Electromechanical Behavior of Organic Mixed Ionic-Electronic Conductors

Licentiate thesis, 2025

Organic mixed ionic-electronic conductors (OMIECs) are a new class of organic materials that connect the hard, rigid world of traditional electronics with the soft, ion-conducting nature of biological systems. Because they can move both electronic and ionic charges, they are especially well suited for interacting with living tissues and have become important to the growing field of organic bioelectronics. A key device based on OMIECs is the organic electrochemical transistor (OECT), which has become the benchmark for evaluating material performance in applications ranging from biosensing to neuromorphic computing.

While the electrical properties of OMIECs are well known, their mechanical properties — and how these change during device operation — are still not fully understood and are essential for a stable, long-term integration with biological tissues without damage, such as tissue scarring.  The electrochemical redox processes that come with OECT operation involve ion and solvent uptake, which can lead to swelling, plasticization, and microstructural changes that directly affect the material’s mechanical properties.

This thesis aims to investigate the fundamental coupling between electrical and mechanical properties in OMIECs during electrochemical operation. OECTs are used as a model system to study ionic-electronic transport, while in situ techniques such as electrochemical nanoindentation (EC-NI) and electrochemical atomic force microscopy (EC-AFM) are applied to track changes in mechanical properties, concretely the elastic modulus. The work focuses on a thiophene based copolymer p(g3TT-T2) (PTTEG) while also exploring how side chain design affects both electrical and mechanical behavior.

Overall, this work shows that OMIECs can be engineered so their mechanical properties are tunable, even stabilized, across redox cycles. By combining device physics, material characterization, and fabrication, this thesis offers a way to understand electromechanical coupling in OMIECs; insights that are key for designing future bioelectronic devices.