LIGHT-EMITTING DIODE BASED ON OLIGO-PHENYLENE VINYLENE AND BUTYL-PBD BLENDS

We have fabricated light-emitting diodes (LEDs) using organic material s; a polymer blend dispersing oligo-phenylene vinylene (oligo-PV), 1,4 -distyrylbenzene and iphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazol e (butyl-PBD) as emissive materials into a soluble polyimide mixed wit h polyaniline (PANI) of emeraldine salt used as a hole transport mater ial. These polymer dispersed materials were sandwiched between In and indium-tin-oxide (ITO) electrodes. In order to increase the electron i njection into the emissive material, we have inserted a thin Mg layer between In and polymer blends. The electroluminescence (EL) spectra of LEDs showed noticeable enhancement of the oscillator strength of olig o-PV peak at 2.76 eV. This implies improved quantum efficiency of this blue light-emitting diode, resulting from the excitonic migration fro m butyl-PBD to oligo-PV. We have found that the EL device with host po lymers, polyimide and PANI, displayed increasing device performance, l owering the turning point in I-V characteristics, compared to that of LED without PANI. Under normal illumination conditions, our devices wi th PANI showed visible blue-violet color at-room temperature after app lying a bias exceeding 8 V. (C) 1997 Elsevier Science Ltd.