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The following quote was obtained by the news editors from the background information supplied by the inventors: "
"OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
"One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as 'saturated' colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.
"One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)3, which has the following structure:
"In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.
"As used herein, the term 'organic' includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. 'Small molecule' refers to any organic material that is not a polymer, and 'small molecules' may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the 'small molecule' class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a 'small molecule,' and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
"As used herein, 'top' means furthest away from the substrate, while 'bottom' means closest to the substrate. Where a first layer is described as 'disposed over' a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is 'in contact with' the second layer. For example, a cathode may be described as 'disposed over' an anode, even though there are various organic layers in between.
"As used herein, 'solution processible' means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
"A ligand may be referred to as 'photoactive' when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as 'ancillary' when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.
"As used herein, and as would be generally understood by one skilled in the art, a first 'Highest Occupied Molecular Orbital' (HOMO) or 'Lowest Unoccupied Molecular Orbital' (LUMO) energy level is 'greater than' or 'higher than' a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A 'higher' HOMO or LUMO energy level appears closer to the top of such a diagram than a 'lower' HOMO or LUMO energy level.
"As used herein, and as would be generally understood by one skilled in the art, a first work function is 'greater than' or 'higher than' a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a 'higher' work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a 'higher' work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.
"More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "According to aspects of the disclosed subject matter, a graded emissive layer deposition device is provided that includes a first nozzle configured to eject a first mixture over a first region of a substrate, the mixture containing a host and an organic dopant. A second nozzle configured to eject a second mixture containing the host and organic dopant over the first region is also provided such that the first mixture has a different ratio of host to organic dopant than the second mixture. A plurality of nozzles, such as the first and second nozzles, may be configured to eject mixtures in a sequential order, and the order may be based on the host-to-dopant ratio of the mixture in each nozzle. The order may be based on a highest to lowest concentration of host-to-dopant ratio in the mixture in each nozzle. The plurality of nozzles may be configured to translate relative to an area of a substrate. The host may be made up of a plurality of component materials such as a plurality of host materials and the organic dopant may be made up of a primary organic dopant and one or more co-dopants
"According to aspects of the disclosed subject matter, a graded emissive layer deposition technique is provided that includes depositing a plurality of mixtures over a first region of a substrate, each mixture containing at least a carrier gas, an organic emissive first material, and a host second material such that each mixture contains a different ratio of the organic emissive first material to the host second material. Each mixture may be deposited through a separate nozzle towards the substrate and plurality of nozzles may be translated relative to each other, each nozzle ejecting one of the plurality of mixtures over the first region of the substrate in an ordered sequence, one mixture at a time.
"According to aspects of the disclosed subject matter, a graded emissive layer deposition technique is provided that includes depositing a first electrode over a substrate. A first mixture containing an organic emissive first material, a host second material, and a carrier gas may be ejected from a first nozzle towards the first electrode. A second mixture containing the organic emissive first material, the host second material, and a carrier gas may be ejected from a second nozzle over the organic emissive first material such that the second mixture has a different concentration of the organic emissive material than the first mixture. Additionally, a second electrode may be deposited over the organic emissive first material. The first electrode may comprise one or more additional layers such as a hole transport layer (HTL), electron transport layer (ETL), or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 shows an organic light emitting device.
"FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.
"FIG. 3 shows an illustrative example of graded organic layers deposited over an electrode according to an embodiment of the invention.
"FIG. 4 shows an illustrative example of a multi-nozzle implementation for graded deposition according to an embodiment of the invention.
"FIG. 5 shows an illustrative example of a multi-nozzle grid implementation for graded depositions according to an embodiment of the invention.
"FIG. 6a shows a graphical representation of different material in a graded emissive layer according to an embodiment of the invention.
"FIG. 6b shows a graphical representation of different material in a graded emissive layer deposited by multiple nozzles according to an embodiment of the invention.
"FIG. 7 shows a graphical representation of different concentrations of material in a graded emissive layer according to an embodiment of the invention."
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