U.S. patent application number 12/902643 was filed with the patent office on 2011-02-03 for inverted bottom-emitting oled device.
Invention is credited to Peter J. Cowdery-Corvan, Therese M. Feller, Lee W. Tutt.
Application Number | 20110024770 12/902643 |
Document ID | / |
Family ID | 42666740 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110024770 |
Kind Code |
A1 |
Tutt; Lee W. ; et
al. |
February 3, 2011 |
Inverted Bottom-Emitting OLED Device
Abstract
A method of making an inverted bottom-emitting OLED device,
comprising: providing a substrate; providing one or more first
electrodes driven by n-type transistors on the substrate; providing
an electron-transporting layer over the substrate and first
electrode(s), wherein the electron-transporting layer comprises an
n-type inorganic semiconductive material with a resistivity in the
range of 1 to 10.sup.5 ohm-cm and a bandgap greater than 2.5 eV;
providing an organic light-emitting layer over the
electron-transporting layer; providing a hole-transporting layer
over the organic emitting layer; and providing a second electrode
over the hole-transporting layer.
Inventors: |
Tutt; Lee W.; (Webster,
NY) ; Feller; Therese M.; (Rochester, NY) ;
Cowdery-Corvan; Peter J.; (Webster, NY) |
Correspondence
Address: |
MCKENNA LONG & ALDRIDGE LLP
1900 K STREET, NW
WASHINGTON
DC
20006
US
|
Family ID: |
42666740 |
Appl. No.: |
12/902643 |
Filed: |
October 12, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12394077 |
Feb 27, 2009 |
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12902643 |
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Current U.S.
Class: |
257/79 ;
257/E51.018 |
Current CPC
Class: |
H01L 27/3262 20130101;
H01L 51/5048 20130101; H01L 51/005 20130101 |
Class at
Publication: |
257/79 ;
257/E51.018 |
International
Class: |
H01L 51/50 20060101
H01L051/50 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. An inverted bottom-emitting OLED device, comprising: a. a
substrate; b. one or more first electrodes driven by n-type
transistors on the substrate; c. an electron-transporting layer
over the substrate and first electrode(s), wherein the
electron-transporting layer comprises an n-type inorganic
semiconductive material with a resistivity in the range of 1 to
10.sup.5 ohm-cm and a bandgap greater than 2.5 eV; d. an organic
light-emitting layer over the electron-transporting layer; e. a
hole-transporting layer over the organic emitting layer; and f. a
second electrode over the hole-transporting layer.
11. The device of claim 10 wherein the one or more first electrodes
are cathodes and the second electrode is an anode.
12. (canceled)
13. (canceled)
14. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to forming an OLED device with
efficient electron transport.
BACKGROUND OF THE INVENTION
[0002] Organic electroluminescent (EL) devices are known to be
highly efficient and are capable of producing a wide range of
colors. Useful applications such as flat-panel displays have been
contemplated. Representative of earlier organic EL devices are
Gurnee et al U.S. Pat. No. 3,172,862; Gurnee U.S. Pat. No.
3,173,050; Dresner, "Double Injection Electroluminescence in
Anthracene," RCA Review, Vol. 30, pp. 322-334, 1969; and Dresner
U.S. Pat. No. 3,710,167. Typical organic emitting materials were
formed of a conjugated organic host material and a conjugated
organic activating agent having condensed benzene rings. The
organic emitting material was present as a single layer medium
having a thickness much above 1 micrometer. Thus, this organic EL
medium was highly resistive and the EL device required an extremely
high voltage (>100 volts) to operate.
[0003] More recent discoveries in organic EL device construction
have resulted in devices having the organic EL medium consisting of
extremely thin layers (<1.0 micrometer in combined thickness)
separating the anode and cathode. The thin organic EL medium offers
reduced resistance, permitting higher current densities for a given
voltage. In a basic two-layer EL device structure, one organic
layer is chosen to inject and transport holes and the other organic
layer is chosen to inject and transport electrons. The interface
between the two layers provides an efficient site for the
recombination of the injected hole-electron pair and resultant
electroluminescence. Examples are provided by U.S. Pat. Nos.
4,356,429; 4,539,507; 4,720,432; 4,885,211; 4,950,950; 5,047,687;
5,059,861; 5,061,569; 5,073,446; 5,141,671; 5,150,006 and
5,151,629.
[0004] The simple structure can be modified to a three-layer
structure, in which an additional luminescent layer is introduced
between the hole- and electron-transporting layers to function
primarily as the site for hole-electron recombination and thus
electroluminescence. In this respect, the functions of the
individual organic layers are distinct and can therefore be
optimized independently. Thus, the luminescent or recombination
layer can be chosen to have a desirable EL color as well as a high
luminance efficiency. Likewise, the electron- and hole-transporting
layers can be optimized primarily for the carrier transporting
property.
[0005] One inherent drawback of the organic EL devices is that
electron mobility in organic materials is extremely low, so that a
high voltage is required to produce a strong electric field. For
instance, the electron mobility in tris(8-quinolinolato)aluminum
(Alq) is in the range of 10.sup.-6-10.sup.-7 cm.sup.2/VS, and thus
a field of 1.times.10.sup.6 V/cm is necessary for efficient
electron transport. The thickness of the organic medium can be
reduced to lower the voltage level required for device operation,
but the reduction results in low quantum efficiency due to
radiative quenching by a conducting surface, high leakage current,
or device shorting.
[0006] In the simplest form, an organic electroluminescent (EL)
device is comprised of organic electroluminescent media disposed
between first and second electrodes. The first and second
electrodes serve as an anode for hole injection and a cathode for
electron injection. The organic electroluminescent media supports
recombination of holes and electrons that yield emissions of light.
These devices are also commonly referred to as organic
light-emitting diodes, or OLEDs. A basic organic EL element is
described in U.S. Pat. No. 4,356,429. In order to construct a
pixilated OLED display device that is useful as a display such as,
for example, a television, computer monitor, cell phone display, or
digital camera display, individual organic EL elements can be
arranged as pixels in a matrix pattern. These pixels can all be
made to emit the same color, thereby producing a monochromatic
display, or they can be made to produce multiple colors such as a
three-pixel red, green, blue (RGB) display. For purposes of this
disclosure, a pixel is considered the smallest individual unit,
which can be independently stimulated to produce light. As such,
the red pixel, the green pixel, and the blue pixel are considered
as three distinct pixels.
[0007] OLED devices are typically formed as a layered structure
with the anode closest to the substrate and the cathode as the
outermost active layer. In this configuration, holes flow away from
the substrate while electrons flow toward the substrate.
Transistors to drive such a device are typically connected to the
anodes, which means that high voltage is necessary, e.g. provided
by p-type transistors. This is not the desired current direction if
one wishes to drive the display by n-type semiconductors.
[0008] Zinc oxide has been shown to be useful as a transparent
conductive electrode for OLED devices. Bolink et al. in Applied
Physics Letter, 91, 223501 (2007), showed it can be used as the
cathode material for a polymer single component emissive layer.
Conductivity of the zinc oxide is paramount when used as a cathode.
Therefore, doping of the zinc oxide must be high enough that the
material acts as a metal, giving a uniform conduction both
laterally and vertically.
[0009] In U.S. Pat. No. 6,069,442, Hung et al. used zinc oxide as
an electron-transporting layer (ETL) in a typical OLED structure.
The resistivity was in the range of 1 to 10.sup.5 ohm-cm indicating
it was acting more as a semiconductor and an ETL than as a cathode.
In Hung's examples, the metal oxide was coated on top of the
organic materials before application of the cathode. A problem with
this approach is that the organic materials tend to be very fragile
and reactive, and can therefore be damaged by the conditions
necessary to apply zinc oxide.
SUMMARY OF THE INVENTION
[0010] There is a need for a simplified OLED device wherein a
stable substrate can be premanufactured and not be reactive with
the organics while also being more suitable for integration with
n-type semiconductors such as zinc oxide and amorphous silicon
transistors.
[0011] This object is achieved by a method of making an inverted
bottom-emitting OLED device, comprising:
[0012] a. providing a substrate;
[0013] b. providing one or more first electrodes activated by
N-type transistors on the substrate;
[0014] c. providing an electron-transporting layer over the
substrate and first electrode(s), wherein the electron-transporting
layer comprises an N-type inorganic semiconductive material with a
resistivity in the range of 1 to 10.sup.5 ohm-cm and a bandgap
greater than 2.5 eV;
[0015] d. providing an organic emitting layer over the
electron-transporting layer;
[0016] e. providing a hole-transporting layer over the organic
emitting layer; and
[0017] f. providing a second electrode over the hole-transporting
layer.
ADVANTAGES
[0018] It is an advantage of this invention that a device made
thereby exhibits reduced air sensitivity during some of the process
steps, as well as a better n-type semiconductor compatibility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a cross-sectional view of a prior art OLED
device;
[0020] FIG. 2 shows a block diagram of the method of making an
inverted bottom-emitting OLED device according to this
invention;
[0021] FIG. 3 shows a cross-sectional view of one embodiment of an
inverted OLED device prepared according to the method of this
invention; and
[0022] FIG. 4 shows a cross-sectional view of another embodiment of
an inverted OLED device prepared according to the method of this
invention.
[0023] Since feature dimensions such as layer thicknesses are
frequently in sub-micrometer ranges, the drawings are scaled for
ease of visualization rather than dimensional accuracy.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Turning now to FIG. 1, there is shown a cross-sectional view
of a typical prior-art OLED device 200 on a substrate 170.
Electron-injecting layer (EIL) 110 injects electrons from cathode
100 to electron-transporting layer (ETL) 120. The ETL transports
the electrons into light-emitting layer 130. On the other side,
hole-injecting layer (HIL) 150 generates holes by donating an
electron into anode 160 and injecting the hole into
hole-transporting layer (HTL) 140. The HTL transports the holes to
the light-emitting layer. In light-emitting layer 130, the hole and
electron combine to yield an exciton which can be captured by a
dopant or host and can release the energy as either a photon or as
heat. However, it is well-known that OLED device 200 is most
efficient with p-type transistors when driving and controlling this
device from the substrate side. It is often desirable to use n-type
transistors, and thus a device of this structure is not well-suited
for such an application.
[0025] Turning now to FIG. 2, there is shown a block diagram of the
method of making an inverted bottom-emitting OLED device according
to this invention. At the start of method 300, a substrate is
provided (Step 310). One or more first electrodes are provided over
the substrate (Step 320) and an inorganic electron-transporting
layer comprising an n-type inorganic semiconductive material is
provided over the substrate and first electrode(s) (Step 330). The
first electrodes can be driven by n-type transistors. The n-type
inorganic semiconductive material can be deposited by means of
atomic-layer deposition, usefully at a temperature greater than
150.degree. C. At this point, it is possible to remove the
partially-completed OLED device, if desired or convenient for the
manufacturing process, from the manufacturing apparatus and even
expose the partially-completed device to air with no negative
effects (Step 340). Thus, the n-type semiconductive material
deposition can be completed in a first manufacturing process, and
subsequent steps (described below) can be performed in a second
manufacturing process at a later time or in another location. With
most OLED device manufacturing processes, the device must be kept
in a vacuum during the entire process as exposing a
partially-completed device to air or moisture at any step in the
process can render the device useless. Thus, it is en advantage of
the present invention that is provides additional options in the
manufacturing process.
[0026] Next, after reintroducing the partially-completed device to
vacuum, the device is provided with an organic light-emitting layer
(Step 350), a hole-transporting layer (Step 360) and a second
electrode (Step 370). The latter steps are all performed in a
vacuum. The device can then be sealed, after which it can again be
exposed to the air. Further details of the individual layers will
be discussed below.
[0027] Turning now to FIG. 3, there is shown a cross-sectional view
of one embodiment of an inverted OLED device prepared according to
the method of this invention. Inverted OLED device 220 comprises
substrate 170, a first electrode, e.g. cathode 100, a second
electrode, e.g. anode 160, and emissive layers 230 between the
electrodes. Emissive layers 230 include inorganic
electron-transporting layer 180, light-emitting layer 130, and
hole-transporting layer 140. Light-emitting layer 130 serves as the
recombination layer where holes and electrons recombine. In the
present invention both hole-transporting layer 140 and
light-emitting layer 130 are formed of organic materials, while
electron-transporting layer 180 is formed of inorganic materials.
Electron-transporting layer 180 is formed before light-emitting
layer 130. The anode and the cathode are connected to an external
AC or DC power source (not shown). The power source can be pulsed,
periodic, or continuous.
[0028] In operation, inverted OLED device 220 can be viewed as a
diode which is forward biased when the anode 160 is at a higher
potential than the cathode 100. Under these conditions, holes
(positive charge carriers) are injected from the anode into
hole-transporting layer 140, and electrons are injected into
electron-transporting layer 180. The injected holes and electrons
migrate toward the oppositely charged electrode. This results in
hole-electron recombination and a release of energy in part as
light, thus producing electroluminescence.
[0029] Devices often have a common top electrode and only vary the
potential on the bottom electrode. This is because the top
electrode is difficult to pattern by anything other than a shadow
mask without damaging the organic materials. It is well known that
the organic materials are sensitive to oxygen and water, and ion
bombardment, temperature, and other chemically reactive species can
also do damage.
[0030] Substrate 170 for inverted OLED device 220 is electrically
insulating and light transparent. The light-transparency property
is desirable for viewing the EL emission through the substrate.
Transparent glass or plastic is commonly employed in such cases.
One useful embodiment in this invention is a glass substrate coated
with a layer of semiconductor material, e.g. amorphous silicon
(a-Si) that can be patterned into an array of n-type transistors
for driving an active-matrix display.
[0031] A first electrode, e.g. cathode 100, is formed over
substrate 170. As light emission is viewed through the cathode 100
and substrate 170, the cathode 100 must be transparent or nearly
transparent. For such applications, metals must be thin or one must
use transparent conductive oxides such as indium tin oxide or tin
oxide, as disclosed by Gurnee et al. in U.S. Pat. No. 3,172,862,
Gurnee in U.S. Pat. No. 3,173,050, Dresner in "Double Injection
Electroluminescence in Anthracene", RCA Review, Volume 30, pages
322-334, 1969; and Dresner in U.S. Pat. No. 3,710,167, or a
combination of these materials. Optically transparent cathodes have
been described in more detail in U.S. Pat. No. 5,776,623. Cathode
materials can be 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.
5,276,380 and EP 0 732 868, laser ablation, and selective chemical
vapor deposition.
[0032] Inorganic electron-transporting layer 180 is an essential
part of this invention. Preferred materials for use in forming the
electron-transporting layer are inorganic n-type semiconductive
materials. The materials should have a resistivity in the range of
1 to 10.sup.5 ohm-cm, be transmissive or semi-transmissive to
visible light, and be inert with respect to the organic luminescent
layer. For transmissivity to visible light, it is desirable that
the material have a bandgap greater than 2.5 eV.
[0033] An important relationship for choosing an inorganic n-type
semiconductive material to form the electron-transporting layer
adjacent to an organic luminescent layer (e.g. light-emitting layer
130) is the comparison of the electron affinity of the inorganic
material and the energy level of the lowest unoccupied molecular
orbital (E.sub.LUMO) of the organic material. The electron affinity
should not be greater than the E.sub.LUMO) by 1.5 eV in order to
achieve efficient electron transport.
[0034] The inorganic n-type semiconductive materials can be a metal
oxide, metal nitride, zinc sulfide, or zinc selenide. For those
materials, the electron mobility is several orders of magnitude
greater than that of organic materials, and the resistivity can be
readily adjusted by impurity doping or controlling the process
temperature or the ambient atmosphere. Suitable metal oxides
include zinc oxide and indium oxide. Other materials can be
titanium oxide, strontium titanium oxide, barium titanium oxide,
gallium nitride, or indium gallium nitride. Combinations of two or
more of these materials also can be useful.
[0035] The thickness of the inorganic ETL layer is so selected that
it would provide a sufficient space separation between the
luminescent layer and the bottom cathode. A desirable range of the
thickness is from 10 to 2000 nm, usefully 10-500 nm. This inorganic
layer can be deposited by many conventional means, such as
evaporation, atomic-layer deposition, sputtering, laser ablation,
and chemical vapor deposition.
[0036] Light-emitting layer 130 of inverted OLED device 220 is an
organic light-emitting layer and comprises a luminescent or
fluorescent material where electroluminescence is produced as a
result of electron-hole pair recombination in this region. In the
simplest construction, the luminescent layer comprises of a single
component, that is a pure material with a high fluorescent
efficiency. A well known material is tris(8-quinolinato)aluminum
(Alq), which produces excellent green electroluminescence. A useful
embodiment of the light-emitting layer comprises a multi-component
material with a host material doped with one or more components of
fluorescent dyes. Using this method, highly efficient OLED devices
can be constructed. Simultaneously, the color of the OLED devices
can be tuned by using fluorescent dyes of different emission
wavelengths in a common host material. This dopant scheme has been
described in considerable details for OLED devices using Alq as the
host material by Tang et al. [J. Applied Physics, Vol. 65, Pages
3610-3616, 1989; U.S. Pat. No. 4,769,292].
[0037] Hole-transporting layer 140 of inverted OLED device 220
contains at least one hole-transporting aromatic tertiary amine,
where the latter is understood to be a compound that has at least
one trivalent nitrogen atom 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
monarylamine, diarylamine, triarylamine, or a polymeric arylamine.
Exemplary monomeric triarylamines are illustrated by Klupfel at al.
in U.S. Pat. No. 3,180,730. Other suitable triarylamines
substituted with vinyl or vinyl radicals and/or containing at least
one active hydrogen containing group are disclosed by Brantley at
al. in U.S. Pat. Nos. 3,567,450 and 3,658,520.
[0038] A second electrode, e.g. anode 160, is formed over
hole-transporting layer 140. As EL emission is viewed through the
bottom electrode, the transmissive characteristics of the anode
material 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. The anode can have multiple
layers to allow better conductivity. For example, silver can be
applied for good reflectivity but be backed with aluminum to
provide further conduction and prevent tarnishing. The preferred
anode materials, transmissive or otherwise, have a work function of
4.1 eV or greater. Desired anode materials can be deposited by any
suitable means such as evaporation, sputtering chemical vapor
deposition, or electrochemical means.
[0039] Turning now to FIG. 4, there is shown a cross-sectional view
of another embodiment of an inverted OLED device prepared according
to the method of this invention. Inverted OLED device 250 includes
the features of inverted OLED device 220 described above, as well
as some additional optional layers. Inverted OLED device 250 can
include active matrix control circuitry. Active matrix layer 190
contains all the layers necessary to form an active matrix,
including metals, semiconductors, insulators, and leveling
materials. In such a structure, active matrix layer 190 presents a
plurality of individually controlled areas, or pixels, in inverted
OLED device 250. In this structure, cathode 100 will in actuality
be a plurality of cathodes, while anode 160 will be common to the
entire device. The transistors formed in active matrix layer 190,
which drive the device through cathodes 100, are n-type
transistors. They can be made from an n-type inorganic
semiconductive material, e.g. amorphous silicon or zinc oxide, and
can be of the same material used in electron-transporting layer
180, or a different material. If the transistors are made from a
wide bandgap material such as zinc oxide, and the metal electrodes
are formed from a transparent metal such as ITO, then the
transistors can be directly under the OLED device for
through-substrate viewing. Otherwise the active matrix will need to
be beside the OLED devices to provide some aperture through the
substrate.
[0040] Since cathode 100 is the electrode closest to the substrate,
this is the easiest electrode to connect to the drive transistors
of active matrix layer 190. In this configuration, anode 160 can be
common to an entire display. By pulling the cathode to ground and
providing a positive voltage on the anode, one can easily drive the
OLED. This requires n-type transistors for adequate performance.
Both zinc oxide and amorphous silicon are n-type semiconductors and
therefore will work well as n-type transistors.
[0041] Electron injecting layer 110, if present, should be an
inorganic material such that the electrons are efficiently injected
into the electron-transporting material, which is an inorganic
oxide. Examples of this are alkali or alkaline fluorides, which
include lithium fluoride, sodium fluoride, potassium fluoride,
rubidium fluoride, cesium fluoride, magnesium fluoride, calcium
fluoride, strontium fluoride and barium fluoride.
[0042] Holo-injecting layer 150 can also be present to aid in the
injection of holes from the anode to the hole-transporting layer.
Examples of hole-injecting materials are molybdenum oxide and
hexacyanohexaazatriphenylene. Other HIL materials are porphyrinic
compounds. A porphyrinic compound is any compound, natural or
synthetic, which is derived from or includes a porphyrin structure,
including porphine itself. Any of the porphyrinic compounds
disclosed by Adler in U.S. Pat. No. 3,935,031 or Tang in U.S. Pat.
No. 4,356,429, the disclosures of which are here incorporated by
reference, can be employed. Other HIL materials are presented in EP
0 891 121 A1 and EP 1 029 909 A1 and incorporated by reference.
EXAMPLES
[0043] The glass substrates, precoated with indium tin oxide 40-80
nm in an electrode pattern, were obtained from Polytronix Co.
(Richardson, Tex.). In all cases, the ZnO was deposited by a
spatial atomic-layer deposition head as described in U.S. Pat. No.
7,413,892 and U.S. Patent Application 2007/0238311 A1 using diethyl
zinc and ammoniated water as the two gasses, separated by a
nitrogen purge. The substrate was heated to 200.degree. C. and the
head oscillated over the surface at a rate of approximately 1 cycle
per second, which yielded a growth rate of 0.3 nm per cycle. A
sheet resistivity of >1 Meg ohms/square and thickness of 40 mm
(resistivity of >4 ohm-cm) was obtained after 133 cycles.
Example 1
Comparative
[0044] An OLED device was constructed in the following manner:
[0045] 1. A clean glass substrate with an ITO pattern was placed in
a vacuum chamber and evacuated to 5.times.10.sup.-6 torr. [0046] 2.
The above-prepared substrate was treated by vacuum depositing a 60
nm including 94% 2-phenyl-9,10-bis(2-naphthyl)anthracene (PBNA) as
host with 2%
4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-
-4H-pyran (DCJTB, a red dopant) as a light-emitting layer. [0047]
3. The above-prepared substrate was further treated by
vacuum-depositing a 120 nm layer of
4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) as a
hole-transporting layer. [0048] 4. The above-prepared substrate was
further treated by vacuum-depositing a 10 nm layer of
hexacyanohexaazatriphenylene (CHATP) as a hole-injecting layer
(HIL).
[0048] ##STR00001## [0049] 5. A 60 nm silver anode layer was
deposited onto the sample by vacuum evaporation.
Example 2
Inventive
[0050] An OLED device was constructed as described in Example 1,
except that the following step was added between Steps 1 and 2:
[0051] 1a. A 40 nm layer of unpatterned ZnO was deposited uniformly
on the substrate.
[0052] After deposition, a positive voltage was applied to the top
(anode) electrode and a negative voltage to the bottom (cathode)
electrode at a constant current of 20 ma/cm.sup.2. Any spectral
output was measured. Example 1, the comparative example did not
emit. Inventive Example 2 emitted orange light with a spectral
maximum at 593 nm wavelength and a luminance of 61 candela/m.sup.2.
This shows that the zinc oxide layer, which is an
electron-transporting layer, enables this device to function.
Example 3
Comparative
[0053] An OLED device was constructed in the following manner:
[0054] 1. A clean glass substrate with an ITO pattern was placed in
a vacuum chamber and evacuated to 5.times.10.sup.-6 torr. [0055] 2.
The above-prepared substrate was treated by vacuum depositing a 40
nm PBNA layer with 0.75% green-emitting dopant GED-1 as a
light-emitting layer.
[0055] ##STR00002## [0056] 3. The above-prepared substrate was
further treated by vacuum-depositing a 75 nm layer of NPB as a
hole-transporting layer. [0057] 4. A 10 nm hole-injecting layer of
CHATP was vacuum-deposited onto the substrate at a coating station.
[0058] 5. A 40 nm silver anode layer was deposited onto the sample
by vacuum evaporation. [0059] 6. A 30 nm aluminum conductive
protective layer was deposited onto the sample by vacuum
evaporation.
Example 4
Inventive
[0060] An OLED device was constructed as described in Example 3,
except that the following step was added between Steps 1 and 2:
[0061] 1a. A 40 nm layer of unpatterned ZnO was deposited uniformly
on the substrate. The sample was briefly dipped in deionized water
and then dried before placing in a vacuum chamber.
[0062] After deposition, a positive voltage was applied to the top
(anode) electrode and a negative voltage to the bottom (cathode)
electrode at a constant current of 20 ma/cm.sup.2. Any spectral
output was measured. Example 3, the comparative example, did not
emit. Inventive Example 4 emitted green light with a spectral
maximum at 535 nm wavelength and a luminance of 2800
candela/m.sup.2. Example 4 shows the robustness of the completed
device to humidity exposure of the intermediate inorganic coated
portion of the OLED. This allows one to premanufacture a substrate
with active matrix electronics and an electron-transporting layer,
and store it without extraordinary precautions against air or
moisture, for later addition of the organic moisture- and
temperature-sensitive organic materials. This is a distinct
advantage over prior-art inverted OLED devices, which utilized a
moisture-sensitive organic electron-transporting layer. Such prior
art devices required that the electron-transporting layer be
manufactured together with the remainder of the OLED device.
Example 5
Comparative
[0063] An OLED device was constructed in the following manner:
[0064] 1. A clean glass substrate with an ITO pattern was placed in
a vacuum chamber and evacuated to 5.times.10.sup.-6 torr. [0065] 2.
The above-prepared substrate was treated by vacuum depositing a 40
nm PNBA layer with 1% tetra-t-butylperylene (TBP) as a blue
light-emitting layer. [0066] 3. The above-prepared substrate was
treated by vacuum depositing a 20 nm NPB layer with 1%
yellow-orange emitting dopant diphenyltetra-t-butylrubrene (PTBR)
as a yellow light-emitting layer.
[0066] ##STR00003## [0067] 4. The above-prepared substrate was
further treated by vacuum-depositing a 40 nm layer of NPB as a
hole-transporting layer. [0068] 5. A 10 nm hole-injecting layer of
CHATP was vacuum-deposited onto the substrate at a coating station.
[0069] 6. A 100 nm silver anode layer was deposited onto the sample
by vacuum evaporation.
Example 6
Inventive
[0070] An OLED device was constructed as described in Example 5,
except that the following step was added between Steps 1 and 2:
[0071] 1a. A 40 nm layer of unpatterned ZnO was deposited uniformly
on the substrate.
[0072] After deposition, a positive voltage was applied to the top
(anode) electrode and a negative voltage to the bottom (cathode)
electrode at a constant current of 20 ma/cm.sup.2. Any spectral
output was measured. Example 5, the comparative example, did not
emit. Inventive Example 6 shows the use of a double emission layer,
which provides multiple emission peaks, with the inorganic
electron-transporting layer. Example 6 emitted a color of about
0.46 CIEx, 0.46 CIEy, which is an approximation of white, at 20
ma/cm.sup.2 and a luminance of 137 candela/m.sup.2.
[0073] 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. For example, the electron
transporting layer can be a single inorganic layer or an inorganic
layer with another underlying organic layer.
PARTS LIST
[0074] 100 cathode [0075] 110 electron-injecting layer [0076] 120
electron-transporting layer [0077] 130 light-emitting layer [0078]
140 hole-transporting layer [0079] 150 hole-injecting layer [0080]
160 anode [0081] 170 substrate [0082] 180 inorganic
electron-transporting layer [0083] 190 active matrix layer [0084]
200 OLED device [0085] 220 inverted OLED device [0086] 230 emissive
layers [0087] 250 inverted OLED device [0088] 300 method [0089] 310
step [0090] 320 step [0091] 330 step [0092] 340 step [0093] 350
step [0094] 360 step [0095] 370 step
* * * * *