Effect of dipole layer of Alq3 and metal on organic electroluminescence

The effect of dipole layer of Alq3 and metal on organic electroluminescence in organic light-emitting diodes(OLEDs) was discussed. The relations among energy level alignment,interface charge transfer and dipole layer formation were well analyzed. An interface dipole layer and charge transfer were observed by XPS and UPS. As for Alq3 with metallic film such as Al and Mg,N 1s,O 1s and C 1s all move to low binding energy. Both Alq3/Al and Alq3/Mg have different electron spectrum from that of simple Alq3 film. It is really the reason of the interface energy change that the metal atoms located near the interface move to organic layer and then chemically interact with O and C of Alq3. The injection voltage barrier heights of electrons at Alq3/Al and Alq3/Mg interface are 0.1 eV and 0.2 eV,respectively. Charge transfer lowers electrons injection voltage barrier height and forms good electrons injection interfaces. The width of dipole layer is about 5 nm. The knowledge of such interface dipole layer is essential for a proper understanding of the physical processes at the metal/organic interface.