolymers and copolymers including block copolymers and random
copolymers.
[0067] In addition to the triarylamine material, the buffer layer
also includes an electron acceptor material to improve electron
transport. Preferably, such compounds have relatively high electron
affinity and relatively low energy of the lowest unoccupied
molecular orbital (LUMO). Suitable electron acceptor materials
include electron deficient compounds such as, for example,
tetracyanoquinodimethane and derivatives, thiopyranylidines,
polynitrofluorenones, tetracyanoethylene (TCNE), chloranil, and
other compounds commonly used as electron acceptors in charge
transfer materials and electrophotography. Specific examples of
electron acceptor materials include tetracyanoquinodimethane (TCNQ)
(Formula 39), tetrafluoro-tetracyanoquinodimethane (F.sub.4-TCNQ)
(Formula 40), tetracyanoethylene, chloranil,
2-(4-(1-methylethyl)phenyl-6-
-phenyl-4H-thiopyran-4-ylidene)-propanedinitrile-1,1-dioxyide
(PTYPD) (Formula 41), and 2,4,7-trinitrofluorenone (Formula 42).
16
[0068] Preferably, the electron acceptor material is soluble in one
or more organic solvents, more preferably, one or more organic
solvents in which the triarylamine material is also soluble.
Typically, the electron donor material is present in the buffer
layer in the range of 0.5 to 20 wt. % of the triarylamine material.
In some embodiments, the electron donor material is present in the
buffer layer in the range of 1 to 5 wt. % of the triarylamine
material.
[0069] The buffer layer optionally includes a polymeric binder. The
polymeric binder can include inert or electroactive polymers or
combinations thereof. Suitable polymers for the polymeric binder
include, for example, polystyrene, poly(N-vinyl carbazole),
polyfluorenes, poly(para-phenylenes), poly(phenylenevinylenes),
polycarbonates, polyimides, polyolefins, polyacrylates,
polymethacrylates (for example, poly(methylmethacrylate)),
polyethers, polysulfones, polyether ketones, and copolymers or
mixtures thereof. If the triarylamine material includes a
triarylamine-containing polymer, that polymer can act as or in
cooperation with a polymeric binder, if desired. If used, the
polymeric binder is typically provided in the range of 20 to 150
wt. %, preferably 70 to 120 wt. %, of the triarylamine
material.
[0070] In some embodiments, the polymeric binder can be
photochemically or thermally crosslinked with itself or with other
components in the buffer layer. Accordingly, a thermochemical or
photochemical crosslinking agent, such as, for example,
2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone, can optionally
be included in the buffer layer. Crosslinking can be desirable for
one or more purposes, such as decreasing the migration of buffer
layer components out of the buffer layer, decreasing the migration
of other materials into the buffer layer, increasing thermal
stability, increasing mechanical stability, increasing
morphological stability, increasing buffer layer stability, and
increasing layer integrity, particularly during further solution
processing. Crosslinking the buffer layer can also facilitate
manufacture of a device by providing a buffer layer upon which
other layers can be solution coated or cast with substantially less
concern about dissolving the buffer layer.
[0071] The buffer layer can optionally include a color converting
material. This material can be a luminescent or non-luminescent
organic, organometallic, or inorganic compound or combinations
thereof. The color converting material changes the color of
electroluminescence from an emitting layer by selective absorption
of light or by absorption of light and re-emission of the light in
a different spectral range. Suitable materials include, for
example, dyes, pigments, and nanoparticles. Examples of suitable
non-luminescent and luminescent dyes include: azo dyes (e.g. C.I.
Direct Green 26 and others), anthraquinone dyes (e.g. C.I. Reactive
Blue 4 and others), indigoid dyes (e.g. Tyrian Purple and others),
triphenylmethane-based dyes (e.g. Eosin and others), coumarin dyes
(e.g. Coumarin 6 and others), metal porphyrins (e.g. platinum [II]
octaethylporphyrin and others), cyclometalated transition metal
complexes (e.g. iridium tris(2-phenylpyridine) and others), and
other dyes including those discussed in H. Zollinger, Color
Chemistry, 1991, VCH Publishers: New York, and The Chemistry and
Application of Dyes, Ed. By D. R. Waring and G. Halls, 1990, Plenum
Press: New York, both of which are incorporated herein by
reference. Examples of nanoparticles suitable for color conversion
can be found in M. Bruchez et al., Science 281, 2013 (1998),
incorporated herein by reference. The color converting material can
be polymeric with color converting moieties in the backbone, on
pendant chains, or both. The color converting material, if used, is
typically included in the buffer layer in an amount in the range of
0.1 to 100 wt. %, preferably 0.1 to 10 wt. %, of the triarylamine
material.
[0072] The buffer layer can also optionally include scattering
material, such as small particles, nanocrystals, or clusters.
Examples of suitable materials include clays, oxides, metals, and
glasses. Specific examples of suitable materials include titania,
alumina and silica powders having a mean particle size of
approximately 0.05 to 0.2 microns, and added to the buffer layer
composition in a concentration of from 0.1 to 20% by weight, and
preferably from about 1-5% by weight.
[0073] The buffer layer 254 is formed by solution coating the
material of the buffer layer onto the substrate 250. After
formation of the buffer layer 254, additional layers, such as the
hole transport layer 260 or emission layer 256, can be formed on
the buffer layer by a variety of techniques including, for example,
solution coating, physical or chemical vapor deposition, and
thermal transfer, including light-induced thermal transfer as
described below.
[0074] An organic solvent is used to make the solution for the
buffer layer. Examples of suitable organic solvents include carbon
tetrachloride, toluene, chloroform, 1,2-dichloroethane,
1,2-dichlorobenzene, tetrahydrofuran, pyridine, and the like. The
remaining materials of the buffer layer are typically dispersible
or, preferably, soluble in the organic solvent.
[0075] In some conventional device formation methods, layers are
formed using solutions of components in water. A drawback of these
methods is that some of the device materials are degraded in the
presence of water or irreversible physical changes may occur
leading to device degradation. Thus, if a layer is formed using a
water solution, the water generally must be completely removed. On
the other hand according to the invention, organic solvents can be
chosen that are easier to remove or do not degrade materials in the
device or both.
[0076] In other conventional device formation methods, the
materials of a layer are disposed by vapor deposition. A number of
materials are difficult to accurately and consistently deposit by
vapor deposition methods. Included in these materials are a variety
of polymers and ionic compounds. Thus, it can be difficult to
deposit materials such as a polymeric binder and cross-linking
agent using vapor deposition techniques. In addition, the
consistency and uniformity of a vapor deposited composition becomes
increasingly difficult when the composition contains multiple
components. On the other hand according to the invention, forming a
buffer layer by solution coating can facilitate the use of
materials such as polymeric binders, polymeric triarylamine
materials, crosslinking agents, dyes, pigments, scattering
particles, and so on. In addition, the coating technique permits
the use of multi-component systems when all of the components are
soluble or dispersible in the solvent.
[0077] As an alternative to solution coating the buffer layer
material directly onto the substrate or depositing the buffer layer
material using ink jet techniques, the buffer layer material can be
coated onto a donor sheet and then transferred by techniques such
as thermal transfer to the substrate. This can be particularly
useful for patterning the buffer layer onto the substrate. For
example, the buffer layer material can be selectively transferred
from the donor sheet to the substrate according to a pattern by
selective application of, for example, light or heat to the donor
sheet. This can be useful, for example, to pattern individual
buffer layers with a different color converting materials (or lack
of color converting material) onto the substrate. Thus, a
full-color display could be formed using, for example, three
different buffer layers with three different color converting
materials (or two different color converting materials and the
third buffer layer lacking a color converting material). Other
methods of selectively patterning color converting materials in
buffer layer(s) include, for example, thermal diffusion of the
color converting material, inkjet transfer of the buffer material
with (or without) color converting materials onto the substrate,
and selective photobleaching.
[0078] Suitable thermal transfer methods for transferring a buffer
layer or other device layers to the substrate or onto a
previously-formed buffer layer include, for example, thermal head
transfer methods and light-induced thermal transfer methods. The
presence of the buffer layer on the substrate can, at least in some
instances, facilitate the transfer of other layers to the substrate
by these methods. Materials, layers, or other structures can be
selectively transferred from the transfer layer of a donor sheet to
a receptor substrate by placing the transfer layer of the donor
element adjacent to the receptor and selectively heating the donor
element. For example, the donor element can be selectively heated
by irradiating the donor element with imaging radiation that can be
absorbed by light-to-heat converter material disposed in the donor,
often in a separate light-to-heat conversion (LTHC) layer, and
converted into heat. Examples of such methods, donor elements and
receptors, as well as articles and devices that can be formed using
thermal transfer, can be found in U.S. Pat. Nos. 5,521,035,
5,691,098, 5,693,446, 5,695,907, 5,710,097, 5,725,989, 5,747,217,
5,766,827, 5,863,860, 5,897,727, 5,976,698, 5,981,136, 5,998,085,
6,057,067, 6,099,994, 6,114,088, 6,140,009, 6,190,826, 6,194,119,
6,221,543, 6,214,520, 6,221,553, 6,228,543, 6,228,555, 6,242,152,
6,270,934, and 6,270,944 and PCT Patent Applications Publication
Nos. WO 00/69649 and WO 01/39986 and U.S. patent application Ser.
Nos. 09/662,845, 09/662,980, 09/844,100, and 09/931,598, all of
which are incorporated herein by reference. The donor can be
exposed to imaging radiation through the donor substrate, through
the receptor, or both. The radiation can include one or more
wavelengths, including visible light, infrared radiation, or
ultraviolet radiation, for example from a laser, lamp, or other
radiation source.
[0079] Other selective heating methods can also be employed, such
as using a thermal print head or using a thermal hot stamp (e.g., a
patterned thermal hot stamp such as a heated silicone stamp that
has a relief pattern that can be used to selectively heat a donor).
Thermal print heads or other heating elements may be particularly
suited for making lower resolution patterns of material or for
patterning elements whose placement need not be precisely
controlled.
[0080] Material from the transfer layer can be selectively
transferred to a receptor in this manner to imagewise form patterns
of the transferred material on the receptor. In many instances,
thermal transfer using light from, for example, a lamp or laser, to
patternwise expose the donor can be advantageous because of the
accuracy and precision that can often be achieved. The size and
shape of the transferred pattern (e.g., a line, circle, square, or
other shape) can be controlled by, for example, selecting the size
of the light beam, the exposure pattern of the light beam, the
duration of directed beam contact with the donor sheet, or the
materials of the donor sheet. The transferred pattern can also be
controlled by irradiating the donor element through a mask.
[0081] Transfer layers can also be transferred from donor sheets
without selectively transferring the transfer layer. For example, a
transfer layer can be formed on a donor substrate that, in essence,
acts as a temporary liner that can be released after the transfer
layer is contacted to a receptor substrate, typically with the
application of heat or pressure. Such a method, referred to as
lamination transfer, can be used to transfer the entire transfer
layer, or a large portion thereof, to the receptor.
[0082] A donor sheet for light-induced thermal transfer can
include, for example, a donor substrate, an optional underlayer, an
optional light-to-heat conversion (LTHC) layer, an optional
interlayer, and a transfer layer. The donor substrate can be a
polymer film or any other suitable, preferably transparent,
substrate. The donor substrate is also typically selected from
materials that remain stable despite heating of one or more layers
of the donor. However, the inclusion of an underlayer between the
substrate and an LTHC layer can be used to insulate the substrate
from heat generated in the LTHC layer during imaging.
[0083] The underlayer can include materials that impart desired
mechanical or thermal properties to the donor element. For example,
the underlayer can include materials that exhibit a low value for
the mathematical product of specific heat and density or low
thermal conductivity relative to the donor substrate. Such an
underlayer may be used to increase heat flow to the transfer layer,
for example to improve the imaging sensitivity of the donor. The
underlayer can also include materials for their mechanical
properties or for adhesion between the substrate and the LTHC.
[0084] An LTHC layer can be included in donor sheets of the present
invention to couple irradiation energy into the donor sheet. The
LTHC layer preferably includes a radiation absorber that absorbs
incident radiation (e.g., laser light) and converts at least a
portion of the incident radiation into heat to enable transfer of
the transfer layer from the donor sheet to the receptor.
[0085] An optional interlayer can be disposed between the LTHC
layer and transfer layer. The interlayer can be used, for example,
to minimize damage and contamination of the transferred portion of
the transfer layer and may also reduce distortion in the
transferred portion of the transfer layer. The interlayer can also
influence the adhesion of the transfer layer to the rest of the
donor sheet. Typically, the interlayer has high thermal resistance.
Preferably, the interlayer does not distort or chemically decompose
under the imaging conditions, particularly to an extent that
renders the transferred image non-functional. The interlayer
typically remains in contact with the LTHC layer during the
transfer process and is not substantially transferred with the
transfer layer.
[0086] The interlayer can provide a number of benefits, if desired.
The interlayer can be a barrier against the transfer of material
from the light-to-heat conversion layer. It can also modulate the
temperature attained in the transfer layer so that thermally
unstable materials can be transferred. For example, the interlayer
can act as a thermal diffuser to control the temperature at the
interface between the interlayer and the transfer layer relative to
the temperature attained in the LTHC layer. This can improve the
quality (i.e., surface roughness, edge roughness, etc.) of the
transferred layer. The presence of an interlayer can also result in
improved plastic memory in the transferred material.
[0087] The thermal transfer layer includes the buffer material to
form the buffer layer, if desired, or appropriate materials to form
other layers depending on the desired thermal transfer. For
example, other layers of the device, such as the hole transport
layer or the emission layer, can be transferred onto the substrate
or onto the buffer layer or other layers disposed on the substrate
by these methods. Such transfer can be sequential using multiple
donor sheets or, in some embodiments, multiple layers can be
transferred using a single donor sheet with the transfer layer
having individual sublayers.
[0088] The present invention contemplates light emitting OEL
displays and devices. In one embodiment, OEL displays can be made
that emit light and that have adjacent devices that can emit light
having different color. For example, FIG. 5 shows an OEL display
300 that includes a plurality of OEL devices 310 disposed on a
substrate 320. Adjacent devices 310 can be made to emit different
colors of light.
[0089] The separation shown between devices 310 is for illustrative
purposes only. Adjacent devices may be separated, in contact,
overlapping, etc., or different combinations of these in more than
one direction on the display substrate. For example, a pattern of
parallel striped transparent conductive anodes can be formed on the
substrate followed by a striped pattern of a hole transport
material and a striped repeating pattern of red, green, and blue
light emitting LEP layers, followed by a striped pattern of
cathodes, the cathode stripes oriented perpendicular to the anode
stripes. Such a construction may be suitable for forming passive
matrix displays. In other embodiments, transparent conductive anode
pads can be provided in a two-dimensional pattern on the substrate
and associated with addressing electronics such as one or more
transistors, capacitors, etc., such as are suitable for making
active matrix displays. Other layers, including the light emitting
layer(s) can then be coated or deposited as a single layer or can
be patterned (e.g., parallel stripes, two-dimensional pattern
commensurate with the anodes, etc.) over the anodes or electronic
devices. Any other suitable construction is also contemplated by
the present invention.
[0090] In one embodiment, display 300 can be a multiple color
display. As such, it may be desirable to position optional
polarizer 330 between the light emitting devices and a viewer, for
example to enhance the contrast of the display. In exemplary
embodiments, each of the devices 310 emits light. There are many
displays and devices constructions covered by the general
construction illustrated in FIG. 3. Some of those constructions are
discussed as follows.
[0091] OEL backlights can include emissive layers. Constructions
can include bare or circuitized substrates, anodes, cathodes, hole
transport layers, electron transport layers, hole injection layers,
electron injection layers, emissive layers, color changing layers,
and other layers and materials suitable in OEL devices.
Constructions can also include polarizers, diffusers, light guides,
lenses, light control films, brightness enhancement films, and the
like. Applications include white or single color large area single
pixel lamps, for example where an emissive material is provided by
thermal stamp transfer, lamination transfer, resistive head thermal
printing, or the like; white or single color large area single
electrode pair lamps that have a large number of closely spaced
emissive layers patterned by laser induced thermal transfer; and
tunable color multiple electrode large area lamps.
[0092] Low resolution OEL displays can include emissive layers.
Constructions can include bare or circuitized substrates, anodes,
cathodes, hole transport layers, electron transport layers, hole
injection layers, electron injection layers, emissive layers, color
changing layers, and other layers and materials suitable in OEL
devices. Constructions can also include polarizers, diffusers,
light guides, lenses, light control films, brightness enhancement
films, and the like. Applications include graphic indicator lamps
(e.g., icons); segmented alphanumeric displays (e.g., appliance
time indicators); small monochrome passive or active matrix
displays; small monochrome passive or active matrix displays plus
graphic indicator lamps as part of an integrated display (e.g.,
cell phone displays); large area pixel display tiles (e.g., a
plurality of modules, or tiles, each having a relatively small
number of pixels), such as may be suitable for outdoor display
used; and security display applications.
[0093] High resolution OEL displays can include emissive layers.
Constructions can include bare or circuitized substrates, anodes,
cathodes, hole transport layers, electron transport layers, hole
injection layers, electron injection layers, emissive layers, color
changing layers, and other layers and materials suitable in OEL
devices. Constructions can also include polarizers, diffusers,
light guides, lenses, light control films, brightness enhancement
films, and the like. Applications include active or passive matrix
multicolor or full color displays; active or passive matrix
multicolor or full color displays plus segmented or graphic
indicator lamps (e.g., laser induced transfer of high resolution
devices plus thermal hot stamp of icons on the same substrate); and
security display applications.
EXAMPLES
[0094] All chemicals are available from Aldrich Chemical Co.,
Milwaukee, Wis., unless otherwise indicated.
[0095] Preparation of ITO Substrates
[0096] For Examples 1-13, ITO substrates were prepared as follows:
ITO (indium tin oxide) glass substrates (Applied Films Corporation,
CO; ca. 25 .OMEGA./sq.) were rinsed in acetone (Aldrich Chemical
Company), dried with nitrogen, and rubbed with TX1010 Vectra
Sealed-Border Wipers (ITW Texwipe, Upper Saddle River, N.J.) soaked
in methanol (Aldrich Chemical Company, Milwaukee, Wis.), after
which they were subjected to oxygen plasma treatment for four
minutes at 200 mT (about 27 Pa) base oxygen pressure and output
power of 50 W in Technics Micro Reactive Ion Etcher, Series 80
(K&M Company, CA). The OLED's described below were generally 1
to 1.5 cm.sup.2 in size.
Comparative Example 1 and Examples 1-3
Buffer Layers Containing of Triarylamine Materials With
Electrically Inert Polymers
[0097] This Example describes the formation of OLEDs having a
solution-processed hole-injecting buffer layer incorporating
4,4',4"-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (MTDATA)
as a triarylamine material, polystyrene (PS) as an electrically
inert polymer binder, and tetrafluoro-tetracyanoquinodimethane
(F.sub.4-TCNQ) or tetracyanoquinodimethane (TCNQ) as an electron
accepting dopant material.
[0098] The OLED is prepared by vapor depositing, onto an ITO
substrate with a buffer layer, 20 nm of
N,N'-bis(naphthan-2-yl)-N,N'-bis(phenyl)ben- zidine (NPD, H. W.
Sands Corp., Jupiter, Fla.), followed by 30 nm of aluminum
tris(8-hydroxyquinolate) (AlQ, H. W. Sands Corp, Jupiter, Fla.)
doped with ca. 1 wt. % of green-emitting Coumarin 545T (C545T,
Eastman Kodak Co., Rochester, N.Y.), and followed by 20 nm of AlQ.
The OLED was capped with a cathode composed of ca. 0.7 nm of
lithium fluoride (LiF, Alfa Aesar Co., Ward Hill, Mass.) and 200 nm
of aluminum (Al, Alfa Aesar Co., Ward Hill, Mass.). In this OLED
construction, the NPD layer acts as a hole-transport layer and
electron-blocking layer, the layer of AlQ doped with C545T
(AlQ:C545T) acts as a light emitting layer, and the layer of AlQ
acts as an electron injection and transport layer. These OLED
constructions are further referred to as
"/NPD/AlQ:C545T/AlQ/LiF/Al"- .
[0099] All organic and cathode layers except the buffer layers were
fabricated in a standard vacuum-deposition procedure at a base
vacuum of ca. 10.sup.-7 to 10.sup.-5 torr (about 10.sup.-5 to
10.sup.-3 Pa) with evaporation rates of 0.05-0.2 nm/s for organic
materials, 0.05 nm/s for LiF, and 1.5-2 nm/s for Al.
[0100] In Comparative Example 1, polypyrrole (PPY, Aldrich Chemical
Co.) was used as a control hole-injecting buffer layer for purposes
of comparison of the OLED behavior of the devices deposited onto
PPY and onto doped triarylamine-based buffer layers. PPY was
spun-coat from its water suspension after filtering the suspension
through 0.2 .mu.m Nylon microfilters, followed by annealing under
nitrogen gas flow at 110.degree. C. for ca. 15 min.
[0101] In Examples 1-4, OLEDs with buffer layers containing MTDATA,
PS, and TCNQ were prepared and their performance evaluated along
with that of the control PPY-based OLEDs. MTDATA, PS, and TCNQ were
purchased from H W Sands Corp. (Jupiter, Fla.), Polysciences Inc.
(Eppelheim, Germany), and TCI America (Portland, Oreg.),
respectively. The buffer layers were spun-coat from their ca. 1.5
wt. % solutions in toluene at the spin-rate of 2000 RPM (about 33
s.sup.-1) to form ca. 90 nm thick films on the ITO coated
substrates. The device structures are glass-ITO/buffer
layer/NPD/AlQ:C545T/AlQ/LiF/Al. The buffers layers for the Examples
are:
[0102] Comparative Example 1: PPY
[0103] Example. 1: 31 wt. % PS, 62 wt. % MTDATA, and 7 wt. %
TCNQ
[0104] Example 2: 47 wt. % PS, 46 wt. % MTDATA, and 7 wt. %
TCNQ
[0105] Example 3: 62 wt. % PS, 31 wt. % MTDATA, and 7 wt. %
TCNQ
[0106] No short-circuiting was observed in any of the studied
electroluminescent lamps. For Examples 1-3, the OLEDs showed high
operational efficiency and low operational voltages, with
operational voltages decreasing with increasing triarylamine
concentration.
Examples 5-6
Buffer Layers Containing Triarylamines and an Electroactive Polymer
Binder
[0107] High bandgap hole-transporting poly(N-vinylcarbazole) (PVK,
Polymer Source Inc., Dorval, Quebec) having relatively high
oxidation potential (ca. 1V vs. SCE) and low hole mobility (ca.
10.sup.-6-10.sup.-5 cm.sup.2/V*s (about 10.sup.-10-10.sup.-9
m.sup.2/V s)) was used as an electroactive binder in the following
buffer compositions: a) 60 wt. % PVK and 40 wt. % MTDATA, and b) 56
wt. % PVK, 37 wt. % MTDATA, and 7 wt. % F.sub.4-TCNQ. These buffer
layers were spun-coat from their ca. 1.5% wt. solutions in toluene
at the spin-rate of 2000 RPM (about 33 s.sup.-1) to form ca. 90 nm
thick films on the ITO coated substrates.
[0108] OLED devices were made as described above for Comparative
Example 1 and Examples 1-3, except that the buffer layers
corresponded to:
[0109] Example 5: 60 wt. % PVK and 40 wt. % MTDATA
[0110] Example 6: 56 wt. % PVK, 37 wt. % MTDATA, and 7 wt. %
F.sub.4-TCNQ
[0111] No short-circuiting was observed in any of the studied
electroluminescent lamps. Luminance-voltage-current density
screening of the OLEDs indicated that high efficiencies can be
obtained in the composition including triarylamine-based buffers
along with low operational voltages. Doping the PVK:MTDATA blend
with F.sub.4-TCNQ significantly lowered the operational voltage of
the OLEDs. Operational lifetime studies on the triarylamine-based
compositions, in which the OLEDs were driven at a constant current
of ca. 1.8 mA/cm.sup.2 (about 18 A/m.sup.2) under inert atmosphere,
show that projected operation lifetimes of these OLEDs extend into
10.sup.3-10.sup.4 hours range at an initial luminance of several
hundred Cd/m.sup.2.
Examples 7 and 8
Buffer Layers Contains Copolymers With Triarylamine Moieties
Pendant to a Polyolefin Backbone
[0112] In this Example, doped triarylamine buffer layers based on
copolymers incorporating triarylamine moieties as a functionality
pendant to a polyolefin backbone were incorporated into OLEDs.
[0113] A block co-polymer of styrene with diphenylaminostyrene
(PS-pDPAS), having approximately 6:1 molar ratio of the monomers
was synthesized and screened as a triarylamine-containing
polymer.
[0114] All materials are available from Aldrich Chemical Co.,
Milwaukee, Wis., with the exception of p-diphenylaminostyrene, and
as where noted. This monomer was synthesized by a preparation
similar to that described by G. N. Tew, M. U. Pralle, and S. I.
Stupp in Angew. Chem. Int. Ed., 2000, 39, 517, incorporated herein
by reference.
[0115] Synthesis of p-diphenylaminostyrene
[0116] To a mixture of 4-(diphenylamino)benzaldehyde (20.06 g, 73
mmol, Fluka Chemical Co., Milwaukee, Wis.), methyltriphenyl
phosphonium bromide (26.22 g, 73 mmol) and dry tetrahydrofuran (450
mL) under nitrogen was added a IM solution of potassium t-butoxide
in tetrahydrofuran (80 mL, 80 mmol) over 5 minutes. The mixture was
stirred for 17 hours at room temperature. Water (400 mL) was added
and the tetrahydrofuran was removed under reduced pressure. The
mixture was extracted with ether, and the combined organic layers
were dried over MgSO.sub.4 and concentrated under vacuum. The crude
solid was purified by column chromatography on silica gel using a
50/50 mixture of methylene chloride and hexane to give a yellow
solid that was further recrystallized once from hexane (15.37 g,
78%).
[0117] Synthesis of Block Co-Polymer of Styrene With
Diphenylaminostyrene (PS-pDPAS)
[0118] A round-bottom glass reactor was baked out under vacuum at
200.degree. C. for 2 hours, then allowed to cool. The reactor was
filled with dry nitrogen. Subsequently, 71.8 g of cyclohexane and
4.4 mL of tetrahydrofuran (THF) were added to the reactor by
syringe. The THF was distilled from sodium/benzophenone solution
under nitrogen prior to use, in order to scavenge water and oxygen.
The cyclohexane was dried by passage through activated basic
alumina, followed by sparging with nitrogen gas for 30 minutes
prior to use. After addition of the solvents, the reaction flask
was cooled to 3.degree. C. in an ice water bath, after which 0.02
mL of styrene was added to the reactor. The styrene had previously
been passed through activated basic alumina to remove inhibitors
and water, and sparged with nitrogen gas to remove oxygen. A
solution of s-butyllithium in cyclohexane (0.4 mL, 1.3 mol/L) was
subsequently added to the reactor. The solution immediately turned
orange, characteristic of the formation of polystyryl anion. After
stirring at 3.degree. C. for 2 hours, a solution of
p-diphenylaminostyrene (1.61 g) in cyclohexane (20 mL) was added to
the reactor by cannula. This solution had previously been degassed
by repeatedly freezing it with liquid nitrogen and exposing it to
vacuum. The solution was stirred overnight while warming to room
temperature. The reaction was then terminated by addition of
methanol, precipitated into a mixture of methanol and isopropanol,
and dried under in a vacuum oven overnight, yielding 3.2 g of
polymer. The resulting PS-pDPAS block polymer contained 74.1 mol %
styrene and 25.9 mol % p-diphenylaminostyrene, based on .sup.13C
NMR. The molecular weight of the block copolymer was 7700 g/mol,
based on gel permeation chromatography in THF against polystyrene
standards.
[0119] OLED Preparation
[0120] OLEDs were formed as described in the Comparative Example 1
and Examples 1-3 except that the buffer layers were as follows:
[0121] Example 7: PS-pDPAS
[0122] Example 8: 93 wt. % PS-pDPAS and 7 wt. % F.sub.4-TCNQ
[0123] These buffer layers were spun-coat from their ca. 1.5% wt.
solutions in toluene at the spin-rate of 2000 RPM (about 33
s.sup.-1) to form ca. 90 nm thick films on the ITO coated
substrates.
[0124] No short-circuiting was observed in any of the studied
electroluminescent lamps. Luminance-voltage-current density
screening of the OLEDs indicated that high efficiencies and low
operational voltages were obtained. Doping PS-pDPAS with
F.sub.4-TCNQ significantly lowered the operational voltage of the
OLEDs.
Comparative Example 2 and Examples 9 and 10
[0125] Buffer Layers Containing Conjugated Copolymers With
Triarylamine Moieties in the Backbone
[0126] This describes the preparation and characterization of an
OLED with doped co-polymer based triarylamine hole injecting buffer
layers. The buffer layers include PEDT
(poly(3,4-ethylenedioxythiophene) available as CH8000 from Bayer A
G, Leverkusen, Germany), undoped
poly{(9-phenyl-9H-carbazole-3,6-diyl)[N,N'-bis(phenyl-4-yl)-N,N'-bis(4-bu-
tylphenyl)benzene-1,4-diamine]} (Cz-triarylamine), and
Cz-triarylamine doped with F.sub.4-TCNQ. An advantage of using
Cz-triarylamine as a triarylamine-containing co-polymer for hole
injecting buffer layers lies in the presence of phenylenediamine
linkages, which typically cause lower ionization potential (higher
energy of the highest occupied molecular orbital). This provides
favorable conditions for increased conductivity due to doping with
electron acceptors (e.g. F.sub.4-TCNQ).
[0127] 3,6-Dibromo-9-phenylcarbazole was made according to M. Park,
J. R. Buck, C. J. Rizzo, J. Carmelo. Tetrahedron 119, 54 (42),
12707-12714, incorporated herein by reference.
N,N'-bis(4-bromophenyl)-N,N'-bis(4-buty-
lphenyl)benzene-1,4-diamine can be obtained in two steps from
1,4-phenylenediamine as reported in Raymond et al., Polymer
Preprints 2001, 42(2), 587-588, incorporated herein by reference.
Tricaprylylmethylammonium chloride is available from Aldrich
Chemical Company under the trade name Aliquat.RTM. 336. All other
materials were obtained from Aldrich Chemical Company.
[0128] Preparation of
9-Phenyl-3,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9H-carbazole
[0129] A 2L flask was charged with 600 mL dry THF and
3,6-dibrimo-9-phenylcarbazole (60 g, 0.15 mole). This was cooled to
-78.degree. C. with an acetone-dry ice bath. n-Butyllithium (138 mL
of a 2.5M solution in hexanes, 0.34 mole) was added drop-wise via
syringe. The reaction was stirred for 20 minutes and then warmed to
-50.degree. C. The temperature was reduced to -78.degree. C. and
2-isopropoxy-4,4,5,5-tetram- ethyl-1,3,2-dioxaborolane (64 g, 0.34
mole) added via syringe at such a rate as to maintain the
temperature below -60.degree. C. The reaction was maintained at
-78.degree. C. for two hours and then poured into an aqueous
solution of ammonium acetate (90 g in 2100 mL water). The layers
were phase separated and the aqueous phase extracted with methyl
tert-butyl ether (2.times.200 mL). The combined organic phase and
extracts were washed with brine (2.times.200 mL) and dried over
magnesium sulfate. Concentration and re-crystallization of the
solid obtained form acetone gave pure
9-phenyl-3,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
-2-yl)-9H-carbazole (12 g, 16% yield).
[0130] Preparation of
Poly{(9-phenyl-9H-carbazole-3,6-diyl)[N,N'-bis(pheny-
l-4-yl)-N,N'-bis(4-butylphenyl)benzene-1,4-diamine)]}
(Cz-triarylamine--Formula 32 Above)
[0131] In a 50 mL round bottomed flask fitted with a rubber septum
and reflux condenser were introduced
9-phenyl-3,6-bis(4,4,5,5-tetramethyl-1,3-
,2-dioxaborolan-2-yl)-9H-carbazole (0.79 g, 1.59 mmole, 5
equivalents),
N,N'-bis(4-bromophenyl)-N,N'-bis(4-butylphenyl)benzene-1,4-diamine
(0.65 g, 0.952 mmol, 3 equivalents), Aliquat.RTM. 336 (0.16 g,
0.405 mmole, 1.28 equivalents), 2M sodium carbonate solution (5.4
mL, 10.8 mmol, 34 equivalents) and 20 mL toluene. This was purged
with a stream of nitrogen for 30 min. Under a nitrogen purge,
tetrakistriphenylphosphine palladium (0) (10 mg, 0.0.0068 mmole,
0.02 equivalents) was added. The reaction mixture was then refluxed
for 16 hrs. A solution of 0.5 g bromobenzene in 5 mL purged toluene
was added followed by and a further charge of
tetrakistriphenylphosphine paladium (0) (10 mg) and refluxing then
continued for a further 16 hrs.
[0132] The reaction was then cooled to room temperature and 30 mL
water added. The organic layer was separated and washed with water
followed by brine. Precipitation into methanol, filtration and
vacuum drying of the solid thus obtained gave 0.62 g of the
required hole transport polymer. Molecular weight determination by
gel permeation chromatography versus polystyrene standards gave Mw
2.39.times.10.sup.3, Mn 1.49.times.10.sup.3 and polydispersity of
1.67
[0133] OLED Preparation
[0134] OLEDs were formed as described in the Comparative Example 1
and Examples 1-3 except that the buffer layers were as follows:
[0135] Comparative Example 2: PEDT
[0136] Example 9: Cz-triarylamine
[0137] Example 10: 93 wt. % Cz-triarylamine and 7 wt. %
F.sub.4-TCNQ.
[0138] These buffer layers were spun-coat from their ca. 1.5% wt.
solutions in toluene at the spin-rate of 2000 RPM (about 33
s.sup.-1) to form ca. 90 nm thick films on the ITO coated
substrates.
[0139] No short-circuiting was observed in any of the studied
electroluminescent lamps. Devices with both doped and undoped
Cz-triarylamine-based buffer layer showed high external quantum
efficiencies. Devices with undoped Cz-triarylamine buffer layer
showed noticeably higher operational voltages than those made on
PEDT. Upon doping Cz-triarylamine with F.sub.4-TCNQ, operational
voltages decreased to the level of those observed for PEDT-based
LEDs. This indicates that Cz-triarylamine possesses an ionization
potential which is low enough for efficient F.sub.4-TCNQ doping to
increase conductivity in the hole-injecting buffer layer.
[0140] Preliminary operation stability studies on devices
incorporating Cz-triarylamine buffer layer carried out in the
constant current continuous sweep regime at current density levels
of ca. 1.8 mA/cm.sup.2 (luminance of 100-150 Cd/m.sup.2) suggest
that Cz-triarylamine-based buffer layers can be used to achieve
improved operational lifetime in OLEDs.
Examples 11-13
Absorptive Dye Doped Color Converting Buffer Layers
[0141] This Example describes the fabrication of hole-injecting
solution-processed buffer layers based on doped triarylamines
blended with electroactive polymer binder and blended with
color-converting organic dye material in order to tune
electroluminescence energy and CIE color coordinates of the OLEDs
incorporating such buffer layers.
[0142] Three solutions consisting of a) 30 mg poly(vinyl carbazole)
(PVK, Aldrich Chemical Co.), 20 mg MTDATA (H. W. Sands Corp.,
Jupiter, Fla.), 2 mg F.sub.4-TCNQ (TCI America, Portland, Oreg.),
3.7 ml CHCl.sub.3, b) 30 mg PVK, 20 mg MTDATA, 2 mg F.sub.4-TCNQ,
75 mg 1,4-bis(2-methyl-6-ethyl anilino) anthraquinone (Dye), 3.7 ml
CHCl.sub.3 and, c) 30 mg PVK, 20 mg MTDATA, 2 mg F.sub.4-TCNQ, 117
mg 1,4-bis(2-methyl-6-ethyl anilino) anthraquinone (Dye), 3.7 ml
CHCl.sub.3 were prepared. The Dye can be prepared according to U.S.
Pat. No. 5,639,896, incorporated herein by reference and is
available as "Amaplast Blue RFC" supplied by "American Aniline
Products", N.Y., N.Y., a unit of Koppers Co., Pittsburgh, Pa. Each
solution was then spun coat onto cleaned ITO substrates at 3000
R.P.M. for 30 s. A vapor deposited small-molecule OLED with NPD (20
nm, 0.2 nm/s), AlQ (50 nm, 0.1 nm/s), LiF (0.7 nm, 0.05 nm/s), Al
(200 nm, 2 nm/s) was sequentially deposited on top in a standard
vacuum deposition procedure at 10-6 torr (about 10-4 Pa) as
described in Comparative Example 1 and Examples 1-3.
[0143] OLEDs were formed as described in the Comparative Example 1
and Examples 1-3 except that the buffer layers were as follows:
[0144] Example 11: Solution a) corresponding to 58 wt. % PVK, 38
wt. % MTDATA and 4 wt. % F.sub.4-TCNQ
[0145] Example 12: Solution b) corresponding to 24 wt. % PVK, 16
wt. % MTDATA, 2 wt. % F.sub.4-TCNQ, and 58 wt. % Dye
[0146] Example 13: Solution c) corresponding to 18 wt. % PVK, 12
wt. % MTDATA, 1 wt. % F.sub.4-TCNQ, and 69 wt. % Dye.
[0147] Devices containing the dye in the buffer layer exhibit a
clear change in the electroluminescence spectrum and the
corresponding C.I.E coordinates due to selective absorption of the
AlQ emission by the dye. CIE color coordinates for two
hole-injecting buffer layer compositions containing the studied dye
material in different concentrations as well as those for the
control device are shown in Table I.
1TABLE I Color Coordinate Shift Sample CIE (x) CIE (y) Example 11
0.34 0.55 Example 12 0.20 0.56 Example 13 0.17 0.57
Example 14
Preparation of an OLED Device Using Thermal Transfer
[0148] Preparation of a Donor Sheet Without a Transfer Layer
[0149] A thermal transfer donor sheet was prepared in the following
manner:
[0150] An LTHC solution, given in Table II, was coated onto a 0.1
mm thick polyethylene terephthalate (PET) film substrate (M7 from
Teijin, Osaka, Japan). Coating was performed using a Yasui Seiki
Lab Coater, Model CAG-150, using a microgravure roll with 150
helical cells per inch. The LTHC coating was in-line dried at
80.degree. C. and cured under ultraviolet (UV) radiation.
2TABLE II LTHC Coating Solution Parts by Component Trade
Designation Weight carbon black pigment Raven 760 Ultra.sup.(1)
3.55 polyvinyl butyral resin Butvar B-98.sup.(2) 0.63 acrylic resin
Joncryl 67.sup.(3) 1.90 Dispersant Disperbyk 161.sup.(4) 0.32
Surfactant FC-430.sup.(5) 0.09 epoxy novolac acrylate Ebecryl
629.sup.(6) 12.09 acrylic resin Elvacite 2669.sup.(7) 8.06
2-benzyl-2-(dimethylamino- )-1-(4- Irgacure 369.sup.(8) 0.82
(morpholinyl)phenyl)butanone 1-hydroxycyclohexyl phenyl ketone
Irgacure 184.sup.(8) 0.12 2-butanone 45.31 1,2-propanediol
monomethyl ether 27.19 acetate .sup.(1)available from Columbian
Chemicals Co., Atlanta, GA .sup.(2)available from Solutia Inc., St.
Louis, MO .sup.(3)available from S. C. Johnson & Son, Inc.
Racine, WI .sup.(4)available from Byk-Chemie USA, Wallingford, CT
.sup.(5)available from Minnesota Mining and Manufacturing Co., St.
Paul, MN .sup.(6)available from UCB Radcure Inc., N. Augusta, SC
.sup.(7)available from ICI Acrylics Inc., Memphis, TN
.sup.(8)available from Ciba-Geigi Corp., Tarrytown, NY
[0151] Next, an interlayer solution, given in Table III, was coated
onto the cured LTHC layer by a rotogravure coating method using the
Yasui Seiki lab coater, Model CAG-150, with a microgravure roll
having 180 helical cells per lineal inch. This coating was in-line
dried at 60.degree. C. and cured under ultraviolet (UV)
radiation.
3TABLE III Interlayer Coating Solution PARTS BY COMPONENT WEIGHT SR
351 HP (trimethylolpropane triacrylate 14.85 ester, available from
Sartomer, Exton, PA) Butvar B-98 0.93 Joncryl 67 2.78 Irgacure 369
1.25 Irgacure 184 0.19 2-butanone 48.00 1-methoxy-2-propanol
32.00
[0152] Preparation of Solutions for Receptor
[0153] The following solutions were prepared and used in the
preparation of layers on the receptor substrate:
[0154] MTDATA:
(4,4',4"-tris(N-(3-methylphenyl)-N-phenylamino)triphenylami- ne)
(OSA 3939, H. W. Sands Corp., Jupiter, Fla.) 1.0% (w/w) in toluene
was filtered and dispensed through a Whatman Puradisc.TM. 0.45
.mu.m Polypropylene (PP) syringe filter.
[0155] PVK: Poly(9-vinylcarbazole) (Aldrich Chemical Co.,
Milwaukee, Wis.) 1.0% (w/w) in toluene was filtered and dispensed
through a Whatman Puradisc.TM. 0.45 .mu.m Polypropylene (PP)
syringe filter.
[0156] F.sub.4-TCNQ: Tetrafluorotetracyanoquinodimethane (Tokyo
Kasei Kogyo Co., Tokyo, Japan) 0.25% (w/w) in toluene was filtered
and dispensed through a Whatman Puradisc.TM. 0.45 .mu.m
Polypropylene (PP) syringe filter.
[0157] MTDATA/F.sub.4-TCNQ: 98/2 w/w% mixture of
MTDATA/F.sub.4-TCNQ.
[0158] MTDATA/PVK: 65/35 w/w% mixture of MTDATA/PVK
[0159] MTDATA/PVK/F.sub.4-TCNO: 64/35/1 w/w/w% mixture of
MTDATA/PVK/F.sub.4-TCNQ
[0160] Preparation of Receptors
[0161] Receptors were formed as follows: ITO(indium tin oxide)
glass (Delta Technologies, Stillwater, Minn., less than 100
.OMEGA./square, 1.1 mm thick) was processed using photolithography
to provide a patterned ITO structure capable of making an
electroluminescent device. The substrate was ultrasonically cleaned
in a hot, 3% solution of Deconex 12NS (Borer Chemie A G, Zuchwil
Switzerland). The substrates were then placed in the Plasma Science
plasma treater for surface treatment under the following
conditions:
4 Time: 2 minutes Power: 500 watt (165 W/cm.sup.2) Oxygen Flow: 100
sccm
[0162] Immediately after plasma treatment, a solution of material
was applied to the surface of the ITO according to Table IV
below.
5TABLE IV Preparation of receptors Spin Film Receptor Receptor
Coating speed thickness number Solution Composition (RPM) (nm) 1
MTDATA Neat 1000 40 2 MTDATA/F.sub.4- 98/2 w/w % 1000 40 TCNQ 3
MTDATA/PVK 65/35 w/w % 1000 40 4 MTDATA/PVK/F.sub.4- 64/35/1 w/w/w
% 1000 40 TCNQ
[0163] Preparation of Solutions for Transfer Layer
[0164] The following solutions were prepared:
[0165] Covion Super Yellow: Covion PPV polymer PDY 132 "Super
Yellow" (75 mg) from Covion Organic Semiconductors GmbH, Frankfurt,
Germany was weighed out into an amber vial with a PTFE cap. To this
was added 9.925 g of toluene (HPLC grade obtained from Aldrich
Chemical, Milwaukee, Wis.). The solution was stirred over night.
The solution was filtered through a 5 .mu.m Millipore Millex
syringe filter.
[0166] Polystyrene: Polystyrene (250 mg) from Aldrich Chemical,
Milwaukee, Wis. (M.sub.w=2,430) was dissolved in 9.75 g of toluene
(HPLC grade obtained from Aldrich Chemical, Milwaukee, Wis.). The
solution was filtered through a 0.45 .mu.m polypropylene (PP)
syringe filter.
[0167] Preparation of Transfer Layers on Donor Sheet and Transfer
of Transfer Layers.
[0168] Transfer layers were formed on the donor sheets using a
33/67 w/w% blend of the solutions of Covion Super Yellow and
polystyrene from the previous section. To obtain the blends, the
above-described solutions were mixed at the appropriate ratios and
the resulting blend solutions were stirred for 20 min at room
temperature.
[0169] The transfer layers were disposed on the donor sheets by
spinning (Headway Research spincoater) the blend solution at about
2000-2500 rpm for 30 s to yield a film thickness of approximately
100 nm.
[0170] The donor sheets coated with Covion Super Yellow/polystyrene
were brought into contact with each of the receptor substrates
prepared in an above section. Next, the donor sheets were imaged
using two single-mode Nd:YAG lasers. Scanning was performed using a
system of linear galvanometers, with the combined laser beams
focused onto the image plane using an f-theta scan lens as part of
a near-telecentric configuration. The laser energy density was 0.4
to 0.8 J/cm.sup.2. The laser spot size, measured at the 1/e.sup.2
intensity, was 30 micrometers by 350 micrometers. The linear laser
spot velocity was adjustable between 10 and 30 meters per second,
measured at the image plane. The laser spot was dithered
perpendicular to the major displacement direction with about a 100
nm amplitude. The transfer layers were transferred as lines onto
the receptor substrates, and the intended width of the lines was
about 100 nm.
[0171] The transfer layers were successfully transferred in a
series of lines that were in overlying registry with the ITO
stripes on the receptor substrates, resulting in good imaging
transfer.
[0172] Preparation of OEL Devices
[0173] Electroluminescent devices were prepared by depositing
calcium/silver cathodes on top of the LEP (Covion Super Yellow/PS)
transferred in the above section. Approximately 40 nm of calcium
was vapor deposited at a rate of 0.11 nm/s onto the LEP, followed
by approximately 400 nm of silver at a rate of 0.5 nm/s. In all
cases, diode behavior and yellow light emission was observed.
[0174] The present invention should not be considered limited to
the particular examples described above, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention may be applicable will be readily apparent to those of
skill in the art to which the present invention is directed upon
review of the instant specification.
* * * * *