White organic electroluminescent device

1. A white organic electroluminescent device for emitting white light, the device comprising:

a substrate;

an anode placed;

a hole transport layer;

an emission layer having a red sub-emission layer, a green sub-emission layer, and a blue sub-emission layer; and

a cathode,

the anode, the hole transport layer, the emission layer and the cathode being placed on the substrate,

wherein:

the green sub-emission layer is placed to be in contact with the hole transport layer;

the red sub-emission layer is placed to be in contact with the green sub-emission layer;

the blue sub-emission layer is placed to be in contact with the red sub-emission layer;

the green sub-emission layer comprises a delayed fluorescent material;

the red sub-emission layer comprises a phosphorescent light emitting material;

a highest occupied molecular orbital (HOMO) of the delayed fluorescent material is deeper than an HOMO of a material of the hole transport layer; and

the HOMO of the delayed fluorescent material is shallower than an HOMO of the phosphorescent light emitting material.

2. The white organic electroluminescent device according to claim 1 , wherein:

an HOMO of a host material for the green sub-emission layer is deeper than the HOMO of the material of the hole transport layer; and

the HOMO of the host material for the green sub-emission layer is shallower than an HOMO of a host material for the red sub-emission layer.

3. The white organic electroluminescent device according to claim 2 , wherein the cathode comprises a transparent electrode placed on a light extraction side.

4. A display apparatus, comprising:

a display unit including the white organic electroluminescent device according to claim 1 ; and

a TFT for controlling a luminance of the white organic electroluminescent device.