An organic light emitting diode is a solid-state semiconductor device that is around 200 times smaller than a human hair.

They can either two or three layers or organic material.

In a two layer design the layers consist of:

• substrate layer which supports the OLED - this layer is made of clear plastic, glass or foil
• an anode which removes electrons when a current flows through the device. The removal of electrons adds electrons "holes".
• the organic layers which are made of organic molecules or polymers.
  

- the conducting layer is made of organic plastic molecules that transport the holes from the anode . An example of a conducting polymer used in OLED's is polyaniline.
- the emissive layer is made of organic plastic molecules that transport electrons from the cathode. The light is made at this point. An example of a polymer used in the emissive layer is polyfluorene.

• a cathode injects electron when a current flows through the device.