Performance of blue fluorescence and red phosphorescent organic light-emitting diodes using a molecular material with high hole drift mobility

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 (mu = 1.0x10(-2) cm(2)V(-1) s(-1)) among those reported for organic disordered systems. We investigated the doping effect of a red phosphorescent 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/m(2) 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%. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim