Star block copolymer POEGMA-b-P3HT enables tunable charge transport in organic field-effect transistors

Abstract

Organic field-effect transistors (OFETs) are promising for flexible, lightweight, low-cost, and wearable electronic devices. Conjugated polymer-based active layers offer excellent optoelectronic properties, mechanical flexibility, and solution processability. Integrating them into a star-shaped, non-conducting polymer matrix to develope a star-shaped conjugated block copolymer enables distinctive, architecture-tuned physical and optoelectronic characteristics. Therefore, in this study we report the synthesis and characterization of star-shaped conjugated block copolymers comprising four-arm poly(oligo(ethylene glycol) methacrylate) (POEGMA) cores covalently linked to linear poly(3-hexylthiophene) (P3HT) arms. POEGMA cores were synthesized via atom transfer radical polymerization using a tetrafunctional initiator, while alkyne-terminated P3HT was prepared through Kumada catalyst-transfer polymerization. The two blocks were coupled via copper(I)-catalyzed azide–alkyne cycloaddition, yielding well-defined POEGMA-b-P3HT with monomodal molecular weight distributions, confirming controlled polymerization. Structural characterization by NMR, GPC, and FTIR verified composition and integrity, where solid-state analysis revealed isotropic optical behavior and a distinctive spike-like morphology in thin films. AFM imaging showed the highest surface roughness in the star-shaped copolymer, attributed to phase-separated nano/micro-domains induced by branched architecture and partial incompatibility between POEGMA arms and the substrate. Electrical measurements demonstrated ambipolar transport in POEGMA-b-P3HT-based OFETs, with balanced hole and electron conduction, in contrast to the p-type response of linear P3HT devices. The retention of P3HT’s semiconducting characteristics within the star-shaped framework highlights the robustness of this architecture and underscore the critical role of macromolecular design in tailoring optoelectronic behavior and establish star-shaped POEGMA-b-P3HT as a promising material platform for ambipolar OFETs and multifunctional organic semiconductors.