Organic-based devices, such as organic light-emitting diodes, require a transparent conductive layer with a high work function, meaning it promotes injection of electron holes into an organic layer to produce more light.
Research presented on July 8 at the International Conference on Science and Technology of Synthetic Metals in Brazil provides insight into factors that influence the injection efficiency. A balanced injection of positive and negative charge carriers into the organic layer is important to achieve high quantum efficiency, but the interface between the metallic coating and organic layer where the injection occurs is poorly understood.
Placing an organic layer on top of the conductive layer modifies each layer's individual work function, or the minimum energy needed to extract the first electron from the metal.
"Measuring the work functions independently for each layer does not provide an indication of how their energy levels match when they touch each other," explained Jean-Luc Brdas, a computational materials chemist, professor in the Georgia Institute of Technology's School of Chemistry and Biochemistry and Georgia Research Alliance Eminent Scholar.
The energy levels for each layer should align when attached; otherwise, a barrier will form and a higher voltage will be required to send current in.
With funding from the Office of Naval Research, Brdas first developed a theoretical model of the interface between conventional metals and a single layer of organic molecules forming a self-assembled monolayer on the metal. His goal was to determine how the metal work function could be modified by depositing the self-assembled monolayer.
Brdas and postdoctoral research fellow Georg Heimel, who is now at the Humboldt University in Berlin, looked for changes in the work function of gold when they modified the chemical nature of the head group of the organic molecules in the self-assembled monol
|Contact: Abby Vogel|
Georgia Institute of Technology Research News