• 전자공학회논문지 IE
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• 제43권2호
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• pp.1-6
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• 2006

Two-wavelength에 의한 백색 유기발광소자를 청색계열의 발광재료 DPVBi와 오렌지계열의 발광재료 Rubrene 물질을 사용하여 제작하였다. 소자의 구조는 glass/ITO/TPD$(225{\AA})$/DPVBi/Rubrene/BCP$(210{\AA})/Alq_3(225{\AA})/Al(1000{\AA})$로 하였다. 청색 발광층인 DPVBi와 오렌지색 발광층인 Rubrene층의 두께비율를 변화시켜 가면서 백색광을 구현하였다. 청색발광재료 DPVBi층의 두께가 210${\AA}$ 이고 오렌지색 발광재료의 Rubrene 층의 두께가 180${\AA}$일 때 구동전압 15V에서 $1000cd/m^2$ 휘도와 (0.29, 0.33)의 CIE 색좌표값을 갖는 백색광을 얻었다.

• 한국표면공학회지
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• 제48권3호
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• pp.115-120
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• 2015

We studied white tandem organic light-emitting diodes using red and blue fluorescent materials. White 2 units tandem OLEDs were fabricated using $Alq_3$:Rubrene (3 vol.% 5 nm) and SH-1 : BD-2 (3 vol.% 25 nm) as emitting layer (EML). The device with $Alq_3$ : Rubrene (3 vol.% 5 nm) / SH-1 : BD-2 (3 vol.% 25 nm) showed yellowish white emission with a Commission Internationale de l'Eclairage (CIE) coordinates of (0.442, 0.473) at $1,000cd/m^2$, and variation of CIE coordinates was low with ($0.44{\pm}0.002$, $0.472{\pm}0.001$) from 500 to $3,000cd/m^2$. White 3 units tandem OLEDs were fabricated by additory stacking the blue or white layer as EML. CIE coordinates of 3 units tandem OLEDs with stacked blue and white layer was low variation of ($0.293{\pm}0.008$, $0.36{\pm}0.005$) and ($0.412{\pm}0.002$, $0.423{\pm}0.001$) from 500 to $3,000cd/m^2$, respectively. Our findings suggest that stacked OLED was possible to controlling CIE coordinates and producing excellent color stability.

• 한국안전학회지
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• 제27권4호
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• pp.13-19
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• 2012

The purpose of this study is to extract the major factors related to the deterioration mechanism of white organic light-emitting diodes(WOLED) by performing accelerated testing of temperature, voltage, time, etc., and to develop an accelerated life test(ALT) model. The measurement results of the brightness of the WOLED exhibited that their average brightness tended to increase as the operating voltage increased and that the half-life period of the brightness appeared after approximately 400 hours when the operating voltage was 20V and the ambient temperature was $85^{\circ}C$. It could be seen that although the WOLED showed comparatively the same brightness when the initial acceleration began after the operating voltage was applied to it, its brightness changed excessively after the WOLED's thermal storage had been made. In addition, it was observed that the half-life period was reduced as the ambient temperature and applied voltage increased. The strength of the WOLED which had been maintained in the range of visible light at the maximum load was reduced by the deterioration of the organic light emitting material due to the influence of the operating voltage and temperature, and the reduction of emitted light was small at low voltage and temperature. It could be seen that the failure of the WOLED during the ALT was caused by wear due to load accumulation over time, and that Weibull distribution was appropriate for the life distribution and acceleration was established between test conditions. From the WOLED analysis, it is thought that factors influencing the brightness deterioration are voltage, temperature, etc., and that comprehensive analysis considering discharge control, dielectric tangent margin, etc., would further increase the reliability.

• 한국표면공학회지
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• 제49권2호
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• pp.196-201
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• 2016

We studied white tandem organic light-emitting diodes using blue and red phosphorescent materials. Optimized white single phosphorescent OLED was fabricated using CBP : FIrpic (12 vol.%, 9 nm) / CBP : $Ir(mphmq)_2acac$ : $Ir(ppy)_3$ (1 vol.%, 1 vol.%, 1 nm) as emitting layer (EML). The single phosphorescent OLED showed maximum current efficiency of 22.5 cd/A, white emission with a Commission Internationale de l'Eclairage (CIE) coordinates of (0.342, 0.37) at $1,000cd/m^2$, and variation of CIE coordinates with ($0.339{\pm}0.008$, $0.371{\pm}0.001$) from 500 to $3,000cd/m^2$. Optimized white tandem phosphorescent OLED was fabricated using CBP : FIrpic (12 vol.%, 7 nm) / CBP : $Ir(mphmq)_2acac$ : $Ir(ppy)_3$ (1 vol.%, 1 vol.%, 3 nm) as EML. The tandem phosphorescent OLED showed maximum current efficiency of 49.2 cd/A, white emission with a CIE coordinates of (0.376, 0.366) at $1,000cd/m^2$, variation of CIE coordinates with ($0.375{\pm}0.004$, $0.367{\pm}0.002$) from 500 to $3,000cd/m^2$. Maximum current efficiency of tandem phosphorescent OLED was more twice as high as single phosphorescent OLED. Our results suggest that tandem phosphorescent OLED was possible to control CIE coordinates and produce excellent color stability.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2006년도 춘계학술발표회 초록집
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• pp.138-138
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• 2006

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.65-65
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• 2015

In this talk, I will introduce two topics. The first topic is the polymer light emitting diodes (PLEDs) using graphene oxide quantum dots as emissive center. More specifically, the energy transfer mechanism as well as the origin of white electroluminescence in the PLED were investigated. The second topic is the facile synthesis of eco-friendly III-V colloidal quantum dots and their application to light emitting diodes. Polymer (organic) light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nanomaterial without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence (EL) from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions. (Sci Rep., 5, 11032, 2015). New III-V colloidal quantum dots (CQDs) were synthesized using the hot-injection method and the QD-light emitting diodes (QLEDs) using these CQDs as emissive layer were demonstrated for the first time. The band gaps of the III-V CQDs were varied by varying the metal fraction and by particle size control. The X-ray absorption fine structure (XAFS) results show that the crystal states of the III-V CQDs consist of multi-phase states; multi-peak photoluminescence (PL) resulted from these multi-phase states. Inverted structured QLED shows green EL emission and a maximum luminance of ~45 cd/m2. This result shows that III-V CQDs can be a good substitute for conventional cadmium-containing CQDs in various opto-electronic applications, e.g., eco-friendly displays. (Un-published results).

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.482-485
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• 2009

We have fabricated transparent white organic light emitting diodes (WOLEDs) for lighting application. The structure property relationship of hybrid WOLEDs has been investigated and optimized devices showed high efficiency. Introduction of transparent cathode of LiF/Al/Ag into the hybrid WOLED led highly efficient WOLED with good transparency.

• 한국전기전자재료학회논문지
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• 제27권9호
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• pp.571-575
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• 2014

We synthesized new materials of $Zn(HPB)_2$ and Ir-complexes as blue or red emitting material. We fabricated white Organic Light Emitting Diodes (OLED) by using $Zn(HPB)_2$ for the blue emitting layer, Ir-complexes for the red emitting layer and $Alq_3$ for the green emitting layer. We fabricated white OLED by using double emitting layers of $Zn(HPB)_2$:Ir-complexes and $Alq_3$. The doping rate of Ir-complexes was varied, such as 0.2%, 0.4%, 0.6%, and 0.8%, respectively. When the doping rate of $Zn(HPB)_2$:Ir-complexes was 0.6%, white emission was achieved. The Commission Internationale de l'Eclairage (CIE) coordinates of the white emission was (0.322, 0.312).

• 한국전기전자재료학회논문지
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• 제27권12호
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• pp.837-840
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• 2014

Novel materials of $Zn(HPB)_2$ and Ir-complexes were respectively synthesized as blue or red emitting material. White Organic Light Emitting Diodes (OLED) were fabricated by using $Zn(HPB)_2$ for a blue emitting layer, Ir-complexes for a red emitting layer and $Alq_3$ for a green emitting layer. White OLED was fabricated by using double emitting layers of $Zn(HPB)_2$ and $Alq_3:Ir$-complexes, and hole blocking layer of BCP. We also varied the thickness of BCP. When the thickness of BCP layer was 5 nm, white emission was achieved. We obtained a maximum luminance of $3,500cd/m^2$. The CIE coordinates was (0.375, 0.331). From this study, we could propose that the hybrid structure is efficient in lighting application of white OLED by improvement of color purity.

• 한국전기전자재료학회논문지
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• 제20권1호
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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 $200\;cd/m^{2}$.