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This study focuses on the carrier balance factor and transient characteristics of organic light-emitting diodes (OLEDs) utilizing tris[4-(5-phenylthiophen-2-yl)phenyl] amine (TPTPA) as a blue emissive material or a host material of a red phosphorescent dye, which exhibits the highest level of hole drift mobility (µ = 1.0×10-2 cm2V-1s-1) among those reported for organic disordered systems. We investigated the doping effect of a red phos-phorescent material in the TPTPA. The peak wavelengths and the shape of the electroluminescent (EL) spectra agree with those of the photoluminescent spectra, which indicate that the EL originates from the excited state of the TPTPA and dopant. The maximum luminance of approximately 11,000 and 2,000 cd/m2 were achieved for devices without and with dopant. While TPTPA device achieved good carrier balance, the hole current was decreased by doping a red phosphorescent material. Compared with the short response times of TPTPA device, relatively long response times of doped device was observed owing to phosphorescent recombination lifetime of a dopant. The TPTPA device exhibited the relatively high light outcoupling efficiency of approximately 34% (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

This study focuses on the performance of organic light-emitting diodes (OLEDs) using an emissive material with high hole drift mobility, tris[4-(5-phenylthiophen- 2-yl)]amine (TPTPA), which exhibits the highest level of hole drift mobility (1.0 × 10-2 cm2 V-1 s-1) among those reported for organic disordered systems. Clear blue emission was observed from TPTPA which was used as the hole transporting and emissive layer in the OLEDs. The maximum luminance of 1.2 × 104 cd/m2, and the maximum current efficiency of 3.9 cd/A were achieved. The short response times of electroluminescence (ca. 10 ns) were achieved under the application of rectangular-shaped voltages. [ABSTRACT FROM AUTHOR]

The effect of electron injection in polymer light-emitting diodes based on the phosphorescent material of fac-tris(2-phenylpyridine) iridium (Ir(ppy)3) devices with CsF/MgAg/Ag cathodes were investigated. The device with MgAg (1 nm)/CsF (3 nm)/Ag cathode showed almost similar current density-voltage-luminance characteristics to that with CsF (3 nm)/MgAg (1 nm)/Ag cathode. The existence of interface between the organic layer and Cs or CsF results in low turn on voltage. To achieve the efficient electron injection and the low turn on voltage, it is necessary to exist MgAg and CsF interface at the position of about 1 nm from organic layer. To achieve the efficient electron injection, it is necessary to exist Cs layer just on the organic layer. The electron injection effects between devices with CsF and Cs are different. It is suggested that the dipole of CsF affect the efficient electron injection. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics and patterning of organic light-emitting diodes (OLEDs) utilizing a sputter deposited amorphous carbon nitride (a-C:N) as a buffer layer have been discussed. Increased device performance has been achieved in a device of the a-C:N buffer layer that was less than 10 nm in thickness. The device with a 5-nm-thick a-C:N exhibited the maximum luminance of 32,000 cd/m2 and the current efficiency of 4.6 cd/A at the current density of 1.2 A/cm2 and 0.06 A/cm2, respectively. The OLEDs with a-C:N buffer layer are useful for preventing the photodegradation suffered during photolithography process. The patterned emission of the device was obtained by using the a-C:N buffer layer as the protective layer to perform photolithography after deposited organic layer. [Copyright &y& Elsevier]

Abstract: We investigated the transient electroluminescence (EL) and modulation characteristics of red organic light-emitting diodes (OLEDs) consisting of 4-(dicyanomethylene)-2-i-propyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) and 5,6,11,12-tetraphenylnaphthacene (rubrene) doped into tris(8-hydroxyquinoline)aluminum (Alq3). The transient EL waveforms showed two components, an initial overshooting peak followed by a constant component, indicating that the excess amount of accumulated charges simultaneously recombine at the moment of onset. This overshoot effect reduced the rise time of transient EL and enhanced the optical output of the OLEDs, and hence the cutoff frequency was increased when the pulse voltage was applied to the device. We demonstrated that the red OLEDs are suitable for use in high-speed switching applications driven at more than 100 MHz, and in electro-optical conversion devices for transmitting video signals. [Copyright &y& Elsevier]

We demonstrate high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent dye doped into a low-molecule material. Methoxy-substituted 1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB) was selected as the host material for the phosphorescent dopant fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3], and organic films were fabricated by spin-coating. A peak external quantum efficiency of 8.2% (29 cd/A), luminous power efficiency of 17.3 lm/W, and luminance of 33,000 cd/m2 were achieved at 9.4 V with a 90 nm-thick emitting layer. Emission from the host TDAPB material was not observed in the electroluminescence (EL) and photoluminescence (PL) spectra. The decrease in efficiencies at a high current is analyzed using the triplet–triplet annihilation model. The high performance for the simple device structure in this study is attributed to excellent film forming properties of the material and efficient energy transfer from the host to dopants. [Copyright &y& Elsevier]

An organic electroluminescence diode (OLED) fabricated on polyimide substrate has been investigated to realize a flexible electro-optic device for optical links. The device fabricated on polyimide substrate shows similar device characteristic to that on glass substrate. The modulation performance of the OLED was significantly improved by applying a positive, low-level DC bias, which results in a slower falling time. An undershoot voltage applied to the falling edge of the input voltage pulse results in faster falling time and a decrease in intensity of the optical output. We demonstrate that the OLEDs can be applied to short-range optical communication fields, such as electro-optical conversion devices for optical links. [Copyright &y& Elsevier]