• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.682-685
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• 2013

We have fabricated blue phosphorescent organic light-emitting devices (OLEDs) on a plastic substrate. The solution coated poly (9-vinylcarbazole) (PVK) host doped with Bis (3,5-difluoro-2-(2-pyridyl)phenyl_(2-carboxypyridyl)irdium(III) (FIrPic) guest molecules was used as an hole transporting emission layer. The device structure was ITO/PVK:FIrpic (50 nm, xwt%)/TAZ 50 nm)/LiF (0.5 nm)/Al (100 nm). The concentration of FIrpic molecule was varied from 1 wt% to 10 wt%. The OLED on plastic substrate exhibited maximum current efficiency of 18 cd/A with 5 wt% FIrpic molecules were doped into the PVK layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.8
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• pp.678-681
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• 2011

We have investigated the effect of organic thin film on the driving voltage of OLED (organic light emitting diode) by inserting a 5 nm thick 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or triphenylphosphineoxide ($Ph_3PO$) between tris-(8-hydroxyquinoline)aluminum ($Alq_3$) electron transport layer and 4,4'-bis(2,2'-diphyenylvinyl)-1,1'-biphenyl (DPVBi) emission layer. The device with 5 nm thick $Ph_3PO$ layer exhibited higher maximum current efficiency and lower driving voltage than the device with BCP layer, resulting from better electron injection from $Alq_3$ to DPVBi in the device with $Ph_3PO$ layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.352.1-352.1
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• 2016

양자점은 나노미터 크기의 반도체 결정으로 밴드갭에 따라 광학적, 전기적 성질이 달라지는 독특한 성질을 가지는 형광물질으로 활발히 연구되고 있다. 중금속을 기반으로 한 양자점은 높은 발광효율과 광안전성을 가지며, 가시광선 영역에서 빛을 내는 특징을 가지고 있다. 그러나 중금속을 사용하기 때문에 독성이 있어 인체나 환경에 유해하여 응용 연구에 제한적이다. 반면에, 탄소 기반의 양자점은 중금속 기반의 양자점과 비슷한 성질을 가질 뿐만 아니라, 높은 용해도와 낮은 독성으로 인해 생체적합성이 높다는 장점이 있다. 이를 이용하여 발광다이오드(LEDs), 태양전지, 광촉매 뿐만 아니라 바이오이미징, 바이오센서 등 생물학분야에도 응용 될 수 있다. 본 연구에서는 Bottom-up 합성 방법으로 유기전구체를 이용하여 질소를 함유하고 있는 양친매성 탄소 양자점(N-GQDs)을 합성하였다. 합성에 사용한 유기전구체는 기존에 보고된 유기전구체와 다르게 반응 진행 중에도 pH 측정 결과 중성을 나타내며, 반응 온도($225^{\circ}C$)와 유사한 온도에서도 pH 값은 여전히 6.0 이상의 값을 나타냈다. 중성을 띄는 특징으로 인해 추가적인 산제거 과정이나 표면안정화 과정이 필요 없다는 장점을 가지고 있다. 합성된 N-GQDs는 높은 결정성의 원형구조를 가지며, 원자힘현미경(AFM) 분석을 통해 높이가 ~ 1.5 nm 미만으로 3층 이하의 두께로 형성되었음을 확인하였다. 또한, 적외선 분광법(FT-IR) 분석을 통해 O-H기, 방향족 고리의 C = C (또는 C = N)기 및 C-N기가 각각 ~3250, ~1670과 ~1140 cm-1에서 확인할 수 있다. 합성된 양자점을 유기태양전지의 active layer에 소량(2 wt%) 첨가하여 양자점의 광학적, 전기적 성질을 확인하였다. 비교군 유기태양전지보다 N-GQDs가 첨가된 유기태양전지의 외부양자효율(PCE)이 7.3%에서 8.4%로 약 20%가 증가하는 것을 보였다. 이는 양자점이 상대적으로 흡수가 약한 단파장 영역의 빛을 흡수하고 PL을 내어 active layer로 에너지 트랜스퍼 현상이 일어나 전자전달을 원활하게 해 주기 때문이다. 앞으로 본 연구의 가능성과 추가적인 연구를 통해 더 많은 분야에 응용되기를 기대한다.

• Applied Chemistry for Engineering
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• v.35 no.5
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• pp.445-450
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• 2024

The electronic structure calculations for organic light-emitting diode-emitting materials were performed using three different methods: r² SCAN-3c, B3LYP-D3/def2-TZVP, and DLPNO-STEOM-CCSD/def2-SVP. These calculations were used to predict structure optimization, molecular orbitals, and excitation properties. Additionally, the differences among the calculation methods were investigated and compared with experimental values to identify the most suitable computational method. The five selected emitting materials include N,N,N',N'-tetraphenyl-anthracene-9,10-diamine, in which diphenyl amines are substituted on an anthracene chromophore, along with other alkyl groups of varying sizes and positions. The qualitative predictions made by the calculations were mostly consistent with the experimental results, and among them, the B3LYP/def2-TZVP method showed the smallest error in absorption wavelength compared to the experimental results, confirming it as the most suitable calculation method.

• Applied Chemistry for Engineering
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• v.34 no.1
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• pp.94-97
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• 2023

2,7-bis(3',6'-diphenyl-[1,1':2',1"-terphenyl]-4'-yl)-9,9'-spirobi[fluorene] (BTPSF) and 2,7-bis(1,4-diphenyltriphenylen-2-yl)-9,9'-spirobi[fluorene] (BDTSF) were successfully synthesized as novel blue-emission materials for organic light-emitting diodes (OLEDs) based on the spirobifluorene (SBF) moiety. BTPSF and BDTSF were obtained in high purity via a Diels-Alder reaction, without the use of a catalyst. Photoluminescence spectra of the synthesized materials showed maximum emitting wave-lengths of approximately 381 and 407 nm in solution and 395 and 434 nm in the film state, for BTPSF and BDTSF, respectively, indicating ultra-violet and deep blue emission colors. BDTSF was applied as an emissive layer (EML) in non-doped devices and achieved a current efficiency of 0.61 cd/A and an external quantum efficiency (EQE) of 0.46%.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.11
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• pp.1183-1189
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• 2012

Organic light-emitting diodes (OLEDs) using microcavity effect have attracted great attention because they can reduce the width of emission spectra from organic materials, and enhance brightness from the same material. We demonstrate the simulation results of the radiation properties from top-emitting organic light-emitting diodes (TE-OLEDs) with microcavity structures based on the general electromagnetic theory. Organic materials such as N,N'-di (naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) ($Alq_3$) as emitting and electron transporting layer are used to form the OLEDs. The organic materials were sandwiched between anode such as Ni or Au and cathode such as Al, Ag, or Al:Ag. The devices were characterized with electroluminescence phenomenon. We confirmed that the simulation results are consistent with experimental results.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.251-262
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• 2014

최근 유기 발광 다이오드(Organic Light Emitting Diodes; OLED)가 각광받고 있어 이를 개발하기 위한 좀 더 효율적이고 실용적인 OLED 구조의 예측이 필요해지고 있다. 본 연구는 가장 기초적인 OLED dye의 형태인 $Ru(bpy){_3}^{2+}$와 그와 유사한 구조의 발광 물질이 전기화학발광(ECL) 현상을 통해 방출하는 빛의 특성을 계산하는 것을 목적으로 한다. EDISON 화학 서버의 GAMESS 프로그램을 사용하여 $Ru(bpy){_3}^{2+}$와 유도체들의 바닥상태(ground state)와 첫 번째 들뜬 상태(first excited state)를 계산하였다. Basis set으로는 MINI와 3-21G 혹은 SBKJC를 사용하였다. 들뜬 상태 계산은 configuration interaction with single excitation(CIS)을 이용하여 단일항(singlet)과 삼중항(triplet) 상태에서 바닥과 들뜬 상태의 최적 구조에 대한 계산을 수행하였다. 다양한 방법으로 방출 파장을 계산한 결과를 바탕으로 $Ru(bpy){_3}^{2+}$와 다양한 유도체들의 에너지 계산에 어떤 방법이 효율적으로 적용될 수 있을지 탐색하였다. 같은 계산방법들이 중심 금속이 이리듐(Ir)인 분자에도 적용이 될 수 있을지 알아보기 위해 $lr(mppy)_3$에도 적용하였다. 본 연구를 통하여 얻어진 방식은 시간을 절약하고 더 효율적인 $Ru(bpy){_3}^{2+}$ 유도체 계산에도 사용할 수 있을 것이다.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.381-388
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• 2015

Organic Light Emitting Diodes (OLEDs) have been receiving great attention in academic and industrial fields, and it is being actively applied to mobile display, as well as large area TV and next-generation flexible display due to their excellent advantages. In addition, the scope of research on OLED materials and device fabrication technology is getting expanded. This review discusses the principle and basic composition of OLED and also classifies OLED materials with different chemical structures according to their usages. Systematic classification of OLEDs by technical concept and material characteristics can help developing new emitting materials.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.193-199
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• 2014

The net effect of the emitter orientation, Mie scatters, and pillow lenses on the outcoupling efficiency (OCE) of a bottom-emitting OLED having an internal photonic crystal layer was investigated by a combined optical simulation based on the finite-difference time-domain method (FDTD) and the ray-tracing technique. The simulation showed that when the emitter orientation was horizontal with respect to the OLED surface, the OCE could be increased by 54% when a photonic crystal layer was employed, while it could be improved by 86% under optimized conditions of Mie scatters and pillow lenses applied to the glass substrate. The peculiar intensity distribution of the OLED, caused by the periodic lattice structure of the photonic crystal layer, could be ameliorated by inserting Mie scatters into the glass substrate. This study suggests that conventional outcoupling structures combined with control of the emitter orientation could improve the OCE substantially.

• Clean Technology
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• v.18 no.4
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• pp.366-372
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• 2012

Three acrylic copolymers containing tris(8-hydroxyquinoline) aluminum (AlQ3) pendant group (25 wt%), acrylateco-HEMA-$AlQ_3$ (25 wt%), were successfully synthesized by free radical polymerization from acrylates [methyl methacrylate (MMA), acrylonitrile (AN) or 2-hydroxyethyl methacrylate (HEMA)] with HEMA functionalized with AlQ3 pendant groups (HEMA-p-$AlQ_3$). The glass transition temperatures ($T_g$) of MMA-co-HEMA-p-$AlQ_3$ (copolymer 1), AN-co-HEMA-p-$AlQ_3$ (copolymer 2) and HEMA-co-HEMA-p-$AlQ_3$ (copolymer 3) were found to be 158, 150 and $126^{\circ}C$, respectively. They have good thermal stability: a very desirable feature for the stability of OLEDs. Their solubility, thermal properties, UV-visible absorption and photoluminescence behaviors were investigated. They were found to be soluble in various organic solvents such as tetrahydrofuran (THF), dimethylformamide (DMF), toluene and chloroform. It was also found that the UV-visible absorption and photoluminescence behaviors of these copolymers were similar to those of pristine $AlQ_3$. Green organic light-emitting diodes (OLEDs) have also been fabricated using these copolymers as light emission/electron transport components obtained easily by spin coating, and their current density voltage (J-V) curves were compared. The OLED device of the copolymer 3 had the lowest turn-on voltage of about 2 V compared to other copolymer types devices.