Surface modification of indium tin oxide for organic light-emitting diodes

grantor: University of TorontoOrganic light emitting diodes (OLEDs) have attracted a wide spread interest due to their potential applications in multicolor flat panel displays. OLEDs are essentially one or several organic thin film semiconductors sandwiched between two electrodes. The charge carrier injection efficiency of OLEDs is affected by the energy barrier height at the interfaces between thin layers in the device. Indium tin oxide (ITO) is used as the anode for injection of holes into highest occupied molecular orbitals (HOMO) of the organic semiconductors in OLEDs. This thesis deals mainly with surface modification of ITO. By surface modification, the work function of ITO could be increased, and hence the energy barrier between Fermi level of the anode and HOMO of the organic semiconductor is decreased. Accordingly, the drive voltage of OLEDs could be reduced. ITO surfaces were modified by oxygen, ammonia, and argon plasma respectively. X-ray photoelectron spectroscopy (XPS) has been used to characterize these surfaces. A surface band-bending model is proposed based on the XPS information. This band model successfully explains the change in work function of ITO after plasma treatment. Hydrogenated amorphous carbon (a-C:H) films deposited by ethylene plasma under various conditions were also studied in this thesis. The distribution of 'sp'3 and 'sp'2 bonding in these films was investigated using XPS and x-ray absorption near-edge spectroscopy (XANES). The factors affecting the structure of the a-C:H films are discussed.M.A.Sc