Materials, devices and applications of organic electrochemical transistors

The organic electrochemical transistors have attracted much attention due to their high sensitivity and potential to overcome the low-efficiency challenge posed by the von Neumann bottleneck of modern computation systems. Up to now, much effort has been focused on the development of high-performance devices that can be applied in flexible bioelectronics and biosensors. The performance of organic electrochemical transistors is mainly determined by the active layer, which needs to be carefully designed and optimized to achieve the best device performance. To address this issue, we have developed a series of novel conjugated polymers, oligomers, and small molecules to serve as active layers in organic electrochemical transistors, organic thermoelectric devices, and organic artificial synapses. Through backbone engineering, side chain engineering, and solvent engineering, the chemical structure, processing technology, and device structure have been fully optimized to achieve devices with high performance and good stability. For PDI-based n-type small molecules, a high-performance organic electrochemical transistor was achieved by isomerization of diPDI to obtain a highly twisted d-gdiPDI, which has a strong positive effect on the charge storage properties and thus on the performance of organic electrochemical transistors. It is worth mentioning that d-gdiPDI exhibits a high volumetric capacitance of 657 F cm(-3), which is the highest value reported to date for small-molecule OECT materials. For fused n-type small molecules based on naphthalene bis-isatin and rhodanine acceptor units, a high mu C* of 31.6 F cm(-1) V-1 (-1)(s) was achieved by extending the molecular scaffold into the oligomer domain. By optimizing the energy level and side chain engineering of isoindigo-based polymers, organic electrochemical transistors with normalized values of 4.09 F cm(-1) V-1 s(-1), a normalized transconductance of 0.94 S cm(-1), excellent operational stability, and a long shelf-life under ambient conditions were obtained. We also developed the green synthesis of lactone-based conjugated polymers by metal-free aldol polymerization, providing a highly efficient and environmentally friendly polymerization route for highperforming n-type organic electrochemical transistors. By variations of donor units in the donor-acceptor polymers, the optical properties and aggregation behavior of naphthalene tetracarboxylic diimide copolymers were finely tuned, and the performance of aqueous-based electrochemical devices was enhanced. By side chain engineering and a binary-solvent strategy, large-area porous thin films were obtained, thereby enhancing the mu C* value up to 476 F cm(-1) V-1 s(-1) in flexible organic electrochemical transistors. The conjugated polymers we developed can also be utilized as high-performance active layer materials in organic thermoelectric devices and organic synaptic transistors. And by means of UV-vis absorption spectroscopy, cyclic voltammetry, atomic force microscopy, 2D grazing incident wide-angle X-ray scattering, the optoelectrical properties and morphology of these materials were investigated, and the structure-property-performance relationships were established. The novel materials and devices with mixed conductivity we developed are essential for the realization of flexible bioelectronics with high sensitivity, high stability, and low energy consumption for commercialization.