Ink-jet-printable phosphorescent organic light-emitting-diode devices

Takuya SonoyamaMasaki ItoShunichi SekiSatoru MiyashitaSean Xia (SID Member)Jason Brooks (SID Member)Kwang-Ohk CheonRaymond C. Kwong (SID Member)Michael InbasekaranJulie J. Brown (SID Member)

Abstract — A novel method for the fabrication of ink-jet-printed organic light-emitting-diode devicesis discussed. Unlike previously reported solution-processed OLED devices, the emissive layer of OLEDdevices reported here does not contain polymeric materials. The emission of the ink-jet-printedP2OLED (IJ-P2OLED) device is demonstrated for the first time. It shows good color and uniform emis-sion although it uses small-molecule solution. Ink-jet-printed green P2OLED devices possess a highluminous efficiency of 22 cd/A at 2000 cd/m2 and is based on phosphorescent emission. The latestsolution-processed phosphorescent OLED performance by spin-coating is disclosed. The red P2OLEDexhibits a projected LT50 of >53,000 hours with a luminous efficiency of 9 cd/A at 500 cd/m2. Thegreen P2OLED shows a projected LT50 of >52,000 hours with a luminous efficiency of 35 cd/A at1000 cd/m2. Also discussed is a newly developed sky-blue P2OLED with a projected LT50 of >3000hour and a luminous efficiency of 18 cd/A at 500 cd/m2.

Keywords — Printable phosphorescent organic light-emitting-diode device, ink-jet printing, solutionprocess, spin coating, small-molecule-based EML.

DOI # 10.1889/JSID16.12.1229

1 IntroductionOLED devices should be key devices to next-generation display.OLED displays have many advantages, such as fast response,wide viewing angle, low power consumption, no need for aback light, and thin form factor.

Because displays require very low power consump-tion, we have focused on a phosphorescent system to reducethe power consumption of OLED displays. The advantageof phosphorescence is its high efficiency. Compared tofluorescent OLEDs, organic phosphorescent devices offer afour-fold increase in efficiency because the fluorescentOLEDs are limited by the triplet-to-singlet ratio which isapproximately 3:1.1 In 1998, phosphorescent OLEDs(PHOLED™),2 which incorporate heavy-metal organomet-allic compounds as emitters, were discovered and have sinceenabled this efficiency barrier to be surpassed.3 PHOLEDshave been shown to have an internal quantum efficiency of100%.4 Theoretically, the efficiency of PHOLEDs is fourtimes than that of fluorescent OLEDs, and this has nowbeen demonstrated by a number of groups. These highlyefficient PHOLED devices exhibit a lifetime in excess of100,000 hours.5 The technology of PHOLEDs applied tothe solution processes [printable phosphorescent organiclight-emitting-diode (P2OLED™)] was previously reported.6

PHOLEDs exhibit high performance which is fabricated byvacuum thermal evaporation (VTE).

The alignment of shadow masks becomes difficultwith higher resolution and larger area. In order to resolvethis problem, considerable attention has been paid to ink-jet-printing technology which has the potential for direct

patterning of the emitting layers and large-area processingwith high resolution.

And the use of ink-jet printing can suppress the wasteof resources with on-demand technology. Previously, weshowed the possibility of fine pixel patterning of full-colorlarge-area light-emitting polymers by using ink-jet-printingtechnology.7,8

The OLED display will become a more attractive dis-play by combining the high performances of PHOLEDs andthe high-resolution patterning of the large-area processingof ink-jet technology.

We describe the first demonstration of a greenP2OLED using ink-jet-printing technology. The hole injec-tion, hole transport, and emissive layer in P2OLEDs arecomposed of small molecules. Usually, it is difficult to makea uniform film using solution processing of small molecules.Problems such as recrystallization and phase separationneed to be addressed in the case of small molecules. Lack ofuniformity of EML film poses huge obstacles to the pro-gress in P2OLED performance. We were able to obtain uni-form emission from the ink-jet-printed P2OLED coupledwith good efficiency. High luminous efficiency of the greenink-jet-printed P2OLED is achieved by selection of a suit-able solvent for the emissive layer. We selected a suitablesolvent by measuring the absolute photoluminescence (PL)quantum efficiency in ink solution. Having a higher absolutePL quantum efficiency in ink solution is essential in achiev-ing high luminous efficiency for ink-jet-printed P2OLED.Our green ink-jet-printed P2OLED has achieved high lumi-nous efficiency by choosing a suitable solvent which exhib-ited a high absolute PL quantum efficiency.

Revised extended version of a paper presented at the 14th International Display Workshops (IDW ‘07) held December 5–7, 2007 in Sapparo, Japan.

T. Sonoyama, M. Ito, S. Seki, and S. Miyahita are with Seiko Epson Corp., Display Development Center, 281 Fujimi, Fujimi-machi, Suwa-gun,Nagano-ken, 399-0293, Japan; telephone +81-266-61-1211, fax +81-266-62-8966, e-mail: sonoyama.takuya@exc.epson.co.jp.

S. Xia, J. Brooks, K-O. Cheon, R. C. Kwong, M. Inbasekaran, and J. J. Brown are with Universal Display Corp., Ewing, N.J. U.S.A.

© Copyright 2008 Society for Information Display 1071-0922/08/1612-1229$1.00

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In this paper, we also present the status of high-perform-ance red, green, and newly developed sky-blue P2OLEDs byusing a spin-coating process, including their luminous effi-ciency, lifetime, and color chromaticity.

2 Experimental setup for ink-jet-printedP2OLEDs

2.1 Advantages of using small moleculesover polymers

We prepared an ink solution using small molecules for ink-jet-printed P2OLEDs (IJ-P2OLEDs). It is widely knownthat a higher viscosity solution limits the ink-jettability usingpiezo heads. Based on our previous experience, we haveconcluded that a viscosity of 20 mPa-sec is the maximumborderline target for ink-jettability of a solution . In this sec-tion, we focus on the viscosity of ink solutions to highlightthe advantage of using small molecules over polymers forink-jet printing.

Figure 1 illustrates the comparison of ink-concentra-tion dependency of viscosity between a polymer, Poly(2,7-(9,9-di-n-octylfluorene)-(1,4-phenylene-((4-secbutylphenyl)-imino)-1,4-phenylene) (“TFB”), Tris(8-hydroxyquinolinato)-aluminum(III) (“Alq3”) and a printable small molecule. Allthree ink solutions were prepared using dichloromethane asthe common solvent. The viscosity of the solutions wasmeasured by a viscometer (CBC Co., Ltd.; VM-100A labviscometer).

Dichloromethane solvent exhibits a viscosity of 0.81mPa-sec at 20.1°C. In the case of TFB in dichloromethane,the viscosity rises dramatically with an increase in solid con-centration. The viscosity of TFB solution in dichloro-methane reaches 30 mPa-sec at an ink concentration of 2.5wt./wt.%.

On the other hand, Alq3 in dichloromethane does notshow any increase in viscosity when the ink concentrationincreases up to 1%. Alq3 does not dissolve in dichloro-methane at more than 1% concentration.

The developed printable small-molecule material(P2OLED materials) have been modified for high solubilityin organic solvents. An increase in viscosity is hardly observedfor a dichloromethane solution of printable small-moleculematerial even though the ink concentration increases up to2.5 wt./wt.%. So, printable small-molecule material retainsits initial viscosity even at higher concentrations.

One of the advantages of using small-molecule-basedink compared to a polymer ink is to be able to use a highsolid concentration without an increase in viscosity. Thisattribute of small-molecule solution allows us to use a rangeof solvents and ink formulations that are suitable for ink-jetprinting.

2.2 Device structure and fabrication of ink-jet-printed P2OLEDs

Figure 2 shows the basic device structure of solution-proc-essed P2OLEDs.

The sequence of organic layers in P2OLED devicesconstructed on ITO glass substrate is HIL/HTL/EML/BL/ETL/LiF/Al. HIL is the hole injection layer, HTL is the holetransport layer, and EML is the emissive layer. In a previousstudy,6 we disclosed that the EML of a P2OLED is con-structed by a two-component host-guest (phosphorescentemitter) system based on small molecules.

In this section, HIL to EML were fabricated by ink-jetprinting using small-molecule inks. Each functional layerwas processed from organic solvent. After ink-jetting,dropped inks were converted into films by drying and bak-ing. BL is the blocking layer and ETL is the electron-trans-port layer. BL, ETL, and LiF/Al were deposited by vacuumthermal evaporator under high-vacuum conditions (<10–7

torr base pressure). Green ink-jet-printed P2OLEDs were

FIGURE 1 — Comparison of ink concentration dependency of viscositybetween TFB polymer, Alq3, and an ink-jet-printable small molecule.TFB in dichloromethane (black closed circle), Alq3 in dichloromethane(solid red triangle), printable small molecule in dichloromethane (solidblue circle).

FIGURE 2 — The basic device structure of solution-processed P2OLED.HIL to EML are fabricated by ink-jet printing. All ink-jetted layers consistof small molecules.

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encapsulated in a dry nitrogen atmosphere (<1-ppm H2O)using a glass lid and an epoxy resin.

Figure 3 shows a thickness profile of ink-jet-printedfunctional layers from HIL to EML across a single pixel.The film thickness and profile were measured by using asurface profilometer (KLA Tencor; P10). The thickness ofthe ink-jet-printed HIL was 10 nm, the thickness of ink-jet-printed HTL is 30 nm and the thickness of ink-jet-printedEML is 35 nm. The ink-jet-printed HIL, HTL, and EMLshow very flat surfaces.

3 Results and discussion of ink-jet-printedP2OLEDs

3.1 Device performance of a green ink-jet-printed P2OLED

In this first demonstration, the ink-jet-printed P2OLEDachieved a high luminous efficiency approaching that of aspin-coated device. We show the performance of three ink-jet-printed devices using three different solvents for theEML. Table 1 shows the properties of the evaluated solventsfor EML. The EML ink for the spin-coated device was pre-pared by using Toluene. solvent-A, solvent-B, and solvent-Cwere used for preparing the EML inks for ink-jet printing.

These evaluated solvents show good solubility to theprintable material of the EML, and they all have a high boil-ing point of over 200°C.

All prepared EML inks contain two components (hostand guest) with 1.0-wt./wt.% ink concentration. The ink usingToluene for the spin-coating experiment results in a viscos-ity of 0.7 mPa-sec at room temperature. The viscosity of inkusing solvent-A shows 3 mPa-sec at room temperature. The

ink using solvent-B and the ink using solvent-C showed vis-cosities of 6 and 3 mPa-sec, respectively, at room tempera-ture.

Figure 4 shows the normalized electrical luminescentspectra of a green spin-coated P2OLED and ink-jet-printedP2OLEDs.

The green spin-coated device has a peak wavelengthat 520 nm with 1931 Commission International de l’Eclairage(CIE) co-ordinates of (0.34, 0.61). Green ink-jet-printedP2OLEDs using solvent-A exhibited a peak wavelength at518 nm with CIE of (0.33, 0.58). Green ink-jet-printedP2OLED using solvent-B and using solvent-C showed apeak wavelength at 520 nm with CIE of (0.34, 0.61). Thespectra of the ink-jet-printed devices were identical to thatof the spin-coated devices, indicating that the emission waspurely from the phosphorescent dopant. In addition, the

FIGURE 3 — Thickness profile of ink-jet-printed functional layers ingreen P2OLEDs. Solid sky-blue line is the ITO profile. The purple solidline is the HIL profile. The solid blue line is the HTL profile. The solidgreen line is the EML profile. The inset shows the EL emission.

FIGURE 4 — Normalized EL spectra of the green spin-coated P2OLEDand ink-jet-printed P2OLEDs. The spin-coated device was based onToluene for EML (solid black line). Ink-jet-printed devices using solvent-Afor the EML (solid blue line), using solvent-B for EML (solid red line) andusing solvent-C for the EML (solid green line) are shown for comparison.

TABLE 1 — Properties of evaluated organic solvents for theEML.

FIGURE 5 — I–L plots of green P2OLEDs.

Journal of the SID 16/12, 2008 1231

absence of bright spots and irregular emission patterns indi-cated that there was no phase separation or recrystallization.

Figure 5 shows the I–L plots and Fig. 6 shows theL–LE plots of green P2OLEDs. These figures are compari-sons of device performance between spin-coated devicesand ink-jet-printed devices.

The spin-coated green P2OLED device possess aluminous efficiency of 22 cd/A at 1000 cd/m2. The ink-jet-printed green P2OLED with solvent-A possesses a luminousefficiency of 3.5 cd/A at 1000 cd/m2. The ink using solvent-Band the ink using solvent-C yielded efficiencies of 19 cd/Aand 23 cd/A, respectively, at 1000 cd/m2.

The device using solvent-A for the EML exhibits avery poor luminous efficiency. The ink-jet-printed greenP2OLEDs using Solvent-B and solvent-C show almost thesame luminous efficiency as a spin-coated device. We havestudied the difference in luminous efficiency among thefabricated ink-jet-printed devices. Further, we evaluatedthe influence of solvent on the luminous efficiency of ink-jet-printed film and in ink solutions by using the absolutephotoluminescence (PL) quantum efficiency (ηPL).

3.2 Discussion of the luminous efficiencyof a green ink-jet-printed P2OLED

Figure 7 shows the absolute PL quantum efficiency of solid-state films. The absolute PL quantum efficiency of a solid-state film containing the EML component was measuredunder nitrogen gas flow by using an integrating sphere(Hamamatsu Photonics Co., C9920-02). The depositedtris(8-hydroxyquinolinato)aluminum(III) (“Alq3”) film byvacuum thermal evaporation showed an ηPL of 18 ± 1% atan excited wavelength of 365 nm.

The solid-state film using Toluene was formed onquartz substrate by spin-coating. After spin-coating, thespin-coated film was baked at an elevated temperature under

inert gas in a glove box, and the ink-jet-printed solid-statefilm using evaluated solvents were formed on quartz sub-strate too. After ink-jet printing, they were dried in a vac-uum chamber to remove the solvent. After drying, they werebaked at an elevated temperature under inert gas in a glovebox.

The spin-coated film using Toluene exhibited an ηPLof 97 ± 2% at an excited wavelength of 365 nm. The ηPL atan excited wavelength of 365 nm using solvent-B and sol-vent-C were, respectively, 98 ± 1% and 97 ± 1%. On theother hand, ink-jet-printed EML film using solvent-Aexhibited a lower ηPL of 62 ± 1% at an excited wavelengthof 365 nm.

The ηPL of ink-jet-printed green films using by sol-vent-B and solvent-C were as high as the spin-coated EMLusing Toluene. However, using Solvent-A resulted in a lowηPL.

Figure 8 shows the absolute PL quantum efficiency ofink solutions.

Prepared ink solutions contained only guest (dopant)material. Solutions were enclosed in a quartz cell for meas-uring. The absolute PL quantum efficiency was measuredwhile flowing with dried nitrogen gas in a cell. The solutionusing Toluene exhibited an ηPL of 98 ± 1% at an excitedwavelength of 450 nm. The ηPL at an excited wavelength of450 nm using solvent-B and solvent-C were, respectively,95 ± 1% and 97 ± 1%. A solution using solvent-A exhibiteda lower ηPL of 53 ± 2% at an excited wavelength of 450 nm.

An ink solution of Toluene, solvent-B, and solvent-Cshowed a high absolute PL efficiency similar to the result offilm measurement. An ink solution with solvent-A hasalready reduced the luminous efficiency. So, we conclude

FIGURE 6 — L–LE plots of green P2OLEDs. In Figs. 5 and 6, thespin-coated device using Toluene for the EML (solid black circle),ink-jet-printed device using solvent-A for the EML (solid blue circle),using solvent-B for the EML (solid red circle), using solvent-C for the EML(solid green circle). FIGURE 7 — Absolute PL quantum efficiency of spin-coated EML film

and ink-jet-printed EML film using evaluated solvents. The spin-coatedsolid-state film using Toluene (solid black square), ink-jet-printedsolid-state film using solvent-A (solid blue square), ink-jet-printedsolid-state film using solvent-B (solid red square), and using solvent-C(solid green square).

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that the luminous efficiency of film correlates well with theluminous efficiency in ink solution.

Table 2 shows the relationship of the absolute PLquantum efficiencies in ink solution and in film and theluminous efficiency (at 1000 cd/m2) in devices. The highabsolute PL quantum efficiency in ink solution is responsi-ble for the high luminous efficiency of ink-jet-printedP2OLEDs. In Fig. 6, the shapes of the efficiency curves aredifferent between a spin-coated device and an ink-jet-printed device for the evaluated solvents. The use of sol-vent-A for the EML affects the luminous efficiency ofink-jet-printed P2OLED perhaps due to quenching.

4 Progress in the solution-processedphosphorescent-OLED performance byspin-coating

RGB P2OLEDs discussed in this paper are bottom-emittingdevices fabricated on glass substrates. P2OLEDs fabricatedby spin-coating have the same device structure as shown inFig. 2. High-quality films were achieved by using spin-coated HIL, HTL, and EML.

Figure 9 shows the normalized EL spectra of the red,green, and the newly developed sky-blue P2OLEDs meas-ured at 10 mA/cm2 and the 1931 Commission Internationalde l’Eclairage (CIE) co-ordinates.

The red P2OLED has a peak wavelength at 623 nmwith 1931 Commission International de l’Eclairage (CIE)co-ordinates of (0.66, 0.33). The green P2OLED has a peakwavelength at 521 nm with 1931 Commission Internationalde l’Eclairage (CIE) co-ordinates of (0.33, 0.63). The sky-blue P2OLED has a peak wavelength at 474 nm with 1931Commission International de l’Eclairage (CIE) co-ordi-nates of (0.19, 0.40). No cavity was used in this experimentto affect the emission.

One challenge for solution-processed small-moleculedevices is to secure uniform film formation. For the hostand dopant systems, phase separation and recrystallizationcan occur during film formation, resulting in a non-uniformemission pattern and poor lifetime. However, through appro-priate material design, amorphous materials with high glass-transition temperatures can be developed to form excellentfilms.

FIGURE 8 — Absolute PL quantum efficiency of inks for the EML usingToluene and using evaluated solvents. Ink solution using Toluene (solidblack triangle), ink solution using solvent-A (solid blue triangle), inksolution using solvent-B (solid red triangle), and ink solution usingsolvent-C (solid green triangle).

FIGURE 9 — Normalized electroluminescence spectra of red, green, andblue P2OLEDs with CIE coordinates of (0.66, 0.33), (0.33, 0.66), and(0.19, 0.40), respectively, measured at 10 mA/cm2.

TABLE 2 — Relationship of absolute PL quantum efficiencies in inksolution, in film, and luminous efficiency in devices.

FIGURE 10 — Emission images of red, green, and blue P2OLEDs testpixels fabricated by spin-coating.

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Figure 10 shows the images of the red, green, and sky-blue P2OLED test pixels. In each case, the P2OLEDs showeduniform emission without any bright spots, which indicatesthat the solution-processed layers have good film quality.

Table 3 shows a summary of the latest spin-coatedRGB-P2OLED performances.

LT50 represents the stability of P2OLEDs and isdefined as the time to reach half the initial luminance. Thelifetime (LT50) measurement of RGB P2OLEDs was drivenat a constant dc current at room temperature. The redP2OLED possesses a projected LT50 of >53,000 hours withan efficiency of 9 cd/A at 500 cd/m2. The green P2OLEDpossesses a projected LT50 of >52,000 hours with an effi-ciency of 27 cd/A at 1000 cd/m2. The sky-blue P2OLEDpossesses a projected LT50 of >3000 hours with an effi-ciency of 18 cd/A at 500 cd/m2. We are continuing the

development of deeper colors and longer lifetimes in blueP2OLED systems.

The P2OLED performance, especially lifetime, arenot yet competi t ive with our state-of-the-art VTEPHOLEDs results. However, considering the short devel-opment period of P2OLEDs, the improvement of the deviceperformances has been significant.

Figure 11 shows the lifetime progresses of red andgreen P2OLEDs over the past year. As can be seen, for redP2OLEDs, the lifetime more than tripled during the pastyear. It improved from 16,000 hours in December 2006 to53,000 hours in November 2007. Green P2OLED lifetimealso improved from 6000 hours to 52,000 hours during thissame period. With more understanding of the degradationmechanism and improvement of materials and fabricationprocesses, the device performance is expected to improveeven further to meet commercial requirements.

5 ConclusionIn this paper, we have described the first ink-jet-printedgreen P2OLED. Our first demonstration of ink-jet-printedP2OLEDs exhibited good color and uniform emission. Uni-formity of EL emission is produced by the uniformity ofink-jet-printed layers. The uniform dispersion of smallmolecules in the EML resulted in the uniformity of ELemission, and high luminous efficiency is achieved by usingan ink solution with a high absolute PL quantum efficiency.To obtain high-performance IJ-P2OLEDs, the selection ofthe most appropriate solvent is very important. We also dis-cussed solution processing with small molecules forP2OLED devices. P2OLEDs provided RGB full-color setsby using the recently developed sky-blue material. We havemade significant advances towards developing a full-colordisplay based on P2OLED technology.

References1 M. A. Baldo, D. F. O’ Brien, M. E. Thompson, and S. R. Forrest, “The

excitonic singlet–triplet ratio in a semiconducting organic thin film,”Phy. Rev. B 60, 14422–14428 (1999).

2 M. A. Baldo, D. F. O’ Brien, Y. You, A. Shoustikov, S. Sibley, M. E.Thompson, and S. R. Forrest," Highly efficient phosphorescent emis-sion from organic electroluminescent devices," Nature 395, 151–154(1998).

3 M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, and S. R.Forrest, “Very high-efficiency green organic light emitting devicesbased on electrophosphorescence,” Appl. Phys. 75, 4–6 (1999).

4 C. Adachi, M. A. Baldo, M. E. Thompson, and S. R. Forrest, “Nearly100% internal phosphorescence efficiency in organic light-emittingdiode,” J. Appl. Phys. 90, 5048–5051 (2001).

5 M. S. Weaver, V. A. Adamovich, R. C. Kwong, M. Hack, and J. J. Brown,“Latest developments in phosphorescent OLEDs,” Proc. IMID ‘05,1129–1132 (2005).

6 M.-H. Lu, M. S. Weaver, M. Rothman, T. Ngo, H. Yamamoto, J. Brooks,S. Xia, A. Fukase, S. Tomioka, S. Seki, and S. Miyashita, “Ink jetprintable phosphorescent organic light-emitting devices,” Conf. Re-cord IDRC ‘06, 63–66 (2006).

7 http://www.epson.jp/osirase/2004/040518.htm.8 T. Shimoda, S. Kanbe, H. Kobayashi, S. Seki, H. Kiguchi, I. Yudasaka,

M. Kimura, S. Miyashita, R. H. Friend, J. H. Burroughes, and C. R.Towns, “Multicolor pixel patterning of light-emitting polymers by ink-jet printing,” SID Symposium Digest 30, 376–379 (1999).FIGURE 11 — Lifetime progress of red and green P2OLEDs over the past year.

TABLE 3 — Summary of red, green, and sky-blue P2OLEDperformances. Lifetime data were calculated from acceleratedtests.

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Takuya Sonoyama received his M.S. degree inmaterial science from the Japan Advanced Insti-tute of Science and Technology in 1997. Hejoined the Knowledge Cluster Initiative Program,Ueda Nagano, Japan, in 2002. In 2004, he joinedSeiko Epson Corp., Owa, Suwa, Japan, where hehas been working on the development of ink-jet-printing technologies for organic light-emitting di-odes at the OLED development center.

Masaki Ito received his B.S. degree in polymerchemical engineering in 2001. In 2007, he joinedSeiko Epson Corp., Owa, Suwa, Japan, where hehas been working on the development of ink-jet-printing technologies for organic light-emittingdiodes at the OLED development center.

Shunichi Seki received his B.S. and M.S. degreesin physics from the Science University of Tokyo.He had been working on pie-conjugated pigmentand photosensitive proteins in halobacteria at theInstitute of Physical and Chemical Research,Riken, Tsukuba, Japan. In 1997, he joined SeikoEpson Corp., Owa, Suwa, Japan, where he hasbeen working on the development of ink-jet-printing technologies for organic light-emittingdiodes. He is a Manager at the OLED develop-ment center.

Satoru Miyashita received his B.S. degree in appliedchemical engineering from Keio University,Japan, in 1981. In 1982, he joined Seiko EpsonCorp., Owa, Suwa, Japan, where he has beenworking on functional materials research andnovel process development. He is a General Man-ager at the OLED development center.

Sean Xia is a Senior Research Scientist at Univer-sal Display Corp. Prior to joining UDC in 2005,he was a Senior Scientist at BTG International,Inc., where he was working on bipolar electrolu-minescent devices for display and lighting appli-cations. He received his B.S. degree in chemistryfrom the University of Science and Technology ofChina (1998). Dr. Xia received his Ph.D. degree(2002) in organic/polymer chemistry from theUniversity of Alabama at Birmingham under the

advisement of Professor Rigoberto C. Advincula. He has over 30 publi-cations in the fields of conjugated oligomers and polymers, electro-chemistry, nanostructured ultra-thin films, and organic light-emitting-diode devices.

Jason J. Brooks is a senior scientist at UniversalDisplay Corp. Prior to joining UDC in 2002, hereceived his B.A. degree in chemistry in 1996from Northwestern University. In 1997, he beganas a graduate student at the University of SouthernCalifornia where he received his Ph.D. degree inchemistry (2002) under the advisement of Profes-sor Mark E. Thompson. He did his graduate studyon the photophysical properties of platinum com-plexes and their application to organic light-emit-

ting-diode devices. He has contributed to patents pertaining to mono-mer-excimer emission of phosphorescent materials as well as othernovel materials designed to improve the properties of phosphorescentdevices. He has several publications in peer-reviewed journals and hasgiven several invited talks in the field of electronic organic materials.

Kwang-Ohk Cheon is a Senior Scientist at Univer-sal Display Corp. He received his Ph.D. degreefrom Iowa State University where he specializedin condensed matter physics. He was a senior sci-entist at BTG international, Inc., working on bipo-lar organic light-emitting-diode devices, and alsoat Evident Technologies performing quantum-dotresearch for LED applications. In 2007, he joinedUniversal Display Corp. His research interestshave focused on printable phosphorescentOLEDs.

Raymond C. Kwong joined UDC in 2000 as aSenior Scientist and is currently the Director ofPHOLED¿ Materials and Development at Univer-sal Display Corp. He received his B.Sc. andM.Phil. in chemistry from the Chinese Universityof Hong Kong in 1993 and 1995, respectively,and his Ph.D. degree in chemistry from the Uni-versity of Southern California in 2000 under theadvisement of Professor Mark E. Thompson. Hehas over 35 publications and 50 patents and

pending patents in the field of organic light-emitting-diode devices. AtUDC, he leads an R&D team to develop organic electronic materials forhigh-performance OLEDs.

Michael Inbasekaran is the Manager of the Print-able OLEDs Research Department at UniversalDisplay Corp. Prior to joining UDC in 2006, hewas a Senior Scientist at The Dow Chemical Com-pany where he invented Lumation polyfluorenesas materials for RGB PLEDs. The Lumation poly-mer business was acquired by Sumitomo Chemi-cals from Dow Chemical Company in 2005. Hereceived his Ph.D. in organic chemistry (1977)from The University of Alabama and spent several

years as a postdoctoral fellow at Ohio State University, the University ofMichigan, and Princeton University before joining The Dow ChemicalCo. (1983) as Senior Chemist. He has over 60 publications and 50 pat-ents in the fields of heterocyclic chemistry, medicinal chemistry, organicsynthetic methods, optoelectronic materials, and organic light-emitting-diode devices.

Journal of the SID 16/12, 2008 1235

Julie J. Brown is Vice President and Chief Tech-nology Officer at Universal Display Corp. Prior tojoining UDC in 1998, she was a Research Depart-ment Manager at Hughes Research Laboratorieswhere she directed the pilot-line production ofhigh-speed indium-phosphide-based integratedcircuits for insertion into advanced airborne radarand satellite communication systems. She receivedher B.S. degree in electrical engineering from Cor-nell University (1983) and then worked at

Raytheon Company (1983–1984) and AT&T Bell Laboratories (1984–1986) before returning to graduate school. She received her M.S. degree(1988) and Ph.D. degree (1991) in electrical engineering/electrophysicsfrom the University of Southern California under the advisement of Pro-fessor Stephen R. Forrest. She was nominated as an IEEE Fellow in 2006and inducted into the New Jersey High Tech Hall of Fame in February2007. She has over 175 publications and patents in the fields of high-speed compound semiconductor electronic/optoelectronic device,microelectromechanical systems (MEMs), and organic light-emitting-diode devices.

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