Filamentary charge transport and recombination in organic semiconductors

Nontechnical Description This project focuses on understanding how electricity flows in organic semiconductors at the nanoscale. It has the potential to improve the efficiency and lifetime of devices such as organic light-emitting diodes that are used in displays and room lighting. Current knowledge assumes that electricity flows uniformly in these materials, but recent models predict that it breaks into nanoscale hot spots scattered around the film. By combining advances in optical microscopy, organic film growth, and three-dimensional modeling, this research will identify the factors that control filamentary transport in these important semiconductors. This project will support several graduate and undergraduate students, as well as develop educational activities for area high school students. The project thereby strengthens the semiconductor workforce in the United States. Technical Description This project will study electrical conduction at the nanoscale in organic thin film devices such as light-emitting diodes and photovoltaic cells. It will combine super-resolution microscopy from the biological sciences with three-dimensional Monte Carlo models that predict how electrical injection, transport, and recombination take place between individual molecules. The primary objectives are to 1) visualize filamentary charge transport and recombination in disordered organic semiconductors, 2) understand the morphological and energetic factors that influence filamentary behavior, and 3) use the results to test and refine a state-of-the-art conduction model to improve the performance of future organic electronic devices. The work will leverage electroluminescence blinking together with fluctuation-based super-resolution microscopy to observe filamentary recombination. By measuring the characteristics of the recombination hot spots while varying factors such as material morphology and energetic disorder, this research will provide the first direct test of Monte Carlo model predictions of conduction in disordered organic materials. The resulting knowledge will improve the performance and reliability of organic electronic devices, which are important for displays, energy generation, flexible electronics, and energy-efficient room lighting. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.