STUDIES ON EMITTING MATERIALS OF ORGANIC EL CELLS

Fifteen distyrylbenzene (DSB) derivatives which were substituted by alkyl group, electron-acceptor group or electron-donor group were synthesized and examined as an emitter for organic multilayer electroluminescence (EL) cells. We carefully measured the EL spectra and SEM pictures as well as the current-voltage and brightness-current characteristics. Then we conculded that it is very important for an emitting layer not to form exciplex or charge-transfer complex with hole transporting layer in addition to an ability to form a thin film. We found that 4,4'-bis[2-(9-ethyl-3-carbazolyl)vinyl]biphenyl (BCzVBi) among those derivatives was very attractive material because we achieved the bright blue green light for the cell with BCzVBi as an emitting layer. We could obtain the luminance of 2000 cd/m2 at a voltage of 7 V and the maximum EL efficiency of 1. 5 lm/W for the cell with ITO/BCzVBi/2-(4-t-Butylphenyl)-5-(4-biphenylyl)-1, 3, 4-oxadiazole/Mg : Ag. We also achieved the bright blue light and the high luminance of more than 1000 cd/m2 by introducing methyl group to biphenyl unit. Therefore the distyrylbenzene derivatives should be most promising compounds as EL emitting materials in the color range from blue to green.