Light-emitting element, light-emitting device, electronic device, and lighting device
An object is to provide a light-emitting element capable of emitting light with a high luminance even at a low voltage, and having a long lifetime. The light-emitting element includes n EL layers between an anode and a cathode (n is a natural number of two or more), and also includes, between m-th EL layer from the anode and (m+1)-th EL layer (m is a natural number, 1≤m≤n−1), a first layer including a first donor material in contact with the m-th EL layer, a second layer including an electron-transport material and a second donor material in contact with the first layer, and a third layer including a hole-transport material and an acceptor material in contact with the second layer and the (m+1)-th EL layer.
1 . A light-emitting device comprising:
a first electrode;
a first hole-transport layer over the first electrode;
a first light-emitting layer over the first hole-transport layer;
a first electron-transport layer over the first light-emitting layer;
an intermediate layer over the first electron-transport layer, the intermediate layer comprising:
a first region comprising a first electron-transport material;
a second region comprising a second electron-transport material; and
a third region comprising a hole-transport material and a first substance;
a second hole-transport layer over the intermediate layer;
a second light-emitting layer over the second hole-transport layer; and
a second electrode over the second light-emitting layer,
wherein the first region comprises one of an alkaline metal element and an alkaline earth metal element,
wherein the second electron-transport material has one of a perylene skeleton and a phenanthroline skeleton, and
wherein the first substance is a compound having one of a cyano group and a fluoro group or a transition metal oxide compound.
2 . The light-emitting device according to claim 1 , further comprising:
a second electron-transport layer over the second light-emitting layer;
a third hole-transport layer over the second electron-transport layer; and
a third light-emitting layer between the third hole-transport layer and the second electrode.
3 . The light-emitting device according to claim 1 , wherein the one of the perylene skeleton and the phenanthroline skeleton is substituted with one of a cyano group and a fluoro group.
4 . The light-emitting device according to claim 1 , wherein the second electron-transport material has a LUMO level greater than or equal to −5.0 eV and lower than or equal to −3.0 eV.
5 . The light-emitting device according to claim 1 , wherein the third region is in contact with the second hole-transport layer.
6 . An electronic device comprising the light-emitting device according to claim 1 .
7 . A light-emitting device comprising:
a first electrode;
a first electroluminescent unit over the first electrode;
a first intermediate layer over the first electroluminescent unit, the first intermediate layer comprising:
a first region comprising a first electron-transport material;
a second region comprising a second electron-transport material; and
a third region comprising a hole-transport material and a first substance;
a second electroluminescent unit over the first intermediate layer; and
a second electrode over the second electroluminescent unit,
wherein the first region comprises one of an alkaline metal element and an alkaline earth metal element,
wherein the second electron-transport material has one of a perylene skeleton and a phenanthroline skeleton, and
wherein the first substance is a compound having one of a cyano group and a fluoro group or a transition metal oxide compound.
8 . The light-emitting device according to claim 7 , further comprising:
a second intermediate layer between the second electroluminescent unit and the second electrode, the second intermediate layer comprising the first electron-transport material, the second electron-transport material, the hole-transport material and the first substance; and
a third electroluminescent unit between the second intermediate layer and the second electrode.
9 . The light-emitting device according to claim 7 , wherein the one of the perylene skeleton and the phenanthroline skeleton is substituted with one of a cyano group and a fluoro group.
10 . The light-emitting device according to claim 7 , wherein the second electron-transport material has a LUMO level greater than or equal to −5.0 eV and lower than or equal to −3.0 eV.
11 . The light-emitting device according to claim 7 , wherein the third region is in contact with the second electroluminescent unit.
12 . An electronic device comprising the light-emitting device according to claim 7 .
13 . A light-emitting device comprising:
a first electrode;
a first hole-transport layer over the first electrode;
a first light-emitting layer over the first hole-transport layer;
a first electron-transport layer over the first light-emitting layer;
an intermediate layer over the first electron-transport layer, the intermediate layer comprising:
a first region comprising a first electron-transport material;
a second region comprising a second electron-transport material; and
a third region comprising a hole-transport material and a first substance;
a second hole-transport layer over the intermediate layer;
a second light-emitting layer over the second hole-transport layer; and
a second electrode over the second light-emitting layer,
wherein the first region comprises one of an alkaline metal element and an alkaline earth metal element,
wherein the second electron-transport material has one of a perylene skeleton and a nitrogen-containing condensed aromatic ring skeleton,
wherein the second electron-transport material has a LUMO level greater than or equal to −5.0 eV and lower than or equal to −3.0 eV, and
wherein the first substance is a compound having one of a cyano group and a fluoro group or a transition metal oxide compound.
14 . The light-emitting device according to claim 13 , further comprising:
a second electron-transport layer over the second light-emitting layer;
a third hole-transport layer over the second electron-transport layer; and
a third light-emitting layer between the third hole-transport layer and the second electrode.
15 . The light-emitting device according to claim 13 , wherein the one of the perylene skeleton and the nitrogen-containing condensed aromatic ring skeleton is substituted with one of a cyano group and a fluoro group.
16 . The light-emitting device according to claim 13 , wherein the third region is in contact with the second hole-transport layer.
17 . An electronic device comprising the light-emitting device according to claim 13 .