OLEDs are composed of several layers of organic materials with the purpose of transforming electrical current into light.
The electrodes on either side introduce holes and electrons into the device when a voltage is applied. The HTL/EBL play several roles such as optimizing hole injection from the anode to the emissive layer, adjusting the cavity as well as blocking electron ingress into the HTL. The ETL/HBL layer perform a similar function to the HTL/EBL but this time with the opposite charges. The EML contains the light emitting material, which will finally transform the holes and electrons (electrical energy) into light.
