• Title, Summary, Keyword: Top-emitting organic light emitting diodes

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Efficient Top-Emitting Organic Light Emitting Diode with Surface Modified Silver Anode

  • Kim, Sung-Jun;Hong, Ki-Hyon;Kim, Ki-Soo;Lee, Ill-Hwan;Lee, Jong-Lam
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.23 no.7
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    • pp.550-553
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    • 2010
  • The enhancement of quantum efficiency using a surface modified Ag anode in top-emitting organic light emitting diodes (TEOLEDs) is reported. The operation voltage at the current density of $1\;mA/cm^2$ of TEOLEDs decreased from 9.3 V to 4.3 V as the surface of anode coated with $CuO_x$ layer. The work function of these structures were quantitatively determined using synchrotron radiation photoemission spectroscopy. Secondary electron emission spectra revealed that the work function of the Ag/$CuO_x$ structure is higher by 0.6 eV than that of Ag. Thus, the $CuO_x$ structure acts as a role in reducing the hole injection barrier by about 0.6 eV, resulting in a decrease of the turn-on voltage of top-emitting light emitting diodes.

Theoretical Modeling of the Internal Power Flow and Absorption Loss of the Air Mode Based on the Proposed Poynting Vector Analysis in Top-emitting Organic Light-emitting Diodes

  • Kim, Jiyong;Kim, Jungho;Kim, Kyoung-Youm
    • Journal of the Korean Physical Society
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    • v.73 no.11
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    • pp.1663-1674
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    • 2018
  • We propose the Poynting vector analysis of the air mode in a top-emitting organic light-emitting diode (OLED) by combining the transfer matrix method and dipole source term. The spatial profiles of the time-averaged optical power flow of the air mode are calculated inside and outside the multilayer structure of the OLED with respect to the thickness of the semi-transparent top cathode and capping layer (CPL). We elucidate how the micro-cavity effect controlled by the thickness variation of the semi-transparent top cathode or CPL affects the internal optical power and absorption loss inside the OLED multilayer and the external optical power coupled into the air. When the calculated absorption loss and external power obtained by the proposed Poynting vector and currently-used point dipole models are compared, two calculation results are identical, which demonstrates the validity of the two models.

Influence of Electrode and Thickness of Organic Layer to the Emission Spectra in Microcavity Organic Light Emitting Diodes (마이크로캐비티 OLED의 전극과 유기물층 두께가 발광 스펙트럼에 미치는 영향)

  • Kim, Chang-Kyo;Han, Ga-Ram;Kim, Il-Yeong;Hong, Chin-Soo
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.11
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    • pp.1183-1189
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    • 2012
  • Organic light-emitting diodes (OLEDs) using microcavity effect have attracted great attention because they can reduce the width of emission spectra from organic materials, and enhance brightness from the same material. We demonstrate the simulation results of the radiation properties from top-emitting organic light-emitting diodes (TE-OLEDs) with microcavity structures based on the general electromagnetic theory. Organic materials such as N,N'-di (naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) ($Alq_3$) as emitting and electron transporting layer are used to form the OLEDs. The organic materials were sandwiched between anode such as Ni or Au and cathode such as Al, Ag, or Al:Ag. The devices were characterized with electroluminescence phenomenon. We confirmed that the simulation results are consistent with experimental results.

Synchrotron radiation photoelectron spectroscopy study of oxygen doping effect by oxygen plasma treatment to inverted top emitting organic light emitting diodes

  • Hong, Ki-Hyon;Kim, Ki-Soo;Kim, Sung-Jun;Choi, Ho-Won;Tak, Yoon-Heung;Lee, Jong-Lam
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.118-120
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    • 2009
  • We reported that the evidence of oxygen doping to copper-phthalocyanine (CuPc) by $O_2$-plasma treatment to Au electrode of inverted top emitting organic light emitting diodes (ITOLEDs). The operation voltage of OLEDs at 150 mA/$cm^2$ decreased from 16.1 to 10.3 V as oxygen atoms indiffued to CuPc layer using $O_2$-plasma. Synchrotron radiation photoelectron spectroscopy results showed that a new bond of Cu-O appeared and the energy difference between the highest occupied molecular orbital and $E_F$ is lowered by 0.20 eV after plasma treatment. Thus the hole injection barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.

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Inductively Coupled Plasma Chemical Vapor Deposition System for Thin Film Ppassivation of Top Emitting Organic Light Emitting Diodes (전면발광 유기광소자용 박막 봉지를 위한 유도결합형 화학 기상 증착 장치)

  • Kim Han-Ki
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.19 no.6
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    • pp.538-546
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    • 2006
  • We report on characteristics of specially designed inductively-coupled-plasma chemical vapor deposition (ICP-CVD) system for top-emitting organic light emitting diodes (TOLEDs). Using high-density plasma on the order of $10^{11}$ electrons/$cm^3$ generated by linear-type antennas connected in parallel and specially designed substrate cooling system, a 100 nm-thick transparent $SiN_{x}$ passivation layer was deposited on thin Mg-Ag cathode layer at substrate temperature below $50\;^{\circ}C$ without a noticeable plasma damage. In addition, substrate-mask chucking system equipped with a mechanical mask aligner enabled us to pattern the $SiN_x$ passivation layer without conventional lithography processes. Even at low substrate temperature, a $SiN_x$ passivation layer prepared by ICP-CVD shows a good moisture resistance and transparency of $5{\times}10^{-3}g/m^2/day$ and 92 %, respectively. This indicates that the ICP-CVD system is a promising methode to substitute conventional plasma enhanced CVD (PECVD) in thin film passivation process.

TOP-EMISSION CHARACTERISTICS OF ORGANIC LIGHT-EMITTING DIODES (유기발광소자의 전면 발광 특성)

  • Shin, Eun-Chul;Park, Il-Heung;Lee, Ho-Shik;Cho, Sung-Ho;Min, Hang-Gi;Kim, Tae-Wan
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.58-59
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    • 2007
  • We have fabricated top-emission. organic ligth-emitting diodes in a structure of Glass/Al/2-TNATA/TPD/$Alq_3$/LiF/Al/Ag. By varying a film thickness of 2-TNATA and TPD, current efficiency, luminance efficiency, and viewing angle dependence of the device were measured. The top device using $Alq_3$ showed electroluminescent peak wavelengths of 522nm and 505nm at $0^{\circ}$ and $60^{\circ}$ viewing angles, respectively. It is thought that a microcavity effect affects on peak wavelength position for different viewing angles.

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Effects of dielectric capping layer in the phosphorescent top emitting organic light emitting diodes

  • Kim, Sei-Yong;Leem, Dong-Seok;Lee, Jae-Hyun;Kim, Jang-Joo
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.499-502
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    • 2008
  • Effects of a dielectric capping layer on the luminous characteristics of top emitting organic light emitting diodes (TOLEDs) have been analyzed using a classical electromagnetic theory. Special attention was given to the influence of the cavity length on the effectiveness of the capping layer. The luminance characteristics of the TOLEDs influenced by the combined effects of the cavity length and the capping layer thickness. Furthermore, these combined effects also modify the emission spectrum and pattern of the TOLEDs, which result in the improvement of total luminance of the device, but no significant change in the device out-coupling efficiency.

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Plasma Treatment Effects on Tungsten Oxide Hole Injection Layer for Application to Inverted Top-Emitting Organic Light-Emitting Diodes

  • Kim, Joo-Hyung;Lee, You-Jong;Jang, Yun-Sung;Kim, Doo-Hyun;Hong, Mun-Pyo
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.354-355
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    • 2009
  • In the fabrication of inverted top-emitting organic light emitting diodes (ITOLEDs), the sputtering process is needed for deposition of transparent conducting oxide (TCO) as top anode. Energetic particle bombardment, however, changes the physical properties of underlying layers. In this study, we examined plasma process effects on tungsten oxide ($WO_3$) hole injection layer (HIL). From our results, we suggest the theoretical mechanism to explain the correlation between the physical property changes caused by plasma process on $WO_3$ HIL and degradation of device performances.

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Microcavity Effect of Top-emission Organic Light-emitting Diodes Using Aluminum Cathode and Anode

  • Lee, Chang-Jun;Park, Young-Il;Kwon, Jang-Hyuk;Park, Jong-Wook
    • Bulletin of the Korean Chemical Society
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    • v.26 no.9
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    • pp.1344-1346
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    • 2005
  • We report microcavity effect of top emission organic light-emitting diodes (OLEDs) by using Al cathode and anode, which are feasible for not only top emission EL and angle dependant effects but facile evaporation process without ion sputtering. The device in case of $Alq_3$ green emission showed largely shifted EL maximum wavelength as 650 nm maximum emission. It was also observed that detection angle causes different EL maximum wavelength and different CIE values in R, G, B color emission. As a result, the green device using $Alq_3$ emission showed 650 nm emission ($0^{\circ}$) to 576 nm emission ($90^{\circ}$) as detection angle changed. We believe that these phenomena can be also explained with microcavity effect which depends on the different length of light path caused by detection angle.

Electrical, Optical and Structural Properties of Indium Zinc Oxide Top Cathode Grown by Box Cathode Sputtering for Top-emitting OLEDs (박스 캐소드 스퍼터로 성장시킨 전면 발광 OLED용 상부 InZnO 캐소드 박막의 전기적, 광학적, 구조적 특성 연구)

  • Bae Jung-Hyeok;Moon Jong-Min;Kim Han-Ki
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.19 no.5
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    • pp.442-449
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    • 2006
  • Electrical, optical, and structural properties of indium zinc oxide (IZO) films grown by a box cathode sputtering (BCS) were investigated as a function of oxygen flow ratio. A sheet resistance of $42.6{\Omega}/{\Box}$, average transmittance above 88% in visible range, and root mean spare roughness of $2.7{\AA}$ were obtained even in the IZO layers grown at room temperature. In addition, it is shown that electrical characteristics of the top-emitting organic light emitting diodes (TOLEDs) with the BCS grown-IZO top cathode layer is better than that of TOLEDs with DC sputter grown IZO top cathode, due to absence of plasma damage effect. Furthermore the effects of oxygen flow ratio in IZO films are investigated, based on x-ray photoelectron spectroscopy (XPS), ultra violet/visible (UV/VIS) spectro-meter, scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis results.