• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.413-414
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• 2008

We have studied an organic layer thickness dependent optical properties and microcavity effects for top-emission organic light-emitting diodes. Manufactured top emission device, structure is Al(100nm)ITPD(xnm)/$Alq_3$(ynm)/LiF(0.5nm)/Al(23nm). While a thickness of hole-transport layer of TPD was varied from 35 to 65nm, an emissive layer thickness of $Alq_3$ was varied from 50 to 100nm for two devices. 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. View-angle dependent emission spectra were measured for the optical measurements. Top-emission devices show that the emission peak wavelength shifts to longer wavelength as the organic layer thickness increases. For instance, it shifts from 490 to 555nm in the thickness range that we used. View-angle dependent emission spectra show that the emission intensity decreases as the view-angle increases. The organic layer thickness-dependent emission spectra show that the full width at half maximum decreases as the organic layer thickness increases. Top emission devices show that the full width at half maximum changes from 90 to 35nm as the organic layer thickness increases. In top-emission device, the microcavity effect is more vivid as the organic layer thickness increases.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.9
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• pp.802-807
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• 2007

We have developed red phosphorescent top emission organic light-emitting diodes with transparent metal cathodes deposited by using thermal evaporation technique. Phosphorescent guest molecule, BtpIr(acac), was doped in host CBP for the red phosphorescent emission, Ca/Ag, Ba/Ag, and Mg/Ag double layers were used as cathode materials of top emission devices, which were composed of glass/Ni/2TNATA(15 nm)/${\alpha}$-NPD(35 nm)/CBP:BtpIr(acac)(40 nm, 10%)/BCP(5 nm)/$Alq_3$(5 nm)/cathodes. The optical transparencies of these metal cathodes strongly depend on underlying Ca, Ba, and Mg layers. These layers also strongly affect the electrical conduction and emission properties of the red phosphorescent top emission devices.

• Journal of the Semiconductor & Display Technology
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• v.5 no.3 s.16
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• pp.23-27
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• 2006

Recently, Top emission organic light-emitting diode (TEOLED) has been attracted by their potential application for the development of flat panel display (FPD). We have fabricated the high luminance top emission organic-emitting diode (TEOLED) using dual cathode layer and three top emitting structure. These devices were characterized by electroluminescence (EL) and current density-voltage (J-V) measurements. After compared it with Au anode structure, luminance of the device using dual anode was better than using without Al device. Consequently, Al layers are very good candidates for a promising electron-injecting buffer layer for top emission light-emitting diode (TEOLED).

• Transactions on Electrical and Electronic Materials
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• v.10 no.1
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.345-346
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• 2008

We have studied an emission spectra of top-emssion organic light-emitting diodes(TEOLED) due to a change of cathode and organic layer thickness. Device structure is Al(100nm)/TPD(xnm)/$Alq_3$(ynm)/LiF(0.5nm)/cathode. And two different types of cathode were used; one is LiF(0.5nm)/Al(25nm) and the other is LiF(0.5nm)/Al(2nm)/Ag(30nm). While a thickness of hole-transport layer of TPD was varied from 35 to 65nm, an emissive layer thickness of $Alq_3$ was varied from 50 to 100nm for two devices. A ratio of those two layer was kept to be about 2:3. Al and Al/Ag double layer cathode devices show that the emission spectra were changed from 490nm to 560nm and from 490nm to 560nm, respectively, when the total organic layer increase. Full width at half maximum was changed from 67nm to 49nm and from 90nm to 35nm as the organic layer thickness increases. All devices show that view angle dependent emission spectra show a blue shift. Blue shift is strong when the organic layer thickness is more than 140nm. Devece with Al/Ag double layer cathode is more vivid.

• Vacuum Magazine
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• v.1 no.2
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• pp.19-23
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• 2014

Transparent and top emission organic light-emitting device (OLEDs) are the important issues in realizing new display applications such as see-through electronic displays, and flexible displays. The cathode of the transparent and top emission OLEDs should be transparent in the visible light and should not give any damage to the underlying organic layers, in addition to its intrinsic role of injecting electrons into the organic layers. Several authors have investigated the transparent conducting oxide films prepared by sputtering methods. They have introduced the sophisticated sputtering process for reducing the damages. Other groups have developed thermally evaporated transparent cathodes which are believed to be damage free without causing any permanent defect to the organic layers. This review focuses on the vacuum evaporated damage free transparent cathodes.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.543-544
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• 2008

In the fabrication of inverted top emission organic light emitting diodes (ITOLEDs), the organic layers are damaged by high-energy plasma sputtering process for transparent top anode. In this study, the plasma process induced damages on metal oxide hole injection layers (HILs) including $WO_3$, $MoO_3$, and $V_2O_5$ as buffer layer are examined. With the result of IV characteristic of hole-only devices, we propose that $MoO_3$ and $V_2O_5$ are stable materials against plasma sputtering process.

• ETRI Journal
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• v.45 no.6
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• pp.1056-1064
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• 2023

The optical properties of the materials composing organic light-emitting diodes (OLEDs) are considered when designing the optical structure of OLEDs. Optical design is related to the optical properties, such as the efficiency, emission spectra, and color coordinates of OLED devices because of the microcavity effect in top-emitting OLEDs. In this study, the properties of top-emitting blue OLEDs were optimized by adjusting the thicknesses of the thin metal layer and capping layer (CPL). Deep blue emission was achieved in an OLED structure with a second cavity length, even when the transmittance of the thin metal layer was high. The thin metal film thickness ranges applicable to OLEDs with a second microcavity structure are wide. Instead, the thickness of the thin metal layer determines the optimized thickness of the CPL for high efficiency. A thinner metal layer means that higher efficiency can be obtained in OLED devices with a second microcavity structure. In addition, OLEDs with a thinner metal layer showed less color change as a function of the viewing angle.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.4
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• pp.160-164
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• 2008

Insulating and conducting 12CaO ${\cdot}7Al_2O_3$ (Cl2A7)-doped indium tin oxide (ITO) (ITO:Cl2A7 insulator and electride) thin films were deposited on glass substrates by an RF magnetron co-sputtering method with increasing number of insulating and conducting Cl2A7 target chips. The structural, electrical and optical properties of these films were investigated. The carrier concentration decreased and resistivity increased in the films with increasing number of Cl2A7 target chips. The optical transmittance of all of the thin films was above 80 % in the visible wavelength range. The structural property and surface roughness of the films were examined and the decrease of crystallinity and surface roughness was strongly dependent on the change of grain size.