Electroluminescence Properties of Organic Light-Emitting-Diodewith New Benzoxazole Derivatives

The authors synthesized new fluoresent dyes with benzoxazole group and evaluated the electroluminescent (EL) properties of organic light-emitting-diodes (OLED) with new dyes as emitting material. Our OLED devices consist of 50nm-thick triphenyl diamine derivative (TPD) layer and 50nm-thick benzoxazole dye layer. The typical OLED device showed a luminance of over 300cd/m2 at 10V. However, the EL efficiencies of these devices were not necessaarily high. Since these benzoxazole dyes have triphenylamine group, the holes easily flew out from TPD to AlLi cathode through benzoxazole dye layer. This leads to increase in the number of holes which do not contribute to hole-electron recombination. Then we synthesized a new benzoxazole dimer derivative without triphenylamine group. When the dimer devivative was doped into oxadiazole derivative (OXD), a blue (an emission peak, 430nm) but weak luminance was observed.