Display device, display module, and electronic device

1 . A display device comprising:

a first light-emitting device and a second light-emitting device,

wherein the first light-emitting device comprises a first electrode and a common electrode,

wherein the second light-emitting device comprises a second electrode and the common electrode,

wherein the first light-emitting device comprises a first hole-injection layer, a first hole-transport layer, a second hole-transport layer, a first light-emitting layer, and an electron-transport layer between the first electrode and the common electrode,

wherein the second light-emitting device comprises a second hole-injection layer, a third hole-transport layer, a fourth hole-transport layer, and a second light-emitting layer between the second electrode and the common electrode,

wherein the second hole-transport layer is in contact with the first light-emitting layer,

wherein the fourth hole-transport layer is in contact with the second light-emitting layer,

wherein the first light-emitting layer comprises a first organic compound emitting light of a first color,

wherein the second light-emitting layer comprises a second organic compound emitting light of a second color,

wherein the electron-transport layer comprises a third organic compound and a first substance,

wherein the third organic compound is an electron-transport material,

wherein the first substance is a metal, a metallic salt, a metal oxide, or an organometallic salt,

wherein the electron-transport layer comprises a first region and a second region,

wherein the first region and the second region differ in a concentration of the first substance,

wherein the first hole-transport layer and the third hole-transport layer comprise the same compound,

wherein the second hole-transport layer and the fourth hole-transport layer comprise different compounds,

wherein each of the first hole-injection layer and the second hole-injection layer comprises a first compound and a second compound,

wherein the first compound has a property of accepting electrons from the second compound, and

wherein the second compound has a HOMO level higher than or equal to −5.7 eV and lower than or equal to −5.4 eV.

2 . The display device according to claim 1 ,

wherein the first region is positioned closer to the first light-emitting layer than the second region is, and

wherein the first region has a higher concentration of the first substance than the second region.

3 . The display device according to claim 1 ,

wherein the second light-emitting device comprises a layer common to the first light-emitting device between the second electrode and the common electrode.

4 . The display device according to claim 1 ,

wherein the third organic compound has a HOMO level higher than or equal to −6.0 eV, and has an electron mobility higher than or equal to 1×10 −7 cm 2 /Vs and lower than or equal to 5×10 −5 cm 2 /Vs when a square root of electric field strength [V/cm] is 600.

5 . The display device according to claim 1 ,

wherein the first hole-injection layer is in contact with one of the first electrode and the common electrode which is configured to be an anode.

6 . The display device according to claim 5 ,

wherein the first hole-transport layer is positioned between the first hole-injection layer and the first light-emitting layer,

wherein the first hole-transport layer comprises a third compound,

wherein a HOMO level of the third compound is a value lower than or equal to a HOMO level of the second compound, and

wherein a difference between the HOMO level of the third compound and the HOMO level of the second compound is 0.2 eV or less.

7 . The display device according to claim 6 ,

wherein the second compound and the third compound each comprise at least one of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton.

8 . The display device according to claim 6 ,

wherein the second hole-transport layer is positioned between the first hole-transport layer and the first light-emitting layer,

wherein the second hole-transport layer comprises a fourth compound, and

wherein a HOMO level of the fourth compound is lower than the HOMO level of the third compound.

9 . The display device according to claim 8 ,

wherein the second compound, the third compound, and the fourth compound each comprise at least one of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton.

10 . The display device according to claim 1 ,

wherein the first organic compound is a fluorescent substance.

11 . The display device according to claim 1 ,

wherein the first color is blue, and

wherein the second color is red or green.

12 . The display device according to claim 1 ,

wherein the first substance is an organometallic complex comprising an alkali metal or an alkaline earth metal.

13 . The display device according to claim 1 ,

wherein the first substance is an organometallic complex comprising a ligand comprising nitrogen and oxygen, and an alkali metal or an alkaline earth metal.

14 . The display device according to claim 1 ,

wherein the first substance is an organometallic complex comprising a quinolinol ligand, and an alkali metal or an alkaline earth metal.

15 . A display module comprising the display device according to claim 1 , and a connector or an integrated circuit.

16 . An electronic device comprising:

the display module according to claim 15 ; and

at least one of an antenna, a battery, a housing, a camera, a speaker, a microphone, and an operation button.

17 . The display device according to claim 1 ,

wherein the second light-emitting layer further comprises a fourth organic compound and a fifth organic compound, and

wherein a combination of the fourth organic compound and the fifth organic compound forms an exciplex.