U.S. patent application number 10/324317 was filed with the patent office on 2003-08-07 for multilayer structures as stable hole-injecting electrodes for use in high efficiency organic electronic devices.
Invention is credited to Parker, Ian D., Zhang, Chi.
Application Number | 20030146436 10/324317 |
Document ID | / |
Family ID | 22792966 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030146436 |
Kind Code |
A1 |
Parker, Ian D. ; et
al. |
August 7, 2003 |
Multilayer structures as stable hole-injecting electrodes for use
in high efficiency organic electronic devices
Abstract
Multilayer anode structures (104) for electronic devices (100)
such as polymer light-emitting diodes are described. The multilayer
anodes include a high conductivity organic layer (114) adjacent to
the photoactive layer (102) and a low conductivity organic layer
(112) between the high conductivity organic layer and the anode's
electrical connection layer (110). This anode structure provides
polymer light emitting diodes which exhibit high brightness, high
efficiency and long operating lifetime. The multilayer anode
structure of this invention provides sufficiently high resistivity
to avoid cross-talk in passively addressed pixellated polymer
emissive displays; the multilayer anode structure of this invention
simultaneously provides long lifetime for pixellated polymer
emissive displays.
Inventors: |
Parker, Ian D.; (Santa
Barbara, CA) ; Zhang, Chi; (Goleta, CA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
22792966 |
Appl. No.: |
10/324317 |
Filed: |
December 20, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10324317 |
Dec 20, 2002 |
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09881223 |
Jun 14, 2001 |
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60212924 |
Jun 20, 2000 |
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Current U.S.
Class: |
257/72 |
Current CPC
Class: |
H01L 51/5088 20130101;
H01L 51/5215 20130101; H01L 27/3281 20130101 |
Class at
Publication: |
257/72 |
International
Class: |
H01L 029/04 |
Claims
What is claimed is:
1. A multilayer electrode comprising a first layer having a first
layer conductivity, a second layer in contact with the first layer,
said second layer comprising a conductive organic material having a
second layer conductivity, and a third layer in contact with the
second layer, said third layer comprising a conductive organic
material having a third layer conductivity greater than the second
layer conductivity and less than the first layer conductivity.
2. A pixellated display comprising the multilayer electrode of
claim 1.
3. The multilayer electrode of claim 1, wherein the second layer
has a bulk conductivity of from 10.sup.-4 S/cm to 10.sup.-11 S/cm
and wherein the bulk conductivity of the third layer is from about
5 times to about 10.sup.6 times as great as the conductivity of the
second layer.
4. The multilayer electrode of claim 1, wherein said second layer
comprises a blend of conjugated conductive organic polymer with
nonconductive polymer.
5. The multilayer electrode of claim 1, wherein the second layer
comprises a blend of PANI with nonconductive polymer.
6. The multilayer electrode of claim 1, wherein the conductance of
the second layer in combination with the third layer is from 1.25
to about 20 times the conductivity of the second layer alone.
7. The multilayer electrode of claim 1, wherein the first layer
comprises indium-tin oxide, the second layer comprises a
water-soluble PANI blend, and the third layer comprises a
poly(ethylenedioxythiophene).
8. The array of claim 1 wherein the second layer has a thickness of
from about 500 .ANG. to about 5000 .ANG..
9. The array of claim 1 wherein the third layer has a thickness of
from about 2 .ANG.to about 400 .ANG..
10. The array of claim 1 wherein said second layer comprises a
mixture of conjugated conductive organic polymer with a
nonconductive host polymer.
11. An electronic device comprising a photoactive layer between a
cathode and an anode, wherein the anode is a multilayer anode
including a first anode layer comprising high conductivity
transparent inorganic contact layer, a second anode layer adjacent
to the first anode layer, said second anode layer comprising
conjugated conductive organic polymer and having a low conductivity
and a third anode layer between said second anode layer and said
photoactive layer, said third anode layer comprising a conductive
organic polymer and having a higher conductivity resistance than
said second anode layer.
12. The device of claim 11, wherein the cathode comprises a first
cathode layer of low work function material and a second layer of
electron transport/injection material between the photoactive layer
and the first cathode layer, the first anode layer having anode
work function and the low work function material having a cathode
work function such that the anode work function is higher than the
cathode work function.
13. The device of claim 11, wherein said second layer comprises a
blend of conjugated conductive organic polymer with nonconductive
polymer.
14. The device of claim 11, wherein the second layer comprises a
blend of PANI with nonconductive polymer.
15. The device of claim 11, wherein the second layer has a bulk
conductivity of from 10.sup.-4 S/cm to 10.sup.-11 S/cm and wherein
the bulk conductivity of the third layer is from about 5 times to
about 10.sup.6 times as great as the conductivity of the second
layer.
16. The device of claim 11 wherein the conductance of the second
layer in combination with the third layer is from 1.25 to about 20
times the conductivity of the second layer alone.
17. The device of claim 11 wherein the photoactive layer comprises
a poly(phenylenevinylene)-based polymer, the cathode comprises an
alkaline earth metal and the anode comprises a indium-tin oxide
first layer, a water-soluble PANI blend second layer and a
poly(ethylenedioxythiophene) third layer.
18. The device of claim 11, wherein the photoactive layer comprises
an active material is selected from asanthracene, butadienes,
coumarin derivatives, acridine, stilbene derivatives, and
combinatios thereof.
19. The device of claim 11, wherein the photoactive layer a
conjugated polymer active material.
20. An array of polymer emissive diodes comprising an active
emissive polymer layer having a first side in contact with a
patterned cathode and a second side in contact with a patterned
transparent anode, the patterning of said anode and cathode
defining an array of emissive diodes, wherein a multilayer anode
including a first layer comprising a patterned high conductivity
inorganic contact layer, a nonpatterned second layer in contact
with said first layer, said second layer comprising conjugated
conductive organic polymer and having a high resistance and a
nonpatterned transparent third layer in contact with said second
layer and with said active emissive polymer layer, said third layer
comprising a conductive organic polymer and having a lower
resistance than said second layer.
21. The array of claim 20 wherein said second layer comprises a
blend of conjugated conductive organic polymer with nonconductive
polymer.
22. The array of claim 20 wherein said blend is a dispersion of one
polymer in the other.
23. The array of claim 20 wherein said blend is a solution of one
polymer in the other.
24. The array of claim 20 wherein the diode of claim 2 wherein the
second layer comprises a blend of PANI with nonconductive
polymer.
25. The array of claim 24 wherein the diode of claim 2 wherein the
second layer has a bulk conductivity of from 10.sup.-4 S/cm to
10.sup.-11 S/cm and wherein the bulk conductivity of the third
layer is from about 5 times to about 10.sup.6 times as great as the
conductivity of the second layer.
26. The array of claim 25 wherein the conductance of the second
layer in combination with the third layer is from 1.25 to about 20
times the conductivity of the second layer alone.
27. The array of claim 20 wherein said patterned high conductivity
transparent inorganic contact layer is present on a support.
28. The array of claim 25 wherein the second layer has a thickness
of from about 500 .ANG. to about 5000 .ANG..
29. The array of claim 25 wherein the third layer has a thickness
of from about 2 .ANG. to about 400 .ANG..
30. The array of claim 23 wherein said second layer comprises a
mixture of conjugated conductive organic polymer with a
nonconductive host polymer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to organic electronic devices. More
particularly it concerns multilayer hole-injecting electrodes
(anodes) for electronic devices.
DESCRIPTION OF PRIOR ART
[0002] Organic electronic devices, such as light emitting devices,
photodetecting devices and photovoltaic cells, may be formed of a
thin layer of electroactive organic material sandwiched between two
electrical contact layers. Electroactive organic materials are
organic materials exhibiting electroluminescence, photosensitivity,
charge (hole or electron) transport and/or injection, electrical
conductivity, and/or exciton blocking. The material may be
semiconductive. At least one of the electrical contact layers is
transparent to light so that light can pass through the electrical
contact layer to or from the electroactive organic material layer.
Other devices with similar structures include photoconductive
cells, photoresistive cells, photodiodes, photoswitches,
transistors, capacitors, resistors, chemoresistive sensors
(gas/vapor sensitive electronic noses, chemical and biosensors),
writing sensors, and electrochromic devices (smart windows).
[0003] Light-emitting diodes (LEDs) fabricated with conjugated
organic polymer layers as their emissive elements have attracted
attention due to their potential for use in display technology [J.
H. Burroughs, D. D. C. Bradley, A. R. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Burns, and A. B. Holmes, Nature 347,
539 (1990); D. Braun and A. J. Heeger, Appl. Phys. Lett. 58, 1982
(1991)]. Patents covering polymer LEDs include the following: R. H.
Friend, J. H. Burroughs and D. D. Bradley, U.S. Pat. No. 5,247,190;
A. J. Heeger and D. Braun, U.S. Pat. Nos. 5,408,109 and 5,869,350.
These references as well as all additional articles, patents and
patent applications referenced herein are incorporated by
reference.
[0004] In their most elementary form, these diodes employ a layer
of conjugated organic polymer bounded on one side by a
hole-injecting electrode (anode) and on the other by an
electron-injecting electrode (cathode), one of which is transparent
to the light produced in the conjugated polymer layer when a
potential is applied across it.
[0005] In many applications, especially in displays, arrays of
these diodes are assembled. In these applications, there is
typically a unit body of active polymer and the electrodes are
patterned to provide the desired plurality of pixels in the array.
With arrays based on a unit body of active polymer and patterned
electrodes there is a need to minimize interference or "cross talk"
among adjacent pixels. This need has also been addressed by varying
the nature of the contacts between the active polymer body and the
electrodes.
[0006] The desire to improve operating life and efficiency is often
seemingly at cross purposes with the desire to minimize cross talk.
High efficiency and long operating life are promoted by the use of
high conductivity contacts with the active material layer. Cross
talk is minimized when the resistance between adjacent pixels is
high. Structures which favor high conductivity and thus high
efficiency and long operating life are contrary to the conditions
preferred for low cross talk.
[0007] In U.S. Pat. No. 5,723,873 it is disclosed that it is
advantageous to place a layer of conductive polyaniline (PANI)
between the hole-injecting electrode and the layer of active
material to increase diode efficiency and to lower the diode's turn
on voltage.
[0008] Hole-injecting anodes which include conductive polyaniline
can provide sufficiently high resistivity to avoid the disadvantage
of cross talk in pixellated polymer emissive displays. However, the
lifetime of such high resistivity polyaniline devices is not
sufficient for many commercial applications. Moreover, devices
fabricated with polyaniline-layer-containing anodes require high
operating voltages.
[0009] Additional developments using a layer of polyaniline or
blends comprising polyaniline, directly between the ITO and the
light-emitting polymer layer, C. Zhang, G. Yu and Y. Cao [U.S. Pat.
No. 5,798,170] demonstrated polymer LEDs with long operating
lifetimes.
[0010] Despite the advantages of the polymer LED's described in
U.S. Pat. No. 5,798,170, the low electrical resistivity typical of
polyaniline inhibits the use of polyaniline in pixellated displays.
For use in pixellated displays, the polyaniline layer should have a
high electrical sheet resistance, otherwise lateral conduction
causes cross-talk between neighboring pixels. The resulting
interpixel current leakage significantly reduces the power
efficiency and limits both the resolution and the clarity of the
display.
[0011] Making the polyaniline sheet resistance higher by reducing
the film thickness is not a good option since thinner films give
lower manufacturing yield caused by the formation of electrical
shorts. This is demonstrated clearly in FIG. 1, which shows the
fraction of "leaky" pixels in a 96.times.64 array vs thickness of
the polyaniline polyblend layer. Thus, to avoid shorts, it is
necessary to use a relatively thick polyaniline layer with
thickness .about.200 nm.
[0012] In polymer emissive displays, good operating lifetimes and
relatively lower operating voltages have been demonstrated through
the use of a layer of poly(ethylenedioxythiophene) (PEDT) between
an indium/tin-oxide (ITO) anode layer and the emissive polymer
layer. PEDT, as typically prepared, has intrinsically low
electrical resistivity. However, for use in pixellated displays,
the PEDT layer needs to have a high electrical sheet resistance,
otherwise lateral conduction causes cross-talk between neighboring
pixels, and the resulting inter-pixel current leakage significantly
reduces the power efficiency and limits both the resolution and the
clarity of the display.
[0013] Thus, there is a need for anode structures for light
emitting devices which avoid inter-pixel cross-talk, and which
exhibit the low operating voltages and the extended operating
lifetimes consistent with the requirements of commercial
applications.
SUMMARY OF THE INVENTION
[0014] This invention relates generally a multilayer anode
structure useful for organic electronic devices, such as diodes and
pixellated displays.
[0015] The multilayer anode includes a first layer comprising a
high conductivity contact layer having a first layer conductivity,
a second layer in contact with the first layer, said second layer
comprising a conductive organic material having a second layer
conductivity, and a third layer in contact with the second layer,
said third layer comprising a conductive organic polymer having a
third layer conductivity greater than the second layer conductivity
and less than the first layer conductivity.
[0016] The multilayer structure provides sufficiently high
resistivity to avoid cross-talk in passively-addressed pixellated
polymer emissive displays; the multilayer anode structure of this
invention simultaneously provides the low operating voltages and
the long operating lifetime required for pixellated polymer
emissive displays in commercial applications.
[0017] This invention additionally provides an improved
configuration for electronic devices such as pixellated polymer
emissive displays. This configuration leads to high efficiency,
long operating life PED's while at the same time avoids excessive
cross talk. This invention relates generally to the use of the
multilayer anode structure in such devices. Thus, in one aspect
this invention provides an improved polymer emissive diode. This
improved diode is made up of an active emissive polymer layer
having a first side in contact with a cathode and a second side in
contact with a transparent anode. The improvement involves a
multilayer transparent anode itself made up of a high conductivity
transparent first contact layer, a transparent second layer in
contact with the first contact layer and a third layer in contact
with the second layer and the active emissive polymer layer. The
second layer contains conjugated conductive organic polymer blend
and has a high resistance. The third layer is thin and contains a
conductive organic polymer having a lower resistance than the
material of the second layer.
[0018] While the multilayer electrode of the invention is useful in
non-pixelated as well as pixelated electronic devices, the use of
these improved multilayer anode structures is particularly
advantageous when a plurality of diodes are arranged into an array
as occurs in pixellated emissive displays as the anode structure
leads to very low levels of cross talk while at the same time
providing long life and high efficiency as compared to arrays
described heretofore.
[0019] In this aspect this invention provides an improved array of
polymer emissive diodes. This improved diode array is made up of an
active emissive polymer layer having a first side in contact with a
patterned cathode and a second side in contact with a patterned
transparent anode, the patterning of the anode and cathode defining
an array of emissive diodes, the improvement comprising a
multilayer transparent anode including a first layer comprising a
patterned high conductivity transparent contact layer, a
nonpatterned transparent second layer in contact with said first
layer, the second layer comprising a blend of conjugated conductive
organic polymer and having a higher resistance (lower conductivity)
and a nonpatterned transparent third layer in contact with the
second layer and with the active emissive polymer layer, the third
layer comprising a conductive organic polymer and having a lower
resistance (higher conductivity) than the second layer.
[0020] As used herein, the term "organic electroactive material"
refers to any organic material that exhibits the specified
electroactivity, such as electroluminescence, photosensitivity,
charge transport and/or charge injection, electrical conductivity
and exciton blocking. The term "solution-processed organic
electroactive material" refers to any organic electroactive
material that has been incorporated in a suitable solvent during
layer formation in electronic device assembly. The term "charge"
when used to refer to charge injection/transport refers to one or
both of hole and electron transport/injection, depending upon the
context. The term "photoactive" organic material refers to any
organic material that exhibits the electroactivity of
electroluminescence and/or photosensitivity. The terms
"conductivity" and "bulk conductivity" are used interchangeably,
the value of which is provided in the unit of Siemens per
centimeter (S/cm). In addition, the terms "surface resistivity" and
"sheet resistance" are used interchangeably to refer to the
resistance value that is a function of sheet thickness for a given
material, the value of which is provided in the unit of ohm per
square (ohm/sq). Also, the terms "bulk resistivity" and "electrical
resistivity" are used interchangeably to refer to the resistivity
that is a basic property of a specific materials (i.e., does not
change with the dimension of the substance), the value of which
provided in the unit of ohm-centimeter (ohm-cm). Electrical
resistivity value is the inverse value of conductivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] This invention will be described with.about.reference being
made to the drawings. In these drawings,
[0022] FIG. 1 is a graph referenced in the Background which shows
the fraction of "leaky" pixels (in a 96 by 64 array) vs thickness
of a polyaniline layer.
[0023] FIG. 2A is a not-to-scale cross-sectional view of a pixel an
organic electronic device of the invention containing a photoactive
layer.
[0024] FIG. 2B is an enlarged cross section of the pixel of FIG. 2A
focusing on the multilayer anode structure.
[0025] FIG. 2C is a schematic diagram of the architecture of a
passively-addressed, pixellated, organic electronic device of the
invention containing a photoactive layer.
[0026] FIG. 3 is a graph which shows the stress-induced degradation
of three devices, one with a polyaniline (emeraldine-salt) layer
(PANI(ES)), one with a layer made with a blend of polyaniline with
polyacrylamide (PANI(ES)-PAM) and one with a layer of
poly(ethylenedioxythiophene) (PEDT) layer at 70.degree. C. Solid
lines represent operating voltage and dashed lines represent light
output.
[0027] FIG. 4 is a graph which shows the stress-induced degradation
of devices having a PANI(ES)-PAM/PEDT double layer with different
PEDT thickness at 70.degree. C. Solid lines represent operating
voltage and dashed lines represent light output.
[0028] FIG. 5 is a graph which shows the stress-induced degradation
of a series of devices having PANI(ES)-PAM/PEDT double layers with
different PANI(ES)-PAM blends at 80.degree. C. Solid lines
represent operating voltage and dashed lines represent light
output.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] As best seen in FIGS. 2A, 2B, and 2C, an electronic device
100 of this invention comprises a layer of photoactive layer 102
between a cathode 106 and a multilayer anode 104. Anode 104
includes a conductive first layer 110 having a first layer
conductivity, a low conductivity second layer 112 having a second
layer conductivity and a high conductivity third layer 114 having a
third layer conductivity greater than the second layer conductivity
and less than the first layer conductivity. Anode 104 and the
overall diode structure can be carried on a substrate 108.
[0030] Organic polymer-based diode 100 employs a relatively high
work function anode; this high work function anode 104 serving to
inject holes into the otherwise filled .pi.-band of the
semiconducting, luminescent polymer 102. Relatively low work
function materials are preferred as the cathode 106; this low work
function cathode serving to inject electrons into the otherwise
empty .pi.*-band of the semiconducting, luminescent polymer 102.
The holes injected at the anode and the electrons injected at the
cathode recombine radiatively within the active layer and light is
emitted. The criteria for suitable electrodes in the art are
described in detail by I. D. Parker, J. Appl. Phys, 75, 1656
(1994).
[0031] Device Configuration:
[0032] As best seen in FIG. 2C, each individual pixel of an organic
electronic device 100 includes an electron injecting (cathode)
contact 106 as one electrode on the front of a photo active organic
material 102 deposited on a multi layer anode 104 of the invention
to serve as the second (transparent) electron-withdrawing (anode)
electrode. The multilayer anode (made of layers 110, 112 and 114)
is deposited on a substrate 108, which is partially coated with a
first layer 110. Deposited on top of first layer 110 is the low
conductivity second layer 112 and the high conductivity third layer
114. Cathode 106 is electrically connected to contact pads 80, and
anode 110 is electrically connected to contact pads 82. The layers
102, 106, 108, 110, and 112 are then isolated from the environment
by a hermetic seal layer 114. Where the electronic device is a
light-emitting device, upon application of electricity via contact
pads 80, 82, which pads are outside of the hermetic seal 70, light
is emitted from the device in the direction shown by arrow 90.
Where the electronic device is a photodetector, light is received
by the deice in the direction opposite the arrow 90 (not
shown).
[0033] This description of preferred embodiments is organized
according to these various components. More specifically it
contains the following sections:
[0034] The Photoactive layer (102)
[0035] The Multilayer Anode (104)
[0036] The Conductive First Layer (110)
[0037] The Low Conductivity Second Layer (112)
[0038] The High Conductivity Third Layer (114)
[0039] The Cathode (106)
[0040] The Substrate (108)
[0041] Contact Pads (80, 90)
[0042] Optional Layers
[0043] Fabrication Techniques
[0044] The Photoactive Layer (102)
[0045] Depending upon the application of the electronic device, the
photoactive layer 102 can be a light-emitting layer that is
activated by an applied voltage (such as in a light-emitting diode
or light-emitting electrochemical cell), a layer of material that
responds to radiant energy and generates a signal with or without
an applied bias voltage (such as in a photodetector). Examples of
photodetectors include photoconductive cells, photoresistors,
photoswitches, phototransistors, and phototubes, and photovoltaic
cells, as these terms are describe in Markus, John, Electronics and
Nucleonics Dictionary, 470 and 476 (McGraw-Hill, Inc. 1966).
[0046] Where the electronic device is a light-emitting device, the
photoactive layer 102 will emit light when sufficient bias voltage
is applied to the electrical contact layers. Suitable active
light-emitting materials include organic molecular materials such
asanthracene, butadienes, coumarin derivatives, acridine, and
stilbene derivatives, see, for example, Tang, U.S. Pat. No.
4,356,429, Van Slyke et al., U.S. Pat. No. 4,539,507, the relevant
portions of which are incorporated herein by reference.
Alternatively, such materials can be polymeric materials such as
those described in Friend et al. (U.S. Pat. No. 5,247,190), Heeger
et al. (U.S. Pat. No. 5,408,109), Nakano et al. (U.S. Pat. No.
5,317,169), the relevant portions of which are incorporated herein
by reference. The light-emitting materials may be dispersed in a
matrix of another material, with and without additives, but
preferably form a layer alone. In preferred embodiments, the
electroluminescent polymer comprises at least one conjugated
polymer or a co-polymer which contains segments of .pi.-conjugated
moieties. Conjugated polymers are well known in the art (see, e.g.,
Conjugated Polymers, J.-L. Bredas and R. Silbey edt., Kluwer
Academic Press, Dordrecht, 1991). Representative classes of
materials include, but are not limited to the following:
[0047] (i) poly(p-phenylene vinylene) and its derivatives
substituted at various positions on the phenylene moiety;
[0048] (ii) poly(p-phenylene vinylene) and its derivatives
substituted at various positions on the vinylene moiety;
[0049] (iii) poly(arylene vinylene), where the arylene may be such
moieties as naphthalene, anthracene, furylene, thienylene,
oxadiazole, and the like, or one of the moieties with
functionalized substituents at various positions;
[0050] (iv) derivatives of poly(arylene vinylene), where the
arylene may be as in (iii) above, substituted at various positions
on the arylene moiety;
[0051] (v) derivatives of poly(arylene vinylene), where the arylene
may be as in (iii) above, substituted at various positions on the
vinylene moiety;
[0052] (vi) co-polymers of arylene vinylene oligomers with
non-conjugated oligomers, and derivatives of such polymers
substituted at various positions on the arylene moieties,
derivatives of such polymers substituted at various positions on
the vinylene moieties, and derivatives of such polymers substituted
at various positions on the arylene and the vinylene moieties;
[0053] (vii) poly(p-phenylene) and its derivatives substituted at
various positions on the phenylene moiety, including ladder polymer
derivatives such as poly(9,9-dialkyl fluorene) and the like;
[0054] (viii) poly(arylenes) and their derivatives substituted at
various positions on the arylene moiety;
[0055] (ix) co-polymers of oligoarylenes with non-conjugated
oligomers, and derivatives of such polymers substituted at various
positions on the arylene moieties;
[0056] (x) polyquinoline and its derivatives;
[0057] (xi) co-polymers of polyquinoline with p-phenylene and
moieties having solubilizing function;
[0058] (xii) rigid rod polymers such as
poly(p-phenylene-2,6-benzobisthiaz- ole),
poly(p-phenylene-2,6-benzobisoxazole),
poly(p-phenylene-2,6-benzimid- azole), and their derivatives; and
the like.
[0059] More specifically, the active materials may include but are
not limited to poly(phenylenevinylene), PPV, and alkoxy derivatives
of PPV, such as for example,
poly(2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenyleneviny- lene) or
"MEH- PPV" (U.S. Pat. No. 5,189,136). BCHA-PPV is also an
attractive active material. (C. Zhang, et al, J. Electron. Mater.,
22, 413 (1993)). PPPV is also suitable. (C. Zhang et al, Synth.
Met., 62, 35 (1994) and references therein.) Luminescent conjugated
polymer which are soluble in common organic solvents are preferred
since they enable relatively simple device fabrication [A. Heeger
and D. Braun, U.S. Pat. Nos. 5,408,109 and 5,869,350].
[0060] Even more preferred active light-emitting polymers and
copolymers are the soluble PPV materials described in H. Becker et
al., Adv. Mater. 12, 42 (2000) and referred to herein as C-PPV's.
Blends of these and other semi-conducting polymers and copolymers
which exhibit electroluminescence can be used. Where the electronic
device 100 is a photodetector, the photoactive layer 102 responds
to radiant energy and produces a signal either with or without a
biased voltage. Materials that respond to radiant energy and is
capable of generating a signal with a biased voltage (such as in
the case of a photoconductive cells, photoresistors, photoswitches,
phototransistors, phototubes) include, for example, many conjugated
polymers and electroluminescent materials. Materials that respond
to radiant energy and are capable of generating a signal without a
biased voltage (such as in the case of a photoconductive cell or a
photovoltaic cell) include materials that chemically react to light
and thereby generate a signal. Such light-sensitive chemically
reactive materials include for example, many conjugated polymers
and electro- and photo-luminescent materials. Specific examples
include, but are not limited to, MEH-PPV ("Optocoupler made from
semiconducting polymers", G. Yu, K. Pakbaz, and A. J. Heeger,
Journal of Electronic Materials, Vol. 23, pp 925-928 (1994); and
MEH-PPV Composites with CN-PPV ("Efficient Photodiodes from
Interpenetrating Polymer Networks", J. J. M. Halls et al.
(Cambridge group) Nature Vol. 376, pp. 498-500, 1995). The
electroactive organic materials can be tailored to provide emission
at various wavelengths.
[0061] In some embodiments, the polymeric photoactive material or
organic molecular photoactive material is present in the
photoactive layer 102 in admixture from 0% to 75% (w, basis overall
mixture) of carrier organic material (polymeric or organic
molecular). The criteria for the selection of the carrier organic
material are as follows. The material should allow for the
formation of mechanically coherent films, at low concentrations,
and remain stable in solvents that are capable of dispersing, or
dissolving the conjugated polymers for forming the film. Low
concentrations of carrier materials are preferred in order to
minimize processing difficulties, i.e., excessively high viscosity
or the formation of gross in homogeneities; however the
concentration of the carrier should be high enough to allow for
formation of coherent structures. Where the carrier is a polymeric
material, preferred carrier polymers are high molecular weight
(M.W.>100,000) flexible chain polymers, such as polyethylene,
isotactic polypropylene, polyethylene oxide, polystyrene, and the
like. Under appropriate conditions, which can be readily determined
by those skilled in the art, these macromolecular materials enable
the formation of coherent structures from a wide variety of
liquids, including water, acids, and numerous polar and non-polar
organic solvents. Films or sheets manufactured using these carrier
polymers have sufficient mechanical strength at polymer
concentrations as low as 1%, even as low as 0.1%, by volume to
enable the coating and subsequent processing as desired. Examples
of such coherent structures are those comprised of poly(vinyl
alcohol), poly(ethylene oxide), poly-para (phenylene
terephthalate), poly-para-benzamide, etc., and other suitable
polymers. On the other hand, if the blending of the final polymer
cannot proceed in a polar environment, non-polar carrier structures
are selected, such as those containing polyethylene, polypropylene,
poly(butadiene), and the like.
[0062] Typical film thicknesses of the photoactive layers range
from a few hundred .ANG.ngstrom units (200 .ANG.) to several
thousand Angstrom units (10,000 .ANG.) (1 .ANG.ngstrom
unit=10.sup.-8 cm). Although the active film thicknesses are not
critical, device performance can typically be improved by using
thinner films. Preferred thickness are from 300 .ANG. to 5,000
.ANG..
[0063] The Multilayer Anode (104)
[0064] The multilayer anode (104) includes the conductive first
layer (110), a low conductivity second layer (112) and a high
conductivity third layer (114).
[0065] The thickness of each layer 110, 112, 114 is determined by
the desired transparency and resistivity of such layer, such
transparency and resistivity factors are in turn dependent upon the
composition of the layer.
[0066] In the device of the invention that contains a photoactive
layer, one electrode is transparent to enable light emission from
the device or light reception by the device. Most commonly, the
anode is the transparent electrode, although the present invention
can also be used in an embodiment where the cathode is the
transparent electrode.
[0067] As used herein, the term "transparent" is defined to mean
"capable of transmitting at least about 25%, and preferably at
least about 50%, of the amount of light of a particular wavelength
of interest". Thus a material is considered "transparent" even if
its ability to transmit light varies as a function of wave length
but does meet the 25% or 50% criteria at a given wavelength of
interest. As is known to those working in the field of thin films,
one can achieve considerable degrees of transparency with metals if
the layers are thin enough, for example in the case of silver and
gold below about 300 .ANG., and especially from about 20 .ANG. to
about 250 .ANG. with silver having a relatively colorless (uniform)
transmittance and gold tending to favor the transmission of yellow
to red wavelengths. Similarly, for materials such as ITO, PANI and
PEDT, transparency can be achieved with a layer ranging from 100
.ANG. to 10,000 .ANG..
[0068] In addition to the desired transparency, the composition of
layers in the multilayer anode 104 should also be chosen so that
the third layer conductivity is less than the first layer
conductivity and more than the second layer conductivity.
Therefore, the choice of material for one layer of the multilayer
anode depends upon the composition of the other layers in the anode
and the corresponding conductivities of such other layers. Other
factors in determining composition are described below in sections
relating to the specific layers.
[0069] The Conductive First Layer (110)
[0070] The conductive first layer has low resistance: preferably
less than 300 ohms/square and more preferably less than 100
ohms/square.
[0071] The conductive first layer (110) of the composite anode
(104) provides electrical contact with an external electrical
source (not shown) and is a conductive layer made of a high work
function material, most typically an inorganic material with a work
function above about 4.5 eV. The conductive first layer 110 is
preferably made of materials containing a metal, mixed metal,
alloy, metal oxide or mixed-metal oxide. Suitable metals include
the Group 11 metals, the metals in Groups 4, 5, and 6, and the
Group 8-10 transition metals. If the anode 104 is to be
light-transmitting, mixed-metal oxides of Groups 12, 13 and 14
metals, such as indium-tin-oxide, are generally used. The IUPAC
numbering system is used throughout, where the groups from the
Periodic Table are numbered from left to right as 1-18 (CRC
Handbook of Chemistry and Physics, 81.sup.st Edition, 2000). The
first layer 110 may also comprise an organic material such as
polyaniline as described in "Flexible light-emitting diodes made
from soluble conducting polymer," Nature vol. 357, pp 477-479 (Jun.
11, 1992).
[0072] Typical inorganic materials which serve as anodes include
metals such as aluminum, silver, platinum, gold, palladium,
tungsten, indium, copper, iron, nickel, zinc, lead and the like;
metal oxides such as lead oxide, tin oxide, indium/tin-oxide and
the like; graphite; doped inorganic semiconductors such as silicon,
germanium, gallium arsenide, and the like. When metals such as
aluminum, silver, platinum, gold, palladium, tungsten, indium,
copper, iron, nickel, zinc, lead and the like are used, the anode
layer should be sufficiently thin to be semi-transparent. Metal
oxides such as indium/tin-oxide are typically at least
semitransparent.
[0073] Where the anode is transparent, the conductive metal-metal
oxide mixtures can be transparent as well at thicknesses up to as
high as 2500 .ANG. in some cases. Preferably, the thicknesses of
metal-metal oxide (or dielectric) layers is from about 25 to about
1200 .ANG. when transparency is desired.
[0074] The Low Conductivity Second Layer (112)
[0075] The second layer 112 should have sufficient high resistivity
to prevent cross talk or current leakage from the multilayer anode
and provide sufficient hole injection/transport. The low
conductivity second layer preferably has a bulk conductivity of
from about 10.sup.-4 S/cm to 10.sup.-11 S/cm. More preferably, the
second layer has a bulk conductivity of from 10.sup.-5 S/m to
10.sup.-8 S/cm.
[0076] The second layer 112 may comprise polyaniline (PANI) or an
equivalent conjugated conductive polymer such as polypyrole or
polythiophene, most commonly in a blend with one or more
nonconductive polymers. Polyaniline is particularly useful. Most
commonly it is in the emeraldine salt (ES) form. Useful conductive
polyanilines include the homopolymer and derivatives usually as
blends with bulk polymers (also known as host polymers). Examples
of PANI are those disclosed in U.S. Pat. No. 5,232,631.
[0077] In another embodiment, the second layer may include
conductive materials such as N,N'-diphenyl-N,N'-bis(3
-methylphenyl)-[1,1'-biphenyl]- -4,4'-diamine (TPD) and
bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylp- henyl)methane
(MPMP), and hole injection/transport polymers such as
polyvinylcarbazole (PVK), (phenylmethyl)polysilane,
poly(3,4-ethylenedioxythiophene) (PEDOT), and polyaniline
(PANI);electron and hole injection/transporting materials such as
4,4'-N,N'-dicarbazole biphenyl (BCP); or light-emitting materials
with good electron and hole transport properties, such as chelated
oxinoid compounds, such as tris(8-hydroxyquinolato)aluminum
(Alq.sub.3).
[0078] When the terms "polyaniline" or PANI are used herein, they
are used generically to include substituted and unsubstituted
materials, as well as other equivalent conjugated conductive
polymers such as the polypyrroles, or the polythiophenes, for
example poly(ethylenedioxythioph- ene) ("PEDT") unless the context
is clear that only the specific nonsubstituted form is intended. It
is also used in a manner to include any accompanying dopants,
particularly acidic materials used to render the polyaniline
conductive.
[0079] In general, polyanilines are polymers and copolymers of film
and fiber-forming molecular weight derived from the polymerization
of unsubstituted and substituted anilines of the Formula I: 1
[0080] wherein
[0081] n is an integer from 0 to 4;
[0082] m is an integer from 1 to 5 with the proviso that the sum of
n and m is equal to 5; and
[0083] R is independently selected so as to be the same or
different at each occurrence and is selected from the group
consisting of alkyl, alkenyl, alkoxy, cycloalkyl, cycloalkenyl,
alkanoyl, alkythio, aryloxy, alkylthioalkyl, alkylaryl, arylalkyl,
amino, alkylamino, dialkylamino, aryl, alkylsulfinyl, alkoxyalkyl,
alkylsulfonyl, arylthio, arylsulfonyl, alkoxycarbonyl,
arylsulfonyl, carboxylic acid, halogen, cyano, or alkyl substituted
with one or more sulfonic acid, carboxylic acid, halo, nitro, cyano
or epoxy moieties; or carboxylic acid, halogen, nitro, cyano, or
sulfonic acid moieties; or any two R groups together may form an
alkylene or alkenylene chain completing a 3, 4, 5, 6 or 7-membered
aromatic or alicyclic ring, which ring may optionally include one
or more divalent nitrogen, sulfur or oxygen atoms. Without
intending to limit the scope of this invention, the size of the
various R groups ranges from about 1 carbon (in the case of alkyl)
through 2 or more carbons up through about 20 carbons with the
total of n Rs being from about 1 to about 40 carbons.
[0084] Illustrative of the polyanilines useful in the practice of
this invention are those of the Formula II to V: 2
[0085] wherein:
[0086] n, m and R are as described above except that m is reduced
by 1 as a hydrogen is replaced with a covalent bond in the
polymerization and the sum of n plus m equals 4;
[0087] y is an integer equal to or greater than 0;
[0088] x is an integer equal to or greater than 1, with the proviso
that the sum of x and y is greater than 1; and
[0089] z is an integer equal to or greater than 1.
[0090] The following listing of substituted and unsubstituted
anilines are illustrative of those which can be used to prepare
polyanilines useful in the practice of this invention.
1 Aniline 2,5-Dimethylaniline o-Toluidine 2,3-Dimethylaniline
m-Toluidine 2,5-Dibutylaniline o-Ethylaniline 2,5-Dimethoxyaniline
m-Ethylaniline Tetrahydronaphthylamine o-Ethoxyaniline
o-Cyanoaniline m-Butylaniline 2-Thiomethylaniline m-Hexylaniline
2,5-Dichloroaniline m-Octylaniline 3-(n-Butanesulfonic acid)
aniline 4-Bromoaniline 2-Bromoaniline 3-Bromoaniline
2,4-Dimethoxyaniline 3-Acetamidoaniline 4-Mercaptoaniline
4-Acetamidoaniline 4-Methylthioaniline 5-Chloro-2-methoxyaniline
3-Phenoxyaniline 5-Chloro-2-ethoxyaniline 4-Phenoxyaniline
[0091] Illustrative of useful R groups are alkyl, such as methyl,
ethyl, octyl, nonyl, tert-butyl, neopentyl, isopropyl, sec-butyl,
dodecyl and the like, alkenyl such as 1-propenyl, 1-butenyl,
1-pentenyl, 1-hexenyl, 1-heptenyl, 1-octenyl and the like; alkoxy
such as propoxy, butoxy, methoxy, isopropoxy, pentoxy, nonoxy,
ethoxy, octoxy, and the like, cycloalkenyl such as cyclohexenyl,
cyclopentenyl and the like; alkanoyl such as butanoyl, pentanoyl,
octanoyl; ethanoyl, propanoyl and the like; alkylsulfinyl,
alkysulfonyl, alkylthio, arylsulfonyl, arylsulfinyl, and the like,
such as butylthio, neopentylthio, methylsulfinyl, benzylsulfinyl,
phenylsulfinyl, propylthio, octylthio, nonylsulfonyl,
octylsulfonyl, methylthio, isopropylthio, phenylsulfonyl,
methylsulfonyl, nonylthio, phenylthio, ethylthio, benzylthio,
phenethylthio, naphthylthio and the like; alkoxycarbonyl such as
methoxycarbonyl, ethoxycarbonyl, butoxycarbonyl and the like,
cycloalkyl such as cyclohexyl, cyclopentyl, cyclooctyl, cycloheptyl
and the like; alkoxyalkyl such as methoxymethyl, ethoxymethyl,
butoxymethyl, propoxyethyl, pentoxybutyl and the like; aryloxyalkyl
and aryloxyaryl such as phenoxyphenyl, phenoxymethylene and the
like; and various substituted alkyl and aryl groups such as
1-hydroxybutyl, 1-aminobutyl, 1-hydroxylpropyl, 1-hydyroxypentyl,
1-hydroxyoctyl, 1-hydroxyethyl, 2-nitroethyl, trifluoromethyl,
3,4-epoxybutyl, cyanomethyl, 3-chloropropyl, 4-nitrophenyl,
3-cyanophenyl, and the like; sulfonic acid terminated alkyl and
aryl groups and carboxylic acid terminated alkyl and aryl groups
such as ethylsulfonic acid, propylsulfonic acid, butylsulfonic
acid, phenylsulfonic acid, and the corresponding carboxylic
acids.
[0092] Also illustrative of useful R groups are divalent moieties
formed from any two R groups such as moieties of the formula: 3
[0093] wherein n* is an integer from about 3 to about 7, as for
example --(CH.sub.2).sub.-4, --(CH.sub.2).sub.-3 and
--(CH.sub.2).sub.-5, or such moieties which optionally include
heteroatoms of oxygen and sulfur such as --CH.sub.2SCH.sub.2-- and
--CH.sub.2--O--CH.sub.2--. Exemplary of other useful R groups are
divalent alkenylene chains including 1 to about 3 conjugated double
bond unsaturation such as divalent 1,3-butadiene and like
moieties.
[0094] Preferred for use in the practice of this invention are
polyanilines of the above Formulas II to V in which:
[0095] n is an integer from 0 to about 2;
[0096] m is an integer from 2 to 4, with the proviso that the sum
of n and m is equal to 4;
[0097] R is alkyl or alkoxy having from 1 to about 12 carbon atoms,
cyano, halogen, or alkyl substituted with carboxylic acid or
sulfonic acid substituents;
[0098] x is an integer equal to or greater than 1;
[0099] y is an integer equal to or greater than 0, with the proviso
that the sum of x and y is greater than about 4, and
[0100] z is an integer equal to or greater than about 5.
[0101] In more preferred embodiments of this invention, the
polyamline is derived from unsubstituted aniline, i.e., where n is
0 and m is 5 (monomer) or 4 (polymer). In general, the number of
monomer repeat units is at least about 50.
[0102] As described in U.S. Pat. No. 5,232,63 1, the polyaniline is
rendered conductive by the presence of an oxidative or acidic
species. Acidic species and particularly "functionalized protonic
acids" are preferred in this role. A "functionalized protonic acid"
is one in which the counter-ion has been functionalized preferably
to be compatible with the other components of this layer. As used
herein, a "protonic acid" is an acid that protonates the
polyaniline to form a complex with said polyaniline.
[0103] In general, functionalized protonic acids for use in the
invention are those of Formulas VI and VII:
A--R VI
[0104] or 4
[0105] wherein:
[0106] A is sulfonic acid, selenic acid, phosphoric acid, boric
acid or a carboxylic acid group; or hydrogen sulfate, hydrogen
selenate, hydrogen phosphate;
[0107] n is an integer from 1 to 5;
[0108] R is alkyl, alkenyl, alkoxy, alkanoyl, alkylthio,
alkylthioalkyl, having from 1 to about 20 carbon atoms; or
alkylaryl, arylalkyl, alkylsulfinyl, alkoxyalkyl, alkylsulfonyl,
alkoxycarbonyl, carboxylic acid, where the alkyl or alkoxy has from
0 to about 20 carbon atoms; or alkyl having from 3 to about 20
carbon atoms substituted with one or more sulfonic acid, carboxylic
acid, halogen, nitro, cyano, diazo, or epoxy moieties; or a
substituted or unsubstituted 3, 4, 5, 6 or 7 membered aromatic or
alicyclic carbon ring, which ring may include one or more divalent
heteroatoms of nitrogen, sulfur, sulfinyl, sulfonyl or oxygen such
as thiophenyl, pyrolyl, furanyl, pyridinyl.
[0109] In addition to these monomeric acid forms, R can be a
polymeric backbone from which depend a plurality of acid functions
"A." Examples of polymeric acids include sulfonated polystyrene,
sulfonated polyethylene and the like. In these cases the polymer
backbone can be selected either to enhance solubility in nonpolar
substrates or be soluble in more highly polar substrates in which
materials such as polymers, polyacrylic acid or
poly(vinylsulfonate), or the like, can be used.
[0110] R' is the same or different at each occurrence and is alkyl,
alkenyl, alkoxy, cycloalkyl, cycloalkenyl, alkanoyl, alkylthio,
aryloxy, alkylthioalkyl, alkylaryl, arylalkyl, alkylsulfinyl,
alkoxyalkyl, alkylsulfonyl, aryl, arylthio, arylsuldmyl,
alkoxycarbonyl, arylsulfonyl, carboxylic acid, halogen, cyano, or
alkyl substituted with one or more sulfonic acid, carboxylic acid,
halogen, nitro, cyano, diazo or epoxy moieties; or any two R
substituents taken together are an alkylene or alkenylene group
completing a 3, 4, 5, 6 or 7 membered aromatic or alicyclic carbon
ring or multiples thereof, which ring or rings may include one or
more divalent heteroatoms of nitrogen, sulfur, sulEmyl, sulfonyl or
oxygen. R' typically has from about 1 to about 20 carbons
especially 3 to 20 and more especially from about 8 to 20
carbons.
[0111] Materials of the above Formulas VI and VII are preferred in
which:
[0112] A is sulfonic acid, phosphoric acid or carboxylic acid;
[0113] n is an integer from 1 to 3;
[0114] R is alkyl, alkenyl, alkoxy, having from 6 to about 14
carbon atoms; or arylalkyl, where the alkyl or alkyl portion or
alkoxy has from 4 to about 14 carbon atoms; or alkyl having from 6
to about 14 carbon atoms substituted with one or more, carboxylic
acid, halogen, diazo, or epoxy moieties;
[0115] R' is the same or different at each occurrence and is alkyl,
alkoxy, alkylsulfonyl, having from 4 to 14 carbon atoms, or alkyl
substituted with one or more halogen moieties again with from 4 to
14 carbons in the alkyl.
[0116] Among the particularly preferred embodiments, most preferred
for use in the practice of this invention are functionalized
protonic acids of the above Formulas VI and VII in which:
[0117] A is sulfonic acid;
[0118] n is the integer 1 or 2;
[0119] R is alkyl or alkoxy, having from 6 to about 14 carbon
atoms; or alkyl having from 6 to about 14 carbon atoms substituted
with one or more halogen moieties;
[0120] R' is alkyl or alkoxy, having from 4 to 14, especially 12
carbon atoms, or alkyl substituted with one or more halogen,
moieties.
[0121] Preferred functionalized protonic acids are organic sulfonic
acids such as dodecylbenzene sulfonic acid and more preferably
poly(2-acrylamido-2-methyl- 1-propanesulfonic acid)
("PAAMPSA").
[0122] The amount of functionalized protonic acid employed can vary
depending on the degree of conductivity required. In general,
sufficient functionalized protonic acid is added to the
polyaniline-containing admixture to form a conducting material.
Usually the amount of functionalized protonic acid employed is at
least sufficient to give a conductive polymer (either in solution
or in solid form).
[0123] The polyaniline can be conveniently used in the practice of
this invention in any of its physical forms. Illustrative of useful
forms are those described in Green, A. G., and Woodhead, A. E., J.
Chem. Soc., 101, 1117 (1912) and Kobay.ashi, et al., J. Electroanl.
Chem., 177, 281-91 (1984), which are hereby incorporated by
reference. For unsubstituted polyaniline, useful forms include
leucoemeraldine, protoemeraldine, emeraldine, nigraniline and
tolu-protoemeraldine forms, with the emeraldine form being
preferred.
[0124] Copending PCT Patent Application No. PCT/US00/32545 of Cao,
Y. and Zhang, C. discloses the formation of low conductivity blends
of conjugated polymers with non-conductive polymers and is
incorporated herein by reference.
[0125] The particular bulk polymer or polymers added to the
conjugated polymer can vary. The selection of materials can be
based upon the nature of the conductive polymer, the method used to
blend the polymers and the method used to deposit the layer in the
device.
[0126] The materials can be blended by dispersing one polymer in
the other, either as a dispersion of small particles or as a
solution of one polymer in the otehr. The polymer are typically
admixed in a fluid phase and the layer is typically laid out of a
fluid phase.
[0127] We have had our best results using water-soluble or
water-dispensable conjugated polymers together with water-soluble
or water-dispensable bulk polymers. In this case, the blend can be
formed by dissolving or dispersing the two polymers in water and
casting a layer from the solution or dispersion.
[0128] Organic solvents can be used with organic-soluble or organic
dispensable conjugated polymers and bulk polymers. In addition,
blends can be formed using melts of the two polymers or by using a
liquid prepolymer or monomer form of the bulk polymer which is
subsequently polymerized or cured into the desired final
material.
[0129] In those presently preferred cases where the PANI is
water-soluble or water dispersable and it is desired to cast the
PANI layer from an aqueous solution, the bulk polymer should be
water soluble or water dispersible. In such cases, it is selected
from, for example polyacrylamides (PAM), poly(acrylic acid) (PAA)
poly(vinyl pyrrolidone) (PVPd), acrylamide copolymers, cellulose
derivatives, carboxyvinyl polymer, poly(ethylene glycols),
poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), poly(vinyl
methyl ether), polyamines, polyimines, polyvinylpyridines,
polysaccharides, end polyurethane dispersions.
[0130] In the case where it is desired to cast the layer from a
non-aqueous solution or dispersion the bulk polymer may be selected
from, for example liquefiable polyethylenes, isotactic
polypropylene, polystyrene, poly(vinylalcohol),
poly(ethylvinylacetate), polybutadienes, polyisoprenes,
ethylenevinylene-copolymers, ethylene-propylene copolymers,
poly(ethyleneterephthalate), poly(butyleneterephthalate) and nylons
such as nylon 12, nylon 8, nylon 6, nylon 6.6 and the like,
polyester materials, polyamides such as polyacrylamides and the
like.
[0131] In those cases where one polymer is being dispersed in the
other, the common solubility of the various polymers may not be
required.
[0132] The relative proportions of the polyaniline and bulk polymer
or prepolymer can vary. For each part of polyaniline there can be
from 0 to as much as 20 parts by weight of bulk polymer or
prepolymer with 0.5 to 10 and especially 1 to 4 parts of bulk
material being present for each part of PANI.
[0133] Solvents for the materials used to cast this layer are
selected to compliment the properties of the polymers.
[0134] In the preferred systems, the PANI and bulk polymer are both
water-soluble or water-dispersible and the solvent system is an
aqueous solvent system such as water or a mixture of water with one
or more polar organic materials such as lower oxyhydrocarbons for
example lower alcohols, ketones and esters.
[0135] These materials include, without limitation, water mixed
with methanol, ethanol, isopropanol, acetone methyl ethyl ketone
and the like.
[0136] If desired, but generally not preferred, a solvent system of
polar organic liquids could be used.
[0137] In the case of conducting polymers such as PANI and bulk
polymers which are not water-soluble or water-dispersible, nonpolar
solvents are most commonly used.
[0138] Illustrative of useful common nonpolar solvents are the
following materials: substituted or unsubstituted aromatic
hydrocarbons such as benzene, toluene, p-xylene, m-xylene,
naphthalene, ethylbenzene, styrene, aniline and the like; higher
alkanes such as pentane, hexane, heptane, octane, nonane, decane
and the like; cyclic alkanes such as decahydronaphthalene;
halogenated alkanes such as chloroform, bromoform, dichloromethane
and the like; halogenated aromatic hydrocarbons such as
chlorobenzene, o-dichlorobenzene, m-dichlorobenzene,
p-dichlorobenzene and the like; higher alcohols such as 2-butanol,
1-butanol, hexanol, pentanol, decanol, 2-methyl-1-propanol and the
like; higher ketones such as hexanone, butanone, pentanone and the
like; heterocyclics such as morpholine; perfluorinated hydrocarbons
such as perfluorodecaline, perfluorobenzene and the like.
[0139] The thickness of the second layer 112 will be chosen with
the properties of the diode in mind. In those situations where the
composite anode is to be transparent, it is generally preferable to
have the layer of PANI as thin as practically possible bearing in
mind the failure problem noted in FIG. 1. Typical thicknesses range
from about 100 .ANG. to about 5000 .ANG.. When transparency is
desired, thicknesses of from about 100 .ANG. to about 3000 .ANG.
are preferred and especially about 2000 .ANG..
[0140] Where the second layer 112 comprises a PANI(ES) blend and a
film thickness of 200 nm or greater, the electrical resistivity of
the second layer should be greater than or equal to 10.sup.4 ohm-cm
to avoid cross talk and inter-pixel current leakage. Values in
excess of 10.sup.5 ohm-cm are preferred. Even at 10.sup.5 ohm-cm,
there is some residual current leakage and consequently some
reduction in device efficiency. Thus, values of approximately from
10.sup.5 to 10.sup.8 ohm-cm are even more preferred. Values greater
than 10.sup.9 ohm-cm will lead to a significant voltage drop across
the injection/buffer layer and therefore should be avoided.
[0141] The High Conductivity Third Layer (114)
[0142] The material for the third layer 114 should be chosen to
match the energy level of the photoactive layer 102, or to improve
hole injection/transport of the multilayer anode 104, or to improve
the interfacial properties of the interface between the multilayer
anode 104 and photoactive layer 102.
[0143] The third component of the hole-injecting electrode is a
very thin layer of a highly conductive organic polymer having a
resistance that is lower than the resistance of the material of the
second layer 112 and higher than the first layer 110. A
representative conductive organic polymer include pure PANI in its
highly conductive forms, the polypyrroles and preferably
polythiophenes such as PEDT, and any of the other organic materials
described in the previous section for the second layer 112.
[0144] The material from which this layer (114) is formed should
have a bulk conductivity with is from about five times to about
10.sup.6 times as great as the bulk conductivity of the second
layer (112) is formed. Similarly the bulk resistivity should be
from five to 10.sup.6 times lower. Where transparency of the
multilayer anode 104 is desired and the layer comprises PEDT, this
third layer is typically very thin, often so thin as to likely not
be a completely continuous layer. The thickness should be in the
range of from about 5 .ANG. to about 500 .ANG. with thicknesses in
the range of 10 .ANG. to 50 .ANG. generally being preferred.
[0145] The addition of the high conductivity third layer (114) to
second layer (112) yields a multilayer structure has a higher
conductance than is observed with the second layer alone. The ratio
of conductance of the bilayer (112 and 114) structure to the
conductance of second layer 112 alone should range from about 1.25
to 20 with ratios of 1.5 to 15 and especially 2 to 10 being
preferred.
[0146] The Cathode (106)
[0147] Suitable materials for use as cathode materials are any
metal or nonmetal having a lower work function than the first
electrical contact layer (in this case, an anode). Materials for
the cathode layer 106 (in this case the second electrical contact)
can be selected from alkali metals of Group I (e.g., Li, Cs), the
Group 2 (alkaline earth) metals--commonly calcium, barium,
strontium, the Group 12 metals, the rare earths--commonly
ytterbium, the lanthanides, and the actinides. Materials such as
aluminum, indium and copper, silver, combinations thereof and
combinations with calcium and/or barium, Li, magnesium, LiF can be
used. Alloys of low work function metals, such as for example
alloys of magnesium in silver and alloys of lithium in aluminum,
are also useful.
[0148] The thickness of the electron-injecting cathode layer ranges
from less than 15 .ANG. to as much as 5,000 .ANG.. This cathode
layer 106 can be patterned to give a pixellated array or it can be
continuous and overlaid with a layer of bulk conductor such as
silver, copper or preferably aluminum which is, itself,
patterned.
[0149] The cathode layer may additionally include a second layer of
a second metal added to give mechanical strength and
durability.
[0150] The Substrate (108)
[0151] In most embodiments, the diodes are prepared on a substrate.
Typically the substrate should be nonconducting. In those
embodiments in which light passes through it, it is transparent. It
can be a rigid material such as a rigid plastic including rigid
acrylates, carbonates, and the like, rigid inorganic oxides such as
glass, quartz, sapphire, and the like. It can also be a flexible
transparent organic polymer such as polyester--for example
poly(ethyleneterephthalate), flexible polycarbonate, poly (methyl
methacrylate), poly(styrene) and the like.
[0152] The thickness of this substrate is not critical.
[0153] Contact Pads (80, 82)
[0154] Any contact pads 80, 82 useful to connect the electrode of
the device 100 to the power source (not shown) can be used,
including, for example, conductive metals such as gold (Au), silver
(Ag), nickel (Ni), copper (Cu) or aluminum (Al).
[0155] Preferably, contact pads 80, 82 have a height (not shown)
projected beyond the thickness of the high work function electrode
lines 110 below the total thickness of layer.
[0156] Preferably, the dimensions of layers 102, 110, and 112 are
such that contacts pads 80 are positioned on a section of the
substrate 108 not covered by layers 102, 112 and 114. In addition,
the dimensions of layer 106, 102, 110, and 112 are such that the
entire length and width electrode lines 106 and electrode lines 110
have at least one layer 102, 112 intervening between the electrodes
106, 110, while electrical connection can be made between electrode
106 and contact pads 80.
[0157] Other Optional Layers
[0158] An optional layer including an electron injection/transport
material may be provided between the photoactive layer 102 and the
cathode 106. This optional layer can function both to facilitate
electron injection/transport, and also serve as a buffer layer or
confinement layer to prevent quenching reactions at layer
interfaces. Preferably, this layer promotes electron mobility and
reduces quenching reactions. Examples of electron transport
materials for optional layer 140 include metal chelated oxinoid
compounds, such as tris(8-hydroxyquinolato)aluminu- m (Alq.sub.3);
phenanthroline-based compounds, such as
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (DDPA) or
4,7-diphenyl-1,10-phenanthroline (DPA), and azole compounds such as
2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) and
3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole (TAZ),
polymers containing DDPA, DPA, PBD, and TAZ moiety and polymer
blends thereof, polymer blends containing containing DDPA, DPA,
PBD, and TAZ. Alternatively, some or all of anode layers 110, 112,
114, the photoactive layer 102, and cathode layer 106, may be
surface treated to increase charge carrier transport efficiency.
The choice of materials for each of the component layers is
preferably determined by balancing the goals of providing a device
with high device efficiency.
[0159] Fabrication Techniques
[0160] The various elements of the devices of the present invention
may be fabricated by any of the techniques well known in the art,
such as solution casting, screen printing, web coating, ink jet
printing, sputtering, evaporation, precursor polymer processing,
melt-processing, and the like, or any combination thereof.
[0161] In the most common approach, the diodes are built up by
sequential deposit of layers upon a substrate. In a representative
preparation, the conductive first layer 110 of the composite
electrode 104 is laid down first. This layer is commonly deposited
by vacuum sputtering (RF or Magnetron), electron beam evaporation,
thermal vapor deposition, chemical deposition or the like methods
commonly used to form inorganic layers.
[0162] Next, the low conductivity second layer 112 is laid down.
This layer is usually most conveniently deposited as a layer from
solution by spin casting or like technique. In those preferred
cases where the layer is formed from water-soluble or
water-dispersible material water is generally used as the
spin-casting medium. In cases where a non-aqueous solvent is called
for are used such as toluene, xylenes, styrene, aniline,
decahydronaphthalene, chloroform, dichloromethane, chlorobenzenes
and morpholine. This layer can be heat-treated as described in
commonly filed U.S. provisional patent application No.
60/212,934.
[0163] Next, the higher conductivity layer 114 is deposited. Again,
this is typically done from solution with the solvent selected as
described with reference to the deposit of layer 112.
[0164] Next, the photoactive layer 102 of conjugated polymer is
deposited. The conjugated polymer can be deposited or cast directly
from solution. The solvent employed is one which will dissolve the
polymer and not interfere with its subsequent deposition.
[0165] Typically, organic solvents are used. These can include
halohydrocarbons such as methylene chloride, chloroform, and carbon
tetrachloride, aromatic hydrocarbons such as xylene, benzene,
toluene, other hydrocarbons such as decaline, and the like. Mixed
solvents can be used, as well. Polar solvents such as water,
acetone, acids and the like may be suitable. These are merely a
representative exemplification and the solvent can be selected
broadly from materials meeting the criteria set forth above.
[0166] When depositing various polymers on a substrate, the
solution can be relatively dilute, such as from 0.1 to 20% w in
concentration, especially 0.2 to 5% w. Film thicknesses of 500-4000
and especially 1000-2000 .ANG. are typically used.
[0167] Finally the low work function electron-injecting contact is
added. This contact is typically vacuum evaporated onto the top
surface of the active polymer layer.
[0168] These steps can be altered and even reversed if an "upside
down" diode is desired.
[0169] It will also be appreciated that the structures just
described and their fabrication can be altered to include other
layers for physical strength and protection, to alter the color of
the light emission or sensitivity of the diodes or the like. It
will further be appreciated that the present invention is further
useful in organic electronic devices including the multilayer anode
of the present invention do not contain a photoactive layer, such
as transistors, capacitors, resistors, chemoresistive sensors
(gas/vapor sensitive electronic noses, chemical and biosensors),
writing sensors, and electrochromic devices (smart window).
[0170] The invention will be further described by the following
Examples which are presented to illustrate the invention but not to
limit its scope.
EXAMPLE 1
[0171] PANI(ES) was prepared according to the following reference
(Y. Cao, et al, Polymer, 30 (1989) 2307). The emeraldine salt (ES)
form was verified by the typical green color. HCl in this reference
was replaced by poly(2-acrylamido-2-methyl-1-propanesulfonic acid
(PAAMPSA) (Aldrich). First, 30.5 g (0.022 mole) of 15% PAAMPSA in
water (Aldrich ) was diluted to 2.3% by adding 170 ml water. While
stirring, 2.2 g (0.022M) aniline was added into the PAAMPSA
solution. Then, 2.01 g (0.0088M) of ammonium persulfate in 10 ml
water was added slowly into the aniline/PAAMPSA solution under
vigorous stirring. The reaction mixture was stirred for 24 hours at
room temperature. To precipitate the product, PANI(ES), 1000 ml of
acetone was added into reaction mixture. Most of acetone/water was
decanted and then the PANI(ES) precipitate was filtered. The
resulting gum-like product was washed several times with acetone
and dried at 40.degree. C. under dynamic vacuum for 24 hours.
[0172] This Example demonstrates the direct synthesis of
PANI(ES).
EXAMPLE 2
[0173] Four grams (4.0 g) of the PANI(ES) powder prepared in
Example 1 was mixed with 400 g of deionized water in a plastic
bottle. The mixture was rotated at room temperature for 48 hours.
The solutions/dispersions were then filtered through 1 .mu.m
polypropylene filters. Different concentrations of PANI(ES) in
water are routinely prepared by changing the quantity of PANI(ES)
mixed into the water.
[0174] This Example demonstrates that PANI(ES) can be
dissolved/dispersed in water and subsequently filtered through a 1
.mu.m filter.
EXAMPLE 3
[0175] A poly(ethylenedioxythiophene), PEDT (Baytron P. special
grade, commercially available from Bayer), solution was diluted
with an equal amount deionized water. The solution was stirred at
room temperature overnight. The PEDT content of the solution was
0.8%. PEDT solutions were also prepared in which the content of
PEDT was 0.4, 0.2 and 0.16%, respectively. All these solutions can
be filtered through a 0.231 .mu.m filter.
EXAMPLE 4
[0176] Thirty grams (30 g.) of a PANI(ES)solution as prepared in
Example 2 was mixed with 7 g of deionized water and 0.6 g of poly
(acrylamide) (PAM)(M.W. 5,000,000-6,000,000, Polysciences) under
stirring at room temperature for 4-5 days. The weight ratio of
PANI(ES) to PAM in the blend solution is 1:2. Blend solutions were
also prepared in which the weight ratio of PANI(ES) to PAM was 1:1,
1:1.5, 1:2.5, 1:3, 1:4, 1:5, 1:6 and 1:9, respectively.
EXAMPLE 5
[0177] Glass substrates were prepared with patterned ITO
electrodes. Using the PANI, PEDT and PANI blend solutions as
prepared in Examples 2, 3 and 4, layers were spin-cast on top of
the patterned substrates and thereafter, baked at 90.degree. C. in
a vacuum oven for 0.5 hour. The films were then treated at
200.degree. C. in a dry box for 30 minutes. The resistance between
ITO electrodes was measured using a high resistance electrometer.
Thickness of the film was measured by using a Dec-Tac surface
profiler (Alpha-Step 500 Surface Profiler, Tencor Instruments).
Table 1 compares the conductivity and thickness of
PANI(ES),PANI(ES)-PAM blend and PEDT films. As can be seen from
Table, the conductivity of PANI(ES) and PEDT is 10-4 and 10-3 S/cm
respectively. Both values are too high for use in pixellated
displays. The high temperature treated PANI(ES)-PAM blend has ideal
conductivity and thickness for these materials to be used in
pixellated displays.
[0178] This Example demonstrates that a high temperature-treated
PANI(ES) blend has ideal conductivity and thickness for use in
pixellated displays; i.e. sufficiently low that interpixel current
leakage can be limited without need for patterning the PANI(ES)
blend film.
2TABLE 1 Bulk conductivity of PANI(ES), PANI(ES)-PAM blend and PEDT
Thickness Conductivity Blend Baking Condition (.ANG.) (S/cm) PANi
-- 426 5.1 .times. 10.sup.-4 PEDT -- 1221 1.8 .times. 10.sup.-3
PANi-PAM (1:2) 200.degree. C./30 min 2195 7.4 .times. 10-7
EXAMPLE 6
[0179] Light emitting diodes were fabricated using soluble
poly(1,4-phenylenevinylene) copolymer (C-PPV) (H. Becker, H.
Spreitzer, W. Kreduer, E. Kluge, H. Schenk, I.D. Parker and Y. Cao,
Adv. Mater. 12, 42 (2000) as the active semiconducting, luminescent
polymer; the thickness of the C-PPV films were 700-900 .ANG.. C-PPV
emits yellow-green light with emission peak at .about.560 nm.
Indium/tin oxide was used as the anode contact layer. A layer of
PANI, PEDT or PANI-PAM blend was then applied using the solutions
prepared in Examples 2, 3 and 4. These layers were spin-cast on top
of the patterned substrates. The layers were baked at 90.degree. C.
in a vacuum oven for 30 minutes, then treated at 200.degree. C. in
dry box for 30 minutes. The active layer and a metal cathode were
applied. The device architecture was ITO/Polyaniline
blend/C-PPV/metal. Devices were fabricated using both ITO on glass
(Applied ITO/glass) and ITO on plastic, polyethylene teraphthalate,
PET, as the substrate (Courtauld's ITO/PET); in both cases,
ITO/Polyaniline blend bilayer was the anode and the hole-injecting
contact. Devices were made with a layer of either Ca or Ba as the
cathode. The metal cathode film was fabricated on top of the C-PPV
layer using vacuum vapor deposition at pressures below
1.times.10.sup.-6 Torr yielding an active layer with area of 3
cm.sup.2. The deposition was monitored with a STM-100
thickness/rate meter (Sycon Instruments, Inc.). 2,000-5,000 .ANG.
of aluminum was deposited on top of the 15 .ANG. barium layer. For
each of the devices, the current vs. voltage curve, the light vs.
voltage curve, and the quantum efficiency were measured. The
measured operating voltage and efficiencies of the devices with
different blend layer are summarized in the Table 2. As can be seen
from the data, the lowest operating voltage and highest light
output were achieved from the device with the PEDT layer.
[0180] This Example demonstrates that highest performance polymer
LEDs can be fabricated using PEDT as a hole injection (buffer)
layer.
3TABLE 2 Performance of devices fabricated with PANI(ES),
PANI(ES)-PAM blend and PEDT Device Performance at 8.3 mA/cm.sup.2
Blend Baking Condition V cd/A Lm/W PANi -- 4.7 7.4 49 PEDT -- 4.5
7.7 5.2 PANi-PAM (1:2) 200.degree. C./30 min 6.6 7.2 3.6
EXAMPLE 7
[0181] Devices produced in accord with Example 6 were encapsulated
using a cover glass sandwiched by UV curable epoxy. The
encapsulated devices were run at a constant current of 3.3
ma/cm.sup.2 in an oven at a temperature of 70.degree. C. The total
current through the devices was 10 mA with luminance of approx. 200
cd/cm.sup.2. Table 3 and FIG. 3 shows the light output and voltage
increase during operation at 70.degree. C. The light output 300-1,
302-1, 304-1 for devices 300, 302 and 304 respectively are shown in
dashed lines in FIG. 3. The voltage output 300-2, 302-2, 304-2 for
devices 300, 302 and 304 respectively are shown in solid lines in
FIG. 3.
[0182] In contrast to devices with PANI(ES) and PANI(ES)-PAM blend
as anode, which degrade within 160-190 hours of stress at
70.degree. C., the half life of the devices with the PEDT layer
reaches 300 hours with a very low voltage increase (4.3 mV/hour).
It is almost twice longer than the device with PANI(ES)-PAM blend.
However, PEDT layers alone do not have resistance sufficiently high
to avoid inter-pixel current leakage and is not suitable for use in
pixellated displays. From Ahrennius plots of the luminance decay
and voltage increase data collected at 50, 70 and 85.degree. C.,
the temperature acceleration factor was estimated to be ca. 25 at
70.degree. C. Thus, the extrapolated stress life at room
temperature was determined to be approximately 7,500 hours for
devices with the PEDT layer.
[0183] This Example demonstrates that longest lifetimes can be
obtained for polymer LEDS fabricated with PEDT layers. However,
these layers do not have resistance sufficiently high to avoid
inter-pixel current leakage.
4TABLE 3 Stress life of LED devices fabricated with PANI(ES),
PANI(ES)-PAM blend and PEDT Stress Life Baking at 70.degree. C. at
3.3 mA/cm.sup.2 Ref. No. Blend Condition mV/h cd/m.sup.2*
t.sub.1/2(h) 300 PANi -- 7.4 185 186 302 PEDT -- 4.3 185 300 304
PANi-PAM (1:2) 200.degree. C./30 11.3 171 168 min *Initial
Brightness
EXAMPLE 8
[0184] The resistance measurements of Example 5 were repeated, but
the PANI(ES) layer was spin-cast from the blend solutions prepared
in Examples 4 at 1400 rpm. The weight ratio of PANI(ES) to PAM in
the blend solution is 1:2. The film was baked at 200.degree. C. for
30 minutes in dry box after dried in 90.degree. C. vacuum oven for
0.5 hour. The thin PEDT film was spinning cast on the top of the
PANI blend layer from the solution prepared in Example 3. The
thickness of the PEDT layer is ranged from 970 .ANG. to .about.10
.ANG.. The resistance between ITO electrodes was measured using a
high resistance electrometer. Thickness of the film was measured by
using a Dec-Tac surface profiler (Alpha-Step 500 Surface Profiler,
Tencor Instruments). Table 4 shows the surface resistance of
PANI(ES)-blend/PEDT double layer films with different PEDT
thickness. As can be seen from Table, the surface resistance of the
PANI(ES)-blend/PEDT double layer can be controlled over a wide
range, from 10.sup.7 to 10.sup.9 ohm/sq by adjusting the thickness
of PEDT layer. While the thickness of PEDT decrease to below 50
.ANG., the conductivity of the double layer is below 10.sup.8
ohm/sq, which is ideal for use in pixellated displays.
[0185] This Example demonstrates that PANI(ES)-blend/PEDT double
layer films can be prepared with conductivity less than 10.sup.8
ohm/sq.
5TABLE 4 Surface Resistance of PANI(ES)-PAM/PEDT double layer with
different PEDT thickness PEDT Double Solution Spinning PEDT Layer
Surface Concentration Rate Thickness Thickness Resistance (%) (rpm)
(.ANG.) (.ANG.) (ohm/sq) 1.6 800 970 2768 5.8 .times. 10.sup.7 0.8
3000 192 1788 4.0 .times. 10.sup.8 0.8 6000 90 1962 5.8 .times.
10.sup.8 0.4 6000 .about.50 2694 1.4 .times. 10.sup.9 0.2 3000
.about.40 2025 5.3 .times. 10.sup.9 0.2 6000 .about.20 1640 6.1
.times. 10.sup.9 0.16 4000 .about.10 2045 5.8 .times. 10.sup.9
EXAMPLE 9
[0186] The device measurements summarized in Example 6 were
repeated, but the PANI blend layer was replaced with
PANI(ES)-blend/PEDT double layers prepared as in Examples 8. Table
5 shows the device performance of LEDs fabricated from polyblend
films with various double layers. Devices fabricated with PANI
blend/PEDT double layers exhibit the same operating voltage and
light efficiency as devices made with PEDT layers.
[0187] This Example demonstrates that a PANI blend/PEDT double
layer can be used to fabricate polymer LEDs with the same low
operating voltage and high efficiency as devices made with a PEDT
layer.
6TABLE 5 Performance of devices fabricated with PANI(ES)-PAM/PEDT
double layer with different PEDT thickness PEDT Solution Spinning
PEDT Device Concentration Rate Thickness Performance at 8.3
mA/cm.sup.2 (%) (rpm) (.ANG.) V cd/A Lm/W 1.6 800 970 5.3 6.9 4.1
0.8 3000 192 4.3 7.2 5.2 0.8 6000 90 4.2 7.6 5.6 0.4 6000 .about.50
4.2 7.6 8.2 0.2 3000 .about.40 4.9 8.0 5.1 0.2 6000 .about.20 4.7
8.3 5.5 0.16 4000 .about.10 5.0 8.1 5.1
EXAMPLE 10
[0188] The stress measurements summarized in Example 7 were
repeated, but the PANI blend layer (incorporated in device 300 in
Table 3) was replaced by PANI blend/PEDT double layers prepared as
in Examples 8. Table 6 and FIG. 4 show the stress life of devices
fabricated with a PANI blend/PEDT double layer. In FIG. 4, the
light output 302-1, 304-1, 402-1, 404-1, and 406-1 for devices 302
and 304 as shown in Table 3 and devices 402, 404 and 460 as shown
in Table 6, respectively, are shown in dashed lines. The voltage
output 302-2, 304-2, 402-2, 404-2, and 406-2 for devices 302 and
304 as shown in Table 3 and devices 402, 404 and 460 as shown in
Table 6, respectively, are shown in solid lines.
[0189] As can be seen from the data, the voltage increase rate of
the double layer device with an .about.10 .ANG. to 20 .ANG. layer
of PEDT is slightly lower than that of device made from PEDT. The
half-life time of the double layer device is even slightly longer
than that of the PEDT device.
[0190] This Example demonstrates that the PANI blend/PEDT double
layer can combine the high resistance of PANI blend and long life
stress lifetime of PEDTin one device.
7TABLE 6 Stress life of LED devices fabricated with
PANI(ES)-PAM/PEDT double layer with different PEDT thickness FIG.
PEDT 4 Solution Spinning PEDT Stress Life at 70.degree. C. Ref
Concentration Rate Thickness at 8.3 mA/cm.sup.2 No. (%) (rpm)
(.ANG.) MV/h cd/m.sup.2* t.sub.1/2(h) 1.6 800 970 9.2 194 221 0.8
3000 192 5.8 144 300 402 0.8 6000 90 3.8 189 319 404 0.4 6000
.about.50 3.4 171 350 0.2 3000 .about.40 4.7 189 303 406 0.2 6000
.about.20 4.2 190 328 0.16 4000 .about.10 3.8 190 330 *Initial
Brightness
EXAMPLE 11
[0191] The resistance measurements of Example 5 were repeated, but
the PANI(ES) layer was spin-cast from the blend solutions prepared
in Examples 4. The weight ratio of PANI(ES) to PAM in the blend
solution is 1:1.5, 1:2, 1:3,1:4 1:5 and 1:6. The film was baked at
200.degree. C. for 30 minutes in dry box after dried in 90.degree.
C. vacuum oven for 0.5 hour. The thin PEDT film was spinning cast
on the top of the PANI blend layers from the solution prepared in
Example 3. The concentration of PEDT solution is 0.16% and the
spinning rate is 4000 rpm. The thickness of the PEDT layer is
.about.10 .ANG.. The resistance between ITO electrodes was measured
using a high resistance electrometer. Thickness of the film was
measured by using a Dec-Tac surface profiler (Alpha-Step 500
Surface Profiler, Tencor Instruments). Table 7 shows the surface
resistance of PANI blend/PEDT double layer films with different
PANI(ES) to PAM ratio. As can be seen from the Table, the surface
resistance of the PANI blend/PEDT double layer can be controlled
over a wide range, from 10.sup.8 to 10.sup.15 ohm/sq by adjusting
the weight ratio of PANI(ES)-PAM layer.
[0192] This Example demonstrates that PANI blend/PEDT double layer
films can be prepared with conductivity less than 10.sup.8 ohm/sq
and even less than 10.sup.13 ohm/sq.
8TABLE 7 Surface Resistance of PANI(ES)-PAM/PEDT double layer with
different PANI(ES)-PAM blend Double Layer Surface Composition
Thickness Resistance PANI Blend (w:w) (.ANG.) (ohm/sq) PANI-PAM
1:1.5 1822 6.6 .times. 10.sup.8 PANI-PAM 1:2 2078 5.7 .times.
10.sup.9 PANI-PAM 1:3 2252 2.1 .times. 10.sup.13 PANI-PAM 1:4 1621
1.1 .times. 10.sup.15 PANI-PAM 1:5 1734 9.0 .times. 10.sup.14
PANI-PAM 1:6 2422 9.6 .times. 10.sup.14
EXAMPLE 12
[0193] The device measurements summarized in Example 6 were
repeated, but the PANI blend layer was replaced with PANI
blend/PEDT double layers. Table 8 shows the device performance of
LEDs fabricated from polyblend films with different double layers.
When the PANI to PAM ratio was larger than 1:4, devices fabricated
with PANI blend/PEDT double layer exhibited the same operating
voltage and light efficiency as devices made with a PEDT layer
alone. The lower PANI(ES) to PAM ratios result in deterioration of
device performance.
[0194] This Example demonstrates that PANI blend/PEDT double layers
can be used to fabricate polymer LEDs with the same low operating
voltage and high efficiency as devices made with a PEDT layer
alone.
9TABLE 8 Performance of devices fabricated with
PANI(IES)-PAM/PEDTdouble layer with different PANI(ES)-PAM blends
Device Performance Composition Double Layer at 8.3 mA/cm.sup.2 PANI
Blend (w:w) Thickness (.ANG.) V cd/A Lm/W PANI-PAM 1:1.5 1822 6.0
6.4 3.4 PANI-PAM 1:2 2078 5.0 8.1 5.1 PANI-PAM 1:3 2252 5.8 7.9 4.3
PANI-PAM 1:4 1621 5.8 8.8 4.6 PANI-PAM 1:5 2422 8.0 8.7 3.1
PANI-PAM 1:6 2078 8.3 8.2 3.0
EXAMPLE 13
[0195] The stress measurements summarized in Example 7 were
repeated, but the PANI(ES)-blend layer was replaced with PANI
blend/PEDT double layers. Table 9 and FIG. 5 show the stress life
of devices fabricated with the PANI(ES) blend/PEDT double layers at
80.degree. C. The luminance 500-1, 502-1, 504-1, and 506-1 devices
500, 502, 504 and 506 respectively are shown in dashed lines in
FIG. 3. The voltage output 500-2, 502-2, 504-2, and 506-2 for
devices 500, 502, 504 and 506 respectively are shown in solid lines
in FIG. 5. When the PANI to PAM ratio is larger than 1:4, the
voltage increase rate of the double layer device was lower than
that of devices made from PEDT. The half-life time of the double
layer device is even longer than that of the PEDT device at
80.degree. C.
[0196] This Example demonstrates that the PANI(ES) blend/PEDT
double layer can combine the high resistance of PANI blend and the
long life stress life time of PEDT in one device.
10TABLE 9 Stress life of LED devices fabricated with
PANI(ES)-PAM/PEDT double layers with different PANI(ES)-PAM blend
Ref. No. Composition Double Layer Stress Life at 70.degree. C. at
3.3 ma/cm.sup.2: In FIG. 5 PANI Blend (w:w) Thickness (.ANG.) mV/h
cd/m.sup.2* t.sub.1/2(h) 500 PEDT -- -- 19.6 217 80 PANI-PAM 1:1.5
1822 19.8 198 108 502 PANI-PAM 1:2 2078 15.7 210 123 PANI-PAM 1:3
2252 17.9 180 89 504 PANI-PAM 1:4 1621 19.5 229 81 506 PANI-PAM 1:5
2422 67.2 232 61 PANI-PAM 1:6 2087 124.8 210 53 *Initial
Brightness
* * * * *