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

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Roll-to-roll microcontact-printed microlens array for light extraction film of organic light-emitting diodes (유기발광다이오드의 외부 광추출층을 위한 롤투롤 마이크로컨택 방식으로 인쇄된 마이크로렌즈 어레이)

  • Hwa, Subin;Sung, Baeksang;Lee, Jae-Hyun;Lee, Jonghee;Kim, Min-Hoi
    • Journal of IKEEE
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    • v.26 no.2
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    • pp.205-210
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    • 2022
  • We demonstrated roll-to-roll microcontact printed (mCP) microlens array (MLA) to enhance the light extraction of organic light emitting diodes (OLEDs). The commercially provided microlens array is used as a template for polydimethylsiloxane (PDMS) roll stamp. The fluorinated film is formed on the PDMS roll stamp from fluorinated ink with low boiling point and printed onto the bottom side of the organic light emitting diode without high pressure and high thermal treatment. With optimized concentration of ink, the pattern which is almost identical to that of the template MLA was successfully printed. Due to the structure and low optical absorbance of microcontact printed MLA, the external quantum efficiency of OLED was improved by about 18%.

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.

Deep red electrophosphorescent organic light-emitting diodes based on new iridium complexes

  • Gong, Doo-Won;Kim, Jun-Ho;Lee, Kum-Hee;Yoon, Seung-Soo;Kim, Young-Kwan
    • 한국정보디스플레이학회:학술대회논문집
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    • 2006.08a
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    • pp.1075-1078
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    • 2006
  • New iridium complex was synthesized and demonstrated a deep red light emission in organic light-emitting diodes (OLEDs). The maximum luminance of 8320 cd/m2 at 15 V and the luminance efficiency of 2.5 cd/A at 20 mA/cm2 were achieved. The peak wavelength of the electroluminescence was at 626 nm with the CIE coordinates of (0.69, 0.30), and the device also showed a stable color chromaticity with various voltages.

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Correlation between host materials and device performances of phosphorescent white organic light-emitting diodes with blue/orange/blue stacked emitting structure

  • Joo, Chul-Woong;Kim, Sung-Hyun;Yook, Kyoung-Soo;Jeon, Soon-Ok;Lee, Jun-Yeob
    • 한국정보디스플레이학회:학술대회논문집
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    • 2008.10a
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    • pp.439-442
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    • 2008
  • A mixed host structure of TCTA and TPBI was used in orange emitting layer and host composition was critical to device performances of PHWOLEDs. PHWOLEDs with TPBI host in orange emitting layer showed high quantum efficiency of 10.3 % at $1000\;cd/m^2$ with little change of CIE coordinates of (0.32, 0.34) from $100\;cd/m^2$ to $10,000\;cd/m^2$.

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Color stable and efficient white organic light emitting diodes with phosphorescent emitters

  • Lee, Hyun-Koo;Lee, Chang-Hee
    • 한국정보디스플레이학회:학술대회논문집
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    • 2009.10a
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    • pp.415-417
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    • 2009
  • Color stable and efficient two wavelength white organic light emitting diodes (OLEDs) were fabricated using a iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,$C^2$'] picolinate (FIrpic) as a blue phosphorescent emitter and a bis(1-phenylisoquinolinato-$C^2$,N)iridium (acetylacetonate) ((piq)$_2$Ir(acac)) as a red phosphorescent emitter. The emitting layers consist of two blue emitting layers and one red emitting layer which is between the two blue layers. The device reaches the peak efficiencies of 7.84 % and 10.3 cd/A at 0.6 mA/$cm^2$. Furthermore, there was little change of EL spectra according to current density change in the device.

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Organic-layer and reflectivity of transparent electrode dependent, microcavity effect of top-emission organic light-eitting diodes (TE-OLED의 유기물층과 반투명 음전극의 반사도에 따른 마이크로 캐비티 특성)

  • An, Hui-Chul;Na, Su-Hwan;Joo, Hyun-Woo;Mok, Rang-Kyun;Jung, Kyung-Seo;Chio, Seong-Jea;Kim, Tae-Wan
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.06a
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    • pp.299-300
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    • 2009
  • We have studied an organic layer and semitransparent Al cathode thickness dependent optical properties for top-emission organic light-emitting diodes. Device structure is ITO(170nm)/TPD(xnm)/$Alq_3$(ynm)/LiF(0.5nm)/Al(100nm) and Al(100nm)/TPD(xnm)/$Alq_3$(ynm)/LiF(0.5nm)/Al(25nm). While a thickness of total, organic layer was varied from 85nm to 165nm, a ratio of those two layers was kept to be about 2:3. Then it was compared with that of bottom devices. And a thickness of semitransparent Al cathode was varied from 20nm to 30nm for the device with an organic layer thickness of 140nm. We were able to control the emission spectra from the top-emission organic light-emitting diodes.

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Current-Voltage-Luminance Characteristics of Organic Light-Emitting Diodes with a Variation of PVK Concentration Used as a Buffer Layer (버퍼층으로 사용한 PVK의 농도 변화에 따른 유기 발광 소자의 전압-전류-휘도 특성)

  • Kim, Sang-Keol;Hong, Jin-Woong;Kim, Tae-Wan
    • Journal of the Korean Applied Science and Technology
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    • v.19 no.1
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    • pp.68-72
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    • 2002
  • We have seen the effects of buffer layer in organic light-emitting diodes(OLEDs) using poly(N-vinylcarbazole)(PVK) depending on a concentration of PVK. Polymer PVK buffer layer was made using spin casting technique. 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-luminance characteristics and an external quantum efficiency were measured with a variation of spin-casting rpm speeds and PVK concentration. We have obtained an improvement of external quantum efficiency by a factor of four when the PVK concentration is 0.1wt% is used. The improvement of efficiency is expected due to a function of hole-blocking of PVK in OLEDs.

Effects of PEDOT:PSS Buffer Layer and Cathode in a Device Structure of $ITO/PEDOT:PSS/TPD/Alq_3/Cathode$ ($ITO/PEDOT:PSS/TPD/Alq_3/Cathode$ 소자 구조에서 PEDOT:PSS 층과 음전극의 영향)

  • Kim, S.K.;Chung, D.H.;Lee, H.D.;Oh, H.S.;Cho, H.N.;Lee, W.J.;Kim, T.W.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2003.07b
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    • pp.1003-1006
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    • 2003
  • We have investigated the effect of hole-injection buffer layer and cathodes in organic light-emitting diodes u sing poly (3,4-ethylenedioxythiophene) : poly (stylenesulfonate) (PEDOT: PSS) in a device structure of $ITO/PEDOT:PSS/TPD/Alq_3/Cathode$. Polymer PEDOT:PSS buffer layer was made using spin casting method. Current-voltage, luminance-voltage characteristics and efficiency of device were measured at room temperature with a variation of cathode materials. The device with LiF/Al cathode shows an improvement of external quantum efficiency approximately by a factor of ten compared to that of Al cathode only device. Our observation shows that the energy barrier-height in cathode side is important in improving the efficiency of the organic light-emitting diodes.

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Images of deposited layers of organic light-emitting diodes observed by scanning-electron microscope (주사 전자 현미경으로 관찰한 유기 발광 소자의 누적층 모양)

  • Lee, Eun-Hye;Yoon, Hee-Myoung;Han, Wone-Keun;Kim, Tae-Wan;Lee, Won-Jae;Jang, Kyung-Uk;Ahn, Joon-Ho
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.11a
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    • pp.298-299
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    • 2008
  • Images of deposited layers of organic light-emitting diodes were observed by scanning-electron microscope (SEM). We were able to see a clear cross-sectional view of deposited layers. The SEM is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. A thickness of deposited layer measured by thickness monitor is close to a real value measured by a-step surface profiler within 5%. We were able to see a formation of domains of size about 50-100nm from a surface morphology of Al, and pin holes of size about 50nm.

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