• 마이크로전자및패키징학회지
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• 제27권3호
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• pp.69-72
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• 2020

본 연구에서는 SnO₂ nanoparticles (NPs) 위에 TiO₂ NPs를 코팅하여 Quantum Dots Light Emitting Diodes (QLEDs)를 제작하였다. TiO₂ NPs는 SnO₂ NPs보다 conduction band minimum (CBM) 준위가 낮다. 따라서 SnO₂ 층과 발광층의 CBM 준위 사이에 위치해 에너지 장벽을 감소시키고, 전자의 이동을 원활하게 할 것으로 예상하였다. QLEDs는 inverted 구조로 제작되었으며, SnO₂ 단일층을 사용한 경우보다 발광 특성이 향상된 것을 확인하였다. 이중 전자수송층을 적용한 이번 연구를 통해 SnO₂를 QLEDs에 전자수송층으로 적용할 수 있을 것으로 기대한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.246.1-246.1
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• 2014

Over the past several years, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED). In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[1] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QDLEDs, blend of poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo) and poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] are used as hole transporting layer (HTL) to improve hole transporting property. At the operating voltage of 8 V, the QDLED device emitted spectrally orange color lights with high luminance up to 2450 cd/m2, and showed current efficacy of 0.6 cd/A, respectively.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.65-74
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• 2009

Device quality indium tin oxide (ITO) films are deposited on glass substrates and ultra-thin diamond-like carbon films are deposited as a buffer layer on ITO by a pulsed Nd:YAG laser at 355 nm and 532 nm wavelength. ITO films deposited at room temperature are largely amorphous although their optical transmittances in the visible range are > 90%. The resistivity of their amorphous ITO films is too high to enable an efficient organic light-emitting device (OLED), in contrast to that deposited by a KrF laser. Substrate heating at $200^{\circ}C$ with laser wavelength of 355 nm, the ITO film resistivity decreases by almost an order of magnitude to $2{\times}10^{-4}\;{\Omega}\;cm$ while its optical transmittance is maintained at > 90%. The thermally induced crystallization of ITO has a preferred <111> directional orientation texture which largely accounts for the lowering of film resistivity. The background gas and deposition distance, that between the ITO target and the glass substrate, influence the thin-film microstructures. The optical and electrical properties are compared to published results using other nanosecond lasers and other fluence, as well as the use of ultra fast lasers. Molecularly doped, single-layer OLEDs of ITO/(PVK+TPD+$Alq_3$)/Al which are fabricated using pulsed-laser deposited ITO samples are compared to those fabricated using the commercial ITO. Effects such as surface texture and roughness of ITO and the insertion of DLC as a buffer layer into ITO/DLC/(PVK+TPD+$Alq_3$)/Al devices are investigated. The effects of DLC-on-ITO on OLED improvement such as better turn-on voltage and brightness are explained by a possible reduction of energy barrier to the hole injection from ITO into the light-emitting layer.

• 한국산학기술학회논문지
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• 제10권7호
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• pp.1514-1519
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• 2009

400nm 파장을 방출하는 GaN LED를 제조하여, n-GaN층과 p-GaN층의 위에 있는 ITO층 표면에 패턴을 만들어 광 추출 효율을 향상시켰다. 추가적으로, n과 p패드 아래와 칩의 바닥면에 각각 광반사 금속을 설치하였다. 광 추출 효율은 20mA에서 n-GaN의 텍스쳐링에 의해 20% 증가되었고 ITO의 텍스쳐링에 의해 18% 증가되었다. 표면 처리가 않된 LED와 비교해서 n-GaN와 ITO를 함께 표면 텍스쳐링 했을때의 광 추출 효율은 20mA에서 32% 증가되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.51-52
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• 2007

Built-in voltage in organic light-emitting diodes was studied using modulated photocurrent technique ambient conditions. From the bias voltage-dependent photocurrent, built-in voltage of the device is determined. The applied bias voltage when the magnitude of modulated photo current is zero corresponds to a built-in voltage. Built-in voltage in the device is generated due to a difference of work function of the anode and cathode. A device was made with a structure of anode/$Alq_3$/cathode to study a built-in voltage. ITO and ITO/PEDOT:PSS were used as an anode, and Al and LiF/AI were used as a cathode. It was found that an incorporation of PEDOT:PSS layer between the ITO and $Alq_3$ increases a built-in voltage by about 0.4V. This is consistent to a difference of a highest occupied energy states of ITO and PEDOT:PSS. This implies that a use of PEDOT:PSS layer in anode improves the efficiency of the device because of a lowering of anode barrier height. With a use bilayer cathode system LiF/Al, it was found that the built-in voltage increases as the LiF layer thickness increases in the thickness range of 0~1nm. For 1nm thick LiF layer, there is a lowering of electron barrier by about 0.2eV with respect to an Al-only device. It indicates that a very thin alkaline metal compound LiF lowers an electron barrier height.

• 마이크로전자및패키징학회지
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• 제26권3호
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• pp.71-74
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• 2019

본 연구는 발광층으로의 전자 주입을 억제하기 위해 ZnO 나노입자보다 낮은 전자 이동도를 갖는 $TiO_2$ 나노입자를 무기 전자 수송층으로 사용하여 standard와 inverted 두 가지 구조의 양자점 전계발광 소자를 제작하고 그 특성을 비교하였다. Standard 구조의 소자에서는 전류 밀도가 낮은 것에 비해 inverted 구조의 소자에서는 전류 밀도가 매우 높은 것을 확인하였다. 휘도의 경우 inverted 구조의 소자가 standard 구조의 소자보다 더 높았지만 높은 전류 밀도로 인해 낮은 전류 효율을 나타냈다. 또한 전류 밀도가 높은 만큼 구동 전압이 높았으며, 방출 파장 스펙트럼에서 적색 편이를 확인하였다. Standard 구조의 소자에서 나타난 낮은 전류 밀도를 통해, $TiO_2$ 나노입자가 양자점 전계발광 소자에서 전자 주입을 억제할 수 있는 가능성을 확인하였다.

• 센서학회지
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• 제30권5호
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• pp.309-313
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• 2021

Organic semiconductors have received tremendous attention for their research because of their tunable electrical and optical properties that can be achieved by changing their molecular structure. However, organic materials are inherently unstable in the presence of oxygen and moisture. Therefore, it is necessary to develop moisture and air stable semiconducting materials that can replace conventional organic semiconductors. In this study, we developed a NiO_x thin film through a solution process. The electrical characteristics of the NiO_x thin film, depending on the thermal annealing temperature and UV-ozone treatment, were determined by applying them to the hole injection layer of an organic light-emitting diode. A high annealing temperature of 500 ℃ and UV-ozone treatment enhanced the conductivity of the NiO_x thin films. The optimized NiO_x exhibited beneficial hole injection properties comparable those of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN), a conventional organic hole injection layer. As a result, both devices exhibited similar power efficiencies and the comparable electroluminescent spectra. We believe that NiO_x could be a potential solution which can provide robustness to conventional organic semiconductors.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.41-43
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• 2004

Plasma polymerized para-xylene ($PP_PX$) deposited by plasma-enhanced chemical vapor deposition (PECVD) was used as the barrier layer on the polyethylene terephthalate (PET) substrate to improve lifetime of the flexible organic light-emitting diodes (FOLEDs). The $PP_PX$ barrier layer deposited on top of the PET substrate with plasma power of 30 W at deposition pressure of 0.2 torr showed transmittance spectra good enough to be applied in FOLED on PET substrates. FOLEDs with the $PP_PX$ barrier layer (barrier-FOLEDs) showed similar I-V and B-V characteristics to FOLEDs without the $PP_PX$ layer (control-FOLEDs). The lifetime of barrier-FOLED was two times longer than that of the control-FOLED. With $PP_PX$ passivation layers, lifetimes of both control and barrier-FOLEDs were improved by more than 4 times. These results show that PECVD deposited $PP_PX$ layers can be used as barrier layers for FOLEDs on plastic substrates as well as passivation layers for general OLEDs.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.299-300
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• 2009

We have studied an organic layer and semitransparent Al cathode thickness dependent optical properties for top-emission organic light-emitting diodes. Device structure is ITO(170nm)/TPD(xnm)/$Alq_3$(ynm)/LiF(0.5nm)/Al(100nm) and Al(100nm)/TPD(xnm)/$Alq_3$(ynm)/LiF(0.5nm)/Al(25nm). While a thickness of total, organic layer was varied from 85nm to 165nm, a ratio of those two layers was kept to be about 2:3. Then it was compared with that of bottom devices. And a thickness of semitransparent Al cathode was varied from 20nm to 30nm for the device with an organic layer thickness of 140nm. We were able to control the emission spectra from the top-emission organic light-emitting diodes.

• 한국표면공학회지
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• 제47권4호
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• pp.210-214
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• 2014

We investigated emission characteristics of tandem organic light emitting devices (OLEDs) with p-type materials as charge generation layer. The tandem OLEDs were fabricated by using $MoO_x$, $WO_x$, C60 and HATCN as p-type material or not using p-type material for charge generation. When HATCN was used as p-type material, it showed high current density at low applied voltage, but increase of efficiency was small because of charge unbalance in emitting layer. In case of tandem OLED not using p-type material, applied voltage increased remarkably because of difficulty of hole injection. In case of $MoO_x$, $WO_x$ or C60 as p-type material, current emission efficiency increased greatly. In particular, current emission efficiency of tandem OLED using $MoO_x$ as p-type material increased up to 3 times than current emission efficiency of single OLED. The Commission Internationale de l'Eclairage (CIE) 1931 color coordinates were changed by overlapping of 504 nm emission wavelength. As a result, emission efficiency of tandem OLED improved compared with single OLED, but driving voltage also increased by increase of organic layer thickness.