• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 디스플레이 광소자 분야
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• pp.53-56
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• 2002

The effect of $\alpha$-septithiophene (${\alpha}-7T$) layers on the organic light emitting diode(OLED) was studied. The ${\alpha}-7T$ was used for a buffer layer in OLED. Hole injection was investigated and improved emission efficiency. The OLEDs structure can be described as indium tin oxide(ITO)/ buffer layer / hole transporting layer / emitting layer / electron transporting layer / LiF / Al. The hole transporting layer were composed of N,N-diphenyl-N,N-di(3-methylphenyl)-1,1-biphenyl-4,4-diamine(TPD), and N,N-di(naphthalene-1-ly)-N,N-diphenyl-benzidine( ${\alpha}$-NPD). The emitting layer, and electron transporting layer consist of tris(8-hydroxyquinolinato) aluminum($Alq_3$). All organic layer were deposited at a background pressure of less than $10^{-6}$ torr using ultra high vacuum (UHV) system. The ${\alpha}-7T$ layer can substitute the hole blocking layer, and improve hole injection properties.

• 한국전기전자재료학회논문지
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• 제14권8호
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• pp.675-678
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• 2001

We fabricated the organic light emittign diodes (OLEDs) with ITO/Cu-Pc/triphenyl-diamine (TPD)/TPD+tris-(8-hydroxyquinoline) aluminum (Alq$_3$)/Al. The electrical properties of Cu-Pc thin film were studied as a hole injection layer. the energy gap of Cu-Pc thin films is decreased according to the substrate heat treatment temperature increased. It could be controlled the hole mobility by changing the heat treatment condition of Cu-Pc. The emission wavelengths could be controlled by changing hole mobility and recombination zone in emission layer.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.492-495
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• 2008

Efficient top-emitting organic light-emitting diodes were fabricated using copper iodide (CuI) doped NPB as a p-doped hole injection layer to improve hole injection from a silver bottom electrode. The enhanced hole injection is originated from the formation of the charge transfer complex between CuI and NPB. The devices result in high efficiency of 69 cd/A with almost Lambertian emission pattern.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1805-1808
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• 2006

In this paper, we describe a versatile use of fullerene(C60) as a charge transporting material for organic light-emitting diodes. The use of fullerene as a buffer layer for an anode, a doping material for hole transport layer, and an electron transport layer was investigated. Fullerene improved the hole injection from an anode to a hole transport layer by lowering the interfacial energy barrier and enhanced the lifetime of the device as a doping material for a hole transport layer. In addition, it was also effective as an electron transporting material to get low driving voltage in the device.

• 한국전기전자재료학회논문지
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• 제21권9호
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• pp.853-858
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• 2008

The structure of organic light-emitting diodes(OLEDs) with typical heterostructure consists of anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode. 4,4bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl(NPB) used as a hole transport layer and 4'4-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl(DPVBi) used as a blue light emitting layer were graded-mixed at selected ratio. Interface at heterojunction between the hole transport layer and the elecrtron transport layer restricts carrier's transfer. Mixing of the hole transport layer and the emitting layer reduces abrupt interface between the hole transport layer and the electron transport layer. The operating voltage of OLED devices with graded mixed-layer structure is 2.8 V at 1 $cd/m^2$ which is significantly lower than that of OLED device with typical heterostructure. The luminance of OLED devices with graded mixed-layer structure is 21,000 $cd/m^2$ , which is much higher than that of OLED device with typical heterostructure. This indicates that the graded mixed-layer enhances the movement of carriers by reducing the discontinuity of highest occupied molecular orbital(HOMO) of the interface between hole transport layer and emitting layer.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.69-70
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• 2006

We studied increasement of efficiency of Organic Light-emitting Diodes depending on thickness variation of LiF, Material of Electron Injection Layer in structure of ITO/Hole Injection Layer (PTFE)/Hole Transportion Later (TPD)/Emitting Layer (Alq3)/Electron Injection Layer (LiF)/Al. TPD and $Alq_3$ is deposited as rate of 1.3~1.5 [${\AA}/s$] in high vacuum ($5{\times}10^{-6}$ [torr]). In result of these studies, we can know maximum efficiency in 0.7 [nm], thickness of LiF. And samples with electron injection material are increased about 5-fold in maximum efficiency in compare with sample without electron injection material.

• Transactions on Electrical and Electronic Materials
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• 제18권2호
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• pp.89-92
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• 2017

The performance of three-layered organic light-emitting diodes (OLEDs) was investigated using TPD hole-transport and injection layers, Teflon-AF, and the electron-injection layer of $Li_2CO_3$ and LiF. The OLEDs were manufactured in a structure of TPD/$Alq_3$/LiF, TPD/$Alq_3$/$Li_2CO_3$, and AF/$Alq_3$/LiF using low-molecular organic materials. In three different three-layered OLEDs, it was found that the device with the TPD/$Alq_3$/LiF structure shows higher performance in maximum luminance, and maximum external quantum efficiency compared to those of the device with TPD/$Alq_3$/$Li_2CO_3$ and TPD/$Alq_3$/LiF by 35% and 17%, and 193% and 133%, respectively. It is thought that the combined LiF/Al cathode contributes to a reduced work function and improves an electrical conduction mechanism due to the electron injection rather than the hole transport, which then increases a recombination rate of charge carriers.

• 대한전자공학회논문지SD
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• 제45권5호
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• pp.19-25
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• 2008

본 연구에서는 유기반도체인 펜타센과 소스-드레인 금속전극사이에 $C_{60}$을 홀주입층으로 적용한 유기박막트랜지스터를 제작하여 $C_{60}$을 삽입하지 않은 소자와의 전기적특성을 비교하였다. $C_{60}/Au$ 이중전극을 사용한 소자의 경우 Au단일전극을 사용한 소자와 비교하였을 때 전하이동도는 0.298 $cm^2/V{\cdot}s$에서 0.452 $cm^2/V{\cdot}s$ 문턱전압의 경우 -13.3V에서 -10.8V로 향상되었으며, contact resistance를 추출하여 비교하였을 경우 감소함을 확인할 수 있었다. 이러한 성능의 향상은 $C_{60}$을 Au와 pentacene 사이에 삽입하였을 경우 Au-pentacene 간의 원하지 않는 화학적 반응을 막아줌으로써 홀 주입장벽를 감소시켜 홀 주입이 향상되었기 때문이다. 또한 Al을 전극으로 적용한 OTFT도 제작하였다. 기존에 Al은 OTFT에 단일전극으로 사용하였을 경우 둘간의 높은 홀 주입장벽으로 인해 채널이 거의 형성되지 않았으나, $C_{60}/Al$ 이중전극을 사용한 소자의 경우 전하이동도와 전류점멸비은 0.165 $cm^2/V{\cdot}s$, $1.4{\times}10^4$ 으로써 Al를 단일전극으로 사용하는 소자의 전기적 특성에 비해 크게 향상되어진 소자를 제작할 수 있었다. 이는 $C_{60}$과 Al이 접합시에 interface dipole의 형성으로 Al의 vacuum energy level이 변화로 인한 Al의 work function이 증가되어 pentacene과 Al간의 hole injection barrier가 감소되었기 때문이다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.305-306
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• 2009

In this study, we have invastigated the recombination zone in the blue phosphorescent organic light-emitting devices with various partially doped structures. The basic device structure of the blue PHOLED was anode / hole injection layer (HIL) / hole transport layer (HTL) / emittingvastigated the recombination zone in the blue layer (EML) / hole blocking layer (HBL) / electron transport layer (ETL) / electron injection layer (EIL) / cathode. After the preparation of the blue PHOLED, the current density (J) - voltage (V) - luminance (L) and current efficiency characteristics were measured.

• 한국전기전자재료학회논문지
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• 제27권1호
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• pp.50-55
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• 2014

It was firstly found in 1st group element. Recently, it has been reported on the improvement of efficiency of the OLEDs by introducing thin layer of some carbonate materials of alkali metal. In order to improve the efficiency of OLEDs which is one of the next generation displays, we have studied the electrical characteristics of the device depending on the thickness ratio of the hole-injection layer to the electron-injection layer. Teflon-AF was used as the hole-injection material, and alkali-metal carbonates of $Li_2CO_3$ were used as the electron-injection materials. To obtain a proper thickness ratio, we manufactured. Four types of devices with the thickness ratio of HIL to EIL were made to be 1 : 4, 2 : 3, 3 : 2, and 4 : 1. The results of electrical and optical properties showed that the device with the thickness ratio of 4 : 1 is the most excellent result. In addition, to prepare a four-layer device by inserting the ${\alpha}$-NPD is a hole transporting material was compared with three-layer element. As a result, the maximum luminance, the maximum luminous efficiency, maximum external quantum efficiency of about 124 [%], 164 [%], 106 [%] improve was confirmed.