• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.1
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• pp.23-28
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• 2014

In this paper, we discuss on the optimal design scheme of the bilayer OLED (Organic Light Emitting Diodes) with micro-cavity structure. We carried out the optical simulation on the OLED device and calculated optimal scale of devices with taking the micro-cavity effect into account. Our emission model is based upon an ensemble of radiating dipole antennas. Consequently, we applied Maxwell's equation to this sequence, followed by the analysis on the electrical behaviors of OLED device using Poisson's equation. It contains carrier injection and transportation mechanism. In this process, we found out the thickness of each layer can affect the recombination rate at the emission layer. Therefore, we optimized the thickness of each layer to improve the efficiency of the device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.6
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• pp.531-535
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• 2007

To invest the luminescent characteristics of red light emitting OLED device, a dual dopant system was incorporated into the emitting layer. The multiple layer OLED device structure was $ITO(1500\;{\AA})/HIL(200\;{\AA})/a-NPD(600\;{\AA})/EML(300\;{\AA})/Alq_3(200\;{\AA})/LiF(7\;{\AA})/Al(1800\;{\AA})$. The concentrations of the rubrene dopant were tested at 0 vol.%, 3 vol.%, 6 vol.% and 9 vol.%. The maximum device efficiency and life time were obtained at the rubrene dopant concentration of 6 vol.%. Emission spectrum and color coordinate of devices showed no relationship with rubrene dopant concentration. Experiment results show that rubrene dopant absorbs energy from $Alq_3$ host and transfer it to RD1 dopant acting as an energy intermediate and influencing the device efficiency, finally the red light is emitted from the RD1 dopant.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.211-214
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• 2009

In this paper we will outline the opportunities for flexible OLED devices, both for display and solid-state lighting applications. We will present our recent data, and discuss future challenges, for low power consumption phosphorescent OLED technology fabricated on flexible substrates to enable a new generation of energy efficient electronic devices.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.4-6
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• 2003

We have developed the active matrix OLED displays with a high efficiency red emission material which uses an emitting assist (EA) dopant system. The EA dopant (rubrene) did not itself emit but assisted the energy transfer from the host ($Alq_s$) to the red emitting dopant(DCM2). A stable red emission (chromaticity coordinates: x=0.64, y=0.36) was obtained in this cell within the luminance range of 100 - 4000 $cd/m^2$ By using EA dopant system, we can realize the reduction of the power consumption of the OLED display..

• Journal of the Semiconductor & Display Technology
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• v.11 no.1
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• pp.29-33
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• 2012

In this study, we have investigated the structural and electrical characteristics of IZO thin films deposited under hydrogen atmosphere on flexible substrate for the OLED (organic light emitting diodes) devices. For this purpose, PES was used for flexible substrate and IZO thin films were deposited by RF magnetron sputtering under hydrogen ambient gases (Ar, $Ar+H^2$) at room temperature. In order to investigate the influences of the hydrogen, the flow rate of hydrogen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. All the samples show amorphous structure regardless of flow rate. The electrical resistivity of IZO films increased with increasing flow rate of $H^2$ under $Ar+H^2$. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO electrodes made by configuration of IZO/$\acute{a}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show good current density-voltage-luminance characteristics. This suggests that flat surface roughness and low electrical resistivity of a-IZO anode film lead to more efficient anode material in OLED devices.

• Journal of the Korean institute of surface engineering
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• v.41 no.3
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• pp.102-108
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• 2008

In this paper, the LiF and polymer thin film as passivation layer have been evaporated on green OLED devices. HDPE, polyacenaphthylene, polytetrafluoroethylene, poly(2,6-dimethyl-1,4-pheneylene oxide), poly sulfone and poly(dimer-acid-co-alkyl poly-amine) have been used as polymer materials. The optical transmittance of evaporated polymer thin film was very good as an above 90% in visible range. The morphology of polymer thin film was measured by AFM. As a result of the measurement average roughness($R_a$) value of the polysulfone was very low as 2.2 nm. The green OLED devices with a structure of ITO/HIL/HTL/EML/Buffer/Al in series of various passivation films were fabricated and analyzed. It was observed that an OLED device with LiF as first passivation film has shown the good electrical and optical property, and all kind of polymer films did not influence on the I-V-L characteristics and the life time of OLED devices. Therefore, we found that polymer layer played a key role as a buffer layer between the inorganic passivation layers to relieve the stress of the inorganic layers.

• Journal of the Semiconductor & Display Technology
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• v.10 no.3
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• pp.67-74
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• 2011

In this study, we have investigated the effect of the substrate temperature on the structural and the electrical characteristics of IZO thin films for the OLED (organic light emitting diodes) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering under various substrate temperature. The substrate temperature has been changed from room temperature to $400^{\circ}C$. Samples which were deposited under $250^{\circ}C$ show amorphous structure. The electrical resistivity of crystalline-IZO (c-IZO) film was higher than that of amorphous-IZO (a-IZO) film. And the electrical resistivity showed minimum value near $150^{\circ}C$ of deposition temperature. The OLED device was fabricated with different IZO substrates made by configuration of IZO/$\acute{a}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show better current density-voltage-luminance characteristics than that of OLED devices with the commercial crystalline-ITO (c-ITO) anode film. It can be explained that very flat surface roughness and high work function of a-IZO anode film lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers. This suggests that a-IZO film is a promising anode materials substituting conventional c-ITO anode in OLED devices.

• Journal of the Semiconductor & Display Technology
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• v.10 no.2
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• pp.39-44
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• 2011

In this study, we have investigated the structural and electrical characteristics of IZO thin films deposited on flexible substrate for the OLED (organic light emitting diodes) devices. For this purpose, PES was used for flexible substrate and IZO thin films were deposited by RF magnetron sputtering under oxygen ambient gases (Ar, $Ar+O_2$) at room temperature. In order to investigate the influences of the oxygen, the flow rate of oxygen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. All the samples show amorphous structure regardless of flow rate. The electrical resistivity of IZO films increased with increasing flow rate of $O_2$ under $Ar+O_2$. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO electrodes made by configuration of IZO/a-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show better current density-voltage-luminance characteristics than that of OLED devices with the commercial crystalline-ITO (c-ITO) anode film. It can be explained that very flat surface roughness and high work function of a-IZO anode film lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers. This suggests that a-IZO film is a promising anode materials substituting conventional c-ITO anode in OLED devices.

• Journal of the Semiconductor & Display Technology
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• v.9 no.3
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• pp.53-58
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• 2010

In this study, we have investigated the effect of the ambient gases on the characteristics of IZO thin films for the OLED (organic light emitting diodes) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering under various ambient gases (Ar, $Ar+O_2$ and $Ar+H_2$) at $150^{\circ}C$. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0.1sccm to 0.5sccm, respectively. All the samples show amorphous structure regardless of ambient gases. The electrical resistivity of IZO film increased with increasing flow rate of $O_2$ under $Ar+O_2$ while under $Ar+H_2$ atmosphere the electrical resistivity showed minimum value near 0.5sccm of $H_2$. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO substrates made by configuration of IZO/${\alpha}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show better current densityvoltage-luminance characteristics than that of OLED devices with the commercial crystalline-ITO (c-ITO) anode film. It can be explained that very flat surface roughness and high work function of a-IZO anode film lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers. This suggests that a-IZO film is a promising anode materials substituting conventional c-ITO anode in OLED devices.

• Journal of the Korean institute of surface engineering
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• v.46 no.3
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• pp.111-115
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• 2013

To study the encapsulation method for large-area organic light emitting devices (OLEDs), OLED of ITO / 2-TNATA / NPB / $Alq_3$:Rubrene / $Alq_3$ / LiF / Al structure was fabricated, which on $Alq_3$/LiF/Al as protective layer of OLED was deposited to protect the damage of OLED, and subsequently it was encapsulated using attaching film and flat glass. The current density and luminance of encapsulated OLED using attaching film and flat glass has similar characteristics compared with non-encapsulated OLED when thickness of Al as a protective layer was 1200 nm, otherwise power efficiency of encapsulated OLED was better than non-encapsulated OLED. Encapsulation process using attaching film and flat glass did not have any effects on the emission spectrum and the Commission International de L'Eclairage (CIE) coordinate. The lifetime of encapsulated OLED using attaching film and flat glass was 287 hours in 1200 nm Al thickness, which was increased according to thickness of Al protective layer, and was improved 54% compared with 186 hours in same Al thickness, lifetime of encapsulated OLED using epoxy and flat glass. As a result, it showed the improved efficiency and the long lifetime, because the encapsulation method using attaching film and flat glass could minimize the impact on OLED caused through UV hardening process in case of glass encapsulation using epoxy.