Charge Carrier Induced Structural Ordering And Disordering in Organic Mixed Ionic Electronic Conductors

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Chemistry

Background:

• Operational stability is crucial for organic mixed ionic-electronic conductors (OMIECs) in applications like biosensing and neuromorphic computing.
• Understanding the factors affecting OMIEC stability is essential for advancing their use in electronic devices.

Purpose of the Study:

• To investigate the operational stability of a p-type OMIEC material across different molecular weights.
• To elucidate the microstructural mechanisms underlying device instability at high charge densities.

Main Methods:

• Electrochemical transistor measurements were used to assess device performance and stability.
• Operando X-ray scattering techniques were employed to observe structural changes during device operation.
• Varying molecular weights of the OMIEC material were tested.

Main Results:

• Devices showed stable operation for over 300 cycles at low charge densities, irrespective of molecular weight.
• High charge densities led to increased device hysteresis and decreased conductivity due to reduced hole mobility.
• Operando X-ray scattering revealed two regimes: ordering at low carrier densities and irreversible disordering at high densities, linked to polaron interactions.

Conclusions:

• Device stability in OMIECs is maintained below a critical charge density threshold.
• Microstructural disordering at high charge densities, driven by polaron-induced structural changes and charge-charge interactions, is the primary cause of instability.
• This study provides a mechanistic understanding of OMIEC material dynamics and instabilities during operation.