• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.234-234
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• 2012

고효율 저전력 고휘도를 장점으로 가지고 있는 OLED의 개선을 위하여 수많은 재료와 기술이 연구되어 왔다. 전기적 손실의 방지를 위하여 다양한 재료가 연구되고 있지만 그 중에서도 가장 각광받는 것은 그래핀이다. 그래핀(graphene)은 탄소원자가 육각형 벌집 모양 배열의 격자구조를 가지는 원자 단층 두께의 물질이다. 그래핀은 에너지와 역격자의 k 벡터가 선형적으로 비례하며 전도띠(conduction band)와 가전자띠(valence band)가 한 점에서 만나는 구조를 가지는 특징으로 인해 매우 빠른 전하 이동도(Mobility)를 가지고 있다. 이와 같은 그래핀의 특성을 이용하여 전극 층으로 이용함으로써 소자 특성의 개선이 가능할 것으로 예상되었다. $1{\times}1$ inch Glass에 ITO 대신에 그래핀을 증착한 후 Spin coater를 사용하여 PEDOT을 각각 1,000 rpm, 2,000 rpm으로 도포 하였다. 그 후 HTL (Hole transport latey), ETL (Electron-transport layer), EML (Emissive layer), EIL (Electron injection layer)를 순차적으로 증착 하여 소자를 제작하였다. 발광층에는 유기물질 Alq3를 사용하여 녹색광을 방출하도록 하였다. Spin coater의 rpm에 따라 전도성 고분자의 두께가 결정이 되는데, rpm이 높을수록 두께가 얇으며, 얇을수록 소비전력 효율이 낮다. 하지만 전류밀도 특성이 균일하지 못한 것을 확인하였다. 휘도 효율 특성은 PEDOT의 두께가 얇을수록 동일한 전압에서 휘도가 낮은것을 확인 하였다. 또한 ITO를 이용한 동일 공정의 OLED와 비교하였을 때 상대적으로 낮은 휘도와 전류 효율특성을 보였지만, 전류밀도는 상대적으로 그래핀이 높은 것으로 확인되었다. 본 연구를 바탕으로 그래핀 소자의 개선이 이루어진다면 더욱 높은 효율과 휘도를 낼 수 있을 것으로 판단된다.

• 한국전기전자재료학회논문지
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• 제23권12호
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• pp.983-987
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• 2010

In order to investigate the emission characteristics of the phosphorescent white organic light-emitting diodes (PHWOLEDs) according to various hole transport layers (HTLs), PHWOLEDs composed of HTLs whose structure are NPB/TCTA, NPB/mCP and NPB/TCTA/mCP, two emissive layers (EMLs) which emit two-wavelengths of light (blue and red), and electron transport layer were fabricated. The applied voltage, power efficiency, and external quantum efficiency at a current density of $1 mA/cm^2$ for the fabricated PHWOLEDs were 7.5 V, 11.5 lm/W, and 15%, in case of NPB/mCP, 5 V, 14.8 lm/W, and 13.7%, in case of NPB/TCTA, and 5.5 V, 14.6 lm/W, and 15%, in case of NPB/TCTA/mCP in the hole transport layer, respectively. High emission efficiency can be obtained when the amount of hole injection from anode is balanced out by the amount of electron injection from the cathode to EML by using NPB/TCTA/mCP structured HTL.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 춘계학술대회 및 기술 세미나 논문집 디스플레이 광소자
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• pp.27-28
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• 2008

We have studied an organic layer-thickness dependent electrical and optical properties of organic light-emitting diodes in a device structure of ITO/TPD/$Alq_3$/LiF/Al. While a hole-transport layer thickness of TPD was varied from 35 to 65nm, an emissive layer thickness of $Alq_3$ was varied from 50 to 100nm. A ratio of those two layers was kept to about 2:3. Variation of the layer thickness changes a traverse time of injected carriers across the organic layer, so that it may affect on the chance of probability of exciton formation. Current-voltage-luminance characteristics of the devices show that there are typical rectifying behaviors, and the luminance reaches about $30,000cd/m^2$. Thickness-dependent current efficiency shows that there is a gradual increase of the efficiency as the total layer thickness increases. The efficiency becomes saturated to be about 10cd/A when the total thickness is above 140nm. They show that emission was from the $Alq_3$ layer, because the peak wavelength is about 525nm. View angle-dependent emission spectra show that the emission intensity decreases as the angle increases.

• 센서학회지
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• 제29권1호
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• pp.27-32
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• 2020

This study proposes a pixel-patterning method for organic light-emitting diodes (OLEDs) based on thermal transfer. An infrared lamp was introduced as a heat source, and glass type donor element, which absorbs infrared and generates heat and then transfers the organic layer to the substrate, was designed to selectively sublimate the organic material. A 200 nm-thick layer of molybdenum (Mo) was used as the lightto-heat conversion (LTHC) layer, and a 300 nm-thick layer of patterned silicon dioxide (SiO₂), featuring a low heat-transfer coefficient, was formed on top of the LTHC layer to selectively block heat transfer. To prevent the thermal oxidation and diffusion of the LTHC material, a 100 nm-thick layer of silicon nitride (SiN_x) was coated on the material. The fabricated donor glass exhibited appropriate temperature-increment property until 249 ℃, which is enough to evaporate the organic materials. The alpha-step thickness profiler and X-ray reflection (XRR) analysis revealed that the thickness of the transferred film decreased with increase in film density. In the patterning test, we achieved a 100 ㎛-long line and dot pattern with a high transfer accuracy and a mean deviation of ± 4.49 ㎛. By using the thermal-transfer process, we also fabricated a red phosphorescent device to confirm that the emissive layer was transferred well without the separation of the host and the dopant owing to a difference in their evaporation temperatures. Consequently, its efficiency suffered a minor decline owing to the oxidation of the material caused by the poor vacuum pressure of the process chamber; however, it exhibited an identical color property.

• 한국전산구조공학회논문집
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• 제32권2호
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• pp.109-116
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• 2019

본 논문에서는 인체의 열상대역 저피탐을 위한 선행연구로써 인체에서 방사되는 적외선 신호의 특성을 소개한다. 인체에서 방사되는 적외선 신호는 인체 표면의 방사율과 표면온도에 의하여 결정된다. 따라서 적외선 신호해석을 위하여 표면온도를 정확히 도출할 필요가 있고, 이를 위하여 인체의 열적 편안함을 도출하는데 주로 사용 되어온 체온 조절 작용 및 다층 구조 피부 모델을 적용하여 인체의 표면온도 도출에 사용하였다. 기법의 검증을 위하여 비정상 해석 결과와 실험결과의 비교검증을 수행하였으며, 이로부터 체온 조절 작용이 인체의 표면온도 결정에 미치는 영향을 파악하였다. 비정상 해석을 통해 도출된 표면온도와 피부 및 의복의 방사율을 이용하여 적외선 신호를 도출하였으며, 가상의 배경조건에 따라 나타나는 인체의 적외선 신호 특성을 파악하였다. 의복을 착용함으로써 인체는 저방사 배경과의 적외선 신호차이가 작아지는 반면 고방사 조건에서는 역대비로 인해 오히려 피탐지성이 증가하게 된다.

• 전기전자학회논문지
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• 제24권3호
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• pp.706-712
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• 2020

유기전기발광소자(Organic light diodes, OLEDs)의 전기발광특성을 향상시키기 위해, 본 논문에서는 용액 공정 정공주입층으로 신규 hexaazatrinaphthylene(HATNA) 유도체들을 도입한 고효율 녹색인광 OLED소자의 특성을 연구하였다. HATNA 유도체는 Indium Tin Oxide(ITO)의 일함수와 비슷한 낮은 the lowest unoccupied molecular orbital(LUMO) 에너지 준위를 가져 다른 개념의 정공주입 메커니즘을 보여주었다. HATNA 유도체를 hole injection layer(HIL)로 사용한 OLED소자들은 HTL로의 정공주입장벽을 효과적으로 감소시키고 발광층 내에 전자와 정공의 균형을 최적화 시켜 외부양자효율이 10.8%에서 15.6%로, 전류 효율은 34.3 cd/A에서 42.7 cd/A로 소자 효율이 크게 향상 되었다.

• 한국재료학회지
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• 제18권4호
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• pp.199-203
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• 2008

High-efficiency phosphorescent organic light emitting diodes using TCTA-TAZ as a double host and $Ir(ppy)_3$ as a dopant were fabricated and their electro-luminescence properties were evaluated. The fabricated devices have the multi-layered organic structure of 2-TNATA/NPB/(TCTA-TAZ) : $Ir(ppy)_3$/BCP/SFC137 between an anode of ITO and a cathode of LiF/AL. In the device structure, 2-TNATA[4,4',4"-tris(2-naphthylphenyl-phenylamino)-triphenylamine] and NPB[N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine] were used as a hole injection layer and a hole transport layer, respectively. BCP [2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline] was introduced as a hole blocking layer and an electron transport layer, respectively. TCTA [4,4',4"-tris(N-carbazolyl)-triphenylamine] and TAZ [3-phenyl-4-(1-naphthyl)-5-phenyl-1,2,4-triazole] were sequentially deposited, forming a double host doped with $Ir(ppy)_3$ in the [TCTA-TAZ] : $Ir(ppy)_3$ region. Among devices with different thickness combinations of TCTA ($50\;{\AA}-200\;{\AA}$) and TAZ ($100\;{\AA}-250\;{\AA}$) within the confines of the total host thickness of $300\;{\AA}$ and an $Ir(ppy)_3$-doping concentration of 7%, the best electroluminescence characteristics were obtained in a device with $100\;{\AA}$-think TCTA and $200\;{\AA}$-thick TAZ. The $Ir(ppy)_3$ concentration in the doping range of 4%-10% in devices with an emissive layer of [TCTA ($100\;{\AA}$)-TAZ ($200\;{\AA}$)] : $Ir(ppy)_3$ gave rise to little difference in the luminance and current efficiency.

• 센서학회지
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• 제33권4호
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• pp.224-229
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• 2024

Quantum dot light-emitting diodes (QD-LEDs) are emerging as next-generation displays owing to their high color purity, wide color gamut, and solution processability. Enhancing the efficiency of QD-LEDs involves preventing non-radiative recombination mechanisms, such as Auger and interfacial recombination. Generally, ZnO serves as the electron transport layer, which is known for its higher mobility compared to that of organic semiconductors and can lead to excessive electron injection. Some of the injected electrons pass through the quantum dot emissive layer and undergo non-radiative recombination near or within the organic hole transport layer (HTL), resulting in HTL degradation. Therefore, the implementation of electron blocking layers (EBLs) is essential; however, studies on all-solution-processed inverted InP QD-LEDs are limited. In this study, poly(9-vinylcarbazole) (PVK) is introduced as an EBL to mitigate HTL degradation and enhance the emission efficiency of inverted InP QD-LEDs. Using a single-carrier device, PVK was confirmed to effectively inhibit electron overflow into the HTL, even at extremely low thicknesses. The optimization of the PVK thickness also ensured minimal disruption of the hole-injection properties. Consequently, a 1.5-fold increase in the maximum luminance was achieved in the all-solution-processed inverted InP QD-LEDs with the EBL.

• 한국전기전자재료학회논문지
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• 제26권10호
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• pp.745-753
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• 2013

Performance of organic light-emitting diodes incorporating microlens array was simulated using a Light Tools software. Use of microlens array can help the light to escape out of the device. We simulated a reference device that is consisted of reflection layer, emissive layer, and flat transparent substrate. And in this reference device, outcoupled efficiency of 22% was obtained. Several shapes of microlens were applied such as hemisphere, trapezoid, cone, and rectangular parallelepiped. The results showed the improvement of outcoupled efficiency of the device with microlens compared to that of the reference one. And from the analyses of the simulated data, the obtained appropriate shape of microlens is hemisphere, and the improvement of the device with hemispherical lens is 57% higher than that of the reference one.

• 한국신뢰성학회지:신뢰성응용연구
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• 제9권2호
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• pp.131-148
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• 2009

An organic light emitting diode (OLED), also light emitting polymer (LEP) and organic electro luminescence (OEL), is any light emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance that allows suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors. Such systems can be used in television screens, computer displays, small, portable system screens such as cell phones and PDAs, advertising, information and indication. OLEDs can also be used in light sources for general space illumination, and large-area light-emitting elements. In this paper, we develop the general guide line of the accelerated life test for assuring B10 life of AMOLED(Active Matrix Organic Light Emitting Diode) and PMOLED(Passive Matrix Organic Light Emitting Diode) which are widely used for display monitor less than 115 mm.