Light-emitting element, comprising an organometallic complex light-emitting material, a light-emitting device and an electronic device comprising the light-emitting element

A light-emitting element comprising:

• an anode;
• a hole-injection layer over the anode;
• a hole-transporting layer over the hole-injection layer;
• a first light-emitting layer over the hole-transporting layer;
• a second light-emitting layer over the first light-emitting layer;
• and
• a cathode over the second light-emitting layer,
• wherein each of the first light-emitting layer and the second light-emitting layer comprises a host material, a hole-transporting material, and a light-emitting material,
• wherein each of the hole-injection layer and the hole-transporting layer comprises the hole-transporting material,
• wherein the host material is a heteroaromatic compound or a metal complex, and has an electron-transporting property,
• wherein the hole-transporting material is a carbazole derivative,
• wherein the light-emitting material is a compound emitting phosphorescence,
• wherein a mass ratio of the hole-transporting material to the host material in the first light-emitting layer is greater than or equal to 0.25 and less than or equal to 0.5, and
• wherein a mass ratio of the hole-transporting material to the host material in the second light-emitting layer is equal to 0.1.

A light-emitting element comprising:

• an anode;
• a cathode;
• a first light-emitting layer and a second light-emitting layer between the anode and the cathode;
• a hole-injection layer between the anode and the first light-emitting layer;
• and
• a hole-transporting layer between the hole-injection layer and the first light-emitting layer,
• wherein each of the first light-emitting layer and the second light-emitting layer comprises a host material, a hole-transporting material, and a light-emitting material,
• wherein each of the hole-injection layer and the hole-transporting layer comprises the hole-transporting material,
• wherein the host material is a heteroaromatic compound or a metal complex, and has an electron-transporting property,
• wherein the hole-transporting material is a carbazole derivative,
• wherein the light-emitting material is a compound emitting phosphorescence,
• wherein a mass ratio of the hole-transporting material to the host material in the first light-emitting layer is greater than or equal to 0.25 and less than or equal to 0.5, and
• wherein a mass ratio of the hole-transporting material to the host material in the second light-emitting layer is equal to 0.1.

A light-emitting element comprising:

• an anode;
• a cathode;
• and
• a first light-emitting layer and a second light-emitting layer between the anode and the cathode,
• wherein each of the first light-emitting layer and the second light-emitting layer comprises a host material, a hole-transporting material, and a light-emitting material,
• wherein the host material is one of bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) and 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]carbazole,
• wherein the hole-transporting material is one of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl and 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine,
• wherein the light-emitting material is one of (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III), and bis{2-(4-fluorophenyl)-3,5-dimethylpyrazinato}(picolinato) iridium(III),
• wherein a mass ratio of the hole-transporting material to the host material in the first light-emitting layer is greater than or equal to 0.25 and less than or equal to 0.5, and
• wherein a mass ratio of the hole-transporting material to the host material in the second light-emitting layer is equal to 0.1.