Isoindigo-Based Polymers with Small Effective Masses for High-Mobility Ambipolar Field-Effect Transistors

Area of Science:

• Materials Science
• Organic Electronics
• Semiconductor Physics

Background:

• High-mobility conjugated polymers are predominantly p-type semiconductors.
• Advances in high-mobility ambipolar polymers lag behind their p-type counterparts.
• Ambipolar polymers are crucial for developing complementary metal-oxide-semiconductor (CMOS) circuits due to their potential for easy fabrication and low cost.

Purpose of the Study:

• To develop high-mobility ambipolar polymers for high-performance organic field-effect transistors (OFETs).
• To investigate the impact of fluorine incorporation on polymer properties and device performance.
• To explore the relationship between polymer design, energy levels, effective mass, crystallinity, and charge transport.

Main Methods:

• Synthesis of three isoindigo-based polymers: PIID-2FBT, P1FIID-2FBT, and P2FIID-2FBT.
• Incorporation of fluorine atoms into the polymer structure.
• Characterization of polymer properties including coplanarity, energy levels, and crystallinity.
• Fabrication and testing of ambipolar organic field-effect transistors.
• Analysis of charge carrier mobilities (µe for electrons, µh for holes) and effective mass.

Main Results:

• Fluorine incorporation enhanced polymer coplanarity, lowered energy levels, and increased crystallinity, leading to improved electron mobility (µe).
• P2FIID-2FBT demonstrated n-type dominant performance with a µe of 9.70 cm² V⁻¹ s⁻¹.
• P1FIID-2FBT achieved a highly balanced ambipolar performance with µh of 6.41 cm² V⁻¹ s⁻¹ and µe of 6.76 cm² V⁻¹ s⁻¹.
• All synthesized polymers exhibited small effective masses, indicating efficient intramolecular charge transport.

Conclusions:

• High-mobility ambipolar semiconductors can be achieved through strategic polymer design.
• Fine-tuning energy levels, reducing effective mass, and enhancing crystallinity are key factors for high-performance ambipolar polymers.
• The developed isoindigo-based polymers represent significant progress in the field of ambipolar organic electronics.