Revealing the Influence of Electrolyte Solvents and Ions on Electronic and Ionic Transport in Electrochemically Doped Conjugated Polymers

Non-technical Description Electricity is everywhere. Ions, charged atoms and molecules, are the way in which electricity flows through living organisms. Negatively-charged electrons and positively-charged holes flow through semiconductors in electronics such as computers and mobile phones. Materials that conduct both ions and electrons bridge these worlds. This gives them many potential applications that bring together electronics and biology. Blends of semiconducting polymers and charge-balancing electrolytes are a promising class of mixed ionic and electronic conductors. In particular, they can be biocompatible and flexible. This makes them attractive materials for wearable and implantable bioelectronics and possibly even neuromorphic computers inspired by the human brain. Ideally, a mixed conductor could be designed on-demand for a given need. However, the chemistry between polymers and ionic electrolytes is complex and many aspects are poorly understood. These fundamental limits in understanding relationships must be addressed for these materials to reach their full potential. This project brings together an interdisciplinary team that combines material characterization, modeling, and device testing to provide fundamental knowledge into these relationships. The results of this project will be used to advance the technologies in which these material systems are used. Students working in this project will develop in-demand technical, communications and critical thinking skills. All of these are essential for preparing the future STEM workforce. Outreach to the community is an integral component of the project. Annual in-person workshops will provide high school science teachers hands-on experience in making and characterizing devices such as electrochromics and transistors. Follow-through includes materials for teachers to make working devices and circuits and learning modules to accompany these materials and experiments. These learning activities will enhance STEM education by connecting fundamental concepts of chemistry and physics with the everyday lives of the students. Technical Description Electronic and ionic transport in conjugated polymers depends on a complicated web of variables, ranging from polymer structure through the extent of solvent-induced polymer swelling. This project investigates three primary variables that influence electronic and ionic transport, including electrolyte solvent chemistry, electrolyte ion chemistry, and polymer sidechain chemistry. Spectroscopic and device level measurements will be combined with quantum-chemical calculations and molecular dynamics simulations to establish a fundamental understanding that spans from molecular level chemical interactions to device level ionic and electronic transport properties. In terms of electrolyte solvent, the project determines how the dielectric constant of the solvent and the solvent’s ability to swell the polymer impact electronic and ionic transport. In terms of electrolyte ion chemistry, the project determines how ion shape and hydrophobicity impact electronic structure and ionic and electronic transport as a function of polymer sidechain chemistry. The results of this project are essential for building a comprehensive predictive model that can be used to guide materials design and electrolyte selection for various applications of electrochemically doped conjugated polymers. 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.