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a b s t r a c t We have investigated the charge carrier transport mobility and hole-only current behavior of phos- phorescent host-dopant mixture, and evaluated the efficiency and lifetime behavior of organic light emitting device (OLED) containing the corresponding light emitting host-dopant system. The carrier drift mobilities of the phosphorescent host, 4,4 � -N,N

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.

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).

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.

The light emitting efficiency and the stability of the phosphorescent devices, whose emission characteristics are strongly dominated not only by the energy transfer but also by the charge carrier trapping influenced by the heterostructured emissive layers and charge injection layer, are studied in terms of the charge injection behavior, carrier transporting mobility, and balancing of devices. The enhancement of the light emitting properties (higher efficiency and lower driving voltage) by use of heterostructures at emitting layer, either multilayers or mixing of hole- and electron-transporting materials (such as 4,4",4"-tris(N-carbazolyl)-triphenylamine); TCTA and bis(10-hydroxybenzo[h]quinolinate) beryllium; Bebq 2 ) was characterized. By a design of emitting layer structure for recombination, 30~50lm/W efficiency of devices with Ir(ppy) 3 and conventional transporting layer was possible.

The charge conduction properties of the organic phosphorescent emission layer doped with iridium-based green and red phosphorescent emitters, fac-tris(2-phenylpyridine) iridium(III) (Ir(ppy) 3 ) and bis(2-(2'-benzo [4,5-a]thienyl)pyridinato-N,C3')iridium(acetyl-acetonate) (btp 2 Ir(acac)), were studied and compared to those of the reference host of 4,'-N,N'-dicarbazole-biphenyl (CBP). In the CBP host layer, both dopants act as hole traps but they affect the electron transport differently. Compared with the pristine CBP film, the electron mobility is similar for Ir(ppy) 3 -doped CBP but it is more than two orders of magnitude lower for btp2Ir(acac)-doped CBP. Because of such difference in the electrical conduction properties between the Ir(ppy) 3 - and btp2Ir(acac)-doped CBP, the main recombination zone position and the electron-hole balance changes. Based on these findings, we optimized white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which CBP layers doped with Ir(ppy) 3 and btp2Ir(acac) and fluorescent dopant of 4,4'-bis[2-{4-(N,N-diphenylamino)phenyl}vinyl]biphenyl (DPAVBi) were used as green (G), red (R), and blue (B) EMLs, respectively. The white OLEDs with the R/G/B EML sequence show improved electron and hole balance, resulting higher efficiency, better color stability and longer lifetime compared to the G/R/B EML sequence. A high luminous current efficiency of 13.5 cd/A at 100 cd/m 2 was achieved with the R/G/B EML sequence.

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.

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.

Ambipolar conduction in organic field-effect transistor is very important feature to achieve organic CMOS circuitry. We fabricated an ambipolar pentacene field-ef fect transistors consisted of gold source-drain electrodes and double-layered PMMA (Polymethylmethacrylate) / PVA (Polyvinyl Alcohol) organic insulator on the ITO(Indium-tin-oxide)-patterned glass substrate. These top-contact geometry field-effect transistors were fabricated in the vacuum of 10 -6 Torr and minimally exposed to atmosphere before its measurement and characterized in the vacuum condition. Our device showed reasonable p-type ch aracteristics of field-effect hole mobility of 0.2-0.9 cm 2 /Vs and the current ON/OFF ratio of about 10 6 compared to prior reports with similar configurations. For the n-type characteristics, field-effect electron mobility of 0.004-0.008 cm 2 /Vs and the current ON/OFF ratio of about 10 3 were measured, which is relatively high performance for the n-type conduction of pentacene field-effect transistors. We attributed these ambipolar properties mainly to the hydroxyl-free PMMA insulator interface with the pentacene active layer. In addition, an increased insulator capacitance due to double-layer insulator structure with high-k PVA layer also helped us to observe relatively good n-type characteristics. Keywords: pentacene, OTFT, field-effect transistor, ambipolar, mobility

The stability of the organic light-emitting diode (OLED) at the high temperature is important for their applications to automotive displays or various lighting applications which are more susceptible to Joule heating problems. In addition, it is known that the OLED lifetime is limited by the poor therma l stability of the hole-transport layer (HTL) material. Thus, the improvement of the thermal stability of the HTL layer is essential for enhancing both thermal stability and the operation lifetime. Here, we report that the thermal stability of OLED device can be significantly enhanced by introducing an LiF-mixed N,N’-di(1-naphthyl)-N,N’-diphenylbenzidine (.-NPD) as a HTL in the OLED having tris(8-hydroxyquinoline) aluminum (Alq 3 ) as a light-emitting and electron-transport la yer. Compared with the reference device with the Þ -NPD HTL, the device having a double layer of LiF-mixed Þ -NPD and Þ -NPD as a HTL showed an increased thermal stability up to 170 without degrading the quantum efficiency of the electroluminescence. In addition, the driving voltage variation over time (less than 3 V) was significantly suppressed while the reference device shows a variation over 6 V. The improved device stability is attri buted to the enhanced thermal stability of the LiF-mixed .-NPD layer, which could be estimated from the result that the film morphology of LiF-mixed .-NPD film was nearly unchanged after heated above the glass transition temperature of .-NPD while that of .-NPD film was significantly changed. Keywords: Organic Light-emitting-diode (OLED), thermal stability, LiF-mixed HTL

The purpose of RGBW Quad Structure Technology is to realize higher brightness than that of normal panel (RGB stripe structure) by adding white sub-pixel to existing RGB stripe structure. However, there is side effect called 'color shift' resulted from increasing brightness. This side effect degrades general color characteristics due to change of 'Hue', 'Brightness' and 'Saturation' as compared with existing RGB stripe structure. Especially, skin-tone colors show a tendency to get darker in contrast to normal panel. We’ve tried to minimize 'color shift' through use of LUT (Look Up Table) for linear arithmetic processing of input data, data bit expansion to 12-bit for minimizing arithmetic tolerance and brightness weight of white sub-pixel on each R, G, B pixel. The objective of this study is to minimize and keep Δu'v' value (we commonly use to represent a color difference), quantitative basis of color difference between RGB stripe structure and RGBW quad structure, below 0.01 level (existing 0.02 or higher) using Macbeth colorchecker that is general reference of color characteristics.

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.

— Image deformation caused by an outside force is observed to remain for hours at high gray levels for liquid-crystal displays (LCDs) in the multi-domain (MD) vertical-alignment (VA) mode. This so-called moving-image-sticking phenomenon demonstrated a non-symmetric luminance profile for the left and right viewing direction for MDVA-mode LCDs which have original symmetric viewing-angle characteristics. The generation of a stable reverse-tilt domain by an outside force was assumed to be the cause of this phenomenon, and the stability of a reverse-tilt domain under an electric fringe field was calculated by changing the electric-fringe-field distribution which determines the LC tilt direction. The domain of a given tilt direction is calculated to change to other tilt direction induced by a fringe field at a low gray condition, but to remain unchanged at a high gray condition. This agrees with the observed trends of duration time of the moving-image-sticking phenomenon.

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.

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.

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.