• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.4
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• pp.397-402
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• 2023

We have developed inverted green phosphorescent organic light emitting diodes (OLEDs) using 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and bis(carbazole-9-yl)biphenyl (CBP) hole transport layers. The driving voltage, current efficiency, power efficiency, and emission characteristics of devices were investigated. While the driving voltage for the same current density was about 1~2 V lower in the devices with the TAPC layer, the maximum luminance was higher in the device with the CBP layer. The maximum current efficiency and power efficiency were 3.2 and 2.7 times higher in the device with the CBP layer, respectively. The higher efficiency in the CBP device resulted from the enhanced hole-electron balance although weak parasitic recombination takes place in the CBP hole transport layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.983-987
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• 2010

In order to investigate the emission characteristics of the phosphorescent white organic light-emitting diodes (PHWOLEDs) according to various hole transport layers (HTLs), PHWOLEDs composed of HTLs whose structure are NPB/TCTA, NPB/mCP and NPB/TCTA/mCP, two emissive layers (EMLs) which emit two-wavelengths of light (blue and red), and electron transport layer were fabricated. The applied voltage, power efficiency, and external quantum efficiency at a current density of $1 mA/cm^2$ for the fabricated PHWOLEDs were 7.5 V, 11.5 lm/W, and 15%, in case of NPB/mCP, 5 V, 14.8 lm/W, and 13.7%, in case of NPB/TCTA, and 5.5 V, 14.6 lm/W, and 15%, in case of NPB/TCTA/mCP in the hole transport layer, respectively. High emission efficiency can be obtained when the amount of hole injection from anode is balanced out by the amount of electron injection from the cathode to EML by using NPB/TCTA/mCP structured HTL.

• Korean Journal of Materials Research
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• v.20 no.6
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• pp.294-300
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• 2010

In this study, we fabricated a polymer light emitting diode (PLED) and investigated its electrical and optical characteristics in order to examine the effects of the PFO [poly(9,9-dioctylfluorene-2-7-diyl) end capped with N,N-bis(4-methylphenyl)-4-aniline] concentrations in the emission layer (EML). The PFO polymer was dissolved in toluene ranging from 0.2 to 1.2 wt%, and then spin-coated. To verify the influence of the TPBI [2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)]electron transport layer, TPBI small molecules were deposited by thermal evaporation. The current density, luminance, wavelength and current efficiency characteristics of the prepared PLED devices with and without TPBI layer at various PFO concentrations were measured and compared. The luminance and current efficiency of the PLED devices without TPBI layer were increased, from 117 to $553\;cd/m^2$ and from 0.015 to 0.110 cd/A, as the PFO concentration increased from 0.2 to 1.0 wt%. For the PLED devices with TPBI layer, the luminance and current efficiency were $1724\;cd/m^2$ and 0.501 cd/A at 1.0 wt% PFO concentration. The CIE color coordinators of the PLED device with TPBI layer at 1.0 wt% PFO concentration showed a more pure blue color compared with the one without TPBI, and the CIE values varied from (x, y) = (0.21, 0.23) to (x, y) = (0.16, 0.11).

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1103-1107
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• 2007

Highly efficient organic electroluminescent devices (OLEDs) based on 4,7- diphenyl-1, 10- phenanthroline (BPhen) as the electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum ($Alq_3$) as the emission layer (EML) and N,$\acute{N}$-bis-[1-naphthy(-N,$\acute{N}$diphenyl-1,1´-biphenyl-4,4´-diamine)] (NPB) as the hole transport layer (HTL) were developed. The typical device structure was glass substrate/ ITO/ NPB/$Alq_3$/ BPhen/ LiF/ Al. Since BPhen possesses a considerable high electron mobility of $5\;{\times}\;10^{-4}\;cm^2\;V^{-1}\;s^{-1}$, devices with BPhen as ETL can realize an extremely high luminous efficiency. By optimizing the thickness of both HTL and ETL, we obtained a highly efficient OLED with a current efficiency of 6.80 cd/A and luminance of $1361\;cd/m^2$ at a current density of $20\;mA/cm^2$. This dramatic improvement in the current efficiency has been explained on the principle of charge balance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.3
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• pp.151-155
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• 2014

We have developed quantum dot light emitting diodes (QD-LEDs) using a InP/ZnSe/ZnS multi-shell QD emission layer. The hybrid structure of organic hole transport layer/QD/organic electron transport layer was used for fabricating QD-LEDs. Poly(4-butylphenyl-diphenyl-amine) (poly-TPD) and tris[2,4,6-trimethyl-3-(pyridin-3-yl)phenyl]borane (3TPYMB) molecules were used as hole-transporting and electron-transporting layers, respectively. The emission, current efficiency, and driving characteristics of QD-LEDs with 50, 65 nm thick 3TPYMB layers were investigated. The QD-LED with a 50 nm thick 3TPYMB layer exhibited a maximum current efficiency of 1.3 cd/A.

• Advances in Energy Research
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• v.4 no.4
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• pp.275-284
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• 2016

In the present work, ZnO nanoparticles (NPs) have been dispersed alone in the same solvent of the active layer for improving performance parameters of the organic solar cells. Different concentrations of the ZnO NPs have been blended inside active layer of the solar cell based on poly(3-hexylthiophene) (P3HT), which forms the hole-transport network, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which forms the electron-transport network. In the present investigations, the ZnO NPs may represent an efficient tool for improving light harvesting through light scattering inside active layer, electron mobility, and electron acceptance strength which tend to improve photocurrent and performance parameters of the investigated solar cell. The fill factor (FF) of the ZnO-doped solar cell increases nearly 14% compared to the non-doped solar cell when the doping is 50%. The present investigations show that ZnO NPs improve power conversion efficiency of the solar cell from 1.23% to 1.64% with increment around 25% that takes place after incorporation of 40% as a volume ratio of the ZnO NPs inside P3HT:PCBM active layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.3
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• pp.309-313
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• 2024

The key to determining the lifetime of OLED device is how much brightness can be maintained. It can be said that there are internal and external causes for the degradation of OLED devices. The most important cause of internal degradation is bonding and degradation in the excited state due to the electrochemical instability of organic materials. The structure of OLED modeled in this paper consists of a cathode layer, electron injection layer (EIL), electron transport layer (ETL), light emission layer, hole transport layer (HTL), hole injection layer (HIL), and anode layer on a glass substrate from top to bottom. It was confirmed that the temperature generated in OLED was distributed around the maximum of 343.15 K centered on the emission layer. It can be seen that the heat distribution generated in the presented OLED structure has an asymmetrically high temperature distribution toward the cathode, which is believed to be because the sizes of the cathode and positive electrode are asymmetric. Therefore, when designing OLED, it is believed that designing the structures of the cathode and anode electrodes as symmetrically as possible can ensure uniform heat distribution, maintain uniform luminance of OLED, and extend the lifetime. The thermal distribution of OLED was analyzed using the finite element method according to Comsol 5.2.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.311-312
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• 2010

The fabricated photovoltaic cells based on PIN heterojunctions, in this study, have a structure of ITO/poly(3, 4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)/donor/donor:C60(10nm)/C60(35nm)/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline(8nm)/Al(100nm). The thicknesses of an active layer(donor:C60), an electron transport layer(C60), and hole/exciton blocking layer(BCP) were fixed in the organic photovoltaic cells. We investigated the performance characteristics of the PIN organic photovoltaic cells with copper phthalocyanine(CuPc), tetracene and pentacene as a hole transport layer. Discussion on the photovoltaic cells with CuPc, tetracene and pentacene as a hole transport layer is focussed on the dependency of the power conversion efficiency on the deposition rate and thickness of hole transport layer. The device performance characteristics are elucidated from open-circuit-voltage(Voc), short-circuit-current(Jsc), fill factor(FF), and power conversion efficiency($\eta$). As the deposition rate of donor is reduced, the power conversion efficiency is enhanced by increased short-circuit-current(Jsc). The CuPc-based PIN photovoltaic cell has the limited dependency of power conversion efficiency on the thickness of hole transport layer because of relatively short exciton diffusion length. The photovoltaic cell using tetracene as a hole transport layer, which has relatively long diffusion length, has low efficiency. The maximum power conversion efficiencies of CuPc, tetracene, and pentacene-based photovoltaic cells with optimized deposition rate and thickness of hole transport layer have been achieved to 1.63%, 1.33% and 2.15%, respectively. The photovoltaic cell using pentacene as a hole transport layer showed the highest efficiency because of dramatically enhanced Jsc due to long diffusion length and strong thickness dependence.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.3
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• pp.69-72
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• 2020

In this study, the inverted structured electroluminescence (EL) devices were fabricated with double electron transport layers (ETLs). The conduction band minimum (CBM) of TiO₂ NPs is lower than SnO₂ NPs. Therefore, it is expected that inserting TiO₂ NPs between the SnO₂ layer and the emission layer (EML) will reduce the energy barrier and transport electrons smoothly. The quantum dot light emitting diodes (QLEDs) with double ETLs showed the enhanced emission characteristics than those with only SnO₂ layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04a
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• pp.37-38
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• 2008

In this paper, we have developed Organic light-emitting devices(OLEDs) using various thicknesses of new electron transport layer. The device structure of ITO/ 2-TNATA(15nm)/ DPVBi(40nm)/ New ETL(20nm,60nm,100nm)/ LiF(0.5nm)/Al(100nm) has been used. The operating voltage of the device was almost independent of the new ETL thickness, due to its high electron conducting property. For example, the operating voltages of the devices with 20nm and 60nm layers are almost 5V at a current density $200mA/cm^2$. The device with the new ETL shows the low turn-on of 2.5V.