This invention relates to thermal transfer of emissive materials from
donor sheets to receptor substrates.
Pattern-wise thermal transfer of materials from donor sheets to receptor
substrates has been proposed for a wide variety of applications. For example, materials
can be selectively thermally transferred to form elements useful in electronic displays
and other devices. Specifically, selective thermal transfer of color filters, black
matrix, spacers, polarizers, conductive layers, transistors, phosphors, and organic
electroluminescent materials have all been proposed. Selective thermal transfer
of organic light emitters for formation of organic electroluminescent devices has
been shown to be particularly useful.
WO-A-92 06410 discloses a method for transferring a contrasting pattern
of intelligence from a composite ablation-transfer imaging medium to a receptor
element in contiguous registration therewith, said composite ablation-transfer imaging
medium comprising a support substrate (i), at least one intermediate dynamic release
layer (ii) essentially coextensive therewith and a laser radiation-ablative carrier
topcoat (iii) also essentially coextensive therewith, said laser radiation-ablative
carrier topcoat (iii) including an imaging amount of a contrast imaging material
contained therein and comprising at least one laser-ablative binder and at least
one laser absorber/sensitizer, and said at least one dynamic release layer (ii)
absorbing such laser radiation at a rate sufficient to effect the imagewise ablation
mass transfer of at least said carrier topcoat (iii), which method comprises imagewise
laser-irradiating said composite ablation-transfer imaging medium according to such
pattern of intelligence with an intensity sufficient to effect the imagewise ablation
mass transfer of the volume of the imagewise-exposed area of at least the laser
radiation-ablative carrier topcoat (iii) of said imaging medium securedly onto said
receptor element and whereby said transferred contrast imaging material delineates
said pattern of intelligence thereon.
Selective thermal transfer of organic electroluminescent materials
(also referred to as organic light emitters), and more specifically of light emitting
polymers (LEPs), can be important in patterning organic light emitting devices (OLEDs,
also referred to as organic electroluminescent devices). More traditional patterning
methods including photolithographic techniques, shadow mask techniques, screen printing
techniques, and others, have been problematic in patterning organic light emitters,
especially for making OLEDs based on LEPs and/or in making high resolution pixilated
displays. Selective thermal transfer can be a viable patterning method for a wide
variety of organic light emitters and for a wide variety of display constructions.
Some LEPs can be difficult to selectively thermally transfer with
high fidelity in their pure form. In many cases, this might be attributed to physical
and mechanical properties of the film or coating of LEP material being transferred.
Some physical and mechanical properties that may be important include molecular
weight, intra-layer cohesive strength, and the like. The present invention contemplates
blending LEPs with other materials to modify the physical and/or mechanical properties
of the LEP-based emissive layer being patterned to improve thermal transfer fidelity
while maintaining desired functionality of the emissive layer in an OLED.
In one embodiment, the present invention provides a thermal transfer
donor element that includes a substrate and a transfer layer capable of being selectively
thermally transferred from the donor element, the transfer layer including a blend
of a light emitting polymer and an additive that forms domains in the light emitting
polymer. The additive is selected to promote high fidelity thermal transfer of the
transfer layer. The blend is capable of forming the emissive layer of an organic
In another embodiment, the present invention provides a process for
patterning a light emitting polymer, including the steps of providing a thermal
transfer donor element, bringing the donor element into close proximity with a receptor
substrate, and selectively thermally transferring the transfer layer from the donor
to the receptor. The donor element includes a substrate and a transfer layer that
includes a blend of a light emitting polymer and an additive that forms domains
in the light emitting polymer. The additive is selected to promote high fidelity
thermal transfer of the transfer layer. The blend is capable of forming the emissive
layer of an organic electroluminescent device.
The invention may be more completely understood in consideration of
the following detailed description of various embodiments of the invention in connection
with the accompanying drawings, in which:
- FIG. 1 is a schematic cross section of a thermal transfer donor element.
The present invention is believed to be applicable to thermal mass
transfer of LEP materials from a donor element to a receptor to form OLEDs or portions
thereof. In particular, the present invention is directed to thermal mass transfer
of blends of materials that include an LEP and an additive selected to promote thermal
transfer, the blends capable of forming an emissive layer in an OLED. The present
invention provides a donor element that includes a thermal transfer layer that includes
a blend of an LEP and an additive selected to improve the fidelity of pattern-wise
thermal transfer and to maintain device functionality (e.g., as compared to a device
employing the LEP in its pure form) when the blend is transferred as the emissive
layer of an OLED. According to the present invention, selectively thermally transferable
LEP blends can be prepared that include an LEP and a compatible additive such as
another polymer, oligomer, or small molecule organic material that is either inert
or active (e.g., charge carrying, emissive, conductive) in the emissive layer of
an OLED. The additive can be selected to promote thermal transfer properties, for
example by reducing intra-layer cohesive energy in the transfer layer, altering
average molecular weight, enhancing adhesion to the receptor upon transfer, and
Examples of classes of LEP materials that can be used in blends of
the present invention include poly(phenylenevinylene)s (PPVs), poly-para-phenylenes
(PPPs), polyfluorenes (PFs), and co-polymers thereof. Examples of suitable LEP materials
can also be found in J.L. Segura, "The Chemistry of Electroluminescent Organic Materials",
Acta Polym., 49, pp. 319-344 (1998), and A. Kraft et al., "Electroluminescent
Conjugated Polymers―Seeing Polymers in a New Light", Angew. Chem. Int.
Ed., 37, pp. 402-428 (1998). Suitable LEPs can also be molecularly doped, dispersed
with fluorescent dyes, etc. Other types of polymer-based emissive materials include
small molecule light emitters dispersed in a polymer matrix. For example, poly(9-vinylcarbazole),
commonly known as PVK, PVCz, or polyvinylcarbazole, is frequently used as a polymeric
matrix for disposing small molecules for hybrid OLEDs.
Examples of additives that can be used in blends of the present invention
include small molecule organics (inert, conductive, light emitting), oligomers of
the LEP in the blend or of different polymers (inert, conductive, conjugated), other
polymers (inert, conductive, conjugated), plasticizers, tackifying resins, and others.
LEP blends should include compatible materials, for example materials that are soluble
in some of the same solvents and that can be coated to form a uniform film when
LEP blends can be selectively thermally transferred from one or more
donor elements as single layers to form emissive layers in OLEDs, or can be selectively
thermally transferred from one or more donor elements as a layer of multiple layer
stacks (e.g., stacks that include one or more of a charge transport layer, a charge
injection layer, a buffer layer, an electrode layer, an adhesive layer, etc., along
with the emissive LEP blend layer) to form OLEDs.
The ability to blend selected compatible additives with materials
can enable higher fidelity patterning of a wider range of emissive materials for
OLEDs. This can be particularly useful when thermally transferring high molecular
weight LEPs or LEPs that, in their pure form, exhibit a high intra-layer cohesive
strength. In some instances, it may be difficult to thermally transfer such materials.
Because such materials provide functionality, it also may be seen as not desirable
to alter them from their pure form in order to improve their transferability in
thermal patterning operations. The present invention, however, shows that LEP blends
can be made that allow for enhancement of thermal transfer properties by altering
physical and mechanical properties of LEP layers while maintaining, and in some
cases improving, the light emission functionality of the LEP in an OLED.
The present invention contemplates donor elements that include LEP
blends in their transfer layers, processes of selectively transferring LEP blends,
and displays and devices made by selective thermal transfer of LEP blends. FIG.
1 shows an example of a thermal transfer donor 100 suitable for use in the present
invention. Donor element 100 includes a base substrate 110, an optional underlayer
112, a light-to-heat conversion layer (LTHC layer) 114, an optional interlayer 118,
and a transfer layer 116. Other layers can also be present. Exemplary donors are
disclosed in U.S. Pat. Nos. 6,114,088; 5,998,085; and 5,725,989, in International
Publication No. 00/41893, and in U.S. Patent Nos. 6,284,425 and 6,228,555.
In processes of the present invention, materials can be transferred
from the transfer layer of a thermal mass transfer donor element to a receptor substrate
by placing the transfer layer of the donor element adjacent to the receptor and
irradiating the donor element with imaging radiation that can be absorbed by the
LTHC layer and converted into heat. The donor can be exposed to imaging radiation
through the donor substrate, or through the receptor, or both. The radiation can
include one or more wavelengths, including visible light, infrared radiation, or
ultraviolet radiation, for example from a laser, lamp, or other such radiation source.
Material from the thermal transfer layer can be selectively transferred to a receptor
in this manner to imagewise form patterns of the transferred material on the receptor.
In many instances, thermal transfer using light from, for example, a lamp or laser,
is advantageous because of the accuracy and precision that can often be achieved.
The size and shape of the transferred pattern (e.g., a line, circle, square, or
other shape) can be controlled by, for example, selecting the size of the light
beam, the exposure pattern of the light beam, the duration of directed beam contact
with the thermal mass transfer element, and/or the materials of the thermal mass
transfer element. The transferred pattern can also be controlled by irradiating
the donor element through a mask.
Alternatively, a thermal print head or other heating element (patterned
or otherwise) can be used to selectively heat the donor element directly, thereby
pattern-wise transferring portions of the transfer layer. In such a case, the LTHC
layer in the donor sheet is optional. Thermal print heads or other heating elements
may be particularly suited for patterning devices for lower resolution information
displays including segmented displays, emissive icons, and the like.
The mode of thermal mass transfer can vary depending on the type of
irradiation, the type of materials and properties of the LTHC layer, the type of
materials in the transfer layer, etc., and generally occurs via one or more mechanisms,
one or more of which may be emphasized or de-emphasized during transfer depending
on imaging conditions, donor constructions, and so forth. One mechanism of thermal
transfer includes thermal melt-stick transfer whereby localized heating at the interface
between the thermal transfer layer and the rest of the donor element can lower the
adhesion of the thermal transfer layer to the donor in selected locations. Selected
portions of the thermal transfer layer can adhere to the receptor more strongly
than to the donor so that when the donor element is removed, the selected portions
of the transfer layer remain on the receptor. Another mechanism of thermal transfer
includes ablative transfer whereby localized heating can be used to ablate portions
of the transfer layer off of the donor element, thereby directing ablated material
toward the receptor. Yet another mechanism of thermal transfer includes sublimation
whereby material dispersed in the transfer layer can be sublimated by heat generated
in the donor element. A portion of the sublimated material can condense on the receptor.
The present invention contemplates transfer modes that include one or more of these
and other mechanisms whereby the heat generated in an LTHC layer of a thermal mass
transfer donor element can be used to cause the transfer of materials from a transfer
layer to receptor surface.
A variety of radiation-emitting sources can be used to heat thermal
mass transfer donor elements. For analog techniques (e.g., exposure through a mask),
high-powered light sources (e.g., xenon flash lamps and lasers) are useful. For
digital imaging techniques, infrared, visible, and ultraviolet lasers are particularly
useful. Suitable lasers include, for example, high power (≥ 100 mW) single mode
laser diodes, fiber-coupled laser diodes, and diode-pumped solid state lasers (e.g.,
Nd:YAG and Nd:YLF). Laser exposure dwell times can vary widely from, for example,
a few hundredths of microseconds to tens of microseconds or more, and laser fluences
can be in the range from, for example, 0.01 to 5 J/cm2 or more. Other
radiation sources and irradiation conditions can be suitable based on, among other
things, the donor element construction, the transfer layer material, the mode of
thermal mass transfer, and other such factors.
When high spot placement accuracy is required (e.g., for high information
full color display applications) over large substrate areas, a laser is particularly
useful as the radiation source. Laser sources are also compatible with both large
rigid substrates (e.g., 1 m × 1 m × 1.1 mm glass) and continuous or
sheeted film substrates (e.g., 100 µm thick polyimide sheets).
During imaging, the thermal mass transfer element can be brought into
intimate contact with a receptor (as might typically be the case for thermal melt-stick
transfer mechanisms) or the thermal mass transfer element can be spaced some distance
from the receptor (as can be the case for ablative transfer mechanisms or transfer
material sublimation mechanisms). In at least some instances, pressure or vacuum
can be used to hold the thermal transfer element in intimate contact with the receptor.
In some instances, a mask can be placed between the thermal transfer element and
the receptor. Such a mask can be removable or can remain on the receptor after transfer.
A radiation source can then be used to heat the LTHC layer (and/or other layer(s)
containing radiation absorber) in an imagewise fashion (e.g., digitally or by analog
exposure through a mask) to perform imagewise transfer and/or patterning of the
transfer layer from the thermal transfer element to the receptor.
Typically, selected portions of the transfer layer are transferred
to the receptor without transferring significant portions of the other layers of
the thermal mass transfer element, such as the optional interlayer or the LTHC layer.
The presence of the optional interlayer may eliminate or reduce the transfer of
material from the LTHC layer to the receptor and/or reduce distortion in the transferred
portion of the transfer layer. Preferably, under imaging conditions, the adhesion
of the optional interlayer to the LTHC layer is greater than the adhesion of the
interlayer to the transfer layer. In some instances, a reflective interlayer can
be used to attenuate the level of imaging radiation transmitted through the interlayer
and reduce any damage to the transferred portion of the transfer layer that may
result from interaction of the transmitted radiation with the transfer layer and/or
the receptor. This is particularly beneficial in reducing thermal damage which may
occur when the receptor is highly absorptive of the imaging radiation.
Large thermal transfer elements can be used, including thermal transfer
elements that have length and width dimensions of a meter or more. In operation,
a laser can be rastered or otherwise moved across the large thermal transfer element,
the laser being selectively operated to illuminate portions of the thermal transfer
element according to a desired pattern. Alternatively, the laser may be stationary
and the thermal transfer element and/or receptor substrate moved beneath the laser.
In some instances, it may be necessary, desirable, and/or convenient
to sequentially use two or more different thermal transfer elements to form electronic
devices on a receptor. For example, multiple layer devices can be formed by transferring
separate layers or separate stacks of layers from different thermal transfer elements.
Multilayer stacks can also be transferred as a single transfer unit from a single
donor element. Examples of multilayer devices include transistors such as organic
field effect transistors (OFETs), organic electroluminescent pixels and/or devices,
including OLEDs. Multiple donor sheets can also be used to form separate components
in the same layer on the receptor. For example, three different donors that each
have a transfer layer comprising an organic electroluminescent material that emits
a different color (for example, red, green, and blue) can be used to form RGB sub-pixel
OLED elements for a color electronic display. Also, separate donor sheets, each
having multiple layer transfer layers, can be used to pattern different multilayer
devices (e.g., OLEDs that emit different colors, OLEDs and OFETs that connect to
form addressable pixels, etc.). Typically, materials from separate donor sheets
are transferred adjacent to other materials on a receptor for form adjacent devices,
portions of adjacent devices, or different portions of the same device. Alternatively,
materials from separate donor sheets can be transferred directly on top of, or in
partial overlying registration with, other layers or materials previously patterned
onto the receptor either by thermal transfer or some other transfer method. A variety
of other combinations of two or more thermal transfer elements can be used to form
a device, each thermal transfer element forming one or more portions of the device.
It will be understood other portions of these devices, or other devices on the receptor,
may be formed in whole or in part by any suitable process including photolithographic
processes, ink jet processes, and various other printing or mask-based processes.
Referring back to FIG. 1, various layers of the thermal mass transfer
donor element 100 will now be described.
The donor substrate 110 can be a polymer film. One suitable type of
polymer film is a polyester film, for example, polyethylene terephthalate or polyethylene
naphthalate films. However, other films with sufficient optical properties, including
high transmission of light at a particular wavelength, as well as sufficient mechanical
and thermal stability for the particular application, can be used. The donor substrate,
in at least some instances, is flat so that uniform coatings can be formed. The
donor substrate is also typically selected from materials that remain stable despite
heating of the LTHC layer. However, as described below, the inclusion of an underlayer
between the substrate and the LTHC layer can be used to insulate the substrate from
heat generated in the LTHC layer during imaging. The typical thickness of the donor
substrate ranges from 0.025 to 0.15 mm, preferably 0.05 to 0.1 mm, although thicker
or thinner donor substrates may be used.
The materials used to form the donor substrate and an adjacent underlayer
can be selected to improve adhesion between the donor substrate and the underlayer,
to control heat transport between the substrate and the underlayer, to control imaging
radiation transport to the LTHC layer, to reduce imaging defects and the like. An
optional priming layer can be used to increase uniformity during the coating of
subsequent layers onto the substrate and also increase the bonding strength between
the donor substrate and adjacent layers. One example of a suitable substrate with
primer layer is available from Teijin Ltd. (Product No. HPE100, Osaka, Japan).
An optional underlayer 112 may be coated or otherwise disposed between
a donor substrate and the LTHC layer, for example to control heat flow between the
substrate and the LTHC layer during imaging and/or to provide mechanical stability
to the donor element for storage, handling, donor processing, and/or imaging. Examples
of suitable underlayers and methods of providing underlayers are disclosed in U.S.
Patent No. 6,284,425.
The underlayer can include materials that impart desired mechanical
and/or thermal properties to the donor element. For example, the underlayer can
include materials that exhibit a low (specific heat × density) and/or low
thermal conductivity relative to the donor substrate. Such an underlayer may be
used to increase heat flow to the transfer layer, for example to improve the imaging
sensitivity of the donor.
The underlayer may also include materials for their mechanical properties
or for adhesion between the substrate and the LTHC. Using an underlayer that improves
adhesion between the substrate and the LTHC layer may result in less distortion
in the transferred image. As an example, in some cases an underlayer can be used
that reduces or eliminates delamination or separation of the LTHC layer, for example,
that might otherwise occur during imaging of the donor media. This can reduce the
amount of physical distortion exhibited by transferred portions of the transfer
layer. In other cases, however it may be desirable to employ underlayers that promote
at least some degree of separation between or among layers during imaging, for example
to produce an air gap between layers during imaging that can provide a thermal insulating
function. Separation during imaging may also provide a channel for the release of
gases that may be generated by heating of the LTHC layer during imaging. Providing
such a channel may lead to fewer imaging defects.
The underlayer may be substantially transparent at the imaging wavelength,
or may also be at least partially absorptive or reflective of imaging radiation.
Attenuation and/or reflection of imaging radiation by the underlayer may be used
to control heat generation during imaging.
The underlayer can be comprised of any of a number of known polymers
such as thermoset (crosslinked), thermosettable (crosslinkable), or thermoplastic
polymers, including acrylates (including methacrylates, blends, mixtures, copolymers,
terpolymers, tetrapolymers, oligomers, macromers, etc.), polyols (including polyvinyl
alcohols), epoxy resins (also including copolymers, blends, mixtures, terpolymers,
tetrapolymers, oligomers, macromers, etc.), silanes, siloxanes (with all types of
variants thereof), polyvinyl pyrrolidinones, polyesters, polyimides, polyamides,
poly (phenylene sulphide), polysulphones, phenol-formaldehyde resins, cellulose
ethers and esters (for example, cellulose acetate, cellulose acetate butyrate, etc.),
nitrocelluloses, polyurethane, polyesters (for example, poly (ethylene terephthalate),
polycarbonates, polyolefin polymers (for example, polyethylene, polypropylene, polychloroprene,
polyisobutylene, polytetrafluoroethylene, polychlorotrifluoroethylene, poly (p-chlorostyrene),
polyvinylidene fluoride, polyvinylchloride, polystyrene, etc.) and copolymers (for
example, polyisobutene-co-isoprene, etc.), polymerizable compositions comprising
mixtures of these polymerizable active groups (e.g., epoxy-siloxanes, epoxy-silanes,
acryloyl-silanes, acryloyl-siloxanes, acryloyl-epoxies, etc.), phenolic resins (e.g.,
novolak and resole resins), polyvinylacetates, polyvinylidene chlorides, polyacrylates,
, nitrocelluloses, polycarbonates, and mixtures thereof The underlayers may include
homopolymers or copolymers (including, but not limited to random copolymers, graft
copolymers, block copolymers, etc.).
Underlayers may be formed by any suitable means, including coating,
laminating, extruding, vacuum or vapor depositing, electroplating, and the like.
For example, crosslinked underlayers may be formed by coating an uncrosslinked material
onto a donor substrate and crosslinking the coating. Alternatively a crosslinked
underlayer may be initially formed and then laminated to the substrate subsequent
to crosslinking. Crosslinking can take place by any means known in the art, including
exposure to radiation and/or thermal energy and/or chemical curatives (water, oxygen,
The thickness of the underlayer is typically greater than that of
conventional adhesion primers and release layer coatings, preferably greater than
0.1 µm (microns), more preferably greater than 0.5 µm (microns), most preferably
greater than 1 µm (micron). In some cases, particularly for inorganic or metallic
underlayers, the underlayer can be much thinner. For example, thin metal underlayers
that are at least partially reflective at the imaging wavelength might be useful
in imaging systems where the donor elements are irradiated from the transfer layer
side. In other cases, the underlayers can be much thicker than these ranges, for
example when the underlayer is included to provide some mechanical support in the
Referring again to FIG. 1, an LTHC layer 114 can be included in thermal
mass transfer elements of the present invention to couple irradiation energy into
the thermal transfer element. The LTHC layer preferably includes a radiation absorber
that absorbs incident radiation (e.g., laser light) and converts at least a portion
of the incident radiation into heat to enable transfer of the transfer layer from
the thermal transfer element to the receptor.
Generally, the radiation absorber(s) in the LTHC layer absorb light
in the infrared, visible, and/or ultraviolet regions of the electromagnetic spectrum
and convert the absorbed radiation into heat. The radiation absorber materials are
typically highly absorptive of the selected imaging radiation, providing an LTHC
layer with an optical density at the wavelength of the imaging radiation in the
range of 0.2 to 3 or higher. Optical density is the absolute value of the logarithm
(base 10) of the ratio of the intensity of light transmitted through the layer to
the intensity of light incident on the layer.
Radiation absorber material can be uniformly disposed throughout the
LTHC layer or can be non-homogeneously distributed. For example, as described in
U.S. Patent No. 6,228,555, non-homogeneous LTHC layers can be used to control temperature
profiles in donor elements. This can give rise to thermal transfer elements that
have improved transfer properties (e.g., better fidelity between the intended transfer
patterns and actual transfer patterns).
Suitable radiation absorbing materials can include, for example, dyes
(e.g., visible dyes, ultraviolet dyes, infrared dyes, fluorescent dyes, and radiation-polarizing
dyes), pigments, metals, metal compounds, metal films, and other suitable absorbing
materials. Examples of suitable radiation absorbers includes carbon black, metal
oxides, and metal sulfides. One example of a suitable LTHC layer can include a pigment,
such as carbon black, and a binder, such as an organic polymer. Another suitable
LTHC layer includes metal or metal/metal oxide formed as a thin film, for example,
black aluminum (i.e., a partially oxidized aluminum having a black visual appearance).
Metallic and metal compound films may be formed by techniques, such as, for example,
sputtering and evaporative deposition. Particulate coatings may be formed using
a binder and any suitable dry or wet coating techniques. LTHC layers can also be
formed by combining two or more LTHC layers containing similar or dissimilar materials.
For example, an LTHC layer can be formed by vapor depositing a thin layer of black
aluminum over a coating that contains carbon black disposed in a binder.
Dyes suitable for use as radiation absorbers in a LTHC layer may be
present in particulate form, dissolved in a binder material, or at least partially
dispersed in a binder material. When dispersed particulate radiation absorbers are
used, the particle size can be, at least in some instances, 10 µm or less, and may
be 1 µm or less. Suitable dyes include those dyes that absorb in the IR region of
the spectrum. For example, IR absorbers marketed by Glendale Protective Technologies,
Inc., Lakeland, Fla., under the designation CYASORB IR-99, IR-126 and IR-165 may
be used. A specific dye may be chosen based on factors such as, solubility in, and
compatibility with, a specific binder and/or coating solvent, as well as the wavelength
range of absorption.
Pigmentary materials may also be used in the LTHC layer as radiation
absorbers. Examples of suitable pigments include carbon black and graphite, as well
as phthalocyanines, nickel dithiolenes, and other pigments described in U.S. Pat.
Nos. 5,166,024 and 5,351,617. Additionally, black azo pigments based on copper or
chromium complexes of, for example, pyrazolone yellow, dianisidine red, and nickel
azo yellow can be useful. Inorganic pigments can also be used, including, for example,
oxides and sulfides of metals such as aluminum, bismuth, tin, indium, zinc, titanium,
chromium, molybdenum, tungsten, cobalt, iridium, nickel, palladium, platinum, copper,
silver, gold, zirconium, iron, lead, and tellurium. Metal borides, carbides, nitrides,
carbonitrides, bronze-structured oxides, and oxides structurally related to the
bronze family (e.g., WO2.9) may also be used.
Metal radiation absorbers may be used, either in the form of particles,
as described for instance in U.S. Pat. No. 4,252,671, or as films, as disclosed
in U.S. Pat. No. 5,256,506. Suitable metals include, for example, aluminum, bismuth,
tin, indium, tellurium and zinc.
Suitable binders for use in the LTHC layer include film-forming polymers,
such as, for example, phenolic resins (e.g., novolak and resole resins), polyvinyl
butyral resins, polyvinyl acetates, polyvinyl acetals, polyvinylidene chlorides,
polyacrylates, cellulosic ethers and esters, nitrocelluloses, and polycarbonates.
Suitable binders may include monomers, oligomers, or polymers that have been, or
can be, polymerized or crosslinked. Additives such as photoinitiators may also be
included to facilitate crosslinking of the LTHC binder. In some embodiments, the
binder is primarily formed using a coating of crosslinkable monomers and/or oligomers
with optional polymer.
The inclusion of a thermoplastic resin (e.g., polymer) may improve,
in at least some instances, the performance (e.g., transfer properties and/or coatability)
of the LTHC layer. It is thought that a thermoplastic resin may improve the adhesion
of the LTHC layer to the donor substrate. In one embodiment, the binder includes
25 to 50 wt.% (excluding the solvent when calculating weight percent) thermoplastic
resin, and, preferably, 30 to 45 wt.% thermoplastic resin, although lower amounts
of thermoplastic resin may be used (e.g., 1 to 15 wt.%). The thermoplastic resin
is typically chosen to be compatible (i.e., form a one-phase combination) with the
other materials of the binder. In at least some embodiments, a thermoplastic resin
that has a solubility parameter in the range of 18 to 27 (J/cm3) 9 to
13 (cal/cm3)1/2), preferably, 19 to 26 (J/cm3)1/2
(9.5 to 12 (cal/cm3)1/2), is chosen for the binder. Examples
of suitable thermoplastic resins include polyacrylics, styrene-acrylic polymers
and resins, and polyvinyl butyral.
Conventional coating aids, such as surfactants and dispersing agents,
may be added to facilitate the coating process. The LTHC layer may be coated onto
the donor substrate using a variety of coating methods known in the art. A polymeric
or organic LTHC layer is coated, in at least some instances, to a thickness of 0.05
µm to 20 µm, preferably, 0.5 µm to 10 µm, and, more preferably, 1 µm to 7 µm. An
inorganic LTHC layer is coated, in at least some instances, to a thickness in the
range of 0.0005 to 10 µm, and preferably, 0.001 to 1 µm.
Referring again to FIG. 1, an optional interlayer 118 may be disposed
between the LTHC layer 114 and transfer layer 116. The interlayer can be used, for
example, to minimize damage and contamination of the transferred portion of the
transfer layer and may also reduce distortion in the transferred portion of the
transfer layer. The interlayer may also influence the adhesion of the transfer layer
to the rest of the thermal transfer donor element. Typically, the interlayer has
high thermal resistance. Preferably, the interlayer does not distort or chemically
decompose under the imaging conditions, particularly to an extent that renders the
transferred image non-functional. The interlayer typically remains in contact with
the LTHC layer during the transfer process and is not substantially transferred
with the transfer layer.
Suitable interlayers include, for example, polymer films, metal layers
(e.g., vapor deposited metal layers), inorganic layers (e.g., sol-gel deposited
layers and vapor deposited layers of inorganic oxides (e.g., silica, titania, and
other metal oxides)), and organic/inorganic composite layers. Organic materials
suitable as interlayer materials include both thermoset and thermoplastic materials.
Suitable thermoset materials include resins that may be crosslinked by heat, radiation,
or chemical treatment including, but not limited to, crosslinked or crosslinkable
polyacrylates, polymethacrylates, polyesters, epoxies, and polyurethanes. The thermoset
materials may be coated onto the LTHC layer as, for example, thermoplastic precursors
and subsequently crosslinked to form a crosslinked interlayer.
Suitable thermoplastic materials include, for example, polyacrylates,
polymethacrylates, polystyrenes, polyurethanes, polysulfones, polyesters, and polyimides.
These thermoplastic organic materials may be applied via conventional coating techniques
(for example, solvent coating, spray coating, or extrusion coating). Typically,
the glass transition temperature (Tg) of thermoplastic materials suitable
for use in the interlayer is 25 °C or greater, preferably 50 °C or greater, more
preferably 100°C or greater, and, most preferably, 150°C or greater. In some embodiments,
the interlayer includes a thermoplastic material that has a Tg greater
than any temperature attained in the transfer layer during imaging. The interlayer
may be either transmissive, absorbing, reflective, or some combination thereof,
at the imaging radiation wavelength.
Inorganic materials suitable as interlayer materials include, for
example, metals, metal oxides, metal sulfides, and inorganic carbon coatings, including
those materials that are highly transmissive or reflective at the imaging light
wavelength. These materials may be applied to the light-to-heat-conversion layer
via conventional techniques (e.g., vacuum sputtering, vacuum evaporation, or plasma
The interlayer may provide a number of benefits. The interlayer may
be a barrier against the transfer of material from the light-to-heat conversion
layer. It may also modulate the temperature attained in the transfer layer so that
thermally unstable materials can be transferred. For example, the interlayer can
act as a thermal diffuser to control the temperature at the interface between the
interlayer and the transfer layer relative to the temperature attained in the LTHC
layer. This may improve the quality (i.e., surface roughness, edge roughness, etc.)
of the transferred layer. The presence of an interlayer may also result in improved
plastic memory in the transferred material.
The interlayer may contain additives, including, for example, photoinitiators,
surfactants, pigments, plasticizers, and coating aids. The thickness of the interlayer
may depend on factors such as, for example, the material of the interlayer, the
material and properties of the LTHC layer, the material and properties of the transfer
layer, the wavelength of the imaging radiation, and the duration of exposure of
the thermal transfer element to imaging radiation. For polymer interlayers, the
thickness of the interlayer typically is in the range of 0.05 µm to 10 µm. For inorganic
interlayers (e.g., metal or metal compound interlayers), the thickness of the interlayer
typically is in the range of 0.005 µm to 10 µm.
Referring again to FIG. 1, a thermal transfer layer 116 is included
in thermal mass transfer donor elements of the present invention. Transfer layer
116 can include any suitable material or materials, disposed in one or more layers
with or without a binder, that can be selectively transferred as a unit or in portions
by any suitable transfer mechanism when the donor element is exposed to direct heating
or to imaging radiation that can be absorbed by the LTHC layer and converted into
Specifically, the present invention contemplates a transfer layer
that includes a blend of an LEP and an additive. The additive can be selected to
promote thermal transfer of the LEP material. For example, the presence of the additive
can reduce cohesive energy in an LEP, thereby allowing it to be pattern-wise transferred
with higher fidelity. By higher fidelity pattern-wise transfer it is meant that
the pattern of material actually transferred from the thermal transfer donor element
to the receptor more closely matches the intended transfer pattern. The additive
can also improve adhesion of the LEP to the receptor upon thermal transfer, particularly
when the LEP blend is the outermost layer of the thermal transfer donor element.
The selection of an additive generally depends on the choice of LEP
material in the blend. As a first consideration, the additive and LEP should be
compatible. Preferably, the additive and LEP are both soluble in a solvent used
to coat the blend onto donor element when making the donor, and the blend is capable
of forming a uniform film when cast or coated. The additive material forms domains
in the LEP material when blended. For example, the formation of micro-domains of
the additive in the LEP may reduce the intra-layer cohesive strength enough to achieve
high fidelity thermal transfer while also allowing the emissive layer to exhibit
uniform electronic and emissive properties. Other considerations when selecting
blend materials include relative amounts of LEP to additive (and other optional
materials) in the blend, whether to use active materials as additives in the blend,
how the additive might affect the electronic and/or emissive properties of the LEP,
and the like.
Examples of blends of LEPs and suitable additives include the following:
LEPs blended with oligomers of the same LEP material; LEPs blended with inert polymers
(e.g., polyfluorene LEPs blended with polystyrene); LEPs blended with active polymers
such as other LEPs, conductive polymers, and the like; LEPs blended with active
organic small molecule materials; molecularly doped LEPs blended with suitable additives;
fluorescent dye dispersed LEPs blended with suitable additives; co-polymers of LEPs
blended with suitable additives; LEPs that comprise backbone polymers having active
pendent groups blended with suitable additives; and the like.
Examples of other transfer layers that can be selectively patterned
from other thermal mass transfer donor elements, in combination with or in addition
to LEP blends, include colorants (e.g., pigments and/or dyes dispersed in a binder),
polarizers, liquid crystal materials, particles, insulating materials, conductive
materials, charge transport materials, charge injection materials, emissive materials
(e.g., phosphors or organic electroluminescent materials), hydrophobic materials
(e.g., partition banks for ink jet receptors), hydrophilic materials, multilayer
stacks (e.g., layers suitable for multilayer device constructions such as organic
electroluminescent devices), microstructured or nanostructured layers, photoresist,
metals, polymers, adhesives, binders, and other suitable materials or combination
of materials. These and other transfer layers are disclosed in the following documents:
U.S. Pat. Nos. 6,114,088; 5,998,085; 5,725,989; 5,710,097; 5,693,446; 5,691,098;
5,685,939; and 5,521,035; International Publication Nos. WO 97/15173, WO 99/46961,
and WO 00/41893.
Thermal mass transfer according to the present invention can be performed
to pattern one or more materials on a receptor with high precision and accuracy
using fewer processing steps than for photolithography-based patterning techniques,
and for materials that are not well-suited for photolithographic patterning (e.g.,
light emitting polymers), and thus can be especially useful in applications such
as high resolution display manufacture. As such, transfer layers that include LEP
blends can be made so that, upon selective thermal transfer to a receptor, the transferred
materials form one or more layers, including the emissive layer of an OLED. Multiple
OLEDs can be patterned serially (from one or more donor elements) or simultaneously
on a receptor to make segmented or pixilated displays that are monochromatic, multi-color,
or full color.
In particularly suited embodiments, the transfer layer can include
one or more materials useful in emissive displays such as OLED displays. For example,
the transfer layer can include, along with a blend of an LEP and an additive, an
organic small molecule light emitter, an organic charge transport or charge injection
material, as well as other organic conductive or semiconductive materials. Thermal
transfer of materials from donor sheets to receptors for emissive display and device
applications is disclosed in U.S. Pat. Nos. 6,114,088 and 5,998,085, and in International
In at least some instances, an OLED includes a thin layer, or layers,
of one or more suitable organic materials sandwiched between a cathode and an anode.
Electrons are injected into the organic layer(s) from the cathode and holes are
injected into the organic layer(s) from the anode. As the injected charges migrate
towards the oppositely charged electrodes, they may recombine to form electron-hole
pairs which are typically referred to as excitons. These excitons, or excited state
species, may emit energy in the form of light as they decay back to a ground state
(see, for example, T. Tsutsui, MRS Bulletin, 22, pp. 39-45 (1997)). Materials
useful in OLEDs are disclosed by J. L. Segura, "The Chemistry of Electroluminescent
Organic Materials", Acta Polym., 49, pp. 319-344 (1998) and by A. Kraft et
al., "Electroluminescent Conjugated Polymers―Seeing Polymers in a New Light",Angew.
Chem. Int. Ed., 37, pp. 402-428 (1998).
Illustrative examples of OLED constructions include molecularly dispersed
polymer devices where charge carrying and/or emitting species are dispersed in a
polymer matrix (see J. Kido "Organic Electroluminescent devices Based on Polymeric
Materials", Trends in Polymer Science, 2, pp. 350-355 (1994)), conjugated
polymer devices where layers of polymers such as polyphenylene vinylene act as the
charge carrying and emitting species (see J. J. M. Halls et al., Thin Solid Films,
276, pp. 13-20 (1996)), vapor deposited small molecule heterostructure devices (see
U.S. Patent No. 5,061,569 and C. H. Chen et al., "Recent Developments in Molecular
Organic Electroluminescent Materials",Macromolecular Symposia, 125, pp. 1-48
(1997)), light emitting electrochemical cells (see Q. Pei et al., J. Amer. Chem.
Soc., 118, pp. 3922-3929 (1996)), and vertically stacked organic light-emitting
diodes capable of emitting light of multiple wavelengths (see U.S. Patent No. 5,707,745
and Z. Shen et al., Science, 276, pp. 2009-2011 (1997)).
The donor element can also include an optional transfer assist layer,
most typically provided as a layer of an adhesive or an adhesion promoter coated
on the transfer layer as the outermost layer of the donor element. The transfer
assist layer can serve to promote complete transfer of the transfer layer, especially
during the separation of the donor from the receptor substrate after imaging. Exemplary
transfer assist layers include colorless, transparent materials with a slight tack
or no tack at room temperature, such as the family of resins sold by ICI Acrylics
under the trade designation Elvacite (e.g., Elvacite 2776). The transfer assist
layer may also contain a radiation absorber that absorbs light of the same frequency
as the imaging laser or light source. Transfer assist layers can also be optionally
disposed on the receptor.
The receptor substrate may be any item suitable for a particular application
including, but not limited to, glass, transparent films, reflective films, metals,
semiconductors, various papers, and plastics. For example, receptor substrates may
be any type of substrate or display element suitable for display applications. Receptor
substrates suitable for use in displays such as liquid crystal displays or emissive
displays include rigid or flexible substrates that are substantially transmissive
to visible light. Examples of suitable rigid receptors include glass and rigid plastic
that are coated or patterned with indium tin oxide and/or are circuitized with low
temperature polysilicon (LTPS) or other transistor structures, including organic
transistors. Suitable flexible substrates include substantially clear and transmissive
polymer films, reflective films, transflective films, polarizing films, multilayer
optical films, and the like. Flexible substrates can also be coated or patterned
with electrode materials or transistors. Suitable polymer substrates include polyester
base (e.g., polyethylene terephthalate, polyethylene naphthalate), polycarbonate
resins, polyolefin resins, polyvinyl resins (e.g., polyvinyl chloride, polyvinylidene
chloride, polyvinyl acetals, etc.), cellulose ester bases (e.g., cellulose triacetate,
cellulose acetate), and other conventional polymeric films used as supports. For
making OLEDs on plastic substrates, it is often desirable to include a barrier film
or coating on one or both surfaces of the plastic substrate to protect the organic
light emitting devices and their electrodes from exposure to undesired levels of
water, oxygen, and the like.
Receptor substrates can be pre-patterned with any one or more of electrodes,
transistors, capacitors, insulator ribs, spacers, color filters, black matrix, and
other elements useful for electronic displays or other devices.
An active primer layer can also be disposed between the donor and
receptor during thermal transfer operations to facilitate transfer of materials.
The idea of an active primer is disclosed in U.S. Patent No. 6,358,664. An active
primer includes materials to promote adhesion or other transfer properties during
selective thermal mass transfer and to maintain device functionality. In practice,
the active primer layer can be coated onto the transfer layer of the donor sheet,
onto the receptor, or both. Also, the active primer layer can be coated to form
a single continuous layer on the donor or receptor, or the active primer layer can
be patterned on the donor or the receptor. An active primer layer can be patterned
by any suitable technique including photolithography, screen printing, selective
thermal transfer, deposition through a mask, and the like. When using a patterned
active primer layer, it may be desirable to pattern the active primer directly onto
the receptor only in those areas where the transfer layer is to be selectively thermally
When using an active primer layer during transfer of LEP blends of
the present invention, it might be desirable for at least one of the materials included
in the active primer to match at least one of the materials included in the LEP
blend. This type of material matching may improve the quality of the interface formed
between the LEP blend layer and the active primer layer after transfer.
After transfer of the LEP blends, other device layers can be deposited
and/or patterned. Such other device layers can include charge transport materials,
cathode layers, and the like. Insulator ribs can also be patterned after transfer
of emissive layers, for example to electronically isolate adjacent devices before
deposition of a common cathode. Patterning of these and other such layers can be
performed by any suitable method including photolithography, thermal transfer, deposition
through a mask, and the like. For OLEDs, it is often desirable to encapsulate the
devices by coating the finished devices with one or more layers that form a barrier
to water, oxygen, and other elements in the environment to which the patterned devices
may be susceptible.
The following examples illustrate the use of LEP blends as transfer
layers in thermal transfer donor elements that can be used to make OLEDs.
Example 1: Preparation of a Receptor with a PEDT/PSS Buffer Layer
A receptor substrate having a PEDT/PSS buffer layer was prepared in
the following manner.
An indium tin oxide (ITO) striped substrate was spin coated at 33.33
s-1 (2000 r.p.m.) with a buffer solution consisting of poly(3,4-ethylenedioxythiophene)/poly(styrene
sulfonicacid) (PEDT/PSS) in de-ionized water (99.5:0.5 water to PEDT/PSS, by weight).
The PEDT/PSS buffer material was the PEDT/PSS commercially available from Bayer
Corporation under the trade designation Baytron P 4083. The PEDT/PSS coated substrate
was heated at 110°C on a hot plate for 5 minutes in air. The PEDT/PSS coating serves
as a hole injecting buffer layer in OLEDs.
Example 2: Preparation of a Receptor with an Active Primer Layer
A receptor substrate having an active primer layer was prepared in
the following manner.
An indium tin oxide (ITO) striped substrate was spin coated at 33.33
s-1 (2000 r.p.m.) with a buffer solution consisting of PEDT/PSS in de-ionized
water (70:30 water to PEDT/PSS, by weight). The PEDT/PSS coated substrate was heated
at 110°C on a hot plate for 5 minutes in air. The PEDT/PSS coating served as a hole
injecting buffer layer in the patterned OLEDs (see Example 7). An active primer
layer was then coated over the PEDT/PSS coating. The active primer layer was a 1:1
dispersion of bis(3-methylphenyl)N,N' dimethylbenzidine (TPD) in polystyrene (50,000
MW, available from Polysciences). The TPD was obtained from Aldrich Chemical Company,
Milwaukee, WI. The polystyrene used had a 50,000 molecular weight and was obtained
from Polysciences, Warrington, PA. The active primer was spin coated onto the PEDT/PSS
layer out of a 1.5% weight-to-volume toluene solution.
Example 3 (Comparative): Preparation of a Donor Sheet with a PPV Transfer
A thermal transfer donor sheet having a light emitting polymer transfer
layer was prepared in the following manner.
An LTHC solution, given in Table I, was coated onto a 0.1 mm thick
polyethylene terapthalate (PET) film substrate. Coating was performed using a Yasui
Seiki Lab Coater, Model CAG-150, using a microgravure roll with 150 helical cells
per lineal inch (2.54 cm). The LTHC coating was in-line dried at 80°C and cured
under ultraviolet (UV) radiation.
(1)available from Columbian Chemicals Co., Atlanta, GA
(2)available from Solutia Inc., St. Louis, MO
(3)available from S. C. Johnson & Son, Inc., Racine,
(4)available from Byk-Chemie USA, Wallingford, CT
(5)available from Minnesota Mining and Manufacturing Co.,
St. Paul, MN
(6)available from UCB Radcure Inc., N. Augusta, SC
(7)available from ICI Acrylics Inc., Memphis, TN
(8)available from Ciba-Geigy Corp., Tarrytown, NY
LTHC Coating Solution
Parts by Weight
carbon black pigment
Raven 760 Ultra™(1)
polyvinyl butyral resin
epoxy novolac acrylate
Ebecryl 629 ™(6)
Elvacite 2669™ (7)
Irgacure 369™ (8)
1-hydroxycyclohexyl phenyl ketone
Irgacure 184™ (8)
1,2-propanediol monomethyl ether acetate
Next, an interlayer, given in Table II, was coated onto the cured
LTHC layer by a rotogravure coating method using the Yasui Seiki Lab Coater, Model
CAG-150, with a microgravure roll having 180 helical cells per lineal inch (2.54cm).
This coating was in-line dried at 60°C and UV cured.
Interlayer Coating Solution
Parts by Weight
SR 351 HP™ (trimethylolpropane triacrylate ester, available
form Sartomer, Exton, PA)
Next, a PPV light emitting polymer was spin coated out of a 0.9% weight-to-volume
toluene solution onto the cured interlayer. The PPV was one commercially available
from Covion Organic Semiconductors GmbH, Frankfurt, Germany, and identified as COVION
Example 4: Preparation of a Donor Sheet with a PPV/Polystyrene Blend
A thermal transfer donor sheet having a light emitting polymer blend
transfer layer was prepared in the following manner.
An LTHC solution was coated onto a 0.1 mm thick PET film substrate
as in Example 3. Next, an interlayer was coated onto the cured LTHC layer as in
Example 3. Next, a 1:1 by weight blend of a PPV light emitting polymer and polystyrene
was spin coated out of a 0.5% weight-to-volume toluene solution onto the cured interlayer.
The PPV was one commercially available from Covion Organic Semiconductors GmbH,
Frankfurt, Germany, and identified as COVION PDY 132. The polystyrene used had a
50,000 molecular weight and was obtained from Polysciences, Warrington, PA.
Example 5: Thermal Imaging of a PPV and a PPV/Polystyrene Blend onto
The PPV and PPV blend donor elements prepared in Examples 3 and 4
were used to thermally transfer patterns onto receptors in the following manner.
Donor sheets as prepared in Examples 3 and 4 were brought into contact
with receptor substrates as prepared in Examples 1 and 2 for imaging of the PPV
and PPV blend transfer layers onto the receptors. Thus, there were four combinations:
the PPV donor of Example 3 on the buffer receptor of Example 1, the PPV donor of
Example 3 on the active primer receptor of Example 2, the PPV blend donor of Example
4 on the buffer receptor of Example 1, and the PPV blend donor of Example 4 on the
active primer receptor of Example 2.
In each case, the transfer layers of the respective donors were contacting
the buffer layer or the active primer layer of the corresponding receptors Next,
the donors were imaged using two single-mode Nd:YAG lasers. Scanning was performed
using a system of linear galvanometers, with the combined laser beams focused onto
the image plane using an f-theta scan lens as part of a near-telecentric configuration.
The laser energy density was 0.55 J/cm2. The laser spot size, measured
at the l/e2 intensity, was 30 µm (microns) by 350 µm (microns). The linear
laser spot velocity was adjustable between 10 and 30 meters per second, measured
at the image plane. The laser spot was dithered perpendicular to the major displacement
direction with about a 100 µm amplitude. The transfer layers were transferred as
lines onto the receptor substrates, and the intended width of the lines was about
The transfer layers were transferred in a series of lines that were
in overlying registry with the ITO stripes on the receptor substrates. The results
of imaging are given in Table III.
Imaging Results for PPV and PPV Blend
Donor Type (transfer layer)
Receptor (receptor coating)
Example 3 (PPV)
Example 1 (buffer only)
Example 4 (PPV blend)
Example 1 (buffer only)
very little transfer
Example 3 (PPV)
Example 2 (buffer + active primer)
good fidelity transfer
Example 4 (PPV blend)
Example 2 (buffer + active primer)
highest fidelity transfer
The imaging results reported in Table III indicate that the use of
a PPV/polystyrene blend improved transfer onto a receptor that included an active
primer layer versus transfer of the pure PPV onto the active primer substrate. While
good fidelity transfer was noted for the pure PPV onto the active primer substrate,
the highest fidelity transfer was achieved using the PPV blend on the active primer
substrate. The difference in transfer quality for pure PPV versus the PPV blend
onto receptors with no active primer layer was less conclusive.
Example 6: Thermal Imaging of a PF and a PF/Polyslyrene Blend
Donor sheets and receptors were prepared and imaged in a manner identical
to the procedure described in Examples 1 through 5, except that the transfer layers
of the respective donor elements were made by coating dilute solutions of a light
emitting polyfluorene (PF) and a 1:1 by weight blend of PF/polystyrene. Imaging
results are reported in Table IV for the analogues of the four cases discussed in
Imaging Results for PF and PF Blend
Donor Transfer Layer
Receptor (receptor coating)
Example 1 (buffer only)
Example 1 (buffer only)
high fidelity transfer
Example 2 (buffer + active primer)
poor transfer (blocking)
Example 2 (buffer + active primer)
highest fidelity transfer
The imaging results reported in Table IV indicate that for each receptor
type (active primer or buffer only), the PF blend showed significantly improved
transfer as compared to the pure PF. On buffer only receptors, the PF blend exhibited
high fidelity transfer whereas the pure PF showed no transfer. On the active primer
receptors, the PF blend exhibited very high fidelity transfer whereas the pure PF
exhibited poor fidelity transfer. The type of poor transfer exhibited by the pure
PF onto the active primer receptor is referred to as "blocking", and can be described
as significant amounts of the transfer layer being transferred to non-intended areas,
as well as to the intended areas, of the receptor.
Example 7: Preparation of an OLED
An OLED was prepared in the following manner. To make the OLED, the
active primer receptor of Example 2 was imaged using the PPV blend donor element
of Example 4 as described in Example 5.
Insulating ribs were patterned as stripes on top of, and positioned
between each of, the transferred PPV/polystyrene blend lines. A highly filled thermoset
polymer formulation was used for the insulating ribs. The approximately 1.6 µm (micron)
high ribs were patterned using the laser thermal transfer method. The transferred
ribs overlapped the PPV/polystyrene lines by about 10 µm (microns) on each side.
Next, a 40.0 nm (400 Angstrom) thick calcium coating was vapor deposited over the
insulating ribs and PPV stripes. Next, a 400.0 nm (4000 Angstrom) thick aluminum
coating was vapor deposited over the calcium coating. The calcium/aluminum construction
served as a double layer cathode in the OLED. The insulator ribs maintain electrical
isolation between OLED devices. The result was a series of patterned OLEDs on the
glass receptor, each OLED including an ITO anode, a PEDT/PSS buffer layer, an active
primer layer that functioned as a hole transport layer and transfer assist layer,
a light emitting polymer (PPV) blend layer, and a common double layer cathode isolated
by insulator ribs positioned between the OLEDs. Upon application of a bias voltage
across the anode and cathode, bright yellow electroluminescence was observed from
each of the patterned OLEDs.