Patent Application
20050129977
This invention relates to an electro-luminescent device, such as an organic light emitting diode. More particularly, the invention relates to a method of uniformly patterning an electro-luminescent layer of such electro-luminescent devices.
Electro-active devices, such as organic light emitting diodes (referred hereinafter to as “OLEDs”), are widely used in organic transistors, fuel cell components, microelectronics processing, microanalytical test procedures, and in specialty electronics. One of the features of such devices is an electro-luminescent layer, formed from photo-sensitive materials, that emits light on receiving an electrical impulse. In order to facilitate miniaturization, conform to device geometry, and maximize electro-luminescent yield, the electro-luminescent layer must often be patterned to various textures, topography, and geometries.
Electro-luminescent layer patterning has been conventionally performed using stamping or laser ablation. In stamping, a pattern is imprinted upon the layer using mechanical force upon a patterned die or a stamping head, whereas in laser ablation, a patterned photomask covers the area to be patterned while the remaining area is selectively etched using a laser beam.
One problem associated with such patterning of electro-luminescent layers is that stamping leaves behind a substantial amount of material residue on the layer surface. Patterning by stamping also does not guarantee uniform, reproducible, and precise patterning over large specimens. While laser ablation may yield uniform, reproducible, and precisely patterned surfaces, the process needs high vacuum conditions, produces excessive debris around the patterned area, is expensive, and cannot be performed on large specimens or in fieldwork.
The current methods for patterning an electro-luminescent layer in electro-active devices use mechanical or laser-beam techniques that do not enable patterned surfaces to be patterned to precision in minimal turnaround times. Therefore, what is needed is an electro-active device having an electro-luminescent layer that is precisely and quickly patterned to uniform thickness. What is also needed is a method for patterning such an electro-luminescent layer that is applicable to a variety of material compositions with a variety of solvating species. What is also needed is a patterning method that is effectively independent of the processing or forming history of the electro-luminescent film.
The present invention meets these and other needs by providing a patterned electro-luminescent layer of substantially uniform thickness and a method of forming such a patterned electro-luminescent layer on a substrate. Different kinds of electro-luminescent layers can be patterned by this method. An electro-luminescent device, such as a photovoltaic cell or OLED, having at least such one electro-luminescent layer, is also provided. The invention also includes an apparatus for making an electro-luminescent layer by selectively removing at least one coating from a surface of a substrate.
Accordingly, one aspect of the invention is to provide an electro-luminescent device. The electro-luminescent device comprises at least one electrode and an electro-luminescent layer disposed on the at least one electrode. The electro-luminescent layer comprises an electro-luminescent polymeric material and has a first pattern disposed on a surface adjacent to the at least one electrode and has a substantially uniform thickness.
A second aspect of the invention is to provide an electro-luminescent layer for an electro-luminescent device. The electro-luminescent layer comprises an electro-luminescent polymeric material. The electro-luminescent layer is patterned and has a substantially uniform thickness, and is formed by forming a continuous sheet of electro-luminescent polymeric material and removing a portion of the continuous sheet by wiping a surface of the continuous sheet in a direction that is tangential to the surface.
A third aspect of the invention is to provide an electro-luminescent device. The electro-luminescent device comprises at least one electrode; an electro-luminescent layer; and at least one conductive layer disposed between the at least one electrode and the electro-luminescent layer. The electro-luminescent layer comprises an electro-luminescent polymeric material, is patterned, and has a substantially uniform thickness. The electro-luminescent layer is formed by forming a continuous sheet of electro-luminescent polymeric material and removing a portion of the continuous sheet by wiping a surface of the continuous sheet in a direction that is tangential to the surface.
A fourth aspect of the invention is to provide a light source comprising a plurality of electro-luminescent devices. Each electro-luminescent device comprises at least one electrode; an electro-luminescent layer, and at least one conductive layer disposed between the at least one electrode and the electro-luminescent layer. The electro-luminescent layer comprises an electro-luminescent polymeric material, and is patterned and has a substantially uniform thickness. The electro-luminescent layer is formed by forming a continuous sheet of electro-luminescent polymeric material and removing a portion of the continuous sheet by wiping a surface of the continuous sheet in a direction that is tangential to the surface.
A fifth aspect of the invention is to provide a method of selectively removing at least one coating from a surface of a substrate. The method comprises the steps of: providing a substrate having the coating disposed on the surface; tangentially contacting a portion of the coating with a wiping head; and wiping the portion with the wiping head to remove a portion of the coating from the substrate.
A sixth aspect of the invention is to provide an apparatus for selectively removing at least one coating from a surface of a substrate. The apparatus comprises: a means for supplying the substrate having the at least one coating; a wiping head for removing a portion of the coating, wherein the wiping head tangentially contacts the coating; and a means for collecting the substrate after removing the portion.
A seventh aspect of the invention is to provide a wiping head for removing a portion of at least one coating disposed on a surface of a substrate. The wiping head comprises a contact surface for contacting and removing the portion of the coating. The contact surface tangentially contacts the portion and has a predetermined geometry.
These and other aspects, advantages, and salient features of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that terms such as “top”, “bottom”, “outward”, “inward”, and the like are words of convenience and are not to be construed as limiting terms.
Referring to the drawings in general and to
Visible light sources produce light in different ways. Such devices may comprise different components and mechanisms for producing light and some sources may produce light more efficiently than others. Many light sources are made of electro-luminescent materials arranged as coatings or films upon an electro-active substrate (often called an electrode). Consequently, the film may be patterned or textured to suit design requirements.
Common methods of film patterning, such as ink jet printing, deposit the coating one drop at a time, by creating polyimide wells to position the drop on the film surface. This method is commonly used in pixels for displays. Films may also be patterned or textured using methods such as, but not limited to, screen printing, gravure printing, flexographic printing, offset lithographic printing, spin coating, spray coating, meniscus coating, and dip coating. However, it is difficult to dispose and pattern coating layers of uniform thickness using such methods with subsequent solvent deposition in which the solvent creates a crater or channel upon drying. One embodiment of the present invention discloses a patterning method applicable to large area devices with coatings of uniform thickness. A common approach to producing patterned electro-luminescent film is to selectively remove portions of the electro-luminescent coating from a continuous film of the electro-luminescent material. This is conventionally done using laser ablation, plasma etching, scratching the film surface, tape lifting, and lifting off under high temperature or pressure using a die or stamp. However, there are certain disadvantages associated with each of these methods. For instance, laser ablation and plasma etching focus on small working areas of the specimen, and the cost for scaling up the process can be very high. Scratching requires plowing through the continuous coating with a stiff stylus, which can potentially damage the underlying layers or substrates. Stamping and lifting with a rubbery die offer an affordable but qualitatively unacceptable solution. The liftoff process can be uniquely related to the materials of construction of the die and may result in incomplete coating removal with residues deposited on the stamped area. The residues can also affect the final properties and performance of the electro-luminescent device.
The present invention provides a process to selectively remove a portion of a continuous electro-luminescent film and to produce a sharply patterned electro-luminescent film.
The invention also provides a process to remove coating material from a continuous electro-luminescent film via wiping with a ‘moistened’ soft head. In another embodiment, the wiping head contains solvents that solvate (or moisten, using aqueous or non-aqueous solvents) the electro-luminescent film. A tangential wiping action using the wiping head assists in removing the solvated area.
In another embodiment, the invention also provides a solvent system that enables removal of portions of multiple layers of film in a single step. The multiple layers may either be identical or distinct from each other.
In one embodiment of the present invention, shown in
In the embodiment shown in
The electro-luminescent layer 120 comprises a polymeric material such as, but not limited to, conjugated polymers, such as polyfluorenes, polyphenylenes (PPPs), and poly para-(phenylenevinylenes) (PPVs). The conductive layer 140 comprises at least one of poly (3,4-ethylenedioxythiophene) (commonly known as “PEDOT”), poly (3,4-propylenedioxythiophene) (also referred to herein as “PProDOT”), polystyrenesulfonate (also referred to herein as “PSS”), polyvinylcarbazole (also referred to herein as “PVK”), and combinations thereof. In other embodiments of the invention, electro-luminescent device 100 further comprises at least one additional polymer layer that performs conductive, emissive, charge injection, and charge blocking functions in the electro-luminescent device 100. Electrode 110 comprises a high work function material capable of forming ohmic contact with the upper adjacent layer (conductive layer 140). Electrode 110 comprises at least one of: indium tin oxide; tin oxide; zinc oxide; fluorinated zinc oxide; tin doped zinc oxide; cadmium tin oxide; gold; a conductive polymer comprising at least one of PEDOT, PProDOT, PSS, PVK; and combinations thereof. In other embodiments of the invention, electrode 110 is supported by a substrate material such as, but not limited to, a polycarbonate, a polyolefin, a polyester, a polyimide, a polysulfone, an acrylate, glass, metal foil, and combinations thereof.
In another embodiment of the present invention, an electro-luminescent layer 120 is disclosed for an electro-luminescent device 100. The electro-luminescent layer 120 comprises an electro-luminescent polymeric material. The electro-luminescent layer 120 is patterned and has a substantially uniform thickness 200, and is formed by forming a continuous layer 115 of the electro-luminescent polymeric material and removing a portion of the continuous layer 115 by wiping a surface 118 of the continuous layer 115 in a direction that is tangential 210 to the surface, as shown in
Electro-luminescent layer 120 is disposed adjacent to at least one conductive layer 140. Electro-luminescent layer 120 possesses a pattern 130 comprising at least one coated portion 160 having a coated surface area and at least one uncoated portion 170 having an uncoated surface area, wherein the at least one uncoated portion intersects the coated portion to form a first coated area 162 and a second coated area 164. Typically, the coated surface area is greater than the uncoated surface area. Additionally, the uncoated portion 170 comprises at least one channel 180 that cuts through coated portion 160 such that channel 180 has a plurality of walls 190 each of the plurality of walls 190 has a boundary width 220 of less than 20% of the width of channel 180. Coated surface area 160 has a thickness in a range from about 50 nm to about 150 nm.
In one embodiment, electro-luminescent layer 120 is made from a continuous polymer sheet 115. The continuous polymer sheet 115 is formed by depositing a polymeric film, such as PEDOT or the like, on a continuous sheet of a substrate, patterning the polymeric film, and baking the polymeric film at a temperature between about 50° C. and about 200° C. The actual baking temperature depends upon the polymer substrate that is used to support the continuous polymer sheet 115. The polymeric film is then coated with an electro-luminescent material to form electro-luminescent layer 120 on the polymer film, and the electro-luminescent layer 120 is then patterned. The steps of patterning the polymeric film, patterning electro-luminescent layer 120, and baking may be performed in any sequential order. For example, application of polymeric and electro-luminescent films, patterning, and baking may proceed according to any of the sequences shown in Table 1.
To facilitate film removal over a selected area of the electro-luminescent film, a portion of the continuous polymer sheet 115 is solvated by at least one of water, methanol, ethanol, isopropanol, acetone, toluene, xylene, and combinations thereof. The surface of the solvated portion of continuous polymer sheet 115 is wiped by wiping head 230 remove a portion of at least one film, thereby patterning the film, or films. Wiping head 230 comprises at least one of a sponge, elastomer, thermoplastic, thermoset, fiber mat, porous material, polyurethane rubber, synthetic rubber, natural rubber, silicones, polydimethylsiloxane (PDMS), textured materials, and combinations thereof.
In one embodiment of the invention, the solvating species are selected for removing a single layer of film with each wiping action without damaging underlying layers. In another embodiment, the solvating species are selected to facilitate removal of multiple layers with each wiping. For example, an electro-luminescent film in a two-layer structure can be patterned using xylene as a solvent without damaging a PEDOT layer underneath. In yet another embodiment, two polymer layers can also be removed in one step with a solvent system containing water and xylene. In this particular embodiment, isopropanol is used to facilitate mixing of water and xylene to yield a homogeneous solution.
In another embodiment of the claimed invention, a method of selectively removing at least one coating from a surface of a substrate is disclosed and generally shown in
Solvent 250 may be either polar or non-polar. For each polymer coating material, there are usually three solubility parameters that account for the non-polar, polar, and hydrogen bonding strength of the polymer. Similarly, there are three corresponding solubility parameters for each solvent. The best solvent for a polymer is one having solubility parameters that match those of the polymer.
In typical instances, the electro-luminescent layer comprises both (i) a conductive polymer coating, such as PEDOT, which is very polar and dissolves only in hydrogen-bonding solvents like water, and (ii) a light emitting polymer coating that is non-polar, which dissolves only in non-polar solvents such as toluene or xylene. In order to remove multiple polymer coatings having extremely divergent solubility characteristics in a single wipe, suitable solvents for each polymer are dispersed in a third solvent to produce a homogeneous solution. The third, or dispersing, solvent is selected from a number of solvents, such as, but not limited to, alcohols (such as isopropanol, ethanol, methanol, and the like), ketones (such as acetone, methyl ethyl ketone, and the like), acetates, ethers, methylene chloride, or any solvent having intermediate solubility parameters. The solvent ratings for a typical light-emitting plastic and PEDOT are listed in Table 1.
Good solvents include either one-component systems having solubility parameters that closely match the solubility parameters of the polymer film (or films), or multi-component solvent systems having effective solubility parameters that match the solubility parameters of the polymer. The solvents in the multi-component system do not necessarily have to be a good solvent for the polymer. For example, neither CCl4 nor ethanol are good individual solvents for polymethylmethacrylate (PMMA), but a binary mixture of CCl4 and ethanol is a good solvent for PMMA because the effective solubility parameter of the mixture matches that of PMMA.
In this example, a PEDOT layer is spin coated onto an indium tin oxide (ITO) coated glass substrate and baked at 200° C. for 1 hour. A layer of light emitting plastic (i.e., electro-luminescent layer) is then spin-coated on top of the PEDOT layer. The patterned area is wiped by solvent assisted wiping (SAW) in which xylene was the only solvent used to remove portions of the electro-luminescent layer.
The PEDOT layer is spin coated onto an indium tin oxide (ITO) coated glass substrate and baked at 200° C. for 1 hour. A layer of light emitting plastic (or electro-luminescent layer) is spin-coated on top of the PEDOT layer. The patterned area is wiped by solvent assisted wiping (SAW) with a solvent mixture consisting of water, isopropanol, and xylene so as to remove both PEDOT and electro-luminescent layers.
Wiping head 230 comprises at least one of a sponge, an elastomer, a thermoplastic, a thermoset, a fiber mat, a porous material, polyurethane rubber, synthetic rubber, natural rubber, silicones, PDMS, textured materials, and combinations thereof. In one embodiment of the invention, wiping head 230 is a fixed head. In another embodiment, wiping head 230 is movable with respect to substrate 110. Alternatively, wiping head 230 and substrate 110 may be moved simultaneously with respect to each other. In still another embodiment, wiping head 230 is rotatable. In a further embodiment, wiping head 230 is a rotatable wheel.
The step of tangentially contacting a portion 460 (
In one embodiment of the claimed method, the contact surface further includes at least one sidewall 260 disposed on at least one edge of the contact surface 240. In another embodiment, the method further includes the step of premoistening portion 460 (
In another embodiment of the claimed invention, an apparatus is disclosed for selectively removing a portion 460 at least one coating 420 from a surface of a substrate 410. The apparatus comprises a means for supplying the substrate 410 having the at least one coating 420, a wiping head 230 for removing a portion 460 of the at least one coating 420, wherein the wiping head 230 contacts the at least one coating 420 in a tangential direction 210, and a means for collecting the substrate after removing the portion 460.
In another embodiment of the claimed invention, a wiping head 230 is disclosed for removing a portion 460 of at least one coating 420 disposed on a surface of a substrate 410. The wiping head 230 comprises a contact surface 240 for contacting and removing portion 460, wherein contact surface 240 contacts portion 460 in a tangential direction 210, and wherein contact surface 240 has a predetermined structure.
Although the examples described hereinabove are for an electroluminescent device, it is understood that the invention can be used in manufacturing features of other articles and devices, such as, but not limited to, microelectronic devices, photovoltaics, thin film transistors, electronic paper and displays, photonic devices, waveguides, microelectromechanical systems (MEMS), microfluidics devices, and the like.
While typical embodiments have been set forth for the purpose of illustration, the foregoing description should not be deemed to be a limitation on the scope of the invention. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present invention.
