Sung-Hoo Ju

The Effect of Polymer Thin Film for Sealing Buffer on the Characteristics of OLEO Device

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() 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.

Emission Characteristics of White Organic Light-Emitting Diodes Using Micro Lens Array Film

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with co-doping and blue/co-doping emitting layer (EML) structures were fabricated using a host-dopant system. The total thickness of light-emitting layer was 25 nm and the dopant of blue and red was FIrpic and in UGH3, respectively. In case of co-doping structure, applying micro lens array film showed efficiency improvement from the current efficiency 78.5 cd/A and power efficiency 40.4 lm/W to the current efficiency 131.1 cd/A and power efficiency 65 lm/W and blue / co-doping structure showed efficiency improvement from the current efficiency 43.8 cd/A and power efficiency 22 lm/W to the current efficiency 69 cd/A and power efficiency 32 lm/W.

Life Time Characteristics of OLED Device with AlO x Passivation Film Deposited by RF Magnetron Sputtering

We investigated the life time characteristics of OLED device with aluminium oxide (AlO ) passivation film on glass substrate and polyethylene terephthalate (PET) substrate by RF magnetron sputtering for the transparent barrier film applied to flexible OLED device. Basic buffer layer was determined as Alq (500 nm)LiF(300 nm)-Al(1200 nm), and the most suitable aluminium oxide (AlO ) film have been formed when the partial volume ratio of oxygen was 20% and the sputtering power was 100 watt and the minimum thickness of buffer was 2 µm. AlO /epoxy hybrid film was also used as a effective passivation layer for the purpose of improving life time characteristics of OLED devices with the glass substrate and the plastic substrate. Besides, the simultaneous deposition of AlO /epoxy film on back side of PET could result in better improvement of life time.

The Luminescent Properties of Red OLED Devices Doped with Two Dopants

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 . 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 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.

Emission Characteristics of Blue Fluorescent OLED with Anode Materials

We studied the blue fluorescent OLED with Mg:Ag, Al, Ni as anode materials. Blue fluorescent OLEDs were fabricated using Anode / MoO3 (3 nm) / 2-TNATA (60 nm) / NPB (30 nm) / SH-1 : BD-2 (5 vol.%, 30 nm) / Bphen (40 nm) / Liq (1 nm) / Al (150 nm). Current density of OLED with Mg:Ag was not measured due to too low work function, and that of OLED with Al showed 45.2 mA/cm2 at 12 V. Luminance and Current efficiency of OLED with Al showed 385.1 cd/m2 and 0.9 cd/A. Current density of OLED with Ni of 8, 10, 12 nm thickness showed 10, 12.9, 37.2 mA/cm2, respectively. Luminance and Current efficiency of OLED with Ni of 8, 10, 12 nm thickness showed 670.9, 991.2, 1,320 cd/m2 and 6.7, 7.7, 3.6 cd/A, respectively. Transmittance of Al was 52.2% at 476 nm wavelength and that of Ni of 8, 10, 12 nm thickness was 79, 77, 74 %, respectively. In spite of best current density, OLED with Al showed the lowest luminance and current efficiency because of low work function and poor transmittance. When thickness of Ni was increased to 12nm, current efficiency was sharply lower owing to bad transmittance and unbalance of holes and electrons. Finally, OLED with Ni of 10 nm thicknes showed the highest current efficiency.

Emission Characteristics of Fluorescent OLED with Alternating Current Power Source Driving Method

To operate organic light emitting device (OLED) with alternating current (AC) power source without AC/DC(direct current) converter, we fabricated the fluorescent OLED and measured the emission characteristics with AC and DC. The OLED operated by AC showed higher maximum current efficiency of 8.2 cd/A and maximum power efficiency of 8.3 lm/W. But current efficiency and power efficiency of AC driven OLED showed worse than DC driven OLED at high voltage above 10 V. This result can be explained by the peak voltage of AC was   times than DC, In case of low driving voltage the emission characteristics were improved by the peak voltage of AC, but in case of high driving voltage the emission efficiencies were decreased by the roll off phenomena. Finally, serial OLED arrays using twelve OLEDs driven by AC 110 V showed average voltage of 9.17 V, voltage uniformity of 99.0%, average luminance of 1,175 cd/㎡, luminance uniformity of 94.4%.

Emission Properties of White Organic Light-Emitting Diodes with Blue Emitting Layer

To study emission properties of white phosphorescent organic light emitting devices (PHOLEDs), we fabricated white PHOLEDs of ITO(150 nm) / NPB(30 nm) / TcTa(10 nm) / mCP(7.5 nm) / light-emitting layer(25 nm) / UGH3(5 nm) / Bphen(50 nm) / LiF(0.5 nm) / Al(200 nm) structure. The total thickness of light-emitting layer with co-doping and blue-doping/co-doping using a host-dopant system was 25 nm and the dopant of blue and red was FIrpic and (acac) in UGH3 as host, respectively. The OLED characteristics were changed with position and thickness of blue doping layer and co-doping layer as light-emitting layer and the best performance seemed in structure of blue-doping(5 nm)/co-doping(20 nm) layer. The white PHOLEDs showed the maximum current density of , maximum brightness of , maximum current efficiency of 34.8 cd/A, maximum power efficiency of 21.6 lm/W, maximum quantum efficiency of 15.6%, and a Commission International de L`Eclairage (CIE) coordinate of (0.367, 0.436) at .

Emission Characteristics of White PHOLEDs with Different Emitting Layer Structures

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with red/blue, blue/red and red/blue/red emitting layer (EML) structures were fabricated using a host-dopant system. In case of white PHOLEDs with red/blue structure, the best efficiency was obtained at a structure of red (15 nm)/blue (15 nm). But the emission color was blue-shifted white. In case of white PHOLEDs with blue/red structure, the better color purity and efficiency were observed at a blue (29 nm)/red (1 nm) structure. For additional improvement of color purity in white PHOLEDs with blue (29 nm)/red (1 nm) EMLs, we fabricated white PHOLEDs with red (1 nm)/blue (28 nm)/red (1 nm) structure. The current efficiency, external quantum efficiency, and CIE (x, y) coordinate were 27.2 cd/A, 15.1%, and (0.382, 0.369) at 1,000 , respectively.

Emission Characteristics of White Organic Light-Emitting Diodes Using Ultra Wide Band-gap Phosphorescent Material

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. The best blue emitting OLED and red emitting OLED characteristics were obtained at a concentration of 12 vol.% FIrpic and 1 vol.% (acac) in UGH3, respectively. And the optimum thickness of the total emitting layer was 25 nm. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with red/blue/red, blue/red, red/blue and co-doping emitting layer structures were fabricated using a host-dopant system. In case of white PHOLEDs with co-doping structure, the best efficiency was obtained at a structure UGH3: 12 vol. % FIrpic: 1 vol.% (acac) (25 nm). The maximum brightness, current efficiency, power efficiency, external quantum efficiency, and CIE (x, y) coordinate were 13,430 , 40.5 cd/A, 25.3 lm/W, 17 % and (0.49, 0.47) at 1,000 , respectively.

Encapsulation Method of OLED with Inorganic Multi-layered Thin Films Sealed with Flat Glass

To study encapsulation method for large-area organic light emitting diodes (OLEDs), red emitting OLEDs were fabricated, on which LiF and Al were deposited as inorganic protective films. And then the OLED was attached to flat glass by printing method using epoxy. In case of direct coating of epoxy onto OLED by printing method, luminance and current efficiency were remarkably decreased because of the damage to the OLED by epoxy. In case of depositing LiF and Al as inorganic protective films and then coating of epoxy onto OLED, luminance and current efficiency were not changed. OLED lifetime was more increased through inorganic protective films between OLED and flat glass than that without any encapsulation (8.8 h), i.e., 47 (LiF/Al/epoxy/glass), 62 (LiF/Al/LiF/epoxy/glass), and 84 h (LiF/Al/Al/epoxy/glass). The characteristics of OLED encapsulated with inorganic protective films (attached to flat glass) showed the possibility of application of protective films.