U.S. patent application number 14/689582 was filed with the patent office on 2015-08-06 for electroluminescent device with quinazoline complex emitter.
The applicant listed for this patent is Global OLED Technology LLC. Invention is credited to Joseph C. DEATON, Barbara B. LUSSIER.
Application Number | 20150221880 14/689582 |
Document ID | / |
Family ID | 37673186 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150221880 |
Kind Code |
A1 |
DEATON; Joseph C. ; et
al. |
August 6, 2015 |
ELECTROLUMINESCENT DEVICE WITH QUINAZOLINE COMPLEX EMITTER
Abstract
An OLED device comprises a cathode, an anode, and located
therebetween a light-emitting layer containing a host material and
a tris-C N-cyclometallated complex of Ir or Rh wherein at least one
of the ligands comprises a substituted quinazoline moiety. The
device provides useful emission and stability attributes.
Inventors: |
DEATON; Joseph C.; (Apex,
NC) ; LUSSIER; Barbara B.; (Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Global OLED Technology LLC |
Herndon |
VA |
US |
|
|
Family ID: |
37673186 |
Appl. No.: |
14/689582 |
Filed: |
April 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11289023 |
Nov 29, 2005 |
9040170 |
|
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14689582 |
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Current U.S.
Class: |
257/40 ;
544/225 |
Current CPC
Class: |
H05B 33/14 20130101;
H01L 51/5092 20130101; C09K 2211/1044 20130101; H01L 51/5221
20130101; H01L 51/5016 20130101; H01L 51/5096 20130101; C07F
15/0073 20130101; H01L 51/0084 20130101; H01L 51/5088 20130101;
H01L 51/506 20130101; C09K 2211/185 20130101; C07F 15/0033
20130101; H01L 51/5004 20130101; H01L 2251/308 20130101; H01L
51/5206 20130101; H01L 51/5076 20130101; H01L 51/0085 20130101;
C09K 11/06 20130101 |
International
Class: |
H01L 51/00 20060101
H01L051/00; C07F 15/00 20060101 C07F015/00 |
Claims
1. An OLED device comprising a cathode, an anode, and located
therebetween a light-emitting layer containing a) a tris-C
N-cyclometallated complex represented by Formula (2c) ##STR00064##
wherein: each d.sup.1 represents an independently selected
substituent and s is 0-4; each d.sup.2 represents an independently
selected substituent and t is 0-4; and d.sup.3 represents hydrogen
or a substituent; b) an electron-transporting host material, and c)
a hole-transporting host material.
2. The OLED device of claim 1, wherein the electron-transporting
host is a complex represented by Formula (PH-10) ##STR00065##
3. The OLED device of claim 1, wherein the hole-transporting host
is N,N'-di-1-naphthalenyl-N,N'-diphenyl-4,4'-diaminobiphenyl.
4. The OLED device of claim 1, wherein the tris-C N-cyclometallated
complex is ##STR00066##
5. A tris-C N-cyclometallated complex represented by Formula (2c)
##STR00067## wherein: each d.sup.1 represents an independently
selected substituent and s is 0-4; each d.sup.2 represents an
independently selected substituent and t is 0-4; and d.sup.3
represents hydrogen or a substituent.
6. The tris-C N-cyclometallated complex ##STR00068##
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent is a continuation of commonly assigned,
co-pending U.S. Ser. No. 11/289,023, filed Nov. 29, 2005, and
published as U.S. 2007/0122655, which is incorporated herein by
reference.
[0002] Reference is made to commonly assigned U.S. patent
applications U.S. Ser. No. 10/945,337 filed Sep. 20, 2004 (now
abandoned); U.S. Ser. No. 11/016,134 filed Dec. 17, 2004 (now U.S.
Pat. No. 7,579,090); U.S. Ser. No. 10/945,338 filed Sep. 20, 2004
(now abandoned); U.S. Ser. No. 11/015,929 filed Dec. 17, 2004 (now
U.S. Pat. No. 7,767,316), and U.S. Ser. No. 11/214,176, filed Aug.
29, 2005 (published as U.S. 2007/0048544).
FIELD OF THE INVENTION
[0003] This invention relates to an organic light-emitting diode
(OLED) electroluminescent (EL) device comprising a light-emitting
layer containing a host material and a phosphorescent
light-emitting material that can provide desirable
electroluminescent properties.
BACKGROUND OF THE INVENTION
[0004] While organic electroluminescent (EL) devices have been
known for over two decades, their performance limitations have
represented a barrier to many desirable applications. In simplest
form, an organic EL device is comprised of an anode for hole
injection, a cathode for electron injection, and an organic medium
sandwiched between these electrodes to support charge recombination
that yields emission of light. These devices are also commonly
referred to as organic light-emitting diodes, or OLEDs.
Representative of earlier organic EL devices are Gurnee et al. U.S.
Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No.
3,173,050, issued Mar. 9, 1965; Dresner, "Double Injection
Electroluminescence in Anthracene", RCA Review, Vol. 30, pp.
322-334, 1969; and Dresner et al. U.S. Pat. No. 3,710,167, issued
Jan. 9, 1973. The organic layers in these devices, usually composed
of a polycyclic aromatic hydrocarbon, were very thick (much greater
than 1 .mu.m). Consequently, operating voltages were very high,
often >100V.
[0005] More recent organic EL devices include an organic EL element
consisting of extremely thin layers (e.g. <1.0 .mu.m) between
the anode and the cathode. Herein, the term "organic EL element"
encompasses the layers between the anode and cathode electrodes.
Reducing the thickness lowered the resistance of the organic layer
and has enabled devices that operate much lower voltage. In a basic
two-layer EL device structure, described first in U.S. Pat. No.
4,356,429, one organic layer of the EL element adjacent to the
anode is specifically chosen to transport holes, therefore, it is
referred to as the hole-transporting layer, and the other organic
layer is specifically chosen to transport electrons, referred to as
the electron-transporting layer. Recombination of the injected
holes and electrons within the organic EL element results in
efficient electroluminescence.
[0006] There have also been proposed three-layer organic EL devices
that contain an organic light-emitting layer (LEL) between the
hole-transporting layer and electron-transporting layer, such as
that disclosed by Tang et al. [J. Applied Physics, Vol. 65, pp.
3610-3616, 1989]. The light-emitting layer commonly consists of a
host material doped with a guest material. Still further, there has
been proposed in U.S. Pat. No. 4,769,292 a four-layer EL element
comprising a hole-injecting layer (HIL), a hole-transporting layer
(HTL), a light-emitting layer (LEL) and an electron
transport/injection layer (ETL). These structures have resulted in
improved device efficiency.
[0007] Many emitting materials that have been described as useful
in an OLED device emit light from their excited singlet state by
fluorescence. The excited singlet state is created when excitons
formed in an OLED device transfer their energy to the excited state
of the dopant. However, it is generally believed that only 25% of
the excitons created in an EL device are singlet excitons. The
remaining excitons are triplet, which cannot readily transfer their
energy to the singlet-excited state of a dopant. This results in a
large loss in efficiency since 75% of the excitons are not used in
the light emission process.
[0008] Triplet excitons can transfer their energy to a dopant if it
has a triplet excited state that is low enough in energy. If the
triplet state of the dopant is emissive, it can produce light by
phosphorescence. In many cases, singlet excitons can also transfer
their energy to lowest singlet excited state of the same dopant.
The singlet excited state can often relax, by an intersystem
crossing process, to the emissive triplet excited state. Thus, it
is possible, by the proper choice of host and dopant, to collect
energy from both the singlet and triplet excitons created in an
OLED device and to produce a very efficient phosphorescent
emission.
[0009] Singlet and triplet states, fluorescence, phosphorescence,
and intersystem crossing are discussed in J. G. Calvert and J. N.
Pitts, Jr., Photochemistry (Wiley, New York, 1966). Emission from
triplet states is generally very weak for most organic compounds
because the transition from triplet-excited state to singlet ground
state is spin-forbidden. However, it is possible for compounds with
states possessing a strong spin-orbit coupling interaction to emit
strongly from triplet-excited states to the singlet ground state
(phosphorescence). One such strongly phosphorescent compound is
fac-tris(2-phenyl-pyridinato-N C-)Iridium(III) (Ir(ppy).sub.3) that
emits green light (K. A. King, P. J. Spellane, and R. J. Watts, J.
Am. Chem. Soc., 107, 1431 (1985), M. G. Colombo, T. C. Brunold, T.
Reidener, H. U. Giidel, M. Fortsch, and H.-B. Burgi, Inorg. Chem.,
33, 545 (1994)). Organic electroluminescent devices having high
efficiency have been demonstrated with Ir(ppy).sub.3 as the
phosphorescent material and 4,4'-N,N'-dicarbazole-biphenyl (CBP) as
the host (M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson,
S. R. Forrest, Appl. Phys. Lett., 75, 4 (1999), T. Tsutsui, M.-J.
Yang, M. Yahiro, K. Nakamura, T. Watanabe, T. Tsuji, Y. Fukuda, T.
Wakimoto, S. Miyaguchi, Jpn. J. Appl. Phys., 38, L1502 (1999)).
Additional disclosures of phosphorescent materials and organic
electroluminescent devices employing these materials are found in
U.S. Pat. No. 6,303,238 B1, WO 00/57676, WO 00/70655, and WO
01/41512 A1.
[0010] There is a continuing need to develop new phosphorescent
materials for improved stability and to provide a wide range of
hues. S. Seo and co-workers, SID 05 Digest, 806 (2005), Y. Chi et
al., Inorg. Chem., 44, 1344 (2005), C. Chen et al., Adv. Funct.
Mater., 14, 1221 (2004), and C. Cheng et al., Adv. Mater., 15, 224
(2003) describe iridium complexes that include two C
N-cyclometallated quinazoline ligands and one ancillary ligand. The
ancillary ligand is an anionic bidentate ligand that does not
provide a carbon bonded to Ir. Although these materials are
reported to have interesting properties it is generally the case
that bis-cyclometallated metal complexes, although easier to
synthesize, are less stable relative to tris-C N-cyclometallated
metal complexes.
[0011] Fujii et al, U.S. 2005/0191527, describes organometallic
compounds with quinoxaline ligands including tris-C
N-cyclometallated complexes of iridium. Mishima et al., U.S.
2005/0191519, describes triplet emitters with various heterocyclic
ligands. Some of these complexes are also tris-C N-cyclometallated
complexes of iridium, although none of the tris-C N-cyclometallated
complexes include a quinazoline ligand. However, many of the
materials described in these disclosures emit at wavelengths that
are too deep to be useful in a practical OLED device.
[0012] The nature of the host material is also critical to get good
performance from the phosphorescent emitter. For example, U.S. Ser.
Nos. 10/945,337 and 10/945,338 filed Sep. 20, 2004 (both now
abandoned), and U.S. Ser. Nos. 11/015,929 and 11/016,134 filed Dec.
17, 2004 (now U.S. Pat. Nos. 7,767,316 and 7,579,090 respectively),
describe an EL device in which the light-emitting layer includes a
hole-transporting compound, certain aluminum chelate materials, and
a light-emitting phosphorescent compound. U.S. Ser. No. 11/214,176
filed Aug. 29, 2005 (published as U.S. 2007/0048544), describes an
EL device in which the light-emitting layer includes a
hole-transporting compound, certain gallium chelate materials, and
a light-emitting phosphorescent compound.
[0013] Notwithstanding these developments, there remains a need for
new phosphorescent materials to provide useful emission and
stability attributes
SUMMARY OF THE INVENTION
[0014] The invention provides an OLED device that comprises a
cathode, an anode, and located therebetween a light-emitting layer
containing a host material and a tris-C N-cyclometallated complex
of Ir or Rh wherein at least one of the ligands comprises a
substituted quinazoline moiety. The device provides useful emission
and stability attributes.
BRIEF DESCRIPTION OF THE DRAWING
[0015] The FIGURE shows a schematic cross-sectional view of one
embodiment of the device of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The organic light-emitting device (OLED) of the invention
contains a cathode, a light-emitting layer, and an anode as
described above. The light-emitting layer includes a host material
and a tris-C N-cyclometallated complex of Ir or Rh wherein at least
one of the ligands comprises a substituted quinazoline moiety. A
quinazoline nucleus and its ring-numbering is shown below.
##STR00001##
[0017] Desirably, the metal forms a nitrogen-metal bond with one
nitrogen of the quinazoline nucleus, and forms a carbon-metal bond
with a substituent on the quinazoline nucleus. Suitably, the
substituent is at the 2 or the 4 position and includes at least one
carbon-carbon double bond, and the metal is bonded to one carbon of
the double bond. Desirably the substituent is an aromatic group,
such as a phenyl group, naphthyl group, or thienyl group.
[0018] The metal is Ir or Rh. Desirably the metal is Ir. In one
embodiment the complex includes three independently selected
substituted quinazoline moieties, and the metal is bonded to each
of these moieties as described above.
[0019] In another embodiment, the substituted quinazoline moiety is
a 2-phenylquinazoline group or a 4-phenylquinazoline group. In a
similar embodiment, the complex includes three independently
selected 2-phenylquinazoline groups or 4-phenylquinazoline
groups.
[0020] The tris-C N-cyclometallated complex may be a facial or a
meridional isomer. Desirably the complex is a facial isomer, since
they are often found to have higher emission quantum yield than the
meridional isomer.
[0021] In another aspect of the invention, the tris-C
N-cyclometallated complex is represented by Formula (1a) or Formula
(1b).
##STR00002##
[0022] In Formulae (1a) and (1b), M represents Ir or Rh. Each
R.sup.1-R.sup.7 represents hydrogen or an independently selected
substituent group such as a phenyl group, a methyl group, or a
trifluoromethyl group. Two of R.sup.1-R.sup.7 may combine to form a
ring group, such as a fused benzene ring group. In one desirable
embodiment R.sup.6 and R.sup.7 combine to form an aromatic group,
such as a benzene group or thiophene group. In another embodiment,
two of R.sup.1-R.sup.5 do not combine to form a fused ring, and
thus the quinazoline nucleus does not have additional fused
rings.
[0023] In Formulae (1a) and (1b), A represents a substituted or
unsubstituted heterocyclic ring group containing at least one
nitrogen atom, such as a pyridine ring group, a pyrazole ring
group, an isoquinoline ring group, or a quinoline ring group.
[0024] In the Formulae, B represents a substituted or unsubstituted
aromatic or heteroaromatic ring. Examples of B include a phenyl
ring group, a 4,6-difluorophenyl ring group, and a thienyl ring
group. In one suitable embodiment, B represents an aryl group.
[0025] In the Formulae, m is an integer from 1 to 3; and n is an
integer from 0 to 2 such that m+n=3. In one desirable embodiment, m
is 3 and n is 0.
[0026] In a further aspect of the invention, the metal complex is
represented by Formula (2a) or Formula (2b).
##STR00003##
[0027] In Formulae (2a) and (2b), M and R.sup.1-R.sup.7 have been
described previously. In one desirable embodiment, R.sup.6 and
R.sup.7 combine to form an aromatic ring.
[0028] In a another aspect of the invention, the metal complex is
represented by (2c) or (2d):
##STR00004##
[0029] In Formula (2c) and (2d), each d.sup.1 and each d.sup.2
represent independently selected substituents, such as a phenyl
group or methyl group. Preferably, adjacent substituents do not
combine to form a fused ring.
[0030] In Formula (2c) and (2d), s is 0-4, t is 0-4, and d.sup.3
represents hydrogen or a substituent.
[0031] Tris-C N-cyclometallated complexes of iridium and rhodium
may be synthesized by methods described in the literature. However,
it is often found that many of the methods are not generally
applicable and work for only limited types of C N-cyclometallating
ligands. Through diligent experimentation in the synthetic
methodology for tris-C N-cyclometallating iridium complexes, the
inventors have now found that the method recently disclosed in U.S.
Ser. No. 10/879,657, filed Jun. 29, 2004, now U.S. Pat. No.
7,005,522, results in efficient synthesis of the tris-C
N-cyclometallated complexes of the present invention having ligands
that N-coordinate through quinazoline moieties. For cases of tris-C
N-cyclometallated complexes where the three C N-cyclometallating
ligands are not all the same, the methods described in U.S. Pat.
No. 6,835,835, U.S. Ser. Nos. 11/015,910, 11/134,120 (now U.S. Pat.
Nos. 7,417,146 and 7,476,739 respectively), and U.S. Ser. No.
11/240,288 filed Sep. 30, 2005 (now U.S. Pat. No. 7,517,984) may be
used.
[0032] Illustrative examples of Formula (1) and Formula (2)
compounds are listed below.
##STR00005## ##STR00006## ##STR00007## ##STR00008##
##STR00009##
[0033] The light-emitting layer also includes at least one host
material. Desirably the host material has a triplet energy higher
than or equal to the triplet energy of the metal complex. Triplet
energy is conveniently measured by any of several means, as
discussed for instance in S. L. Murov, I. Carmichael, and G. L.
Hug, Handbook of Photochemistry, 2nd ed. (Marcel Dekker, New York,
1993).
[0034] In the absence of experimental data the triplet energies may
be estimated in the following manner. The triplet state energy for
a molecule is defined as the difference between the ground state
energy (E(gs)) of the molecule and the energy of the lowest triplet
state (E(ts)) of the molecule, both given in eV. These energies can
be calculated using the B3LYP method as implemented in the
Gaussian98 (Gaussian, Inc., Pittsburgh, Pa.) computer program. The
basis set for use with the B3LYP method is defined as follows:
MIDI! for all atoms for which MIDI! is defined, 6-31G* for all
atoms defined in 6-31G* but not in MIDI!, and either the LACV3P or
the LANL2DZ basis set and pseudopotential for atoms not defined in
MIDI! or 6-31G*, with LACV3P being the preferred method. For any
remaining atoms, any published basis set and pseudopotential may be
used. MIDI!, 6-31G* and LANL2DZ are used as implemented in the
Gaussian98 computer code and LACV3P is used as implemented in the
Jaguar 4.1 (Schrodinger, Inc., Portland, Oreg.) computer code. The
energy of each state is computed at the minimum-energy geometry for
that state. The difference in energy between the two states is
further modified by Equation 1 to give the triplet state energy
(E(t)):
E(t)=0.84*(E(ts)-E(gs))+0.35 (1)
[0035] For polymeric or oligomeric materials, it is sufficient to
compute the triplet energy over a monomer or oligomer of sufficient
size so that additional units do not substantially change the
computed triplet energy of the material.
[0036] Suitable host materials should be selected so that the
triplet exciton can be transferred efficiently from the host
material to the phosphorescent material. For this transfer to
occur, it is a highly desirable condition that the excited state
energy of the phosphorescent material be lower than the difference
in energy between the lowest triplet state and the ground state of
the host, although efficient emission has been reported for devices
where the host has a lower triplet energy than the dopant by M. A.
Baldo, M. E. Thompson, S. K. Forrest, and co-workers, Appl. Phys.
Lett., 79, 2082 (2001). However, the band gap of the host should
not be chosen so large as to cause an unacceptable increase in the
drive voltage of the OLED. Suitable host materials are described in
WO 00/70655, WO 01/39234, WO 01/93642, WO 02/074015, WO 02/15645,
and U.S. 2002/0117662. Suitable hosts include certain aryl amines,
triazoles, indoles, and carbazole compounds. Examples of desirable
hosts are 4,4'-N,N'-dicarbazole-biphenyl (CBP),
2,2'-dimethyl-4,4'-N,N'-dicarbazole-biphenyl,
m-(N,N'-dicarbazole)benzene, and poly(N-vinylcarbazole), including
their derivatives. In one embodiment, the host material includes a
carbazole derivative.
[0037] Types of triplet host materials may be categorized according
to their charge transport properties. The two major types are those
that are predominantly electron transporting and those that are
predominantly hole transporting. It should be noted that some host
materials, which may be categorized as transporting dominantly one
type of charge, may transport both types of charges, especially in
certain device structures, for example CBP which is described in C.
Adachi, R. Kwong, and S. R. Forrest, Organic Electronics, 2, 37-43
(2001). Another type of host are those having a wide energy gap
between the HOMO and LUMO, such that they do not readily transport
charges of either type, and instead rely on charge injection
directly into the phosphorescent dopant molecules.
[0038] A desirable electron-transporting host may be any suitable
electron-transporting compound, such as benzazole, phenanthroline,
1,3,4-oxadiazole, triazole, triazine, or triarylborane, as long as
it has a triplet energy that is higher than that of the
phosphorescent emitter to be employed.
[0039] A preferred class of benzazoles is described by Jianmin Shi
et al. in U.S. Pat. Nos. 5,645,948 and 5,766,779. Such compounds
are represented by structural formula (PHF-1):
##STR00010## [0040] In formula (PHF-1),
[0041] n is selected from 2 to 8;
[0042] Z is independently O, NR or S;
[0043] R and R' are individually hydrogen; alkyl of from 1 to 24
carbon atoms, for example, propyl, t-butyl, heptyl, and the like;
aryl or hetero-atom substituted aryl of from 5 to 20 carbon atoms,
for example, phenyl and naphthyl, furyl, thienyl, pyridyl,
quinolinyl, and other heterocyclic systems; or halo such as chloro,
fluoro; or atoms necessary to complete a fused aromatic ring;
and
[0044] X is a linkage unit consisting of carbon, alkyl, aryl,
substituted alkyl, or substituted aryl, which conjugately or
unconjugately connects the multiple benzazoles together.
[0045] An example of a useful benzazole is
2,2',2''-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)
represented by a formula (PHF-2) shown below:
##STR00011##
[0046] Another class of electron-transporting materials suitable
for use as a host includes various substituted phenanthrolines as
represented by formula (PHF-3):
##STR00012##
[0047] In formula (PHF-3), R.sub.1-R.sub.8 are independently
hydrogen, alkyl group, aryl, or substituted aryl group, and at
least one of R.sub.1-R.sub.8 is aryl group or substituted aryl
group.
[0048] Examples of suitable materials are
2,9-dimethyl-4,7-diphenyl-phenanthroline (BCP) (see formula (PH-1))
and 4,7-diphenyl-1,10-phenanthroline (Bphen) (see formula
(PH-2)).
##STR00013##
[0049] A triarylborane that functions as an electron-transporting
host may be selected from compounds having the chemical formula
(PHF-4):
##STR00014##
wherein Ar.sub.1 to Ar.sub.3 are independently an aromatic
hydrocarbocyclic group or an aromatic heterocyclic group, which may
have one or more substituent.
[0050] It is preferable that compounds having the above structure
are selected from formula (PHF-5):
##STR00015##
wherein R.sub.1-R.sub.15 are independently hydrogen, fluoro, cyano,
trifluoromethyl, sulfonyl, alkyl, aryl, or substituted aryl
group.
[0051] Specific representative embodiments of the triarylboranes
include:
##STR00016##
[0052] An electron-transporting host may be selected from
substituted 1,3,4-oxadiazoles. Illustrative of the useful
substituted oxadiazoles are the following:
##STR00017##
[0053] An electron-transporting host may be selected from
substituted 1,2,4-triazoles. An example of a useful triazole is
3-phenyl-4-(1-naphthyl)-5-phenyl-1,2,4-triazole represented by
formula (PHF-6):
##STR00018##
[0054] The electron-transporting host may be selected from
substituted 1,3,5-triazines. Examples of suitable materials are:
[0055] 2,4,6-tris(diphenylamino)-1,3,5-triazine; [0056]
2,4,6-tricarbazolo-1,3,5-triazine; [0057]
2,4,6-tris(N-phenyl-2-naphthylamino)-1,3,5-triazine; [0058]
2,4,6-tris(N-phenyl-1-naphthylamino)-1,3,5-triazine; [0059]
4,4',6,6'-tetraphenyl-2,2'-bi-1,3,5-triazine; [0060]
2,4,6-tris([1,1':3',1''-terphenyl]-5'-yl)-1,3,5-triazine.
[0061] In one embodiment, the host material includes a material
that is an aluminum or gallium complex. Particularly useful host
materials are represented by Formula (PHF-7) also referred to
herein as Formula (3).
##STR00019##
[0062] In Formula (3), M.sub.1 represents Al or Ga. R.sub.2-R.sub.7
represent hydrogen or an independently selected substituent.
Desirably, R.sub.2 represents an electron-donating group, such as a
methyl group. Suitably, R.sub.3 and R.sub.4 each independently
represent hydrogen or an electron-donating substituent. Preferably,
R.sub.5, R.sub.6, and R.sub.7 each independently represent hydrogen
or an electron-accepting group. Adjacent substituents,
R.sub.2-R.sub.7, may combine to form a ring group. L is an aromatic
moiety linked to the aluminum by oxygen, which may be substituted
with substituent groups such that L has from 6 to 30 carbon atoms.
Illustrative examples of Formula (3) materials are listed
below.
##STR00020## ##STR00021##
[0063] A suitable class of hole-transporting compounds for use as a
host are aromatic tertiary amines, by which it is understood to be
compounds 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. in U.S. Pat. No. 3,180,730. Other
suitable triarylamines substituted with one or more vinyl radicals
and/or comprising at least one active hydrogen containing group are
disclosed by Brantly et al. in U.S. Pat. Nos. 3,567,450 and
3,658,520.
[0064] 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. 4,720,432 and 5,061,569, such as the
tetraaryldiamines. Desirable tetraaryldiamines include two
diarylamino groups, such as indicated by formula (PHF-8):
##STR00022##
wherein:
[0065] each Are is an independently selected arylene group, such as
a phenylene or anthracene moiety,
[0066] n is selected from 1 to 4, and
[0067] R.sub.1-R.sub.4 are independently selected aryl groups.
[0068] In a typical embodiment, at least one of R.sub.1-R.sub.4 is
a polycyclic fused ring structure, e.g., a naphthalene. However,
when the emission of the dopant is blue or green in color it is
less preferred for the host material to have a polycyclic fused
ring substituent.
[0069] Representative examples of the useful compounds include the
following: [0070] 4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl
(NPB); [0071] 4,4'-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl
(TNB); [0072] 4,4'-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl
(TPD); [0073] 4,4'-Bis-diphenylamino-terphenyl; [0074]
2,6,2',6'-tetramethyl-N,N,N',N'-tetraphenyl-benzidine.4,4',4''-tris[(3-me-
thylphenyl)phenylamino]triphenylamine (MTDATA); [0075]
4,4',4''-tris(N,N-diphenyl-amino)triphenylamine (TDATA); [0076]
N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl--
N'-(3-methylphenyl)-N'-phenyl-1,4-benzenediamine.
[0077] In one desirable embodiment the hole-transporting host
comprises a material of formula (PHF-9):
##STR00023##
[0078] In formula (PHF-9),
[0079] R.sub.1 and R.sub.2 represent substituents, provided that
R.sub.1 and R.sub.2 can join to form a ring. For example, R.sub.1
and R.sub.2 can be methyl groups or can join to form a cyclohexyl
ring;
[0080] Ar.sub.1-Ar.sub.4 represent independently selected aromatic
groups, for example phenyl groups or tolyl groups;
[0081] R.sub.3-R.sub.10 independently represent hydrogen, alkyl,
substituted alkyl, aryl, substituted aryl group.
[0082] Examples of suitable materials include, but are not limited
to: [0083] 1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)cyclohexane
(TAPC); [0084] 1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)cyclopentane;
[0085]
4,4'-(9H-fluoren-9-ylidene)bis[N,N-bis(4-methylphenyl)-benzenamine;
[0086] 1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)-4-phenylcyclohexane;
[0087] 1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)-4-methylcyclohexane;
[0088] 1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)-3-phenylpropane;
[0089]
Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylpenyl)methane;
[0090]
Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)ethane;
[0091] 4-(4-Diethylaminophenyl)triphenylmethane; [0092]
4,4'-Bis(4-diethylaminophenyl)diphenylmethane.
[0093] A useful class of compounds for use as the hole-transporting
host includes carbazole derivatives such as those represented by
formula (PHF-10):
##STR00024##
[0094] In formula (PHF-10),
[0095] Q independently represents nitrogen, carbon, silicon, a
substituted silicon group, an aryl group, or substituted aryl
group, preferably a phenyl group;
[0096] R.sub.1 is preferably an aryl or substituted aryl group, and
more preferably a phenyl group, substituted phenyl, biphenyl, or
substituted biphenyl group;
[0097] R.sub.2 through R.sub.7 are independently hydrogen, alkyl,
phenyl or substituted phenyl group, aryl amine, carbazole, or
substituted carbazole;
[0098] and n is selected from 1 to 4.
[0099] Illustrative useful substituted carbazoles are the
following: [0100]
4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenami-
ne (TCTA); [0101]
4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-
-benzenamine; [0102]
9,9'-[5'-[4-(9H-carbazol-9-yl)phenyl][1,1':3',1''-terphenyl]-4,4''-diyl]b-
is-9H-carbazole. [0103] 3,5-bis(9-carbazolyl)tetraphenylsilane
(SimCP).
[0104] In one suitable embodiment the hole-transporting host
comprises a material of formula (PHF-11):
##STR00025##
[0105] In formula (PHF-11),
[0106] n is selected from 1 to 4;
[0107] Q independently represents phenyl group, substituted phenyl
group, biphenyl, substituted biphenyl group, aryl, or substituted
aryl group;
[0108] R.sub.1 through R.sub.6 are independently hydrogen, alkyl,
phenyl or substituted phenyl, aryl amine, carbazole, or substituted
carbazole.
[0109] Examples of suitable materials are the following: [0110]
9,9'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis-9H-carbazole
(CDBP); [0111] 9,9'[1,1'-biphenyl]-4,4'-diylbis-9H-carbazole (CBP);
[0112] 9,9'-(1,3-phenylene)bis-9H-carbazole (mCP); [0113]
9,9'-(1,4-phenylene)bis-9H-carbazole; [0114]
9,9',9''-(1,3,5-benzenetriyl)tris-9H-carbazole; [0115]
9,9'-(1,4-phenylene)bis[N,N,N',N'-tetraphenyl-9H-carbazole-3,6-diamine;
[0116]
9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;
[0117] 9,9'-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;
[0118]
9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N',N'-tetraphenyl-9H-carbazole-3,6-dia-
mine.
[0119] Host materials that are electron-transporting or
hole-transporting with some electron-transporting properties, such
as carbazoles, are generally more desirable when used as a single
host material. This is especially true for typical phosphorescent
dopants that are hole-trapping or are capable of accepting injected
holes. Less preferable are host materials that are primarily hole
transporting and have little electron-transporting properties, such
as triarlyamines. Injecting electrons into these latter
hole-transporting hosts may be difficult because of their
relatively high LUMO energies.
[0120] Host materials may comprise a mixture of two or more host
materials. Particularly useful is a mixture comprising at least one
each of an electron-transporting and a hole-transporting co-host.
The optimum concentration of the hole-transporting co-host(s) may
be determined by experimentation and may be within the range 5 to
60 volume % of the total of the hole- and electron-transporting
co-host materials in the light-emitting layer, and is often found
to be in the range 15 to 30 vol. %. It is further noted that
electron-transporting molecules and hole-transporting molecules may
be covalently joined together to form single host molecules having
both electron-transporting and hole-transporting properties.
[0121] In one aspect of the invention, the host material of the
light-emitting layer includes a host of Formula (3) and at least
one additional host compound, also referred to as a co-host, is
present. Desirably the co-host is a compound capable of
transporting holes.
[0122] The co-host having hole-transporting properties may be any
suitable hole-transporting compound, such as a triarylamine or
carbazole, as long it has a triplet energy that is higher than that
of the phosphorescent dopant to be employed. The optimum
concentration of the hole-transporting co-host relative to the host
of Formula (3) in the present invention may be determined by
experimentation. The concentration of the hole-transporting co-host
is frequently within the range 5 to 60% of the light-emitting layer
by volume, and is often found to be in the range 10 to 30%, or
commonly in the range of 10 to 20%.
[0123] In one desirable embodiment, the co-host is represented by
Formula (4).
##STR00026##
[0124] In Formula (4),
[0125] each Ar.sup.a and each Ar.sup.b may be the same or different
and each independently represents an aromatic group, such as a
phenyl group or a naphthyl group;
[0126] each R.sup.a and each R.sup.b may be the same or different
and each independently represents a substituent group; and
[0127] n and m independently are 0-4. In one suitable embodiment, n
is 0 and m is 0.
[0128] A wide energy gap host material may be any suitable compound
having a large HOMO-LUMO gap such that the HOMO and LUMO of the
phosphorescent emissive material are within the HOMO and LUMO for
the host. In this case, the phosphorescent emissive material acts
as the primary charge carrier for both electrons and holes, as well
as the site for the trapping of excitons. Often the phosphorescent
dopants for use with the wide energy gap hosts are selected to have
electron-withdrawing substituents to facilitate electron injection.
The "wide energy gap" host material functions as a non-charge
carrying material in the system. Such a combination may lead to
high operation voltage of the device, as the concentration of the
charge-carrying dopant is typically below 10% in the emissive
layer.
[0129] Thompson et al. disclosed in U.S. 2004/0209115 and U.S.
2004/0209116 a group of wide energy gap hosts having triplet
energies suitable for blue phosphorescent OLEDs. Such compounds
include those represented by structural formula (PHF-12):
##STR00027##
[0130] wherein:
[0131] X is Si or Pb; and
[0132] Ar.sub.1, Ar.sub.2, Ar.sub.3, and Ar.sub.4 are each an
aromatic group independently selected from phenyl and high triplet
energy heterocyclic groups such as pyridine, pyrazole, thiophene,
etc.
[0133] It is believed that the HOMO-LUMO gaps in these materials
are large due to the electronically isolated aromatic units and the
lack of any conjugating substituents.
[0134] Illustrative examples of this type of hosts include:
##STR00028##
[0135] In many known hosts and device architectures for
phosphorescent OLEDs, the optimum concentration of the
phosphorescent dopant for luminous efficiency is found to be about
1 to 20 vol. % and often 6 to 8 vol. % relative to the host
material. In one aspect of the invention, wherein a mixture of an
electron-transporting host and a hole-transporting co-host is
present in the light-emitting layer, a phosphorescent material
concentration from about 0.5% to about 6% often provides high
luminous efficiencies.
[0136] In addition to suitable hosts, an EL device employing a
phosphorescent material often is more efficient if there is at
least one exciton- or hole-blocking layer on the cathode side of
the emitting layer. Efficiency can also often be improved if there
are one or more exciton- or electron-blocking layers on the anode
side of the emitting layer. These additional layers help confine
the excitons or electron-hole recombination centers to the
light-emitting layer comprising the host and emitting material.
[0137] An exciton- or hole-blocking layer is desirably placed
between the electron-transporting layer and the light-emitting
layer, Layer 109 in the FIGURE. The ionization potential of the
blocking layer should be such that there is an energy barrier for
hole migration from the host into the electron-transporting layer,
while the electron affinity should be such that electrons pass more
readily from the electron-transporting layer into the
light-emitting layer comprising host and phosphorescent material.
It is further desired, but not absolutely required, that the
triplet energy of the blocking material be greater than that of the
phosphorescent material. Suitable hole-blocking materials are
described in WO 00/70655 A2 and WO 01/93642 A1. Two examples of
useful materials are bathocuproine (BCP) and
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)Aluminum(III)
(BAlq). Metal complexes other than BAlq are also known to block
holes and excitons as described in U.S. 2003/0068528. Depending on
the nature of the electron-transporting material and the
configuration of the LEL, this blocking layer, in certain cases,
can be entirely omitted.
[0138] In another embodiment, an exciton- or electron-blocking
layer would be placed between the hole-transporting layer and the
light-emitting layer (this layer is not shown in the FIGURE). As an
example, U.S. 2003/0175553 describes the use of
fac-tris(1-phenylpyrazolato-N,C.sup.2')iridium(III) (Ir(ppz).sub.3)
in an electron-/exciton-blocking layer. U.S. Ser. No. 11/016,108 of
Marina E. Kondakova et al., filed Dec. 17, 2004 (now U.S. Pat. No.
7,597,967), describes further examples of exciton-blocking layers.
Depending on the nature of the hole-transporting material and the
configuration of the LEL, this blocking layer, in certain cases,
can be entirely omitted.
[0139] Unless otherwise specifically stated, use of the term
"substituted" or "substituent" means any group or atom other than
hydrogen. Unless otherwise provided, when a group, compound, or
formula containing a substitutable hydrogen is referred to, it is
also intended to encompass not only the substituent's unsubstituted
form, but also its form further substituted with any substituent
group or groups as herein mentioned, so long as the substituent
does not destroy properties necessary for device utility. Suitably,
a substituent group may be halogen or may be bonded to the
remainder of the molecule by an atom of carbon, silicon, oxygen,
nitrogen, phosphorous, sulfur, selenium, or boron. The substituent
may be, for example, halogen, such as chloro, bromo or fluoro;
nitro; hydroxyl; cyano; carboxyl; or groups which may be further
substituted, such as alkyl, including straight or branched chain or
cyclic alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl,
3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as
ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy,
butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy,
tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and
2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl,
2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy,
2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy;
carbonamido, such as acetamido, benzamido, butyramido,
tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetamido,
alpha-(2,4-di-t-pentylphenoxy)butyramido,
alpha-(3-pentadecylphenoxy)-hexanamido,
alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,
2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-l-yl,
N-methyltetradecanamido, N-succinimido, N-phthalimido,
2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and
N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,
benzyloxycarbonylamino, hexadecyloxycarbonylamino,
2,4-di-t-butylphenoxycarbonyl-amino, phenylcarbonylamino,
2,5-(di-t-pentylphenyl)carbonylamino,
p-dodecyl-phenylcarbonylamino, p-tolylcarbonylamino,
N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido,
N-hexadecylureido, N,N-dioctadecylureido,
N,N-dioctyl-N'-ethylureido, N-phenylureido, N,N-diphenylureido,
N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,
N,N-(2,5-di-t-pentylphenyl)-N'-ethylureido, and t-butylcarbonamido;
sulfonamido, such as methylsulfonamido, benzenesulfonamido,
p-tolylsulfonamido, p-dodecylbenzenesulfonamido,
N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and
hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,
N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl,
N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,
N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,
N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl,
such as N-methylcarbamoyl, N,N-dibutylcarbamoyl,
N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,
N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl,
such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,
p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,
tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,
3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as
methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,
2-ethylhexyl-oxysulfonyl, phenoxysulfonyl,
2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,
2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,
phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl;
sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy;
sulfinyl, such as methylsulfinyl, octylsulfinyl,
2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl,
phenylsulfinyl, 4-nonylphenylsulfinyl, and p-tolylsulfinyl; thio,
such as ethylthio, octylthio, benzylthio, tetradecylthio,
2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,
2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as
acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,
N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and
cyclohexylcarbonyloxy; amine, such as phenylanilino,
2-chloroanilino, diethylamine, dodecylamine; imino, such as 1
(N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl;
phosphate, such as dimethylphosphate and ethylbutylphosphate;
phosphite, such as diethyl and dihexylphosphite; a heterocyclic
group, a heterocyclic oxy group or a heterocyclic thio group, each
of which may be substituted and which contain a 3 to 7 membered
heterocyclic ring composed of carbon atoms and at least one hetero
atom selected from the group consisting of oxygen, nitrogen, sulfur
or phosphorus, such as pyridyl, thienyl, furyl, azolyl, thiazolyl,
oxazolyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl,
pyrolidinonyl, quinolinyl, isoquinolinyl, 2-furyl, 2-thienyl,
2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such
as triethylammonium; quaternary phosphonium, such as
triphenylphosphonium; and silyloxy, such as trimethylsilyloxy.
[0140] If desired, the substituents may themselves be further
substituted one or more times with the described substituent
groups. The particular substituents used may be selected by those
skilled in the art to attain desirable properties for a specific
application and can include, for example, electron-withdrawing
groups, electron-donating groups, and steric groups. When a
molecule may have two or more substituents, the substituents may be
joined together to form a ring such as a fused ring unless
otherwise provided. Generally, the above groups and substituents
thereof may include those having up to 48 carbon atoms, typically 1
to 36 carbon atoms and usually less than 24 carbon atoms, but
greater numbers are possible depending on the particular
substituents selected.
[0141] It is well within the skill of the art to determine whether
a particular group is electron donating or electron accepting. The
most common measure of electron donating and accepting properties
is in terms of Hammett .sigma. values. Hydrogen has a Hammett a
value of zero, while electron-donating groups have negative Hammett
.sigma. values, and electron-accepting groups have positive Hammett
.sigma. values. Lange's handbook of Chemistry, 12.sup.th Ed.,
McGraw-Hill, 1979, Table 3-12, pp. 3-134 to 3-138, here
incorporated by reference, lists Hammett .sigma. values for a large
number of commonly encountered groups. Hammett .sigma. values are
assigned based on phenyl ring substitution, but they provide a
practical guide for qualitatively selecting electron donating and
accepting groups.
[0142] Suitable electron-donating groups may be selected from --R',
--OR', and --NR'(R'') where R' is a hydrocarbon containing up to 6
carbon atoms and R'' is hydrogen or R'. Specific examples of
electron-donating groups include methyl, ethyl, phenyl, methoxy,
ethoxy, phenoxy, --N(CH.sub.3).sub.2, --N(CH.sub.2CH.sub.3).sub.2,
--NHCH.sub.3, --N(C.sub.6H.sub.5).sub.2,
--N(CH.sub.3)(C.sub.6H.sub.5), and --NHC.sub.6H.sub.5.
[0143] Suitable electron-accepting groups may be selected from the
group consisting of cyano, .alpha.-haloalkyl, .alpha.-haloalkoxy,
amido, sulfonyl, carbonyl, carbonyloxy and oxycarbonyl substituents
containing up to 10 carbon atoms. Specific examples include --CN,
--F, --CF.sub.3, --OCF.sub.3, --CONHC.sub.6H.sub.5,
--SO.sub.2C.sub.6H.sub.5, --COC.sub.6H.sub.5,
--CO.sub.2C.sub.6H.sub.5, and --OCOC.sub.6H.sub.5.
[0144] For the purpose of this invention, also included in the
definition of a heterocyclic ring are those rings that include
coordinate or dative bonds. The definition of a coordinate bond can
be found in Grant & Hackh's Chemical Dictionary, page 91. In
essence, a coordinate bond is formed when electron-rich atoms such
as O or N, donate a pair of electrons to electron-deficient atoms
such as Al or B.
General Device Architecture
[0145] The present invention can be employed in many OLED device
configurations using small molecule materials, oligomeric
materials, polymeric materials, or combinations thereof. These
include very simple structures comprising a single anode and
cathode to more complex devices, such as passive matrix displays
comprised of orthogonal arrays of anodes and cathodes to form
pixels, and active-matrix displays where each pixel is controlled
independently, for example, with thin film transistors (TFTs).
[0146] There are numerous configurations of the organic layers
wherein the present invention can be successfully practiced. The
essential requirements of an OLED are an anode, a cathode, and an
organic light-emitting layer located between the anode and cathode.
Additional layers may be employed as more fully described
hereafter.
[0147] A typical structure, especially useful for of a small
molecule device, is shown in the FIGURE and is comprised of a
substrate 101, an anode 103, a hole-injecting layer 105, a
hole-transporting layer 107, a light-emitting layer 109, a hole- or
exciton-blocking layer 110, an electron-transporting layer 111, and
a cathode 113. These layers are described in detail below. Note
that the substrate may alternatively be located adjacent to the
cathode, or the substrate may actually constitute the anode or
cathode. The organic layers between the anode and cathode are
conveniently referred to as the organic EL element. Also, the total
combined thickness of the organic layers is desirably less than 500
nm.
[0148] The anode and cathode of the OLED are connected to a
voltage/current source 150 through electrical conductors 160. The
OLED is operated by applying a potential between the anode and
cathode such that the anode is at a more positive potential than
the cathode. Holes are injected into the organic EL element from
the anode, and electrons are injected into the organic EL element
at the cathode. Enhanced device stability can sometimes be achieved
when the OLED is operated in an AC mode where, for some time period
in the cycle, the potential bias is reversed, and no current flows.
An example of an AC driven OLED is described in U.S. Pat. No.
5,552,678.
Substrate
[0149] The OLED device of this invention is typically provided over
a supporting substrate 101 where either the cathode or anode can be
in contact with the substrate. The substrate can be a complex
structure comprising multiple layers of materials. This is
typically the case for active matrix substrates wherein TFTs are
provided below the OLED layers. It is still necessary that the
substrate, at least in the emissive pixelated areas, be comprised
of largely transparent materials. The electrode in contact with the
substrate is conveniently referred to as the bottom electrode.
Conventionally, the bottom electrode is the anode, but this
invention is not limited to that configuration. The substrate can
either be light transmissive or opaque, depending on the intended
direction of light emission. The light-transmissive property is
desirable for viewing the EL emission through the substrate.
Transparent glass or plastic is commonly employed in such cases.
For applications where the EL emission is viewed through the top
electrode, the transmissive characteristic of the bottom support
can be light transmissive, light absorbing or light reflective.
Substrates for use in this case include, but are not limited to,
glass, plastic, semiconductor materials, silicon, ceramics, and
circuit board materials. It is necessary to provide in these device
configurations a light-transparent top electrode.
Anode
[0150] When the desired electroluminescent light emission (EL) is
viewed through the anode, the anode 103 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 as
the anode. For applications where EL emission is viewed only
through the cathode, 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. Optionally, anodes may be
polished prior to application of other layers to reduce surface
roughness so as to minimize shorts or enhance reflectivity.
Hole-Injecting Layer (HIL)
[0151] A hole-injecting layer 105 may be provided between the anode
and the hole-transporting layer. 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. 4,720,432, plasma-deposited
fluorocarbon polymers as described in U.S. Pat. Nos. 6,127,004;
6,208,075; and 6,208,077, some aromatic amines, for example, MTDATA
(4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine), and
inorganic oxides including vanadium oxide (VOx), molybdenum oxide
(MoOx), and nickel oxide (NiOx). Alternative hole-injecting
materials reportedly useful in organic EL devices are described in
EP 0 891 121 A1 and EP 1 029 909 A1.
[0152] The thickness of a hole-injection layer containing a
plasma-deposited fluorocarbon polymer can be in the range of 0.2 nm
to 15 nm and suitably in the range of 0.3 to 1.5 nm.
Hole-Transporting Layer (HTL)
[0153] It is usually advantageous to have a hole-transporting layer
107 deposited between the anode and the emissive layer. A
hole-transporting material deposited in said hole-transporting
layer between the anode and the light-emitting layer may be the
same or different from a hole-transporting compound used as a
co-host or in an exciton-blocking layer according to the invention.
The hole-transporting layer may optionally include a hole-injection
layer. The hole-transporting layer may include more than one
hole-transporting compound, deposited as a blend or divided into
separate layers.
[0154] The hole-transporting layer 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.
in U.S. Pat. No. 3,180,730. Other suitable triarylamines
substituted with one or more vinyl radicals and/or comprising at
least one active hydrogen containing group are disclosed by Brantly
et al in U.S. Pat. Nos. 3,567,450 and 3,658,520.
[0155] A more preferred class of aromatic tertiary amines is those
which include at least two aromatic tertiary amine moieties as
described in U.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds
include those represented by structural formula (HT1):
##STR00029##
wherein:
[0156] Q.sub.1 and Q.sub.2 are independently selected aromatic
tertiary amine moieties, and
[0157] G is a linking group such as an arylene, cycloalkylene, or
alkylene group of a carbon to carbon bond.
[0158] In one embodiment, at least one of Q.sub.1 or Q.sub.2
contains a polycyclic fused ring structure, e.g., a naphthalene.
When G is an aryl group, it is conveniently a phenylene,
biphenylene, or naphthalene moiety.
[0159] A useful class of triarylamines satisfying structural
formula (HT1) and containing two triarylamine moieties is
represented by structural formula (HT2):
##STR00030##
wherein:
[0160] R.sub.1 and R.sub.2 each independently represents a hydrogen
atom, an aryl group, or an alkyl group, or R.sub.1 and R.sub.2
together represent the atoms completing a cycloalkyl group; and
[0161] R.sub.3 and R.sub.4 each independently represents an aryl
group, which is in turn substituted with a diaryl substituted amino
group, as indicated by structural formula (HT3):
##STR00031##
wherein R.sub.5 and R.sub.6 are independently selected aryl groups.
In one embodiment, at least one of R.sub.5 or R.sub.6 contains a
polycyclic fused ring structure, e.g., a naphthalene.
[0162] Another class of aromatic tertiary amines is the
tetraaryldiamines. Desirable tetraaryldiamines include two
diarylamino groups, such as indicated by formula (HT3), linked
through an arylene group. Useful tetraaryldiamines include those
represented by formula (HT4):
##STR00032##
wherein:
[0163] each Are is an independently selected arylene group, such as
a phenylene or anthracene moiety,
[0164] n is an integer of from 1 to 4, and
[0165] Ar, R.sub.7, R.sub.8, and R.sub.9 are independently selected
aryl groups.
[0166] In a typical embodiment, at least one of Ar, R.sub.7,
R.sub.8, and R.sub.9 is a polycyclic fused ring structure, e.g., a
naphthalene.
[0167] The various alkyl, alkylene, aryl, and arylene moieties of
the foregoing structural formulae (HT1), (HT2), (HT3), (HT4) can
each in turn be substituted. Typical substituents include alkyl
groups, alkoxy groups, aryl groups, aryloxy groups, and halide such
as fluoride, chloride, and bromide. The various alkyl and alkylene
moieties typically contain from about 1 to 6 carbon atoms. The
cycloalkyl moieties can contain from 3 to about 10 carbon atoms,
but typically contain five, six, or seven ring carbon atoms, such
as cyclopentyl, cyclohexyl, and cycloheptyl ring structures. The
aryl and arylene moieties are usually phenyl and phenylene
moieties.
[0168] The hole-transporting layer can be formed of a single
tertiary amine compound or a mixture of such compounds.
Specifically, one may employ a triarylamine, such as a triarylamine
satisfying the formula (HT2), in combination with a
tetraaryldiamine, such as indicated by formula (HT4). Illustrative
of useful aromatic tertiary amines are the following: [0169]
1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC); [0170]
1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane; [0171]
N,N,N',N'-tetraphenyl-4,4'''-diamino-1,1':4',1'':4'''-quaterphenyl;
[0172] Bis(4-dimethylamino-2-methylphenyl)phenylmethane; [0173]
1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (BDTAPVB);
[0174] N,N,N',N'-Tetra-p-tolyl-4,4'-diaminobiphenyl; [0175]
N,N,N',N'-Tetraphenyl-4,4'-diaminobiphenyl; [0176]
N,N,N',N'-tetra-1-naphthyl-4,4'-diaminobiphenyl; [0177]
N,N,N',N'-tetra-2-naphthyl-4,4'-diaminobiphenyl; [0178]
N-Phenylcarbazole; [0179]
4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB); [0180]
4,4'-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD); [0181]
4,4'-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB); [0182]
4,4'-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl; [0183]
4,4'-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl; [0184]
4,4'-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl; [0185]
1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene; [0186]
4,4'-Bis[N-(9-anthryl)-N-phenylamino]biphenyl; [0187]
4,4'-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl; [0188]
4,4'-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl; [0189]
4,4'-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl; [0190]
4,4'-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl; [0191]
4,4'-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl; [0192]
4,4'-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl; [0193]
4,4'-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl; [0194]
2,6-Bis(di-p-tolylamino)naphthalene; [0195]
2,6-Bis[di-(1-naphthyl)amino]naphthalene; [0196]
2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene; [0197]
N,N,N',N'-Tetra(2-naphthyl)-4,4''-diamino-p-terphenyl; [0198]
4,4'-Bis {N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl; [0199]
2,6-Bis[N,N-di(2-naphthyl)amino]fluorine; [0200]
4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine (MTDATA);
[0201]
N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl--
N'-(3-methylphenyl)-N'-phenyl-1,4-benzenediamine; [0202]
4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine
(TCTA); [0203]
4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-
-benzenamine; [0204]
9,9'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis-9H-carbazole
(CDBP); [0205] 9,9'[1,1'-biphenyl]-4,4'-diylbis-9H-carbazole (CBP);
[0206] 9,9'-(1,3-phenylene)bis-9H-carbazole (mCP); [0207]
9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;
[0208] 9,9'-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;
[0209]
9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N',N'-tetraphenyl-9H-carbazole-3,6-dia-
mine.
[0210] Another class of useful hole-transporting materials includes
polycyclic aromatic compounds as described in EP 1 009 041. Some
hole-injecting materials described in EP 0 891 121 A1 and EP 1 029
909 A1 can also make useful hole-transporting materials. In
addition, polymeric hole-transporting materials can be used
including poly(N-vinylcarbazole) (PVK), polythiophenes,
polypyrrole, polyaniline, and copolymers including
poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also
called PEDOT/PSS.
Exciton-Blocking Layer (EBL)
[0211] As described previously, an optional exciton- or
electron-blocking layer may be present between the HTL and the LEL
(not shown in the FIGURE). Some suitable examples of such blocking
layers are described in U.S. Ser. No. 11/016,108 of Marina E.
Kondavova et al., filed Dec. 17, 2004 (now U.S. Pat. No.
7,597,967).
Light-Emitting Layer (LEL)
[0212] The light-emitting layer has been described previously. The
device may have more than one light-emitting layer. Additional
light-emitting layers may include phosphorescent materials or
fluorescent materials. The term "fluorescent" refers to a material
that emits light from a singlet-excited state.
[0213] Fluorescent materials may be used in the same layer as the
phosphorescent material, in adjacent layers, in adjacent pixels, or
any combination. Care must be taken to select materials that will
not adversely affect the performance of the phosphorescent
materials of this invention. One skilled in the art will understand
that concentrations and triplet energies of materials in the same
layer as the phosphorescent material or in an adjacent layer must
be appropriately set so as to prevent unwanted quenching of the
phosphorescence.
[0214] As more fully described in U.S. Pat. Nos. 4,769,292 and
5,935,721, the light-emitting layer (LEL) of the organic EL element
includes a luminescent fluorescent or phosphorescent 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 emitting material or materials
where light emission comes primarily from the emitting materials
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 emitting material is usually chosen from highly
fluorescent dyes and phosphorescent compounds, e.g., transition
metal complexes as described in WO 98/55561, WO 00/18851, WO
00/57676, and WO 00/70655. Emitting materials are typically
incorporated at 0.01 to 10% by weight of the host material.
[0215] The host and emitting materials can be small non-polymeric
molecules or polymeric materials such as polyfluorenes and
polyvinylarylenes (e.g., poly(p-phenylenevinylene), PPV). In the
case of polymers, small molecule emitting materials can be
molecularly dispersed into a polymeric host, or the emitting
materials can be added by copolymerizing a minor constituent into a
host polymer.
[0216] An important relationship for choosing an emitting material
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 emitting material, a
necessary condition is that the band gap of the dopant is smaller
than that of the host material. For phosphorescent emitters it is
also important that the host triplet energy level be high enough to
enable energy transfer from host to emitting material.
[0217] Host and emitting materials known to be of use include, but
are not limited to, those disclosed in U.S. Pat. Nos. 4,769,292;
5,141,671; 5,150,006; 5,151,629; 5,405,709; 5,484,922; 5,593,788;
5,645,948; 5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721;
and 6,020,078.
[0218] Metal complexes of 8-hydroxyquinoline and similar
derivatives (Formula E) constitute one class of useful host
compounds capable of supporting electroluminescence, and are
particularly suitable for light emission of wavelengths longer than
500 nm, e.g., green, yellow, orange, and red.
##STR00033##
wherein:
[0219] M represents a metal;
[0220] n is an integer of from 1 to 4; and
[0221] Z independently in each occurrence represents the atoms
completing a nucleus having at least two fused aromatic rings.
[0222] From the foregoing it is apparent that the metal can be
monovalent, divalent, trivalent, or tetravalent metal. The metal
can, for example, be an alkali metal, such as lithium, sodium, or
potassium; an alkaline earth metal, such as magnesium or calcium;
an earth metal, such aluminum or gallium, or a transition metal
such as zinc or zirconium. Generally any monovalent, divalent,
trivalent, or tetravalent metal known to be a useful chelating
metal can be employed.
[0223] Z completes a heterocyclic nucleus containing at least two
fused aromatic rings, at least one of which is an azole or azine
ring. Additional rings, including both aliphatic and aromatic
rings, can be fused with the two required rings, if required. To
avoid adding molecular bulk without improving on function the
number of ring atoms is usually maintained at 18 or less.
[0224] Illustrative of useful chelated oxinoid compounds are the
following: [0225] CO-1: Aluminum trisoxine [alias,
tris(8-quinolinolato)aluminum(III)] [0226] CO-2: Magnesium bisoxine
[alias, bis(8-quinolinolato)magnesium(II)] [0227] CO-3: Bis[benzo
{f}-8-quinolinolato]zinc (II) [0228] CO-4:
Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-methyl-8-quinol-
inolato)aluminum(III) [0229] CO-5: Indium trisoxine [alias,
tris(8-quinolinolato)indium] [0230] CO-6: Aluminum
tris(5-methyloxine) [alias,
tris(5-methyl-8-quinolinolato)aluminum(III)] [0231] CO-7: Lithium
oxine [alias, (8-quinolinolato)lithium(I)] [0232] CO-8: Gallium
oxine [alias, tris(8-quinolinolato)gallium(III)] [0233] CO-9:
Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)]
[0234] Derivatives of anthracene (Formula F) constitute one class
of useful host materials capable of supporting electroluminescence,
and are particularly suitable for light emission of wavelengths
longer than 400 nm, e.g., blue, green, yellow, orange, or red.
Asymmetric anthracene derivatives as disclosed in U.S. Pat. No.
6,465,115 and WO 2004/018587 are also useful hosts.
##STR00034##
wherein:
[0235] R.sup.1 and R.sup.2 represent independently selected aryl
groups, such as naphthyl, phenyl, biphenyl, triphenyl, anthracene;
and
[0236] R.sup.3 and R.sup.4 represent one or more substituents on
each ring where each substituent is individually selected from the
following groups:
[0237] Group 1: hydrogen, or alkyl of from 1 to 24 carbon
atoms;
[0238] Group 2: aryl or substituted aryl of from 5 to 20 carbon
atoms;
[0239] Group 3: carbon atoms from 4 to 24 necessary to complete a
fused aromatic ring of anthracenyl, pyrenyl, or perylenyl;
[0240] Group 4: heteroaryl or substituted heteroaryl of from 5 to
24 carbon atoms as necessary to complete a fused heteroaromatic
ring of furyl, thienyl, pyridyl, quinolinyl, or other heterocyclic
systems;
[0241] Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to
24 carbon atoms; and
[0242] Group 6: fluorine or cyano.
[0243] A useful class of anthracenes are derivatives of
9,10-di-(2-naphthyl)anthracene (Formula G).
##STR00035##
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6
represent one or more substituents on each ring where each
substituent is individually selected from the following groups:
[0244] Group 1: hydrogen, or alkyl of from 1 to 24 carbon
atoms;
[0245] Group 2: aryl or substituted aryl of from 5 to 20 carbon
atoms;
[0246] Group 3: carbon atoms from 4 to 24 necessary to complete a
fused aromatic ring of anthracenyl, pyrenyl, or perylenyl;
[0247] Group 4: heteroaryl or substituted heteroaryl of from 5 to
24 carbon atoms as necessary to complete a fused heteroaromatic
ring of furyl, thienyl, pyridyl, quinolinyl, or other heterocyclic
systems;
[0248] Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to
24 carbon atoms; and
[0249] Group 6: fluorine or cyano.
[0250] Illustrative examples of anthracene materials for use in a
light-emitting layer include:
2-(4-methylphenyl)-9,10-di-(2-naphthyl)-anthracene;
9-(2-naphthyl)-10-(1,1'-biphenyl)-anthracene;
9,10-bis[4-(2,2-diphenylethenyl)phenyl]-anthracene;
##STR00036## ##STR00037##
[0251] Distyrylarylene derivatives are also useful hosts, as
described in U.S. Pat. No. 5,121,029. Carbazole derivatives are
particularly useful hosts for phosphorescent emitters.
[0252] Useful fluorescent emitting materials include, but are not
limited to, derivatives of anthracene, tetracene, xanthene,
perylene, rubrene, coumarin, rhodamine, and quinacridone,
dicyanomethylenepyran compounds, thiopyran compounds, polymethine
compounds, pyrilium and thiapyrilium compounds, fluorene
derivatives, periflanthene derivatives, indenoperylene derivatives,
bis(azinyl)amine boron compounds, bis(azinyl)methane compounds, and
carbostyryl compounds. Illustrative examples of useful materials
include, but are not limited to, the following:
TABLE-US-00001 ##STR00038## L1 ##STR00039## L2 ##STR00040## L3
##STR00041## L6 ##STR00042## L4 ##STR00043## L7 ##STR00044## L5
##STR00045## L8 ##STR00046## X R1 R2 L9 O H H L10 O H Methyl L11 O
Methyl H L12 O Methyl Methyl L13 O H t-butyl L14 O t-butyl H L15 O
t-butyl t-butyl L16 S H H L17 S H Methyl L18 S Methyl H L19 S
Methyl Methyl L20 S H t-butyl L21 S t-butyl H L22 S t-butyl t-butyl
##STR00047## X R1 R2 L23 O H H L24 O H Methyl L25 O Methyl H L26 O
Methyl Methyl L27 O H t-butyl L28 O t-butyl H L29 O t-butyl t-butyl
L30 S H H L31 S H Methyl L32 S Methyl H L33 S Methyl Methyl L34 S H
t-butyl L35 S t-butyl H L36 S t-butyl t-butyl ##STR00048## R L37
phenyl L38 methyl L39 t-butyl L40 mesityl ##STR00049## R L41 phenyl
L42 methyl L43 t-butyl L44 mesityl ##STR00050## L45 ##STR00051##
L46 ##STR00052## L47 ##STR00053## L48 ##STR00054## L49 ##STR00055##
L50 ##STR00056## L51 ##STR00057## L52 ##STR00058## L53 ##STR00059##
L54
[0253] In addition to the phosphorescent materials of Formula (1),
additional phosphorescent materials may be present in the same or a
different layer. Examples of other phosphorescent materials are
reported in WO 00/57676, WO 00/70655, WO 01/39234, WO 01/41512, WO
01/93642, WO 02/15645, WO 02/71813, WO 02/74015, EP 1 238 981, EP 1
239 526, EP 1 244 155, U.S. 2002/0100906, JP 2003-073387, JP
2003-073388 (with counterpart U.S. 2003/0152802), JP 2003-059667
(with counterpart U.S. 2004/0239237), JP 2003-073665, U.S.
2002/0121638, U.S. 2002/0197511, U.S. 2003/0017361, U.S.
2003/0040627, U.S. 2003/0054198, U.S. 2003/0059646, U.S.
2003/0068526, U.S. 2003/0068528, U.S. 2003/0068535, U.S.
2003/0072964, U.S. 2003/0124381, U.S. 2003/0141809, and U.S. Pat.
Nos. 6,097,147; 6,413,656; 6,451,415; 6,451,455; 6,458,475;
6,515,298; and 6,573,651.
[0254] The emission wavelengths of cyclometallated Ir(III)
complexes of the type IrL.sub.3 and IrL.sub.2L', such as the
green-emitting fac-tris(2-phenylpyridinato-N,C.sup.2')Iridium(III)
and
bis(2-phenylpyridinato-N,C.sup.2')Iridium(III)(acetylacetonate),
may be shifted by substitution of electron donating or withdrawing
groups at appropriate positions on the cyclometallating ligand L,
or by choice of different heterocycles for the cyclometallating
ligand L. The emission wavelengths may also be shifted by choice of
the ancillary ligand L'. Examples of red emitters are the
bis(2-(2'-benzothienyl)pyridinato-N,C.sup.3')Iridium(III)(acetylacetonate-
) and tris(2-phenylisoquinolinato-N,C)Iridium(III). A blue-emitting
example is
bis(2-(4,6-diflourophenyl)-pyridinato-N,C.sup.2')Iridium(III)(picolinate)-
.
[0255] Other important phosphorescent materials include
cyclometallated Pt(II) complexes such as
cis-bis(2-phenylpyridinato-N,C.sup.2')platinum(II),
cis-bis(2-(2'-thienyl)pyridinato-N,C.sup.3') platinum(II),
cis-bis(2-(2'-thienyl)quinolinato-N,C.sup.5') platinum(II), or
(2-(4,6-diflourophenyl)pyridinato-N,C.sup.2') platinum (II)
acetylacetonate. Pt(II) porphyrin complexes such as
2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum(II) are
also useful phosphorescent materials.
[0256] Still other examples of useful phosphorescent materials
include coordination complexes of the trivalent lanthanides such as
Tb.sup.3+ and Eu.sup.3+ (J. Kido et al., Appl. Phys. Lett., 65,
2124 (1994)).
Hole-Blocking Layer (HBL)
[0257] As described previously, in addition to suitable hosts and
transporting materials, an OLED device according to the invention
may also include at least one hole-blocking layer 110 placed
between the electron-transporting layer 111 and the light-emitting
layer 109 to help confine the excitons and recombination events to
the light-emitting layer comprising hosts or co-hosts and a
phosphorescent emitter. In this case, there should be an energy
barrier for hole migration from hosts or co-hosts into the
hole-blocking layer, while electrons should pass readily from the
hole-blocking layer into the light-emitting layer comprising host
or co-host materials and a phosphorescent emitter. The first
requirement entails that the ionization potential of the
hole-blocking layer 110 be larger than that of the light-emitting
layer 109, desirably by 0.2 eV or more. The second requirement
entails that the electron affinity of the hole-blocking layer 110
not greatly exceed that of the light-emitting layer 109, and
desirably be either less than that of light-emitting layer or not
exceed that of the light-emitting layer by more than about 0.2
eV.
[0258] When used with an electron-transporting layer whose
characteristic luminescence is green, such as an Alq-containing
electron-transporting layer as described below, the requirements
concerning the energies of the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) of the
material of the hole-blocking layer frequently result in a
characteristic luminescence of the hole-blocking layer at shorter
wavelengths than that of the electron-transporting layer, such as
blue, violet, or ultraviolet luminescence. Thus, it is desirable
that the characteristic luminescence of the material of a
hole-blocking layer be blue, violet, or ultraviolet. It is further
desirable that the triplet energy of the hole-blocking material be
greater than that of the phosphorescent material. Suitable
hole-blocking materials are described in WO 00/70655A2, WO 01/41512
and WO 01/93642 A1. Two examples of useful hole-blocking materials
are bathocuproine (BCP) and
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)
(BAlq). The characteristic luminescence of BCP is in the
ultraviolet, and that of BAlq is blue. Metal complexes other than
BAlq are also known to block holes and excitons as described in
U.S. 2003/0068528. When a hole-blocking layer is used, its
thickness can be between 2 and 100 nm, and suitably between 5 and
10 nm.
Electron-Transporting Layer (ETL)
[0259] The electron-transporting material deposited in said
electron-transporting layer between the cathode and the
light-emitting layer may be the same or different from an
electron-transporting host or co-host material. The
electron-transporting layer may include more than one
electron-transporting compound, deposited as a blend or divided
into separate layers.
[0260] Preferred thin film-forming materials for use in
constructing the electron-transporting layer of the organic EL
devices 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, exhibiting high levels of performance, and
are readily fabricated in the form of thin films. Exemplary of
contemplated oxinoid compounds are those satisfying structural
formula (ET1) below:
##STR00060##
wherein:
[0261] M represents a metal;
[0262] n is an integer of from 1 to 4; and
[0263] Z independently in each occurrence represents the atoms
completing a nucleus having at least two fused aromatic rings.
[0264] From the foregoing it is apparent that the metal can be
monovalent, divalent, trivalent, or tetravalent metal. The metal
can, for example, be an alkali metal, such as lithium, sodium, or
potassium; an alkaline earth metal, such as magnesium or calcium;
an earth metal, such aluminum or gallium; or a transition metal
such as zinc or zirconium. Generally any monovalent, divalent,
trivalent, or tetravalent metal known to be a useful chelating
metal can be employed.
[0265] Z completes a heterocyclic nucleus containing at least two
fused aromatic rings, at least one of which is an azole or azine
ring. Additional rings, including both aliphatic and aromatic
rings, can be fused with the two required rings, if required. To
avoid adding molecular bulk without improving on function the
number of ring atoms is usually maintained at 18 or less.
[0266] Illustrative of useful chelated oxinoid compounds are the
following:
[0267] CO-1: Aluminum trisoxine [alias,
tris(8-quinolinolato)aluminum(III)]; [0268] CO-2: Magnesium
bisoxine [alias, bis(8-quinolinolato)magnesium(II)]; [0269] CO-3:
Bis[benzo{f}-8-quinolinolato]zinc (II); [0270] CO-4:
Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-methyl-8-quinol-
inolato)aluminum(III); [0271] CO-5: Indium trisoxine [alias,
tris(8-quinolinolato)indium]; [0272] CO-6: Aluminum
tris(5-methyloxine) [alias,
tris(5-methyl-8-quinolinolato)aluminum(III)]; [0273] CO-7: Lithium
oxine [alias, (8-quinolinolato)lithium(I)]; [0274] CO-8: Gallium
oxine [alias, tris(8-quinolinolato)gallium(III)]; [0275] CO-9:
Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)].
[0276] Other electron-transporting materials suitable for use in
the electron-transporting layer include various butadiene
derivatives as disclosed in U.S. Pat. No. 4,356,429 and various
heterocyclic optical brighteners as described in U.S. Pat. No.
4,539,507. Benzazoles satisfying structural formula (ET2) are also
useful electron-transporting materials:
##STR00061##
wherein:
[0277] n is an integer of 3 to 8;
[0278] Z is O, NR or S;
[0279] R and R' are individually hydrogen; alkyl of from 1 to 24
carbon atoms, for example, propyl, t-butyl, heptyl, and the like;
aryl or hetero-atom substituted aryl of from 5 to 20 carbon atoms
for example phenyl and naphthyl, furyl, thienyl, pyridyl,
quinolinyl and other heterocyclic systems; or halo such as chloro,
fluoro; or atoms necessary to complete a fused aromatic ring;
and
[0280] X is a linkage unit consisting of carbon, alkyl, aryl,
substituted alkyl, or substituted aryl, which conjugately or
unconjugately connects the multiple benzazoles together.
[0281] An example of a useful benzazole is
2,2',2''-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)
disclosed in Shi et al. in U.S. Pat. No. 5,766,779.
[0282] Other electron-transporting materials suitable for use in
the electron-transporting layer 111 include various butadiene
derivatives as disclosed in U.S. Pat. No. 4,356,429 and various
heterocyclic optical brighteners as described in U.S. Pat. No.
4,539,507. Benzazoles satisfying structural formula (G) are also
useful electron-transporting materials. Triazines are also known to
be useful as electron-transporting materials. Further useful
materials are silacyclopentadiene derivatives described in EP 1 480
280, EP 1 478 032, and EP 1 469 533. Substituted
1,10-phenanthroline compounds such as
##STR00062##
are disclosed in JP2001-267080, JP2003-115387, JP2004-311184, and
WO 02/43449. Pyridine derivatives are described in JP2004-200162 as
useful electron-transporting materials.
[0283] In one embodiment, the electron-transporting layer includes
a mixture of materials such as those described by W. Begley et al.
in U.S. Ser. No. 11/076,821 filed Mar. 10, 2005 (now abandoned);
U.S. Ser. No. 11/077,218 filed Mar. 10, 2005 (published as U.S.
2006/0204784); and U.S. Ser. No. 11/116,096 filed Apr. 27, 2005
(published as U.S. 2006/0246315), the disclosures of which are
incorporated herein by reference.
[0284] If both a hole-blocking layer and an electron-transporting
layer 111 are used, electrons should pass readily from the
electron-transporting layer 111 into the hole-blocking layer.
Therefore, the electron affinity of the electron-transporting layer
111 should not greatly exceed that of the hole-blocking layer.
Desirably, the electron affinity of the electron-transporting layer
should be less than that of the hole-blocking layer or not exceed
it by more than about 0.2 eV.
[0285] If an electron-transporting layer is used, its thickness may
be between 2 and 100 nm, and suitably between 5 and 20 nm.
Electron-Injecting Layer (EIL)
[0286] Electron-injecting layers (not shown in the FIGURE), when
present, include those described in U.S. Pat. Nos. 5,608,287;
5,776,622; 5,776,623; 6,137,223; and 6,140,763, the disclosures of
which are incorporated herein by reference. An electron-injecting
layer generally consists of a material having a work function less
than 4.0 eV. A thin-film containing low work-function alkaline
metals or alkaline earth metals, such as Li, Cs, Ca, Mg can be
employed. In addition, an organic material doped with these low
work-function metals can also be used effectively as the
electron-injecting layer. Examples are Li- or Cs-doped Alq. In one
suitable embodiment the electron-injecting layer includes LiF. In
practice, the electron-injecting layer is often a thin layer
deposited to a suitable thickness in a range of 0.1-3.0 nm.
Cathode
[0287] When light emission is viewed solely through the anode 103,
the cathode used in this invention can be comprised of nearly any
conductive material. Desirable 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 useful 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.
4,885,211. Another suitable class of cathode materials includes
bilayers comprising a thin electron-injection layer (EIL) in
contact with an organic layer (e.g., an electron-transporting layer
(ETL)) which is capped with a thicker layer of a conductive metal.
Here, the EIL preferably includes a low work function metal or
metal salt, and if so, the thicker capping 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. 5,677,572. An ETL material doped with an alkali metal, for
example, Li-doped Alq, as disclosed in U.S. Pat. No. 6,013,384, is
another example of a useful EIL. Other useful cathode material sets
include, but are not limited to, those disclosed in U.S. Pat. Nos.
5,059,861; 5,059,862; and 6,140,763.
[0288] When light emission is viewed through the cathode, 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. Nos. 4,885,211; 5,247,190; 5,608,287; 5,677,572; 5,703,436;
5,714,838; 5,739,545; 5,776,622; 5,776,623; 5,837,391; 5,969,474;
5,981,306; 6,137,223; 6,140,763; 6,172,459; 6,278,236; and
6,284,393; and in EP 1 076 368 and JP 3,234,963. Cathode materials
are typically deposited by any suitable methods such as
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.
Other Common Organic Layers and Device Architecture
[0289] In some instances, layers 109 and 111 can optionally be
collapsed into a single layer that serves the function of
supporting both light emission and electron transportation. It also
known in the art that emitting dopants may be added to the
hole-transporting layer, which may serve as a host. Multiple
dopants may be added to one or more layers in order to create a
white-emitting OLED, for example, by combining blue- and
yellow-emitting materials, cyan- and red-emitting materials, or
red-, green-, and blue-emitting materials. White-emitting devices
are described, for example, in EP 1 182 244, EP 1 187 235, U.S.
2002/0186214, U.S. 2002/0025419, U.S. 2004/0009367, and U.S. Pat.
Nos. 5,283,132; 5,405,709; 5,503,910; 5,683,823; and 6,627,333.
[0290] Additional layers such as exciton-, electron- and
hole-blocking layers as taught in the art may be employed in
devices of this invention. Hole-blocking layers are commonly used
to improve efficiency of phosphorescent emitter devices, for
example, as in WO 00/70655 A2, WO 01/93642 A1, U.S. 2002/0015859,
U.S. 2003/0068528, and U.S. 2003/0175553 A1.
[0291] This invention may be used in so-called stacked device
architecture, for example, as taught in U.S. Pat. Nos. 5,703,436
and 6,337,492.
Deposition of Organic Layers
[0292] 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
sublimation "boat" often comprised of a tantalum material, e.g., as
described in U.S. Pat. No. 6,237,529, 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 sublimation
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. 5,294,870),
spatially-defined thermal dye transfer from a donor sheet (U.S.
Pat. Nos. 5,688,551; 5,851,709; and 6,066,357) and inkjet method
(U.S. Pat. No. 6,066,357).
[0293] One preferred method for depositing the materials of the
present invention is described in U.S. 2004/0255857 and U.S. Ser.
No. 10/945,941 (now U.S. Pat. No. 7,288,286) where different source
evaporators are used to evaporate each of the materials of the
present invention. A second preferred method involves the use of
flash evaporation where materials are metered along a material feed
path in which the material feed path is temperature controlled.
Such a preferred method is described in the following co-assigned
patent applications: U.S. Ser. Nos. 10/784,585; 10/805,980;
10/945,940; 10/945,941; 11/050,924; and 11/050,934 (now U.S. Pat.
Nos. 7,232,588; 7,238,389; 7,288,285; 7,288,286; 7,625,601; and
7,165,340 respectively). Using this second method, each material
may be evaporated using different source evaporators, or the solid
materials may be mixed prior to evaporation using the same source
evaporator.
Encapsulation
[0294] Most OLED devices are sensitive to moisture or oxygen, or
both, so they are commonly sealed in an inert atmosphere such as
nitrogen or argon. In sealing an OLED device in an inert
environment, a protective cover can be attached using an organic
adhesive, a metal solder, or a low melting temperature glass.
Commonly, a getter or desiccant is also provided within the sealed
space. Useful getters and desiccants include alkali and alkaline
metals, alumina, bauxite, calcium sulfate, clays, silica gel,
zeolites, alkaline metal oxides, alkaline earth metal oxides,
sulfates, or metal halides and perchlorates. Methods for
encapsulation and desiccation include, but are not limited to,
those described in U.S. Pat. No. 6,226,890. In addition, barrier
layers such as SiOx, Teflon, and alternating inorganic/polymeric
layers are known in the art for encapsulation.
Optical Optimization
[0295] 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 minor 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 in functional relationship
with the light-emitting areas of the display. Filters, polarizers,
and anti-glare or anti-reflection coatings can also be provided
over a cover or as part of a cover.
[0296] The OLED device may have a microcavity structure. In one
useful example, one of the metallic electrodes is essentially
opaque and reflective; the other one is reflective and
semitransparent. The reflective electrode is preferably selected
from Au, Ag, Mg, Ca, or alloys thereof. Because of the presence of
the two reflecting metal electrodes, the device has a microcavity
structure. The strong optical interference in this structure
results in a resonance condition. Emission near the resonance
wavelength is enhanced, and emission away from the resonance
wavelength is depressed. The optical path length can be tuned by
selecting the thickness of the organic layers, or by placing a
transparent optical spacer between the electrodes. For example, an
OLED device of this invention can have ITO spacer layer placed
between a reflective anode and the organic EL media, with a
semitransparent cathode over the organic EL media.
[0297] The entire contents of the patents and other publications
referred to in this specification are incorporated herein by
reference.
[0298] Embodiments of the invention may provide advantageous
features such as higher luminous yield, lower drive voltage, and
higher power efficiency, longer operating lifetimes, or ease of
manufacture. Embodiments of devices useful in the invention can
provide a wide range of hues including those useful in the emission
of white light (directly or through filters to provide multicolor
displays). Embodiments of the invention can also provide an area
lighting device.
[0299] The invention and its advantages are further illustrated by
the specific examples that follow. Unless otherwise specified, the
term "percentage" or "percent" and the symbol "%" of a material
indicate the volume percent of the material in the layer in which
it is present.
Example 1
Synthesis of Inv-1,
fac-tris(2-phenylquinazolinato-N,C.sup.2')iridium(III)
[0300] K.sub.3IrBr.sub.6 (2.80 g, 3.55 mmol) was placed in a 200 mL
round bottom flask with 45 mL of 2-ethoxyethanol, 15 mL water, and
2-phenylquinazoline (8.87 mmol). The mixture was freeze-thaw
degassed, and then refluxed for 4 h under nitrogen atmosphere
during which time an orange precipitate appeared. After cooling,
the precipitate was collected by filtration, washed with 1N
HBr(aq), then water, then ethanol, and dried to yield orange
tetrakis(2-phenylquinazolinato-N,C.sup.2')(.mu.-dibromo)diiridium(III)
(2.29 g, 94% yield based on iridium).
[0301] Then
tetrakis(2-phenylquinazolinato-N,C.sup.2')(.mu.-dibromo)diiridium(III)
(0.85 g, 1.245 mmol) and silver tetrafluoroborate (0.27 g) were
placed in a 100-mL round-bottomed flask. Acetonitrile (30 mL) was
added and the mixture was freeze-thaw degassed, and then refluxed
for 3 h under nitrogen atmosphere. After cooling, the yellow
solution was filtered through celite filter aid to remove white
insoluble material, and the solvent was removed under vacuum. A
yellow powder was collected, and dried to afford
[bis(acetonitrile)bis(2-phenylquinazolinato-N,C.sup.2')iridium(III)]tetra-
fluoroborate (0.953 g, 99% based on iridium). Analysis by H.sup.1
NMR spectroscopy and mass spectrometry confirmed that this material
was
bis(acetonitrile)bis[(2-phenylpyridinato-N,C.sup.2')]iridium(III)
tetrafluoroborate.
[0302] Next, [bis(acetonitrile)bis
(2-phenylquinazolinato-N,C.sup.2')iridium(III)]tetrafluoroborate
(0.615 g, 0.797 mmol) and 2-phenylquinazoline (0.71 g) was placed
in a 100-mL round-bottomed flask with 2-ethoxyethanol (30 mL). The
mixture was freeze-thaw degassed, and then refluxed for 18 h under
nitrogen atmosphere during which time a bright orange precipitate
appeared. After cooling, the precipitate was collected by
filtration, washed with ethanol and water, and dried to afford
fac-tris(2-phenylquinazolinato-N,C.sup.2')iridium(III) (0.433 g,
67.3% yield). Analysis by electrospray mass spectrometry (M+
observed 807 amu) and 1H NMR spectroscopy confirmed the identity of
the product.
Example 2
Synthesis of Inv-2, of
fac-tris(4-phenylquinazolinato-N,C.sup.2')iridium(III)
[0303] K.sub.3IrBr.sub.6 (2.755 g, 3.49 mmol) was placed in a 125
mL round bottom flask with 39 mL of 2-ethoxyethanol, 13 mL water,
and 4-phenylquinazoline (1.80 g, 8.73 mmol). The mixture was
freeze-thaw degassed, and then refluxed for 4 h under nitrogen
atmosphere during which time a dark red precipitate appeared. After
cooling, the precipitate was collected by filtration, washed with
methanol and ligroin, and dried to yield dark red
tetrakis(4-phenylquinazolinato-N,C.sup.2')(.mu.-dibromo)diiridium(III)
(2.265 g, 95% yield based on iridium).
[0304] Next,
tetrakis(4-phenylquinazolinato-N,C.sup.2')(.mu.-dibromo)diiridium(III)
(0.696 g, 1.02 mmol) and silver tetrafluoroborate (0.218 g) were
placed in a 100-mL round-bottom flask. Acetonitrile (30 mL) was
added and the mixture was freeze-thaw degassed, and then refluxed
for 3 h under nitrogen atmosphere. After cooling, the red-orange
solution was filtered through celite filter aid to remove white
insoluble material, and then the solvent was removed under vacuum.
A red-orange was collected, and dried to afford
[bis(acetonitrile)bis
(4-phenylquinazolinato-N,C.sup.2')iridium(III)]tetrafluoroborate
(0.759 g, 96% based on iridium). Analysis by H.sup.1 NMR
spectroscopy and mass spectrometry confirmed that this material was
bis(acetonitrile)bis[(4-phenylpyridinato-N,C.sup.2')]iridium(III)
tetrafluoroborate.
[0305] Then
[bis(acetonitrile)bis(4-phenylquinazolinato-N,C.sup.2')iridium(III)]tetra-
fluoroborate (0.497 g, 0.644 mmol) and 4-phenylquinazoline (0.53 g)
was placed in a 100-mL round-bottom flask with 2-ethoxyethanol (30
mL). The mixture was freeze-thaw degassed, and then refluxed for 18
h under nitrogen atmosphere during which time a dark red
precipitate appeared. After cooling, the precipitate was collected
by filtration, washed with ethanol and water, and dried to afford
fac-tris(4-phenylquinazolinato-N,C.sup.2')iridium(III) (0.375 g,
72% yield). Analysis by electrospray mass spectrometry (M+ observed
807 amu) and .sup.1H NMR spectroscopy confirmed the identity of the
product.
Example 3
Fabrication of Devices 1-1 Through 1-3
[0306] An EL device (1-1) satisfying the requirements of the
invention was constructed in the following manner:
[0307] A glass substrate coated with an 85 nm layer of indium-tin
oxide (ITO) as the anode was sequentially ultrasonicated in a
commercial detergent, rinsed in deionized water, degreased in
toluene vapor, and exposed to oxygen plasma for about 1 min.
[0308] a) Over the ITO was deposited a 1 nm fluorocarbon (CFx)
hole-injecting layer (HIL) by plasma-assisted deposition of
CHF.sub.3.
[0309] b) A hole-transporting layer (HTL) of
N,N'-di-1-naphthalenyl-N,N'-diphenyl-4,4'-diaminobiphenyl (NPB)
having a thickness of 150 nm was then evaporated from a tantalum
boat.
[0310] c) A 35 nm LEL comprised of CBP
(4,4'-N,N'-dicarbazole-biphenyl) and 4 wt % of the phosphorescent
dopant Inv-1 were then deposited onto the hole-transporting layer.
These materials were also evaporated from graphite boats.
[0311] d) A 10 nm hole-blocking layer of
bis(2-methyl-8-quinolinolato) (4-phenylphenolato)aluminum(III)
(BAlq) was deposited onto the LEL. This material was also
evaporated from a graphite boat.
[0312] e) A 40 nm electron-transporting layer (ETL) of
tris(8-quinolinolato)aluminum (III) (Alq.sub.3) was then deposited
onto the light-emitting layer. This material was also evaporated
from a graphite boat.
[0313] f) On top of the Alg.sub.3 layer was deposited a 220 nm
cathode formed of a 10:1 volume ratio of Mg and Ag.
[0314] The above sequence completed the deposition of the EL
device. The device was then hermetically packaged in a dry glove
box for protection against ambient environment. Devices 1-2 and 1-3
were constructed in exactly the same manner as Device 1-1, except
the level of Inv-1 was 6% and 8% respectively.
[0315] The cells thus formed were tested at 20 mA/cm.sup.2 constant
current for efficiency in the form of luminance yield (Cd/A) and
radiant yield (W/A) where radiant yield is the radiant flux (in
watts) produced by the device per ampere of input current, where
radiant flux is the light energy produced by the device per unit
time. Testing also determined the output color, reported in CIEx,
CIEy (Commission Internationale de l'Eclairage) coordinates and
drive voltage. The results are listed in Table 1a and 1b.
[0316] The stability of the devices was also measured by operating
the devices for 430 hrs at a current density of 20 mA/cm.sup.2 and
ambient temperature (.about.23.degree. C.). The percent of
luminance remaining after this time period relative to the initial
luminance is listed in Table 1b as a percentage.
TABLE-US-00002 TABLE 1a Testing data for Devices 1-1, 1-2, 1-3.
Luminance Inv-1 Color Emission Yield Device Level (%) CIEx, y
.lamda..sub.max (nm) (cd/A).sup.1 1-1 4 0.548, 0.424 603 4.66 1-2 6
0.561, 0.415 608 4.50 1-3 8 0.563, 0.413 610 4.17 .sup.1at 20
mA/cm.sup.2
TABLE-US-00003 TABLE 1b Testing data for Devices 1-1, 1-2, 1-3.
Inv-1 Drive Voltage Radiant Stability.sup.2 Device Level (%) (V)
.sup.1 Yield (%) 1-1 4 11.4 0.051 80.2% 1-2 6 11.2 0.053 79.3% 1-3
8 10.6 0.051 78.3% .sup.1 at 20 mA/cm.sup.2 .sup.2Percent luminance
remaining after 430 hours of operation.
[0317] From the data presented in Table 1a and 1b, it can be seen
that the devices according to the invention provide high luminance
yield with high color purity and good stability.
Example 4
Fabrication of Devices 2-1 Through 2-3
[0318] Devices 2-1, 2-2, and 2-3 were fabricated in exactly the
same manner as Device 1-1, 1-2, and 1-3 described above, except
Inv-1 was replaced with Inv-2 in each case. The devices were tested
in the same manner as those in Example 3, and the results are
listed in Table 2a and 2b.
TABLE-US-00004 TABLE 2a Testing data for Devices 2-1, 2-2, 2-3.
Luminance Inv-2 Color Emission Yield Device Level (%) CIE x, y
.lamda..sub.max (nm) (cd/A).sup.1 2-1 4 0.577, 0.388 634 3.38 2-2 6
0.580, 0.385 637 3.15 2-3 8 0.583, 0.383 639 3.20 .sup.1at 20
mA/cm.sup.2
TABLE-US-00005 TABLE 2b Testing data for Devices 2-1, 2-2, 2-3.
Inv-2 Drive Voltage Radiant Stability.sup.2 Device Level (%) (V)
.sup.1 Yield (%) 2-1 4 11.2 0.061 80.2% 2-2 6 11.2 0.062 79.3% 2-3
8 10.6 0.065 78.3% .sup.1 at 20 mA/cm.sup.2 .sup.2Percent luminance
remaining after 430 hours of operation.
[0319] As can be seen from Table 2a and 2b, devices prepared
according to the invention provide high luminance yield with high
color purity and good stability.
Example 5
Fabrication of Devices 3-1 Through 3-6
[0320] EL devices satisfying the requirements of the invention were
constructed in the following manner:
[0321] A glass substrate coated with an 85 nm layer of indium-tin
oxide (ITO) as the anode was sequentially ultrasonicated in a
commercial detergent, rinsed in deionized water, degreased in
toluene vapor, and exposed to oxygen plasma for about 1 min.
[0322] a) Over the ITO was deposited a 1 nm fluorocarbon (CFx)
hole-injecting layer (HIL) by plasma-assisted deposition of
CHF.sub.3.
[0323] b) A hole-transporting layer (HTL) of
N,N'-di-1-naphthalenyl-N,N'-diphenyl-4,4'-diaminobiphenyl (NPB)
having a thickness of 150 nm was then evaporated from a tantalum
boat.
[0324] c) A 35 nm LEL comprised of the co-hosts PH-10 and NPB and
the phosphorescent dopant Inv-2 were then deposited onto the
hole-transporting layer. See Table 3a for the levels of each of
these components. These materials were also evaporated from
graphite boats.
[0325] d) A 10 nm hole-blocking layer of PH-10 was deposited onto
the LEL.
[0326] e) A 40 nm electron-transporting layer (ETL) of
tris(8-quinolinolato)aluminum (III) (Alq.sub.3) was then deposited
onto the light-emitting layer. This material was also evaporated
from a graphite boat.
[0327] f) On top of the Alq.sub.3 layer was deposited a 220 nm
cathode formed of a 10:1 volume ratio of Mg and Ag.
[0328] The above sequence completed the deposition of the EL
device. The device was then hermetically packaged in a dry glove
box for protection against ambient environment.
TABLE-US-00006 TABLE 3a Components used in the LEL. Device PH-10 Wt
% NPB Wt % Inv-2 Wt % 3-1 83 15 2 3-2 81 15 4 3-3 76 20 4 3-4 66 30
4 3-5 74 20 6 3-6 94 0 6 ##STR00063##
[0329] The cells thus formed were tested at 0.5 mA/cm.sup.2
constant current for efficiency in the form of luminance yield
(Cd/A) and radiant yield (W/A). Testing was also determined the
output color reported in CIEx, CIEy coordinates and drive voltage.
The results are listed in Table 3b.
[0330] The stability of the devices was also measured by operating
the devices for 474 hrs at a current density of 20 mA/cm.sup.2. The
percent of luminance remaining after this time period is listed in
Table 3b.
TABLE-US-00007 TABLE 3b Testing data for Devices 3-1 through 3-6.
Luminance Drive Emission Radi- Stabil- De- Color Yield Voltage
.lamda..sub.max ant ity.sup.2 vice CIEx, y (cd/A).sup.1 (V).sup.1
(nm) Yield (%) 3-1 0.661, 0.323 5.27 7.2 636 0.136 87 3-2 0.673,
0.319 4.50 7.2 639 0.131 86 3-3 0.673, 0.318 4.68 6.3 639 0.135 87
3-4 0.674, 0.316 5.07 5.6 638 0.142 84 3-5 0.678, 0.315 4.25 6.4
641 0.135 87 3-6 0.612, 0.362 2.52 8.5 645 0.066 82 .sup.1Measured
at 0.5 mA/cm.sup.2 constant current. .sup.2Percent luminance
remaining after 474 hours of operation.
[0331] It can be seen from Table 3b, that the inventive devices
offer high luminance and excellent stability. In addition, if one
compares Devices 3-1 through 3-5, which have a host material that
is a mixture of PH-10 and NPB, with Device 3-6 which has only a
single host (PH-10), one can see that the mixed host in combination
with the dopant of Formula (1) offers a significant improvement in
luminance yield, efficiency, and stability, as well as reduced
drive voltage.
[0332] 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.
[0333] The patents and other publications referred to are
incorporated herein in their entirety.
PARTS LIST
[0334] 101 Substrate [0335] 103 Anode [0336] 105 Hole-Injecting
layer (HIL) [0337] 107 Hole-Transporting layer (HTL) [0338] 109
Light-Emitting layer (LEL) [0339] 110 Hole-Blocking Layer (HBL)
[0340] 111 Electron-Transporting layer (ETL) [0341] 113 Cathode
[0342] 150 Voltage/Current Source [0343] 160 Electrical
Connectors
* * * * *