Light-emitting element and display device including the light-emitting element
Disclosed is a light-emitting element including an anode, a first functional layer over the anode, an emission layer over and in contact with the first functional layer, an electron-transporting layer over the emission layer, and a cathode over the electron-transporting layer. The first functional layer includes a first hole-transporting material and a hole-trapping material. The emission layer includes a host material, an emission material, and the hole-trapping material. Concentrations of the hole-trapping material are lower than concentrations of the first hole-transporting material and the host material in the first functional layer and the emission layer, respectively. A highest occupied molecular orbital level of the hole-trapping material is higher than a highest occupied molecular orbital level of the first hole-transporting material and a highest occupied molecular orbital level of the host material.
1 . A light-emitting element comprising:
an anode;
a first functional layer over the anode, the first functional layer including a first hole-transporting material and a hole-trapping material;
a second functional layer located between the anode and the first functional layer, in contact with the first functional layer, and including a second hole-transporting material and the hole-trapping material;
an emission layer over and in contact with the first functional layer, the emission layer including a host material, an emission material, and the hole-trapping material;
an electron-transporting layer over the emission layer; and
a cathode over the electron-transporting layer,
wherein concentrations of the hole-trapping material are lower than concentrations of the first hole-transporting material and the host material in the first functional layer and the emission layer, respectively,
a highest occupied molecular orbital level of the hole-trapping material is higher than a highest occupied molecular orbital level of the first hole-transporting material and a highest occupied molecular orbital level of the host material,
a concentration of the hole-trapping material is lower than that of the second hole-transporting layer in the second functional layer, and
a highest occupied molecular orbital of the second hole-transporting material is higher than the highest occupied molecular orbital of the hole-trapping material.
2 . The light-emitting element according to claim 1 ,
wherein a difference between the highest occupied molecular orbital level of the hole-trapping material and the highest occupied molecular orbital level of the first hole-transporting material is equal to or more than 0.2 eV.
3 . The light-emitting element according to claim 1 ,
wherein a lowest unoccupied molecular orbital level of the first hole-transporting material is higher than a lowest unoccupied molecular orbital level of the host material by 0.2 eV or more.
4 . The light-emitting element according to claim 1 ,
wherein the concentrations of the hole-trapping material are each equal to or more than 5 vol % and equal to or less than 30 vol % in the first functional layer and the emission layer.
5 . The light-emitting element according to claim 1 ,
wherein the concentrations of the hole-trapping material are the same as each other in the first functional layer and the emission layer.
6 . The light-emitting element according to claim 1 ,
wherein the concentration of the hole-trapping material in the emission layer is lower than the concentration of the hole-trapping material in the first functional layer.
7 . The light-emitting element according to claim 1 ,
wherein a thickness of the first functional layer is equal to or more than 1 nm and equal to or less than 5 nm.
8 . A display device comprising:
a first pixel including a first light-emitting element; and
a second pixel including a second light-emitting element,
wherein the first light-emitting element comprises:
a first anode;
a first functional layer over the first anode, the first functional layer including a first hole-transporting material and a hole-trapping material;
a second functional layer located between the first anode and the first functional layer, in contact with the first functional layer, and including a second hole-transporting material and the hole-trapping material;
a first emission layer over and in contact with the first functional layer, the emission layer including a first host material, a first emission material, and the hole-trapping material;
an electron-transporting layer over the first emission layer; and
a cathode over the electron-transporting layer,
the second light-emitting element comprises:
a second anode;
a hole-transporting layer over the second anode, the hole-transporting layer including the first hole-transporting material;
a second emission layer over the hole-transporting layer, the second emission layer including a second host material and a second emission material;
the electron-transporting layer over the second emission layer; and
the cathode over the electron-transporting layer,
wherein concentrations of the hole-trapping material are lower than concentrations of the first hole-transporting material and the first host material in the first functional layer and the first emission layer, respectively,
a highest occupied molecular orbital level of the hole-trapping material is higher than a highest occupied molecular orbital level of the first hole-transporting material and a highest occupied molecular orbital level of the first host material,
a concentration of the hole-trapping material is lower than that of the second hole- transporting layer in the second functional layer, and
a highest occupied molecular orbital of the second hole-transporting material is higher than the highest occupied molecular orbital of the hole-trapping material.
9 . The display device according to claim 8 ,
wherein a difference between the highest occupied molecular orbital level of the hole-trapping material and the highest occupied molecular orbital level of the first hole-transporting material is equal to or more than 0.2 eV.
10 . The display device according to claim 8 ,
wherein a lowest unoccupied molecular orbital level of the first hole-transporting material is higher than a lowest unoccupied molecular orbital level of the first host material by 0.2 eV or more.
11 . The display device according to claim 8 ,
wherein the concentrations of the hole-trapping material are each equal to or more than 5 vol % and equal to or less than 30 vol % in the first functional layer and the first emission layer.
12 . The display device according to claim 8 ,
wherein the concentrations of the hole-trapping material are the same as each other in the first functional layer and the first emission layer.
13 . The display device according to claim 8 ,
wherein the concentration of the hole-trapping material in the first emission layer is lower than the concentration of the hole-trapping material in the first functional layer.
14 . The display device according to claim 8 ,
wherein a thickness of the first functional layer is equal to or more than 1 nm and equal to or less than 5 nm.
15 . The display device according to claim 8 ,
wherein an emission peak wavelength of the first emission material is longer than an emission peak wavelength of the second emission material.
16 . The display device according to claim 8 ,
wherein the first emission material is a phosphorescent material.