• 한국전기전자재료학회논문지
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• 제26권6호
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• pp.451-456
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• 2013

To study emission properties of white phosphorescent organic light emitting devices (PHOLEDs), we fabricated white PHOLEDs of ITO(150 nm) / NPB(30 nm) / TcTa(10 nm) / mCP(7.5 nm) / light-emitting layer(25 nm) / UGH3(5 nm) / Bphen(50 nm) / LiF(0.5 nm) / Al(200 nm) structure. The total thickness of light-emitting layer with co-doping and blue-doping/co-doping using a host-dopant system was 25 nm and the dopant of blue and red was FIrpic and $Bt_2Ir$(acac) in UGH3 as host, respectively. The OLED characteristics were changed with position and thickness of blue doping layer and co-doping layer as light-emitting layer and the best performance seemed in structure of blue-doping(5 nm)/co-doping(20 nm) layer. The white PHOLEDs showed the maximum current density of $34.5mA/cm^2$, maximum brightness of $5,731cd/m^2$, maximum current efficiency of 34.8 cd/A, maximum power efficiency of 21.6 lm/W, maximum quantum efficiency of 15.6%, and a Commission International de L'Eclairage (CIE) coordinate of (0.367, 0.436) at $1,000cd/m^2$.

• Bulletin of the Korean Chemical Society
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• 제27권10호
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• pp.1549-1552
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• 2006

We report a new series of blue dopants composed of both electron donating and electron accepting moieties in one molecule, based on nalidixic acid. The EL device derived from the dopant exhibits pure blue light emission (0.15, 0.14) The current efficiency is estimated to be 3.88 cd/A at 100 $cd/m^2$, which shows remarkable enhancement, compared to that of the host itself (2.5 cd/A at 100 $cd/m^2$) under the same conditions. These results demonstrate that the incorporation of a proper guest into the host in a guest-host doped system improves not only the purity of the fluorescent blue emission but also elevates its quantum efficiency, thus improving the OLED performance.

• Journal of Information Display
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• 제9권2호
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• pp.18-21
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• 2008

We report on white organic light-emitting diodes (WOLEDs) based on single white dopants, $Ir(pq)_2$($F_2$-ppy) and $Ir(F_2-ppy)_2$(pq), where $F_2$-ppy and pq are 2-(2,4-difluorophenyl) pyridine and 2-phenylquinoline, respectively. The similar phosphorescent lifetime of two ligands lead to luminescence emission in two ligands simultaneously. However, the emission color of the devices was reddish, because the energy was not transferred efficiently from the 4,4,N,N'-dicarbazolebiphenyl (CBP) to the $F_2$-ppy ligand, due to the small band gap of the CBP. Accordingly, we used 1,4-phenylenesis(triphenylsilane) (UGH2) with a large band gap, instead of CBP as the host material. As a result, it was possible to adjust the emission color by the host material. The luminous efficiency of the device with $Ir(F_2-ppy)_2$(pq) doped in UGH2 was about 11 cd/A at 0.06 cd/$m^2$.

• Bulletin of the Korean Chemical Society
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• 제35권6호
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• pp.1670-1674
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• 2014

Two red emitters, 2-(7-(4-(diphenylamino)styryl)-2-methyl-4H-chromen-4-ylidene)malonitrile (Red 1) and 2-(7-(julolidylvinyl)-2-methyl-4H-chromen-4-ylidene)malonitrile (Red 2) have been designed and synthesized for application as red-light emitters in organic light emitting diodes (OLEDs). In these red emitters, the julolidine and triphenyl moieties were introduced to the emitting core as electron donors, and the chrome-derived electron accepting groups such as 2-methyl-(4H-chromen-4-ylidene)malononitrile were connected to electron donating moieties by vinyl groups. To explore the electroluminescence properties of these materials, multilayered OLEDs using red materials (Red 1 and Red 2) as dopants in $Alq_3$ host were fabricated. In particular, a device using Red 1 as the dopant material showed maximum luminous efficiencies and power efficiencies of 0.82 cd/A and 0.33 lm/W at $20mA/cm^2$. Also, a device using Red 2 as a dopant material presented the CIEx,y coordinates of (0.67, 0.32) at 7.0 V.

• 한국전기전자재료학회논문지
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• 제25권6호
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• pp.456-461
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• 2012

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with red/blue, blue/red and red/blue/red emitting layer (EML) structures were fabricated using a host-dopant system. In case of white PHOLEDs with red/blue structure, the best efficiency was obtained at a structure of red (15 nm)/blue (15 nm). But the emission color was blue-shifted white. In case of white PHOLEDs with blue/red structure, the better color purity and efficiency were observed at a blue (29 nm)/red (1 nm) structure. For additional improvement of color purity in white PHOLEDs with blue (29 nm)/red (1 nm) EMLs, we fabricated white PHOLEDs with red (1 nm)/blue (28 nm)/red (1 nm) structure. The current efficiency, external quantum efficiency, and CIE (x, y) coordinate were 27.2 cd/A, 15.1%, and (0.382, 0.369) at 1,000 $cd/m^2$, respectively.

• 한국표면공학회지
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• 제46권2호
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• pp.93-97
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• 2013

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with co-doping and blue/co-doping emitting layer (EML) structures were fabricated using a host-dopant system. The total thickness of light-emitting layer was 25 nm and the dopant of blue and red was FIrpic and $Bt_2Ir(acac)$ in UGH3, respectively. In case of co-doping structure, applying micro lens array film showed efficiency improvement from the current efficiency 78.5 cd/A and power efficiency 40.4 lm/W to the current efficiency 131.1 cd/A and power efficiency 65 lm/W and blue / co-doping structure showed efficiency improvement from the current efficiency 43.8 cd/A and power efficiency 22 lm/W to the current efficiency 69 cd/A and power efficiency 32 lm/W.

• 한국재료학회지
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• 제30권1호
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• pp.1-7
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• 2020

Doping or incorporation with exotic elements are two manners to regulate the optoelectronic properties of transparent conducting (TCO) cadmium oxide (CdO). Nevertheless, the method of doping host CdO by CdTe semiconductor is of high importance. The structural, optical, and electrical properties of CdTe-doped CdO films are studied for the sake of promoting their conducting parameters (CPs), including their conductivity, carrier concentration, and carrier mobility, along with transparency in the NIR spectral region; these are then compared with the influence of doping the host CdO by pure Te ions. X-ray fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, and electrical measurements are used to characterise the deposited films prepared by thermal evaporation. Numerous results are presented and discussed in this work; among these results, the optical properties are studied through a merging of concurrent BGN (redshift) and BGW (blue shift) effects as a consequence of doping processes. The impact of hydrogenation on the characterisations of the prepared films is investigated; it has no qualitative effect on the crystalline structure. However, it is found that TCO-CPs are improved by the process of CdTe doping followed by hydrogenation. The utmost TCO-CP improvements are found with host CdO film including ~ 1 %Te, in which the resistivity decreases by ~ 750 %, carrier concentration increases by 355 %, and mobility increases by ~ 90 % due to the increase of N_carr. The improvement of TCO-CPs by hydrogenation is attributed to the creation of O-vacancies because of H₂ molecule dissociation in the presence of Te ions. These results reflect the potential of using semiconductor CdTe -doped CdO thin films in TCO applications. Nevertheless, improvements of the host CdO CPs with CdTe dopant are of a lesser degree compared with the case of doping the host CdO with pure Te ions.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.399-405
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• 2013

Two series of new green phosphorescent polymers bearing a bis(2-phenyl-pyridine)iridium(III)(dibenzoylmethane) [$(ppy)_2Irdbm$] complex were designed and synthesized. Poly-carbazole (PCbz) derivative or polyfluorene with pendant carbazole groups (PFCbz) were employed as host polymers for the iridium complex. The iridium complex monomer was copolymerized with the host monomers using varying monomer ratios via a Yamamoto coupling reaction. Efficient energy transfer from host to dopant unit was observed by increasing the ratio of the iridium guest in the copolymers. Electroluminescent devices with the configuration ITO/PEDOT:PSS/polymer/BmPyPB/LiF/Al were fabricated and characterized. The phosphorescent polymers composed of the iridium complex guest and polyfluorene with carbazole pendants as a host performed better than the polymers composed of the same guest and the main chain polycarbazole host. A maximum external quantum efficiency of 0.73%, a luminous efficiency of 1.21 cd/A, and a maximum luminance of 372 $cd/m^2$ were obtained from a device fabricated using one of the synthesized copolymers.

• 공업화학
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• 제5권5호
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• pp.764-771
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• 1994

친핵성용매하에서 p-toluenesulfonic acid나 bezensulfonic acid와 같은 유기산을 지지전해질 겸 dopant로 사용하여 전도성 Polypyrrole필름을 전해중합하였고 분해 특성과 기계적 물성증가에 대하여 고찰하였다. Dimethyformamide/p-toluenesulfonic acid에서 합성한 polypyrrole 필름이 전도도 10-40S/cm, 인장강도 $25N/mm^2$. 연신율은 10%로 가장 좋은 특성을 나타내었다. 또한 전해중합시 최적 조건은 0.5M의 pyrrole과 0.5M의 p-toluenesulfonic acid를 첨가하여 정전류법에서는 $2mA/cm^2$의 전류밀도가, 정전위법으로는 0.9V vs. $Ag/Ag^+$에서 중합할 때였으며 생성된 필름은 공기중에서 안정하였고 도핑, 탈-도핑이 가역적이어서 2차 전지로서의 특성을 갖고 있었다. 온도에 따른 분해과정이 1차 반응으로 dopant 음이온이 분해반응에 관여하지 않아 산화안정성이 좋았으며 분해활성화 에너지는 $1.01JK^{-1}mol^{-1}$, $25^{\circ}C$에서의 분해속도상수는 $3.1{\times}10-7min^{-1}$였다. 여러 가지 host polymer와의 composite를 검토한 결과 인장강도는 50%, 연신율은 100% 정도로 기계적 물성을 증가시킬 수 있었다.

• 마이크로전자및패키징학회지
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• 제15권4호
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• pp.59-64
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• 2008

본 연구에서는 백색 고분자유기 발광다이오드를 제작하여 전기 광학적 특성을 평가하였다. ITO(indium tin oxide)를 양극으로 사용하고 정공수송층으로 PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)]를 발광물질로는 PFO [poly(9,9-dioctylfluorene)]와 MEH-PPV [poly(2-methoxy-5(2-ethylhexoxy)-1,4-phenyl-enevinyle)]를 각각 host와 dopant로 사용하였다. 전자주입층으로 LiF(lithium flouride)와 음극으로 Al(aluminum)을 증착하여 최종적으로 ITO/PEDOT:PSS/PFO:MEH-PPV/LiF/Al 구조를 갖는 백색 고분자 유기발광다이오드를 제작하고 PFO와 MEH-PPV의 농도에 따른 전기 광학적 특성 변화를 조사하였다. 제작된 소자는 9V에서(x=0.36, y=0.35)의 CIE 색좌표를 갖는 백색 발광이 관찰되었으며, 최대 전류밀도와 휘도는 약 13V의 인가전압에서 $740mA/cm^2,\;900cd/m^2$의 값을 나타내었으며, $200cd/m^2$ 휘도에서 0.37 cd/A의 최대 전류효율이 관찰되었다.