Light emitting diode and display device including the same

1. A light emitting diode, comprising:

a first electrode;

a hole transport region disposed on the first electrode;

an emission layer disposed on the hole transport region;

an electron transport region disposed on the emission layer; and

a second electrode disposed on the electron transport region,

wherein the hole transport region comprises:

a first hole transport layer disposed adjacent to the first electrode, the first hole transport layer having a first refractive index;

a second hole transport layer disposed adjacent to the emission layer, the second hole transport layer having a second refractive index; and

a third hole transport layer disposed between the first hole transport layer and the second hole transport layer, the third hole transport layer having a third refractive index which is greater than each of the first refractive index and the second refractive index.

2. The light emitting diode of claim 1 , wherein

a difference between the third refractive index and the first refractive index is greater than about 0.1, and

a difference between the third refractive index and the second refractive index is greater than about 0.1.

3. The light emitting diode of claim 2 , wherein

the first refractive index and the second refractive index are each in a range of about 1.30 to about 1.80 at a wavelength of about 460 nm, and

the third refractive index is in a range of about 1.85 to about 2.40 at a wavelength of about 460 nm.

4. The light emitting diode of claim 2 , wherein the first refractive index and the second refractive index are the same.

5. The light emitting diode of claim 1 , wherein the second hole transport layer is disposed directly below the emission layer.

6. The light emitting diode of claim 5 , wherein

a refractive index of the emission layer is greater than the second refractive index of the second hole transport layer, and

a difference between the refractive index of the emission layer and the second refractive index is greater than about 0.1 at a wavelength of about 460 nm.

7. The light emitting diode of claim 6 , wherein the refractive index of the emission layer is in a range of about 1.80 to about 2.40 at a wavelength of about 460 nm.

8. The light emitting diode of claim 1 , wherein the first hole transport layer is disposed directly above the first electrode.

9. The light emitting diode of claim 8 , wherein

a refractive index of the first electrode is greater than the first refractive index of the first hole transport layer, and

a difference between the refractive index of the first electrode and the first refractive index is greater than about 0.1 at a wavelength of about 460 nm.

10. The light emitting diode of claim 9 , wherein the refractive index of the first electrode is in a range of about 1.80 to about 2.40 at a wavelength of about 460 nm.

11. The light emitting diode of claim 1 , wherein a thickness ratio of the first hole transport layer, the third hole transport layer, and the second hole transport layer is in a range of about 0.1:0.8:0.1 to about 0.45:0.1:0.45.

12. The light emitting diode of claim 1 , wherein

the first electrode is a reflective electrode, and

the second electrode is a transmissive electrode or a transflective electrode.

13. The light emitting diode of claim 1 , wherein the emission layer emits light having a central wavelength in a range of about 430 nm to about 470 nm.

14. The light emitting diode of claim 13 , wherein

a thickness of the first hole transport layer is in a range of about 100 Å to about 1,000 Å,

a thickness of the second hole transport layer is in a range of about 100 Å to about 1,000 Å, and

a thickness of the third hole transport layer is in a range of about 100 Å to about 1,000 Å about 100 Å to about 1,000 Å.

15. The light emitting diode of claim 1 , wherein the first hole transport layer and the second hole transport layer each independently comprises an amine compound represented by Formula 1:

wherein in Formula 1,

Ar a to Ar c are each independently a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 3 to 30 ring-forming carbon atoms,

at least two of R a to R c are each independently an adamantyl group or a cyclohexyl group, and

the remainder of R a to R c is a hydrogen atom, a deuterium atom, a halogen atom, a cyano group, a substituted or unsubstituted oxy group, a substituted or unsubstituted thio group, a substituted or unsubstituted amine group, or a substituted or unsubstituted alkyl group of 1 to 20 carbon atoms.

16. The light emitting diode of claim 15 , wherein Ar a to Ar c are each independently a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted terphenyl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, a substituted or unsubstituted dibenzofuranyl group, or a substituted or unsubstituted dibenzothiophenyl group.

17. The light emitting diode of claim 1 , wherein the first hole transport layer and the second hole transport layer each independently comprises at least one amine compound selected from Compound Group 1:

18. The light emitting diode of claim 1 , wherein the third hole transport layer comprises a compound represented by Formula 2:

wherein in Formula 2,

Ar 1 and Ar 2 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group of 1 to 30 carbon atoms, a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 30 ring-forming carbon atoms, or combined with an adjacent group to form a ring,

Ar 3 is a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 30 ring-forming carbon atoms,

a and b are each independently 0 or 1,

L 1 and L 2 are each independently a substituted or unsubstituted cycloalkylene group of 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted heterocycloalkylene group of 2 to 10 ring-forming carbon atoms, a substituted or unsubstituted cycloalkenylene group of 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted arylene group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroarylene group of 2 to 60 ring-forming carbon atoms,

p and s are each independently an integer from 0 to 4,

q and r are each independently an integer from 0 to 3, and

R 1 to R 5 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted oxy group, a substituted or unsubstituted alkyl group of 1 to 60 carbon atoms, a substituted or unsubstituted heterocycloalkyl group of 3 to 60 ring-forming carbon atoms, a substituted or unsubstituted aryl group of 6 to 60 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 60 ring-forming carbon atoms.

19. The light emitting diode of claim 1 , wherein the third hole transport layer comprises at least one compound selected from Compound Group 2:

20. The light emitting diode of claim 1 , wherein the hole transport region further comprises:

a fourth hole transport layer disposed between the first hole transport layer and the third hole transport layer, the fourth hole transport layer having a refractive index greater than the first refractive index and less than the third refractive index; and

a fifth hole transport layer disposed between the second hole transport layer and the third hole transport layer, the fifth hole transport layer having a refractive index greater than the second refractive index and less than the third refractive index.

21. The light emitting diode of claim 20 , wherein

the first hole transport layer and the second hole transport layer each independently comprises an amine compound represented by Formula 1,

the third hole transport layer comprises a compound represented by Formula 2, and

the fourth hole transport layer and the fifth hole transport layer each independently comprises an amine compound represented by Formula 1 and a compound represented by Formula 2:

wherein in Formula 1,

Ar a to Ar c are each independently a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 3 to 30 ring-forming carbon atoms,

at least two of R a to R c are each independently an adamantyl group or a cyclohexyl group, and

the remainder of R a to R c is a hydrogen atom, a deuterium atom, a halogen atom, a cyano group, a substituted or unsubstituted oxy group, a substituted or unsubstituted thio group, a substituted or unsubstituted amine group, or a substituted or unsubstituted alkyl group of 1 to 20 carbon atoms,

[Formula 2]

wherein in Formula 2,

Ar 1 and Ar 2 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group of 1 to 30 carbon atoms, a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 30 ring-forming carbon atoms, or combined with an adjacent group to form a ring,

Ar 3 is a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 30 ring-forming carbon atoms,

a and b are each independently 0 or 1,

L 1 and L 2 are each independently a substituted or unsubstituted cycloalkylene group of 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted heterocycloalkylene group of 2 to 10 ring-forming carbon atoms, a substituted or unsubstituted cycloalkenylene group of 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted arylene group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroarylene group of 2 to 60 ring-forming carbon atoms,

p and s are each independently an integer from 0 to 4,

q and r are each independently an integer from 0 to 3, and

R 1 to R 5 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted oxy group, a substituted or unsubstituted alkyl group of 1 to 60 carbon atoms, a substituted or unsubstituted heterocycloalkyl group of 3 to 60 ring-forming carbon atoms, a substituted or unsubstituted aryl group of 6 to 60 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 60 ring-forming carbon atoms.

22. The light emitting diode of claim 20 , wherein the first to fifth hole transport layers each have a thickness in a range of about 100 Å to about 1,000 Å.

23. A display device comprising:

a plurality of light emitting diodes, each of the plurality of light emitting diodes including:

a first electrode;

a hole transport region disposed on the first electrode;

an emission layer disposed on the hole transport region;

an electron transport region disposed on the emission layer; and

a second electrode disposed on the electron transport region,

wherein the hole transport region of at least one of the plurality of light emitting diodes comprises:

a first hole transport layer disposed adjacent to the first electrode, the first hole transport layer having a first refractive index;

a second hole transport layer disposed adjacent to the emission layer, the second hole transport layer having a second refractive index; and

a third hole transport layer disposed between the first hole transport layer and the second hole transport layer, the third hole transport layer having a third refractive index which is greater than each of the first refractive index and the second refractive index.

24. The display device of claim 23 , wherein

a difference between the third refractive index and the first refractive index is greater than about 0.1, and

a difference between the third refractive index and the second refractive index is greater than about 0.1.

25. The display device of claim 23 , wherein

the first electrode is a reflective electrode, and

the second electrode is a transmissive electrode or a transflective electrode.

26. The display device of claim 23 , wherein

the first hole transport layer and the second hole transport layer each independently comprises an amine compound represented by Formula 1, and

the third hole transport layer comprises a compound represented by Formula 2:

wherein in Formula 1,

Ar a to Ar c are each independently a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 3 to 30 ring-forming carbon atoms,

at least two of R a to R c are each independently an adamantyl group or a cyclohexyl group, and

the remainder of R a to R c is a hydrogen atom, a deuterium atom, a halogen atom, a cyano group, a substituted or unsubstituted oxy group, a substituted or unsubstituted thio group, a substituted or unsubstituted amine group, or a substituted or unsubstituted alkyl group of 1 to 20 carbon atoms,

wherein in Formula 2,

Ar 1 and Ar 2 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group of 1 to 30 carbon atoms, a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 30 ring-forming carbon atoms, or combined with an adjacent group to form a ring,

Ar 3 is a substituted or unsubstituted aryl group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 30 ring-forming carbon atoms,

a and b are each independently 0 or 1,

L 1 and L 2 are each independently a substituted or unsubstituted cycloalkylene group of 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted heterocycloalkylene group of 2 to 10 ring-forming carbon atoms, a substituted or unsubstituted cycloalkenylene group of 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted arylene group of 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroarylene group of 2 to 60 ring-forming carbon atoms,

p and s are each independently an integer from 0 to 4,

q and r are each independently an integer from 0 to 3, and

R 1 to R 5 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted oxy group, a substituted or unsubstituted alkyl group of 1 to 60 carbon atoms, a substituted or unsubstituted heterocycloalkyl group of 3 to 60 ring-forming carbon atoms, a substituted or unsubstituted aryl group of 6 to 60 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group of 2 to 60 ring-forming carbon atoms.