Enhanced Charge Transport and Stability Conferred by Iron(III)-Coordination in a Conjugated Polymer Thin-Film Transistors

A high performance diketopyrrolopyrrole (DPP)–based semiconducting polymer is modified with ligands to enable metal coordination, and its subsequent effect as field-effect transistors is investigated. In specific, pyridine-2,6-dicarboxamide (PDCA) units are incorporated in a DPP–based polymer backbone with a content from 0 to 30 mol%, and the resulting polymers are then mixed with Fe(II) ions. The coordination and spontaneous oxidation converts Fe(II) to Fe(III) ions to result in Fe(III)-containing metallopolymers. The resulting metallopolymers are observed to show good solubility in organic solvents and can be easily processed as thin films. The charge transport characteristics are subsequently investigated through the fabrication of field–effect transistor devices, in which an enhanced charge carrier mobility with the Fe(III)-containing metallopolymers is observed. In specific, an almost twofold improvement in the charge carrier mobility is obtained for the 20% PDCA-containing polymer after Fe coordination (from 0.96 to 1.84 cm² V⁻¹ s⁻¹). Furthermore, the operation stability of the metallopolymer-based devices is found to be significantly improved with low bias stress. Its superior electrical characteristics are attributed to the doping effect of the Fe ions. This study indicates that incorporation of appropriate metallic ions to polymer presents a viable approach to enhance the performance of polymer–based transistor devices.