Understanding Polymer-Ion Interactions for Improved OMIECs

OMIECs are soft electronic materials that exhibit the capability to solvate and facilitate the transport of ionic species, and this mixed ionic/electronic work environment provides significant research potential for conjugated polymer-based energy storage study. OMIECs’ high degree of structural flexibility and functionality allow them with specific customization across a wide range of electronic applications such as OECTs and OLEDs. The complex nature of OMIEC systems makes it difficult to disentangle how different factors, such as the polymer chemical structure, the choice and concentration of electrolytes, influence the properties of the OMIECs. Efforts have been made to improve stability and performance of devices by tuning the polymer side chain structures to balance the water uptake in aqueous OMIECs systems. However, there are only few research on the impact of electrolyte environments on OMIECs. Moreover, the underlying polymer-ion coupling mechanism still need further understanding to improve the polymer design strategy for better electrochemical performance of OMIECs. In this work, we investigated a series of oxybithiophene based p-type polymers with different length of alkyl side chains to examine the relationship between the hydrophobic side chain structure and different aqueous electrolyte environments, aiming to explore the polymer-ion interactions for OMIECs systems. We will report on the impact of the side chain structure on the redox performance, depth of charge, rate capability, swelling behaviour of the p-type polymers. We calculated the doping ability from specific capacity results of the p-type polymers in different electrolyte environments. With the help of in situ characterization methods, we observed an abnormal swelling trend of one polymer in specific electrolyte environments. This unusual swelling phenomenon can help us to unveil the polymer-ion interactions and provide insights into choices of electrolytes for improved electrochemical performance of OMIECs.