Imprinted Microlens Array Films for Efficient Down-Conversion White Organic Light-Emitting Diodes

홍주희,한주원,김용현 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

White organic light-emitting diodes (OLEDs) have attracted considerable attention due to their important applications in flat panel displays, general lighting. The biggest challenge of conventional OLEDs is the limited light outcoupling efficiency about 20 % while the internal quantum efficiency of OLEDs approaches almost 100 %. In this work, we develop a high performance down-conversion microlens array (DC-MLA) films for white OLEDs. The DC-MLA films are fabricated by a soft imprinting method with breath figure patterns, which are low-cost, simple and quick solution process. Blue OLEDs employing the DC-MLA films exhibit highly enhanced light outcoupling efficiency and high quality of white light. The DC-MLA films improve the external quantum efficiency (EQE) of white OLEDs by a factor of 1.45. In addition, high quality white light with a color rendering index of 84.3 is achieved for the white OLEDs with DC-MLA films.

ITO 표면 처리와 음전극 변화에 따른 OLEDs의 특성 연구

김두석,장윤기,권영수,Kim, Doo-Seok,Jang, Yoon-Ki,Kwon, Young-Soo 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.12

In this study, we report an improved efficiency of Organic light emitting diodes(OLEDs), using $UV/O_3$ treated anode and different cathode. We investigated the efficiency of OLEDs by $UV/O_3$ treatment of ITO surface. We Performed $UV/O_3$ treatment and found that $UV/O_3$ treatment enhanced the performance of OLEDs. The fundamental structure of the OLEDs was ITO $anode/{\alpha}-NPD/Alq_3/Al$ or Li:Al cathode. The Li:Al can improve the OLEDs efficiency dramatically in cathode because it has lower work function than Al. Current-voltage, Luminance-voltage characteristics and luminance efficiency were measured at room temperature.

Light Extraction Structures Based on Nanoparticle-Embedded Hole Transport Layers for Organic Light-Emitting Diodes

이동진,김진희,김용현 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

Organic light-emitting diodes (OLEDs) have attracted considerable attention as a next-generation lighting. Their enhanced organic materials and device structures have led to highly enhanced efficiency and lifetime. However, the biggest challenge of conventional OLEDs is the limited light outcoupling efficiency about 20 % while the internal quantum efficiency of OLEDs approaches almost 100 %. In this work, we report enhanced light outcoupling efficiency in solution-processed organic light emitting diodes by using a nanoparticle-embedded hole transport layer (HTL), which results in corrugated surface of HTLs. Solution-processed green OLEDs with corrugated HTLs exhibit the highly enhanced light outcoupling efficiency due to reduced total internal reflection in layers. We expect that the solution-processable nanoparticle-embedded hole transport layer can be a simple, costeffective approach to realize high performance OLEDs.

전기-광 변환소자 응용을 위한 적색 유기 EL 소자의 광변조 특성

김주승,구할본,Kim, Ju-Seung,Gu, Hal-Bon 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.6

We fabricated red organic light emitting diodes(OLEDs) utilizing tis(8-hydroxyquinoline) aluminum $(Alq_3)$ doped with $5\%$ of (4-(dicyanomethylene)-2-i-propyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran) (DCJTI) and investigated the driving and modulation characteristics for applying to the electro-optical conversion device. To improve the driving characteristics of red OLEDs, 3 V of offset voltage, which is equal to the turn on voltage, Is applied to the device. Offset voltage enhanced the optical EL output and reduced the rise time of EL waveforms of red OLEDs, and hence the cutoff frequency is increased with increasing applied voltage. The optical pulse of 100 MHz has been obtained from red OLEDs. Therefore, we confirmed that the red OLEDs can be applied to the fields of optical communication as an electro-optical conversion device.

Electrical Characteristics of Green Emitting Phosphor $Ir(PPY)_3$ Doped OLEDs

Kim, Jun-Ho,Kim, Yun-Myung,Ha, Yun-Kyung,Kim, Young-Kwan,Kim, Jung-Soo The Korean Institute of Electrical Engineers 2001 KIEE International Transactions on Electrophysics Vol.11C No.3

The organic light-emitting devices (OLEDs) based on fluorescence have low efficiency due to the requirement of spin-symmetry conservation. By using the phosphorescent material, internal quantum efficiency can reach 100%, compared with 25% in the case of the fluorescent material. Thus, phosphorescent OLEDs have recently been extensively studied and shown higher internal quantum efficiency than the conventional OLEDs. In this study, we investigated the characteristics of the phosphorescent OLEDs with the green emitting phosphor, $Ir(ppy)_3$ (tris(2-phenylpyridine)iridium). The device with a structure of ITO/TPD$Ir(ppy)_3$ doped in BCP/BCP/$Alq_3$/Li:Al/Al was fabricated, and its electrical and optical characteristics were studied. By changing the doping concentration of $Ir(ppy)_3$, we fabricated several devices and investigated their characteristics.

Efficient tandem organic light-emitting diode with fluorinated hexaazatrinaphthylene charge generation layer

Gunel Huseynova,Jae Hyun Lee,Akpeko Gasonoo,이현구,Yong Hyun Kim,Jonghee Lee 한국정보디스플레이학회 2022 Journal of information display Vol.23 No.4

We present the fluorinated hexaazatrinaphthylene derivative, 1,2,3,4,7,8,9,10,13,14,15,16- dodecafluoro-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-F12), as a new material to replace another hexaazatrinaphthylene molecule, 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HATCN), which is widely used as an intermediate connector and charge generation layer (CGL) in tandem organic light-emitting diodes (OLEDs). Upon comparison with the reference single emitting layer unit OLED, the tandem device with HATNA-F12 CGL had improved current efficiency and external quantum efficiency of 42.1% and 41.7%, respectively. Our results show that HATNA-F12 is an excellent substitute for HAT-CN and has more promising characteristics as a CGL material for applications in tandem OLEDs. When compared to devices with HAT-CN CGL, the green tandem OLEDs with CGL consisting of HATNA-F12 demonstrated improved current efficiency, power efficacy, and external quantum efficiency values, while the change of the CGL material had almost no effect on the operating voltage, current density, and color coordinates of the OLEDs. We confirm that using the newly suggested HATNA-F12 molecule as a CGL in these OLEDs can enhance device efficiency.

Exciplex hosts for blue phosphorescent organic light-emitting diodes

Mina Jung,Jun Yeob Lee 한국정보디스플레이학회 2020 Journal of information display Vol.21 No.1

The host material of organic light-emitting diodes (OLEDs) has been advanced from a single host to a mixed host for high efficiency and long lifetime. Several types of mixed host have been reported in the literature, but the exciplex host has been popular as the mixed host of OLEDs. The exciplex host has been developed mostly for red and green phosphorescent OLEDs, and has upgraded device performances, but it is difficult to develop the exciplex host for blue phosphorescent OLEDs. Recently, several works demonstrated the potential of the exciplex host for blue phosphorescent OLEDs. In this paper, the exciplex host for blue OLEDs is reviewed, and its prospects are presented.

Effects of surface treatment of ITO anode layer patterned with shadow mask technology on characteristics of organic light-emitting diodes

Park, C.Y.,Lee, J.H.,Choi, B.H. Elsevier Science 2013 Organic electronics Vol.14 No.12

We investigated the effects of various surface treatments of indium tin oxide (ITO) on the electrical and optical characteristics of organic light-emitting diodes (OLEDs). A 150-nm-thick ITO anode layer was patterned directly with a shadow mask during the sputtering process without the use of a conventional photolithography patterning method. The sputtered ITO layer was subjected to thermal and oxygen plasma treatments to reduce the sheet resistance and improve surface roughness. The thermal treatment was performed for 1h at temperatures of 250 and 380<SUP>o</SUP>C, which were chosen so that the glass substrates would not deform from thermal damage. The measured sheet resistance decreased from 30.86Ω/sq for the as-sputtered samples to 8.76Ω/sq for the samples thermally treated at 380<SUP>o</SUP>C for 1h followed by oxygen plasma treatment. The root-mean-square surface roughness measured by atomic force microscopy considerably decreased to 3.88nm with oxygen plasma treatment. The thermal treatment considerably decreased the sheet resistance of the ITO anode layer patterned with the shadow mask. The spike-like structures that are often formed and observed in shadow mask-patterned ITO anode layers were almost all removed by the oxygen plasma treatment. Therefore, a smooth surface for shadow mask-patterned ITO layers with low sheet resistance can be obtained by combining thermal and oxygen plasma treatments. A smooth surface and low sheet resistance improves the electrical and optical characteristics of OLEDs. The surface-treated ITO layer was used to fabricate and characterize green phosphorescent OLED devices. The typical characteristics of OLED devices based on surface-treated shadow mask-patterned ITO layers were compared with those fabricated on untreated and photolithography-patterned ITO layers to investigate the surface treatment effects. The OLED devices fabricated by thermal treatment at 380<SUP>o</SUP>C for 1h followed by oxygen plasma treatment for 180s showed the highest luminance and current density. Furthermore, the leakage current that might be induced by the rough ITO surface was dramatically reduced to 0.112mA/cm<SUP>2</SUP>. Our study showed that the shadow mask-patterned ITO anode layer treated by heat and plasma and having a low sheet resistance and surface roughness yielded excellent electrical and optical properties for OLEDs compared to those based on an untreated ITO layer. The fabricated OLED devices using the surface-treated shadow mask-patterned ITO layer exhibited comparable characteristics to those obtained from a conventional photolithography-patterned ITO anode.

Straight-forward control of the degree of micro-cavity effects in organic light-emitting diodes based on a thin striped metal layer

Lee, J.,Cho, H.,Koh, T.W.,Hofmann, S.,Kim, Y.H.,Yun, C.,Schwab, T.,Reineke, S.,Lussem, B.,Lee, J.I.,Yoo, S.,Leo, K.,Gather, M.C. Elsevier Science 2013 Organic electronics Vol.14 No.10

We investigated the control of micro-cavity (MC) effects in organic light-emitting diodes (OLEDs) with the introduction of a striped thin metal layer between the indium tin oxide (ITO) layer and the hole transporting layer (HTL). With an enhanced MC effect obtained through the inserted metal layer, the forward emission of the OLED became stronger and the angular distribution became more forward-directed, leading to a current efficiency (CE) that was nearly 1.45times higher than that of the reference device without the inserted metal layer. The net CE of the OLEDs with a striped metal layer was found to be determined by the area-weighted average of the CE's of full-cavity-enhanced OLEDs and non-cavity OLEDs. It was also observed that the trade-off between resonance enhancement in efficiency and angle-dependent color stability, often found problematic in MC-based OLEDs, could be mitigated in a straight-forward manner by changing the relative portion of the metal-covered area.

Twin Target Sputtering System with Ladder Type Magnet Array for Direct Al Cathode Sputtering on Organic Light Emitting Diodes

Moon, Jong-Min,Kim, Han-Ki The Korean Infomation Display Society 2007 Journal of information display Vol.8 No.3

Twin target sputtering (TTS) system with a configuration of vertically parallel facing Al targets and a substrate holder perpendicular to the Al target plane has been designed to realize a direct Al cathode sputtering on organic light emitting diodes (OLEDs). The TTS system has a linear twin target gun with ladder type magnet array for effective and uniform confinement of high density plasma. It is shown that OLEDs with Al cathode deposited by the TTS show a relatvely lower leakage current density $({\sim}1{\times}10^{-5}mA/cm^2)$ at reverse bias of -6V, compared to that ($1{\times}10^{-2}{\sim}10^{-3}$ $mA/cm^2$ at -6V) of OLEDs with Al cathodes grown by conventional DC magnetron sputtering. In addition, it was found that Al cathode films prepared by TTS were amorphous structure with nanocrystallines due to low substrate temperature. This demonstrates that there is no plasma damage caused by the bombardment of energetic particles. This indicates that the TTS system with ladder type magnet array could be useful plasma damage free deposition technique for direct Al cathode sputtering on OLEDs or flexible OLEDs.