Blue-green organic light-emitting diodes based on fluorene-oxadiazole compounds

We explore the electroluminescent properties of multilayer vapor-deposited organic light-emitting diodes based on a novel set of blue-green emitting-fluorene-oxadiazole compounds. The compounds were used both for the transport of electrons and for the emission of light; in all cases, arylamines were used for the transport of holes. Reducing the ionization potential of the fluorene-oxadiazole compound suppressed the exciplex formation between the hole-transporting layer (HTL) and the electron transport layer (ETL) and increased the corresponding photometric efficiency from 0.6 to 8.7 cd/A. High power efficiencies of 4.5 lm/ W at a luminance of 200 cd/ m were also achieved at low operating voltages. However, the device lifetime was very limited which was attributed mainly to the exciplex formation in the HTL/ETL interface and the instability of the oxadiazole moiety in the excited state. (C) 1998 American Institute of Physics. [S0003-6951(98)03547-5].