Light-emitting element, light-emitting device, electronic device, and lighting device comprising a metal complex having a metal-oxygen bond and an aromatic ligand

摘要

A light-emitting element which emits light with high luminance and can be driven at low voltage. The light-emitting element includes n (n is a natural number of 2 or more) EL layers between an anode and a cathode, and includes a first layer, a second layer, and a third layer between an m-th (m is a natural number, 1≦m≦n−1) EL layer from the anode and an (m+1)th EL layer. The first layer functions as a charge-generation region, has hole-transport properties, and contains an acceptor substance. The third layer has electron-transport properties and contains an alkali metal or the like. The second layer formed of a metal complex having a metal-oxygen bond and an aromatic ligand is provided between the first and third layers, whereby an injection barrier at the time of injecting electrons generated in the first layer into the m-th EL layer through the third layer can be lowered.

主权项

1. A light-emitting element comprising:
n EL layers between an anode and a cathode, n being a natural number greater than or equal to 2; and a first layer, a second layer, and a third layer between an m-th EL layer from the anode and an (m+1)th EL layer, m being a natural number greater than or equal to 1 and lesser than or equal to (n−1), wherein the first layer is provided between the (m+1)th EL layer and the second layer, is in contact with the (m+1)th EL layer and the second layer, and contains an organic compound and an acceptor substance, wherein the second layer is provided between the first layer and the third layer, is in contact with the first layer and the third layer, and consists essentially of a metal complex having a metal-oxygen bond and an aromatic ligand, wherein the third layer is provided between the second layer and the m-th EL layer, is in contact with the second layer and the m-th EL layer, and contains an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal compound, an alkaline earth metal compound, or a rare earth metal compound, and wherein a LUMO level of the metal complex is greater than or equal to −5.0 eV and less than or equal to −3.0 eV.