Asymmetric side-chain engineering of conjugated polymers with improved performance and stability in organic electrochemical transistors

Abstract

This study rigorously investigated the impact of asymmetric side chain design on the performance of organic electrochemical transistors (OECTs). Hydrophilic and hydrophobic side chains were systematically introduced into poly(isoindigo-bithiophene)-based polymers, and the resulting symmetric and asymmetric side chain combinations were carefully compared. The objective was to enhance coplanarity, mobility, hydrophilicity, and stability to improve OECT device performance. While P(C,C) and P(O,O), with symmetric branched alkyl and oligoether side chains, exhibit effective OECT device functions, the asymmetric side-chain designed P(C,O), with branched alkyl and oligoether side chains, outperforms both symmetric counterparts. P(C,O) demonstrates OECT performance with a pronounced product of mobility and capacitance (μ_hC*) of 65.2 F cm⁻¹ V⁻¹ s⁻¹, excellent hole mobility (μ_h) of 0.78 cm² V⁻¹ s⁻¹, and fast response speed. Specifically, P(C,O) demonstrates superior stability while maintaining good capacitance. The performance retention of P(C,O) after consecutive ON/OFF cycles is 77.5%, which is much higher than 35.2% and 47.0% of P(C,C) and P(O,O). The asymmetric structure contributes to enhancing coplanarity and structural stability, resulting in improved crystalline properties after electrolyte swelling. This study presents a balanced and rigorous approach to balancing the performance and stability in OECTs through asymmetric side chain design.