Strain‐Engineering Induced Anisotropic Crystallite Orientation and Maximized Carrier Mobility for High‐Performance Microfiber‐Based Organic Bioelectronic Devices

Abstract Despite the importance of carrier mobility, recent research efforts have been mainly focused on the improvement of volumetric capacitance in order to maximize the figure‐of‐merit, μC* (product of carrier mobility and volumetric capacitance), for high‐performance organic electrochemical transistors. Herein, high‐performance microfiber‐based organic electrochemical transistors with unprecedentedly large μC* using highly ordered crystalline poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) microfibers with very high carrier mobilities are reported. The strain engineering via uniaxial tension is employed in combination with solvent‐mediated crystallization in the course of drying coagulated fibers, resulting in the permanent preferential alignment of crystalline PEDOT:PSS domains along the fiber direction, which is verified by atomic force microscopy and transmission wide‐angle X‐ray scattering. The resultant strain‐engineered microfibers exhibit very high carrier mobility (12.9 cm² V⁻¹ s⁻¹) without the trade‐off in volumetric capacitance (122 F cm⁻³) and hole density (5.8 × 10²⁰ cm⁻³). Such advantageous electrical and electrochemical characteristics offer the benchmark parameter of μC* over ≈1500 F cm⁻¹ V⁻¹ s⁻¹, which is the highest metric ever reported in the literature and can be beneficial for realizing a new class of substrate‐free fibrillar and/or textile bioelectronics in the configuration of electrochemical transistors and/or electrochemical ion pumps.