OLEDs utilizing direct injection to the triplet state

1. An organic light emitting device comprising:

a) an anode;

b) a cathode;

c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising

i) a phosphorescent dopant having a phosphorescent dopant HOMO energy level, a phosphorescent dopant LUMO energy level, a triplet energy, and a singlet energy; and

ii) an emissive layer host having an emissive layer host HOMO energy level and an emissive layer host LUMO energy level; and

d) a transport layer disposed adjacent to the emissive layer, the transport layer comprising a first material having a first material HOMO energy level and a first material LUMO energy level, wherein electrons and holes introduced into the emissive layer have an energy difference less than the energy required to form a singlet on the dopant, such that the energy difference is sufficient for formation of triplets on the dopant and energetically unfavorable for formation of singlets on the dopant.

2. The device of claim 1 , wherein the energy separation between the emissive layer host LUMO and the phosphorescent dopant HOMO is not more than 0.1 eV less than the triplet energy of the phosphorescent dopant.

3. The device of claim 1 , wherein the energy separation between the emissive layer host HOMO and the phosphorescent dopant LUMO is not more than 0.1 eV less than the triplet energy of the phosphorescent dopant.

4. The device of claim 1 , wherein the transport layer is an electron transport layer, and wherein the energy separation between the first material LUMO and the phosphorescent dopant HOMO is not more than 0.1 eV less than the triplet energy of the phosphorescent dopant.

5. The device of claim 1 , wherein the transport layer is a hole transport layer, and wherein the energy separation between the first material HOMO and the phosphorescent dopant LUMO is not more than 0.1 eV less than the triplet energy of the phosphorescent dopant.

6. The device of claim 1 , comprising two transport layers: an electron transport layer comprising an electron transport material, and a hole transport layer comprising a hole transport material, wherein the energy separation between the electron transport material LUMO and the hole transport material HOMO is not more than 0.1 eV less than the triplet energy of the phosphorescent dopant.

7. The device of claim 6 , wherein the energy separation is at least 0.2 eV less than the singlet energy of the phosphorescent dopant.

8. The device of claim 1 , wherein the phosphorescent dopant has a peak in the emission spectra that is less than 500 nm.

9. The organic light emitting device of claim 1 ,

wherein the transport layer comprises a plurality of materials, each material having a HOMO energy level and a LUMO energy level, wherein at least one energy level of each of the plurality of materials together form a series of energy steps leading to at least one energy level in the emissive layer, wherein each step in the series of energy steps is no more than 0.2 eV.

10. An organic light emitting device, comprising:

a) an anode;

b) a cathode;

c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising

i) a phosphorescent dopant having a phosphorescent dopant HOMO energy level, a phosphorescent dopant LUMO energy level, a triplet energy, and a singlet energy; and

ii) an emissive layer host having an emissive layer host HOMO energy level and an emissive layer host LUMO energy level; and

d) a transport layer disposed adjacent to the emissive layer, wherein the transport layer comprising comprises a plurality of materials, each material having a HOMO energy level and a LUMO energy level, wherein at least one energy level of each of the plurality of materials together form a series of energy steps leading to at least one energy level in the emissive layer, wherein each step in the series of energy steps is no more than 0.2 eV.