Extended OLED operational lifetime through phosphorescent dopant profile management
This disclosure relates, at least in part, an organic light emitting device, which in some embodiments comprises an anode; a cathode; a first emissive layer disposed between the anode and the cathode, the first emissive layer comprising an electron transporting compound and a phosphorescent emissive dopant compound; and wherein the phosphorescent emissive dopant compound has a concentration gradient, in the emissive layer, which varies from the cathode side of the first emissive layer to the anode side of the emissive layer.
1. An organic light emitting device comprising:
an anode;
a cathode;
a first emissive layer disposed between the anode and the cathode, the first emissive layer comprising an electron transporting compound and a phosphorescent emissive dopant compound;
wherein the phosphorescent emissive dopant compound is a hole transporter; and
wherein the phosphorescent emissive dopant compound has a concentration gradient, in the emissive layer, wherein the concentration gradient varies according to a profile selected from the group consisting of: (i) linear towards the cathode side of the first emissive layer; (ii) non-linear towards the cathode side of the first emissive layer, wherein said non-linear profile corresponds to a polynomial function selected from the group consisting of a quadratic function, a cubic function, or a higher order function; and (iii) a step wise form.
2. The organic light emitting device of claim 1 , wherein when the concentration gradient varies in a step wise form, the phosphorescent emissive dopant compound is dispersed in the emissive layer as a plurality of high concentration dopant regions and as a plurality of low concentration dopant regions.
3. The organic light emitting device of claim 1 , wherein when the concentration gradient varies in a step wise form, wherein the phosphorescent emissive dopant compound is dispersed in the emissive layer as a plurality of first dopant regions and as a plurality of second dopant regions, wherein the first dopant regions are wider than the second dopant regions.
4. The organic light emitting device of claim 1 , wherein the emissive layer further comprises a second electron transporting compound, wherein the phosphorescent emissive dopant compound has a HOMO energy level at least 0.5 eV lower than a HOMO level of the second electron transporting compound.
5. The organic light emitting device of claim 1 , wherein the organic light emitting device further comprises a hole injection layer disposed between the anode and the emissive layer.
6. The organic light emitting device of claim 5 , wherein the hole injection layer and the emissive layer have a combined thickness, and wherein the emissive layer has a thickness which is at least 60% of the combined thickness.
7. The organic light emitting device of claim 6 , wherein the emissive layer has a thickness ranging from 10 nm to 150 nm.
8. The organic light emitting device of claim 1 , wherein a hole injection layer is not disposed between the anode and the emissive layer.
9. The organic light emitting device of claim 1 , wherein exciton density is uniformly distributed across the emissive layer compared to an equivalent device that has a uniform concentration of the phosphorescent emissive dopant compound in the emissive layer.
10. The organic light emitting device of claim 1 , wherein the concentration gradient decreases from the cathode side of the first emissive layer to the anode side of the emissive layer.
11. The organic light emitting device of claim 1 , wherein the concentration gradient increases from the cathode side of the first emissive layer to the anode side of the emissive layer.
12. The organic light emitting device of claim 3 , wherein electron transport is performed primarily by the electron transporting compound.
13. The organic light emitting device of claim 5 , wherein hole transport is performed primarily by the phosphorescent emissive dopant compound.
14. The organic light emitting device of claim 1 , further comprising an electron transport layer disposed between the cathode and the emissive layer.
15. The organic light emitting device of claim 1 , wherein the organic light emitting device has an external quantum efficiency of at least 10% higher compared to an equivalent device that has a uniform concentration of the phosphorescent emissive dopant compound in the emissive layer.
16. The organic light emitting device of claim 1 , wherein the organic light emitting device exhibits a time to degrade to 80% of an initial luminance value of 1000 cd/m2 that is at least 3.5 times greater than an equivalent device that has a uniform concentration of the phosphorescent emissive dopant compound in the emissive layer.