• Transactions on Electrical and Electronic Materials
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• 제10권1호
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• pp.28-30
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• 2009

We have studied organic layer-thickness dependent electrical and optical properties of bottom- and top-emission devices. Bottom-emission device was made in a structure of ITO(170 nm)/TPD(x nm)/$Alq_3$(y nm)/LiF(0.5 nm)/Al(100 nm), and a top-emission device in a structure of glass/Al(100 nm)/TPD(x nm)/$Alq_3$(y nm)/LiF(0.5 nm)/Al(25 nm). A hole-transport layer of TPD (N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine) was thermally deposited in a range of 35 nm and 65 nm, and an emissive layer of $Alq_3$ (tris-(8-hydroxyquinoline) aluminum) was successively deposited in a range of 50 nm and 100 nm. Thickness ratio between the hole-transport layer and the emissive layer was maintained to be 2:3, and a whole layer thickness was made to be in a range of 85 and 165 nm. From the current density-luminance-voltage characteristics of the bottom-emission devices, a proper thickness of the organic layer (55 nm thick TPD and 85 nm thick $Alq_3$ layer) was able to be determined. From the view-angle dependent emission spectrum of the bottom-emission device, the peak wavelength of the spectrum does not shift as the view angle increases. However, for the top-emission device, there is a blue shift in peak wavelength as the view angle increases when the total layer thickness is thicker than 140 nm. This blue shift is thought to be due to a microcavity effect in organic light-emitting diodes.

• 마이크로전자및패키징학회지
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• 제15권2호
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• pp.23-28
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• 2008

최적 소자구조에 의한 고분자 발광다이오드의 외부 양자효율 향상을 위해 스핀코팅 방법으로 ITO/EDOT:PSS/(PFO)/PFO:MEH-PPV/LiF/Al 구조의 발광소자를 제작하고 전기, 광학적 특성을 조사하였다. ITO(indium tin oxide) 투명전극을 양극으로 사용하고 정공수송층으로 PEDOT:PSS[poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)]를 사용하였으며, 발광물질로는 PFO[poly(9,9-dioctyl-fluorene)]와 MEH-PPV [poly(2-methoxy-5(2-ethylhexoxy)-1,4-phenylenevinyle)]를 각각 호스트와 도펀트로 사용하였다. PFO:MEH-PPV 발광층의 두께를 약 $400{\AA}$으로 형성하였고, MEH-PPV의 농도는 9wt%로 고정하여 도핑하였다. PFO 발광층의 두께를 $200{\sim}300{\AA}$의 범위로 변화시켜 전계발광 특성을 비교 해 본 결과, 두께가 약 $250{\AA}$ 부근에서 가장 우수한 광학적 특성이 관찰되었으며, 13V의 인가전압에서 각각 약 $400mA/cm^2$의 전류밀도와 $1500cd/m^2$의 휘도가 관찰되었다 또한 PFO 발광층을 2중으로 구성한 소자(PFO/PFO:MEH-PPV)가 단일 발광층을 갖는 소자 (PFO:MEH-PPV)에 비해 발광휘도 및 전류 효율에서 약 3배의 향상된 특성을 보여주었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.147-147
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• 2015

The multilayer structure of the organic light emitting diode has merits of improving interfacial characteristics and helping carriers inject into emission layer and transport easier. There are many reports to control hole injection from anode electrode by using transition metal oxide as an anode buffer layer, such as V2O5, MoO3, NiO, and Fe3O4. In this study, we apply thin films of LiF which is usually inserted as a thin buffer layer between electron transport layer(ETL) and cathode, as an anode buffer layer to reduce the hole injection barrier height from ITO. The thickness of LiF as an anode buffer layer is tested from 0 nm to 1.0 nm. As shown in the figure 1 and 2, the luminous efficiency versus current density is improved by LiF anode buffer layer, and the threshold voltage is reduced when LiF buffer layer is increased up to 0.6 nm then the device does not work when LiF thickness is close to 1.0 nm As a result, we can confirm that the thin layer of LiF, about 0.6 nm, as an anode buffer reduces the hole injection barrier height from ITO, and this results the improved luminous efficiency. This study shows that LiF can be used as an anode buffer layer for improved hole injection as well as cathode buffer layer.

• 한국전기전자재료학회논문지
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• 제27권1호
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• pp.45-49
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• 2014

We have fabricated white organic light-emitting diodes (OLEDs) using several thicknesses of electron-transport layer. The multi-emission layer structure doped with red and blue phosphorescent guest emitters was used for achieving white emission. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as an electron-transport layer. The thickness of BCP layer was varied to be 20, 55, and 120 nm. The current efficiency, emission and recombination characteristics of multi-layer white OLEDs were investigated. The BCP layer thickness variation results in the shift of emission spectrum due to the recombination zone shift. As the BCP layer thickness increases, the recombination zone shifts toward the electron-transport layer/emission-layer interface. The white OLED with a 55 nm thick BCP layer exhibited a maximum current efficiency of 40.9 cd/A.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.1343-1346
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• 2005

Self assembled monolayers (SAM) are generally used at the anode/organic interface to enhance the carrier injection in organic light emitting devices, which improves the electroluminescence performance of organic devices. This paper reports the use of SAM of 1-decanethiol (H-S(CH2)9CH3) at the cathode/organic interface to enhance the electron injection process for organic light emitting devices. Aluminum (Al), tris-(8-hydroxyquionoline) aluminum (Alq3), N,N'-diphenyl-N,N'-bis(3 -methylphenyl)-1,1'- diphenyl-4,4'-diamine (TPD) and indium-tin-oxide (ITO) were used as bottom cathode, an emitting layer (EML), a hole-transporting layer (HTL) and a top anode, respectively. The results of the capacitancevoltage (C-V), current density -voltage (J-V) and brightness-voltage (B-V), luminance and quantum efficiency measurements show a considerable improvement of the device performance. The dipole moment associated with the SAM layer decreases the electron schottky barrier between the Al and the organic interface, which enhances the electron injection into the organic layer from Al cathode and a considerable improvement of the device performance is observed. The turn-on voltage of the fabricated device with SAM layer was reduced by 6V, the brightness of the device was increased by 5 times and the external quantum efficiency is increased by 0.051%.

• 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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.158-161
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• 2004

We have studied a lifetime in organic light-emitting diodes depending on buffer layer. A transparent electrode of indium-tin-oxide(ITO) was used as an anode. And the cathode for electron injection was LiAl. Phthalocyanine Copper(CuPc), Poly(3,4-ethylenedioxythiophene):poly (PEDOT:PSS), or poly (9-vinylcarbazole)(PVK) material was used as a buffer layer. A thermal evaporation was performed to make a thickness of 40nm of TPD layer at a rate of $0.5{\sim}1\;{\AA}/s$ at a base pressure of $5{\times}10^{-6}\;torr$. A material of tris(8-hydroxyquinolinate) Aluminum($Alq_3$) was used as an electron transport and emissive layer. A thermal evaporation of $Alq_3$ was done at a deposition rate of $0.7{\sim}0.8[{\AA}/s]$ at a base pressure of $5{\times}10^{-6}\;torr$. By varying the buffer material, hole injection at the interface could be controlled because of the change in work function. Devices with CuPc and PEDOT:PSS buffer layer are superior to the other PVK buffer layer.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.940-943
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• 2003

We report the fabrication and the characterization of white organic light-emitting devices consisting of a red-emitting layer of a new DCM derivative doped into 4,4'bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (${\alpha}-NPD$) and a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi). The device structure is ITO/PEDOT:PSS/${\alpha}-NPD$ (50 nm)/${\alpha}-NPD$:DCM (5 nm, 0.2 %)/DPVBi (x)/Alq3 (40 nm)/LiF (0.5 nm)/Al. The electroluminescence (EL) spectra consist of two broad peaks around 470 nm and 580 nm with the spectral emission depending on the thickness of DPVBi. The device with the DPVBi thickness of about 20 nm show a white light-emission with the Commission Internationale d'Eclairage(CIE) chromaticity coordinates of (0.33, 0.36). The external quantum efficiency is 2.6% and luminous efficiency is 2.0 lm/W at a luminance of 100 $cd/m^{2}$. The maximum luminance is about 30,270 $cd/m^{2}$ at 13.9 V.

• ETRI Journal
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• 제34권5호
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• pp.690-695
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• 2012

We investigate the light-emitting performances of blue phosphorescent organic light-emitting diodes (PHOLEDs) with three different electron injection and transport materials, that is, bathocuproine(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) (Bphen), 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (Tm3PyPB), and 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy), which are partially doped with cesium metal. We find that the device characteristics are very dependent on the nature of the introduced electron injection layer (EIL) and electron transporting layer (ETL). When the appropriate EIL and ETL are combined, the peak external quantum efficiency and peak power efficiency improve up to 20.7% and 45.6 lm/W, respectively. Moreover, this blue PHOLED even maintains high external quantum efficiency of 19.6% and 16.9% at a luminance of $1,000cd/m^2$ and $10,000cd/m^2$, respectively.

• Transactions on Electrical and Electronic Materials
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• 제10권6호
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• pp.208-211
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• 2009

The authors have demonstrated the various characteristics of hybrid white organic light-emitting diodes (HWOLED) using fluorescent blue and phosphorescent red emitters. We also demonstrated that two devices showed different characteristics in accordance with thickness of the 4,4′-N,N′-dicarbazole-biphenyl (CBP) spacer (CS) inserted between the blue and the red emitting layer. It was found that the device with a CS thickness of 70 $\AA$ showed a current efficiency 2.5 times higher than that of the control device with a CS thickness of 30 $\AA$ by preventing the triplet Dexter energy transfer from the red to the blue emitting layer. The HWOLED with the CS thickness of 70 $\AA$ exhibited a maximum luminance of 24500 cd/$m^2$, a maximum current efficiency of 42.9 cd/A, a power efficiency of 37.5 lm/W, and Commission Internationale de I'Eclairage coordinates of (0.37, 0.42).