• Journal of the Korean Applied Science and Technology
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• v.19 no.1
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• pp.68-72
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• 2002

We have seen the effects of buffer layer in organic light-emitting diodes(OLEDs) using poly(N-vinylcarbazole)(PVK) depending on a concentration of PVK. Polymer PVK buffer layer was made using spin casting technique. Two device structures were fabricated; one is ITO/TPD/$Alq_{3}$/Al as a reference, and the other is ITO/PVK/TPD/$Alq_{3}$/Al to see the effects of buffer layer in organic light-emitting diodes. Current-voltage-luminance characteristics and an external quantum efficiency were measured with a variation of spin-casting rpm speeds and PVK concentration. We have obtained an improvement of external quantum efficiency by a factor of four when the PVK concentration is 0.1wt% is used. The improvement of efficiency is expected due to a function of hole-blocking of PVK in OLEDs.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.49-55
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• 2015

This paper reports solution-processed, high-efficiency organic light-emitting diodes (OLEDs) fabricated by a knife coating method under ambient air conditions. In addition, indium tin oxide (ITO), traditionally used as the anode, was substituted by optimizing the conductivity enhancement treatment of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films on a polyethylene terephthalate (PET) substrate. The transmittance and sheet resistance of the optimized PEDOT:PSS anode were 83.4% and $27.8{\Omega}/sq$., respectively. The root mean square surface roughness of the PEDOT:PSS anode, measured by atomic force microscopy, was only 2.95 nm. The optimized OLED device showed a maximum current efficiency and maximum luminous density of 5.44 cd/A and $8,356cd/m^2$, respectively. As a result, the OLEDs created using the PEDOT:PSS anode possessed highly comparable characteristics to those created using ITO anodes.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.837-838
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• 2009

In this work, pyromellitic dianhydride (PMDA) was used as a cathode interfacial layer in the organic light emitting diodes (OLEDs) and its thickness was optimized. Various electrical and optical characterizations of the OLEDs having various thicknesses of the PMDA cathode interfacial layer revealed that the best OLED performance could be achieved by using 0.5 nm-thick PMDA layer compared to the control device without any interfacial layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.184-187
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• 2009

In this paper, we study effect of charge balance on performance of blue phosphorescent organic light emitting diodes (OLEDs). Charge balance determines the location of recombination zone in the OLEDs. By tuning the charge balance in iridium (III) bis[(4,6-difluorophenyl)-pyridinate-N,C2']picolinate (FIrpic) based blue phosphorescent organic light-emitting devices (PHOLEDs) with a high mobility and high triplet energy electron transporting material, we were able to achieve a high current efficiency of 60 cd/A which is a 3X improvement over previous devices with 3,5'-N,N'-dicarbazole-benzene (mCP) host.

• Journal of IKEEE
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• v.24 no.3
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• pp.706-712
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• 2020

To improve light-emitting performance of green phosphorescent organic light-emitting diodes (OLEDs), we introduced new hole injection materials-hexaazatrinaphthylene (HATNA) derivatives as a solution processed hole injection layer (HIL). The HATNA derivative has a low the lowest unoccupied molecular orbital (LUMO) energy level, similar to the work function of Indium Tin Oxide (ITO), showing a different concept of hole injection mechanism. It was confirmed that the device efficiency of OLEDs using HATNA-HIL showed the improved external quantum efficiency from 10.8% to 15.6% and current efficiency from 32.7 cd/A to 42.7 cd/A due to the balance of electrons and holes in the emissive layer.

• Current Optics and Photonics
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• v.6 no.3
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• pp.227-235
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• 2022

To investigate the aging-related physiological functions of organic light-emitting diodes (OLEDs), we examined mRNA expression changes in aging-related genes due to oxidative stress inhibition by 630-nm red light OLEDs. As a result of irradiating 630-nm OLED with an intensity of 5 mW/cm² for 15 min, the viability of dermal fibroblasts significantly increased by 1.3-fold. In addition, reactive oxygen species generated by H₂O₂ were significantly reduced about 4.9-fold by irradiation with 630-nm OLED. Quantitative reverse-transcription polymerase chain reaction results showed that 630-nm OLEDs altered aging-related gene mRNA expression levels through antioxidant activity. The mRNA expression levels of matrix metalloproteinase1 (MMP1) and MMP9 decreased significantly, by about 2.2- and 2.5-fold, compared to the control group, whereas those of collagen, type I, and alpha 1 increased significantly, by 4.9-fold. The mRNA expression levels of cancer suppression genes p16 and p53 in dermal fibroblasts were also significantly reduced by 630-nm OLED irradiation, by about 1.4- and three-fold, respectively, compared to the control. Overall, it was confirmed that 630-nm OLED irradiation lowered the level of ROS formation induced by H₂O₂ in dermal fibroblasts, and that this antioxidant effect could regulate the mRNA expression levels of aging- and tumor suppression-related genes. This study shows a link between 630-nm OLED irradiation and anti-aging physiological functions such as antioxidant function, and suggests the potential of OLEDs as a useful light source for skin care.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.750-753
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• 2002

The chemical vapor condensation process of Parylene-N thin films was investigated and applied to the passivation of the organic light emitting diodes (OLEDs). The effects of process variables on the deposition rate were studied, and it was found that the deposition rate of Parylene increases with increasing precursor sublimation temperature but decreases with increasing substrate temperature. The Parylene film was used as a passivation layer for OLEDs, and as a result, the lifetime of the passivated OLEDs was increased by a factor of about 2.3 compared with that of non-passivated OLEDs.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.69.2-69.2
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• 2012

Graphene films have a strong potential to replace indium tin oxide anodes in organic light-emitting diodes (OLEDs), to date. However, the luminous efficiency of OLEDs with graphene anodes has been limited by a lack of efficient methods to improve the low work function and reduce the sheet resistance of graphene films to the levels required for electrodes. Here, we fabricate flexible OLEDs by modifying the graphene anode to have a high work function and low sheet resistance, and thus achieve extremely high luminous power efficiencies (37.2 lm/W in fluorescent OLEDs, 102.7 lm/W in phosphorescent OLEDs), which are significantly higher than those of optimized devices with an indium tin oxide anode (24.1 lm/W in fluorescent OLEDs, 85.6 lm/W in phosphorescent OLEDs). We also fabricate flexible white OLED lighting devices using the graphene anode. These results demonstrate the great potential of graphene anodes for use in a wide variety of high-performance flexible organic optoelectronics.

• Bulletin of the Korean Chemical Society
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• v.26 no.9
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• pp.1344-1346
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• 2005

We report microcavity effect of top emission organic light-emitting diodes (OLEDs) by using Al cathode and anode, which are feasible for not only top emission EL and angle dependant effects but facile evaporation process without ion sputtering. The device in case of $Alq_3$ green emission showed largely shifted EL maximum wavelength as 650 nm maximum emission. It was also observed that detection angle causes different EL maximum wavelength and different CIE values in R, G, B color emission. As a result, the green device using $Alq_3$ emission showed 650 nm emission ($0^{\circ}$) to 576 nm emission ($90^{\circ}$) as detection angle changed. We believe that these phenomena can be also explained with microcavity effect which depends on the different length of light path caused by detection angle.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.3
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• pp.257-262
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• 2007

Organic light-emitting diodes (OLEDs) with the high efficieney and long lifetime are of growing interest in next-generation displays. Among the factors influencing OLEDs properties, one of unstable factor is $Alq_3$ cationic species caused by the excess holes resided in $Alq_3$ layer. Therefore, we suppressed the accumulation of excess holes by using the mixed-hole transporting layer (MHTL) of NPB and CBP in multilayer green OLEDs. The devices with MHTL showed improved characteristics in the luminous efficiency and lifetime. More characteristics and the carrier transport mechanism will be discussed.