Organic electroluminescent device
The invention provides an organic electroluminescent device having high luminous efficiency, being able to drive at a low voltage and being excellent in driving durability including, between an anode and cathode, a luminescent layer containing a luminescent material, an electron-transport layer (ETL1) and an organic thin film layer (ETL2) in this order from the anode side, wherein the organic thin film layer (ETL2) contains an electron-transport material and has a thickness of 0.01 to 3 nm, and the ratio (ETL1/ETL2) of the thickness of the electron-transport layer (ETL1) to the thickness of the organic thin film layer (ETL2) is in the range of 5 to 500.
1. An organic electroluminescent device comprising a luminescent layer containing a luminescent material, an electron-transport layer (ETL1) and an organic thin film layer (ETL2) in this order from an anode side between a pair of electrodes, wherein:
the organic thin film layer (ETL2) contains an electron transporting material and has a thickness of 0.01 to 3 nm;
the ratio (ETL1/ETL2) of the thickness of the electron-transport layer (ETL1) to the thickness of the organic thin film layer (ETL2) is in the range of 5 to 500;
an electron affinity (ETL1 (Ea)) of the electron-transport layer (ETL1) and an electron affinity (ETL2 (Ea)) of the organic thin film layer (ETL2) satisfy the relationship represented by the following equation (2); and
the organic thin film layer (ETL2) is adjacent to a cathode layer:
ETL 1( Ea )> ETL 2( Ea ) (2)
wherein an electron transporting material contained in the electron-transport layer (ETL1) is a metal complex of an 8-quinolinol derivative, and the electron transporting material contained in the organic thin film layer (ETL2) is a metal complex containing at least one of bipyrene, carbazole, imidazopyridine, a derivative thereof, or a derivative of 2-(2-phenolato)imidazopyridine.
2. The organic electroluminescent device of claim 1 , wherein the work function of a material constituting the cathode layer is in the range of 2.5 to 4.5 eV.
3. The organic electroluminescent device of claim 1 , wherein the ratio (ETL1/ETL2) of the thickness of ETL1 to the thickness of ETL2 is in the range of 7 to 70.
4. The organic electroluminescent device of claim 1 , wherein the ratio (ETL1/ETL2) of the thickness of ETL1 to the thickness of ETL2 is in the range of 10 to 50.
5. The organic electroluminescent device of claim 1 , wherein the organic thin film layer (ETL2) contains at least one selected from pyrene, carbazole, imidazopyridine, a derivative thereof, or a metal complex thereof.
6. The organic electroluminescent device of claim 1 , wherein the electron-transport layer (ETL1) contains a metal complex.