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Song, Wook,Lee, Jun Yeob,Kim, Taekyung,Lee, Yoonkyoo,Jeong, Hyein Elsevier 2018 ORGANIC ELECTRONICS Vol.57 No.-
<P><B>Abstract</B></P> <P>Comprehensive study to understand the degradation mechanism of high efficiency blue organic light-emitting diodes by charge transport layers was carried out by managing the device parameters and charge transport materials. Although it has been generally accepted that the charge transport layers are important for long lifetime, the degradation mechanism was not clear. From this work, it was revealed that exciton quenching of emitters by the degradation products of charge transport layers is the main degradation pathway of blue phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes. It was described that the degradation of the blue devices by the charge transport layers would be largely avoided by separating the exciton generating emitters from the charge transport layers by shifting the exciton formation zone to the center of the emitting layer. Eventually, the lifetime of the blue devices with the emission zone fall apart from the charge transport layers was not affected by the charge transport layers because exciton quenching by the degradation products of the charge transport layers was suppressed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Exciton quenching by degradation of hole and electron transport materials. </LI> <LI> Relationship between recombination zone and degradation by charge transport materials. </LI> <LI> Management of recombination zone to suppress degradation by charge transport materials. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Song, Wook,Lee, Jun Yeob Elsevier 2017 Organic electronics Vol.49 No.-
<P><B>Abstract</B></P> <P>A lifetime extending device structure by suppressing positive polaron induced triplet exciton-polaron annihilation was developed for improved lifetime in blue phosphorescent organic light-emitting diodes. A blue triplet emitter doped hole transport layer was introduced to control the triplet exciton-polaron annihilation of blue phosphorescent emitters in the emitting layer, which extended the lifetime of the blue phosphorescent devices. Current and ultraviolet light/current aging tests of hole and electron only devices proved that the lifetime extending mechanism of the blue triplet emitter doped hole transport layer is suppression of triplet exciton-positive polaron annihilation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lifetime extension of blue phosphorescent device by suppression of triplet-positive polaron annihilation. </LI> <LI> Device structure with a blue triplet emitter doped in the hole transport layer. </LI> <LI> Improved stability of the blue device under current aging and ultraviolet-visible aging. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Song, Wook,Lee, Woochul,Kim, Kong Kyeom,Lee, Jun Yeob Elsevier 2016 ORGANIC ELECTRONICS Vol.37 No.-
<P><B>Abstract</B></P> <P>Origin of doping concentration dependence of lifetime of thermally activated delayed fluorescent (TADF) devices was examined using a TADF emitter doped in a hole transport type and a bipolar host material. Lifetime of the hole transport type host based TADF device was increased according to doping concentration of TADF emitter, while that of the bipolar host based TADF device was decreased according to doping concentration of TADF emitter. The doping concentration dependence of the lifetime could be correlated with recombination zone of the emitting layer. Broad recombination zone at high doping concentration in the hole transport type host and at low doping concentration in the bipolar host was proposed as the main contributor of the doping concentration dependence of the lifetime.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lifetime increase in thermally activated delayed fluorescent devices with a unipolar host according to doping concentration. </LI> <LI> Constant lifetime in thermally activated delayed fluorescent device with a bipolar host according to doping concentration. </LI> <LI> Correlation of recombination zone broadening with lifetime of thermally activated delayed fluorescent devices. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Song, Wook,Lee, In Ho,Hwang, Seok-Ho,Lee, Jun Yeob Elsevier 2015 ORGANIC ELECTRONICS Vol.23 No.-
<P><B>Abstract</B></P> <P>Fluorescent white organic light-emitting diodes having a blue thermally activated delayed fluorescent emitter and a yellow fluorescent emitter was developed by co-doping the blue and yellow emitters in a single emitting layer. The blue delayed fluorescent device showed high quantum efficiency of 22.6% at a very high doping concentration of 50% and the white devices exhibited a high quantum efficiency of 15.5% even though a fluorescent yellow emitter was doped in the blue thermally activated delayed fluorescent emitting layer. Minimized charge trapping and Dexter energy transfer by low yellow doping concentration of 0.05% as well as efficient Förster energy transfer could develop the high efficiency fluorescent white organic light-emitting diodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> White devices with a blue delayed fluorescent emitter and yellow fluorescent emitter. </LI> <LI> Singlet energy transfer from a blue emitter to yellow emitter. </LI> <LI> High quantum efficiency above 15% in the fluorescent white organic light-emitting diodes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Song, Wook,Kim, Taekyung,Lee, Jun Yeob,Lee, Yoonkyoo,Jeong, Hyein THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.68 No.-
<P><B>Abstract</B></P> <P>Lifetime study of blue phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes was carried out to understand the dominant degradation process during electrical operation of the devices. Doping concentration dependence of the phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes was studied, which demonstrated long lifetime at low doping concentration in the phosphorescent devices and at high doping concentration in the thermally activated delayed fluorescent devices. Detailed mechanism study of the two devices described that triplet–triplet annihilation is the main degradation process of phosphorescent organic light-emitting diodes, whereas triplet–polaron annihilation is the key degradation factor of the thermally activated delayed fluorescent devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lifetime dependence on doping concentration in the phosphorescent and TADF organic light-emitting diodes. </LI> <LI> Triplet–triplet annihilation as dominant degradation mechanism of phosphorescent devices. </LI> <LI> Triplet–polaron annihilation as dominant degradation mechanism of TADF devices </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Song, Wook,Lee, Jun Yeob ELSEVIER 2017 ORGANIC ELECTRONICS Vol.51 No.-
<P><B>Abstract</B></P> <P>A novel triplet exciton guiding mixed host managing triplet exciton-polaron annihilation by separating the triplet excitons and polarons in the different host was developed. A high triplet energy/narrow gap host and a low triplet energy/wide gap host were mixed to isolate the triplet excitons and polarons, which could improve the extrapolated lifetime of the phosphorescent organic light emitting diodes by more than twice. The triplet exciton-polaron annihilation reducing mechanism was confirmed by triplet energy transfer, single carrier device test and triplet exciton-polaron annihilation rate constant study of the singlet host and mixed host.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Triplet exciton guiding mixed host for improved lifetime in phosphorescent organic light-emitting diodes. </LI> <LI> Triplet exciton and polaron separation by managing energy levels and triplet energy of hosts. </LI> <LI> Lifetime improvement by suppressed triplet exciton-polaron annihilation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
영한 기계 번역 품사 집합과 펜트리뱅크 코퍼스 품사 집합간의 품사 대응
이성욱(Songwook Lee),이공주(Kong Joo Lee),서정연(Jungyun Seo) 한국정보과학회 1999 한국정보과학회 학술발표논문집 Vol.26 No.2Ⅱ
펜트리뱅크 코퍼스를 기계 번역에서 품사 태깅의 통계 정보 추출에 이용하기 위해서는 펜트리뱅크 코퍼스의 품사 집합과 기계 번역의 품사 집합의 품사 대응이 필요하다. 본 연구는 기계 번역의 품사 태그 집합과 펜트리뱅크의 48개의 품사 태그를 서로 적절히 대응하여 펜트리뱅크 코퍼스의 통계 정보를 이용하는 품사 태깅 시스템을 구축하는데 발생하는 문제점과 그 해결 방안을 제안한다.