• Title, Summary, Keyword: Hole injection layer

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Efficiency Improvement of Organic Light-emitting Diodes depending on Thickness of Hole Injection Materials

  • Kim, Weon-Jong;Yang, Jae-Hoon;Kim, Tag-Yong;Jeong, Joon;Lee, Young-Hwan;Hong, Jin-Woong;Park, Ha-Yong;Kim, Tae-Wan
    • Transactions on Electrical and Electronic Materials
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    • v.6 no.5
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    • pp.233-237
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    • 2005
  • In the device structure of ITO/hole injection layer/N, N'-biphenyl-N, N'-bis-(1-naphenyl)-[1,1'-biphenyl]4,4'-diamine(NPB)/tris(8-hydroxyquinoline) aluminum$(Alq_3)/Al$, we investigated an effect of hole-injection materials (PTFE, PVK) on the electrical characteristics and efficiency of organic light-emitting diodes. A thermal evaporation was performed to make a thickness of NPB layer with a evaporation rate of $0.5\~1.0\;\AA/s$ in a base pressure of $5\times10^{-6}$ Torr. We measured current-voltage characteristics and efficiency with a thickness variation of hole-injection layer. The PTFE and PVK hole-injection layer improve a performance of the device in several aspects, such as good mechanical junction, reducing the operating voltage and energy band adjustment. Compared with the devices without a hole-injection layer, we have obtained that an optimal thickness of NPB was 20 nm in the device structure of $ITO/NPB/Alq_3/Al$. And using the PTFE or PVK hole-injection layer, the external quantum efficiencies of the devices were improved by $24.5\%\;and\;51.3\%$, respectively.

Efficient Organic Light-Emitting Diodes with a use of Hole-injection Buffer Layer

  • Kim, Sang-Keol;Chung, Dong-Hoe;Chung, Taek-Gyun;Kim, Tae-Wan
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.766-769
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    • 2002
  • We have seen the effects of hole-injection buffer layer in organic light-emitting diodes using copper phthalocyanine(CuPc), poly(vinylcarbazole)(PVK), and Poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS) in a device structure of ITO/buffer/TPD/$Alq_3$/Al. Polymer PVK and PEDOT:PSS buffer layer was made using spin casting method and the CuPc layer was made using thermal evaporation. Current-voltage characteristics, luminance-voltage characteristics and efficiency of device were measured at room temperature with a thickness variation of buffer layer. We have obtained an improvement of the external quantum efficiency by a factor of two, four, and two and half when the CuPc, PVK, and PEDOT:PSS buffer layer are used, respectively. The enhancement of the efficiency is attributed to the improved balance of holes and elelctrons due to the use of hole-injection buffer layer. The CuPc and PEDOT:PSS layer functions as a hole-injection supporter and the PVK layer as a hole-blocking one.

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Interfacial Electronic Structures for Electron and Hole Injection in Organic Devices: Nanometer Layers of CsN3 and 1,4,5,8,-naphthalene-tetracarboxylic-dianhydride (NTCDA)

  • Yi, Yeon-Jin;Jeon, Pyeongeu;Lee, Jai-Hyun;Jeong, Kwang-Ho;Kim, Jeong-Won
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.90-90
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    • 2012
  • The electron/hole injections in organic electronic devices have long been an issue due to the large energy level mismatches between electrode and organic layer. To utilize the organic materials in electronic devices, functional thin layers have been used, which reduce the electron/hole injection barrier from electrode to organic material. Typically, inorganic compounds and organic molecules are used as an electron and hole injection layer, respectively. Recently, CsN3 and 1,4,5,8,- naphthalene-tetracarboxylic-dianhydride (NTCDA) are reported as a potential electron and hole injection layers. CsN3 shows unique properties that it breaks into Cs and N and thus Cs can dope organic layer into n-type. On the other side, hole injection anode, NTCDA forms gap states with anode material. In this presentation, we show the electronic structure changes upon the insertion of CsN3 and NTCDA at proper interfaces to reduce the charge injection barriers. These barrier reductions are correlated with device characteristics.

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The Real Role of 4,4'-Bis[N-[4-{N,N-bis(3-methylphenyl)amino}phenyl]-N-phenylamino] biphenyl (DNTPD) Hole Injection Layer in OLED: Hole Retardation and Carrier Balancing

  • Oh, Hyoung-Yun;Yoo, Insun;Lee, Young Mi;Kim, Jeong Won;Yi, Yeonjin;Lee, Seonghoon
    • Bulletin of the Korean Chemical Society
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    • v.35 no.3
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    • pp.929-932
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    • 2014
  • We explored interfacial electronic structures in indium tin oxide (ITO)/DNTPD/N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB) layer stack in an OLED to clarify the real role of an aromatic amine-based hole injection layer, DNTPD. A hole injection barrier at the ITO/DNTPD interface is lowered by 0.20 eV but a new hole barrier of 0.36 eV at the DNTPD/NPB is created. The new barrier at the DNTPD/NPB interface and its higher bulk resistance serve as hole retardation, and thus those cause the operation voltage for the ITO/DNTPD/NPB to increase. However, it improves current efficiency through balancing holes and electrons in the emitting layer.

Electroluminescent Properties of Organic Light-emitting Diodes with Hole-injection Layer of CuPc

  • Lee, Jung-Bok;Lee, Won-Jae;Kim, Tae-Wan
    • Transactions on Electrical and Electronic Materials
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    • v.15 no.1
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    • pp.41-44
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    • 2014
  • Emission properties of the organic light-emitting diodes were investigated with the use of a hole-injection layer of copper(II)-phthalocyanine (CuPc). The manufactured device structure is indium-tin-oxide (ITO) (180 nm)/CuPc (0~50 nm)/N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) (40 nm)/tris-(8-hydroxyquinoline) aluminum (III) ($Alq_3$) (60 nm)/Al(100 nm). We investigated the luminescence properties of $Alq_3$ which is affected by the CuPc hole-injection layer. Also, we studied the influence of light-emission properties in the structure of an ITO/CuPc/TPD/$Alq_3$/Al device depending on the several thicknesses of CuPc (0~50 nm) layer. As a result, it was found that the hole injection occurs smoothly in the device with 20 nm thick CuPc layer, and the properties become significantly worse in the device with a CuPc layer thickness higher than 40 nm. We studied the topography and external quantum efficiency depending on the layer thickness of CuPc. Also, we analyzed the electroluminescent characteristics in the low and high-voltage range.

Efficient Organic Light-emitting Diodes using Hole-injection Buffer Layer

  • Chung, Dong-Hoe;Kim, Sang-Keol;Lee, Joon-Yng;Hong, Jin-Woong;Cho, Hyun-Nam;Kim, Young-Sik;Kim, Tae-Wan
    • Journal of Information Display
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    • v.4 no.1
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    • pp.29-33
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    • 2003
  • We have investigated the effects of hole-injection buffer layer in organic light-emitting diodes using copper phthalocyanine (CuPc), poly(vinylcarbazole)(PVK), and Poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) in a device structure of $ITO/bufferr/TPD/Alq_3/Al$. Polymer PVK and PEDOT:PSS buffer layer were produced using the spin casting method where as the CuPc layer was produced using thermal evaporation. Current-voltage characteristics, luminance-voltage characteristics and efficiency of device were measured at room temperature at various a thickness of the buffer layer. We observed an improvement in the external quantum efficiency by a factor of two, four, and two and half when the CuPc, PVK, and PEDOT:PSS buffer layer were used, respectively. The enhancement of the efficiency is assumed to be attributed to the improved balance of holes and elelctrons resulting from the use of hole-injection buffer layer. The CuPc and PEDOT:PSS layer function as a hole-injection supporter and the PVK layer as a hole-blocking one.

Development of Blue Organic Light-Emitting Diodes(OLEDs) Due to Change in Mixed Ratio of HTL:EML(DPVBi:NPB) Layers (HTL:EML(DPVBi:NPB) 층의 조성비 변화에 따른 청색 유기 발광 소자 개발)

  • Lee, Tae-Sung;Lee, Byoung-Wook;Hong, Chin-Soo;Kim, Chang-Kyo
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.31-32
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    • 2008
  • The structure of OLEDs with conventional heterostructure consists of anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode. NPB used as a hole transport layer and DPVBi used as a blue light emitting layer were graded-mixed at selected ratio. Interface at heterojunction between the hole transport layer and the elecrtron transport layer restricts device's stability. Mixing of the hole transport layerand the emitting layer removes abrupt interface between the hole transport. layer and the electron transport layer. The stability of OLED with graded mixed-layer developed in this study was improved.

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Electroluminescent Properties of Organic Light-emitting Diodes Depending on the Thickness of CuPc Hole-injection Layer (정공 주입층 CuPc 두께 변화에 따른 유기 발광 소자의 발광 특성)

  • Lee, Jung-Bok;Kim, Kyung-Hwan;Kim, Tae-Wan;Lee, Won-Jae
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.26 no.12
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    • pp.899-903
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    • 2013
  • We investigated the luminescence properties of $Alq_3$ in the device structure of ITO/CuPc/TPD/$Alq_3$/Al. The CuPc as a hole-injection material and TPD as hole-transport material. Emission properties were measured by varying a layer thickness of CuPc (0 nm to 50 nm), which is the hole-injection layer. As a result, it was found that the hole injection occurs smoothly when the layer thickness was 20 nm among the thicknesses from 0 nm to 50 nm.

High performance top-emitting OLEDs with copper iodide-doped hole injection layer

  • Lee, Jae-Hyun;Leem, Dong-Seok;Kim, Jang-Joo
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.492-495
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    • 2008
  • Efficient top-emitting organic light-emitting diodes were fabricated using copper iodide (CuI) doped NPB as a p-doped hole injection layer to improve hole injection from a silver bottom electrode. The enhanced hole injection is originated from the formation of the charge transfer complex between CuI and NPB. The devices result in high efficiency of 69 cd/A with almost Lambertian emission pattern.

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Dielecric properties depending on applied voltage of OLEDs with Hole Injection Layer (유기발광소자에서 정공주입층의 인가전압에 따른 유전특성)

  • Cha, Ki-Ho;Lee, Young-Hwan;Kim, Won-Jong;Lee, Jong-Yong;Kim, Gwi-Yeol;Hong, Jin-Woong
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.309-310
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    • 2006
  • We studied dielectric properties of OLEDs(Organic Light-emitting Diodes) depending on applied voltage (AC) of PTFE(Polytetrafluoroethylene), material of hole injection layer in structure of ITO/hole injection layer (PTFE)/emitting layer, Alq3(Tris(8-hydroxyquinolibe) Alumin)/Al. PTFE is deposited 2 [nm] as rate of 0.2~03 [${\AA}/s$] and $Alq_3$ is deposited 100 [nm] as rate of 1.3~1.5 [${\AA}/s$] m high vacuum ($5{\times}10^{-6}$[torr]). In result of these studies, we can know dielectric properties of OLEDs. Impedance is decreased depending on applied voltage variation, dielectric loss showed peak in specified voltage and showed cole-cole plot of a specimen.

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