AVS 45th International Symposium
    Organic Electronic Materials Topical Conference Monday Sessions
       Session OE+EM-MoM

Paper OE+EM-MoM9
XPS and AFM Investigation of Stability Mechanism of tris-(8-hydroxyquinoline) Aluminium Based Light-Emitting Devices

Monday, November 2, 1998, 11:00 am, Room 327

Session: Organic Thin Film Devices I: Light Emitters
Presenter: Q.T. Le, University of Rochester
Authors: Q.T. Le, University of Rochester
F.M. Avendano, University of Rochester
E.W. Forsythe, University of Rochester
L. Yan, University of Rochester
Y. Gao, University of Rochester
C.W. Tang, Eastman Kodak Company
Correspondent: Click to Email
Stability is an essential issue in the application of organic light-emitting devices (OLEDs). We have investigated the indium tin oxide (ITO) surface for operated and un-operated OLEDs that consist of ITO/phenyl-diamine (NPB)/tris-(8-hydroxyquinoline) aluminium (Alq@sub 3@)/Mg:Ag with NPB thickness varied from 0 to 300 Å using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The ITO surface was exposed by removing the organic and metal layers with dichloromethane, an organic solvent in which NPB and Alq@sub 3@ are highly soluble. Electroluminescence (EL) characterization demonstrates that the NPB layer substantially enhanced the stability. XPS analysis shows that for the device made without NPB and after 90 hours of operation, there exists an insoluble organic material on the ITO surface. This organic material is not observed on the ITO of un-operated cells nor of the operated NPB-containing devices. Lateral force AFM also shows a striking difference between the ITO surface of devices with and without NPB after operation. The XPS and AFM results suggest that the organic residue is the degradation product of Alq@sub 3@ that act as quenching sites at the ITO/Alq@sub 3@ interface, which may lead to the early failure of the single layer devices. This work was supported in part by DARPA DAAL 0196K0086 and NSF grant DMR-9612370.