Highly Stable Organic Electrochemical Transistors Based on Cyclopenta Dithiophene and Benzothiadiazole Donor–Acceptor Copolymer with Optimized Glycol Side Chain Length

The glycolated cyclopenta dithiophene (gCPDT) and benzothiadiazole (BT) donor-acceptor copolymers have been synthesized by the method of direct arylation polymerization, and served as highly stable active material of accumulation mode organic electrochemical transistor (OECT). Structure characterization, optical/electrochemical measurements, and density functional theory calculation demonstrate that the glycol side chain length does not have obvious effects on the backbone structure and charge delocalization, but exhibits crucial contribution to the film structural order, oxidation current, and ion doping capacity. The CPDT-BT copolymer with optimized glycol side chain length (P3gCPDT-BT) shows the best OECT performances with the normalized peak transconductance of 134.2 ± 3.2 S cm^-1, charge carrier mobility and volumetric capacitance, µC* of 479.3 ± 11.6 F V^-1 cm^-1 s^-1. The P3gCPDT-BT is also applied to flexible OECT and shows no signs of degradation when operated for 15 000 pulse cycles at ambient conditions, autoclave sterilization procedure, 2 h of ultrasonic treatment, 500 bending cycles, and 60 days long-term storage. These performances should pave the way for the practice applications of OECT in the bio-organic electronic devices.