Light-emitting element, light-emitting device, display device, and electronic apparatus

1. A light-emitting element, comprising:

a cathode;

an anode; and

a light-emitting unit provided between the cathode and the anode to emit light when a driving voltage is applied,

wherein the light-emitting unit includes a first light-emitting layer emitting first light, an intermediate layer, a second light-emitting layer emitting second light having a different color from the first light, and a third light-emitting layer emitting third light having a different color from the first light, which are laminated from the anode side to the cathode side,

wherein each of the second and third light-emitting layers is configured to contain a luminescent material, a host material, and an assist dopant material,

wherein the intermediate layer is configured to contain the host material and the assist dopant material,

wherein one of the host material and the assist dopant material is material having high electron transportability, and the other thereof is a material having high hole transportability, and

wherein, when the concentrations of the assist dopant materials contained in the second light-emitting layer, the third light-emitting layer, and the intermediate layer are respectively expressed by C Assist (EML2), C Assist (EML3), and C Assist (IML), the following Relational Expression (A) is satisfied:

C Assist ( IML )> C Assist ( EML 2)≧ C Assist ( EML 3)  (A).

2. The light-emitting element according to claim 1 ,

wherein the host material is a material having high electron transportability, and the assist dopant material is a material having high hole transportability.

3. The light-emitting element according to claim 2 ,

wherein, in each of the second and third light-emitting layers and the intermediate layer, when mobility of holes is expressed by μh and mobility of electrons is expressed by μe, in the intermediate layer and the second light-emitting layer, the following Relational Expression (1) is satisfied:

0.01≦μ e/μh≦ 100  (1).

4. The light-emitting element according to claim 3 ,

wherein, in the third light-emitting layer, the following Relational Expression (2) is satisfied:

μ e/μh≧ 100  (2).

5. The light-emitting element according to claim 1 ,

wherein, when the thicknesses of the second and third light-emitting layers are respectively expressed by T(EML2) and T(EML3), the following Relational Expression (B) is satisfied:

T ( EML 2)≦ T ( EML 3)  (B).

6. The light-emitting element according to claim 1 ,

wherein the host material is an acene-based compound.

7. The light-emitting element according to claim 1 ,

wherein the assist dopant material is an amine-based compound.

8. The light-emitting element according to claim 7 ,

wherein the amine-based compound is a compound represented by the following Formula (4)

9. The light-emitting element according to claim 1 ,

wherein the luminescent materials respectively contained in the second light-emitting layer and the third light-emitting layer are the same as each other.

10. The light-emitting element according to claim 1 , wherein the luminescent materials respectively contained in the second light-emitting layer and the third light-emitting layer are different from each other.

11. A light-emitting device, comprising the light-emitting element according to claim 1 .

12. A light-emitting device, comprising the light-emitting element according to claim 2 .

13. A light-emitting device, comprising the light-emitting element according to claim 3 .

14. A light-emitting device, comprising the light-emitting element according to claim 4 .

15. A light-emitting device, comprising the light-emitting element according to claim 5 .

16. A light-emitting device, comprising the light-emitting element according to claim 6 .

17. A light-emitting device, comprising the light-emitting element according to claim 7 .

18. A light-emitting device, comprising the light-emitting element according to claim 8 .

19. A display device, comprising the light-emitting device according to claim 11 .

20. An electronic apparatus, comprising the display device according to claim 19 .