Despite the growing attention on organic electrochemical transistors (OECTs), most research has focused on the design of p-type active materials, and the number of high-performance n-type materials is limited. Herein, a series of naphthalene diimide-based polymers incorporated with asymmetrically branched oligo(ethylene glycol) (OEG) side chains are developed to enable green-solvent-processed, high-performance n-type OECTs. The branched OEG side chains afford sufficient solubility in eco-friendly ethanol/water solvent mixtures. Importantly, taking advantage of the amphiphilic nature of OEGbased polymers, ethanol/water solvents selectively solvate hydrophilic OEG side chains, while producing assembled π−π stacks of hydrophobic backbones. This enables highly ordered polymer packing with a preferential edge-on orientation, and thus excellent lateral charge transport. In particular, the fine-tuned OEG side chains of P(NDIMTEG-T) provide compact backbone packing, effective polaron generation, and superior electrochemical stability with optimized swelling capability. The resultant n-type OECT shows the best electrical/ electrochemical performance in the family, represented by a high transconductance (g m ) of 0.38 S cm −1 and a large figure-of-merit (µC*) of 0.56 F V −1 cm −1 s −1 .This study demonstrates the use of aqueous processing in OECTs, for the first time, and suggests important guidelines for the design of n-type organic mixed ionic-electronic conductors with excellent OECT characteristics.

Emergent bioelectronic technologies are underpinned by the organic electrochemical transistor (OECT), which employs an electrolyte medium to modulate the conductivity of its organic semiconductor channel.Here we utilize postpolymerization modification (PPM) on a conjugated polymer backbone to directly introduce glycolated or anionic side chains via fluoride displacement. The resulting polymers demonstrated increased volumetric capacitances, with subdued swelling, compared to their parent polymer in ptype enhancement mode OECTs. This increase in capacitance was attributed to their modified side chain configurations enabling cationic charge compensation for thin film electrochemical oxidation, as deduced from electrochemical quartz crystal microbalance measurements. An overall improvement in OECT performance was recorded for the hybrid glycol/ionic polymer compared to the parent, owing to its low swelling and bimodal crystalline orientation as imaged by grazing-incidence wide-angle X-ray scattering, enabling its high charge mobility at 1.02 cm 2 •V −1 •s −1 . Compromised device performance was recorded for the fully glycolated derivative compared to the parent, which was linked to its limited face-on stacking, which hindered OECT charge mobility at 0.26 cm 2 •V −1 •s −1 , despite its high capacitance. These results highlight the effectiveness of anionic side chain attachment by PPM as a means of increasing the volumetric capacitance of p-type conjugated polymers for OECTs, while retaining solid-state macromolecular properties that facilitate hole transport.

Despite the growing interest in dynamic behaviors at the frequency domain, there exist very few studies on molecular orientation-dependent transient responses of organic mixed ionic–electronic conductors. In this research, we investigated the effect of ion injection directionality on transient electrochemical transistor behaviors by developing a model mixed conductor system. Two polymers with similar electrical, ionic, and electrochemical characteristics but distinct molecular orientations were successfully synthesized by varying the co-monomer unit (2,2’-bithiophene or phenylene) in conjunction with a novel 1,4-dithienylphenylene-based monomer. The comprehensive electrochemical analysis suggests that the molecular orientation affects the length of the ion-drift pathway, which is directly correlated with ion mobility, resulting in peculiar OECT transient responses. These results provide the general insight into molecular orientation-dependent ion movement characteristics as well as high-performance device design principles with fine-tuned transient responses.