Polymorph-Dependent Multi-Level Supramolecular Self-Assembly and Local Charge Transport of a Conjugated Polymer in Solution and Solid States

Abstract

The polymorphic behavior of conjugated polymers enables tunable optoelectronic properties, but their transport mechanism remains elusive due to the inherent complexity and uncontrollability of polymorphic self-assembly behaviors and electronic processes at various length scales, alongside the ambiguous relationship between solution and solid states. Herein, precise control of multi-level supramolecular self-assembly of a polymorphic conjugated polymer, N-PDPP4T-HD with two distinct semi-crystalline aggregated phases (β1 and β2) via solvent engineering is demonstrated. β1 forms 1D worm-like nanostructures in solution, whereas β2 generates 2D nanoscale lamellar configuration, confirmed by experimental observation and molecular dynamic simulation. Such solution-state features are inherited in the solid state (1D nanofibers for β1 and 2D granular-like structures for β2). X-ray characterizations reveal larger crystalline domains on the nanometer scale, reduced π-stacking distance on the Ångstrom scale, and diminished paracrystallinity disorder for solid-state β2. Going beyond conventional DC transistor characterizations, contact-free ultrafast terahertz spectroscopy to unveil AC short-range, intrinsic transport properties is employed. Longer charge carrier scattering time and thus intrinsic mobility of β2 result in threefold higher short-range photoconductivity than β1. This work establishes the “solution structure – solid structure – local transport” relation in polymorphic conjugated polymers and provides new opportunities for high-performance plastic electronic devices.