Abstrict This invention provides a top-emitting OLED display device that
includes a substrate; an array of OLED elements disposed on one
side of the substrate; and a desiccant material provided in a patterned
arrangement over the array of OLED elements on the same side of
the substrate such that the desiccant material does not interfere
with the light emitted by the OLED elements.
Claims What is claimed is:
1. A top-emitting OLED display device comprising: a) a substrate;
b) an array of OLED elements disposed over one side of the substrate;
and c) desiccant material provided in a patterned arrangement over
the array of OLED elements on the same side of the substrate such
that the desiccant material does not interfere with the light emitted
by the OLED elements.
2. The display device claimed in claim 1 wherein the desiccant
is provided around the perimeter of the device.
3. The display device claimed in claim 2 wherein the desiccant
material is light absorbing.
4. The display device claimed in claim 1 wherein the desiccant
material is black.
5. The display device claimed in claim 1 wherein the OLED elements
comprise a plurality of layers including one or more insulating
layers and the desiccant material comprises one or more of the insulating
layers.
6. The display device claimed in claim 1 wherein the organic light
emitting elements comprise a plurality of layers and the patterned
arrangement of desiccant material is located within one of the plurality
of layers.
7. A top-emitting OLED display device comprising: a) a substrate;
b) an array of OLED elements disposed over one side of the substrate
wherein the light-emitting area of each OLED element defines a light-emitting
pixel area; and c) desiccant material provided in a patterned arrangement
over the array of OLED elements on the same side of the substrate,
such that the desiccant material is provided between the light-emitting
pixel areas.
8. The display device claimed in claim 7 wherein the desiccant
material is black.
9. The display device claimed in claim 7 wherein the organic light
emitting elements comprise a plurality of layers including one or
more insulating layers and the patterned arrangement of desiccant
material comprises one or more of the insulating layers.
10. The display device claimed in claim 7 wherein the desiccant
material is light absorbing and serves as a black matrix for improving
contrast.
11. The display device claimed in claim 10 wherein the desiccant
material includes a light absorber selected from the group consisting
of dyes and pigments.
12. The display device claimed in claim 10 wherein the desiccant
material includes a light absorber selected from the group consisting
of carbon black, graphite, metal oxides, and metal sulfides.
13. The display device claimed in claim 7 wherein the desiccant
is also provided a round the perimeter of the device.
14. The display device claimed in claim 7 wherein the array of
OLED elements comprises: a) an array of first electrodes; b) an
array of organic electro-luminescent elements deposited over the
array of first electrodes; c) a transparent, common second electrode
provided over the array of organic electro-luminescent elements;
and d) wherein the desiccant is provided in contact with the second
electrode.
15. The display device claimed in claim 7 wherein the array of
OLED elements comprises: a) an array of first electrodes; b) an
array of organic electro-luminescent elements deposited over the
array of first electrodes; c) a transparent, common second electrode
provided over the array organic electro-luminescent elements; and
d) a transparent protection layer provided over the common second
electrode; wherein the desiccant is provided in contact with the
transparent protection layer.
16. The display device claimed in claim 7 wherein the top-emitting
OLED display device includes a transparent cover provided over the
OLED elements and the patterned arrangement of desiccant material
is located on the inside of the transparent cover.
17. The display device claimed in claim 7 wherein the patterned
arrangement of desiccant material comprises a plurality of layers.
18. The display device claimed in claim 7 wherein the patterned
arrangement of desiccant material is a thick film layer.
19. The display device claimed in claim 7 wherein the desiccant
material includes a desiccant selected from the group consisting
of alkaline metal oxides, alkaline earth metal oxides, sulfates,
metal halides, and perchlorates.
20. The display device claimed in claim 7 wherein the desiccant
material includes a moisture absorption rate enhancing or maintaining
binder selected from the group consisting of cellulose acetates,
epoxies, phenoxies, siloxanes, methacrylates, sulfones, phthalates,
and amides.
21. The display device claimed in claim 20 wherein the moisture
absorption rate enhancing or maintaining binder is a radiation-curable
binder selected from the group consisting of radiation-curable photoresist
compositions.
22. The display device claimed in claim 7 wherein the desiccant
material includes a moisture-absorption rate-enhancing radiation-curable
binder selected from the group consisting of acrylates, methacrylates,
cyclized polyisoprenes, polyvinyl cinnamates, epoxies, silicones,
and adhesives.
23. The display device claimed in claim 7 wherein the desiccant
material is conformable to the surface of the materials deposited
over the substrate.
24. The display device claimed in claim 7 further comprising a
transparent cover that is conformable to the surface of the materials
deposited over the substrate.
25. A top-emitting OLED display device comprising: a) a substrate;
b) an array of thin film transistors provided over the substrate;
c) a patterned first insulating layer provided over the array of
thin film transistors; d) an array of first electrodes in electrical
contact with the thin film transistors; e) a second insulating layer
provided over the array of first electrodes, wherein the second
insulating layer is patterned to expose at least a portion of the
first electrodes, the area of which defines the light-emitting pixel
area; f) an array of organic electro-luminescent elements deposited
over the array of first electrodes; g) a transparent, common second
electrode provided over the array of organic electro-luminescent
elements; and h) desiccant material provided in a patterned arrangement
over the second electrode, such that the desiccant material is provided
between the light-emitting pixel areas.
26. The display device claimed in claim 25 wherein the light-emitting
pixel areas are located in recessed areas, the patterned second
insulating layer defines raised areas, and the desiccant is applied
to the raised areas by contact printing.
27. A top-emitting OLED display device comprising: a) a substrate;
b) an array of thin film transistors provided over the substrate;
c) a patterned first insulating layer provided over the array of
thin film transistors; d) an array of first electrodes in electrical
contact with the thin film transistors; e) a second insulating layer
provided over the array of first electrodes, wherein the second
insulating layer is patterned to expose at least a portion of the
first electrodes, the area of which defines a light-emitting pixel
area; f) an array of organic electro-luminescent elements deposited
over the array of first electrodes; g) a transparent, common second
electrode provided over the array organic electro-luminescent elements;
and h) wherein the first insulating layer or the second insulating
layer or both comprise a desiccant material.
28. A method of manufacturing a top-emitting OLED display device,
comprising the steps of: a) providing a substrate; b) forming an
array of OLED elements on one side of the substrate, wherein the
light-emitting area of each OLED element defines the light-emitting
pixel area; and c) forming a patterned arrangement of desiccant
material on the same side of the substrate and arranged between
the light-emitting pixel areas such that the desiccant material
does not interfere with the light emitted by the OLED elements.
29. The method claimed in claim 28 wherein photo-lithographic
processes are used to deposit the patterned arrangement of desiccant
material.
30. The method claimed in claim 28 wherein the desiccant material
is applied to the substrate as a liquid and is cured to form a solid.
31. The method claimed in claim 28 wherein thick film screen printing
processes are used to deposit the patterned arrangement of desiccant
material.
32. The method claimed in claim 28 wherein the desiccant material
is applied to raised portions of the OLED device by contact printing.
33. The method claimed in claim 28 wherein the desiccant material
is applied using a thermal transfer process from a donor substrate.
34. A top-emitting OLED display device, comprising: a) substrate;
b) an array of first electrodes provided over the substrate; c)
an array of organic electro-luminescent elements deposited on the
array of first electrodes such that there are gaps formed between
the organic electro-luminescent elements; d) desiccant material
provided within the gaps formed between the organic electro-luminescent
elements; and e) a transparent, common second electrode provided
over the array of electro-luminescent elements and desiccant material.
Description FIELD OF THE INVENTION
[0001] The present invention relates to organic light emitting
diode (OLED) displays, and more particularly, to improving the performance,
reliability, and robustness of such displays by preventing moisture
from degrading the light-emitting OLED materials and improving the
contrast of the display.
BACKGROUND OF THE INVENTION
[0002] Organic light-emitting diode (OLED) display devices require
humidity levels below about 1000 parts per million (ppm) to prevent
premature degradation of device performance within a specified operating
and/or storage life of the device. Control of the environment to
this range of humidity levels within a packaged device is typically
achieved by encapsulating the device or by sealing the device and
a desiccant within a cover. Desiccants such as, for example, metal
oxides, alkaline earth metal oxides, sulfates, metal halides, and
perchlorates are used to maintain the humidity level below the above
level. See for example U.S. Pat. No. 6226890 B1 issued May 8
2001 to Boroson et al. describing desiccant materials for moisture-sensitive
electronic devices. The device disclosed in FIG. 2 of Boroson et
al. is a so-called bottom emitting OLED device that emits light
through a transparent substrate. The desiccant material is located
over the organic light emitting materials in an enclosure that is
sealed to the back-side of the substrate.
[0003] In a so-called top emitting OLED the organic material is
also located on a substrate, but the light is emitted from the surface
of the substrate through a transparent cover plate that also serves
as part of the sealed enclosure. In this arrangement, desiccant
materials located in the enclosure over to the organic materials
will interfere with the light emitted by the OLED.
[0004] There is a need therefore for an improved means to provide
desiccation in a top-emitting OLED display device.
SUMMARY OF THE INVENTION
[0005] The need is met by providing a top-emitting OLED display
device, that includes a substrate; an array of OLED elements disposed
on one side of the substrate; and a desiccant material provided
in a patterned arrangement over the array of OLED elements on the
same side of the substrate such that the desiccant material does
not interfere with the light emitted by the OLED elements.
[0006] According to a preferred embodiment of the invention, the
patterned arrangement of desiccant material performs the function
of a black matrix for increasing the contrast of the display.
ADVANTAGES
[0007] The present invention has the advantage that it increases
the lifetime of a top-emitting OLED display device by providing
desiccation of the OLED elements. In a preferred embodiment, the
contrast of the display is also improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 illustrates a partial cross section of a prior art
conventional top-emitting OLED display device;
[0009] FIG. 1A is a cross section view of a typical OLED element
known in the art that illustrates some of the various layers that
can be used to construct an OLED element;
[0010] FIG. 2 is a partial cross section of a display having desiccant
material applied to the top layer of the OLED substrate according
to a first embodiment of the present invention;
[0011] FIG. 3 is a top view of a display shown in FIG. 2;
[0012] FIG. 4 is a partial cross section of a display with desiccant
material applied to the inside of the display device cover according
to a second embodiment of the present invention;
[0013] FIG. 5 is a partial cross section of a display with desiccant
material used within other layers according to a third embodiment
of the present invention;
[0014] FIG. 6 is a partial cross section of a display with desiccant
material on the top layer, on a cover, and within other layers;
[0015] FIG. 7 is a cross section of a display illustrating the
desiccant material used around the perimeter of the display device;
[0016] FIG. 8 is a partial cross section of a display with desiccant
material applied to the top layer of the OLED substrate and a conformal
cover; and
[0017] FIG. 9 is a partial cross section of a display where the
desiccant material is contact printed.
[0018] It will be understood that the figures are not to scale
since the individual layers are too thin and the thickness differences
of various layers too great to permit depiction to scale.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Referring to FIG. 1 a prior art top-emitting OLED display
device 10 is shown with a substrate 12 and a thin-film transistor
(TFT) active matrix layer 14 comprising an array of TFTs that provides
power to OLED elements. A patterned first insulating layer 16 is
provided over the TFT active matrix layer, and an array of first
electrodes 18 are provided over insulating layer 16 and in electrical
contact with the TFT active matrix layer. A patterned second insulating
layer 17 is provided over the array of first electrodes 18 such
that at least a portion of the each of the first electrodes 18 is
exposed.
[0020] Over the first electrodes and insulating layers are provided
red, green, and blue-emitting organic electroluminescent (EL) elements,
19R, 19G, and 19B, respectively. Herein, the collection of organic
EL elements may also be referred to as the organic EL layer The
light-emitting pixel area is generally defined by the area of the
first electrode 18 in contact with the organic EL elements. Over
the organic EL layer is provided a transparent, common second electrode
30 that has sufficient optical transparency to allow transmission
of the generated red, green, and blue light. Each first electrode
in combination with its associated organic EL element and second
electrode is herein referred to as an OLED element. A typical top-emitting
OLED display device comprises an array of OLED elements wherein
each OLED element emits red, green or blue. However, monochrome
display devices are also known where the array of OLED elements
emit the same color light, for example, white.
[0021] In operation, the thin-film transistors in TFT layer 14
allow current to flow between the first electrode 18 each of which
can be selectively addressed, and the common second electrode 30.
Holes and electrons recombine within the organic EL elements to
emit light.
[0022] Referring to FIG. 2 a first embodiment of the top-emitting
OLED device of the present invention includes a transparent protection
layer 32 provided over the second electrode, and further provides
a patterned layer of light-absorbing desiccant 40 in contact with
the transparent protection layer 32. A transparent cover 36 is provided
over OLED device with a gap maintained between the device and the
cover. Attachment of the cover to the device at the edges of the
display is not shown in this partial view.
[0023] The transparent protection layer 32 is optional and the
patterned layer of desiccant can instead be provided in direct contact
with the second electrode 30. When provided, the protection layer
32 may comprise inorganic materials such as SiOx or SiNx, for example,
as disclosed in JP 2001126864. Alternatively, the protection layer
32 may comprise organic materials such as polymers, including but
not limited to, Teflon.RTM., polyimides, and polymers disclosed
in JP 11-162634. Protection layer 32 may comprise multiple layers
of organic or inorganic materials, or combinations thereof. Alternating
inorganic and organic layers, for example, as disclosed in U.S.
Pat. No. 6268295 and WO 00/36665 are useful as protection layer
32. In all cases, the protection layer 32 should have high optical
transparency, preferably greater than 70% transmittance. For convenience,
the combination of layers from the substrate through the optional
protection layer is referred to herein as the OLED substrate.
[0024] The light-absorbing desiccant 40 is provided in a patterned
arrangement between the light-emitting pixel areas, designated 24R,
G, and B of the device such that it does not interfere with the
light emitted by the OLED elements 19R, G, and B. As previously
mentioned, the light-emitting pixel area is generally defined by
the area of the first electrode in contact with the organic EL elements.
A top view of the result is shown in FIG. 3. Referring to FIG. 3
the display device 10 has a patterned array of light-emitting pixel
areas 24R, 24G, and 24B that emit red, green, and blue light, respectively.
The light-absorbing desiccant material 40 is patterned between the
pixels or OLED elements so as to allow light to be emitted from
the pixels through the cover (not shown in FIG. 3). The light-absorbing
desiccant material need not be deposited over the entire available
area, and may be deposited on only a portion of the available device
area not used by the light emitting pixel areas. The desiccant material
need not be deposited in a planar layer, but can be conformable
to the surface of the materials deposited over the substrate. The
desiccant material may be deposited and patterned using thick film
manufacturing techniques such as screen-printing as are known in
the art. The light-absorbing desiccant can be deposited much more
thickly and heavily than the OLED layers. In general, the more material
that is deposited, the better desiccation and light absorption is
provided.
[0025] The light-absorbing desiccant material 40 may be deposited
in a pattern using photolithographic techniques known in the art.
For example, light absorbing desiccant material may be coated as
a liquid on the entire surface and exposed to radiation through
a mask to polymerize portions of the coating. Portions of the material
exposed to the radiation are cured and the remainder is washed away.
Dry film photolithography may also be used. In addition, patterned
thermal transfer can be used, for example, by coating desiccant
material 40 onto a donor substrate, placing the donor substrate
in contact or close proximity to the OLED substrate, and selectively
heating the donor with a laser to cause transfer of the desiccant
material to the OLED substrate. The desiccant material 40 may comprise
a plurality of thinner layers deposited by sequential deposition
of desiccant materials.
[0026] As shown in FIG. 7 the cover 36 forms a cavity over the
OLED pixel areas 24. The light absorbing desiccant material 40 can
be used as a desiccant seal material 40' around the perimeter of
the device, further improving desiccation. Sealing is done under
inert atmosphere conditions, for example, under nitrogen or argon,
so that the gap contains little to no water or oxygen. The light-absorbing
desiccant materials may, or may not, actually touch the cover 36.
If they do touch, each pixel area becomes an independent cavity.
For simplicity, the TFT layers, organic EL layers, second electrode
and the optional protection layer are depicted in FIG. 7 as a single
combined layer 13.
[0027] Many desiccants may be used in this invention, but currently
preferred solid desiccants are selected from the group consisting
of alkaline metal oxides, alkaline earth metal oxides, sulfates,
metal chlorides, and perchlorates. Preferred binders are moisture-permeable
and radiation-curable, i.e., they may be cured by exposure to heat
or to electromagnetic radiation such as infra-red, visible, or ultraviolet
light. Preferred binders include radiation-curable, commercially
available photoresist compositions, or radiation-curable acrylates,
methacrylates, cyclized polyisoprenes, polyvinyl cinnamates, epoxies,
silicones, and adhesives. The desiccant material may include a moisture
absorption rate enhancing or maintaining binder selected from the
group consisting of cellulose acetates, epoxies, phenoxies, siloxanes,
methacrylates, sulfones, phthalates, and amides.
[0028] This invention does not require desiccant material 40 or
desiccant seal material 40' to have light-absorbing properties,
and it may instead be transparent or translucent. Providing desiccant
material 40 with light-absorbing properties is useful to increase
the contrast of the device. A preferred light-absorbing desiccant
material in the present invention has a black color. Patterned light-absorbing
desiccant material 40 serves as a black matrix for improving contrast
by absorbing ambient light. The terms "black" or "black
matrix" are not meant to imply perfect light absorption at
all wavelengths, but rather, to imply that the matrix appears dark
to an observer and has little hue. The present invention provides
advantages over the art in this regard in that contrast is enhanced
without the loss of light through the use of circular polarizers
or other light-absorbing layers as known in the art. Moreover, light-absorbing
desiccant materials will also absorb light emitted or being guided
through other layers of the display device. This will have the effect
of reducing the level of stray light in the device, improving its
sharpness.
[0029] While black is preferred, other desiccant colors may be
used to yield a desired feature. A light absorber may be an additive
to the desiccant/binder matrix and can be selected from the group
comprising dyes and pigments. Pigments can include, for example,
carbon black, graphite, metal oxides, metal sulfides, and metal
complexes such as phthalocyanines. Alternatively, one may select
a desiccant or a binder that intrinsically possesses light absorbing
properties.
[0030] In a second embodiment, the light-absorbing desiccant material
is applied to the inside of transparent cover 36 rather than the
top layer on the OLED substrate. Referring to FIG. 4 the cover
may be prepared separately from the OLED substrate. A similar masking
technique as described above may be used to deposit patterned desiccant
material 40 onto the cover 36. The cover 36 is aligned with the
OLED substrate when the cover is affixed to the substrate to ensure
that the light-absorbing desiccant does not occlude the light from
the pixels.
[0031] Alternatively, the light-absorbing desiccant materials are
deposited so that the desiccant materials touch both the top layer
of the substrate and the cover (not shown). If this is done over
all of the display, each pixel element will be enclosed separately
within a cavity. It is also possible to deposit light-absorbing
desiccant material that touches both the substrate and the cover
only on the perimeter (not shown) so that a physical barrier to
moisture exists around the periphery of the OLED display device
but the pixel elements are all exposed to the gap in common.
[0032] Referring to FIG. 5 according to a further embodiment,
a light-absorbing desiccant 40 is patterned in conjunction with
one or more of the layers comprising the organic EL layer such that
the patterned desiccant layer is provided between the pixel areas
24. The desiccant material may comprise all or a portion of one
or more layers, i.e. it can comprise the layer, or be located within
one of the layers. In this case, the process by which the device
is made is conventional; the only difference being is that the material
that is used to fill the gaps between pixel areas has desiccating
properties.
[0033] According to another embodiment, second insulating layer
17 comprises an insulating light-absorbing desiccant. Because the
second insulating layer defines the pixel areas by defining the
exposed area of the first electrode, the patterned desiccant layer
is necessarily provided between the pixel areas. The purpose of
the second insulating layer 17 is to smooth the edges of the first
electrode 18 and to assist in preventing a short circuit to the
second electrode 30. The desiccant material can be, for example,
one of the desiccants described above, or an acrylic binder mixed
with one of the desiccants described above. Any polymer used as
the second insulating layer can be used as the binder. The desiccant
and binder may be deposited and patterned using conventional photolithography,
or any means normally used to deposit and pattern the second insulating
layer. Similarly, the first insulating layer 16 may also comprise
a desiccant material.
[0034] As shown in FIG. 6 the various embodiments of the present
invention are not mutually exclusive and can be combined in a single
device. For example, light-absorbing desiccant material 40 may be
patterned on the top layer of the substrate, on the cover, and within
other layers. Combining the various embodiments provides further
desiccation and contrast enhancement in the display device. A shown
in FIG. 6 there are gaps formed between the organic electro-luminescent
elements 19R, G, B and the desiccant material 40 is provided within
the gaps.
[0035] A second insulating layer is not required in this invention.
When it is used, it should be appreciated that it is generally much
thicker than the combined thickness of the organic EL elements,
second electrode and optional protection layer. When this is the
case, a three-dimensional relief pattern is created with the light-emitting
pixel areas in recessed regions and the second insulating layers
representing the raised areas. This is shown in FIG. 9. The organic
EL elements, second electrode, and optional protection layer are
shown collectively as combined layer 15 which is deposited in a
conformable manner over the structure. When such a relief pattern
is present, contact printing of the light-absorbing desiccant 40
can be performed through well-known methods. This is advantageous
because it greatly simplifies the desiccant-patterning step.
[0036] For example, desiccant 40 may be coated onto a donor sheet,
which is placed in physical contact with the OLED substrate. Transfer
of the desiccant only takes place at the raised portions because
that is where the contact takes place. The OLED substrate surface
may be treated with an adhesion promoter to aid transfer. Heat may
be used to aid the transfer of the desiccant from the donor to the
OLED substrate. Alternatively, the desiccant material 40 may be
roller coated onto the raised areas from a roller surface coated
with the desiccant.
[0037] While transparent cover 36 is typically glass or plastic
sheet, the cover can comprise materials that are deposited in a
conformable manner over the surface of the materials deposited over
the substrate, i.e., over OLED substrate with patterned desiccant
material 40. The same materials useful as protection layer 32 can
be used as the transparent conformable cover 36'. This is illustrated
in FIG. 8.
[0038] This invention is advantageously practiced with top-emitting
OLED active matrix devices. However, it is readily apparent to one
skilled in the art that this invention may be used in any top-emitting
OLED device including simple matrix or passive matrix devices.
[0039] OLED Element Architecture
[0040] There are numerous configurations of the layers within each
OLED element wherein the present invention can be successfully practiced.
A typical, non-limiting, structure is shown in FIG. 1A and is comprised
of an anode layer 103 a hole-injecting layer 105 a hole-transporting
layer 107 a light-emitting layer 109 an electron-transporting
layer 111 and a cathode layer 113. These layers are described in
detail below. The total combined thickness of the organic layers
is preferably less than 500 nm. The first electrode 18 may be either
the cathode or anode, and the second electrode 30 is necessarily
the opposite. A voltage/current source 250 is required to energize
the OLED element and conductive wiring 260 is required to make electrical
contact to the anode and cathode. The TFT layers and associated
wiring serve these functions.
[0041] Substrate
[0042] Because the OLED elements are not viewed through the substrate,
substrate 12 can either be light transmissive or opaque. Substrates
for use in this case include, but are not limited to, glass, plastic,
semiconductor materials, ceramics, and circuit board materials.
[0043] Anode
[0044] When the anode layer 103 serves as second electrode 30
the anode should be transparent or substantially transparent to
the emission of interest. Common transparent anode materials used
in this invention are indium-tin oxide (ITO), indium-zinc oxide
(IZO) and tin oxide, but other metal oxides can work including,
but not limited to, aluminum- or indium-doped zinc oxide, magnesium-indium
oxide, and nickel-tungsten oxide. In addition to these oxides, metal
nitrides, such as gallium nitride, and metal selenides, such as
zinc selenide, and metal sulfides, such as zinc sulfide, can be
used in layer 103. When anode layer serves the function of the first
electrode 18 the transmissive characteristics of layer 103 are
immaterial and any conductive material can be used transparent,
opaque or reflective. Example conductors for this application include,
but are not limited to: gold, iridium, molybdenum, palladium, and
platinum. Typical anode materials, transmissive or otherwise, have
a work function of 4.1 eV or greater. Desired anode materials are
commonly deposited by any suitable means such as evaporation, sputtering,
chemical vapor deposition, or electrochemical means. Anodes can
be patterned using well-known photolithographic processes.
[0045] Hole-Injecting Layer (HIL)
[0046] It is often useful that a hole-injecting layer 105 be provided
between anode 103 and hole-transporting layer 107. The hole-injecting
material can serve to improve the film formation property of subsequent
organic layers and to facilitate injection of holes into the hole-transporting
layer. Suitable materials for use in the hole-injecting layer include,
but are not limited to: porphyrinic compounds as described in U.S.
Pat. No. 4720432 and plasma-deposited fluorocarbon polymers as
described in U.S. Pat. No. 6208075. Alternative hole-injecting
materials reportedly useful in organic EL devices are described
in EP 0 891 121 A1 and EP 1 029 909 A1.
[0047] Hole-Transporting Layer (HTL)
[0048] The hole-transporting layer 107 contains at least one hole-transporting
compound such as an aromatic tertiary amine, where the latter is
understood to be a compound containing at least one trivalent nitrogen
atom that is bonded only to carbon atoms, at least one of which
is a member of an aromatic ring. In one form the aromatic tertiary
amine can be an arylamine, such as a monoarylamine, diarylamine,
triarylamine, or a polymeric arylamine. Exemplary monomeric triarylamines
are illustrated by Klupfel et al. U.S. Pat. No. 3180730. Other
suitable triarylamines substituted with one or more vinyl radicals
and/or comprising at least one active hydrogen containing group
are disclosed by Brantley et al. in U.S. Pat. No. 3567450 and
U.S. Pat. No. 3658520. A more preferred class of aromatic tertiary
amines are those which include at least two aromatic tertiary amine
moieties as described in U.S. Pat. No. 4720432 and U.S. Pat. No.
5061569. Illustrative of useful aromatic tertiary amines include,
but are not limited to, the following:
[0049] 11-Bis(4-di-p-tolylaminophenyl)cyclohexane
[0050] 11-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane
[0051] 44'-Bis(diphenylamino)quadriphenyl
[0052] Bis(4-dimethylamino-2-methylphenyl)-phenylmethane
[0053] N,N,N-Tri(p-tolyl)amine
[0054] 4-(di-p-tolylamino)-4'-[4(di-p-tolylamino)-styryl]stilbene
[0055] N,N,N',N'-Tetra-p-tolyl-4-4'-diaminobiphenyl
[0056] N,N,N',N'-Tetraphenyl-44'-diaminobiphenyl
[0057] N,N,N',N'-tetra-1-naphthyl-44'-diaminobiphenyl
[0058] N,N,N',N'-tetra-2-naphthyl-44'-diaminobiphenyl
[0059] N-Phenylcarbazole
[0060] 44'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl
[0061] 44'-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl
[0062] 44"-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl
[0063] 44'-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl
[0064] 44'-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl
[0065] 15-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
[0066] 44'-Bis[N-(9-anthryl)-N-phenylamino]biphenyl
[0067] 44"-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl
[0068] 44'-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl
[0069] 44'-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl
[0070] 44'-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl
[0071] 44'-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl
[0072] 44'-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl
[0073] 44'-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl
[0074] 26-Bis(di-p-tolylamino)naphthalene
[0075] 26-Bis[di-(1-naphthyl)amino]naphthalene
[0076] 26-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene
[0077] N,N,N',N'-Tetra(2-naphthyl)-44"-diamino-p-terphenyl
[0078] 44'-Bis{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl
[0079] 44'-Bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl
[0080] 26-Bis[N,N-di(2-naphthyl)amine]fluorene
[0081] 15-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
[0082] Another class of useful hole-transporting materials includes
polycyclic aromatic compounds as described in EP 1 009 041. In addition,
polymeric hole-transporting materials can be used such as poly(N-vinylcarbazole)
(PVK), polythiophenes, polypyrrole, polyaniline, and copolymers
such as poly(34-ethylenedioxythiophene)/poly(4-styrenesul- fonate)
also called PEDOT/PSS.
[0083] Light-Emitting Layer (LEL)
[0084] As more fully described in U.S. Pat. No. 4769292 and U.S.
Pat. No. 5935721 the light-emitting layer (LEL) 109 of the organic
EL element comprises a luminescent or fluorescent material where
electroluminescence is produced as a result of electron-hole pair
recombination in this region. The light-emitting layer can be comprised
of a single material, but more commonly consists of a host material
doped with a guest compound or compounds where light emission comes
primarily from the dopant and can be of any color. The host materials
in the light-emitting layer can be an electron-transporting material,
as defined below, a hole-transporting material, as defined above,
or another material or combination of materials that support hole-electron
recombination. The dopant is usually chosen from highly fluorescent
dyes, but phosphorescent compounds, e.g., transition metal complexes
as described in WO 98/55561 WO 00/18851 WO 00/57676 and WO 00/70655
are also useful. Dopants are typically coated as 0.01 to 10% by
weight into the host material. Iridium complexes of phenylpyridine
and its derivatives are particularly useful luminescent dopants.
Polymeric materials such as polyfluorenes and polyvinylarylenes
(e.g., poly(p-phenylenevinylene), PPV) can also be used as the host
material. In this case, small molecule dopants can be molecularly
dispersed into the polymeric host, or the dopant could be added
by copolymerizing a minor constituent into the host polymer.
[0085] An important relationship for choosing a dye as a dopant
is a comparison of the bandgap potential which is defined as the
energy difference between the highest occupied molecular orbital
and the lowest unoccupied molecular orbital of the molecule. For
efficient energy transfer from the host to the dopant molecule,
a necessary condition is that the band gap of the dopant is smaller
than that of the host material.
[0086] Host and emitting molecules known to be of use include,
but are not limited to, those disclosed in U.S. Pat. No. 4768292
U.S. Pat. No. 5141671 U.S. Pat. No. 5150006 U.S. Pat. No.
5151629 U.S. Pat. No. 5405709 U.S. Pat. No. 5484922 U.S.
Pat. No. 5593788 U.S. Pat. No. 5645948 U.S. Pat. No. 5683823
U.S. Pat. No. 5755999 U.S. Pat. No. 5928802 U.S. Pat. No.
5935720 U.S. Pat. No. 5935721 and U.S. Pat. No. 6020078.
[0087] Metal complexes of 8-hydroxyquinoline and similar oxine
derivatives constitute one class of useful host compounds capable
of supporting electroluminescence, and are particularly suitable.
Illustrative of useful chelated oxinoid compounds are the following:
[0088] CO-1: Aluminum trisoxine [alias, tris(8-quinolinolato)aluminum(III)-
]
[0089] CO-2: Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)]
[0090] CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)
[0091] CO-4: Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-met-
hyl-8-quinolinolato) aluminum(III)
[0092] CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]
[0093] CO-6: Aluminum tris(5-methyloxine) [alias, tris(5-methyl-8-quinolin-
olato) aluminum(III)]
[0094] CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]
[0095] CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]
[0096] CO-9: Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)]
[0097] Other classes of useful host materials include, but are
not limited to: derivatives of anthracene, such as 910-di-(2-naphthyl)anthracene
and derivatives thereof, distyrylarylene derivatives as described
in U.S. Pat. No. 5121029 and benzazole derivatives, for example,
22',2"-(135-phenylene)tris[1-phenyl-1H-benzimidazole].
[0098] Useful fluorescent dopants include, but are not limited
to: derivatives of anthracene, tetracene, xanthene, perylene, rubrene,
coumarin, rhodamine, quinacridone, dicyanomethylenepyran compounds,
thiopyran compounds, polymethine compounds, pyrilium and thiapyrilium
compounds, fluorene derivatives, periflanthene derivatives and carbostyryl
compounds.
[0099] Electron-Transporting Layer (ETL)
[0100] Preferred thin film-forming materials for use in forming
the electron-transporting layer 111 of the organic EL elements of
this invention are metal chelated oxinoid compounds, including chelates
of oxine itself (also commonly referred to as 8-quinolinol or 8-hydroxyquinoline).
Such compounds help to inject and transport electrons, exhibit high
levels of performance, and are readily fabricated in the form of
thin films. Exemplary oxinoid compounds were listed previously.
[0101] Other electron-transporting materials include various butadiene
derivatives as disclosed in U.S. Pat. No. 4356429 and various
heterocyclic optical brighteners as described in U.S. Pat. No. 4539507.
Benzazoles and triazines are also useful electron-transporting materials.
[0102] In some instances, layers 111 and 109 can optionally be
collapsed into a single layer that serves the function of supporting
both light emission and electron transport. These layers can be
collapsed in both small molecule OLED systems and in polymeric OLED
systems. For example, in polymeric systems, it is common to employ
a hole-transporting layer such as PEDOT-PSS with a polymeric light-emitting
layer such as PPV. In this system, PPV serves the function of supporting
both light emission and electron transport.
[0103] Cathode
[0104] The cathode 113 serves as the first electrode 18 it need
not be transparent and can comprise nearly any conductive material.
Desirable cathode materials have good film-forming properties to
ensure good contact with the underlying organic layer, promote electron
injection at low voltage, and have good stability. Useful cathode
materials often contain a low work function metal (<4 0 eV) or
metal alloy. One preferred cathode material is comprised of a Mg:Ag
alloy wherein the percentage of silver is in the range of 1 to 20%,
as described in U.S. Pat. No. 4885221. Another suitable class
of cathode materials includes bilayers comprising a thin electron-injection
layer (EIL) and a thicker layer of conductive metal. The EIL is
situated between the cathode and the organic layer (e.g., ETL).
Here, the EIL preferably includes a low work function metal or metal
salt, and if so, the thicker conductor layer does not need to have
a low work function. One such cathode is comprised of a thin layer
of LiF followed by a thicker layer of Al as described in U.S. Pat.
No. 5677572. Other useful cathode material sets include, but are
not limited to, those disclosed in U.S. Pat. Nos. 5059861 5059862
and 6140763.
[0105] When cathode layer 113 serves as the second electrode 30
the cathode must be transparent or nearly transparent. For such
applications, metals must be thin or one must use transparent conductive
oxides, or a combination of these materials. Optically transparent
cathodes have been described in more detail in U.S. Pat. No. 4885211
U.S. Pat. No. 5247190 JP 3234963 U.S. Pat. No. 5703436
U.S. Pat. No. 5608287 U.S. Pat. No. 5837391 U.S. Pat. No.
5677572 U.S. Pat. No. 5776622 U.S. Pat. No. 5776623 U.S.
Pat. No. 5714838 U.S. Pat. No. 5969474 U.S. Pat. No. 5739545
U.S. Pat. No. 5981306 U.S. Pat. No. 6137223 U.S. Pat. No.
6140763 U.S. Pat. No. 6172459 EP 1 076 368 and U.S. Pat.
No. 6278236. Cathode materials are typically deposited by evaporation,
sputtering, or chemical vapor deposition. When needed, patterning
can be achieved through many well known methods including, but not
limited to, through-mask deposition, integral shadow masking as
described in U.S. Pat. No. 5276380 and EP 0 732 868 laser ablation,
and selective chemical vapor deposition.
[0106] Deposition of Organic Layers
[0107] The organic materials mentioned above are suitably deposited
through a vapor-phase method such as sublimation, but can be deposited
from a fluid, for example, from a solvent with an optional binder
to improve film formation. If the material is a polymer, solvent
deposition is useful but other methods can be used, such as sputtering
or thermal transfer from a donor sheet. The material to be deposited
by sublimation can be vaporized from a sublimator "boat"
often comprised of a tantalum material, e.g., as described in U.S.
Pat. No. 6237529 or can be first coated onto a donor sheet and
then sublimed in closer proximity to the substrate. Layers with
a mixture of materials can utilize separate sublimator boats or
the materials can be pre-mixed and coated from a single boat or
donor sheet. Patterned deposition can be achieved using shadow masks,
integral shadow masks (U.S. Pat. No. 5294870), spatially-defined
thermal dye transfer from a donor sheet (U.S. Pat. Nos. 5851709
and 6066357) and inkjet method (U.S. Pat. No. 6066357). While
all organic layers may be patterned, it is most common that only
the layer emitting light is patterned, and the other layers may
be uniformly deposited over the entire device.
[0108] Optical Optimization
[0109] OLED devices of this invention can employ various well-known
optical effects in order to enhance its properties if desired. This
includes optimizing layer thicknesses to yield maximum light transmission,
providing dielectric mirror structures, replacing reflective electrodes
with light-absorbing electrodes, providing anti-glare or anti-reflection
coatings over the display, providing a polarizing medium over the
display, or providing colored, neutral density, or color conversion
filters over the display. Filters, polarizers, and anti-glare or
anti-reflection coatings may be specifically provided over the cover
or as part of the cover. In another embodiment of this invention,
the OLED elements may emit white light and a RGB filter array is
provided over the white-emitting OLED elements to provide a full
color display device.
[0110] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will
be understood that variations and modifications can be effected
within the spirit and scope of the invention. |