Light-emitting device, light-emitting apparatus, electronic device, and lighting device
A novel light-emitting device is provided. A light-emitting device with high emission efficiency is provided. A light-emitting device with a long lifetime is provided. A light-emitting device with low driving voltage is provided. The light-emitting device includes an anode, a cathode, and an EL layer between the anode and the cathode. The EL layer includes a hole-injection layer, a light-emitting layer, and an electron-transport layer. The hole-injection layer is positioned between the anode and the light-emitting layer. The electron-transport layer is positioned between the light-emitting layer and the cathode. The hole-injection layer contains a first substance and a second substance. 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. The second substance exhibits an electron-accepting property with respect to the first substance. The electron-transport layer contains a material whose resistance decreases with current flowing therethrough.
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 light-emitting layer and an electron-transport layer,
wherein the electron-transport layer is positioned between the light-emitting layer and the cathode,
wherein the electron-transport layer contains a material whose resistance decreases with current flowing therethrough, and
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.
2. The light-emitting device according to claim 1 ,
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.
3. The light-emitting device according to claim 2 ,
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.
4. 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.
5. 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 light-emitting layer;
a hole-injection layer between the anode and the light-emitting layer; and
an electron-transport 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 electron-transport layer contains a material whose resistance decreases with current flowing therethrough, and
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.
6. 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 light-emitting layer;
a hole-injection layer between the anode and the light-emitting layer; and
an electron-transport 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 electron-transport layer contains a material whose resistance decreases with current flowing therethrough,
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, and
wherein the first substance and the second substance are selected in such a way that a carrier recombination region in the light-emitting device extends to the electron-transport layer at an initial driving stage.
7. The light-emitting device according to claim 1 ,
wherein the organic compound having an electron-transport property is represented by the following Chemical Formula:
and
wherein the organometallic complex of an alkali metal or an alkaline earth metal is represented by the following Chemical Formula:
8. The light-emitting device according to claim 5 ,
wherein the organic compound having an electron-transport property is represented by the following Chemical Formula:
and
wherein the organometallic complex of an alkali metal or an alkaline earth metal is represented by the following Chemical Formula:
9. The light-emitting device according to claim 6 ,
wherein the organic compound having an electron-transport property is represented by the following Chemical Formula:
and
wherein the organometallic complex of an alkali metal or an alkaline earth metal is represented by the following Chemical Formula:
10. The light-emitting device according to claim 1 ,
wherein the organic compound having an electron-transport property is represented by the following Chemical Formula:
and
wherein the organometallic complex of an alkali metal or an alkaline earth metal is represented by the following Chemical Formula:
11. The light-emitting device according to claim 5 ,
wherein the organic compound having an electron-transport property is represented by the following Chemical Formula:
and
wherein the organometallic complex of an alkali metal or an alkaline earth metal is represented by the following Chemical Formula:
12. The light-emitting device according to claim 6 ,
wherein the organic compound having an electron-transport property is represented by the following Chemical Formula:
and
wherein the organometallic complex of an alkali metal or an alkaline earth metal is represented by the following Chemical Formula: