Organic Light Emitting Diodes (OLED) are built up in layers. The layers of an OLED
are responsible for the injection and transport of the charge carriers. As with semiconductors, electrons and false electrons (holes) serve as charge carriers. The electrons are generated in the cathode and injected into the Electron Transport Layer (ETL); the holes in the anode and Hole In jection Layer (HIL) and drift through the Hole Transport Layer (HTL) to the Emission Layer (EML), where they recombine with the electrons, emitting light. The Hole Transport Layer thus has a transport function for the holes.