Paper OF+TF-ThM1
Characterization and Modification of ITO Surfaces: Use of Chemisorbed Probe Molecules as Indicators of Electron Transfer Rates and Their Use in Improving OLED Performance
XPS characterization of ITO surfaces, following various pretreatments, shows that the surface coverage of hydroxyl groups, and oxygen defects, can be varied significantly. Probe molecules, such as ferrocene dicaroboxylic acid (Fc(COOH)2) can be chemisorbed to these surfaces through hydrogen bonding interactions, at coverages up to 40% of a compact monolayer. The coverage and electron transfer rates of these chemisorbed molecules vary by up to 100% depending upon pretreatments used. Organic light emitting diodes, prepared by spin coating single polymer layers (PVK), doped with Alq3, and its tri-sulfonamide analog, Al(qs)3, show signficant lowering of onset potentials for electroluminescence for ITO films modified with the Fc(COOH)2 probe, following air plasma cleaning. These differences in onset potential are most significant for devices where electron injection is not the chief limitation to electroluminescence.