Molar Mass Improves the Performance of n‑Type Organic Electrochemical Transistors

We report on the synthesis and use of two side-chain-free ionenes with varying heteroatoms, PFu and PTh, for n-type accumulation-mode OECTs. Compared to PTh, PFu is more challenging to make, less stable, and shows increased water solubility. The optical properties and surface morphologies of the two derivatives are comparable, but their microstructures vary distinctly in terms of ordering and backbone orientation. While the backbones of PTh show a preferential face-on orientation, PFu is significantly less ordered. The OECT performance of PTh is improved by 1 order of magnitude compared to PFu, as indicated by μC* values of 116.16 and 10.66 F cm^-1 V^-1 s^-1, respectively. Further increasing the molar mass of PTh doubles the performance, resulting in a record-high μC* value of 225.71 F cm^-1 V^-1 s^-1 and a high μ value of 0.58 cm² V^-1 s^-1, highlighting the crucial role of molecular weight control for enhancing device performance.