Uncovering Ion-Electron Interactions in Organic Mixed Conductors

Project Information

UMICs

Grant agreement ID: 101022365

DOI

10.3030/101022365

Project closed

EC signature date 2 March 2021

Start date 10 May 2021

End date 9 May 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 224 933,76

EU contribution

€ 224 933,76

Coordinated by

THE CHANCELLOR MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom

Periodic Reporting for period 1 - UMICs (Uncovering Ion-Electron Interactions in Organic Mixed Conductors)

Reporting period: 2021-05-10 to 2023-05-09

Summary of the context and overall objectives of the project

Organic mixed ionic-electronic conductors (OMIECs) have risen as a promising material choice for bioelectronic and biochemical devices due to their low impedance, soft mechanical properties, and ability to transduce ionic signals to electronic currents. The ion-electron interactions, which are unique to mixed conductors, have been exploited to produce high performance sensors and physiological recording devices. However, the fundamental interactions between ions and electrons that determine the performance of these materials is still poorly understood, impeding their translation from academic research to commercial use. The proposal addresses this gap in knowledge using state-of-the-art electronic and chemical analysis at the nanoscale to better understand the macroscale materials properties.

Our methodology focused on the kinetics of bioelectronic device operation. We found an accurate way to predict speed of operation by understanding how ion-electron interactions alter the transport properties in OMIECs. Furthermore, we discovered a new fundamental speed limit for switching bioelectronic devices from the OFF to the ON state. We show that the quickest path to overcoming this speed limit is to maximize the homogeneity of the OMIEC nanostructure. The fundamental insights resulting from this project inform the design of next-generation high-speed bioelectronic devices and materials, helping them advance beyond the lab into commercial and clinical applications.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Using a newly developed optical microscopy methodology, we made two important discoveries regarding the kinetics of OMIEC operation. The results from the new method resulted in a more accurate interpretation of commonly used experimental technique to characterize ion transport enabling improved engineering of devices and benchmarking of materials. First, we found that charging and discharging rates are determined by the diffusion coefficient of charge paired ions and electrons. When paired, electronic charges move via diffusion due to large chemical energy required to charge the OMIEC, while ions followed the motion of electrons via drift which is must faster than ionic diffusion. The results are currently under review at an open access journal for eventual dissemination.

We used the optical microscopy to study a handful of OMIECs and found that the technique can differentiate between ionic and electronic limited motion. From this, we found that at very low electronic carrier concentrations, electronic motion is slower than ionic motion thereby limiting the operational speed of a device. We used diffraction-based transmission electron microscopy to image the nanoscale order of OMIECs, revealing that heterogenous order causes the slow electronic motion.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Organic mixed ionic-electronic conductors (OMIECs) have risen as a promising material choice for bioelectronic devices due to their low impedance, soft mechanical properties, and ability to transduce ionic signals to electronic currents. The ion-electron interactions, which are unique to mixed conductors, have been exploited to produce high performance sensors and electrophysiological recording devices. Our research has shown how these ion-electron interactions impact the performance of devices. We found that the switching kinetics of OMIEC devices is largely dependent of the ion-electron coupling. We propose several new ways to improve the speed of operation for bioelectronics, including controlling the materials microstructure and using optimised device operating parameters.

The insights from the research performed in this project will aid in the design of novel organic electronic materials for bioelectronic devices. With better materials, we expect organic bioelectronics to have great impact on the future of healthcare. Organic materials can be used to make bioelectrodes which cause much lower immune response compared to their metal counterparts. Additionally, the volumetric scaling of the charge capacity of OMIECs enables stimulation electrodes with orders of magnitude higher charge injection capacity that can operate at low frequencies down to 1 Hz. These properties of OMIECs open the path towards chronically stable implantable electronics, and the better understanding resulting from the project will directly help to translate these devices from research to clinical applications.

Relationship between microstructure and switching speed in conjugated polymers

Artist illustration of electrons and holes conducting in a conjugated polymer