Enhanced solid-state order and field-effect hole mobility through control of nanoscale polymer aggregation

Area of Science:

• Organic electronics
• Materials science
• Polymer chemistry

Background:

• Efficient charge transport in organic field-effect transistors (OFETs) relies on ordered polymer thin films with in-plane π-π stacking.
• General strategies for controlling π-stacking orientation in polymer films are limited.

Purpose of the Study:

• To investigate how side-chain engineering in furan-containing diketopyrrolopyrrole (DPP) polymers affects solubility, solid-state packing, and OFET performance.
• To establish a generalizable method for enhancing π-stacking and charge carrier mobility in organic electronic materials.

Main Methods:

• Synthesis of DPP polymers with linear hexadecyl (C16) and branched 2-butyloctyl (BO) side chains.
• Characterization of polymer solubility, thin-film morphology (AFM, GIXD), and device performance (field-effect mobility).
• Investigation of solution properties, including nanoscale aggregation, and its correlation with film structure.

Main Results:

• DPP polymers with linear side chains exhibited lower solubility, larger crystalline domains, and enhanced in-plane π-π packing.
• A direct correlation was found between early-onset nanoscale aggregation in polymer solutions and the formation of highly oriented in-plane π-stacked films.
• Inducing aggregation in less soluble polymers significantly improved nanostructural order, π-π orientation, and field-effect hole mobility (up to 2.25 cm²/V·s).

Conclusions:

• Side-chain engineering is a viable strategy to tune polymer solubility and control π-stacking orientation in OFETs.
• Controlled nanoscale aggregation in solution is a powerful approach to achieve highly ordered solid-state structures and enhance charge transport in organic semiconductors.
• This aggregation-induced strategy holds broad applicability for improving the performance of various π-conjugated organic electronic materials.