Red Phosphorescent Organic Light-Emitting Diodes Using Mixture System of Small-Molecule and Polymer Host

We study two types of polymer materials, poly(n-vinylcarbazole) (PVK) and starburst small-molecule 1,3,5-tris[4(diphenylamino)phenyl]benzene (TDAPB), as the host for electrophosphorescent organic light-emitting diodes (PHOLEDs) doped with red-emitting phosphor tris(1-phenylisoquinoline) iridium (III) [Ir(piq)3]. PHOLEDs employed a PVK and TDAPB blend as the host exhibited a maximum red light emission at a wavelength of 630 nm. The external quantum efficiency of 6.3% and power efficiency of 3.0 lm/W have been achieved. The electroluminescent (EL) spectra were not changed at high current and the luminance reached 8,800 cd/m at the voltage of 13V. We found that the roughness of the surface as estimated by means of atomic force microscopy (AFM) smoothened with increasing TDAPB doping concentration, and a slight exciplex emission between TDAPB and an electron transport material 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4,-oxadiazole (PBD) was observed at the wavelength of approximately 530 nm. [DOI: 10.1143/JJAP.44.2790]