Acceptor-Acceptor-Type Conjugated Polymers for Energy Level Modulation in Semiconducting Carbon Nanotube Transistors

Area of Science:

• Materials Science
• Nanotechnology
• Polymer Chemistry

Background:

• Polymer wrapping is a key method for purifying semiconducting single-walled carbon nanotubes (s-SWCNTs).
• The influence of frontier orbital energy levels on polymer wrapping and s-SWCNT sorting is not well understood.
• Designing conjugated polymers with tunable energy levels is crucial for selective s-SWCNT separation.

Purpose of the Study:

• To investigate how tuning frontier orbital energy levels in naphthalene diimide (NDI)-based copolymers affects their interaction with s-SWCNTs.
• To compare the sorting efficiency and device performance of NDI-copolymers with different backbone structures.
• To establish a structure-property relationship for designing high-performance polymers for s-SWCNT sorting.

Main Methods:

• Synthesis and characterization of four NDI-based copolymers with varying donor/acceptor units.
• Optical characterization (UV-Vis, photoluminescence) to assess s-SWCNT purity and chirality selectivity.
• Fabrication and testing of field-effect transistors (FETs) using sorted s-SWCNTs to evaluate device performance.

Main Results:

• PNDI-BTI achieved >99% s-SWCNT purity, surpassing PNDI-2T.
• PNDI-BTI demonstrated stronger aggregation and formed more uniform s-SWCNT networks compared to PNDI-2T.
• PNDI-BTI preferentially sorted large-diameter s-SWCNTs, while PNDI-2T sorted small-diameter ones.
• FETs with PNDI-BTI/s-SWCNTs exhibited high hole mobility (2.1 cm² V^-1 s^-1) and stable on/off ratios (9 × 10³).

Conclusions:

• Tuning frontier orbital energy levels is an effective strategy for enhancing s-SWCNT sorting selectivity.
• PNDI-BTI's lower energy levels and stronger π-π interactions contribute to superior sorting and device performance.
• The study provides insights for designing advanced acceptor-acceptor type conjugated polymers for s-SWCNT applications.