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Kim, Gyeong Woo,Lampande, Raju,Choe, Dong Cheol,Bae, Hyeong Woo,Kwon, Jang Hyuk Elsevier 2015 THIN SOLID FILMS - Vol.589 No.-
<P><B>Abstract</B></P> <P>In this paper, we demonstrate a design and synthesis of efficient hole injecting material, 5,10,15-trimethyl-5H-diindolo[3,2-a:3’,2’-c] carbazole (TMDI), for blue fluorescent organic light emitting diodes (OLEDs). Our synthesized TMDI material has good hole mobility of about 8.9 x10<SUP>−4</SUP> cm<SUP>2</SUP>/Vs and compatible highest occupied molecular orbital level of −5.1eV, which are important parameters for excellent hole injection layer (HIL) in the OLED applications. The fabricated blue fluorescent OLEDs with TMDI yield about 8% reduction in operating voltage and 39% of improvement in power efficiency as compare to the widely used HIL material 4,4’,4”-tris-(N-(naphthalen-2-yl)-N-phenyl-amino) triphenylamine. Such performance enhancements are mainly attributed to good hole mobility of TMDI.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 5,10,15-trimethyl-5H-diindolo[3,2-a:3',2'-c] carbazole (TMDI) as efficient hole injection material. </LI> <LI> Excellent hole mobility and a good HOMO level of 5.1eV </LI> <LI> 8% reduction in the operating voltage of blue fluorescent OLED. </LI> <LI> 39% power efficiency improvement in the blue fluorescent OLED. </LI> </UL> </P>
Technical status of top-emission organic light-emitting diodes
Kim Seong Keun,Lampande Raju,Kwon Jang Hyuk 한국정보디스플레이학회 2021 Journal of information display Vol.22 No.3
Top-emission organic light-emitting diodes (TEOLEDs) that contain semi-transparent metal top cathodes and highly reflective anodes have been actively researched for display applications due to their many advantages such as their high aperture ratio, good color purity, and high efficiency. In this research, the technical design of TEOLEDs used in organic light-emitting diode (OLED) displays is reviewed, covering the optical theory with the microcavity effect, optical losses, and the importance of the Purcell effect in the optical calculation. The key methodologies for addressing the high efficiency and low driving voltage of TEOLEDs are also discussed.
An efficient nano-composite layer for highly transparent organic light emitting diodes
Kim, Gyeong Woo,Lampande, Raju,Boizot, Julien,Kim, Gyeong Heon,Choe, Dong Cheol,Kwon, Jang Hyuk The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.7
We report highly transparent and low resistive new cathode structures, which basically consist of nano-composite layer/Ag/WO3 for transparent organic light-emitting diode (TOLED) applications. Our new cathode structure exhibits an extremely high transmittance of 91.2% at 550 nm, a low sheet resistance of 5.4 Omega square(-1), and excellent electron injection properties. Such a high transmittance along with a low resistivity of the fabricated new cathode could be explained by surface-modifying behavior with the generation of a nano-composite thin silver oxide layer during Ag deposition. Chemical interaction at the interface between the electron injection layer and the electron transport layer results in good electron injection properties in TOLEDs. The fabricated TOLEDs with our new cathode structures have a full device transmittance of 85-87% at 550 nm.
Kim, G.H.,Lampande, R.,Kang, B.Y.,Bae, H.W.,Lee, J.Y.,Kwon, J.H.,Park, J.H. Elsevier Science 2016 Organic Electronics Vol.31 No.-
<P>We report bipolar host materials with robust indenocarbazole and biphenyl moiety as hole-electron-transporting unit for phosphorescent yellow organic light-emitting diodes (OLEDs). New host materials demonstrated an excellent morphological stability with high glass transition temperature of 207 degrees C. Simultaneously, it also revealed appropriate triplet energy of about 2.6 eV for ideal triplet energy transfer to yellow phosphorescent dopant. A phosphorescent yellow OLED with new host ICBP1 (and ICBP2) and conventional yellow dopant iridium(III) bis(4-(4-t-butylphenyl) thieno[3,2-c] pyridinato-N, C2') acetylacetonate (Ir(tptpy)(2)acac) shows a low driving voltage of 3.4 (and 3.6 V) at 1000 cd/m(2), and maximum external quantum efficiency as high as 26.4%. Such efficient performance of phosphorescent yellow OLEDs is attributed to a good charge balance and high electron transport properties of host materials. (c) 2016 Elsevier B.V. All rights reserved.</P>
Im, Joon Beom,Lampande, Raju,Kim, Gyeong Heon,Lee, Ju Young,Kwon, Jang Hyuk American Chemical Society 2017 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.121 No.2
<P>To investigate the influence of intramolecular charge transfer (CT) characteristics, rigidity, and polarity of a molecule on photophysical properties, we designed and synthesized two types of thermally activated delayed fluorescence (TADF) emitters with malononitrile and acrylonitrile moieties as electron accepting units. Their photophysical properties such as singlettriplet energy split (?EST), photoluminescence quantum yields (PLQYs), and electronic structures were theoretically and experimentally evaluated. Among the synthesized materials, the emitters with an acrylonitrile moiety as an acceptor and phenoxazine, dimethylacridine, and tert-butylcarbazole as a donor revealed small ?EST values, good PLQYs, and efficient TADF performances. In contrast, the malononitrile derivatives demonstrated high ?EST values, very low PLQYs, and relatively poor TADF performances even though they have strong intramolecular CT characteristics and high polarity. We found that high molecular polarity and strong intramolecular CT characteristics are not essential factors for attaining good TADF performances over molecular rigidity.</P>
Kong, J.H.,Kim, G.W.,Lampande, R.,Kim, G.H.,Park, M.J.,Bae, H.W.,Kwon, J.H. Elsevier Science 2015 Organic electronics Vol.21 No.-
We report new electron injection lithium complexes, lithium 2-(2-pyridyl)-3-pyridinolate (LIPPy) and lithium 4-phenyl-2-(2-pyridyl)phenolate (LIPPP) for low driving voltage and better stability of organic light emitting diodes (OLEDs). These materials were designed with the help of molecular simulation of anion formation energy and lithium binding energy calculations. Small anion formation energy and low binding energy of lithium complexes show good correlation with expected experimental driving voltage of the OLEDs. Fabricated OLEDs with these new lithium complexes exhibit lower driving voltage, higher power efficiency and longer lifetime as compare to the widely used and commercially available lithium 8-quinolate (Liq) and lithium 2-(2-pyridyl)phenolate (LIPP).
Kim, Kwang Jong,Kim, Gyeong Heon,Lampande, Raju,Ahn, Dae Hyun,Im, Joon Beom,Moon, Ji Su,Lee, Jae Kyun,Lee, Jae Yeol,Lee, Ju Young,Kwon, Jang Hyuk The Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.6
<P>In this communication, we report an excellent new highly conjugated and rigid electron donor (diindolocarbazole) for thermally activated delayed fluorescence (TADF) emitters. The donor-acceptor structure with diindolocarbazole donor induces high oscillator strength as well as high probability for the radiative transition, suitable frontier molecular overlap with proper intramolecular charge transfer and a large dihedral angle with out-of-plane structure between electron donor and acceptor; this results in high photoluminescence quantum yield, small singlet-triplet energy splitting, and extremely short delayed fluorescence exciton lifetime. The fabricated organic light emitting diode with new donor applied green emitter exhibits a remarkably high external quantum efficiency of 31.4% without any out-coupling technique. It also shows extremely low efficiency roll-off characteristics with the highest luminance of 71 160 cd m<SUP>−2</SUP> as well as good operational device stability.</P>
Efficient blue phosphorescent organic light emitting diodes with host engineering
김영재,손영훈,김신혜,이정민,Raju Lampande,노창호,김성한,권장혁 한국물리학회 2015 Current Applied Physics Vol.15 No.1
We demonstrate as much as possible blue color and high efficiency phosphorescent organic lightemitting diodes (PHOLEDs) by using well-known iridium(III)bis[(3,5-difluoro-4-cyanophenyl)-pyridinato- N,C0]picolinate (FCNIrpic) dopant and previously reported good host materials. For the control of blue color and efficiency, various host materials, 1,3-bis(carbazole-9-yl)benzene (mCP), 9-(3-(9Hcarbazole- 9-yl)phenyl)-3-(dibromophenylphosphoryl)-9H-carbazole (mCPPO1), and 2,8-di(9H-carbazol- 9-yl)dibenzo[b,d]furan (DFCz), bis(4-(N-carbazole)phenyl)dimethylsilane (2MCBP) are selected and investigated their performances. A maximum external quantum efficiency (EQE) of 23.9% and power efficiency of 30.2 lm/W are achieved from 2MCBP device with Commision Internationale de L'Eclairage color coordinates (CIEx,y) of (0.14, 0.21). The deepest color with color coordinate of (0.14, 0.19) is obtained for the mCP device.