Organic light emitting element

An organic light emitting element comprising:

• a first electrode;
• a plurality of hole transport layers disposed on the first electrode;
• an emission layer disposed on the plurality of hole transport layers;
• a hole blocking layer disposed on the emission layer;
• an electron transport layer disposed on the hole blocking layer;
• and
• a second electrode disposed on the electron transport layer, wherein
• the plurality of hole transport layers comprise:
• a first hole transport layer having a first refractive index;
• a second hole transport layer disposed between the emission layer and the first hole transport layer, the second hole transport layer having a second refractive index less than the first refractive index;
• and
• a third hole transport layer disposed between the first hole transport layer and the first electrode, the third hole transport layer having a third refractive index less than the first refractive index,
• the second refractive index, the third refractive index, a refractive index of the emission layer, and a refractive index of the electron transport layer are each in a range of about 1.2 to about 1.7,
• the first refractive index and a refractive index of the hole blocking layer are each in a range of about 1.7 to about 2.2, and
• the second refractive index, the third refractive index, the refractive index of the emission layer, and the refractive index of the electron transport layer are each less than the first refractive index.