• Title, Summary, Keyword: Organic light-emitting diodes

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AC-Based Characterization of Quantum-Dot Light-Emitting Diodes

  • Hwang, Hee-Soo;Lee, Ki-Hun;Park, Chan-Rok;Yang, Heesun;Hwang, Jinha
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.466-466
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    • 2013
  • Quantum-dot materials have introduced novel applications in organic light-emitting diodes and solar cells. The size controllability and structure modifications have continuously been upgrading the applicability to optoelectronic and flat-panel displays. In particular, quantum-dot organic light-emitting diodes (QLEDs) are a device driven through the electrical field applied to the electrical diodes. The QLEDs are affected by the constituent materials and the corresponding device structures. Conventionally, the electrical properties are characterized only in terms of dc-based current-voltage characteristics. The dynamic change in light-emitting diodes should be characterized in emitted and non-emitted states. Therefore, the frequency-dependent impedance can offer different information on the electrical performance in QLED. The current work reports an auxiliary information on the electrical and optical features originating from quantum-dot organic light-emitting diodes. The empirical characterizations are discussed towards an experimental tool in optimizing the light-emitting diodes.

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Charge Trapping Host Structure for High Efficiency in Phosphorescent Organic Light-Emitting Diodes

  • Lee, Jun-Yeob
    • Journal of Information Display
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    • v.9 no.2
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    • pp.14-17
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    • 2008
  • A charge trapping host structure was developed to improve the light-emitting efficiency of green phosphorescent organic light-emitting diodes. N, N'-dicarbazolyl-3,5-benzene(mCP) and a spirobifluorene based triplet host(PHl) were co-deposited as hosts in the emitting layer and the device performance was examined according to the composition mCP and PH1. The results showed that the quantum efficiency could be improved by 30 % using a mixed host of mCP and PH1.

Cathode interface engineering for stable and efficient organic light-emitting diodes

  • Qiu, Yong;Duan, Lian;Li, Yang
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.1199-1202
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    • 2007
  • The improvement of the electron injection is of critical importance for obtaining efficient and stable organic light-emitting diodes(OLEDs). Here, we report some of our recent results on the development of new cathode interlayer materials for OLEDs. Some of our new materials show performance superior to that of LiF.

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Simplified Bilayer White Phosphorescent Organic Light-Emitting Diodes

  • Lee, Jonghee;Sung, Woo Jin;Joo, Chul Woong;Cho, Hyunsu;Cho, Namsung;Lee, Ga-Won;Hwang, Do-Hoon;Lee, Jeong-Ik
    • ETRI Journal
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    • v.38 no.2
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    • pp.260-264
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    • 2016
  • We report on highly efficient blue, orange, and white phosphorescent organic light-emitting diodes consisting only two organic layers. Hole transporting 4, 4,' 4"-tris (N-carbazolyl)triphenylamine (TcTa) and electron transporting 2-(diphenylphosphoryl) spirofluorene (SPPO1) are used as an emitting host for orange light-emitting bis(3-benzothiazol-2-yl-9-ethyl-9H-carbazolato) (acetoacetonate) iridium ((btc)2(acac)Ir) and blue light-emitting iridium(III)bis(4,6-difluorophenyl-pyridinato-N,C2') picolinate (FIrpic) dopant, respectively. Combining these two orange and blue light-emitting layers, we successfully demonstrate highly efficient white PHOLEDs while maintaining Commission internationale de l'eclairage coordinates of (x = 0.373, y = 0.443). Accordingly, we achieve a maximum external quantum, current, and power efficiencies of 12.9%, 30.3 cd/A, and 30.0 lm/W without out-coupling enhancement.

High efficiency deep blue and pure white phosphorescent organic light emitting diodes

  • Yook, Kyoung-Soo;Jeon, Soon-Ok;Joo, Chul-Woong;Kim, Myung-Seop;Choi, Hong-Seok;Lee, Seok-Jong;Han, Chang-Wook;Tak, Yoon-Heung;Lee, Nam-Yang;Lee, Jun-Yeob
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.486-488
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    • 2009
  • High efficiency deep blue and pure white phosphorescent organic light emitting diodes were developed using a new deep blue phosphorescent dopant, tris((3,5-difluoro-4-cyanophenyl)pyridine) iridium (FCNIr). A high quantum efficiency of 9.1 % with a color coordinate of (0.15, 0.16) at 1,000 cd/$m^2$ was obtained in the deep blue device and a high quantum efficiency of 15.2 % with a color coordinate (0.30, 0.32) was obtained in the pure white organic light-emitting diodes. The quantum efficiency of the pure white device is the best quantum efficiency value reported in the pure white device up to now.

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Double Hole Transport Layers Deposited by Spin-coating and Thermal-evaporating for Flexible Organic Light Emitting Diodes

  • Chen, Shin Liang;Wang, Shun Hsi;Juang, Fuh Shyang;Tsai, Yu Sheng
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.741-744
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    • 2007
  • The research applied the processes of spin-coating and thermal-evaporating in proper order to deposit the hole transport material N,N'-Bis(naphthalen-1-yl)- N,N'-bis(phenyl)-benzidine (NPB) on the ITO substrate to make flexible organic light emitting diodes (FOLED) with double hole transport layer.

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Numerical Modeling and Simulations of Electrical Characteristics of Multi-layer Organic Light Emitting Diodes

  • Lee, Hyun-Jung;Lee, Yong-Soo;Park, Jae-Hoon;Choi, Jong-Sun
    • Journal of Information Display
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    • v.8 no.3
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    • pp.11-16
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    • 2007
  • Theoretical simulations of spatial distribution of charge carriers and recombination rate, and J-V characteristics of the multi-layer organic light emitting diodes are carried out. Drift-diffusion current transport, field-dependent carrier mobility, exponential and Gaussian trap distribution, and Langevin recombination models are included in this computer model. The simulated results show good agreement with the experimental data confirming the validity of the physical models for organic light emitting diodes.

Effects of Buffer layer in Organic Light-Emitting Diodes (유기 전기발광 소자에서 버퍼층이 미치는 영향)

  • 김상걸;정동회;이호식;정택균;김태완;민항기;박종욱;송미종;이준웅
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.174-177
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    • 2001
  • We have seen the effects of buffer layer in organic light-emitting diodes using poly(N-vinylcarbazole)(PVK). Polymer PVK buffer layer was made using spin casting techniques. Two different types of spin casting have been applied; static coating and dynamic coating. Two device structures were fabricated; one is ITO/TPD/Alq$_3$/Al as a reference, and the other is ITO/PVK/TPD/Alq$_3$/Al to see the effects of buffer layer in organic light-emitting diodes. Current-voltage characteristics and luminous efficiency were measured with a variation of spin-casting methods and rpm speeds. We have obtained an improvement of luminous efficiency by a factor of two and half when the PVK buffer layer is used.

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Effects of Buffer Layer in Organic Light-Emitting Diodes Using Poly(N-vinylcarbazole)

  • Chung, Dong-Hoe;Hong, Jin-Woong;Kim, Tae-Wan
    • Journal of the Korean Applied Science and Technology
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    • v.20 no.2
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    • pp.173-176
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    • 2003
  • We have seen the effects of buffer layer in organic light-emitting diodes using poly(N-vinylcarbazole)(PVK). Polymer PVK buffer layer was made using static spin-casting method. Two device structures were made; one is ITO/TPD/Alq3/Al as a reference and the other is ITO/PVK/TPD/Alq3/Al to see the effects of buffer layer in organic light-emitting diodes. Current-voltage characteristics, luminance-voltage characteristics and luminous efficiency were measured with a variation of spin-casting speeds. We have obtained an improvement of luminous efficiency by a factor of two and half when the PVK buffer layer is used.

Dielectric Properties depending on Bias Voltage in Organic Light-emitting Diodes (유기 발광 소자의 바이어스 전압에 따른 유전 특성)

  • Oh, Yong-Cheul;Lee, Joon-Ung
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.18 no.11
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    • pp.1038-1042
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    • 2005
  • We have investigated dielectric properties depending on bias voltage in organic light-emitting diodes using 8-hydroxyquinoline aluminum $(Alq_3)$ as an electron transport and emissive material. We analyzed the dielectric properties of organic light-emitting diodes using impedance of characteristics. Impedance characteristics was measured complex impedance Z and phase $\theta$ in the frequency range of 40 Hz to $10^8$ Hz. We obtained complex electrical conductivity, dielectric constant, and loss tangent $(tan\delta)$ of the device at room temperature. From these analyses, we are able to interpret a conduction mechanism and dielectric properties contributed by an interfacial and orientational polarization.