Impact of the Conjugated Polymer Sidechain Composition on the Performance Metrics of Organic Electrochemical Transistors With Vertical vs. Conventional Architectures

Organic electrochemical transistors (OECTs) efficiently convert ionic signals into measurable electronic currents, enabling applications in bioelectronic sensors, neuromorphic devices, and low‐voltage integrated circuits. High device performance relies on conjugated polymer structures capable of balanced mixed ionic‐electronic conduction, motivating side‐chain engineering design strategies. Here we report a systematic study comparing the properties of DPP‐EDOT polymers in which branched alkyl side chains are progressively replaced by linear glycolated EG 5 substituents (0%–100%) and evaluate their performance metrics in both conventional (cOECT) and vertical (vOECT) device architectures. Increasing EG 5 content monotonically increases both steady‐state ( g m, max, norm = 1.27 → 70.73 S·cm −1 ) and transient performance ( τ ON/ τ OFF = 903.91/473.9 → 2.4/0.4 ms) in cOECTs. In contrast, vOECTs exhibit a more pronounced composition‐dependent transition: the vertical architecture delivers outstanding performance only when EG 5 content exceeds ∼50%, revealing a critical hydrophilicity requirement imposed by the reduced ion‐injection area and extended lateral ion‐transport pathways intrinsic to the vertical geometry. These findings establish architecture‐dependent molecular design principles for effectively pairing OMIECs with planar and vertical OECT configurations.