Probing Film Morphology and Ionic Transport in Organic Semiconductors

University Of Washington, Seattle WA

Investigators

Abstract

Nontechnical description: Polymers that simultaneously conduct both electrons and ions are of technological interest as signal transducers that can interface biological systems with the world of modern digital electronics. The project uses unique microscopy tools to provide a fundamental understanding of how the processing and structure of these polymers affects their ability to conduct ions, and how the transport of ions in turn affects the conduction of electrons through the material. The scientific knowledge from this project impacts technological applications for improving the materials performance of polymers in bioelectronics, and also stands to benefit broader applications such as polymer binders for use in electrochemical energy storage, and potentially also electronic materials for energy harvesting applications. This project additionally builds on the strong track record of the principal investigator in education by developing distinct scalable outreach materials as part of a recently created ambassadors project that trains students to conduct outreach. The project includes direct support for undergraduate research, and addresses pipeline issues facing under-represented groups in the sciences by cementing a successful partnership the principal investigator has undertaken with the Rainier Scholars organization. Technical description: The scientific goal of this project is to gain a fundamental understanding of the relationship between film processing, local structure, and ion transport in conjugated polymer thin films, with an emphasis on understanding the role of local heterogeneity. Conjugated polymers have recently emerged as promising materials for transducing signals at the interface between the biological and digital environments. This project explores fundamental structure/function properties of these materials as relevant to such applications by applying a unique set of scanning probe microscopy methods. Specifically, the project employs electrochemical strain microscopy to make local measurements of ion motion in conjugated polymer films. In addition, local scanning probe potentiometry of planar device structures doped with ions enables better understanding of structural origins of dispersive ionic transport. Finally, the unique capabilities of time-resolved electrostatic force microscopy are exploited to study electronic, ionic, and structural relaxation dynamics occurring over more than 6 orders of magnitude in time, but with sub-diffraction resolution. Importantly, the project studies the coevolution of structure and function using in situ imaging with environmental (temperature, solvent, dopant, bias) control to understand how structure and function correlate in mixed ionic / electronic transport materials properties in real space.