This research will study the basic physical mechanisms and effectiveness of plasma surface treatments and nanoscale interfacial layers for improving hole injection from Earth abundant, inexpensive, zinc oxide based transparent conducting oxides. Transparent conducting oxides that allow good positive charge (holes) injection are critical for high efficiency organic light emitting diodes that can be used as energy efficient, general lighting sources. Indium-tin-oxide is currently the dominant transparent conducting oxide. However, it is expensive because of the Earth?s limited supply of indium, and alternatives are urgently needed for both organic light emitting diodes and solar cells. The experiments will use a combination of x-ray, ultraviolet and electron spectroscopies to measure the structural and chemical changes induced by the surface modification treatments, and electrical measurements to correlate these changes with the expected improvements in the zinc oxide hole injection properties. Device physics studies will be performed to measure how the expected improvements in the hole injection properties of the zinc oxide films influence the turn-on voltage, brightness, and power efficiency of complete organic light emitting diode test structures. Computational modeling and simulations using based on Density Functional Theory will assist the understanding obtained from the experimental research.
The combination of experimental and computational studies is expected to provide predictive models that facilitate rationally designed reductions in turn-on voltage, and power efficiency improvements in second generation organic light emitting diodes with zinc oxide anodes, and, fewer device layers. Fewer device layers and zinc oxide anodes are expected to translate into significantly reduced materials and processing costs. In turn, reduced organic light emitting diode cost is expected to encourage their widespread use for general lighting, which can have a significant impact on reducing the amount of fossil fuel consumed by general lighting.
