Organic light emitting diode devices with improved luminance efficiency

An organic light emitting device comprising:

• (a) a substrate;
• (b) an anode and a cathode disposed over the substrate;
• (c) a luminescent layer disposed between the anode and the cathode wherein the luminescent layer includes a host and at least one dopant;
• (d) the host of the luminescent layer being selected to include a solid organic material comprising a mixture of at least two components wherein;
• (i) the first component of the mixture is a benzenoid compound that is capable of transporting both electrons and holes and that is substantially non-polar, said luminescent comprising at least 50% by volume of the first host component;
• and
• (ii) th second component of the mixture is an oganic compound that is more polar than the first component, said second component being either
• a heterocyclic benzenoid having the molecular structure
• wherein
• Z is O, NR″or S;
• R and R′, are individually hydrogen;
• alkyl of from 1 to 24 carbon atoms;
• aryl or hetero-atom substituted aryl of from 5 to 20 carbon atoms;
• halo, or atoms necessary to complete a fused aromatic ring;
• and R″ is hydrogen;
• alkyl of from 1 to 24 carbons atoms;
• or aryl of from 5 to 20 carbon atoms, or
• an oxinoid compound having the molecular structure:
• wherein
• Me represents a metal;
• n is an integer of from 1 to 3;
• and
• Z independently in each occurrent represents the atoms completing a nucleus having at least two fused aromatic rings;
• and
• (e) the dopant of the luminescent layer is selected to produce light from the light emitting device.