This patent application is assigned to
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).sub.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 an embodiment, a compound having the formula Os(L).sub.n is disclosed; wherein Os is Osmium (IV) metal, L is a ligand coordinating to the Os atom, and n is an integer from 1 to 6; wherein each L can be same or different; wherein at least one L is a multidentate ligand; and wherein the compound is neutral.
"According to another aspect, a first device comprising a first organic light emitting device is provided. The first organic light emitting device can comprise an anode, a cathode, and an organic layer, disposed between the anode and the cathode. The organic layer can comprise a compound having the formula Os(L).sub.n, wherein Os is Osmium (IV) metal, L is a ligand coordinating to the Os atom, and n is an integer from 1 to 6, wherein each L can be same or different, wherein at least one L is a multidentate ligand, and wherein the compound is neutral. The first device can be a consumer product, an organic light-emitting device, and/or a lighting panel.
"Many osmium(II) based phosphorescent emitters for OLED applications are known. However, because of the shallow HOMO level of Os(II) resulting in a small band gap, tuning the color of the emission of osmium(II) based emitters to blue region can be difficult. The inventors have found that osmium(IV) complexes have deeper HOMO than Os(II) and therefore, it is easier to achieve blue emission. Compared to Os(II) based emitters, Os(IV) complexes have deeper HOMO which enables the incorporation of main stream organic hosts; i.e. a host with HOMO level around -5.39 eV and LUMO level around -1.21 eV. Also, because of the deeper HOMO, OLEDs utilizing Os(IV) based emitters are more immune from formation of exciplex in the device. Os(IV) complexes in general is more difficult to oxidize than Os(II) complexes because of the higher oxidation state; therefore; the band gap is potentially wider than Os(II) and easier to achieve blue emission than Os(II).
"Since Os(II) complexes in general has a very shallow HOMO level. It's very difficult to tune emission energy to blue region due to the small band gap. On the other hand, HOMO level of Os(IV) complexes are deeper and potentially easier to reach blue region.
"Osmium(H) complexes have been investigated for OLED applications. The octahedral ligand arrangement of the Os(II) complexes resembles that of Ir(III) complexes. Os(II) complexes generally exhibit low oxidation potential, i.e. shallow HOMO energy level than Ir(III) complexes. Os(IV) complexes offers a great deal of flexibility for color tuning and bring the HOMO level to proper alignment in the device.
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 a Molecular structure of complex trihydride."
URL and more information on this patent application, see: TSAI, Jui-Yi; XIA, Chuanjun; ESTERUELAS, Miguel A. Osmium (Iv) Complexes for Oled Material. Filed
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