News Column

Patent Issued for Triplet-Triplet Annihilation up Conversion (TTA-UC) for Display and Lighting Applications

June 18, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- Universal Display Corporation (Ewing, NJ) has been issued patent number 8742657, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Xia, Chuanjun (Lawrenceville, NJ); Weaver, Michael S (Princeton, NJ); Brooks, Jason (Philadelphia, PA).

This patent was filed on October 11, 2010 and was published online on June 3, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

"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 structure:

"##STR00001##

"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."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Devices using triplet-triplet annihilation up-conversion (TTA-UC) to covert emission from a light source, e.g., an OLED, to an emission with shorter wavelength are provided. A first device is provided, comprising a first organic light emitting device comprising a first material that is an emitting material having a first emissive spectrum, and a first triplet-triplet annihilation up-conversion layer disposed adjacent to the first organic light emitting device such that light emitted by the organic light emitting device is incident on the first up-conversion layer. The first triplet-triplet annihilation up-conversion layer comprising a first donor material and a first acceptor material, and the first donor material has an absorption spectrum that overlaps with the first emissive spectrum.

"In one aspect, the device further comprises a pixel, which further comprises three subpixels. The first subpixel comprises the first organic light emitting device and the first up conversion layer disposed adjacent to the first organic light emitting device. The second subpixel comprises a second organic light emitting device comprising a second material that is an emitting material having a second emissive spectrum. Preferably, the second subpixel does not include an up-conversion layer or a down conversion layer. The third subpixel comprises a third organic light emitting device comprising a third material that is an emitting material having a third emissive spectrum.

"In another aspect, the third subpixel further comprises a first down conversion layer disposed adjacent to the third organic light emitting device such that light emitted by the third organic light emitting device is incident on the first down conversion layer.

"In yet another aspect, the first material, the second material, and the third material have an emissive spectrum having a peak wavelength of about 500 nm to about 600 nm. Preferably, the first material, the second material, and the third material are the same material.

"In a further aspect, the first and the second materials have an emissive spectrum having a peak wavelength of about 500 nm to about 600 nm, and the third material has an emissive spectrum having a peak wavelength of about 600 nm to about 700 nm. Preferably, the second subpixel does not comprise an up-conversion layer or a down conversion layer.

"In one aspect, the first subpixel has an emissive spectrum that has a peak wavelength of about 400 nm to about 500 nm, the second subpixel has an emissive spectrum that has a peak wavelength of about 500 nm to about 600 nm, and the third subpixel has an emissive spectrum that has a peak wavelength of about 600 nm to about 700 nm.

"In another aspect, the first material, the second material, and the third material have an emissive spectrum having a peak wavelength of about 500 nm to about 600 nm. In the first subpixel, the first material emits light having a peak wavelength of about 500 to about 600 nm. The first up-conversion layer absorbs light having a peak wavelength of about 500 nm to about 600 nm and emits light having a peak wavelength of about 400 nm to about 500 nm, such that the first subpixel emits light having a peak wavelength of about 400 nm to about 500 nm. The second subpixel does not include an up-conversion or a down conversion layer, and the second material emits light having a peak wavelength of about 500 nm to about 600 nm, such that the second subpixel emits light having a wavelength of about 500 nm to about 600 nm. The third subpixel includes a down conversion layer, which absorbs light having a peak wavelength of about 500 nm to about 600 nm and emits light having a peak wavelength of about 600 nm to about 700 nm, such that the third subpixel emits light having a peak wavelength of about 600 nm to about 700 nm. Preferably, the first material, the second material, and the third material are the same material.

"In one aspect, the first triplet-triplet annihilation up-conversion layer absorbs between about 80 percent and about 100 percent of the light emitted from the organic light emitting device.

"In another aspect, the device further comprises at least one filter that absorbs light having a peak wavelength of about 500 nm to about 600 nm.

"In yet another aspect, the device further comprises at least one microcavity that absorbs light having a peak wavelength of about 500 nm to about 600 nm.

"In a further aspect, the device absorbs 99 percent of the emitted light emitted by the first material.

"In one aspect, the organic light emitting device is capable of emitting a first spectrum of light having a first peak wavelength when voltage is applied to the device. The first triplet-triplet annihilation up-conversion layer is capable of absorbing the first spectrum of light and emitting a second spectrum of light with a second peak wavelength. The second peak wavelength is shorter than the first peak wavelength.

"In another aspect, the first triplet-triplet annihilation up-conversion layer absorbs between about 20 percent and about 80 percent of the light emitted by the first material.

"In one aspect, the device has CIE coordinates of x=0.10-0.40, y=0.05-0.40.

"In another aspect, the device has a CRI of about 80 to about 100.

"In one aspect, the first triplet-triplet annihilation up-conversion layer is a solution. In another aspect, the first triplet-triplet annihilation up-conversion layer is a solid film.

"In one aspect, the light source is a green organic light emitting device or red organic light emitting device.

"In another aspect, the first material emits light having CIE coordinates of within a seven step McAdam ellipse centered on the black body curve with a correlated color temperature (CCT) in the range of 2500-7400K, and the first device emits light having CIE coordinates of within a seven step McAdam ellipse centered on the black body curve with a correlated color temperature (CCT) at least 50K higher than that of the emission of the first material.

"In yet another aspect, the first material emits light having a peak wavelength of about 500 nm to about 700 nm, and the first device emits light having CIE coordinates of within a seven step McAdam ellipse centered on the black body curve with a correlated color temperature (CCT) in the range of 2500-7000K.

"In one aspect, the first device further comprises a filter deposited over the organic light emitting device.

"In one aspect, the first device is an area emitting device.

"In one aspect, the first triplet-triplet annihilation up-conversion layer and the organic light emitting device are deposited on the same substrate. In another aspect, the first triplet-triplet annihilation up-conversion layer is vertically-stacked upon the organic light emitting device. In yet another aspect, the first triplet-triplet annihilation up-conversion layer and the organic light emitting device are positioned side by side.

"In one aspect, the first device is a display. In another aspect, the first device is suitable for general illumination purposes.

"In one aspect, the first triplet-triplet annihilation up-conversion layer has a linear or circular light polarization function.

"In one aspect, the first material is a small molecule. In another aspect, the first material is a phosphorescent molecule.

"In one aspect, up-conversion is achieved through triplet-triplet annihilation.

"In one aspect, the first donor materials are selected from the group consisting of:

"##STR00002## ##STR00003##

"The first donor materials may be substituted or unsubstituted.

"In another aspect, the first acceptor materials are selected from the group consisting of:

"##STR00004## ##STR00005##

"The first acceptor materials may be substituted or unsubstituted.

"Methods of operating a device are also provided. The methods comprise driving an organic light emitting device to generate light, absorbing the light in a first triplet-triplet annihilation up-conversion layer, shortening the wavelength of the light using triplet-triplet annihilation up-conversion, and emitting the light."

For the URL and additional information on this patent, see: Xia, Chuanjun; Weaver, Michael S; Brooks, Jason. Triplet-Triplet Annihilation up Conversion (TTA-UC) for Display and Lighting Applications. U.S. Patent Number 8742657, filed October 11, 2010, and published online on June 3, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8742657.PN.&OS=PN/8742657RS=PN/8742657

Keywords for this news article include: Universal Display Corporation.

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Source: Journal of Engineering


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