Enhanced Electrochemical Response and Device Speed in Diketopyrrolopyrrole/PEO Composite Channels

Achieving efficient charge conduction in organic electrochemical transistor (OECT) channel materials requires a delicate balance between electronic conduction and ion uptake. Common approaches to this challenge focus on tethering hydrophilic side chains to conjugated backbones, often resulting in complex synthetic routes. Herein, an alternative strategy is presented using composite mixed-conductive materials. Specifically, polyethylene oxide (PEO), a hydrophilic polymer, and a diketopyrrolopyrrole-based semiconductor, renowned for electronic conduction and processability, are used in varying ratios to form composite films with tunable mixed conduction and enhanced OECT performance. The effect of incorporating PEO on the composite's morphology and OECT performance in both aqueous and non-aqueous electrolytes is investigated. At the nanoscale, PEO is found to not only enhance channel hydrophilicity and ion uptake but also electrochemical gating speed, leading to improved OECT performance. These enhancements in electrochemical performance are correlated with the morphological properties of the composite via structural and in-situ spectro-electrochemical characterizations. Furthermore, the composite's response is found to vary with the electrolyte environment: in organic electrolytes such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), it exhibits high-speed performance suitable for neuromorphic applications, while in aqueous electrolytes, it achieves robust ion uptake ideal for bioelectronics. These findings highlight the potential of composite designs for optimized OECT functionality across applications.