• ETRI Journal
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• 제33권1호
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• pp.32-38
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• 2011

We investigated the light-emitting performances of blue phosphorescent organic light-emitting diodes, known as PHOLEDs, by incorporating an N,N'-dicarbazolyl-3,5-benzen interlayer between the hole transporting layer and emitting layer (EML). We found that the effects of the introduced interlayer for triplet exciton confinement and hole/electron balance in the EML were exceptionally dependent on the host materials: 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, 9-(4-tert-butylphenyl)-3,6-ditrityl-9H-carbazole, and 4,4'-bis-triphenylsilanyl-biphenyl. When an appropriate interlayer and host material were combined, the peak external quantum efficiency was greatly enhanced by over 21 times from 0.79% to 17.1%. Studies on the recombination zone using a series of host materials were also conducted.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.843-845
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• 2009

A polymeric host for triplet emitters composed of N-alkylcarbazole and tetramethylbenzene units was successfully synthesized. Efficient energy transfer was observed between this polymeric host and green phosphorescent dyes. The device fabricated using 5 wt% green 1 in the polymeric host as the emitting layer showed the best performance. Thin films of this host-guest system, exhibiting clear stripe patterns could be prepared through the LITI process. The patterned films were then used to fabricate electrophosphorescent devices, which show performance characteristics similar to those of spin-coated devices. The new host material is a good candidate to be used in polymer-based full-color electrophosphorescent light-emitting displays.

• Journal of Electrical Engineering and Technology
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• 제4권4호
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• pp.552-558
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• 2009

We proposed a semi-blind digital image watermarking technique for copyright protection. The proposed algorithm embedded a binary sequence watermark into significant wavelet coefficients by using a quantization method. The main idea of the quantization method was to quantize a middle coefficient of the triplet of a significant wavelet coefficient according to the watermark's value. Unlike an existing algorithm, which used a random location table to find a coefficient in which the watermark bit will be embedded: the proposed algorithm used quad-tree decomposition to find a significant wavelet coefficient for embedding. For watermark detection, an original host image was not required. Thanks to the usage of significant wavelet coefficients, the proposed algorithm improved the correlation value, up to 0.43, in comparison with the existing algorithm.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.184-187
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• 2009

In this paper, we study effect of charge balance on performance of blue phosphorescent organic light emitting diodes (OLEDs). Charge balance determines the location of recombination zone in the OLEDs. By tuning the charge balance in iridium (III) bis[(4,6-difluorophenyl)-pyridinate-N,C2']picolinate (FIrpic) based blue phosphorescent organic light-emitting devices (PHOLEDs) with a high mobility and high triplet energy electron transporting material, we were able to achieve a high current efficiency of 60 cd/A which is a 3X improvement over previous devices with 3,5'-N,N'-dicarbazole-benzene (mCP) host.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
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• pp.1474-1477
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• 2007

We demonstrate relaxation of roll-off characteristics by controlling the dopant concentrations and the thickness of an emitter layer in electrophosphorescence diodes composed of 2,6-dicarbazolo-1,5-pyridine (PYD2)-host doped with 25 wt%-Iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-$N,C^2$] picolinate (FIrpic).

• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3290-3294
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• 2011

The properties of monomeric and dimeric salen-aluminum complexes, [salen(3,5-$^tBu)_2$Al(OR)], R = $OC_6H_4-p-C_6H_6$ (H1) and R = [salen(3,5-$^tBu$)AlOPh]C$(CH_3)_2$ (H2) (salen = N,N'-bis-(salicylidene)-ethylenediamine) as host layer materials in red phosphorescent organic light-emitting diodes (PhOLEDs) were investigated. H1 and H2 exhibit high thermal stability with decomposition temperature of 330 and $370^{\circ}C$. DSC analyses showed that the complexes form amorphous glasses upon cooling of melt samples with glass transition temperatures of 112 and $172^{\circ}C$. The HOMO (ca. -5.2~-5.3 eV) and LUMO (ca. -2.3~-2.4 eV) levels with a triplet energy of ca. 1.92 eV suggest that H1 and H2 are suitable for a host material for red emitters. The PhOLED devices based on H1 and H2 doped with a red emitter, $Ir(btp)_2$(acac) (btp = bis(2-(2'-benzothienyl)-pyridinato-N,$C^3$; acac = acetylacetonate) were fabricated by vacuum-deposition and solution process, respectively. The device based on vacuum-deposited H1 host displays high device performances in terms of brightness, luminous and quantum efficiencies comparable to those of the device based on a CBP (4,4'-bis(Ncarbazolyl) biphenyl) host while the solution-processed device with H2 host shows poor performance.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.229.2-229.2
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• 2016

본 연구에서는 Host와 Dopant $Ir(ppy)_3$의 도핑 위치 변화에 따른 bottom emission 인광 OLED를 제작하여 발광 효율 및 특성을 분석하였다. 소자의 EML은 $Ir(ppy)_3/CBP$와 $CBP/Ir(ppy)_3$ 순으로 증착하여 제작하였다. $Ir(ppy)_3/CBP$은 낮은 구동 전압에서 큰 전류밀도와 큰 luminance을 측정하였고, 반대로 $CBP/Ir(ppy)_3$은 높은 구동 전압에서 $CBP/Ir(ppy)_3$은 큰 전류밀도와 큰 luminance가 측정되었다. 이는 $Ir(ppy)_3/CBP$에서 HTL과 EML 사이에 hole direct injection이 발생으로 Hole이 증가하지만 charge balance 불일치로 roll-off가 발생하고, $CBP/Ir(ppy)_3$에서 electron direct injection에 의한 electron 증가로 charge balance가 향상된다. EL spectrum 측정에서 $Ir(ppy)_3$은 파장 512nm 발광이 일어나고, CBP와 NPB은 각각 파장 380nm, 433nm로 분석된다. 각 물질의 triplet의 전달은 energy level이 큰 곳에서 작은 곳으로 전달되는데 이러한 이유로 전압에 따른 recombination zone 변화로 각 물질에서 나오는 파장의 intensity가 달라지는 것을 확인하였다. $Ir(ppy)_3/CBP$은 낮은 전류 밀도에서는 CBP의 영향으로 380nm 파장대가 크고, 높은 전류 밀도에서는 $Ir(ppy)_3$의 영향으로 512nm 파장대가 크게 나오는 것을 확인했고, $CBP/Ir(ppy)_3$에서는 낮은 전류 밀도에서 512nm 파장대가 커지고, 큰 전류 밀도에서는 CBP에서 NPB로의 triplet 에너지 전달의 증가로 433nm 파장대가 커지는 것을 확인하였다.

• 한국응용과학기술학회지
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• 제30권2호
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• pp.244-250
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• 2013

본 연구에서는 전하 조절층을 이용하여 녹색 인광 유기발광다이오드의 효율의 향상을 나타냈다. 양극성의 4,4,N,N'-dicarbazolebiphenyl (CBP)를 호스트와 전하 조절층으로 사용하여 발광층 내에서 전하의 이동을 원활하게 할 수 있다. 게다가 전하 조절층의 삽입으로 엑시톤을 효과적으로 발광층 내에 제한하여, 삼중항-삼중항 소멸 현상을 억제할 수 있음을 확인하였다. 발광층의 전체 두께는 유지하고, 전하 조절층의 변화를 준 다섯 개의 소자를 제작하여 최적화된 전하 조절층의 두께를 이용한 Device D는 외부 양자 효율 16.22%와 휘도 효율 55.76 cd/A의 성능을 보였다.

• 한국전기전자재료학회논문지
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• 제27권6호
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• pp.377-382
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• 2014

We have investigated the effects of spacer layer inserted between blue and red doped emission layers on the emission and efficiency characteristics of phosphorescent OLEDs. N,N'-di-carbazolyl-3,5-benzene (mCP) was used as a host layer. Iridium(III)bis[(4,6-di-fluorophenyl)- pyridinato-N,$C^2$']picolinate (FIrpic) and tris(1-phenyl-isoquinolinato-$C^2$,N)iridium(III) [Ir(piq)3] were used as blue and red dopants, respectively. The emission layer structure was mCP (1-x) nm/mCP:$Ir(piq)_3$ (5 nm, 10%)/mCP (x nm)/mCP:FIrpic (5 nm, 10%). The thickness of mCP spacer layer was varied from 0 to 15 nm. The emission from $Ir(piq)_3$ and the efficiency of the device were dominated by energy transfer from mCP host and FIrpic molecules, and by diffusion of mCP host triplet excitons.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.196-199
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• 2009

We report the multiple quantum well (MQW) structure for highly efficient red phosphorescent OLEDs. Various triplet quantum well devices from a single well to five quantum wells are realized using a wide band-gap hole and electron transporting layers, narrow band-gap host and dopant material, and charge control layers (CCL). The maximum external quantum efficiency of 14.8 % with a two quantum well device structure is obtained, which is the highest value among the red phosphorescent OLEDs using same dopant.