Nanoscale Correlative Microscopy to Visualize Spatial Distributions of Ionic and Electronic Species in Organic Mixed Conductors

The performance of organic mixed ionic-electronic conductors (OMIECs) depends on the nanoscale transport of ionic and electronic species through a complex polymer matrix. These transport processes strongly depend on the arrangement of crystalline and amorphous regions in OMIEC thin film and are challenging to probe due to the small length scales associated with crystalline and amorphous features. Using photoinduced force microscopy (PiFM), we map the presence of ionic and electronic charge carriers in OMIEC thin films with approximately 10 nm spatial resolution. By correlating local crystallinity with nanoscale stiffness mapping and ion concentration with infrared PiFM, we find that ions preferentially reside in crystalline regions of the polymer likely due to their higher HOMO level compared to that of disordered regions. Our study provides nanoscale insights into the mechanism of electrochemical doping and how the arrangement of ionic and electronic species impacts performance.