Abstract
Organic light emitting devices (OLEDs) has superiority to traditional LEDs by its low power consumption and wide viewing angle. Alq3 is the most popular material for the electron transport layer in OLED, which was constructed by three quinolines and an aluminum atom. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of Alq3 band are located on the phenoxide site and pyridrl site on Alq3 molecule, respectively. We have focused on the interface between Alq3 and the metal cathode in this research, which dominates the barrier of electron injection from metal cathode to the organic layer. We used the synchrotron radiation to take our data and investigate the how Alq3 interact with Ag with different thickness.According to our experiment, we differentiate Ag deposition on Alq3 into two stages. In stage I, Ag atom diffuses into thick Alq3 film and causes band bending of Alq3. In stage II, the Ag dopant grows as clusters on the top of the Alq3 than diffusing into it. In the process of Ag dopant becomes more to decrease the inevitable charging effect of thick organic layer. On the other hand, the Ag donate charge to the N atom in Alq3, which forms the cluster-induced dipole with magnitude 0.24 eV. This leads us to detect the vacuum level (VL) difference between Ag and Alq3 including work function difference and cluster-induced dipole, which with magnitude 0.6eV. By the way, the large cluster size of Ag would elongate the Al - O bond and make a new component appear in O 1s spectrum.