Heume-Il Baek

Electroluminescence characteristics of n-type matrix materials doped with iridium-based green and red phosphorescent emitters

The electroluminescence characteristics of various n-type matrix materials with various orders of electron mobility doped with the phosphorescent green emitter fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3] and the phosphorescent red emitter bis(2-(2′-benzo [4,5-a] thienyl)pyridinato-N,C3′)iridium(acetyl-acetonate) [btp2Ir(acac)] were evaluated and compared to those of the p-type 4,4″-N,N′-dicarbazole-biphenyl (CBP) reference matrix. For Ir(ppy)3, the device with the n-type matrix 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene was found to have the highest efficiency and operational lifetime, whereas for btp2Ir(acac) the device with the p-type matrix CBP was found to have the highest efficiency. Our study of hole- and electron-dominant devices and analyses of electroluminescence spectra show that the main recombination zone position and the electron-hole balance change as the matrix material changes, resulting in changes in the characteristics of the organic light emitting diodes.

Simple white organic light emitting diodes with improved color stability and efficiency using phosphorescent and fluorescent emitters

White organic light emitting diodes (WOLEDs) with both phosphorescent and fluorescent emitting layers (EML) usually adopt an interlayer between them to achieve high efficiency by preventing mutual quenching, but insertion of the interlayer causes a higher operating voltage as well as additional fabrication steps. Here, we demonstrate that simple-structure WOLEDs without an interlayer could be achieved using the combination of phosphor-sensitized-fluorescent red and phosphorescent blue EMLs. In addition, the main cause of the color shift with increasing current density was identified, and the color shift of the WOLED was successfully suppressed by properly balancing emission from the red and blue EMLs. Consequently, a maximum external quantum efficiency of 6.2% (a current efficiency of 14.3 cd/A) and very stable color coordinates of (0.32±0.01,0.42±0.002) were achieved. However, the elimination of an interlayer for the combination with a fluorescent blue EML causes about 50% decrease in the efficiency and ...

P-186: Enhanced Efficiency and Stability of Organic Light-Emitting Diodes with Copper Hexadecafluorophthalocyanine Doped Hole Transport Layer

We report the enhancement of the electroluminescence (EL) efficiency and the device stability of organic light-emitting diodes (OLEDs) by inserting a copper hexadecafluorophthalocyanine (F16CuPC)-doped N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD) layer between an indium-tin oxide and α-NPD. Compared with the reference device consisting of the bilayer structure of α-NPD and tris(8-hydroxyquinoline) aluminum (Alq3), the devices having F16CuPC-doped α-NPD show not only an increased EL efficiency (∼4.5 cd/A compared with ∼3.8 cd/A for the reference device) and lower driving voltage but also a longer lifetime and smaller operating voltage variation over time. It is suggested that the improved device performance can be attributed to the higher hole-injection efficiency and thermal stability of the F16CuPC-doped α-NPD layer.

Three white organic light‐emitting diodes with blue‐green fluorescent and red phosphorescent dyes

Abstract This paper reports that well‐balanced white emission with three primary colors can be achieved with a simple white organic light‐emitting diode (WOLED) structure of ITO / α‐NPD (50 nm) / α‐NPD: Btp2Ir(acac) (8 wt%, 6 nm) / α‐NPD (5 nm) / BCP (3 nm) / Alq3: C545T (0.5 wt%, 10 nm) / Alq3 (40 nm) / LiF (0.5 nm) / Al (100 nm). The external quantum efficiency of the device reached 3.8% at a current density (luminance) of 4.6 mA/cm2 (310 cd/m2), and the maximal luminance of the device reached 19,000 cd/m2 at 11.5 V. The insignificant blue shift of the emitting color with an increasing current density can be attributed to the narrowing of the exciton formation zone width.

Multilayer white organic light emitting diode with optimum emitting layer sequence

Yellow organic light emitting diode (OLED) with red/green emitting layer (EML) sequence showed higher efficiency than device with green/red EML sequence because of the electrical carrier conduction difference in EMLs. Based on this result white OLED with additional blue emitter was demonstrated with maximum efficiency of 18.3 cd/A at 100 cd/m2 and good color stability.

Strain relaxation and quantum size effect studied by two-photon laser scanning photoluminescence microscopy

Nanoscale excitation by the simultaneous absorption of two photons was employed to investigate the spatially resolved role of strain relaxation and quantum size effect (QSE) in affecting luminescence from ZnO nanorods (NRs).

Shadow excitation of nanoneedles: Roguing localization and strain effects from photoluminescence

In order to pinpoint the spatially resolved role of strain, localization, and quantum confinement (QC) in tapered nanoneedles (NNs), angle-resolved photoluminescence (PL) was adapted as a function of temperature.

P‐83: The Correlation of MPRT and Moving Picture Resolution with Actually Perceived Moving Image Qualities

The motion picture response time (MPRT) methods have been widely used to evaluate the degree of motion blurs in display devices such as liquid crystal displays (LCDs) and plasma display panels (PDPs). Recently, APDC (Advanced PDP development center Corporation) announced the moving picture resolution method to represent the moving image quality of FPDs by using a resolving power as a measure. However, there are some differences in evaluation results of these two methods for same display devices. In this study, we measured the moving picture resolutions of five different FPDs which have different MPRT values and compared these results with actually perceived moving image qualities. The results show that the MPRT has higher correlation with actually perceived moving image qualities than the moving picture resolution method.

Methods for balanced charge carriers and enhanced efficiency of organic phosphorescent devices

In this paper, the light emitting efficiency, spectrum, and the lifetime of the phosphorescent devices, whose emission characteristics are strongly dominated not only by the energy transfer but also by the charge carrier trapping induced by the emissive dopant, are explained by differences in the energy levels of the host, dopant, and nearby transport layers. On the basis of our finding on device performance and photocurrent measurement data by time-of-flight (TOF), we suggest a detailed emission mechanism, along with a physical interpretation and practical design scheme for improving the efficiency and lifetime of devices. Moreover, the effects of the modification of charge (both hole and electrons) transporting layers which results in a drop of operating voltage and improved efficiency on the performance of electrophosphorescent device are investigated experimentally. Using the Ir-based phosphorescent emitter, vacuumevaporated, solution-processed, and composition of their hybrid structures are designed for better charge carrier balance and efficient exciton blocking behavior.

Carrier Transport Properties in Organic Phosphorescent Emissive Layer and Their Application to Efficient Organic Phosphorescent Devices

We studied electrical properties of OLEDs consisting of the emission layer doped with phosphorescent molecules. Different doping profile is necessary for better efficiency and lifetime due to different conduction properties of Ir(ppy)3- and btp2Ir(acac)-doped CBP.