Light-emitting device, light-emitting apparatus, electronic device, and lighting device

1. A light-emitting device comprising:

an anode;

a cathode; and

an EL layer between the anode and the cathode,

wherein the EL layer includes a hole-injection layer, a light-emitting layer, and an electron-transport layer,

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

wherein the electron-transport layer is positioned between the light-emitting layer and the cathode,

wherein the hole-injection layer contains a first substance and a second substance,

wherein the first substance is an organic compound which has a hole-transport property and a HOMO level higher than or equal to −5.7 eV and lower than or equal to −5.4 eV,

wherein the second substance exhibits an electron-accepting property with respect to the first substance, and

wherein the electron-transport layer contains a material whose resistance decreases with current flowing therethrough.

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

wherein the material whose resistance decreases with current flowing therethrough contains an organometallic complex of an alkali metal or an alkaline earth metal.

3. The light-emitting device according to claim 1 ,

wherein the material whose resistance decreases with current flowing therethrough contains an organic compound having an electron-transport property and an organometallic complex of an alkali metal or an alkaline earth metal.

4. The light-emitting device according to claim 2 ,

wherein the organometallic complex of an alkali metal or an alkaline earth metal forms a cluster.

5. The light-emitting device according to claim 2 ,

wherein the organometallic complex of an alkali metal or an alkaline earth metal is a metal complex including a ligand containing nitrogen and oxygen and an alkali metal or an alkaline earth metal.

6. The light-emitting device according to claim 2 ,

wherein the organometallic complex of an alkali metal or an alkaline earth metal is a metal complex including a monovalent metal ion and a ligand having an 8-hydroxyquinolinato structure.

7. The light-emitting device according to claim 2 ,

wherein the organometallic complex of an alkali metal or an alkaline earth metal is a lithium complex including a ligand having an 8-hydroxyquinolinato structure.

8. The light-emitting device according to claim 2 ,

wherein the electron-transport layer includes a first layer and a second layer,

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

wherein the second layer is positioned between the first layer and the cathode, and

wherein a concentration of the organometallic complex of an alkali metal or an alkaline earth metal in the first layer is different from that in the second layer.

9. The light-emitting device according to claim 8 ,

wherein the concentration of the organometallic complex of an alkali metal or an alkaline earth metal in the first layer is higher than that in the second layer.

10. The light-emitting device according to claim 1 ,

wherein the second substance is an organic compound.

11. The light-emitting device according to claim 1 ,

wherein the light-emitting layer contains a host material and a light-emitting substance, and

wherein the light-emitting substance emits blue fluorescence.

12. An electronic device comprising:

the light-emitting device according to claim 1 ; and

a sensor, an operation button, a speaker, or a microphone.

13. A light-emitting apparatus comprising:

the light-emitting device according to claim 1 ; and

a transistor or a substrate.

14. A lighting device comprising:

the light-emitting device according to claim 1 ; and

a housing.