Side Chains Override Crystallinity in n-Type Organic Mixed Conductors

Area of Science:

• Materials Science
• Organic Electronics
• Bioelectronics

Background:

• Crystallinity in organic semiconductors typically enhances charge transport.
• The role of crystallinity in organic mixed ionic-electronic conductors (OMIECs) for bioelectronic devices is not fully understood.
• OMIECs are crucial for developing advanced bioelectronic interfaces.

Purpose of the Study:

• To investigate the impact of controlled crystallinity on charge transport in OMIECs.
• To determine if enhanced crystallinity universally improves OMIEC performance.
• To establish design principles for high-performance, scalable bioelectronic devices.

Main Methods:

• Controlled crystallinity using thermal annealing in three electron-transporting OMIECs.
• Varied side-chain architectures (branched vs. linear ethylene glycol) to influence ion transport.
• Employed in-operando physicochemical characterization to analyze charge transport and material properties.

Main Results:

• Thermal annealing uniformly increased crystallinity across all tested OMIECs.
• Mixed charge transport improved only in polymers with linear side chains, doubling electronic charge mobility.
• Branched side-chain polymers showed reduced mobility, low water uptake, and significant bipolaron formation after annealing.

Conclusions:

• Crystallinity's effect on mixed conductivity is dependent on side-chain architecture, not solely backbone chemistry.
• The assumption that higher crystallinity always benefits charge transport in OMIECs is challenged.
• Findings provide design rules for OMIECs compatible with high-temperature fabrication and sterilization, enabling reliable bioelectronics.