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 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,
the patterned arrangement of desiccant material being black and
serving as a black matrix for improving contrast by absorbing ambient
light.
2. The method claimed in claim 1 wherein photolithographic processes
are used to deposit the patterned arrangement of desiccant material.
3. The method claimed in claim 1 wherein the desiccant material
is applied to the substrate as a liquid and is cured to form a solid.
4. The method claimed in claim 1 wherein thick film screen printing
processes are used to deposit the patterned arrangement of desiccant
material.
5. The method claimed in claim 1 wherein the desiccant material
is applied to raised portions of the OLED device by contact printing.
6. The method claimed in claim 1 wherein the desiccant material
is applied using a thermal transfer process from a donor substrate.
Description FIELD OF THE INVENTION
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
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.
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.
There is a need therefore for an improved means to provide desiccation
in a top-emitting OLED display device.
SUMMARY OF THE INVENTION
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.
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
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
FIG. 1 illustrates a partial cross section of a prior art conventional
top-emitting OLED display device;
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;
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;
FIG. 3 is a top view of a display shown in FIG. 2;
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;
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;
FIG. 6 is a partial cross section of a display with desiccant material
on the top layer, on a cover, and within other layers;
FIG. 7 is a cross section of a display illustrating the desiccant
material used around the perimeter of the display device;
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
FIG. 9 is a partial cross section of a display where the desiccant
material is contact printed.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
OLED Element Architecture
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.
Substrate
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.
Anode
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.
Hole-Injecting Layer (HIL)
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.
Hole-Transporting Layer (HTL)
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. Nos. 3567450 and
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. Nos. 4720432 and 5061569. Illustrative
of useful aromatic tertiary amines include, but are not limited
to, the following: 11-Bis(4-di-p-tolylaminophenyl)cyclohexane 11-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane
44'-Bis(diphenylamino)quadriphenyl Bis(4-dimethylamino-2-methylphenyl)-phenylmethane
N,N,N-Tri(p-tolyl)amine 4-(di-p-tolylamino)-4'-[4(di-p-tolylamino)-styryl]stilbene
N,N,N',N'-Tetra-p-tolyl-4-4'-diaminobiphenyl N,N,N',N'-Tetraphenyl-44'-diaminobiphenyl
N,N,N',N'-tetra-1-naphthyl-44'-diaminobiphenyl N,N,N',N'-tetra-2-naphthyl-44'-diaminobiphenyl
N-Phenylcarbazole 44'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl
44'-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl 44"-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl
44'-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl 44'-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl
15-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene 44'-Bis[N-(9-anthryl)-N-phenylamino]biphenyl
44"-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl 44'-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl
44'-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl 44'-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl
44'-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl 44'-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl
44'-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl 26-Bis(di-p-tolylamino)naphthalene
26-Bis[di-(1-naphthyl)amino]naphthalene 26-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene
N,N,N',N'-Tetra(2-naphthyl)-44"-diamino-p-terphenyl 44'-Bis{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl
44'-Bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl 26-Bis[N,N-di(2-naphthyl)amine]fluorene
15-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
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-styrenesulfonate)
also called PEDOT/PSS.
Light-Emitting Layer (LEL)
As more fully described in U.S. Pat. Nos. 4769292 and 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.
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.
Host and emitting molecules known to be of use include, but are
not limited to, those disclosed in U.S. Pat. Nos. 4768292 5141671
5150006 5151629 5405709 5484922 5593788 5645948
5683823 5755999 5928802 5935720 5935721 and 6020078.
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:
CO-1: Aluminum trisoxine [alias, tris(8-quinolinolato)aluminum(III)]
CO-2: Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)]
CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)
CO-4: Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-methyl-8-quinoli
nolato) aluminum(III)
CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]
CO-6: Aluminum tris(5-methyloxine) [alias, tris(5-methyl-8-quinolinolato)
aluminum(III)]
CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]
CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]
CO-9: Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)]
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].
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.
Electron-Transporting Layer (ETL)
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.
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.
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.
Cathode
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.
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.
Deposition of Organic Layers
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.
Optical Optimization
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.
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.
Parts List 10 top-emitting OLED device 12 substrate 13 combined
layer 14 TFT active matrix layer 15 combined layer 16 first insulating
layer 17 second insulating layer 18 first electrode 19B blue-emitting
organic EL element 19G green-emitting organic EL element 19R red-emitting
organic EL element 24 pixel area 24B blue-emitting pixel area 24G
green-emitting pixel area 24R red-emitting pixel area 30 transparent
second electrode 32 protection layer 36 transparent cover 36' transparent
conformable cover 40 desiccant material 40' desiccant seal material
103 anode layer 105 hole-injecting layer 107 hole-transporting layer
109 light-emitting layer 111 electron-transporting layer 113 cathode
layer 250 voltage/current source 260 conductive wiring.
|