• Title/Summary/Keyword: Organic light emitting diodes (OLEDs)

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Tandem Organic Light-Emitting Devices Having Increased Power Efficiency

  • Liao, Liang-Sheng;Klubek, Kevin P.
    • 한국정보디스플레이학회:학술대회논문집
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    • 2008.10a
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    • pp.1015-1018
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    • 2008
  • Tandem organic light-emitting diodes (OLEDs) do not always improve power efficiency over their conventional OLED counterparts. When a tandem OLED utilizes optimized EL units, increased power efficiency can only be achieved if the intermediate connector in the device has excellent charge injection capability.

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Development of Fluorescent or Phosphorescent Materials for Non-Dopant Red Organic Light-Emitting Diodes

  • Chen, Chin-Ti
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07b
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    • pp.1133-1137
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    • 2005
  • In this paper, a renovated approach in the fabrication of red organic light-emitting diodes (OLEDs) is described. The hard-to-control doping process required for dopant-based red OLEDs can be avoided due to the novel red fluorophores that are not concentration quenching in solid state. Doping is in general a must for phosphorescence OLEDs because of the triplet-triplet annihilation, a common problem for phosphorophore dopants. However, we have recently found that extraordinary red iridium complex showing relatively short emission lifetime render the non-doped phosphorescence red OLED possible.

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Correlation between optimized thicknesses of capping layer and thin metal electrode for efficient top-emitting blue organic light-emitting diodes

  • Hyunsu Cho;Chul Woong Joo;Byoung-Hwa Kwon;Chan-mo Kang;Sukyung Choi;Jin Wook Sin
    • ETRI Journal
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    • v.45 no.6
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    • pp.1056-1064
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    • 2023
  • The optical properties of the materials composing organic light-emitting diodes (OLEDs) are considered when designing the optical structure of OLEDs. Optical design is related to the optical properties, such as the efficiency, emission spectra, and color coordinates of OLED devices because of the microcavity effect in top-emitting OLEDs. In this study, the properties of top-emitting blue OLEDs were optimized by adjusting the thicknesses of the thin metal layer and capping layer (CPL). Deep blue emission was achieved in an OLED structure with a second cavity length, even when the transmittance of the thin metal layer was high. The thin metal film thickness ranges applicable to OLEDs with a second microcavity structure are wide. Instead, the thickness of the thin metal layer determines the optimized thickness of the CPL for high efficiency. A thinner metal layer means that higher efficiency can be obtained in OLED devices with a second microcavity structure. In addition, OLEDs with a thinner metal layer showed less color change as a function of the viewing angle.

Performance of Organic light-emitting diode by various surface treatments of indium tin oxide (Indium tin oxide 기판의 표면처리에 따른 유기 발광다이오드의 특성)

  • Kim, Sun-Hyuk;Han, Jeong-Whan
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.39 no.9
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    • pp.1-10
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    • 2002
  • We have done various treatments of indium tin oxide (ITO) surface for organic light-emitting diodes (OLEDs), and investigated the surface states by different surface treatments using atomic force microscopy (AFM) and Auger electron spectroscopy (AES). We have fabricated OLEDs deposited by ultra-high vacuum molecular beam deposition system and studied the characteristics of the OLEDs. We have observed the dramatical improvement of the performance of OLEDs fabricated on ITO substrates treated by $O_2$ plasma treatment reduces the carbon comtamination of ITO surfaces and increases the work function of ITO.

Finite Element Method (FEM) Study on Space Charge Effects in Organic Light Emitting Diodes (OLED)

  • Kim, Kwang-Sik;Hwang, Young-Wook;Won, Tae-Young
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.12 no.4
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    • pp.467-472
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    • 2012
  • In this paper, we present a finite element method (FEM) study on the space charge effects in organic light emitting diodes. The physical model covers all the key physical processes in OLEDs, namely charge injection, transport and recombination, exciton diffusion, transfer and decay as well as light coupling, and thin-film-optics. The exciton model includes generation, diffusion, and energy transfer as well as annihilation. We assumed that the light emission originates from oscillation which thus is embodied as exciton in a stack of multilayer. We discuss the accumulation of charges at internal interfaces and their signature in the transient response as well as the electric field distribution. We also report our investigation on the influence of the insertion of the emission layer (EML) in the bilayer structure.

Large Size and High Resolution Organic Light Emitting Diodes Based on the In-Ga-Zn-O Thin Film Transistors with a Coplanar Structure

  • Hong Jae Shin
    • Korean Journal of Materials Research
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    • v.33 no.12
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    • pp.511-516
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    • 2023
  • Amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) with a coplanar structure were fabricated to investigate the feasibility of their potential application in large size organic light emitting diodes (OLEDs). Drain currents, used as functions of the gate voltages for the TFTs, showed the output currents had slight differences in the saturation region, just as the output currents of the etch stopper TFTs did. The maximum difference in the threshold voltages of the In-Ga-Zn-O (a-IGZO) TFTs was as small as approximately 0.57 V. After the application of a positive bias voltage stress for 50,000 s, the values of the threshold voltage of the coplanar structure TFTs were only slightly shifted, by 0.18 V, indicative of their stability. The coplanar structure TFTs were embedded in OLEDs and exhibited a maximum luminance as large as 500 nits, and their color gamut satisfied 99 % of the digital cinema initiatives, confirming their suitability for large size and high resolution OLEDs. Further, the image density of large-size OLEDs embedded with the coplanar structure TFTs was significantly enhanced compared with OLEDs embedded with conventional TFTs.

Organic Electroluminescence Device using Dye doped Emitting (색소 doped 유기EL 소자에 의한 고효율화)

  • 임장순;강성종;노병규;오환술
    • Proceedings of the IEEK Conference
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    • 2000.11b
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    • pp.261-264
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    • 2000
  • Organic light emitting diodes(OLEDs) have been expected to find an application as a new type of display since C. W. Tang and VanSlyke first reported on high performance OLEDs. This paper has been stuied a green organic EL device using dye doped emitting layer such as C6(Coumarin 6). In the Alq-based e]ectroluminescence diodes, we applied highly fluorescent molecular(Coumarin 6) and obtained enhancement in the electroluminescence efficiency.

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Solution-processible corrugated structure and scattering layer for enhanced light extraction from organic light-emitting diodes

  • Hyun, Woo Jin;Im, Sang Hyuk;Park, O Ok;Chin, Byung Doo
    • Journal of Information Display
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    • v.13 no.4
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    • pp.151-157
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    • 2012
  • A simple method of fabricating out-coupling structures was demonstrated via solution-processing to enhance light extraction from organic light-emitting diodes (OLEDs). Scattering layers were easily obtained by spin-coating an $SiO_2$ sol solution that contained $TiO_2$ particles. By introducing the scattering layer and the solution-processible corrugated structure as internal and external extraction layers, the OLEDs showed increased external quantum efficiency without a change in the electroluminescence spectrum compared to conventional devices. Using these solution-processible out-coupling structures, nearly all-solution-processed OLEDs with enhanced light extraction could be fabricated. The light extraction enhancement is attributed to the suppression by the out-coupling structures of the light-trapping that arose at the interface of the glass substrate and the air.

Efficient Organic Light-emitting Diodes with Aluminum-doped Zinc Oxide Anodes (알루미늄 도핑된 산화아연 양극을 적용한 고효율 유기발광다이오드)

  • Lee, Ho-Nyeon;Lee, Young-Gu;Jung, Jong-Guk;Lee, Seung-Eui;Oh, Tae-Sik
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.20 no.8
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    • pp.711-715
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    • 2007
  • Properties of organic light-emitting diodes (OLEDs) with aluminum-doped zinc oxide (ZnO:Al) anodes showed different behaviors from OLEDs with indium tin oxide (ITO) anodes according to driving conditions. OLEDs with ITO anodes gave higher current density and luminance in lower voltage region and better EL and power efficiency under lower current density conditions, However, OLEDs with ZnO:Al anodes gave higher current density and luminance in higher voltage region over about 8V and better EL and power efficiency under higher current density over $200mA/cm^2$. These seemed to be due to the differences in conduction properties of semiconducting ZnO:Al and metallic ITO. OLEDs with ZnO:Al anodes showed nearly saturated efficiency under high current driving conditions compared with those of OLEDs with ITO anodes. This meant better charge balance in OLEDs with ZnO:Al anodes. These properties of OLEDs with ZnO:Al anodes are useful in making bright display devices with efficiency.

Conduction mechanism in organic light-emitting diode in ITO/PEDOT/PSS/TPD/Alq$_3$/LiAl structure (ITO/PEDOT/PSS/TPD/Alq$_3$/LiAl 구조의 유기 발광 소자에서 전도 메카니즘)

  • 정동회;김상걸;정택균;오현석;이원재
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.07a
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    • pp.198-201
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    • 2002
  • We have studied the temperature dependence of current-voltage and luminance-voltage characteristics of Organic Light Emitting Diodes(OLEDs). The OLEDS are based on the molecular compounds, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as a hole transport, tris(8-hydroxyquinolinoline) aluminum(III) (Alq$_3$) as an electron transport, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a buffer layer. The current-voltage and luminance-voltage characteristics were measured in the temperature range of 10[K] and 300[K]. A conduction mechanism in OLEDs has been interpreted in terms of space-charge-limited current(SCLC) and tunneling mechanism.

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