• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.283-283
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• 2011

The n-doping effect by doping metal carbonate into an electron-injecting organic layer can improve the device performance by the balanced carrier injection because an electron ohmic contact between cathode and an electron-transporting layer, for example, a high current density, a high efficiency, a high luminance, and a low power consumption. In the study, first, we investigated an electron-ohmic property of electron-only device, which has a ITO/$Rb_2CO_3$-doped $C_{60}$/Al structure. Second, we examined the I-V-L characteristics of all-ohmic OLEDs, which are glass/ITO/$MoO_x$-doped NPB (25%, 5 nm)/NPB (63 nm)/$Alq_3$ (32 nm)/$Rb_2CO_3$-doped $C_{60}$(y%, 10 nm)/Al. The $MoO_x$doped NPB and $Rb_2CO_3$-doped fullerene layer were used as the hole-ohmic contact and electron-ohmic contact layer in all-ohmic OLEDs, respectively, Third, the electronic structure of the $Rb_2CO_3$-doped $C_{60}$-doped interfaces were investigated by analyzing photoemission properties, such as x-ray photoemission spectroscopy (XPS), Ultraviolet Photoemission spectroscopy (UPS), and Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy, as a doping concentration at the interfaces of $Rb_2CO_3$-doped fullerene are changed. Finally, the correlation between the device performance in all ohmic devices and the interfacial property of the $Rb_2CO_3$-doped $C_{60}$ thin film was discussed with an energy band diagram.

• Proceedings of the KIEE Conference
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1438-1439
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• 2011

In this paper, we studied effects on the efficiency, according to thickness of the electron injection layer(EIL) for improving efficiency of Organic Light Emitting Diodes(OLEDs). For the first time, after confirming the optimum thickness of the EIL material $Cs_2CO_3$, we designed OLED devices having a structure of ITO/TPD/$Alq_3/Cs_2CO_3$/Al. And we manufactured devices applying for the optimum thickness of the material in the simulation with thermal evaporating method. And we investigated how the EIL material $Cs_2CO_3$ effects on efficiency of OLEDs in the EIL. As the result, because the EIL material $Cs_2CO_3$ reduces energy potential barrier of the EIL, it facilitated the electron transfer. And, as blocking the hole transfer contributes to an increased recombination, we confirmed that the efficiency of OLEDs increased. And compared to the device without using the EIL material, the device using thickness 1.0 nm of $Cs_2CO_3$ in the EIL shows the excellent efficiency. Therefore, we confirmed that the luminance and the external quantum efficiency increase about 600% and 500% respectively.

• Journal of the Korean Applied Science and Technology
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• 제17권3호
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• pp.174-177
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• 2000

The effect of a-sexithiophene(${\alpha}-6T$) layers on the light emitting diode (LED) were studied. The ${\alpha}-6T$ was used for a buffer layer in electroluminescent (EL) devices. Enhanced carrier (hole) injection and improved emission efficiency were observed. Carrier injection characteristics were investigated as a function of ${\alpha}-6T$ later thickness. The efficiency of the electroluminescence was proportional to the thickness of ${\alpha}-6T$ layer. The highest efficiency was observed 600A of ${\alpha}-6T$ later, which was about 1.5 times higher than that of device without ${\alpha}-6T$ later. The device with a-6T showed an operation voltage lowered by 2V. The ${\alpha}-6T$ layer can substitute hole blocking layer, and control charge injection properties.

• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2267-2270
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• 2013

A series of blue fluorescent emitters based on triphenylene derivatives were synthesized via the Diels-Alder reaction in moderate yields. The electronic absorption and emission characteristics of the new functional materials were affected by the nature of the substituent on the triphenylene nucleus. Multilayered OLEDs were fabricated with a device structure of: ITO/NPB (50 nm)/EML (30 nm)/Bphen (30 nm)/Liq (2.0 nm)/Al (100 nm). All devices showed efficient blue emissions. Among those, a device using 1 gives the best performances with a high brightness (978 cd $m^{-2}$ at 8.0 V) and high efficiencies (a luminous efficiency of 0.80 cd/A, a power efficiency of 0.34 lm/W and an external quantum efficiency of 0.73% at 20 $mA/cm^2$). The peak wavelength of the electroluminescence was 455 nm with CIEx,y coordinates of (0.17, 0.14) at 8.0 V.

• Proceedings of the KIEE Conference
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1359-1360
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• 2006

lTO(Indium-Tin-Oxide) was used as anode material for OLED. Characteristics of ITO have great effect on efficiency of OLEDS(Organic light emitting diodes). ITO surface was treated by Nd:YAG laser in order to improve its chemical properties, wettability, adhesive property and to remove the surface contaminants while maintaining its original function. In this study, main purpose was to improve the efficiency of OLEDs by the ITO surface treatment: ITO surface was treated using a Nd:YAG(${\lambda}=266nm$, pulse) with a fixed power of 0.06[w] and various stage scanning velocities. Surface morphology of the ITO was investigated by AFM. Test OLEDs with surface treated ITO were fabricated by deposition of TPD (HTL), Ald3 (ETL/TML) and Al (cathode) thin films. Device performance of the OLEDs such as V-I-L was investigated using Source Measurement Unit (SMU: Keithly. Model 2400) and Luminance Measurement (TOPCON. BM-8).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2006년도 학술대회 및 기술세미나 논문집 디스플레이 광소자
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• pp.54-55
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• 2006

Organic light-emitting diodes(OLEOs) are attractive because of possible application in display with low operating voltage, low power consumption, self-emission and capability of multicolor emission by the selection of emissive material. We investigated the effects of deposition rate on the electrical characteristics, physical characteristics and optical characteristics of OLEOs in the ITO(indium-tin-oxide)/N.N'-diphenyl-N,N'-bis(3-methyphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline)aluminum($Alq_3$)/Al device. We measured current density, luminous flux and luminance characteristics of devices with varying deposition rates of TPD and $Alq_3$. It has been found that optimal deposition rate of TPD and $Alq_3$ were respectively $1.5{\AA}/s$ from the device structure. An AFM measurement results, surface roughness of the deposited film was the lowest when deposition rate was $1.5{\AA}/s$.

• Proceedings of the KIEE Conference
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1735-1737
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• 1999

In this study, several lanthanide complexes such as Eu$(TTA)_3$(Phen). Tb$(ACAC)_3$(Cl-Phen) were synthesized and the white-light electroluminescence (EL) characteristics of their thin films were investigated. where the devices having structures of anode/TPD/Tb$(ACAC)_3$(Cl-Phen)/Eu$(TTA)_3$(Phen)/$Alq_3$ or $Bebq_2$/ cathode and the low work function metal alloy such as Li:Al was used as the electron injecting electrode (cathode). Details on the white-light-emitting characteristics of these device structures were explained by the energy band diagrams of various materials used in these structures, where the energy levels of new materials such as ionization potential (IP) and electron affinity (EA) were measured by cyclic voltametric method.

• Journal of the Microelectronics and Packaging Society
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• 제14권4호
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• pp.37-42
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• 2007

We fabricated the polymer light emitting diodes (PLEDs) with ITO/PEDOT:PSS/PVK/PFO:MEH-PPV/LiF/Al structures. The effect of the thickness of PEDOT:PSS hole injection layer(HIL) on the electrical and optical properties of PLEDs was investigated. In addition, PVK hole transport layer(HTL) was introduced in the PLED device, and compared the properties of the PLEDS with and without PVX layer. All organic film layers were prepared by the spin coating method on the plasma treated ITO/glass substrates. As the thickness of PEDOT:PSS film layer decreased from about 80 nm to 50 nm, the luminance of PLED device increased from $220cd/m^2$에서 $450cd/m^2$. This may be ascribed to the increased transportation efficiency of the holes into the emission layer of PLED. The maximum current density and luminance were obtained fir the PLED device with PVX hole transport layer, showing that the current density and luminance were $268mA/cm^2\;and\;540cd/m^2$ at 12V, respectively. This values were improved by about 14% and 22% in current density and luminance compared with the PLED device without PVK layer.

• Journal of the Korean Chemical Society
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• 제54권3호
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• pp.291-294
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• 2010

In this study, we demonstrated high-efficiency blue organic light-emitting diodes (OLEDs) employing BCzVBi as a blue fluorescent dye doped into blue host material, DPVBi with various concentration. The optimized blue OLED device having high-efficiency was constructed with structure of NPB (500 ${\AA}$) / DPVBi:BCzVBi-6% (150 ${\AA}$)/$Alq_3$(300 ${\AA}$) / Liq (20 ${\AA}$) / Al (1000 ${\AA}$). The maximum luminescence of blue OLED was 13200 cd/$m^2$ at 13.8 V and current density and maximum efficiency were 26.4 mA/$cm^2$ at 1000 cd/$m^2$ and 4.24 cd/A at 3.9 V, respectively. Luminous efficiency shows two times higher than comparing with non-doped BCzVBi blue OLED whereas $CIE_{x,y}$ coordinate was similar with bare DPVBi blue OLED such as (0.16, 0.19). Electroluminescence of BCzVBi-6% doped blue OLED has two major peaks at 445 nm and 470 nm whereas pure DPVBi's blue peak appears at 456 nm and it is happened through endothermic Forster energy transfer by molecule's vibration between LUMO of DPVBi as host material and LUMO of BCzVBi as dopant in device.

• Journal of the Korean Vacuum Society
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• 제19권3호
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• pp.184-189
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• 2010

Organic light-emitting diodes (OLEDs) with single emissive layer structures using two fluorescent dopants were fabricated and the device was composed of ITO / NPB ($700{\AA}$) / MADN : C545T - 1.0% : DCJTB - 0.3% ($300{\AA}$) / Bphen ($300{\AA}$) / LiF ($10{\AA}$) /Al ($1,000{\AA}$). C545T and DCJTB were functioned as green fluorescent dye and red fluorescent dye under MADN as host material. Concentrations of C545T and DCJTB was changed in emissive layer of MADN. Optimized OLED device using two fluorescence dopants shows emission efficiency of 8.42 cd/A and luminescence of 3169 cd/$m^2$at 6 V with CIE color coordinate, (0.43, 0.50). Electroluminescence of optimized OLED showed two peak at 500 and 564 nm according to C545T and DCJTB. These results indicate that F$\ddot{o}$ster energy transfer energy transfer was from MADN to C545T and rather than to DCJTB continuously.