Ester-End-Capped Semiconducting Polymers for High-Performance Field-Effect Transistors Processed from Nonhalogenated...

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• High-performance polymer semiconductors often suffer from poor solubility in eco-friendly nonhalogenated solvents.
• Optimizing molecular packing is crucial for achieving high charge carrier mobility in polymer semiconductors.
• Traditional processing methods frequently rely on halogenated solvents, posing environmental concerns.

Purpose of the Study:

• To develop high-performance, nonhalogenated solvent-processable polymer semiconductors using diketopyrrolopyrrole (DPP) building blocks.
• To investigate the effect of ester-end-capping on polymer solubility, molecular packing, and thin-film morphology.
• To evaluate the performance of resulting polymer semiconductors in organic field-effect transistors (OFETs).

Main Methods:

• Synthesis of DPP-based polymers with benzoate ester end-groups.
• Solubility testing in various nonhalogenated solvents (toluene, p-xylene).
• Characterization of molecular packing and solid-state morphology using techniques like cryogenic transmission electron microscopy (cryo-TEM).
• Fabrication and electrical characterization of OFET devices.

Main Results:

• Ester-end-capping significantly improved polymer solubility (>12 mg·mL⁻¹ in toluene and p-xylene).
• End-capped polymers exhibited enhanced π-π stacking and increased crystallite coherence length (CCL) due to ordered molecular packing.
• Linear alkyl ester chains (DPPTT-Ester-L) promoted better molecular ordering and larger CCL compared to branched chains (DPPTT-Ester-B).
• OFETs based on DPPTT-Ester-L processed in p-xylene achieved a high hole mobility of 3.19 cm²V⁻¹s⁻¹, outperforming unmodified polymers and those processed with halogenated solvents.

Conclusions:

• Ester-end-capping is an effective strategy for enhancing the solubility and processability of DPP-based polymer semiconductors in nonhalogenated solvents.
• Tailoring the alkyl chain structure of end-groups allows fine-tuning of solution-state aggregation and solid-state molecular packing.
• This approach enables the development of high-performance, environmentally friendly polymer electronic devices.