Neutron Reflectometry for In-Depth Porosity and Figure-of-Merits Correction of Organic Electrochemical Transistors

Abstract

A porous channel structure enhances the performance of organic electrochemical transistors (OECTs). However, the complex spatial arrangement and volume fraction of the active material in the thin film render the volumetric figure of merit undetermined. To resolve this critical issue, two characterization approaches, including topographical analysis and neutron reflectometry, are employed to quantitatively evaluate the porosity of a porous channel with salt additives. These methods haven’t been employed in OECT characterizations. Accordingly, the model channel comprises dense, porous, and nanofibrillar microstructures, along with the inclusion of chaotropic salts, to enhance the volumetric doping characteristics of OECTs with a p-type conjugated polymer matrix. This combined channel provides a clear platform for estimating the volumetric figure of merit. The results indicate that the topographical method indicates an approximate surface coverage of 58.5% of the porous thin film. Notably, neutron reflectometry provides a more precise quantification of porosity within the bulk structure (66.3%), underscoring the mutual validation of these two methods and the necessity of volumetric assessment beyond topographical analysis. Beyond quantifying porosity, neutron reflectometry excels at analyzing heterogeneous channels with salt inclusion and hybrid composite channels, thereby providing insight into the extent of ion injection/ejection. Finally, the nanofibrillar channel with salt inclusion can be precisely evaluated with a volumetric capacitance (74 F cm−3), carrier mobility (2.7 cm2 s−1 V−1), and a reliable product of 267 F s−1 cm−1 V−1. The findings provide a practical framework for advancing mixed ionic–electronic conductors and deepen the fundamental understanding of OECTs.