US Patent 7960038 Light emitting device and electronic appliance using the same

The light emitting element includes a first electrode and a second electrode, between which a light emitting layer, a hole transporting layer provide in contact with the light emitting layer, an electron transporting layer provided in contact with the light emitting layer, and a mixed layer provided between the electron transporting layer and the second electrode. The mixed layer includes an electron transporting substance and a substance showing an electron donating property with respect to the electron transporting substance. The light emitting layer includes an organometallic complex represented in General Formula (1) and a host. R1 and R2 each represent an electron-withdrawing substituent group. R3 and R4 each represent any of hydrogen or an alkyl group having 1 to 4 carbon atoms. L represents any of a monoanionic ligand having a beta-diketone structure, a monoanionic bidentate chelating ligand having a carboxyl group, or a monoanionic bidentate chelating ligand having a phenolic hydroxyl group.