EAGER: Workfunction Modification of ZnO for Anode Applications in Second Generation Organic Light Emitting Diodes for Solid State Lighting

University Of North Texas, Denton TX

Investigators

Abstract

This EArly-concept Grants for Exploratory Research (EAGER) grant provides funding to assess the effectiveness of oxygen plasma as a means of tuning the workfunction, and therefore charge injection properties of zinc oxide (ZnO) films for potential use as anodes in organic light emitting diodes (OLEDs). Measurements of the workfunction, composition, structure, conductivity and luminescent properties of pulsed laser deposited and magnetron sputtered ZnO films before and after they had been exposed to oxygen plasma treatments of specific duration, plasma density and applied power will determine the induced workfuction alterations, as well as correlate structural modifications with changes in electro-optical properties. To gain insight to the charge injection mechanism, temperature dependent current-voltage measurements of "hole-only" structures with as-deposited ZnO films will be compared to structures with plasma treated films and known workfunction changes. In parallel, Density Functional Theory (DFT) simulations of defected ZnO surfaces will compute properties such as defect structure and workfunction changes due to surface modification by oxygen plasma. This work addresses the need for significantly reduced OLED materials and processing costs. The combination of experimental methods and computational techniques is expected to provide predictive models for the ZnO surface modification and properties changes due to oxygen plasma processing, and a deeper understanding of the basic mechanisms involved. The results will indicate the feasibility of using ZnO for hole injection instead of the typical ITO/organic hole injector/ organic hole transporter multilayer stack. The higher ZnO thermal conductivity compared to organic materials can be expected to reduce device operating temperature, and increase device stability and lifetime. Its relatively low cost compared to ITO and organic hole injectors can be expected to have a significant positive impact on OLED commercialization. As such, ZnO anodes could potentially be the foundation for a second generation of low cost OLEDs.