A Competitive n-Type OECT Material via Copolymerization of Electron Deficient Building Blocks

Abstract

The classical acceptor motifs diketopyrrolopyrrole (DPP) and thienopyrrolodione (TPD) are copolymerized to yield the acceptor–acceptor polymer “Poly(DPP-TPD).” The fundamental design idea is to maximize the electron affinity (EA), thus increasing the ambient stability of the reduced state against oxygen and water while ensuring high ion compatibility through the incorporation of hydrophilic oligoethylene glycol N-substituents. Additionally, a highly planarized polymer structure is anticipated, due to the extended noncovalent interactions (conformational locking) between the carbonyl oxygen and the thiophene protons. Cyclic voltammetry, spectroelectrochemistry, ultraviolet photoelectron spectroscopy, ultraviolet-visible absorption spectroscopy, and organic field effect transistor (OFET) characterization demonstrate the suitability for n-type organic electrochemical transistor (OECT) devices. High EA, ionization potential, and good electron mobility (µe(OFET)) are shown, in addition to the electrochemical reduction of polymer films in aqueous electrolyte. In n-type OECTs, poly(DPP-TPD) demonstrates a moderate threshold voltage of Vth = 0.58 V and an outstanding µC* value of 7.62 F cm−1 V−1 s−1. Cycling studies consisting of pulsed on- and off-switching of the device at gate voltages between Vg = 0.6–0.8 V in the saturation regime reveal high stability for more than 2700 cycles with rapid switching kinetics.