• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.324-325
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• 2006

In order to develop high efficiency white organic light-emitting diodes (OLEDs), OLED devices consisted of red and blue emitting layers (EMLs) were fabricated and the effect of respective layer thickness and the order of layer stacking on the luminous efficiency was evaluated Red/blue structure showed higher efficiency than blue/red, due to the higher exiton formation. In the blue layer of red/blue structure. However, the efficiency of the red/blue significantly depended on the thickness of the red layer, whereas the thickness of the blue layer was not affect so much. The optimum thickness of the red layer was 20 ${\AA}$, where the luminous and power efficiencies were 155 cd/A and 10.51 lm/W at 1000~3000$cd/m^2$ respectively and the maximum luminance was about 80,000 $cd/m^2$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.1
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• pp.15-21
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• 2012

In this study, the characteristics of the 2-wavelength white organic light-emitting diod (WOLED) with two colors of yellow and blue were compared and analyzed with 3-wavelength WOLED with three colors of red, green, and blue. The results indicated that the power efficiency of the 2-wavelength WOLED was 1.6 times higher than 3-wavelength WOLED. In addition, the colot coordinate of the 2-wavelenth WOLED which was (0.34, 0.39) was found closer to the optimal color coordinate for the white-lighting application when compared with that of the 3-wavelength WOLED.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.100-101
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• 2008

We have developed low voltage driving white organic light emitting diode with new electron transport layer. The with light emission was realized with a yellow dopant, rubrene and blue-emitting DPVBi layer. The new electron transport layer results in very high current density at low voltage, causing a reduction of driving voltage. The device with new electron transport layer shows a brightness of 1000 cd/m2 at 4.3 V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.4
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• pp.232-237
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• 2014

We have fabricated white organic light-emitting diodes (OLEDs) by co-doping of red and blue phosphorescent guest emitters into the single host layer. Tris(2-phenyl-1-quinoline) iridium(III) [$Ir(phq)_3$] and iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-$N,C^{2^{\prime}}$]picolinate (FIrpic) were used as red and blue dopants, respectively. The effects of dopant concentration on the emission, carrier conduction and external quantum efficiency characteristics of the devices were investigated. The emissions on the guest emitters were attributed to the energy transfer to the guest emitters and direct excitation by trapping of the carriers on the guest molecules. The white OLED with 5% FIrpic and 2% $Ir(phq)_3$ exhibited a maximum external quantum efficiency of 19.9% and a maximum current efficiency of 45.2 cd/A.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.45-49
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• 2014

We have fabricated white organic light-emitting diodes (OLEDs) using several thicknesses of electron-transport layer. The multi-emission layer structure doped with red and blue phosphorescent guest emitters was used for achieving white emission. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as an electron-transport layer. The thickness of BCP layer was varied to be 20, 55, and 120 nm. The current efficiency, emission and recombination characteristics of multi-layer white OLEDs were investigated. The BCP layer thickness variation results in the shift of emission spectrum due to the recombination zone shift. As the BCP layer thickness increases, the recombination zone shifts toward the electron-transport layer/emission-layer interface. The white OLED with a 55 nm thick BCP layer exhibited a maximum current efficiency of 40.9 cd/A.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.6
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• pp.511-514
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• 2008

2-wavelength type white OLED devices have been made consisted of two layers; a layer with blue light emitting DPVBi host and other EML layer with yellow emitting rubrene dopant. New method to get white emitting device has been suggested by varying thicknesses of the DPVBi layer. The ITO/2-TNATA($150{\AA}$)/NPB($350{\AA}$)/DPVBi($35{\AA}$)/DPVBi:rubrene (2wt%,$200{\AA}$)/DPVBi($100{\AA}$)/Alq_3($50{\AA}$)/LiF($5{\AA}$)/Al($1000{\AA}$) structure has showed optimum results in CIE coordinates of (0.3233, 0.33). OLED devices with this structure has properties of $1.2d/m^2$ at turn-on voltage of 3.9V and $1037cd/m^2$ at 7.9V. This structure has advantages of simple fabrication and easy to emit the white color.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.7
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• pp.616-621
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• 2003

The white-light-emitting organic LED with two-wavelength was fabricated using blue emitting material(DPVBi) and a series of orange color fluorescent dye(Rubrene) by vacuum evaporation processes. The basic structure of white-light-emitting OLED was ITO/NPB(150$\AA$)/DPVBi(150$\AA$)/Alq$_3$:Rubrene(150$\AA$)/BCP(100$\AA$)/Alq$_3$(150$\AA$)/Al(600$\AA$). The changes of the CIE coordiante strongly depended on the doping concentration of Rubrene and the thickness of NPB layer. We obtained the white-light-emitting OLED close to the pure white color light and the CIE coordinate of the device was (0.315, 0.330) at applied voltage of 13V when the doping concentration of Rubrene was 0.5wt% and the thickness of NPB layer is 200$\AA$. At a current of 100mA/$\textrm{cm}^2$, the quantum efficiency was 0.35%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.11
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• pp.910-915
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• 2012

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.% $Bt_2Ir$(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.% $Bt_2Ir$(acac) (25 nm). The maximum brightness, current efficiency, power efficiency, external quantum efficiency, and CIE (x, y) coordinate were 13,430 $cd/m^2$, 40.5 cd/A, 25.3 lm/W, 17 % and (0.49, 0.47) at 1,000 $cd/m^2$, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.274-274
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• 2011

백색 유기발광소자는 일반적으로 적색, 청색 및 녹색의 삼원색을 혼합하여 제작하거나 청색 유기발광소자의 빛을 일부 변환시켜 적색 혹은 녹색을 발생하여 백색을 발광하는 구조를 가진다. 백색을 구현하기 위한 삼원색 조합법은 소자의 구조가 복잡하고 제조단가가 상승하며 제작 된 백색 유기 발광 소자내의 발광 영역을 담당하는 물질의 빠른 열화 때문에 발광 스펙드럼에 변화가 생길 수 있다. 본 연구에서 제안하는 색변환 방법은 최적화된 청색 유기발광소자에서 발광된 빛을 색변환 무기물 형광체 층에 의해 재흡수하고 재발광하는 과정에 의해 빛이 발생되기 때문에 색변환 무기물 형광체 층을 사용한 유기발광소자는 구조가 단순하며 무기물 형광체가 외부노출에 안정하기 때문에 상대적으로 안정된 동작이 가능하다. 청색 유기 발광 소자의 효율이나 휘도를 개선하면 소자의 성능이 향상될 수 있는 구조적 장점이 있다. 그러나 기존에 일반적으로 제조하던 방법인 고상반응법에 의한 형광체입자의 크기는 ${\mu}m$ 이상이며 형태도 불규칙한 단점이 있다. 본 연구에서는 졸겔방법으로 녹색 무기물 형광체 $Zn_2SiO_4:Mn$를 제작하였고 청색 형광 유기 발광 소자에 적용하였다. X-선 회절측정 결과는 형성된 녹색 무기물 형광체내의 Zn 이온이 도핑된 Mn 이온에 대체되었음을 보여주었다. 제작된 진청색 형광 OLED의 전계발광 스펙트럼은 461nm에서 발광 스펙트럼을 나태내고 녹색 무기물 형광체는 470 nm에서 여기되어 Mn 이온의 $^4T_1-^6A_1$ 전이에 의하여 526 nm에서 발광을 한다. 이 과정에서 색변환층의 두께가 0.3 mm 이상일 때 461 nm의 발광스펙트럼의 세기가 급격히 줄어들었다. 이 결과는 제작된 녹색 무기물 형광체를 진청색 유기발광소자와 결합하고 색변환층의 두께를 변화하여 제작된 유기발광소자의 발광색을 조절할 수 있음을 보여주었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.53-56
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• 2007

We have fabricated organic white light emitting diodes by mixing two colors from very thin rubrene doped and non-doped DPVBi layers. The device structure was ITO/2-TNATA(15 nm)/${\alpha}$-NPD(35 nm)/DPVBi:rubrene(5 nm)/DPVBi(30 nm)/$Alq_{3}(5\;nm)$/BCP(5 nm)/LiF(0.5 nm)/Al(150 nm). The yellow-emitting rubrene of 0.7 wt % was doped into the blue-emitting DPVBi host for the white light. CIE coordinate of the device was (0.31, 0.33) at 8 V. The color coordinates were stable at wide ranges of driving voltages. The luminance was over $1,000\;cd/m^{2}$ at 8 V and increases to $14,500\;cd/m^{2}$ at 12 V. The maximum current efficiency of the device was 8.2 cd/A at $200\;cd/m^{2}$.