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Jonghee Lee,Jeong-Ik Lee,Hye Yong Chu 한국전자통신연구원 2009 ETRI Journal Vol.31 No.6
Highly efficient white phosphorescent organic lightemitting diodes with a mixed-host structure are developed and the device characteristics are studied. The introduction of a hole-transport-type host (N, N'- dicarbazolyl-3-3-benzen (mCP)) into an electrontransport- type host (m-bis-(triphenylsilyl)benzene (UGH3)) as a mixed-host emissive layer effectively achieves higher current density and lower driving voltage. The peak external quantum and power efficiency with the mixed-host structure improve up to 18.9% and 40.9 lm/W, respectively. Moreover, this mixed-host structure device shows over 30% enhanced performance compared with a single-host structure device at a luminance of 10,000 cd/m² without any change in the electroluminescence spectra.
Who are Steered to a Risky Credit Alternative?
Lee, Jonghee The Korean Home Economics Association 2013 International Journal of Human Ecology Vol.14 No.2
The market for a payday advance, regarded as both a convenient and short term-loan for immediate financial help, has grown incredibly since the 1990's. Despite its popularity by borrowers and the possible benefits, it has received negative publicity. Some borrowers have been caught in a debt trap for a long-term period and at tripledigit interest rates. The objective of this study is to shed light on the borrowers' profiles and their demand for a payday advance. Based on the 2010 household level data from the U.S. Federal Reserve Board, this study finds that payday advance users are pronounced as seemingly risky people. Payday advance users tend to be college drop-outs, African Americans, and non-homeowners compared to non-payday advance users. They are more likely to overspend above their income and have a favorable attitude toward conspicuous spending than non-payday advance users. They tend not to shop at all nor perform even moderate shopping for credit before using a payday advance service as opposed to non-payday advance users.
Lee, Jongtaek,Lee, Junyoung,Yang, Jonghee,Park, Taehun,Ahn, Sang Jung,Yi, Whikun American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.8
<P>We synthesized three-dimensional (3-D) SWNT networks suspended on Si pillar architecture. The pillar arrays on Si substrate were formed by a standard photolithography technique using a patterned chrome mask and plasma etching in a SF6:C4F8 gas mixture. Successively, 3-D SWNT networks were synthesized between pillar arrays by a thermal chemical vapor deposition. We investigated the optical properties and formation of 3-D SWNT networks suspended on Si pillar arrays through controlling catalyst deposition methods between pillar arrays by using scanning electron microscopy and Raman spectroscopy. We confirmed that the bridging and connecting of SWNTs between Si pillars, suggesting the effective growth of the 3-D SWNT networks on Si pillar architecture for application to large scale and well-organized devices.</P>
Improvements of phosphorescent white OLEDs performance for lighting application.
Lee, Jonghee,Chu, Hye Yong,Lee, Jeong-Ik,Song, Ki-Im,Lee, Su Jin American Scientific Publishers 2008 Journal of Nanoscience and Nanotechnology Vol.8 No.10
<P>We developed white OLED device with high power efficiency, in which blue and orange phosphorescent emitters were used. By introduction of multi-functional interlayer which has partial doping of orange dopant inside EBL, we report WOLEDs with peak external efficiencies up to (14.1% EQE, 31.3 Im/W) without light out-coupling technique. At 1000 cd/m2, the performance achieved was 11.9% EQE, 18.7 Im/W with CIE = (0.39, 0.44). We also found that WOLED performances are related with doping ratio of the orange dopant that was inserted inside EBL.</P>
Lee, Keunsoo,Shin, Jin-Wook,Park, Jun-Hwan,Lee, Jonghee,Joo, Chul Woong,Lee, Jeong-Ik,Cho, Doo-Hee,Lim, Jong Tae,Oh, Min-Cheol,Ju, Byeong-Kwon,Moon, Jaehyun American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.27
<P>We propose and fabricate a random light scattering layer for light extraction in organic light-emitting diodes (OLEDs) with silver nanodots, which were obtained by melting silver nanowires. The OLED with the light scattering layer as an internal light extraction structure was enhanced by 49.1% for the integrated external quantum efficiency (EQE). When a wrinkle structure is simultaneously used for an external light extraction structure, the total enhancement of the integrated EQE was 65.3%. The EQE is maximized to 65.3% at a current level of 2.0 mA/cm(2). By applying an internal light scattering layer and wrinkle structure to an OLED, the variance in the emission spectra was negligible over a broad viewing angle. Power mode analyses with finite difference time domain (FDTD) simulations revealed that the use of a scattering layer effectively reduced the waveguiding mode while introducing non-negligible absorption. Our method offers an effective yet simple approach to achieve both efficiency enhancement and spectral stability for a wide range of OLED applications.</P>
Enhanced and balanced efficiency of white bi-directional organic light-emitting diodes.
Lee, Jonghee,Cho, Hyunsu,Koh, Tae-Wook,Yun, Changhun,Hofmann, Simone,Lee, Jae-Hyun,Kim, Yong Hyun,L?ssem, Bj?rn,Lee, Jeong-Ik,Leo, Karl,Gather, Malte C,Yoo, Seunghyup Optical Society of America 2013 Optics express Vol.21 No.23
<P>We report on the characteristics of enhanced and balanced white-light emission from bi-directional organic light-emitting diodes (BiOLEDs) enabled by the introduction of micro-cavity effects. The insertion of an additional metal layer between the indium tin oxide anode and the hole transporting layer results in similar light output of our BiOLEDs in both top and bottom direction and in reduced distortion of the electroluminescence spectrum. Furthermore, we find that by utilizing MC effects, the overall current efficiency can be improved by 26.2% compared to that of a conventional device.</P>
Lee, Hyunkoo,Maeng, Min-Jae,Hong, Jong-Am,Najnin, Rokeya,Moon, Jaehyun,Cho, Hyunsu,Lee, Jonghee,Yu, Byoung-Gon,Park, Yongsup,Cho, Nam Sung The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.38
<▼1><P>Highly efficient green, blue, and white phosphorescent inverted organic light-emitting diodes were demonstrated by improving charge injection and balance.</P></▼1><▼2><P>To improve the performance of inverted organic light-emitting diodes (OLEDs), we investigated the electrical, optical, and interfacial properties of three different lithium (Li)-doped electron transport materials (ETMs): tris(3-(3pyridyl)mesityl)borane (3TPYMB), 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), and 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB). The electron injection barriers (EIBs) between indium-tin-oxide and the ETMs were deduced for both pristine and Li-doped cases from ultraviolet photoelectron spectroscopy measurements and optical band gap values. The Li-doped ETMs showed EIB values of approximately 0.03 eV, 0.77 eV, and 0.81 eV for 3TPYMB, TmPyPB, and BmPyPB, respectively, which are much lower than those of their pristine counterparts of 0.94 eV, 1.14 eV, and 1.48 eV, respectively. The Li-doped ETMs were employed as electron injection layers (EILs) of inverted bottom-emission OLEDs (IBE-OLEDs) with green phosphorescence. IBE-OLEDs with 3TPYMB, TmPyPB, and BmPyPB EILs exhibited driving voltages of 3.6 V, 4.0 V, and 4.5 V at 1000 cd m<SUP>−2</SUP> and maximum external quantum efficiencies (EQEs) of 20.3%, 19.7%, and 16.5%, respectively. From the low EIB of Li-doped 3TPYMB, we also demonstrated highly efficient blue and white phosphorescent IBE-OLEDs. We optimized the device structure to improve the charge balance and out-coupling efficiency by changing the hole injection layer and the thickness of the hole and electron transport layers with optical simulation. The blue device showed a maximum EQE and luminous current efficiency of 22.9% and 43.1 cd A<SUP>−1</SUP>, respectively. In addition, the white device exhibited a high EQE and luminous efficacy of 19.3% and 37.8 lm W<SUP>−1</SUP> at 3 mA cm<SUP>−2</SUP> (∼1000 cd m<SUP>−2</SUP>), respectively. To the best of our knowledge, the efficiencies of these green, blue, and white devices are the highest values obtained to date with a low driving voltage for IBE-OLEDs without any additional light-extraction structure. Since the Li-doped 3TPYMB has an extremely low EIB and shows good device performance, it can be utilized as an effective EIL in inverted-structure devices.</P></▼2>
Lee, Jonghee,Kim, Yong Hyun Elsevier 2018 Synthetic metals Vol.242 No.-
<P><B>Abstract</B></P> <P>We report high performance white organic light-emitting diodes (OLEDs) based on high conductivity poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films optimized by a solvent post treatment. The device stack is carefully optimized with high efficiency tandem structures including red, yellow/green, and blue emissive materials. The OLED with the PEDOT:PSS transparent electrode achieves a high power efficiency of 26.1 lm/W and an external quantum efficiency of 19.3%, which are comparable to the reference indium tin oxide (ITO)-based OLEDs. In addition, it is observed that the angular emission characteristic of PEDOT:PSS-based OLEDs is closer to Lambertian distribution compared to that of the ITO-based OLED. We show that the optimized device stack together with post-treated PEDOT:PSS transparent electrodes can realize high performance ITO-free white OLEDs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Efficient ITO-free white OLEDs prepared with conductive polymers are presented. </LI> <LI> The device efficiency is boosted by using the optimized tandem structure. </LI> <LI> The optimized device stack results in the high efficiency of ITO-free white OLEDs. </LI> </UL> </P>
Lee, Chang-Whan,Lee, Mihui,Yoon, Sung-Pil,Ham, Hyung-Chul,Choi, Sun Hee,Han, Jonghee,Nam, Suk Woo,Yang, Dong-Yol Elsevier 2017 Journal of industrial and engineering chemistry Vol.51 No.-
<P><B>Abstract</B></P> <P>The effect of current collectors of molten carbonate fuel cells (MCFCs) was studied through three-dimensional computational fluid dynamics and experiments. Three types of current collectors such as a sheet with sheared protrusions and perforated sheets were employed and performances of MCFCs were compared. A current collector structure with a large gas open area to electrodes improves diffusion characteristics between electrodes and gas flow channels. As a result, differences of gas mole fractions between gas flow channels and electrodes were decreased. Finally, Nernst loss and cathode polarization loss decreased, and the performance was enhanced. Using these results, current collector structures for improved performance and long-term operation were discussed.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>