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

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⁻¹V⁻¹s⁻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.