White organic light-emitting device and display device using the same

1. A white organic light-emitting device comprising:

a first electrode and a second electrode facing each other; and

a plurality of emission stacks, separated from each other by charge generation layers interposed therebetween, the plurality of emission stacks between the first electrode and the second electrode, wherein:

at least one of the emission stacks is a phosphorescent stack;

the phosphorescent stack comprises a hole transport layer, and a first phosphorescent layer, a second phosphorescent layer, and a third phosphorescent layer sequentially provided on the hole transport layer to each emit light having a longer wavelength than blue light;

the first phosphorescent layer comprises a first red dopant having a highest occupied molecular orbital (HOMO) energy level lower than or equal to a HOMO energy level of the hole transport layer; the second phosphorescent layer comprises a second red dopant having a HOMO energy level higher than the HOMO energy level of the first red dopant; and the third phosphorescent layer comprises a third dopant having a luminescence peak at a shorter wavelength than the first red dopant and the second red dopant,

wherein: the first phosphorescent layer comprises only an electron transport host; and each of the second phosphorescent layer and the third phosphorescent layer comprises an electron transport host and a hole transport host.

2. The white organic light-emitting device according to claim 1 , wherein:

the phosphorescent stack further comprises a fourth phosphorescent layer on the third phosphorescent layer; and

the third phosphorescent layer and the fourth phosphorescent layer emit light having a shorter wavelength than the light emitted from the first phosphorescent layer and the second phosphorescent layer.

3. The white organic light-emitting device according to claim 2 , wherein the second to fourth phosphorescent layers sequentially emit shorter-wavelength light.

4. The white organic light-emitting device according to claim 1 , wherein the HOMO energy level of the second red dopant is higher than the HOMO energy level of the hole transport layer.

5. The white organic light-emitting device according to claim 1 , wherein: the electron transport host is a compound having a triazine core; and the hole transport host is a phenylamine compound or a biphenylamine compound.

6. The white organic light-emitting device according to claim 1 , wherein: the first red dopant of the first phosphorescent layer is contained in a concentration equal to or greater than a concentration of the second red dopant of the second phosphorescent layer; the first red dopant and the second red dopant are contained in an amount of 2 wt % to 9 wt % in the first phosphorescent layer and the second phosphorescent layer, respectively; and the third dopant is contained in an amount of 5 wt % to 19 wt % in the third phosphorescent layer.

7. The white organic light-emitting device according to claim 1 , wherein: the second phosphorescent layer comprises the electron transport host in a larger amount than the hole transport host; and the third phosphorescent layer comprises the hole transport host in a larger amount than the electron transport host.

8. The white organic light-emitting device according to claim 1 , wherein the first red dopant is a compound containing a combination of iridium and thieno-pyrimidine.

9. The white organic light-emitting device according to claim 1 , wherein the first phosphorescent layer and the second phosphorescent layer comprise the same electron transport host.

10. The white organic light-emitting device according to claim 1 , further comprising, between the first electrode and the second electrode, at least one first blue emission stack between the first electrode and the phosphorescent stack, and at least one second blue emission stack between the phosphorescent stack and the second electrode,

wherein each of the first blue emission stack and the second blue emission stack comprises a blue fluorescent layer.

11. The white organic light-emitting device according to claim 1 , further comprising, between the first and second electrodes, at least one blue emission stack between the first electrode and the phosphorescent stack or between the phosphorescent stack and the second electrode,

wherein the blue emission stack comprises a blue fluorescent layer.

12. The white organic light-emitting device according to claim 1 , wherein:

the first phosphorescent layer and the second phosphorescent layer each have a luminescence peak at a wavelength of 600 nm to 640 nm; and

the third phosphorescent layer has a luminescence peak at a wavelength of 500 nm to 540 nm.

13. The white organic light-emitting device according to claim 1 , wherein:

the first phosphorescent layer and the second phosphorescent layer each have a luminescence peak at a wavelength of 600 nm to 640 nm; and

the third phosphorescent layer has a luminescence peak at a wavelength of 540 nm to 580 nm.

14. The white organic light-emitting device according to claim 3 , wherein;

the first phosphorescent layer and the second phosphorescent layer each have a luminescence peak at a wavelength of 600 nm to 640 nm;

the third phosphorescent layer has a luminescence peak at a wavelength of 540 nm to 580 nm; and

the fourth phosphorescent layer has a luminescence peak at a wavelength of 500 nm to 540 nm.

15. A display device comprising:

a substrate having a thin film transistor in each of a plurality of sub-pixels;

a first electrode connected to the thin film transistor in the sub-pixel, and a second electrode spaced apart from the first electrode and provided across the sub-pixels; and

a plurality of emission stacks, separated from each other by charge generation layers interposed therebetween, the plurality of emission stacks between the first electrode and the second electrode, wherein:

at least one of the emission stacks is a phosphorescent stack;

the phosphorescent stack comprises a hole transport layer, and a first phosphorescent layer, a second phosphorescent layer, and a third phosphorescent layer sequentially provided on the hole transport layer to each emit light having a longer wavelength than blue light;

the first phosphorescent layer comprises a first red dopant having a highest occupied molecular orbital (HOMO) energy level lower than or equal to a HOMO energy level of the hole transport layer;

the second phosphorescent layer comprises a second red dopant having a HOMO energy level higher than the HOMO energy level of the first red dopant; and

the third phosphorescent layer comprises a third dopant having a luminescence peak at a shorter wavelength than the first red dopant and the second red dopant,

wherein: the first phosphorescent layer comprises only an electron transport host; and each of the second phosphorescent layer and the third phosphorescent layer comprises an electron transport host and a hole transport host.

16. The display device according to claim 15 , further comprising color filters, individually provided in the sub-pixels, beneath the first electrode or above the second electrode, so that each of the color filters transmits light having passed through the first electrode or the second electrode to emit a different color of light from sub-pixels adjacent to the color filter.

17. The display device according to claim 15 , wherein:

the phosphorescent stack further comprises a fourth phosphorescent layer on the third phosphorescent layer; and

the third phosphorescent layer and the fourth phosphorescent layer emit light having a shorter wavelength than the light emitted from the first phosphorescent layer and the second phosphorescent layer.

18. The display device according to claim 15 , wherein the HOMO energy level of the second red dopant is higher than the HOMO energy level of the hole transport layer.