The relationship between ionic-electronic coupling and transport in organic mixed conductors

Area of Science:

• Materials Science
• Electrochemistry
• Condensed Matter Physics

Background:

• Organic mixed ionic-electronic conductors (OMIECs) facilitate charge conversion via electrochemical doping.
• Applications span bioelectronics, neuromorphic computing, and energy storage.
• Simultaneous ionic and electronic transport in OMIECs is not well understood.

Purpose of the Study:

• To develop a self-consistent model for combined ionic and electronic transport in OMIECs.
• To identify the key driving forces for mixed charge transport.
• To understand space charge region formation in OMIECs.

Main Methods:

• In situ electrochemical (de)doping measurements on an archetypal OMIEC.
• Development of a quasi-field drift-diffusion model informed by experimental data.
• Numerical simulations of charge transport at device-relevant scales.

Main Results:

• The model accurately captures experimentally measured ion transport across various potentials.
• Hole chemical potential, modulated by doping, is a primary driver of mixed transport.
• Competition between hole drift and diffusion creates diffuse space charge regions.

Conclusions:

• Mobile ions screen electrostatic driving forces in OMIECs.
• Diffuse space charge regions are a unique characteristic of mixed conductors.
• This work provides a framework for understanding and designing OMIEC devices.