• Applied Chemistry for Engineering
• /
• v.25 no.3
• /
• pp.233-236
• /
• 2014

Organic light emitting diodes (OLEDs) received much attention from both academia and industry as the next-generation flat panel displays. However, to produce high quality OLEDs, there are still many challenges to overcome. Especially, in full color OLEDs, the intrinsic wide band gap of the blue emitting materials results in inferior efficiency compared to those of green and red emitting materials. Therefore, extensive research efforts have been devoted to develop efficient blue emitting materials. This review briefly summarizes the basics of OLEDs and introduces highlights of research efforts in blue-emitting materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.7
• /
• pp.486-489
• /
• 2018

Solution-processed organic light-emitting diodes (OLEDs) have the advantages of low cost, fast fabrication, and large-area devices. However, most studies on solution-processed OLEDs have mainly focused on solution-processable hole transporting materials or emissive materials. Here, we report fully solution-processed green OLEDs including hole/electron transport layers and emissive layers. The electrical and optical properties of OLEDs based on solution-processed TPBi (2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) as the electron transport layer were investigated with respect to the spin speed and the number of layers. The performance of OLEDs with solution-processed TPBi exhibits a power efficiency of 9.4 lm/W. We believe that the solution-processed electron transport layers can contribute to the development of efficient fully solution-processed multilayered OLEDs.

• Proceedings of the IEEK Conference
• /
• 2000.11b
• /
• pp.261-264
• /
• 2000

Organic light emitting diodes(OLEDs) have been expected to find an application as a new type of display since C. W. Tang and VanSlyke first reported on high performance OLEDs. This paper has been stuied a green organic EL device using dye doped emitting layer such as C6(Coumarin 6). In the Alq-based e]ectroluminescence diodes, we applied highly fluorescent molecular(Coumarin 6) and obtained enhancement in the electroluminescence efficiency.

• Applied Chemistry for Engineering
• /
• v.26 no.6
• /
• pp.725-729
• /
• 2015

Organic light emitting diodes (OLEDs) are regarded as the next generation display and solid-state lighting due to their superb achievements from extensive research efforts on improving the efficiency and stability of OLEDs in addition to developing new materials. Herein, efficient green phosphorescent OLEDs were obtained by using hexaazatrinaphthylene (HAT) derivatives as a hole injection layer. External quantum and current efficiencies of OLEDs were enhanced from 8.8% and 30.8 cd/A to 13.6% and 47.7 cd/A, respectively by inserting a thin layer of HAT derivatives between the ITO and hole transporting layer. The enhancement of OLEDs was found to be originated from the inserted HAT derivatives, which resulted in the optimized hole-electron balance inside the emission layer.

• Bulletin of the Korean Chemical Society
• /
• v.26 no.9
• /
• pp.1344-1346
• /
• 2005

We report microcavity effect of top emission organic light-emitting diodes (OLEDs) by using Al cathode and anode, which are feasible for not only top emission EL and angle dependant effects but facile evaporation process without ion sputtering. The device in case of $Alq_3$ green emission showed largely shifted EL maximum wavelength as 650 nm maximum emission. It was also observed that detection angle causes different EL maximum wavelength and different CIE values in R, G, B color emission. As a result, the green device using $Alq_3$ emission showed 650 nm emission ($0^{\circ}$) to 576 nm emission ($90^{\circ}$) as detection angle changed. We believe that these phenomena can be also explained with microcavity effect which depends on the different length of light path caused by detection angle.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2003.07a
• /
• pp.901-902
• /
• 2003

Three-color organic light-emitting diodes (OLEDs) of metal-semiconductor-metal (MSM) structure have been favricated by using m-MTDATA [4,4',4"-tris (3-methylphenylphenylamino) triphenylamine] as hole injection layer(HIL). The mMTDATA is shown to be an effective hole injecting material, in that the insertion of mMTDATA greatly reduces the roughness of anode surface and improves the device performance. Red, green and blue OLEDs were fabricated, and their color coordinates in CIE chromaticity were found to be (0.600, 0.389), (0.240, 0.525), and (0.171, 0.171), respectively. The luminous efficiencies of the fabricated OLEDs were 1.4 lm/W at 106 $cd/m^{2}$ for red, 1.4 lm/W at 100 $cd/m^{2}$ for green, and 2.0 lm/W at 104 $cd/m^{2}$ for blue.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2006.08a
• /
• pp.1813-1818
• /
• 2006

We demonstrate a new approach to form gradient hole injection layer (HIL) in organic light-emitting diodes (OLEDs). Single spincoating of hole-injecting conducting polymer compositions with a perfluorinated ionomer results in gradient workfunction through the layer by self-organization, which lead to remarkably efficient single layer polymer light-emitting diodes (PLEDs) (${\sim}21$ cd/A). The device lifetime was significantly improved (${\sim50$ times) compared with the conventional hole injection layer, poly(3,4-ethylenedioxy-thiophene)/polystyrene sulfonate. This solution processed HIL also produced dramatically enhanced luminous efficiency (${\sim}34$ cd/A) in vacuum- deposited green fluorescent OLEDs while the vacuum deposited HIL gave the luminous efficiency of ${\sim}23$ cd/A in the same device structure.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2009.10a
• /
• pp.787-790
• /
• 2009

High contrast red, green and blue organic light-emitting diodes were fabricated using inorganic metal multi layer composed of thin Al, KCl and thick Al and then were compared to optical and electrical characteristics with the attached polarizer and conventional OLEDs. Ambient light reflection of OLED using inorganic metal layer, polarizer and conventional metal layer were 29.2, 31.1 and 82.5% respectively. Optical characteristics of OLEDs using inorganic metal layer were max luminescence of 13040 cd/m2 and luminous efficiency of 2.12 cd/A at 8V whereas OLEDs using polarizer has 8456 cd/m2 and 1.43 cd/A at 8V each. OLEDs including inorganic metal multi layers show significant technical advantages in achieving high performance of OLED display with improved contrast ratio of 251:1, specifically in Red OLED.

• Journal of the Microelectronics and Packaging Society
• /
• v.23 no.1
• /
• pp.11-15
• /
• 2016

The organic light emitting diodes (OLEDs) have been studied as large flexible displays, light source and hard wares of internet of things. However, OLEDs show some drawbacks in terms of external environments due to the low work function of the metals and the reactive organic materials. In particular, the operation functions of the OLEDs tend to deteriorate rapidly by exposing the oxygen and moisture. So as to prevent it, domestic and overseas studies underway in various method such as ALD, PVD, CVD. But it has complex process and high cost. Therefore In order to protect devices from the external environments, it is important to develop the passivation thin films of low-cost and simple process which can prevent the devices from the penetration of the oxygen and moistures. In this study, to improve the reliability, passivation thin films were coated onto the green OLEDs by spin coating method and investigated the changes of the optical properties of the prepared devices at various doping concentrations of sodium alginate (SA). The passivation solutions were synthesized by using polyvinyl alcohol (PVA) host material with a dopant of SA which were added with the amounts of 10, 20 and 40 wt% into the PVA. As a result, the best barrier properties of the OLEDs were obtained for the samples with 40 wt% SA. Finally, the passivation films can be optimized by using the mixture solution of PVA and SA materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.20 no.3
• /
• pp.257-262
• /
• 2007

Organic light-emitting diodes (OLEDs) with the high efficieney and long lifetime are of growing interest in next-generation displays. Among the factors influencing OLEDs properties, one of unstable factor is $Alq_3$ cationic species caused by the excess holes resided in $Alq_3$ layer. Therefore, we suppressed the accumulation of excess holes by using the mixed-hole transporting layer (MHTL) of NPB and CBP in multilayer green OLEDs. The devices with MHTL showed improved characteristics in the luminous efficiency and lifetime. More characteristics and the carrier transport mechanism will be discussed.