An Amorphous n-Type Conjugated Polymer with an Ultra-Rigid Planar Backbone

Area of Science:

• Materials Science
• Organic Electronics
• Polymer Chemistry

Background:

• High charge carrier mobility in polymer semiconductors is typically associated with semi-crystalline structures.
• Amorphous conjugated polymers offer alternative charge transport mechanisms.
• Developing amorphous polymers with efficient charge transport remains a challenge.

Purpose of the Study:

• To report the first near-amorphous n-type conjugated polymer with significant electron mobility.
• To investigate the relationship between polymer backbone rigidity and charge transport properties.
• To introduce a new molecular design strategy for amorphous polymer semiconductors.

Main Methods:

• Copolymerization of electron-accepting, planar fused-ring building blocks: double B←N bridged bipyridine (BNBP) and benzobisthiazole (BBTz).
• Fabrication and characterization of organic field-effect transistors (OFETs) using the synthesized polymer.
• Analysis of polymer backbone structure, π-π stacking, and molecular weight.

Main Results:

• A novel alternating copolymer of BNBP and BBTz was synthesized, exhibiting a near-amorphous nature.
• The polymer demonstrated a respectable electron mobility of 0.34 cm² V^-1 s^-1 in OFETs.
• The material features an exceptionally rigid, straight, and planar polymer backbone.

Conclusions:

• The synthesized near-amorphous polymer exhibits excellent electron transporting properties, challenging the semi-crystalline paradigm.
• Ultrahigh backbone stiffness, small π-π stacking distance, and high molecular weight are key factors contributing to the observed electron mobility.
• This work opens new avenues for designing high-performance amorphous polymer semiconductors for organic electronics.