Evaluating the Impact of Surface Treatments on a Fluorinated Silicon Phthalocyanine Organic Mixed Ionic-Electronic Conductor

Small-molecule organic mixed ionic-electronic conductors (OMIECs) offer an interesting alternative to polymers for the fabrication of reliable organic electrochemical transistors (OECTs) thanks to their minimal batch-to-batch variability. The environmental and operational stability of the devices remains a significant issue, particularly in n-type OMIECs, prompting the molecular design of materials with lower LUMO levels and tighter intermolecular forces. In this work, we apply a common strategy that achieves these goals, fluorination, to our previously developed silicon phthalocyanine OMIEC and use silane-based surface treatments as a case study for the effect of surface treatment on the performance of small-molecule OECTs. When compared to the non-fluorinated material, bis(2-[2-(2-methoxyethoxy)ethoxy]acetate) silicon tetrafluoro phthalocyanine (MEEA-F4SiPc) OECTs fabricated on SiO2 demonstrate a lower threshold voltage (VT) at 0.406 ± 0.056 V and better cycling stability. Using surface treatments resulted in faster uptake of ions when swelling as evidenced by EIS and Raman spectroscopy. Though this also resulted in slight improvements in the transient characteristics of the OECTs through faster τon values, the steady-state characteristics of the OECTs were unchanged. This study suggests surface treatment as a strategy for improved small-molecule OECT performance.