Balancing Ionic and Electronic Conduction for High‐Performance Organic Electrochemical Transistors. (28th January 2020) - Savva, Achilleas
Abstract: Conjugated polymers that support mixed (electronic and ionic) conduction are in demand for applications spanning from bioelectronics to energy harvesting and storage. To design polymer mixed conductors for high‐performance electrochemical devices, relationships between the chemical structure, charge transport, and morphology must be established. A polymer series bearing the same p‐type conjugated backbone with increasing percentage of hydrophilic, ethylene glycol side chains is synthesized, and their performance in aqueous electrolyte gated organic electrochemical transistors (OECTs) is studied. By using device physics principles and electrochemical analyses, a direct relationship is found between the OECT performance and the balanced mixed conduction. While hydrophilic side chains are required to facilitate ion transport—thus enabling OECT operation—swelling of the polymer is not de facto beneficial for balancing mixed conduction. It is shown that heterogeneous water uptake disrupts the electronic conductivity of the film, leading to OECTs with lower transconductance and slower response times. The combination of in situ electrochemical and structural techniques shown here contributes to the establishment of the structure–property relations necessary to improve the performance of polymer mixed conductors and subsequently of OECTs. Abstract : Organic electrochemical transistors (OECTs) rely on conjugated polymers that support ionic and electronic conduction. While swelling of the polymer film is required to promote the transport of electrolyte ions, extreme hydration can hinder electronic charge transport, lowering the OECT performance. Fine‐tuning of the hydrophilicity of the polymer balances the ionic and electronic conduction necessary to build high‐performance devices.