Materials and structures for enhancing the performance or organic light emitting devices

A device, comprising:

• an anode;
• a cathode;
• an first organic layer disposed between the anode and the cathode, wherein 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, wherein the second organic layer is in direct contact with the first organic layer, and wherein the second organic layer comprises a material having the structure:
• wherein:
• x is an integer from 2 to 4, defining a number of quinolate ligands;
• y is an integer from 0 to 3;
• M is a metal selected from the group consisting of Ca, Sr, Ba, Ti, Zr, Hf, V, Nb, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Ni, Pd, Pt, Zn, Cd, Hg, Ge, Sn, and Pd;
• i ranges from 1 to x;
• Rai and Rbi each represent no substitution, mono-, di-, or tri-substitution, and wherein the substituents are independently selected from the group consisting of:
• alkyl and aryl groups.

A device, comprising:

• an anode;
• a cathode;
• an first organic layer disposed between the anode and the cathode, wherein 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, wherein the second organic layer is in direct contact with the first organic layer, and wherein the second organic layer comprises a material having the structure:

A device, comprising:

• an anode;
• a cathode;
• an first organic layer disposed between the anode and the cathode, wherein 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, wherein the second organic layer is in direct contact with the first organic layer, and wherein the second organic layer comprises a material having the structure

A device, comprising:

• an anode;
• a cathode;
• an first organic layer disposed between the anode and the cathode, wherein 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, wherein the second organic layer is in direct contact with the first organic layer, and wherein the second organic layer comprises an organic material having a dipole moment less than about 2.0 debyes, and a highest occupied molecular orbital energy level that is not more than 0.7 eV less than the highest occupied molecular orbital energy level of the organic material in the first organic layer.