A device is provided, having an anode, a cathode, and a first organic layer disposed
between the anode and the cathode. The first organic layer is capable of phosphorescent
emissive when a voltage is applied between the anode and the cathode. A second
organic layer disposed between the first organic layer and the cathode is also
provided. The second organic layer is in direct contact with the first organic
layer. The second organic layer may comprise a material having the structure:
##STR1##
M may be selected from the group Ti, Zr, Hf, Nb, Re, Sn and Ge. The substituents
R1 through R10 may be selected from the group consisting of alkyl and aryl groups.
Each of R1 through R10 may represent no substitution, mono-, di-, or tri-substitution.
The second organic layer may comprise a material having a dipole moment less than
about 2.0 debyes, such that the device has an unmodified external quantum efficiency
of at least about 3% and a lifetime of at least about 1000 hours at an initial
photon flux of about 1018 photons/sr-sec. The second organic layer may
comprise a metal complex having a plurality of ligands, wherein each ligand makes
the same contribution to the highest occupied molecular orbital and the lowest
unoccupied molecular orbital of the metal complex. The second organic layer may
be in direct contact with the cathode, or there may be a separate organic layer
between the second organic layer and the cathode. Other metal complexes having
quinolate ligands may be used.
